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/).

Ten explosions were recorded . . . in March . . . . The month's highest ash cloud rose 1,900 m on 13 March. Seismicity was more vigorous than usual, with volcanic earthquake swarms recorded almost daily from 14 to 29 March, each lasting 4-5 hours.

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.

Small steam-and-ash emissions were observed periodically through mid-April, beginning at 1645 on 8 March, when a pilot flying near the volcano reported a small steam plume, possibly containing ash, that rose about 2 km above the summit. One hour later, only minor steaming was observed during a flight directly over the crater. A second flight at 1806 reported ash covering snow on the SW side of the crater. Minor steaming continued to be visible during flights at 1915 and 2006, rising to ~150 m. No activity was observed the following morning. Small steam and ash plumes, mostly <100 m high, were noted on 11-12 March.

Fishing vessels reported ashfall off Akutan Island on 22 March, following a pilot's report of a 4.3-km-high ash plume at 1637. No ashfall was reported 16 km NE, in Akutan village. A NOTAM was issued at 1224 on 24 March, prohibiting air traffic within 18 km of the volcano, up to 18 km altitude.

Activity was reported again on 7 April, when an Akutan village resident noted ash plumes rising 450-550 m above the volcano. Two days later, at 1000, a pilot reported an ash cloud at about 3-3.5 km altitude, drifting NW. A single lightning strike was recorded at the time of the eruption, by AVO's detection system.

Geologic Background. One of the most active volcanoes of the Aleutian arc, Akutan contains 2-km-wide caldera with an active intracaldera cone. An older, largely buried caldera was formed during the late Pleistocene or early Holocene. Two volcanic centers are located on the NW flank. Lava Peak is of Pleistocene age, and a cinder cone lower on the flank produced a lava flow in 1852 that extended the shoreline of the island and forms Lava Point. The 60-365 m deep younger caldera was formed during a major explosive eruption about 1600 years ago and contains at least three lakes. The currently active large cinder cone in the NE part of the caldera has been the source of frequent explosive eruptions with occasional lava effusion that blankets the caldera floor. A lava flow in 1978 traveled through a narrow breach in the north caldera rim almost to the coast. Fumaroles occur at the base of the caldera cinder cone, and hot springs are located NE of the caldera at the head of Hot Springs Bay valley and along the shores of Hot Springs Bay.

Information Contacts: AVO; FAA.

The two lava flows active in February continued to descend the W and WSW flanks in March (figures 45 and 46). The WSW-flank flow bifurcated, with one tongue advancing 50 m in early March to 730 m elevation, before stopping in mid-month. Near 1,100 m elevation, the W-flank flow also divided; one lobe advanced W down a valley, while the other diverged to the WSW, overflowing the September 1991-March 1992 flows (figure 46). The lava flow advanced an estimated 10-20 m daily on the upper slope, and 2-5 m daily on the gentler, lower slope. The most active, northern- and southern-most, lobes extended to 870 m and 830 m elevation, respectively, the first time in several years that lava had reached that elevation on the WSW flank.

Figure 45. Photograph of Arenal by G. Soto, showing its summit craters and active lava flows, 16 March 1992. Courtesy of ICE.

Figure 46. Map of late 1991-March 1992 lava flows at Arenal. Courtesy of ICE.

Strombolian activity continued at a significantly decreased rate and intensity, consisting primarily of sudden or rhythmic degassing events, with little or no pyroclastic ejection. In addition to intense fumarolic activity in Crater C (the active crater), intense steaming was observed between craters C and D (300 m E of Crater C).

Seismic activity was at moderate levels, with an average of 15 earthquakes recorded daily (at station FOR, 4 km E), and peaks on 4, 25, and 30 March. Increases in tremor were recorded on 11, 13, and 18 March.

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: G. Soto and R. Barquero, ICE; G. Alvarado, GEOMAR, Germany; M. Fernández, Univ de Costa Rica.

Most of the following is from R. Romano.

The fissure eruption ... was continuing in mid-April. Lava production from the main vent at 2,100 m altitude (in the W wall of the Valle del Bove) has remained almost constant, accompanied by degassing of varying intensity. By mid-April, 85 x 10⁶ m³ of lava that had emerged at an average rate of 8 m³/s was estimated to cover an area of >7 km².

From March through mid-April, lava from the main vent immediately entered a complex tube system, reappearing through ephemeral vents ~ 5 km downslope, below the Valle del Bove. The vents formed on the edge of the Salto della Giumenta, at the head of the Val Calanna a few kilometers from Zafferana Etnea, population ~ 7,000 (see figure 43). No ephemeral vents or lava overflows have been observed since the end of February in the wide lava field that had developed in the S part of the Valle del Bove.

On 14 March, lava reached the base of the barrier constructed in early January at the bottom of the Val Calanna. During the second half of March and the first few days of April, lava from the ephemeral vents gradually filled the area from the base of the Salto della Giumenta to the barrier. On 3 April, vents began to form within the Salto della Giumenta, feeding flows inside the Val Calanna. By the morning of 7 April, lava was only a few meters from the top of the barrier, with an active front along the barrier's entire length. That afternoon, lava flowed around the S side of the barrier and began to advance along the access road in the Val Calanna. The next afternoon, lava spilled over the central part of the barrier, and began to move down the gorge of the neighboring Portella Calanna valley. Lava advanced rapidly, aided by the steep slope, covering 1 km in 5 days. At least six earth barriers were built to contain the lava, but none were successful. By 14 April, lava was overflowing the last barrier, at ~ 780 m elevation, 1.5 km from the inhabited center of Zafferana Etnea and 7.5 km from the main vent.

Efforts were also made to slow or halt the advancing lava by disrupting the feeder tube system. Experiments with directed explosives, designed to blast holes in the lava field and encourage lava breakouts, began on 13 April in the upper Valle del Bove and Val Calanna. Lava destroyed two isolated houses above Zafferana on 14 April and covered nearby orchards, but the lobe threatening the town had virtually stopped by the next day and evacuation plans were postponed. New lava approached Zafferana over earlier flows in the succeeding days, and was again within a kilometer of the town by 20 April.

