Volcanism at Sheveluch has been ongoing for the past 20 years. Previous activity consisted of pyroclastic flows, explosions, moderate gas-and-steam emissions, and lava dome growth, according to the Kamchatka Volcanic Eruptions Response Team (KVERT). Between May 2018 and mid-December 2018 activity levels were low, with intermittent low-power thermal anomalies and gas-and-steam emissions. Activity increased in the second half of December 2018, remaining high through at least April 2019.

Activity intensified beginning in late December through April 2019, which included increased and more frequent thermal anomalies, according to KVERT and the MIROVA system (figure 50). On 30 December 2018, video data from KVERT showed explosions producing an ash cloud that rose up to 11 km altitude and drifted 244 km WSW and 35 km NE. Eruptive activity included incandescent lava flows and hot avalanches. The ash cloud that drifted WSW resulted in ashfall over Klyuchi Village (50 km SW) and Kozyrevsk (100 km SW).

Figure 50. Thermal anomalies at Sheveluch increased in late December 2018, as seen on this MIROVA Log Radiative Power graph for the year ending 5 April 2019. The elevated thermal activity continued through March 2019. Courtesy of MIROVA.

Beginning in early January and going through April 2019, the lava dome at the northern part of the volcano continued to grow, extruding incandescent, viscous lava blocks (figure 51). Throughout these months, KVERT reported that satellite imagery and video data showed strong fumarolic activity, as well as strong gas-and-steam plumes containing some amount of ash; gas-and-steam plumes rose as high as 7 km. According to the KVERT Daily Reports on 3 and 4 January 2019, a gas-and-steam plume containing ash drifted NE up to about 600 and 400 km, respectively. Gas-and-steam plumes noted in the KVERT Daily Report, Weekly Releases, and Volcano Observatory Notice for Aviation (VONA), drifted 50-263 km in different directions. On 9 November 2018, the KVERT Daily Report recorded an ash plume drifting 461 km E from the volcano and on 26 December 2018, the KVERT Weekly Information Release recorded an ash cloud drifting 300 km NW. The KVERT Weekly Information Release reported that on 10 April 2019 an ash cloud drifted up to 1,300 km SE.

Figure 51. Incandescent avalanches from the lava dome and an ash plume can be seen in this photo of Sheveluch on 22 February 2019. Photo by Yu. Demyanchuk; courtesy of the Institute of Volcanology and Seismology FEB RAS, KVERT.

Thermal anomalies based on MODIS satellite instruments analyzed using the MODVOLC algorithm were frequent beginning on 28 December 2018. In just three days in late December (28-31 December 2018) there were 34 thermal alerts. Hotspots were detected 21-27 days each month between January-April 2019. A majority of these hotspot pixels occurred within the summit crater.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

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

Steep-sloped and symmetrical Mayon has recorded historical eruptions back to 1616 that range from Strombolian fountaining to basaltic and andesitic flows, as well as large ash plumes, and devastating pyroclastic flows and lahars. A phreatic explosion with an ash plume in mid-January 2018 began the latest eruptive episode which included the growth of a lava dome with pyroclastic flows down the flanks and lava fountaining (BGVN 43:04). Activity tapered off during March; occasional ash emissions continued through August 2018. Minor ash emissions and summit incandescence were intermittent from October 2018-April 2019, the period covered in this report. Information is provided primarily by the Philippine Institute of Volcanology and Seismology (PHIVOLCS).

Pyroclastic density currents were reported in early November 2018; ash plumes were produced from phreatic events a few times during both November and December 2018. Emissions produced SO₂ anomalies during January-March 2019; a series of events in early March generated several small ash plumes. Satellite images showing a thermal anomaly at the summit were recorded multiple times each month from October 2018-April 2019 (figure 44).

Figure 44. Small but distinct persistent thermal anomalies were recorded in satellite imagery from the summit of Mayon during October 2018-April 2019. Top left: 12 October 2018. Top right: 26 November 2018. Middle left: 11 December 2018. Middle right: 30 January 2019. Bottom left: 14 February 2019. Bottom right: 25 April 2019. All images are using the "Atmospheric penetration" filter (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Very little activity was reported at Mayon during October 2018. Steam plumes rose daily from 250-750 m above the summit before drifting with the prevailing winds and dissipating. Incandescence was observed at the summit most nights during the month, and seismicity remained low with only a few earthquakes reported. Leveling data obtained during 30 August-3 September indicated significant short-term deflation of the volcano relative to 17-24 July 2018. New leveling data obtained on 22-31 October indicated inflation of the SE quadrant and short-term deflation on the N flank relative to the 30 August-3 September data. The volcano remained inflated compared with 2010 baseline data. Electronic tilt data showed pronounced inflation of the mid-slopes beginning 25 June 2018.

Activity increased during November 2018. In addition to steam plumes rising to 750 m and an incandescent glow at the summit most nights, pyroclastic density currents and ash plumes were reported. The seismic monitoring network recorded pyroclastic density currents on 5 and 6 November. On 8 November around noontime, a small, short-lived brownish ash plume, associated with degassing, drifted WSW from the summit. A seismic event on the morning of 11 November was associated with a short-lived fountaining event that produced a brownish-gray ash plume that drifted SW. Another similar plume was reported on the morning of 12 November, also drifting SW before dissipating. Two phreatic events were observed on the morning of 26 November. They produced grayish to grayish-white ash plumes that rose 300-500 m above the summit before drifting SW. The following morning, another event produced a grayish ash plume 500 m above the summit that drifted SW. On 30 November a 1-minute-long ash emission event produced a grayish white plume that also drifted SW.

Steam plume emissions and incandescence at night continued at Mayon during December 2018. The seismic network recorded a four-minute-long event shortly after noon on 9 December that produced a grayish-brown ash plume which drifted W. Precise leveling data obtained on 8-13 December 2018 indicated a slight inflation of the volcano relative to 22-31 October 2018. A 30-second-long ash emission event in the afternoon on 18 December produced a brownish ash plume. Two phreatic events were observed on the morning of 27 December. They produced grayish to grayish-white ash plumes that rose 600 and 200 m above the summit, before drifting SW (figure 45).

Figure 45. Ash plumes rose a few hundred m from the summit of Mayon on 27 December 2018. Courtesy of Twitter users "k i t" (left) and "georgianne" (right).

Very little surface activity except for white steam-laden plumes that crept downslope and drifted NW or SW was noted during January 2019. Incandescence at the summit, visible with the naked eye, became more frequent during February 2019, along with continued steam plumes. Precise leveling data obtained on 25 January-3 February 2019 indicated a slight deflation relative to 8-13 December 2018. However, continuous GPS and electronic tilt data showed inflation of the mid-slopes since June 2018. Small SO₂ plumes were detected by the TROPOMI satellite instrument a few times during January-March 2019 (figure 46).

Figure 46. Emissions of SO2 that exceeded 2 DU (Dobson Units) occurred a few times at Mayon during January-March 2019. Top left: 25 January. Top right: 16 February. Lower left: 4 March. Lower right: 15 March. Courtesy of NASA Goddard Space Flight Center.

Steam plumes rose 250-500 m above the summit and drifted generally W in early March 2019; incandescence continued daily at the summit. Phreatic events occurred on 7 and 8 March, producing ash plumes that rose 500 and 300 m from the summit before drifting SW (figure 47). Three more phreatic events occurred on the afternoon of 12 March; they produced light brown to grayish ash plumes that rose 500, 1,000, and 500 m, respectively, and drifted SW. Six phreatic events occurred throughout the day on 13 March, producing ash plumes that rose 200-700 m above the summit and drifted W. A single explosion the next day produced a 500-m-tall ash plume. The Tokyo VAAC reported an ash plume visible for several hours in satellite imagery drifting W at 3.7 km altitude on 13 March (UTC). An increase in the daily number of rockfall events from 1-2 per day to 5-10 per day was noted during the second half of March. Precise leveling data obtained on 20-26 March 2019 indicated a slight inflation relative to 25 January-3 February 2019.

Figure 47. A small ash emission at Mayon was reported by PHIVOLCS on 8 March 3019; the plume rose 300 m from the summit and drifted SW. Courtesy of PHOVOLCS.

Steam plumes drifted SW or NW throughout April, rising 200-400 m from the summit. Incandescence could be observed at night for the first half of the month. Leveling data obtained during 9-17 April 2019 indicated a slight inflation relative to 20-26 March 2019. Seismicity remained low during the month with only occasional volcanic earthquakes and rockfall events. Lenticular clouds around the summit were observed (figure 48), but these are an unusual meteorological occurrence caused by weather conditions not related to volcanic activity.

Figure 48. A double lenticular cloud surrounded the summit of Mayon early in the morning on 23 April 2019 and was captured by a local observer; it was not related to volcanic activity. Courtesy of Twitter user Ivan.

Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

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/); 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/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Twitter user "Ivan", Naga City, Philippines (URL: https://twitter.com/ivanxlcsn); Twitter user "k i t", Legazpi City, Philippines (URL: https://twitter.com/jddmgc); Twitter user "georgianne", Costa Leona, Philippines (URL: https://twitter.com/xolovesgia_).

Remote Tinakula lies 100 km NE of the Solomon Trench at the N end of the Santa Cruz Islands, which are part of the country of the Solomon Islands located 400 km to the W. It has been uninhabited since an eruption with lava flows and ash explosions in 1971 when the small population was evacuated (CSLP 87-71). The nearest communities live on Te Motu (Trevanion) Island (about 30 km S), Nupani (40 km N), and the Reef Islands (60 km E); residents occasionally report noises from explosions at Tinakula. Ashfall from larger explosions has historically reached these islands. The most recent eruptive episode was a large ash explosion and substantial SO₂ plume during 21-26 October 2017; satellite imagery suggested that a flow of some type traveled down the scarp on the W flank. Renewed thermal activity that was recognized in satellite imagery beginning in December 2018 continued intermittently through June 2019 and is covered in this report. Satellite imagery and thermal data are the primary sources of information for this volcano. It is occasionally visited by members of the National Disaster Management Office (NDMO) of the Solomon Islands Government, tourists, and research vessels who are able to capture ground-based information.

Satellite images from December 2018 to February 2019 show thermal anomalies at the summit vent. Excellent ship-based photographs of the island on 24-25 January 2019 provided by a crewmember from the R/V Petrel identify numerous volcanic features and show a steam-and-gas plume at the vent. Satellite images from April and May 2019 show thermal anomalies at both the summit vent and along the W flank scarp suggesting flow activity during that time.

A stream of incandescence on the NW flank of Tinakula in a Sentinel 2 satellite image on 24 October 2017 confirmed that some type of high-temperature flow accompanied the explosions and eruptive activity of 21-25 October 2017 (BGVN 43:02). Satellite imagery during most of 2018 recorded steam plumes drifting in several directions from the summit, but no thermal activity (figure 24). There was no further evidence of activity in satellite visible or thermal data until almost exactly one year later when the MIROVA project recorded two thermal alerts in the third week of October 2018 (figure 25). Satellite images from that week were cloudy and did not confirm any surface activity.

Figure 24. Sentinel-2 satellite imagery of Tinakula provides valuable information about activity at this remote volcano in the South Pacific. A large explosion with ash plumes and flows occurred during 21-26 October 2017. Top left: a strong E-W linear thermal anomaly suggesting a flow event from the summit was evident on the NW flank on 24 October 2017. Top right: a small steam plume rose from the summit vent on a cloudless 11 February 2018. Bottom left: a dense steam plume drifted SE from the summit vent on 4 September 2018. Bottom right: clouds and dense steam obscure the summit on 24 October 2018, about the same time that MIROVA reported a thermal anomaly. Top left image uses bands 12, 11, 8A, others use 12, 4, 2. Courtesy of Sentinel Hub Playground.

Figure 25. The MIROVA project recorded the first thermal anomaly in a year from Tinakula during the third week of October 2018. Courtesy of MIROVA.

The first satellite imagery confirming renewed thermal activity appeared on 8 December 2018, around the same time as a small MIROVA anomaly. After that, several images during January and February 2019 confirmed moderately strong thermal activity at the summit (figure 26). Whether the anomalies were the result of active lava effusion or strong incandescent gases from the summit vent is uncertain.

Figure 26. Thermal anomalies at the summit vent of Tinakula were recorded six times between early December 2018 and early February 2019 with Sentinel-2 satellite images. Top row: 8 December 2018 and 2 January 2019. Middle row: 12 (anomaly is just below date) and 27 January 2019. Bottom row: 1 and 6 February 2019. All images are bands 12, 4, 2. Courtesy of Sentinel Hub Playground.

Visual confirmation of activity at Tinakula is rare, but the research vessel R/V Petrel sailed past the volcano on 24 and 25 January 2019 and a crewmember provided detailed images of the W flank and vent area. The summit vent is located at the top of a W facing scarp, and steam is frequently observed rising from the vent (figures 27). Recent flows and volcaniclastic deposits were visible in the ravine on the W flank (figures 28 and 29). Fresh-looking lava was also visible near the summit vent on top of older deposits (figure 30). Eroded volcaniclastic deposits near the base of the scarp on the W flank were visible on top of older veined and layered volcanic rocks (figure 31). Crewmembers on the vessel R/V Petrel could clearly see an incandescent glow from the summit crater at night (figure 32).

Figure 27. A view from the SW of the W flank of Tinakula on 24-25 January 2019. The summit vent is at the top of a W facing scarp, the steam plume drifted E. Used with permission from Paul G Allen's Vulcan Inc.

Figure 28. The W flank of Tinakula as seen from the W on 24-25 January 2019. The steam plume drifted E. Recent flows and volcaniclastic deposits appeared dark in the steep ravine on the W face (left side). Used with permission from Paul G Allen's Vulcan Inc.

Figure 29. Steam and gas rose from the summit vent at Tinakula on 24-25 January 2019. Recent lava deposits are visible in front of the plume and in the ravine on the left (the W flank). Used with permission from Paul G Allen's Vulcan Inc.

Figure 30. The edge of the summit vent of Tinakula on 24-25 January 2019 had recent lava on older deposits; steam and gas is rising from the vent in the background. Used with permission from Paul G Allen's Vulcan Inc.

Figure 31. The W flank of Tinakula on 24-25 January 2019. Eroded volcaniclastic deposits overlie older veined and layered volcanic rocks. Used with permission from Paul G Allen's Vulcan Inc.

