Sangeang Api is located in the eastern Sunda-Banda Arc in Indonesia, forming a small island in the Flores Strait, north of the eastern side of West Nusa Tenggara. It has been frequently active in recent times with documented eruptions spanning back to 1512. The edifice has two peaks – the active Doro Api cone and the inactive Doro Mantori within an older caldera (figure 37). The current activity is focused at the summit of the cone within a horseshoe-shaped crater at the summit of Doro Api. This bulletin summarizes activity during May 2019 through January 2020 and is based on Darwin Volcanic Ash Advisory Center (VAAC) reports, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, or CVGHM) MAGMA Indonesia Volcano Observatory Notice for Aviation (VONA) reports, and various satellite data.

Figure 37. A PlanetScope satellite image of Sangeang Api with the active Doro Api and the inactive Doro Mantori cones indicated, and the channel SE of the active area that contains recent lava flows and other deposits. December 2019 monthly mosaic copyright of Planet Labs 2019.

Thermal anomalies were visible in Sentinel-2 satellite thermal images on 4 and 5 May with some ash and gas emission visible; bright pixels from the summit of the active cone extended to the SE towards the end of the month, indicating an active lava flow (figure 38). Multiple small emissions with increasing ash content reached 1.2-2.1 km altitude on 17 June. The emissions drifted W and WNW, and a thermal anomaly was also visible. On the 27th ash plumes rose to 2.1 km and drifted NW and the thermal anomaly persisted. One ash plume reached 2.4 km and drifted NW on the 29th, and steam emissions were ongoing. Satellite images showed two active lava flows in June, an upper and a lower flow, with several lobes descending the same channel and with lateral levees visible in satellite imagery (figure 39). The lava extrusion appeared to have ceased by late June with lower temperatures detected in Sentinel-2 thermal data.

Figure 38. Sentinel-2 satellite thermal images of Sangeang Api on 20 May and 9 June 2019 show an active lava flow from the summit, traveling to the SE. False color (urban) image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 39. PlanetScope satellite images of Sangeang Api show new lava flows during June and July, with white arrows indicating the flow fronts. Copyright Planet Labs 2019.

During 4-5 July the Darwin VAAC reported ash plumes reaching 2.1-2.3 km altitude and drifting SW and W. Activity continued during 6-9 July with plumes up to 4.6 km drifting N, NW, and SW. Thermal anomalies were noted on the 4th and 8th. Plumes rose to 2.1-3 km during 10-16th, and to a maximum altitude of 4.6 km during 17-18 and 20-22. Similar activity was reported during 24-30 July with plumes reaching 2.4-3 km and dispersing NW, W, and SW. The upper lava flow had increased in length since 15 June (see figure 39).

During 31 July through 3 September ash plumes continued to reach 2.4-3 km altitude and disperse in multiple directions. Similar activity was reported throughout September. Thermal anomalies also persisted through July-September, with evidence of hot avalanches in Sentinel-2 thermal satellite imagery on 23 August, and 9, 12, 22, and 27 September. Thermal anomalies suggested hot avalanches or lava flows during October (figure 40). During 26-28 October short-lived ash plumes were reported to 2.1-2.7 km above sea level and dissipated to the NW, WNW, and W. Short-lived explosions produced ash plumes up to 2.7-3.5 km altitude were noted during 30-31 October and 3-4 November 2019.

Figure 40. Sentinel-2 satellite thermal images of Sangeang Api on 7 and 22 October 2019 show an area of elevated temperatures trending from the summit of the active cone down the SE flank. False color (urban) image rendering (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Discrete explosions produced ash plumes up to 2.7-3.5 km altitude during 3-4 November, and during the 6-12th the Darwin VAAC reported short-lived ash emissions reaching 3 km altitude. Thermal anomalies were visible in satellite images during 6-8 November. A VONA was released on 14 November for an ash plume that reached about 2 km altitude and dispersed to the west. During 14-19 November the Darwin VAAC reported short-lived ash plumes reaching 2.4 km that drifted NW and W. Additional ash plumes were observed reaching a maximum altitude of 2.4 km during 20-26 November. Thermal anomalies were detected during the 18-19th, and on the 27th.

Ash plumes were recorded reaching 2.4 km during 4-5, 7-9, 11-13, and 17-19 December, and up to 3 km during 25-28 December. There were no reports of activity in early to mid-January 2020 until the Darwin VAAC reported ash reaching 3 km on 23 January. A webcam image on 15 January showed a gas plume originating from the summit. Several fires were visible on the flanks during May 2019 through January 2020, and this is seen in the MIROVA log thermal plot with the thermal anomalies greater than 5 km away from the crater (figure 41).

Figure 41. MIROVA log plot of radiative power indicates the persistent activity at Sangeang Api during April 2019 through March 2020. There was a slight decline in September-October 2019 and again in February 2020. Courtesy of MIROVA.

Geologic Background. Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, Doro Api and Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent historical eruptions have been recorded since 1512, most of them during in the 20th century.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/).

Shishaldin is located near the center of Unimak Island in Alaska and has been frequently active in recent times. Activity includes steam plumes, ash plumes, lava flows, lava fountaining, pyroclastic flows, and lahars. The current eruption phase began on 23 July 2019 and through September included lava fountaining, explosions, and a lava lake in the summit crater. Continuing activity during October 2019 through January 2020 is described in this report based largely on Alaska Volcano Observatory (AVO) reports, photographs, and satellite data.

Minor steam emissions were observed on 30 September 2019, but no activity was observed through the following week. Activity at that time was slightly above background levels with the Volcano Alert Level at Advisory and the Aviation Color Code at Yellow (figure 17). In the first few days of October weak tremor continued but no eruptive activity was observed. Weakly elevated temperatures were noted in clear satellite images during 4-9 October and weak tremor continued. Elevated temperatures were recorded again on the 14th with low-level tremor.

Figure 17. Alaska Volcano Observatory hazard status definitions for Aviation Color Codes and Volcanic Activity Alert Levels used for Shishaldin and other volcanoes in Alaska. Courtesy of AVO.

New lava extrusion was observed on 13 October, prompting AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch. Elevated surface temperatures were detected by satellite during the 13th and 17-20th, and a steam plume was observed on the 19th. A change from small explosions to continuous tremor that morning suggested a change in eruptive behavior. Low-level Strombolian activity was observed during 21-22 October, accompanied by a persistent steam plume. Lava had filled the crater by the 23rd and began to overflow at two places. One lava flow to the north reached a distance of 200 m on the 24th and melted snow to form a 2.9-km-long lahar down the N flank. The second smaller lava flow resulted in a 1-km-long lahar down the NE flank. Additional snowmelt was produced by spatter accumulating around the crater rim. By 25 October the northern flow reached 800 m, there was minor explosive activity with periodic lava fountaining, and lahar deposits reached 3 km to the NW with shorter lahars to the N and E (figure 18). Trace amounts of ashfall extended at least 8.5 km SE. There was a pause in activity on the 29th, but beginning at 1839 on the 31st seismic and infrasound monitoring detected multiple small explosions.

Figure 18. PlanetScope satellite images of Shishaldin on 3 and 29 October 2019 show the summit crater and N flank before and after emplacement of lava flows, lahars, and ashfall. Copyright PlanetLabs 2019.

Elevated activity continued through November with multiple lava flows on the northern flanks (figure 19). By 1 November the two lava flows had stalled after extending 1.8 km down the NW flank. Lahars had reached at least 4 km NW and trace amounts of ash were deposited on the north flank. Elevated seismicity on 2 November indicated that lava was likely flowing beyond the summit crater, supported by a local pilot observation. The next day an active lava flow moved 400 m down the NW flank while a smaller flow was active SE of the summit. Minor explosive activity and/or lava fountaining at the summit was indicated by incandescence during the night. Small explosions were recorded in seismic and infrasound data. On 5 November the longer lava flow had developed two lobes, reaching 1 km in length. The lahars had also increased in length, reaching 2 km on the N and S flanks. Incandescence continued and hot spatter was accumulating around the summit vent. Activity continued, other than a 10-hour pause on 4-5 November, and another pause on the 7th. The lava flow length had reached 1.3 km on the 8th and lahar deposits reached 5 km.

Figure 19. Sentinel-2 thermal satellite images show multiple lava flows (orange) on the upper northern flanks of Shishaldin between 1 November and 1 December 2019. Blue is snow and ice in these images, and partial cloud cover is visible in all of them. Sentinel-2 Urban rendering (bands 21, 11, 4) courtesy of Sentinel Hub Playground.

After variable levels of activity for a few days, there was a significant increase on 10-11 November with lava fountaining through the evening and night. This was accompanied by minor to moderate ash emissions up to around 3.7 km altitude and drifting northwards, and a significant increase in seismicity. Activity decreased again during the 11-12th while minor steam and ash emissions continued. On 14 November minor ash plumes were visible on the flanks, likely caused by the collapse of accumulated spatter. By 15 November a large network of debris flows consisting of snowmelt and fresh deposits extended 5.5 km NE and the collapse of spatter mounds continued. Ashfall from ash plumes reaching as high as 3.7 km altitude produced thin deposits to the NE, S, and SE. Activity paused during the 17-18th and resumed again on the 19th; intermittent clear views showed either a lava flow or lahar descending the SE flank. Activity sharply declined at 0340 on the 20th.

Seismicity began increasing again on 24 November and small explosions were detected on the 23rd. A small collapse of spatter that had accumulated at the summit occurred at 2330 on the 24th, producing a pyroclastic flow that reached 3 km in length down the NW flank. A new lava flow had also reached several hundred meters down the same flank. Variable but elevated activity continued over 27 November into early December, with a 1.5-km-long lava flow observed in satellite imagery acquired on the 1st. On 5 December minor steam or ash emissions were observed at the summit and on the north flank, and Strombolian explosions were detected. Activity from that day produced fresh ash deposits on the northern side of the volcano and a new lava flow extended 1.4 km down the NW flank. Three small explosions were detected on the 11th.

At 0710 on 12 December a 3-minute-long explosion produced an ash plume up to 6-7.6 km altitude that dispersed predominantly towards the W to NW and three lightning strokes were detected. Ash samples were collected on the SE flank by AVO field crews on 20 December and analysis showed variable crystal contents in a glassy matrix (figure 20). A new ash deposit was emplaced out to 10 km SE, and a 3.5-km-long pyroclastic flow had been emplaced to the north, containing blocks as large as 3 m in diameter. The pyroclastic flow was likely a result from collapse of the summit spatter cone and lava flows. A new narrow lava flow had reached 3 km to the NW and lahars continued out to the northern coast of Unimak island (figure 21). The incandescent lava flow was visible from Cold Bay on the evening of the 12th and a thick steam plume continued through the next day.

Figure 20. An example of a volcanic ash grain that was erupted at Shishaldin on 12 December 2019 and collected on the SE flank by the Alaska Volcano Observatory staff. This Scanning Electron Microscope images shows the different crystals represented by different colors: dark gray crystals are plagioclase, the light gray crystals are olivine, and the white ones are Fe-Ti oxides. The groundmass in this grain is nearly completely crystallized. Courtesy of AVO.

Figure 21. A WorldView-2 satellite image of Shishaldin with the summit vent and eruption deposits on 12 December 2019. The tephra deposit extends around 10 km SE, a new lava flow reaching 3 km NW with lahars continuing to the N coast of Unimak island. Pyroclastic flow deposits reach 3.5 km to the N and contain blocks as large as 3 m. Courtesy of Hannah Dietterich, AVO.

A new lava flow was reported by a pilot on the night of 16 December. Thermal satellite data showed that this flow reached 2 km to the NW. High-resolution radar satellite images over the 15-17th showed that the lava flow had advanced out to 2.5 km and had developed levees along the margins (figure 22). The lava channel was 5-15 m wide and was originating from a crater at the base of the summit scoria cone, which had been rebuilt since the collapse the previous week. Minor ash emissions drifted to the south on the 19tt and 20th (figure 23).

Figure 22. TerraSAR-X radar satellite images of Shishaldin on 15 and 17 December 2019 show the new lava flow on the NW flank and growth of a scoria cone at the summit. The lava flow had reached around 2.5 km at this point and was 5-15 m wide with levees visible along the flow margins. Pyroclastic flow deposits from a scoria cone collapse event on 12 December are on the N flank. Figure courtesy of Simon Plank (German Aerospace Center, DLR) and Hannah Dietterich (AVO).

Figure 23. Geologist Janet Schaefer (AVO/DGGS) collects ash samples within ice and snow on the southern flanks of Shishaldin on 20 December 2019. A weak ash plume is rising from the summit crater. Photo courtesy of Wyatt Mayo, AVO.

On 21 December a new lava flow commenced, traveling down the northern slope and accompanied by minor ash emissions. Continued lava extrusion was indicated by thermal data on the 25th and two lava flows reaching 1.5 km and 100 m were observed in satellite data on the 26th, as well as ash deposits on the upper flanks (figure 24). Weak explosions were detected by the regional infrasound network the following day. A satellite image acquired on the 30th showed a thick steam plume obscuring the summit and snow cover on the flanks indicating a pause in ash emissions.

Figure 24. This 26 December 2019 WorldView-2 satellite image with a close-up of the Shishaldin summit area to the right shows a lava flow extending nearly 1.5 km down the NW flank and a smaller 100-m-long lava flow to the NE. Volcanic ash was deposited around the summit, coating snow and ice. Courtesy of Matt Loewen, AVO.

In early January satellite data indicated slow lava extrusion or cooling lava flows (or both) near the summit. On the morning of the 3rd an ash plume rose to 6-7 km altitude and drifted 120 km E to SE, producing minor amounts of volcanic lightning. Elevated surface temperatures the previous week indicated continued lava extrusion. A satellite image acquired on 3 January showed lava flows extending to 1.6 km NW, pyroclastic flows moving 2.6 km down the western and southern flanks, and ashfall on the flanks (figure 25).

Figure 25. This WorldView-2 multispectral satellite image of Shishaldin, acquired on 3 January 2019, shows the lava flows reaching 1.6 km down the NW flank and an ash plume erupting from the summit dispersing to the SE. Ash deposits cover snow on the flanks. Courtesy of Hannah Dietterich, AVO.

On 7 January the most sustained explosive episode for this eruption period occurred. An ash plume rose to 7 km altitude at 0500 and drifted east to northeast then intensified reaching 7.6 km altitude with increased ash content, prompting an increase of the Aviation Color Code to Red and Volcano Alert Level to Warning. The plume traveled over 200 km to the E to NE (figure 26). Lava flows were produced on the northern flanks and trace amounts of ashfall was reported in communities to the NE, resulting in several flight cancellations. Thermal satellite images showed active lava flows extruding from the summit vent (figure 27). Seismicity significantly decreased around 1200 and the alert levels were lowered to Orange and Watch that evening. Through the following week no notable eruptive activity occurred. An intermittent steam plume was observed in webcam views.

Figure 26. This Landsat 8 satellite image shows a detached ash plume drifts to the NE from an explosive eruption at Shishaldin on 7 January 2020. Courtesy of Chris Waythomas, AVO.

Figure 27. This 7 January 2019 Sentinel-2 thermal satellite image shows several lava flows on the NE and NW flanks of Shishaldin, as well as a steam plume from the summit dispersing to the NE. Blue is snow and ice in this false color image (bands 12, 11, 4). Courtesy of Sentinel-Hub playground.

Eruptive activity resumed on 18 January with lava flows traveling 2 km down the NE flank accompanied by a weak plume with possible ash content dispersing to the SW (figure 28). A steam plume was produced at the front of the lava flow and lahar deposits continued to the north (figures 29 to 32). Activity intensified from 0030 on the 19th, generating a more ash-rich plume that extended over 150 km E and SE and reached up to 6 km altitude; activity increased again at around 1500 with ash emissions reaching 9 km altitude. AVO increased the alert levels to Red/Warning. Lava flows traveled down the NE and N flanks producing meltwater lahars, accompanied by elevated seismicity (figures 33). Activity continued through the day and trace amounts of ashfall were reported in False Pass (figure 34). Activity declined to small explosions over the next few days and the alert levels were lowered to Orange/watch shortly after midnight. The next morning weak steam emissions were observed at the summit and there was a thin ash deposit across the entire area. Satellite data acquired on 23 January showed pyroclastic flow deposits and cooling lava flows on the northern flank, and meltwater reaching the northern coast (figure 35).

Figure 28. This Worldview-3 multispectral near-infrared satellite image acquired on 18 January 2020 shows a lava flow down the NE flank of Shishaldin. A steam plume rises from the end of the flow and lahar deposits from snowmelt travel further north. Courtesy of Matt Loewen, AVO.

Figure 29. Steam plumes from the summit of Shishaldin and from the lava flow down the NE flank on 18 January 2020. Lahar deposits extend from the lava flow front and towards the north. Photo courtesy of Matt Brekke, via AVO.

Figure 30. A lava flow traveling down the NE flank of Shishaldin on 18 January 2020, seen from Cold Bay. Photo courtesy of Aaron Merculief, via AVO.

Figure 31. Two plumes rise from Shishaldin on 18 January 2020, one from the summit crater and the other from the lava flow descending the NE Flank. Photos courtesy of Woodsen Saunders, via AVO.

Figure 32. A low-altitude plume from Shishaldin on the evening of 18 January 2020, seen from King Cove. Photo courtesy of Savannah Yatchmeneff, via AVO.

Figure 33. This WorldView-2 near-infrared satellite image shows a lava flow reaching 1.8 km down the N flank and lahar deposits filling drainages out to the Bering Sea coast (not shown here) on 19 January 2020. Ash deposits coat snow to the NE and E. Courtesy of Matt Loewen, AVO.