Degassing from the summit craters has gradually decreased following the collapse episode in Northeast Crater at the end of February (17:02). Additional Northeast Crater collapses 21-29 March triggered ash ejections accompanied by distinctive seismicity. Moderate gas emission from the summit vents observed by B. Behncke on 21 March was punctuated around 0900 by several low-energy ash emissions from Northeast Crater. At 1230 on 24 March, a dark-gray, convoluted ash plume rose to ~ 1 km above the summit within ~ 5 minutes, and also appeared to spread laterally at its base. The plume gradually dissipated during the following 30 minutes, depositing tephra to the E.

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: R. Romano, T. Caltabiano, and M. Porto, IIV; P. Carveni and M. Grasso, Univ di Catania; B. Behncke, GEOMAR, Kiel; Il Mattino, Napoli; AP; UPI; Reuters.

Seismic energy release and the number of long-period events fluctuated widely in March, similar to behavior in January-February. Tremor remained at low levels throughout the month. Eleven high-frequency earthquakes were recorded (M 1.2-2.2), centered primarily N and NE of the crater. Electronic tiltmeter measurements [at Crater Station] showed 21.8 µrad deflation in the N component, while measurements [at Peladitos Station] were essentially stable, with a slight tendency toward inflation (11 and 6 µrad for the two components). SO₂ flux from the volcano was variable in March, ranging from 120 to ~2,500 t/d, but showed a general increase late in the month.

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: J. Romero, INGEOMINAS-Observatorio Vulcanológico del Sur.

Sulfurous odors were occasionally detected up to 90 km S and SE of the volcano, beginning 10 April and increasing to a peak at 1100 on 13 April. Residents of Murta (60 km SSE) and Puerto Tranquilo (80 km SSE) reported headaches and nausea at 1500. The Civil Aviation Administration confirmed the intense sulfur odor SE of the volcano, but direct observation of the summit on 13 April revealed no visible eruptive activity. At 1700 on 14 April, an abnormal increase in river flow volume and turbidity was reported from Puerto Ibáñez, 90 km SE. Geologists suggested that the observed phenomena were a result of increased thermal and fumarolic activity beneath the caldera glacier (10 km diameter), combined with the abnormally dry weather conditions.

In late March, aeolian re-suspension of ash from Hudson's August 1991 eruption continued in Argentinian Patagonia. The following is from a report by the Patagonian Volcanism Project.

At about 1030 on 30 March, the crew of flight TAN 404 (Malargue to Neuquen), noted a brown "dust veil" ~50 km S of Malargue, at ~ 6,000 m altitude. Finely dispersed, light-brown volcanic ash formed a well-defined layer ~100 m thick and 300 km wide that spanned the horizon. The layer was rather homogeneous and perfectly visible against the cloud-free blue sky, but once within it the layer was no longer evident. The pilot reported that the layer had not originated from nearby surface dust, but was the result of Hudson ash again being transported to high altitudes from Argentinian Patagonia following calm weather that had prevailed in late March.

The ash was not from a recent eruption, but was entirely due to reworking of volcanic ash in dry, windy Santa Cruz Province, Argentina. On 21 March, re-suspended ash was deposited in Comodoro Rivadavia, accompanying local precipitation and a drop in temperature. At that time, strong southerly winds in Southern Patagonia suspended the ash, which preferentially traveled N along Argentina's Atlantic coastline and the Andean foothills. Other atmospheric effects included lowering of the dust layer during cold morning conditions, followed by ascent during the day due to surface heating, and fiery-red to pink high-level clouds seen in Comodoro Rivadavia at dawn on 31 March.

Volcanic bombs from the Hudson area contain black streaks in highly vesicular lighter-colored pumice. However, microprobe data indicate that the clear and dark glasses have essentially identical high-K dacite compositions.

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: J. Naranjo, SERNAGEOMIN; P. Bitschene, A. Arizmendi, M. Fernández, N. Arias, and A. Nillni, Patagonian Volcanism Proyect, Argentina.

Fumarolic activity continued in March. The crater lake's water level was several centimeters lower than in February, with an average temperature of 28°C and a pH of 3.7 on 2 April. The 141 earthquakes recorded in March (at station IRZ2, 5 km W of the crater), included M 2.0-2.5 events on 2, 15, and 21-22 March. The larger earthquakes were centered 6-7 km NW, 1.5 km SE, and 3 km NE of the crater, at 0-17 km depth. Low-frequency seismicity continued beneath the crater.

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: E. Fernández, J. Barquero, and V. Barboza, OVSICORI; G. Soto and R. Barquero, ICE; Guillermo Alvarado, GEOMAR, Christian-Albrechts-Universität, Germany; Mario Fernández, Sección de Sismología y Vulcanología, Escuela Centroamericana de Geología, Univ de Costa Rica.

Episode 51 . . . began on the afternoon of 7 March, four days after an intrusion in the upper East rift marked the end of the previous episode. A new fissure vent developed on the W flank of Pu`u `O`o, directly upslope from the E-50 vent, and lava within Pu`u `O`o rose to within 55 m of the rim. Lava production apparently stopped at about 2100, but resumed by midnight. Fieldwork the next day revealed an active fissure 34 m long with a spatter rampart 6 m high. Lava ponded W of the vent, while channelized flows moved south and new lava briefly filled the E-50 aa channel.

Lava production stopped at least four times during the following weeks. Active periods that sometimes lasted little more than a day were separated by repose intervals of 16-67 hours. Summit tilt consistently showed slight inflation during repose periods. The E-51 vent built a small shield on the W flank of Pu`u `O`o. Most of the small braided lava streams that covered the shield were fed by a summit lava pond, on the uprift (W) side of the active fissure. Large flows advanced in all directions from the new vent, expanding the W and S margins of the E-50-51 lava field (figure 85). Some flows emerged from the vent without passing through the pond. These wrapped around the base of Pu`u `O`o. On 13 April, a large pahoehoe flow was moving south and was nearing a forested area.

The level of lava inside Pu`u `O`o fluctuated between 35 and 60 m below the spillway on the crater rim, sustaining frequent gas-piston events and vigorous spattering. The lava level apparently dropped during two of the repose periods, then rose with renewed activity at the E-51 vent. On 12 April, several lava overflows briefly covered the crater floor before lava again retreated deeper into the vent.

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, HVO.

Steam emission from Shinmoe-dake cone's summit crater . . . produced a continuous 100-200-m-high plume in March. Seismicity was at low levels, with a monthly total of 27 small earthquakes, similar to February . . . . Two weak tremor episodes were recorded on 6 and 17 March. Fine ash emissions . . . were not observed in March.

