Ethiopia's Erta Ale basaltic shield volcano has had at least one active lava lake since the mid-1960s, and possibly much earlier. Two active craters (North Pit and South Pit) within the larger oval-shaped Summit Caldera have exhibited periodic lava fountaining and lava lake overflows over the years. A new eruptive event located about 3 km SE of the Summit Crater appeared on 21 January 2017. Activity at the eruption site increased during subsequent months, sending lava flows several kilometers NE and SW from a newly formed lava lake. This report discusses activity from February 2017 through March 2018 as the flows traveled as far as 16 km from the main vent. Information comes from satellite thermal and visual imagery, and photographs and reports from ground-based expeditions that periodically visit the site.

Summary of activity, February 2017-March 2018. The 21 January 2017 activity at Erta Ale was the first time a vent outside of the Summit Caldera has been observed (figure 50). The initial vent or vents created multiple lava flows that traveled generally NE and SW from their sources, creating at least one lava lake that persisted for about a year (figure 51). The flows began inside an older caldera at a location about 3 km SE of the South Pit Crater, but eventually overflowed the caldera rim in multiple directions. As the flow fields enlarged, thermal imagery captured hot-spots along the flows that were likely produced by breakouts, skylights into lava tunnels, and hornitos, as well as multiple surges of flows across the growing fields (figure 52). The imagery also showed the locations of the advancing flow fronts which had reached over 5 km SW of the source by August 2017 and over 16 km NE of the source by March 2018, eventually reaching the alluvial plain NE of Erta Ale. Thermal anomaly data indicated that the maximum thermal energy output happened in April 2017, gradually decreasing through March 2018. The far NE front of the northeast flow field was still active at end of March 2018.

Figure 50. The summit of Erta Ale has two oblong NW-trending calderas. The northern Summit Caldera contains the North Pit Crater and the South Pit Crater. The North Pit Crater has had a solidified lava lake with a large hornito emitting magmatic gases and incandescence at night, and the South Pit Crater has had an active lava lake for many years that last overflowed its rim during mid-January 2017. The new eruption began at vents located about 3 km SE of the South Pit Crater near the northern rim of a second caldera referred to here as the Southeast Caldera, on 21 January 2017. The new eruption had not yet begun in this 16 January 2017 image. See figure 46 (BGVN 42:07) for additional images the following week that show the first flows from the new vents. Images copyright by Planet Labs Inc., 3 m per pixel resolution, and used with permission under a Creative Commons license (CC BY-SA 4.0), annotated by GVP.

Figure 51. A new lava lake formed during late January 2017 at the new eruption site about 3 km SE of the South Pit Crater at Erta Ale, inside the Southeast Caldera. This view is likely from the rim of the Southeast Caldera, looking SE or E. Visitors were not able to get closer to the vent due to the active flows for several months. Photo by Stefan Tommasini taken during February 2017, courtesy of Volcano Discovery (Erta Ale volcanic activity: 2017 overview and June update, 27 June 2017).

Figure 52. An active new pahoehoe lava field flowed over older lava flows inside the Southeast Caldera at Erta Ale during February 2017. This photo was likely taken from the northern or western rim of the Southeast Caldera. Photo by Stefan Tommasini, courtesy of Volcano Discovery (Erta Ale volcanic activity: 2017 overview and June update, 27 June 2017).

When the new eruptive episode began, the lava lake at the South Pit Crater drained rapidly to around 80-100 m below the rim, according to visitors to the site a few weeks later. The crater was emitting a strong thermal signal by early March 2017 as the lake level rose again. Visitors in April witnessed a fluctuating lake level rising and falling by up to 20 m every 30 minutes over several days. The thermal signal remained strong at the South Pit Crater through March 2018. Due to significant political instability in the area, ground visits are intermittent, but high-quality photographs were taken in February 2017, December 2017, and January 2018 that show the new lava lake and parts of the new flow fields.

Activity during late January-March 2017. The new eruptive event at Erta Ale began in late January 2017 at the northern end of the Southeast Caldera located; the first lava flows observed were locatedabout 3 km SE from the main Summit Caldera (figure 45 (BGVN 42:07) and figure 50). Two separate vent areas appeared active initially. The northern vent sent lava flows to the NE for several kilometers and to the SW a much shorter distance. The southern vent sent a stream of lava to the S. By the end of January 2017 the North and South Pit Craters at the Summit Caldera were still thermally active, but the signals were much stronger from the new vent areas in the Southeast Caldera (figure 53). A faint thermal signal from about 5 km E of the northern vent suggested the extent of the new flows in that direction.

Figure 53. A Sentinel-2 image from 29 January 2017 shows the initial activity at the new Southeast Caldera vents of Erta Ale (labelled Event 1 and Event 2). Weak thermal signals are apparent from the North and South Pit Craters (Pit Crater Nord, Pit Crater Sud) within the Summit Caldera, and much stronger thermal signals are evident from two areas inside the Southeast Caldera. A faint signal from about 5 km E of the new vents indicates possible flow activity breaking out of lava tubes in that region (Skylight). Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Le point sur l'activité des volcans Etna, Erta Ale, Fuego, Piton de la Fournaise et Bogoslof, 3 février 2017).

A small group of travelers led by Ethiopian geologist Enku Mulugeta visited Erta Ale during the first half of February 2017. They reported that within the main Summit Caldera, the hornito in the North Pit Crater had collapsed and the lava lake in the South Pit Crater was about 80-100 m below the caldera floor level. The eruption in the Southeast Caldera was still very active, and they photographed the sizable new lava field which contained numerous pahoehoe flows, actively spattering hornitos, and a large lava lake (figures 51, 52, and 54). During the following months activity remained high both at the new eruption site and at the Summit Caldera where the lava lake in the South Pit Crater gradually rose back up to about 50 m below the caldera floor. Culture Volcan annotated a series of Sentinel-2 satellite thermal images which show the progression of the lava flows through the following year.

Figure 54. A large new lava field quickly formed inside the Southeast Caldera at Erta Ale after the beginning of the new eruptive event in late January 2017. When photographed here in February 2017, pahoehoe flows had spread outward from a central vent area (glow at top center) for over a kilometer in multiple directions. View is likely to the E from the W rim of the Southeast Caldera. Photo by Stefan Tommasini, February 2017, courtesy of Volcano Discovery (Erta Ale volcanic activity: 2017 overview and June update, 27 June 2017).

By 10 March 2017 only the southern vent area was active inside the Southeast Caldera. It continued to feed the lava field; lava was actively flowing S from the vent towards the W rim of the Southeast Crater, and NE, breaking out from lava tubes which blocked the thermal signal until about 2.6 km NE of the vent (figure 55). Thermal signals from both the North and South Pit Craters were distinct and stronger than in late January.

Figure 55. The thermal signals at both the North and South Pit Craters at Erta Ale were stronger in this 10 March 2017 image than in late January. Only one main source of lava is apparent at the Southeast Caldera. Lava flows directly from the primary vent SW towards the W rim of the caldera, and also surfaces from tunnels about two kilometers NE in an actively moving lava front. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Un point sur l'activité des volcans Etna et Erta Ale, 13 mars 2017).

A site visit to the South Pit Crater on 20 March 2017 demonstrated that the lake level had risen significantly since its drop in early February, and was once again actively convecting (figure 56). By the end of March 2017, satellite thermal imagery made clear the increasing thermal signal at the South Pit Crater, and in the Southeast Caldera, the major increase in effusion to the NE from the main vent. The width of the flow field had increased to about 1,400 m, and the farthest front was about 3,400 m NE from the vent (figure 57). The lava at the source measured about 180 x 75 m in size, suggesting a lava lake; a smaller overflow to the SW appeared to have reached the W rim of the Southeast Caldera by 30 March 2017 near the area where a new flow had first appeared in a 23 January 2017 satellite image (see figure 46, BGVN 42:07).

Figure 56. The South Pit Crater of Erta Ale on 20 March 2017 had risen significantly from its drop in February and was actively convecting. Photo by Jean-Michel Escarpit, courtesy of Cultur Volcan (Un point sur l'activité des volcans Fuego, Manam et Erta Ale, 22 mars 2017).

Figure 57. The thermal signal at the South Pit Crater continued to increase in this 30 March 2017 satellite image of Erta Ale. The main vent in the Southeast Caldera had dimensions of about 180 x 75 m, suggesting a lake had formed. A large increase in the thermally active area to the NE indicated that the flow field was expanding significantly in that direction, with a few small thermal anomalies between the lake and lava field suggesting a number of small flows or lava tube breakouts. Flow activity also continued to the SW reaching the W rim of the Southeast Crater where lava had flowed past the crater rim in late January (see figure 46, BGNV 42:07). Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Un point sur l'activité des volcans Klyuchevskoy et Erta Ale, 31 mars 2017).

Activity during April-May 2017. In the next Sentinel-2 satellite image from 9 April (figure 58), the distance to the farthest front of the lava flow had increased to about 4,600 m from the lava lake, and a new flow had appeared a few hundred meters east of the lake that extended about 1,100 m ENE from its source. Lava also flowed SW from the source to the SW rim of the Southeast Crater, appearing to pond against and flow slightly beyond the rim.

Figure 58. The lava flows continued to extend NE from their source inside the Southeast Crater at Erta Ale in this Sentinel-2 satellite image from 9 April 2017. The farthest edge of the northeast flow front was about 4,600 m from the lake. A new arm of lava flowed more than a kilometer ENE from its source close to the lake. Another thermal signature SW of the lake indicated an accumulation of lava near or slightly spilling over the SW rim of the Southeast Crater. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Le point sur l'activité des volcans Erta Ale et Bogoslof, 16 avril 2017).

A group visited Erta Ale during 11-15 April 2017 in collaboration with Addis Ababa University geologist Enku Mulugeta. They noted that fluctuating lava lake levels at the South Pit Crater were cycling every 30 minutes or so between 40 and 50 m below the caldera floor (figures 59 and 60). Lava tubes from the walls of the crater would feed the lake with fresh lava after it drained. Two coalesced hornitos, about 7 m high, were present in the NE part of the crater, emitting SO2 gas and occasional lava. At the North Crater Pit, noisy degassing of SO2 from several hornitos at the center of the solidified crust was apparent. Observers at the Southeast Caldera could see the lava lake with the top about 10 m below its crater rim, and minor fountaining during the night, but they were not able to get closer than about 700 m due to the active flows.

Figure 59. The lava lake level at the South Pit Crater at Erta Ale during April 2017 was fluctuating by 10-20 m every 30 minutes or so. The high-stand of the lava is shown here. Courtesy of Toucan Photo.

Figure 60. The lava lake level at the South Pit Crater at Erta Ale during April 2017 was fluctuating by 10-20 m every 30 minutes or so. The low stand of the lava is shown here as the lava drains away. Courtesy of Toucan Photo.

By the end of April 2017 satellite thermal imagery indicated that the northeast flow field at the Southeast Caldera extended more than 7 km NE from the lake and was curving towards the E (figure 61). The lava lake was still thermally active, as was the South Pit Crater to the NW.

Figure 61. Sentinel-2 satellite imagery of Erta Ale on 29 April 2017 shows the growth of the northeast lava field from earlier in the month to more than 7 kilometers from its source. The South Pit Crater was still active, as was the source of the northeast lava field. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (L'activité effusive reste soutenue à l'Erta Ale, 3 mai 2017).

Eleven days later, activity was quite different in the Southeast Caldera. Satellite imagery from 9 May 2017 (figure 62) showed a new, relatively narrow but bright lava flow moving NE for 2-3 km originating in a location slightly NE of the original lava lake; activity farther NE had diminished from the previous image. A subsequent image on 18 May looked similar, but by 19 May the narrow flow had been replaced by a much broader area of thermal anomaly in the region immediately E of the source. By 29 May 2017, the source of the lava appeared to have shifted several hundred meters SE of the earlier location, and a strong thermal signal once again extended NE across the northeast flow field from the new source for about two kilometers (figure 63).

Figure 62. A Sentinel-2 satellite image of Erta Ale on 9 May 2017 showed a shift to the NE in the location of the source of the active flows. A new narrow flow had traveled 2-3 km NE from a source located NE of the lava lake. The more distant northeast flow field had a much smaller thermal signature than on 29 April. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Breakout sur le volcan Erta Ale, 11 mai 2017).

Figure 63. A significant shift to the SE in the location of the lava source from a few weeks earlier is apparent in this Sentinel-2 satellite image of Erta Ale captured on 29 May 2017. A strong thermal anomaly trended NE across the northeast flow field for about two kilometers. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Erta Ale: une éruption vraiment exceptionnelle, 11 juin 2017).

Activity during June-August 2017. The rapidly changing flow field was significantly different again less than two weeks later in satellite imagery captured on 8 June 2017. Lava was flowing N, SE, and S across the northeast lava field, extending beyond the rim of the Southeast Caldera to the N and E. Another very strong thermal signal emerged from the SW corner of the Southeast Caldera where lava was flowing W and S outside the caldera rim forming a new southwest lava field (figure 64).

Figure 64. A Sentinel-2 satellite image of Erta Ale on 8 June 2017 shows significant changes in the location of the active flow fields from less than two weeks earlier. The South Pit Crater in the Summit Caldera still had a strong thermal signal suggesting an active lake in the crater. Flows in the Southeast Caldera appeared to be moving N, E, and S across the northeast lava field, and a new area with flows moving S and W from the SW rim of the Southeast Caldera formed the new Southwest lava field. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Erta Ale: une éruption vraiment exceptionnelle, 11 juin 2017).

During June 2017, the most aggressive flow activity contributed to significant growth of the southwest lava field. By 28 June, infrared imaging detected flow fronts 4,500 m SW of the vent; they had extended to about 5,100 m, nearing the base of the SW flank of Erta Ale, by 5 July (figure 65). Flow activity also persisted in the northeast flow field with activity concentrated about 1.5 km NE of the vent on 28 June. Movement increased at the northeast flow field beginning in late June and it had extended to about 3.5 km NE of the lava lake by 5 July 2017.

Figure 65. Lava flow activity at the Southeast Caldera of Erta Ale during June 2017 was concentrated in the growing southwest flow field which had extended about 5,100 m from its lava lake source by 5 July 2017 in this Landsat 8 satellite image. The northeast flow field began extending farther NE during the first week of July, reaching 3,500 m from the lake by 5 July. Courtesy of ESA/Copernicus and NASA/USGS with annotations provided by Culture Volcan (Un point sur l'activité des volcans Copahue et Erta Ale, 8 juillet 2017).

Significant movement to the NE in the northeast flow field was apparent in satellite images beginning on 21 July 2017; the head of the flow had reached about 9.5 km from the lava lake by 28 July 2017, mostly focused in a narrow channel (figure 66). Activity decreased in the southwest flow field during July; the lava front had advanced only a few hundred meters by the end of July from its position on 5 July.

Figure 66. The northeast flow field at Erta Ale lengthened significantly during July 2017; the leading edge was about 9.5 km NE of the lava lake by 28 July 2017, as captured in this Sentinel-2 satellite image. The southwest flow field had extended just a few hundred meters SW from its location on 5 July. The distance between the South Pit Crater and the Southeast Caldera lava lake is about 2.7 km. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Les actus du jour: Katla en alerte jaune et quelques changements à l'Erta Ale, 29 juillet 2017).

During August 2017, lava continued to flow from the Southeast Caldera lava lake in two directions. The northeast flow front extended to 12 km from the vent by 17 August and had reached over 14 km by 7 September. The southwest flow field, while it remained in roughly the same area, had a decreased but still significant thermal signature in early September, suggesting continued but diminished activity throughout the period (figures 67).

Figure 67. During August 2017, lava continued to flow in two directions from the Southeast Caldera lava lake at Erta Ale. The northeast flow field had reached over 14 km from the lake by 7 September 2017 when this Landsat 8 satellite image was taken. The Southwest flow field, while it remained in roughly the same area, still had a significant thermal signature suggesting continued activity. Courtesy of ESA/Copernicus and NASA/USGS with annotations provided by Culture Volcan (volcan Erta Ale: ça continue; Fernandina: c'est moins sûr, 12 septembre 2017).

Activity during September-December 2017. In a Sentinel-2 satellite image from 26 September 2017, it was clear that the South Crater Pit was still thermally active, and that the southwest flow field had largely cooled with only a small area on its NW edge still producing a thermal anomaly (figure 68). In contrast, the northeast flow field had advanced about 1 km in the previous three weeks and was less than a kilometer from the edge of the valley alluvium. It finally reached the edge of the older lava field and began to advance across the alluvium NE of the volcano, more than 16 km from the lava lake, on 16 October 2017 (figure 69). Based on satellite imagery, Cultur Volcan interpreted that activity slowed significantly during November 2017, and while the thermal signal remained strong near the head of the flow, it did not advance significantly across the alluvium.

Figure 68. The South Pit Crater at Erta Ale still had an active lava lake on 26 September 2017 in this Sentinel-2 satellite image. The southwest lava field had largely cooled, with only a small thermal anomaly along it NW edge. The northeast lava field continued to be active; it had advanced about 1 km NE in about three weeks and was about 650 m from the edge of the alluvium. A significant number of hotspots along the northeast lava flow suggest that several skylights existed into lava tubes or there were small breakouts. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Les actus du jour: Heard Island, Erta Ale, Pacaya, Fuego, Sangay, Ol Doynio Lengai, 5 octobre 2017).

Figure 69. Erta Ale's northeast flow field reached the alluvium about 16 km E of the Southeast Caldera lava lake by 16 October 2017, as recorded in this Sentinel-2 satellite image. The distance between the ends of the two easternmost tongues of lava is about 1 km. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Erta Ale: ça y est, le champ de lave entre dans la plaine!, 18 octobre 2017).

Visitors to the South Pit Crater in mid-December 2017 reported that its lava lake continued to be active and its level was about 60 m below the rim. They were also able to visit the Southeast Caldera lava lake, 2.7 km SE of the South Pit Crater, and take photographs from its rim; it was about 200 m long and 100 m wide and filled with slowly convecting lava (figures 70, 71). Satellite imagery from 25 December 2017 showed the active lake at the South Pit Crater, the active lake at the Southeast Caldera, and numerous skylights and overflows along the 16-km-long northeast flow field (figure 72).

Figure 70. The Southeast caldera lava lake at Erta Ale, its surface crusted over with slightly cooled lava, with dimensions of about 200 x 100 m in mid-December 2017. Photograph by FB88, courtesy of Culture Volcan (Un point sur l'activité à l'Erta Ale, 31 décembre 2017).

Figure 71. The Southeast Caldera lava lake at Erta Ale was slowly convecting during mid-December 2017. Photographed by FB88, courtesy of Culture Volcan (Un point sur l'activité à l'Erta Ale, 31 décembre 2017).

Figure 72. Sentinel-2 satellite imagery from 25 December 2017 of Erta Ale showed the active lake at the South Pit Crater (Summit lava lake), the active lake at the Southeast Caldera (Rift-Zone lava lake), and numerous skylights and overflows along the 16-km-long northeast flow field. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Un point sur l'activité à l'Erta Ale, 31 décembre 2017).

Activity during January-March 2018. By mid-January 2018 thermal activity was concentrated a few kilometers back from the front of the northeast flow, about 12 km from the lava lake (figure 73). A Volcano Discovery tour group visited during 13-26 January 2018 and was able to access and photograph both the North and South Pit Craters and the new lake and flow fields around the Southeast Caldera with ground-based and aerial drone photography (figures 74-84).

Figure 73. By 19 January 2018, thermal activity at Erta Ale's northeast flow field was concentrated a few kilometers back from the front of the flow, about 12 km from the Southeast Caldera lava lake. The South Pit Crater and Southeast Caldera lava lakes are visible on the left. Small hot-spots near the Southeast Caldera lava lake could be hornitos or skylights into lava tubes. Courtesy of ESA/Copernicus with annotations provided by Culture Volcan (Le point sur l'activité des volcans Erta Ale, Kadovar (Mis à jour) et Nevados de Chillan, 21 janvier 2018).

Figure 74. In this aerial view taken in January 2018 by a drone of the central part of Erta Ale's Summit Caldera, steam plumes rose from the North Pit Crater (left) and South Pit Crater (right). The fresh black lava around the South Pit Crater overflowed onto the caldera floor in January 2017 shortly before the beginning of the eruptive events in the Southeast Caldera a few kilometers to the south. Photograph by Stefan Tommasini taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 75. The North Pit Crater inside the Summit Caldera at Erta Ale contained a large collapsed vent in January 2018 that formed after the magma drained away from the crater in January 2017. Photograph by Stefan Tommasini taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 76. The lava lake in the South Pit Crater of Erta Ale's Summit Caldera was tens of meters below the rim in January 2018. Magma drained away and parts of the crater walls collapsed in January 2017, followed by repeated filling and draining of the lava lake during 2017. Photograph by Stefan Tommasini taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 77. This aerial view by drone shows the large lava lake that formed at Erta Ale's Southeast Caldera during 2017; it was still slowly convecting in January 2018. The lake dimensions were about 100 x 200 m. Photograph by Stefan Tommasini taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 78. Recently cooled black crust is overrun and consumed by molten lava that quickly cools and crusts over in Erta Ale's Southeast Caldera lava lake in January 2018. Photograph by Stefan Tommasini taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 79. Lava appears to flow into the Southeast Caldera lava lake at Erta Ale from a vent at the far edge and slowly spread across the lake during January 2018. Photograph by Stefan Tommasini taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 80. Lava splashes as it flows into the Southeast Caldera lava lake at Erta Ale in January 2018. Photograph by Anastasia Ganuschenko taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 81. Downwelling consumes lava inside the Southeast Caldera lava lake at Erta Ale in January 2018. Photograph by Stefan Tommasini taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 82. Incandescence is visible inside a hornito that formed through lava spattering along the new flows in the Southeast Caldera at Erta Ale in January 2018. Photograph by Anastasia Ganuschenko taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 83. Many layers of fresh Pahoehoe lava flows were cool enough to walk on in some areas of the Southeast Caldera lava fields in January 2018. Photograph by Stefan Tommasini taken during 13-26 January 2018, courtesy of Volcano Discovery.

Figure 84. Fresh lava flows were easily distinguished from older ones by their silver hue and dark black crust at Erta Ale's Southeast Caldera lava fields in January 2018. Photograph by Stefan Tommasini taken during 13-26 January 2018, courtesy of Volcano Discovery.

By late March 2018 no thermal signal appeared in satellite imagery at the site of the Southeast Caldera lava lake, although the South Pit Crater was still visible. A large increase in the area of fresh flows and multiple thermal anomalies were present at the flow front of the northeast lava field 14-16 km from the former lava lake (figure 85). During the second half of March, the flow progressed several hundred meters out into the alluvial plain.

Figure 85. Sentinel-2 satellite imagery captured on 15 March 2018 showed a large increase in the area of fresh lava flows at the NE front of the northeast lava field at Erta Ale when compared with an image from 19 January 2018. Over the next ten days, images showed the narrow finger of lava that just touches the alluvium in this image creep about a kilometer out into the alluvial plain. Courtesy of Courtesy of ESA/Copernicus, published by Cultur Volcan (Les actus volcaniques du jour: Erta Ale, Maly-Semiachik, Suwanose-Jima et Ebeko, 28 mars 2018).

MIROVA thermal anomaly data. The MIROVA thermal anomaly data captures information about the distance of the anomalies from the summit as well as the radiative power released from Erta Ale. Both sets of information agree well with observations from the Sentinel-2 and Landsat satellite data. The plot of distance from the summit (figure 86) shows that during August 2016-mid-January 2017 the thermal anomalies were located very close to the summit point, representing heat flow from both the South and North Pit Craters within the Summit Caldera. Beginning on 21 January 2017, the jump in location of the anomalies corresponded with the beginning of the eruption in the Southeast Caldera. The MIROVA thermal anomalies progressed farther from the summit point during March and April 2017, when the northeast flow field was lengthening to the NE. The thermal signal jumps back closer to the summit point in early May corresponding to when new breakouts were spotted near the Southeast Caldera lava lake; the flows again traveled away from the lake during June and July 2017. Active lava flows from mid-August 2017 through March 2018 were visible in satellite imagery 12-16 km from the lava lake, which is reflected in the MIROVA data (figure 86).

Figure 86. MIROVA data showing the distance from the summit point of thermal anomalies at Erta Ale. Upper graph is the year ending 18 July 2017. Lower graph is the year ending 9 March 2018. They correspond well with locations of thermal anomalies that appear in numerous satellite images during that time. Note the distance scale change. See text and earlier figures for details. Courtesy of MIROVA.

The MIROVA data for the radiative power released from Erta Ale during August 2016-March 2018 also corresponds well with satellite and ground observations (figure 87). The levels of radiative power were moderate and constant during August 2016 to mid-January 2017 when only the lava lake and hornitos at the South and North Pit Craters were active (see also figure 47, BGVN 42:07). A moderate spike in the radiative power corresponds to the overflow of the South Pit Crater during 16-20 January 2017, followed by a large spike in radiative power on 21 January when the eruption started in the Southeast Caldera. This was followed by an extended period of increased radiative power as extensive flow fields formed in the Southeast Caldera. The graph is also able to distinguish the movement of the flows from near the Southeast Caldera lava lake to farther away and then near again during March-June 2017. The radiative power graph from 10 March 2017-9 March 2018 clearly shows a gradual decrease in the amount of radiative power over the period, suggesting a decline in flow activity, which corresponds well to satellite observations.

Figure 87. MIROVA plots of radiative power at Erta Ale for 18 July 2016-18 July 2017 (upper) and 9 March 2017-9 March 2018 (lower). Note the different y-axis scales for VRP due to the large spike on 21 January 2017 at the beginning of the Southeast Caldera eruptive episode. The plots record both the movement of the flow fields away from and closer to the summit point during March-June 2017, and then the gradual decrease in radiative energy from May 2017 through early March 2018. Courtesy of MIROVA.

Geologic Background. Erta Ale is an isolated basaltic shield that is the most active volcano in Ethiopia. The broad, 50-km-wide edifice rises more than 600 m from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The volcano contains a 0.7 x 1.6 km, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera is renowned for one, or sometimes two long-term lava lakes that have been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: European Space Agency (ESA), Copernicus (URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus; Robert Simon, Sr., Data Visualization Engineer, Planet Labs Inc. (URL: http://www.planet.com/) [Images used under https://creativecommons.org/licenses/by-sa/4.0/]; Cultur Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.com); Toucan Photo (URL: www.toucan.photo); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

The first confirmed historical eruption at Kadovar began around mid-day local time on 5 January 2018, according to witnesses. The steeply-sloped island is approximately 1.4 km in diameter and is located about 25 km NNE from the mouth of the Sepik River on the mainland of Papua New Guinea (figure 1). This report covers activity from the beginning of the eruption on 5 January through March 2018. Information about the eruption is provided by the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), satellite sources, news reports, and local observers. A possible eruption was witnessed by explorers in 1700; no other activity was reported until an outbreak of thermal activity in 1976 (NSEB 01:14-01:11, SEAN 03:09) and a short period of seismic unrest in 2015, according to RVO.

Figure 1. Kadovar Island is located about 25 km NNE from the mouth of the Sepik River on the mainland of Papua New Guinea. Nearby active volcanoes include Blup Blup (12 km N) and Bam (21 km W); residents of Kadovar were evacuated initially to Blup Blup before being moved to an area near Wewak, the nearest community on the mainland, about 105 km W. The red triangles are Holocene volcanoes, and the blue (cyan) triangles are Pleistocene volcanoes. Base map courtesy of Google Earth.

Ash and steam emissions from Kadovar were first reported on 5 January 2018. After about 24 hours, more than half of the island was covered by volcanic debris. Activity intensified over the next two weeks; RVO identified five distinct vents located at the summit and along the SE coast. Dense ash plumes and steam rose from the summit vents, and a slowly-extruding lava flow emerged from a vent near the shoreline on the SE flank. Persistent steam and intermittent ash plumes were produced from the summit vent through the end of March. The lava flow grew outward from the shore for tens of meters before collapsing in early February, but it reappeared a few days later. By the end of the first week of March 2018 the flow was about 17 m above sea level; its growth rate had slowed, adding only one meter by late March.

The NOAA/CIMSS Volcanic Cloud Monitoring system generated an alert for an ash cloud moving WNW, as imaged by S-NPP VIIRS, at 0330 UTC on 5 January 2018; Himawari-8 imagery subsequently showed that the eruption began around 0220 UTC. The Darwin VAAC reported two discrete ash plumes drifting W at 2.1 km altitude during the day. After local reports of the eruption Samaritan Airlines flew administrators from the Wewak district to investigate, enabling photographs of ash and steam emissions (figure 2).

Figure 2. Steam and ash emerged from a vent near the summit of Kadovar Island and drifted WNW on 5 January 2018. The view is looking NW with the SE flank of Kadovar in the foreground. In the upper photo, the island in the background is Viai Island about 30 km NW. Photo by Ricky Wobar, administrator of the Wewak district. Courtesy of Samaritan Aviation, posted on Facebook on 5 January 2018.

The following day, 6 January 2018, photos from a Samaritan Air flight showed that dark gray ash and steam plumes rising from a crater on the SE side of the summit had intensified (figures 3 and 4). It was estimated that 50 or 60% of the island was covered in volcanic debris, which appeared to be primarily ash along with some pyroclastic flows. According to the International Federation of Red Cross and Red Crescent Societies (IFRC), the entire population of Kadovar, about 600 people who lived on the N side of the island, was relocated to nearby Blup Blup Island which is home to about 800 residents. RVO reported minor ashfall on Kairiru and Mushu islands (115 km WNW), and on mainland Papua New Guinea at Mt. Uru in Yangoru (130 km W), Woginara (140 km W), and the Wewak District (100 km W).

Figure 3. Ash and steam plumes rose from distinct vents on the SE side of the summit at Kadovar. View is to the NE, with Blup Blup volcano located about 12 km in the distance. Photo by Ricky Wobar likely taken on 6 January 2018, published by ABC News on 8 January 2018. Courtesy of ABC News.

Figure 4. Ash and steam emissions intensified from vents at the summit of Kadovar Island on 6 January 2018. Posted on Facebook, 6 January 2018 by Samaritan Aviation.

Also on 6 January 2018, missionary Brandon Buser set out from Wewak to visit Bam by boat. He observed the steam and ash plumes of Kadovar from about 75 km away. About 25 km W of the island, he felt falling ash. From a few hundred meters offshore he witnessed the ash and steam plumes rising from near the summit as he circled the S and E sides of the island (figures 5-8).

Figure 5. Locations of the following photographs of the eruption at Kadovar on 6 January 2018 correspond closely to the purple spots where the boat slowed down on its trip around the island. North is to the top. Numbers indicate approximate locations of the following figures 6-12. Courtesy of Brandon Buser. Base map courtesy of Google Earth.

Figure 6. An ash plume drifted NW from the summit of Kadovar as viewed from a boat a few hundred meters off the SW flank on 6 January 2018. Courtesy of Brandon Buser.

Figure 7. Ash drifted WNW from Kadovar and also covered the vegetation on the SSW flank on 6 January 2018 in this view from a boat a few hundred meters off the SSW flank. Courtesy of Brandon Buser.

Figure 8. Dark ash and white steam both rose from vents at the summit of Kadovar on 6 January 2018. Debris and ashfall killed and denuded the trees on the SE flank, and covered the ground. View is from a boat a few hundred meters off the SE flank. Courtesy of Brandon Buser.

While preparing to head E to Bam, Buser witnessed an explosion that sent large plumes of ash and steam skyward from the SE flank, and a significant cloud of volcanic debris was ejected outward and down the SE flank; large boulders fell into the ocean. Heading rapidly E away from the eruption, he took additional photographs (figures 9-12).

Figure 9. Dark gray ash and white steam billowed up from a vent near the summit of Kadovar on 6 January 2018 at the start of an explosion. The denuded vegetation and bare slopes on the SE flank indicated the extent of the recent activity. The view is from a boat a few hundred meters offshore of the NE flank. Courtesy of Brandon Buser.

Figure 10. An explosion witnessed at Kadovar on 6 January 2018. Steam rose from a vent near the summit (right), dark gray ash billowed up from the SE flank, and brown dust and debris descended the SE flank into the ocean (left) in this view from a few hundred meters off the NE flank. Courtesy of Brandon Buser.

