Japan’s Nishinoshima volcano, located about 1,000 km S of Tokyo in the Ogasawara Arc, erupted above sea level in November 2013 after 40 years of dormancy. Activity lasted for two years followed by two brief eruptions in 2017 and 2018. The next eruption, from early December 2019 through August 2020, included ash plumes, incandescent ejecta, and lava flows; it produced a large pyroclastic cone with a wide summit crater and extensive lava flows that significantly enlarged the island. This report covers the end of the eruption and cooling during September 2020-January 2021. Information is provided primarily from Japan Meteorological Agency (JMA) monthly reports and the Japan Coast Guard (JCG), which makes regular observation overflights.

Ash emissions were last reported on 27 August 2020. The very high levels of thermal energy from numerous lava flows, ash, and incandescent tephra that peaked during early July decreased significantly during August and September. Continued cooling of the fresh lava and the summit crater lasted into early January 2021 (figure 107). Monthly overflights and observations by scientists confirmed areas of steam emissions at the summit and on the flanks and discolored water around the island, but no eruptive activity.

Figure 107. High levels of thermal activity at Nishinoshima during June and July 2020 resulted from extensive lava flows and explosions of incandescent tephra. Although the last ash emission was reported on 27 August 2020, cooling of new material lasted into early January 2021. The MIROVA log radiative power graph of thermal activity covers the year ending on 3 February 2021. Courtesy of MIROVA.

Thermal activity declined significantly at Nishinoshima during August 2020 (BGVN 45:09). Only two days had two MODVOLC alerts (11 and 30), and four other days (18, 20, 21, 29) had single alerts. During JCG overflights on 19 and 23 August there were no ash emissions or lava flows observed, although steam plumes rose over 2 km above the summit crater during both visits. The last ash emission was reported by the Tokyo VAAC on 27 August 2020. No eruptive activity was observed by JMA during an overflight on 5 September, but steam plumes were rising from the summit crater (figure 108). No significant changes were observed in the shape of the pyroclastic cone or the coastline. Yellowish brown discolored water appeared around the western half of the island, and high temperature was still measured on the inner wall of the crater. Faint traces of SO₂ plumes were present in satellite images in early September; the last plume identified was on 18 September. Six days with single MODVOLC alerts were recorded during 3-19 September, and the final thermal alert appeared on 1 October 2020.

Figure 108. No eruptive activity was observed during a JMA overflight of Nishinoshima on 5 September 2020, but steam rose from numerous places within the enlarged summit crater (inset). Courtesy of JMA and JCG (Monthly report of activity at Nishinoshima, September 2020).

Steam plumes and high temperatures were noted at the summit crater on 28 October, and brown discolored water was present around the S coast of the island (figure 109), but there were no other signs of volcanic activity. Observations from the sea conducted on 2 November 2020 by researchers aboard the Maritime Meteorological Observatory marine weather observation ship "Ryofu Maru" confirmed there was no ongoing eruptive activity. In addition to steam plumes at the summit, they also noted steam rising from multiple cracks on the cooling surface of the lava flow area on the N side of the pyroclastic cone (figure 110). Only steam plumes from inside the summit crater were observed during an overflight on 24 November.

Figure 109. On a JCG overflight above Nishinoshima on 28 October 2020 there were no signs of eruptive activity; steam plumes were present in the summit crater and brown discolored water was visible around the S coast of the island. Courtesy of JMA and JCG (Monthly report of activity at Nishinoshima, October 2020).

Figure 110. Observations of Nishinoshima by staff aboard the Maritime Meteorological Observatory ship "Ryofu Maru" on 2 November 2020 showed a steam plume rising from the lava flow area on the N side of the pyroclastic cone (arrow) and minor steam above the cone. Courtesy of JMA (Monthly report of activity at Nishinoshima, November 2020).

JMA reduced the warning area around the crater on 18 December 2020 from 2.5 to 1.5 km due to decreased activity. On 7 December a steam plume rose from the inner wall of the summit crater and thermal imaging indicated the area was still hot. Brown discolored water was observed on the SE and SW coasts. Researchers aboard a ship from the Earthquake Research Institute at the University of Tokyo and the Marine Research and Development Organization reported continued steam plumes in the summit crater, around the lava flows on the N flank, and along the S coast during 15-29 December (figure 111). Steam plumes and elevated temperatures were still measured inside the summit crater during an overflight by the Japan Coast Guard on 25 January 2021, and discolored water persisted on the SE and SW coasts; there was no evidence of eruptive activity.

Figure 111. Observations of Nishinoshima from the sea by researchers from the Earthquake Research Institute (University of Tokyo) and the Marine Research and Development Organization, which took place from 15-29 December 2020, showed fumarolic acitivity not only inside the summit crater, but also in the lava flow area on the N side of the pyroclastic cone (left, 20 December) and in places along the southern coast (right, 23 December). (Monthly report of activity at Nishinoshima, December 2020).

Geologic Background. The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Another eruption that began offshore in 2013 completely covered the previous exposed surface and enlarged the island again. Water discoloration has been observed on several occasions since. The island is the summit of a massive submarine volcano that has prominent satellitic peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the sea surface 9 km SSE.

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); Japan Coast Guard (JCG) Volcano Database, Hydrographic and Oceanographic Department, 3-1-1, Kasumigaseki, Chiyoda-ku, Tokyo 100-8932, Japan (URL: http://www.kaiho.mlit.go.jp/info/kouhou/h29/index.html); Volcano Research Center (VRC-ERI), Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/topics/ASAMA2004/index-e.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA 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/).

Nyiragongo is a stratovolcano in the DR Congo with a deep summit crater containing a lava lake and a small active cone. During June 2018-May 2020, the volcano exhibited strong thermal signals primarily due to the lava lake, along with incandescence, seismicity, and gas-and-steam plumes (BGVN 44:05, 44:12, 45:06). The volcano is monitored by the Observatoire Volcanologique de Goma (OVG). This report summarizes activity during June-November 2020, based on satellite data.

Infrared MODIS satellite data showed almost daily strong thermal activity during June-November 2020 from MIROVA (Middle InfraRed Observation of Volcanic Activity), consistent with a large lava lake. Numerous hotspots were also identified every month by MODVOLC. Although clouds frequently obscured the view from space, a clear Sentinel-2 image in early June showed a gas-and-steam plume as well as a strong thermal anomaly (figure 76).

Figure 76. Sentinel-2 satellite imagery of Nyiragongo on 1 June 2020. A gas-and-steam is visible in the natural color image (bands 4, 3, 2) rising from a pit in the center of the crater (left), while the false color image (bands 12, 11, 4) reveals a strong thermal signal from a lava lake (right). Courtesy of Sentinel Hub Playground.

During the first half of June 2020, OVG reported that SO₂ levels had decreased compared to levels in May (7,000 tons/day); during the second half of June the SO₂ flux began to increase again. High levels of sulfur dioxide were recorded almost every day in the region above or near the volcano by the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Copernicus Sentinel-5 Precursor satellite (figure 77). According to OVG, SO₂ flux ranged from 819-5,819 tons/day during June. The number of days with a high SO₂ flux decreased somewhat in July and August, with high levels recorded during about half of the days. The volume of SO₂ emissions slightly increased in early July, based on data from the DOAS station in Rusayo, measuring 6,787 tons/day on 8 July (the highest value reported during this reporting period), and then declined to 509 tons/day by 20 July. The SO₂ flux continued to gradually decline, with high values of 5,153 tons/day in August and 4,468 tons/day in September. The number of days with high SO₂ decreased further in September and October but returned to about half of the days in November.

Figure 77. TROPOMI image of SO2 plume on 27 June 2020 in the Nyiragongo-Nyamulagira area. The plume drifted SSE. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

During 12-13 July a multidisciplinary team of OVG scientists visited the volcano to take measurements of the crater using a TCRM1102 Plus2 laser. They noted that the crater had expanded by 47.3 mm in the SW area, due to the rise in the lava lake level since early 2020. The OVG team took photos of the small cone in the lava lake that has been active since 2014, recently characterized by white gas-and-steam emissions (figure 78). OVG noted that the active lava lake had subsided roughly 20 m (figure78).

Figure 78. Photos (color corrected) of the crater at Nyiragongo showing the small active cone generating gas-and-steam emissions (left) and the active lava lake also characterized by white gas-and-steam emissions on 12 July 2020 (right). Courtesy of OVG (Rapport OVG Juillet 2020).

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

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

Kerinci, located in Sumatra, Indonesia, has had numerous explosive eruptions since 1838, with more recent activity characterized by gas-and-steam and ash plumes. The current eruptive episode began in April 2018 and has recently consisted of intermittent brown ash emissions and white gas-and-steam emissions (BGVN 45:07); similar activity continued from June through November 2020. Information primarily comes from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data.

Activity has been characterized by dominantly white and brown gas-and-steam emissions and occasional ash plumes, according to PVMBG. Near daily gas-and-steam emissions were observed rising 50-6,400 m above the crater throughout the reporting period: beginning in late July and continuing intermittently though November. Sentinel-2 satellite imagery showed frequent brown emissions rising above the summit crater at varying intensities and drifting in different directions from July to November (figure 21).

Figure 21. Sentinel-2 satellite imagery of brown emissions at Kerinci from July through November 2020 drifting in multiple directions. On 27 July (top left) the brown emissions drifted SW. On 31 August (top right) the brown emissions drifted W. On 2 September (bottom left) slightly weaker brown emissions drifting W. On 4 November (bottom right) weak brown emissions mostly remained within the crater, some of which drifted E. Images using “Natural Color” rendering (bands 4, 3, 2), courtesy of Sentinel Hub Playground.

During June through July the only activity reported by PVMBG consisted of white gas-and-steam emissions and brown emissions. On 4 June white gas-and-steam emissions rose to a maximum height of 6.4 km above the crater. White-and-brown emissions rose to a maximum height of 700 m above the crater on 2 June and 28 July.

Continuous white-and-brown gas-and-steam emissions were reported in August that rose 50-1,000 m above the crater. The number of ash plumes reported during this month increased compared to the previous months. In a Volcano Observatory Notice for Aviation (VONA) issued on 7 August at 1024, PVMBG reported an ash plume that rose 600 m above the crater and drifted E, SE, and NE. In addition, the Darwin VAAC released two notices that described continuous minor ash emissions rising to 4.3 km altitude and drifting E and NE. On 9 August an ash plume rose 600 m above the crater and drifted ENE at 1140. An ash plume was observed rising to a maximum of 1 km above the crater, drifting E, SE, and NE on 12 August at 1602, according to a PVMBG VONA and Darwin VAAC advisory. The following day, brown emissions rose to a maximum of 1 km above the crater and were accompanied by a 600-m-high ash plume that drifted ENE at 1225. Ground observers on 15 August reported an eruption column that rose to 4.6 km altitude; PVMBG described brown ash emissions up to 800 m above the crater drifting NW at 0731 (figure 22). During 20-21 August pilots reported an ash plume rising 150-770 m above the crater drifting NE and SW, respectively.

Figure 22. Webcam image of an ash plume rising above Kerinci on 15 August 2020. Courtesy of MAGMA Indonesia.

Activity in September had decreased slightly compared to the previous month, characterized by only white-and-brown gas-and-steam emissions that rose 50-300 m above the crater; solely brown emissions were observed on 30 September and rose 50-100 m above the crater. This low level of activity persisted into October, with white gas-and-steam emissions to 50-200 m above the crater and brown emissions rising 50-300 m above the crater. On 16 October PVMBG released a VONA at 0340 that reported an ash plume rising 687 m above the crater and drifting NE. On 17 October white, brown, and black ash plumes that rose 100-800 m above the crater drifted NE according to both PVMBG and a Darwin VAAC advisory (figure 23). During 18-19 October white, brown, and black ash emissions rose up to 400 m above the crater and drifted NE and E.

Figure 23. Webcam image of a brown ash emission from Kerinci on 17 October 2020. Courtesy of MAGMA Indonesia.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Whakaari/White Island, located in the Bay of Plenty 50 km offshore of North Island, has been New Zealand’s most active volcano since 1976. Activity has been previously characterized by phreatic activity, explosions, and ash emissions (BGVN 42:05). The most recent eruption occurred on 9 December 2019, which consisted of an explosion that generated an ash plume and pyroclastic surge that affected the entire crater area, resulting in 21 fatalities and many injuries (BGVN 45:02). This report updates information from February through November 2020, which includes dominantly gas-and-steam emissions along with elevated surface temperatures, using reports from the New Zealand GeoNet Project, the Wellington Volcanic Ash Advisory Centre (VAAC), and satellite data.

Activity at Whakaari/White Island has declined and has been dominated by white gas-and-steam emissions during the reporting period; no explosive eruptive activity has been detected since 9 December 2019. During February through 22 June, the Volcanic Activity Level (VAL) remained at a 2 (moderate to heightened volcanic unrest) and the Aviation Color Code was Yellow. GeoNet reported that satellite data showed some subsidence along the W wall of the Main Crater and near the 1914 landslide scarp, though the rate had reduced compared to previous months. Thermal infrared data indicated that the fumarolic gases and five lobes of lava that were first observed in early January 2020 in the Main Crater were 550-570°C on 4 February and 660°C on 19 February. A small pond of water had begun to form in the vent area and exhibited small-scale gas-and-steam-driven water jetting, similar to the activity during September-December 2019. Gas data showed a steady decline in SO₂ and CO₂ levels, though overall they were still slightly elevated.

Similar activity was reported in March and April; the temperatures of the fumaroles and lava in the Main Crater were 746°C on 10 March, the highest recorded temperature to date. SO₂ and CO₂ gas emissions remained elevated, though had overall decreased since December 2019. Small-scale water jetting continued to be observed in the vent area. During April, public reports mentioned heightened gas-and-steam activity, but no eruptions were detected. A GeoNet report issued on 16 April stated that high temperatures were apparent in the vent area at night.

Whakaari remained at an elevated state of unrest during May, consisting of dominantly gas-and-steam emissions. Monitoring flights noted that SO₂ and CO₂ emissions had increased briefly during 20-27 May. On 20 May, the lava lobes remained hot, with temperatures around 500°C; a nighttime glow from the gas emissions surrounding the lava was visible in webcam images. Tremor levels remained low with occasional slightly elevated episodes, which included some shallow-source volcanic earthquakes. Satellite-based measurements recorded several centimeters of subsidence in the ground around the active vent area since December 2019. During a gas observation flight on 28 May there was a short-lived gas pulse, accompanied by an increase in SO₂ and CO₂ emissions, and minor inflation in the vent area (figure 96).

Figure 96. Photo of a strong gas-and-steam plume rising above Whakaari/White Island on 28 May 2020. Courtesy of GeoNet.

An observation flight made on 3 June reported a decline in gas flux compared to the measurements made on 28 May. Thermal infrared images taken during the flight showed that the lava lobes were still hot, at 450°C, and continued to generate incandescence that was visible at night in webcams. On 16 June the VAL was lowered to 1 (minor volcanic unrest) and on 22 June the Aviation Color Code had decreased to Green.

Minor volcanic unrest continued in July; the level of volcanic tremors has remained generally low, with the exception of two short bursts of moderate volcanic tremors in at the beginning of the month. Temperatures in the active vents remained high (540°C) and volcanic gases persisted at moderate rate, similar to those measured since May, according to an observation flight made during the week of 30 July. Subsidence continued to be observed in the active vent area, as well as along the main crater wall, S and W of the active vents. Recent rainfall has created small ponds of water on the crater floor, though they did not infiltrate the vent areas.

Gas-and-steam emissions persisted during August through October at relatively high rates (figures 97 and 98). A short episode of moderate volcanic tremor was detected in early August, but otherwise seismicity remained low. Updated temperatures of the active vent area were 440°C on 15 September, which had decreased 100°C since July. Rain continued to collect at the crater floor, forming a small lake; minor areas of gas-and-steam emissions can be seen in this lake. Ongoing subsidence was observed on the Main Crater wall and S and W of the 2019 active vents.

Figure 97. Photo of an observation flight over Whakaari/White Island on 8 September 2020 showing white gas-and-steam emissions from the vent area. Photo courtesy of Brad Scott, GeoNet.

Figure 98. Image of Whakaari/White Island from Whakatane in the North Island of New Zealand showing a white gas-and-steam plume on 26 October 2020. Courtesy of GeoNet.