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

Information Contacts: JMA.

"Activity increased in March with Crater 3 becoming more active. Emissions from Crater 3 consisted of weak to moderate white-grey vapour and ash with occasional blue vapour. Weak to moderate explosion noises were frequently heard throughout the month. At night, weak to moderate red glow over the crater and occasional incandescent lava ejections were seen. A new lava flow on the cone's N flank began on 6 March and was still advancing at the end of the month. Emissions from Crater 2 consisted of low to moderate volumes of white-grey vapour and ash clouds. Thick black ash clouds were emitted towards the end of the month, resulting in ashfall on the SE side of the volcano. Rumbling and explosion noises associated with some of the emissions were heard throughout the month. Steady weak red crater glow was observed on clear nights, with incandescent lava ejections occurring on 21 and 22 March. Seismic activity was at a higher level than in January and February."

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: I. Itikarai, P. de Saint-Ours, and C. McKee, RVO; ICAO.

Growth of a new dome and fumarolic activity were observed in the active central crater (800 m wide, 350 m deep) during 26 Feb-8 March observations. The new dome, at the base of the crater's S wall, had a fresh surface of black spines and an apparent diameter of <1/3 the size of the dome erupted in 1989 (~200 m). Estimation of its size and shape was difficult because of its position directly below the observation point. The dome was apparently in an early stage of extrusion, and local authorities were warned of the possibility of large explosions within the next few months, similar to those in September 1986 and February 1990.

Fumarolic activity and sulfur deposition occurred along ring fractures elsewhere in the crater, and a strong sulfur odor was noted on the volcano's N and S flanks. White steam emissions to 300-500 m above the rim were punctuated by sporadic vigorous pulses of alternating white and dark gray columns, which rose to 2,500 m. Gentle summer winds primarily carried the plumes SE, although plumes extending northward were commonly observed in the morning. Although activity was vigorous, the jet fumaroles seen in the crater during a previous dome-building episode in 1989 (14:11) were not evident in 1992. No night glow was observed nor was seismicity recorded during the February-March observation period. Although there is no current seismic monitoring in the area, visual observations continue from nearby villages.

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: M. Gardeweg, SERNAGEOMIN, Santiago; S. Sparks and R. Thomas, Univ of Bristol; M. Murphy, Univ College, Dublin.

Lava bubbled from a new vent (T20) [but see 17:6] in the center of the crater floor (figure 24) . . . on 12 March. A very recent lava flow (F33) extended from the new vent across the S depression, and was still cracking, suggesting that it had formed the previous day. The new vent was in roughly the same position as former vent T18 (observed in June-October 1991, but not in December 1991, perhaps after being covered by flow F32; 16:8 and 17:02), and may represent a renewal of activity from that vent. The largest of the remaining cones (T5/T9), estimated at 20 m high, had heat waves emanating from its vents. None of the other cones showed visible signs of activity

Figure 24. Sketch map of the summit craters of Ol Doinyo Lengai, 12 March 1992. Prepared by M. Peterson, with modifications from C. Nyamweru. Sketch from an oblique airphoto taken 24 July 1992, looking N across Ol Doinyo Lengai's crater. Fresh lava is shown emerging from hornito T20. The former feature T11 is no longer visible. Courtesy of F. LeGuern.

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

Information Contacts: C. Nyamweru, St. Lawrence Univ; M. Peterson, Arusha.

"A build-up of activity at Southern Crater led to a series of brief phases of moderate-strong Strombolian activity starting on 23 March. Weak Strombolian eruptive activity started at Southern Crater on the evening of 29 February. Incandescent lava ejections were weak to moderate (up to 200 m above the crater), and intermittent (every few minutes or up to 6/minute) throughout the first 20 days of March. During the day, incandescence was not seen, but each burst produced a "puff" of brown ash-laden vapour that rose to between 500 and 1,000 m above the crater and produced fine ashfalls in coastal areas downwind. The ash consisted of ~45% black lithic material, 35% oxidized fragments, apparently from older rocks, and ~20% fresh-looking glass shards and crystals.

"The seismicity was at a moderate level, with 400-1,100 small, low-frequency events per day. Starting on 21 March, a definite build-up in seismicity (1,200-1,400 events/day of larger amplitude) was recorded in association with more forceful ash-laden ejections. Incandescent lava fragments rose to 500 m above the crater. The seismicity became sub-continuous in the afternoon of 23 March, moderately strong explosion sounds started to rattle the walls of Tabele Observatory . . . , and dark grey-brown ash clouds rose forcefully to 900-1,000 m above the crater. From 1615 to 2000 this crater produced sub-continuous emissions of incandescent scoriae to ~1,100 m above the crater rim, with flashing arcs a few seconds apart accompanying each explosion. Scoria avalanches descended into the upper SE and SW valleys, and ash and lapilli fell into coastal areas. The lapilli were as large as 3 cm in size and consisted of light, highly vesiculated, grey glassy pumices with ~5% crystals. The maximum thickness of the lapilli-ash deposit was ~0.5 cm. At the end of this eruptive phase, the seismicity dropped dramatically, but resumed six hours later when another similar phase of activity (of lesser intensity) started and continued for ~30 minutes.

"During the following week, a new pattern of activity was observed. Periods of sub-continuous Strombolian eruptions, with low frequency events in such close succession as to look like monochromatic tremor of fluctuating amplitude (lasting about an hour each) were separated by periods of irregular duration (0.5-22.75 hours) during which no emissions or night glow were seen over the crater and virtually no seismicity was recorded. Altogether there were 24 periods of sub-continuous Strombolian activity (counted from the periods of seismicity that characteristically accompanied them) between 23 and 30 March. Some of these active phases were followed by periods of intermittent, mild Strombolian activity lasting a few hours. After 30 March, the more usual pattern of regular Strombolian activity and seismicity (1,300-1,400 small events/day) resumed."

The crew of Qantas flight 59 reported a moderately dense black plume rising . . . to ~2.5 km altitude on 1 April at 1417. A NOTAM was issued several hours later. The observer at Manam reported sub-continuous ejection of thick gray-brown ash clouds to 400-500 m above the summit on 1 April, consistent with the aircraft report. Seismograms that day showed an even distribution of small volcanic earthquakes, not indicative of strong Strombolian activity.