Figure 32. Incandescence was clearly visible from the summit vent at Tinakula on 24-25 January 2019. Used with permission from Paul G Allen's Vulcan Inc.

During April and May 2019, both the MIROVA project and MODVOLC measured a number of thermal anomalies (figure 33) using MODIS satellite data. MODVOLC alerts were issued on 4 and 20 April, and 11, 18, and 27 May. Sentinel-2 satellite images during the period confirmed that a flow on the W flank was a likely source of the thermal energy in addition to the summit vent (figure 34). Thermal anomalies appeared again at the end of June in MIROVA data, but no satellite images showed anomalies at that time.

Figure 33. The number and intensity of MIROVA thermal anomalies increased at Tinakula during April and May 2019. After a short pause, they returned at the end of June. Courtesy of MIROVA.

Figure 34. Sentinel-2 satellite images captured thermal anomalies at the summit and on the W flank of Tinakula during April and May 2019 suggesting the presence of an incandescent flow down the W scarp. Top row: 7 and 22 April 2019 (bands 12, 8, 4). Bottom row: 27 April and 12 May 2019 (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

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

Information Contacts: 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); Vulcan Inc. (URL: https://www.vulcan.com/), additional details about the R/V Petrel (URL: https://www.paulallen.com/).

Short pulses of intermittent eruptive activity have characterized Piton de la Fournaise, the large basaltic shield volcano on La Réunion Island in the western Indian Ocean, for several thousand years. For the last 20 years, frequent effusive basaltic eruptions have occurred on average twice per year. The activity is characterized by lava fountains and lava flows, and occasional explosive eruptions that shower blocks over the summit area and produce ash plumes. Almost all of the recent activity has occurred within the Enclos Fouqué caldera, although past eruptions in 1977, 1986, and 1998 have occurred at vents outside of the caldera. Four separate eruptive episodes were reported during 2018; from 3-4 April, 27 April-1 June, 13 July, and 15 September-1 November (BGVN 43:12, 43:09). Two episodes from 2019 during February-March and June are covered in this report, with information provided primarily by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) as well as satellite instruments.

Piton de la Fournaise experienced two eruptions during November 2018-June 2019. The first lasted from 18 February to 10 March 2019, and the second episode was 11-13 June. The episode in February-March started consisted of multiple fissures opening on the E flank of the Dolomieu crater on 18 February with lava flows that traveled several hundred meters. After a brief pause, one new fissure opened nearby on 19 February and produced up to 3 million m³ of lava in a little over four days. Although the flow rate then declined, the eruption continued until 10 March. During the last three days, 7-10 March, two new fissures opened nearby and produced large volumes of lava, bringing the total eruptive volume to about 14.5 million m³. After little activity during April and May, a small eruption occurred on the SSE outer slope of Dolomieu crater that lasted for about 48 hours on 11-13 June; multiple small flows traveled about 1,000 m down the steep flank before ceasing. The MIROVA thermal anomaly graph of log radiative power clearly showed the abruptness of the beginning and ends of the last three eruptive episodes at Piton de la Fournaise from August 2018 through June 2019 (figure 165).

Figure 165. The MIROVA graph of thermal energy from Piton de la Fournaise from 30 July 2018 through June 2019 shows the last three eruptive episodes at the volcano. From 15 September through 1 November 2018 fissures and flows were active on the SW flank of Dolomieu crater near Rivals crater (BGVN 43:12). Fissures opened on the E flank of the crater on 18 February 2019, and after a brief pause resumed on 19 February at the foot of Piton Madoré. Lava flows remained active until 10 March 2019. A short episode of lava effusion occurred on 11-12 June 2019 on the SSE outer slope of Dolomieu crater. Courtesy of MIROVA.

Activity during November 2018-March 2019. Following the end of the 15 September-1 November 2018 eruption, seismic activity immediately below the summit remained low (with only 20 shallow and two deep earthquakes during November). The inflationary signal recorded since the beginning of September stopped, and the OVPF deformation networks did not record any significant deformation. There were 35 shallow earthquakes (0-2 km depth) below the summit crater during December, and one deep earthquake. Only 12 shallow earthquakes and one deep earthquake (greater than 2 km below the surface) were reported in January.

OVPF reported an increase in CO₂ concentrations beginning in December 2018, and noted the beginning of inflation on 13 February 2019. A seismic swarm of 379 earthquakes accompanied by minor but rapid deformation (less than 1 cm) was reported on 16 February 2019. A new seismic swarm of 208 earthquakes began early on 18 February with a much larger ground deformation (10 cm of elongation of the summit zone). A volcanic tremor indicative of the arrival of magma near the surface began at 0948 that morning. Webcams indicated that eruptive fissures had opened in the NE part of the Enclos Fouqué caldera. The onset of the eruption was marked by a sudden drop in CO₂ flux which then stabilized. The eruptive sites were confirmed visually around 1130. Three fissures with actively flowing lava opened on the E flank of Dolomieu Crater; the fountains of lava were less than 30 m high. The front of the longest flow had reached 1,900 m elevation after one hour. The eruption lasted a little over 12 hours and was over by 2200 that evening; it covered about 150-200 m of the hiking trail to the summit.

Seismicity remained high after the event ended, and at 1500 on 19 February 2019 another seismic swarm of 511 deep earthquakes located under the E flank at about 2.5 km depth occurred. It was not accompanied by a significant amount of deformation. At 1710 tremor signals appeared on the observatory seismographs and the first gas plumes and lava ejection were observed at 1750 and 1912, respectively. During an overflight the next day (20 February), OVPF team members observed the new eruptive site at an elevation of 1,800 m at the foot of Piton Madoré. One fissure and one fountain were active at 0620 on 20 February and the flow front was at 1,300 m elevation (figure 166). During the night of 20-21 February the flow front crossed over the "Grandes Pentes" area in the eastern half of the Enclos Fouque (figure 167).

Figure 166. The eruption which began on 19 February 2019 on the E flank of Dolomieu crater at Piton de la Fournaise produced a lava fountain and flow which traveled down at least 500 m of elevation by the next morning when this photo was taken at 0620 local time. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du mercredi 20 février 2019 à 11h00, Heure locale).

Figure 167. The active fissure at Piton de la Fournaise was producing lava fountains and an active flow during the evening of 20 February 2019. Overnight the flow crossed over the "Grandes Pentes" area of the caldera. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du jeudi 21 février 2019 à 14H00, Heure locale).

OVPF reported on 22 February 2019 that 22 shallow earthquakes had been reported since the eruption began on 19 February. Surface flow rates estimated from satellite data, via the HOTVOLC system (OPGC - University of Auvergne), were between 2.5 and 15 m³/s. The quantity of lava emitted between 19 and 22 February was between 1 and 3 million m³. OVPF observed the growth of an eruptive cone that was filled with a small lava lake producing ejecta during a morning overflight on 22 February. A channelized flow moved downstream from the cone and split into two lobes about 1 km from (and 200 m below) the cone (figure 168). The split in the flow occurred near the Guyanin crater. The N flowing lobe, about 50 m wide, had an actively flowing front located at 1,320 m elevation; the incandescent flow was travelling over a recent flow (likely from the previous night). The S-flowing lobe spread to 200 m wide and split into two tongues 300 m SE of Guyanin crater.

Figure 168. During an overflight on the morning of 22 February 2019 scientists from OVPF observed a growing spatter cone with a small lava lake at Piton de la Fournaise. A channelized flow moved downstream from the fissure and split into two flows. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 22 février 2019 à 13h30, Heure locale).

Incandescent ejecta from the cone was captured in a webcam image overnight on 22-23 February 2019 (figure 169). The rate of advance of the flow slowed significantly by 24 February, but the intensity of the eruptive tremor remained relatively constant. Mapping of the lava flow on 28 February carried out by the OI2 platform (OPGC - University Clermont Auvergne) from satellite data confirmed the slow progress of the flow after 24 February (300 m in 5 days) (figure 170). The flow front was located at 1,200 m elevation, and only the N arm was active; the lava had traveled about 2.2 km from the vent by 28 February.

Figure 169. Incandescent ejecta from the eruptive cone at Piton de la Fournaise was captured in the webcam in the early hours of 23 February 2019. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du samedi 23 février 2019 à 13h30, Heure locale).

Figure 170. Contours of the lava flows at Piton de la Fournaise from 18-28 February 2019 were determined from satellite data by the OI2 platform (Université Clermont Auvergne), dated 18 (red) and 19 (blue) February (top image); 20 (green), 21 (red), 22 (blue), 27 (turquoise), and 28 (pink) February (bottom image). Courtesy of and copyright by OVPF/IPGP. Top: Bulletin d'activité du vendredi 22 février 2019 à 13h30 (Heure locale); bottom: Bulletin d'activité du jeudi 28 février 2019 à 16h30 (Heure locale).

Between 28 February and 1 March 2019 a third lobe of lava appeared flowing NE from the vent on the N side of the new flow area; it split into two lobes sometime on 1 March. Very little new lava was recorded on the other lobes. By 4 March the flow rate estimated by satellite data was about 7.5 m³/s. During a site visit on the morning of 5 March OVPF scientists sampled the N lobe of the flow and bombs and tephra near the cone, and acquired infrared and visible images. They noted the continued growth of the cone which still had an open vent at the summit and a base 100 m in diameter. It was 25 m high with a 50-m-wide eruptive vent at the top (figure 171). High-temperature gas emissions and strong Strombolian activity issued from the vent. Steam emissions were present around the base of the cone, suggesting the presence of lava tunnels. A single lobe of lava flowed N from the cone.

Figure 171. The eruptive cone at Piton de la Fournaise on 5 March 2019 had a 100-m-diameter base, 25 m of vertical height, and 50-m-wide vent at the summit. Courtesy of and copyright by OVPF/IPGP, (Bulletin d'activité du mardi 5 mars 2019 à 17h30, Heure locale).

A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré was first observed on the morning of 6 March (figure 172); OVPF concluded that it had opened late on 5 March. A small cone was forming and a new flow traveled N from the main eruptive site. At least six new emission points were noted the following morning (7 March) around the Piton Madoré. Poor weather prevented confirmation by aerial reconnaissance that day, but in a site visit on 8 March OVPF scientists determined that the new fissure from 5 March remained active; a small cone about 10 m high had two flow lobes on the W and N sides (figure 173). A fissure that opened on 7 March was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March with two 50-m-high lava fountains (figure 174). Samples collected by OVPF indicated that the vents of 5 and 7 March produced lava of different compositions.

Figure 172. A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré at Piton de la Fournaise was first observed on the morning of 6 March 2019; OVPF concluded that it had opened late on 5 March. A small cone was forming on the flank of an old one and a new flow traveled N from the main eruptive site. Courtesy of OVPF/IPGP, copyright by Helicopter Coral (Bulletin d'activité du jeudi 7 mars 2019 à 15h00 Heure locale).

Figure 173. The 5 March 2019 fissure at Piton de la Fournaise on the NW flank of Piton Madoré still had two active flow lobes emerging from it and heading N and W on 8 March 2019. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

Figure 174. A fissure that opened on 7 March 2019 at Piton de la Fournaise was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March 2019 with two 50-m-high lava fountains. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

There was a strong increase in the eruptive tremor intensity on 7 March, related to the opening of the two new fissures on 5 and 7 March (figure 175). As a result, the surface flow estimates made from satellite data increased significantly to high values greater than 50 m³/s, with the average values on 7-8 March of around 20-25 m³/s. The increased flow rates resulted in the flows traveling much greater distances. By the morning of 9 March the active flow had reached 650-700 m above sea level. The flow front had traveled about 1 km in 24 hours. Strong seismicity had been increasing under the summit zone for the previous 48 hours. After a phase of very strong surface activity observed overnight on 9-10 March that included lava fountains 50-100 m high (figure 176), surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. OVPF noted that sudden increases in seismicity and flow rates near the end of an eruption have occurred at about half of the eruptions at Piton de la Fournaise in recent years. Lava volumes emitted on the surface between 18 February and 10 March 2019 were estimated at about 14.5 million m³ (figure 177).

Figure 175. An infrared view of the eruptive site on the E flank of Dolomieu crater at Piton de la Fournaise on 8 March 2019 clearly showed the original fissure from 19 February (bottom right of center), the fissure on Piton Madore that opened on 5 March (right) and the fissures that opened on 7 March (upper, right of center). The combined activity produced significant thermal and seismic activity at the volcano. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 8 mars 2019 à 17h00, Heure locale).

Figure 176. Lava fountains 50-100 m high were the result of very strong surface activity observed overnight on 9-10 March 2019 at Piton de la Fournaise. Surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. Photo taken on 9 March 2019 around midnight from the RN2. Courtesy of OVPF/IPGP, copyright by A. Finizola LGSR/IPGP (Bulletin d'activité du dimanche 10 mars 2019 à 19h30 Heure locale).

Figure 177. A sudden increase in the flow rate at the end of the 18 February-10 March 2019 eruption at Piton de la Fournaise was recorded by researchers at the Université Clermont Auvergne. OVPF noted this was typical of about half of the eruptions at Piton de la Fournaise. Courtesy of OVPF/IPGP, copyright by HOTVOLC, Université Clermont Auvergne (OVPF Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

Significant SO₂ plumes were captured by the TROPOMI instrument on the Sentinel 5-P satellite throughout the 18 February-10 March eruption (figure 178). After the surface eruption ceased, shallow seismicity continued at a lower rate of about 12 earthquakes per day. The end of the eruption (7-10 March) was accompanied by a marked deflation, interpreted by OVPF as the rapid emptying of the magma reservoir. Following the end of the eruption, inflation resumed for the rest of March but then ceased. Seismicity continued at a lower level during April with an average of six shallow earthquakes per day.

Figure 178. Multiple days of high DU value SO2 plumes were recorded by the TROPOMI instrument on the Sentinel 5-P satellite during the 18 February-10 March 2019 eruption at Piton de la Fournaise. Top row: during 18, 21, and 22 February SO2 plumes drifted SE. Middle row: during 23, 24, and 25 February the wind direction changed from SE through S to SW and left a curling trail of SO2. Bottom row: 5, 7, and 8 March showed an increase in SO2 emissions that corresponded with increased seismicity and lava flow output before the eruption ceased.