Figure 34. An ash plume (top) and gas-and-steam plumes (bottom) at Shishaldin on 19 January 2020. Courtesy of Matt Brekke, via AVO.

Figure 35. A Landsat 8 thermal satellite image (band 11) acquired on 23 January 2019 showing hot lava flows and pyroclastic flow deposits on the flanks of Shishaldin and the meltwater flow path to the Bering Sea. Figure courtesy of Christ Waythomas, AVO.

Activity remained low in late January with some ash resuspension (due to winds) near the summit and continued elevated temperatures. Seismicity remained above background levels. Infrasound data indicated minor explosive activity during 22-23 January and small steam plumes were visible on 22, 23, and 26 January. MIROVA thermal data showed the rapid reduction in activity following activity in late-January (figure 36).

Figure 36. MIROVA thermal data showing increased activity at Shishaldin during August-September, and an even higher thermal output during late-October 2019 to late January 2020. Courtesy of MIROVA.

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

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/); Simon Plank, German Aerospace Center (DLR) German Remote Sensing Data Center, Geo-Risks and Civil Security, Oberpfaffenhofen, 82234 Weßling (URL: https://www.dlr.de/eoc/en/desktopdefault.aspx/tabid-5242/8788_read-28554/sortby-lastname/); 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/); Planet Labs, Inc. (URL: https://www.planet.com/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Nevados de Chillán is a complex of late-Pleistocene to Holocene stratovolcanoes in the Chilean Central Andes. An eruption started with a phreatic explosion and ash emission on 8 January 2016 from a new crater (Nicanor) on the E flank of the Nuevo crater, which lies on the NW flank of the cone of the large stratovolcano referred to as Volcán Viejo. Strombolian explosions and ash emissions continued throughout 2016 and 2017; a lava dome within the Nicanor crater was confirmed in early January 2018. Explosions and pyroclastic flows continued during 2018 and the first half of 2019. This report covers continuing activity from June-December 2019 when ongoing explosive events produced ash plumes, lava, and pyroclastic flows. Information for this report is provided primarily by Chile's Servicio Nacional de Geología y Minería (SERNAGEOMIN)-Observatorio Volcanológico de Los Andes del Sur (OVDAS), and by the Buenos Aires Volcanic Ash Advisory Center (VAAC).

Nevados de Chillán was relatively quiet during June 2019, generating only a small number of explosions with ash plumes. This activity continued during July; some events produced incandescent ejecta around the crater. By August a distinct increase in activity was noticeable; ash plumes were larger and more frequent, and incandescent ejecta rose hundreds of meters above the summit a number of times. Frequent explosions were typical during September; the first of several blocky lava flows emerged from the crater mid-month. Inflation that began in mid-July continued with several centimeters of both horizontal and vertical displacement. By October, pyroclastic flows often accompanied the explosive events in addition to the ash plumes, and multiple vents opened within the crater. Three more lava flows had appeared by mid-November; explosions continued at a high rate. Activity remained high at the beginning of December but dropped abruptly mid-month. MODVOLC measured three thermal alerts in September, two in October, seven in November, and six in December. This period of increased thermal activity closely matches the thermal anomaly data reported by the MIROVA project (figure 37), which included an increase at the end of August 2019 that lasted through mid-December before stopping abruptly. Several lava flows and frequent explosions with incandescent ejecta and pyroclastic flows were reported throughout the period of increased thermal activity.

Figure 37. MIROVA thermal anomaly data for Nevados de Chillán from 3 February through December 2019 show low activity during June-August and increasing activity from August through mid-December. This correlates with ground and satellite observations of lava flows, incandescent explosions, ash plumes, and pyroclastic flows during the period of increased thermal activity. Courtesy of MIROVA.

Activity during June-August 2019. Nevados de Chillán remained relatively quiet during June 2019 with a few explosions of ash. At the active Nicanor crater, located on the E flank of the Volcán Nuevo dome, predominantly white steam plumes were observed daily in the nearby webcams. The growth rate of the dome inside the crater was reported by SERNAGEOMIN as continuing at about 260 m³/day. They noted an explosion on 3 June; the Buenos Aires VAAC reported a puff of ash seen from the webcam drifting SE at 3.7 km altitude (figure 38). The webcam indicated sporadic weak emissions continuing that day and the next. Minor explosions were also reported on 7-8 June and included incandescence observed at night and ejecta deposited around the crater rim. The Buenos Aires VAAC reported a narrow ash plume drifting ENE in multispectral imagery under clear skies late on 7 June. The webcams showed sporadic emissions of ash at 3.4 km altitude on 19 June that dissipated rapidly.

Figure 38. Explosions at Nevados de Chillán on 3 (left) and 20 (right) June 2019 produced ash plumes that quickly dissipated in the strong winds. Courtesy of the SERNAGEOMIN Portezuelo webcam, Pehuenia Online (left) and Eco Bio Bio La Red Informativa (right).

Minor pulsating explosive activity continued during July 2019 with multiple occurrences of ash emissions. Ash emissions rose to 3.7 km altitude on 4 July and were seen in the SERNAGEOMIN webcam; the VAAC reported an emission on 8 July that rose to 4.3 km altitude and drifted SE. Monitoring stations near the complex recorded an explosive event early on 9 July; incandescence with gases and ejecta were deposited around the crater and an ash plume rose to 3.9 km and drifted SE. Small ash plumes from sporadic puffs on 12 July rose to 4.6 km altitude. An explosive event on 14 July also produced incandescent ejecta around the crater along with weak sporadic ash emissions. Single ash emissions on 18 (figure 39) and 22 July at 3.7 km altitude drifted ESE from summit before dissipating; another emission on 26 July was reported at 4.3 km altitude.

Figure 39. Local news sources reported ash emissions at Nevados de Chillán on 18 July 2019. Courtesy of INF0SCHILE (left) and Radio Ñuble (right).

A distinct increase in the intensity and frequency of explosive activity was recorded during August 2019. SERNAGEOMIN noted ash emissions and explosions during 3-4 August in addition to the persistent steam plumes above the Nicanor crater (figure 40). The Buenos Aires VAAC reported a single puff on 3 August that was seen in the webcam rising to 3.9 km altitude and dissipating quickly. The next day a pilot reported an ash plume estimated at 5.5 km altitude drifting E. It was later detected in satellite imagery; the webcam revealed continuous emission of steam and gas with intermittent puffs of ash. SERNAGEOMIN issued a special report (REAV) on 6 August noting the increase in size and frequency of explosions, some of which produced dense ash plumes that rose 1.6 km above the crater along with incandescent ejecta. They also reported that satellite imagery indicated a 1.5-km-long lahar that traveled down the NNE flank as a result of the interaction of the explosive ejecta with the snowfall near the summit.

Figure 40. Climbers captured video of a significant explosion at Nevados de Chillán on 4 August 2019. Courtesy of CHV Noticias.

Beginning on 9-10 August 2019, and continuing throughout the month, SERNAGEOMIN observed explosive nighttime activity with incandescent ejecta scattered around the crater rim along with moderate levels of seismicity each day. A diffuse ash plume was detected in satellite imagery by the VAAC on 9 August drifting NW at 4.9 km altitude. SERNAGEOMIN issued a new warning on 12-13 August that the recent increase in activity since the end of July suggested the injection of a new magmatic body that could lead to larger explosive events with pyroclastic and lava flows. They reported pyroclastic ejecta from multiple explosions on 13 August rising 765 and 735 m above the crater. Drone images taken between 4 and 12 August showed the destruction of the summit dome from multiple explosions with the Nicanor Crater (figure 41). The VAAC reported sporadic pulses of volcanic ash drifting N during 12-14 August, visible in satellite imagery estimated at 4.3 km altitude. By 17-18 August, they noted constant steam emissions interspersed with gray plumes during explosive activity.

Figure 41. Drone images taken at Nevados de Chillán between 4 and 12 August 2019 showed destruction of the dome caused by multiple explosions at the summit crater. Courtesy of Movisis.org Internacional.

An increase in seismicity, especially VT events, during 21-22 August 2019 resulted in multiple special REAV reports from SERNAGEOMIN. They noted on 21 August that an explosion produced gas emissions and pyroclastic material that rose 1,400 m above the crater; the next day material rose 450 m. That night, in addition to incandescent ejecta around the crater, they reported small high-temperature flows on the N flank which extended to the NNE flank a few days later. The VAAC reported pulses of ash plumes moving SE on 22 August at 4.3 km altitude. A faint ash cloud was visible in satellite imagery on 29 August drifting E at 3.7 km altitude (figure 42). The cloud was dissipating rapidly as it moved away from the summit. Sporadic ash emissions from intermittent explosions continued moving ESE then N and NE; they were reported daily through 5 September. They continued to rise in altitude to 3.9 km on 30 August, 4.3 km on 1 September, and 4.6 km on 3 September.

Figure 42. Incandescence at the summit of Nevados de Chillán and ashfall covering snow to the E was captured in Sentinel-2 satellite imagery on 29 August 2019. Courtesy of Copernicus EMS.

Activity during September-October 2019. Frequent explosions from Nicanor crater continued during September 2019, producing numerous ash plumes and small high-temperature flows along the NNE flank. A webcam detected a small lateral vent on the NNE flank about 50 m from the crater rim emitting gas and particulates on 2-3 September. Multiple explosions during 3-5 September were associated with gas and ash emissions and incandescent ejecta deposited around the crater rim (figure 43). The network of GNSS stations recording deformation of the volcanic complex confirmed on 3-4 September that inflation, which had been recorded since mid-July 2019, was continuing at a rate of about 1 cm/month. Blocks of incandescent ejecta from numerous explosions were observed rolling down the N flank on 6-7 September and the E flank the following night.

Figure 43. Activity at Nevados de Chillán on 3 September 2019 included ash and steam explosions (left) and incandescent ejecta at the summit (right). Courtesy of Carlos Bustos and SERNAGEOMIN webcams.

SERNAGEOMIN reported on 9-10 September that satellite imagery revealed a new surface deposit about 130 m long trending NNE from the center of crater. They reported an increase in the level of seismicity from moderate to high on 10-11 September and observed incandescent ejecta at the summit during several explosions (figure 44). During a flyover on 12 September scientists confirmed the presence of a new blocky lava flow emerging from Nicanor Crater and moving down the NNE flank of Nuevo volcano. The flow was about 600 m long, 100 m wide, and 5 m thick with a blocky surface and incandescent lava at the base within the active crater. Measurements with a thermal camera indicated a temperature around 800°C within the active crater, and greater than 100°C on the surface of the flow. Frequent high-energy explosions that day produced incandescent ejecta that could be seen from Las Trancas and Shangri-La (figure 45). Ashfall 0.5 cm thick was reported 2 km from the volcano to the SW. The flow was visible from the webcam located N of Nicanor on 16-17 September. Satellite imagery indicated the flow was about 550 m long and moving at a rate of about 21 m/day.

Figure 44. A blocky lava flow moved down the NNE flank of Nevados de Chillán on 11 September (left); incandescent ejecta covered the summit area the next night (right). Courtesy of EarthQuakesTime (left), Red Geocientifica de Chile (right) and SERNAGEOMIN Webcams.

Figure 45. The SERNAGEOMIN Portezuelo webcam revealed the blocky lava flow, incandescent ejecta and ash emissions at Nevados de Chillán on 12 September 2019. Courtesy of American Earthquakes (left), PatoArias (right), and SERNAGEOMIN.

During 18-22 September 2019 multiple special reports of seismicity were released each day with incandescent ejecta, gas, and particulate emissions often observed at the summit crater; the lava flow remained active. On 24 September ashfall was reported about 15 km NW in communities including Las Trancas; small pyroclastic flows were observed the following day. Horizontal inflation of 2.4 cm was reported on 25 September, and vertical inflation was measured at 3.4 cm since mid-July. SERNAGEOMIN noted that while the frequency of explosions had increased, the energy released had decreased. Morphological changes in Nicanor crater suggested that it was growing at its SW edge and eroding the adjacent Arrau crater; the NE edge of the crater was unstable.

Plumes of steam and ash continued along with the explosions for the remainder of the month. During the night, incandescent ejecta was observed, and the low-velocity lava flow continued to move. Multiple VAAC reports were issued virtually every day of September. Pulses of ash were moving SE at 4.3 km altitude on 7-8 September. For most of the rest of the month sporadic emissions with minor amounts of ash were observed in either the webcam or satellite images at an altitude of 3.7 km, occasionally rising to 4.3 km. They drifted generally SE but varied somewhat with the changing winds. Continuous ash emissions were observed during 24-25 September that rose as high as 4.9 km altitude and drifted E, clearly visible in satellite imagery. After that, the altitude dropped back to 3.7 km and the plume was only faintly and intermittently visible in satellite imagery.

Low-altitude gray ash plumes were observed rising from Nicanor crater almost every day that weather permitted during October 2019. Incandescent ejecta was frequently observed at night. Beginning on 6-7 October, SERNAGEOM reported pyroclastic flows traveling short distances from the crater most days. They traveled 1.13 km down the NNE flank, 0.42 km down the NNW flank and 0.88 km down the SW flank. The blocky lava flow on the NNE flank was no longer active (figure 46). During 9-12 October, multiple special reports of increased seismic activity (REAVs) were issued each day. Inflation continued throughout the month. On 10 October the total horizontal deformation (since mid-July) was 3 cm, with a rate of movement a little over 1 cm/month; the total vertical displacement was 4.5 cm, with a rate of 1.93 cm/month during the previous 30 days.

In a special report issued on 11 October, SERNAGEOMIN mentioned that analysis of satellite imagery indicated a new emission center within the Nicanor crater adjacent to the dome vent active since December 2017 and to the lava flow of September. The new center was oval shaped with an E-W dimension of 60 m and a N-S dimension of 55 m, located about 90 m SE of the old, still active center, and was the site of the explosive activity reported since 30 September.

Figure 46. Drone footage posted 10 October 2019 from Nevados de Chillán shows steam emissions from the Nicanor crater and a blocky lava flow down NNE flank. The snow-covered cone in background is Volcan Baños. Courtesy of Volcanologia Chile and copyright by Nicolas Luengo V.

On 16 October a new blocky flow was observed on the NE flank of the Nicanor Crater; it was about 70 m long, moving about 30 m/day. By 21 October it had reached 130 m in length, and its rate of advance had slowed significantly. Beginning on 25 October seismicity decreased noticeably and much less surface activity was observed at the crater. Explosions at the end of the month produced steam plumes, gas emissions and minor pulsating ash emissions.

The Buenos Aires VAAC reported a puff of ash at 4.9 km altitude on 1 October moving SE. Continuous emission of steam and gas with sporadic puffs of ash that rose to around 3.7-4.3 km altitude were typical every day after that until 25 October usually drifting S or E; they were most often visible in the webcams, and occasionally visible in satellite imagery when weather conditions permitted. A diffuse plume of ash was detected on 16 October drifting SE at 4.6 km altitude. The VAAC reported incandescence visible at the summit in webcam images on 22 October; a significant daytime explosion on 24 October produced a large incandescent ash cloud (figure 47). The next day the VAAC detected weak pulses of ash plumes in satellite images extending E from the summit for 130 km. Intermittent ash emissions were reported drifting SE at 3.7-4.3 km each day from 29-31 October.

Figure 47. A large incandescent ash plume at Nevados de Chillán on 24 October 2019 sent ejecta around the summit (left); a dense ash plume was produced during an explosion on 30 October 2019 (right). Courtesy of Cristian Farian (left) and SERNAGEOMIN (right); both images taken from the SERNAGEOMIN webcams.

Activity during November-December 2019. Moderate seismicity continued during November 2019 with recurrent episodes of pulsating gas and ash emissions. Incandescent ejecta was visible many nights that the weather conditions were favorable (figure 48). In the Daily Report (RAV) issued on 6 November, SERNAGEOMIN noted that the original 700-m-long blocky lava flow on the NNE flank active during September had been partly covered by another flow, about 350 m long. They also reported that pyroclastic density currents were observed in the area immediately around the crater extending in several directions. They extended 850 m down the SW flank, 670 m down the NW flank, 1,680 m down the N flank, and 440 m to the NNE.

Changes in the crater area indicated a growth of the SW edge of the Nicanor Crater, continuing to erode the Arrau crater, with the constant emission of gas, ash, and incandescent ejecta that produced plumes up to 1.8 km high. SERNAGEOMIN also observed activity from a vent at the NE edge of the crater that included gas emission and ejecta, but no lava flow. The fourth lava flow observed in recent months (L4) was identified on the NNE slope on 13 November adjacent to the earlier flows; it was about 70 m long and slowly advancing. By 19 November L4 consisted of two lobes and extended about 90 m from the edge of the Nicanor crater advancing at an average rate of 0.4 m/hour. The vent producing L4 was located about 60 m SSE of the vent that produced the earlier flows (L1, L2, and L3). By 28 November the flow had reached a length of 165 m and was no longer advancing. A series of explosions reported on 25-27 and 30 November produced ejecta that rose 800, 1,000, 1,300, and 700 m above the crater.

Figure 48. Incandescent ejecta at Nevados de Chillán was clearly visible at night on 3 November 2019. Courtesy of Claudio Kanisius.

Ash emissions were reported by the Buenos Aires VAAC during most of November, usually visible from the webcams, but often also seen in satellite imagery. The plumes generally reached 3.7-4.6 km altitude and drifted SSE. They usually occurred as continuous emission of steam and gas accompanied by sporadic pulses of ash but were sometimes continuous ash for several hours. They were visible about 100 km E of the summit on 2 November, and over 200 km SE the following day. A narrow plume of ash was seen in visual satellite imagery extending 50 km E of the summit on 9 November. Intermittent incandescence at the summit was seen from the webcam on 18 November. Pulses of ash were detected in satellite imagery extending 125 km SE on 22 November. Strong puffs of ash briefly rose to 4.9 km altitude and drifted NE on 26 November (figure 49); incandescence during the nighttime was visible in the webcam on 28 November.