"Aerial and ground inspections were conducted between 28 and 30 March. Southern Crater, which since at least 1975 has had an open funnel shape with a diameter of ~50 m, was bowl-shaped, clogged with agglutinated scoriae, and the active vent was only ~15 m wide and 8 m deep. There was no emission from the crater area between eruptions. The summit area was mantled with scoriae, but these deposits did not extend in any significant thickness lower than about the 1,000-m level, and no lava flows were produced. Only one small debris flow deposit was recognized in the SE valley; the flow descended a gully along its southern margin. Although the nose of the flow stopped at 950 m elev, a lighter hot cloud overriding it apparently continued to ~900 m elev, scorching vegetation. Other small debris flows may have contributed to the apron of pyroclastic debris on the upper part of the SE valley. A few small debris flows would have, similarly, cascaded down the steep rock face at the head of the SW valley and come to a stop in its amphitheatre, at ~900 m elev.

"Throughout March (and since April 1991), Main Crater was totally inactive, and its floor covered with debris eroded from the crater walls. Tilt recordings showed no significant change throughout the month, although 3 µrad of radial inflation were recorded at Tabele in the 3.5 months preceding the onset of the eruption. In late March, two short leveling lines (~500 m long) were laid out radially to the volcano on the lower E and NW flanks for further ground deformation monitoring in the upcoming months.

"The previous most significant activity from Manam occurred in June 1987. On 30 June, after a period of ~1.5 months of mild Strombolian activity, an intense Strombolian eruptive phase (of similar character to the latest activity) produced numerous scoria flows into the SE and SW valleys down to ~300 m elev. This phase also produced a short viscous basaltic lava flow, lapilli, and ashfalls that caused some damage to subsistence gardening areas near the coast (between 4 and 5 km radial distance from the crater). In comparison, the latest eruption was of lesser magnitude. It produced less than half the amount of material (<2-5 x 10⁶ m³) and no significant damage to gardens or inhabited areas."

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

Information Contacts: I. Itikarai, P. de Saint-Ours, and C. McKee, RVO; ICAO.

Glowing rockfalls continued from Merapi's 1992 dome. They were channeled into the headwaters of rivers on the NW (Senowo), W (Putih), and SW (Bebeng) flanks, extending 300-2,000 m from the dome. The number of rockfalls and multiphase earthquakes generally decreased after late February, although they still dominated seismic records (figure 5). Occasional avalanche-generated pyroclastic flows remained relatively small and traveled a maximum of 2,000 m downslope. The plume was low (to 550 m height), relatively thin, and white. The average SO₂ flux measured by COSPEC (figure 6) was 324 t/d through mid-April, with individual measurements ranging from 32 to 419 t/d, the highest on 2 April. As of mid-April, Merapi remained at a Level-1 Alert (see 17:2 for details of the alert system), with summit climbs by the public prohibited.

Figure 5. Merapi's daily number of glowing rockfalls, multiphase earthquakes, and pyroclastic flow events, with amplitudes x durations of glowing rockfalls, January-April 1992. Courtesy of MVO.

Figure 6. Daily average SO2 flux measured by COSPEC at Merapi, December 1991-early April 1992. Courtesy of MVO.

[1988 and 1990-91 seismicity and deformation data were moved to follow 15:7]

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

Information Contacts: B. Voight, Pennsylvania State Univ.

Violent Strombolian activity occurred at the volcano on 9-12 April, and resumed at lower intensity on 13-14 April. Heavy ashfall forced the evacuation of 28,000 people [but see BGVN 17:04] from nearby towns and from parts of León (18 km WSW; figure 3), the second-largest city in Nicaragua, between 10 and 12 April. No fatalities directly related to the eruption were reported, although there were two accidental deaths during the evacuation. The volcano was quiet as of 20 April.

Figure 3. Map showing locations of Cerro Negro and neighboring volcanoes, with nearby cities and towns affected by the eruption. Contour interval, 200 m. Based on sheet ND16-15 (Managua), U.S. Defense Mapping Agency series 1501, Joint Operations Graphic (Ground).

9-12 April 1992. No instrumental seismic data were available before the eruption, but 5 earthquakes were felt in villages within 5 km of the volcano at about 2300 on 9 April, signalling the onset of activity. The first explosion occurred at 2320, and was quickly followed by the eruption of incandescent material with the development of a large ash cloud. The initial eruption plume rose an estimated 4000 m above the cone, and contained material up to bomb-size.

The ash cloud was visible on weather-satellite images beginning at 0000 on 10 April, and by 0530, the cloud extended 300 km to the WSW (264° azimuth), with a maximum width of about 200 km, at an estimated initial altitude of 6 km. Both ground and satellite observations indicated that the eruption was vigorous and nearly continuous. The eruption column, clearly visible from Managua (60 km SE) much of the time, was estimated from the ground to be approximately 7 km high. Satellite images showed that the plume extended 400 km W on 11-12 April. Material ejected to about 7.5 km during more energetic pulses of the eruption was carried roughly 50 km NE by higher-altitude winds. SO₂ plumes that are significantly below the tropopause (roughly 16 km at this latitude) are difficult to detect with NASA's Total Ozone Mapping Spectrometer, and none were evident during the Cerro Negro eruption.

Ash began falling in León within 1 hour of the onset of activity, and formed deposits up to 4 cm thick by 1700 the next day. Very fine ashfall was reported as far away as the Pacific Coast (50 km W, in Corinto). Late on 10 April, the wind direction changed from WSW to W and ash accumulations were recognized in Telica (16 km W). That evening, 15 houses and several other structures, including a few large storage buildings, collapsed in León and surrounding areas. Collapses of numerous farm buildings, rural homes, and school buildings were reported over the next several days.

Ashfall continued W of the volcano, with accumulations of 2.5 cm of ash in Telica, 1.5 cm in Quezalguaque (20 km W), and 0.1 cm in Chinandega (50 km WNW) by 12 April. A change in wind direction to the SW during the night of 11 April caused the first ashfall S of León. That evening, incandescent material was observed consistently rising 300 m above the crater. Activity continued the following day, but was intermittent and less vigorous, finally ceasing at about 1800 on 12 April. During the 9-12 April activity, the crater diameter increased from approximately 100 m to 300-400 m.