Activity during November was primarily characterized by persistent, moderate-to-large gas-and-steam plumes that drifted downwind for several kilometers but did not reach the mainland. The SO₂ flux was 618 tons/day and the CO₂ flux was 2,390 tons/day. New observations on 11 November noted some occasional ash deposits on the webcams in conjunction with mainland reports of a darker than usual plume (figure 99). Satellite images provided by MetService, courtesy of the Japan Meteorological Agency, confirmed the ash emission, but later images showed little to no apparent ash; GNS confirmed that no eruptive activity had occurred. Initial analyses indicated that the ash originated from loose material around the vent was being entrained into the gas-and-steam plumes. Observations from an overflight on 12 November showed that there was no substantial change in the location and size of the active vents; rainfall continued to collect on the floor of the 1978/90 Crater, reforming the shallow lake. A small sequence of earthquakes was detected close to the volcano with several episodes of slightly increased volcanic tremors.

During 12-14 November the Wellington VAAC issued multiple advisories noting gas, steam, and ash plumes that rose to 1.5-1.8 km altitude and drifted E and SE, based on satellite data, reports from pilots, and reports from GeoNet. As a result, the VAL was increased to 2 and the Aviation Color Code was raised to Yellow. Scientists on another observation flight on 16 November reported that small amounts of ash continued to be present in gas-and-steam emissions, though laboratory analyses showed that this ash was resuspended material and not from new eruptive or magmatic activity. The SO₂ and CO₂ flux remained above background levels but were slightly lower than the previous week’s measurements: 710 tons/day and 1,937 tons/day. Seismicity was similar to the previous week, characterized by a sequence of small earthquakes, a larger than normal volcanic earthquake located near the volcano, and ongoing low-level volcanic tremors. During 16-17 November plumes with resuspended ash were observed rising to 460 m altitude, drifting E and NE, according to a VAAC advisory (figure 99). During 20-24 November gas-and-steam emissions that contained a minor amount of resuspended ash rose to 1.2 km altitude and drifted in multiple directions, based on webcam and satellite images and information from GeoNet.

Figure 99. Left: Photo of a gas observation flight over Whakaari/White Island on 11 November 2020 showing some dark particles in the gas-and-steam plumes, which were deposited on some webcams. Photo has been color corrected and straightened. Courtesy of GeoNet. Right: Photo showing gas, steam, and ash emissions rising above the 2019 Main Crater area on 16 November 2020. Courtesy of GNS Science (17 November 2020 report).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows a total of eleven low-power thermal anomalies during January to late March 2020; a single weak thermal anomaly was detected in early July (figure 100). The elevated surface temperatures during February-May 2020 were detected in Sentinel-2 thermal satellite images in the Main Crater area, occasionally accompanied by gas-and-steam emissions (figure 101). Persistent white gas-and-steam emissions rising above the Main Crater area were observed in satellite imagery on clear weather days and drifting in multiple directions (figure 102). The small lake that had formed due to rainfall was also visible to the E of the active vents.

Figure 100. Low-power, infrequent thermal activity at Whakaari/White Island was detected during January through late March 2020, as reflected in the MIROVA data (Log Radiative Power). A single thermal anomaly was shown in early July. Courtesy of MIROVA.

Figure 101. Sentinel-2 thermal satellite images in the Main Crater area of Whakaari/White Island show residual elevated temperatures from the December 2019 eruption, accompanied by gas-and-steam emissions and drifting in different directions during February-May 2020. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 102. Sentinel-2 images showing persistent white gas-and-steam plumes rising from Main Crater area of Whakaari/White Island during March-November 2020 and drifting in multiple directions. A small pond of water (light blue-green) is visible in the vent area to the E of the plumes. On 11 November (bottom right), the color of the plume is gray and contains a small amount of ash. Images using “Natural color” rendering (bands 4, 3, 2). 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/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html); 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); Brad Scott, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: https://twitter.com/Eruptn).

Suwanosejima, an andesitic stratovolcano in Japan's northern Ryukyu Islands, was intermittently active for much of the 20th century, producing ash plumes, Strombolian explosions, and ashfall. Continuous activity since October 2004 has included intermittent explosions which generate ash plumes that rise hundreds of meters above the summit to altitudes between 1 and 3 km. Incandescence is often observed at night and ejecta periodically reaches over a kilometer from the summit. Ashfall is usually noted several times each month in the nearby community on the SW flank of the island. Ongoing activity for the second half of 2020, which includes significantly increased activity in December, is covered in this report with information provided by the Japan Meteorological Agency (JMA), the Tokyo Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

A steady increase in activity was reported during July-December 2020. The number of explosions recorded increased each month from only six during July to 460 during December. The energy of the explosions increased as well; ejecta was reported 600 m from the crater during August, but a large bomb reached 1.3 km from the crater at the end of December. After an increased period of explosions late in December, JMA raised the Alert Level from 2 to 3 on a 5-level scale. The MIROVA graph of thermal activity indicated intermittent anomalies from July through December 2020, with a pulse of activity in the second half of December (figure 48).

Figure 48. MIROVA thermal activity for Suwanosejima for the period from 3 February through December 2020 shows pulses of activity in February and April, with intermittent anomalies until another period of frequent stronger activity in December. Courtesy of MIROVA.

Six explosions were recorded during July 2020, compared with only one during June. According to JMA, the tallest plume rose 2,000 m above the crater rim. Incandescent ejecta was occasionally observed at night. The Tokyo VAAC reported a number of ash plumes that rose to 1.2-2.7 km altitude and drifted NW and W during the second half of the month (figure 49). Activity increased during August 2020 when thirteen explosions were reported. The Tokyo VAAC reported a few ash plumes during 1-6 August that rose to 1.8-2.4 km altitude and drifted NW; a larger pulse of activity during 18-22 August produced plumes that rose to altitudes ranging from 1.8 to over 2.7 km. Ashfall was reported on 19 and 20 August in the village located 4 km SSW of the crater; incandescence was visible at the summit and ash plumes drifted SW in satellite imagery on 19 August (figure 50). A MODVOLC thermal alert was issued on 19 August. On 21 August a large bomb was ejected 600 m from the Otake crater in an explosion early in the day; later that afternoon, an ash plume rose to more than 2,000 m above the crater rim. During 19-22 August, SO₂ emissions were recorded each day by the TROPOMI instrument on the Sentinel-5P satellite (figure 51).

Figure 49. An ash emission at Suwanosejima rose to 2.7 km altitude and drifted NW on 27 July 2020. Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, July 2020).

Figure 50. Ash drifted SW from the summit crater of Suwanosejima on 19 August 2020 and a bright thermal anomaly was present at the summit. Residents of the village 4 km SW reported ashfall that day and the next. Courtesy of Sentinel Hub Playground.

Figure 51. A period of increased activity at Suwanosejima during 19-22 August 2020 produced SO2 emissions that were measured by the TROPOMI instrument on the Sentinel-5P satellite. Nishinoshima, was also producing significant SO2 at the same time. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Thirteen explosions were recorded during September 2020, with the highest ash plumes reaching 2,000 m above the crater rim, and bombs falling 400 m from the crater. Ashfall was recorded on 20 September in the community located 4 km SSW. The Tokyo VAAC reported intermittent ash plumes during the month that rose to 1.2-2.1 km altitude and drifted in several directions. Incandescence was frequently observed at night (figure 52). Explosive activity increased during October with 22 explosions recorded. Ash plumes rose over 2,000 m above the crater rim, and bombs reached 700 m from the crater. Steam plumes rose 2,300 m above the crater rim. Ashfall and loud noises were confirmed several times between 2 and 14 October in the nearby village. A MODVOLC thermal alert was issued on 6 October. The Tokyo VAAC reported multiple ash plumes throughout the month; they usually rose to 1.5-2.1 km altitude and drifted in many directions. The plume on 28 October rose to over 2.7 km altitude and was stationary.

Figure 52. Incandescence at night and ash emissions were observed multiple times at Suwanosejima during September and October 2020 including on 21 and 26 September (top) and 29 October 2020. Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, September and October 2020).

Frequent explosions occurred during November 2020, with a sharp increase in the number of explosions to 105 events compared with October. Ash plumes rose to 1,800 m above the crater rim and bombs were ejected 700 m. Occasional ashfall and loud noises were reported from the nearby community throughout the month. Scientists measured no specific changes to the surface temperature around the volcano during an overflight early on 5 November compared with the previous year. At 0818 on 5 November a small ash explosion at the summit crater was photographed by the crew during an observation flight (figure 53). On 12 and 13 November, incandescent ejecta fell 600 m from the crater and ash emissions rose 1,500 m above the crater rim (figure 54).

Figure 53. A minor explosion produced a small ash plume at Suwanosejima during an overflight by JMA on the morning of 5 November 2020. The thermal activity was concentrated at the base of the explosion (inset). Image taken from off the E coast. Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, November 2020).

Figure 54. On 12 and 13 November 2020 incandescent ejecta from Suwanosejima reached 600 m from the crater (top) and ash emissions rose 1,500 m above the crater rim (bottom). Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, November 2020).

During December 2020 there were 460 explosions reported, a significant increase from the previous months. Ash plumes reached 1,800 m above the summit. Three MODVOLC thermal alerts were issued on 25 December and two were issued the next day. The number of explosions increased substantially at the Otake crater between 21 and 29 December, and early on 28 December a large bomb was ejected to 1.3 km SE of the crater (figure 55). A second explosion a few hours later ejected another bomb 1.1 km SE. An overflight later that day confirmed the explosion, and ash emissions were still visible (figure 56), although cloudy weather prevented views of the crater. Ashfall was noted and loud sounds heard in the nearby village. A summary graph of observations throughout 2020 indicated that activity was high from January through May, quieter during June, and then increased again from July through the end of the year (figure 57).

Figure 55. Early on 28 December 2020 a large explosion at Suwanosejima sent a volcanic bomb 1.3 km SE from the summit (bright spot on left flank in large photo). Thermal imaging taken the same day showed the heat at the eruption site and multiple fragments of warm ejecta scattered around the crater area (inset). Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, December 2020).

Figure 56. Ash emissions were still visible midday on 28 December 2020 at Suwanosejima during a helicopter overflight by the 10th Regional Coast Guard. Image taken from the SW flank of the volcano. Two large explosions earlier in the day had sent ejecta more than a kilometer from the crater. Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, December 2020).

Figure 57. Activity summary for Suwanosejima for January-December 2020 when 764 explosions were recorded. Black bars represent the height of steam, gas, or ash plumes in meters above the crater rim, gray volcano icons represent explosions, usually accompanied by an ash plume, red icons represent large explosions with ash plumes, orange diamonds indicate incandescence observed in webcams. Courtesy of JMA (Suwanosejima volcanic activity annual report, 2020).

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 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/); 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); NASA 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/).

Karangetang (also known as Api Siau) is located on the island of Siau in the Sitaro Regency, North Sulawesi, Indonesia and consists of two active summit craters: a N crater (Kawah Dua) and a S crater (Kawah Utama, also referred to as the “Main Crater”). More than 50 eruptions have been observed since 1675. The current eruption began in November 2018 and has recently been characterized by frequent incandescent block avalanches, thermal anomalies in the crater, and gas-and-steam plumes (BGVN 45:06). This report covers activity from June through November 2020, which includes dominantly crater anomalies, few ash plumes, and gas-and-steam emissions. Information primarily comes from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and various satellite data.

Activity decreased significantly after mid-January 2020 and has been characterized by dominantly gas-and-steam emissions and occasional ash plumes, according to PVMBG. Daily gas-and-steam emissions were observed rising 25-600 m above the Main Crater (S crater) during the reporting period and intermittent emissions rising 25-300 m above Kawah Dua (N crater).

The only activity reported by PVMBG in June, August, and October was daily gas-and-steam emissions above the Main Crater and Kawah Dua (figure 47). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows intermittent low-power thermal anomalies during June through late July, which includes a slight increase in power during late July (figure 48). During 14-15 July strong rumbling from Kawah Dua was accompanied by white-gray emissions that rose 150-200 m above the crater. Crater incandescence was observed up to 10 m above the crater. According to webcam imagery from MAGMA Indonesia, intermittent incandescence was observed at night from both craters through 25 July. In a Volcano Observatory Notice for Aviation (VONA) issued on 5 September, PVMBG reported an ash plume that rose 800 m above the crater.

Figure 47. Webcam image of gas-and-steam plumes rising above the two summit craters at Karangetang on 16 June 2020. Courtesy of MAGMA Indonesia.

Figure 48. Intermittent low-power thermal anomalies at Karangetang were reported during June through July 2020 with a slight increase in power in late July, according to the MIROVA graph (Log Radiative Power). No thermal activity was detected during August to late October; in mid-November a short episode of increased activity occurred. Courtesy of MIROVA.

Thermal activity increased briefly during mid-November when hot material was reported extending 500-1,000 m NW of the Main Crater, accompanied by gas-and-steam emissions rising 200 m above the crater. Corresponding detection of MODIS thermal anomalies was seen in MIROVA graphs (see figure 48), and the MODVOLC system showed alerts on 13 and 15 November. On 16 November blue emissions were observed above the Main Crater drifting W. Sentinel-2 thermal images showed elevated temperatures in both summit craters throughout the reporting period, accompanied by gas-and-steam emissions and movement of hot material on the NW flank on 19 November (figure 49). White gas-and-steam emissions rose to a maximum height of 300 m above Kawah Dua on 22 November and 600 m above the Main Crater on 28 November.

Figure 49. Persistent thermal anomalies (bright yellow-orange) at Karangetang were detected in both summit craters using Sentinel-2 thermal satellite imagery during June through November 2020. Gas-and-steam emissions were also occasionally detected in both craters as seen on 17 June (top left) and 20 September (bottom left) 2020. On 19 November (bottom right) the Main Crater (S) showed a hot thermal signature extending NW. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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).

Colombia’s broad, glacier-capped Nevado del Ruiz has an eruption history documented back 8,600 years, including documented observations since 1570. Ruiz remained quiet for 20 years after the deadly September 1985-July 1991 eruption until a period of explosive activity from February 2012 into 2013. Renewed activity beginning in November 2014 included ash and gas-and-steam plumes, ashfall, and the appearance of a slowly growing lava dome inside the Arenas crater in August 2015. Additional information has caused a revision to earlier reporting that eruptive activity ended in May 2017 and began again that December (BGVN 44:12); activity appears to have continued throughout 2017 with intermittent ash emissions and thermal evidence of dome growth. Periods of increased thermal activity alternated with periods of increased explosive activity during 2018-2019 and into 2020; SO₂ emissions persisted at significant levels. The lava dome has continued to grow through 2020. This report covers ongoing activity from July-December 2020 using information from reports by the Servicio Geologico Colombiano (SGC) and the Observatorio Vulcanológico y Sismológico de Manizales, the Washington Volcanic Ash Advisory Center (VAAC) notices, and various sources of satellite data.

Gas and ash emissions continued throughout July-December 2020; they generally rose to 5.8-6.1 km altitude with the highest reported plume at 6.7 km altitude on 7 December. SGC interpreted repeated episodes of “drumbeat seismicity” as an indication of continued dome growth throughout the period. Satellite thermal anomalies also suggested that dome growth continued. The MIROVA graph of thermal activity suggests that the dome was quiet in July and early August, but small pulses of thermal energy were recorded every few weeks for the remainder of 2020 (figure 115). Plots of the cumulative number and magnitude of seismic events at Nevado del Ruiz between January 2010 and November 2020 show a stable trend with periodic sharp increases in activity or magnitude throughout that time. SGC has adjusted the warning levels over time according to changes in the slope of the curves (figure 116).

Figure 115. Thermal energy shown in the MIROVA graph of log radiative power at Nevado del Ruiz from 3 February 2020 through the end of the year indicates that higher levels of thermal energy lasted through April 2020; a quieter period from late May-early August was followed by low-level persistent anomalies through the end of the year. Courtesy of MIROVA.

Figure 116. Changes in seismic frequency and energy at Nevado del Ruiz have been monitored by SGC for many years. Left: the cumulative number of daily VT, LP-VLP, TR, and HB seismic events, recorded between 1 January 2010 and 30 November 2020. The arrows highlight the days with the highest number of seismic events; the number and type of event is shown under the date. Right: The cumulative VT and HB seismic energy recorded between 1 January 2010 and 30 November 2020. The arrows highlight the days with the highest energy; the local magnitude of the event is shown below the date. SGC has adjusted the warning levels over time (bar across the bottom of each graph) according to changes in the slope of the curves. Courtesy of SGC (INFORME TÉCNICO – OPERATIVO DE LA ACTIVIDAD VOLCÁNICA, SEGMENTO VOLCÁNICO NORTE DE COLOMBIA – NOVIEMBRE DE 2020).