Activity during May-June 2019. OVPF reported slight inflation near the summit beginning in early May, and an increase in CO₂ concentration in the soil near Plaine des Cafres and Plaine des Palmistes. Strong shallow seismicity reappeared on 27 May 2019 and recurred on 30 and 31 May. Two small seismic swarms were measured on 31 May in the early morning. A new seismic swarm beginning at 0603 on 11 June accompanied by rapid deformation suggested a new eruption was imminent. A tremor near the summit area was first noted at 0635 local time; the webcams indicated a plume of gas, but poor visibility prevented evidence of fresh lava. Around 0930 that morning OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at elevations ranging from 2480 to 2025 m (figure 179). The flow fronts were not visible due to weather. Lava fountains under 30 m in height and lava flows were present in the three lowest fissures. The flows traveled rapidly down the steep flank of the crater (figure 180).

Figure 179. Around 0930 on the morning of 11 June 2019 OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at Piton de la Fournaise at elevations ranging from 2480 to 2025 m. Courtesy of and copyright by OVPF-IPGP and Imazpress (Bulletin d'activité du mardi 11 juin 2019 à 11h00).

Figure 180. Thermal imaging of the 11-12 June 2019 eruptive site at Piton de la Fournaise showed multiple streams of lava traveling rapidly down the steep flank from several fissures on 11 June 2019. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 11h00).

The intensity of the eruptive tremor decreased throughout the day, and by 1530 only the lowest elevation fissure was still active (figure 181). The next afternoon (12 June) images in the OVPF webcam located in Piton des Cascades indicated the flow front was at about 1,200-1,300 m elevation. Seismographs indicated that the eruption stopped around 1200 on 13 June. Poor weather obscured visibility of the flow activity. Seismic activity decreased following the eruption, but appeared to increase again beginning on 21 June, with 10 events detected on 30 June. SO₂ plumes were recorded in satellite data on 11 and 12 June 2019.

Figure 181. The intensity of the eruptive activity at Piton de la Fournaise on 11 June 2019 decreased throughout the day, and by 1530 only the lowest elevation fissure was still active. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 17h45 Heure locale).

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

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); 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/).

Heard Island, in the Southern Indian Ocean, includes the large Big Ben stratovolcano and the smaller, apparently inactive, Mt. Dixon. Because of the island's remoteness, satellites are the primary monitoring tool. Big Ben has been active intermittently since 1910, and was active during October 2017-September 2018 (BGVN 43:10). Activity continued during October 2018-March 2019.

Satellite photos using Sentinel Hub showed hotspots every month between October 2018 and March 2019. Because the area was frequently covered by a heavy cloud layer, most of the hotspot signals were partially obscured. Though thermal anomalies are usually seen at summit vents, on 18 October 2018 an anomaly was present about 300 m down the E flank. Similarly, on 1 January 2019, a weak anomaly beginning about 200 m down the NW flank was about 300 m long (figure 40).

The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected three hotspots, two in October and one in early November 2018, all of low radiative power. There were no MODVOLC alert pixels during this period.

Figure 40. Sentinel-2 L1C image of Heard Island's Big Ben volcano on 1 January 2019 one summit hotspot and an elongated thermal anomaly to the NW. Scale bar (bottom right) is 200 m. The photo was taken in atmospheric penetration view (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

Geologic Background. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon volcano lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben volcano because of its extensive ice cover. The historically active Mawson Peak forms the island's 2745-m high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported in historical time at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Information Contacts: Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

The ongoing eruption at Semeru has been characterized by numerous ash explosions and thermal anomalies, but activity apparently diminished in 2018 (BGVN 43:01 and 43:09); this decreased activity continued through at least February 2019. The current report summarizes activity from 24 August 2018 to 28 February 2019.

The Indonesian volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), reported ongoing daily seismicity, dominated by explosion earthquakes and emission-related events from late November through February (figure 35). Ash plumes resulting in aviation advisories by the Darwin Volcanic Ash Advisory Centre (VAAC) were reported on 4, 6-7, and 19 September, and 12 October 2018. The next significant ash plume reported by the VAAC wasn't until 24 February 2019 (table 23).

Figure 35. Seismicity recorded at Semeru during 28 November 2018-26 February 2019. Plot shows explosion earthquakes ('Letusan'), emission-related events ('Hembusan'), felt earthquakes ('Gempa Terasa'), local tectonic events ('Tektonic Lokal'), and distant tectonic events ('Tektonic Jauh'). Courtesy of PVMBG and MAGMA Indonesia.

Table 23. Summary of ash plumes at Semeru during 25 August 2018 through February 2019. The summit is at 3,657 m elevation. Data courtesy of Darwin VAAC.

Thermal anomalies using MODIS satellite instruments processed by the MODVOLC algorithm were only recorded on 26, 28, and 30 August 2018, and 22 and 31 October 2018. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected numerous hotspots within 5 km of the volcano during August and early September, with a significant decrease in frequency through October (figure 36); only a few scattered hotspots were recorded from November 2018 through February 2019.

Figure 36. MIROVA plot of thermal anomalies (Log Radiative Power) at Semeru during July 2018-February 2019. Courtesy of MIROVA.

Geologic Background. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

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/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

The eruption at Dukono that began in 1933 has showered the area with ash from frequent explosions (BGVN 43:04, 43:12). The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM), is responsible for monitoring this volcano.

This long-term pattern of intermittent ash explosions continued during October 2018-March 2019, with ash plumes rising to between 1.5 and 2.7 km altitude, or about 300-1,500 m above the summit (table 19). Although meteorological clouds often obscured views, satellite imagery captured typical ash plumes on 28 September 2018 (figure 10) and 5 February 2019 (figure 11). Instruments aboard NASA satellites (TROPOMI and OMPS) detected high levels of sulfur dioxide near or directly above the volcano on multiple days during January-March 2019. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to remain outside of the 2-km exclusion zone.

Table 19. Monthly summary of reported ash plumes from Dukono for October 2018-March 2019. The direction of drift for the ash plume through each month was highly variable. Data courtesy of the Darwin VAAC and PVMBG.

Figure 10. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 28 September 2018 with the plume blowing towards the NE. Courtesy of Sentinel Hub Playground.

Figure 11. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 5 February 2019, with the plume blowing SW. Courtesy of Sentinel Hub Playground.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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).

Intermittent small phreatic explosions from the acid lake of Rincón de la Vieja's active crater has most recently occurred since 2011 (BGVN 42:08, 43:03, and 43:09). This activity continued through at least February 2019. The volcano is monitored by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), and the information below comes from its weekly bulletins between 18 August 2018 and 28 February 2019. Weather conditions often prevented webcam views and estimates of plume heights. The volcano was in Activity Level 3 throughout the reporting period (volcano erupting, steady state).

According to OVSICORI-UNA, two distinct, 2-minute-long explosions occurred on 31 August 2018 beginning at 0434 and 1305. Several hours after the eruption tremor became continuous but low-frequency long-period (LP) earthquakes ceased. OVSICORI-UNA reported a gas emission late on 7 September. An unconfirmed small phreatic explosion occurred on 11 September at 0634, and another on 17 September at 1014. The seismic record showed continuous background tremor and very sporadic LP earthquakes.

Intermittent background tremor was recorded during the first half of October, along with a few emissions and phreatic explosions. Deformation measurements during October showed a contraction between the N and S of the volcano, with subsidence. On 17 October there was another phreatic explosion, and thereafter tremor disappeared and seismicity decreased. On 23 and 27 October seismic stations signaled additional possible phreatic explosions.

OVSICORI-UNA reported that a series of explosions began at 1945 on 4 November and consisted of at least three 2-minute-long episodes. The next day at 1511 a plume of water vapor and diffuse gas, recorded by a webcam and visible to residents to the N, rose about 100 m above the crater rim and drifted W. On 9 November a 2-minute-long explosion began at 1703. Another explosion on 27 November at 0237 produced a plume of water vapor and gas that rose 600 m above the crater rim and drifted SW. A short 1-minute explosion began at 1054 on 3 December.

Based on OVSICORI-UNA weekly bulletins, activity remained stable in January 2019 with small-amplitude phreatic explosions on 11, 12, and 14 January. More energetic phreatomagmatic explosions on 17 and 20 January produced lahars. Several small-amplitude explosions were detected at the end of the month. During January, a few LPs, no VTs, and intermittent tremor were recorded.

OVSICORI-UNA reported that two small-scale explosions occurred on 1 February, along with possible events at 1906 and 1950 on 5 February and at 0120 on 6 February. An event at 0000 on 6 February was also recorded; the report noted that poor weather conditions prevented visual observations of the crater. On 16 and 17 February strong degassing was observed. No LPs were recorded, but two significant VTs were detected on 17 and 22 February near or under the crater.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of 1916-m-high Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A plinian eruption producing the 0.25 km3 Río Blanca tephra about 3500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).

This report summarizes activity at Turrialba during September 2018-February 2019. During this period there was similar activity as described earlier in 2018 (BGVN 43:09), with occasional ash explosions and numerous, sometimes continuous, periods of gas-and-ash emissions (table 8). Data were provided by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA).

Table 8. Ash emissions at Turrialba, September 2018-February 2019. Cloudy weather sometimes obscured observations. Maximum plume height is above the crater rim. Information courtesy of OVSICORI-UNA.

According to OVSICORI-UNA's annual summary for 2018, a slow decline in activity occurred after the volcano reached its highest emission rate during 2016. Activity during 2018 was consistent with an open system, generating frequent passive ash emissions. The volcano emitted ash on 58% of the days during the year. Some explosions were large enough to eject ballistics more than 400 m around the crater. Typical activity can be seen in a photo from 11 September 2018 (figure 50) and satellite imagery on 7 November 2018 (figure 51).

Figure 50. Photo of an ash explosion at Turrialba taken on 11 September 2018. Courtesy of Red Sismologica Nacional (RSN: UCR-ICE), Universidad de Costa Rica.

Figure 51. Sentinel-2 satellite image of an ash emission from Turrialba on 7 November 2018, taken in natural color (gamma adjusted). Courtesy of Sentinel Hub Playground.

During January into early February 2019, passive ash emissions continued irregularly and with less intensity and duration. Emissions sometimes lacked ash. In their report of 4 February 2019, OVSICORI-UNA indicated that passive ash emissions were weak and slow. For the rest of February, they characterized ash emissions as frequent, but of low intensity.

Seismic activity. On 1 November 2018 OVSICORI-UNA reported that seismicity remained high, and involved low-amplitude banded volcanic tremor along with long-period (LP) and volcano-tectonic (VT) earthquakes. In late January-early February 2019, OVSICORI-UNA reported that seismicity remained relatively stable, although a small increase was associated with the hydrothermal system. VT earthquakes were absent, and tremors had decreased in both energy and duration. The number of low-frequency LP volcanic earthquakes remained stable, although they had decreasing amplitudes. No explosions were documented, and emissions were weak and had short durations and very dilute ash content.

Thermal anomalies. No thermal anomalies were recorded during the reporting period using MODIS satellite instruments processed by MODVOLC algorithm. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected five scattered hotspots during September-October 2018, none during November-December 2018, and two during January-February 2019. All were within 2 km of the volcano and of low radiative power.

Gas measurements. Significant sulfur dioxide levels near the volcano were recorded by NASA's satellite-borne ozone instruments only on 29 September 2018 (both NPP/OMPS and Aura/OMI instruments) and on 11 February 2019 (Sentinel 5P/TROPOMI instrument). OVSICORI-UNA's gas measuring instruments were compromised in September 2018 through January 2019 due to vandalism. In early February, however, they detected hydrogen sulfide for the first time since 2016.

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

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Red Sismologica Nacional (RSN) a collaboration between a) the Sección de Sismología, Vulcanología y Exploración Geofísica de la Escuela Centroamericana de Geología de la Universidad de Costa Rica (UCR), and b) the Área de Amenazas y Auscultación Sismológica y Volcánica del Instituto Costarricense de Electricidad (ICE), Costa Rica (URL: https://rsn.ucr.ac.cr/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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://hotspot.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/); Costa Rica Star (URL: https://news.co.cr); The Tico Times (URL: https://ticotimes.net).

San Cristóbal has produced occasional weak explosions since 1999, with intermittent gas-and-ash emissions. The only reported explosion during the first half of 2018 was on 22 April, the first since November 2017 (BGVN 43:03). The current report covers activity between 1 August 2018 and 1 May 2019. The volcano is monitored by the Instituto Nicaragüense de Estudios Territoriales (INETER).

According to INETER, a series of explosions occurred on 9 January 2019 that lasted several hours. INETER stated that one explosion occurred at 1643; the Washington VAAC's first advisory stated that an explosion occurred at 1145 (local time). The weak explosions, which occurred after a period of heightened seismic activity, generated an ash plume that reached 200 m above the edge of the crater and drifted W. The Washington VAAC reported volcanic ash plumes on 10-11 January extending about 92 km SW, and on 24-25 January extending about 185 km WSW. A low-energy explosion was detected by the seismic network at 1550 on 4 March 2019. The event produced a gas-and-ash plume that rose 400 m above the crater rim and drifted SW.

Monitoring data reported by INETER (table 6) showed elevated levels of seismicity during October 2018 through January 2019. Sulfur dioxide was also measured at higher levels in January 2019.

Table 6. Monthly sulfur dioxide measurements and seismicity reported at San Cristóbal during August 2018-March 2019. "Most" indicates that type of seismicity was dominant that month. Data courtesy of INETER.

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

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://webserver2.ineter.gob.ni/vol/dep-vol.html); 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).

The remote Semisopochnoi comprises the uninhabited volcanic island of the same name, ~20 km in diameter, in the Rat Islands group of the western Aleutians (figure 1). Plumes had been reported several times in the 18th and 19th centuries, and most recently observed in April 1987 from Sugarloaf Peak (SEAN 12:04). The volcano is dominated by an 8-km diameter caldera that contains a small lake (Fenner Lake) and a number of post-caldera cones and craters. Monitoring is done by the Alaska Volcano Observatory (AVO) using an on-island seismic network along with satellite observations and lightning sensors. An infrasound array on Adak Island, about 200 km E, may detect explosive emissions with a 13 minute delay if atmospheric conditions permit.