13-14 April 1992. Only very light fumarolic activity was observed in the crater, and the volcano was otherwise quiet until explosions reportedly resumed around 2200-2300 on 13 April. An infrared satellite image at 2300 showed an already developed eruption cloud, which extended to about 350 km SSW by 0700 on 14 April. Remnants of the ash cloud produced by the more violent 9-12 April eruption were still evident 500 km W of the volcano on satellite images at 0800. Strombolian activity on 13-14 April ejected bombs to about 300 m height and produced a light ash cloud about 3.5 km high, but the interval between explosions (5 seconds early on 14 April), and their intensity, decreased throughout the day. The maximum recorded rate of ashfall in León, 2.4 gm/m²/minute, was measured at 1000. Although the plume appeared to be disconnected from the volcano on a satellite image at 1200, ground observations indicated that the eruption continued at lesser intensity until about 1730. Only light fumarolic activity was observed the following day.

Deposit thicknesses were 1 m, 1.2 km W; 15 cm, 13 km WSW; 5 cm, 20 km WSW; and 1 cm, 39 km WSW of the volcano. Rough calculations based on preliminary isopach mapping by INETER suggest a total erupted volume of approximately 0.03 km³ DRE.

Seismicity. Seismic stations were installed around the volcano on 10-11 April. During 10-12 April, low-frequency, low-amplitude seismic tremor was nearly continuous. Some B-type earthquakes were also recorded. The tremor rate declined on 12 April and tremor ceased on 13 April.

Several A-type events were recorded in the hours before the renewed eruption on 13 April. Tremor accompanied the eruption, and ceased at the end of explosive activity. Seismic data collected on 13-15 April (figure 4) show a very rapid rate of increase in seismic energy release immediately prior to the resumption of the eruption on the 13th, nearly steady-state energy release for the duration of the eruption, and a very rapid decrease to background levels following cessation of activity on the evening of the 14th. Geologists suggest that these data support the existence of a relatively open conduit that rapidly delivers magma from depth, and the current lack of any voluminous magma body close to the surface. On 17 April, 40 earthquakes were recorded near the volcano, a significant increase from seismicity on 15-16 April.

Figure 4. Real-time Seismic Amplitude Measurements (RSAM) at Cerro Negro, 13-15 April 1992. Courtesy of C. Connor.

Geologic Background. Nicaragua's youngest volcano, Cerro Negro, was created following an eruption that began in April 1850 about 2 km NW of the summit of Las Pilas volcano. It is the largest, southernmost, and most recent of a group of four youthful cinder cones constructed along a NNW-SSE-trending line in the central Marrabios Range. Strombolian-to-subplinian eruptions at intervals of a few years to several decades have constructed a roughly 250-m-high basaltic cone and an associated lava field constrained by topography to extend primarily NE and SW. Cone and crater morphology have varied significantly during its short eruptive history. Although it lies in a relatively unpopulated area, occasional heavy ashfalls have damaged crops and buildings.

Information Contacts: Claudio Gutiérrez (Director); Helman Taleno L., Fabio Segura M., Martha Navarro C., Oscar Urbina L., and Wilfried Strauch, INETER, Aptdo. 2110, Managua, Nicaragua; Patricio Jerez, IRENA, Kilómetro 12, Carretera Norte, Managua, Nicaragua; C.B. Connor, FIU, Miami; J. Lynch, Thomas Baldwin, and Charles Kadin, SAB; S. Doiron, NASA GSFC; Deborah Jerez, 9808 Natick Rd., Burke, VA 22015 USA.

A seismic swarm recorded between 0200 and 0400 on 19 March consisted of 10 earthquakes beneath and around the island (figure 3). Several of the events were felt by island residents, the largest, M 2.5, at 0349. No surface anomalies were observed.

Figure 3. Epicenter map of earthquakes near Nii-jima, 19 March 1992. Courtesy of JMA.

Geologic Background. The elongated island of Niijima, SSW of Oshima, is 11 km long and only 2.5 km wide. It is comprised of eight low rhyolitic lava domes that are clustered in two groups at the northern and southern ends of the island, separated by a low, flat isthmus. The flat-topped domes give the island the appearance of two large plateaus bounded by steep cliffs. The Mukaiyama complex at the southern end of the island and Achiyama lava dome at the northern end were formed during Niijima's only historical eruptions in the 9th century CE. Shikineyama and Zinaito domes form small islands immediately to the SW and west, respectively, during earlier stages of volcanism. Earthquake swarms occurred during the 20th century.

Information Contacts: JMA.

On 4 April, rainfall triggered a lahar in a NE-flank drainage (Sacobia). The lahar disrupted a portion of the extensive June 1991 pyroclastic-flow deposits, producing a secondary explosion and reportedly a secondary pyroclastic flow. The press described an ash cloud that rose about 1,200 m, and darkened the Angeles area (25 km E of the summit). The lahar also destroyed two sabo dams that were being constructed to reduce future mudflow damage downslope, but no casualties or additional property damage were reported.

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; Reuters.

Small phreatic explosions, observed in the crater lake in February, were concentrated in March at mud pots exposed by the continued decline in lake water level. Lake temperature measurements oscillated between 65 and 75°C. Gas emission continued, producing plumes that rose to >1 km and extended W and SW. Residents on the W and SW flanks reported that acid rain and mist affected vision, caused skin rashes, and damaged agricultural areas. On average, 237 earthquakes were recorded daily in March (at station POA2, 2.7 km SW of the crater), with a maximum of 398 on 4 March. A M 2.5 earthquake was recorded at 0652 on 3 March, centered 3.5 W of the crater at 7 km depth.

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: E. Fernández, J. Barquero, and V. Barboza, OVSICORI.

"Seismic activity increased slightly in March. The month's total number of caldera earthquakes was 267 . . .. The maximum daily count was 72, recorded on 7 March. None of the events was large enough to be felt. The strongest earthquake for the month was a M_L 2.7 event recorded on 12 March."

Geologic Background. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the 688-m-high asymmetrical pyroclastic shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: I. Itakarai, P. de Saint-Ours, and C. McKee, RVO; ICAO.

Rumbling and small explosions were reported on several occasions in March. Portable seismometers at Proyecto Geotérmico Miravalles (35 km SE of the active crater) recorded small earthquakes, possibly associated with explosions, on 13-16, 20, and 26 March. A maximum of five events was recorded, on 16 March.