Activity during July-December 2020. Seismic energy increased during July compared to June 2020 with events localized around the Arenas crater. The depth of the seismicity varied from 0.3-7.8 km. Some of these signals were associated with small emissions of gas and ash, which were confirmed through webcams and by reports from officials of the Los Nevados National Natural Park (NNNP). The Washington VAAC reported a possible ash emission on 8 July that rose to 6.1 km altitude and drifted NW. On 21 July a webcam image showed an ash emission that rose to the same altitude and drifted W; it was seen in satellite imagery possibly extending 35 km from the summit but was difficult to confirm due to weather clouds. Short- to moderate-duration (less than 40 minutes) episodes of drumbeat seismicity were recorded on 5, 13, 17, and 21 July. SCG interprets this type of seismic activity as related to the growth of the Arenas crater lava dome. Primarily WNW drifting plumes of steam and SO₂ were observed in the webcams daily. The gas was occasionally incandescent at night. The tallest plume of gas and ash reached 1,000 m above the crater rim on 30 July and was associated with a low-energy tremor pulse; it produced ashfall in parts of Manizales and nearby communities (figure 117).

Figure 117. Images captured by a traditional camera (top) and a thermal camera (bottom) at Nevado del Ruiz showed a small ash emission in the early morning of 30 July 2020. Ashfall was reported in Manizales. The cameras are located 3.7 km W of the Arenas crater. Courtesy of SGC (Emisión de ceniza Volcan Nevado del Ruiz Julio 30 de 2020).

Seismicity increased in August 2020 with respect to July. Some of the LP and TR (tremor) seismicity was associated with small emissions of gas and ash, confirmed by web cameras, park personnel, and the Washington VAAC. The Washington VAAC received a report from the Bogota MWO of an ash emission on 1 August that rose to 6.1 km altitude and drifted NW; it was not visible in satellite imagery. Various episodes of short duration drumbeat seismicity were recorded during the month. The tallest steam and gas plume reached 1,800 m above the rim on 31 August. Despite the fact that in August the meteorological conditions made it difficult to monitor the surface activity of the volcano, three ash emissions were confirmed by SGC.

Seismicity decreased during September 2020 with respect to August. Some of the LP and TR (tremor) seismicity was associated with small emissions of gas and ash, confirmed by web cameras, park personnel and the Washington VAAC. The Washington VAAC reported an ash emission on 16 September that rose to 6.1 km altitude and drifted NW. A minor ash emission on 20 September drifted W from the summit at 5.8 km altitude. A possible emission on 23 September drifted NW at 6.1 km altitude for a brief period before dissipating. Two emissions were reported drifting WNW of the summit on 26 September at 5.8 and 5.5 km altitude. Continuous volcanic tremors were registered throughout September, with the higher energy activity during the second half of the month. One episode of drumbeat seismicity on 15 September lasted for 38 minutes and consisted of 25 very low energy earthquakes. Steam and gas plumes reached 1,800 m above the crater rim during 17-28 September (figure 118). Five emissions of ash were confirmed by the webcams and park officials during the month, in spite of difficult meteorological conditions; three of them occurred between 15 and 20 September.

Figure 118. A dense plume of steam rose from Nevado del Ruiz in the morning of 17 September 2020. Courtesy of Gonzalo.

Seismicity increased during October with respect to September. A few of the LP and tremor seismic events were associated with small emissions of gas and ash, confirmed by web cameras, park personnel, and the Washington VAAC. The Washington VAAC issued advisories of possible ash emissions on 2, 6, 9, 11, 15, 17, 18, and 21 October. The plumes rose to 5.6-6.4 km altitude and drifted primarily W and NW. Steam plumes were visible most days of the month (figure 119). Only a few were visible in satellite data, but most were visible in the webcams. Several episodes of drumbeat seismicity were recorded on 13, 22-25, and 27 October, which were characterized by being of short duration and consisting of very low energy earthquakes. The tallest plume during the month rose about 2 km above the crater rim on 18 October. Ash emissions were recorded eight times during the month by SGC.

Figure 119. A steam plume mixed with possible ash drifted SE from Nevado del Ruiz on 7 October 2020. Courtesy of vlucho666.

During November 2020, the number of seismic events decreased relative to October, but the amount of energy released increased. Some of the seismicity was associated with small emissions of gas and ash, confirmed by webcams around the volcano. The Washington VAAC reported ash emissions on 22 and 30 November; the 22 November event was faintly visible in satellite images and was also associated with an LP seismic event. They rose to 5.8-6.1 km altitude and drifted W. Various episodes of drumbeat seismicity registered during November were short- to moderate-duration, very low energy, and consisted of seismicity associated with rock fracturing (VT). Multiple steam plumes were visible from communities tens of kilometers away (figure 120).

Figure 120. Multiple dense steam plumes were photographed from communities around Nevado del Ruiz during November 2020, including on 18 (top) and 20 (bottom) November. Top image courtesy of Jose Fdo Cuartas, bottom image courtesy of Efigas Oficial.

Seismic activity increased in December 2020 relative to November. It was characterized by continuous volcanic tremor, tremor pulses, long-period (LP) and very long-period (VLP) earthquakes. Some of these signals were associated with gas and ash emissions, one confirmed through the webcams. The Washington VAAC reported ash emissions on 5 and 7 December. The first rose to 5.8 km altitude and drifted NW. The second rose to 6.7 km altitude and drifted W. A single discrete cloud was observed 35 km W of the summit; it dissipated within six hours. Drumbeat seismic activity increased as well in December; the episode on 3 December was the most significant. Steam and gas emissions continued throughout the month; a plume of gas and ash reached 1,700 m above the summit on 20 December, and drifted NW.

Sentinel-2 satellite data showed at least one thermal anomaly inside the Arenas crater each month during August-December 2020, corroborating the seismic evidence that the dome continued to grow throughout the period (figure 121). Sulfur dioxide emissions were persistent, with many days every month recording DU values greater than two with the TROPOMI instrument on the Sentinel 5-P satellite (figure 122).

Figure 121. Thermal anomalies at Nevado del Ruiz were recorded at least once each month during August-December 2020 suggesting continued growth of the dome within the Arenas crater at the summit. Courtesy of Sentinel Hub Playground.

Figure 122. Sulfur dioxide emissions were persistent at Nevado del Ruiz during August-December 2020, with many days every month recording DU values greater than two with the TROPOMI instrument on the Sentinel 5-P satellite. Ecuador’s Sangay had even larger SO2 emissions throughout the period. Dates are at the top of each image. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Additional reports of activity during 2017. Activity appears to have continued during June-December 2017. Ash emissions were reported by the Bogota Meteorological Weather Office (MWO) on 13 May, and by SGC on 28 May. During June, some of the recorded seismic events were associated with minor emissions of ash; these were confirmed by webcams and by field reports from both the staff of SGC and the Los Nevados National Natural Park (PNNN). Ash emissions were confirmed in webcams by park officials on 3, 16, and 17 June. Gas emissions from the Arenas crater during July 2017 averaged 426 m above the crater rim, generally lower than during June. The emissions were mostly steam with small amounts of SO₂. Emissions were similar during August, with most steam and gas plumes drifting NW. No ash emissions were reported during July or August.

SGC reported steam and gas plumes during September that rose as high as 1,650 m above the crater rim and drifted NW. On 21 September the Washington VAAC received a report of an ash plume that rose to 6.4 km altitude and drifted NNW, although it was not visible in satellite imagery. Another ash emission rising to 6.7 km altitude was reported on 7 October; weather clouds prevented satellite observation. An episode of drumbeat seismicity was recorded on 9 October, the first since April 2017. While SGC did not explicitly mention ash emissions during October, several of the webcam images included in their report show plumes described as containing ash and gas (figure 123).

Figure 123. Plumes of steam, gas, and ash rose from Arenas crater at Nevado del Ruiz most days during October 2017. Photographs were captured by the webcams installed in the Azufrado Canyon and Cerro Gualí areas. Courtesy of SGC (INFORME DE ACTIVIDAD VOLCANICA SEGMENTO NORTE DE COLOMBIA, OCTUBRE DE 2017).

The Washington VAAC received a report from the Bogota MWO of an ash emission that rose to 6.1 km altitude and drifted NE on 8 November 2017. A faint plume was visible in satellite imagery extending 15 km NE from the summit. SGC reported that plumes rose as high as 2,150 m above the rim of Arenas crater during November. The plumes were mostly steam, with minor amounts of SO₂. A diffuse plume of ash was photographed in a webcam on 24 November. SGC did not report any ash emissions during December 2017, but the Washington VAAC reported “a thin veil of volcanic ash and gases” visible in satellite imagery and webcams on 18 December that dissipated within a few hours. In addition to the multiple reports of ash emissions between May and December 2017, Sentinel-2 thermal satellite imagery recorded at least one image each month during June-December showing a thermal anomaly at the summit consistent with the slowly growing dome first reported in August 2015 (figure 124).

Figure 124. Thermal anomalies from the growing dome inside Arenas crater at the summit of Nevado del Ruiz appeared at least once each month from June-December 2017. A strong anomaly was slightly obscured by clouds on 3 June (top left). On 2 August, a steam plume obscured most of the crater, but a small thermal anomaly is visible in its SE quadrant (top right). Strong anomalies on 30 November and 20 December (bottom) have a ring-like form suggestive of a growing dome. Atmospheric penetration rendering (bands 12, 11, 8A), courtesy of Sentinel Hub Playground.

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

Information Contacts: 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); 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/); Gonzalo (URL: https://twitter.com/chaloc22/status/1306581929651843076); Jose Fdo Cuartas (URL: https://twitter.com/JoseFCuartas/status/1329212975434096640); Vlucho666 (URL: https://twitter.com/vlucho666/status/1313791959954268161); Efigas Oficial (URL: https://twitter.com/efigas_oficial/status/1329780287920873472).

Mount Ibu is an active stratovolcano located along the NW coast of Halmahera Island in Indonesia. After a two-day eruption in 1911, Ibu was quiet until 1998-1999 when explosions produced ash emissions, a lava flow and dome growth began inside the summit crater. Although possible dome growth occurred in 2001 and 2004, little activity was reported until ash emissions began in April 2008. These were followed by thermal anomalies beginning the next month; ash emissions and dome growth have continued for 12 years and the dome now fills the summit crater (BGVN 45:07). Activity continued throughout 2020, consisting of frequent white-and-gray emissions, ash explosions, ash plumes, and small lava flows. This report updates activity through December 2020, using 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 satellite instruments.

Activity throughout July-December 2020 was very consistent and similar to activity reported earlier in the year. Tens of daily explosions produced white and gray ash emissions that rose 200-800 m above the summit (figure 25). Occasional larger explosions were reported in VONAs and VAAC notices. The MIROVA graph of log radiative power for the period shows consistent thermal anomalies the entire time (figure 26). Satellite imagery from Sentinel-2 identified thermal anomalies inside the summit crater every month, usually a larger central one and a smaller one to the NW, suggesting continued dome growth and lava flow activity (figure 27).

Figure 25. Between 60 and 90 explosions occurred most days at Ibu during 1 July-31 December 2020. White and gray plumes rose 200-800 m above the summit crater every day. Data courtesy of PVMBG daily reports.

Figure 26. The MIROVA graph of Log Radiative Power at Ibu from 3 February through December 2020 indicated a constant ongoing heat source from the summit of the crater. Courtesy of MIROVA.

Figure 27. Thermal anomalies persisted at the summit of Ibu throughout July-December 2020. One central anomaly was usual accompanied by a smaller one slightly NW of the central spot. Atmospheric penetration rendering (bands 12, 11a, and 8), courtesy of Sentinel Hub Playground.

The Darwin VAAC observed multiple minor ash emissions in satellite imagery drifting W on 6 July 2020 at 1.8 km altitude. A series of discrete puffs of ash were observed on 15 July also at 1.8 km altitude drifting W. Ongoing minor emissions were discernible on visible and RGB imagery at 2.1 km altitude drifting W on 20 July. On 30 July ash plumes rose to 1.8 km altitude drifted NW and a hotspot was present at the summit. A single MODVOLC alert was issued on 8 July. Single MODVOLC alerts were also issued on 11, 18, and 27 August 2020. PVMBG issued a VONA on 5 August, reporting an ash cloud that rose to 1.8 km altitude and drifted N (figure 28). The Darwin VAAC reported an ash emission later that day that rose to 4.3 km altitude and drifted NW for several hours before dissipating. Multiple discrete emissions were identified in satellite imagery drifting N at 2.1 km altitude on 11 August; they dissipated quickly. During 22-25 August intermittent ash emissions rose to 1.5-1.8 km altitude and drifted NW and W. Minor continuous emissions were again reported on 28 August.

Figure 28. Ash plumes rose from the summit of Ibu many days during July and August 2020, including on 8 July (top) and 5 August (bottom). Courtesy of PVMBG.

Many ash emissions during September and October 2020 were not accompanied by VONAs or VAAC advisories (figure 29). PVMBG issued a VONA on 20 September for an ash emission that rose to 1.5 km altitude and drifted N. Continuous discrete ash emissions over several days drifted SW to NW during 25-29 September at 1.8-2.1 km altitude, as reported in multiple VONAs and VAAC advisories. Single MODVOLC alerts were issued on 26 and 30 September. The Darwin VAAC issued an ash advisory on 8 October for intermittent ash emissions rising to 2.1 km altitude and drifting NW. A single MODVOLC alert was issued the next day. On 20 October ash emissions again rose to 2.1 km altitude and drifted NE.

Figure 29. Ash emissions at Ibu were photographed in webcams on 6 September (left) and 12 October (right) 2020. Courtesy of PVMBG.

The Darwin VAAC reported intermittent ash emissions to 1.8 km altitude during 3-5, 12-13, 18-19, and 22 November 2020 that drifted SSW for several hours before dissipating. PVMBG also issued a VONA for an ash cloud on 27 November that rose to 2.1 km altitude and drifted W. They reported faint rumbling at the PGA Ibu station on 10 November and loud rumbling on 16 and 18 November. During December, minor ash emissions rose to 1.8-2.1 km altitude and drifted E on 4 and 6 December, SW on 11 December, and SE on 12-13 December. PVMBG issued a VONA on 19 December for a white to gray ash cloud drifting N at 1.7 km altitude. Single MODVOLC alerts were issued on 10, 13, and 22 December. Numerous ash emissions were captured by the webcams (figure 30).

Figure 30. Ash emissions at Ibu were recorded in webcams on 17 November (top) and 5 December (bottom) 2020. Courtesy of PVMBG.

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/); 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).

Etna, on the island of Sicily, Italy, and has had documented eruptions dating back 3,500 years. Its most recent eruptive period began in September 2013 and has continued through November 2020, characterized by frequent Strombolian explosions, effusive activity, and ash plumes. Activity has commonly originated from the summit areas, including the Northeast Crater (NEC), the Voragine-Bocca Nuova (or Central) complex (VOR-BN), the Southeast Crater (SEC, formed in 1978), and the New Southeast Crater (NSEC, formed in 2011). The newest crater, referred to as the "cono della sella" (saddle cone), emerged during early 2017 in the area between SEC and NSEC. This report from August through November 2020 updates activity consisting of frequent Strombolian explosions, ash plumes, summit crater incandescence, degassing, and some ashfall based on information primarily from weekly reports by the Osservatorio Etneo (OE), part of the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV).

Summary of activity during August-November 2020. Intra-crater Strombolian explosions that varied in frequency and intensity throughout the reporting period, and the accompanying ash emissions that rose to a maximum altitude of 4.5 km, primarily originated from the Northeast Crater (NEC), the New Southeast Crater (NSEC), and intermittently from the Voragine Crater (VOR). Degassing of variable intensity typically occurred at the VOR and the Bocca Nuova (BN) Crater. At night, occasional summit crater incandescence was visible in webcam images, accompanied by explosions and gas-and-ash emissions. On 14 August strong Strombolian explosions produced an ash plume that rose to 4.5 km altitude and drifted SE, resulting in ashfall between Pedara, Trecastagni, and Viagrande. INGV reported that the central pit crater at the bottom of BN continued to widen, and on 9 September scientists observed that a new pit crater had formed NW of the central depression and was widening due to crater wall collapses. During late October to 1 November, INGV reported that small lava flows originated from scoria cones in the NEC and were visible from the edge of the crater but did not spill over.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows frequent thermal activity of varying strength throughout the reporting period (figure 308). In late October, the frequency of the thermal anomalies increased, and continued through November. According to the MODVOLC thermal algorithm, a total of 31 alerts were detected in the summit craters during August through November; thermal anomalies were reported for five days in August, four days in September, four days in October, and eight days in November. Frequent Strombolian activity contributed to distinct SO₂ plumes that drifted in multiple directions (figure 309).