Figure 49. An explosion on 26 November 2019 at Nevados de Chillán produced a dense ash plume and small pyroclastic flows down the flank. Courtesy of Volcanes de Chile and the SERNAGEOMIN Portezuelo webcam.

Pulsating emissions of gas and ejecta continued into December 2019. Five explosions were reported on 1 December that produced gas plumes which rose 300-800 m above the crater. Three more explosions occurred on 3 December sending gas plumes 500-1,000 m high. SERNAGEOMIN reported on 4 December that explosive activity was observed from four vents within the Nicanor crater. This activity triggered new pyroclastic flows that extended 1,100 m E and 400 m S. By 5 December the total vertical inflation reported since July was 8 cm. A large explosion on 5 December sent material 1.6 km above the summit and pyroclastic flows down the flanks (figure 50). The webcams at Andarivel and Portezuelo showed a pyroclastic flow moving 400 m W, a direction not previously observed; this was followed by additional pyroclastic flows to the N and E.

Figure 50. A large explosion at Nevados de Chillán on 5 December 2019 produced an ash plume that rose 1.6 km above the summit and sent pyroclastic flows down the flanks. Courtesy of SERNAGEOMIN.

On 9 December SERNAGEOMIN noted that the increase to four active vents was causing erosion on the S and SE edges of the crater making the most affected areas to the SW, S, SE and E of the crater. Major explosions reported that day produced pyroclastic flows that descended down the E and ESE flanks and particulate emissions that rose 1 km. The SW flank near the crater was also affected by ejecta and pyroclastic debris carried by the wind. The most extensive pyroclastic flows travelled down the E flank for the next several days; explosions on 10 December sent material 1.2 km high. Three explosions were noted on 11 December; the first sent incandescence close to 200 m high, and the second produced a column of particulate material 1.2 km high. The first of two explosions on 12 December sent material 1.8 km above the crater and pyroclastic flows down the flanks (figure 51). Although explosions were reported on 13 and 14 December, cloudy skies prevented observations of the summit.

Figure 51. A large explosion at Nevados de Chillán on 12 December 2019 produced an ash plume that rose 1.8 km above the summit and sent pyroclastic flows down the flanks. Courtesy of Volcanes de Chile and SERNAGEOMIN.

Intermittent ash emissions were reported by the Buenos Aires VAAC during 1-13 December 2019. They rose to 3.7-4.3 km and drifted generally E. Pulses of ash were detected at 4.9 km altitude moving S in satellite imagery on 9 December. The last reported ash emission for December was on the afternoon of 12 December; puffs of ash could be seen in satellite imagery moving E at 4.6 km altitude. A decrease in particulate emissions and explosions was reported beginning on 14 December, and no further explosions were recorded by infrasound devices after 15 December. The deposits from the earlier pyroclastic flows had reached 600 m E and 300 m W of the crater. Seismic activity was recorded as low instead of moderate beginning on 25 December. A total horizontal inflation of about 6 cm since July was measured at the end of December.

Geologic Background. The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

Information Contacts: 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/), Twitter: @Sernageomin; 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/); Cristian Farias Vega, Departamento de Obras Civiles y Geología, Universidad Católica de Temuco, Vilcún, Región de La Araucanía, Chile (URL: https://twitter.com/cfariasvega/status/1187471827255226370); Copernicus Emergency Management Service (Copernicus EMS), Joint Research Centre, European Union (URL: https://emergency.copernicus.eu/, https://twitter.com/CopernicusEMS/status/1168156474817818624); Volcanes de Chile, Proyectos de la Fundación Volcanes de Chile, Chile (URL: https://www.volcanesdechile.net/, https://twitter.com/volcanesdechile/status/1199496839491395585); Pehuenia Online, Pehuenia, Argentina (URL: http://pehueniaonline.com.ar/, https://twitter.com/PehueniaOnline/status/1135703309824745472); Eco Bio Bio La Red Informativa, Bio Bio Region, Chile (URL: http://emergenciasbiobio.blogspot.com/, https://twitter.com/Eco_BioBio_II/status/1141734238590574593); INF0SCHILE (URL: https://twitter.com/INF0SCHILE/status/1151849611482599425); Radio Ñuble AM y FM, Chillán, Chile (URL: http://radionuble.cl/linea/, lhttps://twitter.com/RadioNuble/status/1151858189299781632); CHV Noticias, Santiago, Chile (URL: https://www.chvnoticias.cl/, https://twitter.com/CHVNoticias/status/1159263718015819777); Movisis.org Internacional, Manabi, Ecuador (URL: https://movisis.org/, https://twitter.com/MOVISISEC/status/1160778823031558144); Carlos Bustos (URL: https://twitter.com/cbusca1970/status/1168932243873644548); EarthQuakesTime (URL: https://twitter.com/EarthQuakesTime/status/1171654504841908229); Red Geocientifica de Chile (URL: https://twitter.com/RedGeoChile/status/1171972482875703296); American Earthquakes (URL: https://twitter.com/earthquakevt/status/1172271139760091136); PatoArias, Talca, Chile (URL: https://twitter.com/patoarias/status/1172287142191665153); Volcanologia Chile, (URL: http://www.volcanochile.com/joomla30/, https://twitter.com/volcanologiachl/status/1182707451554078720); Claudio Kanisius (URL: https://twitter.com/ClaudioKanisius/status/1191182878346031104).

The large Asosan caldera reaches around 23 km long in the N-S direction and contains a complex of 17 cones, of which Nakadake is the most active (figure 58). A recent increase in activity prompted an alert level increase from 1 to 2 on 14 April 2019. The Nakadake crater is the site of current activity (figure 59) and contains several smaller craters, with the No. 1 crater being the main source of activity during July-December 2019. The activity during this period is summarized here based on reports by the Japan Meteorological Agency and satellite data.

Figure 58. Asosan is a group of cones and craters within a larger caldera system. January 2010 Monthly Mosaic images copyright Planet Labs 2019.

Figure 59. Hot gas emissions from the Nakadake No. 1 crater on 25 June 2019 reached around 340°C. Courtesy of the Japan Meteorological Agency (July 2019 monthly report).

Small explosions were observed at the No. 1 vent on the 4, 5, 9, 13-16, and 26 July. There was an increase in thermal energy detected near the vent leading to a larger event on the 26th (figures 60 and 61), which produced an ash plume up to 1.6 km above the crater rim and continuing from 0757 to around 1300 with a lower plume height of 400 m after 0900. Light ashfall was reported downwind. Elevated activity was noted during 28-29 July, and an ash plume was seen in webcam footage on the 30th. Incandescence was visible in light-sensitive cameras during 4-17 and after the 26th. A field survey on 5 July measured 1,300 tons of sulfur dioxide (SO₂) per day. This had increased to 2,300 tons per day by the 12th, 2,500 on the 24th, and 2,400 by the 25th. A sulfur dioxide plume was detected in Sentinel-5P/TROPOMI satellite data acquired on 28 July (figure 62).

Figure 60. Thermal images taken at Asosan on 26 July 2019 show the increasing temperature of emissions leading to an explosion. Courtesy of the Japan Meteorological Agency (July 2019 monthly report).

Figure 61. An eruption from the Nakadake crater at Asosan on 26 July 2019. Courtesy of the Japan Meteorological Agency (July 2019 monthly report).

Figure 62. A sulfur dioxide plume was detected from Asosan (to the left) on 28 July 2019. The larger plume (red) to the right is not believed to be associated with volcanism in this area. NASA Sentinel-5P/TROPOMI satellite image courtesy of the NASA Goddard Space Flight Center.

The increased eruptive activity that began on 5 July continued to 16 August. There were 24 eruptions recorded throughout the month, with eruptions occurring on 18-23, 25, and 29-31 August. An ash plume at 2100 on 4 August reached 1.5 km above the crater rim. Detected SO₂ increased to extremely high levels from late July to early August with 5,200 tons per day recorded on 9 August, but which then reduced to 2,000 tons per day. Ashfall occurred out to around 7 km NW on the 10th (figure 63). Activity continued to increase at the Nakadake No. 1 crater, producing incandescence. High-temperature gas plumes were detected at the No. 2 crater.

Figure 63. Ashfall from Asosan on 10 August 2019 near Otohime, Aso city, which is about 7 km NW of the Nakadake No. 1 crater that produced the ash plume. The ashfall was thick enough that the white line in the parking lot was mostly obscured (lower photo). Courtesy of the Japan Meteorological Agency (August 2019 monthly report).

Thermal activity continued to increase, and incandescence was observed at the No. 1 crater throughout September. There were 24 eruptions recorded throughout August. Light ashfall occurred out to around 8 km NE on the 3rd and ash plumes reached 1.6 km above the crater rim during 10-13, and again during 25-30 (figures 64 and 65). During the later dates ashfall was reported to the NE and NW. The SO₂ levels were back down to 1,600 tons per day by 11 September and increased to 2,600 tons per day by the 26th.

Figure 64. Ash plumes at Asosan on 29 September 2019. Courtesy of Volcanoverse.

Figure 65. Activity at Asosan in late September 2019. Left: incandescence and a gas plume at the Nakadake No. 1 crater on the 28th. Right: an eruption produced an ash plume at 0839 on the 30th. Aso Volcano Museum surveillance camera image (left) and Kusasenri surveillance camera image (right) courtesy of the Japan Meteorological Agency (September 2019 monthly report).

Similar elevated activity continued through October with ash plumes reaching 1.3 km above the crater and periodic ashfall reported at the Kumamoto Regional Meteorological Observatory, and out to 4 km S to SW on the 19th and 29th. Temperatures up to 580°C were recorded at the No. 1 crater on 23 October and incandescence was occasionally visible at night through the month (figure 66). Gas surveys detected 2,800 tons per day of SO₂ on 7 October, which had increased to 4,000 tons per day by the 11th.

Figure 66. Drone images of the Asosan Nakadake crater area on 23 October 2019. The colored boxes show the same vents and the photographs on the left correlate to the thermal images on the right. The yellow box is around the No. 1 crater, with temperature measurements reaching 580°C. The emissions in the red box reached 50°C, and up to 100°C on the southwest crater wall (blue box). Courtesy of the Japan Meteorological Agency (October 2019 monthly report).

Ash plume emission continued through November (figure 67 and 68). Plumes reached 1.5 to 2.4 km above sea level during 13-18 November and ashfall occurred downwind, with a maximum of 1.4 km above the crater rim for the month. Ashfall was reported near Aso City Hall on the 27th. Incandescence was observed until 6 November. During the first half of October sulfur dioxide emissions were slightly lower than the previous month, with measurements detecting under 3,000 tons per day. In the second half of the month emissions increased to 2,000 to 6,300 tons per day. This was accompanied by an increase in volcanic tremor.

Figure 67. Examples of ash plumes at Asosan on 2, 8, 9, and 11 November 2019. The plume on 2 November reached 1.3 km above the crater rim. Kusasenri surveillance camera images courtesy of the Japan Meteorological Agency.

Figure 68. Ash emissions from the Nakadake crater at Asosan on 15 and 17 November 2019. The continuous ash emission is weak and is being dispersed by the wind. Copyright Mizumoto, used with permission.

Throughout December activity remained elevated with ash plumes reaching 1.1 km above the Nakadake No. 1 crater and producing ashfall. The maximum gas plume height was 1.8 km above the crater. A total of 23 eruptions were recorded, and incandescence at the crater was observed through the month. Sulfur dioxide emissions continued to increase with 5,800 tons per day recorded on the 27th, and 7,400 tons per day recorded on the 31st.

Overall, eruptive activity has continued intermittently since 26 July and SO₂ emissions have increased through the year. Incandescence was seen at the crater since 2 October and this is consistent with an increase in thermal energy detected by the MIROVA algorithm around that time (figure 69).

Figure 69. Thermal anomalies were low through 2019 with a notable increase around October to November. Log radiative power plot courtesy of MIROVA.

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), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); 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/); 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/); Planet Labs, Inc. (URL: https://www.planet.com/); Mizumoto, Kumamoto, Kyushu, Japan (Twitter: https://twitter.com/hepomodeler); Volcanoverse (URL: https://www.youtube.com/channel/UCi3T_esus8Sr9I-3W5teVQQ).

Remote Tinakula lies 100 km NE of the Solomon Trench at the N end of the Santa Cruz Islands, which are part of the South Pacific 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. A large ash explosion during 21-26 October 2017 was a short-lived event; renewed thermal activity was detected beginning in December 2018 and intermittently throughout 2019. This report covers the ongoing activity from July-December 2019. Since ground-based observations are rarely available, satellite thermal and visual data are the primary sources of information.

MIROVA thermal anomaly data indicated intermittent but ongoing thermal activity at Tinakula during July-December 2019 (figure 35). It was characterized by pulses of multiple alerts of varying intensities for several days followed by no activity for a few weeks.

Figure 35. The MIROVA project plot of Radiative Power at Tinakula from 2 March 2019 through the end of the year indicated repeated pulses of thermal energy each month except for August 2019. It was characterized by pulses of multiple alerts for several days followed by no activity for a few weeks. Courtesy of MIROVA.

Observations using Sentinel-2 satellite imagery were often prevented by clouds during July, but two MODVOLC thermal alerts on 2 July 2019 corresponded to MIROVA thermal activity on that date. No thermal anomalies were reported by MIROVA during August 2019, but Sentinel-2 satellite images showed dense steam plumes drifting away from the summit on four separate dates (figure 36). Two distinct thermal anomalies appeared in infrared imagery on 9 September, and a dense steam plume drifted about 10 km NW on 14 September (figure 37).

Figure 36. Sentinel-2 satellite imagery for Tinakula recorded ongoing steam emissions on multiple days during August 2019 including 10 August (left) and 20 August (right). The island is about 3 km in diameter. Left image is natural color rendering with bands 4,3,2, right image is atmospheric penetration with bands 12, 11, and 8a. Courtesy of Sentinel Hub Playground.

Figure 37. A bright thermal anomaly at the summit and a weaker one on the nearby upper W flank of Tinakula on 9 September 2019 (left) indicated ongoing eruptive activity in Sentinel-2 satellite imagery. While no thermal anomalies were visible on 14 September (right), a dense steam plume originating from the summit drifted more than 10 km NW. Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

During October 2019 steam emissions were captured in four clear satellite images; a weak thermal anomaly was present on the W flank on 9 October (figure 38). MODVOLC recorded a single thermal alert on 9 November. Stronger thermal anomalies appeared twice during November in satellite images. On 13 November a strong anomaly was present at the summit in Sentinel-2 imagery; it was accompanied by a dense steam plume drifting NE from the hotspot. On 28 November two thermal anomalies appeared part way down the upper NW flank (figure 39). Thermal imagery on 3 December suggested that a weak anomaly remained on the NW flank in a similar location; a dense steam plume rose above the summit, drifting slightly SW on 18 December (figure 40). A thermal anomaly at the summit on 28 December was accompanied by a dense steam plume and corresponded to multiple MIROVA thermal anomalies at the end of December.

Figure 38. A weak thermal anomaly was recorded on the upper W flank of Tinakula on 9 October 2019 in Sentinel-2 satellite imagery (left). Dense steam drifted about 10 km NW from the summit on 29 October (right). Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Figure 39. On 13 November 2019 a strong anomaly was present at the summit of Tinakula in Sentinel-2 imagery; it was accompanied by a dense steam plume drifting NE from the hotspot (left). On 28 November two thermal anomalies appeared part way down the upper NW flank (right). Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Figure 40. Thermal imagery on 3 December 2019 from Tinakula suggested that a weak anomaly remained in a similar location to one of the earlier anomalies on the NW flank (left); a dense steam plume rose above the summit, drifting slightly SW on 18 December (center). A thermal anomaly at the summit on 28 December was accompanied by a dense steam plume (right) and corresponded to multiple MIROVA thermal anomalies at the end of December. Atmospheric penetration rendering (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).

Heightened continuing activity at Ibu since March 2018 has been dominated by frequent ash explosions with weak ash plumes, and numerous thermal anomalies reflecting one or more weak lava flows (BGVN 43:05, 43:12, and 44:07). This report summarizes activity through December 2019, and is based on data from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Darwin Volcanic Ash Advisory Centre (VAAC), and various satellites.

Typical ash plumes during the reporting period of July-December 2019 rose 800 m above the crater, with the highest reported to 1.4 km in early October (table 5). They were usually noted a few times each month. According to MAGMA Indonesia, explosive activity caused the Aviation Color Code to be raised to ORANGE (second highest of four) on 14, 22, and 31 August, 4 and 30 September, and 15 and 20 October.

Table 5. Ash plumes and other volcanic activity reported at Ibu during December 2018-December 2019. Plume heights are reported above the crater rim. Data courtesy of PVMBG and Darwin VAAC.

Thermal anomalies were sometimes noted by PVMBG, and were also frequently obvious in infrared satellite imagery suggesting lava flows and multiple active vents, as seen on 22 November 2019 (figure 19). Thermal anomalies using MODIS satellite instruments processed by the MODVOLC algorithm were recorded 2-4 days every month from July to December 2019. In contrast, the MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected numerous hotspots on most days (figure 20).

Figure 19. Example of thermal activity in the Ibu crater on 22 November 2019, along with a plume drifting SE. One or more vents in the crater are producing small lava flows, an observation common throughout the reporting period. Sentinel-2 false color (urban) images (bands 12, 11, 4), courtesy of Sentinel Hub Playground.

