Frequent activity at Ecuador's Sangay has included pyroclastic flows, lava flows, ash plumes, and lahars reported since 1628. Its remoteness on the east side of the Andean crest make ground observations difficult; remote cameras and satellites provide important information on activity. The current eruption began in March 2019 and continued through December 2019 with activity focused on the Cráter Central and the Ñuñurco (southeast) vent; they produced explosions with ash plumes, lava flows, and pyroclastic flows and block avalanches. In addition, volcanic debris was remobilized in the Volcan river causing significant damming downstream. This report covers ongoing similar activity from January through June 2020. Information is provided by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), and a number of sources of remote data including the Washington Volcanic Ash Advisory Center (VAAC), the Italian MIROVA Volcano HotSpot Detection System, and Sentinel-2 satellite imagery. Visitors also provided excellent ground and drone-based images and information.

Throughout January-June 2020, multiple daily reports from the Washington Volcanic Ash Advisory Center (VAAC) indicated ash plumes rising from the summit, generally 500-1,100 m. Each month one or more plumes rose over 2,000 m. The plumes usually drifted SW or W, and ashfall was reported in communities 25-90 km away several times during January-March and again in June. In addition to explosions with ash plumes, pyroclastic flows and incandescent blocks frequently descended a large, deep ravine on the SE flank. Ash from the pyroclastic flows rose a few hundred meters and drifted away from the volcano. Incandescence was visible on clear nights at the summit and in the ravine. The MIROVA log radiative power graph showed continued moderate and high levels of thermal energy throughout the period (figure 57). Sangay also had small but persistent daily SO₂ signatures during January-June 2020 with larger pulses one or more days each month (figure 58). IG-EPN published data in June 2020 about the overall activity since May 2019, indicating increases throughout the period in seismic event frequency, SO₂ emissions, ash plume frequency, and thermal energy (figure 59).

Figure 57. This graph of log radiative power at Sangay for 18 Aug 2018 through June 2020 shows the moderate levels of thermal energy through the end of the previous eruption in late 2018 and the beginning of the current one in early 2019. Data is from Sentinel-2, courtesy of MIROVA.

Figure 58. Small but persistent daily SO2 signatures were typical of Sangay during January-June 2020. A few times each month the plume was the same or larger than the plume from Columbia’s Nevado del Ruiz, located over 800 km NE. Image dates are shown in the header over each image. Courtesy of NASA’s Global Sulfur Dioxide Monitoring Page.

Figure 59. A multi-parameter graph of activity at Sangay from May 2019 to 12 June 2020 showed increases in many types of activity. a) seismic activity (number of events per day) detected at the PUYO station (source: IG-EPN). b) SO2 emissions (tons per day) detected by the Sentinel-5P satellite sensor (TROPOMI: red squares; source: MOUNTS) and by the IG-EPN (DOAS: green bars). c) height of the ash plumes (meters above crater) detected by the GOES-16 satellite sensor (source: Washington VAAC). d) thermal emission power (megawatt) detected by the MODIS satellite sensor (source: MODVOLC) and estimate of the accumulated lava volume (million M3, thin lines represent the error range). Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2020 - N°3, “Actualización de la actividad eruptiva”, Quito, 12 de junio del 2020).

Activity during January-March 2020. IG-EPN and the Washington VAAC reported multiple daily ash emissions throughout January 2020. Gas and ash emissions generally rose 500-1,500 m above the summit, most often drifting W or SW. Ashfall was reported on 8 January in the communities of Sevilla (90 km SSW), Pumallacta and Achupallas (60 km SW) and Cebadas (35 km WNW). On 16 January ash fell in the Chimborazo province in the communities of Atillo, Ichobamba, and Palmira (45 km W). Ash on 28 January drifted NW, with minor ashfall reported in Púngala (25 km NW) and other nearby communities. The town of Alao (20 km NW) reported on 30 January that all of the vegetation in the region was covered with fine white ash; Cebadas and Palmira also noted minor ashfall (figure 60).

Figure 60. Daily ash plumes and repeated ashfall were reported from Sangay during January 2020. Top left: 1 January 2020 (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-2, JUEVES, 2 ENERO 2020). Top right: 20 January 2020 (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-21, MARTES, 21 ENERO 2020). Bottom left: 26 January-1 February 2020 expedition (Martes, 18 Febrero 2020 12:21, EXPEDICIÓN AL VOLCÁN SANGAY). Bottom right: 30 January 2020, minor ashfall was reported in the Province of Chimborazo (#IGAlInstante Informativo VOLCÁN SANGAY No. 006, JUEVES, 30 ENERO 2020). Courtesy of IG-EPN.

A major ravine on the SE flank has been the site of ongoing block avalanches and pyroclastic flows since the latest eruption began in March 2019. The pyroclastic flows down the ravine appeared incandescent at night; during the day they created ash clouds that drifted SW. Satellite imagery recorded incandescence and dense ash from pyroclastic flows in the ravine on 7 January (figure 61). They were also reported by IG on the 9th, 13th, 26th, and 28th. Incandescent blocks were reported in the ravine several times during the month. The webcam captured images on 31 January of large incandescent blocks descending the entire length of the ravine to the base of the mountain (figure 62). Large amounts of ash and debris were remobilized as lahars during heavy rains on the 25th and 28th.

Figure 61. Sentinel-2 satellite imagery of Sangay from 7 January 2020 clearly showed a dense ash plume drifting W and ash and incandescent material from pyroclastic flows descending the SE-flank ravine. Left image uses natural color (bands 4, 3, 2) rendering and right images uses atmospheric penetration (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Figure 62. Pyroclastic flows at Sangay produced large trails of ash down the SE ravine many times during January 2020 that rose and drifted SW. Top left: 9 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-9, JUEVES, 9 ENERO 2020). Top right: 13 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-14, MARTES, 14 ENERO 2020). On clear nights, incandescent blocks of lava and pyroclastic flows were visible in the ravine. Bottom left: 16 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-17, VIERNES, 17 ENERO 2020). Bottom right: 31 January (#IGAlInstante Informativo VOLCÁN SANGAY No. 007, VIERNES, 31 ENERO 2020). Courtesy of IG-EPN.

Observations by visitors to the volcano during 9-17 January 2020 included pyroclastic flows, ash emissions, and incandescent debris descending the SE flank ravine during the brief periods when skies were not completely overcast (figure 63 and 64). More often there was ash-filled rain and explosions heard as far as 16 km from the volcano, along with the sounds of lahars generated from the frequent rainfall mobilizing debris from the pyroclastic flows. The confluence of the Rio Upano and Rio Volcan is 23 km SE of the summit and debris from the lahars has created a natural dam on the Rio Upano that periodically backs up water and inundates the adjacent forest (figure 65). A different expedition to Sangay during 26 January-1 February 2020 by IG personnel to repair and maintain the remote monitoring station and collect samples was successful, after which the station was once again transmitting data to IG-EPN in Quito (figure 66).

Figure 63. Hikers near Sangay during 9-17 January 2020 witnessed pyroclastic flows and incandescent explosions and debris descending the SE ravine. Left: The view from 40 km SE near Macas showed ash rising from pyroclastic flows in the SE ravine. Right: Even though the summit was shrouded with a cap cloud, incandescence from the summit crater and from pyroclastic flows on the SE flank were visible on clear nights. Courtesy of Arnold Binas, used with permission.

Figure 64. The steep ravine on the SE flank of Sangay was hundreds of meters deep in January 2020 when these drone images were taken by members of a hiking trip during 9-17 January 2020 (left). Pyroclastic flows descended the ravine often (right), coating the sides of the ravine with fine, white ash and sending ash billowing up from the surface of the flow which resulted in ashfall in adjacent communities several times. Courtesy of Arnold Binas, used with permission.

Figure 65. Debris from pyroclastic flows that descended the SE Ravine at Sangay was carried down the Volcan River (left) during frequent rains and caused repeated damming at the confluence with the Rio Upano (right), located 23 km SE of the summit. These images show the conditions along the riverbeds during 9-17 January 2020. Courtesy of Arnold Binas, used with permission.

Figure 66. An expedition by scientists from IG-EPN to one of the remote monitoring stations at Sangay during 26 January-1 February 2020 was successful in restoring communication to Quito. The remote location and constant volcanic activity makes access and maintenance a challenge. Courtesy of IG-EPN (Martes, 18 Febrero 2020 12:21, EXPEDICIÓN AL VOLCÁN SANGAY).

During February 2020, multiple daily VAAC reports of ash emissions continued (figure 67). Plumes generally rose 500-1,100 m above the summit and drifted W, although on 26 February emissions were reported to 1,770 m. Ashfall was reported in Macas (40 km SE) on 1 February, and in the communities of Pistishi (65 km SW), Chunchi (70 km SW), Pumallacta (60 k. SW), Alausí (60 km SW), Guamote (40 km WNW) and adjacent areas of the Chimborazo province on 5 February. The Ecuadorian Red Cross reported ash from Sangay in the provinces of Cañar and Azuay (60-100 km SW) on 25 February. Cebadas and Guamote reported moderate ashfall the following day. The communities of Cacha (50 km NW) and Punín (45 km NW) reported trace amounts of ashfall on 29 February. Incandescent blocks were seen on the SE flank multiples times throughout the month. A pyroclastic flow was recorded on the SE flank early on 6 February; additional pyroclastic flows were observed later that day on the SW flank. On 23 February a seismic station on the flank recorded a high-frequency signal typical of lahars.

Figure 67. Steam and ash could be seen drifting SW from the summit of Sangay on 11 February 2020 even though the summit was hidden by a large cap cloud. Ash was also visible in the ravine on the SE flank. Courtesy of Sentinel Hub Playground, natural color (bands 4, 3, 2) rendering.

A significant ash emission on 1 March 2020 was reported about 2 km above the summit, drifting SW. Multiple ash emissions continued daily during the month, generally rising 570-1,170 m high. An emission on 12 March also rose 2 km above the summit. Trace ashfall was reported in Cebadas (35 km WNW) on 12 March. The community of Huamboya, located 40 km ENE of Sangay in the province of Morona-Santiago reported ashfall on 17 March. On 19 and 21 March ashfall was seen on the surface of cars in Macas to the SE. (figure 68). Ash was also reported on the 21st in de Santa María De Tunants (Sinaí) located E of Sangay. Ash fell again in Macas on 23 March and was also reported in General Proaño (40 km SE). The wind changed direction the next day and caused ashfall on 24 March to the SW in Cuenca and Azogues (100 km SW).

Figure 68. Ashfall from Sangay was reported on cars in Huamboya on 17 March 2020 (left) and in Macas on 19 March (right). Courtesy IG-EPN, (#IGAlInstante Informativo VOLCÁN SANGAY No. 024, MARTES, 17 MARZO 2020 and #IGAlInstante Informativo VOLCÁN SANGAY No. 025, JUEVES, 19 MARZO 2020).

Incandescence from the dome at the crater and on the SE flank was noted by IG on 3, 4, and 13 March. Remobilized ash from a pyroclastic flow was reported drifting SW on 13 March. The incandescent path of the flow was still visible that evening. Numerous lahars were recorded seismically during the month, including on days 5, 6, 8, 11, 15, 30 and 31. Images from the Rio Upano on 11 March confirmed an increase from the normal flow rate (figure 69) inferred to be from volcanic debris. Morona-Santiago province officials reported on 14 March that a new dam had formed at the confluence of the Upano and Volcano rivers that decreased the flow downstream; by 16 March it had given way and flow had returned to normal levels.

Figure 69. Images from the Rio Upano on 11 March 2020 (left) confirmed an increase from the normal flow rate related to lahars from Sangay descending the Rio Volcan. By 16 March (right), the flow rate had returned to normal, although the large blocks in the river were evidence of substantial activity in the past. Courtesy of IG (#IGAlInstante Informativo VOLCÁN SANGAY No. 018, MIÉRCOLES, 11 MARZO 2020 and #IGAlInstante Informativo VOLCÁN SANGAY No. 023, LUNES, 16 MARZO 2020).

Activity during April-June 2020. Lahar activity continued during April 2020; they were reported seven times on 2, 5, 7, 11, 12, 19, and 30 April. A significant reduction in the flow of the Upano River at the entrance bridge to the city of Macas was reported 9 April, likely due to a new dam on the river upstream from where the Volcan river joins it caused by lahars related to ash emissions and pyroclastic flows (figure 70). The flow rate returned to normal the following day. Ash emissions were reported most days of the month, commonly rising 500-1,100 m above the summit and drifting W. Incandescent blocks or flows were visible on the SE flank on 4, 10, 12, 15-16, and 20-23 April (figure 71).

Figure 70. A significant reduction in the flow of the Upano River at the entrance bridge to the city of Macas was reported on 9 April 2020, likely due to a new dam upstream from lahars related to ash emissions and pyroclastic flows from Sangay. Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 032, JUEVES, 9 ABRIL 2020).

Figure 71. Incandescent blocks rolled down the SE ravine at Sangay multiple times during April 2020, including on 4 April (left). Pyroclastic flows left two continuous incandescent trails in the ravine on 23 April (right). Courtesy of IG-EPN (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-95, SÁBADO, 4 ABRIL 2020 and INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-114, JUEVES, 23 ABRIL 2020).

Activity during May 2020 included multiple daily ash emissions that drifted W and numerous lahars from plentiful rain carrying ash and debris downstream. Although there were only a few visible observations of ash plumes due to clouds, the Washington VAAC reported plumes visible in satellite imagery throughout the month. Plumes rose 570-1,170 m above the summit most days; the highest reported rose to 2,000 m above the summit on 14 May. Two lahars occurred in the early morning on 1 May and one the next day. A lahar signal lasted for three hours on 4 May. Two lahar signals were recorded on the 7th, and three on the 9th. Lahars were also recorded on 16-17, 20-22, 26-27, and 30 May. Incandescence on the SE flank was only noted three times, but it was cloudy nearly every day.

An increase in thermal and overall eruptive activity was reported during June 2020. On 1 and 2 June the webcam captured lava flows and remobilization of the deposits on the SE flank in the early morning and late at night. Incandescence was visible multiple days each week. Lahars were reported on 4 and 5 June. The frequent daily ash emissions during June generally rose to 570-1,200 m above the summit and drifted usually SW or W. The number of explosions and ash emissions increased during the evening of 7 June. IG interpreted the seismic signals from the explosions as an indication of the rise of a new pulse of magma (figure 72). The infrasound sensor log from 8 June also recorded longer duration tremor signals that were interpreted as resulting from the descent of pyroclastic flows in the SE ravine.

Figure 72. Seismic and infrasound signals indicated increased explosive and pyroclastic flow activity at Sangay on 7-8 June 2020. Left: SAGA station (seismic component) of 7 and 8 June. The signals correspond to explosions without VT or tremor signals, suggesting the rise of a new magma pulse. Right: SAGA station infrasound sensor log from 8 June. The sharp explosion signals are followed a few minutes later (examples highlighted in red) by emergent signals of longer duration, possibly associated with the descent of pyroclastic material in the SE flank ravine. Courtesy if IG-EPN (Informe Especial del Volcán Sangay - 2020 - N°3, “Actualización de la actividad eruptiva”, Quito, 12 de junio del 2020).

On the evening of 8 June ashfall was reported in the parish of Cebadas and in the Alausí Canton to the W and SW of Sangay. There were several reports of gas and ash emissions to 1,770 m above the summit the next morning on 9 June, followed by reports of ashfall in the provinces of Guayas, Santa Elena, Los Ríos, Morona Santiago, and Chimborazo. Ashfall continued in the afternoon and was reported in Alausí, Chunchi, Guamote, and Chillanes. That night, which was clear, the webcam captured images of pyroclastic flows down the SE-flank ravine; IG attributed the increase in activity to the collapse of one or more lava fronts. On the evening of 10 June additional ashfall was reported in the towns of Alausí, Chunchi, and Guamote (figure 73); satellite imagery indicated an ash plume drifting W and incandescence from pyroclastic flows in the SE-flank ravine the same day (figure 74).

Figure 73. Ashfall from Sangay was reported in Alausí (top left), Chunchi (top right) and Guamote (bottom) on 10 June 2020. Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 049, MIÉRCOLES, 10 JUNIO 2020).

Figure 74. Incandescent pyroclastic flows (left) and ash plumes that drifted W (right) were recorded on 10 June 2020 at Sangay in Sentinel-2 satellite imagery. Courtesy of Sentinel Hub Playground.

Ashfall continued on 11 June and was reported in Guayaquil, Guamote, Chunchi, Riobamba, Guaranda, Chimbo, Echandía, and Chillanes. The highest ash plume of the report period rose to 2,800 m above the summit that day and drifted SW. That evening the SNGRE (Servicio Nacional de Gestion de Riesgos y Emergencias) reported ash fall in the Alausí canton. IG noted the increase in intensity of activity and reported that the ash plume of 11 June drifted more than 600 km W (figure 75). Ash emissions on 12 and 13 June drifted SW and NW and resulted in ashfall in the provinces of Chimborazo, Cotopaxi, Tungurahua, and Bolívar. On 14 June, the accumulation of ash interfered with the transmission of information from the seismic station. Lahars were reported each day during 15-17 and 19-21 June. Trace amounts of ashfall were reported in Macas to the SE on 25 June.

Figure 75. The ash plume at Sangay reported on 11 June 2020 rose 2.8 km above the summit and drifted W according to the Washington VAAC and IG (left). Explosions and high levels of incandescence on the SE flank were captured by the Don Bosco webcam (right). Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 055, JUEVES, 11 JUNIO 2020 and INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-164, VIERNES, 12 JUNIO 2020).

During an overflight of Sangay on 24 June IG personnel observed that activity was characterized by small explosions from the summit vent and pyroclastic flows down the SE-flank ravine. The explosions produced small gas plumes with a high ash content that did not rise more than 500 m above the summit and drifted W (figure 76). The pyroclastic flows were restricted to the ravine on the SE flank, although the ash from the flows rose rapidly and reached about 200 m above the surface of the ravine and also drifted W (figure 77).