Figure 11. A large explosion at Kadovar witnessed on 6 January 2018. Light gray steam and ash rose from near the summit and drifted NW covering the N half of the island in ash; a large eruption of dark gray ash shot upward from a different vent on the SE flank surrounded by dust and debris that traveled outward at its base. Larger debris caused splashing in the water off the SE flank (left). View is from a few kilometers off the NE flank. Courtesy of Brandon Buser.

Figure 12. The plumes of steam, ash, and debris from the explosion moments earlier at Kadovar on 6 January 2018 rose and began to drift NW covering the island. Blocks landing in the ocean on the SE flank created spray along the shoreline (left). View is from a boat a few kilometers NE of the island. Courtesy of Brandon Buser.

The Darwin VAAC reported on 6 January 2018 that a continuous ash plume was identifiable in satellite imagery moving W and WNW at 2.1 km altitude. By 7 January, the plume could be identified about 220 km WNW in satellite images (figure 13). During their return trip from Bam on 8 January 2018, the missionaries again circled the island and noted that the eruption seemed to be occurring from different vents. The island was covered in ash, and they became covered with wet ash as they traveled under the drifting ash plume. The Darwin VAAC reported the plume drifting WNW extending about 185 km on 8 January. They also noted that the influence of the sea breeze was also spreading minor ash to the SW. Continuous ash emissions were observed by the Darwin VAAC through 11 January, drifting W and NW at 2.1 km altitude.

Figure 13. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured the eruption of Kadovar that began two days earlier on 7 January 2018 as a plume of ash and steam that streamed NW from its crater. A second smaller plume, also drifting NW, is visible SE of Kadovar from unrelated activity at nearby Manam, one of Papua New Guinea's most active volcanos. Brown-green plumes visible in the water S of Kadovar near the coast of the mainland, are caused by sediment from the Sepik and Ramu rivers on the mainland. Courtesy of NASA Earth Observatory.

RVO reported a significant escalation in activity during 12-13 January 2018. An explosion during the previous night ejected large incandescent boulders from the fracture on the SE flank. Residents on Blup Blup (15 km N) could see incandescence high on the volcano's flank. During a flyover on 13 January, RVO noted variable steam and gas emissions rising to 1 km above the Main Crater and identified five distinct vents (figure 14). The SE Coastal Vent was very active with dense white steam emissions rising 600 m from the vent (figure 15). A dome of lava was visible at the base of the steam plume, but no incandescence was observed. The Southern Coastal Vent had been vigorously steaming a few days earlier, and RVO interpreted it to be the source of the incandescent blocks in the explosion a few days before.

Figure 14. A sketch map of the five newly identified vents at Kadovar, 14 January 2018, from an RVO overflight the previous day. Courtesy of RVO (VOLCANO INFORMATION BULLETIN- No. 08 14/01/2018).

Figure 15. A vigorous steam plume rose from the SE Coastal Vent at Kadovar on 13 January 2018 while an ash plume rose from Main Crater at the summit. Photo by the office of Allan Bird, Governor of East Sepik Province. Courtesy of RVO (VOLCANO INFORMATION BULLETIN- No. 08 14/01/2018).

Reports of continuous ash emissions at 2.1 km altitude drifting WNW from the Darwin VAAC resumed on 16 January. A brief emission to 3.7 km was also noted that day. Pilot reports on 17 and 18 January indicated that ash was still in the area as high as 3-3.7 km altitude drifting W. The reports of emissions from the Darwin VAAC continued through 24 January. Ash emissions were generally continuous at altitudes from 2.4 to 3 km, although low level emissions of primarily steam and gas were observed on 20 January that included intermittent phases of increased ash content. The plume drift direction was variable, with periods when ash drifted S and SE in addition to the generally prevailing NW and W directions.

During 18-22 January 2018, the Main Crater continued to produce moderate to dark gray ash plumes that rose 500-800 m above the summit, drifting locally S and SE, and a continuous steam plume from the SE Coastal Vent rose as high as 800 m above the island. An incandescent lava flow slowly extruded from the SE Coastal Vent. By the last week of January, the ash plumes were only rising about 100 m above the Main Crater and drifting W; weak incandescence was still observed at night. The white steam plume from the SE Coastal Vent rose closer to 400 m above the island. RVO estimated that the lava flow had risen to about 50 m above sea level and extended 150-200 m out from the coast.

In their report on 2 February 2018, RVO noted that the lava flow continued to grow. A distinct lobe had pushed out from the seaward nose of the flow, by about 20-30 m; it appeared to be channeled by levees which had developed at the flow's sides. At 1830 local time on 1 February, a collapse of the side of the flow facing Blup Blup was observed; it resulted in a plume of gray ash and then vigorous steaming at the collapse site, which also was incandescent at night. The main body of the flow significantly bulged upwards, with a distinct 'valley' visible between the bulge and the island's flank.

RVO reported that on 9 February the lava flow at the SE Coastal Vent had collapsed, causing 5-6 minor tsunamis less than 1 m high that were observed by residents on Blup Blup's E and W coasts. The waves were reported at 1050, before the main collapse of the dome. In a 12 February report, RVO noted that activity from Main Crater consisted of white plumes rising 20 m and drifting a few kilometers SE accompanied by weak nighttime crater incandescence. Activity renewed at the SE Coastal Vent shortly after the collapse of the flow on 9 February 2018; lava re-emerged a few days later, connecting a lava island to the coastline again. Continuous steam emissions from both the Main Crater and the SE Coastal Vent were interrupted by dark ash plumes on 16 and 20-22 February, and occasional explosions were heard by residents on nearby islands. Minor ashfall was reported on Blup Blup on 21 and 22 February.

Eruptive activity continued during March 2018, although at a slower rate. The Main Crater generally produced continuous emissions of white steam and intermittent explosions with dark ash plumes; incandescence was usually visible at night from Blup Blup. According to the Darwin VAAC, a pilot reported an ash plume at 3.9 km altitude drifting SE on 2 March; it was not visible in satellite imagery due to meteoric clouds. The lava flow extruding from the SE Coastal Vent continued to grow, creating a dome that grew from 7-8 m above sea level to 10-17 m above sea level by 8 March. Dark ash emissions from the vent and nighttime incandescence were common. The growth rate slowed later in the month, and only one meter of change was observed between 10 and 20 March.

Satellite data. The MIROVA project recorded thermal anomalies from Kadovar in early January and early March 2018 (figure 16). MODVOLC thermal alerts were issued on three days; 15 and 22 January, and 7 February 2018. During January, small SO₂ plumes were recorded by NASA satellites on four occasions (figure 17).

Figure 16. The MIROVA project thermal anomaly graph for Kadovar from 11 May 2017 through March 2018. The first anomaly in early January 2018 correlates with observations of the first reported explosion. Courtesy of MIROVA.

Figure 17. SO2 plumes from Kadovar were detected several times during January 2018 by the OMI instrument on NASA's Aura satellite. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. Kadovar is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. The village of Gewai is perched on the crater rim. A 365-m-high lava dome forming the high point of the andesitic volcano fills an arcuate landslide scarp that is open to the south, and submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. No certain historical eruptions are known; the latest activity was a period of heightened thermal phenomena in 1976.

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea, Contact: steve_saunders@mineral.gov.pg, ima_itikarai@mineral.gov.pg; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); NOAA, Cooperative Institute for Meteorological Satellite Studies (CIMSS), Space Science and Engineering Center (SSEC), University of Wisconsin-Madison, 1225 W. Dayton St., Madison, Wisconsin 53706, USA (URL: http://cimss.ssec.wisc.edu/); International Federation of Red Cross and Red Crescent Societies (IFRC) (URL: http://www.ifrc.org/); Samaritan Aviation (URL: http://samaviation.com/, https://www.facebook.com/samaritanaviation/); Brandon Buser (URL: https://ethnos360.org/missionaries/brandon-and-rachel-buser, https://www.facebook.com/brandon.buser.35); ABC News (URL: http://www.abc.net.au/news/2018-01-08/tsunami-warning-for-communities-near-erupting-png-volcano/9311544); Google Earth (URL: https://www.google.com/earth/).

Indonesia's Sinabung volcano has been highly active since its first confirmed Holocene eruption during August and September 2010; ash plumes initially rose up to 2 km above the summit, and falling ash and tephra caused fatalities and thousands of evacuations (BGVN 35:07). It remained quiet after the initial eruption until 15 September 2013, when a new eruptive phase began that has continued uninterrupted through February 2018. Ash plumes rising several kilometers, avalanche blocks falling several kilometers down the flanks, and deadly pyroclastic flows travelling more than 4 km have all been documented repeatedly during the last several years. Details of events during October 2017-March 2018, including the largest explosion to date on 19 February 2018, are covered in this report. Information is provided by, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), referred to by some agencies as CVGHM or the Indonesian Center of Volcanology and Geological Hazard Mitigation, the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB). Additional information comes from satellite instruments and local observers.

When activity began in 2010, and again when eruptions resumed in 2013, many news accounts included statements that Sinabung had last been active 400 years ago, or even saying specifically that the last eruption was in 1600 CE. Those claims appear to have been caused by a misunderstanding related to the boundary time that Indonesian volcanologists use to categorize volcanoes. Those volcanoes with historical activity, defined as being about 400 years ago (corresponding to the beginning of the Dutch East India Company era), are in the "Type A" group. Those in the "Type B" group, including Sinabung prior to 2010, have not had reported activity in more than 400 years. Using charcoal associated with the most recent pyroclastic flow, Hendrasto et al. (2012) determined that the last previous eruptive activity was 1200 years before present using carbon dating techniques, or 740-880 CE (at 1 sigma).

Although activity remained high from October 2017 through March 2018, a gradual decline in the overall eruptive activity from the beginning of 2017 was apparent. The number of explosions per month generally declined, with no explosions reported during March 2018, for the first time since August 2013 (figure 45). The thermal anomaly record was similar; periods of high heat flow persisted through mid-November 2017, followed by a gradual reduction in the amount of thermal activity, although the intensity remained consistent, according to the MIROVA project (figure 46). Much of the heat flow was attributed to the dome growth at the summit; the dome was destroyed in the large explosion of 19 February 2018.

Figure 45. The number of explosions per month at Sinabung as reported by PVMBG from January 2017-March 2018. Only partial data was reported for 18-31 January 2018, and no explosions were observed during March 2018.

Figure 46. Thermal anomaly data at Sinabung from satellite-based MODIS instruments, plotted on a Log Radiative Power scale, persisted through the end of 2017 and then decreased in frequency through the end of February 2018. Much of the heat flow was attributed to a dome near the summit which was destroyed in the 19 February 2018 explosion. Graph shows thermal anomalies between 11 May 2017 and 1 April 2018. Courtesy of MIROVA.

Throughout the period from October 2017 through 19 February 2018, steam plumes were constantly rising to heights of 1,000-2,400 m above the summit. Avalanche blocks were ejected daily down the E and S flanks from 500-3,500 m, and multiple pyroclastic flows each month traveled between 1,000 and 4,600 m down the SE flank. Tens of explosions occurred monthly, generating ash plumes that rose from 500 to 5,000 m above the summit. Explosive activity was more intermittent during February than the previous months, until 19 February when the largest explosion to date occurred; it included an ash plume that rose to at least 16.8 km altitude and at least ten pyroclastic flows. In spite of the size of the explosion, no injuries or fatalities were reported as most nearby communities had been evacuated from the ongoing activity. Activity decreased substantially during March 2018; there were no explosions, block avalanches, or pyroclastic flows reported, only steam plumes rising 1,000 m above the summit.

Activity during October 2017-January 2018. During October 2017, steam plume heights reached 1,500 m above the summit. Avalanche blocks traveled down the E and S flanks 500-2,500 m, and eight pyroclastic flows traveled 1,000-4,500 m down the SE and S flanks. Ash plume heights ranged from 500 to 3,600 m above the summit. The Darwin VAAC issued 38 aviation alerts during the month. On 1 October they reported an ash plume drifting both NW at 4.6 km altitude and NE at 3.7 km. The next day, the webcam observed an ash emission that rose to 5.5 km altitude. On 4 October an ash plume was spotted in the webcam rising to 5.8 km altitude and drifting ENE. Later that day it had detached from the volcano and was seen drifting NW in satellite imagery. An ash plume on 5 October rose to 3.9 km altitude and drifted ESE. Two ash emission were reported on 7 October; the first rose to 3 km altitude, the second rose to 4.3 km, they both dissipated quickly. On 8 October, three plumes were reported. The first rose to 4.6 km and drifted WSW, the second rose to 3 km and drifted S and the third rose to 3.4 km and also drifted S. The following day, an ash plume rose to 4.6 km and drifted E. BNPB stated that on 11 October, an event at Sinabung generated an ash plume that rose 1.5 km above the crater and drifted ESE, causing ashfall in several local villages. On 12 October an event produced an ash plume that rose 2 km above the crater and was followed by pyroclastic flows traveling 1.5 and 2 km down the S and ESE flanks, respectively.

PVMBG reported ash plumes rising to 3.7 km on 11, 12, and 13 October 2017. Later on 13 October the Jakarta MWO reported an ash plume at 4.3 km. The next day PVMBG reported an ash plume at 5.5 km altitude. A plume on 15 October rose to 3 km and drifted E. A steam plume on 16 October drifted down the SE flank before drifting SE no 16 October (figure 47). On 17 October, a discrete emission rose a few hundred meters above the summit drifted NE. Later that day, an ash plume was seen in the webcam moving SE at 3.4 km. On 18 October, two ash emissions were reported. The first rose to 3.7 km and drifted E, the second rose to 3.9 km and drifted W. An ash plume rose to 4.6 km altitude on 21 October, and to 3.9 km, drifting S, on 23 October. The next day, three ash plumes were reported; the first rose to 3 km, the second to 4.6 km, and the third to 3.7, all drifting E. After five days of quiet, the webcam observed ash plumes that rose to 4.3 km on 30 October, and to 3.9 km on 31 October. Only two MODVOLC thermal alerts were issued, on 20 and 27 October.

Figure 47. A steam plume drifted down the SW flank of Sinabung before moving SE on 16 October 2017. View is from the SE. Courtesy of PVMBG.

Steam plumes were higher during November 2017, rising 2,400 m above the summit. Block avalanches traveled 500-3,000 m down the E and S flanks most days, and ten pyroclastic flows traveled between 2,000-3,500 m down the ESE and S flanks. The ash plumes rose 700-3,200 m above the summit. The Darwin VAAC issued 41 aviation alerts in November. Near-daily ash plumes were observed mostly in the webcam and occasionally in satellite imagery. They generally rose to 3.4-4.9 km altitude; the most common drift directions were S and SW. A number of times, multiple ash plumes were reported in a single day. On 14 November, four ash plumes were observed. The first rose to 3.7 km, the second and third rose to 4.6 km and drifted S and SSW, the last rose to 3.9 km and also drifted SSW. On 20 November a discrete emission produced an ash plume that rose to 5.5 km altitude and drifted SSW. Three ash plumes were recorded the next day, rising 3.9-4.6 km and drifting in multiple directions under variable winds. An ash plume on 23 November was reported by PVMBG at 6.7 km altitude drifting W, the highest noted for the month. MODVOLC thermal alerts appeared twice on 5 November, once on 14 November, and three times on 17 November.

Activity during December 2017 was similar to the previous two months; steam plumes rose 2,000 m above the summit, block avalanches traveled 500-3,500 m down the E and S flanks numerous times, and nine pyroclastic flows descended the ESE and S flanks distances ranging from 2,000 to 4,600 m. Ash plume heights were from 700-4,000 m above the summit. The Darwin VAAC issued 43 aviation alerts in December 2017. They reported ash plume heights of 3.4-4.9 km altitude on most days. Every day during 10-19 December, ash plumes were reported at altitudes of 4.6-5.5 km drifting SW, E or SE. PVMBG reported ash plumes on 26, 27 and 28 December that rose to 3.9, 5.2, and 5.5 km, respectively. BNPB reported pyroclastic flows on 27 December that traveled 3.5-4.6 km SE, and ashfall was reported in many nearby villages including Sukanalu Village (20 km SE), Tonggal Town, Central Kuta, Gamber (4 km SE), Berastepu (4 km SE), and Jeraya (6 km SE). The highest ash plume of the month rose to 6.4 km altitude on 29 December and drifted E. This was followed by another discrete ash emission the same day that rose to 5.8 km and two plumes the next day that rose to 5.2 km and drifted W. There was only one MODVOLC thermal alert issued on 7 December.

The Darwin VAAC issued 56 aviation alerts for January 2018. Multiple discrete ash emissions were reported on most days. Plume altitudes generally ranged from 3.4 to 5.5 km. A 6.1 km altitude plume was visible in satellite imagery on 18 January (figure 48). The drift directions were highly variable throughout the month. Most plumes dissipated within six hours. Incandescent blocks were reported by PVMBG falling 500-1,500 m down the ESE flank on most days when the summit was visible. They also reported a pyroclastic flow on 27 January that traveled 2,500 m ESE from the summit (figure 49). Three MODVOLC thermal alerts were issued on 6 January, and one on 12 January.

Figure 48. An ash plume rose 3,000 m from the summit of Sinabung on 18 January 2018 in this view looking at the SE flank. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 49. A pyroclastic flow descended 2,500 m down the SE flank of Sinabung on 27 January 2018 while an ash plume also drifts SE in this view of the SE flank. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Activity during February 2018. During most of February, steam plumes rose only 1,000 m above the summit, and avalanche blocks traveled 500-2,500 m down the ESE and S flanks. Far fewer ash emissions were reported than previous months, but the largest explosive event recorded to date took place on 19 February (figure 50). The Darwin VAAC issued 29 aviation alerts during February 2018. Short-lived ash emissions were reported on 1, 3, 5, 11, and 15 February. The ash plume heights ranged from 3.4-4.6 km altitude, and they drifted S or SW.

Figure 50. A very large ash plume rose to 16.8 km altitude from Sinabung on 19 February 2018. Image is from several tens of kilometers from the volcano a few hours after the eruption. No fatalities were reported. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

The large explosion was first reported by the Darwin VAAC at 0255 UTC on 19 February 2018. It produced an ash plume, which was clearly observed in satellite imagery (figure 51), that quickly rose to at least 16.8 km altitude and began drifting NW (figure 52). It also produced a large SO2 plume that was recorded by satellite instruments (figure 53). Over the next 15 hours the plume dispersed in three different directions at different altitudes. The highest part of the plume drifted NW at 13.7 km and was visible over 300 km from the summit. The lower part of the plume drifted S initially at 6.7 km and gradually lowered to 4.3 km; it was visible 75 km from the summit before dissipating. A middle part of the plume drifted NW at 9.1 km during the middle of the day. Three subsequent minor ash emissions were observed on 20 and 25 February that rose to 3.4 km altitude. There were no VAAC reports issued during March 2018. A MODVOLC thermal alert issued on 11 February was the last for several months.

Figure 51. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured this natural-color image of the ash plume at Sinabung at 0410 UTC on 19 February 2018, just a few hours after it began. The ash plume rose over 16 km high and drifted in multiple directions. Courtesy of NASA Earth Observatory.

Figure 52. The large ash plume of 19 February 2018 at Sinabung, viewed here from within a few kilometers of the summit in the first hour or so after the eruption, rose quickly to over 16 km altitude. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 53. Two different Ozone Monitoring Instruments measured the SO2 plume released by Sinabung in the explosion on 19 February 2018. The upper left image was recorded about three hours after the explosions (0616-0621 UTC, 19 February 2018) by the Ozone Mapper Profiler Suite (OMPS) instrument on the Suomi NPP satellite. The upper right image was recorded about 27 hours after the explosion (0619-0802 UTC, 19 February 2018) by the Ozone Monitoring Instrument (OMI) on the Aura satellite, and shows the multi-directional dispersal of the SO2 plume during that time. The lower image uses the data captured at the same time as the upper left image and displays it using different software and detailed background information. The maximum gas concentrations reached 140 Dobson Units. Upper images courtesy of NASA Goddard Space Flight Center, and lower image courtesy of NASA Earth Observatory.

As many as 10 pyroclastic flows were observed during the 19 February explosion, traveling as far as 4.9 km SSE and 3.5 km E (figures 54 and 55). Ash and tephra as large as a few millimeters in diameter fell in areas downwind, including Simpang Empat (7 km SE), the Namanteran district, Pqyung (5 km SSW), Tiganderket (7 km W), Munthe, Kutambaru (20 km NW), Perbaji (4 km SW), and Kutarayat (figure 56 and 57).

Figure 54. A pyroclastic flow traveled several kilometers SSE from Sinabung on 19 February 2018 as tephra fell from the rising ash cloud in this view from several kilometers away to the NE. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 55. The dark gray ash plume rose skyward while the large brown pyroclastic flows traveled SE from Sinabung on 19 February 2018 as viewed from the town of Kutarakyat located 5 km NE of the volcano. Photo by Endro Rusharyanto, courtesy of the Associated Press (AP).

Figure 56. Small tephra fragments fell on the village of Gurukinayan (13 km E) and other villages SE of Sinabung during the eruption of 19 February 2018. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 57. Ash from the eruption at Sinabung on 19 February 2018 covered vegetable plants the following day in the village of Payung (5 km SSW). Photograph by Antara Foto, Ahmad Putra via Reuters.

Villagers were temporarily evacuated from nearby villages, but were able to return a few days later (figure 58). Conditions in five districts were so dark that visibility was reduced to about 5 m. In addition, ashfall was recorded as far away as the town of Lhokseumawe, 260 km N. Magma Indonesia reported that the lava dome that had been growing at the summit for some time was destroyed in the 19 February explosion (figure 59). A PVMBG volcanologist reported the volume of the destroyed lava dome was at least 1.6 million cubic meters.

Figure 58. Villagers from Gurukinayan (13 km E) were evacuated as ash spread over the town from the eruption of Sinabung on 19 February 2018, but they returned to their homes a few days later. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 59. The summit of Sinabung, before (top) and after (bottom) the large explosion of 19 February 2018. The dome size in the upper photo is similar to that shown figure 43 (BGVN 42:12) from September 2017. The lower image was taken within a week after the explosion. Courtesy of MAGMA Indonesia, via Twitter.

Reference: Hendrasto M, Surono, Budianto A, Kristianto, Triastuty H, Haerani N, Basuki A, Suparman Y, Primulyana S, Prambada O, Loeqman A, Indrastuti N, Andreas A S, Rosadi U, Adi S, Iguchi M, Ohkura T, Nakada S, Yoshimoto M, 2012. Evaluation of Volcanic Activity at Sinabung Volcano, After More Than 400 Years of Quiet. Journal of Disaster Research, vol. 7, no. 1, p. 37-44.

Geologic Background. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Sutopo Purwo Nugroho, Head of Information Data and Public Relations Center of BNPB via Twitter (URL: https://twitter.com/Sutopo_PN); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Associated Press (AP), Endro Rusharyanto, Photographer (URL: http://www.ap.org/); Reuters (http://www.reuters.com/).

Ebeko volcano is located on the remote N end of Paramushir Island in the Kuril Islands and contains many craters, lakes, and thermal features. Eruptions and ash plumes were observed at Ebeko in early July 2010 (BGVN 36:07). No additional activity was reported from Ebeko until October 2016, marking the start of the more recent eruptive cycle. New explosive eruptions accompanied by ash fall began on 20 October 2016 through April 2017 (BGVN: 42:08). Explosive eruptions, ash plumes, ash falls were observed and reported at a regular frequency during this reporting period from May through November 2017 (table 4). Eruptions were reported by observations from residents in the town of Severo-Kurilsk, located about 7 km E of Ebeko, by volcanologists and by satellite imagery. The Kamchatkan Volcanic Eruption Response Team (KVERT) is responsible for monitoring Ebeko, and is the primary source of information. The Aviation Color Code (ACC) remained at Orange throughout this reporting period. This color is the second highest level of the four color scale.

Table 4. Summary of activity at Ebeko volcano from May 2017 to November 2017. Aviation Color Code (ACC) is a 4-color scale. Data courtesy of KVERT.

Explosives events, bursts of ash, ashfall, and ash plumes were reported throughout this period, and were quite variable in appearance (figures 12-16). Minor amounts of ash fell in Severo-Kurilsk on 25 April, 2-3, 6-7, 16, and 18 September, and 22 November. Ash plume altitudes during this reporting period ranged from 1.5 to 4 km; with the highest altitude of 4 km recorded on 2 September (table 4).

Figure 12. Ash plume from an explosive event at Ebeko on 15 May 2017. Ash plume altitude reached 2 km. Photo by L. Kotenko, courtesy of Institute of Volcanology and Seismology IVS FEB RAS.

Figure 13. Ash plume from an explosive event at Ebeko on 23 May 2017. Ash plume altitude reached 2 km. Photo by L. Kotenko, courtesy of Institute of Volcanology and Seismology IVS, FEB, RAS.

Figure 14. Ash explosions from Ebeko on 10 August 2017 as seen from Severo-Kurilsk, 7 km E. Photo by V. Rashidov, courtesy of Institute of Volcanology and Seismology IVS FEB RAS.

Figure 15. Ash bursts up to 2 km on 22 August 2017. Photo by T. Kotenk. Courtesy of Institute of Volcanology and Seismology IVS FEB RAS.

Figure 16. Active crater of Ebeko volcano on 13 September 2017. Ash plume altitude reached 2.2 km. Photo by Ivan and Nataliya Cherkashiny. Courtesy of Institute of Volcanology and Seismology IVS FEB RAS.

MIROVA only identified two low-power thermal anomalies in the past year, one in late February 2017 and the other in late March 2017. A weak thermal anomaly was reported by KVERT on 31 July 2017.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Short pulses of intermittent eruptive activity have characterized Piton de la Fournaise, the large basaltic shield volcano on Reunion Island in the western Indian Ocean, for several thousand years. The most recent episode occurred during 31 January-27 February 2017 with an active vent located inside the Enclos caldera on the S flank, about 1 km SE of Château Fort and about 2.5 km ENE of Piton de Bert (BGVN 42:07). The next episode, discussed here, began on 14 July 2017 and lasted for about six weeks. Activity through February 2018 is covered in this report. Information is provided by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) and satellite instruments.

A new fissure eruption began on 14 July 2017 on the S flank inside the caldera about 850 m W of Château Fort and lasted through 28 August. The fissure was initially 450 m long with seven active lava fountains. Within 48 hours the flow had reached its farthest extent, about 2.8 km from the fissure. Activity continued from the southernmost cone of the fissure with three active vents for a few weeks. Surface lava flows diminished, and activity was concentrated in lava tubes flowing SE from the cone with occasional breakouts and ephemeral vents along the flow field. The tremor signal briefly spiked with lava fountains on 16-17 August, and then ceased altogether on 28 August. A brief seismic swarm during 24 August-1 September led OVPF to conclude that magma had moved but did not open a new fissure. Inflation was intermittent through December, and then increased significantly during January before leveling off during February 2018.

Activity during June-July 2017. The brief seismic swarm of 17-18 May 2017 was followed by another brief increase in seismicity during the first few days of June 2017, but no surface eruption was reported. The inflation that occurred during the May event tapered off by early June. The volcano remained quiet until seismicity began increasing on 10 July 2017; this was accompanied by inflation recorded at the GPS stations as well. The observatory (OVPF) noted the beginning of seismic tremors, indicative of a new eruption, around 0050 on 14 July 2017. Webcams revealed that eruptive fissures opened on the S flank of the cone inside the Enclos caldera. A reconnaissance flight conducted later in the morning on 14 July indicated that the eruptive site was located 750 m SE of the Kala-Pele peak and 850 m W of Château Fort, about 2.2 km NE of Piton Bert (Figure 110).

Figure 110. Location of the Piton de la Fournaise eruption that began on 14 July 2017. Courtesy of OVPF/IPGP (Bulletin d'activité du vendredi 14 juillet 2017 à 15h30 Heure locale).

By 0930 that morning, the fissure extended over a total length of approximately 450 m. Seven lava fountains with a maximum height of 30 m were active (figure 111). The fountain farthest downstream began to build a cone with two arms of flowing lava. Satellite measurements indicated an initial flow rate of about 22-30 m³/s at the beginning of the eruption.

Figure 111. A new fissure opened on the S flank of the cone inside the Enclos caldera at Piton de la Fournaise on 14 July 2017. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 14 juillet 2017 à 15h30 Heure locale).

The tremor intensity decreased significantly the following day; this was reflected in the decrease in the flow rates and the distribution of activity on the fissure. Only three lava fountains were active on 15 July 2017 near the downstream end of the fissure; they began to form two small cones with lava flows that merged into a single channel (figure 112). The fountains did not exceed 30 m in height. By 1400 on 15 July the flow front was 2.2 km SE from the fissure. Satellite instrument measurements suggested the flow rate had dropped to two m³/s. Sulfur dioxide anomalies were measured by the OMI satellite instrument during 14-16 July (figure 113).

Figure 112. Lava emerged from two vents and merged into a single flow at the eruptive site at Piton de la Fournaise on 15 July 2017 at 1400 local time. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du samedi 15 juillet 2017 à 16h30 Heure locale).

Figure 113. Sulfur dioxide anomalies were captured by the OMI instrument on the Aura satellite by NASA on 14 (left) and 16 (right) July 2017 at the beginning of the eruption at Piton de la Fournaise. Courtesy of NASA Goddard Space Flight Center.

Tremors fluctuated over the next few days with changes related to the growth and collapse of various the cones along the fissure. On 18 July, there were six active fountains (figure 114). The flow rate remained approximately 1-3 m³/s. Fountains reached 20 m high on 19 July and a third vent was visible forming on the N side of the main cone. During an overflight on 21 July, OVPF noted that all three vents were active, but lava was only flowing SE from the central one (figure 115). Lava tubes had begun to form downstream of the cone, with numerous breakouts creating small lateral expansion arms.

Figure 114. Six fountains were active along the fissure zone on 18 July 2017 at Piton de la Fournaise. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du mardi 18 juillet 2017 à 16h00 Heure locale).

Figure 115. Lava flowed SE from the central vent of three in the fissure zone at Piton de la Fournaise on 21 July 2017. The magmatic gases are drifting SSE to the upper left of the image. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 21 juillet 2017 à 16h30 Heure locale).

OVPF measured the flow dimensions on 22 July as 2.8 km long and 0.6 km wide (figure 116); the flow front had not advanced in the previous seven days. A fourth vent on the N side of the cone was periodically emitting ejecta, and two flows were active; one moving SE towards Château Fort and the other moving towards the SW inside a lava tube. On 24 July OVPF measured the flow rate as 1-4 m³/s, and the total volume of lava to date as 5.3 ± 1.9 million m³. On 25 July 2017, local observers reported that the main vent on the SE flank of the cone was visible, as well as a second vent on the N flank of the growing cone. The main lava channel was clearly visible downstream of the cone with frequent overflows (figure 117), and active flow continued inside the lava tubes.

Figure 116. An outline of the active lava flow at Piton de la Fournainse on 22 July 2017. Base map courtesy of Google Earth. Annotations courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du samedi 22 juillet 2017 à 17h00 Heure locale).

Figure 117. The main lava channel flowed SE from the eruptive vent at Piton de la Fournaise on 25 July 2017. Photo copyright by Cité du Volcan/Arthur Vaitilingom). Courtesy of OVPF/IPGP (Bulletin d'activité du mercredi 26 juillet 2017 à 16h00 Heure locale).

By 30 July the flow intensity had decreased to about half of its original flow rate. The cone continued to grow, but no surface lava flows were observed (figure 118). The main vent rarely produced ejecta. Active lava was flowing in tunnels with a few minor breakouts near the cone. The flow front remained 2.8 km from the eruptive vent.

Figure 118. The eruptive vent of Piton de la Fournaise on 30 July 2017 showed no surface flows, but activity continued in lava tunnels. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du dimanche 30 juillet 2017 à 16h00 Heure locale).

Activity during August 2017-February 2018. The intensity of the tremors associated with the eruption continued to taper off into early August to levels below 20% of what they were at the beginning of the eruption, and this corresponded to a decrease in observed activity in the field. During an OVPF overflight on 2 August 2017 no flows or ejecta from the eruptive cone were seen, but a number of surface breakouts from lava tubes were still visible; the nearest to the cone was 520 m to the SE (figure 119). The main vent was completely blocked, but the smaller vent still had visible incandescence and strong degassing (figure 120).