Figure 20. Thermal anomalies recorded at Ibu by the MIROVA system using MODIS infrared satellite data for the year 2019. Courtesy of MIROVA.

Geologic Background. The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

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

Lateiki (Metis Shoal) is one of several submarine and island volcanoes on the W side of the Tonga trench in the South Pacific. It has produced ephemeral islands multiple times since the first confirmed activity in the mid-19th century. Two eruptions, in 1967 and 1979, produced islands that survived for a few months before eroding beneath the surface. An eruption in 1995 produced a larger island that persisted, possibly until a new eruption in mid-October 2019 destroyed it and built a new short-lived island. Information was provided by the Ministry of Lands, Survey and Natural Resources of the Government of the Kingdom of Tonga, and from satellite information and news sources.

Review of eruptions during 1967-1995. The first reported 20th century eruption at this location was observed by sailors beginning on 12 December 1967 (CSLP 02-67); incandescent ejecta rose several hundred meters into the air and "steam and smoke" rose at least 1,000 m from the ocean surface. The eruption created a small island that was reported to be a few tens of meters high, and a few thousand meters in length and width. Eruptive activity appeared to end in early January 1968, and the island quickly eroded beneath the surface by the end of February (figure 6). When observed in April 1968 the island was gone, with only plumes of yellowish water in the area of the former island.

Figure 6. Waves break over Lateiki on 19 February 1968, more than a month after the end of a submarine eruption that began in December 1967 and produced a short-lived island. Photo by Charles Lundquist, 1968 (Smithsonian Astrophysical Observatory).

A large steam plume and ejecta were observed on 19 June 1979, along with a "growing area of tephra" around the site with a diameter of 16 km by the end of June (SEAN 04:06). Geologists visited the site in mid-July and at that time the island was about 300 m long, 120 m wide, and 15 m high, composed of tephra ranging in size from ash to large bombs (SEAN 04:07); ash emissions were still occurring from the E side of the island. It was determined that the new island was located about 1 km E of the 1967-68 island. By early October 1979 the island had nearly disappeared beneath the ocean surface.

A new eruption was first observed on 6 June 1995. A new island appeared above the waves as a growing lava dome on 12 June (BGVN 20:06). Numerous ash plumes rose hundreds of meters and dissipated downwind. By late June an elliptical dome, about 300 x 250 m in size and 50 m high, had stopped growing. The new island it formed was composed of hardened lava and not the tuff cones of earlier islands (figure 7) according to visitors to the island; pumice was not observed. An overflight of the area in December 2006 showed that an island was still present (figure 8), possibly from the June 1995 eruption. Sentinel-2 satellite imagery confirming the presence of Lateiki Island and discolored water was clearly recorded multiple times between 2015 and 2019. This suggests that the island created in 1995 could have lasted for more than 20 years (figure 9).

Figure 7. An aerial view during the 1995 eruption of Lateiki forming a lava dome. Courtesy of the Government of the Kingdom of Tonga.

Figure 8. Lateiki Island as seen on 7 December 2006; possibly part of the island that formed in 1995. Courtesy of the Government of the Kingdom of Tonga and the Royal New Zealand Air Force.

Figure 9. Sentinel-2 satellite imagery confirmed the existence of an island present from 2015 through 2019 with little changes to its shape. This suggests that the island created in 1995 could have lasted for more than 20 years. Courtesy of Sentinel Hub Playground.

New eruption in October 2019. The Kingdom of Tonga reported a new eruption at Lateiki on 13 October 2019, first noted by a ship at 0800 on 14 October. NASA satellite imagery confirmed the eruption taking place that day (figure 10). The following morning a pilot from Real Tonga Airlines photographed the steam plume and reported a plume height of 4.6-5.2 km altitude (figure 11). The Wellington VAAC issued an aviation advisory report noting the pilot's observation of steam, but no ash plume was visible in satellite imagery. They issued a second report on 22 October of a similar steam plume reported by a pilot at 3.7 km altitude. The MODVOLC thermal alert system recorded three thermal alerts from Lateiki, one each on 18, 20, and 22 October 2019.

Figure 10. NASA's Worldview Aqua/MODIS satellite imagery taken on 14 October 2019 over the Ha'apai and Vava'u region of Tonga showing the new eruption at Lateiki. Neiafu, Vava'u, is at the top right and Tofua and Kao islands are at the bottom left. The inset shows a closeup of Late Island at the top right and a white steam plume rising from Lateiki. Courtesy of the Government of the Kingdom of Tonga and NASA Worldview.

Figure 11. Real Tonga Airline's Captain Samuela Folaumoetu'I photographed a large steam plume rising from Lateiki on the morning of 15 October 2019. Courtesy of the Government of the Kingdom of Tonga.

The first satellite image of the eruption on 15 October 2019 showed activity over a large area, much bigger than the preexisting island that was visible on 10 October (figure 12). Although the eruption produced a steam plume that drifted several tens of kilometers SW and strong incandescent activity, no ash plume was visible, similar to reports of dense steam with little ash during the 1968 and 1979 eruptions (figure 13). Strong incandescence and a dense steam plume were still present on 20 October (figure 14).

Figure 12. The first satellite image of the eruption of Lateiki on 15 October 2019 showed activity over a large area, much bigger than the preexisting island that was visible on 10 October (inset). The two images are the same scale; the island was about 100 m in diameter before the eruption. Image uses Natural Color Rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

Figure 13. The steam plume from Lateiki on 15 October 2019 drifted more than 20 km SE from the volcano. A strong thermal anomaly from incandescent activity was present in the atmospheric penetration rendering (bands 12, 11, 8a) closeup of the same image (inset). Courtesy of Sentinel Hub Playground.

Figure 14. A dense plume of steam drifted NW from Lateiki on 20 October 2019, and a strong thermal signal (inset) indicated ongoing explosive activity. Courtesy of Annamaria Luongo and Sentinel Hub Playground.

A clear satellite image on 30 October 2019 revealed an island estimated to be about 100 m wide and 400 m long, according to geologist Taaniela Kula of the Tonga Geological Service of the Ministry of Lands, Survey and Natural Resources as reported by a local news source (Matangitonga). There was no obvious fumarolic steam activity from the surface, but a plume of greenish brown seawater swirled away from the island towards the NE (figure 15). In a comparison of the location of the old Lateiki island with the new one in satellite images, it was clear that the new island was located as far as 250 m to the NW (figure 16) on 30 October. Over the course of the next few weeks, the island's size decreased significantly; by 19 November, it was perhaps one-quarter the size it had been at the end of October. Lateiki Island continued to diminish during December 2019 and January 2020, and by mid-month only traces of discolored sea water were visible beneath the waves over the eruption site (figure 17).

Figure 15. The new Lateiki Island was clearly visible on 30 October 2019 (top left), as was greenish-blue discoloration in the surrounding waters. It was estimated to be about 100 m wide and 400 m long that day. Its size decreased significantly over subsequent weeks; ten days later (top right) it was about half the size and two weeks later, on 14 November 2019 (bottom left), it was about one-third its original size. By 19 November (bottom right) only a fraction of the island remained. Greenish discolored water continued to be visible around the volcano. Courtesy of Sentinel Hub Playground.

Figure 16. The location of the new Lateiki Island (Metis Shoal), shown here on 30 October 2019 in red, was a few hundred meters to the NW of the old position recorded on 5 September 2019 (in white). Courtesy of Annamaria Luongo and Sentinel Hub Playground.

Figure 17. Lateiki Island disappeared beneath the waves in early January 2020, though plumes of discolored water continued to be observed later in the month. Courtesy of Sentinel Hub Playground.

Geologic Background. Lateiki, previously known as Metis Shoal, is a submarine volcano midway between the islands of Kao and Late that has produced a series of ephemeral islands since the first confirmed activity in the mid-19th century. An island, perhaps not in eruption, was reported in 1781 and subsequently eroded away. During periods of inactivity following 20th-century eruptions, waves have been observed to break on rocky reefs or sandy banks with depths of 10 m or less. Dacitic tuff cones formed during the first 20th-century eruptions in 1967 and 1979 were soon eroded beneath the ocean surface. An eruption in 1995 produced an island with a diameter of 280 m and a height of 43 m following growth of a lava dome above the surface.

Information Contacts: Government of the Kingdom of Tonga, PO Box 5, Nuku'alofa, Tonga (URL: http://www.gov.to/ ); Royal New Zealand Air Force (URL: http://www.airforce.mil.nz/); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Annamaria Luongo, Brussels, Belgium (Twitter: @annamaria_84, URL: https://twitter.com/annamaria_84 ); Taaniela Kula, Tonga Geological Service, Ministry of Lands, Survey and Natural Resources; Matangi Tonga Online (URL: https://matangitonga.to/2019/11/06/eruption-lateiki).

Sakurajima is a highly active stratovolcano situated in the Aira caldera in southern Kyushu, Japan. Common volcanism for this recent eruptive episode since March 2017 includes frequent explosions, ash plumes, and scattered ejecta. Much of this activity has been focused in the Minamidake crater since 1955; the Showa crater on the E flank has had intermittent activity since 2006. This report updates activity during July through December 2019 with the primary source information from monthly reports by the Japan Meteorological Agency (JMA) and various satellite data.

During July to December 2019, explosive eruptions and ash plumes were reported multiple times per week by JMA. November was the most active, with 137 eruptive events, seven of which were explosive while August was the least active with no eruptive events recorded (table 22). Ash plumes rose between 800 m to 5.5 km above the crater rim during this reporting period. Large blocks of incandescent ejecta traveled as far as 1.7 km from the Minamidake crater during explosions in September through December. The Kagoshima Regional Meteorological Observatory (11 km WSW) reported monthly amounts of ashfall during each month, with a high of 143 g/m² during October. Occasionally at night throughout this reporting period, crater incandescence was observed with a highly sensitive surveillance camera. All explosive activity originated from the Minamidake crater; the adjacent Showa crater produced mild thermal anomalies and gas-and-steam plumes.

Table 22. Monthly summary of eruptive events recorded at Sakurajima's Minamidake crater in the Aira caldera, July through December 2019. The number of events that were explosive in nature are in parentheses. No events were recorded at the Showa crater during this time. Ashfall is measured at the Kagoshima Local Meteorological Observatory (KLMO), 10 km W of Showa crater. Data courtesy of JMA (July to December 2019 monthly reports).

An explosion that occurred at 1044 on 4 July 2019 produced an ash plume that rose up to 3.2 km above the Minamidake crater rim and ejected material 1.1 km from the vent. Field surveys conducted on 17 and 23 July measured SO₂ emissions that were 1,200-1,800 tons/day. Additional explosions between 19-22 July generated smaller plumes that rose to 1.5 km above the crater and ejected material 1.1 km away. On 28 July explosions at 1725 and 1754 produced ash plumes 3.5-3.8 km above the crater rim, which resulted in ashfall in areas N and E of Sakurajima (figure 86), including Kirishima City (20 km NE), Kagoshima Prefecture (30 km SE), Yusui Town (40 km N), and parts of the Kumamoto Prefecture (140 km NE).

Figure 86. Photo of the Sakurajima explosion at 1725 on 28 July 2019 resulting in an ash plume rising 3.8 km above the crater (left). An on-site field survey on 29 July observed ashfall on roads and vegetation on the N side of the island (right). Photo by Moto Higashi-gun (left), courtesy of JMA (July 2019 report).

The month of August 2019 showed the least activity and consisted of mainly small eruptive events occurring up to 800 m above the crater; summit incandescence was observed with a highly sensitive surveillance camera. SO₂ emissions were measured on 8 and 13 August with 1,000-2,000 tons/day, which was slightly greater than the previous month. An extensometer at the Arimura Observation Tunnel and an inclinometer at the Amida River recorded slight inflation on 29 August, but continuous GNSS (Global Navigation Satellite System) observations showed no significant changes.

In September 2019 there were 32 eruptive events recorded, of which 11 were explosions, more than the previous two months. Seismicity also increased during this month. An extensometer and inclinometer recorded inflation at the Minamidake crater on 9 September, which stopped after the eruptive events. On 16 September, an eruption at 0746 produced an ash plume that rose 2.8 km above the crater rim and drifted SW; a series of eruptive events followed from 0830-1110 (figure 87). Explosions on 18 and 20 September produced ash plumes that rose 3.4 km above the crater rim and ejecting material as far as 1.7 km from the summit crater on the 18th and 700 m on the 20th. Field surveys measured an increased amount of SO₂ emissions ranging from 1,100 to 2,300 tons/day during September.

Figure 87. Webcam image of an ash plume rising 2.8 km from the Minamidake crater at Sakurajima on 16 September 2019. Courtesy of Weathernews Inc.

Seismicity, SO₂ emissions, and the number of eruptions continued to increase in October 2019, 41 of which were explosive. Field surveys conducted on 1, 11, and 15 October reported that SO₂ emissions were 2,000-2,800 tons/day. An explosion at 0050 on 12 October produced an ash plume that traveled 1.7 km from the Minamidake crater. Explosions between 16 and 19 October produced an ash plume that rose up to 3 km above the crater rim (figure 88). The Japan Maritime Self-Defense Force 1st Air group observed gas-and-steam plumes rising from both the Minamidake and Showa craters on 25 October. The inflation reported from 16 September began to slow in late October.

Figure 88. Photos taken from the E side of Sakurajima showing gas-and-steam emissions with some amount of ash rising from the volcano on 16 October 2019 after an explosion around 1200 that day (top). At night, summit incandescence is observed (bottom). Courtesy of Bradley Pitcher, Vanderbilt University.

November 2019 was the most active month during this reporting period with increased seismicity, SO₂ emissions, and 137 eruptive events, 77 of which were explosive. GNSS observations indicated that inflation began to slow during this month. On 8 November, an explosion at 1724 produced an ash plume up to a maximum of 5.5 km above the crater rim and drifted E. This explosion ejected large blocks as far as 500-800 m away from the crater (figure 89). The last time plumes rose above 5 km from the vents occurred on 26 July 2016 at the Showa crater and on 7 October 2000 at the Minamidake crater. Field surveys on 8, 21, and 29 November measured increased SO₂ emissions ranging from 2,600 to 3,600 tons/day. Eruptions between 13-19 November produced ash plumes that rose up to 3.6 km above the crater and ejected large blocks up 1.7 km away. An onsite survey on 29 November used infrared thermal imaging equipment to observe incandescence and geothermal areas near the Showa crater and the SE flank of Minamidake (figure 90).

Figure 89. Photos of an ash plume rising 5.5 km above Sakurajima on 8 November 2019 and drifting E. Photo by Moto Higashi-gun (top left), courtesy of JMA (November 2019 report) and the Geoscientific Network of Chile.

Figure 90. Webcam image of nighttime incandescence and gas-and-steam emissions with some amount of ash at Sakurajima on 29 November 2019. Courtesy of JMA (November 2019 report).

Volcanism, which included seismicity, SO₂ emissions, and eruptive events, decreased during December 2019. Explosions during 4-10 December produced ash plumes that rose up to 2.6 km above the crater rim and ejected material up to 1.7 km away. Field surveys conducted on 6, 16, and 23 December measured SO₂ emissions around 1,000-3,000 tons/day. On 24 December, an explosion produced an ash plume that rose to 3.3 km above the crater rim, this high for this month.

Sentinel-2 natural color satellite imagery showed dense ash plumes in late August 2019, early November, and through December (figure 91). These plumes drifted in different directions and rose to a maximum 5.5 km above the crater rim on 8 November.

Figure 91. Natural color Sentinel-2 satellite images of Sakurajima within the Aira caldera from late August through December 2019 showed dense ash plumes rising from the Minamidake crater. Courtesy of Sentinel Hub Playground.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent thermal anomalies beginning in mid-August to early September 2019 after a nearly two-month hiatus (figure 92). Activity increased by early November and continued through December. Three Sentinel-2 thermal satellite images between late July and early October showed distinct thermal hotspots within the Minamidake crater, in addition to faint gas-and-steam emissions in July and September (figure 93).

Figure 92. Thermal anomalies at Sakurajima during January-December 2019 as recorded by the MIROVA system (Log Radiative Power) started up in mid-August to early September after a two-month break and continued through December. Courtesy of MIROVA.

Figure 93. Sentinel-2 thermal satellite images showing small thermal anomalies and gas-and-steam emissions (left and middle) at Sakurajima within the Minamidake crater between late July and early October 2019. All images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Weathernews Inc. (Twitter: @wni_jp, https://twitter.com/wni_jp, URL: https://weathernews.jp/s/topics/201608/210085/, photo posted at https://twitter.com/wni_jp/status/1173382407216652289); Bradley Pitcher, Vanderbilt University, Nashville. TN, USA (URL: https://bradpitcher.weebly.com/, Twitter: @TieDyeSciGuy, photo posted at https://twitter.com/TieDyeSciGuy/status/1185191225101471744); Geoscientific Network of Chile (Twitter: @RedGeoChile, https://twitter.com/RedGeoChile, Facebook: https://www.facebook.com/RedGeoChile/, photo posted at https://twitter.com/RedGeoChile/status/1192921768186515456).

Suwanosejima, located south of Japan in the northern Ryukyu Islands, is an active andesitic stratovolcano that has had continuous activity since October 2004, typically producing ash plumes and Strombolian explosions. Much of this activity is focused within the Otake crater. This report updates information during July through December 2019 using monthly reports from the Japan Meteorological Agency (JMA), the Tokyo Volcanic Ash Advisory Center (VAAC), and various satellite data.

White gas-and-steam plumes rose from Suwanosejima on 26 July 2019, 30-31 August, 1-6, 10, and 20-27 September, reaching a maximum altitude of 2.4 km on 10 September, according to Tokyo VAAC advisories. Intermittent gray-white plumes were observed rising from the summit during October through December (figure 40).