Figure 76. A dense ash plume rose 500 m from the summit of Sangay on 24 June 2020 and drifted W during an overflight by IG-EPN personnel. The aerial photograph is taken from the SE; snow-covered Chimborazo is visible behind and to the right of Sangay. Photo by M Almeida, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

Figure 77. Pyroclastic flows descended the SE flank ravine at Sangay during an overflight by IG-EPN personnel on 24 June 2020. Ash from the pyroclastic flow rose 200 m and drifted W, and infrared imagery identified the thermal signature of the pyroclastic flow in the ravine. Photo by M Almeida, IR Image by S Vallejo, courtesy of IG EPN (Jueves, 25 Junio 2020 12:24, SOBREVUELO AL VOLCÁN SANGAY).

Infrared imagery taken during the overflight on 24 June identified three significant thermal anomalies in the large ravine on the SE flank (figure 78). Analysis by IG scientists suggested that the upper anomaly 1 (125°C) was associated with explosive activity that was observed during the flight. Anomaly 2 (147°C), a short distance below Anomaly 1, was possibly related to effusive activity of a small flow, and Anomaly 3 (165°C) near the base of the ravine that was associated with pyroclastic flow deposits. The extent of the changes at the summit of Sangay and along the SE flank since the beginning of the eruption that started in March 2019 were clearly visible when images from May 2019 were compared with images from the 24 June 2020 overflight (figure 79). The upper part of the ravine was nearly 400 m wide by the end of June.

Figure 78. A thermal image of the SE flank of Sangay taken on 24 June 2020 indicated three thermal anomalies. Anomaly 1 was associated with explosive activity, Anomaly 2 was associated with effusive activity, and Anomaly 3 was related to pyroclastic-flow deposits. Image prepared by S Vallejo Vargas, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

Figure 79. Aerial and thermal photographs of the southern flank of the Sangay volcano on 17 May 2019 (left: visible image) and 24 June 2020 (middle: visible image, right: visible-thermal overlay) show the morphological changes on the SE flank, associated with the formation of a deep ravine and the modification of the summit. Photos and thermal image by M Almeida, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

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, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); 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); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Arnold Binas (URL: https://www.doroadventures.com).

The Karangetang andesitic-basaltic stratovolcano (also referred to as Api Siau) at the northern end of the island of Siau, north of Sulawesi, Indonesia, has had more than 50 observed eruptions since 1675. Frequent explosive activity is accompanied by pyroclastic flows and lahars, and lava-dome growth has created two active summit craters (Main to the S and Second Crater to the N). Rock avalanches, observed incandescence, and satellite thermal anomalies at the summit confirmed continuing volcanic activity since the latest eruption started in November 2018 (BGVN 44:05). This report covers activity from December 2019 through May 2020. Activity is monitored by Indonesia's Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), and ash plumes are monitored by the Darwin VAAC (Volcanic Ash Advisory Center). Information is also available from MODIS thermal anomaly satellite data through both the University of Hawaii's MODVOLC system and the Italian MIROVA project.

Increased activity that included daily incandescent avalanche blocks traveling down the W and NW flanks lasted from mid-July 2019 (BGVN 44:12) through mid-January 2020 according to multiple sources. The MIROVA data showed increased number and intensity of thermal anomalies during this period, with a sharp drop during the second half of January (figure 40). The MODVOLC thermal alert data reported 29 alerts in December and ten alerts in January, ending on 14 January, with no further alerts through May 2020. During December and the first half of January incandescent blocks traveled 1,000-1,500 m down multiple drainages on the W and NW flanks (figure 41). After this, thermal anomalies were still present at the summit craters, but no additional activity down the flanks was identified in remote satellite data or direct daily observations from PVMBG.

Figure 40. An episode of increased activity at Karangetang from mid-July 2019 through mid-January 2020 included incandescent avalanche blocks traveling down multiple flanks of the volcano. This was reflected in increased thermal activity seen during that interval in the MIROVA graph covering 5 June 2019 through May 2020. Courtesy of MIROVA.

Figure 41. An episode of increased activity at Karangetang from mid-July 2019 through mid-January 2020 included incandescent avalanche blocks traveling up to 1,500 m down drainages on the W and NW flanks of the volcano. Top left: large thermal anomalies trend NW from Main Crater on 5 December 2019; about 500 m N a thermal anomaly glows from Second Crater. Top center: on 15 December plumes of steam and gas drifted W and SW from both summit craters as seen in Natural Color rendering (bands 4,3,2). Top right: the same image as at top center with Atmospheric penetration rendering (bands 12, 11, 8a) shows hot zones extending WNW from Main Crater and a thermal anomaly at Second Crater. Bottom left: thermal activity seen on 14 January 2020 extended about 800 m WNW from Main Crater along with an anomaly at Second Crater and a hot spot about 1 km W. Bottom center: by 19 January the anomaly from Second Crater appeared slightly stronger than at Main Crater, and only small anomalies appeared on the NW flank. Bottom right: an image from 14 March shows only thermal anomalies at the two summit craters. Courtesy of Sentinel Hub Playground.

A single VAAC report in early April noted a short-lived ash plume that drifted SW. Intermittent low-level activity continued through May 2020. Small SO₂ plumes appeared in satellite data multiple times in December 2019 and January 2020; they decreased in size and frequency after that but were still intermittently recorded into May 2020 (figure 42).

Figure 42. Small plumes of sulfur dioxide were measured at Karangetang with the TROPOMI instrument on the Sentinel-5P satellite multiple times during December 2019 (top row). They were less frequent but still appeared during January-May 2020 (bottom row). Larger plumes were also detected from Dukono, located 300 km ESE at the N end of North Maluku. Courtesy of Global Sulfur Dioxide Monitoring Page.

PVMBG reported in their daily summaries that steam plumes rose 50-150 m above the Main Crater and 25-50 m above Second Crater on most days in December. The incandescent avalanche activity that began in mid-July 2019 also continued throughout December 2019 and January 2020 (figure 43). Incandescent blocks from the Main Crater descended river drainages (Kali) on the W and NW flanks throughout December. They were reported nearly every day in the Nanitu, Sense, and Pangi drainages, traveling 1,000-1,500 m. Incandescence from both craters was visible 10-25 m above the crater rim most nights.

Figure 43. Incandescent block avalanches descended the NW flank of Karangetang as far as 1,500 m frequently during December 2019 and January 2020. Left image taken 13 December 2019, right image taken 6 January 2020 by PVMBG webcam. Courtesy of PVMBG, Oystein Anderson, and Bobyson Lamanepa.

A few blocks were noted traveling 800 m down Kali Beha Barat on 1 December. Incandescence above the Main crater reached 50-75 m during 4-6 December. During 4-7 December incandescent blocks appeared in Kali Sesepe, traveling 1,000-1,500 m down from the summit. They were also reported in Kali Batang and Beha Barat during 4-14 December, usually moving 800-1,000 m downslope. Between 5 and 14 December, gray and white plumes from Second Crater reached 300 m multiple times. During 12-15 December steam plumes rose 300-500 m above the Main crater. Activity decreased during 18-26 December but increased again during the last few days of the month. On 28 December, incandescent blocks were reported 1,500 m down Kali Pangi and Nanitu, and 1,750 m down Kali Sense.

Incandescent blocks were reported in Kali Sesepi during 4-6 January and in Kali Batang and Beha Barat during 4-8 and 12-15 January (figure 44); they often traveled 800-1,200 m downslope. Activity tapered off in those drainages and incandescent blocks were last reported in Kali Beha Barat on 15 January traveling 800 m from the summit. Incandescent blocks were also reported traveling usually 1,000-1,500 m down the Nanitu, Sense, and Pangi drainages during 4-19 January. Blocks continued to occasionally descend up to 1,000 m down Kali Nanitu through 24 January. Pulses of activity occurred at the summit of Second Crater a few times in January. Steam plumes rose 25-50 m during 8-9 January and again during 16-31 January, with plumes rising 300-400 m on 20, 29, and 31 January. Incandescence was noted 10-25 m above the summit of Second Crater during 27-30 January.

Figure 44. Incandescent material descends the Beha Barat, Sense, Nanitu, and Pangi drainages on the NW flank of Karangetang in early January 2020. Courtesy of Bobyson Lamanepa; posted on Twitter on 6 January 2020.

Activity diminished significantly after mid-January 2020. Steam plumes at the Main Crater rose 50-100 m on the few days where the summit was not obscured by fog during February. Faint incandescence occurred at the Main Crater on 7 February, and steam plumes rising 25-50 m from Second Crater that day were the only events reported there in February. During March, steam plumes persisted from the Main Crater, with heights of over 100 m during short periods from 8-16 March and 25-30 March. Weak incandescence was reported from the Main Crater only once, on 25 March. Very little activity occurred at Second Crater during March, with only steam plumes reported rising 25-300 m from the 22nd to the 28th (figure 45).

Figure 45. Steam plumes at Karangetang rose over 100 m above both summit craters multiple times during March, including on 26 March 2020. Courtesy of PVMBG and Oystein Anderson.

The Darwin VAAC reported a continuous ash emission on 4 April 2020 that rose to 2.1 km altitude and drifted SW for a few hours before dissipating. Incandescence visible 25 m above both craters on 13 April was the only April activity reported by PVMBG other than steam plumes from the Main Crater that rose 50-500 m on most days. Steam plumes of 50-100 m were reported from Second Crater during 11-13 April. Activity remained sporadic throughout May 2020. Steam plumes from the Main Crater rose 50-300 m each day. Satellite imagery identified steam plumes and incandescence from both summit craters on 3 May (figure 46). Faint incandescence was observed at the Main Crater on 12 and 27 May. Steam plumes rose 25-50 m from Second Crater on a few days; a 200-m-high plume was reported on 27 May. Bluish emissions were observed on the S and SW flanks on 28 May.

Figure 46. Dense steam plumes and thermal anomalies were present at both summit craters of Karangetang on 3 May 2020. Sentinel 2 satellite image with Natural Color (bands 4, 3, 2) (left) and Atmospheric Penetration rendering (bands 12, 11, 8a) (right); courtesy of Sentinel Hub Playground.

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); 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/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Bobyson Lamanepa, Yogyakarta, Indonesia, (URL: https://twitter.com/BobyLamanepa/status/1214165637028728832).

Masaya, which is about 20 km NW of the Nicaragua’s capital of Managua, is one of the most active volcanoes in that country and has a caldera that contains a number of craters (BGVN 43:11). The Santiago crater is the one most currently active and it contains a small lava lake that emits weak gas plumes (figure 85). This report summarizes activity during February through May 2020 and is based on Instituto Nicaragüense de Estudios Territoriales (INETER) monthly reports and satellite data. During the reporting period, the volcano was relatively calm, with only weak gas plumes.

Figure 85. Satellite images of Masaya from Sentinel-2 on 18 April 2020, showing and a small gas plume drifting SW (top, natural color bands 4, 3, 2) and the lava lake (bottom, false color bands 12, 11, 4). Courtesy of Sentinel Hub Playground.

According to INETER, thermal images of the lava lake and temperature data in the fumaroles were taken using an Omega infrared gun and a forward-looking infrared (FLIR) SC620 thermal camera. The temperatures above the lava lake have decreased since November 2019, when the temperature was 287°C, dropping to 96°C when measured on 14 May 2020. INETER attributed this decrease to subsidence in the level of the lava lake by 5 m which obstructed part of the lake and concentrated the gas emissions in the weak plume. Convection continued in the lava lake, which in May had decreased to a diameter of 3 m. Many landslides had occurred in the E, NE, and S walls of the crater rim due to rock fracturing caused by the high heat and acidity of the emissions.

During the reporting period, the MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system recorded numerous thermal anomalies from the lava lake based on MODIS data (figure 86). Infrared satellite images from Sentinel-2 regularly showed a strong signature from the lava lake through 18 May, after which the volcano was covered by clouds.

Figure 86. Thermal anomalies at Masaya during February through May 2020. The larger anomalies with black lines are more distant and not related to the volcano. Courtesy of MIROVA.

Measurements of sulfur dioxide (SO2) made by INETER in the section of the Ticuantepe - La Concepción highway (just W of the volcano) with a mobile DOAS system varied between a low of just over 1,000 metric tons/day in mid-November 2019 to a high of almost 2,500 tons/day in late May. Temperatures of fumaroles in the Cerro El Comalito area, just ENE of Santiago crater, ranged from 58 to 76°C during February-May 2020, with most values in the 69-72°C range.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Shishaldin is located near the center of Unimak Island in Alaska, with the current eruption phase beginning in July 2019 and characterized by ash plumes, lava flows, lava fountaining, pyroclastic flows, and lahars. More recently, in late 2019 and into January 2020, activity consisted of multiple lava flows, pyroclastic flows, lahars, and ashfall events (BGVN 45:02). This report summarizes activity from February through May 2020, including gas-and-steam emissions, brief thermal activity in mid-March, and a possible new cone within the summit crater. The primary source of information comes from the Alaska Volcano Observatory (AVO) reports and various satellite data.

Volcanism during February 2020 was relatively low, consisting of weakly to moderately elevated surface temperatures during 1-4 February and occasional small gas-and-steam plumes (figure 37). By 6 February both seismicity and surface temperatures had decreased. Seismicity and surface temperatures increased slightly again on 8 March and remained elevated through the rest of the reporting period. Intermittent gas-and-steam emissions were also visible from mid-March (figure 38) through May. Minor ash deposits visible on the upper SE flank may have been due to ash resuspension or a small collapse event at the summit, according to AVO.

Figure 37. Photo of a gas-and-steam plume rising from the summit crater at Shishaldin on 22 February 2020. Photo courtesy of Ben David Jacob via AVO.

Figure 38. A Worldview-2 panchromatic satellite image on 11 March 2020 showing a gas-and-steam plume rising from the summit of Shishaldin and minor ash deposits on the SE flank (left). Aerial photo showing minor gas-and-steam emissions rising from the summit crater on 11 March (right). Some erosion of the snow and ice on the upper flanks is a result of the lava flows from the activity in late 2019 and early 2020. Photo courtesy of Matt Loewen (left) and Ed Fischer (right) via AVO.

On 14 March, lava and a possible new cone were visible in the summit crater using satellite imagery, accompanied by small explosion signals. Strong thermal signatures due to the lava were also seen in Sentinel-2 satellite data and continued strongly through the month (figure 39). The lava reported by AVO in the summit crater was also reflected in satellite-based MODIS thermal anomalies recorded by the MIROVA system (figure 40). Seismic and infrasound data identified small explosions signals within the summit crater during 14-19 March.

Figure 39. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show a bright hotspot (yellow-orange) at the summit crater of Shishaldin during mid-March 2020 that decreases in intensity by late March. Courtesy of Sentinel Hub Playground.

Figure 40. MIROVA thermal data showing a brief increase in thermal anomalies during late March 2020 and on two days in late April between periods of little to no activity. Courtesy of MIROVA.

AVO released a Volcano Observatory Notice for Aviation (VONA) stating that seismicity had decreased by 16 April and that satellite data no longer showed lava or additional changes in the crater since the start of April. Sentinel-2 thermal satellite imagery continued to show a weak hotspot in the crater summit through May (figure 41), which was also detected by the MIROVA system on two days. A daily report on 6 May reported a visible ash deposit extending a short distance SE from the summit, which had likely been present since 29 April. AVO noted that the timing of the deposit corresponds to an increase in the summit crater diameter and depth, further supporting a possible small collapse. Small gas-and-steam emissions continued intermittently and were accompanied by weak tremors and occasional low-frequency earthquakes through May (figure 42). Minor amounts of sulfur dioxide were detected in the gas-and-steam emissions during 20 and 29 April, and 2, 16, and 28 May.

Figure 41. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show occasional gas-and-steam emissions rising from Shishaldin on 26 February (top left) and 24 April 2020 (bottom left) and a weak hotspot (yellow-orange) persisting at the summit crater during April and early May 2020. Courtesy of Sentinel Hub Playground.

Figure 42. A Worldview-1 panchromatic satellite image showing gas-and-steam emissions rising from the summit of Shishaldin on 1 May 2020 (local time) (left). Aerial photo of the N flank of Shishaldin with minor gas-and-steam emissions rising from the summit on 8 May (right). Photo courtesy of Matt Loewen (left) and Levi Musselwhite (right) via AVO.

Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Krakatau, located in the Sunda Strait between Indonesia’s Java and Sumatra Islands, experienced a major caldera collapse around 535 CE, forming a 7-km-wide caldera ringed by three islands. On 22 December 2018, a large explosion and flank collapse destroyed most of the 338-m-high island of Anak Krakatau (Child of Krakatau) and generated a deadly tsunami (BGVN 44:03). The near-sea level crater lake inside the remnant of Anak Krakatau was the site of numerous small steam and tephra explosions. A larger explosion in December 2019 produced the beginnings of a new cone above the surface of crater lake (BGVN 45:02). Recently, volcanism has been characterized by occasional Strombolian explosions, dense ash plumes, and crater incandescence. This report covers activity from February through May 2020 using information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), the Darwin Volcanic Ash Advisory Center (VAAC), and various satellite data.

Activity during February 2020 consisted of dominantly white gas-and-steam emissions rising 300 m above the crater, according to PVMBG. According to the Darwin VAAC, a ground observer reported an eruption on 7 and 8 February, but no volcanic ash was observed. During 10-11 February, a short-lived eruption was detected by seismograms which produced an ash plume up to 1 km above the crater drifting E. MAGMA Indonesia reported two eruptions on 18 March, both of which rose to 300 m above the crater. White gas-and-steam emissions were observed for the rest of the month and early April.