Figure 119. Lava tubes and small breakouts at Piton de la Fournaise on 2 August 2017 (N to the lower right). The breakouts were several hundred meters SE of the main vent. The eroded cone in the upper right is visible in the upper left of figure 115 showing the relative location compared with the main fissure. See also figure 121 for relative location. 1) A hornito formed from overpressure in an underlying lava tube. 2) A 20-m-long flow from a breakout over an active tunnel. 3) Two ephemeral vents had recently opened in the roof of the tunnel just prior to this photo being taken. 4-5-6) The longest breakout flow observed was 220 m long and began at an ephemeral vent located downstream of points 1, 2, and 3. The flow surface was 10 m wide near 4), spreading out and cooling farther downstream (5 and 6). Incandescent lava was still visible near the flow front (6) in two lobes. 7-8) Two other breakout flows from ephemeral vents 520 meters from the main vent were also visible, 50 and 180 m long, respectively. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du mercredi 2 août 2017 à 16h30 Heure locale).

Figure 120. Visible incandescence and strong degassing were apparent from the smaller vent at the eruptive site on 2 August 2017 at Piton de la Fournaise. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du mercredi 2 août 2017 à 16h30 Heure locale).

Estimates of the flow rates during the first week of August were less than 1-2 m³/s, and the total lava volume emitted on the surface was measured at 7.2 +/- 2.3 million m³. A larger breakout from a tunnel on 5 August was visible in the OVPF webcams and fed a surface flow over several hundred meters for several hours. By 6 August 2017 the activity was focused mainly in lava tunnels with a few surface breakouts, although incandescence was visible from the small vent seen in imagery available in Google Earth (figure 121). Small ejecta was observed during 7-9 August from the remaining active small vent on the N flank of the cone (figure 122).

Figure 121. Imagery from Google Earth captured on 6 August 2017 showed incandescence and degassing from the small vent at the S end of the fissure at Piton de la Fournaise (left plume), as well as degassing from surface breakouts along the still active lava tunnels to the SE. Courtesy of Google Earth.

Figure 122. Only the small vent on the N side of the cone was still incandescent at Piton de la Fournaise on 9 August 2017. N is to the upper right. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du mercredi 9 août 2017 à 17h00 Heure locale).

Observations made on 14 August 2017 indicated lava was still active in tunnels as pahoehoe flows were observed about 2 km from the active vent. A brief increase in seismic and surface activity occurred on 16 August. The Piton de Bert webcam captured short-lived lava fountains at the E edge of the eruptive cone. Seismic tremor intensity increased rapidly and then oscillated during 16-17 August. The minor inflation of the cone that had been observed since 1 August ceased by 18 August. Field measurements on 21 August demonstrated a significant decrease in flow activity since 12 August. The volcanic tremor signal was stable at a low level on 25 August; it decreased significantly on 27 August and disappeared altogether about 0300 local time on 28 August 2017, leading OVPF to conclude the eruptive phase had ended.

A number of indications led OVPF to conclude that two migrations of magma that did not reach the surface occurred between 16 August and 1 September. Increased seismicity began on 16 August and was accompanied by a measured increase in SO₂; satellite measurements showed two areas of inflation SE of the active fissure between 7 and 25 August. A seismic swarm in the same area was recorded during 24 and 25 August (figure 123). Overflights by OVPF on 25 August did not identify any new fissures associated with the seismic events and inflation.

Figure 123. A seismic swarm on 24 and 25 August 2017 at Piton de la Fournaise led OVPF to conclude that magma was moving beneath the surface in an area SE of the active fissure zone. Courtesy of and copyright by OVPF/IPGP (Bulletin mensuel du lundi 2 octobre 2017).

After the seismic swarm, the number of daily seismic events decreased to less than one per day by the end of September 2017. OVPF reported minor inflation during the second half of October along with a slight increase in seismicity. Inflation stabilized in November but increased again during January 2018 (figure 124). A gradual increase in shallow seismicity beneath the summit craters was recorded during the second half of February. It was accompanied by an increase in CO₂ concentrations in the soil as well, which rose to some of the highest levels since measurements began in 2015.

Figure 124. Deformation at Piton de la Fornaise from 14 July 2017 to 28 February 2018. The eruption of 14 July- 28 August 2017 is shown in yellow. The y-axis measures the change in length in centimeters of a N-S line crossing the Dolomieu crater between two GPS receivers. The raw data is shown in black and the blue line is the data smoothed over a week. A rise means elongation and therefore swelling of the volcano; conversely, a decrease indicates contraction and therefore deflation of the volcano. Courtesy of and copyright by OVPF/IPGP (Bulletin mensuel du jeudi 1 mars 2018).

Thermal anomaly data. The MIROVA project thermal anomaly record shows both the episodic nature of the activity and the cooling signature of the flows that continued beyond 28 August 2017 when OVPF noted the cessation of tremors associated with eruptive activity (figure 125). The MODVOLC thermal alerts first appeared on 13 July 2017 and continued persistently with multiple daily alerts until 23 August 2017.

Figure 125. MIROVA thermal anomaly data for Piton de la Fournaise for the year ending 5 January 2018. The eruption of February 2017 had very little cooling after the tremors ceased at the end of February, but the July eruption had significant cooling evident for more than two months after the cessation of seismic tremors on 28 August 2017. Courtesy of MIROVA.

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise (OVPF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Hawaii's Kilauea volcano continued its eruptive activity, intermittent for thousands of years and continuous since 1983, throughout 2017. The summit caldera formed about 500 years ago, and the East Rift Zone (ERZ) has been active for much longer. Lava lakes were intermittent in and around Halema'uma'u crater at the summit until 1982. Lava has been continuously flowing from points along the ERZ since 1983, and the episode 61g flow was still vigorous through the end of 2017. A large explosion within Halema'uma'u Crater in March 2008 resulted in a new vent with a lava lake that has been continuously active through 2017.

The US Geological Survey's (USGS) Hawaii Volcano Observatory (HVO) has been monitoring and researching the volcano for over a century, since 1912. Quarterly Kilauea reports for July-December 2017, written by HVO scientists Carolyn Parcheta and Lil DeSmither, form the basis of this report. MODVOLC, MIROVA, and NASA Goddard Space Flight Center (GSFC) provided additional satellite information about thermal anomalies and SO₂ plumes.

The lava lake inside the Overlook vent at Halema'uma'u Crater continued to rise and fall during the second half of 2017 with no significant lake level changes and a few periods of spattering. The lake level overall was lower at the end of the year than during much of the year, reflecting long-term deflation of the summit. There were no major explosive events from rockfalls, but smaller sloughs of veneer (thin layers of recently cooled lava that adhere to the vent walls) without accompanying explosions were common. Ongoing subsidence at Pu'u 'O'o, especially around the West Pit prompted moves of monitoring equipment, but little else changed at the cone.

The episode 61g lava flow continued with numerous surface breakouts from areas near the vent all the way down over the pali and into the ocean at the Kamokuna delta during July-December 2017. Changes in the subsurface flow in lava tubes contributed to changing locations of surface breakouts, which were still active at the end of the year. The lava flowing into the ocean at Kamokuna slowed and finally ended in November with changes occurring on the delta in the final weeks of its activity.

Activity at Halema'uma'u. For the second half of 2017, activity at the lava lake inside the Overlook crater continued with little change from January-June. The lake's surface circulation pattern was typical, with upwelling in the N and subsidence of the crust along the southern lake margin, but also around the entire edge of the lake depending on the upwelling location (figure 292). There were often "sinks" a few tens of meters from the SW edge of the lake where the crust folds in on itself and sinks, pulling material away from the wall. A noticeable lava veneer buildup often occurred on the southern margin, where the surface crust was most consistently subducting. Short-term spattering events lasted minutes to hours and occasionally altered the surface crust motion by creating localized subsidence. Throughout the period, spattering was often confined to a grotto at the SE sink. On most days, two or more spattering sites were active simultaneously.

Figure 292. Commonly referenced features and geographic nomenclature at the Halema'uma'u lava lake which is inside the Overlook vent at Kilauea. Geographic directions are faded gray arrows inside the lake with white labels N, S, E, and W, and are distinct from nomenclature cardinal directions (black arrows) used in the text. Satellite image from DigitalGlobe taken on 20 October 2017. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

The lava lake level generally rose and fell over periods of hours to days in response to gas-piston action and to inferred changes in summit lava pressure indicated by deflation-inflation (DI) events. There were a few periods with exceptions when the lake level remained constant for many days at a time, heating up the surrounding walls enough to produce thermal cracking and popping sounds. The total range of the lake level varied between 35 and 40 m during July-December 2017, with the highest level about 17 m below the rim in early September (elevation 1,020 m), and the lowest levels, about 57 m below the rim in late July and September (elevation 977 m) (figure 293).

Figure 293. Halema'uma'u lava lake level measurements for 2017 in meters above sea level at Kilauea. X-axis represents the count of the calendar days, 0 is 1 January 2017. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

There were no significant explosive events triggered by rockfalls, but smaller collapses of veneer and the wall were common, particularly during deflationary phases when the lake level was low and exposed larger areas of the walls. A few larger collapses in September 2017 were big enough to change the geometry of the lake slightly (figure 294). The first, on 8 September at 1806 HST, was a collapse of the large ledge attached to the wall in the southern corner of the lake. This event produced a plume containing ash, a composite seismic event, and lake surface agitation. The following day, 9 September, there was another collapse at 0509. This involved an area of the E Overlook rim composed of mainly lithic deposits, directly above the Southeast sink, which produced a dusty plume, a composite seismic event, and lake surface agitation. On 12 September a thin slice of the southwest lake rim collapsed at 1420, producing a dusty plume, an agitated lake surface for about 10 minutes, and a composite seismic event.

Figure 294. Small changes were visible in the geometry of the Overlook vent at Halema'uma'u from veneer and wall collapses in September 2017 at Kilauea. Left image taken 31 May 2017 by T. Orr shows the areas where the largest collapses took place in September 2017. A large shelf collapsed on 8 September, and the other two dates highlight areas where portions of the lake's lithic wall collapsed. The right photo was taken on 21 September 2017 by L. DeSmither. The photo views are looking SE. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for July-September 2017).

An interesting effect observed on two veneer collapses occurred on 24 October 2017 at 1617 and 1623. Both were silent events but were noticed because they visually depressed the lake as they fell in and sent a small "wave" propagating outward before spattering began a few seconds later. The wave did not make it more than half way across the lake in either case, and both spattering events lasted only a few minutes. Several veneer ledges built up and subsequently collapsed around the lakes perimeter but were most notable on the SW corner of the lake. Three collapses, on 5 December at 0400 and 7 December at 1856 and 2024, enlarged the NNE edge of the lake towards true N, but did not produce a spatter deposit or explosion (figure 295). Another rockfall occurred on the N margin of the lake on 23 December 2017 at 1552 and triggered a large spattering event.

Figure 295. View from the SW time-lapse camera at Kilauea into the lava lake at Halema'uma'u showing the locations of two collapses in early December 2017 that expanded the Overlook vent towards the NNE. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

Activity at Pu'u 'O'o. During July-December 2017, there were only minor changes in the main crater of Pu'u 'O'o as recorded by the PO webcam, PT webcam, and the West Pit time-lapse camera. Due to slight subsidence, altered ground, and widening cracks first noted in August, the West Pit time-lapse camera was relocated 20 m to the SE on 12 October, and roughly 25 m further back from the rim on 1 November after new crack expansion was observed.

During the month of August 2017 there was slight subsidence of the W portion of the crater floor, and around 20 August a crack opened up in the S embayment with three heat locations. There appeared to be slight subsidence of the E side of West Pit from the time-lapse imagery spanning 22 November to 12 December. This subsidence accelerated during 15-17 December, but then was slower through the end of the year. The deformation data confirmed subsidence at Pu'u 'O'o, but it seemed to be confined to the land bridge separating the main crater and the West Pit lava pond. The lava pond inside of the west pit rose slightly during the period from around an elevation of 847 m in early August to 849.5 m on 12 December when measured during site visits about every three weeks. A thick surface crust and sluggish plate motion was typical at the lava pond.

The time-lapse camera located on the E rim of the lava pond (through October) captured three rockfalls in July and two in August that disturbed the pond's surface. On 30 September 2017 a collapse of the west pit's SE rim also broke off a portion of the ledge below, as it was impacted by the falling rocks (figure 296). The collapse was large enough to agitate the pond surface for several tens of minutes, and produced a small step in the tilt at the POC tiltmeter.

Figure 296. The West Pit lava pond time-lapse camera at Kilauea's Pu'u 'O'o crater captured the area of the rim that collapsed (circled in upper left corner) at 0054 HST on 30 September 2017. The larger circle shows where the lower ledge broke off as a result of the impact. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for July-September 2017).

The pond surface was also disturbed from rockfalls on 22, 28, and 31 October 2017. The first two events were on the N side of the West Pit rim, and the events on 31 October were on the S side of the rim. A small rockfall that triggered minor spattering was witnessed during an overflight on 1 November (figure 297). After 1 November, when the camera was moved away from the rim, it no longer had direct views of the pond. One of the E spillway spatter cones collapsed into the lava tube that was feeding the 61g flow on 20 November and provided a skylight into the tube for a day before it crusted over. On 12 December, a large talus pile on the NNE side of West Pit was evidence of rock falls near the original time-lapse camera site. The talus, likely resulting from several rock falls, piled up onto the lava coated bench.

Figure 297. A rockfall witnessed at Kilauea's Pu'u 'O'o cone during a 1 November 2017 overflight. A small event on the W side of the pond triggered minor spattering. The surface of the pond had large plates with wide cracks. Left photo by L. DeSmither, right photo by C. Parcheta. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

Activity at the East Rift Zone, episode 61g flow field. The 13 June 2017 breakout that had started on the upper flow field, approximately 1.1 km from the vent, was the largest area of active surface flows on the 61g flow during July-September. Ranging between 2.6–5.8 km from the vent, the breakout significantly expanded the upper flow fields western flow margin. This breakout remained active through the end of September (figure 298). On 26 June 2017 a breakout started near the top of Royal Gardens and quickly advanced down the pali, east of the main flow field. By 6 July the front of the breakout had extended 500 m beyond the pali base with fluid pahoehoe at the front, and a small a'a channel on the steep part of the pali. Slow advancement of the flow placed it approximately 1.5 km from the emergency road near the coast by 9 August before the flow front stalled. When mapped again on 15 August, the closest active flows were about 2.1 km uphill from the road. Intermittently during 1-20 September the breakout produced channelized flows on the steep part of the pali, sometimes as often as every 24 hours. By the end of September active surface flows had advanced to approximately 1.6 km from the emergency road (figure 298).

Figure 298. Changes to the extent of Kilauea's active episode 61g flow field between 2 July and 28 September 2017, showing the flow margin expansion in red. The yellow line indicates the active lava tube beneath the surface flow. During this time, the flow field expanded an additional 165 hectares from the previous 1,007 hectares (as of 2 July), to a total of 1,172 hectares, increasing the flow field area by 16 percent. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for July-September 2017).

Two other breakouts that started near the episode 61g vent were also active during July-September 2017. The 5 March breakout, which had advanced downslope during its 4 months of activity, was weakly active on 10 July, with two small lava pads observed approximately 4.8 km from the vent. By the time of the overflight on 9 August, the breakout was inactive. On 26 July around 1025 HST, a new breakout started about 1.1 km from the vent and remained active through the end of September with flow activity located 1.1-2.5 km from the vent. On 27 August at roughly 0945 a breakout began on the steep part of the pali originating from the main 61g tube. By 1 September the breakout was at the base of the pali and spreading onto the coastal plain. A few other channels were reported on this area of the pali, and activity continued through the end of September with very little advancement across the coastal plain (figure 299).

Figure 299. A view looking NW at the breakouts on the Pulama Pali and the coastal plain of Kilauea's East Rift Zone. The majority of the 61g surface flows that spread across the coastal plain were supplied by the 26 June 2017 breakout (right of the kipuka, green area, center right); the breakout that started on 27 August (left of the kipuka, steaming) supplied a smaller pad of flows closer to the base of the pali. A 'kipuka' is an Hawai'ian term for an "island" of land completely surrounded by one or more younger lava flows. Photo taken on 21 September 2017 by L. DeSmither. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for July-September 2017).

The 26 June 2017 breakout remained active and stable through the end of 2017, forming a tube from its breakout point to midway down the pali on the E side of the 61g flow. The area where breakouts from 5 March, 13 June, and 26 July occurred (1.1 km from vent) also remained intermittently active through the end of 2017 (figure 300).

Figure 300. The lava flow field expansion for the 61g lava flow at Kilauea between 1 October and 31 December 2017. In addition to continued activity from the longer-lived breakouts fueling the expansion shown in red, nearly 90 known shorter-lived surface breakouts occurred, based on observations from webcams, overflights, and satellite data. Changes in the breakout locations are seen in the progression of orange, red, and purple dots after the 61g tube became blocked by a graben collapse on the delta near the end of September (see discussion in next section). The yellow lines indicate lava tube locations underneath the surface flow. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

Numerous overflows originating on the sea cliff began in early October 2017. These breakouts occurred within 310 m of the sea cliff and persisted for nearly a month. There were also approximately 20 short-lived breakouts in October above the sea cliff, each lasting 1-3 days. They were located mostly in clusters on the upper flow field at 1, 2, and 3.5 km from the vent, along the top and base of the pali, and from the coastal tube.

An estimated 35 tube breakouts occurred during November 2017; they typically lasted 2- 10 days, and were located inland of the October breakouts. Locations of activity were in the upper flow field almost entirely between 2 and 3.5 km from vent, with three closer breakouts at 0.5, 0.8, and 1 km from vent. The two active tubes on the pali continued to have breakouts at the top and base of the cliff, but also started breakouts midway downslope (figure 301). At 0805 on 7 November, a viscous breakout occurred approximately 500 m above the sea cliff. The small breakout came directly from the 61g tube and lasted for roughly four and a half days. Another viscous breakout from the tube occurred approximately 950 m upslope of the sea cliff from 18-23 November. A week after that, a third viscous breakout occurred about 2 km from the sea cliff. By the end of November, there was no further breakout activity on the delta or the distal half of the coastal plain.

Figure 301. A pali breakout from the 61g lava tube observed during a 20 November 2017 overflight at Kilauea. The photographer estimated the active breakout at tens of meters across. Photograph by C. Parcheta. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

During December 2017, an estimated 30 breakouts were recorded from the 61g flow tube, however these were often longer, lasting up to a week on the upper flow field, and with near perpetual breakouts on the pali throughout the month, which made quantifying the exact number difficult. A new breakout occurred 500 m from the 61g vent on 1 December and lasted through 20 December. This breakout, and the whole area between 500-1,200 m from the vent, poured lava onto the eastern upper flow field (figure 300). Most of the upper flow field activity was focused very close to the vent, between 350-800 m; additional activity also occurred at the 1 km location and a few continued breakouts were noted from the 2-3.5 km region. The coastal flow field activity was sluggish and mostly a result of the near-constant pali tube breakouts reaching the base. On 9 December a new voluminous breakout began near the top of the pali that burned through the kipuka near the center of the flow field (figures 302 and 303). This major breakout lasted through the end of the year and produced mostly 'a'a channels on the pali with pahoehoe at the pali base. Pali tube breakouts occurred at nearly every elevation but seemed to move higher up the slope as the month came to a close. Activity did not advance more than 400 m from the base of the pali.

Figure 302. A small channel of lava burned through the kipuka on Kilauea's Pulama Pali on 21 December 2017. Figure 299 shows the kipuka on 21 September, still intact. Photograph by C. Parcheta. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

Figure 303. Close up of the 'a'a flow front near the base of the pali at Kilauea, which burned the remaining trees within the kipuka. Photograph by M. Patrick on 21 December 2017. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

Time series thermal maps of the 61g flow field overlaid on all of the tubes mapped from the field to date suggested to HVO scientists that some of the many breakouts during October-December 2017 may have come from reactivation of an earlier tube thought to be inactive since at least April 2017 (figure 304). Breakout locations coincided with the former tube trace, and happened at least five times between 21 September and 5 January 2018.

Figure 304. A time series of thermal maps from overflights at Kilauea with all 61g tubes overlaid. Solid white lines are tubes active as of the image date, indicated by a thermal trace. Long dashed white line is the main (western) tube that became blocked at the end of September 2017. Dotted lines are older tubes from 2016 that were active when the 61g flow first crossed the coastal plain. These tubes were no longer noted in public maps by April 2017. In all thermal maps from October-December 2017, there was activity (indicated by black arrows) located above the older tube down the center of the flow field suggesting to HVO scientists that this tube may have been still producing breakouts from backlogged lava in the system. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

Activity at the East Rift Zone, Kamokuna ocean entry. By the end of June 2017, flows from multiple breakouts had resurfaced the delta of the Kamokuna ocean entry, covering earlier cracks, and building up and steepening the delta's landward side. These surface breakouts continued into early July, but by 10 July several new cracks had appeared, two of which visibly spanned the width of the delta (figure 305). Slumping of the seaward half of the delta and expansion of the cracks was visible in time-lapse camera images until the end of September.

Figure 305. The Kamokuna ocean entry delta at Kilauea with visible large coast-parallel cracks which span most of the delta's width. On the W (left) side of the delta, the largest crack has been partially buried by the 'a'a flow produced by the 19 August 2017 breakout which started on the sea cliff roughly 100 m inland (lighter in color). Photo taken on 1 September 2017 by L. DeSmither. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for July-September 2017).

On 19 August 2017 around 0405 HST a breakout started on the sea cliff approximately 100 m upslope of the ramp, and five minutes later lava was spilling over the sea cliff and onto the delta. The breakout point and the lava falls over the cliff were both on the W side of the 61g tube. The lava produced a small 'a'a flow on the delta (figure 305), during its short-lived activity that lasted roughly 9.5 hours. Late on 19 August, the time-lapse camera also captured two images of littoral explosions in the center of the delta that produced a large spatter deposit on the delta's surface.

Three more sea cliff breakouts started on 23 September 2017. The first was brief "firehose-like" activity that began in the early morning hours. Based on the delta surface flows it produced, activity lasted less than 24 hours. Later views of the cliff face revealed that the "firehose" came out of a narrow horizontal crack E of the ramp, that was less than a meter below the top of the cliff. Later that day, on the sea cliff near the ocean entry, two new breakouts started, one to the E and one to the W of the tube. The E breakout originated roughly 70 m upslope of the sea cliff, and the breakout point had been fractured and depressed. Its thin pahoehoe flow spread out behind the littoral cone and came close to the edge of the cliff but did not spill over. The W breakout was visible in the time-lapse camera images on 23 September from around noon until midnight, producing only a few small dribbles of lava over the sea cliff. The breakout point was roughly 100 m upslope of the sea cliff, and buried the breakout from 19 August with thick, viscous pahoehoe. By the end of September, surface flows again covered much of the delta until most of the cracks were obscured, and only the ramp and a small area of the eastern delta close to the sea cliff were still uncovered.

Beginning in late August 2017, the ocean entry plume started to fluctuate regularly, and the plume was often weak or would briefly shut down. A shatter ring (a raised rim depression that forms over active lava tubes) began forming near the front of the delta on 21 August. By 30 August, the repeated uplifting and subsidence of the delta had broken the surface flows and built up a large rubble pile. On 26 September 2017 a bulge formed on the back half of the delta where the slope was steepest (figure 306). This inflationary feature produced steam and a delta surface flow from a crack at its base.

Figure 306. Changes at the Kamokuna ocean entry at Kilauea between 26 June (left) and 26 September 2017 (right). The delta grew about 1.62 hectares (4 acres) in size, but also thickened from multiple breakouts resurfacing the delta. The delta cracks are not visible in either photo because the delta had been newly resurfaced in both images. Photos taken by L. DeSmither. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for July-September 2017).

HVO scientists concluded that the bulge observed on 26 September 2017 was the result of the formation of a spreading-induced graben in the middle of the delta that obstructed the 61g tube between 23 and 26 September 2017 (figure 307, top row). During the first part of October, additional breakouts from the tube above the sea cliff produced lava falls that poured down on the W side of the tube (figure 307, middle row). A few breakouts in the latter half of October flowed to the E side of the tube (figure 307, bottom row). The delta did not expand much in area during October-December 2017, but it thickened greatly due to the added volume from the lava falls breakouts and several small sluggish breakouts on the delta. The maximum extent that the delta reached was a little over 4 hectares in October, and then it began to shrink from waves crumbling its edges. By the end of December, the delta had lost about 0.4 hectares (1 acre) of land.

Figure 307. Activity at the Kamokuna ocean entry of Kilauea during September-October 2017. Top: before (left, 19 September 2017) and after (right, 26 September 2017) the graben formation induced by delta slumping. The yellow (left) and orange (right) lines indicate the topographic profile through the middle of the delta. Middle: Aerial photograph (left, C. Parcheta) and thermal image (right, M. Patrick) from a 12 October 2017 overflight showing the extent of lava falls both E and W of the tube. Once the tube became blocked, the whole delta was resurfaced by this outpouring of lava. Bottom: The last of the lava falls occurred on the E side of the tube. The western falls had solidified but were illuminated on the left in this image during the first activity of the eastern lava falls. Image taken by the Kamokuna time-lapse camera on 10 October 2017 at 1842. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

The ocean entry was thought to have fully ceased activity shortly after 12 November 2017. The plume had its first pause in activity on 23 September, and quickly resumed but with decreasing vigor. By 26 September the plume was noticeably weaker and beginning to show intermittent pauses, which continued and became more prolonged through 4 November. The following day (5 November) was the first day with no plume visible in the HPcam, and 6 November was the last day an ocean entry plume was visible in the HP webcam. Ocean entry was active and observed during field visits between 6-11 November, but its weak, diffuse plume was not visible to the HP camera. The time-lapse camera stopped taking photos during the end of the Kamokuna delta activity in the late afternoon on 11 November (figure 308). This malfunction was discovered during a field visit on 12 November; the batteries were replaced a week later. The last photo of known lava activity on the delta was taken on 12 November, and the delta was likely completely inactive within a day or two.

Figure 308. Kamokuna delta at Kilauea on 11 November 2017 shortly before the edges began to crumble from the continuous wave action. Photograph by Kamokuna time-lapse camera. Courtesy of HVO (Hawaiian Volcano Observatory Quarterly Report for October-December 2017).

During a 12 December 2017 overflight, an HVO scientist witnessed a collapse of a small portion of the sea cliff east of the tube into a yellow talus pile on the back portion of the delta, removing the evidence of the lava falls.

Satellite thermal and SO₂ data. In addition to field observations, satellite-based thermal and SO₂ data provide important insights into the ongoing activity at Kilauea. The many MODVOLC thermal alerts issued during July-December 2017 show the varying intensity and locations through time of the many breakouts along the episode 61g flow field from near the vent at the base of Pu'u 'O'o all the way down to the Kamokuna ocean entry delta (figure 309).

Figure 309. MODVOLC thermal alert pixels for the episode 61g lava flow at Kilauea during various weeks of July-December 2017. Green grid squares each represent 1 square km. Areas of activity discussed in the earlier text are labelled. Each image represents seven days of thermal alerts. Upper left: 2-8 July 2017, the 13 June breakout expands the upper flow field, and the front of the 26 June breakout has extended beyond the base of the pali. Upper right: 23-29 July 2017, the 26 July breakout appears about 1 km E of the vent, breakouts are active on the pali, and surface flows are active on the Kamokuna delta. Center left: 27 August-2 September 2017, extensive new breakouts along the base of the pali created multiple alerts in that area. Center right: 1-7 October 2017, abundant breakouts just above the delta create lava falls over the delta after the graben formed in late September. Lower left: 12-18 November 2017, many breakouts were observed near the vent and on the pali during November. Lower right: 17-23 December 2017, breakouts were focused on the upper slope and the pali where the kipukas burned up in December, and lava was no longer flowing into the ocean at the delta. Courtesy of HIGP, MODVOLC.

The MIROVA project thermal anomaly graph of distance from the summit also shows the multiple sources of heat at Kilauea and the migration of those sources over time (figure 310). The MIROVA center point for relative distances described here is about 10 km (0.1°) E of Halema'uma'u crater. The anomaly locations at about 10 km distance from this point correspond to both the lava pond at Pu'u 'O'o crater and the Halema'uma'u crater lava lake. Those about 20 km away correspond to the Kamokuna ocean entry. Anomalies that migrate over time between 10 and 20 km distance trace the movement of the many episode 61g flow breakouts between Pu'u 'O'o and the Kamokuna ocean entry during July-December 2017.

Figure 310. The MIROVA project thermal anomaly graph of distance from the summit shows the multiple sources of heat at Kilauea and the migration of those sources from 1 June 2017-15 January 2018. The MIROVA center point for relative distances described here is about 10 km (0.1°) E of western Halema'uma'u crater. The anomaly locations at about 10 km distance (y-axis) correspond to both the lava pond at Pu'u 'O'o crater and the Halema'uma'u crater lava lake. Those about 20 km away correspond to the Kamokuna ocean entry. Anomalies that migrate over time between 10 and 20 km distance trace the movement of the many episode 61g flow breakouts between Pu'u 'O'o and the Kamokuna ocean entry during July-December 2017.

Kilauea emits significant SO₂ that is recorded by both ground-based and satellite instruments. Sulfur dioxide emissions exceeded density levels of two Dobson Units (DU) multiple times every month during the period (figure 311). Increases in SO₂ flux are caused by many factors including increases in the number and size of surface lava breakouts as well as activity at the summit crater.

Figure 311. Sulfur dioxide emissions generally exceeded density levels of two Dobson Units (DU) multiple times every month at Kilauea and are recorded daily in satellite data. Increases in SO2 emissions are caused by many factors including increases in the number and size of surface lava breakouts as well as activity at the summit crater. A few of the SO2 plumes captured by the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite with DU greater than 2 during July-December 2017 are shown. The prevailing winds on Hawaii blow from NE to SW, so plumes generally drift SW. UR: 23 July 2017, UL: 12 September 2017, LR: 9 October 2017 and LL: 28 December 2017. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: http://hvo.wr.usgs.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Nicaragua's San Cristóbal volcanic complex has exhibited sporadic eruptive activity dated back to the early 16th century. More consistent modern record keeping has documented short-lived eruptive episodes every year since 1999. Small explosions with intermittent gas-and-ash emissions are typical. Three single-day explosive events were reported in 2015; a series of explosions on 5 March 2015 generated a 500 m high ash plume, 41 explosions on 6 June 2015 ejected ash 200 m above the summit, and the first of two explosions on 12 June 2015 sent an ash plume 2,000 m above the summit. The next eruption did not occur until 22 April 2016 when 11 explosions were recorded, with the largest sending an ash plume 2,000 m above the summit. Activity from July 2016-December 2017 is covered in this report. Information is provided by the Instituto Nicaragüense de Estudios Territoriales (INETER), and the Washington Volcanic Ash Advisory Center (VAAC).

Following little activity during the remainder of 2016 after the 22 April explosions, small explosions with minor ash were reported in February, March, and April 2017. Significant explosions during 18-19 August sent ash plumes over 200 km W and deposited ash in numerous communities. Seismicity was high during October-December 2017, but ash-bearing explosions were only reported on 7 and 11 November.

After the 22 April 2016 explosions, San Cristóbal remained quiet for the remainder of 2016. In the month's they were measured, 45-72 degassing-type seismic events were recorded. During a field visit on 29 November 2016, new landslides around the crater rim, both inside the crater and down the outer flanks, were observed. These were interpreted by INETER scientists as resulting from a major tectonic earthquake that occurred offshore in mid-November that was felt in nearby Chinandega (16 km SW), and not from volcanic activity.

Seismic activity increased slightly in January 2017 with 100 degassing events recorded. INETER reported 15 small ash-and-gas explosions during 18-19 February and 153 degassing events. There were no reports of ashfall in the nearby communities. Only 27 degassing seismic events were reported in March; three small gas explosions with minor ash occurred on 16, 25, and 28 March 2017.