Figure 40. Surveillance camera images of white gas-and-steam emissions rising from Suwanosejima on 10 December 2019 (left) and up to 1.8 km above the crater rim on 28 December (right). At night, summit incandescence was also observed on 10 December. Courtesy of JMA.

An explosion that occurred at 2331 on 1 August 2019 ejected material 400 m from the crater while other eruptions on 3-6 and 26 August produced ash plumes that rose up to a maximum altitude of 2.1 km and drifted generally NW according to the Tokyo VAAC report. JMA reported eruptions and summit incandescence in September accompanied by white gas-and-steam plumes, but no explosions were noted. Eruptions on 19 and 29 October produced ash plumes that rose 300 and 800 m above the crater rim, resulting in ashfall in Toshima (4 km SW), according to the Toshima Village Office, Suwanosejima Branch Office. Another eruption on 30 October produced a similar gray-white plume rising 800 m above the crater rim but did not result in ashfall. Similar activity continued in November with eruptions on 5-7 and 13-15 November producing grayish-white plumes rising 900 m and 1.5 km above the crater rim and frequent crater incandescence. Ashfall was reported in Toshima Village on 19 and 20 November; the 20 November eruption ejected material 200 m from the Otake crater.

Field surveys on 14 and 18 December using an infrared thermal imaging system to the E of Suwanose Island showed hotspots around the Otake crater, on the N slope of the crater, and on the upper part of the E coastline. GNSS (Global Navigation Satellite Systems) observations on 15 and 17 December showed a slight change in the baseline length. After 2122 on 25-26 and 31 December, 23 eruptions, nine of which were explosive were reported, producing gray-white plumes that rose 800-1,800 m above the crater rim and ejected material up to 600 m from the Otake crater. JMA reported volcanic tremors occurred intermittently throughout this reporting period.

Incandescence at the summit crater was occasionally visible at night during July through December 2019, as recorded by webcam images and reported by JMA (figure 41). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed weak thermal anomalies that occurred dominantly in November with little to no activity recorded between July and October (figure 42). Two Sentinel-2 thermal satellite images in early November and late December showed thermal hotspots within the summit crater (figure 43).

Figure 41. Surveillance camera image of summit incandescence at Suwanosejima on 31 October 2019. Courtesy of JMA.

Figure 42. Weak thermal anomalies at Suwanosejima during January-December 2019 as recorded by the MIROVA system (Log Radiative Power) dominantly occurred in mid-March, late May to mid-June, and November, with two hotspots detected in late September and late December. Courtesy of MIROVA.

Figure 43. Sentinel-2 thermal satellite images showing small thermal anomalies (bright yellow-orange) within the Otake crater at Suwanosejima on 8 November 2019 (left) and faintly on 23 December 2019 behind clouds (right). Both images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Barren Island is a remote stratovolcano located east of India in the Andaman Islands. Its most recent eruptive episode began in September 2018 and has included lava flows, explosions, ash plumes, and lava fountaining (BGVN 44:02). This report updates information from February 2019 through January 2020 using various satellite data as a primary source of information.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent thermal anomalies within 5 km of the summit from mid-February 2019 through January 2020 (figure 41). There was a period of relatively low to no discernible activity between May to September 2019. The MODVOLC algorithm for MODIS thermal anomalies in comparison with Sentinel-2 thermal satellite imagery and Suomi NPP/VIIRS sensor data, registered elevated temperatures during late February 2019, early March, sparsely in April, late October, sparsely in November, early December, and intermittently in January 2020 (figure 42). Sentinel-2 thermal satellite imagery shows these thermal hotspots differing in strength from late February to late January 2020 (figure 43). The thermal anomalies in these satellite images are occasionally accompanied by ash plumes (25 February 2019, 23 October 2019, and 21 January 2020) and gas-and-steam emissions (26 April 2019).

Figure 41. Intermittent thermal anomalies at Barren Island for 20 February 2019 through January 2020 occurred dominantly between late March to late April 2019 and late September 2019 through January 2020. Courtesy of MIROVA.

Figure 42. Timeline summary of observed activity at Barren Island from February 2019 through January 2020. For Sentinel-2, MODVOLC, and VIIRS data, the dates indicated are when thermal anomalies were detected. White areas indicated no activity was observed, which may also be due to meteoric clouds. Data courtesy of Darwin VAAC, Sentinel Hub Playground, HIGP, and NASA Worldview using the "Fire and Thermal Anomalies" layer.

Figure 43. Sentinel-2 thermal images show ash plumes, gas-and-steam emissions, and thermal anomalies (bright yellow-orange) at Barren Island during February 2019-January 2020. The strongest thermal signature was observed on 23 October while the weakest one is observed on 26 January. Sentinel-2 False color (bands 12, 11, 4) images courtesy of Sentinel Hub Playground.

The Darwin Volcanic Ash Advisory Center (VAAC) reported ash plumes rising from the summit on 7, 14, and 16 March 2019. The maximum altitude of the ash plume occurred on 7 March, rising 1.8 km altitude, drifting W and NW and 1.2 km altitude, drifting E and ESE, based on observations from Himawari-8. The VAAC reports for 14 and 16 March reported the ash plumes rising 0.9 km and 1.2 km altitude, respectively drifting W and W.

Geologic Background. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/).

Whakaari/White Island has been New Zealand's most active volcano since 1976. Located 48 km offshore, the volcano is a popular tourism destination with tours leaving the town of Whakatane with approximately 17,500 people visiting the island in 2018. Ten lives were lost in 1914 when part of the crater wall collapsed, impacting sulfur miners. More recently, a brief explosion at 1411 on 9 December 2019 produced an ash plume and pyroclastic surge that impacted the entire crater area. With 47 people on the island at the time, the death toll stood at 21 on 3 February 2019. At that time more patients were still in hospitals within New Zealand or their home countries.

The island is the summit of a large underwater volcano, with around 70% of the edifice below the ocean and rising around 900 m above sea level (figure 70). A broad crater opens to the ocean to the SE, with steep crater walls and an active Main Crater area to the NW rear of the crater floor (figure 71). Although the island is privately owned, GeoNet continuously monitors activity both remotely and with visits to the volcano. This Bulletin covers activity from May 2017 through December 2019 and is based on reports by GeoNet, the New Zealand Civil Defence Bay of Plenty Emergency Management Group, satellite data, and footage taken by visitors to the island.

Figure 70. The top of the Whakaari/White Island edifice forms the island in the Bay of Plenty area, New Zealand, while 70% of the volcano is below sea level. Courtesy of GeoNet.

Figure 71. This photo from 2004 shows the Main Crater area of Whakaari/White Island with the vent area indicated. The crater is an amphitheater shape with the crater floor distance between the vent and the ocean entry being about 700 m. The sediment plume begins at the area where tour boats dock at the island. Photo by Karen Britten, graphic by Danielle Charlton at University of Auckland; courtesy of GeoNet (11 December 2019 report).

Nearly continuous activity occurred from December 1975 to September 2000, including the formation of collapse and explosion craters producing ash emissions and explosions that impacted all of the Main Crater area. More recently, it has been in a state of elevated unrest since 2011. Renewed activity commenced with an explosive eruption on 5 August 2012 that was followed by the extrusion of a lava dome and ongoing phreatic explosions and minor ash emissions through March 2013. An ash cone was seen on 4 March 2013, and over the next few months the crater lake reformed. Further significant explosions took place on 20 August and 4, 8, and 11 October 2013. A landslide occurred in November 2015 with material descending into the lake. More recent activity on 27 April 2016 produced a short-lived eruption that deposited material across the crater floor and walls. A short period of ash emission later that year, on 13 September 2016, originated from a vent on the recent lava dome. Explosive eruptions occur with little to no warning.

Since 19 September 2016 the Volcanic Alert Level (VAL) was set to 1 (minor volcanic unrest) (figure 72). During early 2017 background activity in the crater continued, including active fumaroles emitting volcanic gases and steam from the active geothermal system, boiling springs, volcanic tremor, and deformation. By April 2017 a new crater lake had begun to form, the first since the April 2016 explosion when the lake floor was excavated an additional 13 m. Before this, there were areas where water ponded in depressions within the Main Crater but no stable lake.

Figure 72. The New Zealand Volcanic Alert Level system up to date in February 2020. Courtesy of GeoNet.

Activity from mid-2017 through 2018. In July-August 2017 GeoNet scientists carried out the first fieldwork at the crater area since late 2015 to sample the new crater lake and gas emissions. The crater lake was significantly cooler than the past lakes at 20°C, compared to 30-70°C that was typical previously. Chemical analysis of water samples collected in July showed the lowest concentrations of most "volcanic elements" in the lake for the past 10-15 years due to the reduced volcanic gases entering the lake. The acidity remained similar to that of battery acid. Gas emissions from the 2012 dome were 114°C, which were over 450°C in 2012 and 330°C in 2016. Fumarole 0 also had a reduced temperature of 152°C, reduced from over 190°C in late 2016 (figure 73). The observations and measurements indicated a decline in unrest. Further visits in December 2017 noted relatively low-level unrest including 149°C gas emissions from fumarole 0, a small crater lake, and loud gas vents nearby (figures 74 and 75). By 27 November the lake had risen to 10 m below overflow. Analysis of water samples led to an estimate of 75% of the lake water resulting from condensing steam vents below the lake and the rest from rainfall.

Figure 73. A GeoNet scientists conducting field work near Fumarole 0, an accessible gas vent on Whakaari/White Island in August 2017. Courtesy of GeoNet (23 August 2017 report).

Figure 74. GeoNet scientists sample gas emissions from vents on the 2012 Whakaari/White Island dome. The red circle in the left image indicates the location of the scientists. Courtesy of GeoNet (23 August 2017 report).

Figure 75. Active fumaroles and vents in the Main Crater of Whakaari/White Island including Fumarole 0 (top left). The crater lake formed in mid-2017 and gas emissions rise from surrounding vents (right). Courtesy of GeoNet (22 December 2017 report).

Routine fieldwork by GeoNet monitoring teams in early March 2018 showed continued low-level unrest and no apparent changes after a recent nearby earthquake swarm. The most notable change was the increase in the crater lake size, likely a response from recent high rainfall (figure 76). The water remained a relatively cool 27°C. Temperatures continued to decline at the 2012 dome vent (128°C) and Fumarole 0 (138°C). Spring and stream flow had also declined. Deformation was observed towards the Active Crater of 2-5 mm per month and seismicity remained low. The increase in lake level drowned gas vents along the lake shore resulting in geyser-like activity (figure 77). GeoNet warned that a new eruption could occur at any time, often without any useful warning.

In mid-April 2018 visitors reported loud sounds from the crater area as a result of the rising lake level drowning vents on the 2012 dome (in the western side of the crater) and resulting in steam-driven activity. There was no notable change in volcanic activity. The sounds stopped by July 2018 as the geothermal system adjusted to the rising water, up to 17 m below overfill and filling at a rate of about 2,000 m³ per day, rising towards more active vents (figure 78). A gas monitoring flight taken on 12 September showed a steaming lake surrounded by active fumaroles along the crater wall (figure 79).

Figure 76. The increase in the Whakaari/White Island crater lake size in early March 2018 with gas plumes rising from vents on the other side. Courtesy of GeoNet (19 March 2018 report).

Figure 77. The increasing crater lake level at Whakaari/White Island produced geyser-like activity on the lake shore in March 2018. Courtesy of Brad Scott, GeoNet.

Figure 78. Stills taken from a drone video of the Whakaari/White Island Main Crater lake and active vents producing gas emissions. Courtesy of GeoNet.

Figure 79. Photos taken during a gas monitoring flight with GNS Science at Whakaari/White Island show gas and steam emissions, and a steaming crater lake on 12 September 2018. Note the people for scale on the lower-right crater rim in the bottom photograph. Copyright of Ben Clarke, University of Leicester, used with permission.

Activity during April to early December 2019. A GeoNet volcanic alert bulletin in April 2019 reported that steady low-level unrest continued. The level of the lake had been declining since late January and was back down to 13 m below overflow (figure 80). The water temperature had increased to over 60°C due to the fumarole activity below the lake. Fumarole 0 remained steady at around 120-130°C. During May-June a seismic swarm was reported offshore, unrelated to volcanic activity but increasing the risk of landslides within the crater due to the shallow locations.

Figure 80. Planet Labs satellite images from March 2018 to April 2019 show fluctuations in the Whakaari/White Island crater lake level. Image copyright 2019 Planet Labs, Inc.

On 26 June the VAL was raised to level 2 (moderate to heightened volcanic unrest) due to increased SO₂ flux rising to historically high levels. An overflight that day detected 1,886 tons/day, nearly three times the previous values of May 2019, the highest recorded value since 2013, and the second highest since measurements began in 2003. The VAL was subsequently lowered on 1 July due to a reduction in detected SO₂ emissions of 880 tons/day on 28 June and 693 tons/day on 29 June.

GeoNet reported on 26 September that there was an increase in steam-driven activity within the active crater over the past three weeks. This included small geyser-like explosions of mud and steam with material reaching about 10 m above the lake. This was not attributed to an increase in volcanic activity, but to the crater lake level rising since early August.

On 30 October an increase in background activity was reported. An increasing trend in SO₂ gas emissions and volcanic tremor had been ongoing for several months and had reached the highest levels since 2016. This indicated to GeoNet that Whakaari/White Island might be entering a period where eruptive activity was more likely. There were no significant changes in other monitoring parameters at this time and fumarole activity continued (figure 81).

Figure 81. A webcam image taken at 1030 on 30 October 2019 from the crater rim shows the Whakaari/White Island crater lake to the right of the amphitheater-shaped crater and gas-and-steam plumes from active fumaroles. Courtesy of GeoNet.

On 18 November the VAL was raised to level 2 and the Aviation Colour Code was raised to Yellow due to further increase in SO₂ emissions and volcanic tremor. Other monitoring parameters showed no significant changes. On 25 November GeoNet reported that moderate volcanic unrest continued but with no new changes. Gas emissions remained high and gas-driven ejecta regularly jetting material a few meters into the air above fumaroles in the crater lake (figure 82).

Figure 82. A webcam image from the Whakaari/White Island crater rim shows gas-driven ejecta rising above a fumarole within the crater lake on 22 November 2019. Courtesy of GeoNet.

GeoNet reported on 3 December that moderate volcanic unrest continued, with increased but variable explosive gas and steam-driven jetting, with stronger events ejecting mud 20-30 m into the air and depositing mud around the vent area. Gas emissions and volcanic tremor remained elevated and occasional gas smells were reported on the North Island mainland depending on wind direction. The crater lake water level remained unchanged. Monitoring parameters were similar to those observed in 2011-2016 and remained within the expected range for moderate volcanic unrest.

Eruption on 9 December 2019. A short-lived eruption occurred at 1411 on 9 December 2019, generating a steam-and-ash plume to 3.6 km and covering the entire crater floor area with ash. Video taken by tourists on a nearby boat showed an eruption plume composed of a white steam-rich portion, and a black ash-rich ejecta (figure 83). A pyroclastic surge moved laterally across the crater floor and up the inner crater walls. Photos taken soon after the eruption showed sulfur-rich deposits across the crater floor and crater walls, and a helicopter that had been damaged and blown off the landing pad (figure 84). This activity caused the VAL to be raised to 4 (moderate volcanic eruption) and the Aviation Colour Code being raised to Orange.

Figure 83. The beginning of the Whakaari/White Island 9 December 2019 eruption viewed from a boat that left the island about 20-30 minutes prior. Top: the steam-rich eruption plume rising above the volcano and a pyroclastic surge beginning to rise over the crater rim. Bottom: the expanded steam-and-ash plume of the pyroclastic surge that flowed over the crater floor to the ocean. Copyright of Michael Schade, used with permission.

Figure 84. This photo of Whakaari/White Island taken after the 9 December 2019 eruption at around 1424 shows ash and sediment coating the crater floor and walls. The helicopter in this image was blown off the landing pad and damaged during the eruption. Copyright of Michael Schade, used with permission.

A steam plume was visible in a webcam image taken at 1430 from Whakatane, 21 minutes after the explosion (figure 85). Subsequent explosions occurred at 1630 and 1749. Search-and-Rescue teams reached the island after the eruption and noted a very strong sulfur smell that was experienced through respirators. They experienced severe stinging of any exposed skin that came in contact with the gas, and were left with sensitive skin and eyes, and sore throats. Later in the afternoon the gas-and-steam plume continued and a sediment plume was dispersing from the island (figure 86). The VAL was lowered to level 3 (minor volcanic eruption) at 1625 that day; the Aviation Colour Code remained at Orange.

Figure 85. A view of Whakaari/White Island from Whakatane in the North Island of New Zealand. Left: there is no plume visible at 1410 on 9 December 2019, one minute before the eruption. Right: A gas-and-steam plume is visible 21 minutes after the eruption. Courtesy of GeoNet.

Figure 86. A gas-and-steam plume rises from Whakaari/White Island on the afternoon of 9 December 2019 as rescue teams visit the island. A sediment plume in the ocean is dispersing from the island. Courtesy of Auckland Rescue Helicopter Trust.

During or immediately after the eruption an unstable portion of the SW inner crater wall, composed of 1914 landslide material, collapsed and was identified in satellite radar imagery acquired after the eruption. The material slid into the crater lake area and left a 12-m-high scarp. Movement in this area continued into early January.

Activity from late 2019 into early 2020. A significant increase in volcanic tremor began at around 0400 on 11 December (figure 87). The increase was accompanied by vigorous steaming and ejections of mud in several of the new vents. By the afternoon the tremor was at the highest level seen since the 2016 eruption, and monitoring data indicated that shallow magma was driving the increased unrest.