Figure 308. Strong and frequent thermal activity at Etna was detected during August through November 2020, as reflected in the MIROVA data (Log Radiative Power). Beginning in late October, the frequency of the thermal anomalies increased compared to the previous months. Courtesy of MIROVA.

Figure 309. Distinct SO2 plumes from Etna were detected on multiple days during August to November 2020 due to frequent Strombolian explosions, including 29 August (top left), 8 September (top right), 1 October (bottom left), and 11 November (bottom right) 2020. SO2 plumes were observed drifting in multiple directions. Captured by the TROPOMI instrument on the Sentinel 5P satellite, courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Activity during August-September 2020. During August, INGV reported intra-crater Strombolian explosions in the NEC, VOR, and NSEC (including the cono della sella) craters, which produced discontinuous ash emissions rising above each crater (figure 310). Gas-and-steam emissions were the dominant activity in the BN crater. INGV noted that the central pit crater on the floor of BN had been gradually widening since April. On 2 August a slight increase in explosivity resulted in minor ashfall in Trecastagni and Acicastello. Explosive activity occasionally ejected material above the crater rim up to several tens of meters. On the morning of 7 August incandescent Strombolian activity was visible in the NSEC (figure 311). During the evening of 10-11 August surveillance cameras showed the explosions ejecting incandescent material on the surrounding flanks. On 14 August intense Strombolian activity in the saddle cone of the NSEC produced an ash plume that rose to 4-4.5 km altitude and drifted SE, resulting in ashfall between Pedara, Trecastagni, and Viagrande. By the evening activity had sharply declined, according to a VONA (Volcano Observatory Notice for Aviation) report, though sporadic ash emissions continued. A new series of ash emissions associated with explosions of varying intensity began on 15 August in the NSEC. A resulting ash plume rose to 4-4.5 km altitude and drifted ESE. On 17 August gas-and-steam emissions were seen rising above the VOR crater, accompanied by persistent Strombolian explosions. Between the afternoon and early morning of 20-21 August surveillance cameras showed an increased intensity and frequency of ash emissions above the NSEC and NEC that rose to 4-4.5 km altitude and drifted SSE. INGV-OE scientists reported minor ashfall in Trecastagni, Viagrande, and Catania. During 24-30 August ground observers reported that the intra-crater explosions in the NEC originated from two explosive vents; the BN crater exhibited gas-and-steam emissions from the central pit crater, which continued to widen. During 25-26 August explosive activity increased at the NSEC with ash emissions rising to 4.5 km and drifting SSE, which resulted in modest ashfall in Catania, Viagrande, and Trecastagni; by morning, the volume of ash emissions had decreased, though explosions persisted. During 28-29 August discontinuous and modest ash emissions originating from the NSEC rose 4.5 km altitude drifting E and ENE but did not result in ashfall. Emissions had stopped by 1747 on 29 August, though intense gas-and-steam emissions continued, occasionally accompanied by mild explosive activity (figure 312).

Figure 310. An ash plume accompanied Strombolian explosions at Etna on 3 August (top left) and 4 August (top right) and as seen from the Montagnola (EMOV) thermal camera in the NSEC. Continuous Strombolian activity and summit crater incandescence was observed on 7 August (bottom left); an ash plume was visible in the Monte Cagliato surveillance camera during the day on 9 August (bottom right). Courtesy of INGV (Report 33/2020, ETNA, Bollettino Settimanale, 03/08/2020 – 09/08/2020, data emissione 11/08/2020).

Figure 311. Strombolian explosions and summit crater incandescence was observed at Etna’s New Southeast Crater (NSEC “cono della sella”) during the early morning of 7 August 2020 seen from Tremestieri Etneo. Photo by Boris Behncke, INGV.

Figure 312. Photo of the S edge of the Bocca Nuova Crater at Etna on 29 August 2020 showing degassing in the pit crater. The main scoria cone within the Voragine Crater is visible in the background. Courtesy of INGV (Report 36/2020, ETNA, Bollettino Settimanale, 24/08/2020 – 30/08/2020, data emissione 01/09/2020).

Strombolian activity of varying intensity continued in the NSEC and NEC during September, producing sporadic ash emissions (figure 313). The BN and VOR craters were characterized by gas-and-steam emissions. Explosions in the NSEC ejected coarse pyroclastic material above the crater rim several tens of meters, some of which were deposited on the S flank, and accompanied by sporadic ash emissions; these explosions continued to widen the depression in the saddle cone of the NSEC. Intermittent nighttime crater incandescence was observed in the NSEC. Sporadic and weak ash emissions were observed in the VOR. On 9 September INGV scientists reported intense degassing from the center pit crater in the BN. To the NW of this center depression, a new pit crater had formed and began to widen due to the collapse of the crater walls (figure 314). On 26 September explosions in the NSEC produced an ash plume that rose to 4 km altitude and drifted E, though no ashfall was reported.

Figure 313. Webcam image showing explosions in the New Southeast Crater and resulting ash emissions on 1 September 2020. Courtesy of INGV (Report 37/2020, ETNA, Bollettino Settimanale, 31/08/2020 – 06/09/2020, data emissione 08/09/2020).

Figure 314. Photos of the bottom of the W edge of the Bocca Nuova Crater at Etna on 9 September 2020. Gas-and-steam emissions are visible rising above the pit crater in the background. In the foreground a new pit crater had formed to the NW of the central pit crater (yellow dotted line). Photo was taken from the S edge of the BN crater. Courtesy of INGV (Report 38/2020, ETNA, Bollettino Settimanale, 07/09/2020 – 13/09/2020, data emissione 15/09/2020).

Activity during October-November 2020. Similar variable Strombolian activity continued into October in the NSEC (cono della sella) and NEC; isolated and weak ash emissions were visible in the VOR crater and gas-and-steam emissions continued in both the VOR and BN craters. On 1 October an increase in explosive activity in the NSEC occurred around 0800, which produced an ash plume rising to 4.5 km altitude, drifting E. Ash emissions on 3 October were mostly confined to the summit crater, but some drifted toward the Valle del Bove. On 7 October Strombolian explosions in the NSEC generated an ash plume that rose to 4.5 km altitude drifting E and ESE. INGV personnel reported ashfall as a result in the Citelli Refuge. On 9 October drone observations showed at least three active scoria cones on the floor of the NEC with diameters of 30-40 m and heights of 10 m; a fourth vent was later reported in November (figure 315). INGV reported that activity characterized by Strombolian explosions and spatter was fed by these vents, accompanied by intense intra-crater fumarolic activity.

Figure 315. Map of the summit craters of Etna showing the active vents and the area of cooled lava flows (light green) updated on 9 October 2020. The base is modified from a 2014 DEM created by Laboratorio di Aerogeofisica-Sezione Roma 2. The hatch marks indicate the crater rims: BN = Bocca Nuova; VOR = Voragine; NEC = North East Crater; SEC = South East Crater; NSEC = New South East Crater. Red circles indicate areas with ash emissions and/or Strombolian activity, yellow circles indicate steam and/or gas emissions only. Courtesy of INGV (Report 44/2020, ETNA, Bollettino Settimanale, 19/10/2020 – 25/10/2020, data emissione 27/10/2020).

During 12-18 October surveillance cameras captured incandescence in the NEC and pyroclastic material seen during more intense explosions. During the week of 19-25 October several thermal anomalies were detected on the NEC and BN crater floor. Particularly at night, thermal and surveillance cameras observed incandescent ejecta rising above the NSEC (figure 316). On 23 October a helicopter overflight along the W side of Etna showed continued explosions at the NSEC, which produced both ash emissions and incandescent shreds of lava. An associated ash plume rose to 4.5 km altitude and drifted SSE. Sporadic ash emissions were also observed in the BN crater (figure 316). During 26 October to 1 November occasional Strombolian activity resumed in the VOR which ejected material over the crater rim. The BN crater activity was characterized by small intra-crater collapses and consequent ash emissions. In the NEC, similar explosive activity persisted with the addition of small lava flows from the scoria cones, which were visible from the crater edge, though activity remained confined to the crater.

Figure 316. Photos showing Strombolian activity at the New Southeast Crater at Etna on 25 October 2020 (top left); ash emissions were observed during 22 October 2020 (top right). Ash emissions rose above the Bocca Nuova Crater on 22 October (bottom left) and weak ash emissions were seen above the Voragine Crater on 22 October (bottom right). Courtesy of INGV (Report 44/2020, ETNA, Bollettino Settimanale, 19/10/2020 – 25/10/2020, data emissione 27/10/2020).

Activity in November continued with variable Strombolian explosions accompanied by discontinuous ash emissions from the NSEC, NEC, and BN. During more intense explosions, ejecta reached several tens of meters above the crater, sometimes falling just outside the crater rim. Intensive degassing in the BN crater revealed occasional reddish ash in the new W pit crater that formed in September. The central pit crater was primarily characterized by intense gas-and-steam emissions and intra-crater wall collapses. Four vents were observed on the bottom of the NEC during 2-8 November, though only three of them produced Strombolian explosions, the fourth was quiet. On 5 November Strombolian explosions in BN originated from the W pit crater; coarser material was ejected above the pit crater rim. By 12 November Strombolian activity had decreased, explosions in the BN had deposited material on the S flank. Out of the three active NEC scoria cones, only one was continuously exploding, the second had discontinuous explosions, and the third was primarily emitting gas-and-steam. On 15 November faint ash emissions from the E side of the NSEC were observed (figure 317). On 20 November sporadic explosive activity continued from the NSEC and BN, the former of which occasionally ejected material above the crater rim (figure 318).

Figure 317. Webcam images of the New Southeast Crater at Etna on 14 (left) and 15 (right) November 2020 showing Strombolian activity in the cono della sella (left) and the E vent shown by the black arrow (right). Images were taken by the Montagnola webcam. Courtesy of INGV (Report 47/2020, ETNA, Bollettino Settimanale, 09/11/2020 – 15/11/2020, data emissione 17/11/2020).

Figure 318. Drone image of the New Southeast Crater at Etna on 21 November 2020 showing an ash plume rising above the inner crater rim (black line). Fallout is visible within the crater rim (small red circles). Courtesy of INGV (Report 48/2020, ETNA, Bollettino Settimanale, 16/11/2020 – 21/11/2020, data emissione 24/11/2020).

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: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/); 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/); 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/); Boris Behncke, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: https://twitter.com/etnaboris).

Copahue is an elongated composite cone located along the Chile-Argentina border. The E summit crater consists of an acidic 300-m-wide crater lake which is characterized by intense fumarolic activity. Previous activity consisted of continuous gas-and-ash emissions during early November 2019, accompanied by nighttime incandescence, minor SO₂ plumes, and the reappearance of the lake in the El Agrio crater during early December 2019 (BGVN 45:03). This report, covering March-November 2020, describes an eruption with gas-and-ash plumes from mid-June through late October, accompanied by thermal anomalies visible in satellite imagery and small SO₂ plumes. Primary information for this report comes from the Servicio Nacional de Geología y Minería (SERNAGEOMIN) Observatorio Volcanológico de Los Andes del Sur (OVDAS), the Buenos Aires Volcanic Ash Advisory Center (VAAC), and various satellite data.

Activity during March-May 2020 was relatively low and consisted primarily of seismicity, sulfur dioxide emissions, and occasional white gas-and-steam emissions rising 300-900 m above the El Agrio crater. On 20 March a series of volcano-tectonic seismic events were detected SSW of the volcano; satellite images showed a decrease in the size of the crater lake. SO₂ emissions had daily averages of 487-636 tons, with the highest value reaching 1,884 tons/day on 16 May. During April slight subsidence was reported in the crater, occurring at a maximum rate of 0.3 cm/month.

Activity during most of June and July consisted of occasional white gas-and-steam emissions rising 350-500 m above the El Agrio crater and SO₂ emissions averaging 592-1,950 tons/day; a high value of 1,897 tons/day was reported on 13 June. However, on 16 June a period of increased seismicity was accompanied by crater incandescence and gas emissions containing some ash. SO₂ plumes increased slightly in July with values of 2,100 and 1,713 tons/day on 2 and 4 July, respectively. Another ash plume was observed by local residents on 16 July, accompanied by elevated seismicity and SO₂ emissions of 4,684 tons/day. On 20 July residents of La Araucanía described an odor that indicated hydrogen sulfide gas emissions. A photo on 23 July showed an ash plume rising above the crater (figure 55).

Figure 55. Photo of a gas-and-ash plume rising from Copahue on 23 July 2020. Courtesy of Valentina Sepulveda, taken from Caviahue, Argentina.

Beginning in early August, and continuing through September 2020, the Sentinel-2 MODIS Thermal Volcanic Activity graph provided by the MIROVA system identified a small cluster of thermal anomalies in the summit area (figure 56). Thermal anomalies during this time were also captured in Sentinel-2 thermal satellite imagery, showing a persistent hotspot of varying strength in the summit crater (figure 57). This thermal activity was accompanied by small sulfur dioxide plumes identified by the TROPOMI instrument on the Sentinel-5P satellite, which exceeded two Dobson Units (DU). Distinct SO₂ emissions greater than two DUs were detected on 6, 11, 21, 22, and 29 August, 1 and 6 September, and 4 and 15 October (figure 58).

Figure 56. A small cluster of thermal anomalies were detected in the summit area of Copahue (red dots) during early August through September 2020 as recorded by the Sentinel-2 MODIS Thermal Volcanic Activity data (bands 12, 11, 8A). Courtesy of MIROVA.

Figure 57. Sentinel-2 thermal satellite imagery showed a thermal anomaly (bright yellow-orange) at Copahue during August-October 2020. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 58. Small SO2 plumes were recorded at Copahue during August-October 2020. Top row: 11 August and 1 September 2020. Bottom row: 6 September and 15 October 2020. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

During August, approximately 133 explosive events were detected, in addition to the gas-and-steam and SO₂ emissions (figure 59). On 3 August pulses of ash emissions were reported by SERNAGEOMIN, which resulted in a 2.2-km-long tephra deposit estimated to have a volume of 1 km³. Gray gas-and-ash emissions were observed on 6 August, followed by a thermal anomaly detected in satellite imagery beginning on 8 August. Sulfur dioxide emissions were elevated compared to previous months, measuring an average of 2,641 tons/day with high values of 4,498 tons/day on 12 August that increased to 4,627 tons/day by 27 August. During 16-31 August webcams recorded gas-and-ash plumes rising as high as 1.7 km altitude and were sometimes accompanied by nighttime crater incandescence. Plumes drifted in multiple directions as far as 4.3 km N, 9 km NE, 8 km E, 4 km SE, 4 km SW, 9 km W, and 4.4 km NW.

Figure 59. Photo of a white gas-and-steam plume rising from Copahue on 12 August 2020. Courtesy of Valentina Sepulveda, taken from Caviahue, Argentina.

Elevated activity continued into September with 2-10 explosive events detected during the month; during 1-15 September webcams recorded gas-and-ash plumes rising to 1.1 km altitude, drifting 6-15 km SW and SE, which were sometimes accompanied by nighttime crater incandescence (figure 60). On 7 September a Buenos Aires VAAC advisory reported an ash plume rising to 3.7 km altitude drifting SE. On 11 September a webcam showed a weak gas emission, possibly containing some ash. Three episodes of gas-and-steam plumes were reported, rising 100-1,040 m above the crater, sometimes accompanied by incandescence. SO₂ emissions were in the 1,499-1,714 tons/day range, with a high value of 4,522 tons/day on 28 September. SERNAGEOMIN reported repetitive explosions in the acid lake area alongside fumarolic activity, ejecting some material 1.7 km N, 1.2 km SE, and 4 km E of the crater.