Eight small explosions with gas and minor ash took place during April 2017 on days 13, 15, 16 and 19, but no damage was reported in nearby communities. Very low values of SO₂ (averaging 147 tons/day) were measured at the end of April 2017, far less than values of 854 and 642 measured in September and October 2016. Degassing-type seismic events increased sharply beginning on 20 April, totaling 1,931 events; they remained elevated through 25 April.

Volcano-tectonic (VT) earthquakes increased significantly to 235 recorded events during May, from values in the single digits earlier in the year. Minor fumarolic activity occurred at the S side of the summit crater on 27 May 2017 (figure 33). Two small gas explosions were recorded on 20 and 27 May, but no ash emissions were reported. A significant increase to 2,349 degasification-type earthquakes was reported during June 2017; slightly fewer (1,981) were reported during July.

Figure 33. Minor fumarolic activity was observed at the S side of the summit crater at San Cristóbal during a field visit by INETER on 27 May 2017. Courtesy of INETER (Boletín mensual, Sismos y Volcanes de Nicaragua, Mayo 2017).

Significant explosions early on 18 August 2017 were observed from Chinandega with notable gas and ash emissions (figure 34), and ashfall was deposited around the region (figure 35). Communities affected by the ashfall were located to the W and SW of the volcano and included Belén, La Mora, La Bolsa, El Viejo (18 km WSW), La Grecia, Realejo (25 km SW) and Corinto (30 km SW). Ash plumes rose between 300 and 600 m above the crater rim and drifted W and SW. Additional explosions occurred the next day but had ceased by 20 August.

Figure 34. Explosion and ash plume at San Cristóbal at 1330 on 18 August 2017. Courtesy of INETER (Boletín mensual, Sismos y Volcanes de Nicaragua, Agosto, 2017).

Figure 35. Ash was collected by INETER scientists from the 18 August 2017 explosion at San Cristóbal. Courtesy of INETER (Boletín mensual, Sismos y Volcanes de Nicaragua, Agosto, 2017).

A small plume was noted in satellite imagery by the Washington VAAC on 18 August 2017 moving NW. Later imagery showed gas and ash drifting W at an estimated altitude of 2.1 km. It extended approximately 265 km W of the summit before dissipating. Ground measurements of SO₂ made during 18-20 August showed increases to a peak of 3,519 metric tons per day on 19 August before dropping back to more typical background values below 700 t/d. INETER scientists used GOES and AVHRR satellite images to identify the maximum extent of the ash plume from the eruptive event. The ash cloud covered the area W of San Cristóbal, approximately 2,960 Km², and extended more than 80 km offshore, with a total length of 125 km and a maximum width of 33 km (figure 36). Seismometers recorded 3,880 degassing-type seismic events during August 2017. Seismicity decreased slightly during September 2017 to 2,604 measured events, of which 2,415 were degassing-type, 187 were VT events, and two explosions were recorded on 1 September, but no ashfall was reported.

Figure 36. The extent of the ash plume from the 18-20 August 2017 eruptive episode at San Cristóbal, identified in satellite imagery by INETER scientists. Courtesy of INETER (Boletín mensual, Sismos y Volcanes de Nicaragua, Agosto, 2017).

An order-of-magnitude increase in seismicity occurred during October-December 2017, with the monthly totals of the numbers of events ranging from 17,000-21,000 (figure 37). INETER reported a series of 14 explosions during the evening of 7 November. Ashfall was reported to the W in Los Farallones, San Agustín, La Mora, El Naranjo and the city of Chinandega. The Washington VAAC subsequently reported an ash plume that models suggested rose to 6.7 km and drifted W on 11 November.

Figure 37. Numbers of daily seismic events at San Cristóbal during October-December 2017. Event types include VT (volcano-tectonic), degasification, and tremor. Note scale in each graph as different symbols and colors are used for the same type each month. Total seismic events for October (top) was 17,815, November (middle) was 19,206, and December (bottom) was 20,925. Ash bearing explosions were reported by INETER on 7 November, and the Washington VAAC reported an ash plume on 11 November that possibly rose to 6.7 km altitude and drifted W. Courtesy of INETER (Boletín mensual, Sismos y Volcanes de Nicaragua, Octubre, Noviembre, Diciembre, 2017).

Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).

Suwanosejima, an andesitic stratovolcano in Japan's northern Ryukyu Islands, was intermittently active for much of the 20th century, producing ash plumes, Strombolian explosions, and ash deposits. Continuous activity since October 2004 (figure 24) has consisted generally of multiple ash plumes most months rising hundreds of meters above the summit to altitudes between 1 and 3 km, and tens of reported explosions. The rate of activity began increasing during 2014; the frequency of explosions and the height of the plumes have continued to increase through 2017, which is covered in this report. Information is provided primarily by the Japan Meteorological Agency (JMA), and the Tokyo Volcanic Ash Advisory Center (VAAC).

Figure 24. Eruptive history at Suwanosejima from January 2003-December 2017. Black bars represent the height of the emissions in meters above the crater rim, gray volcanoes indicate an explosion, usually accompanied by an ash plume, and the red volcanoes represent large explosions with ash plumes. Courtesy of JMA (Suwanosejima volcanic activity report, December 2017).

Activity at Suwanosejima has been persistent and generally increasing during 2014-2017 (figure 25). During 2017, ash emissions rose from a few hundred to nearly 3 km above the Ontake crater rim. Large explosions were reported 32 times by JMA, including 12 during August. Most explosions sent ash emissions to less than 1,000 m above the crater rim, but the highest ash plume, on 3 August 2017, rose 2.8 km above the crater rim, and was the highest recorded since observations began in 2003. Incandescence was observed at the crater from a thermal camera throughout the year and was witnessed locally many times. Many of the explosions, large and small, were heard in the nearby village. Ashfall was confirmed in the village to the SSW on nine different occasions during the year.

Figure 25. Eruptive history at Suwanosejima for 2014-2017. Black bars represent height of steam, gas, or ash plumes in meters above crater rim, gray arrows or volcanoes represent an explosion, usually accompanied by an ash plume, red arrows or volcanoes represent a large explosion with an ash plume, red bars or orange diamonds indicate incandescence observed in webcams. From top to bottom: Eruptive activity during 2014, 2015, 2016, and 2017. Courtesy of JMA (Suwanosejima volcanic activity reports, December 2014, 2015, 2016, and 2017).

Activity during January-April 2017. There were no large explosions at Suwanosejima during January 2017, but occasional minor ash emissions rose as high as 1,300 m above the Ontake crater rim. Incandescence was visible from the webcam on most clear nights. Ashfall was reported in the village 4 km S on 17 and 26 January. The Tokyo VAAC reported ash emissions four times in January. Ash plumes rose to 1.2 km altitude and drifted SE on 4 January; to 1.8 km and drifted W on 5 January; to 1.2 km and drifted S on 16-17 January; and to 2.1 km and drifted SE on 25 January.

In contrast with January, five large explosions were reported by JMA during February 2017. The first, on 9 February, sent an ash plume to 700 m above the crater rim. An ash emission on 18 February rose to 1,200 m above the rim (figure 26). People in the nearby village reported hearing explosions on 18, 20, 27, and 28 February. The largest explosions occurred during 27-28 February when ejecta was scattered 600 m from the crater rim. The Tokyo VAAC reported ash emissions drifting SE several times: on 9 February at 1.5 km altitude, on 16 and 17 February at 1.8 km, and during 27-28 February at 1.5 km.

Figure 26. An ash emission from Suwanosejima was captured by the 'Campground' webcam on 18 February 2017. Courtesy of JMA (Suwanosejima volcanic activity report, February 2017).

Intermittent ash emissions occurred during March 2017, but no large explosive events were reported. Ejecta was scattered around the edge of the crater on 4 March and an ash plume rose 1,000 m. Small ash plumes were noted rising 900 m on 12 and 15 March; explosions were heard in the village on 14 and 16 March, and ashfall was reported there on 25 March. Incandescence was observed at the summit intermittently throughout the month. During a field survey on 21 and 22 March, JMA noted minor thermal anomalies at the Ontake Crater, the N slope of the Ontake crater, and just above the coastline on the E flank (figure 27). The Tokyo VAAC reported ash emissions three times during March; on 3 March ash plumes rose to 1.5-1.8 km altitude and drifted SE and on both 28 and 31 March they rose to 1.8 km altitude and drifted SE and E.

Figure 27. Thermal anomalies were apparent from the Ontake crater (upper left), the north slope of the crater (upper right), and just above the coastline on the E flank (lower left) in this thermal image of Suwanosejima taken on 22 March 2017 from the NE. Courtesy of JMA (Suwanosejima volcanic activity report, March 2017).

Only minor ash emissions and occasional incandescence was reported during April 2017. Two emission events on 1 April sent ash plumes to 1,200 m above the crater rim. A tremor that lasted nine minutes occurred on 11 April and a small seismic swarm was recorded on 13 April. Small explosions were also reported on 17 and 19 April, with the 19 April event heard at the nearby village; another small explosion was reported on 30 April. There were no reports issued by the Tokyo VAAC.

Activity during May-August 2017. Activity increased slightly during May 2017; two large explosions were recorded by JMA. A small explosion was reported on 1 May, and the highest plume rose to 1,900 m above the crater rim on 10 May during a larger event. Incandescence was observed from the local village on 16 May, and explosions were heard from the village on 16 and 18 May, and again on 28 and 29 May; no ashfall was reported. The Tokyo VAAC reported ash emissions on 7, 8, and 10 May. On 7 May they reported an ash plume located 45 km S at 1 km altitude extending SW. A few hours later ash extended N at 1.5 km. An explosion on 8 May sent an ash plume to 2.1 km where it remained stationary over the volcano for much of the day before dissipating. A higher ash plume was reported on 10 May at 2.7 km altitude drifting E.

Small ash explosions occurred at Ontake Crater on 8 and 21 June 2017, but there were no larger explosive events. Ash plume heights rose to only 600 m above the crater rim, and occasional nighttime incandescence was reported. No reports were issued by the Tokyo VAAC. JMA reported that the highest ash plume during July rose 2.1 km above the summit crater on 17 July, but no large explosions were recorded. Incandescence was observed intermittently throughout the month. A small explosion on 2 July sent an ash plume to 1.9 km above the crater rim. Intermittent ash emissions were noted during 17-19, 22 and 25 July. The Tokyo VAAC reported ash emissions during 2 and 16-18 July. They reported the plumes on 2 July at 1.8-2.4 km altitude, extending N for most of the day. A new explosion on 16 July sent an ash plume to 2.7 km altitude that drifted E. Intermittent ash emissions continued to drift E through 18 July at altitudes ranging from 1.8-2.1 km.

Activity increased substantially during August 2017; JMA reported 12 large explosions, nine of which occurred during the last week. Ashfall was reported in the nearby village on 2 August. The highest plume of the month was reported on 3 August, 2.8 km above the crater rim. Explosions were heard in the village on 3 and 19 August. A small explosion was reported on 12 August. Large explosions occurred on 19, 20, and 24 August in addition to the nine events during the last week. A single MODVOLC thermal alert was reported on 18 August, and the MIROVA system reported thermal anomalies during several days of the last week of the month (figure 28). The Washington VAAC reported ash on 1 August that rose to 2.4 km altitude and drifted SW. A higher plume on 3 August rose to 3.7 km and drifted W. They reported another ash plume that first rose to 3.0 km on 24 August; subsequent emissions that day were drifting NE at 2.1-2.4 km altitude. A new plume on 25 August extended E at 2.4 km. Continuing ash emissions from multiple explosions during 28-31 August rose to 1.2-3.0 km altitude and drifted SE.

Figure 28. Log Radiative Power plot from the MIROVA project for Suwanosejima for 24 May 2017-15 February 2018 shows increased thermal activity during late August 2017, and intermittent pulses of activity from late May-September. Courtesy of MIROVA.

Activity during September-December 2017. Four large explosions were recorded during the first week of September 2017, after which a number of smaller ash emission events were reported. Ashfall was reported four times in the nearby village on 2, 4, 29, and 30 September. The Tokyo VAAC reported explosions on 1, 4, 6, and 29 September. The ash plume from the explosion on 6 September rose to 1.5 km altitude and drifted E; on 29 September, it rose to 2.4 km altitude, also drifting E.

JMA reported four large explosions during October 2017. Two explosions occurred on 11 October; one of the ash plumes rose 1,900 m above the crater rim (figure 29). Explosions were heard in the nearby village on 12 and 31 October, and ashfall was reported on 13 October. During the large explosion of 31 October incandescent ejecta was scattered around the crater rim and the ash plume rose 1,900 m. The Tokyo VAAC reported an explosion with ash on 10 October (UTC) that rose to 2.7 km altitude and remained stationary until dissipating a few hours later. They noted that the explosion on 31 October produced a plume that rose over 1.5 km and drifted NW.

Figure 29. An ash plume from an explosion on 11 October 2017 rises 1.9 km above the Ontake crater of Suwanosejima. Courtesy of JMA (Suwanosejima volcanic activity report, October 2017).

JMA reported five large explosions during November 2017. Incandescent ejecta was seen around the crater rim during the explosion of 1 November, and the plume rose to 2 km above the rim. Loud explosions were heard from the nearby village on 3, 5, 6, 15, and 16 November, and ashfall was reported there on 14, 15, and 20 November. A small explosion was reported on 10 November; intermittent explosions with ash plumes rising 700 m were observed on 20 and 21 November. The Tokyo VAAC reported ash plumes at 1.5 km drifting W on 1 and 5 November, and at 1.8 km altitude drifting NW on 10 November, the last VAAC report issued for 2017.

Only small explosions were reported from Ontake crater during December 2017. The highest plume rose 700 m above the crater rim. Small explosions were heard a number of times in the nearby village on 8-9, 11-13, and 26-30 December. JMA scientists visiting during 8-10 December heard intermittent explosions and witnessed incandescence visible to the naked eye. They also observed ashfall in the village on the morning of 10 December. During a field survey on 14 December, no significant changes were noted from the previous survey in March 2017 (figures 30 and 31).

Figure 30. The summit of Suwanosejima with steam rising from Ontake Crater taken from the W on 14 December 2017. Courtesy of JMA (Suwanosejima volcanic activity report, December 2017).

Figure 31. Steam rises from the Ontake Crater of Suwanosejima viewed from the E on 14 December 2017. Courtesy of JMA (Suwanosejima volcanic activity report, December 2017).

Geologic Background. The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit of the volcano is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Manam is a basaltic-andesitic stratovolcano that lies 13 km off the northern coast of mainland Papua New Guinea; it has a 400-year history of recorded evidence for recurring low-level ash plumes and occasional Strombolian emissions, lava flows, pyroclastic avalanches, and large ash plumes. Activity during 2016 included only two episodes of ash emissions, during early March and mid-July, but persistent thermal activity (strongest between March and July 2016) was intermittent throughout the year (BGVN 42:03). Activity from January 2017-January 2018, discussed below, included increased Strombolian activity, lava flows, and ash emissions during February-May 2017 that led to evacuations and concern for local residents. Information about Manam is primarily provided by Papua New Guinea's Rabaul Volcano Observatory (RVO), part of the Department of Mineral Policy and Geohazards Management (DMPGM). This information is supplemented with aviation alerts from the Darwin Volcanic Ash Advisory Center (VAAC). MODIS thermal anomaly satellite data is recorded by the University of Hawai'i's MODVOLC thermal alert recording system, and the Italian MIROVA project; sulfur dioxide monitoring is done by instruments on satellites managed by NASA's Goddard Space Flight Center.

Summary of 2017 activity. A strong surge in thermal activity beginning in mid-February 2017 lasted through mid-June. Low levels of intermittent activity continued for the rest of 2017, with a short-lived increase during late December 2017 and early January 2018 (figure 35). Strong multi-pixel daily MODVOLC thermal alerts began on 17 February and continued through 29 May 2017. Plumes of SO₂ were detected with satellite instruments in late February, early March, and during the second half of May.

Figure 35. The MIROVA project Log Radiative Power signal for Manam increased significantly during late February 2017 and remained elevated through mid-June. Significant ash plumes and Strombolian activity were reported from early March-late May, after which only a few low-level ash plumes were reported through the end of 2017. Log Radiative Power graph of the year ending 17 January 2018. The occasional points shown in black indicate thermal sources located more than 5 km from the summit, and are likely unrelated to volcanic activity. Courtesy of MIROVA.

The first report of ash emissions in 2017 was on 2 March. Activity increased in late March, and again during the second half of April. Most of the many ash plume events that took place during May rose to 2-5 km altitude, but on 4 and 26 May they rose to over 12 km altitude. Ash plumes were noted on only two days during June, and none during July. Minor low-level ash emissions resumed in early and mid-August. The final VAAC report of 2017 was issued on 2 September.

RVO reported incandescent activity, Strombolian explosions, lava and pyroclastic flows, and ash emissions during February-May 2017 from both the Main and Southern craters (figures 36 and 37), and steam-and-gas emissions throughout the year. Activity during late February to mid-April occurred at both craters; most of the activity during late April and May came from Southern Crater. The events of mid-May caused ashfall across the island. Lava flows and pyroclastic flows in mid-April and mid-May led to evacuations from several villages. Incandescence was observed once from Southern Crater in November and once from Main Crater in December.

Figure 36. Activity at Main Crater of Manam during 2017. The five graphs represent the rate (right y-axis) and intensity (left y-axis) of various activity at the volcano. Steam-and-gas emissions were observed throughout the year (bottom graph; green bars, blue circles). Explosions were heard during mid-February-April (second from bottom graph; blue bars, green circles). Ash emissions were reported from mid-February through April, and at the end of May (middle graph; purple bars, black crosses). Incandescence was observed from mid-February-April, once at the end of May and once in early December (second from top graph; black bars, red x's). Incandescent bombs, lava flows or pyroclastic flows were observed during mid-February-April and at the end of May (top graph; red bars, black diamonds). Courtesy of Steve Saunders, RVO.

Figure 37. Activity at Southern Crater of Manam during 2017. The five graphs represent the rate (right y-axis) and intensity (left y-axis) of various activity at the volcano. Steam-and-gas emissions were observed throughout the year (bottom graph; green bars, blue circles). Explosions were heard during February-May and in mid-July (second from bottom graph; blue bars, green circles). Ash emissions were reported from mid-January through May (middle graph; purple bars, black crosses). Incandescence was observed in early January, from late January-May, and once in early November (second from top graph; black bars, red x's). Incandescent bombs, lava flows, or pyroclastic flows were observed from mid-February-mid May (top graph; red bars, black diamonds). Courtesy of Steve Saunders, RVO.

Activity during February-March 2017. After a break during much of December 2016, low-to-moderate pulses of thermal anomalies were recorded briefly by the MIROVA project early in January 2017 (BGVN 42:03, figure 34). Activity increased again in mid-February with stronger MIROVA anomalies and multi-pixel MODVOLC thermal alerts. Sulfur dioxide plumes were released on 25 February and 4 March 2017 (figure 38).

Figure 38. Sulfur dioxide emissions from Manam increased in late February 2017 along with increased thermal activity. SO2 plumes were captured by the OMI instrument on the Aura satellite on 25 February 2017 (left) and 4 March 2017 (right). Another emission, partly obscured, on 4 March is likely from Bagana on Bougainville Island to the SE. Courtesy of NASA Goddard Space Flight Center.

MODVOLC thermal alerts were issued on 13 days during March, many days had 3-6 alerts. The Darwin VAAC issued the first Volcanic Ash Advisory of 2017 on 2 March based on a pilot report of ash extending N of the volcano at 3 km altitude. The next report, on 20 March, indicated an ash plume visible in satellite imagery moving NE at 2.4 km altitude. It extended 80 km E of the summit the following day. Mostly-steam emissions with minor ash content were reported on 23 March, extending 75 km SE at the same altitude.

Activity during April 2017. Intense multi-pixel MODVOLC thermal alerts continued into April 2017; days with multiple alerts included 2, 14, 22-23, and 25-26 April. RVO released a Volcano Information Bulletin on 16 April 2017 noting a sudden increase in RSAM values beginning on 15 April, and indicating that a small-to-moderate eruption was ongoing from Main Crater. Incandescence was visible during most nights of April from both Main and Southern craters. RSAM values increased by two orders of magnitude during 16-17 April (figure 39). During that night, a brief report from Dugulava village on the SE side of the island indicated that large incandescent lava fragments were falling into valleys to the N and SW, accompanied by loud explosions. Strombolian activity at Southern Crater increased on 18 April, and was accompanied by emissions of dark ash plumes that rose a few hundred meters above the crater and drifted NW. Two small pyroclastic flows were channeled into valleys on the SE and SW flanks, and terminated at about 1,000 m elevation. Strombolian activity subsided by late afternoon, but weak gray ash emissions continued. At Main Crater, white-gray ash plumes continued with bursts of incandescence at about 5-minute intervals.

Figure 39. A spike in RSAM values during 16-17 April 2017 coincided with increased Strombolian activity from Southern Crater at the summit of Manam. Courtesy of RVO-DMPGM (Volcano Information Bulletin-No. 06-042017, Issue Date: 19th April 2017).

RVO reported that activity diminished after 18 April but continued at low levels through 21 April; explosions were still heard from both Main and Southern Craters. Both craters were incandescent, but only Southern Crater ejected incandescent tephra, which became briefly intense during the morning of 20 April. Pale gray-to-brown plumes containing minor amounts of ash rose from both craters and drifted SE. RSAM values began to rise again on 22 April, and Strombolian activity continued during 22-24 April (figure 40). According to a news article from 25 April (The National) the Alert Level was raised to Stage 3, and an official on the island noted that evacuations of women and children had begun to Bogia, about 16 km SW on the mainland.

Figure 40. An explosion at Manam on 22 April 2017. Incandescence at the summit and steam emissions are visible beneath the meteoric clouds. Photo: USGS/Landsat-8 OLI. Courtesy of Radio New Zealand.

The Darwin VAAC reported an ash plume at 4.6 km altitude extending about 35 km SE from the summit on 24 April. The next day, an ash plume was observed drifting a similar distance SW at 3 km altitude. The drift direction changed to WSW then W during 26 April, and the plume was last observed about 65 km from the summit. Infrared imagery indicated ongoing activity at the summit.

Strombolian activity and strong, dark-gray ash emissions continued during 24-25 April; activity declined for a few days before the next pulse began during the early morning of 28 April with Strombolian explosions that were heard at the Bogia Government Station. Most of the lava fell back into the crater, but some traveled down the SW and SE valleys, and minor amounts of ash fell on the SE and W parts of the island.

A pulse of moderately-high Strombolian activity occurred from Southern Crater during the early morning of 30 April 2017. The episode lasted about two hours and produced a small pyroclastic flow that was channeled into the SW valley and stopped at about 200 m elevation. Ejected incandescent lava fragments landed mostly within the crater, but some traveled down the SW and SE valleys. Ash and scoria up to 40 mm in diameter fell on the E side of the island in Abaria and Boakure.

Activity during May 2017. The strongest thermal activity of the year was recorded during May 2017. MODVOLC thermal alerts were issued on 4, 5, 9, 13, 14, 17, 18, 25, and 29 May, with 21 alerts issued on 18 May and a single alert on 29 May that was the last issued for the year. RVO reported a Strombolian event from Southern Crater, lasting from about 1700 on 4 May to 0700 the following morning. A lava flow descended into the SW valley to 600 m above sea level, and minor amounts of ash fell in areas stretching between Warisi to the E, Dugulaba on the S, and Boda and Baliab on the NW parts of the island.

The Darwin VAAC reported an ash plume drifting E at 3 km altitude late on 4 May 2017 (UTC). About an hour later, they reported a much higher altitude ash plume moving S from the summit at 12.5 km altitude, in addition to continuous ash moving E at 3 km altitude. The high-level ash plume dissipated after about five hours, but the lower-level emission continued to be visible in satellite imagery drifting E, then NE at least 25 km from the summit through 7 May, after which activity subsided. RVO reported steam-and-gas emissions from Southern Crater on 13 May. Incandescent lava fragments were ejected during the early morning of 14 May, generating a lava flow that traveled down the SW valley to an elevation of 600-700 m.

The next VAAC report, on 14 May 2017, noted an ash plume drifting NW at 4.6 km altitude 35 km from the summit. Later in the day, they reported another short-lived ash plume that rose to 5.5 km altitude drifting almost 100 km W, and a large hotspot over the summit. The lower-altitude plume lasted for another day before dissipating. RVO reported light gray to dark gray ash plumes during 15-18 May. The Darwin VAAC reported multiple plumes moving W at 2.1-2.4 km altitude on 17 May, and continuous emissions extending WNW on 18 May. RVO reported explosive activity on 18 May; a small lava flow traveled down the SW valley, but not as far as the 13-14 May flow. A weak ash emission, which dissipated after a few hours, was reported on 19 May drifting W at 2.7 km altitude. The Darwin VAAC reported that a substantial ash emission on 26 May 2017 was seen in satellite images drifting 55-75 km W at 12.2 km altitude. A second plume from a continuous lower-level eruption was reported later in the day rising to 4.6 km altitude. Both plumes dissipated by the end of the day. Sulfur dioxide emissions were captured by satellite instruments on 18 and 27 May (figure 41).

Figure 41. SO2 plumes from Manam were captured on 18 (left) and 27 (right) May 2017 by the OMI instrument on the Aura satellite. Eruptive activity was reported by RVO and ash emissions were reported by the Darwin VAAC on 18 May, and a large ash emission was reported by the Darwin VAAC on 26 May. Courtesy of NASA Goddard Space Flight Center.

Activity during June-December 2017. Activity decreased significantly after May 2017 and was low for the remainder of the year. RVO noted weak-to-moderate steam plumes on the rare clear-weather days during June; there was no observed incandescence, and very low seismicity. The Darwin VAAC reported an ash plume that rose to 5.5 km altitude and drifted W on 6 June. Later in the day the plume extended WNW at about 2.4 km altitude. It was last observed early on 7 June before dissipating. No further ash emissions were noted by the Darwin VAAC or RVO until 5 August 2017 when the Darwin VAAC observed minor ash emissions moving NW at 2.1 km altitude. The emissions were visible that day and the next before dissipating. A new ash emission was reported late on 7 August, drifting W at 1.8 km altitude for about 8 hours before dissipating early the next day. Another minor plume on 12 August briefly extended 35 km NW at 2.1 km altitude. During 21-22 August, a similar plume was seen at the same altitude. A minor ash emission on 1 September, which also rose to 2.1 km altitude, was only visible for a few hours before dissipating, and was the last emission reported in 2017.

RVO noted incandescence at Southern Crater once in early November, and once at Main Crater in early December. The MIROVA data showed a cluster of thermal anomalies during late December2017 and early January 2018 (figure 35) suggesting a renewed pulse of thermal activity during that time.

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys" channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Radio New Zealand (URL: http://www.radionz.co.nz); The National (URL: http://www.thenational.com.pg).

Periodic eruptive activity at Ecuador's remote Sangay has included frequent explosions with ash emissions and occasional andesitic block lava flows. Eruptive activity from late March to mid-November 2016 included multiple ash emissions and persistent thermal signals through July 2016 (BGVN 42:08). A new episode of ash emissions and thermal anomalies, that began on 20 July 2017 (BGVN 42:08) and lasted through late October 2017, is covered in this report. Subsequent activity through February 2018 included a single ash-emission event near the end of the month. Information is provided by Ecuador's Instituto Geofísico (IG) and the Washington Volcanic Ash Advisory Center (VAAC); thermal data from the MODIS satellite instrument is recorded by the University of Hawaii's MODVOLC system and the Italian MIROVA project.

The first ash plume of the latest eruptive episode at Sangay was reported on 20 July 2017. VAAC reports were issued on 20 and 21 July, eleven days in August, six days in September, and on 13 October. Thermal activity first appeared in a MIROVA plot during the last week of July and continued through 26 October. Multiple MODVOLC thermal alerts were issued between 2 August and 19 October. IG reported that low-energy ash emissions rising 1 km or less above the summit crater were typical throughout the period. They also repeatedly noted two distinct thermal hot spots in satellite data. A single ash emission on 25 February 2018 was the only additional activity through the end of February 2018.

Activity during July-October 2017. The Washington VAAC reported an ash emission on 20 July 2017 that rose to 8.2 km altitude and drifted about 80 km W. A plume was reported on 1 August by the Guyaquil MWO near the summit at about 5.3 km altitude, but was obscured by clouds in satellite imagery. The following day an ash plume was observed at 7.6 km altitude centered about 15 km NW of the summit. An ash emission was reported on 6 August, but was not visible in satellite imagery. The MWO reported an ash emission on 12 August at 6.4 km altitude moving SW, but no ash was detected in satellite imagery under partly cloudy conditions. The Washington VAAC observed an ash plume on 13 August extending around 50 km SW at 6.1 km altitude and a well-defined hotpot. IG reported an ash emission drifting W on 16 August, but clouds obscured satellite views of the plume. Hotspots continued to be observed in shortwave infrared (SWIR) imagery. The Washington VAAC reported an ash plume at 8.2 km altitude on 17 August. The imagery showed an initial puff moving NW followed by several smaller puffs. On 19 August, the Guayaquil MWO reported an ash plume at 5.8 km altitude drifting SW. The next day, another explosion was reported with ash rising again to 5.8 km and drifting W, and a hotspot was observed in satellite imagery.

The Washington VAAC reported a possible ash plume extending 30 km SW of the summit at 7 km altitude on 22 August. It had dissipated the next day, but they noted that a hotspot was visible in SWIR imagery. The next ash plume was reported by the MWO on 1 September at 5.2 km altitude but was not observed in satellite imagery. The next day, the Washington VAAC observed an ash plume at 6.1 km altitude extending 15 km NW of the summit. The Guayaquil MWO reported an ash plume to 7.3 km altitude on 6 September. On 20 September, a possible ash plume could be seen in GOES-16 imagery extending about 150 km W from the summit at 6.1 km altitude. Another plume extended 15 km SW from the summit later in the day at the same altitude. By the end of the day, continuous ash emissions were reported drifting W at 5.8 km altitude. The following day, occasional ash emissions were still reported drifting W and dissipating within 35 km of the summit. A new emission late on 21 September sent an ash plume 25 km W of the summit at 6.1 km altitude. Possible ongoing emissions were reported on 22 September, but not visible in satellite imagery. After three weeks of quiet, the Washington VAAC reported an ash emission on 13 October drifting S at 6.1 km altitude along with a bright hot spot visible for part of the day. This was the last report of ash emissions for 2017.

The eruption that began on 20 July 2017 was characterized by explosions from the central crater and lava emissions from the Ñuñurco dome on the E side of the summit. IG reported two areas of hot spots visible in thermal images during August and September. Around 65 seismic explosions and 25 long-period events were recorded daily during most of this time, along with a few harmonic tremors. Low-energy ash emissions rising 1 km or less above the summit crater were typical. Ashfall was reported to the SW and NW in Culebrillas (75 km SW), and Licto (35 km NW). New lava flows were interpreted to be on the ESE flank by IG based on the repeated hot spots visible in satellite imagery and darkened areas in the snow in the webcam images (figure 20).

Figure 20. A dark streak in the snow near the summit (left side, arrow) of Sangay indicates recent ejecta of blocks or flows on the upper ESE flank of the cone on 1 October 2017. View is from the ECU911 webcam located in Huamboya, 40 km E. Courtesy of IG-EPN (Informe Especial del Volcán Sangay, 2017-2, Continúa la erupción, se observan dos ventos, 4 de octubre del 2017).

Thermal activity measured from satellite instruments support the interpretation of significant lava emissions as blocks or flows at Sangay during late July-October 2017. The MODVOLC system reported 11 thermal alerts beginning on 14 August, 15 during September, and 13 between 3 and 19 October. A similar signal of thermal activity was recorded by the MIROVA system during the same period (figure 21).

Figure 21. The MIROVA project graph of thermal anomalies in MODIS data from Sangay for the year ending on 17 November 2017 (lower graph) clearly shows the period of increased heat flow between late July and late October. The last anomaly appeared on 26 October 2017 (upper graph). Courtesy of MIROVA.

Activity on 25 February 2018. The Washington VAAC reported an ash plume rising to 6.1 km altitude and drifting NE from the summit on 25 February 2018. The plume was visible 170 km NE before dissipating by the end of the day.