On 16 September 2018 increased seismicity was detected at 0831, prompting AVO to raise the Aviation Color Code (ACC) to Yellow and Volcano Alert Level (VAL) to Advisory. Retrospective analysis of satellite data acquired on 10 September revealed small ash deposits on the N flank of Mount Cerberus, possibly associated with two bursts of tremor recorded on 8 September (figure 5). This new information, coupled with intensifying seismicity and a strong tremor signal recorded at 1249 on 17 September, resulted in AVO raising the ACC to Orange and the VAL to Watch. Seismicity remained elevated on 18 September with nearly constant tremor recorded by local sensors. At the same time, no ash emissions were observed in cloudy satellite images and no eruptive activity was recorded on regional pressure sensors at Adak.

Figure 1. Minor ash deposits can be seen on the south and west flanks of the N cone of Mount Cerberus, Semisopochnoi Island, in this ESA Sentinel-2 image from 1200 on 10 September 2018. Also note probable minor steam emissions obscuring the crater of the N cone. Image courtesy of AVO.

During 19-25 September 2018 seismicity remained elevated, alternating between periods of continuous and intermittent bursts of tremor. Tremor bursts at 1319 on 21 September and at 1034 on 22 September produced airwaves detected on a regional infrasound array on Adak Island; no ash emissions were identified above the low cloud deck in satellite data, and the infrasound detections likely reflected an atmospheric change instead of volcanic activity.

Seismicity remained elevated during 3-9 October 2018, with intermittent bursts of tremor. No volcanic activity was detected in infrasound or satellite data. On 11 October satellite data indicated partial erosion of a tephra cone in the crater of Cerberus's N cone. A crater lake about 90 m in diameter filled the vent. The data also suggested that the vent had not erupted since 1 October. Seismicity remained elevated and above background levels. The next day AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory, noting the recent satellite data results and lack of tremor recorded during the previous week. AVO reported that unrest continued during 11-24 October.

An eruptive event began at 2047 on 25 October 2018, identified based on seismic data; strong volcanic tremor lasted about 20 minutes and was followed by 40 minutes of weak tremor pulses. A weak infrasound signal was detected by instruments on Adak Island. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale) and Volcano Alert Level was raised to Watch (the second highest level on a four-level scale). A dense meteorological cloud deck prevented observations below 3 km, but a diffuse cloud was observed in satellite data rising briefly above the cloud deck, though it was unclear if it was related to eruptive activity. Tremor ended after the event, and seismicity returned to low levels.

Small explosions were detected by the seismic network at 2110 and 2246 on 26 October 2018, and 0057 and 0603 on 27 October. No ash clouds were identified in satellite data, but the volcano was obscured by high meteorological clouds. Additional small explosions were detected in seismic and infrasound data during 28-29 October; no ash clouds were observed in partly-cloudy-to-cloudy satellite images.

AVO reported on 31 October 2018 that unrest continued. Two small explosions were detected, one just before 0400 and the other around 1000. Satellite views were obscured by clouds at the time, and no ash clouds were observed. Unrest continued through 1 November, at which time the satellite link and the seismic line failed. On 21 November the ACC was lowered to Yellow and the VAL was lowered to Advisory.

Geologic Background. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is 1221-m-high Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked 774-m-high Mount Cerberus volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. Other post-caldera volcanoes include the symmetrical 855-m-high Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

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/).

Japan's 24-km-wide Asosan caldera on the island of Kyushu has been active throughout the Holocene. Nakadake has been the most active of 17 central cones within the caldera for 2,000 years. Historical eruptions have been primarily basaltic to basaltic-andesitic ash eruptions, with periodic Strombolian activity, all from Nakadake Crater 1. The most recent major eruptive episode began in late November 2014 and continued through 1 May 2016. Another eruption, with the largest ash plume in 20 years, occurred on 8 October 2016. Asosan remained quiet until renewed activity from Crater 1 began in mid-April 2019; it is covered in this report, through the end of June 2019. The Japan Meteorological Agency (JMA) provides monthly reports of activity; the Tokyo Volcanic Ash Advisory Center (VAAC) issues aviation alerts reporting on possible ash plumes.

Asosan remained quiet during 2017 and 2018 with steam plumes rising a few hundred meters from Crater 1 and low levels of SO₂ emissions; a warm acidic lake was present within the crater. Fumarolic activity from two areas on the S and SW wall of the crater rim generated occasional thermal anomalies in satellite data and incandescence at night. A brief period of increased seismicity was reported in mid-March 2019. An increase in seismic amplitude on 14 April 2019 preceded a small explosion on 16 April; it produced an ash plume which rose 200 m above the crater rim and drifted NW. It was followed by additional small explosions on 19 April. A new explosion on 3 May produced minor ashfall in adjacent communities; ash emissions were reported multiple times during May with plumes reaching 1,400 m above the crater rim. No additional ash emissions were reported in June.

Activity during 2017 and 2018. JMA reported that no eruptions occurred during 2017. Amplitudes of volcanic tremor increased somewhat during March but were generally low for the rest of the year. The earthquake hypocenters were mostly located near the active crater at around sea level. SO2 emissions were slightly less than 1,000 tons per day (t/d) from January through April; for the rest of the year they ranged from 600 to 2,500 t/d. The Alert Level had been lowered from 2 to 1 on 7 February 2017 where it remained throughout the year. Steam plumes generally rose no more than 600 m above the active crater rim (figure 42). JMA noted that from January to June they often observed crater incandescence at night with a high-sensitivity surveillance camera; Sentinel-2 satellite images also captured thermal anomalies a few times (figure 43). The green lake inside the crater persisted throughout the year with water temperatures of 50-60°C. Two fumaroles were present with high-temperature gas emissions on the SW and S crater walls. Temperatures at the S crater wall were over 600°C from February to May; they decreased to 320-560°C during the rest of the year (figure 44). Sulfur deposits were visible around the SW crater wall fumarole during July.

Figure 42. Steam plumes that rose around 600 m above Nakadake Crater 1 at Asosan were typical activity throughout 2017. Images taken with JMA webcam on 9 June (top left), 22 August (top right), 12 November (bottom left), and 20 December (bottom right) 2017. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 43. Sentinel-2 images captured thermal anomalies at the S rim of the green lake at Asosan's Nakadake Crater 1 on 16 February (left) and 27 May 2017 (right). JMA reported that incandescence was occasionally visible during the night from January-June from the same area. Courtesy of Sentinel Hub Playground.

Figure 44. High-temperature gas and steam from fumaroles on the S wall of the Nakadake Crater 1 at Asosan on 24 August (top) and 17 November 2017 (bottom) were persistent all year, with temperatures ranging from 300 to over 600°C. The green lake inside the crater persisted throughout the year as well with water temperatures of 50-60°C. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

The Alert Level did not change at Asosan during 2018, and no eruptions were reported. Sulfur dioxide emissions fluctuated between 400 and 1,800 t/d throughout the year. Steam plumes generally rose less than 500 m above the active crater (figure 45); incandescence was observed at night during May-October and sometimes observed in satellite imagery as thermal anomalies (figure 46). The temperature of the green lake inside the crater ranged from 58 to 75°C throughout the year. The thermal anomaly on the S wall of the crater was consistently in the 300-500°C range, and had a high temperature in April of 580°C; in December the high temperature had risen to 738°C (figure 47). A brief increase in the number of isolated tremors occurred during March, with 1,044 reported on 4 March, exceeding the previous maximum of 1,000 on 27 October 2014. Seismicity also increased briefly during June, with more than 400 events reported each day on 8, 18, and 20 June. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1, continued to produce modest steam plumes throughout 2017 and 2018 (figure 48).

Figure 45. Typical steam plumes at Asosan during 2018 rose around 500 m above the Nakadake Crater 1. Images are from 4 March (top left), 22 July (top right), 17 August (lower left), and 13 September 2018 (lower right). Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 46. Nighttime incandescence was reported by JMA during May-October 2018 from the S rim of Nakadake Crater 1 at Asosan; Sentinel-2 satellite images (bands 12, 4, 2) captured thermal anomalies from the same area numerous times during 2018 including on 16 June (top left), 26 July and 19 September (middle row), and 18 and 23 November (bottom row). JMA photographed incandescence at night on 17 July 2018 at the S fumarole area (top right). Courtesy of Sentinel Hub Playground and JMA (Aso volcano Monthly Report for July 2018).

Figure 47. The "Green Tea Pond" inside Nakadake Crater 1 at Asosan had temperatures that ranged from 58 to 75°C during 2018 (top row, 26 March 2018); the thermal anomaly on the S wall of the crater consistently had temperatures measured in the 300-500°C range and the SW fumarole area had somewhat lower temperatures (bottom row, 22 June 2018). Courtesy of JMA (monthly Asosan reports for March, May, and June 2018).

Figure 48. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1 at Asosan, continued to produce modest steam plumes throughout 2017 and 2018. It is shown here on 20 December 2017 (top) and 12 March 2018 (bottom). Courtesy of JMA (December 2017 and March 2018 monthly volcano reports).

Activity during 2019. Steam plumes rose to 800 m above the crater rim during January 2019. Overall activity increased slightly during February; SO₂ emissions peaked at 2,200 t/d early in the month; they ranged from 800 to 1,800 t/d for most of the month. The amplitude of volcanic tremor also increased slightly during February. A further increase in tremor amplitude on 11 March 2019 prompted JMA to raise the Alert Level from 1 to 2 the following morning. Volcanic tremor amplitude decreased on 15 March; JMA determined that activity had decreased, and the Alert Level was lowered back to 1 on 29 March 2019. The amount of water in the crater decreased significantly between 27 February and 20 March, exposing part of the crater floor.

The surface temperature of the lake rose during the first part of 2019; it was 78°C in February and 84°C in March. Steam plumes rose to 1,200 m above the crater rim during March and April. SO₂ emissions rose to 4,500 t/d on 12 March but dropped to a lower range of 1,300-2,400 for the rest of the month. Another surge in SO₂ emissions on 12 April 2019 to 3,600 t/d prompted a special report from JMA the following day. SO₂ emissions varied from about 1,700 to 4,100 t/d during the month; values remained high during the second half of the month. JMA noted that the color of the water in the lake inside Nakadake Crater 1 changed from green to gray after 4 April. Fountains of muddy water were periodically observed; they reached 15 m high on 9 April. The temperatures of both the lake (82°C) and around the two fumarole areas (S area about 530°C, SW area about 310°C) remained constant during April and similar to March.

A large increase in the amplitude of volcanic tremor early on 14 April 2019 prompted JMA to raise the Alert Level from 1 to 2 later in the day. The epicenters of the earthquakes were very shallow, located within 1 km beneath the crater. A small eruption occurred at 1828 on 16 April at Nakadake Crater 1; it produced a gray and white plume that rose 200 m above the crater rim and was the first eruption since 8 October 2016 (figure 49). Incandescence was observed inside the crater on 3 and 17 April. The amplitude of seismic tremors decreased on 18 April. Three very small eruptions on 19 April produced ash and steam plumes that rose 500 m above the crater rim. During a site visit that day JMA measured a high-temperature area that produced incandescence from the bottom of the crater at night (figure 50).

Figure 49. The first eruption since October 2016 at Nakadake Crater 1 at Asosan on 16 April 2019 sent an ash plume 200 m above the crater rim (top). Incandescent gas appeared on the crater floor the next day (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 50. Three small explosions on 19 April 2019 at Asosan's Nakadake Crater 1 produced small ash emissions that rose 500 m above the crater rim (top). A strong thermal signal also appeared from the bottom of the crater. Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

A new eruption began at 1540 on 3 May that lasted until 0620 on 5 May (figure 51). Initially the ash plume rose 600 m above the crater rim, but a few hours later the volume of ash increased, and the plume reached 2 km above the crater rim for a brief period. Incandescence was visible from the webcam. The Tokyo VAAC reported the ash plume at 3 km altitude drifting SE on 3 May. Later in the day it rose to 3.7 km altitude and drifted SW. During a field survey the following day (4 May) JMA reported a steam and ash plume rising from the center of the active crater. The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (figure 52).

Figure 51. An explosion at Asosan's Nakadake Crater 1 on 3 May 2019 produced an ash plume that reached 2 km above the crater rim (top) and incandescence visible from the webcam (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 52. During a site visit on 4 May 2019, staff from JMA witnessed an ash and steam plume rising from the bottom of Nakadake Crater 1 at Asosan (top). The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (bottom). Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Ash fell on the S flank, and a small amount of ashfall on 4 May was confirmed by evidence on a car windshield in Takamori Town (6 km S), Kumamoto Prefecture (figure 53). Ashfall was also reported in Takamori-machi, Minami Aso village (9 km SW), and part of Yamato-cho (25 km SW), also in the Kumamoto Prefecture. SO₂ emissions were measured as high as 4,000 t/d on 4 May. Additional explosions with ash plumes were reported from Asosan on 9, 12-16, 29, and 31 May; the plumes rose from 200 to 1,400 m above the crater rim but were not visible in satellite imagery. The TROPOMI instrument on the Sentinel-5 satellite captured SO₂ plumes on 3 and 26 May 2019 (figure 54).

Figure 53. Ashfall was reported on 4 May 2019 in Takamori Town, Kumamoto Prefecture, from the eruption at Asosan's Nakadake Crater 1 on 3 May 2019. Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 54. Plumes of SO2 from Asosan were recorded by the TROPOMI instrument on the Sentinel-5P satellite on 3 (left) and 26 (right) May 2019. Courtesy of NASA Goddard Space Flight Center.

Steam plumes rose to 1,700 m above the crater rim during June 2019 (figure 55). During field visits on 6 and 25 June diffuse ash emissions were observed rising from the center of the active crater, but they did not extend significantly above the crater rim (figure 56). The maximum temperature of the plume was measured at about 340°C with a thermal imaging camera. Almost all of the water in the crater bottom had evaporated since early May; incandescence continued to be observed within the crater at night with the high-resolution webcam (figure 57).

Figure 55. Steam plumes rose to 1,700 m above the crater rim at Asosan's Nakadake Crater 1 on 10 June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 56. Plumes of gas and minor ash were visible at Asosan's Nakadake Crater 1 during site visits by JMA on 6 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 57. Incandescent gas was visible from the vent at Asosan's Nakadake Crater 1 on 18 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); 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/).