Figure 60. Photos of gas-and-steam plumes rising from Copahue on 6 September (top) and 28 September (bottom) 2020. Courtesy of Valentina Sepulveda, taken from Caviahue, Argentina.

Persistent activity in October consisted of gas-and-steam plumes, ash emissions, and SO₂ emissions. The gas-and-steam plumes rose 1.4 km above the crater, occasionally accompanied by nighttime incandescence. On 5 October the SO₂ emissions were at a high value of 3,824 tons/day. During 12-15 October ash emissions resulted in a wide distribution of ashfall that reached 6.8 km NE, 7 km SE, and 6.7 km SW (figure 61). A pilot reported an ash plume rose to 3.7 km altitude drifting SE, according to a VAAC advisory, though the plume was not visible in satellite data. Sentinel-2 satellite imagery recorded strong gas-and-ash plumes during August-October, drifting generally S and E, which resulted in ash deposits on the nearby flanks (figure 62). Continued emissions had covered all of the flanks with ash by late October.

Figure 61. Photos of a gas-and-ash plume rising from Copahue on 13 October (top) and 15 October (bottom) 2020. Courtesy of Valentina Sepulveda, taken from Caviahue, Argentina.

Figure 62. Sentinel-2 images showing ash gas-and-ash plumes rising from Copahue during August-October 2020, resulting in some ashfall in the nearby areas. The ash plume on 31 August (top left) is drifting S with ashfall observed on the N and S flanks. The ash plume on 7 September (top right) is drifting SE with ashfall on the E and S flanks. The ash plume on 27 September (bottom left) is drifting E and N with ashfall on the NE flanks. The ash plume on 20 October (bottom right) is drifting S with ashfall on all the flanks due to continued activity. Images using “Natural color” rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

Similar activity during November decreased, primarily characterized by gas-and-steam plumes and SO₂ emissions. White gas-and-steam emissions, possibly with some ash content, were observed with a webcam on 9 and 12 November, accompanied by low but continuous seismicity. During 11-12 November SO₂ emissions were at a high value of 904 tons/day. A white gas-and-steam plume was observed on 15 November rising 760 m above the crater; typical degassing rose 200-300 m above the crater, according to SERNAGEOMIN. The daily average of SO₂ emissions ranged 366-582 tons.

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

Information Contacts: 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/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Valentina Sepulveda, Hotel Caviahue, Caviahue, Argentina (URL: https://twitter.com/valecaviahue, Twitter: @valecaviahue).

Masaya, located in Nicaragua, includes the Nindirí, San Pedro, and San Juan craters, as well as the currently active Santiago crater. The Santiago crater has contained an active lava lake since December 2015 (BGVN 41:08), and often produces gas-and-steam emissions. Similar activity is described in this report which updates information from June through November 2020 using reports from the Instituto Nicareguense de Estudios Territoriales (INETER) and various satellite data.

Volcanism at Masaya has been relatively quiet and primarily characterized by an active lava lake and gas-and-steam emissions. From January to November 2020 there were 8,551 seismic events recorded. A majority of these events were described as low-frequency earthquakes, though a few were classified as volcano-tectonic. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed few low-power thermal anomalies during June through November (figure 87). A small cluster of low-power thermal activity was detected in July and consisted of seven thermal anomalies out of a total of thirteen thermal anomalies recorded during the reporting period. Thermal activity was also observed in Sentinel-2 satellite imagery, which showed a constant thermal anomaly in the Santiago crater at the lava lake during July through October, occasionally accompanied by a gas-and-steam plume (figure 88). Small and intermittent sulfur dioxide emissions appeared in satellite data during each month of the reporting period, excluding July, some of which exceeded two Dobson Units (DU) (figure 89). On 6 July, 11 and 13 August, 7 September, during October, and 9 and 13 November, INETER scientists took SO₂ measurements by making several transects using a mobile DOAS spectrometer that sampled for gases downwind of the volcano. Average values during these months were 1,202 tons/day (t/d), 1,383 t/d, 2,089 t/d, 950 t/d, and 819 t/d, respectively, with the highest average reported in September.

Figure 87. Few thermal anomalies were detected at Masaya between June and November 2020 with a small cluster of thermal activity in July. A total of thirteen low-power thermal anomalies were shown on the MIROVA graph (Log Radiative Power) during the reporting period. Courtesy of MIROVA.

Figure 88. Sentinel-2 thermal satellite imagery showed the active lava lake at the summit crater of Masaya during July through October 2020, occasionally accompanied by gas-and-steam emissions, as seen on 27 July (top left) and 30 September (bottom left). Images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 89. Intermittent sulfur dioxide emissions were captured from Masaya during June through November 2020 by the TROPOMI instrument on the Sentinel-5P satellite. These images show SO2 emissions reaching up to 2 Dobson Units (DU). Top left: 9 June 2020. Top right: 23 August 2020. Bottom left: 7 September 2020. Bottom right: 15 November 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

During June and July persistent gas-and-steam emissions were reported rising above the open lava lake in the Santiago crater (figure 90). On 20 June INETER scientists measured the gases on the S side, inside the Nindirí crater (SW side), and La Cruz (NW side). A perceptible gas-and-steam plume was noted rising above the Nindirí crater and drifting W. Crater wall collapses were observed on the E wall of the Santiago crater; the lava lake remained, but the level of the lake had decreased compared to previous months. During July, thermal measurements were taken of the fumaroles and near the lava lake using a FLIR SC620 thermal camera. INETER reported that the temperature measured 576°C, which had significantly increased from 163°C noted in the previous month.

Figure 90. Images of the lava lake at Masaya during June 2020, accompanied by gas-and-steam emissions (left) and a gas-and-steam plume rising above the Santiago crater (right). Courtesy of INETER (Boletín Sismológico, Vulcanológico y Geológico Junio, 2020).

Small crater wall collapses were detected on the NW and E wall of the Santiago crater, accompanied by abundant gas-and-steam emissions during August (figure 91). On 7 August thermal measurements were taken of the fumaroles and near the lava lake, which showed another temperature increase to 771°C. Continuous collapse of the crater walls began to excavate depressions in the crater floor and along the walls. Similar activity was observed in September with abundant gas-and-steam emissions in the Santiago crater, as well as collapses of the E wall (figure 91). Temperature measurements taken during this month had decreased slightly compared to August, to 688°C.

Figure 91. Photos of the Santiago crater at Masaya during August (left) and September (right) 2020 showing a) an internal collapse on the N wall of the crater floor; b) an internal collapse on the S wall of the crater floor, forming a depression; c) newly excavated crater floor due to wall collapses; and d) an internal collapse on the S wall. In September a significant amount of gas-and-steam emissions originating from the N side of the crater were observed compared to the previous months. Courtesy of INETER (Boletín Sismológico, Vulcanológico y Geológico Agosto and Septiembre, 2020).

Activity in October and November remained consistent with continued wall collapses in the Santiago crater, particularly on the S and E wall, due to fractures in the rocks and erosion, accompanied by gas-and-steam emissions. INETER reported that the level of the lava lake had decreased due to continuous internal wall collapses, which had caused some obstruction in the lava lake and allowed for material to accumulate within the crater. On 9 October thermal measurements were taken of the fumaroles and near the lava lake using a FLIR SC620 thermal camera (figure 92). The temperature had increased again compared to September, to 823°C. By 26 November, the temperature had decreased slightly to 800°C, though activity remained similar.

Figure 92. Thermal measurements of the active lava lake and fumaroles taken in the Santiago crater at Masaya on 1 October 2020 with a FLIR SC620 thermal camera. Temperatures reached up to 823°C. Courtesy of INETER (Boletín Sismológico, Vulcanológico y Geológico Octubre, 2020).

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

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Nevados de Chillán, located in the Chilean Central Andes, is a volcanic complex composed of late-Pleistocene to Holocene stratovolcanoes. On 8 January 2016 an explosion created the Nicanor Crater on the NW flank of Volcán Viejo. Recent activity consists of explosions, ash plumes, pyroclastic flows, and a new lava dome in the Nicanor Crater (BGVN 45:07). This report covers July through October 2020; activity is characterized by frequent explosions, ash plumes, a lava flow on the N flank, and continued lava dome growth. The primary source of information comes from the Servicio Nacional de Geología y Minería (SERNAGEOMIN)-Observatorio Volcanológico de Los Andes del Sur (OVDAS), the Buenos Aires Volcanic Ash Advisory Center (VAAC), and satellite data.

Since 27 June webcams have showed an active lava flow that originated from the Nicanor Crater and descended the N flank. Activity during July consisted of 210-473 volcano-tectonic seismic events and 565-614 explosive events. Ash plumes rising 1.1-1.2 km above the crater and were accompanied by day and nighttime incandescence on the E edge of the Nicanor Crater. Due to these explosions, SERNAGEOMIN reported that tephra and other pyroclastic deposits were deposited within 400 m to the E of the crater. On 1 July a Buenos Aires VAAC advisory reported that a webcam showed ash emissions rising to 4.3 km altitude. Continuous explosions the next day produced ash plumes that rose 500 m above the crater. During 1-2 July the active lava flow had reached 40 m long and descended at a rate of 0.2 m³ per second. On 6 July an explosion at 0837 generated a gas-and-ash plume that rose 1.2 km above the crater and drifted SE; sporadic ash emissions were also observed on 7 July, according to a VAAC advisory. SERNAGEOMIN webcams showed that the lava flow that began on 27 June continued down the N flank, while a new lobe 55-194 m long moved toward the NE flank of Nicanor Crater. Gas plumes were also observed rising above the active crater, as noted on 20 July (figure 63). On 29 July weak ash emissions rose 3.9 km altitude and drifted SE, according to a VAAC report. During that day, the volume of the lava dome measured 400,000 m³ and grew at a rate of 0.1 m³ per second. Throughout the month, the lava flow continued to descend the N flank of the Nicanor Crater, reaching 520 m at a rate of 0.7-0.6 m per hour. Some unconsolidated blocks up to a meter in size detached from the front of the flow and moved up to 240 m. Sulfur dioxide emissions during the month averaged 823 tons/day with a high value of 1,815 tons/day reported on 29 July.

Figure 63. A white gas-and-steam plume was observed at Nevados de Chillán on 20 July 2020. Courtesy of SERNAGEOMIN webcam, posted by Volcanology Chile.

During August SERNAGEOMIN reported 68-75 volcano-tectonic seismic events and 497-578 explosive events, the latter of which ejected material as far as 300 m E and NE from Nicanor Crater. Associated ash plumes rose 800-980 m above the crater and were accompanied by day and nighttime crater incandescence. The lava dome continued to grow during the month, reaching a thickness of 41 m, according to SERNAGEOMIN. SO₂ emissions were an average value of 134-205 tons/day with a high value of 245 tons/day reported on 3 August. On 15 August a VAAC advisory reported weak and sporadic gas-and-ash emissions at the summit; on 20 August a hotspot was detected in satellite imagery, though an ash plume was not observed. The active lava flow on the N flank extended 490-495 m and moved at a rate of 0.07-0.06 m per hour. On 31 August a webcam showed an ash plume rising above the volcano, accompanied by the advancing lava flow on the N flank (figure 64).

Figure 64. An explosion at Nevados de Chillán produced an ash plume on 31 August 2020. A lava flow accompanies the ash plume on the N flank. Courtesy of SERNAGEOMIN.

Similar activity continued into September, with 45-48 volcano-tectonic and 591-621 explosive events. Ash plumes rose to 1.5 km above the crater and were accompanied by day and nighttime incandescence on the E edge of Nicanor Crater. During 1-15 September explosions at the lava dome produced ash plumes that rose to less than 1.5 km altitude, resulting in ashfall within 300 m E and NE of the crater; ejecta from larger explosions was also observed to the ESE. Satellite images showed partial destruction of the lava dome as well as loss of some material due to successive explosions at the beginning of the month. Overall, the dome continued to increase in size, reaching a volume of 180,000 m³ and a thickness of 45 m since August (41 m). The lava dome measured 93 m NW-SE and 104 m SW-NE. By 15 September the 500-m-long lava flow had descended the NNE flank and continued to advance at a rate of 1.7 m per hour. The W levee of the flow channel had ruptured, which caused the toe of the lava flow to thicken. On 20 September ash emissions rose to 3.7 km altitude and drifted NE and ENE, according to a VAAC advisory. On 22 September gas emissions, weak and sporadic ash emissions, and occasional explosions accompanied the lava flow. Through the remainder of the month, the lava flow persisted, measuring 615 m, and advancing at a rate of 0.4 m per hour; its volume was 487,000 m³ (figure 65). SO₂ emissions were an average value of 111-358 tons/day with a high value of 503 tons/day reported on 22 September.

Figure 65. Photo (color corrected) of the incandescent lava flow at night descending the NNE flank of Nevados de Chillán on 21 September 2020. Photo by Jose Fauna, courtesy of Volcanology Chile.

During October there were 34-61 volcano-tectonic seismic events reported, as well as 607-644 explosive events, seven of which generated ash plumes that rose 1-1.5 km above the crater. Day and nighttime incandescence in the E edge of Nicanor Crater remained. Ash deposits associated with the explosive activity were distributed to the E and NE as far as 300 m from the crater; denser pyroclastic deposits from stronger explosions were located to the N and NE. The lava flow on the N slope persisted, extending 614-683 m from the crater rim at a rate of 0.1-0.82 m per hour with a width of 80.2 m near the crater rim and up to 112.8 m near the toe. The lava dome also continued to grow since it was last measured in September; it was 115 m wide at the base by 107 m high. SO₂ emissions were an average value of 167-355 tons/day with a high value of 588 tons/day reported on 26 October. On 29 October an ash plume was detected in satellite imagery and rose to 3.7 km altitude and drifted W, according to a VAAC advisory (figure 66). SERNAGEOMIN reported that a 25-m-diameter subcrater had formed on the E inner edge of Nicanor Crater at the top of the lava dome. On 30 October, intermittent gas-and-ash emissions were visible at the summit in satellite imagery, rising to 3.9 km altitude and drifting SE.

Figure 66. Webcam image of an explosion at Nevados de Chillán on 29 October 2020 that produced an ash plume that rose 360 m above the crater and drifted SW. Courtesy of SERNAGEOMIN.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows frequent low-power thermal activity beginning in early June and continuing through October 2020 due to frequent explosions, the continued lava dome growth in Nicanor Crater, and the lava flow that descended the N flank (figure 67). On clear weather days, two thermal anomalies in the summit craters are observed in Sentinel-2 thermal satellite imagery; one represents the growing lava dome and the other is the lava flow on the N flank (figure 68). On 25 September an ash plume was observed drifting S.

Figure 67. Frequent low-power thermal activity at Nevados de Chillán continued during July through October 2020, according to the MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 68. Sentinel-2 satellite imagery showed a persistent thermal anomaly (bright yellow-orange) in the summit crater of Nevados de Chillán during July through October 2020. On 29 July (top left), a third faint thermal anomaly was detected on the N flank, indicating a lava flow. On 25 September (bottom left) an ash plume was visible drifting S. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

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/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); 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); Volcanology Chile (URL: https://twitter.com/volcanologiachl); Jose Fauna, Caracol sector, San Fabián de Alicom, Chile (URL: https://twitter.com/josefauna).

The following summarizes activity at Sakura-jima during January-June 1998 and January-May 1999. Information concerning events in 1998 were provided through communications from Yosihiro Sawada forwarded by Dan Shackelford. More recent information is available at the Japanese Meteorological Agency website.

The amount of tephra deposited around the volcano peaked during 1991-92 (up to 5.8 x 10⁶ tons/month) but has since decreased; present deposits are <3 x 10⁵ tons/month.

Activity during January-June 1998. Ten explosions and eruptions were recorded in January 1998. One explosion, on 7 January, produced a plume that rose 1,200 m above the summit. An explosive outburst on 24 January produced a column of incandescent ejecta accompanied by volcanic lightning. The total ashfall measured at Kagoshima Local Meteorological Observatory (KLMO) during January amounted to 10 g/m².

Silent ash emissions (eruptions without explosions) occurred on 8, 16, 25, and 27 February 1998. A plume on 16 February rose 1,400 m above the crater. In March 1998, 22 eruptions (without explosions) were recorded. Eruption plumes on 2 and 3 March rose 1,200 m. KLMO recorded 37 g/m² of ash for March. In April 1998, there were 19 eruptions, including eight explosions. The highest plume during April was observed 1,500 m above the crater on 30 April. April ashfall totaled only 1 g/m².