Geologic Background. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec ); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Remote Tinakula lies 100 km NE of the Solomon Trench at the N end of the Santa Cruz Islands, part of the country of the Solomon Islands, which generally lie 400 km to the W. It has been uninhabited since an eruption with lava flows and ash explosions in 1971 when the small population was evacuated (CSLP 87-71). The nearest inhabitants live on Te Motu (Trevanion) Island (about 30 km S), Nupani (40 km N), and the Reef Islands (60 km E); they occasionally report explosion noises from Tinakula. Ashfall from larger explosions has historically reached these islands. The last reported evidence of activity came from MODVOLC thermal alerts between August 2010 and October 2012, and observations of incandescent lava blocks rolling into the sea in May 2012. A new eruptive episode with a large ash explosion and substantial SO₂ plume during 21-26 October 2017 is reported below, along with newly available historical newspaper accounts of earlier eruptions.

Reports of ash plumes are issued by the Wellington Volcanic Ash Advisory Center (VAAC); the National Disaster Management Office (NDMO) of the Solomon Islands Government also issues situation reports when significant activity is reported. Satellite data from infrared, visual, and SO₂ monitoring instruments are an important source of information for this remote volcano. News reports from local (and social) media are often the only sources of information for the smaller events. Recently identified 19th- and 20th-century newspaper accounts of eruptive activity witnessed by sailors passing nearby is a valuable new resource for previously unreported events.

Eruption of 21-26 October 2017. Reports of a substantial explosion with an ash plume from Tinakula appeared on social media and in the local press during 22-26 October 2017. Staff from the Lata Met Service Office approached the island by boat on 23 October to make direct observations (figures 17-19). A video clip from the Himawari8 Satellite showing the ash plume explosion was posted by Stephan Armbruster on Twitter on 22 October. The Solomon Islands NDMO issued a situation report on 26 October showing ashfall covering vegetation on the island. According to the NDMO, ashfall was concentrated on the island, although a small amount of ash drifted SE and was reported to briefly contaminate drinking water in several communities in the nearby Reef Islands (60 km ENE) . Ashfall was also reported on Fenualoa Island (50 km ENE) (Radio New Zealand). The eruption was categorized by NMDO as a VEI 3. A team of geologists from NDMO brought seismic monitoring equipment to Tinakula in early November, and measured a high frequency volcanic tremor on 5 November 2017.

Figure 17. View from the SE of the eruption at Tinakula on 23 October 2017 during a site visit by staff from the Lata Office of the Solomon Islands Meteorological Service. Photo by Okano Gamara.

Figure 18. Ash and steam emissions rose from Tinakula on 23 October 2017 during a site visit by staff from the Lata Office of the Solomon Islands Meteorological Service. Photo by Okano Gamara.

Figure 19. Ash emission from Tinakula on 23 October 2017 during a site visit by staff from the Lata Office of the Solomon Islands Meteorological Service. Photo by Okano Gamara.

The Wellington VAAC first reported an ash plume visible in satellite imagery shortly after midnight (UTC) on 21 October 2017. The plume was estimated to be at 4.6 km altitude and drifting N. About 90 minutes later they reported a second eruption with a much higher plume drifting SE at 10.7 km altitude using IR imagery cloud top temperatures to estimate the altitude. They reported ongoing ash emissions visible in satellite imagery drifting SE at 6.1 km altitude throughout the morning, dropping to 3 km altitude by the end of the day. The following day, 22 October, intermittent ash emissions were reported at 3.7 km altitude moving E. By that afternoon, they had dropped to 2.4 km, and had lowered to 1.8 km by late on 23 October. Ongoing low-level ash emission (2.1 km altitude) continued through 25 October; by early on 26 October, there was no further evidence of ongoing activity.

No MODVOLC thermal alerts were associated with this event, but there was a brief MIROVA signal from the MODIS infrared data during 20-23 October 2017 (figure 20). A major SO₂ plume was released from Tinakula on 21 October, and a smaller one was recorded on 28 October as well (figure 21).

Figure 20. Moderate thermal signals were recorded from Tinakula on 20 and 23 October 2017 (top graph) by the MIROVA system that captures MODIS infrared satellite data. Another signal reported during the first week of March 2017 (bottom graph) could also have been an eruptive event, but no other corroborating evidence is available. Courtesy of MIROVA.

Figure 21. Major SO2 plumes from Tinakula and the Vanatu volcanoes of Ambae and Ambrym were released during October 2017. A substantial SO2 plume drifted in several directions from Tinakula on 21 October 2017 (left). Much smaller plumes are also visible from Ambae and Ambrym which are located farther south. On 28 October (right), a smaller SO2 plume was drifting SE from Tinakula while much larger plumes were apparent from Ambae and Ambrym. Data gathered by the OMI instrument on the Aura Satellite. Courtesy of NASA Goddard Space Flight Center.

Summary of activity during 1971-2012. After the 1971 eruption, intermittent ash emissions, lava bombs, and pyroclastic flows were reported by geologists and sailors passing nearby in 1984, 1985, 1989-1990, 1995, and 1999. Infrared MODIS thermal data was first reported as MODVOLC thermal alerts beginning in 2000 and has provided satellite-based confirmation of thermal activity since then. Months with thermal activity included February 2000-May 2001, February 2006-November 2007, September-November 2008, August 2009, and January 2010-October 2012 (figure 22). No additional thermal alerts were issued through 2017. Since 2004, SO₂ data has been gathered by satellite instruments and processed by NASA Goddard Space Flight Center; in February and April 2006 small SO₂ plumes were recorded (figure 23).

Figure 22. Months with MODVOLC thermal alerts from MODIS infrared data for Tinakula, during January 2000-December 2017. The orange boxes indicate months where at least one MODVOLC thermal alert was issued; the number of alerts is indicated inside the square. Months highlighted in green represent contiguous periods of time of three months or greater with no recorded MODVOLC thermal alerts. Pale orange squares indicate months with no MODVOLC thermal alerts issued, but within a three-month buffer of an earlier thermal alert. Data courtesy of MODVOLC.

Figure 23. SO2 emission data captured by the OMI instrument on the Aura satellite indicated small plumes from Tinakula (top center of images) on 12 and 14 February 2006 (top) and 21 and 23 April 2006 (bottom). Small plumes were also visible from Ambrym on 12 February, and from Ambae and Ambrym on 14 February and 21 and 23 April 2006. Courtesy of NASA Goddard Space Flight Center.

Eruption reports during 1868-1932. Reports of eruptions at Tinakula between 1868 and 1932 have recently been found in 19th and 20th century newspaper accounts from Australia and New Zealand (table 6). The accounts describe incandescence, water discoloration of the sea, explosions, ash plumes, and lava flows extending from the summit to the ocean.

Table 6. Newly discovered historical newspaper accounts of volcanic activity from ships passing near Tinakula between 1868 and 1932. This is not a full eruptive history for the time period. Online links provided in the References section. Courtesy of Steve Hutcheon.

References. The Age (Melbourne, Victoria) 10 November 1868, page 2b (URL: http://nla.gov.au/nla.news-article177002744).

The Empire (Sydney, NSW) 27 October 1869, page 2a, (URL: http://nla.gov.au/nla.news-article60895166).

The Sydney Morning Herald (NSW) 19 Februay 1872, page 6a (URL: http://nla.gov.au/nla.news-article13252748).

The Daily Telegraph (Sydney, NSW) 1887 20 July, page 4f (URL: http://nla.gov.au/nla.news-article239817295).

The Daily Telegraph (Sydney, NSW) 1 September 1910, page 7a (URL: http://nla.gov.au/nla.news-article237993807; http://nla.gov.au/nla.news-article15183461 ).

The New Zealand Herald (Auckland, NZ) 27 June 1932, page 6a (URL: https://paperspast.natlib.govt.nz/newspapers/NZH19320627.2.19 ).

The Auckland Star (NZ) 10 September 1932, page 1h (Supplement) (URL: https://paperspast.natlib.govt.nz/newspapers/AS19320910.2.180.6 ).

Geologic Background. The small 3.5-km-wide island of Tinakula is the exposed summit of a massive stratovolcano at the NW end of the Santa Cruz islands. Similar to Stromboli, it has a breached summit crater that extends from the summit to below sea level. Landslides enlarged this scarp in 1965, creating an embayment on the NW coast. The satellitic cone of Mendana is located on the SE side. The dominantly andesitic volcano has frequently been observed in eruption since the era of Spanish exploration began in 1595. In about 1840, an explosive eruption apparently produced pyroclastic flows that swept all sides of the island, killing its inhabitants. Frequent historical eruptions have originated from a cone constructed within the large breached crater. These have left the upper flanks and the steep apron of lava flows and volcaniclastic debris within the breach unvegetated.

Information Contacts: National Disaster Management Office (NDMO), Solomon Islands Government, Prince Philip Highway, Ranadi, Solomon Islands (URL: http://www.ndmo.gov.sb); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: http://so2.gsfc.nasa.gov/index.html ); Radio New Zealand (URL: http://www.radionz.co.nz/international/pacific-news/342267/solomons-pm-calls-for-calm-in-communities-close-to-volcano); Solomon Islands Broadcasting Corporation, SIBC Voice of the Nation, Honiara, Solomon Islands (URL: http://www.sibconline.com.sb/no-its-not-snow-in-the-solomons-its-ash-from-the-tinakula-volcano/); Andy Prata, AIRES Atmospheric Industrial Research and Environmental Solutions, Melbourne, Australia (URL: https://www.aires.space/, https://twitter.com/andyprata/status/922177129944625157); Gamara Okzman Bencarson, Facebook.

Regular monitoring reports about Yasur from the Vanuatu Meteorology and Geo-Hazards Department (VMGD) indicated that the centuries-long eruptive activity continued from mid-June 2017 through January 2018. VMGD volcano bulletins on 21 July, 30 August, 29 September, 31 October, and 8 December 2017, and 30 January 2018, stated that major unrest was continuing, and the Alert Level remained at 2 (on a scale of 0-4). Based on seismic data, explosions continued to be intense. Visitors were reminded of the closed 395-m-radius Permanent Exclusion Zone (figure 48) and that volcanic ash and gas could impact other areas near the volcano due to trade winds.

Figure 48. Oblique aerial photograph of Yasur with an overlay of designated hazard zones that may be closed depending on the level of eruptive activity. Courtesy of Vanuatu Meteorology and Geo-Hazards Department.

During the reporting period thermal anomalies based on MODIS satellite instruments analyzed using the MODVOLC algorithm were numerous every month. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system also detected numerous hotspots every month (figure 49).

Figure 49. Thermal anomalies detected in MODIS data by the MIROVA system (log radiative power) at Yasur for the year ending 23 February 2018. Courtesy of MIROVA.

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department, Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Radio New Zealand (URL: https://www.radionz.co.nz); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

The Kamchatka Volcanic Eruptions Response Team (KVERT) characterized Bezymianny as having weak activity from mid-June 2014 through the end of 2015, including weak or moderate gas-and-steam emissions (figures 17 and 18) and, when not obscured by clouds, weak thermal anomalies (BGVN 41:01). Observations here through May 2017 come from KVERT reports and Tokyo Volcanic Ash Advisory Center (VAAC) advisories.

Figure 17. View of the summit showing fumarolic activity at Bezymianny on 16 September 2014. Photo by Yu. Demyanchuk; courtesy of IVS FEB RAS, KVERT.

Figure 18. Moderate gas-and-steam activity at Bezymianny on 15 April 2015. Photo by Yu. Demyanchuk; courtesy of IVS FEB RAS, KVERT.

Activity during 2016. KVERT reported that weak volcanic activity continued into January 2016, with moderate gas-and-steam activity through 12 December 2016. During this time, satellite data by KVERT showed a weak thermal anomaly over the volcano on most days, although on some days KVERT described the volcano as "quiet." Often the volcano was obscured by clouds.

The Tokyo VAAC reported that on 30 July an ash plume rose to an altitude of 3 km and drifted E, an observation based on information from the Yelizovo Airport (UHPP). Weak fumarolic activity continued in late August (figure 19).

Figure 19. A small, weak, fumarolic plume could be seen rising from Bezymianny on 24 August 2016. Photo by O. Girina; courtesy of IVS FEB RAS, KVERT.

Based on KB GS RAS (Kamchatka Branch of Geophysical Services, Russian Academy of Sciences) data, KVERT noted that seismicity began to increase on 18 November. The thermal anomaly temperature detected in satellite images also increased on 5 December, and then significantly increased on 13 December, probably caused by lava-dome extrusion. This activity prompted KVERT to raise the Aviation Color Code from Yellow, where it had been since 17 July 2014, to Orange (second highest level).

According to KVERT, a gas-and-steam plume containing a small amount of ash drifted about 118 km W on 15 December. The Tokyo VAAC noted that ash plumes rose as high as 6.1 km that same day. KVERT reported strong gas-and-steam emissions during 16-31 December (figure 20); a gas-and-steam plume drifted about 60 km SW on 18 December. A daily thermal anomaly was detected over the volcano.

Figure 20. A strong gas-and-steam plume was seen rising from Bezymianny on 19 December 2016. Photo by V. Buryi; courtesy of IVS FEB RAS, KVERT.

Activity during January-May 2017. According to KVERT, lava-dome extrusion likely continued into January 2017. Strong gas-and-steam emissions continued through 19 January 2017 and a thermal anomaly was detected over the volcano during most days. On 12 January, KVERT noted that activity had gradually decreased after an intensification during 5-24 December 2016, and thus the Aviation Color Code was lowered to Yellow. Thereafter, KVERT characterized the volcano as having moderate gas-steam activity. On 23 February, KVERT reported that the effusive eruption continued and that lava was flowing on the S flank of the lava dome.

On 9 March at about 1330, an explosive eruption occurred (figure 21). Based on webcam observations, at 1454 an ash plume rose to altitudes of 6-7 km and drifted 20 km NE. The Aviation Color Code was raised to Orange. About 30 minutes later, at 1523, an ash plume rose to altitudes of 7-8 km and drifted 60 km NW. KVERT raised the Aviation Color Code to Red, the highest level. Satellite data showed a 14-km-wide ash plume drifting 112 km NW at an altitude of 7 km. Later that day a 274-km-long ash plume identified in satellite images drifted NW at altitudes of 4-4.5 km; the majority of the leading part of the plume contained a significant amount of ash. Lava flowed down the NW part of the lava dome. The Aviation Color Code was lowered to Orange. Ash plumes drifted as far as 500 km NW.

Figure 21. The start of an explosive eruption from Bezymianny was captured in this image taken from a webcam video on 9 March 2017. Video from KB GS RAS; courtesy of IVS FEB RAS, KVERT.

KVERT reported that lava continued to advance down the NW flank of the lava dome during 10 March-21 April, and gas-and-steam plumes rose from the crater. A thermal anomaly was visible most days in satellite images. The Aviation Color Code was lowered to Yellow on 25 May. According to a KVERT report on 26 May, the volcano became quiet after the 9 March episode, although strong gas-and-steam emissions and daily thermal anomalies continued.

Thermal anomalies. Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were almost daily events during January through 2 November 2016, except none were reported in March through 19 May 2016. On many days, multiple pixels were reported (13 pixels on 1 September). The number of events diminished in December (only six days), and except for a brief period during 9-12 March 2017, none were reported after 20 December through at least 26 May 2017.

The Mirova (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, reported several hotspots each month during May-August 2016, with a significant increase in September through early November (figure 22). Numerous hotspots were again reported in December, but only a few in January and February, except for a narrow cluster during the middle of February. In contrast to the MODIS/MODVOLC data, numerous hotspots were reported in March, April, and May 2017. The vast majority of hotspots during the past 12 months were within 5 km of the volcano and were of low power.

Figure 22. Thermal anomalies at Bezymianny recorded by the MIROVA system (log radiative power) for the year ending 5 May 2017. Note stronger frequent activity in the second half of December 2016 and the stronger anomalies associated with the March 2017 activity. Courtesy of MIROVA.

Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Kamchatka Branch of the Geophysical Service, Russian Academy of Sciences (KB GS RAS) (URL: http://www.emsd.ru/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

The remote island of Chirinkotan is in the Northern Kuril Islands at the southern end of the Sea of Okhotsk, about 320 km SW of the tip of Kamchatka, Russia. It is an outlier about 40 km NW of the main Kuril Islands Arc. There have been very few historical observations of activity at Chirinkotan, although there is at least one confirmed 19th century observation of lava flows. A short-lived event that resulted in a small, low-level ash plume-and-gas plume was seen in satellite imagery on 20 July 2004 (Neal et al., 2005). Volcanic activity resumed in mid-2013, with intermittent ash plumes, thermal anomalies, and block lava flows reported through April 2017. The volcano is monitored by the Sakhalin Volcanic Eruption Response Team (SVERT) of the Institute of Marine Geology and Geophysics (Far Eastern Branch, Russian Academy of Science), and aviation alerts are issued by the Tokyo Volcanic Ash Advisory Center (VAAC).

A new eruptive phase began with a likely ash emission on 11 June 2013. Intermittent thermal anomalies and gas-and-steam emissions were reported for the next 12 months, sometimes drifting up to 100 km, usually SE. Renewed thermal anomalies and gas emissions were recorded during clear weather beginning on 21 November 2014. Two ash plumes observed in late July 2015 were the likely sources of fresh ashfall and block lava flows sampled during a visit by Russian geoscientists on 9 August 2015. A gas-and-steam plume on 17 November 2015 was the last activity observed, except for low-level thermal anomalies, until a substantial ash plume was captured in satellite data at 8.8 km altitude over a year later on 29 November 2016. Additional ash plumes were observed in satellite data once in late January, and twice each in March and April 2017.

Activity during May 2013-June 2014. After no reports of activity since July 2004, SVERT observed gas-and-steam emissions in satellite imagery beginning in late May 2013. They raised the Alert Level from Green to Yellow (on the four level Green-Yellow-Orange-Red scale) sometime between 27 May and 10 June. The first likely ash emission was reported on 11 June, followed by a thermal anomaly detected on 13 June. Thermal anomalies continued to be detected by SVERT during June and July 2013. The first MODVOLC thermal alert was reported on 22 July; they were reported monthly after that through 11 December 2013, with several days of multiple-pixel alerts. SVERT also noted thermal anomalies and gas-and-steam emissions during August through December, including plumes drifting 30-60 km SE during 17-19 October, 55-100 km SE during 5-6 November, and more than 50 km SE on 25 November.

From the beginning of January 2014 through early June, persistent thermal anomalies were observed in clear imagery nearly every week by SVERT, along with intermittent steam-and-gas emissions. Several times during March, plumes were observed drifting 80-170 km SE. MODVOLC thermal alerts were reported on 8 February, 4 days in March (four pixels on 8 March), and twice on 27 May. SVERT reported that beginning on 24 May, gas emissions containing ash were detected in satellite images. A decrease in thermal anomalies observed by SVERT led them to lower the Alert Level to Green on 5 June 2014.

Activity during November 2014-July 2015. SVERT raised the Alert Level back to Yellow in late November 2014, citing new thermal anomalies beginning on 21 November followed by intermittent steam-and-gas emissions. A plume was observed drifting 40 km SE on 27 November. A new MODVOLC thermal alert appeared on 4 December. SVERT reported thermal anomalies and diffuse gas-and-steam plumes during December 2014 and January-February 2015. Emissions were detected 3 km above Chirinkotan drifting SE on 5 January 2015. MODVOLC reported two thermal alert pixels on 7 January and one on 10 January.

SVERT briefly lowered the Alert Level to Green between 4 and 20 March when no activity was detected. Thermal anomalies were reported again beginning on 19 March; they were noted weekly along with intermittent gas-and-steam emissions through mid-May when the Alert Level was lowered back to Green again on 19 May.

MODVOLC reported a three-pixel thermal alert on 20 July 2015 (local time). The Tokyo VAAC reported an eruption on 21 July (local time) with an ash plume rising to 3.7 km altitude drifting SE. The plume was observed in satellite imagery for about 2 hours before dissipating. SVERT reported a thermal anomaly and steam-and-gas emissions on 22 July, and the Alert Level was raised to Yellow. Another ash plume was reported by the Tokyo VAAC on 26 July rising to an altitude of 4.6 km and drifting NW for several hours before dissipating.

Expedition during August 2015. Scientists from the Institute of Marine Geology and Geophysics (IMGiG) of the Far Eastern Branch of the Russian Academy of Sciences visited Chirinkotan on 9 August 2015. While there, they observed steaming from a recent blocky lava flow near the coast (figure 3), hiked to the summit, and collected data about volcanic and biological activity on the island. A group of researchers climbed to the edge of the summit crater at 600 m elevation, where clouds prevented clear views of the crater (figure 4), however the strong odor of sulfur and noise from fumarolic activity was noted. The scientists sampled the fresh pyroclastic rocks. When the visibility improved, the depth of the crater was observed to be about 150 m; an extrusive dome in the center had a vent on the top emitting gas.

Figure 3. Steam rising from recent lava flow at Chirinkotan that reached the coastline, 9 August 2015. Courtesy of IMGiG (Diary of the Kurils 2015 Expedition, 7-9 August 2015, http://imgg.ru/ru/news/111 ).

Figure 4. Fieldwork at the summit crater rim of Chirinkotan, 9 August 2015. Courtesy of IMGiG. (Diary of the Kurils 2015 Expedition, 7-9 August 2015, http://imgg.ru/ru/news/111 ).

The upper flank of the volcano was strewn with ash and bombs (from 2-3 cm to several meters in diameter). Scientists observed recently buried and charred living vegetation, and nesting birds freshly killed by volcanic ash and bombs, indicating a very recent event (figure 5). The botanists in the research group noted that all of the vegetation on the upper and middle flanks had been killed 2-3 years ago in a major event, likely during the start of the 2013 eruptive cycle. Ash deposits ranged in thickness from a few centimeters near the coast to 8-15 cm near the summit. During a survey of a pyroclastic flow on the SW coast, scientists noted that it was still hot on the surface (40-60°?) and consisted of block lava, bombs, and volcanic ash (figure 6).

Figure 5. Evidence of recent explosive activity at Chirinkotan. Top: recently burned vegetation from a volcanic bomb on the flank. Bottom: living vegetation buried in recent volcanic ash, 9 August 2015. Courtesy of IMGiG (Diary of the Kurils 2015 Expedition, 7-9 August 2015, http://imgg.ru/ru/news/111 ).

Figure 6. Still-hot debris from a block lava flow on Chirinkotan, 9 August 2015. Courtesy of IMGiG (Diary of the Kurils 2015 Expedition, 7-9 August 2015, http://imgg.ru/ru/news/111 ).

Activity during November 2015-April 2017. As a result of the direct observations of the recent eruption on the island, SVERT raised the Alert Level to Orange on 11 August 2015. There were no further reports available from SVERT until 17 November when gas-and-steam emissions were detected, and the Aviation Color Code was reported as Yellow. SVERT reported on 7 December 2015 that the ACC had been lowered to Green. Although SVERT did not report renewed activity from Chirinkotan until it issued a VONA on 29 November 2016 and raised the Alert Level to Yellow, the MIROVA thermal anomaly detection system indicated intermittent low-level anomalies between late May and early October 2016 (figure 7), indicating a heat source on the island.

Figure 7. MIROVA data of Log Radiative Power at Chirinkotan for the year ending on 31 January 2017 showing a weak but persistent thermal anomaly between late May and early October 2016. Courtesy of MIROVA.

The Tokyo VAAC issued a report of a volcanic ash plume from an eruption on 29 November (local time) 2016. The plume rose to 8.8 km altitude and drifted N. It was observed in satellite imagery for about 9 hours before dissipating. SVERT briefly raised the ACC to Yellow between 29 November and 2 December. They noted that the ash plume was observed drifting 39 km N. A new report of ash emissions came from the Tokyo VAAC on 26 January 2017, with an ash plume at 3.7 km drifting SE observed in the Himawari-8 satellite imagery. SVERT raised the alert level to Yellow on 27 January (UTM) 2017 and also noted ash emissions on 29 January drifting SE to a maximum distance of 105 km. They lowered the Alert Level to Green on 1 February 2017.

A new ash plume was observed by the Tokyo VAAC on 1 March (local time) 2017 at an altitude of 5.5 km. When SVERT raised the Aviation Color Code to Yellow on 2 March, they noted that the plume had drifted 165 km E. They lowered the ACC back to Green on 6 March. The Tokyo VAAC reported a new ash plume at 6.1 km extending SE early on 21 March 2017. SVERT reported the emission at 15 km E of the volcano when they raised the ACC to Yellow a short while later. They noted on 24 March, when they lowered the ACC to Green, that the maximum extent of the ash cloud had been about 50 km SE.

On 31 March 2017, the Tokyo VAAC issued an advisory for an ash plume at 6.7 km altitude drifting E, and SVERT raised the Alert Level to Yellow the next day. They reported the ash plume drifting 165 km NE before dissipating. Another plume on 7 April was observed by the Tokyo VAAC at 3.7 km altitude drifting SE. SVERT reported the plume at 5 km altitude drifting NE. SVERT lowered the ACC to Green on 24 April 2017.

Reference: Neal C A, McGimsey R G, Dixon J, Melnikov D, 2005. 2004 volcanic activity in Alaska and Kamchatka: summary of events and response of the Alaska Volcano Observatory. U S Geol Surv, Open-File Rpt, 2005-1308: 1-67.

Geologic Background. The small, mostly unvegetated 3-km-wide island of Chirinkotan occupies the far end of an E-W volcanic chain that extends nearly 50 km W of the central part of the main Kuril Islands arc. It is the emergent summit of a volcano that rises 3000 m from the floor of the Kuril Basin. A small 1-km-wide caldera about 300-400 m deep is open to the SW. Lava flows from a cone within the breached crater reached the shore of the island. Historical eruptions have been recorded since the 18th century. Lava flows were observed by the English fur trader Captain Snow in the 1880s.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT), Institute of Marine Geology and Geophysics, Far Eastern Branch, Russian Academy of Science, Nauki st., 1B, Yuzhno-Sakhalinsk, Russia, 693022 (URL: http://www.imgg.ru/en/, http://www.imgg.ru/ru/svert/reports); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Institute of Marine Geology and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, (FEB RAS IMGiG), 693 022 Russia, Yuzhno-Sakhalinsk, ul. Science 1B (URL: http://imgg.ru/ru); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Eruptive activity at Dukono has continued since 1933. As previously reported, ash explosions were frequently observed, and thermal anomalies were intermittent, from September 2011 through July 2014 (BGVN 39:06). Similar activity has continued through March 2017. Monitoring is conducted by the Indonesian Center for Volcanology and Geological Hazard (PVMBG, also known as CVGHM) from an observation post 11 km away. The Alert Level has remained at 2 (on a scale of 1-4), with residents and tourists advised to not approach the crater within a radius of 2 km.

PVMBG reported that in March-April 2015 seismicity remained high and consisted of explosion signals, volcanic earthquakes, and tremor, accompanied by roaring heard at the observation post. A powerful explosion on 23 May 2015 was followed by minor ashfall in areas to the E. During 1-5 July 2015 white-and-gray plumes rose as high as 600 m; minor ashfall was reported in northern areas on 1 July. Ashfall was reported in areas from the Galela District to Tobelo town (NNW) in August 2015 and at the observation post in September. Seismicity fluctuated at high levels, with elevated periods during 15-22 August, 28 August-5 September, and 15-25 October 2015.

As summarized by PVMBG, the period from 1 January to 19 December 2016 exhibited white-and-gray plumes rising as high as 1.2 km above the rim of the Malupang Warirang crater, accompanied by roaring heard at the observation post. The eruption plume height generally fluctuated though, was higher during periods in May and from late November into December; ashfall increased during the periods of higher plume heights, and was noted in villages within 11 km N, NE, and SW. Seismicity remained high.

Nearly daily aviation advisories from the Darwin VAAC (Volcanic Ash Advisory Centre) since July 2014 confirmed the PVMBG reports. As identified in satellite imagery, white and gray ash plumes were seen rising to altitudes of 1.5-4 km from the Malupang Warirang crater, and drifting in various directions for tens to hundreds of kilometers. Data compiled from VAAC reports and summarized by month for April 2016-March 2017 (table 15) reveal plume altitudes between 1.5 and 3.7 km with visible drift distances up to 300 km away.

Table 15. Monthly summary of reported ash plumes from Dukono for April 2016-March 2017. The direction of drift for the ash plume was highly variable. Data from Darwin VAAC and PVMBG.

Intermittent thermal anomalies, typically single pixels, were recorded by MODVOLC (table 16) in the months of April and June 2014, January-March 2015, December 2015, and November 2016. MODIS thermal data recorded by the MIROVA system during the year of April 2016-March 2016 (figure 6) showed intermittent low-power anomalies in May and August 2016, and then in every month from October 2016 through March 2017. It should be noted that the MODIS satellite thermal sensors cannot penetrate cloud cover, which is frequent over Dukono much of the year.

Table 16. Thermal anomalies at Dukono based on MODIS data processed by MODVOLC, August 2014-March 2017. Courtesy of Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System.

Figure 6. Thermal anomalies (Log Radiative Power) detected by MODIS and recorded by the MIROVA system for year ending 5 April 2017. Courtesy of MIROVA.

Vistors to the crater in March 2016 photographed ash rising form an incandescent vent (figure 7). Patrick Marcel reported that "the vents at the bottom of the crater emitted a sustained, extremely noisy jet of gas, steam and ash, and ejected incandescent bombs to up to 500 m height. Some of them landed outside the crater rim." The "You&MeTraveling2" blog posted a trip journal that described a late-August 2016 visit to Dukono, including photos and a video looking down into the crater that showed activity similar to that seen by Marcel in March 2016.

Figure 7. View into Dukono's crater on 12 March 2016. Photo by Patrick Marcel (color adjusted from original); courtesy of Volcano Discovery.

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Volcano Discovery (URL: http://www.volcanodiscovery.com/); You&MeTraveling2 (URL: http://youandmetraveling2.com/).

The existence of an anorthoclase phonolite lava lake in the summit crater of Mount Erebus was first reported in 1972, and it has been thought to be continuously active since that time. Antarctica's best known volcano is located on Ross Island, 90 km E of the continent, offshore of the Scott Coast. McMurdo station, run by the United States Antarctic Program, is about 40 km S on the tip of Ross Island (figure 16). During the history of observations, lava lake(s) have generally persisted, although changes in size and shape over time reflect variations in volcanic activity.

Figure 16. On 31 December 2013, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite acquired visible near-infrared images of the western end of Ross Island in austral mid-summer. McMurdo Station is about 40 km S of the summit of Mount Erebus. Courtesy of NASA Earth Observatory.

This report briefly summarizes research activity at Mount Erebus, and volcanic activity observed since 1972. Photographs from expeditions between 2010 and 2016 show more recent activity at the volcano. Observations from MODVOLC data collected from 2000 through 2016 are also discussed.

Summary of research activity. For most years since the 1970's, scientists have visited Erebus during the austral summer (November-February) and gathered samples, taken SO₂ and other geochemical measurements, collected GPS data, and made observations and overflights to evaluate the condition of the volcano.

Seismometers were initially installed by a joint project of United States, New Zealand, and Japanese scientists in 1980-1981. Between 1980 and 2016 as many as 10 seismic stations were recording activity at Erebus; they were monitored by the Mount Erebus Volcano Observatory (MEVO) run by the New Mexico Institute of Mining and Technology (New Mexico Tech). During the early 2000s MEVO also used infrasonic recordings to capture data on the frequency of eruptions. Researchers from New Mexico Tech, the University of Cambridge, and University College London made yearly expeditions there between 2003 and 2016.

The Mount Erebus Volcano Observatory closed in 2016. A final report was submitted to the National Science Foundation (NSF) on the past research and ideas for future research (Mattioli and LaFemina, 2016), and includes a comprehensive list of scientific publications about Erebus. One area of ongoing volcanology research relates to studying the behavior of the lava lake with a variety of on-site monitoring equipment (figure 17).

Figure 17. Radar altimeter installed at the crater rim of Erebus in December 2016. There are two dishes, to both transmit and receive data. Several other devices are seen in the background, all trained on the lava lake on the floor of the crater. Courtesy of the University of Cambridge Department of Geography.

Summary of activity, 1972-2009. During the 1970's, the lava lake was observed to be about 130 m long and oval shaped, producing occasional Strombolian explosions. Bombs up to 10 m in in diameter were ejected near the vent, and ones up to 30 cm in diameter were thrown out over the main crater. Oscillations of the lake level of up to 2 m were observed.