Aira caldera encompasses the northern half of Kagoshima Bay in Kyushu, Japan. During the Holocene activity has been focused at Sakurajima volcano along the southern rim of the caldera, and more recent activity has occurred at the Minamidake and Showa summit craters (figure 59). Minamidake crater has been persistently active since 1955, and activity at Showa crater resumed in 2006. Sakurajima is one of Japan's most active volcanoes and frequently deposits ash over the nearby Kagoshima city. This report covers activity that occurred through 2017 and is based on reports issued by the Japan Meteorological Agency (JMA).

Figure 59. The active Minamidake and Showa craters of Sakurajima volcano at Aira. Three incandescent vents within the craters are visible in this Sentinel-2 false color thermal image (bands 12, 11, 4) that was acquired on 13 December 2017. Courtesy of Sentinel Hub Playground.

Typical activity largely consists of Vulcanian explosions that produce ash plumes and small pyroclastic flows. Prior to a decrease in activity in August 2016, the volcano typically produced tens of explosions per month. The last recorded explosion in 2016 was a low-level ash plume on 22 August at 1.2 km altitude, reported by the Tokyo Volcanic Ash Advisory Center (VAAC). Sakurajima has remained on Activity Alert Level 3 (do not approach) on an alert level scale of 1 (little to no activity) to 5 (eruption or imminent eruption causing significant damage to residential areas).

Activity has been low since August 2016. No eruptions were observed through January and February 2017, and both seismicity and SO₂ emission levels remained low.

Eruptive activity resumed on 25 March 2017 at 1803 local time, when the Minamidake crater produced an ash plume to 500 m above the crater and a pyroclastic flow travelled approximately 1,100 m to the south (figure 60). Several additional small ash emission events were noted after this event.

Figure 60. Eruption at the Minamidake crater of Sakurajima (Aira caldera) on 25 March 2017 at 1803 local time. The ash plume reached 500 m above the crater and a pyroclastic flow traveled 1,100 m to the south. Image taken by the Kaigata surveillance camera, courtesy of JMA (March 2017 Monthly Sakurajima report).

Showa crater resumed activity at 0511 on 26 April 2017; 19 more events occurred through the month, including two larger explosive events. One explosive event produced an ash plume to 3,200 m above the crater on 28 April at 1101 local time. Two events occurred at the Minamidake crater through April.

Activity continued at the Showa crater in May, with 47 ash emission events, with nine of these being explosive events. One event on 2 May produced a 4,000-m-high plume that deposited ash on nearby communities (figure 61). Several larger explosions ejected blocks out to 500-800 m from the Showa crater. Activity continued at Minamidake crater, with ash reaching 2,500 m above the crater during an event on 5 May.

Figure 61. Eruption of Sakurajima in the Aira caldera on 2 May 2017 at 0320 local time. The ash plume reached 4,000 m above the crater. Image taken by the Tarumi Ararazaki surveillance camera, courtesy of JMA (May 2017 Monthly Sakurajima report).

Through June, the Showa crater produced 14 events, including two explosive events. An explosion on 6 June produced an ash plume up to 3,200 m above the crater and blocks were deposited out to 800 m from the crater. One small event occurred at Minamidake. Activity was reduced in July, with seven events at Showa crater and none at Minamidake.

During August no events took place at Minamidake. However, Showa crater remained active with 98 events, including 20 that were explosive. Activity through September was similar with no activity in Minamidake crater and 170 events at Showa, including 38 explosive events.

Activity declined again from October through December. During October there were 37 events from Showa crater, with five being explosive (figure 62). One event at Minamidake crater on 31 October produced an ash plume up to 1,000 m above the crater. During November, five events occurred at Minamidake crater, and one at Showa crater that produced an ash plume to 1,300 m above the crater. In December, one event occurred at the Showa crater and Minamidake produced one small event.

Figure 62. An explosive event is seen in this webcam image from the Sakurajima volcano Showa crater (Aira caldera) on 1 October, 2135 local time. Incandescent blocks were deposited out to 1,300 m from the crater. Image taken by the Tarumi Arasaki surveillance camera, courtesy of JMA (October 2017 Monthly Sakurajima report).

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Information Contacts: Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Ambae (Aoba) is a large basaltic shield volcano in the New Hebrides arc that has generated periodic phreatic and pyroclastic explosions originating in the summit crater lakes Manaro Lakua and Voui during the last 25 years; the central edifice with the active summit craters is often referred to as Manaro Voui. A pyroclastic cone appeared in Lake Voui during November 2005-February 2006 (figure 30, BGVN 31:12). The volcano remained mostly quiet until an explosive eruption from a new pyroclastic cone in the lake began in mid-September 2017 and lasted through mid-November (BGVN 43:02). Activity included high-altitude ash emissions (9.1 km), lava flows, and Strombolian activity. After a quieter December, ash emissions resumed during January-April 2018. This report summarizes activity from January to June 2018, with information provided by the Vanuatu Geohazards Observatory of the Vanuatu Meteorology and Geo-Hazards Department (VMGD), the Wellington Volcanic Ash Advisory Center (VAAC), satellite data from several sources, and social media photographs.

Ongoing steam and intermittent ash emissions were observed during January and February 2018; incandescent ejecta continued from the pyroclastic cone at the summit. An increase in the frequency and volume of ash emissions in March led VMGD to raise the Alert Level to 3 (on a 0-5 level scale) by the middle of the month. Ash plume heights ranged from 3-5 km altitude. Heavy rains on 30 March caused a large lahar that significantly damaged a village on the N side of the island. A high-altitude plume on 31 March was measured at 13.7 km altitude. Significant ashfall around the island caused infrastructure damage and health hazards to humans, livestock, and plants. An explosion in early April produced another high-altitude ash plume observed in satellite imagery at 12.2 km altitude and one of the largest SO₂ plumes measured in several years. A major ash plume on 11 April rose to 9.1 km altitude and enveloped much of the island in ash-laden meteoric clouds. The pyroclastic cone growing in Lake Voui had bisected the lake by March, and continued to fill it in. By late May, only two remnants of the lake remained, and a nearby smaller lake was dry. A low-level ash emission in late June signaled the beginning of a new, larger eruptive episode that began on 1 July 2018.

Activity during January-February 2018. The Wellington VAAC reported an ash plume at Ambae on 2 January 2018 drifting E at 3.1 km altitude that dissipated after a few hours. A plume on 8 January estimated at the same altitude resulted in reports of ashfall on the N and NE areas of the island; meteoric clouds prevented observations of the plume. Ongoing steam emissions were reported for the rest of January. On 7 February a continuous ash plume was observed in satellite data at 2.7 km altitude moving N. The following day, it was visible spreading E from the summit. A pilot confirmed observation of the plume continuing to spread to the E at 3.1 km altitude late on 8 February. Another low-level emission on 10 February extended NE at 2.1 km for a few hours. An ash plume on 13 February was clearly visible drifting N in satellite imagery; its altitude was estimated at 3.1 km.

A larger eruption on 16 February generated an ash plume that rose to 4.6 km altitude and initially drifted NE. Continuous ash emission extended as high as 5.5 km through 17 February and drifted SE and then S. By the next day, the constant emissions were still visible in satellite imagery, estimated at 4.6 km altitude; the main plume was drifting E with a remnant moving to the SW, finally dissipating on 19 February (figure 54). Ash emissions were visible in infrared imagery at about 3.9 km altitude on 23 February. Ongoing explosions were observed in the webcam on 23 and 24 February; ash was visible in satellite imagery until the end of the day on 24 February. A brief explosion observed in the webcam around sunrise on 27 February generated a small ash plume that rose to 3.1 km altitude and drifted SE. Moderate sulfur dioxide emissions were recorded a number of times during January and February (figure 55).

Figure 54. On 18 February 2018, the pyroclastic cone at Ambae had grown significantly since 1 October 2017 (see figure 46 BGVN 43:02) (upper image) and actively ejected pyroclastic material along with magmatic gas and steam (lower image). Courtesy of pilot David Sarginson, Facebook.

Figure 55. SO2 plumes from Vanuatu's Ambae, Ambrym, and Gaua volcanoes were all substantial enough sometime during January and February 2018 to be recorded by the OMI instrument on NASA's Aura satellite. Emissions on 2 January 2018 (top left) were drifting slowly SW from Ambae (upper plume) and Ambrym (lower plume); only Ambae had a plume drifting W on 11 January (top right); both Ambae and Ambrym SO2 plumes drifted NE on 17 February (bottom left); on 19 February (bottom right) Gaua (top plume) produced an emission that drifted E while Ambae and Ambrym generated SO2 that drifted SW. Courtesy of NASA Goddard Space Flight Center.

Activity during March 2018. The frequency and volume of ash emissions increased significantly during March 2018. Ash plumes were visible in satellite imagery during 3-6 March 2018. The initial plume rose to 3.7 km altitude and drifted NE, rising to 3.9 on 4 March and drifting N. The following day plumes rose to 4.6 km. By 6 March the plume was lower, drifting NW at 2.4 km altitude. A series of continuous low-level ash emissions were visible in satellite and webcam imagery every day from 11-19 March (figure 56). They initially drifted SE and SW and then moved to the W on 15 March at altitudes of generally 2.4-3.1 km, occasionally higher. The plumes drifted N and W during 17-19 March. This increase in ash emissions affecting local villages led VMGD to raise the alert level from 2 to 3 on 18 March 2018. They noted that activity was similar to the previous October but with more sustained ash emissions.

Figure 56. Continuous ash emissions from Ambae beginning on 11 March 2018 (10 March UTC shown here) were visible in satellite imagery for over a week. Courtesy of European Space Agency, Copernicus EMS.

Local observers reported an explosion on 21 March that rose to 3.4 km altitude and drifted SW (figures 57-59). Continuous emissions through the end of the month were discernible in either satellite imagery or the webcam each day. Plume altitudes ranged from 3.1 to 4.9 km altitude, drifting in several directions. Significant ashfall began affecting local villages, destroying crops and livestock, and collapsing structures during the second half of March.

Figure 57. A strong explosion on 21 March 2018 at Ambae produced an ash plume that rose several kilometers above the crater. Ashfall affected villagers in many communities on the island. Image courtesy VMGD Saratamata webcam located 22 km NE on the NE tip of Ambae Island, annotations by Cultur Volcan.

Figure 58. A major ash plume rose from the crater of the pyroclastic cone in Lake Voui on Ambae on 21 March 2018. Photo courtesy of Robson S Tigona (VMGD), posted on Facebook.

Figure 59. The dense ash plume from the explosion on 21 March 2018 at Ambae caused significant localized ashfall on the SW of the island as seen from Nduidui wharf in W Ambae. Courtesy of Dan McGarry, Vanuatu Daily Post.

Local news reports on 25 March noted that ejecta from the previous evening was visible over 70 km away to the SW by residents on Espiritu Santo Island, and small amounts of ash fell on Pentecost Island, 60 km SE (figure 60). According to the Vanuatu Independent, Virgin Australia cancelled flights to Vanuatu on 25 March. The New Zealand Defence Force did an aerial survey on 26 March and observed a large ash plume rising several kilometers (figure 61). Radio New Zealand reported on 30 March that large amounts of ashfall and acid rain had damaged crops, water supplies and buildings on Ambae (figures 62). A New Zealand GNS Science volcanologist reported that gardens were covered by ash and limbs on trees were broken. Some of the roofs over buildings and water supplies had collapsed due to the weight of the volcanic ash. Heavy ashfall in the S and NW parts of the island at the end of the month resulted in evacuations of several villages in the affected areas.

Figure 60. Ashfall was observed on Pentecost Island, 60 km SE of Ambae after significant explosions overnight during 24-25 March 2018. Courtesy of Dan McGarry, Vanuatu Daily Post via twitter.

Figure 61. The New Zealand Defence Force photographed this large ash plume rising from the summit of Ambae during an aerial survey on 26 March 2018. Courtesy of the New Zealand Defence Force (NZDF).

Figure 62. Dense volcanic ash fell at the Penama Adventist College (PAC) in Red Cliff on Ambae in late March 2018. The upper image was taken on 14 April 2017, the lower image on 27 March 2018. Photos by John Metojoe, Vanuatu Police Force, and PAC. Courtesy of Philipson Bani (IRD/LMV).

The village of Waluebue on the N side of Ambae was badly damaged by a lahar during the night of 30-31 March. Homes and churches were destroyed from the mud and large boulders in the debris flow. All residents were safely evacuated (figures 63-67).

Figure 63. A large lahar deposited boulders and damaged many buildings in the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photo courtesy of Clifford Tarisimbi.

Figure 64. As seen in this example of a building undercut on one side and partially buried on the other, a large lahar damaged many buildings in the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photos courtesy of Clifford Tarisimbi.

Figure 65. Mud and boulders buried some buildings to the roofline when a large lahar damaged passed through the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photos courtesy of Clifford Tarisimbi.

Figure 66. Boulders a meter or more in diameter destroyed buildings when large lahar traveled through the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photo courtesy of Clifford Tarisimbi.

Figure 67. Boulders a meter or more in diameter destroyed buildings when large lahar traveled through the village of Waluebue on the N side of Ambae during the night of 30-31 March 2018. Photo courtesy of Clifford Tarisimbi.

A new series of high-altitude ash emissions were reported by the Washington VAAC beginning on 30 March (figure 68). Early reports from satellite images and webcams indicated an ash plume at 6.1 km altitude. This was followed within the hour of confirmation from satellite imagery of the plume at 13.7 km altitude moving NW. By the following morning, two plumes were visible, one drifting S at 6.1 km and a second drifting NW at 13.7 km altitude. Meteoric clouds prevented observations later that day, but by 1 April, intermittent explosions were producing plumes moving E at an estimated altitude of 3.0 km, and SE estimated at 6.1 km altitude.

Figure 68. A 13.7-km-high ash plume was visible from the VMGD Webcam at Ambae on 31 March 2018. Satellite imagery showed plumes drifting in multiple directions. Courtesy of VMGD.