On 10 April PVMBG reported two eruptions, at 2158 and 2235, both of which produced dark ash plumes rising 2 km above the crater followed by Strombolian explosions ejecting incandescent material that landed on the crater floor (figures 108 and 109). The Darwin VAAC issued a notice at 0145 on 11 April reporting an ash plume to 14.3 km altitude drifting WNW, however this was noted with low confidence due to the possible mixing of clouds. During the same day, an intense thermal hotspot was detected in the HIMAWARI thermal satellite imagery and the NASA Global Sulfur Dioxide page showed a strong SO₂ plume at 11.3 km altitude drifting W (figure 110). The CCTV Lava93 webcam showed new lava flows and lava fountaining from the 10-11 April eruptions. This activity was evident in the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph of MODIS thermal anomaly data (figure 111).

Figure 108. Webcam (Lava93) images of Krakatau on 10 April 2020 showing Strombolian explosions, strong incandescence, and ash plumes rising from the crater. Courtesy of PVMBG and MAGMA Indonesia.

Figure 109. Webcam image of incandescent Strombolian explosions at Krakatau on 10 April 2020. Courtesy of PVMBG and MAGMA Indonesia.

Figure 110. Strong sulfur dioxide emissions rising from Krakatau and drifting W were detected using the TROPOMI instrument on the Sentinel-5P satellite on 11 April 2020 (top row). Smaller volumes of SO2 were visible in Sentinel-5P/TROPOMI maps on 13 (bottom left) and 19 April (bottom right). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 111. Thermal activity at Anak Krakatau from 29 June-May 2020 shown on a MIROVA Log Radiative Power graph. The power and frequency of the thermal anomalies sharply increased in mid-April. After the larger eruptive event in mid-April the thermal anomalies declined slightly in strength but continued to be detected intermittently through May. Courtesy of MIROVA.

Strombolian activity rising up to 500 m continued into 12 April and was accompanied by SO₂ emissions that rose 3 km altitude, drifting NW according to a VAAC notice. PVMBG reported an eruption on 13 April at 2054 that resulted in incandescence as high as 25 m above the crater. Volcanic ash, accompanied by white gas-and-steam emissions, continued intermittently through 18 April, many of which were observed by the CCTV webcam. After 18 April only gas-and-steam plumes were reported, rising up to 100 m above the crater; Sentinel-2 satellite imagery showed faint thermal anomalies in the crater (figure 112). SO₂ emissions continued intermittently throughout April, though at lower volumes and altitudes compared to the 11th. MODIS satellite data seen in MIROVA showed intermittent thermal anomalies through May.

Figure 112. Sentinel-2 thermal satellite images showing the cool crater lake on 20 March (top left) followed by minor heating of the crater during April and May 2020. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

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/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); 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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Taal volcano is in a caldera system located in southern Luzon island and is one of the most active volcanoes in the Philippines. It has produced around 35 recorded eruptions since 3,580 BCE, ranging from VEI 1 to 6, with the majority of eruptions being a VEI 2. The caldera contains a lake with an island that also contains a lake within the Main Crater (figure 12). Prior to 2020 the most recent eruption was in 1977, on the south flank near Mt. Tambaro. The United Nations Office for the Coordination of Humanitarian Affairs in the Philippines reports that over 450,000 people live within 40 km of the caldera (figure 13). This report covers activity during January through February 2020 including the 12 to 22 January eruption, and is based on reports by Philippine Institute of Volcanology and Seismology (PHIVOLCS), satellite data, geophysical data, and media reports.

Figure 12. Annotated satellite images showing the Taal caldera, Volcano Island in the caldera lake, and features on the island including Main Crater. Imagery courtesy of Planet Inc.

Figure 13. Map showing population totals within 14 and 17 km of Volcano Island at Taal. Courtesy of the United Nations Office for the Coordination of Humanitarian Affairs (OCHA).

The hazard status at Taal was raised to Alert Level 1 (abnormal, on a scale of 0-5) on 28 March 2019. From that date through to 1 December there were 4,857 earthquakes registered, with some felt nearby. Inflation was detected during 21-29 November and an increase in CO₂ emission within the Main Crater was observed. Seismicity increased beginning at 1100 on 12 January. At 1300 there were phreatic (steam) explosions from several points inside Main Crater and the Alert Level was raised to 2 (increasing unrest). Booming sounds were heard in Talisay, Batangas, at 1400; by 1402 the plume had reached 1 km above the crater, after which the Alert Level was raised to 3 (magmatic unrest).

Phreatic eruption on 12 January 2020. A seismic swarm began at 1100 on 12 January 2020 followed by a phreatic eruption at 1300. The initial activity consisted of steaming from at least five vents in Main Crater and phreatic explosions that generated 100-m-high plumes. PHIVOLCS raised the Alert Level to 2. The Earth Observatory of Singapore reported that the International Data Center (IDC) for the Comprehensive test Ban Treaty (CTBT) in Vienna noted initial infrasound detections at 1450 that day.

Booming sounds were heard at 1400 in Talisay, Batangas (4 km NNE from the Main Crater), and at 1404 volcanic tremor and earthquakes felt locally were accompanied by an eruption plume that rose 1 km; ash fell to the SSW. The Alert Level was raised to 3 and the evacuation of high-risk barangays was recommended. Activity again intensified around 1730, prompting PHIVOLCS to raise the Alert Level to 4 and recommend a total evacuation of the island and high-risk areas within a 14-km radius. The eruption plume of steam, gas, and tephra significantly intensified, rising to 10-15 km altitude and producing frequent lightning (figures 14 and 15). Wet ash fell as far away as Quezon City (75 km N). According to news articles schools and government offices were ordered to close and the Ninoy Aquino International Airport (56 km N) in Manila suspended flights. About 6,000 people had been evacuated. Residents described heavy ashfall, low visibility, and fallen trees.

Figure 14. Lightning produced during the eruption of Taal during 1500 on 12 January to 0500 on 13 January 2020 local time (0700-2100 UTC on 12 January). Courtesy of Chris Vagasky, Vaisala.

Figure 15. Lightning strokes produced during the first days of the Taal January 2020 eruption. Courtesy of Domcar C Lagto/SIPA/REX/Shutterstock via The Guardian.

In a statement issued at 0320 on 13 January, PHIVOLCS noted that ashfall had been reported across a broad area to the north in Tanauan (18 km NE), Batangas; Escala (11 km NW), Tagaytay; Sta. Rosa (32 km NNW), Laguna; Dasmariñas (32 km N), Bacoor (44 km N), and Silang (22 km N), Cavite; Malolos (93 km N), San Jose Del Monte (87 km N), and Meycauayan (80 km N), Bulacan; Antipolo (68 km NNE), Rizal; Muntinlupa (43 km N), Las Piñas (47 km N), Marikina (70 km NNE), Parañaque (51 km N), Pasig (62 km NNE), Quezon City, Mandaluyong (62 km N), San Juan (64 km N), Manila; Makati City (59 km N) and Taguig City (55 km N). Lapilli (2-64 mm in diameter) fell in Tanauan and Talisay; Tagaytay City (12 km N); Nuvali (25 km NNE) and Sta (figure 16). Rosa, Laguna. Felt earthquakes (Intensities II-V) continued to be recorded in local areas.

Figure 16. Ashfall from the Taal January 2020 eruption in Lemery (top) and in the Batangas province (bottom). Photos posted on 13 January, courtesy of Ezra Acayan/Getty Images, Aaron Favila/AP, and Ted Aljibe/AFP via Getty Images via The Guardian.

Magmatic eruption on 13 January 2020. A magmatic eruption began during 0249-0428 on 13 January, characterized by weak lava fountaining accompanied by thunder and flashes of lightning. Activity briefly waned then resumed with sporadic weak fountaining and explosions that generated 2-km-high, dark gray, steam-laden ash plumes (figure 17). New lateral vents opened on the N flank, producing 500-m-tall lava fountains. Heavy ashfall impacted areas to the SW, including in Cuenca (15 km SSW), Lemery (16 km SW), Talisay, and Taal (15 km SSW), Batangas (figure 18).

Figure 17. Ash plumes seen from various points around Taal in the initial days of the January 2020 eruption, posted on 13 January. Courtesy of Eloisa Lopez/Reuters, Kester Ragaza/Pacific Press/Shutterstock, Ted Aljibe/AFP via Getty Images, via The Guardian.

Figure 18. Map indicating areas impacted by ashfall from the 12 January eruption through to 0800 on the 13th. Small yellow circles (to the N) are ashfall report locations; blue circles (at the island and to the S) are heavy ashfall; large green circles are lapilli (particles measuring 2-64 mm in diameter). Modified from a map courtesy of Lauriane Chardot, Earth Observatory of Singapore; data taken from PHIVOLCS.

News articles noted that more than 300 domestic and 230 international flights were cancelled as the Manila Ninoy Aquino International Airport was closed during 12-13 January. Some roads from Talisay to Lemery and Agoncillo were impassible and electricity and water services were intermittent. Ashfall in several provinces caused power outages. Authorities continued to evacuate high-risk areas, and by 13 January more than 24,500 people had moved to 75 shelters out of a total number of 460,000 people within 14 km.

A PHIVOLCS report for 0800 on the 13th through 0800 on 14 January noted that lava fountaining had continued, with steam-rich ash plumes reaching around 2 km above the volcano and dispersing ash SE and W of Main Crater. Volcanic lighting continued at the base of the plumes. Fissures on the N flank produced 500-m-tall lava fountains. Heavy ashfall continued in the Lemery, Talisay, Taal, and Cuenca, Batangas Municipalities. By 1300 on the 13th lava fountaining generated 800-m-tall, dark gray, steam-laden ash plumes that drifted SW. Sulfur dioxide emissions averaged 5,299 metric tons/day (t/d) on 13 January and dispersed NNE (figure 19).

Figure 19. Compilation of sulfur dioxide plumes from TROPOMI overlaid in Google Earth for 13 January from 0313-1641 UT. Courtesy of NASA Global Sulfur Dioxide Monitoring Page and Google Earth.

Explosions and ash emission through 22 January 2020. At 0800 on 15 January PHIVOLCS stated that activity was generally weaker; dark gray, steam-laden ash plumes rose about 1 km and drifted SW. Satellite images showed that the Main Crater lake was gone and new craters had formed inside Main Crater and on the N side of Volcano Island.

PHIVOLCS reported that activity during 15-16 January was characterized by dark gray, steam-laden plumes that rose as high as 1 km above the vents in Main Crater and drifted S and SW. Sulfur dioxide emissions were 4,186 t/d on 15 January. Eruptive events at 0617 and 0621 on 16 January generated short-lived, dark gray ash plumes that rose 500 and 800 m, respectively, and drifted SW. Weak steam plumes rose 800 m and drifted SW during 1100-1700, and nine weak explosions were recorded by the seismic network.

Steady steam emissions were visible during 17-21 January. Infrequent weak explosions generated ash plumes that rose as high as 1 km and drifted SW. Sulfur dioxide emissions fluctuated and were as high as 4,353 t/d on 20 January and as low as 344 t/d on 21 January. PHIVOLCS reported that white steam-laden plumes rose as high as 800 m above main vent during 22-28 January and drifted SW and NE; ash emissions ceased around 0500 on 22 January. Remobilized ash drifted SW on 22 January due to strong low winds, affecting the towns of Lemery (16 km SW) and Agoncillo, and rose as high as 5.8 km altitude as reported by pilots. Sulfur dioxide emissions were low at 140 t/d.

Steam plumes through mid-April 2020. The Alert Level was lowered to 3 on 26 January and PHIVOLCS recommended no entry onto Volcano Island and Taal Lake, nor into towns on the western side of the island within a 7-km radius. PHIVOLCS reported that whitish steam plumes rose as high as 800 m during 29 January-4 February and drifted SW (figure 20). The observed steam plumes rose as high as 300 m during 5-11 February and drifted SW.

Sulfur dioxide emissions averaged around 250 t/d during 22-26 January; emissions were 87 t/d on 27 January and below detectable limits the next day. During 29 January-4 February sulfur dioxide emissions ranged to a high of 231 t/d (on 3 February). The following week sulfur dioxide emissions ranged from values below detectable limits to a high of 116 t/d (on 8 February).

Figure 20. Taal Volcano Island producing gas-and-steam plumes on 15-16 January 2020. Courtesy of James Reynolds, Earth Uncut.

On 14 February PHIVOLCS lowered the Alert Level to 2, noting a decline in the number of volcanic earthquakes, stabilizing ground deformation of the caldera and Volcano Island, and diffuse steam-and-gas emission that continued to rise no higher than 300 m above the main vent during the past three weeks. During 14-18 February sulfur dioxide emissions ranged from values below detectable limits to a high of 58 tonnes per day (on 16 February). Sulfur dioxide emissions were below detectable limits during 19-20 February. During 26 February-2 March steam plumes rose 50-300 m above the vent and drifted SW and NE. PHIVOLCS reported that during 4-10 March weak steam plumes rose 50-100 m and drifted SW and NE; moderate steam plumes rose 300-500 m and drifted SW during 8-9 March. During 11-17 March weak steam plumes again rose only 50-100 m and drifted SW and NE.

PHIVOLCS lowered the Alert Level to 1 on 19 March and recommended no entry onto Volcano Island, the area defined as the Permanent Danger Zone. During 8-9 April steam plumes rose 100-300 m and drifted SW. As of 1-2 May 2020 only weak steaming and fumarolic activity from fissure vents along the Daang Kastila trail was observed.

Evacuations. According to the Disaster Response Operations Monitoring and Information Center (DROMIC) there were a total of 53,832 people dispersed to 244 evacuation centers by 1800 on 15 January. By 21 January there were 148,987 people in 493 evacuation. The number of residents in evacuation centers dropped over the next week to 125,178 people in 497 locations on 28 January. However, many residents remained displaced as of 3 February, with DROMIC reporting 23,915 people in 152 evacuation centers, but an additional 224,188 people staying at other locations.

By 10 February there were 17,088 people in 110 evacuation centers, and an additional 211,729 staying at other locations. According to the DROMIC there were a total of 5,321 people in 21 evacuation centers, and an additional 195,987 people were staying at other locations as of 19 February.

The number of displaced residents continued to drop, and by 3 March there were 4,314 people in 12 evacuation centers, and an additional 132,931 people at other locations. As of 11 March there were still 4,131 people in 11 evacuation centers, but only 17,563 staying at other locations.

Deformation and ground cracks. New ground cracks were observed on 13 January in Sinisian (18 km SW), Mahabang Dahilig (14 km SW), Dayapan (15 km SW), Palanas (17 km SW), Sangalang (17 km SW), and Poblacion (19 km SW) Lemery; Pansipit (11 km SW), Agoncillo; Poblacion 1, Poblacion 2, Poblacion 3, Poblacion 5 (all around 17 km SW), Talisay, and Poblacion (11 km SW), San Nicolas (figure 21). A fissure opened across the road connecting Agoncillo to Laurel, Batangas. New ground cracking was reported the next day in Sambal Ibaba (17 km SW), and portions of the Pansipit River (SW) had dried up.

Figure 21. Video screenshots showing ground cracks that formed during the Taal unrest and captured on 15 and 16 January 2020. Courtesy of James Reynolds, Earth Uncut.

Dropping water levels of Taal Lake were first observed in some areas on 16 January but reported to be lake-wide the next day. The known ground cracks in the barangays of Lemery, Agoncillo, Talisay, and San Nicolas in Batangas Province widened a few centimeters by 17 January, and a new steaming fissure was identified on the N flank of the island.

GPS data had recorded a sudden widening of the caldera by ~1 m, uplift of the NW sector by ~20 cm, and subsidence of the SW part of Volcano Island by ~1 m just after the main eruption phase. The rate of deformation was smaller during 15-22 January, and generally corroborated by field observations; Taal Lake had receded about 30 cm by 25 January but about 2.5 m of the change (due to uplift) was observed around the SW portion of the lake, near the Pansipit River Valley where ground cracking had been reported.

Weak steaming (plumes 10-20 m high) from ground cracks was visible during 5-11 February along the Daang Kastila trail which connects the N part of Volcano Island to the N part of the main crater. PHIVOLCS reported that during 19-24 February steam plumes rose 50-100 m above the vent and drifted SW. Weak steaming (plumes up to 20 m high) from ground cracks was visible during 8-14 April along the Daang Kastila trail which connects the N part of Volcano Island to the N part of the main crater.

Seismicity. Between 1300 on 12 January and 0800 on 21 January the Philippine Seismic Network (PSN) had recorded a total of 718 volcanic earthquakes; 176 of those had magnitudes ranging from 1.2-4.1 and were felt with Intensities of I-V. During 20-21 January there were five volcanic earthquakes with magnitudes of 1.6-2.5; the Taal Volcano network (which can detect smaller events not detectable by the PSN) recorded 448 volcanic earthquakes, including 17 low-frequency events. PHIVOLCS stated that by 21 January hybrid earthquakes had ceased and both the number and magnitude of low-frequency events had diminished.

Geologic Background. Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Disaster Response Operations Monitoring and Information Center (DROMIC) (URL: https://dromic.dswd.gov.ph/); United Nations Office for the Coordination of Humanitarian Affairs, Philippines (URL: https://www.unocha.org/philippines); James Reynolds, Earth Uncut TV (Twitter: @EarthUncutTV, URL: https://www.earthuncut.tv/, YouTube: https://www.youtube.com/user/TyphoonHunter); Chris Vagasky, Vaisala Inc., Louisville, Colorado, USA (URL: https://www.vaisala.com/en?type=1, Twitter: @COweatherman, URL: https://twitter.com/COweatherman); Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Avenue, Singapore (URL: https://www.earthobservatory.sg/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Relief Web, Flash Update No. 1 - Philippines: Taal Volcano eruption (As of 13 January 2020, 2 p.m. local time) (URL: https://reliefweb.int/report/philippines/flash-update-no-1-philippines-taal-volcano-eruption-13-january-2020-2-pm-local); Bloomberg, Philippines Braces for Hazardous Volcano Eruption (URL: https://www.bloomberg.com/news/articles/2020-01-12/philippines-raises-alert-level-in-taal-as-volcano-spews-ash); National Public Radio (NPR), Volcanic Eruption In Philippines Causes Thousands To Flee (URL: npr.org/2020/01/13/795815351/volcanic-eruption-in-philippines-causes-thousands-to-flee); Reuters (http://www.reuters.com/); Agence France-Presse (URL: http://www.afp.com/); Pacific Press (URL: http://www.pacificpress.com/); Shutterstock (URL: https://www.shutterstock.com/); Getty Images (URL: http://www.gettyimages.com/); Google Earth (URL: https://www.google.com/earth/).