Figure 87. This RSAM (Real-Time Seismic Amplitude) time series plot represents the energy produced at Whakaari/White Island from 11 November to 11 December 2019 with the Volcanic Activity Levels and the 9 December eruption indicated. The plot shows the sharp increase in seismic energy during 11 December. Courtesy of GeoNet (11 December 2019 report).

The VAL was lowered to 2 on the morning of 12 December to reflect moderate to heightened unrest as no further explosive activity had occurred since the event on the 9th. Volcanic tremor was occurring at very high levels by the time a bulletin was released at 1025 that day. Gas emissions increased since 10 January, steam and mud jetting continued, and the situation was interpreted to be highly volatile. The Aviation Colour Code remained at Orange. Risk assessment maps released that day show the high-risk areas as monitoring parameters continued to show an increased likelihood of another eruption (figure 88).

Figure 88. Risk assessment maps of Whakaari/White Island show the increase in high-risk areas from 2 December to 12 December 2019. Courtesy of GeoNet (12 December 2019 report).

The volcanic activity bulletin for 13 December reported that volcanic tremor remained high, but had declined overnight. Vigorous steam and mud jetting continuing at the vent area. Brief ash emission was observed in the evening with ashfall restricted to the vent area. The 14 January bulletin reported that volcanic tremor had declined significantly over night, and nighttime webcam images showed a glow in the vent area due to high heat flow.

Aerial observations on 14 and 15 December revealed steam and gas emissions continuing from at least three open vents within a 100 m² area (figure 89). One vent near the back of the crater area was emitting transparent, high-temperature gas that indicated that magma was near the surface, and produced a glow registered by low-light cameras (figure 90). The gas emissions had a blue tinge that indicated high SO₂ content. The area that once contained the crater lake, 16 m below overflow before the eruption, was filled with debris and small isolated ponds mostly from rainfall, with different colors due to the water reacting with the eruption deposits. The gas-and-steam plume was white near the volcano but changed to a gray-brown color as it cooled and moved downwind due to the gas content (figure 91). On 15 December the tremor remained at low levels (figure 92).

Figure 89. The Main Crater area of Whakaari/White Island showing the active vent area and gas-and-steam emissions on 15 December 2019. Gas emissions were high within the circled area. Before the eruption a few days earlier this area was partially filled by the crater lake. Courtesy of GeoNet (15 December 2019 report).

Figure 90. A low-light nighttime camera at Whakaari/White Island imaged "a glow" at a vent within the active crater area on 13 December 2019. This glow is due to high-temperature gas emissions and light from external sources like the moon. Courtesy of GeoNet (15 December 2019 report).

Figure 91. A gas-and-steam plume at Whakaari/White Island on 15 December 2019 is white near the crater and changes to a grey-brown color downwind due to the gas content. Courtesy of GeoNet (15 December 2019 report).

Figure 92. The Whakaari/White Island seismic drum plot showing the difference in activity from 12 December (top) to 15 December (bottom). Courtesy of GeoNet (15 December 2019 report).

On 19 December tremor remained low (figure 93) and gas and steam emission continued. Overflight observations confirmed open vents with one producing temperatures over 650°C (figure 94). SO₂ emissions remained high at around 15 kg/s, slightly lower than the 20 kg/s detected on 12 December. Small amounts of ash were produced on 23 and 26 December due to material entering the vents during erosion.

Figure 93. This RSAM (Real-Time Seismic Amplitude) time series plot represents the energy produced at Whakaari/White Island from 1 November to mid-December 2019. The Volcanic Alert Levels and the 9 December eruption are indicated. Courtesy of GeoNet.

Figure 94. A photograph and thermal infrared image of the Whakaari/White Island crater area on 19 December 2019. The thermal imaging registered temperatures up to 650°C at a vent emitting steam and gas. Courtesy of GeoNet.

The Aviation Colour Code was reduced to Yellow on 6 January 2020 and the VAL remained at 2. Strong gas and steam emissions continued from the vent area through early January and the glow persisted in nighttime webcam images. Short-lived episodes of volcanic tremor were recorded between 8-10 January and were accompanied by minor explosions. A 15 January bulletin reported that the temperature at the vent area remained very hot, up to 440°C, and SO₂ emissions were within normal post-eruption levels.

High temperatures were detected within the vent area in Sentinel-2 thermal data on 6 and 16 January (figure 95). Lava extrusion was confirmed within the 9 December vents on 20 January. Airborne SO₂ measurements on that day recorded continued high levels and the vent temperature was over 400°C. Observations on 4 February showed that no new lava extrusion had occurred, and gas fluxes were lower than two weeks ago, but still elevated. The temperatures measured in the crater were 550-570°C and no further changes to the area were observed.

Figure 95. Sentinel-2 thermal infrared satellite images show elevated temperatures in the 9 December 2019 vent area on Whakaari/White Island. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Information Contacts: New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/); GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Bay of Plenty Emergency Management Group Civil Defense, New Zealand (URL: http://www.bopcivildefence.govt.nz/); Auckland Rescue Helicopter Trust, Auckland, New Zealand (URL: https://www.rescuehelicopter.org.nz/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Ben Clarke, The University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom (URL: https://le.ac.uk/geology, Twitter: https://twitter.com/PyroclasticBen); Michael Schade, San Francisco, USA (URL: https://twitter.com/sch).

Kadovar is an island volcano north of Papua New Guinea and northwest of Manam. The first confirmed historical activity began in January 2018 and resulted in the evacuation of residents from the island. Eruptive activity through 2018 changed the morphology of the SE side of the island and activity continued through 2019 (figure 36). This report summarizes activity from May through December 2019 and is based largely on various satellite data, tourist reports, and Darwin Volcanic Ash Advisory Center (VAAC) reports.

Figure 36. The morphological changes to Kadovar from 2017 to June 2019. Top: the vegetated island has a horseshoe-shaped crater that opens towards the SE; the population of the island was around 600 people at this time. Middle: by May 2018 the eruption was well underway with an active summit crater and an active dome off the east flank. Much of the vegetation has been killed and ashfall covers a lot of the island. Bottom: the bay below the SE flank has filled in with volcanic debris. The E-flank coastal dome is no longer active, but activity continues at the summit. PlanetScope satellite images copyright Planet Labs 2019.

Since this eruptive episode began a large part of the island has been deforested and has undergone erosion (figure 37). Activity in early 2019 included regular gas and steam emissions, ash plumes, and thermal anomalies at the summit (BGVN 44:05). On 15 May an ash plume originated from two vents at the summit area and dispersed to the east. A MODVOLC thermal alert was also issued on this day, and again on 17 May. Elevated temperatures were detected in Sentinel-2 thermal satellite data on 20, 21, and 30 May (figure 38), with accompanying gas-and-steam plumes dispersing to the NNW and NW. On 30 May the area of elevated temperature extended to the SE shoreline, indicating an avalanche of hot material reaching the water.

Figure 37. The southern flank of Kadovar seen here on 13 November 2019 had been deforested by eruptive activity and erosion had produced gullies down the flanks. Copyrighted photo by Chrissie Goldrick, used with permission.

Figure 38. Sentinel-2 thermal satellite images show elevated temperatures at the summit area, and down to the coast in the top image. Gas-and-steam plumes are visible dispersing towards the NW. Sentinel-2 false color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel-Hub Playground.

Throughout June cloud-free Sentinel-2 thermal satellite images showed elevated temperatures at the summit area and extending down the upper SE flank (figure 38). Gas-and-steam plumes were persistent in every Sentinel-2 and NASA Suomi NPP / VIIRS (Visible Infrared Imaging Radiometer Suite) image. MODVOLC thermal alerts were issued on 4 and 9 June. Similar activity continued through July with gas-and-steam emissions visible in every cloud-free satellite image. Thermal anomalies appeared weaker in late-July but remained at the summit area. An ash plume was imaged on 17 July by Landsat 8 with a gas-and-ash plume dispersing to the west (figure 39). Thermal anomalies continued through August with a MODVOLC thermal alert issued on the 14th. Gas emissions also continued and a Volcano Observatory Notice for Aviation (VONA) was issued on the 19th reporting an ash plume to an altitude of 1.5 km and drifting NW.

Figure 39. An ash plume rising above Kadovar and a gas plume dispersing to the NW on 17 July 2019. Truecolor pansharpened Landsat 8 satellite image courtesy of Sentinel Hub Playground.

An elongate area extending from the summit area to the E-flank coastal dome appears lighter in color in a 7 September Sentinel-2 natural color satellite image, and as a higher temperature area in the correlating thermal bands, indicating a hot avalanche deposit. These observations along with the previous avalanche, persistent elevated summit temperatures, and persistent gas and steam emissions from varying vent locations (figure 40) suggests that the summit dome has remained active through 2019.

Figure 40. Sentinel-2 visible and thermal satellite images acquired on 7 September 2019 show fresh deposits down the east flank of Kadovar. They appear as a lighter colored area in visible, and show as a hot area (orange) in thermal data. Sentinel-2 natural color (bands 4, 3, 2) and false color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel-Hub Playground.

Thermal anomalies and emissions continued through to the end of 2019 (figure 41). A tour group witnessed an explosion producing an ash plume at around 1800 on 13 November (figure 42). While the ash plume erupted near-vertically above the island, a more diffuse gas plume rose from multiple vents on the summit dome and dispersed at a lower altitude.

Figure 41. The summit area of Kadovar emitting gas-and-steam plumes in August, September, and November 2019. The plumes are persistent in satellite images throughout May through December and there is variation in the number and locations of the source vents. PlanetScope satellite images copyright Planet Labs 2019.

Figure 42. An ash plume and a lower gas plume rise during an eruption of Kadovar on 13 November 2019. The summit lava dome is visibly degassing to produce the white gas plume. Copyrighted photos by Chrissie Goldrick, used with permission.

While gas plumes were visible throughout May-December 2019 (figure 43), SO₂ plumes were difficult to detect in NASA SO₂ images due to the activity of nearby Manam volcano. The MIROVA thermal detection system shows continued elevated temperatures through to early December, with an increase during May-June (figure 44). Sentinel-2 thermal images showed elevated temperatures through to the end of December but at a lower intensity than previous months.

Figure 43. This photo of the southeast side Kadovar on 13 November 2019 shows a persistent low-level gas plume blowing towards the left and a more vigorous plume is visible near the crater. This is an example of the persistent plume visible in satellite imagery throughout July-December 2019. Copyrighted photo by Chrissie Goldrick, used with permission.

Figure 44. The MIROVA plot of radiative power at Kadovar shows thermal anomalies throughout 2019 with some variations in frequency. Note that while the black lines indicate that the thermal anomalies are greater than 5 km from the vent, the designated summit location is inaccurate so these are actually a the summit crater and on the E flank. Courtesy of MIROVA.

Geologic Background. The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. It is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the andesitic volcano, filling an arcuate landslide scarp open to the south; submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. A period of heightened thermal phenomena took place in 1976. An eruption began in January 2018 that included lava effusion from vents at the summit and at the E coast.

Information Contacts: 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/); Planet Labs, Inc. (URL: https://www.planet.com/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Worldview (URL: https://worldview.earthdata.nasa.gov); Chrissie Goldrick, Australian Geographic, Level 7, 54 Park Street, Sydney, NSW 2000, Australia (URL: https://www.australiangeographic.com.au/).

The 32 recorded explosions . . . in October . . . caused no damage. The month's highest ash cloud rose 4 km above the crater. Ash deposition [at KLMO] was 93 g/m² . . . . Swarms of volcanic earthquakes were recorded on 2, 4, 10, and 18 October. Explosions became less frequent in November, with only three as of the 17th . . . .

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: JMA.

Lava effusion continued through October. Two blocky flows were observed descending the WNW and SSW flanks in September, and continued to spall blocks from the advancing fronts in October. September fieldwork revealed that only blocks from the SSW-flank flow that was active in May and June reached the forest edge, and that the flow itself did not enter the forest. This flow was still hot in September and emitted vapor from its surface. Rapid erosion continued in flank ravines, carrying sediment downstream, where 14 cm of material has been deposited in Laguna Cedeño (2.5 km N) during the last 9 months.

Strombolian and fumarolic activity continued in Crater C, although explosions weakened at the end of September. During observations on 23-25 October, explosions were separated by 25-100 minutes. The daily number of earthquakes recorded by the ICE network was relatively low in September, averaging 10 (maximum 18), increasing to an average of 20 (maximum 55) in October. Significant tremor episodes occurred on 18-20 September, and 6, 12, and 26-29 October.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: R. Barquero and G. Soto, ICE.

SANE provided additional information . . . from passing ships and aircraft, and occasional visits. The eruption's start date remained uncertain, but the first reported activity consisted of gusts of hot air from the N end of the crater on 28 March, and "smoke" observed from a Coast Guard aircraft on 6 April. By 1 May, intensified activity and bigger plumes were seen from ships, and pilots observed numerous dead fish near the island on 9 May. When a GSI team reached Barren Island on 16 May, lava had covered an 800 x 200 m area, and by their next visit on 26 June (16:5 & 8) lava had reached the sea. Continued lava production was reported through July, and accompanying pulsating columns of incandescent tephra were ejected to roughly 60 m height twice in five minutes during observations from Navy aircraft on 30 July. Little information was available on August and September activity.

The eruption was continuing on 24 October, but the 1991 cone collapsed shortly thereafter and only small amounts of "smoke" were intermittently observed during the first week in November.

Geologic Background. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

Information Contacts: S. Acharya, SANE; D. Shackelford, Fullerton, CA.

The rainy season limited summit observations in August and September, often cloaking the volcano in clouds, and severely damaging the unpaved access road. By October, however, aerial reconnaissance and distant ground observations indicated changes to summit morphology. Some landslides had apparently occurred along the 1975 flow levees on the main cone's SE flank, and weak steam clouds rose from points along the 1975 lava. The SSW flank was occupied by the March-April 1991 lava flow, which stopped after descending to 2,600 m altitude. The flow is about 100-125 m wide and reaches a maximum thickness of 25 m, with a central depression about 10 m deep. [Deposits produced after the partial collapse of the summit lava dome on 16 April were eroded during the rainy season, leaving new ravines 5-15 m deep. See follow-up report in BGVN 17:06.]

Fumarolic activity has been irregular, appearing strong on some days, weaker on others. Fumaroles were concentrated in the area of the 1991 lava flow outlet and on the NE part of the summit dome. Weak fumaroles were also visible on zones of expansion on the main dome.

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: J. Flores, J. Hernández, R. Saucedo, A. Cortés, C. Valencia, and R. García, CICT, Universidad de Colima; Z. Jiménez, Instituto de Geofísica, UNAM.

An 8-19 October resurvey of a 46-line EDM network on the upper S flank showed little movement since July, with maximum line-length changes of ~0.0015%. Activity at the summit craters was more energetic than in July but had the same general characteristics. Continued Strombolian activity in the NE sector of Southeast Crater periodically increased in strength, with large incandescent blebs of lava rising tens of meters above the crater rim. The open vent in Northeast Crater was degassing strongly and incandescent at night, while the two vents on the floor of Bocca Nuova had mild to strong Strombolian activity. E of Bocca Nuova, a single vent on the floor of La Voragine displayed weak Strombolian activity and daylight incandescence.

Further Reference. McGuire, W., Murray, J., Pullen, A., and Saunders, S., 1991, Ground deformation monitoring at Mt. Etna: evidence for dyke emplacement and slope instability: Journal of the Geological Society, London, v. 148, p. 577-583.

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: S. Saunders, West London Institute; W. McGuire, Cheltenham and Gloucester College of Higher Education.

An 18 October overflight by the JMSA revealed discolored green water over the submarine volcano.

Geologic Background. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the pyramidal island of Minami-Ioto. Water discoloration is frequently observed from the volcano, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.

Information Contacts: JMA.

The summit crater lava dome continued to grow through the second week of November, and was ~50 m thick by 23 October (figure 46). The surface of the dome was covered by angular blocks, some >4 m in diameter, most notable on the dome's E and SE edges. The central portion of the dome was covered by smaller fragments. The dome was first observed during an overflight on 9 October, but the start of dome growth may have been 3-4 October when high levels of sustained tremor (episodes of ~2 Hz lasting to 30 minutes) were recorded.

Figure 46. Sketch of the crater area of Galeras, showing dome and fumarole locations on 23 October 1991. Courtesy of INGEOMINAS.

Gas and ash emissions occurred from different points on the dome surface, occasionally ejecting blocks to short distances. Surface activity closely corresponded with tremor and long-period seismic events that were recorded about 10-15 times/hour. Seismic energy release and the number of earthquakes continued to increase in October (see figure 52), again establishing new monthly highs at Galeras.

Electronic tiltmeters showed continued deformation during October, with 234 µrad of accumulated inflation at 190° azimuth measured [at Crater Station]; (figure 47), and 41 µrad at 292° azimuth measured [at Peladitos Station]. Slight inflation was also measured 2.3 km E of the crater (at "Piedras"). A decrease in the rate of inflation at Crater Station occurred on 9 October.

Figure 47. Tangential (top curve) and radial (bottom curve) deformation measured 0.9 km E of the crater (by the "Crater" electronic tiltmeter) at Galeras, October 1991. Courtesy of INGEOMINAS.

The daily average SO₂ flux varied widely from ~100 t/d (23 October) to ~1,700 t/d (28 October; figure 48), reaching higher values than in August or September (maxima of 370 and 1,045 t/d respectively). Airborne COSPEC measurements on 12 November indicated SO₂ fluxes of up to 2,500 t/d.

Figure 48. Daily average SO2 flux at Galeras, October 1991. No measurements were made on days without data. Courtesy of INGEOMINAS.