Activity during April-June 2018. New eruptions occurred overnight during 5-6 April 2018 that generated an ash plume and a large distinct SO₂ plume. Meteoric clouds and darkness prevented observation of the ash plume, but the SO₂ signal was clearly visible on false-color satellite imagery. The plume initially rose to 7.3 km altitude and drifted W; a few hours later, it rose to 12.2 km. With a Dobson Unit measurement of 52.55 units, it was one of the strongest SO₂ plumes measured on the planet since 2015, according to Simon Carn of Michigan Technological University (figure 69). An ongoing eruption was visible in the webcam on 6 April, but meteoric clouds again prevented observation in satellite data. A cluster of lightning strikes was detected by the World Wide Lightning Location Network (WWLLN) around the reported time of the eruption, according to Simon Carn. Intermittent low-level ash emissions were confirmed in the webcam on 8 April, estimated to be moving NE and E at 3.0-4.9 km altitude.

Figure 69. The largest SO2 plume recorded since 2015 erupted from Ambae during 5-6 April 2018. Courtesy of NASA Goddard Space Flight Center.

Ash from a continuous low-level eruption during 9-10 April 2018 was clearly visible in the webcam and partly visible in satellite imagery drifting E and NE at 4.3-4.9 km altitude. The SO₂ plume from the eruption stretched across most of the South Pacific (figure 70). Ashfall from the plume spread across a large area of the island causing substantial damage in local communities (figures 71 and 72).

Figure 70. A sulfur dioxide plume from Ambae in Vanuatu stretched across the South Pacific in this 9 April 2018 image from the OMI instrument on the Aura satellite. Courtesy of NASA Goddard Space Science Center and Simon Carn.

Figure 71. Ashfall from continuous emissions at Ambae during 9-10 April 2018 spread across much of the island, damaging local communities. Image posted on 10 April 2018. Courtesy of Wilfred Woodrow, Facebook.

Figure 72. Ashfall from continuous emissions during 9-10 April 2018 at Ambae spread across much of the island, damaging local communities. Photo from Ghevin Banga, posted by Bani Philipson (IRD/LMV).

The ash plume height increased significantly on 11 April to 9.1 km altitude and drifted SE according to the Wellington VAAC. Planet Lab images showed the plume covering the N half of the island a short time later (figure 73). The following day, the plume altitude gradually lowered from 4.6 to 1.8 km and drifted N, then NW. Local communities reported intermittent low-level ash emissions and localized ashfall late on 12 April; this was the last report of ash emissions for April. Thick meteoric and ash clouds enveloped much of the island as seen in social media video on 12 April.

Figure 73. Three satellite images from Planet Labs Inc. show the changes at Ambae between September 2017 and April 2018. On 30 September 2017 (top), the pyroclastic cone in Lake Voui was still an island within the lake. By 10 March 2018 (middle), the lake had been divided in two by the growth of the cone, the lake was discolored, and ashfall covered a large area several kilometers in diameter around the lake. A major ash emission on 11 April 2018 (bottom) rose to 9.1 km altitude and covered the N half of the island. Courtesy of Planet Labs Inc. posted on Twitter at Planet@planetlabs.

According to the Vanuatu Daily Post on 16 April 2018, the Council of Ministers for Vanuatu declared their intent to seek help from International Relief Organizations to evacuate the island's population after the latest episodes of extensive ashfall destroyed much of the infrastructure. Photographs from an overflight by VGMD on 21 April 2018 showed the increased size of the pyroclastic cone inside Lake Voui dividing the lake into two segments, one nearly consumed by the cone (figure 74). They reported small eruptions on 23 and 27 April; these were the last ash emissions until the end of June 2018.

Figure 74. Aerial images of the active pyroclastic cone at Ambae were captured by VMGD during an overflight on 21 April 2018. Only dense steam emissions were observed in the view to the E across the summit, and the original Lake Voui was in two segments split by the pyroclastic cone. Courtesy of VMGD.

The thermal activity recorded by the MODVOLC and MIROVA systems corresponded with the observations of explosions and ash emissions. There were MODVOLC thermal alerts issued each month from January through 10 April 2018, with strong, multi-alert periods in February and March; these data were similar to the MIROVA signal for the period, which also showed increased activity during the same time (figure 75).

Figure 75. Data from the MIROVA project show significant pulses of heat flow from Ambae during February-April 2018. Inset photo shows the large ash plume of 9 April as viewed from the VMGD webcam, which corresponds to the largest heat flow in April shown on the graph. Courtesy of MIROVA and VMGD.

By the end of May 2018, Manaro Ngoru, the small water body on the W side of the summit was dry; Lake Voui, divided into two segments by the pyroclastic cone, had a small amount of orange-brown water in the W half, and muddy brown water in the E half (figures 76 and 77). Steam plumes rose continuously from the cone, but no ash emissions were observed.

Figure 76. The summit of Ambae on 22 May 2018 was covered with ash over a large area; former Lake Voui was divided in two by the pyroclastic cone, and only a modest steam plume rose from the top of the cone. Manaro Ngoru, the former lake on the W side of the summit, was completely dry. Courtesy of Planet Labs.

Figure 77. The W side of Lake Voui on Ambae on 29 May 2018 was a small area of dark reddish brown water around the pyroclastic cone. View is to the S. Courtesy of Bani Philipson (IRD/LMV). =

VMGB issued a volcano alert on 7 June 2018, announcing that they had lowered the Alert Level from 3 to 2, due to the reduced activity at Ambae during late April and May. Radio New Zealand reported that on 9 June, the Vanuatu government announced plans to move its Penama Province capital due to the ongoing eruption. The Penama Council agreed to relocate its headquarters from Saatamaa in Eastern Ambae to Loltong in North Pentacost. The Penama Province is one of six in Vanuatu and includes the three islands of Ambae, Maewo, and Pentecost.

The Wellington VAAC issued an ash advisory from a low-level ash emission on 21 June 2018. It was clearly visible in satellite imagery, and rose to 3 km altitude, drifting SE. That was the last activity reported until a large new ash plume was recorded in the webcam on 1 July 2018.

Geologic Background. The island of Ambae, also known as Aoba, is a massive 2500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); European Space Agency (ESA), Copernicus (URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus; 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/); New Zealand Defence Force (NZDF), Wellington, New Zealand (URL: http://www.nzdf.mil.nz/, Twitter: @NZDefenceForce); Vanuatu Daily Post (URL: http://dailypost.vu/news/flash-appeal/article_7c929c1e-dda3-5eab-925b-c814e04eeacb.html); Dan McGarry, Vanuatu Daily Post (Twitter: @dailypostdan); Vanuatu Independent News Magazine, Port Vila, Vanuatu (URL: https://vanuatuindependent.com/2018/03/26/flight-cancelled-due-to-volcanic-ash/); Simon Carn, Dept of Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, USA (URL: http://www.volcarno.com/, http://so2.umbc.edu/omi/); Radio New Zealand, 155 The Terrace, Wellington 6011, New Zealand (URL: https://www.radionz.co.nz/international/pacific-news/359231/vanuatu-provincial-capital-moves-due-to-volcano); Bani Philipson, Observatoire de Physique du Globe de Clermont-Ferrand (OPGC) and Institut de Recherche pour le Developpement (IRD), Laboratoire Magmas et Volcans (LMV), University Campus of Cézeaux, 6 Blaise Pascal Avenue, TSA 60026 - CS 60026, 63178 AUBIERE Cedex, France (URL: http://lmv.univ-bpclermont.fr/bani-philipson/, Twitter: @philipsonbani); David Sarginson (Facebook: URL: https://www.facebook.com/david.sarginson.16); Clifford Tarisimbi (Facebook: https://www.facebook.com/profile.php?id=100009930510696); Wilfred Woodrow (Facebook: https://www.facebook.com/groups/558036627684741/permalink/974980079323725); Planet Labs Inc. (URL: http://www.planet.com/).

Ambrym volcano, located in Vanuatu along the New Hebrides Island Arc, consists of a large 12-km-diameter caldera with two active craters, Marum and Benbow. Historical activity has occurred at summit and flank vents, producing moderate explosive eruptions and lava flows that reach the coast. Historically important eruptions date back two centuries, including extra-caldera W-flank lava flows that caused destruction in coastal areas in 1820, 1894, 1913, and 1929. Since then, there have not been extra-caldera lava eruptions, although the areas around Marum and Benbow craters remain hazardous. The Vanuatu Meteorology and Geo-Hazards Department (VMGD) located in Port Vila, Vanuatu, is responsible for monitoring ongoing activity at Ambrym.

During January through June 2018, volcanic activity was confined to the eruptive vents of Benbow and Marum craters, including ongoing lava lake activity inside the active vents, substantial degassing, and emission of steam clouds. The Volcanic Alert Level remained at Level 2 on a scale from 0 to 5 with five being the highest (figure 30). At Level 2 ('Major Unrest') the danger is restricted to the active craters and the Permanent Exclusion Zones, which are located within a 1 km radius around Benbow crater and about a 2.7 km radius around Marum crater (figure 38).

Figure 38. A "Safety Map" showing Benbow and Marum craters at Ambrym with the locations of both designated permanent exclusion zones and danger zones. Courtesy of Vanuatu Meteorology and Geo-Hazards Department.

VMGD reported that the lava lakes in Benbow and Marum craters continued to be active and produced gas and steam emissions on 30 January, 19 March, and 25 April 2018. More sustained and substantial emissions were reported on 7 June.

During the reporting period, numerous thermal anomalies were detected by the MODIS satellite instruments and subsequently analyzed using the MODVOLC algorithm, possibly reflecting lava lake activity in Benbow and Marum craters (figures 39 and 40). The MIROVA (Middle InfraRed Observation of Volcanic Activity) system also detected numerous hotspots almost every day (figure 41).

Figure 39. Showing two active craters of Ambrym, Benbow and Marum. Red areas indicate approximate locations of Thermal Anomaly detections with the number of detections from MODVOLC Thermal Alert System from the period January through June 2018. Courtesy of HIGP - MODVOLC Thermal Alerts System.

Figure 40. MODVOLC thermal alerts detected during the reporting period from January to June 2018 showing hot spots located at Benbow and Marum craters. Courtesy of HIGP - MODVOLC Thermal Alerts System.

Figure 41. Plot of MODIS thermal infrared data analyzed by MIROVA showing the log radiative power of thermal anomalies at Ambrym for the year ending on 29 August 2018. Courtesy of MIROVA.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides arc. A thick, almost exclusively pyroclastic sequence, initially dacitic, then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major plinian eruption with dacitic pyroclastic flows about 1900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the caldera floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

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

Activity at Bezymianny has been frequent over the past 60 years, and almost continuous since May 2010. The Kamchatka Volcanic Eruptions Response Team (KVERT) reported that ash plumes from the 20 December 2017 explosive eruption (BGVN 43:01) rose as high as 15 km and drifted 320 km NE (figure 24). On 29 December activity included moderate gas-and-steam emissions; a lava flow likely continued to effuse onto the N flank of the lava dome. A thermal anomaly over the volcano was identified in satellite images in late December 2017.

Figure 24. Explosions from Bezymianny sent ash plumes up to 15 km altitude on 20 December 2017. Photo by Yu. Demyanchuk; courtesy of IVS FEB RAS, KVERT.

KVERT reported on 5 April 2018 that moderate gas-and-steam activity was continuing. Satellite data showed a thermal anomaly over the volcano on 29-30 March and 2-3 April, but the volcano was obscured by clouds in the other days of week. Fumarolic plumes were also seen on 13 April (figure 25). No MODVOLC thermal alerts were measured during the first half of 2018, and MIROVA analysis shows only low level radiative power anomalies for the same period (figure 26).

Figure 25. Thermal anomalies at Bezymianny recorded by the MIROVA system (log radiative power) for the year ending 2 February 2018 (top) and 28 June 2018 (bottom). Courtesy of MIROVA.

Figure 26. Thermal anomalies at Bezymianny recorded by the MIROVA system (log radiative power) for the year ending 28 June 2018. Courtesy of MIROVA.

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

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

Cleveland, at the western end of the isolated Chuginadak Island in the Aleutian Islands, is characterized by frequent small explosions that are monitored using local seismic and infrasound sensors, and by elevated surface temperatures that are monitored by satellite-based infrared sensors. The current eruptive period began in April 2016 and has continued through at least July 2018. The Alaska Volcano Observatory (AVO) is responsible for monitoring, and issues regular reports describing activity.

Small explosions in mid-December 2017 were followed by elevated surface temperatures later in the month and a lava flow in the summit crater that began effusing on 5 January 2018 (table 9). Thermal anomalies and other signs of unrest continued through 24 February, when a small explosion was detected. Another explosion was reported on 2 March with a plume rising to 4.6 km altitude and drifting ENE. Satellite data continued to identify elevated temperatures in early March. Small explosions were identified using seismic and infrasound data on 14 March and 4 April. The ash cloud on 4 April rose to 4.6 km altitude and drifted SW; hot material was ejected onto the W flank.

Thermal anomalies were ongoing in June. A small circular lava flow (~80 m in diameter) in the summit crater was reported on 25 June; a thermal anomaly noted during 29 June-2 July extending SW downslope within the crater was consistent with a lava flow, according to AVO. Weakly elevated surface temperatures were reported on many days during 7-23 July, along with some small steam plumes (figure 25). A small deposit of blocks, within the summit crater and just below the E crater rim, seen using satellite imagery during 18-23 July suggested to AVO that there had been a very small explosion not recorded using seismic or pressure sensor monitors.

Table 9. Observations of dome growth and other crater activity at Cleveland, December 2017-July 2018. Note that the absence of observable activity from satellites is often due to cloud cover. Data courtesy of Alaska Volcano Observatory (AVO).

Figure 25. Worldwide-3 satellite image of the summit crater of Cleveland volcano on 10 July 2018. The 80-m-diameter circular lava flow extruded in late June 2018 can be seen as well as minor steam emissions. Courtesy of Alaska Volcano Observatory / U.S. Geological Survey (Image 117311, color adjusted).

Geologic Background. The beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Joined to the rest of Chuginadak Island by a low isthmus, Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

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://www.dggs.alaska.gov/); Anchorage Volcanic Ash Advisory Center (VAAC), Alaska Aviation Weather Unit, NWS NOAA US Dept of Commerce, 6930 Sand Lake Road, Anchorage, AK 99502-1845 USA (URL: http://vaac.arh.noaa.gov/).

The most recent activity from Copahue originates in the El Agrio crater, which has permanent fumarolic activity and an acidic lake. During 2017, ash emissions began in early June, but decreased after July, although tremor and degassing with occasional ash continued for the remainder of the year (BGVN 43:01). The volcano is monitored by the Servicio Nacional de Geología y Minería (SERNAGEOMIN). This report discusses activity during January-June 2018.