In the northern Tonga region, approximately 80 km NW of Vava’u, large areas of floating pumice, termed rafts, were observed starting as early as 7 August 2019. The area of these andesitic pumice rafts was initially 195 km² with the layers measuring 15-30 cm thick and were produced 200 m below sea level (Jutzeler et al. 2020). The previous report (BGVN 44:11) described the morphology of the clasts and the rafts, and their general westward path from 9 August to 9 October 2019, with the first sighting occurring on 9 August NW of Vava’u in Tonga. This report updates details regarding the submarine pumice raft eruption in early August 2019 using new observations and data from Brandl et al. (2019) and Jutzeler et al. (2020).

The NoToVE-2004 (Northern Tonga Vents Expedition) research cruise on the RV Southern Surveyor (SS11/2004) from the Australian CSIRO Marine National Facility traveled to the northern Tonga Arc and discovered several submarine basalt-to-rhyolite volcanic centers (Arculus, 2004). One of these volcanic centers 50 km NW of Vava’u was the unnamed seamount (volcano number 243091) that had erupted in 2001 and again in 2019, unofficially designated “Volcano F” for reference purposes by Arculus (2004) and also used by Brandl et al. (2019). It is a volcanic complex that rises more than 1 km from the seafloor with a central 6 x 8.7 km caldera and a volcanic apron measuring over 50 km in diameter (figures 19 and 20). Arculus (2004) described some of the dredged material as “fresh, black, plagioclase-bearing lava with well-formed, glassy crusts up to 2cm thick” from cones by the eastern wall of the caldera; a number of apparent flows, lava or debris, were observed draping over the northern wall of the caldera.

Figure 19. Visualization of the unnamed submarine Tongan volcano (marked “Volcano F”) using bathymetric data to show the site of the 6-8 August 2020 eruption and the rest of the cone complex. Courtesy of Philipp Brandl via GEOMAR.

Figure 20. Map of the unnamed submarine Tongan volcano using satellite imagery, bathymetric data, with shading from the NW. The yellow circle indicates the location of the August 2019 activity. Young volcanic cones are marked “C” and those with pit craters at the top are marked with “P.” Courtesy of Brandl et al. (2019).

The International Seismological Centre (ISC) Preliminary Bulletin listed a particularly strong (5.7 Mw) earthquake at 2201 local time on 5 August, 15 km SSW of the volcano at a depth of 10 km (Brandl et al. 2019). This event was followed by six slightly lower magnitude earthquakes over the next two days.

Sentinel-2 satellite imagery showed two concentric rings originating from a point source (18.307°S 174.395°W) on 6 August (figure 21), which could be interpreted as small weak submarine plumes or possibly a series of small volcanic cones, according to Brandl et al. (2019). The larger ring is about 1.2 km in diameter and the smaller one measures 250 m. By 8 August volcanic activity had decreased, but the pumice rafts that were produced remained visible through at least early October (BGVN 44:11). Brandl et al. (2019) states that, due to the lack of continued observed activity rising from this location, the eruption was likely a 2-day-long event during 6-8 August.

Figure 21. Sentinel-2 satellite image of possible gas/vapor emissions (streaks) on 6 August 2019 drifting NW, which is the interpreted site for the unnamed Tongan seamount. The larger ring is about 1.2 km in diameter and the smaller one measures 250 m. Image using False Color (urban) rendering (bands 12, 11, 4); courtesy of Sentinel Hub Playground.

The pumice was first observed on 9 August occurred up to 56 km from the point of origin, according to Jutzeler et al. (2020). By calculating the velocity (14 km/day) of the raft using three satellites, Jutzeler et al. (2020) determined the pumice was erupted immediately after the satellite image of the submarine plumes on 6 August (UTC time). Minor activity at the vent may have continued on 8 and 11 August (UTC time) with pale blue-green water discoloration (figure 22) and a small (less than 1 km²) diffuse pumice raft 2-5 km from the vent.

Figure 22. Sentinel-2 satellite image of the last visible activity occurring W of the unnamed submarine Tongan volcano on 8 August 2019, represented by slightly discolored blue-green water. Image using Natural Color rendering (bands 4, 3, 2) and enhanced with color correction; courtesy of Sentinel Hub Playground.

Continuous observations using various satellite data and observations aboard the catamaran ROAM tracked the movement and extent of the pumice raft that was produced during the submarine eruption in early August (figure 23). The first visible pumice raft was observed on 8 August 2019, covering more than 136.7 km² between the volcanic islands of Fonualei and Late and drifting W for 60 km until 9 August (Brandl et al. 2019; Jutzeler 2020). The next day, the raft increased to 167.2-195 km² while drifting SW for 74 km until 14 August. Over the next three days (10-12 August) the size of the raft briefly decreased in size to less than 100 km² before increasing again to 157.4 km² on 14 August; at least nine individual rafts were mapped and identified on satellite imagery (Brandl et al. 2019). On 15 August sailing vessels observed a large pumice raft about 75 km W of Late Island (see details in BGVN 44:11), which was the same one as seen in satellite imagery on 8 August.

Figure 23. Map of the extent of discolored water and the pumice raft from the unnamed submarine Tongan volcano between 8 and 14 August 2019 using imagery from NASA’s MODIS, ESA’s Sentinel-2 satellite, and observations from aboard the catamaran ROAM (BGVN 44:11). Back-tracing the path of the pumice raft points to a source location at the unnamed submarine Tongan volcano. Courtesy of Brandl et al. (2019).

By 17 August high-resolution satellite images showed an area of large and small rafts measuring 222 km² and were found within a field of smaller rafts for a total extent of 1,350 km², which drifted 73 km NNW through 22 August before moving counterclockwise for three days (figure f; Jutzeler et al., 2020). Small pumice ribbons encountered the Oneata Lagoon on 30 August, the first island that the raft came into contact (Jutzeler et al. 2020). By 2 September, the main raft intersected with Lakeba Island (460 km from the source) (figure 24), breaking into smaller ribbons that started to drift W on 8 September. On 19 September the small rafts (less than 100 m x less than 2 km) entered the strait between Viti Levu and Vanua Levu, the two main islands of Fiji, while most of the others were stranded 60 km W in the Yasawa Islands for more than two months (Jutzeler et al., 2020).

Figure 24. Time-series map of the raft dispersal from the unnamed submarine Tongan volcano using multiple satellite images. A) Map showing the first days of the raft dispersal starting on 7 August 2019 and drifting SW from the vent (marked with a red triangle). Precursory seismicity that began on 5 August is marked with a white star. By 15-17 August the raft was entrained in an ocean loop or eddy. The dashed lines represent the path of the sailing vessels. B) Map of the raft dispersal using high-resolution Sentinel-2 and -3 imagery. Two dispersal trails (red and blue dashed lines) show the daily dispersal of two parts of the raft that were separated on 17 August 2019. Courtesy of Jutzeler et al. (2020).

References: Arculus, R J, SS2004/11 shipboard scientists, 2004. SS11/2004 Voyage Summary: NoToVE-2004 (Northern Tonga Vents Expedition): submarine hydrothermal plume activity and petrology of the northern Tofua Arc, Tonga. https://www.cmar.csiro.au/data/reporting/get file.cfm?eovpub id=901.

Brandl P A, Schmid F, Augustin N, Grevemeyer I, Arculus R J, Devey C W, Petersen S, Stewart M , Kopp K, Hannington M D, 2019. The 6-8 Aug 2019 eruption of ‘Volcano F’ in the Tofua Arc, Tonga. Journal of Volcanology and Geothermal Research: https://doi.org/10.1016/j.jvolgeores.2019.106695

Jutzeler M, Marsh R, van Sebille E, Mittal T, Carey R, Fauria K, Manga M, McPhie J, 2020. Ongoing Dispersal of the 7 August 2019 Pumice Raft From the Tonga Arc in the Southwestern Pacific Ocean. AGU Geophysical Research Letters: https://doi.orh/10.1029/2019GL086768.

Geologic Background. A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about 35 km S of Fonualei and 60 km NE of Late volcano. The site of the eruption is along a NNE-SSW-trending submarine plateau with an approximate bathymetric depth of 300 m. T-phase waves were recorded on 27-28 September 2001, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the E.

Information Contacts: Jan Steffen, Communication and Media, GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Klyuchevskoy is part of the Klyuchevskaya volcanic group in northern Kamchatka and is one of the most frequently active volcanoes of the region. Eruptions produce lava flows, ashfall, and lahars originating from summit and flank activity. This report summarizes activity during October 2019 through May 2020, and is based on reports by the Kamchatkan Volcanic Eruption Response Team (KVERT) and satellite data.

There were no activity reports from 1 to 22 October, but gas emissions were visible in satellite images. At 1020 on 24 October (2220 on 23 October UTC) KVERT noted that there was a small ash component in the ash plume from erosion of the conduit, with the plume reaching 130 km ENE. The Aviation Colour Code was raised from Green to Yellow, then to Orange the following day. An ash plume continued on the 25th to 5-7 km altitude and extending 15 km SE and 70 km SW and reached 30 km ESE on the 26th. Similar activity continued through to the end of the month.

Moderate gas emissions continued during 1-19 November, but the summit was obscured by clouds. Strong nighttime incandescence was visible at the crater during the 10-11 November and thermal anomalies were detected on 8 and 10-13 November. Explosions produced ash plumes up to 6 km altitude on the 20-21st and Strombolian activity was reported during 20-22 November. Degassing continued from 23 November through 12 December, and a thermal anomaly was visible on the days when the summit was not covered by clouds. An ash plume was reported moving to the NW on the 13th, and degassing with a thermal anomaly and intermittent Strombolian activity then resumed, continuing through to the end of December with an ash plume reported on the 30th.

Gas-and-steam plumes continued into January 2020 with incandescence noted when the summit was clear (figure 33). Strombolian activity was reported again starting on the 3rd. A weak ash plume produced on the 6th extended 55 km E, and on the 21st an ash plume reached 5-5.5 km altitude and extended 190 km NE (figure 34). Another ash plume the next day rose to the same altitude and extended 388 km NE. During 23-29 Strombolian activity continued, and Vulcanian activity produced ash plumes up to 5.5 altitude, extending to 282 km E on the 30th, and 145 km E on the 31st.

Figure 33. Incandescence and degassing were visible at Klyuchevskoy through January 2020, seen here on the 11th. Courtesy of KVERT.

Figure 34. A low ash plume at Klyuchevskoy on 21 January 2020 extended 190 km NE. Courtesy of KVERT.

Strombolian activity continued throughout February with occasional explosions producing ash plumes up to 5.5 km altitude, as well as gas-and-steam plumes and a persistent thermal anomaly with incandescence visible at night. Starting in late February thermal anomalies were detected much more frequently, and with higher energy output compared to the previous year (figure 35). A lava fountain was reported on 1 March with the material falling back into the summit crater. Strombolian activity continued through early March. Lava fountaining was reported again on the 8th with ejecta landing in the crater and down the flanks (figure 36). A strong persistent gas-and-steam plume containing some ash continued along with Strombolian activity through 25 March (figure 37), with Vulcanian activity noted on the 20th and 25th. Strombolian and Vulcanian activity was reported through the end of March.

Figure 35. This MIROVA thermal energy plot for Klyuchevskoy for the year ending 29 April 2020 (log radiative power) shows intermittent thermal anomalies leading up to more sustained energy detected from February through March, then steadily increasing energy through April 2020. Courtesy of MIROVA.

Figure 36. Strombolian explosions at Klyuchevskoy eject incandescent ash and gas, and blocks and bombs onto the upper flanks on 8 and 10 March 2020. Courtesy of IVS FEB RAS, KVERT.

Figure 37. Weak ash emission from the Klyuchevskoy summit crater are dispersed by wind on 19 and 29 March 2020, with ash depositing on the flanks. Courtesy of IVS FEB RAS, KVERT.

Activity was dominantly Strombolian during 1-5 April and included intermittent Vulcanian explosions from the 6th onwards, with ash plumes reaching 6 km altitude. On 18 April a lava flow began moving down the SE flank (figures 38). A report on the 26th reported explosions from lava-water interactions with avalanches from the active lava flow, which continued to move down the SE flank and into the Apakhonchich chute (figures 39 and 40). This continued throughout April and May with sustained Strombolian and intermittent Vulcanian activity at the summit (figures 41 and 42).

Figure 38. Strombolian activity produced ash plumes and a lava flow down the SE flank of Klyuchevskoy on 18 April 2020. Courtesy of IVS FEB RAS, KVERT.

Figure 39. A lava flow descends the SW flank of Klyuchevskoy and a gas plume is dispersed by winds on 21 April 2020. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Figure 40. Sentinel-2 thermal satellite images show the progression of the Klyuchevskoy lava flow from the summit crater down the SE flank from 19-29 April 2020. Associated gas plumes are dispersed in various directions. Courtesy of Sentinel Hub Playground.

Figure 41. Strombolian activity at Klyuchevskoy ejects incandescent ejecta, gas, and ash above the summit on 27 April 2020. Courtesy of D. Bud'kov, IVS FEB RAS, KVERT.

Figure 42. Sentinel-2 thermal satellite images of Klyuchevskoy show the progression of the SE flank lava flow through May 2020, with associated gas plumes being dispersed in multiple directions. Courtesy of Sentinel Hub Playground.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank 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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Nyamuragira (also known as Nyamulagira) is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo and consists of a lava lake that reappeared in the summit crater in mid-April 2018. Volcanism has been characterized by lava emissions, thermal anomalies, seismicity, and gas-and-steam emissions. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

According to OVG, intermittent eruptive activity was detected in the lava lake of the central crater during December 2019 and January-April 2020, which also resulted in few seismic events. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows thermal anomalies within the summit crater that varied in both frequency and power between August 2019 and mid-March 2020, but very few were recorded afterward through late May (figure 88). Thermal hotspots identified by MODVOLC from 15 December 2019 through March 2020 were mainly located in the active central crater, with only three hotspots just outside the SW crater rim (figure 89). Sentinel-2 thermal satellite imagery also showed activity within the summit crater during January-May 2020, but by mid-March the thermal anomaly had visibly decreased in power (figure 90).

Figure 88. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira during 27 July through May 2020 shows variably strong, intermittent thermal anomalies with a variation in power and frequency from August 2019 to mid-March 2020. Courtesy of MIROVA.

Figure 89. Map showing the number of MODVOLC hotspot pixels at Nyamuragira from 1 December 2019 t0 31 May 2020. 37 pixels were registered within the summit crater while 3 were detected just outside the SW crater rim. Courtesy of HIGP-MODVOLC Thermal Alerts System.

Figure 90. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity (bright yellow-orange) at Nyamuragira from February into April 2020. The strength of the thermal anomaly in the summit crater decreased by late March 2020, but was still visible. Courtesy of Sentinel Hub Playground.

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: Information contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/exp.

Nyiragongo is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo, part of the western branch of the East African Rift System and contains a 1.2 km-wide summit crater with a lava lake that has been active since at least 1971. Volcanism has been characterized by strong and frequent thermal anomalies, incandescence, gas-and-steam emissions, and seismicity. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

In the December 2019 monthly report, OVG stated that the level of the lava lake had increased. This level of the lava lake was maintained for the duration of the reporting period, according to later OVG monthly reports. Seismicity increased starting in November 2019 and was detected in the NE part of the crater, but it decreased by mid-April 2020. SO₂ emissions increased in January 2020 to roughly 7,000 tons/day but decreased again near the end of the month. OVG reported that SO₂ emissions rose again in February to roughly 8,500 tons/day before declining to about 6,000 tons/day. Unlike in the previous report (BGVN 44:12), incandescence was visible during the day in the active lava lake and activity at the small eruptive cone within the 1.2-km-wide summit crater has since increased, consisting of incandescence and some lava fountaining (figure 72). A field survey was conducted on 3-4 March where an OVG team observed active lava fountains and ejecta that produced Pele’s hair from the small eruptive cone (figure 73). During this survey, OVG reported that the level of the lava lake had reached the second terrace, which was formed on 17 January 2002 and represents remnants of the lava lake at different eruption stages. There, the open surface lava lake was observed; gas-and-steam emissions accompanied both the active lava lake and the small eruptive cone (figures 72 and 73).

Figure 72. Webcam image of Nyiragongo in February 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG February 2020).

Figure 73. Webcam image of Nyiragongo on 4 March 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG Mars 2020).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data continued to show frequent strong thermal anomalies within 5 km of the summit crater through May 2020 (figure 74). Similarly, the MODVOLC algorithm reported multiple thermal hotspots almost daily within the summit crater between December 2019 and May 2020. These thermal signatures were also observed in Sentinel-2 thermal satellite imagery within the summit crater (figure 75).

Figure 74. Thermal anomalies at Nyiragongo from 27 July through May 2020 as recorded by the MIROVA system (Log Radiative Power) were frequent and strong. Courtesy of MIROVA.