Forty-one eruptions were observed in May 1998, including 27 explosive eruptions. The highest plume observed rose 2,500 m above crater on 24 May. A volcanic earthquake swarm lasted seven hours on 19-20 May. The total May ashfall was 105 g/m². All five eruptions recorded during June were explosive. On 6 June an eruption plume rose 1,100 m above the crater. The total June ashfall deposit was 5 g/m² thick.

Activity during January-May 1999. January 1999 was characterized by a low level of volcanic earthquakes, although 13 eruptions occurred. During February-April 1999 observers recorded 44 eruptions, including 15 explosions. Eruptive activity was relatively high during 11-16 March when there were 10 eruptions, including eight explosions. An eruption column rose 1,800 m on 20 April.

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: Yosihiro Sawada, Volcanological Division, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (URL: http://www.jma.go.jp/); Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Dan Shackelford, 3124 E. Yorba Linda Blvd., Apt. H-33, Fullerton, CA 92831-2324 USA.

Deception has been monitored for part of every austral summer since 1987; its flooded caldera forms a 5 x 9 km bay that is breached to the SW, giving Deception Island a ring shape. In December 1998, as part of the Spanish Antarctic Research Project, a new seismic network was deployed to monitor activity on the island. The instrumentation included two seismic antennas and two continuous-recording stations.

The latest seismic survey was conducted under the auspices of the Spanish Antarctic Project; it revealed a significant increase in the daily number of seismic events (i.e., volcano-tectonic (VT) earthquakes, volcanic tremor, and long-period (LP) events when compared with activity recorded during previous summer field surveys. The noteworthy increase started in early January 1999 (BGVN 24:01) and continued in February (figure 14).

Figure 14. Change in the number of seismic events during 31 December 1998-19 February 1999 at Deception Island. Earthquakes shown encompass long period (LP) and volcano-tectonic (VT). Courtesy of the Spanish Antarctic Research Project.

The active area is in a region between Fumarolic Bay and Murature Point and the seismic activity appears to be located near the boundary of the geological structure activated by the 1970 eruption.

The focal depth of the seismic events was shallow (less than 1 km). The seismic energy release was higher than observed in the recent past, and a few shocks were felt. The maximum magnitude of the VT earthquakes is estimated to be ~3.5. Some episodes of volcanic tremor were felt by the scientific staff while working close to the site at Murature Point. An anomalous increase of dead krill was noticed in the bay a few days before the seismic crisis.

Members of the project interpreted these observations in the following manner: A fresh intrusion of magma occurred at a depth of ~500 m. The VT earthquakes are the brittle response of the shallow structure surrounding this injection, and the LP events and volcanic tremor result from the interaction of the shallow aquifer of the island with this injection of hot material. This implies a significant evolution of activity, marked by a change from stable stationary geothermal processes to a more dynamic intrusive process.

Geologic Background. Ring-shaped Deception Island, one of Antarctica's most well known volcanoes, contains a 7-km-wide caldera flooded by the sea. Deception Island is located at the SW end of the Shetland Islands, NE of Graham Land Peninsula, and was constructed along the axis of the Bransfield Rift spreading center. A narrow passageway named Neptunes Bellows provides entrance to a natural harbor that was utilized as an Antarctic whaling station. Numerous vents located along ring fractures circling the low, 14-km-wide island have been active during historical time. Maars line the shores of 190-m-deep Port Foster, the caldera bay. Among the largest of these maars is 1-km-wide Whalers Bay, at the entrance to the harbor. Eruptions from Deception Island during the past 8700 years have been dated from ash layers in lake sediments on the Antarctic Peninsula and neighboring islands.

Information Contacts: Jesus Ibañez, Gerardo Alguacil, José Morales, José Peña, Javier Almendros and Enrique Carmona, Instituto Andaluz de Geofísica, Univ. de Granada, Spain; Alicia Garcia and Ramón Ortiz, Dpto. de Volcanologia, MNCN-CSIC, José Gutierrez Abascal 2, 28006 Madrid, Spain; Edoardo del Pezzo and Marcello Martini, Osservatorio Vesuviano, Napoles, Italy; Bernard Chouet, USGS, Menlo Park, CA 94025 USA; Gilberto Saccorotti, Univ. Salerno, 84100 Baronissi (Salerno), Italy.

The following report summarizes activity observed at Etna from March through May 1999. The information for this report was compiled by Boris Behncke at the Dipartimento di Scienze Geologiche (formerly Istituto di Geologia e Geofisica), University of Catania (DSGUC), and posted on his internet web site. The compilation was based on personal visits to the summit, observations from Catania, and other sources cited in the text.

Almost all activity has been limited to the eruptive fissure that became active on 4 February at the southeastern base of Southeast Cone (SEC). During early March, lava continued to flow into the Valle del Bove, forming a lava field (figure 77) composed of numerous lobes. The activity was visible from Catania and other locations on 5 March, with the flow field incandescent over its length from the W rim of Valle del Bove down to ~2,000 m elevation.

Figure 77. Sketch map of Etna showing the Valle del Bove and the area of lava flow-field that has developed since 4 February 1999, as of 4 June 1999. The lavas erupted during 1989-93 are shown in various shades of gray, previous flows (since 1971) are shown in lighter shades. 1995 to early 1999 lavas are not shown. Key: NE=Northeast Crater; V=Voragine; BN=Bocca Nuova; SE=Southeast Cone; TDF=Torre del Filosofo; MO=Montagnola; RS=Rifugio Sapienza; MC=Monti Centenari. Courtesy of Boris Behncke.

Observations on 3 March. On 3 March, the area of activity was visited by Giovanni Sturiale and Boris Behncke (DSGUC), and Christophe Baudin, a visitor from Belgium. The most recent lava to flow through the notch in the N rim of SEC, on 4 February, was covered with a thin layer of reddish ash and showed no heat emission. The inclined floor of the notch was ~3-5 m wide and covered with rubble; the width at its rim was 15-20 m. Only a few glimpses were caught of the interior of the crater, but at several tens of meters depth there was an inner terrace surrounding a narrow central pit. The width of the crater at its rim was at most 50 m. Gas and vapor escaped from several fumarolic areas on the SW and E crater rims. On the SE side of the crater there was a fuming pit ~15-20 m wide. Below this pit, on the outer flank of the cone, a vigorously steaming fissure segment extended ~100 m downslope; below this was the oval-shaped main vent of the 4 February episode.

Eruptive activity from the 4 February fissure consisted of very weak, and intermittent, ejections of pyroclastics, and quiet outflow of degassed lava. A cluster of about 10 hornitos at the upper end of the fissure were covered with sulfur. Relatively regular observations during 27 February-3 March (information from Giuseppe Scarpinati, Carmelo Monaco, and Christophe Baudin) indicated irregular activity at the hornitos. There was vigorous spattering at one of the main hornitos on 27 February, a new hornito began to grow on 28 February about 70-80 m downslope from the main group, and on 2 March a short-lived lava extrusion occurred from the base of one of the uppermost hornitos. On these occasions the hornitos were the site of high-pressure gas emissions that produced loud hissing.

During the 3 March visit, all hornitos were unusually quiet. High-pressure gas emission occurred from a few locations 50-80 m downslope. No flowing lava was visible, but a row of skylights lay 100-150 m downslope from the hornitos. About 100 m farther downslope the lava appeared at the surface in a well-defined flow channel. Several other lava flows were slowly moving across the lava field. At the rim of the Valle del Bove one main flow spilled into this vast depression, forming a pronounced ridge where it disappeared in another lava tube. Lava resurfaced a few hundred meters further downslope through numerous ephemeral vents, forming narrow flows that extended to the floor of the Valle. The farthest active lava was at ~2,000 m elevation, above the Monti Centenari, a cluster of 1852-53 cinder cones of which only the summits now protrude (figure 77).

The mean output was several cubic meters per second; the volume of lava produced in one month of activity was between 5 and 10 x 10⁶ m³. Although this is a very rough estimate, with an error of ~50%, it indicates more production than other long-lived effusive eruptions in the summit area, which had effusion rates of < 1 m³/s.

Observations on 11 and 13 March. A group of DSGUC geologists (Behncke, Mariangela Porravecchio, Giuseppe Paradiso, and Antonella Lentini) visited the eruptive fissure at the base of the SEC on 11 March. Above the rim of Valle del Bove, all lava was flowing in tubes. There are apparently two main lava tubes ~30 m apart at the rim of Valle del Bove. The more southerly tube ended just above the crest of the Valle where the lava appeared at the surface, and two ephemeral vents emitted lava further downslope. The northerly lava tube extended much further into the Valle, and surface flows appeared halfway down its W slope, at ~2,500 m elevation. The active flow-fronts appeared to be somewhere above 2,000 m elevation. No activity had occurred at the hornitos in the uppermost part of the fissure, but degassing occurred from several incandescent fumaroles. Geologists from Palermo University measured temperatures of ~1,030°C in one of these fumaroles.

There appeared to be little activity elsewhere, although something that appeared to be a phreatic steam explosion came from Bocca Nuova's southeastern vent area. It formed a convoluted cloud but contained little or no ash, and it produced no sound.

On the late afternoon of 13 March the eruptive fissure was again visited by DSGUC geologists (Behncke, Monaco, Betty Giampiccolo, and Marcello Bianca). There were only minor changes compared to two days earlier. The southern lava flow sent numerous branches spilling over the rim of Valle del Bove. Little had changed at the northern lava flow. The output was still as high as 5 m³/s, and the effusive episode that began on 4 February was estimated to have produced >15 x 10⁶ m³ of lava, an amount typical of a "slow" flank eruption (Etnean flank eruptions are generally classified into those with relatively low effusion rates, such as the 1983 and 1991-93 eruptions, and high-effusion rate eruptions like those of 1981 or 1989).

During late March lava continued to flow into Valle del Bove. While a major flow issued from an ephemeral vent about halfway down the W slope of Valle del Bove, several smaller lobes were visible on the crest of the Valle on the evening of 24 March.

Observations on 7 April. Effusive activity continued in early April, though at a slightly diminishing rate. Lava flows continued to spill into the Valle del Bove, but their fronts stopped before reaching the base of the steep slope. A visit was made on 7 April by Behncke and geologists of Catania and Switzerland together with Marco Fulle (Trieste Astronomical Observatory) and Roberto Carniel (Stromboli On-line). Numerous small surface flows were active in two areas above the rim of Valle del Bove, one about halfway between the rim and the hornitos at the upper end of the 4 February fissure, and the other just above the rim. In the lower area, three or four small flows slowly advanced a short distance from their vents, which lay around spectacular tumulus, or pressure ridges, formed as magma pushed from below, raising blocks and slabs of older lava up to 5 m. The constant effusion since 4 February had formed an impressive, delta-like ridge on the Valle del Bove rim.

The upper area of activity, at ~2,850 m elevation, had five or six vents around a smaller tumulus. Two vents produced voluminous flows that descended tens of meters and had spectacular cascades. A small vent produced a flow that moved in a 20-cm-wide, S-shaped channel; this vent froze over in less than two hours, and a new ephemeral vent became active 20 m downslope. Strong gas emission occurred from two places in the upper part of the 4 February fissure. The cluster of hornitos at the end of the fissure was quiet while profuse steaming occurred from the upper part of the fracture that split the southeastern side of SEC on 4 February. On the W wall of the Valle del Bove, lava issued from a number of ephemeral vents about halfway down the slope, feeding flows that advanced a few hundred meters.

While lava effusion continued unabated, the rate of lava production appeared lower than during the first six weeks of the eruption, possibly in the range of 1-3 m³/s. The volume of lava produced thus far exceeded 20 x 10⁶ m³.

Observations on 14 April. Decreased lava effusion from the 4 February fissure was observed by Behncke and a German television team on 14 April. Near the W rim of Valle del Bove, lava came to the surface in a few places and produced very small flows. Halfway between the Valle del Bove rim and the hornitos, two main vents fed chanellized flows. Activity was more vigorous than the lower area, but had decreased markedly since one week before.

A notable feature is the formation of pressure ridges, tumuli, and small-volume extrusions from cracks in older lavas. Most of this was caused by very slow intrusion of lava from tubes towards the surface once the tube was blocked or slowed, forcing the lava upwards. Lava oozed through the cracks and formed new flows, but in many cases the lava formed bulbous protuberances which often resembled the lobes of pillow lavas forming underwater.

Observations on 30 April. Behncke and others descended into the Valle del Bove on 30 April. One main effusive vent, at ~2,700 m elevation (~100 m below the rim of Valle del Bove), was feeding several flows which in part disappeared into lava tubes and resurfaced tens of meters downslope. The mean effusion rate appeared to be around 1 m³/s or slightly less. The maximum flow length was ~300 m. The farthest flow fronts were stagnant above the floor of the Valle del Bove. There was no explosive activity around the effusive vents. Only one feeder tube appeared to be active, located in the central part of the field on the W slope of Valle del Bove.

Observations on 12 May. During early May, little significant change affected the activity. Lava flowing from the area of the 4 February fissure through a lava tube appeared at the surface at ~2,600 m elevation on the W wall of Valle del Bove. Active lava fronts did not extend below 2,000 m.

On 12 May, Behncke and Scarpinati visited the summit area, including Bocca Nuova and SEC, and entered the Valle del Bove. The summit craters were quiet, apart from near-continuous passive emissions of light brown ash from the NW vent of Bocca Nuova. This activity, which was most likely caused by internal collapse, was entirely noiseless and ash plumes barely rose above the crater rim. A deposit several centimeters thick covered the S, SE, and E sides of the main summit cone.

After descending from the main summit cone to the saddle which separates it from the SE Cone, Behncke climbed to the summit of the SEC. The crater was practically gas-free, so it could be seen that its floor had collapsed and the conduit was no longer open. There was, however, some gas and vapor emission from the upper part of the fracture which had split the SE flank of the cone on 4 February.

There was no visible activity anywhere above the Valle del Bove rim, the only surface flows appearing ~200-250 m below the original eruptive fissure, in Valle del Bove. Lava was issuing from two ephemeral vents on the N and E sides of a large tumulus. It was ~10-15 m across and consisted of uplifted, tilted, craggy blocks of older lava and minor volumes of more recent smooth-surfaced pahoehoe. The N vent fed a small well-channelized flow while from the vent on the E side of the tumulus lava was squeezed out like toothpaste.

Behncke and Scarpinati heard continuous cracking and knocking sounds from below, and small rockfalls from the sides of the tumulus were frequently observed; rocks at the surface of the tumulus were slowly fracturing. It was evident that magma was forcefully pushing from below, and lava was rising slowly within cracks between the blocks at the surface. After about 15 minutes of observation, Behncke and Scarpinati left the unstable tumulus area and continued their observation from 15 m upslope. For another 20-30 minutes, the tumulus gradually extended in all directions. Fracturing on the slope above the tumulus indicated a larger volume of magma arriving at the end of the feeder tube and nearing the surface.

After about 35-45 minutes of observation, the large blocks of older lava began to fall apart while ever larger rockfalls and collapses occurred on the flanks of the tumulus. After this, the entire tumulus area became highly mobile, and its E and SE sides, perched above the steep Valle del Bove slope, began to slide downhill, producing spectacular cascades of incandescent blocks and exposing the fluid, incandescent interior. The most dramatic phase, which lasted no longer than 5 minutes, saw the virtual unfolding of the whole structure as older blocks slipped into the Valle del Bove. Where the observers had walked only 30 minutes before, an incandescent chasm 15 m wide and 5-6 m deep opened, and lava slowly flowed from draining lava tubes. Fresh lava welled up at the W end of the collapse depression, rapidly filling it and spilling over its SE rim, causing further rockfalls. Some rocks at least 20 m³ in volume fell, with fresh incandescent lava attached to them. The overflowing lava appeared to be more voluminous than that which had previously issued from the two vents.

The previously active flows, cut off from their supply, soon stagnated, and small lava tubes with still-incandescent walls became visible. Fresh lava spilled down in a southeasterly direction, forming two branches which traveled 100-150 m in about 30 minutes.

Observations on 15-19 May. Surface activity resumed at the 4 February fissure on 15 May, after about a month of lava flowing through tubes to the Valle del Bove. A luminous spot in the hornito area was sighted through binoculars on the evening of 15 May by Giuseppe Scarpinati from his home in Acireale. Earlier that day Harry Pinkerton (Environmental Sciences Division, University of Lancaster) and others working in the area had noted no active lava. The next day (16 May), lava was slowly extruded from three small vents. The rate of emission increased during the following two days, and a larger vent fed sluggish flows that advanced across the N part of the flow-field.