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

Information Contacts: G. Soto and R. Barquero, ICE; Guillermo Alvarado, GEOMAR, Christian-Albrechts-Universität, Germany; Mario Fernández, Univ. de Costa Rica.

Increased thermal activity began in early January, peaked around 23-26 February, and concluded about 8 March. Several minor phreatic eruptions were observed beginning on 8 February, including several since 11 February fieldwork. Steam clouds were observed over Crater Lake at 1500-1600 on 12 February by Dept of Conservation staff. On 18 February, airplane pilots (Darren Kirkland and Ross Bateup) reported a phreatic eruption generating a steam column and waves 0.6-0.9 m high at around 1100, and two large "bubbles" and a pulse of steam at 1822. During a visit on 20 February, Dr. Ockens (Univ of Sydney) heard an airplane engine-like noise, followed by steam emission from the lake and a sulfur odor. Kirkland observed an eruption that produced large waves at 1200 on 23 February, and after a week of relative quiet, reported the lake to be vigorously active at 1600-1800 on 6 March, producing dense steam clouds and large waves. Steam clouds were noted rising from the lake that day at about 1330, by Roger Smith (from near the lake shore) and Keith McKenzie (from a helicopter, at a distance). Smith also reported the appearance of sulfurous, yellow-green patches in the lake.

During fieldwork on 24 March, Crater Lake appeared pale gray, with upwelling (three or four cells) and yellow slicks over the N vent area. New snow was visible at the water's edge and there was no evidence of recent activity. The temperature data logger recorded a peak of 47°C on 23 and 26 February, then temperature fell, plateauing briefly at ~44°C on 2-8 March, and reaching 31.5°C (direct measurement) on 24 March (figure 12). Water analyses indicated no significant changes in Mg or Cl concentrations during the February-March activity.

EDM measurements showed moderate inflation associated with the February/March activity. Seismicity has remained at background levels since 11 February, with low-level volcanic tremor or small volcanic earthquakes recorded on most days. No signals related to reported activity were seen. Geologists noted that the February/March activity was similar to the minor events that occurred every 5-10 months between 1985 and January 1990.

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The 110 km3 dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: P. Otway, DSIR Wairakei.

In January-February 1992, seismic activity was at the highest levels since the start of monitoring in 1980, although there is no indication that an eruption is imminent. This activity followed a significant increase in August 1991, when earthquakes began to occur beneath Crater Peak, a region that had been almost quiescent since monitoring began (figures 1 and 2). During January-July 1991, within a 10-km radius of the volcano, an average of 2 earthquakes (M>0) were recorded every 10 days. This average increased to 7 earthquakes/10 days in August-November 1991, and again to 20 earthquakes/10 days in December 1991-February 1992. Most of the earthquakes had magnitudes <1 and depths <5 km. Since November 1991, the majority of the earthquakes have been centered beneath the main summit and Crater Peak, with a zone of lesser activity 5 km N of the main summit.

Figure 1. Map of earthquake epicenters near Spurr, 1981-August 1991. Filled rectangles labeled with 3-letter codes mark nearby seismic stations. Printed by permission of the Scientist-in-Charge, Alaska Volcano Observatory.

Figure 2. Time vs. distance plot of hypocenters at Spurr, 1981-August 1991. Distance is measured by projecting events on a N-S line in figure 1. The number of seismic stations operating in the Spurr area is shown along the top. Hypocenters for the 1989 swarm could not be determined as only two stations were operating at the time. Printed by permission of the Scientist-in-Charge, Alaska Volcano Observatory.

Seismicity at Spurr has been characterized by large fluctuations in the number of events. Large earthquake swarms were recorded in early 1982 (>140 events recorded) and in early 1989 (not shown in figure 2), both centered 3 km N of the main summit. Normal seismicity has tended to concentrate beneath the main summit.

On 9 July 1953, a brief explosive eruption from Crater Peak produced a 21-km-high plume that dropped ash in Anchorage (120 km E). A mudflow blocked the Chakachatna River (S flank), forming a lake 8 km long.

Reference. Nye, C.J., and Turner, D.L., 1990, Petrology, geochemistry, and age of the Spurr Volcanic Complex, eastern Aleutian Arc: BV, v. 52, p. 205-226.

Geologic Background. The summit of Mount Spurr, the highest volcano of the Aleutian arc, is a large lava dome constructed at the center of a roughly 5-km-wide horseshoe-shaped caldera open to the south. The volcano lies 130 km W of Anchorage and NE of Chakachamna Lake. The caldera was formed by a late-Pleistocene or early Holocene debris avalanche and associated pyroclastic flows that destroyed an ancestral edifice. The debris avalanche traveled more than 25 km SE, and the resulting deposit contains blocks as large as 100 m in diameter. Several ice-carved post-caldera cones or lava domes lie in the center of the caldera. The youngest vent, Crater Peak, formed at the breached southern end of the caldera and has been the source of about 40 identified Holocene tephra layers. Eruptions from Crater Peak in 1953 and 1992 deposited ash on the city of Anchorage.

Information Contacts: AVO.

Visitors ... in mid-March reported that activity was at a low level, with only a few eruptive episodes an hour. Despite frequent heavy rains, no dark, ash-laden phreatomagmatic eruption plumes were observed. When viewed from a ferryboat for about an hour during the morning of 18 March, the volcano erupted only once, shortly after 0730, otherwise emitting only a gas plume.

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: B. Behncke, GEOMAR, Kiel.

Low-frequency seismicity continued at levels similar to February. An average of 1-2 events were recorded daily (at station VTU, 0.5 km E of the crater), with a maximum of four events on 6 March.

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

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI.

Lava extrusion . . . was continuing in mid-April 1992. Dome 5 . . . swelled by intrusion, pushing the N half of dome 4 eastward, while dome 6 (formed 3 December 1991) thickened by new surface flows (figure 41). The length of dome 6 did not increase significantly, and the complex "petal" surface structures remained close to the vent, now the highest point in the dome complex. Increased seismicity in early April preceded the extrusion of a new dome (7), which was growing rapidly at mid-month.

Figure 41. Sketch of the dome complex at Unzen, 12 April 1992. Individual domes are numbered. Courtesy of Setsuya Nakada.