During a period of increased activity between September 1984 and January 1985, several large explosions were recorded by the seismic network, and there were reports of mushroom-shaped clouds rising as much as 2 km above the summit. During September 1984, numerous large explosions sent ejecta as high as 600 m above the summit, and incandescence was visible from 70 km away. Ash also covered the NW flank down to 3,400 m elevation. Observations in October 1984 indicated that much of the lava lake had solidified, and that the surface was covered with ejecta from the recent explosions. Seismicity remained above average through January 1985. During this period of increased activity, bombs averaging 2 m in diameter (but some as large as 10 m in diameter) were ejected up to 1.2 km from within the inner crater. The eruptions were witnessed from 60 km away and explosions could be heard up to 2 km from the volcano (SEAN 11:03). A small lava lake about 15 m in diameter reappeared late in 1985.

Two primary lakes of phonolitic lava, and a third transient lake, were present inside the crater during the late 1980s (see figure 9, SEAN 13:02), and infrequent Strombolian eruptions with small bombs were captured by a remote video camera mounted on the crater rim. Small ash eruptions were observed from an active vent near the lava lakes in January 1991. On 19 October 1993, two moderate phreatic eruptions created a new crater ~80 m in diameter on the main crater floor and ejected debris over the northern crater rim. These were the first known phreatic eruptions at Erebus, and probably resulted from steam build-up associated with melting snow in the crater (BGVN 20:11).

Vent and lava lake eruptions were recorded by MEVO during the late 1990s and early 2000s. The largest peaks in terms of numbers of eruptions were during 1995, 1997, 1998, 2000, and a broad peak beginning in late 2005 that continued into late 2006 (BGVN 31:12).

Activity during 2010-2016. The two primary lava lakes remained active at Erebus. The one in the NE sector of the inner crater has been persistent almost continuously since first reported in 1972. The second lake is more in the center of the main crater and is intermittently active. During a visit in 2010, only the NE sector lake was active (BGVN 36:09). During clear weather, a steady steam plume is often observed (figure 18).

Figure 18. Mount Erebus with a steam plume rising from the summit crater, viewed from the Lower Erebus Hut (LEH), 6 December 2010. Courtesy of Mount Erebus Volcano Observatory.

Visits during 2011-2016 have confirmed the ongoing Strombolian activity and convection at the lava lakes nearly every year. During 2011 the glowing lava lake emitted steam and magmatic gases from the bottom of a vent at the main crater (figure 19). An eruption on 2 January 2012 at the lava lake was captured by the remote video cameras managed by MEVO (figure 20). Several bombs were ejected on 18 December 2013 and landed close to monitoring equipment run by MEVO. Researchers were able to open a hot bomb and see the molten interior (figure 21).

Figure 19. The lava lake at Erebus, photographed in December 2011. Image by Clive Oppenheimer/Volcanofiles; courtesy of Erik Klemetti.

Figure 20. An eruption from the lava lake at Erebus, captured on the MEVO video cameras on 2 January 2012. Courtesy of MEVO and Volcano Discovery.

Figure 21. Several bombs erupted from Erebus on 18 December 2013 and landed close to monitoring equipment run by MEVO. Researchers were able to open a hot bomb and see the molten interior. Images courtesy of Aaron Curtis, MEVO, 18 December 2013 (posted on Facebook).

When UNAVCO (a non-profit university-governed consortium) flew over Erebus in December 2015, steam and magmatic gas plumes indicated that both lava lakes were active (figure 22). The two incandescent crater vents at were observed in greater detail during January 2016 by researchers associated with the University of Cambridge (figure 23).

Figure 22. The crater of Erebus, with active steam plumes from two lava lakes on 7 December 2015, photographed during an overflight by UNAVCO (a non-profit university-governed consortium). Photo by Annie Zaino, UNAVCO (posted on Facebook).

Figure 23. Two lava lakes at Erebus were observed on 14 January 2016 by researchers associated with the University of Cambridge. Lower image is a close-up of the right vent in the upper image. Courtesy of Kayla Iacovino and Tehnuka Ilanko (posted on Facebook).

MODVOLC data, 2000-2016. With the remoteness of Erebus, satellite imagery serves as one of the few year-round tools currently available to assess longer-term activity. The University of Hawaii's MODVOLC thermal alert system has been processing MODIS infrared satellite data since 2000. Mount Erebus has had a strong and nearly continuous MODVOLC signature throughout 2000-2016 (table 3), confirming its ongoing eruptive activity.

Table 3. Number of MODVOLC thermal alert pixels recorded per month from 1 January 2000 to 31 December 2016 by the University of Hawaii's thermal alert system for Erebus. Table compiled by GVP from data provided by MODVOLC. Spurious data from 25 October 2014 was omitted.

The MODVOLC thermal alert data show that thermal activity at Erebus has waxed and waned several times during the 2000-2016 interval (figure 24). Activity was very low during 2000, but increased steadily through mid-2005 to more than 20 times as many annual thermal alert pixels since 2000. Activity dropped off substantially from late 2005 and remained low through early 2007, when another increase began that peaked at an even higher level (2514 pixels during 2009) in mid-2009. Another drop in activity occurred during 2010, and since 2011 there have been fewer than 300 pixels per year, with numbers below 200 for 2015 and 2016.

Figure 24. The number of MODVOLC thermal alert pixels per year, colored by month, reported for Erebus from 2000 through 2016. Activity was very low during 2000, but increased steadily through mid-2005. Activity dropped off substantially from late 2005 through early 2007, when another increase began that peaked at an even higher level in mid-2009. Another drop in activity occurred during 2010, and since 2011, there have been fewer than 300 pixels per year. Data courtesy of MODVOLC.

Another trend in the MODVOLC data is also apparent when the number of pixels are plotted by month, as opposed to year, for this time period (figure 25). From November through February, during the austral summer, the number of pixels per month never exceeds 150 (see table 3, highest value is 125). From March through October, during the Austral winter, the number of pixels recorded per month can be much higher (the highest value is 458). The average number of 'summer' pixels per month (November-February, 2000-2016) is 30. The average number of 'winter' pixels per month for the same period (March-October) is 108, more than three times greater.

Figure 25. The number of MODVOLC thermal alert pixels per month for the period 2000-2016, colored by year. The total average number of pixels per month from 1 March through 31 October (1732) is three times the average total number of pixels per month from 1 November through 28 February (480). Data courtesy of MODVOLC.

References: Mattioli, G.S., and LaFemina, P.C., 2016, Final Report submitted to the National Science Foundation, Community Workshop: "Scientific Drivers and Future of Mount Erebus Volcano Observatory (MEVO)" (URL: https://www.unavco.org/community/meetings-events/2016/mevo/2016-MEVO-Final-Report.pdf)

Geologic Background. Mount Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island. The 3794-m-high Erebus is the largest of three major volcanoes forming the crudely triangular Ross Island. The summit of the dominantly phonolitic volcano has been modified by one or two generations of caldera formation. A summit plateau at about 3200 m elevation marks the rim of the youngest caldera, which formed during the late-Pleistocene and within which the modern cone was constructed. An elliptical 500 x 600 m wide, 110-m-deep crater truncates the summit and contains an active lava lake within a 250-m-wide, 100-m-deep inner crater. The glacier-covered volcano was erupting when first sighted by Captain James Ross in 1841. Continuous lava-lake activity with minor explosions, punctuated by occasional larger strombolian explosions that eject bombs onto the crater rim, has been documented since 1972, but has probably been occurring for much of the volcano's recent history.

Information Contacts: Mt. Erebus Volcano Observatory (MEVO), New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA; Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); The University of Cambridge Department of Geography (URL: http://www.geog.cam.ac.uk/research/projects/lavalakes/); Erik Klemetti, Eruptions Blog, Wired (URL: https://www.wired.com/author/erikvolc/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301-5394 (URL: http://www.unavco.org/); Kayla Iacovino and Tehnuka Ilanko, The Volcanofiles (URL: http://www.volcanofiles.com/).

Volcán de Fuego has been erupting continuously since 2002. Historical observations of eruptions date back to 1531, and radiocarbon dates are confirmed back to 1580 BCE. These eruptions have resulted in major ashfalls, pyroclastic flows, lava flows, and damaging lahars. Fuego was continuously active from June 2014-December 2015. Ash plumes rose to 6 km altitude, ashfall was reported in communities as far as 90 km away, pyroclastic flows descended multiple drainages at least four times, Strombolian activity rose to 800 m above the summit, lava flows descended a few kilometers down five different drainages numerous times, and three different lahars damaged roadways (BGVN 42:05). This report continues with a summary of similar activity during January-June 2016. In addition to regular reports from INSIVUMEH, the Washington Volcanic Ash Advisory Center (VAAC) provides aviation alerts. Locations of towns and drainages are listed in table 12 (BGVN 42:05).

Daily weak and moderate explosions generating ash plumes to about 800 m above the summit (4.6 km altitude) that dissipated within about 10 km were typical activity for Fuego during January-June 2016. In addition, ten eruptive episodes were recorded during this time. Each episode lasted 24-72 hours, with all but one including incandescent material rising 200-400 m above the summit feeding lava flows down the larger drainages for several kilometers. Most also included pyroclastic flows down the larger drainages. One of the episodes consisted of only large pyroclastic eruptions (with an accompanying ash plume) that issued directly from the summit crater and down the ravines; all included ash plumes rising over 5 km in altitude. Several lahars were reported during late April-June.

Activity during 30 December 2015. INSIVUMEH reported a significant increase in activity on 30 December 2015. A series of pyroclastic flows descended the Las Lajas and El Jute drainages on the SE flank, and a dense ash plume rose to 5 km altitude and drifted 20 km W. Ashfall was reported in multiple communities on the flanks, including Panimache I and II (8 km SW), Morelia (9 km SW), and Santa Sofía (12 km SW).

Activity during January 2016. Two eruptive episodes with explosions that generated ash plumes, pyroclastic flows, Strombolian activity, lava flows, and ashfall were documented by INSIVUMEH during January 2016. The first eruption began with an increase in seismicity early in the morning of 3 January. Moderate to strong explosions were accompanied by an ash plume that rose to 4.8 km altitude (about 1 km above the summit) and drifted W and SW. Two lava flows emerged from the summit crater and traveled down the Las Lajas and Trinidad ravines. Moderate to strong explosions continued during 3 January. By the afternoon, dense plumes of ash were reported at 6 km altitude drifting SW and SE more than 40 km. Ashfall was reported in the villages of Panimaché I and II, Morelia, Santa Sofia, El Porvenir, La Rochela, Osuna, El Zapote and Rodeo. Also later in the day, incandescence was observed 400 m above the crater; it fed three lava flows in the Santa Teresa, Trinidad, and Las Lajas canyons that reached 2.5 km in length. Eruptive activity diminished after about 37 hours with weak bursts of ash rising to 4.6-4.7 km altitude on 5 January that drifted S, SW, and SE.

A smaller explosive event during 15-17 January produced block avalanches and created ash plumes that rose 450-750 m above the crater and drifted up to 12 km N and NE; four to five explosions per hour were detected. The second eruptive episode began with increased activity on 19 January; incandescent material was ejected 400-500 m above the summit, generating new lava flows to the same three canyons as the earlier eruption (Santa Teresa, Trinidad and Las Lajas) (figure 36). Ash emissions rose to 4.9 km altitude and drifted NE. Pyroclastic flows also descended the Las Lajas and El Jute canyons (figure 37).

Figure 36. Lava flows towards Las Lajas Canyon on 19 January 2016 as viewed from the SE flank. Courtesy of INSIVUMEH-OVFGO (Informe Mensual De La Actividad Del Volcán Fuego, January 2016).

Figure 37. A pyroclastic flow descends towards the Las Lajas and El Jute ravines on the SE flank of Fuego on 19 January 2016 in this thermal image captured by INSIVUMEH. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, January 2016).

The second episode continued throughout 20 January 2016 when the largest ash plume rose to 6.7 km altitude and drifted NE more than 90 km according to the Washington VAAC. Ashfall was reported in San Miguel, Las Dueñas, Alotenango, Acatenango, and Antigua. Ash plumes from the pyroclastic flows also generated ashfall on the S and SW flanks (figure 38). By the morning of 21 January, the lava flows had ceased advancing at about 3 km length, although a hot spot was still clearly visible in satellite imagery. Weak explosions generated ash plumes that rose only a few hundred meters above the summit and drifted NNE. During January, the Observatorio del Volcan de Fuego installed a second webcam on the SE side of Fuego at the Finca La Reunión, a resort about 8 km from the summit. The first webcam is located about 10 km SW of the summit at the Observatorio del Volcan de Fuego in the community of Panimache.

Figure 38. A pyroclastic flow on 20 January 2016 travels down the SE flank of Fuego, creating an ash cloud in the ravine. Additional ash emissions drifted in multiple directions. A recent lava flow is also visible in the ravine. View is from the La Reunión webcam, 8 km SE of the summit. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, January 2016).

Activity during February-March 2016. Explosions increased in number and energy on 5 February 2016, classified by INSIVUMEH as the 3rd episode of the year. Six moderate to strong explosions per hour were reported, sending ash emissions to 4.5 km altitude, drifting W, NW, and N more than 12 km, and avalanche blocks down the flanks to the base. The third eruptive episode of the year began with moderate explosions on 9 February 2016; it generated ash plumes which rose to 4.7 km altitude and dispersed up to 35 km NNW. Ashfall was reported in Chimaltenango, Zaragoza, Ciudad Vieja, San Pedro las Huertas, San Miguel Las Dueñas, San Juan Alotenango, Antigua Guatemala and the Capital City as far as 35 km N and NE. The explosions were accompanied by incandescent material rising to 300 m above the summit and feeding lava flows that traveled towards the Trinidad, Las Lajas, and Santa Teresa canyons, reaching lengths of 800 to 3,000 meters (figure 39).

Figure 39. Incandescence rises 300 m above the crater at Fuego, generating lava flows down the Trinidad, Las Lajas and Santa Teresa canyons on 9 February 2016. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Febrero 2016).

The following day (10 February 2016), pyroclastic flows descended the El Jute and Las Lajas ravines (figure 40) while ash plumes rose to 5.2 km altitude and incandescent material was ejected 400 m above the crater. Although activity decreased throughout the day, explosions continued to generate ash plumes to 4.9 km altitude that dispersed ash up to 45 km N and NE. Minor ash emissions were reported by the Washington VAAC on 17 February at 4.6-4.9 km altitude drifting SE about 40 km, and on 24 February at 4.6 km drifting about 25 km SW.

Figure 40. Pyroclastic flows descend the Las Lajas and El Jute ravines at Fuego on 10 February 2016 as viewed from the webcam at Finca la Reunión, 8 km SE. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Febrero 2016).

On 29 February 2016, moderate to strong explosions at a rate of 6-10 per hour were heard more than 14 km away. They were accompanied by an ash plume that rose to 4.8 km and drifted 12 km E, and a lava flow that traveled 500 m towards Las Lajas ravine. This 4th eruptive episode (according to INSIVUMEH) lasted more than 72 hours (figure 41). On 2 March, several ash plumes rose to different altitudes and dispersed in different directions. The largest ash plume, was observed by the Washington VAAC at 7.3 km altitude; it was visible 400 km N before it dissipated into weather clouds. Lower altitude plumes rose to 4.6 km and drifted 75 km SW before dissipating. Ash fell in the communities of Morelia, Santa Sofia, La Rochela, Panimaché I and II, Sangre de Cristo, La Soledad and Yepocapa. The incandescent activity fed two lava flows; the first in the direction of Las Lajas reached 3 km, the second flowed towards El Jute ravine and reached 2 km in length. Pyroclastic flows also travelled down these two canyons and block avalanches descended the Honda Canyon. Explosive activity diminished during 3-6 March; ash emissions rose to 550 m above the summit and drifted 8-10 km W, SE, and SE.

Figure 41. RSAM values spiked at Fuego during 29 February-3 March 2016 during eruptive episode 4. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Marzo 2016).

During 10 March 2016, moderate to strong Vulcanian explosions generated an ash plume that rose to 4.4 km altitude and drifted E. The Washington VAAC observed ash emissions in multispectral satellite imagery on 15 March at 4.3 km altitude extending about 80 km SW from the summit as well as hot spots and pyroclastic flows visible in the INSIVUMEH webcam. An increase in activity on 21 March generated weak and moderate explosions that produced ash plumes that rose to 4.3-4.7 km and drifted W. This activity was recorded as an increase in RSAM tremor amplitude and duration at the FG3 seismic station, but was not considered an eruptive episode by INSIVUMEH (figure 42).

Figure 42. Increases in RSAM tremor amplitude and duration at Fuego were recorded during 21 and 22 March, and eruptive episode 5 was recorded during 26 and 27 March 2016. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Marzo 2016).

Eruptive episode 5 began on 26 March 2016 and lasted more than 24 hours (figure 42). Strombolian eruptions rose up to 500 m above the crater (figure 43), feeding three lava flows that traveled 2 km down Las Lajas, 1.3 km down the Santa Theresa, and 1 km down the Trinidad ravines. Ash plumes rose to 6.1 km altitude and drifted up to 150 km W (figure 44); ash fell on the villages of Morelia, Santa Sofia, San Predro Yepocapa, Panimaché I and II. By the end of 27 March, eruptive activity had diminished to background conditions, which included weak and moderate explosions generating ash plumes to about 800 m above the summit (4.6 km altitude) that dissipated within about 10 km WSW. On 29 March ashfall was reported Sangre de Cristo and Panimaché I and II.

Figure 43. Strombolian activity rises 300 m above the crater at Fuego on 26 March 2016. Photo by Gustavo Chigna, courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Marzo 2016).

Figure 44. An ash plume at Fuego rose to over 6 km altitude on 26 March 2016 and drifted 150 km W before dissipating. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Marzo 2016).

Activity during April-May 2016. The Washington VAAC reported diffuse volcanic ash emissions in satellite and webcam imagery on 2 April 2016. The ash plume drifted W at 4.3 km altitude, and extended 75 km from the summit before dissipating. Increased eruptive activity during 6-7 April 2016 resulted in moderate and strong explosions which produced ash plumes rising to 4.6-4.8 km altitude that drifted W and SW 15 km. The explosions were audible more than 20 km from the volcano; roofs and windows vibrated within 12 km. INSIVUMEH received reports of ashfall from the villages of Morelia, Sangre de Cristo, and Panimche I and II.

An explosion on 8 April created an ash plume that rose to 5.8 km and drifted SSW about 35 km. Successive bursts of ash on 9 April rose to 4.9 km altitude and drifted W. Emissions on 11 April were reported at 4.3 km altitude about 15 km SW from the summit; the next day they rose to 4.9 km and drifted SW to a distance of 45 km. INSIVUMEH reported variable activity beginning on 11 April with high levels of explosive activity on 12 April marking the beginning of the sixth eruptive episode of the year, which lasted for three days. An incandescent fountain persisted 100-300 m above the crater and fed two lava flows during the event; one traveled 2 km down the Las Lajas ravine, and the other reached 1 km in length in the Santa Teresa ravine. Avalanches were constant along the flanks during this episode. Continuous ash emissions were observed as well; plumes generally rose no higher than 5.8 km (2 km above the summit). Ashfall was reported in La Rochela, Ceylon, Morelia, Hagia Sophia, Sangre de Cristo, Panimaché I and II. On 13 April the ash plume extended 185 km SW from the summit. A brilliant hotspot was observed in satellite imagery on 14 April after which no further VAAC reports were issued until early May. On 29 April, after more than a week of rain, a lahar descended the Las Lajas drainage but no damage was reported.

Activity at Fuego increased significantly during May 2016, and included three eruptive episodes that generated ash plumes, pyroclastic and lava flows, and increased rainfall that resulted in lahars. Ash plumes rose above 5.5 km altitude (more than 2 km above the summit) and dispersed to the S, SW, and SE. Seismic activity increased on 5 May in the form of internal vibrations caused by lava which flowed more than 1.2 km down the Las Lajas ravine, and moderate to strong explosions that produced ash plumes which rose to 4.8 km altitude and drifted S for 12 km. The Washington VAAC reported diffuse ash extending 65 km SE from the summit.

The 7th eruptive episode of the year began on 6 May 2016 with incandescent material rising 300 m above the summit crater, causing two lava flows. One traveled down Las Lajas ravine more than 3 km; the second descended the Trinidad ravine for 1.5 km. Block avalanches were constant around the crater rim. The episode lasted for more than 32 hours (figure 45); the moderate to strong explosions ejected ash to altitudes above 5.5 km that drifted S and SW. Ashfall was reported in Escuintla and its surroundings. There were no pyroclastic flows during this episode. The Washington VAAC reported emissions extending 65 km SE of the summit at 5 km altitude on 6 May.

Figure 45. RSAM values during 2 May-6 June 2016 helped INSIVUMEH to define eruptive episodes for 2016 at Fuego, along with observed activity. Eruptive episode 7, consisting of Strombolian activity, lava flows, and ash plumes, occurred during 6-7 May 2016. Episode 8 comprised ash plumes and several large pyroclastic flows that descended the S flank during 18 and 19 May, but no seismic explosive activity. Increases in explosive activity on 21 May marked the beginning of episode 9, which lasted through 23 May 2016 and included incandescent fountains, lava flows, and ash plumes. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Mayo 2016).

The next eruptive episode (8) did not involve seismic explosive activity (figure 45). Instead, several large pyroclastic flows overflowed the crater rim on 18 and 19 May 2016 and descended the flanks towards Las Lajas and Honda ravines (figure 46) resulting in ashfall reported to the S, SW, and W, in villages more than 30 km away. A large ash plume reached more than 5.5 km altitude and drifted 15 km SSW on 19 May (figure 47). Ashfall was reported in the villages of El Rodeo, La Rochela, Osuna, Panimaché, Morelia, Sangre de Cristo and Yepocapa. By late in the day, the Washington VAAC noted that the plume was centered about 90 km SW at 5.8 km altitude.

Figure 46. A pyroclastic flow descends Las Lajas ravine on the S flank of Fuego on 18 May 2016 in these images taken from Finca La Reunión. Lower photo by Basilo Sul, both images courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Mayo 2016).

Figure 47. An ash plume drifts SW from Fuego on 19 May 2016 after a series of pyroclastic flows and ash emissions sent ash plumes to over 5 km altitude. The Operational Land Imager instrument on Landsat 8 captured this image. Courtesy of NASA Earth Observatory.

The ninth eruptive episode of 2016 generated incandescent fountains 200-300 m above the summit; they fed a 2-km-long lava flow down the Las Lajas ravine (figure 48). Seismic activity began to increase on 21 May and lasted through 23 May (see figure 45). Moderate and strong explosions created an ash plume that rose to 5.5 km altitude and drifted SW and W. The Observatory reported ashfall in Morelia, El Porvenir, Santa Sofia, Los Yucales, Panimaché I and II. The Washington VAAC reported an ash plume visible in satellite imagery at 5.5 km altitude, drifting 75 km S beyond the coast on 23 May 2016. A lahar descended the Las Lajas ravine on 20 May and was recorded by the seismic station FG3, but no damage was reported.

Figure 48. Landsat band 7 (top) and band 10 (bottom) images of the still-cooling lava flow in Las Lajas ravine at Fuego on 26 May 2016. Courtesy of Rudiger Escobar, Michigan Technological University and INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Mayo 2016).

Activity during June 2016. A significant rainfall combined with the plentiful ash from recent pyroclastic flows, resulted in lahars descending Las Lajas and El Jute ravines on 5 June 2016. They transported blocks, branches, and tree trunks, and a strong sulfur smell was reported by nearby residents. Another lahar was reported on 18 June that was 15 m wide and had a 1.5-m-high front. An increase in seismic activity during the afternoon of 24 June signaled the beginning of eruptive episode 10. This was followed by about 30 hours of moderate to strong explosive activity that could be heard and felt as far as 12 km away. A dense ash plume on 25 June rose to 5.5 km altitude and drifted S, SW, and W more than 40 km. Ashfall was reported in San Pedro Yepocapa, Sangre de Cristo, Morelia, Santa Sofia, Panimaché I and II. The Washington VAAC observed the ash plume in multispectral imagery on 25 June extending 120 km WSW from the summit. NASA Goddard Space Flight Center captured a small but distinct SO₂ plume from Fuego on 25 June as well (figure 49). Incandescent material rose 300 m above the summit crater during this episode and fed three lava flows; the first descended Las Lajas ravine 2.5 km, the second traveled 2.3 km down El Jute ravine, and the third flowed down Taniluyá ravine for 600 meters. Seismic activity from episode 10 decreased on 26 June.

Figure 49. A small but distinct SO2 anomaly was measured from Fuego on 25 June 2016. INSIVUMEH reported the 10th eruptive episode of the year during that time with a dense ash plume and lava flows emerging from the summit crater. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3763-m-high Fuego and its twin volcano to the north, Acatenango. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at Acatenango. In contrast to the mostly andesitic Acatenango, eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo (DRC) is part of the western branch of the East African Rift System (EARS). Nyamuragira (or Nyamulagira), a high-potassium basaltic shield volcano on the W edge of VVP, includes a lava field that covers over 1,100 km² and contains more than 100 flank cones in addition to a large central crater (see figure 54, BGVN 40:01). A large lava lake that had been active for many years emptied from the central crater in 1938. Numerous flank eruptions have been observed since that time, the last during November 2011-March 2012 on the NE flank. This report covers the substantial SO₂ emissions from both Nyamuragira and nearby Nyiragongo (15 km SE) between November 2011 and April 2016, and the onset of eruptive activity, including a new lava lake, at the summit crater beginning in May 2014. Activity is described through April 2017.

On-the-ground information about Nyamuragira is intermittent due to the unstable political climate in the region, but some information is available from the Observatoire Volcanologique de Goma (OVG), MONUSCO (the United Nations Organization working in the area), geoscientists who study Nyamuragira, and travelers who visit the site. The most consistent data comes from satellite – thermal data from the MODIS instrument processed by the MODVOLC and MIROVA systems, SO₂ data from the AURA instrument on NASA's OMI satellite, and NASA Earth Observatory images from a variety of satellites.

A substantial flank eruption took place from November 2011 through March 2012. This was followed by a period of degassing with SO₂-rich plumes, but no observed thermal activity, from April 2012 through April 2014. Increased seismicity and minor thermal activity was observed at the central crater during April 2014; lava fountains first seen in early July 2014 continued through September. A lava lake in the crater was confirmed on 6 November 2014, and it produced a consistent and strengthening thermal anomaly through the first week of April 2016, when it stopped abruptly. Thermal activity suggesting reappearance of the lava lake began again in early November 2016, and strengthened in both frequency and magnitude into early January 2017, continuing with a strong signal through April 2017.

Activity during November 2011-March 2012. Nyamuragira erupted from cones and fissures on the NE flank between early November 2011 and mid-March 2012 (BGVN 39:03). The vent area, 12 km ENE of the central crater, was an E-W fissure 500-1,000 m long. Lava fountains up to 300 m high produced flows that advanced nearly 12 km N in the first 10 days. Three scoria cones formed adjacent to the fissure during the eruption, and a small lava lake appeared in the center of the largest cone. During January 2012, lava flowed from the vent area and from numerous small breakouts within 2 km of the cones (figures 58, 59). Dario Tedesco reported that the eruptions ceased in March 2012 after a series of explosion earthquakes recorded by the OVG had ended; the last MODVOLC thermal alert in the area of the eruption was captured on 14 March 2012, and none were reported again until 2014.

Figure 58. Lava fountain and active lava flow emerging from the breach of the erupting flank cone of Nyamuragira volcano on 8 January 2012. Courtesy of Volcano Discovery.

Figure 59. Lava fountains around 150 m high erupt on 8 January 2012 from the active flank vent during the 2011-2012 eruption of Nyamuragira. Photo by Lorraine Field, courtesy of Volcano Discovery.

Activity during April 2012-May 2014. Periodic field surveys at Nyamuragira have been carried out since 2009 by helicopter, thanks to the support of the United Nations Organization Stabilization Mission in the DR Congo (MONUSCO). Since 2013, observations of the crater have also been done once or twice a month by helicopter. The team has included researchers from the OVG, Dario Tedesco, and other international scientists. This area is a high-risk sector due to the presence of armed groups, and it is impossible, due to the lack of security, to make detailed field surveys (Coppola et al., 2016).

Dario Tedesco reported SO₂-rich fumaroles in Nyamuragira's central crater beginning in early March 2012, shortly before the NE-flank fissure eruptions ended (BGVN 40:01). A progressive collapse of the 400-m-wide, 50-80 m deep pit crater located in the NE part of the caldera began as soon as the eruptions ended. They noted that during the second half of April, large SO₂ plumes continuously emerged from the pit crater.

NASA's Global Sulfur Dioxide Monitoring program captured major SO₂ plumes from the area for an extended period between November 2011 and February 2014. The plumes represent combined emissions from both Nyamuragira and Nyiragongo, which are too close together to distinguish the source in the satellite data. Campion (2014), however, noted that SO₂ emissions from the VVG increased several fold after the end of the 2011-2012 Nyamuragira eruption; they interpreted that 60-90 % of these emissions should be attributed to Nyamuragira.

Significant areas of SO₂ plumes with DU > 2 (shown as red pixels on the Aura/OMI images, figure 60) were captured by the OMI instrument at the beginning of the November 2011 eruption and continued through February 2012. Beginning in April 2012 elevated values occurred more than 20 days per month through December 2012. Values were more variable in both frequency and magnitude during 2013 with a notable surge of activity during 6-19 June 2013 that resulted in daily SO₂ plumes. Details of monthly SO₂ values are given in the last section of this report (see table 3).

Figure 60. Large SO2 plumes from Nyamuragira and Nyiragongo between November 2011 and December 2013. Four of the dates correspond to the Maximum DU days for that month (see table 3), and two represent other days of the month with substantial plumes. Courtesy of NASA/GSFC.

Activity during June 2014-April 2017. Incandescence at the summit and increased seismicity was reported again in April 2014, along with increasing SO₂ values. A strong MODVOLC thermal alert signal appeared on 22 June 2014, and a satellite image from 30 June showed clear hotspots at both Nyamuragira and Nyiragongo (figure 61).

Figure 61. Hot spots from both Nyamuragira and Nyiragongo on 30 June 2014. This false-color image combines shortwave-infrared, near-infrared, and green light as red, green, and blue, respectively. Since shortwave- and near- infrared light penetrates hazy skies better than visible light, more surface detail is visible in this image than would be in natural-color. Because very hot surfaces glow in shortwave-infrared, the lava within both summit craters appear bright red. The dark lava flows spreading from Nyamuragira were erupted within the past 50 years, some as recently as 2012. Vegetation is bright green. The image was collected by Landsat 8. Courtesy of NASA Earth Observatory.

An extended series of MIROVA thermal anomaly data beginning in May 2014 clearly shows the episodic periods of active heat flow at Nyamuragira from late May 2014 through April 2017 (figure 62). During the first episode, from late May to early September 2014, lava fountains were observed in early July, and reported to be active through September (BGVN 40.01). Campion (2014) and Smets and others (2014) debated whether the lava lake first appeared in April or not until November. On 6 November 2014 a small lava lake was confirmed at the base of the summit pit when sighted during an OVG helicopter survey. Both MODVOLC and MIROVA thermal anomalies appeared again in early November and persisted through the end of the year.

Figure 62. MIROVA thermal anomaly data from Nyamuragira from May 2014 through April 2017. Vertical black bar on each chart show the ending date of the previous chart. Chart "A" was previously published (BGVN 40:01, figure 57); other charts were captured via Volcano Discovery, Erik Klemetti, and Culture Volcan. Courtesy of MIROVA.

Thermal anomalies were persistent throughout 2015, with a noted increase in both frequency and magnitude during July (figure 62 C). A NASA Earth Observatory image from 9 February 2015 clearly shows active plumes venting from both Nyamuragira and Nyiragongo (figure 63). MONUSCO-supported summit crater visits by researchers on 2 April 2015, and photographer Oliver Grunwald on 10 July 2015, confirmed the presence of an active lava lake during both visits (figure 64, and video link in Information Contacts).