On 19 May, Behncke, Antonella Lentini, Mariangela Porravecchio (DGSUC), Valentina Giambarresi (Catania University), and others visited Etna's summit area and the effusive vents. A part of this group climbed to the SEC summit. Since the previous visit by Behncke on 12 May, all emissions of vapor from the obstructed crater floor had ceased. The crater floor was ~70 m below the W rim, and the crater walls were vertical in most places. Fumarolic activity was occurring from numerous locations around the crater rim.

While the group stayed on the SEC summit, ash emissions from Bocca Nuova and Northeast Crater produced dilute plumes ~100-150 m above the respective crater rims. Rumbling sounds came from the direction of the Voragine or (less likely) Northeast Crater. No visible emissions were associated with the noise, and no more sounds were heard when everybody had returned to the hornito area.

The new vent 80-100 m below the hornitos lay in a drained channel ~3 m wide in its central portion. The shift of the currently active vent downslope was evident in the form of a ridge built by a series of crusted-over vents. The emission of lava was frequently accompanied by strong degassing, indicating that the lava here was more gas-rich than that issuing from the ephemeral vent on the Valle del Bove slope. Some 20 m downslope from this active vent, one of the initial three vents (of 16 May) was still extruding small amounts of bulbous lava, forming a tumulus.

The visit to the ephemeral vent on the Valle del Bove slope was highly instructive regarding the properties of effusive vents and lava channels. Lava was still flowing from two vents on the floor of the depression formed during the 12 May collapse of the large tumulus. Flow fronts did not extend to the Valle del Bove floor. Four or five well-channelized flows ~1 m wide were moving down the slope; towards their fronts two of these flows were seen to thicken and broaden to 2-3 m height and 5 m width.

The floor of the depression left after the tumulus collapse was partially covered with new lava, mostly aa with one small lobe of very smooth pahoehoe, and the main effusive vent had shifted ~2 m downslope. A second effusive vent 4-5 m downflow produced a small volume of lava.

Investigation of what remained of the collapsed tumulus revealed that the two effusive vents observed on 12 May had not been completely destroyed. Vent 1 lay on the N side of the tumulus, and while still active it had fed lava into a well-defined channel. Vent 2, on the E side of the tumulus, had squeezed out lava much like toothpaste, which had spilled down the steep E face of the tumulus. Both vents were cut off from lava supply as the tumulus collapsed, and when the area of vent 1 was observed shortly thereafter, lava was still draining from the flow channel. Observation on 19 May revealed that the channel had completely drained, its depth being ~1.5 m (compared to a width of 0.8-0.9 m). This is a much higher depth-width ratio than in most other lava channels on Etna and many other volcanoes, but normally lava channels are not drained as completely as in this case since the supply of lava decreases gradually, allowing some of the lava to remain and "freeze" on the channel floor.

Vent 2, one week after the cessation of its activity, was a roughly circular hole open towards the downslope side, and evolving into a thoroughly drained flow channel that had been hidden under the lava when observed before the tumulus collapse. Like at vent 1, this flow channel was deeper than wide. The vent 2 channel is on much steeper terrain, but this apparently had no effect on the depth and width of the flow channel. The vent itself, ~1.5 m wide at its rim, widened at depth to a subcircular cavity from whose floor some bulbous lava had oozed, probably, at some stage of the tumulus collapse. This indicates that there had been a lava pocket ~1 m below the vent. Vent 2 was surrounded by peculiar lava features. There was something like a "basal" lava type, of chocolate brown color, and with a very smooth ripply surface, onto which patches of black, scoriaceous lava were attached. Many of these features are almost certainly related to the frequent and rapid shifting of the locus of extrusion, and the shearing of actively extruding lava along solidified lava on the vent or flow channel walls.

Effusive activity from the 4 February fissure continued at a slowly decreasing rate through the end of May. This decrease was accompanied by an apparent increase of activity in the summit craters, possibly caused by the rise of the magma in the central conduit system below these craters, as less magma escaped through the 4 February fissure. A new surge of activity at this fissure occurred in mid-June; more detail will be provided in a future Bulletin.

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: Boris Behncke, Dipartimento di Scienze Geologiche, Palazzo delle Scienze, Università di Catania, Corso Italia 55, 95129 Catania, Italy.

During March and April 1999, seismic activity continued at low levels, similar to those reported in previous months (BGVN 24:02). The biggest source of seismic energy release, 2.1 x 10¹⁵ ergs, was associated with volcano-tectonic (VT) events attributed to fracturing. In total, 75 VT earthquakes were registered, located at depths between 0.4 and 20 km below the summit. The largest event, on 3 April, had a magnitude of 2.7 and was located SW of the volcano. During this two-month period the sum of the seismic energy released by 46 long-period events and 27 tremor episodes amounted to 9.8 x 1013 ergs. Radon-222 emissions at four stations located around the volcano measured between 23 and 3,608 pCi/l, values similar to those seen in previous months.

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: Observatorio Vulcanológico y Sismológico de Pasto (OVSP), Carrera 31, 18-07 Parque Infantil, PO Box 1795, Pasto, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).

"White ash emissions" were noted between 9 March and 24 May, rising as high as 700 m above the crater rim but more often 100-200 m. On 11 March it was noted that larger eruptions, accompanied by booming noises and thick ash emission, had decreased to every 10-15 minutes from every 5 minutes during the previous observations on 2 February. Signals from seismic events were dominated by those from the eruptive events, which occurred at a rate of over 100 per day in March and reduced to half that number in April and May.

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: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

A large tectonic earthquake near Iwate on 3 September 1998 (BGVN 23:09) was followed by elevated rates of seismicity and ground deformation that declined in subsequent months (figure 3). In late 1998 volcanic tremor was recorded up to ten times per month and earthquakes around the Moho discontinuity occurred >10 times per month.

Figure 3. Daily numbers of earthquakes at Iwate (recorded at the Matsukawa station) during 1 January 1998-14 May 1999. Courtesy JMA.

At 1909 on 22 May 1999, a M 3.6 earthquake occurred around the W edge of Nishi-Iwate. The earthquake was followed 8 minutes later by another of M 2.2. These volcanic earthquakes were the largest of a swarm centered at 3-6 km depth. No episodes of tremor were observed and no surface manifestations were detected by video monitoring or during a helicopter flight.

The National Coordination Committee for Prediction of Volcanic Eruption said that the largest earthquakes in the swarm occurred in the W region of the volcano, where shallow (5-10 km in depth) low-frequency volcanic earthquakes had been increasing (figure 4). They also observed that deep (~30 km in depth) low-frequency earthquakes had been occurring regularly with some minor increases and decreases in frequency. GPS observation showed relatively low but steady ground-deformation in the western region of the volcano. Gas measurement showed an increase in below-ground temperature and also indicated the gas chemistry had become more magmatic since September 1998. Their conclusion was that Iwate was showing a slight increase in activity.

Figure 4. Hypocenters of earthquakes around Iwate during 1 April-13 May 1999. Courtesy JMA.

Geologic Background. Viewed from the east, Iwatesan volcano has a symmetrical profile that invites comparison with Fuji, but on the west an older cone is visible containing an oval-shaped, 1.8 x 3 km caldera. After the growth of Nishi-Iwate volcano beginning about 700,000 years ago, activity migrated eastward to form Higashi-Iwate volcano. Iwate has collapsed seven times during the past 230,000 years, most recently between 739 and 1615 CE. The dominantly basaltic summit cone of Higashi-Iwate volcano, Yakushidake, is truncated by a 500-m-wide crater. It rises well above and buries the eastern rim of the caldera, which is breached by a narrow gorge on the NW. A central cone containing a 500-m-wide crater partially filled by a lake is located in the center of the oval-shaped caldera. A young lava flow from Yakushidake descended into the caldera, and a fresh-looking lava flow from the 1732 eruption traveled down the NE flank.

Information Contacts: Hiroyuki Hamaguchi, Faculty of Science, Tohoku University, Sendai 980, Japan; Kazuo Sekine, Sendai District Meteorological Observatory, Japan Meteorological Agency, 1-3-15 Gorin, Miyagino-ku, Sendai 983, Japan; Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html).

Between 9 March and 24 May, a "thick white ash plume" was emitted from the main crater and rose to 300-500 m, while a "thin white ash plume" rose to ~150 m from Crater II. Occasionally incandescence was seen in the column rising from the main crater to heights of 25 m. Some A-type earthquakes occurred throughout the reporting period, but seismicity was dominated by tectonic events that frequently exceeded 200/week.

Karangetang (Api Siau) lies at the northern end of the island of Siau, N of Sulawesi, and contains five summit craters strung along a N-S line. One of Indonesia's most active volcanoes, Karangetang has had more than 40 recorded eruptions since 1675. Twentieth century eruptions have included frequent explosions, sometimes accompanied by pyroclastic flows and lahars.

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

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

The following summarizes activity at Satsuma-Iwo-jima (also called Tokara-Iwo-jima), an island on the NW rim of Kikai Caldera. Information concerning events in 1997-98 was provided through communications from Yosihiro Sawada, forwarded by Dan Shackelford. More recent information is available at the Japanese Meteorological Agency (JMA) website.

JMA initiated seismic observation at Kikai in September 1997; from the beginning, several volcanic earthquakes were recorded each day. The number of earthquakes increased suddenly in April 1998 to 60-80/day with some days having more than 100 events. Earthquakes were at this high level during a field inspection on 4-5 May 1998. High numbers of earthquakes continued well into June, then gradually waned, before returning to levels seen in March (~10 events/day). Events decreased to <20/day by late June 1998, but increased again to 20-40/day during September, and to more than 60/day in late 1998.

During the inspection in May 1998, JMA staff found a newly deposited ash layer 5 cm thick around the crater, suggesting that an eruption had occurred in late-April or early-May. The Geological Survey of Japan (GSJ) analyzed the ash and concluded that it was composed of silicic and altered lava fragments of Iwo-dake lava (rhyolite). Residents of this volcanic island witnessed ash falls in August and October 1998. In early November GSJ scientists saw intermittent ash emissions from the crater and found ash deposits in the middle of the SE flank.

Volcanic earthquakes occurred 50-100 times/day during January and February 1999, and 90-130 times/day after February. Hypocenters of these earthquakes were located just below Iwo-dake. Island residents observed ash falling on 24 January [and 14 February 1999].

Geophysical activity is monitored by the Sakura-jima Volcano Observatory, Kyoto University, and JMA; geochemical data are maintained by GSJ.

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

Information Contacts: Yosihiro Sawada, Volcanological Division, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (URL: http://www.jma.go.jp/); Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Dan Shackelford, 3124 E. Yorba Linda Blvd., Apt. H-33, Fullerton, CA 92831-2324 USA.

The eruption of Pu`u `O`o continued to generate a variety of effects on the pali (cliff or fault scarp) and coastal plain during April and May as lava traveled from the vent through a lava-tube system to the ocean. At the coastal lava-entry area the lava bench repeatedly changed as new deposits built up and collapsed. Frequent explosions threw lava fragments into the ocean, onto the bench, and to the top of the adjacent sea cliff.

In the past, the supply of magma to the vent has been cut off for short periods; the 23rd such pause in the eruption began at about 1300 on 4 May and ended around 2200 on 5 May, only about 33 hours. That was long enough for both the steam plume at the ocean-entry area to stop (figure 136) and for a sluggish 6-week-old pahoehoe flow on the coastal plain to cease advancing. The eruption resumed slowly, and as lava moved through the tube system, only a few small sluggish flows broke out onto the pali and coastal plain (figure 137). Lava finally reached the ocean through the preexisting tube system on 7 May.

Figure 136. View of Kilauea on the island of Hawaii's SE flank looking W on the morning of 6 May 1999, about 12 hours after the eruptive pause ended. The entire area from the ocean and lava bench (bottom) to Pu`u `O`o (top) can be seen. Courtesy of HVO.

Figure 137. A short-lived pahoehoe flow at Kilauea that began after pause #23 (4-5 May 1999) had ended. Courtesy of HVO; photograph by S.R. Brantley.

Figure 138. A pahoehoe flow from Kilauea on the coastal plain emerging after pause #23 and inflating with new lava. Note the crack at the top of the flow; this crack formed when the top crust fractured as the molten interior of the flow swelled or inflated with new lava. Courtesy of HVO.

Figure 139. Another view of the same Kilauea pahoehoe flow shown on figure 138 taken as the lava spread laterally. Typical of pahoehoe flows, this moved forward as lava spread across the ground in budding toes and small sheets. The lava flow inflated as molten material continued to move through its main body. Courtesy of HVO.

Figure 140. Location of the source of a breakout from the main lava tube on the coastal plain as seen on 31 March. The surface of the new pahoehoe flow is about 2 m below the top of the rise at its source. Courtesy of HVO; photograph by J. Kauahikaua.

Lava broke out from the tube system on 26 March about 2 km from the ocean. The breakout fed a wide, slow-moving pahoehoe flow for the next five weeks. The flow had advanced to within ~700 m of the ocean when the supply of lava was shut off by the pause on 4 May.

No significant changes have occurred recently at the Pu`u `O`o cone. Observations into the deep crater of Pu`u `O`o are usually not possible because of the thick plume of steam and SO₂ gas. The vent continued to release an average of 2,000 tons of SO₂ gas each day during April and May. Lava was sometimes visible in the northernmost pit on the crater floor; and when viewed on 6 May, a small spatter cone was visible in this pit.

Explosions at lava bench on 13 April. A series of strong explosions from the active lava bench on 13 April was likely related to the progressive collapse of the leading edge of the delta. As the lava tubes were sheared off by the collapses, seawater entered the tube system and a much larger than usual volume of lava was suddenly exposed to seawater. Both processes led to strong steam-driven explosions that hurled lava bombs and hot rocks into the air as high as 80 m and inland nearly 100 m from the bench's edge (figure 141). These ballistics did not land behind the warning signs posted by the National Park Service about 90 m from the sea cliff above the bench.

Figure 141. Lava bombs flying inland from the site of steam explosions at the ocean entry point on 13 April. Courtesy of HVO; photograph by J. Wightman.

USGS observers said that when they arrived at the ocean entry area at 1400 on 13 April two plumes rose from the edge of the active bench. The widest part of the bench was ~40-45 m, where a few hours earlier the bench was as wide as 80 m. Starting just before 1600 the W plume area began venting steam from a hole (probably a skylight) just inland from the outer edge of the bench; the venting sounded like a jet engine. A few moments later explosions from this new vent hurled spatter into the air and formed bubble fountains as large as 10-15 m in diameter.

This activity turned highly explosive within a few minutes, hurling spatter and rocks into the air (average height of spatter was between 50 and 60 m). Ejected materials fell to the ground atop the sea cliff more than 75 m from the source. Explosive activity continued steadily for about 90 minutes and returned intermittently during the next few hours. One explosive episode caused lightning in the plume. When the witnesses returned to their car, parked 5 km away at the end of the Chain of Craters road, they found a thin layer of tiny brown flakes of glass from the explosions on the windshield.

Background. Kilauea is one of five coalescing volcanoes that comprise the island of Hawaii. Historically its eruptions originate primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the caldera to the sea. The latest Kilauea eruption began in January 1983 along the east rift zone. The eruption's early phases, or episodes, occurred along a portion of the rift zone that extends from Napau Crater on the uprift (toward the summit) end to ~8 km E on the downrift end (toward the sea). Activity eventually centered on the area and crater that were later named Pu`u `O`o. Between July 1986 and January 1992, the Kupaianaha lava lake was active ~3 km NE (downrift) of Pu`u `O`o. It was during this period that the town of Kalapana and most of the 181 homes lost were destroyed. In December 1991, one month before the shutdown of Kupaianaha, eruptive activity returned to Pu`u `O`o. More than 1 km³ of lava was erupted from January 1983 through January 1997.

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

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii Volcanoes National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/).

Seismicity at Kliuchevskoi was above background levels during most of May. Earthquakes were concentrated near the summit crater and at depths of 25-30 km. On 29-30 April, a plume rose 200-400 m above the crater. An ash explosion began at 1330 on 1 May and on the evening of 2 May a fumarolic plume rose 2,700 m above the crater. During 3-5 May plumes rose 200-1,500 m above the crater before extending a few kilometers NE.