Figure 75. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) showed ongoing thermal activity (bright yellow-orange) in the summit crater at Nyiragongo during January through April 2020. Courtesy of Sentinel Hub Playground.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Kavachi is a submarine volcano located in the Solomon Islands south of Gatokae and Vangunu islands. Volcanism is frequently active, but rarely observed. The most recent eruptions took place during 2014, which consisted of an ash eruption, and during 2016, which included phreatomagmatic explosions (BGVN 42:03). This reporting period covers December 2016-April 2020 primarily using satellite data.

Activity at Kavachi is often only observed through satellite images, and frequently consists of discolored submarine plumes for which the cause is uncertain. On 1 January 2018 a slight yellow discoloration in the water is seen extending to the E from a specific point (figure 20). Similar faint plumes were observed on 16 January, 25 February, 2 March, 26 April, 6 May, and 25 June 2018. No similar water discoloration was noted during 2019, though clouds may have obscured views.

Figure 20. Satellite images from Sentinel-2 revealed intermittent faint water discoloration (yellow) at Kavachi during the first half of 2018, as seen here on 1 January (top left), 25 February (top right), 26 April (bottom left), and 25 June (bottom right). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Activity resumed in 2020, showing more discolored water in satellite imagery. The first instance occurred on 16 March, where a distinct plume extended from a specific point to the SE. On 25 April a satellite image showed a larger discolored plume in the water that spread over about 30 km², encompassing the area around Kavachi (figure 21). Another image on 30 April showed a thin ribbon of discolored water extending about 50 km W of the vent.

Figure 21. Sentinel-2 satellite images of a discolored plume (yellow) at Kavachi beginning on 16 March (top left) with a significant large plume on 25 April (right), which remained until 30 April (bottom left). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

Information Contacts: Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Kuchinoerabujima encompasses a group of young stratovolcanoes located in the northern Ryukyu Islands. All historical eruptions have originated from the Shindake cone, with the exception of a lava flow that originated from the S flank of the Furudake cone. The most recent previous eruptive period took place during October 2018-February 2019 and primarily consisted of weak explosions, ash plumes, and ashfall. The current eruption began on 11 January 2020 after nearly a year of dominantly gas-and-steam emissions. Volcanism for this reporting period from March 2019 to April 2020 included explosions, ash plumes, SO₂ emissions, and ashfall. The primary source of information for this report comes from monthly and annual reports from the Japan Meteorological Agency (JMA) and advisories from the Tokyo Volcanic Ash Advisory Center (VAAC). Activity has been limited to Kuchinoerabujima's Shindake Crater.

Volcanism at Kuchinoerabujima was relatively low during March through December 2019, according to JMA. During this time, SO₂ emissions ranged from 100 to 1,000 tons/day. Gas-and-steam emissions were frequently observed throughout the entire reporting period, rising to a maximum height of 1.1 km above the crater on 13 December 2019. Satellite imagery from Sentinel-2 showed gas-and-steam and occasional ash emissions rising from the Shindake crater throughout the reporting period (figure 7). Though JMA reported thermal anomalies occurring on 29 January and continuing through late April 2020, Sentinel-2 imagery shows the first thermal signature appearing on 26 April.

Figure 7. Sentinel-2 thermal satellite images showed gas-and-steam and ash emissions rising from Kuchinoerabujima. Some ash deposits can be seen on 6 February 2020 (top right). A thermal anomaly appeared on 26 April 2020 (bottom right). Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

An eruption on 11 January 2020 at 1505 ejected material 300 m from the crater and produced ash plumes that rose 2 km above the crater rim, extending E, according to JMA. The eruption continued through 12 January until 0730. The resulting ash plumes rose 400 m above the crater, drifting SW while the SO₂ emissions measured 1,300 tons/day. Ashfall was reported on Yakushima Island (15 km E). Minor eruptive activity was reported during 17-20 January which produced gray-white plumes that rose 300-500 m above the crater. On 23 January, seismicity increased, and an eruption produced an ash plume that rose 1.2 km altitude, according to a Tokyo VAAC report, resulting in ashfall 2 km NE of the crater. A small explosion was detected on 24 January, followed by an increase in the number of earthquakes during 25-26 January (65-71 earthquakes per day were registered). Another small eruptive event detected on 27 January at 0148 was accompanied by a volcanic tremor and a change in tilt data. During the month of January, some inflation was detected at the base on the volcano and a total of 347 earthquakes were recorded. The SO₂ emissions ranged from 200-1,600 tons/day.

An eruption on 1 February 2020 produced an eruption column that rose less than 1 km altitude and extended SE and SW (figure 8), according to the Tokyo VAAC report. On 3 February, an eruption from the Shindake crater at 0521 produced an ash plume that rose 7 km above the crater and ejected material as far as 600 m away. As a result, a pyroclastic flow formed, traveling 900-1,500 m SW. The previous pyroclastic flow that was recorded occurred on 29 January 2019. Ashfall was confirmed in the N part of Yakushima Island with a large amount in Miyanoura (32 km ESE) and southern Tanegashima. The SO₂ emissions measured 1,700 tons/day during this event.

Figure 8. Webcam images from the Honmura west surveillance camera of an ash plume rising from Kuchinoerabujima on 1 February 2020. Courtesy of JMA (Weekly bulletin report 509, February 2020).

Intermittent small eruptive events occurred during 5-9 February; field observations showed a large amount of ashfall on the SE flank which included lapilli that measured up to 2 cm in diameter. Additionally, thermal images showed 5-km-long pyroclastic flow deposits on the SW flank. An eruption on 9 February produced an ash plume that rose 1.2 km altitude, drifting SE. On 13 February a small eruption was detected in the Shindake crater at 1211, producing gray-white plumes that rose 300 m above the crater, drifting NE. Small eruptive events also occurred during 20-21 February, resulting in gas-and-steam emissions that rose 200 m above the crater. During the month of February, some horizontal extension was observed since January 2020 using GNSS data. The total number of earthquakes during this month drastically increased to 1225 compared to January. The SO₂ emissions ranged from 300-1,700 tons/day.

By 2 March 2020, seismicity decreased, and activity declined. Gas-and-steam emissions continued infrequently for the duration of the reporting period. The SO₂ emissions during March ranged from 700-2,100 tons/day, the latter of which occurred on 15 March. Seismicity increased again on 27 March. During 5-8 April 2020, small eruptive events were detected, generating ash plumes that rose 900 m above the crater (figure 9). The SO₂ emissions on 6 April reached 3,200 tons/day, the maximum measurement for this reporting period. These small eruptive events continued from 13-20 and 23-25 April within the Shindake crater, producing gray-white plumes that rose 300-800 m above the crater.

Figure 9. Webcam images from the Honmura Nishi (top) and Honmura west (bottom) surveillance cameras of ash plumes rising from Kuchinoerabujima on 6 March and 5 April 2020. Courtesy of JMA (Weekly bulletin report 509, March and April 2020).

Geologic Background. A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km W of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. All historical eruptions have occurred from Shindake, although a lava flow from the S flank of Furudake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shindake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, 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 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

This report, our first for this volcano, covers the low-level activity of Cerro Bravo and monitoring efforts during 2006-2012 based on reporting by the Servicio Geológico Colombiano (SGC). Cerro Bravo was non-eruptive and the Alert Level remained at IV (Green; "volcanically active with stable behavior") due to minimal seismicity, gas emissions, and deformation.

Data availability. Government and academic investigations during 1980-1990 established the geology and preliminary hazard analysis for Cerro Bravo. Monthly SGC technical bulletins were available online from March 2006 through December 2012 and documented an increasing diversity of datasets that developed as the monitoring network expanded. Those bulletins highlighted low-level seismicity that was frequently dominated by surficial activity (rockfalls and other mass-wasting events); fluctuations in radon gas emissions were also noted and baseline data was established for emission rates. As of December 2012, three seismometers (two short-period and one triaxial station), one tiltmeter, two EDM leveling lines, and 10 diffuse radon detectors comprised the monitoring effort (figure 1).

Figure 1. Location map of Cerro Bravo and the monitoring network maintained by the Servicio Geológico Colombiano (SGC). One seismic station (CAJO) was ~6 km S of the edifice, beyond this map view. The town of Letras (~6 km SW) was the largest community proximal to the volcano. The yellow road crossing the region is Route 50 which continues to Manizales (25 km W of Cerro Bravo) and to Bogota (140 km SE of Cerro Bravo). This map was modified from the original that appeared in the December 2012 Activity Report of the SGC.

Thouret and others (1990) presented a framework for regional volcanic activity after conducting an assessment of the Ruiz-Tolima Massif (figure 2). The investigators determined that, within a 2 Ma-long period, "recent explosive activity has migrated towards the intersections of the Palestina strike-slip fault and the N 50°W normal faults, first around [the volcanic centers] Quindío and Tolima, secondly in the Cerro Espana area, and most recently close to Cerro Bravo and Ruiz." Holocene activity at Cerro Bravo was characterized as dacitic with evidence of magma mixing. They also highlighted the role of caldera collapse within the region, including the case of Quebrada Seca Caldera, a major bounding feature of Cerro Bravo (figure 3). The concluding remarks included an emphasis on mass wasting at Cerro Bravo and lahar hazards for the ice-clad volcanoes in the region, mainly Nevado del Ruiz and Nevado del Tolima.

Figure 2. This map of seven volcanoes includes Cerro Bravo (red triangle) in the far NE region. Fault lines (dashed green lines) cross the area and are labeled with the following abbreviations: P.F.=Palestina Fault; O.-T.-F.=Otun-Pereira Fault; T.F.=Toche Fault; R.-T.F.=Recio-Tolima Fault. The city of Manizales is marked with a blue square in the NE corner. Modified from Thouret and others, 1995.

Figure 3. Two views of Cerro Bravo's SW flank from Letras, a town ~6 km SW of the summit. (A) This profile of merged photos was taken in July 2011; note that the youngest domes in the structure comprise the highest peaks on the left-hand side of the photo (northernmost peaks). Courtesy of Maria Luisa Monsalve, SGC. (B) Panorama view of Cerro Bravo annotated with major structural features by Monsalve (1991).

A government report prepared by Monsalve (1991) assessed the geology of the area and presented several hazard maps for pyroclastic flow, pyroclastic fall, ballistic projectiles, dome collapse, and lahar scenarios. Although ashfall could reach Manizales (~25 km W), most hazards in this study were centrally located around the immediate region of Cerro Bravo, for example pyroclastic flows and flank failures (figure 4). Hazard zones for lahars included the Río Guarino, Río Aguacatal, and Río Gualí which could extend as far as the town of Honda (~80 km E).

Figure 4. This map of hazard zones for Cerro Bravo highlights pyroclastic flow scenarios. The summit of Cerro Bravo is marked with a red star; nearby towns and communities are labeled with green text. Modified from Monsalve (1991).

Seismicity during 2006-2012. During this reporting period, seismicity occurred at very low levels with 0-9 volcano-tectonic events (VT) recorded per month (table 1). Long-period earthquakes (LP) occurred more frequently with 0-80 events recorded per month. The SGC noted avalanche and rockfall signatures and, relative to the other years reviewed during this report, 2008 and 2011 had a notable number of surficial seismic signatures attributed to small avalanches and rockfalls. An average of 22 avalanche and 14 rockfall events occurred per month whereas the averages were between 1.5 and 10.7, respectively, during other years. The largest single rockfall event occurred in May 2012 and lasted for 34 seconds.

Table 1. Monthly seismicity at Cerro Bravo was tabulated by the occurrence of events: volcano-tectonic (VT), long-period (LP), rockfall, and largest earthquake magnitude. Courtesy of SGC.

The largest recorded earthquake magnitude, M 3.4, was recorded in December 2008. The average magnitude during this reporting period was M 1.7. An anomalous 2-hour-long signal was recorded in June 2006; that month, seismicity was slightly elevated (3 VT, 11 LP, and 37 rockfalls).

The SGC August 2008 bulletin highlighted a seismic swarm within the region of Cerro Bravo. The swarm was detected on 9 August 2008 comprising 65 earthquakes at an undetermined distance NE of Paramillo del Quindío (located ~40 km S of Cerro Bravo) at relatively shallow depths (2-5 km). The earthquakes had small magnitudes; the largest was M 1.14. A second swarm occurred on 30 December 2008, when ~80 LP earthquakes were detected. The largest event, an M 2.3 earthquake, occurred S of Cerro Bravo and caused shaking that was noted by residents of Manizales (particularly those in tall buildings).

A swarm of 67 earthquakes occurred during 17-29 November 2010. The SGC noted that rockfalls and avalanches were likely responsible for these events. That month, there were five LP earthquakes but no VT earthquakes were detected.

Rockfalls and avalanches were attributed to elevated seismicity in June 2011 when 40 events were detected that month. While those earthquakes were occurring, there were no associated geophysical or geochemical changes observed at the edifice.

Geochemical monitoring efforts. Radon and carbon dioxide data were recorded by the SGC during 2005 through 2012 (figure 5), although CO₂ data became unavailable after October 2009. The SGC reported that background level emissions were classified as values 2 data rarely coincided with radon except for a prominent increase around June 2008 at that Cerro Bravo 2 station CO₂ measured ~2.7% volume and the radon peak was ~900 pCi/L.

Figure 5. Radon and carbon dioxide emissions from Cerro Bravo during April 2005 - May 2010 (Cerro Bravo 1 Station) and June 2005-May 2010 (Cerro Bravo 2 Station). Note that, at both stations, CO2 data ended in October 2009. Courtesy of SGC.

Figure 6. This plot of radon emissions for 2005-2012 includes increasingly more radon stations over time. Installation of eight new stations occurred in June 2011 at a time when radon emissions were peaking around 2,000 pCi/L. Courtesy of SGC.

Surface deformation monitoring. In October 2009, the SGC installed reflectors and base stations for two EDM (Electronic Distance Measurement) lines (figure 1). An EDM survey was conducted three months later, beginning the establishment of long-term surface deformation monitoring. During 2009-2012, eight EDM surveys were conducted from the El Doce base and four EDM surveys were conducted from El Porton; the SGC stated that no significant changes were calculated from these datasets.

Monitoring with an electronic tilt station began in late March 2011 with an installation on the E flank (figure 1). Stable conditions were recorded by the tiltmeter up until December 2011 when decreasing trends suddenly began from both N and E components (figure 7). The SGC noted that from December 2011 to early April 2012 there was a total change of -5 & mu;m and -8 & mu;m (N and E components respectively). During April-December 2012, generally stable conditions resumed.

Figure 7. The electronic tilt record from CBRE station (located on the E flank). With the exception of December 2011-April 2012 (when significant decreasing trends persisted), this record showed fluctuations within expected range of the instrument. Courtesy of SGC.

References. Lescinsky, D., 1990, Geology, volcanology and petrology of Cerro Bravo, a young dacitic stratovolcano in West-Central Colombia [Master's Thesis]: Hanover, NH, Dartmouth College, 244 pp.

Monsalve, M.L., 1991. Mapa preliminar de amenaza volcánica del Volcán Cerro Bravo, INGEOMINAS, Prepared for the Government of Tolima and CRE-Tolima.

Thouret, J.C., Cantagrel, J-M., Robin, C., Murcia, A., Salinas, R., and Cepeda, H., 1995, Quaternary eruptive history and hazard-zone model at Nevado del Tolima and Cerro Machin volcanoes, Colombia. Journal of Volcanology Geothermal Research, 66 (1-4):397-426.

Thouret, J.C., Murcia, A., Salinas, R., Parra, E., Cepeda, H., and Cantagrel, J-M., Stratigraphy and quaternary eruptive history of the Ruiz-Tolima volcanic massif (Colombia): Implications for assessment of volcanic hazards. Symposium International Géodynamique Andine: Résumés des communications. 15-17 May 1990, Grenoble, France. p. 391-393.

Geologic Background. Cerro Bravo is a relatively low dominantly dacitic lava-dome complex north of Nevado del Ruiz that was constructed within the Pleistocene Quebrada Seca caldera. A series of moderate plinian eruptions during the Holocene were accompanied by pyroclastic flows and lava dome growth. Although historical records of the roughly 4000-m-high Cerro Bravo eruptions have not been found, stratigraphic evidence indicates that it last erupted sometime between the 1595 and 1845 eruptions of Ruiz.

Information Contacts: María Luisa Monsalve, Gloria Patricia Cortés, and Cristian Mauricio López, Servicio Geológico Colombiano (SGC), Volcanological and Seismological Observatory, Avenida 12 Octubre 15-47, Manizales, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).

According to the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO), several large active submarine volcanoes, spreading ridges, and rift zones have been discovered in the Northwest Lau back-arc basin, NE of Fiji Island (figure 1), by a team of Australian and American scientists aboard the CSIRO Marine National Facility Research Vessel Southern Surveyor during a research cruise in Spring 2008 (CSIRO, 2008b). While mapping previously uncharted areas for submarine volcanic and hot spring activity with multibeam sonar and various other techniques, the team located several active volcanoes, one of which they named Dugong. The depth of Dugong is given in the InterRidge Vents Database [Ver. 3.1] (2013), and its location was plotted on figure 1 based on coordinates given in Lupton and others (2012).

Figure 1. Two maps showing (lower left) North Island, New Zealand (in black) and selected plate tectonic features along the Kermadec and Tonga trenches (hachured line with teeth on upthrown side) and (larger map) Dugong (white square) and other features such as the main spreading centers, geographical features, and subaerial volcanoes (open yellow triangles). Note Niuafo'ou volcano and island. The base maps in figure 1 came from Keller and others (2008), a study primarily discussing the area in the rectangle on the larger map. The sea floor was mapped with multibeam sonar (soundings normal to the ship's track). Abbreviations are as follows: VFR - Valu fa ridge; ELSC - East Lau spreading center; ILSC - Intermediate Lau spreading center; CLSC - Central Lau spreading center; LETZ - Lau Extensional transform zone; PR - Peggy Ridge; NWLSC - Northwest Lau spreading center; NSC - Niuafo'ou spreading center (location of Rochambeau Rifts); NELSC - Northeast Lau spreading center; FSC - Fonualei spreading center; and MTJ - Mangatolu triple junction. Courtesy of Keller and others (2008).