Figure 63. On 9 February 2015, clear skies afforded an unobstructed view from space of plumes venting from both Nyamuragira (north) and Nyiragongo (south) volcanoes in the Democratic Republic of the Congo. The lower image shows a close-up view of Nyamuragira, which is topped with a small caldera with walls about 100 m high. In 1938, a lava lake within the caldera drained during a large, long-lasting fissure eruption that sent lava flows all the way to Lake Kivu. Satellite observations and helicopter overflights in 2014 confirmed that the caldera again contained a small but vigorous lava lake. Courtesy of NASA Earth Observatory.

Figure 64. An active lava lake at Nyamuragira crater on 2 April 2015. Courtesy of MONUSCO/Abel Kavanagh (URL: https://www.flickr.com/photos/monusco/17118082715/).

The MIROVA and MODVOLC thermal anomaly data suggest that the lava lake at Nyamuragira was active until 4 April 2016 when the signals abruptly ended (figure 62 D). This also corresponds closely in time to when the major SO₂ emissions captured by NASA also ceased. Observations by Dario Tedesco at the summit on 6 April 2016, during a UNICEF and MONUSCO-sponsored helicopter overflight, showed only an incandescent vent releasing hot gases, and no active lava lake. A small lava lake was again visible in the pit crater on 27 April 2016 when observed by Sebastien Valade of the University of Florence on another MONUSCO-sponsored flight (figure 65).

Figure 65. Nyamuragira's pit crater with a small lava lake observed on 27 April 2016; volcanologist Sebastien Valade takes thermal measurements from the rim. Photo by Abel Kayanagh/MONUSCO. Courtesy of MONUSCO via Culture Volcan.

Thermal anomaly data from MIROVA suggest a pulse of activity during late April through early June 2016 (figure 62 D). This was followed by a period from early June through early November 2016 with no record of activity at Nyamuragira. The MIROVA signal reappeared in early November, followed by intermittent MODVOLC thermal alerts beginning on 27 November. A new pulse of thermal activity, with values similar to those observed during July 2015-April 2016, reappeared in early January 2017 (figure 62 E) and continued through April 2017. On an OVG-sponsored visit to the summit crater on 11 March 2017, independent journalist Charly Kasereka photographed the summit crater with incandescent lava covering the crater floor (figure 66).

Figure 66. Effusive activity at the bottom of the summit crater of Nyamuragira on 11 March 2017. Additional image available at https://laculturevolcan.blogspot.fr/2017/04/quelques-nouvelles-des-volcans.html shows minor spattering of molten lava near the vent on the crater floor. Photo by Charly Kasereka; courtesy of Cultur Volcan.

Sulfur dioxide and thermal anomaly data. Abundant sulfur dioxide emissions at Nyamuragira during November 2011-April 2017 show large variations in both magnitude and frequency during the period (table 3). A plot of the SO₂ data (figure 67) reveals a sharp increase in both the number of days per month with DU greater than 2 and the actual maximum DU value during the active flank eruption between November 2011 and February 2012. After lower values during March 2012, they rise steadily and remain significantly elevated for all of 2013. Values drop briefly in early 2014 and then rise again during April 2014, remaining elevated through February 2016 before dropping off significantly.

Figure 67. Sulfur dioxide data for Nyamuragira and Nyiragongo, October 2011 through April 2017. Blue bars represent the number of days each month where DU > 2 was captured in the Aura/OMI data (left axis). The orange points represent the highest DU value for the months where SO2 emissions had DU values > 2 for at least one day. See table 3 for details of Dobson Units (DU), and text for discussion of values. The two volcanos are less than 20 km apart, and thus the individual sources of SO2 cannot be distinguished in the satellite data.

A similar plot of the number of monthly MODVOLC thermal alert pixels for Nyamuragira from November 2011 through April 2017 (figure 68) shows that there were no thermal alerts for the period from April 2012-February 2014 when SO₂ emissions were large and frequent. In contrast, there were frequent thermal alerts from June 2014-April 2016 when SO₂ emissions were also high.

Figure 68. Number of MODVOLC thermal alert pixels per month at Nyamuragira from October 2011 through April 2017. Data courtesy of MODVOLC.

Table 3. Days per month that SO₂ values over the Nyamuragira and Nyiragongo area exceeded 2 Dobson Units (DU), October 2011-April 2017, and maximum DU values for each month. Data represent minimum values due to OMI row anomaly missing data (gray stripes), and missing days. SO₂ is measured over the entire earth using NASA's Ozone Monitoring Instrument (OMI) on the AURA spacecraft. The gas is measured in Dobson Units (DU), the number of molecules in a square centimeter of the atmosphere. If you were to compress all of the sulfur dioxide in a column of the atmosphere into a flat layer at standard temperature and pressure (0 C and 1013.25 hPa), one Dobson Unit would be 0.01 millimeters thick and would contain 0.0285 grams of SO₂ per square meter.

References: Campion, R., 2014, New lava lake at Nyamuragira volcano revealed by combined ASTER and OMI SO₂ measurements, 7 November 2014, Geophysical Research Letters (URL: http://onlinelibrary.wiley.com/doi/10.1002/2014GL061808/full).

Coppola, D., Campion, R., Laiolo, M., Cuoco, E., Balagizi, C., Ripepe, M., Cigolini, C., Tedesco, D., 2016, Birth of a lava lake:Nyamulagira volcano 2011-2015. Bull Volcanol (2016) 78: 20. doi:10.1007/s00445-016-1014-7.

Smets, B., d'Oreye, N., Kervyn, F., 2014, Toward Another Lava Lake in the Virunga Volcanic Field?, 21 October 2014, EOS, Transactions American Geophysical Union (URL: http://onlinelibrary.wiley.com/doi/10.1002/2014EO420001/pdf)

Smets, B., d'Oreye, N., Kervyn, F., Kervyn, M., Albino, F., Arellano, S., Bagalwa, M., Balagizi, C., Carn, S.A., Darrah, T.H., Fernández, J., Galle, B., González, P.J., Head, E., Karume, K., Kavotha, D., Lukaya, F., Mashagiro, N., Mavonga, G., Norman, P., Osodundu, E., Pallero, J.L.G., Prieto, J.F., Samsonov, S., Syauswa, M., Tedesco, D., Tiampo, K., Wauthier, C., Yalire, M.M., 2014. Detailed multidisciplinary monitoring reveals pre- and co-eruptive signals at Nyamulagira volcano (North Kivu, Democratic Republic of Congo). Bull Volcanol 76 (787): 35 pp.

Smets, B., Kervyn, M., Kervyn, F., d'Oreye, N., 2015. Spatio-temporal dynamics of eruptions in a youthful extensional setting: Insights from Nyamulagira volcano (D.R. Congo), in the western branch of the East African Rift. Earth-Science Review 150, 305-328. doi:10.1016/j.earscirev.2015.08.008

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Erik Klemetti, Eruptions Blog, Wired (URL: https://www.wired.com/author/erikvolc/); Cultur Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.com/); MONUSCO, United Nations Organization Stabilization Mission in the DR Congo (URL: https://monusco.unmissions.org/en/); Oliver Grunewald, Video filmed on 10 July 2015 (URL: https://laculturevolcan.blogspot.fr/2015/07/le-lac-de-lave-du-volcan-nyamuragira.html).

The andesitic Volcán El Reventador lies well east of the main volcanic axis of the Cordillera Real in Ecuador and has historical observations of eruptions of numerous lava flows and explosive events going back to the 16th century. The largest historical eruption took place in November 2002 and generated a 17-km-high eruption cloud, pyroclastic flows that traveled 8 km, and several lava flows. This report briefly summarizes activity between 2002 and June 2014, and covers details of activity from July 2014 through December 2015. The volcano is monitored by the Instituto Geofisico-Escuela Politecnicia Nacional (IG) of Ecuador, and the Washington Volcanic Ash Advisory Center (VAAC).

Summary of 2002-2014 activity. Intermittent activity including pyroclastic flows, ash plumes, lava flows and explosive events took place between 2003 and 2008. Since July 2008 there have been persistent gas-and-ash plumes, dome growth, and both pyroclastic and lava flows. Lahars are also very common in this high-rainfall area, and cause damage to infrastructure on a regular basis. A lava dome was first observed growing in September 2009 within the crater that formed during the 2002 eruption. By July 2011, it had reached the height of the highest part of the crater rim; by January 2013 it filled the crater and formed a new summit, 100 m above the E rim. This led to lava blocks travelling down the flanks, in addition to the lava flows and pyroclastic flows traveling down the flanks of the cone inside the crater during 2012-2014. A summary of thermal anomalies compiled from MIROVA data (figure 46) demonstrates the ongoing but intermittent nature of heat flow between 2002 and 2014.

Figure 46. Thermal activity detected by the MIROVA system at Reventador, January 2002-January 2014. Courtesy of IG (Informe Especial del Volcan Reventador No. 3, 7 July 2014).

Summary of June 2014-December 2015 activity. Activity was very consistent throughout the period of June 2014 through December 2015. The thermal webcam captured images of lava flows, pyroclastic flows and ejected incandescent blocks nearly every month. MODVOLC thermal alerts were reported every month except March 2015. Satellite imagery of hot spots were common as well. The Washington VAAC reported observations of ash plumes every month, although they generally rose only to altitudes below 5.6 km (2 km above the summit). IG reported seismicity as varying between moderate and high during the period.

Activity during June-December 2014. Activity during June 2014 was characterized by numerous explosions and small pyroclastic flows that descended the flanks of the cone. The Washington VAAC issued two series of reports on 11-12 and 19-20 June. A pilot reported an ash plume on 11 June rising 2.8 km above summit at 6.4 km altitude and drifting W, and the next day ash was observed 1.8 km above the summit. Weather generally obscured satellite views. On 19 June, multiple small emissions of volcanic ash were seen in the observatory webcam along with incandescent material on the flanks. MODVOLC thermal alerts were issued on 5, 21, and 30 June.

IG reported a new lava flow on 2 July 2014 descending 400 m on the SSW flank. A pyroclastic flow was also reported on 2 July (figure 45, BGVN 39:07) extending 1,500 m down the S flank. IG noted ash emissions on 2, 4, 9-12, 18, 22-24, and 27 July rising 800 m to 2 km above the summit. MODVOLC reported multi-pixel thermal alerts on 2, 16, and 27 July, and single pixel alerts on 10 and 25 July. In addition to the ash plumes reported by IG, the Washington VAAC reported on-going ash emissions and detected hotspots at the crater on 31 July.

The Washington VAAC issued a report of hot spots visible in satellite imagery on 1 August 2014 and a pilot report of an ash plume at 6.1 km altitude (2.5 km above the summit) on 25 August. The only MODVOLC thermal alerts were issued on 31 August. IG reported lower level plumes (300-800 m above the summit) with minor ash on 6 other days during the month.

Activity increased during September 2014. The Washington VAAC issued reports during 2-4, 18, and 23 September. On 2 September, ash plumes were observed extending about 45 km W of the summit at 5.5 km altitude. Another faint plume of volcanic ash was observed within 20 km of the summit the next day. An ongoing hotspot with possible small ash emissions was noted on 4 September. IG reported an explosion on the morning of 5 September that generated a plume and ejected blocks from the crater that fell ~500 m below the summit on the W flank. A thermal camera detected an explosion on the following day that also included ballistics. MODVOLC thermal alerts were issued on eight days during September. Steam plumes with minor ash rose to around 1 km above the summit and dispersed generally W several times during the month.

A single MODVOLC thermal alert was reported on 6 October 2014. The Washington VAAC reported short 2-3 minute bursts of minor volcanic ash on 19 October which was seen drifting WNW and dispersing within 16 km of the summit below 5.8 km altitude. An additional single pixel thermal alert was issued on 25 October, and a three-pixel alert appeared on 29 October.

IG reported steam-and-ash plumes rising up to 1 km above the summit a few times during the month, which were visible on the rare clear-weather days (figure 47). Only two days in November, 5 and 21, had MODVOLC thermal alerts. The Washington VAAC, however, issued reports during 11-12, 18-19, and 27 November of possible low-level ash-bearing plumes. The IG webcam LAVA on the SE flank captured images of pyroclastic flows on 20 and 25 November (figure 48).

Figure 47. The active cone at Reventador on 9 November 2014 with a low-level steam plume. Image taken from the IG Webcam LAVA on the SE flank. Courtesy of IG via La Culture Volcan.

Figure 48. Pyroclastic flows at Reventador, 20 (left) and 25 (right) November 2014 taken from the IG LAVA webcam on the SE flank. Courtesy of IG via Culture Volcan.

On 5 December 2014 a webcam recorded a steam-and-gas emission associated with an incandescent lava flow on the E flank. MODVOLC thermal alert pixels appeared on four days in December 2014 (3, 7, 14, and 23), and VAAC reports of ash plumes were issued on 5, 13-14, 21-22, and 30 December. The largest plume, on 14 December, rose to 6.1 km (2.5 km above the summit) and drifted NE. IG reported moderate seismicity and low-level steam plumes with minor ash content on several occasions.

Activity during 2015. Moderate seismic activity continued during January 2015 with low-level steam-and-ash plumes from explosions rising a few hundred meters above the summit, according to IG. A larger explosion reported by IG on 16 January generated an ash plume that rose 2 km and drifted SE. The Washington VAAC reported activity from 14-18 January, and again on 26 January. Their reports were of small puffs of ash within a kilometer of the summit drifting for a few hours before dissipating. MODVOLC thermal alerts were issued on 15 and 29 January.

Steam plumes containing minor amounts of ash were recorded a few times during February 2015 during periods of moderate seismicity. The Washington VAAC issued several reports, during 7-9, 13-17, 19-21, 24, and 26-28 February, noting occasional plumes with ash rising to less than one km above the summit, and hot-spots seen in satellite imagery on 13-14, 17, 19, and 27 February. An aircraft reported volcanic ash on 19 February at 6.1 km altitude. A new lava flow first observed on the SW flank on 11 February had advanced 1 km by 19 February. This is consistent with the four-pixel MODVOLC thermal alert issued on 18 February. Single pixel alerts were issued on 7, 19, and 23 February as well.

No MODVOLC thermal alerts were issued during March 2015, but the Washington VAAC continued to note low-level small bursts of ash emissions several times a week within 15 km of the summit, as reported by IG. The webcam captured a hotspot at the summit on 11 March. A thermal camera image of a lava flow taken on 13 March showed the visible part of it to be over 500 m long (figure 49), and IG noted in their 13 March report that is was actually about 1.5 km long that day.

Figure 49. Annotated thermal camera image at Reventador of an 11 March 2015 lava flow. Camera is located SE of the volcano. Courtesy of IG (Informe especial del Volcan Reventador No. 1, 13 March 2015).

Activity during April 2015 included moderate seismicity and incandescence at the crater reported by IG. A lava flow on the SW flank was visible with the infrared camera during the first week; this agrees with the 5-pixel MODVOLC thermal alert recorded on 5 April and the bright hotspot observed in both satellite imagery and the webcam during 3-5 April. Hot spots were observed via satellite and webcam several additional times during the month. Additional thermal alerts also appeared on 10 and 21 April. Steam-and-ash plumes rising to 1 km above the summit were intermittent throughout the month, mostly observed from the webcam.

Multi-pixel MODVOLC thermal alerts appeared during 2-3, 20, and 30 May, indicating continued sources of heat from lava flows. In a special report issued on 19 May, IG noted a new lava flow during the previous week that descended the S flank, forming a fan with three lobes on the SE and SW flanks. The length was greater than 1,000 m from the summit on 19 May, although the flows remained on the flanks of the summit cone within the caldera (figure 50). IG noted an increase in emission tremor on 17 May which may have been related to the extrusion of the lava, but weather conditions prevented visual confirmation. During 17-30 May, intermittent low-level gas-and-ash plumes within 15 km of the summit were reported on most days.

Figure 50. Annotated thermal image of the summit cone of Reventador on 19 May 2015 showing a 3-lobed lava flow descending the S flank of the cone for more than 1 km. Courtesy of IG (Informe especial del Volcan Reventador No. 2, 19 May 2015).

MODVOLC thermal alerts diminished during June 2015, occurring only on 8 and 15 June. Nonetheless, thermal images showed lava flows down the SW and S flanks of the cone several times, and hot spots were observed in satellite images and on the webcam when the weather permitted. Steam-and-ash plumes were generally reported to rise to 1 km or less above the summit and drift usually NW or SW within 15 km of the volcano. A pilot reported volcanic ash on 30 June at 6.7 km, but no ash was seen in satellite imagery under cloudy conditions. IG issued a special report on 24 June noting increased seismicity in the form of increased tremor signal and explosions on 23 June. The thermal camera located in the area of El Copete, 5 km S of the crater, showed an increase in surface activity characterized by several lava flows on the SW, S, and SE flanks exceeding one km in length (figure 51).

Figure 51. Thermal image of Reventador taken on 23 June at 1950 by the webcam near El Copete. Courtesy of IG (Informe especial del Volcan Reventador No. 3, 24 June 2015).

Seismic activity was reported as high during July 2015 by IG, and included explosions, tremor, long-period earthquakes, harmonic tremor, and emission signals. During the first week, incandescent material was visible more than 1 km down the SE flank in thermal images. On 17 July, light gray deposits possibly from a pyroclastic flow were observed; on 21 July explosions again ejected incandescent material onto the flanks. Steam and ash emissions were intermittent and generally remained below 5.1 km altitude. MODVOLC thermal alerts appeared on 1, 3, 15, and 17 July.

High levels of seismic activity continued during August 2015. The Washington VAAC reported possible ash plumes on 14 days during the month, and MODVOLC thermal alerts were issued on six dates, including four-pixel alerts on 4 and 27 August suggestive of lava flows and/or incandescent material on the flanks of the cone. A discrete volcanic ash emission on 6 August was reported by the Washington VAAC at 7 km altitude (3.4 km above the summit) with a plume extending about 25 km NW of the summit. Other plumes that were reported by pilots (on 25 August at 8.8 km altitude moving NW, and on 26 August at 6.7 km moving W) were not observed in cloudy satellite imagery.

Ash-and-gas emissions were reported by the Washington VAAC during 14 days in September 2015, generally drifting N and W at altitudes less than 2 km above the crater (5.6 km altitude); high levels of seismicity also continued, according to IG. The Guayaquil MWO reported volcanic ash at 6.1 km on 19 September. Puffs of ash seen in the webcam were reported at 7.3 km altitude on 25 September and thought to have quickly dissipated. MODVOLC thermal alerts appeared on seven days during the month; five of them were two- or three-pixel alerts. An SO₂ plume drifting WNW from Reventador was captured by NASA's OMI instrument on 22 September (figure 52).

Figure 52. An SO2 plume drifting W from Reventador on 22 September 2015. Reventador is represented by the triangle south of the NW-SE trending Ecuador/Columbia border in the bottom center of the image near longitude 78 W just south of the equator. A small plume in the top half of the image is likely SO2 from Nevado del Ruiz. Courtesy of NASA/GSFC.

A series of VAAC reports of low-level minor ash emissions were issued during 1-5 October 2015. After two weeks of no activity, multi-pixel MODVOLC thermal alerts and VAAC reports increased during 20-30 October. The peak MODVOLC activity included 4-6 daily pixels during 26-28 October, and the VAAC reports noted a bright hotspot on the satellite images beginning on 20 October and present for most of the rest of the month. Continuous emissions were observed in the webcam during 22-26 October, generally below 4.6 km, moving NW, and extending up to 40 km from the summit. Continuous emissions appeared again on 30 October at 5.1 km moving W.

During the last two weeks of November 2015, steam, gas, and ash emissions rose to less than 2 km above the summit and incandescent blocks rolled 500 m down the flanks of the cone. MODVOLC thermal alerts were reported for five days between 15 and 29 November. Similar activity was reported during December, although the Washington VAAC only issued reports on four different days, and MODVOLC thermal alerts were recorded only on 6 and 24 December. VAAC reports noted hotspots in satellite imagery on 7 December. The VAAC reports on 11 and 16 December indicated ash plumes at 5.5 km moving W and SW.

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Culture Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.fr/).

A February 2012 ash explosion of Columbia's Nevado del Ruiz volcano was the first confirmed ash emission in over 20 years. The broad, glacier-capped volcano has an eruption history documented back 8,600 years, and historical observations since 1570. Notably, a large explosion at night in heavy rain on 13 November 1985 generated large lahars that washed down 11 flank valleys, inundating most severely the town of Armero where over 20,000 residents were killed. It remains the second deadliest volcanic eruption of the 20th century after Mt. Pelee in 1902 killed 28,000.

This report summarizes and concludes the February 2012-April 2014 eruption (BGVN 37:08, 39:07), and then describes details of new activity beginning in November 2014, through December 2015. The volcano is monitored by the Servicio Geologico Colombiano (SGC) and aviation reports are provided by the Washington Volcanic Ash Advisory Center (VAAC).

Summary of activity, November 1985-June 2012. After the large explosions and deadly lahars of November 1985, activity at Ruiz continued with intermittent ash emissions and significant seismic activity through July 1991. Seismicity, deformation, and SO₂ emissions have been closely monitored since the 1985 eruption. Between 1991 and February 2012 intermittent high-frequency seismic events (earthquake swarms) were recorded, but no ash emissions were observed. In September 2010, seismicity notably increased in frequency and diversity of event type until early 2012 when fresh ashfall was observed. INGEOMINAS (Instituto Colombiano de Geología y Minería, precursor to SGC) also noted an inflationary trend in the geodetic data from October 2010 through 2011.

A March 2012 overflight by INGEOMINAS noted minor amounts of ash-covered snow on the E flank, which they surmised came from an explosion on 22 February (BGVN 37:08). During March, long-period seismicity underwent a 20-fold increase. SO₂ emissions also dramatically increased between March and June 2012. Several ash emissions from the summit were observed during April-June 2012 (BGVN 37:08). An ash plume that rose to 11 km altitude on 29 May caused ashfall in over 20 communities to the NW and closures at three nearby airports. Widespread ashfall during June covered solar panels on field equipment. An EO-1 satellite image from 6 June 2012 shows a plume and significant ashfall around the summit (figure 71).

Figure 71. Satellite image of Nevado del Ruiz taken on 6 June 2012 showing an active ash plume from the Arenas crater and ash deposits NW of the summit. It was acquired by the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite. Courtesy NASA Earth Observatory.

Summary of activity, July 2012-December 2015.Explosions and seismic tremor with ash emissions continued during July and August 2012. Ashfall was reported within 30 km on numerous occasions. From September 2012 through early July 2013 minor amounts of ashfall were reported a few times each month, mostly in the immediate vicinity of the volcano. After a larger explosion on 11 July 2013, sparse and intermittent ash emissions were reported between August 2013 and April 2014. Between May and October 2014 there were no reports of ash emissions or thermal anomalies.

A significant increase in seismicity occurred during the second week of November 2014, and ash was seen at the summit during an overflight on 19 November. Ash fell in communities within 30 km several times each month through December 2015. Seismic evidence suggesting possible lava dome extrusion first appeared in August 2015, and stronger signals were recorded on 22 October. Thermal anomalies around the summit crater increased in frequency and magnitude during the last three months of 2015.

Activity during July 2012-October 2014.A large ash plume on 30 June 2012 prompted evacuation warnings to several communities within 30 km and closed three nearby airports for the second time within 30 days. On 2 July the Washington VAAC reported a 7.5-km-wide ash plume at 6.1 km altitude drifting 75 km W (BGVN 37:08). Additional VAAC reports were issued on 8, 9, and 10 July for SO₂ emissions containing minor volcanic ash. SGC noted that explosions and ash emissions continued throughout the month in spite of a decrease in seismicity. Ashfall was reported near the volcano, and in municipalities in the departments of Caldas (W) and Risaralda (SW), steadily throughout the month.

Tremors associated with continuing gas and ash emissions occurred throughout August 2012; ash plumes were observed rising 200-800 m above the summit crater. During 3-6 August, gas and ash emissions were seen from Manizales (30 km NW) and Chinchiná (30 km WNW). On 12 August, a gas-and-ash plume observed with a webcam rose 1 km above the crater and drifted W, and ashfall was reported in Brisas (50 km SW). A layer of ash was deposited at the Observatorio Vulcanológico y Sismológico de Manizales (OVSM) on 13 August; they also reported ash emissions associated with seismic signals the next evening. Webcams showed gas-and-ash plumes rising 400 m and drifting W and NW during 15-16 August.

Minor amounts of ashfall were reported by SGC in areas around the volcano each month during September 2012 through 11 July 2013 (table 4), when a larger ash emission occurred. A noted increase in seismicity beginning on 13 April 2013 was also reported by SGC. The ash emission on 11 July was captured by the webcam in the Parque Nacional Natural Los Nevados (PNNN) (figure 72), and fine ash fell in Manizales. The Washington VAAC reported the ash plume at 6.1 km altitude. Multispectral imagery showed the plume extending 55 km NW. After 12 July 2013 there were no further reports from the Washington VAAC until December 2014.

Table 4. Ash emission events at Ruiz during September 2012-July 2013. Data compiled from various sources as shown.

Figure 72. Ash emission at Ruiz on 11 July 2013 at 1143. The column of gases and gray ash stands out among the white clouds. Photo by Julián Peña, courtesy of SGC (Informe-Technico, July 2013).

Evidence for ash emissions between August 2013 and April 2014 is sparse and intermittent. The SGC Monthly reports during this time mention pulses of low-energy tremor associated with emissions of gases, steam, and small amounts of ash every month except November, when they reported only steam and gas, but no specific dates are given. SGC's Technical Information Monthly reports mention occasional grayish coloration, suggesting ash in the gas-and-steam plumes during August-October 2013. Tremors associated with small amounts of ash and grayish coloration in the plumes are again noted from January through April 2014 without describing specific events.

The weekly activity reports issued by SGC make no mention of ash from August through November 2013. They note in weekly reports for 2-8 and 9-15 December that gray emissions possibly associated with ash in plumes of mostly water vapor and gases were observed. During the week of 16-23 December they recorded low-energy tremors associated with the output of small amounts of ash, which were reported in trace quantities in Manizales. In their 31 December 2013-6 January 2014 and 10-16 February 2014 weekly reports they noted the occurrence of tremors associated with ash and gas. There is no mention of ash in their March or April 2014 weekly reports. There is also no mention of ash emission in SGC monthly reports during May-October 2014. The MIROVA thermal anomaly data do show minor thermal anomalies in latest August and more persistent anomalies at the beginning of October 2014 (figure 73) prior to the reports of ash emissions during November.

Figure 73. MIROVA signal of MODIS data for the year ending on 15 May 2015. Persistent thermal anomalies are present between late October 2014 and mid-April 2015. Courtesy of the MIROVA project supported by the Centre for Volcanic Risk of the Italian Civil Protection Department via SGC (Informe de Actividad, April 2015).

Activity during November 2014-December 2015.A significant change in seismicity occurred beginning in the second week of November 2014. There was an increase in the number of long-period (LP) earthquakes, pulses of volcanic tremor, and several periods of continuous tremor (lasting for hours or even days) associated with fluid movement, and with emissions of gas and ash (table 5). Several of these periods were preceded by an LP event. The first significant pulse of volcanic tremor began on the evening of 18 November following an LP event and lasted more than 12 hours.

Table 5. Periods of continuous tremor associated with ash emissions at Ruiz during November 2014. Some of the tremor episodes were preceded by long-period (LP) events. Courtesy of SGC (Informe de Actividad, November 2014).

The Unidad Nacional de Gestion de Riesgo de Desastres (UNGRD, National Disaster Risk Management Unit) coordinated an overflight during 19-21 November 2014 and observed fresh ash deposits on the S flank. Ash emissions were also verified in satellite imagery (figure 74) and by reports from nearby communities. The ash dispersed generally SE and SW during 18-21 November. Ash was again observed on the N side of the Arenas crater on 29 November in the early morning after a lengthy period of continuous tremor was recorded the previous day (see table 5).

Figure 74. Image of Ruiz on 24 November 2014 taken by the OLI-TIRS sensor on the Landsat 8 Satellite at 1018 local time. Ash deposits are dispersed SE and SW of the summit crater, and the steam plume is drifting W. Courtesy of SGC (Informe de Actividad, November 2014).

During the second half of December 2014, SGC reported significant concentrations of ash in the emissions that were associated with continuous tremor episodes. On 15 December seismic signals indicating ash emissions were detected, and then confirmed by a local webcam and nearby residents. The Washington VAAC also noted an ash emission based on a pilot observation extending 16 km S at 7.6 km altitude. The next day they reported a narrow plume of minor volcanic ash extending 22 km SW of the summit at 6.1 km altitude. On 18 and 19 December the Washington VAAC reported ash plumes to altitudes of 7.9 and 9.1 km, respectively, that drifted SSW and dissipated within a few hours. A faint thermal anomaly was also detected. A satellite image taken on 26 December 2014 clearly shows ash deposits in nearly all directions from the Arenas crater (figure 75). Ashfall was reported during this time in the Caldas (W) and Risaralda (SW) departments.

Figure 75. An ASTER image from the OLI-TIRS Sensor on the Landsat 8 satellite taken on 26 December 2014 of Ruiz (N is to the top) showing fresh ash deposits covering the summit glacier in nearly all directions. Courtesy of SGC (Informe de Actividad, December 2014).

According to the news source Prensa Latina, increased ash emissions at Ruiz prompted closure of the La Nubia airport (22 km NW) on 7 January 2015. On 14 January, the Washington VAAC reported an ash plume visible in satellite imagery extending 16 km SW of the summit at 6.7 km altitude. SGC reported seven episodes of continuous tremor on 4, 7, 14, 24, 26, 28, and 29 January, almost all of which were associated with ash emissions (figures 76). Ashfall was reported several times after these episodes in the Eje Cafetero area to the W of Ruiz.

Figure 76. Ash emissions on six different dates during January 2015 at Ruiz. Photographs taken by the webcam located in the Azufrado sector (NW). Courtesy of SGC (Informe de Actividad, January 2015).

Occasional minor ash emissions were reported during February 2015 during periods of continuous tremor, but most of the emissions were steam and gas. On 9 February, ashfall was reported in El Libano (29 km E), El Oso (10 km SE), and Murillo (17 km E). Although seismic tremors were diminished during March from the previous month, emissions associated with these tremors contained gases and minor amounts of ash from 8 March through the end of the month. Ashfall was reported after a tremor in the evening on 8 March by personnel from the Parque Nacional Natural Los Nevados (PNNN), the Observatorio Vulcanológico y Sismológico de Manizales (OVSM), and from the municipalities of Manizales and Villamaria (27 km NW).

An increase in several types of seismicity was observed by SGC during April 2015. Volcanic tremor, associated with gas and ash emissions, were confirmed through photographs taken by the webcams (figure 77), and by officials at PNNN and SGC. Ashfall was reported on 20 April in the municipalities of Manizales and Villamaría. The Washington VAAC reported a small puff of gas and minor amounts of ash visible in satellite imagery on 22 April at 7.3 km altitude drifting W about 40 km before dissipating. The MIROVA signal from the MODIS thermal anomaly data shows persistent thermal activity from late October 2014 through mid-April 2015 (figure 73).

Figure 77. Plumes of ash-and-gas from Ruiz during April 2015. Confirmed ash emissions were observed on 9, 22, 27, and 29 April. Courtesy of SGC (Informe de Actividad, April 2015).

Ash emissions were photographed by the webcams located in the Azufrado and Cerro Guali regions on at least eleven dates during May 2015. The Washington VAAC reported possible emissions on 19 and 26 May, but extensive weather clouds prevented satellite observations. Most of the frequent episodes of volcanic tremor during June were also associated with ash emissions which were photographed at least six times during the month. The Observatory at Manizales reported ash moving WNW on 6 June at about 800 m above the summit; weather clouds obscured satellite observations by the Washington VAAC.