Short-lived explosive eruptions began at 1143 on 7 May, as seen from the nearby town of Klyuchi [(30 km NNE)]. Activity began with a powerful gas-and-steam blowout that became dark gray as ash mixed with steam rose above the summit. Ash explosions continued to occur every three minutes until the series ended abruptly at 1217. The height of the ash column reached 3,000 m and the plume extended 8 km NW. Authorities increased the color-coded warning level to yellow. Less vigorous gas-and-steam explosions, with plume heights of 400-700 m, occurred during the day at intervals of 7-10 minutes. At 1453 an ash-poor explosion column rose 2,500 m above the crater. Explosions were observed every 3-5 minutes with plumes 200-1,000 m above the crater during much of 8-9 May. A plume released on 8 May extended 30 km to the S and at 1230 on 9 May a plume rose 2,000 m above the crater. Moderate seismic and fumarolic activity returned and continued until the end of May.

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

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.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.

Following several months of intense activity that began on 5 February (BGVN 24:04), Anak Krakatau became relatively quiet in late April. From the end of April until the end of May, only several explosions were heard. On 26 April a weak explosion sent a white-gray ash plume 200-500 m high. Between 4 and 17 May there were two blasts per week, each accompanied by a glow and white-gray ash reaching between 100 and 400 m high. In the week from 18 to 24 May, in addition to two explosions, a shock on the morning of 20 May registered at 2 on the MMI scale.

Anak Krakatau was very active from 1992 to 1997, depositing 6.8 x 10⁶ m³ of lava flows. The island was enlarged by 378,527 m² and the height of the cone increased from 159 to ~300 m.

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

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

The current phase of activity at Lewotobi Lakilaki began at 0547 on 21 March, when observers noted a vigorous steam plume rising 250 m above the summit. This was noteworthy because when the volcano is in a non-active phase its steam plume rises no higher than ~25 m. On 30 March a rumbling noise was heard and the volcano's status was raised to Level II, or "Alert." The following day observers twice noted ash plumes ~250 m high accompanied by a rumbling noise. On 1 April observers saw such plumes at three different times.

From 27 April to 3 May the ash eruption continued. The observed ash was whitish-gray, of weak to moderate pressure, and extending 300 m above the summit. Eruption events were sometimes accompanied by detonations. On 29 April, glowing material was ejected 50-75 m above the crater and it fell over an area with 50 m radius. Thin ash fell over the Boru area the following day at 1600. The seismic record totals for the week showed four volcanic type-B, nine tectonic, four eruption, and nine emission events.

Ash eruptions reached heights of 500 m during 4-10 May and were sometimes accompanied by strong detonations. On 7 and 9 May glowing materials were again ejected to 50-75 m heights, falling within a 50 m radius. On 7 May ash fell around the areas of Boru, Riang Boru, Hokeng, and Wolorona. Deposits were ~1 mm thick. Seismic events for the week decreased, with three eruptive and five emission events. From 11 through 17 May ash eruptions continued to reach heights of 500 m and were sometimes accompanied by strong detonations. During the week of 18-24 May emission heights decreased to 300 m and blast sounds became less frequent. Thin ash fell during 19 May on the Boru and Riagulu regions.

Geologic Background. The Lewotobi "husband and wife" twin volcano (also known as Lewetobi) in eastern Flores Island is composed of the Lewotobi Lakilaki and Lewotobi Perempuan stratovolcanoes. Their summits are less than 2 km apart along a NW-SE line. The conical Lakilaki has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has erupted only twice in historical time. Small lava domes have grown during the 20th century in both of the crescentic summit craters, which are open to the north. A prominent flank cone, Iliwokar, occurs on the E flank of Perampuan.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

During 9 March-24 May visual observations suggested stable conditions, with a "white ash plume" rising 25-75 m above the crater rim. But the seismic record showed extreme variation. Between 9 March and 23 March, volcanic A-type events increased from 7 to 53 and volcanic B-type events rose from 15 to 64. Tectonic events decreased from 34 to 17 in that same period. During the week of 23-29 March event numbers dropped to 23 for A-type and 43 for B-type. Tectonic events rose to 35. Weekly event incidence declined in May, hovering under 10 for A-type, under 20 for B-type, and under 25 for tectonic.

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

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

Activity of Marapi volcano was subdued during the period from late April to late May. From 27 April-3 May, only the emissions events increased (from 21 to 30) from the previous week; volcanic type-A, type-B, and tectonic events, along with eruptions, all decreased. During 4-17 May observed activity was limited to thin white-gray ash emissions that rose 100-400 m above the summit.

Geologic Background. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

Merapi remained active throughout the reporting period of 9 March through 24 May. Although no deaths were reported, the volcano continually threatened surrounding populated areas with lahars, lava avalanches, and pyroclastic flows. Throughout the period, Merapi exhibited weakly pressured, thick, white, sulfur-tinted ash plumes extending 100-700 m above the summit.

During the week of 9-15 March a vigorous "white ash plume" was observed, weakly pressured, with 550 m maximum height above the summit. Observers additionally identified lava glowing along the SW flank, in the direction of the Blongkeng, Lamat, and Sat drainages (the maximum run-out distance was 0.8 km). On 11 March a small pyroclastic flow was noted traveling SW with 0.8 km of run-out distance. During this week multiphase events dominated seismic activity, presumably resulting from the emission of lava and glowing debris. A small lahar traveled down the Sat drainage on 13 March.

During 16-22 March, ash emissions and lava avalanches continued. Avalanches again traveled SW, with maximum run-out distances of 0.4 km. Glow at the lava dome was weak. Surface shocks (assumed to be from lava avalanches) dominated seismicity. From 23 to 29 March the lava avalanches continued in the direction of the SW-flank rivers with 1.8 km maximum run-out distances. These drainages glowed at night. On 24 March a small pyroclastic flow started at the edge of the lava dome, moved in the direction of the Sat River, and attained a 0.6 km run-out distance; no glow was observed at the dome. Seismicity was dominated by surface events mostly interpreted as lava avalanches.

During the week of 27 April to 3 May, sulfur-tinted ash plumes reached their highest point during the recording period, 700 m above the summit. Lava avalanches continued in the direction of Blongkeng, Sat, and Lamat with 0.9 km run-out distances; again night glow was observed in these drainages. In contrast, the body of the lava dome lacked glowing areas. A small pyroclastic flow from the edge of the 1998 lava moved downslope SW for a distance of 1.3 km. Surface events continued to dominate seismicity. A small lahar buried two trucks and a digging machine at Putih on 1 May; no injuries were reported.

Lava avalanches during 4-17 May continued towards the SW-flank drainages with 1-km maximum distances each week. There was a weak glow on the lava dome during the first week and none the second. There was one small pyroclastic flow each week from the edge of the 1998 lava, which again moved SW out to 1 km distance. From 18 to 24 May lava avalanches had 1.8 km run-out distances. Glow within cracks on the lava dome was weak. Seismicity during May continued to be dominated by multiphase shocks and surface events identified as lava avalanches.

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 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent 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.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

During 9 March-24 May activity initially increased but later diminished. Volcanic activity increased during 9-15 March and people in the local settlement heard booming noises about 20 times/day. From 16 to 22 March, volcanic activity continued at the same scale, but the booming noises weakened. The seismic record also illustrated decreased intensity. Activity continued through the week of 23-29 March without diminishing, but the booming noises ceased. Volcanic and tectonic events increased, with volcanic type-B earthquakes rising from 6 to 15 and tectonic events increasing from 1 to 18. From 27 April to 3 May volcanic earthquakes increased and an eruption emitted white-gray ash to 200 m.

Activity began tapering during 4-10 May. A white plume was observed at heights of 10-20 m. Volcanic shocks decreased. Activity continued to decline during 11-17 May, with a plume ranging from 10 to 200 m heights. Volcanic activity was not recorded during 18-24 May, but observers reported 14 "thin white ash plumes" rising 10-50 m.

The Peuet Sague stratovolcano contains four summit peaks. The crater believed to be active resides SE of one of the peaks of the lava dome (Mount Tutung). This narrow crater has a diameter of about 70 m and a depth of 80 m. The last major eruption occurred in 1918-21 when ash was emitted, a lava dome was formed, and pyroclastic flows spilled into surrounding uninhabited forests. A 1975 team that reached the peak found no eruptive activity, but documented a lake (500 x 800 m) at the foot of Mount Tutung. Within Tutung's crater they found a small (40 x 75 m) blue lake surrounded by four solfataras. Scientists inspecting the summit area in 1984 found burned trees surrounding the main crater, likely due to a 1979 eruption. Local eyewitnesses and pilots reported ash columns above the summit in 1979, 1986, and 1991.

Geologic Background. Peuet Sague is a large volcanic complex in NW Sumatra. The volcano, whose name means "square," contains four summit peaks, with the youngest lava dome being located to the N or NW. This extremely isolated volcano lies several days journey on foot from the nearest village and is infrequently visited. The first recorded historical eruption took place from 1918-21, when explosive activity and pyroclastic flows accompanied summit lava-dome growth. The active crater is located NE of the Gunung Tutung lava dome and has typically produced small-to-moderate explosive eruptions.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

During May, Popocatépetl generally displayed low activity. Seismicity included small, isolated exhalations of gas, steam, and ash. The alert status remained at "Yellow" with a 7-km radius of restricted access.

A gas-and-steam exhalation at 1315 on 5 May lasted 12 minutes and produced a plume to ~1 km above the crater. Gas-and-steam exhalations at 1435 and 1623 on 6 May lasted 30 and 14 minutes, respectively, and both produced plumes rising ~1 km above the crater. Separate seismic events at 2053 and 2133 on 10 May were possibly rockfalls on the S flank. Visibility was obstructed by clouds. The next morning a steam column from the crater was seen rising about 500 m above the summit. Beginning at 2200 on 13 May, a sequence of seismic events with variable amplitudes was accompanied by high-frequency tremor. Stable seismic conditions returned after about an hour.

Activity increased on 15 May and included small rivulets of meltwater. At 0246 on 16 May a moderately large explosion occurred. Later (at 0706) a moderate exhalation, lasting three minutes, produced an ash column rising 2,500 m above the summit before dispersing to the SW. No ashfall was reported. Several volcano-tectonic events were recorded on 17 May; their signals possibly related to small rivulets of meltwater descending the N flank.

During the night of 23 May a swarm of three tectonic earthquakes was centered 2.5 km E of the crater. The first, at 2251, had M 1.7 and was located at a depth of 4.5 km; the next occurred at 2338, had M 1.9, and was located at a depth of 5.2 km; and the last was at 2339, had M 2.0, and was located at a depth of 5.8 km.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Servando De la Cruz-Reyna^1,2, Roberto Quaas^1,2; Carlos Valdés G.², and Alicia Martinez Bringas¹. 1-Centro Nacional de Prevencion de Desastres (CENAPRED), Delfin Madrigal 665, Col. Pedregal de Santo Domingo, Coyoacán, 04360, México D.F. (URL: https://www.gob.mx/cenapred/); 2-Instituto de Geofisica, UNAM, Coyoacán 04510, México D.F., México.

As of 21 February the seismograph was under repair so the volcano was monitored visually. During 9 March-24 May a "white ash plume" rose 10-150 m above the summit. During 27 April - 3 May the plume remained thin, but after 4 May it vacillated between thick and thin.

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 volcanic cones, 1,949-m-high Doro Api and 1,795-m-high 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.

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 eruptions have been recorded since 1512, most of them during in the 20th century.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

Due to increased seismicity, officials raised the status to "Caution" during the week of 23-29 March. Earlier, during the week of 9-15 March a white-gray ash plume attained heights of 400-500 m and the number of events involving debris flows rose from 6 to 42 (with a maximum run-out of 2 km). In addition, weekly volcanic B-type events increased from 1 to 35, tectonic events went from 9 to 27, and explosions increased from 280 to 385. From 23 to 29 March there were 224 earthquakes related to emissions. In addition there was one volcanic A-type, one volcanic B-type, and 14 events associated with moving debris.

On 19 April the Darwin Volcanic Ash Advisory Center (VAAC) issued an advisory to aviators, citing reported eruption ash clouds at 9 km. There was no evidence of the ash cloud from satellite imagery.

Seismic events decreased during 27 April-3 May, but a white-gray ash plume continued to reach up to 600 m. There was a marked increase in seismic events from 4-17 May. From 18-24 May the ash plume varied from white-gray to white-brown and extended to between 400 and 600 m above the summit. Eruptions dominated the seismic record, with a decrease in volcanic events. During the week pilots reported occasional ash clouds drifting NW. On 24 May the plume height reached ~6 km, drifting NW.

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

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

Mount Slamet has been predominantly quiet since its last eruption in 1989. During the week of 27 April-3 May, however, the volcano's status was raised to "Alert." That week and the next, "white ash emissions" reached 400 m and hot-spring temepratures ranged from 40 to 81°C. Tremors constituted the dominate seismic events. Slamet ejected black ash from its crater over 1-2 May, prompting concern. Government officials warned residents to stay away from the area following several outbursts within a 10-day period.

During 4-17 May seismicity was dominated by tremor with 4- to 30-mm amplitudes, and "thin-to-thick white ash plumes" reached 400 m height. During 18-24 May ash plumes only rose 25-100 m; tremor amplitudes declined to 0.5-20 mm. There was an increase in volcanic events, with B-type events increasing from 9 to 68 and A-type increasing from 10 to 26.

Geologic Background. Slamet, Java's second highest volcano at 3428 m and one of its most active, has a cluster of about three dozen cinder cones on its lower SE-NE flanks and a single cinder cone on the western flank. It is composed of two overlapping edifices, an older basaltic-andesite to andesitic volcano on the west and a younger basaltic to basaltic-andesite one on the east. Gunung Malang II cinder cone on the upper E flank on the younger edifice fed a lava flow that extends 6 km E. Four craters occur at the summit of Gunung Slamet, with activity migrating to the SW over time. Historical eruptions, recorded since the 18th century, have originated from a 150-m-deep, 450-m-wide, steep-walled crater at the western part of the summit and have consisted of explosive eruptions generally lasting a few days to a few weeks.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

January, February, and March were characterized by sporadic low-intensity events and little seismic activity. In early- to mid-January (7, 13, 14, 15, and 16) there was a series of small explosive eruptions, some generating substantial ash clouds. These events were followed by episodes of ash venting and correlated with seismic tremors. There were occasional small-volume pyroclastic flows (mostly generated by dome collapse, but some perhaps due to fountain collapse during earlier eruptions). Several pyroclastic-flow signals (for example, 7 January) had low-frequency precursors and observers heard associated booming noises in the S of the island. Subsequent vigorous ash venting suggested that the collapses came from violent degassing of the dome. SO₂ levels generally decreased during January, although they remained elevated. Ash samples were coarse with lithic and crystal fragments up to 6 mm in size in the Richmond Hills and St. Georges area; those from the dome-collapse pyroclastic flows were very fine-grained.

At the end of January the observatory conducted an extensive photographic and theodolite survey at 12 sites; they also used a GPS-equipped helicopter. The information was used to produce a detailed dome map. The researchers gauged the dome's volume at 76.8 x 10⁶ m³ and measured its highest point (at the top of the White River Valley) at 977 m. Also noted was a deep split in the dome from the 3 July 1998 collapse and subsequent events. The N part of the split comprised two-thirds of the total dome volume (including the three main buttresses above Gages, the N flank, and the Tar River). The scar cuts 100 m into the older English's Crater and has removed a minimum of 5.4 x 10⁶ m³ of old rock.

February activity consisted of a short period of ash venting and pyroclastic flows, and two small mudflows. There was reduced deformation, and the SO₂ flux continued to decline.

Activity in March was dominated by 23 small explosive and ash-venting episodes on 1, 7, 12, 26, and 30 March. The largest produced a 7-km-tall ash cloud, ashfall as far as Salem and Runaway Ghaut, lightning, and pyroclastic flows reaching the Tar River delta. Deformation rates decreased, gas emissions were moderate, and SO₂ fluxes dropped. Seismicity was dominated by signals from ash venting. Events had impulsive origins with gradual declines in amplitude toward the signal's end.

Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

Information Contacts: Montserrat Volcano Observatory (MVO), Mongo Hill, Montserrat, West Indies (URL: http://www.mvo.ms/).