Reference. Calvache, M.L., 1990, Geology and volcanology of the recent evolution of Galeras volcano, Colombia: M.S. Thesis, Louisiana State University, Baton Rouge, LA, 172 p.

Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.

Information Contacts: INGEOMINAS-OVP; S. Williams and M. Calvache, Arizona State Univ.

The following report about the effects of ash from Hudson's 12-15 August eruption on livestock is from the U.S. Centers for Disease Control.

"Large numbers of livestock deaths were reported in Santa Cruz province, Argentina, in the weeks immediately following the initial eruptions of Hudson. In response to reports that large numbers of sheep deaths were due to high fluoride levels from ash, an investigation was conducted by U.S. Centers for Disease Control personnel in cooperation with the Office of Foreign Disaster Assistance.

"Analysis of sheep urine and ash samples collected between 17 and 22 September revealed low levels of fluoride. Mean fluoride urine levels of 5.7 mg/L fall within the normal range for ruminants. Preliminary fluoride analyses on ash samples collected at different distances from Hudson were performed both before and after rainfall. Ion chromatography using acetic acid extraction revealed fluoride levels ranging from nondetectable to 14 ppm in the samples collected 17-20 September. Although this ash analysis is preliminary, the results indicate that fluoride levels in these samples are well below toxic concentrations. The maximally tolerable range for fluoride concentrations in ruminant feed is between 40 and 50 ppm.

"These results, in combination with clinical impressions, lead to the conclusion that a great many of the sheep deaths are possibly due to a complex set of environmental, topographical, and husbandry conditions that were exacerbated by the presence of large amounts of volcanic ash. The sheep in Santa Cruz had just survived a particularly harsh winter and were going into the spring lambing season feeding on overgrazed land that had undergone a period of prolonged drought. Pregnant ewes are typically very susceptible to toxemia late in gestation and the unavailability of food and water due to ashcover for even a short period of time is sufficient to trigger this often fatal condition. Clinical observations of sheep deaths in the area of volcano ashfall are consistent with death due to complications of pregnancy, greatly exacerbated by the physical presence of ash. Pregnancy toxemia is a condition with a very poor prognosis and no easy and certain treatment."

Geologic Background. The ice-filled, 10-km-wide caldera of the remote Cerro Hudson volcano was not recognized until its first 20th-century eruption in 1971. It is the southernmost volcano in the Chilean Andes related to subduction of the Nazca plate beneath the South American plate. The massive volcano covers an area of 300 km2. The compound caldera is drained through a breach on its NW rim, which has been the source of mudflows down the Río de Los Huemeles. Two cinder cones occur N of the volcano and others occupy the SW and SE flanks. This volcano has been the source of several major Holocene explosive eruptions. An eruption about 6700 years ago was one of the largest known in the southern Andes during the Holocene; another eruption about 3600 years ago also produced more than 10 km3 of tephra. An eruption in 1991 was Chile's second largest of the 20th century and formed a new 800-m-wide crater in the SW portion of the caldera.

Information Contacts: C. Rubin and E. Noji, Centers for Disease Control, Atlanta.

Fumarolic activity continued within the crater through October, with no significant changes, although there was an apparent slight temperature decrease from 90.0-91.6°C in September, to 83.8-90.4°C in October. The hottest and most vigorous fumarole was located in an alluvial fan on the crater's N side. Crater lake level increased in September, and stabilized through October at a maximum depth of 14 m. Small fluctuations were noted, corresponding with rainfall. Seismicity continued to decline in September, reaching very low levels in October.

Geologic Background. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: R. Barquero and G. Soto, ICE.

"Geologists visited Satsuma-Iwo-jima 7-10 November. Several large fumarole fields exist within and around the 300-m-diameter crater. Accessible fumaroles had temperatures ranging from 100 to > 800°C. Several types of sampling were conducted to geochemically characterize the emissions. GSJ geologists had used a COSPEC to measure a maximum SO₂ flux of 500 t/d in May 1990, similar to . . . 15 years previously. In addition to geochemical samples, a portable spectrometer was used to collect spectra of various features to provide ground truth for satellite images of the region. The major summit geomorphological change since last year's visit by GSJ geologists was the formation of a 15 x 30 m pit crater in the SE corner of the main summit crater. Local silica-mine workers first noticed the new pit crater in June or July 1991. A large plume was continuously emitted from the pit crater."

Geologic Background. Kikai is a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. It was the source of one of the world's largest Holocene eruptions about 6,300 years ago when rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake lava dome and Inamuradake scoria cone, as well as submarine lava domes. Historical eruptions have occurred at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km E of Tokara-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Tokara-Iojima.

Information Contacts: R. Andres, Michigan Technological Univ; H. Shinohara, R. Symonds, and B. Ritchie, GSJ.

New fissure vents opened on 8 November between the East rift zone's two active vents (Kupaianaha and Pu`u `O`o), feeding aa flows that advanced into the remnants of Royal Gardens subdivision (figure 81). Lava from Kupaianaha vent continued to emerge from tubes on the W side of the flow field, but the lava pond in Pu`u `O`o drained rapidly and was no longer visible by 11 November.

Figure 81. Lava produced by Kilauea's East Rift eruption, 1983-91 (stippled). The area of October surface lava flow activity from Kupaianaha vent is indicated by a diagonal pattern. Arrows indicate flow in tubes. Crosses mark the discontinuous fissure vents that opened between Pu`u `O`o and Kupaianaha on 8 November. Lava extruded by the new fissures as of mid-November is black. Courtesy of HVO.

October activity. Lava from Kupaianaha vent moved downslope through tubes and emerged onto the W side of the flow field through October, feeding surface flows between ~400 m (1,300 ft) altitude and the coastal plain (figure 81). Lava that broke out of the main (Wahaula) tube at ~270 m (900 ft) destroyed one of the remaining houses in Royal Gardens subdivision on 27 October. Breakouts behind the flow front destroyed a nearby house 4 days later. The two destroyed houses, and two others that remained intact nearby, had been isolated by 1990 flows. Three houses in Royal Gardens remained inhabited at the end of October, one within 1 km of recent flows. In the past few months, flows in this area have extended the margin of the lava field ~700 m to the W, but have been blocked from reaching the ocean by 1989 lava.

Kupaianaha vent's lava pond remained frozen during October. During an 11 October overflight, two small skylights were seen next to the former pond: one in large cracks on the faulted, uprift side of the pond, and the other (emitting heavy fume) in the crater wall on the pond's SE side. The lava pond in Pu`u `O`o crater fluctuated between 1 and 10 m below the crater floor, 36 m below the 1986 spillway. The vigorous degassing episodes noted in previous months were not as common in October. Fieldwork on 25 October revealed a large pile of spatter in the former spillway, and tephra that included Pele's tears and reticulite were found along the downrift side of the crater rim (figure 82).

Figure 82. Pu`u `O`o's crater floor, 25 October 1991. Tephra deposits in and around the 1986 spillway are shown. Periodic overflows of the active pond have coated much of the crater floor. Sketch by Mauro Coltelli; courtesy of HVO.

Fissure eruption beginning 8 November. Seismic activity preceding the fissure eruption began with a short burst of shallow summit tremor on 8 November at about 0200, followed by small earthquakes that became frequent beneath the summit and upper East rift zone. The summit began to deflate at about 0430 as magma moved into the upper east rift. The fissures opened from W to E starting before 0445, with the easternmost fissures opening about 0500. Glow was reported just downrift from Pu`u `O`o at 0450. A plume of dust rose roughly 400 m above Pu`u `O`o at about 0715, as the crater floor collapsed. Helicopter pilots reported that at 0745 the pond at Pu`u `O`o had drained and a fissure eruption was underway, initially from a discontinuous series of fissures ~1.5 km long. Volcanic tremor intensified beneath the summit and in the vent area that night. The next day, lava fountains were <5 m high, and by the morning of 10 November the eastern fissures were feeding lava directly into a pond nearly 15 m deep. Late that day, the pond was stagnant NE of the fissures, but to the SE, two wide channelized aa flows were moving slowly toward the coast. The pond had drained into a rapidly advancing aa flow by the morning of 11 November, and fountains had again emerged above the subsided pond.

By 1600 on 11 November, the flows had advanced 3 km to ~400 m (1,300 ft) altitude, at the top of Royal Gardens subdivision, and trees were burning along the subdivision's E side. Two days later, the flows had advanced another 200 m into Royal Gardens. As of 14 November, the flow front was stagnant, but new aa flows were advancing atop earlier lava, and were particularly active ~125 m above the multilobate terminus. Lava was issuing quietly into a channel ~30 m wide that fed the flows downslope, but fountaining had stopped. The deflation rate at the summit had slowed during 8-10 November, accelerated on 11 November, but was slowing again as of the 14th. Volcanic tremor, indicating magma migration, continued at moderate levels beneath the summit and upper East rift zone, but amplitudes decreased on 13 November.

The level of lava in the tube extending from Kupaianaha to the flat area near the coast has dropped somewhat since the onset of fissure activity. Pahoehoe flows originating at Kupaianaha remained active on the E side of Royal Gardens subdivision on 14 November, but other Kupaianaha flows had stagnated along the coastal plain. [see also 16:11]

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: T. Mattox and P. Okubo, HVO.

An earthquake swarm occurred 24-25 October in the sea 7 km N of Kozu-shima (figure 1). The largest shocks (M 4.9) were recorded at 1746 and 1754 on the 24th. Changes in surface activity were not observed on the island or in the epicentral area. The seismicity was the first for the area since 23 April . . . .

Geologic Background. A cluster of rhyolitic lava domes and associated pyroclastic deposits form the small 4 x 6 km island of Kozushima in the northern Izu Islands. Kozushima lies along the Zenisu Ridge, one of several en-echelon ridges oriented NE-SW, transverse to the trend of the northern Izu arc. The youngest and largest of the 18 lava domes, 574-m-high Tenjoyama, occupies the central portion of the island. Most of the older domes, some of which are Holocene in age, flank Tenjoyama to the north, although late-Pleistocene domes are also found at the southern end of the island. Only two possible historical eruptions, from the 9th century, are known. A lava flow may have reached the sea during an eruption in 832 CE. Tenjosan lava dome was formed during a major eruption in 838 CE that also produced pyroclastic flows and surges. Earthquake swarms took place during the 20th century.

Information Contacts: JMA.

"Moderate to strong activity persisted throughout October. Crater 2 activity consisted of continuous release of white vapour, producing a small emission column that frequently (5-15 times/hour) turned into a forceful jet of ash-laden vapour, generating a whooshing sound. Occasionally, a discontinuous tremor-like signal was recorded by the 1-km-distant LAN seismometer. Light ashfalls were experienced in coastal areas 10 km downwind. On most nights this Vulcanian activity was accompanied by dull glow above the crater, becoming brighter at times when incandescent lava fragments were ejected onto the flanks of the cone.

"Activity at Crater 3 was intermittent, with periods of 5-15 minutes devoid of any emission separated by sudden forceful explosive emissions of thick, mushrooming, dark grey ash clouds that rose 400-650 m above the crater rim. The crater was more strongly active 4-10 October, when small pyroclastic flows were generated at the base of the strongest explosions, but these did not advance beyond the cone's upper flanks. Intermittent glow from the crater was accompanied by incandescent projections to ~100 m above the crater rim. Crater 3 explosions were recorded as distinct impulsive signals (5-50/day) by the LAN seismic station, with the strongest ones (1-12/day) recorded 9 km away (CGA station).

"Seismic activity dropped significantly in October. The intermittent tremor recorded since June disappeared in September but reappeared sporadically in October. Most of the seismicity consisted of discrete earthquakes. The daily totals of these events ranged from 15 to 60.

"Aerial and ground inspections were carried out 10-11 October. The main change noted since the last inspection, in mid-August, concerned Crater 3. Of the 2 active vents previously observed in the mound of lava filling the original crater, the N one (which seemed the most active in August) was inactive, while a 50-m explosion crater had formed around the S vent, which was the source of the reported Vulcanian activity. This new crater was bowl-shaped, ~6 m deep, and filled with loose debris-blocks and ash. Similar debris also extended in short tongues to <100 m outside the crater rim and probably was deposited by small pyroclastic flows such as those reported earlier in October. Within the crater were irregular arcuate ridges of loose debris that may have been deposited by pyroclastic flows. The active vent area was only ~5 m across. Although it remained glowing for a short time after each explosion, the maximum temperature measured with an infrared thermometer from 30 m distance was only 500°C when erupting, and 270°C when quiet. The temperature of the crater floor was 140-170°C.

"The short lava flow observed 12 August on the cone's N flank had cooled, but a few rootless fumaroles remained on its surface, which was partly buried under airfall blocks and ash. The flow had the rugged surface features of aa lava and was ~300 m long, extending from the crater rim (~1,100 m elev) to 950 m elev. Its thickness decreased from 2.5 m (where it spilled over the crater rim) to <1 m at its front. The volume of the flow is estimated to be <=15,000 m³.

"Crater 2 was estimated to be 130 m wide and 30 m deep. Its floor is now at the level of the upper bench described in the last ground inspection, in June 1989 (SEAN 14:06). Several small vents (<=1 m in diameter), although closely grouped at the base of the crater, were activated independently. At the times of the strongest emissions however, up to four vents erupted concurrently with a deafening jet engine noise, generating air and ground vibrations recorded by the summit seismic station as emergent periods of tremor-like signals. The westernmost vent was directing its jet of ash-laden vapour at an angle of 15° toward the SE, resulting in the backfall of blocks and spatter-like scoriae on the SE crater rim and beyond. The maximum measured temperature at the base of the jet (although glowing at times) was only 240°C, and 70°C higher up in the plume."

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: P. de Saint-Ours and C. McKee, RVO.

At 1620-1625 on 21 October, an explosion and a roughly 2,000-m-high dark gray column were observed by Santos Soza, a Minsal Ltda. employee based 35 km NW of the volcano (in Toconao). Wind carried the plume NE, and completely dispersed it within 20 minutes. The explosion was not audible, but it was accompanied by a small shock, with a duration of a few seconds, felt at Toconao. A second, smaller eruption column was observed the following day at about 1400 without accompanying felt seismicity or an audible explosion.

Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Information Contacts: J. Naranjo, SERNAGEOMIN, Santiago; V. Letelier, Minsal Ltda., Toconao.

Vigorous explosions on 24 October ejected ash to ~2 km height, and may have generated a pyroclastic flow on 25 October, before a decline in activity noted at 2000. As much as 1 m of tephra was reportedly deposited near the summit, but only 2.5 cm of ash fell 4 km E (at Kinilaw). The airport at Manado (15 km NE; figure 1) was closed until 29 October, because of poor visibility and minor ashfall. By 29 October, more than 1900 buildings and roughly 3 km² of clove trees and coconut palms had been damaged; ~10,000 people were evacuated. Ash and incandescent material ejected on 6 November reached 300 m height. Large explosions on 17 and 20 November produced ash columns 1,000 and 2,500 m high, respectively, panicking residents of nearby villages, who had recently returned to their homes. Ash emissions continued the next day, but were less frequent and less intense. Vivianne Clavel, a Swiss volcanologist studying the eruption, was reported missing on 24 October, and had not been located by searchparties at press time.

Figure 1. Map of Lokon-Empung, based on a portion of the Manado, Indonesia 1:250,000 sheet (Joint Operations Graphic-Ground, series 1501, sheet NA 51-12, Army Map Service, Washington). Contour interval, 200 m.

[Despite rescue efforts, no signs of V. Clavel were found. According to a witness, she was killed by falling blocks and buried by ash.]

Geologic Background. The twin volcanoes Lokon and Empung, rising about 800 m above the plain of Tondano, are among the most active volcanoes of Sulawesi. Lokon, the higher of the two peaks (whose summits are only 2 km apart), has a flat, craterless top. The morphologically younger Empung volcano to the NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks. Historical eruptions have primarily produced small-to-moderate ash plumes that have occasionally damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred. A ridge extending WNW from Lokon includes Tatawiran and Tetempangan peak, 3 km away.

Information Contacts: N. MacLeod, Ridgefield WA, USA; T. Casadevall, USGS; U.S. Embassy, Jakarta; UPI; Reuters; AP.

[The eruption] has continued without explosive venting visible from a distance. Observers on a boat that passed Marchena on 7 or 8 November reported vigorous steaming at the W coast. Water near the flow front was too hot to touch and numerous fumaroles were evident inland. Since David Day's 28-30 September visit, lava had formed a single broad front at the coast, closing the small bay where Day had landed.

Reports collected by Day provided additional information about the timing and characteristics of the early phases of the eruption. The first reported activity was a "suspicious" large cloud seen over Marchena on 25 September at 1840 from ~65 km S (at Bartolomé). An explosion was observed at 1905 from ~90 km SSE (Turtle Cove, Santa Cruz Island). A low white cloud near the coast was seen with infrared binoculars at about 2100. Witnesses at three sites ~65 km S reported 7-8 evenly spaced vents that remained active throughout the night. Incandescent ejecta appeared to rise roughly the equivalent of the island's elevation (~350 m), with height increases of ~25% during the strongest activity. A more vigorous vent, lying W of the others, was first seen at about 0300 on 26 September. Ejecta heights from the W vent appeared to exceed those from the other vents by ~50%.

Geologic Background. The low shield volcano forming Marchena Island contains one of the largest calderas of the Galápagos Islands. The 6 x 7 km caldera and its outer flanks have been largely buried by a cluster of pyroclastic cones and associated lava flows. Its first historical eruption occurred in 1991. Other young lava flows, some of which may be only a few thousand, or even a few hundred years old, filled the caldera and flowed down its outer forested flanks, in some cases to the sea.