A significant increase in ashfall was reported during July 2015 (figure 78), including in the regions of Caldas, Tolima, and Risaralda, as well as by officials in the Park (PNNN). The Observatory at Manizales (OVSM) reported an ash plume on 6 July at about 7.3 km altitude, but it was not observed in satellite data due to weather. The Washington VAAC noted ash emissions visible in satellite data and the webcam on 13 July, with a plume at 7 km altitude drifting NW a few tens of kilometers before dissipating. OVSM reported plumes at about 6 km moving S and W during 18-20 July. Seismic signals indicating emissions were reported on 23 July and observed in the webcam, according to the Washington VAAC. SGC noted seismic tremors and a plume on the morning of 26 July that rose to 3 km above the summit (8.2 km altitude) (figure 79); near summit-level emissions were also observed via the webcam on 26 and 27 July. Seismic data indicated continued occasional bursts of ash drifting W to WSW during the next few days. Ashfall was reported downwind in the municipalities of Chinchina (33 km NW), Palestina (35 km NW), Santa Rosa de Cabal (33 km W), Dosquebradas (40 km WSW), and Pereira (40 km WSW). A bright thermal anomaly was reported in satellite imagery on 31 July, but no ash was observed.

Figure 78. Gas, steam, and ash plumes from the Arenas crater at Ruiz during July 2015. Photographs captured by the cameras located in the area of Azufrado, Cerro Gualí, and in the OVSM. Courtesy of SGC (Informe de Actividad, July 2015).

Figure 79. Seismic and visual images of tremors that produced ash emissions at Ruiz between 0800 and 1559 on 26 July 2015. The digital seismogram and spectrogram are from station BIS (2 km W of Arenas Crater) and show a characteristic spasmodic tremor (1, 2, and 3) that was associated with ash emissions recorded on the Piranha-Azufrado webcamera in the lower images. Courtesy of SGC (Informe de Actividad, July 2015).

SGC reported greater instability at Ruiz compared with previous months during August 2015. Seismicity related to fracturing and fluid flow both increased during the month. Energy levels for spasmodic tremor related to gas and ash emissions were also generally higher. The Washington VAAC reported ash visible in satellite imagery on 6 August at 7.3 km altitude moving NW as far as 20 km for about 10 hours before dissipating. They noted another possible plume with minor ash on 12 August at 6.7 km drifting 55 km NW from the summit. Ashfall was reported on 23 August from officials of PNNN and residents of Pereira. A brief emission containing minor ash on 28 August, observed in a webcam, was reported by the Washington VAAC as extending about 35 km W. Ongoing emissions rising a few hundred meters above the summit with occasional small bursts of ash continued for the next two days.

The tremor event on 31 August 2015 was the largest since 18 November 2014; ashfall affected numerous cities and municipalities, including Manizales (30 km NW) (with the largest particle sizes towards the E side of the city), La Linda, La Cabaña (36 km NW), and trace amounts in Santagueda (40 km NW), Arauca (48 km NW), Kilómetro 41, Villamaría (27 km NW), Chinchiná, Palestina, and Neira (36 km NW) (figure 80). A news article reported that the La Nubia airport closed that day due to ash emissions. Most ash emissions during the month affected the regions of Caldas and Risaralda NW of the volcano.

Figure 80. Ashfall was recorded in a number of cities during the 31 August 2015 emission event at Ruiz. The four left images are from the city of Manizales. The six right images are from different towns in the department of Caldas. Courtesy of SGC (Informe de Actividad, August 2015).

The Washington VAAC issued advisory reports on 3, 12-15, 17, 23-24, 27, and 29-30 September 2015. Most reports were based on observations from the webcams near the volcano and/or seismic activity, but many events were not visible in satellite imagery due to weather clouds. Plume altitudes ranged from 5.5 to 7.9 km. Incandescence observed in a webcam on 4 September was followed by a high-energy tremor. The ash plumes reported by the Washington VAAC on 12 and 13 September rose to 7.9 km and drifted in several directions. Ash was moving to the NW below 5.2 km and extended for over 90 km; between 5.2 and 7.9 km altitude it extended about 80 km SW. Ongoing emissions with small bursts of ash continued through 15 September with a new emission to 7.6 km around 1600 that day.

The OVSM reported a strong seismic signal at 0728 on 17 September, but weather clouds blocked observation from satellite imagery of the potential ash plume. The largest tremor of the month occurred in the afternoon of 18 September and ash emissions were verified in the webcams as well as by SGO officials doing fieldwork in the area; ash emissions were also observed in the webcam on 19 September at 1556. SGO reported a seismic event on 22 September that produced water-vapor, gas, and ash plumes that rose 2 km above the crater and drifted mainly NW. An ash plume was confirmed by the Washington VAAC in a satellite image on 27 September extending about 70 km WNW at 6.1 km altitude. An advisory issued on 29 September noted ash to 8.5 km within 16 km of the summit. SGO noted that the 29 September emissions were observed both E and W of the volcano.

The Washington VAAC confirmed continuous ash emissions on 5 October 2015 at 7 km altitude extending about 25 km W of the summit. A gas, steam, and ash plume rose 1.7 km and drifted NW on 8 October. Another report of volcanic ash early on 9 October was not visible in satellite imagery, although a thermal anomaly persisted and seismicity was elevated. A small ash emission was spotted in imagery data drifting WNW late on 9 October. A gas, steam, and ash plume rose 1.8 km and drifted NW on 17 October. A discrete emission of ash rose to 9.1 km altitude on 22 October and drifted N. SGO reported ash emissions observed in webcams on 26 October, but weather clouds prevented satellite observation by the Washington VAAC. A gas, steam, and ash plume rose 1.7 km and drifted NW on 30 October.

SGC first noticed an unusual pattern of seismicity known as a "drumbeat" signal, for which they issued a special report on 20 August 2015. The "drumbeat" signal is characterized by discrete episodes of short duration (about 30 minutes each) that repeat at regular time intervals and show similar waveforms and energy. They are interpreted by volcanologists to represent phenomena associated with the ascent of high-viscosity magma to the surface and thus are an indicator of near-surface extrusion or dome building. SGC recorded the same signal on 8 September, and then again on 22 October (figure 81). Thermal anomalies near the Arenas crater were observed by SGO on 26, 28, and 30 September, and were again recorded on 7, 9, and 10 October 2015.

Figure 81. Episodes of seismic "drumbeats" at Ruiz recorded on 22 October 2015. The top box is the vertical component seismic record from station BIS, the larger yellow shaded box highlights the entire 'drumbeat' episode. The seismogram from the OLLETA station (lower left) shows a clearer view of the first episode (1). The lower right images show details of the signal at three different time intervals highlighted in smaller boxes in the top image. This signal is interpreted to represent phenomena associated with the ascent of high-viscosity magma to the surface and thus are an indicator of near-surface extrusion or dome building over the emission conduit. Courtesy of SGC (Informe de Actividad, October 2015).

Seismic activity decreased slightly during November 2015, but there still were episodes of volcanic tremor associated with gas and ash emissions that were recorded by the webcams and personnel at PNNN. Continuous tremor signal was recorded on 1 and 4 November. The "drumbeat" signal was again briefly recorded on 13 November. Thermal anomalies increased in frequency and were observed on 4, 18, 20, 22, 26, and 27 November. SGC confirmed ash emissions on 5, 10, 14, 27, and 29 November. The Washington VAAC reported an ash plume on 14 November at 6.4 km altitude moving SW. SGC captured images of the ash plume from two different webcams (figure 82).

Figure 82. Photographs of the ash emission at Ruiz of 14 November 2015 at 0537 from two different webcams. Top image is from the Azufrado webcam (5 km NE) and the lower image is from the Pitayo webcam. Courtesy of SGC (Informe de Actividad, November 2015).

Thermal alerts captured by the University of Hawai'i's MODVOLC system appeared in December 2015 for the first time in several years. They were recorded on 3, 22, 26, and 31 December. Additionally, the MIROVA thermal anomaly system showed significant increases in anomalies at Ruiz during the last three months of 2015 (figure 83).

Figure 83. MIROVA data for the year ending 2 January 2016 showing the substantial increase in frequency and magnitude of thermal anomalies at Ruiz during the last three months of 2015. Courtesy of MIROVA via SGC (Informe de Actividad, December 2015).

Minor episodes of volcanic tremor with ash emissions were reported by SGC during the first two weeks of December 2015. A significant volcanic tremor with ash emissions occurred on 20 December, and ashfall was reported by SGC officials, PNNN personnel, and residents near the volcano and in the city of Manizales. The Washington VAAC noted the ash plume at 6.1 km altitude with 25 km of the summit. A gas, steam and ash plume rose 1.7 km and drifted NW on 28 December.

Sulfur Dioxide emissions, June 2012-2015. Persistent, large SO₂ plumes were captured from Ruiz many times during June 2012-December 2015 (figure 84 and 85). Every month during this period the OMI (Ozone Measuring Instrument) on the Aura satellite recorded days with SO₂ emissions exceeding 2 DU (Dobson Units); many months had more than half of the recording days with values > 2 DU. Dobson Units are the number of molecules in a square centimeter of the atmosphere. If you were to compress all of the sulfur dioxide in a column of the atmosphere into a flat layer at standard temperature and pressure, one Dobson Unit would be 0.01 millimeters thick and contain 0.0285 grams of SO₂ per square meter.

Figure 84. Select Aura/OMI images of SO2 plumes from Ruiz, 2012-2013. Top left: 14 June 2012, the SO2 plume drifts NW. Top right: 18 August 2012, the SO2 plume from Ruiz drifts W. An SO2 plume is also visible drifting W from Ecuador's Cotopaxi in the lower left corner of the image. Bottom left: A 10.26 DU (Dobson Unit) SO2 plume sits directly over Ruiz on 7 December 2012. Bottom right: The SO2 plume drifts south on 19 December 2013. See text above for description of Dobson Units. Courtesy of NASA Goddard Space Flight Center (NASA/GSFC).

Figure 85. Select Aura/OMI images of SO2 plumes from Ruiz, 2014-2015. Top left: On 3 February 2014 an SO2 plume from Ruiz drifts due W while another plume drifts NE from Guagua Pichincha in northern Ecuador. Top right: A 24 September 2014 SO2 plume drifts NW from Ruiz as far as the coastline. Bottom left: On 5 March 2015, a plume drifts slightly W from Ruiz. Bottom right: A W-drifting SO2 plume from Ruiz on 4 October 2015 is visible along with W-drifting plumes from both Cotopaxi and Tungurahua in Ecuador. Courtesy of NASA/GSFC.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: Servicio Geologico Colombiano (SGC), Observatorio Vulcanologico Y Sismologico Manizales, Diagonal 53 N0. 34 - 53 - Bogotá D.C. Colombia (URL: http://www2.sgc.gov.co/Manizales.aspx); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Prensa Latina, Agencia Informativa Latinoamericana (URL: http://www.plenglish.com/).

Strong fumarolic activity characterized activity at Costa Rica's Turrialba for several decades before a phreatic eruption in January 2010 resulted in ashfall tens of kilometers from the volcano. Since the January-March 2010 eruption, there have been one or two brief eruptive episodes with ash emissions each year, generally lasting days to weeks. An episode from 29 October through 8 December 2014 began with an ash explosion, followed by continuous emissions on 30 and 31 October. Several additional explosions with ash emissions occurred during November, followed by a strong Strombolian explosion on 8 December that included ashfall up to 1 cm thick in places, and ballistics deposited 300 m from the vent (BGVN 40:04). This report covers the increasing ash-emission activity during 2015 and 2016. Information comes primarily from the Observatorio Vulcanologico y Sysmologico de Costa Rica-Universidad Nacional (OVSICORI-UNA). Aviation alerts are issued by the Washington Volcanic Ash Advisory Center (VAAC).

Turrialba began a new eruptive episode with an ash plume on 8 March 2015. Frequent, intermittent ash-bearing events continued through mid-May, and tapered off during June, with a final event reported on 22 June 2015. The larger plumes rose 2-2.5 km above the vent rim and drifted in many different directions, leading to ashfall throughout the region as far as 40 km from the volcano. A 'bubble of magmatic gas' dispersed accumulated ash from the vent on 15 August 2015. An eruption on 16 October 2015 was the largest in a year, and the start of a new series of emissions that persisted through the end of October, dispersing ash for tens of kilometers in most directions. A brief period of ash emissions between 2 and 8 February 2016 deposited ash within a few kilometers of the summit crater. Ash emissions and frequent small explosions between 28 April and 7 May preceded a longer series of emissions that began with a significant explosion on 16 May, included significant ashfall in regions within 30 km, and lasted until late July 2016. Strombolian activity and pyroclastic flows were also reported during late May; ashfall was reported up to 100 km SW. A new series of explosions and ash emissions began on 13 September that continued nearly uninterrupted through the end of the year, although ashfall reports were greatest in October 2016.

Activity during 2015. Little activity was reported during January and February 2015. Seismicity slowly increased from short-duration, low-amplitude, higher-frequency events in January to more lower-frequency events in February. Very-long-period earthquakes (VLP's) began to register in February and became more pronounced during March, when some were associated with explosions and ash emissions. The first, short, effusive emissions with low ash content occurred on 8 March. The largest events with prolonged ash emissions occurred on 12 (figure 43) and 15 March.

Figure 43. Eruption at Turrialba on 12 March 2015. Webcam image courtesy of OVSICORI (Boletín de Vulcanología Estado de los Volcanes de Costa Rica, January, February, March 2015).

Based on webcam views, weather models, and OVSICORI-UNA updates, the Washington VAAC reported that on 8 March diffuse ash emissions rose from the Cráter Oeste (West Crater) and seismicity increased. OVSICORI-UNA reported more ash emissions on 11 and 12 March. Almost continuous ash emissions were observed in the afternoon of 12 March punctuated by two noticeable explosions. Ash plumes rose as high as 2 km above the crater and drifted NW. Ashfall also occurred in the Valle Central and in the capital of San José (30 km WSW), and caused the closure of the Juan Santamaria International Airport (48 km W), which reopened during the evening on 13 March. The local Tobias Bolanos airport (40 km WSW) closed intermittently. On 13 March three short-duration explosions were reported. According to the Washington VAAC, ash plumes that day drifted 45 km NE at an altitude of 9.1 km, and drifted over 35 km W at an altitude of 6.1 km.

On 18 March, OVSICORI-UNA reported that gas, vapor, and ash plumes rose from Cráter Oeste and seismicity remained high. Observers in Finca La Central (2 km SW) noted gas-and-steam emissions. On 19 March two gas-and-water-vapor emissions were observed; one from Cráter Central contained a small amount of ash. At 1400 the webcam recorded strong emissions of gas, vapor, and tephra from Cráter Oeste. On 23 March a gas, vapor, and ash plume rose from Cráter Oeste, causing ashfall in areas E and SE of the crater including in the Cráter Central and El Mirador. In addition, a dense and vigorous gas-and-vapor plume caused Parque Nacional Volcán Turrialba authorities to recommend masks for protection against gas inhalation.

There were 11 gas-and-ash eruptions and 10 additional smaller ash emissions during April 2015. OVSICORI-UNA reported that a small ash eruption occurred on 3 April, causing ashfall in nearby areas including Silvia and La Central. On 5 April, an eruption generated a plume that rose 500 m and caused ashfall in Curridabat (31 km WSW), Granadilla (29 km WSW), San Pedro, Desamparados (35 km WSW), Aserrí (40 km SW), San Sebastián (37 km WSW), and Escazú (42 km WSW). The eruption of 7 April was the largest of the month (figure 44), and although it occurred at night, the visible ash plume rose to about 2.5 km above the summit. Ash and sulfur odors were reported in many areas of the city of San José (30-40 km WSW). The largest quantities of ash fell in the La Picada and La Silvia communities a few kilometers NNE of the volcano, and affected several hundred cows and other animals at dairy farms. Small ash emissions occurred on 8, 16, and 18 April, and every day during 20-24 April. The ash on 20 April dispersed N and affected Guápiles (20 km N). On 23 and 24 April, ash dispersed NW and affected the inhabitants of the Valle Central, and was reported at Tobias Bolanos and San Juan Santamaria international airports.

Figure 44. Nightime eruption of ash and hot volcanic blocks from Turrialba on 7 April 2015 that began at 0205 and lasted until 0241. Webcam image courtesy of OVSICORI-UNA, (Boletín de Vulcanología, Estado de los Volcanes de Costa Rica, April 2015)

During May 2015, OVSICORI-UNA recorded 39 eruptions with ash emissions. In general, the plumes did not rise more than 500 m above the crater, and a few were accompanied by small pyroclastic flows. The largest events were on 1 and 4 May when emissions lasted for 4 and 23 minutes, respectively. The 4 May event produced an ash plume that rose 2.5 km and drifted SW. The eruption ejected ballistics 1 km from the crater. Most of the ashfall occurred around the crater. Reports of minor ashfall and sulfur odors came from communities 30-40 km WSW around the city of San José (Moravia, Coronado, Mata de Plátano, La Uruca, Guadalupe, Tibás, Calle Blancos, San Pedro Montes de Oca, Sabanilla Montes de Oca, Pavas, Zapote, Escazú, Paso Ancho, Curridabat, Santa Ana), and a few localities in the eastern region of Heredia (40 km W). Additional ash emissions were reported on 6, 11, 14, and 18 May. Although the multiple emissions on 18 May lasted as long or longer than earlier events (23 and 25 minutes), they were lower energy, and the plumes rose only 400-500 m above the summit crater.

OVSICORI-UNA reported that ash emissions occurred on 1, 4, 7, and 22 June 2015. The eruption on 1 June was the largest, and the small ash eruption on the afternoon of 22 June deposited ash mainly in the vicinity of the volcano to the SW (figure 45). They also reported a significant decrease in the seismic activity, such that by late June, the RSAM values had returned to levels similar to October 2014, prior to the start of the most recent eruptive events. Significant rains after April 2015 led to a shallow lake forming in the Cráter Oeste. Images taken in July of the Cráter Central showed deposits of eruptive material more than 2 m thick compared with May 2014.

Figure 45. Eruption at Turrialba on 22 June 2015. Webcam image courtesy of OVSICORI-UNA (Boletín de Vulcanología, Estado de los Volcanes de Costa Rica, June 2015).

Seismicity continued to decrease during August 2015. However, an event on 15 August comprised nine hours of tremor associated with the ascent and escape of a bubble of magmatic gas, according to OVSICORI-UNA. The resulting ash ejection was believed to be material that had accumulated at the bottom of the crater. Seismicity remained low during September, with no reported ash emissions.

An increase in seismicity began on 1 October 2015, and until a large eruption on 16 October (figure 46). This was followed on 23 October by a lengthy sequence of ash emissions that continued until 31 October. The 16 October eruption was the largest in terms of energy since the 30 October 2014 eruption. Most of the ash fell on the summit, but a plume headed NW and minor ashfall was reported in parts of the Valle Central such as la Unión, Concepción de Tres Ríos, Montes de Oca (30 km WSW), San Rafael de Coronado (26 km WSW), and Moravia (27 km W). A strong odor of sulfur was reported in Tierra Blanca (18 km SW), Pacayas (12 km SSW), Moravia, and Guadalupe (32 km WSW).

Figure 46. A Google Earth image of Turrialba annotated with images from the 16 and 26 October 2015 eruptions. a) 20-cm- diameter impact from volcanic ejecta. b) Solar panel destroyed by impacts. c) Ash deposit. d) Pyroclastic flow deposit. e) Hot material deposited by the pyroclastic flow. f) Thermal image of an eruption on 26 Of October (Photos: G.Avard). Courtesy of OVSICORI-UNA (Boletín de Vulcanología, Estado de los Volcanes de Costa Rica, October 2015).

Seismicity increased between 16 and 23 October, when new ash emissions began and were accompanied by pyroclastic flows. Between 23 and 31 October, OVSICORI-UNA reported 57 small emissions and 120 explosions of varying size and characteristics. The Washington VAAC was unable to see most of the emissions in satellite imagery due to weather clouds, however the plumes on 31 October were reported at 4.3 km altitude moving W. Both seismic and eruptive activity declined considerably during November 2015. OVSICORI-UNA reported one small eruption on 27 November and a small explosion on 30 November; they did not mention ash related to either event.

Activity during 2016. OVSICORI-UNA reported a brief emission of gases and volcanic ash to 500 m above the crater on 2 February 2016. Residents of La Silva (2 km NW) reported a sulfur odor and ashfall on 5 February, and additional emissions above Cráter Oeste on 6 February. The Washington VAAC noted gray emissions on 8 February. The next report, on 3 April, described an explosion lasting less than one minute that generated a small gas-and-ash plume. Seismicity increased on 28 April, followed by ash emissions and frequent small explosions on 30 April and 1 May from Cráter Oeste. Gas-and-tephra emissions increased on 1 May with minor amounts of ash deposited in La Central (4 km SW) and La Pastora (6 km SSE). A larger ash plume on 2 May rose 2 km above the summit, and was followed by frequent explosions producing 1-km-high ash plumes the next day. Frequent explosions were again recorded during 3-5 May with ash plumes rising up to 1 km above Cráter Oeste. Small lahars were reported on 7 May, and small, frequent ash emissions accompanied spasmodic tremor on 8 May.

A significant explosion on 16 May 2016, that caused abundant ashfall on farms 2.5 km WNW, was the start of a new episode that lasted for more than two months. Frequent ash emissions continued the next day, although seismic tremor amplitude decreased substantially from the initial explosion. Numerous gas-and-ash emissions were reported during 17-19 May. Ashfall was reported in areas of Valle Central (30-40 km W), including Coronado, Guadalupe, and Heredia (38 km W). On 20 May a Strombolian phase began, producing an ash-and-gas plume that rose 3 km and drifted W. The eruptive column collapsed, generating pyroclastic flows that reached the nearby ranches of La Silva and La Picada, and the Cráter Central. According to a news article, some airlines canceled or delayed flights into the Juan Santamaría International Airport (48 km W).

Gas-and-ash emissions continued during 21-22 May; plumes rose as high as 600 m above the summit. Villagers reported ashfall in areas of San José (40 km WSW), Cartago (25 km SW), Alajuela (49 km W), Heredia (38 km W), Puriscal (65 km WSW), and Jaco (100 km SW). Ash plumes rose as high as 1 km and drifted W and SW on 23 May, causing ashfall in areas downwind including Tapezco (Zarcero-Alfaro Ruíz, 70 km WNW), Guácima de Alajuela (55 km WSW), Barva (39 km W), Finca Lara (17 km W), Finca Laguna (23 km WNW), Grecia, and Naranjo. A strong explosion on 24 May generated new ash plumes that rose 3.5 km and drifted SW. This event ejected large rocks around the crater and led to ashfall in multiple areas including Santa Rosa de Oreamuno, Santa Cecilia de Heredia, and San Francisco de Heredia, tens of kilometers to the W. Large amounts of ash (deposits 2-7 mm thick) fell in Carthage, Heredia (38 km W), San José (40 km W), and Alajuela (49 km W) from more explosions on 25 May that also ejected incandescent material.

A small explosion on 1 June 2016 began a new sequence of ash emissions, with plumes rising 1-2 km, that lasted until 4 June. Ashfall was reported in a number of communities including San Rafael de Moravia (31 km WSW), Sabana (38 km WSW), Buenos Aires (17 km N), and Pococí (45 km N) during 2-3 June. Ash emissions and explosions on 10 June caused ashfall and/or a sulfur odor in multiple areas of Valle Central including San Luis, Santo Domingo, Moravia, San Francisco, and Coronado. OVSICORI-UNA reported increased seismic activity on 16 June; the webcam showed areas of incandescence. Morning satellite imagery showed a diffuse ash plume extending 45 km WNW of the summit that dissipated by mid-afternoon. Tremor increased on 23 June, followed by a lengthy sequence of tremor episodes and ash emissions that lasted through 26 June; ashfall was reported in several neighborhoods in San José and Heredia. Increased tremor on 28 June was likely accompanied by ash emissions, but darkness and clouds obscured views from the webcam.

Strong tremor on 7 July 2016 was followed by an ash plume that rose 1 km above the crater and likely drifted WNW and WSW. Ashfall was recorded in many neighborhoods downwind, in San José, Heredia, and Turrubares. Emissions of large amounts of ash were visible in the webcam the next day, and ashfall was reported in many of the same areas as the day before. The Washington VAAC issued daily reports from 7 to 15 July of diffuse ash emissions observed in the webcam, generally rising less than 500 m above the summit. A new series of explosions during 22-25 July were recorded seismically, but visual observations were difficult due to fog. Hot rock fragments, gas, and ash were noted as high as 500 m above the crater on 24 July. Ash plumes rose to 3 km above the crater and drifted NW, W, and SW the next day. OVSICORI-UNA reported possible volcanic ash again on 29 July and 1 August, but weather clouds prevented views in satellite imagery.

Another new series of explosions and ash emissions began on 13 September 2016. They were reported daily from 15 September to the end of the month. Most plumes rose less than 1 km above the crater, but explosions on 19 September generated ash plumes that rose as high as 4 km and resulted in ashfall in many communities in the Valle Central, including those in San José (35 km WSW), Heredia (38 km W), Alajuela, and Cartago (25 km SW). According to news articles, flights in and out of the Juan Santamaría International Airport were canceled; the airport remained closed at least through the morning of 20 September. The Pavas San José Tobías Bolaños Airport in San José was also temporarily closed. Plumes that rose as high as 2 km were reported on 22, 26, and 27 September.

During a 22-24 September field visit OVSICORI-UNA scientists observed a significant lahar in the Rio Toro Amarillo which flows NW from Turrialba, that mobilized logs and large rocks in a 1.5-m-deep flow (figure 47). They had observed 3 cm of fresh ash in the drainage prior to the start of the rainfall on 22 September.

Figure 47. The abrupt change in flow conditions was observed by OVSICORI-UNA scientists on 22 September 2016 when heavy rains generated a lahar in the Rio Toro Amarillo at Turrialba. The inset photo shows the same area about an hour before the flooding. Photo by E. Duarte, courtesy of OVSICORI-UNA (Algunos Efectos Proximales y Distales por Acumulación de la Ceniza: Volcán Turrialba, Reporte de campo: 22-24 de setiembre de 2016).

From 26 September through 24 November 2016 multiple reports were issued by the Washington VAAC virtually every day, usually reporting minor emissions of gas and ash. OVSICORI reported intermittent steam, gas, and ash emissions rising 500-1,000 m during all of October 2016. Ashfall was reported in Guadeloupe on 11 October. On 16 October OVSICORI-UNA noted that the almost constant ash emission in the previous few days affected the operation and communication of various scientific instruments installed at the top of the volcano and surrounding areas; communication with two seismic stations located near the summit was lost. Webcams showed continuing ash emissions rising as high as 1 km during 16-18 October. During 18-25 October, passive ash emissions continued, causing ashfall in Siquirres (30 ENE), Guacimo (23 km NNE), Guapiles (21 km N), Moravia (27 km W), San José (36 km WSW), Tibás (35 km WSW), Guadalupe (32 km WSW), Curridabat (32 km WSW), Tres Ríos (27 km SW), San Pedro (32 km WSW), and various areas of the Valle Central. Ashfall was reported in Nubes de Coronado (25 km W) on 28 October.

There were fewer reports of ashfall during November, although many areas of the Valle Central reported ashfall during 9-13 November. A small quantity of ash fell in Cartago and Paraiso de Cartago (25 km SE) on 20 November. The Washington VAAC again issued near-daily reports of ash and gas plumes between 6 December and the end of 2016. The weak and sporadic emissions generally rose only a few hundred meters, drifting in multiple directions, and there were few reports of ashfall in the surrounding communities.

Geologic Background. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

Murray Ford, a coastal geomorphologist from New Zealand's Auckland University, reported in a Radio New Zealand story on 1 February 2017 that satellite imagery showed a large plume of discolored water between Tongatapu and the volcanic Hunga Tonga-Hunga Ha'apai islands. The activity seen by Murray was on a Landsat 8 OLI (Operational Land Imager) satellite image acquired on 27 January 2017 (figure 2). which showed a bright area of discolored water above the summit and a broader area of discolored water immediately NW, likely from previous events. According to volcanologist Brad Scott (GNS Science) there are additional satellite images from 23, 26, 28, and 29 January 2017, indicating that the eruption had been ongoing for over a week. His colleagues in Tonga indicated a possible associated steam plume, but cloud cover made observations uncertain.

Figure 2. Landsat 8 OLI satellite image a submarine plume from an unnamed seamount in Tonga on 27 January 2017, about 33 km NW of Tongatapu island. A small bright area of discolored water is directly over the summit (bottom center), with a small plume immediately N, and a broad area of discolored water to the NW, likely from previous eruptive events. The larger plume to the NW measures 30 km long and 20 km wide. Courtesy of NASA Earth Observatory (https://earthobservatory.nasa.gov/IOTD/view.php?id=89565).

A report prepared by Taylor (2000) noted that there had been four previous reports of activity from this location: submarine activity in August 1911, a steam plume in July 1923, discolored water in 1970, and an ephemeral island near the end of an eruptive episode during 27 December 1998-14 January 1999 (also see BGVN 24:03). In a blog post about the latest eruption, Brad Scott (GNS Science) also stated that there had been discolored water and felt earthquakes sometime in 2007.

Reference: Taylor, P., 2000, A volcanic hazards assessment following the January 1999 eruption of Submarine Volcano III, Tofua Volcanic Arc, Kingdom of Tonga, Australian Volcanological Investigations (AVI) Occasional Report No. 99/01, 5 August 2000, 7 p.

Geologic Background. An unnamed submarine volcano is located 35 km NW of the Niu Aunofo lighthouse on Tongatapu Island. Tongatapu is a coral island at the southern end of an island chain paralleling the Tofua volcanic arc to the E. The volcano was constructed at the S end of a submarine ridge segment of the Tofua volcanic arc extending NNE to Falcon Island. The first documented eruptions took place in 1911 and 1923; an ephemeral island was formed in 1999.

Information Contacts: NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Brad Scott, New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/, http://www.geonet.org.nz/news/1usjOmF4LqaI64qScMocuW); Radio New Zealand (URL: http://www.radionz.co.nz/international/pacific-news/323569/scientist-discovers-underwater-eruption-in-tonga).

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

References. Newman, S., 1997, Earthweek, a diary of the planet (week ending 12 September): syndicated newspaper column (URL: http://www.earthweek.com/).

Manila Bulletin, 4 Sept. 1997, Dante's Peak (URL: http://www.mb.com.ph/).

Simkin, T., and Siebert, L., 1994, Volcanoes of the world, 2nd edition: Geoscience Press in association with the Smithsonian Institution Global Volcanism Program, Tucson AZ, 368 p.

Information Contacts: Emmanuel G. Ramos, Deputy Director, Philippine Institute of Volcanology and Seismology, Department of Science and Technology, PHIVOLCS Building, C. P. Garcia Ave., University of the Philippines, Diliman campus, Quezon City, Philippines.

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

Information Contacts: Xinhua News Agency, 5 Sharp Street West, Wanchai, Hong Kong; Giday WoldeGabriel, EES-1/MS D462, Geology-Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545; Ayalaw Yiman, Ethiopian Embassy, 2134 Kalorama Rd. NW, Washington DC 20008.

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

References. Omlin, A, Damm, E., Mienert, J., and Lukas, D., 1999, In-situ detection of methane releases adjacent to gas hydrate fields on the Norwegian margin: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Yalciner, A.C., Borrero, J., Kukano, U., Watts, P., Synolakis, C. E., and Imamura, F., 1999, Field survey of 1999 Izmit tsunami and modeling effort of new tsunami generation mechanism: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Gold, T., 1998, The deep hot biosphere: Springer Verlag, 256 p., ISBN: 0387985468.

Gold, T., 2000, Eye-witness accounts of several major earthquakes (URL: http://www.people.cornell.edu/ pages/tg21/eyewit.html).

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

References. Devyatkin, E.V. and Smelov, S.B., 1979, Position of basalts in sequence of Cenozoic sediments of Mongolia: Izvestiya USSR Academy of Sciences, geological series, no. 1, p. 16-29. (In Russian).

Logatchev, N.A., Devyatkin, E.V., Malaeva, E.M., and others, 1982, Cenozoic deposits of Taryat basin and Chulutu river valley (Central Hangai): Izvestiya USSR Academy of Sciences, geological series, no. 8, p. 76-86. (In Russian).

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Information Contacts: Alexei V. Ivanov, Institute of the Earth Crust SB, Russian Academy of Sciences, Irkutsk, Russia; Bekhtur andM. Ulziibat, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulan-Bator, Mongolia; M. Ganzorig, Institute of Informatics MAS, Ulan-Bator, Mongolia.

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.

Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8, B-9000, Belgium; Chris Newhall, USGS, Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; The Daily Nation (URL: http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL: http://www.visituganda.com/).