As shown in figure 2, the greater Dugong structure is dominated by a 5-km-diameter caldera at a depth of 1,100 m. Dugong volcano is located ~60 km E of Lobster volcano, ~20 km WNW of Niuafo'ou volcano/island, and ~680 km NE of Suva, Fiji.

Figure 2. Multibeam sonar three-dimensional (30 kHz swathmap) image of submarine volcano Dugong. A Global Positioning System (GPS) and an Inertial Motion Unit (IMU) were used to monitor the ship's position and attitude. The large volcano, 45 km in diameter, is located 25 km NW of the subaerial back-arc island volcano of Niuafo'ou. A 5 km diameter crater forms the summit region of the volcano, with a small hydrothermal plume near its base. The mapping revealed an enormous structure with hundreds of individual eruptive blobs and transected by numerous faults. A dredge of the SW floor of the caldera recovered a few fresh basaltic pillow fragments, volcanic glass, and small pieces of pumice. There is no color scale for the image for conversion to depth, although dark green is the deepest, trending upwards through yellow, orange, red, and tan. Location and distance scales are also missing from the figure. Image from CSIRO (2008b); with ancillary information from Arculus (2008).

During the 6 week research expedition in the Pacific Ocean, scientists from the Australian National University (ANU), CSIRO Exploration & Mining, and the United States collaborated to survey the topography of the seafloor, analyzing rock types and formations, and monitoring deep sea hot spring activity around an area known as the North Lau Basin, 400 km NE of Fiji.

References. Arculus, R.J., 2008, Marine National Facility RV Southern Survey 2008 Program: Voyage Summary SS07/2008 Northern Lau Vents Expedition (NoLauVE), 23 p (URL: http://www.cmar.csiro.au/datacentre/process/data_files/cruise_docs/SS200807sum.pdf).

CSIRO, 2008a, Active submarine volcanoes found near Fiji, CSIRO web site (URL: http://www.csiro.au/Organisation-Structure/Divisions/Earth-Science--Resource-Engineering/SubmarineVolcanoes.aspx).

CSIRO, 2008b, Active submarine volcanoes found near Fiji, CSIRO media release (URL: http://www.scienceimage.csiro.au/mediarelease/mr08-93.html).

de Ronde, C.E.J, Baker, ET, Massoth, G.J, Lupton, J.E, Wright, I.C., Feely, R.A., and Greene, R.R., 2001, Intra-oceanic subduction-related hydrothermal venting, Kermadec volcanic arc, New Zealand, Earth and Planetary Science Letters, v. 193, p. 359-369.

Graham, I.J., Reyes, A.G., Wright, I.C., Peckett, K.M., Smith, I.E.M., and Arculus, R.J., 2008, Structure and petrology of newly discovered volcanic centers in the northern Kermadec-southern Tofua arc, South Pacific Ocean, Journal of Geophysical Research, v. 113, B08S02, doi:10.1029/2007JB005453.

InterRidge Vents Database Ver. 3.1, 2013, Vent Fields (URL: http://www.interridge.org/irvents/ventsfields?).

Keller, N.S., Arculus, R.J., Hermann, J., and Simon, R., 2008, Submarine back arc lava with arc signature: Fonualei Spreading Center, northeast Lau Basin, Tonga, Journal of Geophysical Research, v. 113, B08S07, doi:10.1029/2007JB005451.

Lupton, J.E., Arculus, R.J., Resing, J., Massoth, G.J., Greene, R.R., Evans, L.J., and Buck, N., 2012, Hydrothermal activity in the Northwest Lau Backarc Basin: Evidence from water column measurements, Geochemistry, Geophysics, Geosystems, v. 13, no. 5, doi: 10.1029/2011GC003891. Information Contacts. Commonwealth Scientific and Industrial Research Organization (CSIRO) (URL: http://www.csiro.au).

Geologic Background. This volcano was discovered during an Australian research cruise in 2008. The overall edifice is 45 km in diameter, with a 5-km-diameter summit caldera.

Information Contacts: Commonwealth Scientific and Industrial Research Organization (CSIRO) (URL: http://www.csiro.au); National Oceanic and Atmospheric Agency (NOAA) (URL: http://www.CSC.noaa.gov/crs/rs_apps/sensors/multi_beam.htm); Richard Arculus, Australian National University Research School of Earth Sciences; and Frederick Stein, Director, Marine National Facility, CSIRO.

This volcano is well known for three summit crater lakes, each a different color. We last reported minor bubbling in a crater lake Tiwu Nua Muri Kooh Tai lake in 1995 (BGVN 20:06). Between 15 and 19 May 1995, rescuers searched for the body of a Dutch tourist who had fallen into the crater lake but they did not find it.

2013 activity.The Center of Volcanology and Geological Hazard Mitigation (CVGHM) reported that on 6, 10, and 12 June 2013, and during 14 June-9 July 2013, the color of the water in Kelimutu's Crater II (Tiwu Nua Muri Kooh Tai Crater) was bluish white. Diffuse white plumes rose as high as 50 m above the lake's surface and in some areas the water appeared or sounded like it was boiling. A sulfur odor was also reported. The water in Crater I (Tiwu Ata Polo) was light green and churned, and the water in Crater III (Tiwu Ata Mbupu) was mossy green.

On 3 June 2013, a change was observed in the color of the lake water in Crater II, going from blue to a café au lait (light tan), accompanied by white smoke under weak to medium pressure, rising 50 meters above the surface of the lake. From the southern side of Crater II a bubbling sound of boiling was heard near the wall separating Crater I from Crater II. The smell of sulphur gas was quite sharp in the vicinity of the crater and at nighttime a weak to medium smell of this gas could be discerned in Pemo Village which is 3 kms from the peak of Kelimutu. On 4 June 2013 at 1400 hours local time the status of Kelimutu was upgraded from Alert Level 1 (Normal) to Alert Level 2 (Waspada).

On 6 June 2013 water in Crater II was a bluish white (like a salty egg), with sparse to medium white smoke under weak to strong pressure extending up 10-35 meters above the lake surface. A weak to strong bubbling sound of boiling water was heard on the southern side of the crater. A medium to sharp smell of sulphurous gas was evident as was the withering vegetation.

On 10 June 2013 water in Crater II was still a bluish white with medium to dense white smoke extending up 40-50 m above the lake surface. A bubbling sound of boiling water could be heard on the southern side of the crater. A medium smell of sulphurous gases was discernible.

On 12 June 2013, smoke rising from the surface of the lake extended to only about 10-30 meters above the lip of the crater. There was a rather acrid smell of sulphurous fumes. Eruptive and hot air noises were audible two times and the water in the crater lake still appeared to be boiling.

From 14 June to 9 July 2013, water in Crater II visually still appeared bluish white with sparse white smoke rising from the surface of the lake about 2-10 meters into the atmosphere (dominant height was not observed). There was a weak to medium (with weak dominating) smell of sulphurous gases. At one point bubbling water was noticeable but it was clearly under weak pressure. Water from Crater III was calm and moss-green in color.

During 22-29 June 2013 sulfur dioxide concentrations in Crater II were occasionally 2.8 ppm, when the wind blew the gas towards the sensor. CVGHM noted that plumes rising from the lakes became lower and barely visible during 3 June-9 July, and that the hissing or "rustling sound" of water from near the dividing wall of craters I and II had gradually faded away. Based on visual observations, seismicity, and gas emissions, CVGHM lowered the Alert Level to 1 (on a scale of 1-4) on 12 July (figure 4).

Figure 4. Kelimutu has three summit crater lakes seen in this photo. The lake Tiwi Ata Mbupu (left) is commonly blue. Tiwu Nua Muri Kooh Tai and Tiwu Ata Polo, which share a common crater wall, are typically green and red-colored, respectively. Photo courtesy of https://www.tripping.com. Posted 1 June 2013.

During 13 - 18 June 2013, local tectonic quakes peaked at 139 before undergoing a decrease as of 17 June 2013. Shallow (VB) and deep (VA) volcanic earthquakes occurred intensely each day, reaching a a peak of 13 shallow volcanic quakes 19-24 June 2013 and then tended to decline (figure 5). Deep volcanic quakes peaked at 14 during 1-6 July 2013 and then subsided.

Figure 5. A plot of seismicity at Kelimutu during 1 June 2013 through 11 July 2013. Courtesy of CVGHM.

No thermal alerts were recorded by MODVOLC for the past twelve months beginning in mid-July 2012.

Figure 6. First photo (A) is Tiwu Ata Polo Lake (water color change from red to green), second photo (B) is between Tiwu Ata Polo Lake and Tiwu Nua Muri Kooh Fai Lake, and third photo (C) is Tiwu Nua Muri Kooh Fai Lake (water color change from green to white). Pictures taken on 6 June 2013 by Kristianto.

Geologic Background. Kelimutu is a small, but well-known, Indonesian compound volcano in central Flores Island with three summit crater lakes of varying colors. The western lake, Tiwi Ata Mbupu (Lake of Old People) is commonly blue. Tiwu Nua Muri Kooh Tai (Lake of Young Men and Maidens) and Tiwu Ata Polo (Bewitched, or Enchanted Lake), which share a common crater wall, are commonly colored green and red, respectively, although lake colors periodically vary. Active upwelling, probably fed by subaqueous fumaroles, occurs at the two eastern lakes. The scenic lakes are a popular tourist destination and have been the source of minor phreatic eruptions in historical time. The summit is elongated 2 km in a WNW-ESE direction; the older cones of Kelido (3 km N) and Kelibara (2 km S).

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); and Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822 USA (URL: http;//hotspot.higp.hawaii.edu/).

We recently noted that Frederick Belton's web site on Ol Doinyo Lengai has been supplemented by a web site from the Ngare Sero Village Council entitled "Oldoinyo Lengai - The Mountain of God." This new web site has information on climbing, mountain safety, guides, equipment, and fees, as well as activity of the volcano as observed by guides and visitors. According to Belton, Lazaro Saitoti is maintaining the web site from both Arusha and Engare Sero, and it represents a potentially useful source of local information, with an emphasis on tourism.

Abigail Church forwarded to us two aerial photographs of Lengai's active crater and summit, one taken in June 2013 (figure 166) and the other in 28 July 2013 (figure 167). On 29 July, Church reported that she had flown over Lengai a few times in the last year or so, and that Lengai appeared to have small active vents still emitting lava. In addition, these aerial views recorded little other activity except for slippage off the steep walls. She noted that she was in touch with a number of pilots that are often flying over Lengai and that might contact her if they see anything unusual.

Figure 166. Aerial photograph of the crater and summit of Lengai taken in June 2013, looking almost S. In the background one can see the summit of Lengai, due S of the crater (see map, figure 154 of BGVN 37:11). Courtesy of Andy Allan.

Figure 167. Aerial photograph of the crater and summit of Lengai taken 28 July 2013, looking almost S. In the background one can see the summit of Lengai, due S of the crater (see map, figure 154 of BGVN 37:11). Courtesy of Phil Mathews, Heliprops Ltd.

On 10 April 2013, Bonnie Betts climbed Lengai and, on Belton's web site is quoted as reporting: "We started at midnight in a thunderstorm with light rain, but it cleared up. You could hear the lava sloshing around inside the crater before getting to the top; also dark smoke could be seen coming from the crater while ascending in the night . . . Looking into the crater, you can see the lava sloshing back and forth in the dark, black tunnel, and then some would flow out with a different flowing swishing sound." Local guides expressed concerns to Betts that an extensive crack seen in the crater may be the beginning of a collapse of the inner wall of the pit crater. Figures 168 and 169 show photos taken during Betts' climb.

Figure 168. A tall spatter cone was formed 10 April 2013 near the crater wall, as seen looking W from the crater rim, located on the W side of the pit. The flank of that cone had also ruptured and an active lava flow exited the cone. Note that the vent is also present in the photo of the same area taken 14-15 September 2012 (see figure 158 of BGVN 37:11). Photo courtesy of Bonnie Betts.

Figure 169. Photo taken 10 April 2013, looking W from the crater rim. A steaming fissure crossed the photo in mid-ground near the crater rim. Just to the right of center of the photo are the Pearly Gates, cut in the crater rim atop the former climbing route on the W side of the volcano (see figure 154 of BGVN 37:11). Photo courtesy of Bonnie Betts.

Belton received some photos and a description by Gian Schachenmann of a visit to Lengai on 17-18 June 2013. Schachenmann noted sloshing lava sounds from the spatter cone and big cracks on the rim where gases escaped (figure 170).

Figure 170. Photo taken 17 or 18 June 2013 (in the same area as figure 168, above), showing that the tall spatter cone no longer has the vent that was present on the photo taken 10 April 2013. Thus, it also appears that there has been only slight growth of the cone during the two months between the photographs. Photo courtesy of Gian Schachenmann.

Death of John Barry Dawson, Lengai Legend. According to the Mitchell (2013), John B. Dawson, Emeritus Professor of Geology, Lakehead University, Thunder Bay, Ontario, Canada, died 2 February 2013. Excerpts from that obituary are found below.

Dawson was known for his extensive knowledge of kimberlite geology. Subsequent to graduation in 1960, Barry joined the Tanganyika Geological Survey, where he was employed to map areas of the then remote Angata Salei region near Lake Natron, a location of an active volcano. "The first ever descent into the crater of this volcano, Oldoinyo Lengai, (the Maasi Mountain of God), was made by Barry and Ray Pickering in October 1960. It was during this visit that he recognized the unique sodium carbonate volcanism and earned himself a permanent place in petrological history with the publication of his paper on these extraordinary rocks in the journal Nature (Dawson, 1962). Subsequently, he maintained an active research program on the petrology of Oldoinyo Lengai and other volcanoes in the Gregory Rift Valley."

"During this work he narrowly survived one violent silicate ash eruption of Oldoinyo Lengai in 1966, and was fortunate enough to observe, some 40 years later in 2007, the return to silicate pyroclastic activity from the quiet effusive natrocarbonatite eruptions. To the time of his death, Barry was actively involved in studies of Oldoinyo Lengai, Kerimasi, Mosonik and other Tanzanian volcanoes. He was especially pleased with the publication in 2009 [sic] of his comprehensive review of volcanic activity in the Gregory Rift" (Dawson, 2008).

References. Belton, F., 2013, Ol Doinyo Lengai, web site, URL: http://www.oldoinyolengai.pbworks.com.

Dawson, J.B., 1962. Sodium Carbonate Lavas from Oldoinyo Lengai, Tanganyika, Nature, v. 195, pp. 1075-1076.

Dawson, J.B., 2008, The Gregory Rift Valley and Neogene-Recent Volcanoes of Northern Tanzania, Geological Society, London, Memoir 33, pp. viii 102.

Mitchell, R.H., 2013, John Barry Dawson 1932-2013, Mineralogical Magazine, v. 77, no. 3, pp. 401-402.

Ngare Sero Village Council, 2013, Oldoinyo Lengai - The Mountain of God, web site, URL: http://www.oldoinyo-lengai.org

Geologic Background. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Information Contacts: Abigail Church, The Ker and Downey Safari Tradition, James Robertson, chairman, P.O. Box 86, Karen 00502, Kenya (URL: http://www.kerdowneysafaris.com/); Frederick A. Belton, University Studies Department, Middle Tennessee State University, Murfreesboro, TN (URL: http://www.oldoinyolengai.pbworks.com); Lazaro Saitoti, Chairman, Ngare Sero Village Council, and Lemra Kingi, Chairman Tourism, Ngare Sero Village Council, Arusha and Engare Sero, Tanzania (URL: http://www.oldoinyo-lengai.org); and Bonnie Betts (no contact information).

The Australian Commonwealth Scientific and Industrial Research Organization (CSIRO) announced in press releases that several large active submarine volcanoes, spreading ridges, and rift zones had been discovered in the Northwest Lau back-arc basin, NE of Fiji Island (figure 1). The discoveries were made by a team of Australian and American scientists aboard the CSIRO Marine National Facility Research Vessel Southern Surveyor in Spring 2008 (CSIRO, 2008a). While mapping previously uncharted areas for submarine volcanic and hot spring activity, the team located several volcanoes, one of which they named Lobster. The depth of Lobster is given as 1,500 m in the InterRidge Vents Database [Ver. 3.1] (2013). The location of Lobster is shown in figure 1, based on coordinates given in Lupton and others (2012). The base maps in figure 1 came from Keller and others (2008), a study primarily discussing the area in the rectangle on the larger map. The sea floor was mapped with multibeam sonar. Lobster is located ~75 km NNW of Niuafo'ou volcano/island and ~680 km NE of Suva, Fiji (figure 1). Dugong volcano lies ~60 km E of Lobster.

Figure 1. Two maps showing (lower left) North Island, New Zealand (in black) and selected plate tectonic features along the Kermadec and Tonga trenches (hachured line with teeth on upthrown side) and (larger map) Lobster (white square) and other features such as the main spreading centers, geographical features, and subaerial volcanoes (open yellow triangles). Note Niuafo'ou volcano and island, and the location of Lobster (and Dugong, a neighboring volcano discussed in a separate Bulletin report and plotted on a larger map). Abbreviations are as follows: VFR - Valu fa ridge; ELSC - East Lau spreading center; ILSC - Intermediate Lau spreading center; CLSC - Central Lau spreading center; LETZ - Lau Extentional transform zone; PR - Peggy Ridge; NWLSC - Northwest Lau spreading center; NSC - Niuafo'ou spreading center (location of Rochambeau Rifts); NELSC - Northeast Lau spreading center; FSC - Fonualei spreading center; and MTJ - Mangatolu triple junction. Courtesy of Keller and others (2008).

Lobster volcano's caldera is 2x2.5 km in diameter with a floor at 1.5 km depth (figure 2). It was described as residing amid four radiating rift zones.