Frequent partial collapse of the front and sides of dome 6, and rarely the E and NE side of dome 5, generated pyroclastic flows that descended SE (toward the Akamatsu River) and sometimes ESE (along the Mizunashi River). During March, 504 pyroclastic flows were seismically recorded, up from 344 in February. The SE slope of the Akamatsu Valley was almost filled by block-and-ash-flow deposits by early April. A large pyroclastic flow, generated by collapse of large blocks between domes 5 and 6 on 1 April, traveled 3 km down the Mizunashi River, reaching the evacuated town of Kita-Kamikoba (where 43 people were killed by the 3 June 1991 flows). The 1 April block-and-ash-flow deposit was thinner, and its ash-cloud surge deposit was thinner and distributed over a much smaller area than those from the 3 June 1991 flows. The 1 April pyroclastic flow was the largest since the 15 September 1991 flows, whose deposit surface and lava blocks continued to steam as of early April. Small pit craters (to 30 cm diameter) were visible on the surface of the September 1991 deposit.

Heavy rainfall triggered three large debris flows in March. The 1 March debris flow reached a point 100 m from the coast (8 km E of the summit) crossing Routes 57 and 251, and burying a 200-m section of the Shimabara Railway. At 1000 on 15 March, 30 mm/hour of rainfall triggered a debris flow of similar size and route. Both highways were crossed, and a 140-m section of the railway was buried by 0.3 m of mud, remaining closed until 14 April. A smaller debris flow occurred along the same route on the morning of 23 March, burying a 30-m section of Route 251. Roughly 7,600 people remained evacuated as of mid-April.

During March, 5,663 earthquakes were recorded on the dome complex, down slightly from 6423 in February. Seismicity declined through mid-March, increased to the highest level of the eruption, and then declined again at the end of the month. The number of earthquakes increased during the first few days of April, before declining once more on 6 April, as a new dome (7) began to emerge. The new dome had grown to 100 x 150 m by 12 April (figure 41).

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: S. Nakada, Kyushu Univ; JMA.

Vigorous fumarolic activity was continuing from the N rim of the historically active crater (Fossa Grande) and from thermal areas on the upper N flank during a visit on the afternoon of 18 March. Most of the fumaroles were concentrated along the N crater rim, inside the N part of the crater, and on the N flank of the wall of tephra built during Vulcano's last eruption, in 1888-90. The main fumarole field appears to have extended a short distance to the E along the N crater rim, where new vents had formed since Behncke's last visit in November 1990. A new linear zone of high-pressure gas emission has developed roughly parallel to the large fissure that formed after 1988 on the N crater wall. Fumarolic activity from scattered vents on the upper N flank seemed to have increased since November 1990, and a less-prominent thermal area on the outer SE flank included at least 7 weak fumarolic vents.

Intense hydrothermal alteration and erosional undercutting have occurred on the upper N flank, around the S rim of the 18th-century Forgia Vecchia craters. Extension cracks have appeared within a few meters of the steep N slope, and deep gullies extend toward the coastal town of Porto di Levante.

Geologic Background. The word volcano is derived from Vulcano stratovolcano in Italy's Aeolian Islands. Vulcano was constructed during six stages during the past 136,000 years. Two overlapping calderas, the 2.5-km-wide Caldera del Piano on the SE and the 4-km-wide Caldera della Fossa on the NW, were formed at about 100,000 and 24,000-15,000 years ago, respectively, and volcanism has migrated to the north over time. La Fossa cone, active throughout the Holocene and the location of most of the historical eruptions, occupies the 3-km-wide Caldera della Fossa at the NW end of the elongated 3 x 7 km island. The Vulcanello lava platform forms a low, roughly circular peninsula on the northern tip of Vulcano that was formed as an island beginning in 183 BCE and was connected to Vulcano in about 1550 CE. Vulcanello is capped by three pyroclastic cones and was active intermittently until the 16th century. The latest eruption from Vulcano consisted of explosive activity from the Fossa cone from 1898 to 1900.

Information Contacts: B. Behncke, GEOMAR, Kiel.

Explosive activity continued through early March from Wade and TV1 Craters.... Distinct emissions of gray and reddish ash were observed during regular visits to the island and from nearby fishing vessels. A larger event on 20 February produced a tall plume (estimates ranged up to 5,000 m) and ejected blocks and juvenile bombs. Numerous E-type seismic signals were recorded through mid-Mar.

Observations. On 3 February, R. Fleming (Waimana Helicopters) noted gray ash, not present during a 1 February visit, covering the W and SW walls of the main crater. Two eruption columns were reported the next day, the first at 0740 by R. Pollack (MV Pursuit), and a stronger one at 1318 by V. Froude (Dept of Conservation; MV Takapu). Froude observed another eruption column at 0737 on 5 February. TV1 Crater was the source of a light gray ash cloud, 50-100 m high, during an island visit at 1040-1730 on 7 February. Ash again emerged from TV1 during a 12 February visit. Light pink-brown ash emission began at about 1229, and increased slightly during the afternoon. The next day, Fleming reported the emission of red ash from TV1 (at 1530). Strong red ash emissions were reported at 1900-2000 by John Baker (MV Ma Cherie). Wade Crater, inactive earlier in the month, erupted light pink-red ash during a 17 February visit (1030-1546), while TV1 emitted only white steam.

The eruption on 20 February began abruptly at about 1004 without any visible precursors. The initial dark eruptive pulse rose rapidly from TV1 Crater, accompanied by an uprushing noise. Ballistics, white lithic blocks, and dark (not visibly incandescent) juvenile bombs, were ejected to 400-500 m height. Another 3-5 more-dilute, block-free pulses of activity occurred over the next 5 minutes, feeding a high convective plume that traveled SSE. By 1010, several observers along the Bay of Plenty coast had seen the eruption cloud, estimating heights of 1,600-5,000 m. R. Martin and M. Stringfellow (Bay of Plenty Regional Council staff) measured elevation angles of 4.8-5°, yielding column heights of 4,200-4,300 m. Fleming estimated that the initial eruptive pulse rose 1,700-1,800 m before expanding. By 1020, activity had decreased to an ash-free, very weakly convoluting, low eruptive plume. High levels of steam and gas emission continued for 1.5 hours after the explosion, before a dramatic decrease in mid-afternoon.