According to the Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI), SERNAGEOMIN reported that a hydrothermal explosion was recorded on 24 March 2018, along with increased tremor. The Alert Level was raised to Yellow (second highest level on a four-color scale); SERNAGEOMIN recommended no entry into a restricted area within 1 km of the crater. ONEMI maintained its own Alert Level of Yellow (the middle level on a three-color scale) for the municipality of Alto Biobío (25 km SW).

Based on SERNAGEOMIN information, ONEMI reported that during 1-31 March 2018 there were 83 volcano-tectonic events recorded and 204 earthquakes indicting fluid movement. Tremor levels increased on 24 March, the same day as a phreatic explosion, though by the next day it had decreased to baseline levels. Webcams recorded gas plumes rising from El Agrio crater as high as 1 km. During an overflight on 3 April, scientists observed continuous white gas plumes rising almost 400 m.

The Buenos Aires Volcanic Ash Advisory Center (VAAC) reported that on 24 June diffuse steam emissions possibly containing ash were visible in webcam views rising to an altitude of 3.6 km.

Geologic Background. Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Information Contacts: Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), Beaucheff 1637/1671, Santiago, Chile (URL: http://www.onemi.cl/); Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php).

Kerinci has produced intermittent ash explosions in recent years, including December 2011, June 2013, March-June 2016, and November 2016 (BGVN 42:04). The Darwin Volcanic Ash Advisory Centre (VAAC) has issued the only reports on activity between December 2016 and July 2018, and these have been based on satellite data. The Indonesia volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), has kept the Alert Level at 2 (on a scale of 1-4) since 9 September 2007.

According to the Darwin VAAC, on 13 August 2017, an ash plume rose to an altitude of 4.3 km and drifted WSW.

Sentinel-2 satellite imagery showed what appeared to be a small ash plume rising from the crater on 21 April 2018 (figure 4). The Darwin VAAC also reported that on 5 June 2018 a minor ash emission rose to an altitude of 4.3 km and drifted W (figure 5). On 10 June an ash plume rose to an altitude of 4 km and drifted W.

Figure 4. Natural color satellite image from Sentinel-2 on 21 April 2018 showing a small light-brown ash plume rising from the Kerinci summit crater. Courtesy of Sentinel Hub.

Figure 5. A brown ash plume is visible in this natural color Sentinel-2 satellite image of the Kerinci crater on 5 June 2018. Courtesy of Sentinel Hub.

During the reporting period, no significant sulfur dioxide levels near the volcano were recorded by NASA's satellite-borne ozone instruments, and no thermal anomalies were detected.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

Information Contacts: 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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Open lava lakes at the Kilauea summit caldera along with a lava lake and flows from the East Rift Zone (ERZ) have been almost continuous since the current eruption began in 1983, and the rift zone has been intermittently active for at least two thousand years. The period from January-April 2018 included the ending of activity in one part of the ERZ and the beginning of a new episode. March 2018 marked the tenth year of the active lava lake inside the Overlook vent at Halema'uma'u. Information for this report comes primarily from the US Geological Survey's (USGS) Hawaii Volcano Observatory (HVO) which provides daily reports, volcanic activity notices, and photo and video data.

At the end of 2017, the lava lake inside the Overlook vent at Halema'uma'u crater maintained the typical activity it had exhibited throughout the year, with a consistent lava circulation pattern, and occasional spattering events from hardened lava falling into the lake from the pit walls. The lake level rose and fell by a few meters over periods of hours to days, ending the year about 30 m below its level at the beginning of the year. Longer-term subsidence of the Pu'u 'O'o cone on the East Rift Zone was also apparent during 2017, although there was little change in the elevation of the lava pond inside the west pit area of the crater; occasional rockfalls triggered minor spattering. At the end of 2017 the East Rift Zone episode 61g surface lava flow activity persisted on the upper portions of the flow field near Pu'u 'O'o, on the pali, and in scattered areas along the coastal plain. Changes in the subsurface flow in lava tubes contributed to frequent changes to surface breakout locations. The lava flowing into the ocean at Kamokuna slowed and finally ended in November 2017.

During January-April 2018, the lava lake level inside the Overlook vent of Halema'uma'u crater rose and fell daily with alternating periods of inflation and deflation, with a gradual overall inflationary trend. Inflation intensified at the end of April, and the lake overflowed onto the floor of the crater during 21-27 April. The lake level had dropped several meters below the rim of the vent by the last day of the month. Activity of the episode 61g lava flow decreased gradually throughout the period. The flow remained active at the base of the pali and on the upper flow field through February, but activity tapered off on the coastal plain. By the end of March, only the upper flow field was still active. Notable inflationary tilt began at Pu'u 'O'o on 12 March 2018. Lava flowed out of vents on the main crater floor and also created a perched lava pond in the west pit. In mid-April HVO noted that the inflation resulted from increased pressurization of the magma under Pu'u 'O'o and in the past this had led to the formation of new vents and lava flows along the East Rift Zone. A marked increase in seismicity and ground deformation at Pu'u 'O'o on the afternoon of 30 April was followed by the collapse of the crater floor, dispersing red ash a significant distance around the cone. Following the collapse, HVO seismometers and tiltmeters recorded a substantial increase in seismic activity and deformation from Kilauea's summit to an area about 10-16 km downrift (east) of Pu'u 'O'o which propagated eastward overnight along the Lower East Rift Zone (LERZ), marking the beginning of a major new eruptive phase.

Activity during January 2018. Consistent activity continued into January 2018 with few notable changes. The lava lake inside the Overlook vent at Halema'uma'u crater rose and fell by a few meters over hours and days; on the East Rift Zone the lava pond persisted at Pu'u 'O'o cone, and scattered breakouts from the episode 61g lava flow continued. Early on 19 January two earthquakes of magnitude 2.4 and 2.5 occurred on the lower East Rift Zone near Leilani Estates. Also on 19 January, a rockfall from the wall of Halema?uma?u crater plunged into the lava lake producing a short-lived explosion of spatter and wallrock that blanketed an area around the former visitor overlook. Debris fell as far as the Halema'uma'u parking lot (figure 312).

Figure 312. Spatter up to about 30 cm in size was thrown onto the rim of Halema'uma'u crater at Kilauea during explosive events on 19 January 2018. Some fragments were thrown or blown farther downwind, reaching as far as the closed section of Crater Rim Drive in Hawai'i Volcanoes National Park. The boot of an HVO scientist, who entered the area to check on HVO's webcameras, is shown here for scale. Courtesy of HVO.

HVO noted that spattering from the lava lake at Halema'uma'u was visible from the visitor overlook overnight during 25-26 January. Spatter appeared again briefly the next day, and overnight during 29-30 January. Four spattering sites were visible on a clear 30 January day (figure 313). Webcam views overnight on 30-31 January showed that incandescence persisted from the small lava pond on the W side of the Pu'u 'O'o crater. On the morning of 26 January a new breakout from the episode 61g flow appeared on the pali. By the end of January, most of the breakouts from the episode 61g flow field were concentrated at the base of the pali and on the upper flow field, with little activity on the coastal plain.

Figure 313. Clear views at the summit of Kilauea on 30 January 2018 revealed four spattering sites visible on the surface of the Halema'uma'u lava lake inside the Overlook vent. Through the gas plume, a visible scar (light-colored wall rock) from the 19 January rockfall that triggered an explosive event, could be seen on the southern Overlook vent wall. Another, smaller scar on the northeastern lake wall (left), resulted from two small rock falls on 24 January. Courtesy of HVO.

Activity during February 2018. The lake level inside the Overlook vent continued with daily fluctuations of several meters, between 31 and 42 m below the Halema'uma'u crater floor, during February 2018. A small veneer collapse (rockfall) into the lava lake on 23 February was visible in lava lake webcam images. Throughout the month, persistent incandescence was observed in the webcam at the Pu'u 'O'o west pit lava pond (figure 314). On 10 February a large portion of the NE rim of the west pit collapsed. Prior to and during the rim collapse, the adjacent ground also subsided. The episode 61g flow remained active at the base of the pali (figure 315) and in the upper flow field. A new breakout on the upper flow field, 1-2 km from the vent, appeared early on 26 February. A small swarm of earthquakes occurred in the upper East Rift Zone on 21 February; the largest event was a M 2.3. Seismicity throughout the volcano was otherwise at normal rates throughout the month.

Figure 314. Incandescence from the west pit at Kilauea's Pu'u 'O'o cone on 19 February 2018 was typical of that observed during clear weather throughout the month. Courtesy of HVO.

Figure 315. 'A'a flows at the base of Pulama pali at Kilauea on 20 February 2018 produced shimmers of heat (top center) and incandescent fragments. Rubble from the flow rolled downhill, as the molten center slowly pushed forward. Courtesy of HVO.

Activity during March 2018. A brief swarm of small earthquakes occurred in the upper East Rift Zone on 2 March 2018. An ongoing long-period earthquake swarm at 5-10 km depth beneath the caldera began late on 6 March and continued into the next day. At the Halema'uma'u crater, the lava lake fluctuated daily, with levels ranging from a low of 40.5 m below the crater floor to a high of 20 m below it. Changes in levels of up to 10 m in a 24-hour period were common. Vigorous spattering was observed on 6 March (figure 316). On 16 March, the lava lake rose high enough (26 m below the crater floor) for active spattering to be visible in webcams mounted in the HVO tower, located across the crater from the vent. The 10th anniversary of the eruption within Halema'uma'u crater was marked on 19 March. When the vent first opened on 19 March 2008, it formed a small pit about 35 m wide. Over the following decade, the pit (informally called the "Overlook crater") grew to about 280 x 200 m in size (see figure 313).

Figure 316. Within Kilauea volcano's summit lava lake at the Halema'uma'u crater, vigorous spattering on 6 March 2018 was occurring on the southern margin where a ledge of solidified lava had built out from the vent wall. Courtesy of HVO.

Notable inflationary tilt at Pu'u 'O'o cone began on 12 March 2018; GPS stations also started recording extension across the cone on that date. A small increase in seismic events was observed at Pu'u 'O'o on the evening of 21 March. Increased views of spattering from the west pit lava pond were visible beginning the following day, likely due to subsidence over the previous months as reported by HVO. During the evening of 25 March lava flowed out of a vent in the SE part of the crater floor and continued to expand for the rest of the month (figure 317). Inflationary tilt slowed significantly on 27 March. Cracks along the ridge between the main crater and the west pit continued to grow throughout the month as the ridge continued to subside (figure 318).

Figure 317. On 25 March 2018 a small lava flow began erupting onto the Pu'u 'O'o crater floor at Kilauea for the first time since May 2016. In this thermal image, taken by the PTcam on 26 March 2018 at 1318, the flow (bright color) appears to be supplied by one of the small spatter cones in the crater's south embayment. The lava flow did not extend beyond the crater. This type of activity is not unusual for Pu'u 'O'o. Courtesy of HVO.

Figure 318. At Pu'u 'O'o on Kilauea's East Rift Zone, the ridge separating the main crater (top) from the west pit (bottom) had been subsiding over the previous several months due to small rockfalls and unstable ground when this image was taken on 27 March 2018. As the ground shifted, cracks along the ridge and on both sides of it continued to open. The lava pond within the west pit rose several meters during March and produced overflows (darker lava) onto the floor of the pit as it rose. A small lava flow also erupted onto the floor of the main crater on 25 March and remained active through 27 March, visible as the lava darker in color in the foreground of the main crater floor. Courtesy of HVO.

By 20 March surface lava flow activity from the episode 61g flow near the base of the pali appeared to have diminished, and only sparse lava flow activity on the coastal plains was noted after 23 March. Activity on the upper flow field, closer to Pu'u 'O'o, continued (figure 319). A 30 March overflight by HVO confirmed no flow activity on the coastal plain or the pali.

Figure 319. Active lava breakouts were scarce across the episode 61g flow field on Kilauea's East Rift Zone, with active flows confined to an area approximately 1-2 km from Pu'u 'O'o during March 2018. This breakout from the lava tube consisted of fluid pahoehoe and was photographed on 27 March 2018 during an overflight. The incandescent area is several meters across. Courtesy of HVO.

Activity during 1-16 April 2018. Constant spattering at the Overlook vent lava lake (figure 320) was intermittently visible from HVO and the Jagger Museum during April 2018 as the lake level rose and fell several meters on a daily basis. Its lowest level of the month was 32 m below the crater floor, and a general inflationary trend throughout the month resulted in significant overflows onto the floor of Halema'uma'u crater at the end of the month. A rockfall in the morning of 6 April triggered an explosion at the summit lava lake that damaged the power system to the Halema'uma'u crater rim webcams (figure 321). A moderate swarm of over 200 earthquakes occurred on 11 April at depths of 7-9 km below the summit; the largest event in the sequence was M 2.4. Seismicity returned to its background rate in the early morning of 12 April. Three minor ledge collapses, common while the lava lake level is lowering, occurred on 12 April.

Figure 320. A clear view of Kilauea's summit lava lake in the Overlook vent on 4 April 2018 revealed spattering on the N side and center of the lake surface, a departure from its more common location on the SE side of the lake; this occasionally happened when the surface flow direction reversed. Spattering is caused by gas bubbles bursting within the lava lake. Courtesy of HVO.

Figure 321. On 6 April 2018 at 1028 HST a partial collapse of the southern Overlook crater wall triggered an explosive event at Kilauea's summit lava lake. A large plume of gas, ash, and lava fragments rose from the lava lake and was visible from the Jaggar overlook. The explosion threw debris onto the Halema'uma'u crater rim at the old visitor overlook, which has been closed due to ongoing volcanic hazards such as this explosive event. Courtesy of HVO.

For the first half of April 2018, steady minor inflation continued at Pu'u 'O'o, interrupted by brief episodes of sharp deflation that appeared related to small lava flows on the crater floor. During an overflight on 13 April HVO geologists viewed a perched lava pond inside the west pit (figure 322). A slight increase in seismicity in the Upper East Rift Zone began overnight during 15-16 April; the largest event was a M 2.9 earthquake.