Figure 2. (a) Multibeam sonar three-dimensional (30 kHz swathmap) image made in 2008 of Lobster which sits in what was described as the center of a rift zone and astride a spreading ridge to its W (CSIRO, 2008). Image lacks scale for depth values, but in relative terms light blue is the deepest, trending upwards through dark-to-light green, yellow, orange, and then red as the shallowest. Image from news release of CSIRO (2008b). (b) Shaded relief, contour map of Lobster caldera on the Rochambeau rifts showing part of a survey track completed in 2010 by the research vessel Dorado Discovery. Taken from Lupton and others (2012). (c) Detail map of Lobster Caldera showing locations and profiles for two chemistry hydrocasts. Inserts show vertical profiles of δ3He (deviation of the 3He/4He ratio measured at depth from the atmospheric ratio), total Mn (manganese), and %T transmission of light (a measure of suspended particles) plotted versus depth. Taken from Lupton and others (2012).

The caldera's rim is about 100 m high on the W side whereas only ~20 m high on the E side.

Dredge samples from Lobster recovered in 2008 contained olivine and plagioclase in pillow basalts. A dredge sample taken on the smooth caldera floor recovered fresh flows as well as thick, black aphyric pillows with glassy rinds.

Age. According to Arculus (2008) and Lupton and others (2012), active venting was identified in the form of high helium anomalies (δ³He), suspended particles (%T), and trace metals (manganese and iron) at 60 m off the bottom in the SE corner of the summit caldera. Lupton and others (2012) reported, in 2012, that the site was still active.

The expedition mapped the seafloor using a 30 kHz multibeam sonar with Global Positioning System (GPS) and an Inertial Motion Unit (IMU) to track the ship's position and attitude. They also made vertical conductivity, temperature, and depth (CTD) measurements as well as rock dredging. In addition, by lowering the CTD package up and down a few hundred meters from the bottom, while moving the ship, they obtained a far greater density of data. This technique, often informally referred to as a CTD tow-yo, is effective for mapping and sampling hydrothermal plumes.

References. Arculus, R.J., 2008, Marine National Facility RV Southern Survey 2008 Program: Voyage Summary SS07/2008 Northern Lau Vents Expedition (NoLauVE), 23 p (URL: http://www.cmar.csiro.au/datacentre/process/data_files/cruise_docs/SS200807sum.pdf).

CSIRO, 2008a, Active submarine volcanoes found near Fiji, CSIRO web site (URL: http://www.csiro.au/Organisation-Structure/Divisions/Earth-Science--Resource-Engineering/SubmarineVolcanoes.aspx).

CSIRO, 2008b, Active submarine volcanoes found near Fiji, CSIRO media release (URL: http://www.scienceimage.csiro.au/mediarelease/mr08-93.html).

de Ronde, C.E.J, Baker, ET, Massoth, G.J, Lupton, J.E, Wright, I.C., Feely, R.A., and Greene, R.R., 2001, Intra-oceanic subduction-related hydrothermal venting, Kermadec volcanic arc, New Zealand, Earth and Planetary Science Letters, v. 193, p. 359-369.

Graham, I.J., Reyes, A.G., Wright, I.C., Peckett, K.M., Smith, I.E.M., and Arculus, R.J., 2008, Structure and petrology of newly discovered volcanic centers in the northern Kermadec–southern Tofua arc, South Pacific Ocean, Journal of Geophysical Research, v. 113, B08S02, doi:10.1029/2007JB005453.

InterRidge Vents Database Ver. 3.1, 2013, Vent Fields (URL: http://www.interridge.org/irvents/ventsfields?).

Keller, N.S., Arculus, R.J., Hermann, J., and Simon, R., 2008, Submarine back-arc lava with arc signature: Fonualei Spreading Center, northeast Lau Basin, Tonga, Journal of Geophysical Research, v. 113, B08S07, doi:10.1029/2007JB005451.

Lupton, J.E., Arculus, R.J., Resing, J., Massoth, G.J., Greene, R.R., Evans, L.J., and Buck, N., 2012, Hydrothermal activity in the Northwest Lau Backarc Basin: Evidence from water column measurements, Geochemistry, Geophysics, Geosystems, v. 13, no. 5, doi: 10.1029/2011GC003891.

Geologic Background. Active hydrothermal venting was noted when this volcano was first discovered in 2008 by an Australian research expedition.

Information Contacts: Commonwealth Scientific and Industrial Research Organization (CSIRO) (URL: http://www.csiro.au).

Our last report on Manan (BGVN 36:06) discussed field observations through 11 January 2011. The following summarizes available Rabaul Volcano Observatory (RVO) reports issued since that time through May 2013.

Pyroclastic flows took place during the reporting interval, specifically four times on 16 June 2012, and another four times on 30 July 2012, all of which traveled down the SE valley. No injuries were reported. In addition there were lava fountains, several lava flows, and some cases of sustained emissions lasting hours.

Occasional ash plumes triggered the Darwin Volcanic Ash Advisory Centre (Darwin VAAC) to issue notices. Some ash plumes drifted over 200 km (figure 29).

Figure 29. This ALI satellite photo was taken of Manam on 17 September 2009. Courtesy of NASA-EOS.

Loud noises, rumbling, tephra ejected above or outside the confines of the crater, and night glow were common observations.

2011 activity. During 1-19 August 2011, RVO reported Manam's summit area was obscured by weather clouds on most days. When the summit was clear to viewers on the mainland, 15-20 km away from Manam, both vents emitted white vapor plumes. Main Crater produced light-gray ash clouds during 13 and 17-18 August, and bright, steady incandescence was visible on most clear nights. August seismicity was dominated by volcanic tremor, but discrete high-frequency volcano-tectonic earthquakes were also recorded which, RVO noted, are not very common for Manam. An electronic tiltmeter located ~4 km SW from the summit craters continued to show inflation.

Based on analysis of satellite imagery, the Darwin VAAC reported a series of ash plumes which, during 18-21 August, rose to altitudes of 1.8-2.1 km and drifted 45-90 km NW and W.

The VAAC next reported that on 18 October, ash plumes rose to 3.7 km altitude and drifted 150-170 km NW. During 19-21 October ash plumes rose to an altitude of 3.7 km and drifted 150-220 km W. For 11 November 2011, using both satellite imagery and a pilot observation, the VAAC reported an ash plume to an altitude of 3 km drifting up to ~90 km NE.

Activity continued in December 2011. Seismicity was assessed by Real-time Seismic Amplitude Measurements (RSAM) and varied at high levels between 200-350 RSAM. Both craters produced ash and lava fragments. The ash clouds rose to several hundred meters above the vents. Both vents often glowed at night, and expelled glowing fragments. Brown and grey ash was deposited in areas down wind. There were reports of a possible lava flow from the Southern Crater, with the 'V' shaped channel created by the 2005 blast being filled up.

2012 activity. RVO reported continued activity during January 2012. White vapor and grey-to-black ash emissions rising less than 200 m were observed from both craters throughout the month, sometimes with accompanying weak incandescent projections. From the Southern Crater, more sustained emissions on the evening of 20 January occurred with mainly black ash up to 400 m, trending to the SE. At that time low-energy projections observed at 3-4 minute intervals fell back inside the crater. Main Crater produced a bright steady glow and released thick white vapor with a strong blue tinge. On 23 January observers noted that there were possibly three vents emitting columns of vapor and ash. Seismicity during this time remained moderate to high, with a variable RSAM of 200-350.

RVO next reported mainly mild activity at Southern Crater during the first two weeks of May 2012. Diffuse white and blue vapor emerged during 5-6 and 13-14 May, and gray and gray-brown ash clouds were observed on 7, 9, and 12 May. Observers noted incandescence on the nights of 6, 8, 10-11, and 13-14 May, and glowing tephra occasionally falling outside of the crater.

Activity increased on 16 May 2012. Ash cloud colors changed from gray and gray-brown to gray and black. On 27 and 30 May Strombolian emissions occurred and, for periods lasting 1-2 hours, continuously ejected incandescent tephra. On 30 May two vents at the Southern Crater produced lava fountains. Ash plumes rose 100-400 m above the crater and drifted NW. Most of the tephra fell back into the crater, but some was channeled into the SE and SW valleys. Emissions from Main Crater were milder and characterized by white plumes and gray to gray-brown ash plumes noted during 6, 10-11, 13, 26, 28-29, and 31 May. Ash fell on the NW part of the island.

Seismicity during May 2012 maintained a moderate to moderately-high level and was associated with discrete low-frequency earthquakes and low-level, sporadic volcanic tremor in the background occurring during 1-9 May. Daily low frequency totals ranged between 880 and 970. The steady increase in RSAM observed in April continued until about 16 May, and fluctuated in an upward trend thereafter. The fluctuations reflected phases or episodes of low and moderate activity. The highest RSAM of 500 was reached on the 30th. After 30 May RSAM declined again to reach 350 by the end of May. Around this time tremor became dominant and overshadowed the discrete events, making it difficult to conduct event counts. The electronic tiltmeter (located 4 km SW) continued to show gentle uptilt towards the summit.

RVO reported low to moderate activity during 1-15 June 2012. Emissions consisted of gray and sometimes black ash clouds that rose from the crater on most days. Plumes drifted SE on 2 June and NW during 6-15 June. Ash fell in areas downwind between Yassa (WSW) and Baliau (NNW), and Warisi (ESE). Incandescent material was also ejected from the crater.

Pyroclastic flows on 16 June 2012 (at 0700, 0725, 0727, and 0729) all channelled into the SE valley. The last pyroclastic flow was perhaps the largest. It reached the lowest elevation, 300-400 m above sea level, but came to rest far from populated areas. Ash plumes from the pyroclastic flows rose ~1,000 m and drifted WSW and WNW. Small amounts of ash fell in villages between Dugulava (on the SW side of the island) and Yassa. Fine ash also fell in downwind areas on the mainland, including the Bogia government station (25 km SSW, on the mainland). Emissions from Main Crater were milder and mostly characterized by white and bluish plumes. Light gray plumes were noted during 2 and 8-9 June.

Ash fell in the NW part of the island. Weaker emissions occurred on 17 June, mostly consisting of steam with occasional ash. During 18-30 June gray and occasionally black ash clouds rose 100-150 m above the crater and drifted mainly NW. Incandescent tephra was ejected from the crater on most nights. Activity during 28-29 June was almost sub-Plinian. Emissions from Main Crater were milder and mostly characterized by white and bluish plumes. Gray ash plumes were emitted during 18, 23, 26-27, and 29 June. Incandescence from the crater was visible during 18, 20-22, and 24 June. Ash again fell in the NW part of the island. Seismic recording ceased during 12-27 June 2012 due to equipment failure at Bogia apparently caused by a lightning strike. During the period of data recording, seismicity remained at moderate to moderately high level, dominated by sub-continuous to continuous volcanic tremor. RSAM fluctuated between 250 and 550. High peaks in the RSAM between 4 and 10 June were associated with moderate to strong phases of eruptive activity described above. The electronic tiltmeter was generally stable during reporting period, but the long term trend showed slow inflation towards the summit area. When seismic recording resumed on 28 June 2012, the level of seismicity had risen slightly: RSAM 400-600. The high RSAM values corresponded to some of the moderate summit activity reported above. Seismicity was dominated by sub-continuous to continuous volcanic tremor. Around this time, the electronic tiltmeter remained out of service.

During the first half of June RVO recommended authorities declare a Stage 2 alert level. The level remained at Stage 2 for the remainder of June 2012.

In their next available report, RVO noted that activity increased slightly during 15-31 July, except during 18-20 July when ash emissions decreased. During most of the reporting period, when visibility was clear, gray-to-sometimes-black ash plumes were observed rising 300-700 m above the crater discharging from two vents. The plumes mainly drifted NW, mainly affecting villages between Yassa and Kuluguma. Rumbling was heard on 25 July from Bogia. Bright glow visible at night was attributed to ejected incandescent tephra. Sub-Plinian activity occurred on most nights during 21-31 July. Small lava flows descended the SW flank.

Four pyroclastic flows traveled down the SE flank on 30 July (at 0638, 0640, during 1200-1300, and at 1428). The first event was the largest, and generated an ash plume that rose 1.8 km above the crater and drifted NW. As before, all four flows were again channeled into the SE valley. Emissions from Main Crater were milder and mostly characterized by white and bluish plumes, and occasional gray ash plumes. The Alert Level remained at Stage 2. Seismicity fluctuated, and was very high during 16-17 July 2012, dominated by sub-continuous to continuous volcanic tremors. RSAM ranged between 500 and 700. It declined thereafter to 150-300 units between 18 and 20 July before increasing again rapidly to 700 on the 21st. The reduced seismicity between 18 and 20 coincided with the reduced summit activity. Seismicity remained at a very high level (700 RSAM units) for the next few days before declining again to another low (300 RSAM units) on 26 July. There was one more phase of high activity (700 RSAM units) between 28 - 30 July, before RSAM became steady at 450 until the end of the month. The electronic tiltmeter remained out of service.

2013 activity. RVO reported that dark gray ash plumes were occasionally emitted from Manam's Southern Crater during 8-12 January. At about 1000 on 12 January a sub-Plinian eruption generated ash plumes that rose 1.4-1.5 km above the crater; activity peaked between 1200 and 1300. The ash plumes drifted SW, S, and SE, producing ashfall on the island in areas downwind and light ashfall in Bogia (23 km SSW). Activity decreased after 1600, and ash plumes rose only 500 m above the crater. At night ejected incandescent material was observed. Ejected material and ashfall was deposited in the SE and SW valleys. Ash plumes drifted S during 13-14 January. White vapor plumes rose from Main Crater during the reporting period. Based on observations of satellite imagery and wind data analyses, the Darwin VAAC reported that an ash plume rose to an altitude of 3 km a.s.l. on 28 January and drifted 22 km E. The next day an ash plume drifted 93 km NE, and then later another ash plume drifted 55 km NE at an altitude of 4.3 km a.s.l.

Seismicity was low on 8 January with RSAM value was 80. But beginning on 9 January it started to gradually increase, reaching a moderate level early on the 11th. RSAM had by then reached 200. Seismicity continued to increase, as RSAM reached 550 between 1000 and 1100, which coincided with the commencement of the small sub-Plinian eruption reported above. RSAM reached a peak of 620 at about 2300 on 12 January before it subsided to about 320 at 0500 on 13 January. RSAM fluctuated between 230 and 600 until the end of the reporting period.

Seismicity was characterised by frequent small low frequency earthquakes during low to moderate seismicity and by sub-continuous to continuous volcanic tremors during high seismicity. Data from the electronic tiltmeter did not show any significant changes.

Based on observations of satellite imagery and wind data analyses, the Darwin VAAC reported that an ash plume rose to an altitude of 10.1 km a.s.l. on 12 February and drifted 55 km SW. On 16 February an ash plume rose to an altitude of 3.4 km a.s.l. and drifted over 35 km NW.

RVO reported that on 1 March Main and Southern Craters emitted small amounts of diffuse white vapor; the craters were either partially or totally obscured by meteorological cloud cover. On 4 and 7 March intermittent gray ash plumes rose 300 m, above the cloud cover. RSAM values remained at a near-background level of 120. A gradual increase began on 2 March, reaching a peak of about 350 on 6 March before declining again to 300 on 7 March. The increase in RSAM on the 6 March was attributed to a increase in the number and size of low frequency earthquakes and occasional sub-continuous volcanic tremors. Ground deformation data from the electronic tiltmeter fluctuated within a steady trend.

Based on analysis of satellite images, pilot observations, and wind data analyses, the VAAC reported that on 14 March an ash plume rose to altitudes of 6.1-7.6 km a.s.l. and drifted 110-150 km ESE.

Based on analysis of satellite imagery (MT Sat) and wind data analyses, the Darwin VAAC reported that on 10-11 April an ash plume rose to altitudes of ~ 2 km and and drifted 75 km W. RVO reported that Manam's high level of activity continued on 15 April. Ash plumes rose 500 m above the crater. A loud explosion was heard at 0804. At about 1950 dense ash plumes rose 2 km and drifted SW. At night loud jet-like noises were reported by residents in Bogia. Lava was observed flowing from a new vent on the headwall of SW valley during a brief clear period from 1800 to 1850. Ash and scoria fell in most villages between Dugulava, on the SW side of the island, and Kuluguma on the NW side. Similar activity continued during the first half of 16 April, including a small pyroclastic flow that occurred around 1359 that was channeled into SE valley. Thereafter, the activity was characterized by gentle light gray ash emissions until 20 April.

During the high activity between 13 and 16 April, the formation of two new sub-terminal vents was reported. The exact timing is unclear due to occasional cloud cover around the summit area. The first vent probably formed on 13 April on the side of the headwall of SW valley. The vent was seen releasing lava effusively into SW valley. The second vent formed sometime during the evening of the 15 April E of Southern Crater in SE valley at an approximately similar elevation as those formed in mid 2012.

Seismicity, reflecting activity at the summit, was high on 15 April with RSAM readings fluctuating ~ 700. It declined slowly from 16 April and, as of the 18 April, it reached a moderate level with RSAM of 370, then declined again to 220. The down-tilt or deflation towards the summit area stopped around 15 April. Subsequently, information from the electronic tiltmeter was stable.

RVO reported that on 23 April dense white vapor plumes occasionally rose from Southern Crater. During 25-28 April ash clouds rose from the new sub-terminal vent E of Southern Crater inside the SE valley. The ash clouds rose 600 m and drifted NW. Loud booming noises were heard each day; however, between 0700 and 1900 on 27 April the noises became more frequent, louder, and explosive in nature, and were heard at Bogia. Seismicity remained high and swung around in the latter part of 25 April and increased steadily until it reached peak activity on the 28 April, before dropping slightly. Corresponding RSAM values increased from 220 on the 25 April, to 650 on the 28 April, and thereafter dropped to 500. Seismicity was characterized by small to moderate low frequency earthquakes.