Voluminous light-brown ash emissions completely obscured the main crater during an afternoon visit on 27 February. On 1 March, thick dark ash emissions were reported by Pollack at 0847. Wade Crater erupted a cloud of pink/brown ash 500-700 m high while TV1 emitted white steam, during a visit at 1125-1515 on 3 March. Nearly continuous ashfall occurred E of the crater. Maximum particle sizes were ~1 mm. Occasional roaring and thumping noises were heard. Fumarole temperatures ranged to >300°C, and analyses of gas samples showed high gas/water ratios, with one sample yielding a strong magmatic signature. The floor of May 91 Crater was nearly flat, reaching 30-35 m below its SE rim. During a 5 March visit at 1020-1605, Wade emitted a weak ash-tinged plume and conspicuously blue fume, accompanied by loud, pulsating degassing noises. Dense ash-free steam from TV1 often obscured half of the 1978/90 Crater Complex. No ash was observed during a 10 March visit, although a steam plume rose to 300-400 m.

Seismicity. B-type seismicity increased from 5-6 events recorded daily 18-24 January to >15/day 1-5 February, while the daily number of recorded A-type earthquakes remained at 2-4. Medium-frequency volcanic tremor began on 6 February. B-type earthquakes declined sharply in number, and were absent from records on 12-17 February. Volcanic tremor amplitude increased after 11 February to a peak on 16 February, coinciding with an 11-hour period (15-16 February) when 4-6 microearthquakes were recorded per minute. Tremor, predominantly medium-frequency (4-7 Hz) with occasional lower frequency signals lasting 1-5 hours, declined to background levels by 21 February. The level of seismic activity remained similar (0-6 A-type and 0-5 B-type events daily) through 3 March, when a swarm of >40 B-type events was recorded.

E-type (eruption) events were recorded every several days during late January-early February [six from 30 January-4 February], were rare in mid-February [one on 14 February], then occurred almost daily from late February through mid-March [20 from 20 February-15 March, with seven on 29 February]. The event that accompanied the production of the large ash-laden column on 20 February was similar to, but larger than, the 17 January seismic event. Of the two predominant varieties of E-type signals during this period, the more common had a low-frequency onset followed by a high-frequency coda; the other was dominantly high-frequency and had a more impulsive onset.

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: I. Nairn and B. Scott, DSIR Rotorua.

In 1985, a new superheated fumarole formed on the upper E margin of the Mushpots thermal area, which lies on the E side of the caldera associated with the youngest of Yellowstone's three cycles of voluminous rhyolitic volcanism, 0.6 million years ago. The presence of vegetation and the limited extent of bare thermal ground indicated that heat flow near the site of the new fumarole had been moderate to low for at least the previous 15 years. Interviews with park personnel strongly suggested that activity began about 3 July 1985. The steam cloud from the vent may have inspired a false report of smoke from the area, but the vent was not discovered until 5 October 1986, during fieldwork by C. Craig-Hunter and Roderick Hutchinson. At that time, the fumarole's transparent dry-steam jet was directed upslope N35°W at an approximate angle of 21°. A small, reddish-brown, iron-stained cone of hydrothermally altered sand-sized material had grown ~ 0.5 m above the uphill side of the rectangular 1.35 x 1.9-m vent, which dipped at an angle under the lower S rim. Just below the fumarole, on the floor of an old thermal zone, were numerous new or recently enlarged, small, steaming, thermal and mud pot vents, covering an area ~ 10 m in diameter. Sulfate and/or yellow elemental sulfur deposits covered most of the area and nearby slopes to the W, SW, and NW. A second area of new or rejuvenated thermal vents was also discovered in the drainage to the south.

Many trees had been killed in line with the fumarole's directed plume and around the margins of the old thermal zone. Mature trees as much as 87 cm in diameter were snapped off at ground level or uprooted, and tops were broken on other trees 40 m from the rim of the old thermal zone (54 m from the fumarole). A narrow zone of hydrothermally altered white chips of glacial till was found among the toppled trees up to 40 m from the thermal zone rim. These ejecta were 6 cm deep on the rim in 1986.

Geologists returned on 12 February 1987, after a nearby Univ of Utah seismograph . . . detected an isolated episode resembling volcanic tremor. The fumarole's temperature had increased (figure 1) and more elemental sulfur and iron sulfates had been deposited in the old thermal zone, but no other changes were evident. Since then, a biannual survey has been conducted in the area.

Figure 1. Temperatures measured at Mushpot Fumarole, Yellowstone National Park, 5 October 1986-28 March 1992. Courtesy of R. Hutchinson.

During fieldwork on 28 March 1992, a quiet cloud of wet, 93°C vapor filled the 1985 fumarole's vent. However, less than 30 m downslope (S), on the E margin of the old thermal zone's floor, the ground was shaking violently with the formation and growth of a new mud pot. Bursts of thick, viscous mud were typically doming to 2 m and occasionally to 5 m in diameter before exploding to 3-6 m height. Each explosion shook the ground in all directions. Branches of thermally killed trees shook 50 m away, the ground was visibly moving 8-10 m from the rim, and within 4 m of the rim was behaving like pudding, with violent shaking causing surface oscillations of 1-2 cm. During 90 minutes of observations, the surface area of the mud pot increased by ~ 50%, to an estimated 11 x 7 m. It had a depth of at least 2 m. The minimal amount of ejected mud surrounding the crater and the intense shaking suggested that development of the mud pot had begun within the last 24 hours.

Geologic Background. The Yellowstone Plateau volcanic field developed through three volcanic cycles spanning two million years that included some of the world's largest known eruptions. Eruption of the over 2450 km3 Huckleberry Ridge Tuff about 2.1 million years ago created the more than 75-km-long Island Park caldera. The second cycle concluded with the eruption of the Mesa Falls Tuff around 1.3 million years ago, forming the 16-km-wide Henrys Fork caldera at the western end of the first caldera. Activity subsequently shifted to the present Yellowstone Plateau and culminated 640,000 years ago with the eruption of the over 1000 km3 Lava Creek Tuff and the formation of the present 45 x 85 km caldera. Resurgent doming subsequently occurred at both the NE and SW sides of the caldera and voluminous (1000 km3) intracaldera rhyolitic lava flows were erupted between 150,000 and 70,000 years ago. No magmatic eruptions have occurred since the late Pleistocene, but large hydrothermal eruptions took place near Yellowstone Lake during the Holocene. Yellowstone is presently the site of one of the world's largest hydrothermal systems including Earth's largest concentration of geysers.

Information Contacts: Roderick A. Hutchinson, Yellowstone National Park.

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/).