Information Contacts: D. Day, Isla Santa Cruz.

The following paragraph, from M. Kasahara, K. Tanaka, and N. Zana supplements last month's report.

After 25 months of quiet, an eruption began at 0130 on 20 September, from a N30°E fissure [see slightly revised trend in 17:1] ~15 km NE of the summit caldera and 5 km NE of the 1958 (Kitsimbanyi) eruption site (figure 8). An earthquake swarm began about a week before the eruption (figure 9), but gradually declined between 16 September and eruption's onset, with changing seismic waveforms reflecting a shift to lower frequencies. The start of the eruption was witnessed from ~10 km SE (at Rumangabo) and clearly recognized by the appearance of continuous tremor on a seismograph (BLG) operated by the CRSN 40 km SSW of the eruption site. Tremor amplitude was half its initial value a day after the eruption began, but tremor was continuing in late September (figure 10). Lava fountain activity continued at the N end of the fissure [but see 17:1], producing a new cone and two lava flows. During the first week of the eruption, the new cone (named Mikombe; "many bats") grew to 60-70 m height with basal dimensions of 400 x 300 m (figure 11). Lava extended 6-7 km NE, along and over the 1958, 1967, and 1980 flows. The eruption remained vigorous on 30 September when initial field studies ended.

Figure 9. Daily number of earthquakes recorded at a seismic station (BLG), ~40 km SW of Nyamuragira's 1991 eruption site, 9-27 September 1991. Courtesy of M. Kasahara.

Figure 10. Hourly variation in tremor amplitude recorded (at station KTL) roughly 15 km ESE of Nyamuragira's 1991 eruption site, from 12 hours after the onset of the eruption through early 28 September. Courtesy of M. Kasahara.

Figure 11. Topographic sketch map of the Mikombe cone 15 km NE of Nyamuragira's summit, 27 September 1991. Contour interval is 10 m, with 0 representing the pre-eruption base level. Data points are elevations, in meters above base level. Courtesy of M. Kasahara.

Airline flight crews reported plumes to 7.5 km altitude on 15 and 20 October. On 21 October, CRSN geologists reported that activity was increasing, and lava had cut the road to Tongo. A new vent, SW of Mikombe, opened on 23 October [see also 17:1] and, as of 31 October, activity continued to increase at both vents. Pilot reports suggested that the ash cloud was only 200 m high by 2 November.

Given the first week's lava output, geologists expected the total volume to be of the same order as previous eruptions. The current eruption was believed to be a continuation of the highly active period that began with the 1976 eruption. Since then, seven flank eruptions have occurred in 15 years, 2-3 times the 1900-76 rate (Krafft, 1990).

Reference. Krafft, M., 1990, Führer zu den Virunga-Vulkanen: Ferdinand Enke Verlag, Stuttgart, 192 p.

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

Information Contacts: M. Kasahara and K. Tanaka, Hokkaido Univ; ICAO; H-L. Hody, GEOVAR, Kigali, Rwanda.

Although no explosions occurred within the caldera formed by the mid-June paroxysmal eruption, secondary explosions continued at pyroclastic-flow deposits through early November, causing ashfall, sulfur odors, and poor visibility. Seismicity and caldera steam emission continued to decline. Debris flows traveled down all major drainages during October, but observations suggested that the majority of the flows were more water-rich than in previous months.

7-13 October. Geologists entered the caldera for the first time on 8 October. The caldera rim elevation ranges from 1,100 m to about 1,000 m, with the lowest point on the NW side, and the caldera lake at roughly 800 m elevation. Strong steaming was observed on the S wall and along the lake shore, with numerous bubbles rising elsewhere in the lake. No ambient sulfur odor was detected when standing upwind of the fumaroles. Analyses of the caldera lake water revealed a temperature of 40°C and a pH of 6 (table 6), suggesting a primarily meteoric origin, although the plume's SO₂ flux dropped from roughly 100 t/d to 10 t/d when the lake formed. Most of the 1991 deposits within the caldera are composed of old dome rock, with almost no pumice present. No distinct ring faults are apparent.

Table 6. Chemistry of Pinatubo caldera lake water, 8 October 1991. Analyses by M. Campita, L. Ringer, and L. Tansinsin, PHIVOLCS.

Several small secondary explosions from the Sacobia valley pyroclastic-flow deposits (NE flank) were observed on 13 October; the largest, at 1247, produced a plume 2,000 m high. By about 1400, a sulfurous odor was detected, and moderate ashfall occurred at Clark Air Base. Secondary explosion signals were recorded seismically on 7 and 8 October but were not visually confirmed, while at other times during the week, small explosions were observed but not seismically recorded.

Seismicity continued to decline, with an average of 55 earthquakes recorded daily, compared to 63/day the previous week (figure 24). The earthquakes occurred at 2-10 km depth and most had magnitudes < 2. Two shocks of intensity I (modified Rossi-Forel scale) were felt at Clark Air Base.

Figure 24. Number of earthquakes (top) and Real-time Seismic Amplitude Measurement (bottom) at Pinatubo, 16 June-3 November 1991. Courtesy of PHIVOLCS.

Relatively small debris flows occurred in the NE, SE, and SW quadrants following heavy rainfall. Residents of Tarlac (45 km NE) noted that no large lahars had passed in the previous several weeks to months. Floods were reported along the E flank's Pasig-Potrero River (2/3 m deep) on 7 October, and the NE flank's Bamban River (waist-chest deep). Small flows occurred on the Pasig-Potrero River on 12 October, and the Sacobia, Abacan (both NE flank), and Pasig-Potrero Rivers on 13 October. The debris dam on the SE flank's Mapanuepe River began breaching again on 12 October.

14-20 October. Secondary explosions occurred in the upper Marella pyroclastic-flow deposits (SW flank) around midmorning on 14 October. One hour later, ashfall, accompanied by a sulfur odor and reduced visibility (500 m), were reported at Sitio Danalaon (18 km SW of the summit). By 1600, ash fell in Castillejos and San Marcelino (both ~30 km SW of the summit), and by 1800, ash fell in Subic (~35 km SSW). Additional explosions occurred in the upper Marella deposits on 16 and 18 October when a 500-m grayish ash cloud was produced. Ashfall from other secondary explosions was also reported in Angeles (25 km E) on 15 October.

Seismicity during the week declined to a daily average of 44 earthquakes, with most events at 5-10 km depths and M < 2. Earthquakes continued to occur in clusters. One large shock (M 3.4) on 15 October, centered about 4 km NE of the summit, was felt (intensity IV) at Clark Air Base. Other earthquakes were felt (intensities I-II) on 15, 16, 18, and 20 October.

Heavy rains on 16 October triggered small lahars on the NE, SW, and SE flanks. One large lahar, about 3 m high, traveled down the upper Pasig-Potrero River, transporting boulders up to 1 m in diameter. Small floods of muddy water were observed on the Marella River on the 14th.

21 October-3 November. An aerial survey of the caldera on 23 October showed that the lake level had risen, covering some large rocks that had been visible in August and September. Steam emissions on the S wall had decreased, and some had stopped. Some fresh talus extended into the lake. Observers 20 km SW (at Sitio Danalaon) reported pulsating weak to moderate steam emission from the caldera on 2 November.

Moderate-sized secondary explosions occurred in the Sacobia and Marella valley pyroclastic-flow deposits on 28 October, coincident with heavy rainfall. Near the Sacobia valley, sand-sized ashfall from secondary explosions was quite heavy during the early evening, and poor visibility caused drivers to stop their vehicles. Smaller explosions were observed in the Sacobia valley on 22 and 31 October, and in the Marella valley on 2 November when a dirty cloud 200 m high was produced.

The number of earthquakes averaged 37/day, at 5-10 km depths and mostly M < 2. The earthquakes occurred in clusters E, SSE, SW, N, and NW of the caldera (figure 25). Four shocks were felt at Clark Air Base, the largest (M 3.4) with intensity IV on 1 November, the other three (M 2.9-3.0, intensity I) on 25 and 31 October and 3 November.

Figure 25. Epicenters of 515 earthquakes at Pinatubo, 21 October-3 November 1991. Courtesy of PHIVOLCS.

Heavy rain from typhoon Ruth triggered lahars down most drainages on 28 October. On the SW flank, following 8 cm of rain in a 24-hour period, a hot lahar was observed travelling down the Marella River, a lahar up to 1 m high was observed on the Sto. Tomas River, and the debris dam on the Mapanuepe River was completely swept away. Lahars on the Pasig-Potrero River grew from ~0.5 m high at 1400, to a peak of 3 m high at 1654, and carried .5m-diameter pumice clasts and logs 3 m long and 30 cm in diameter. A lahar >1 m high was reported on the Porac River and a 65 cm hyperconcentrated flow was reported on the Gumain River (both SE flank). On the NE flank, lahars were reported on the Abacan and O'Donnell Rivers, and reached 3 m high on the Sacobia River. Flows were reported NW of the volcano, but they were more water-rich than previously, and there was no significant deposition. Small lahars occurred for several days following the 28th.

Geologic Background. Prior to 1991 Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located 100 km NW of Manila with no records of historical eruptions. The 1991 eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2.5-km-wide summit caldera whose floor is now covered by a lake. Caldera formation lowered the height of the summit by more than 300 m. Although the eruption caused hundreds of fatalities and major damage with severe social and economic impact, successful monitoring efforts greatly reduced the number of fatalities. Widespread lahars that redistributed products of the 1991 eruption have continued to cause severe disruption. Previous major eruptive periods, interrupted by lengthy quiescent periods, have produced pyroclastic flows and lahars that were even more extensive than in 1991.

Information Contacts: R. Punongbayan, PHIVOLCS.

Fumarolic activity in the yellowish-green crater lake continued through October, and mats of sulfur were observed floating on the water's surface. In September, strong bubbling was observed in the N- and NW-central parts of the lake, which was at 76.3°C with a pH <0.5. Lake measurements on 16 October indicated that the lake level had fallen 15 cm since 18 September, despite continued rains; water temperature was 74.4°C. Fumaroles on the 1953-55 dome ranged to 90.6°C in September and 88.4°C in October.

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: R. Barquero and G. Soto, ICE.

Vigorous ash emissions, rising to 300-600 m, were observed from an aircraft on 3 October.

Geologic Background. Raung, one of Java's most active volcanoes, is a massive stratovolcano in easternmost Java that was constructed SW of the rim of Ijen caldera. The unvegetated summit is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the W flank produced a large debris avalanche that traveled 79 km, reaching nearly to the Indian Ocean. Raung contains several centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively.

Information Contacts: N. MacLeod, Ridgefield WA, USA.

Although seismicity remained at very low levels in October (figure 46), there was a slight relative increase in long-period activity. High-frequency earthquakes were centered NE and SW of the summit. The SO₂ flux varied between moderate and low values, and deformation measurements showed no significant changes.

Figure 46. Daily seismic energy release (top) and number of earthquakes (bottom) recorded at Ruiz, January-October 1991. Horizontal lines indicate classification thresholds (used in previous Bulletins) for different levels of activity. Courtesy of INGEOMINAS.

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

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.

The number of recorded explosion shocks increased irregularly through October (figure 23), a continuation of the generally increasing trend that followed the low activity of mid-July to mid-August. Tremor amplitude also increased (figure 24). The number of seismometer-saturating events was quite low and concentrated during the last week of October, when tremor was stronger and explosions were more frequent.

Figure 23. Average number of explosion shocks/hour at Stromboli, 25 September-31 October, 1991. The mean value for the period is shown by the dotted line. Courtesy of M. Riuscetti.

Figure 24. Number of seismometer-saturating events/day (lower curve) and average daily tremor amplitude in volts (upper curve) at Stromboli, 25 September-31 October, 1991. Courtesy of M. Riuscetti.

A team from the Univ di Udine climbed the volcano during the first week in October. Two vents were active in Crater 1, the first near the E rim, the second a 30-m-high cone on its NW flank (facing the Sciara del Fuoco). Explosions produced plumes 100-150 m high, and ejected lapilli and sand-sized tephra. Crater 2 was still marked by two radial fissures with clearly visible night glow, but its rim was no longer well-defined. Cone 1 in Crater 3 continued to produce white vapor from two vents. The westernmost vent of Crater 3 appeared to be the most active, and was at the center of a rapidly enlarging chasm. It ejected clouds of black, sand-sized tephra to a maximum height of 300 m.

Along the ridge extending E from Pizzo sopra la Fossa (the observation point SE of the active craters), a zone that once consisted of a few isolated hot spots had evolved to a thermal anomaly in September (16:08) and a continuous line of fumaroles in October.

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5,000 years ago due to a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: M. Riuscetti, Univ di Udine.

Late-October explosions from the summit cone of On-take produced ash clouds a few hundred meters high and caused slight ashfalls on the island. The explosions were the most vigorous since similar events in January.

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

Information Contacts: JMA.

"A buildup of seismicity observed toward the end of September continued through the first week of October, but the volcano remained in a non-erupting state, releasing vapour in small to moderate volumes. The increased seismicity consisted of periods of frequent discrete, low-frequency earthquakes. The maximum daily number of recorded events was ~350. Despite their increase in number, there was no marked increase in amplitude. This activity waned after a week and by the end of the month was at a low level, with earthquake counts of <30/day. High-frequency volcanic earthquakes were recorded occasionally throughout October."

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: P. de Saint-Ours and C. McKee, RVO.

Growth of the lava dome . . . continued through mid-November and partial dome collapses frequently generated pyroclastic flows. Seismicity had declined to relatively low levels since extrusion of dome 4 started in mid-September. A seismic swarm began beneath the dome on 24 October, gradually increasing through mid-November. The seismicity buildup was similar to those of August and September, which culminated in the appearance of domes 3 and 4, respectively, although the rate of increase was slower for the current swarm. Uplift at the boundary between domes 3 and 4, first noted from the air on 25 October, was continuing in mid-November, suggesting magma intrusion under or into dome 4. As of 14 November, dome 4 was 500 m long, 400 m wide, and 250 m high. Dome and pyroclastic flow volumes were used to estimate a total of about 4 x 107 m³ of magma erupted between May and the end of October.

Pyroclastic flows, mainly from dome 4, moved down the Oshiga and Mizunashi valleys, as in September. Most have been relatively small since the eruption's largest pyroclastic flow on 15 September. Ash clouds generated by the larger flows reached about 2 km height. The number of pyroclastic flows, counted seismically, declined gradually through October (to 439, from 521 in September) and markedly since 11 November.

Geologic Background. The massive Unzendake volcanic complex comprises much of the Shimabara Peninsula east of the city of Nagasaki. An E-W graben, 30-40 km long, extends across the peninsula. Three large stratovolcanoes with complex structures, Kinugasa on the north, Fugen-dake at the east-center, and Kusenbu on the south, form topographic highs on the broad peninsula. Fugendake and Mayuyama volcanoes in the east-central portion of the andesitic-to-dacitic volcanic complex have been active during the Holocene. The Mayuyama lava dome complex, located along the eastern coast west of Shimabara City, formed about 4000 years ago and was the source of a devastating 1792 CE debris avalanche and tsunami. Historical eruptive activity has been restricted to the summit and flanks of Fugendake. The latest activity during 1990-95 formed a lava dome at the summit, accompanied by pyroclastic flows that caused fatalities and damaged populated areas near Shimabara City.

Information Contacts: JMA.

A new active crater formed in the S part of the 1978/91 Crater complex between visits by geologists on 9 and 23 October. The crater (named Wade; figure 14) had developed at the site of the former R.F. Crater, active January 1989-mid 1990. The onset of activity at the new crater was not documented, but may have been marked by E-type seismic events recorded on 18 October. The captain of the Island Princess reported that red ash had been falling for at least four days before 23 October.

Figure 14. Map of White Island's Main Crater, showing the new (Wade) crater. The position of the 1978/91 Crater rim is as of 28 November 1990. Dots labeled with Roman numerals are levelling sites; only some are shown. Courtesy of B. Scott.

As geologists approached the island on 23 October, activity was initially limited to moderate steam emission. At about 1120, an eruptive episode sent a red-brown steam/ash column to ~1 km above sea level. Long trains of low- to medium-frequency, low-amplitude earthquakes were recorded between 1115 and 1127, with a burst of stronger, higher frequency tremor at about 1118. During field studies between about 1230 and 1500, quiet emission of reddish ash-rich gas continued from the new circular crater, roughly 30-50 m in diameter and at least 30 m deep. Recently fallen red-brown ash was visible on all of the outer slopes of White Island. About 4 cm of ash had fallen at a site roughly 200 m SE of the new crater, thickening to 14 cm on the S rim of 1978/91 Crater. No significant juvenile component was evident in the ash.

A small amount of recently fallen ballistic tephra, including andesitic scoriae that are probably juvenile and accessory blocks, was found within 20 m of the SE rim of 1978/91 Crater. The orientation of ash thrown from the impact craters suggested an origin for the ballistic clasts in the direction of TV1 crater (roughly 100 m NE of the new crater), perhaps during the late-morning eruptive episode. TV1 may also have been the source of a layer of lithic gravel within a gray ash matrix, deposited to its E between layers of reddish ash. TV1 emitted only white steam until about 1315, when it began to erupt voluminous clouds of gray-brown ash. Ash emission was continuous for at least the next 30 minutes, and the color of the ash was noticeably different from that emerging from the simultaneously erupting new crater. TV1 had formed on 2 October 1990 and erupted again in February 1991, but had been relatively quiet since then. Little gas emerged from May 91 crater during the 23 October fieldwork, although it was the site of vigorous gas emission during the previous visit on 9 October.

Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Information Contacts: C. Wood, DSIR Geology & Geophysics, Rotorua.

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/).