Information from the electronic tiltmeter did not show any significant movements. RVO reported that during 29 April-16 May activity at Manam was low, characterized by white and occasionally blue vapor plumes rising from Southern Crater. White vapor plumes also rose from Main Crater. Seismicity fluctuated at high level between 29 April and 1 May; RSAM ranged between 500-700. After 1 May it started to decline, reaching a low level on 4 May and remaining low for the remainder of the reporting period. The corresponding RSAM at low level ranged between 50 and 100. RVO reminded people to stay away from the four main radial valleys, and especially the SE and SW ones, because most products from the activity at Southern Crater were channeled into these two valleys. No significant surface deformation was detected by the electronic tiltmeter.

Digital book in press. A new academic, digital book has sections that clearly relate to Manam (Johnson, 2013, in press). From the table of contents, those sections are (9) Tony Taylor and an Eruption Time Cluster: 1951-1966, Evacuation of Manam and the 1956-66 Eruptions and (14) Eruptions of the Early Twenty-first Century: 1998-2008. Manam, 2004-5: Abandoning a Volcanic Island?

Reference. Johnson, RW, (2013, in press), Fire Mountains of the Islands: A History of Volcanic Eruptions and Disaster Management in Papua New Guinea and the Solomon Islands, Australian National University E-press (ANU E Press (URL: http://epress.anu.edu.au/).

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 basaltic-andesitic stratovolcano to its lower flanks. These 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 observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent 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), PO Box 386, Rabaul, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC) (URL: http://www.bom.gov.au/info/vaac/).

The last report on Reventador covered activity through 26 April 2012 (BGVN 37:03) and this one covers activity through April 2013.

In its Special Report of 9 November 2012, Ecuador's Instituto Geofísico-Escuela Politécnica Nacional (IG) summarized the new phase of activity that began in February 2012. The Special Report noted that lava flows traveled as far as 2 km from the crater down the N and S flanks. Later reports noted that in November-December 2012, lava flows reached 1.3 km in length; in January 2013 they reached up to 1.1 km in length. During this reporting interval, ash plumes rose as high as 5.2 km altitude both in August 2012 and November 2013.

The lava dome in the interior of the crater continued to grow and between November 2012 and January 2013 established a new summit that reached to at least 100 m above the E rim, having completely filled the crater developed in November 2002. This enabled blocks from the lava dome to roll down the flanks.

Table 6. A non-comprehensive synthesis of Reventador's steam and ash plumes generated during the reporting period. Courtesy of IG and the Washington VAAC.

Between late April and early August 2012, activity at Reventador remained moderate, and although cloud cover often obscured visual observations, there were occasional reports of steam emissions rising to as high as 1 km above the crater. Long-period (LP) earthquakes occurred with moderate-to-high intensity, a behavior interpreted as the movement of fluids at depths. Seismic signals attributed to rock fall were also prominent, inferred to come from lava flows that descended the N flank, as aerial observers witnessed on both 29 May and 4 June.

Based on analysis of satellite imagery, the Washington Volcanic Ash Advisory Center (VAAC) reported that on 12 August they detected a well-defined thermal anomaly. Thermal images obtained in overflights carried out on 17 and 18 October 2012 revealed a lava flow that descended the flank of the cone and verified that another flow had descended during the preceding days or weeks and at the moment of observation was still warm. The flows did not exceed 1 km in length, and in light of their location within the crater, were not a danger to the public (figure 39).

Figure 39. A) On the left photo, the S flank of Reventador seen on 19 October 2012. A lava flow descending on the upper flank covered much of the flows from previous days and weeks. At right is a corresponding thermal image, permitting definition of the extent of the new hotter flows. Photo and image, courtesy of P. Ramon (Instituto Geofisico).

On 17 and 18 October, IG also verified the presence of a previously known lava dome within the crater, with steep slopes, the top of which was then the highest point of the volcano. Similar observations were carried out on 19 October by IGEPN technicians maintaining the monitoring network, who also stressed the continuous flow of lava blocks spilling off both the fronts of new flows and from the lava dome.

During 31 October-11 December 2012, the IG reported that although cloud cover often prevented visual observations, ash plumes were often seen.

Seismicity increased during this time period. Around 5 November, the seismic network detected an increase in the magnitude of volcanic tremor. IG reported that seismicity indicated falling rock and explosions during 14-15 November. Beginning 16 November IG's seismic network indicated a significant increase in tremor and in signals indicative of emissions and explosions. IG reported that scientists aboard an overflight on 23 November observed intense fumarolic activity and a new crater at the summit of the dome, which contained ash and large blocks. A thermal camera measured temperatures at the dome of ~ 300°C. Lava flows continued to be active on the dome flanks, and elongated block-and-ash deposits were also visible on the flanks. IG reported high seismicity during 5-11 December 2012, indicating multiple explosions almost daily. At least one lava flow was generated between November - December 2012 that descended the N flank to ~1.3 km in length.

2013. Throughout this January-April 2013 reporting period, cloud cover often prevented visual surface observations. The lava dome grew between November 2012 through January 2013 to at least 100 m above the E rim, completely filling the crater generated by the eruption of November 2002. Between November 2002 and 31 January 2013, ~ 20 lava flows had traveled down the N, SE, and S flanks, and affected zones within the caldera.

IG reported moderate seismicity during 16-21 January 2013. During the morning of 22 January seismicity, including tremor, increased significantly, signals indicating that rock falls were detected. Low frequency, high-energy tremor was detected by seismic stations around the volcano with an average of 20 seismic events and an average of 29 explosions. Explosions were heard. Lava flows traveled down the SW and N flanks. Observers reported lava fountains in the crater and lava flows on the flanks, both of which became more intense at 1800. Explosions produced white-to-light-gray plumes that rose 2 km and drifted W (figure 40).

Figure 40. Emission column seen late in the day on 22 January 2013 associated with the explosive activity at Reventador. Courtesy Walter Garcia Synohidro and Instituto Geofisico.

During the night of 22 January a lava flow descending the SE flank had reached a width of 350 m and extended at least 1.1 km (figure 41). Other smaller lava flows up to 200 m long were observed on the N and S flanks.

Figure 41. Thermal image of Reventador on 22 January 2013 shows the dome from which a lava flow descends to the SE. Courtesy S. Vallejo, Instituto Geofisico (IG-EPN).

During 23 January-7 February 2013 seismicity remained high. Lava flows were visible at night. Crater incandescence was observed at night during 29-30 January.

IG reported that seismicity became more moderate during 8-12 February; explosions were detected daily. Ashfall was reported in areas near the volcano on 9 February. Between 16-20 February, activity remained moderate, with continued ash emissions, but an absence of reported ashfall. For the remainder of February 2013, no reports of surface activity were received, and seismic signals ceased transmission.

According to the Washington VAAC, the IG reported that on 2 March lava flows were observed. IG reported that the seismic network recorded multiple explosions during 13-17 March. Observers reported falling and rolling incandescent material on Reventador's S flanks on 12 March. On 15 and 17 March explosions were detected by the seismic network. IG characterized activity as being at a moderate level for most of the remainder of March.

IG noted that moderate activity continued into April 2013 (table 6). Through 12 April seismicity remained moderate. On 15 April IG reported an increase in the number of seismic events. Seismic and surface activity remained moderate to high through 24 April, but became more moderate thereafter and remained so for the remainder of April 2013.

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-Escuela Politécnica Nacional (IG), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); and Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

During 2005-2012, Nevado del Tolima was non-eruptive and the Alert Level remained at IV (Green; "volcanically active with stable behavior") due to minimal seismicity and deformation. The Servicio Geológico Colombiano (SGC) monitored Tolima with a seismic network, tilt measurements, and regular field observations. The greatest changes at Tolima during this time period were related to the summit glacier that generated significant seismicity and surface activity. Volcano-tectonic (VT) and long-period (LP) earthquakes were also detected with the monitoring network, although these events were frequently too small to locate.

In this report, we also highlight geological hazards investigations by Thouret and others (1995); among the hazards, runout distances for lahars were determined as well as potential ash distribution areas. Further, we include the results of long-term studies focused on the summit glacier (figure 2); investigators noted significant retreat based on aerial photos and later, with Landsat image analysis.

Figure 2. A) A view toward the S flank of the glacier-clad summit of Tolima taken on 18 February 2010. Fresh snowfall highlights the morphology that includes lava flows and debris fans. B) A view of the N flank taken on 22 January 2010. The extent of the glacier appears in bright contrast to the yellow-gray and red colors of the altered summit rock. Courtesy of SGC.

Seismicity during March 2006 - December 2012. Based on volcano-tectonic (VT) and long-period (LP) earthquake counts, the SGC reported that low-level seismicity persisted during this reporting period (table 1). The occurrence of earthquakes was highest during 2006 when 22-90 VT and 5-20 LP events per month were recorded. From 2007 through 2012, VT and LP events occurred at a lower rate (0-73 VT per month and 0-17 LP per month).

Table 1. Monthly seismicity at Nevado del Tolima was tabulated by the occurrence of events: volcano-tectonic (VT), long-period (LP), Glacier & Rockfall, Unclassified, and Largest Earthquake magnitude. Events considered "Unclassified" are attributed to icequakes or rockfalls that do not fulfill the amplitude or duration parameters in order to be included in the SGC database. Note that these values have been corrected by the SGC database and differ from "Technical Bulletin" reports. Courtesy of SGC.

Seismic signals attributed to glacial changes ("icequakes") and rockfalls dominated the records during 2006-2012. Frequently, more than 1,000 events were recorded per month. During 2008-2010, such events were slightly less frequent; an average of 313 earthquakes occurred per month. Coincidentally, LP events were significantly less frequent during that time period as well (less than one event per month). From March 2006 to July 2007, rockfall signals were attributed to surface activity mainly occurring on the N flank and related to small avalanches of ice and rock. The SGC noted that the general summit area was the source of shallow seismicity from mid 2010 through 2012.

Because of sparse activity and low-magnitude events, hypocentral depths of VT earthquakes were rarely calculated during 2006-2012 (table 2). Five earthquakes were located in September 2012, the most to be located in a single month. Three of these earthquakes were located > 5 km of the summit (NW and SE), while 2 were within 1 km (figure 3). That month, seismicity was relatively high compared with previous months; the SGC reported 27 VT earthquakes and 1,077 "Glacier & Rockfall" signals.

Table 2. The number of located VT earthquakes from Tolima during 2011-2012. Located earthquake information was not available for 2006-2010. Courtesy of SGC.

Figure 3. This map shows five located VT earthquakes in the region of Tolima during September 2012. Red and yellow circles indicate hypocenters and epicenters (colors relate to depths; circle size relates to event magnitude); black squares mark the locations of two seismic stations (ESME and NIDO); the summits of Nevado del Tolima and Nevado del Quindío (~10 km NW) are labeled and marked with green stars; approximate locations of towns are indicated by blue text. Courtesy of SGC.

Surface deformation monitoring. An electronic tilt station was installed in 2011 and, by May 2011, data from the Esmeralda station (~2 km W) was being relayed to the SGC Manizales observatory (figure 4). Through the rest of 2011 and 2012, tilt data suggested the effects of local temperatures and fluctuations were within the expected range of the instrument. Changes of 70-95 and 75-100 μrad from the N and E components, respectively, were recorded on a monthly basis. During August-December 2012, fluctuations in tilt were associated with changes in the summit glacier's mass as well as variability due to local temperature changes.

Figure 4. Tilt data from Nevado del Tolima was recorded from the Esmeralda (ESME) station during May 2011 through December 2012. Primary fluctuations in this data were caused by local temperature variations and changes in glacial mass; a data gap occurred during August-October 2012 due to network problems. Courtesy of SGC.

Hazard assessment. Geologic mapping and a hazards analysis were conducted by Thouret and others (1995) (figure 5). They emphasized that they relied on the same appraisal methods as applied by Parra and others (1986) for Nevado del Ruiz. Three scenarios were developed based on three known events of different magnitudes (VEI 3, VEI 3-4, and VEI 4-5); the two plots within the lower left-hand inset map of figure 6 show the major characteristics of those scenarios.

Figure 5. Stratigraphic, volcanic, and geomorphic map of Nevado del Tolima. Town locations are marked with yellow circles. Abbreviations of labeled faults within the blue-outlined inset map refer to the following: P.F.=Palestina Fault; O.-T.-F.=Otun-Pereira Fault; T.F.=Toche Fault; R.-T.F.=Recio-Tolima Fault. Modified from Thouret and others, 1995.

Figure 6. This hazard map for Nevado del Tolima also includes Cerro Machín (located ~20 km SSW). Based on the work by Thourest and others (1995), the small circles drawn around Nevado del Tolima and Cerro Machín encompass areas likely to be affected by subplinian ballistic ejecta, whereas larger circles encompass areas likely to be seriously affected by plinian tephra-fall. Modified from Thouret and others, 1995.

Parameters for possible pyroclastic surges and ash-cloud surges were assessed for major valleys in the region, particularly Río Combeima, Río Totare and Río San Romualdo valleys, and the headwaters of Río Toche valleys (figure 6).

Rock or debris avalanches and lahars were also considered in the study; the authors stated that such events could be triggered by an earthquake or intrusion, and mobilized material had the likelihood of channelization within the deep Río Combeima gorge, a dangerous scenario due to the connectivity of the drainages that influence areas as distant as Ibague and Río Coello. Recent debris-flow deposits from volcanic and glacial sources dominated the aerial extent of the mapped region, particularly along the N slopes and within channels.

Thouret and others (1995) determined that lava flows would be the least hazardous phenomenon likely to occur; "extrusive activity [at Tolima] has been short-lived and is likely to produce block-lava flows such as those of young-Tolima age. Highly viscous and slow-moving block-lava flows could reach only 5-6 km when channeled, and likely move to the southeast or south. However, the very steep south flank would enable lava flows to travel more than 6 km if the chemical composition, physical properties, and hence viscosity of erupted magma changed."

Tolima glacial retreat. While hazards due to glacial ice interactions and volcanism were noted by some investigators (Thouret and others, 1995), other investigations of glaciers were conducted in this region due to interests in global climate change. An assessment conducted in 1976 concluded that five snowcapped volcanoes were present within the Parque Nacional de los Nevados: Tolima, Nevado del Ruiz (~25 km N of Tolima), Santa Isabel (~18 km NNW of Tolima), El Cisne (~20 km N of Tolima), and El Quindío (~10 km W of Tolima) (Hoyos-Patiño, 1998). According to Hoyos-Patiño (1998), El Cisne and El Quindío had almost lost their ice caps by 1976, maintaining less than 1 km² of ephemeral snow- and ice-covered areas.

Glaciers and snowfields mapped by Landsat images of Tolima's summit in 1976 calculated a total area of 3.8 km²; aerial photo analysis from 1978 determined that 11 glaciers were present with a total area of 2.22 km². Based on 2001 Landsat 7 image analysis by Morris and others (2006), the area of glacial extent was 1.26 km²; they calculated a loss of 43% from 1959 to 2001 (figure 7). For comparison, the largest ice loss from this region of Colombia occurred at Nevado del Ruiz, where ice coverage decreased from 21.4 km² to 10.92 km² during 1959-2001.

Figure 7. Glacier and generalized drainages of Tolima as drawn from 1959 aerial photography. Area 1 represents the total icecap area of 7 km2 as determined in 1959. Area 2 was thin ice that deglaciated between 1959 and 1987. Area 3 was glaciated during the Little Ice Age. Area 4 was Holocene and uppermost Pleistocene tephra incised by snowmelt-fed, narrow, deep gullies. Area 5 represents the prehistorical scar, mounds, and deposits resulting from a rockslide-debris avalanche off the NE flank. Area 6 includes young and deeply carved deposits from debris flows and tephra-laden ice-and-snow avalanches near the crater and on the SW flank. Area 7 includes high, steep, eroded intrusions, necks, and lava flows, from the pre-existing summit. From Thouret and others, 1995.

References. Hoyos-Patiño, F., 1998: Glaciers of Colombia, p. I:11-30, in R. S. Williams and J. G. Ferrigno, eds: Satellite Image Atlas of Glaciers of the World: South America, U.S. Geological Survey Prof. Paper 1386-1, 1206 pp.

Morris, J.N., Poole, A.J., and Klein, A.G., 2006, Retreat of Tropical Glaciers in Colombia and Venezuela from 1984 to 2004 as Measured from ASTER and Landsat Images, 63rd Eastern Snow Conference, Newark, Delaware.

Thouret, J.C., Cantagrel, J-M., Robin, C., Murcia, A., Salinas, R., and Cepeda, H., 1995, Quaternary eruptive history and hazard-zone model at Nevado del Tolima and Cerro Machín volcanoes, Colombia. Journal of Volcanology Geothermal Research, 66 (1-4):397-426.

Geologic Background. The steep-sided, glacier-clad Nevado del Tolima volcano contrasts with the broad profile of Nevado del Ruiz to the north. The andesitic-dacitic younger Tolima formed during the past 40,000 years, rising above and largely obscuring a 3-km-wide late-Pleistocene caldera. The summit consists of a cluster of late-Pleistocene to Holocene lava domes that were associated with thick block-lava flows on the N and E flanks, and extensive pyroclastic-flow deposits. The summit contains a funnel-shaped crater 200-300 m deep. Holocene activity has included explosive eruptions ranging in size from moderate to plinian. The last major eruption took place about 3600 years ago. Lava dome growth has produced block-and-ash flows that traveled primarily to the NE and SE. Minor explosive eruptions have been recorded in the 19th and 20th centuries.

Information Contacts: María Luisa Monsalve, Gloria Patricia Cortés, and Lina Constanza García, Servicio Geológico Colombiano (SGC), Volcanological and Seismological Observatory, Avenida 12 Octubre 15-47, Manizales, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).