Figure 322. During an overflight of Kilauea on 13 April 2018 geologists from HVO observed that lava within the west pit at Pu'u 'O'o had formed a perched lava pond (center) contained within a levee. This levee, formed by an accumulation of hardened lava, confined molten lava to the perched pond, which allowed the lava surface to rise higher than the west pit floor. If the pond rises high enough, lava can spill over the levee, forming small flows around the margin of the perched pond. Courtesy of HVO.

At the beginning of April 2018 the episode 61g lava flow was active only above the Pulama pali. The areas of the upper flow field with active lava flows were located within the Kahauale'a Natural Area Reserve, which has been closed to the public since 2007 due to volcanic hazards. On 13 April 2018, geologists observed scattered breakouts from the 61g flow within about 2.2 km from Pu'u 'O'o and another sluggish breakout about 5 km from Pu'u 'O'o (figure 323).

Figure 323. An HVO geologist photographed an active pahoehoe breakout on 13 April 2018 at Kilauea after taking a lava sample nearby. This breakout was located approximately 0.4 km from the episode 61g vent. As the flow inflated, internal pressure cracked the rigid crust of the flow allowing molten lava to ooze out. Courtesy of HVO.

Activity during 17-30 April 2018. Beginning in mid-April 2018 seismometers recorded an increase in the number of small earthquakes beneath the summit and upper East Rift Zone reflecting increased pressurization. Kilauea's summit and East Rift Zone magma systems are connected, with changes at one sometimes leading to changes at the other. Tiltmeters, GPS, web cameras, and field observations, continued to record inflation at the Halema'uma'u crater, at Pu'u 'O'o, and at the upper portion of the episode 61g lava tube system. HVO noted that this inflation could lead to the opening of a new vent on or near Pu'u 'O'o that could cause a significant drop in the summit lake level.

At the Halema'uma'u crater, inflation significantly outpaced deflation for the second half of April. In the afternoon of 18 April the lake level was at 25 m below the crater floor. A lengthy episode of inflation brought the lava to within 6 m of the floor on the afternoon of 21 April. As the level continued to rise, a small overflow along the S crater rim occurred about midnight overnight on 21-22 April (figure 324). The lava lake was below the rim again the next morning but spilled out several times over the next several days to the N, S, and SW. The flows, similar to those produced during the last significant overflow event in April-May 2015, consisted of lobate sheets of shelly pahoehoe traveling as far as 375 m across the floor of Halema'uma'u. A small overflow had also occurred in October 2016.

Figure 324. The rising summit lava lake levels first peaked overnight on 21-22 April 2018, producing small overflows onto the floor of Halema'uma'u Crater at Kilauea. The largest overflow, on the N side of the Overlook vent (shown here), reached about 80 m from the lake margin. Image taken on 22 April 2018, courtesy of HVO.

The summit lava lake spilled out of the Overlook crater rim multiple times during 22-27 April, caused by repeated inflation-deflation cycles (figures 325-327). Between overflows, the lava column receded below the crater rim. An overflight during the afternoon of 23 April showed that the overflows covered about 30% of the Halema'uma'u crater floor, approximately 16 ha. The height of the lava lake, on the floor of Halema'uma'u crater, was 79 m below the rim of the crater on 25 April. HVO estimated that only about one quarter of the floor of the crater remained uncovered by new flows as of 26 April. Summit tiltmeters continued to record an overall inflationary trend with brief periods of deflation until turning to more sustained deflation around midnight overnight on 26-27 April. A magnitude 3.2 earthquake occurred around 1308 HST on 26 April but did not cause any eruptive changes. Seismometers recorded a few small earthquakes in the upper East Rift Zone and south part of the caldera during 25-29 April.

Figure 325. On 24 April 2018 between around 2030 and 2300, Kilauea's summit lava lake overflowed again. The large overflow spread W (to the right) from the lava lake onto the floor of Halema'uma'u around 2230 in this image. The bright (yellow-white) spot is spattering along the S margin of the lava lake. USGS photo by M. Patrick, courtesy of HVO.

Figure 326. Beginning at approximately 0615 on 26 April 2018 a new overflow began covering about 36 hectares (90 acres) of Kilauea's Halema'uma'u crater floor with lava, continuing for about four hours and covering about two-thirds of crater floor. This was the largest overflow since the summit eruption began in 2008. In this view to the S taken later in the day, the gas plume was being produced by the lava lake in the SE crater floor (upper left). Courtesy of HVO.

Figure 327. This thermal image (looking S) taken on 26 April 2018 at Kilauea shows the active overflows from the lava lake (upper left) onto the Halema'uma'u crater floor. View is toward the south. Courtesy of HVO.

The summit lake level dropped 16 m during 27-28 April, ending the period of inflation that produced the overflows onto the crater floor. The lake level remained about 15 m below the floor when skies cleared on 30 April and permitted a view from the webcam (figure 328). Slight inflation returned later in the day and the lake level rose to just beneath the vent rim.

Figure 328. A break in the weather on the morning of 30 April 2018 allowed HVO's webcam to capture this image of the lava lake within Halema'uma'u at the summit of Kilauea. Following multiple overflows of the lava lake the previous week, the lake level dropped after summit deflation. Early that morning, the lava lake level was estimated to be about 15 m below the vent rim, but shortly thereafter, the summit switched to inflation, and the lake level rose to just below the vent rim. Courtesy of HVO.

HVO released a Volcanic Activity Notice, in addition to their regular daily report, midday on 17 April 2018. They noted that observations and measurements at Pu'u 'O'o during the previous month suggested that the magma system had become increasingly pressurized, raising the possibility that a new vent could form at any time, either on the Pu'u 'O'o cone or along adjacent areas. Since mid-March there had been uplift of the Pu'u 'O'o crater floor by several meters. Similar episodes of inflation and uplift at Pu'u 'O'o occurred in May-June 2014, prior to the start of the June 27th flow (active 2014-2016) and May 2016 before the start of the ongoing episode 61g flow.

When measured during a site visit on 18 April the pond level in the west pit at Pu'u 'O'o was 7 m higher than it had been in late March as a result of lava overflows building up the surrounding levee. An overflight on 23 April showed the perched lava pond with overflows slowly filling the pit (figure 329), and significant cracks on the NE part of the crater rim (figure 330). The pond had another overflow that remained in the pit on 24 April, and the floor continued to rise. Inflationary tilt continued at Pu'u 'O'o until it leveled off around midnight during 26-27 April, but the crater floor continued to rise for the next four days.

Figure 329. On the East Rift Zone of Kilauea, the perched lava pond in Pu'u 'O'o's west pit persisted during the second half of April, seen here on 23 April 2018. Overflows of the pond levees were slowly filling the bottom of the west pit and raising the floor. Courtesy of HVO.

Figure 330. Ongoing uplift of the crater floor of Pu'u 'O'o at Kilauea beginning in mid-March 2018 generated numerous cracks on the crater floor and around the rim. These cracks cut through both recent lava flows (darker color) and older flows on the crater floor. Image taken on 23 April 2018, courtesy of HVO.

Just after 1400 on 30 April 2018, a marked increase in seismicity and ground deformation began at Pu'u 'O'o. A few minutes later, a thermal webcam (PTcam) located on the crater rim showed the first of two episodes of floor collapse; the second collapse began at 1520 and lasted about an hour. Webcam views into the crater and surrounding area were frequently obscured by poor weather conditions. However, shortly after 1600 the PTcam recorded images that were likely the signature of small explosions from the western side of the crater as the floor collapsed.

Following the collapse there was an increase in seismicity and deformation from the summit to an area about 10-16 km downrift (east) of Pu'u 'O'o. Overnight, this activity continued to propagate eastward along the rift zone. The largest earthquake of this sequence was a magnitude 4.0 just offshore south of Pu'u 'O'o at 0239 on the morning of 1 May. HVO field crews were turned back the next morning by ash in the air above Pu'u 'O'o, likely due to continuing collapse within the crater and vigorous gas emissions. Reddish ash was also noted in abundance on the ground around Pu'u 'O'o.

Lava flow activity in the episode 61g flow continued on the upper flow field through the end of April 2018. Activity was focused above the pali and closer to Pu'u 'O'o, within 2 km of the vent. After the explosion and collapse of the crater floor at Pu'u 'O'o on 30 April, a large amount of red ash was deposited around the cone and covered over some of the active breakouts of the 61g flow (figure 331).

Figure 331. The collapse of the Pu'u 'O'o crater floor at Kilauea on 30 April 2018 produced a large amount of red ash that was deposited around Pu'u 'O'o, as well as blown farther downwind, with a thin dusting of ash reaching uprift (west) as far as Mauna Ulu. On 1 May 2018, a layer of red ash covered active 61g lava flow surface breakouts in an area between 1-2 km from the 61g vent. Courtesy of HVO.

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

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: http://hvo.wr.usgs.gov/).

Three volcanoes in the Kirishimayama volcanic complex experienced heightened activity during late 2017 and early 2018. There were explosions at Shinmoedake during September-October 2017 and March-May 2018, an explosion at Iwo-yama in April 2018, and heightened seismicity at Ohachi in February 2018 (BGVN 43:06). Activity weakened afterwards, and by the beginning of July the three volcanoes were relatively quiet except for some fumarolic activity and seismic activity. This report documents activity between June and November 2018. Most of the information was provided in Japan Meteorological Agency (JMA) monthly reports.

Activity at Shinmoedake during June 2018. JMA reported that an explosion at 0909 on 22 June generated an ash plume that rose 2.6 km above the crater rim and drifted E. Tephra was ejected 1.1 km away, and shock waves were felt in the Miyazaki region. Minor amounts of ash fell in Kirishima prefecture and Kagoshima prefecture to the S, Miyakonojo city (Miyazaki prefecture) to the E, and Takahara Town. Another explosion at 1534 on 27 June generated a plume that rose 2.2 km above the crater rim.

According to JMA, since the beginning of May the rate of deformation had slowed, and tiltmeter data showed no change. In addition, sulfur dioxide emissions had decreased from 1,000 tons/day on mid-March to 80 tons/day on 1 June. Based on the data, JMA believed the magma supply had declined, decreasing the possibility of an eruption affecting an area outside a radius of 2 km. Thus, on 28 June, JMA lowered the Alert Level from 3 to 2.

Activity at Iwo-yama during June-July 2018. Activity weakened in May, and no volcanic explosions occurred after 27 April. However, active fumarolic activity and ejection of mud continued through November from the vent on the S side. During 23-30 July, white plumes rose 300-500 m above the vent. Also on the S side, the hot lake, which was muddy in May, became transparent in June, but was cloudy again in July. Fumarolic activity also occurred at a vent 500 W of the crater.

Volcanic earthquakes slightly increased in late May. According to measurements by the Global Navigation Satellite System (GNSS), the volcano, which had been contracting, began to expand slowly at the beginning of June. The Alert Level remained at 2.

Geologic Background. Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located Karakunidake being the highest. Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html).

After a major eruption on 26 October 2010 that subsided in early December of that year, Merapi erupted regularly amid elevated seismicity between 13 June 2011 and April 2014; seismicity returned to normal levels in May 2014 (BGVN 39:10). Renewed activity in the form of phreatic explosions took place during May-June 2018.

Lahar in October 2016. According to the Badan Nasional Penanggulangan Bencana (BNPB) (National Disaster Management Agency), a lahar on 27 October 2016 induced by moderate to heavy rain swept nine sand mining trucks down the Bebeng River on the SW flank; at least one truck was buried and six were severely damaged. There were no fatalities as the miners and other people at the scene escaped. Material at the summit and on the flanks produced during the October-November 2010 eruption was an estimated 20-25 million cubic meters, contributing to the continuing high potential of lahars during heavy rain. BNPB recommended that the public remain vigilant during rainy weather because a lahar formed on the upper flanks of Merapi can reach the bottom in less than 30 minutes. The Alert Level remained at 1 (on a scale of 1-4).

Phreatic explosions during May-June 2018. The volcano was apparently quiet between November 2016 and April 2018. According to the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), an explosion occurred at 0740 on 11 May 2018. The eruption began with a small roar and vibrations that were felt at the observation post for 10 minutes. A plume rose to 5.5 km above the summit. There was no seismic precursor and no subsequent seismic activity. According to a news account (The Jakarta Post) on 11 May, the increased activity caused Yogyakarta's Adisutjipto International Airport (27 km S) to close, resulting in the cancellation of eight Garuda Indonesia flights. PVMBG did not increase the alert level from Green/Normal; they interpreted the explosion as being a minor event triggered by the accumulation of volcanic gases, and unlikely to result in subsequent explosions. High levels of sulfur dioxide in the vicinity of the volcano were detected by the satellite-based Ozone Monitoring Instrument (OMI) on 11 May; concentrations reached as high as 2.0 Dobson Units.

On 21 May a phreatic explosion began at 0125 and lasted for 19 minutes, generating an ash plume that rose 700 m above the crater and drifted W. At 0938, another phreatic explosion began that lasted six minutes and produced an ash plume that rose 1.2 km above the crater. Ashfall from both events was reported in areas 15 km downwind. A third event, detected at 1750, lasted three minutes and produced a plume of unknown height. After these events, one volcano-tectonic (VT) earthquake and one tremor event were recorded. The seismicity along with increased phreatic events prompted PVMBG to raise the Alert Level to 2.

According to PVMBG, on 23 May, at 1349 the Babadan observation post heard a two-minute-long phreatic explosion. A plume was not visible due to inclement weather, though minor ashfall was reported at the Ngepos observation post. On 24 May an event at 0256 generated an ash plume that rose 6 km above the crater rim and drifted W. Roaring was heard at all the Merapi observation posts. A two-minute-long event at 1048 produced an ash plume that rose 1.5 km and drifted W. PVMBG recommended the evacuation of everyone within 3 km of the summit.

PVMBG reported that on 1 June, at 0820, an event generated an ash plume that rose at least 6 km above the crater rim and drifted NW, then SW (figure 68). Ashfall was reported at the Selo observation post. Observers noted white smoke rising from a forested area 1.5 km NW, possibly indicating burning vegetation. PVMBG indicated that VT events were occurring at about 3 km below the crater. Later that day at 2024, an ash plume from a 1.5-minute-long event rose 2.5 km above the crater rim and drifted NE and W. At 2100, an ash plume rose 1 km and drifted NW. The Alert Level remained at 2.

Figure 68. Photo of an explosion at Merapi on 1 June 2018. Courtesy of Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); The Jakarta Post (URL: http://www.thejakartapost.com/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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