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).

Ambrym, a volcanic island in the archipelago of Vanuatu with a large caldera (figure 35) is frequently active. Since at least 2001 the caldera has been the site of two lava lakes (BGVN 29:06, 32:05, and 40:06). The Vanuatu Geohazards Observatory (VGO) is responsible for monitoring the volcano, and the Wellington Volcanic Ash Advisory Center (VAAC) tracks ash plumes to provide aviation warnings.

Figure 35. Map of the Ambrym caldera showing features and lava flows through 1989. The insert shows an outline of the island with a fracture zone passing through an outline of the circular caldera in the center of the triangular island. Courtesy of Stromboli Online; original source unknown.

On 21 February 2015 the VGO issued a notice reminding the public that a minor eruption was occurring from a new vent inside the caldera. The Alert Level was raised from 2 to 3 (on a new scale of 0-5; see figure 30 in BGVN 40:06). Hazardous areas were near and around the active vents (Benbow, Maben-Mbwelesu, Niri-Mbwelesu and Mbwelesu), and downwind areas prone to ashfall. VGO reported both on 2 March 2015 and 27 May 2016 that activity at Ambrym had slightly decreased but remained elevated. The Alert Level was lowered to 2. Areas deemed hazardous were near and around the active vents, and in downwind areas prone to ashfall.

The Wellington VAAC reported that low-level ash emissions from Ambrym were identified in satellite images on 12 July 2016, 11-13 October 2016, and 3 April 2017. MODIS satellite thermal sensors have measured nearly continuous thermal anomalies over the past year ending in mid-April 2017, evident in both MIROVA (figure 36) and MODVOLC data (figure 37); similar levels of thermal anomalies are present in MODVOLC records since 2009.

Figure 36. Plot of MODIS thermal infrared data analyzed by MIROVA showing log radiative power for Ambrym for the year ending 18 April 2017. Courtesy of MIROVA.

Figure 37. MODVOLC thermal alerts measured during mid-January to mid-April 2017, as an example of similar densities of thermal alerts since about 2009. More than approximately 160 thermal alert pixels (red/orange squares) for this 3-month period are centered over the Marum and Benbow craters. Courtesy of (HIGP), MODVOLC Thermal Alerts System.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Information Contacts: Vanuatu Geohazards Observatory (VGO), Geo-Hazards office, Vanuatu Meteorology and Geo-Hazards Department (URL: http://www.vmgd.gov.vu/vmgd/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://vaac.metservice.com/); 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/); Stromboli Online (URL: http://www.swisseduc.ch/stromboli/perm/van/links-en.html).

Japan's 24-km-wide Asosan caldera on the island of Kyushu has been active throughout the Holocene. Nakadake has been the most active of 17 central cones within the caldera for 2,000 years. Historical eruptions have been primarily basaltic to basaltic-andesitic ash eruptions, with periodic Strombolian activity. Minor ash emissions during May-June 2011, January-February 2014, and August-September 2014 preceded a major eruptive episode which began in late November 2014 and continued through 1 May 2016. Another eruption, with the largest ash plume in 20 years, occurred on 8 October 2016. The Japan Meteorological Agency (JMA) provides regular reports of activity; the Tokyo Volcanic Ash Advisory Center (VAAC) issues aviation alerts reporting on possible ash plumes. This report covers the period from the beginning of the late 2014 episode through March 2017.

Minor ash eruptions occurred at Asosan during 13 January-19 February 2014 and 30 August-6 September 2014. Trace ashfall was reported on 24 October 2014. A new large eruptive episode began in late November with ash plumes and Strombolian activity that continued from 25 November 2014 through late May 2015. Ash explosions also occurred on 28 June, 8 August, and 3 and 10-11 September 2015. A large explosion with pyroclastic flows occurred on 14 September. This was followed by intermittent ash plumes until 23 October 2015. Minor ash explosions took place on 7 and 25 December 2015. More explosions with ash were recorded on 17-18 February, 4 March, 16 and 30 April, and 1 May 2016. Nakadake crater was then quiet until a large explosion with an 11.9-km-high ash plume on 8 October 2016, after which no further explosive activity was reported through March 2017.

Activity during January-October 2014. After no activity during 2012 and 2013, increased seismicity in December 2013 preceded a series of minor ash eruptions between 13 January and 19 February 2014 (BGVN 40:02). The largest, on 29 January, rose 2.7 km and drifted NW. The next episode began on 30 August and lasted for only a week until 6 September 2014. The ash plumes were continuous during most of this brief time, but only rose as high as 2.1 km, and drifted N and NE. Other than a small amount of ashfall reported on 24 October, only steam plumes issued from Nakadake between early September and 25 November, the beginning of a lengthy eruptive episode.

Activity during November 2014-May 2015. The details of the beginning of this episode have been covered in a previous Bulletin report (BGVN 40:02). Ashfall was reported from ash plumes in several directions (NE, WSW, SW) as far as 38 km away, although plume heights were seldom above 2.4 km altitude (figure 36). Incandescence was observed at night from the webcams. Strombolian activity occurred from two active vents at Nakadake, producing frequent explosions of incandescent material onto the crater rim (figure 37). Blocks up to 10 cm wide were observed by JMA scientists within 1.2 km SW of the crater in mid-December 2014.

Figure 36. Ash plume from Asosan on 26 November 2014. Image taken from Kumamoto University webcam located about 1 km SW of Nakadake crater. Courtesy of Volcano Discovery.

Figure 37. Strombolian activity at the Nakadake crater at Asosan on 27 December 2014. Image taken from the Kyoto University webcam located at Nakadake crater which was destroyed during a subsequent eruption. Courtesy of Volcano Discovery.

Ash plumes and Strombolian activity continued from 25 November 2014 through late May 2015. The Tokyo VAAC issued near-daily reports through early May, when they became more intermittent until a month-long break beginning on 26 May. Plume heights were rarely higher than 1.5 km above the rim (3 km altitude). Field surveys noted intermittent ejecta from the Strombolian activity as high as 300 m above the crater rim. Ashfall was reported in the surrounding Kumamoto (W), Oita (NE), and Miyazaki (SE) prefectures (figure 38).

Figure 38. A dense ash plume drifting S from Asosan on 13 January 2015. The ash plume is visible for at least 30 km. Upper image is the inset box of lower image. Courtesy of NASA Earth Observatory.

The JMA report for February 2015 noted that observations conducted by Kumamoto University indicated that as much as 1,500,000 tons of ash fell from the start of the eruption on 25 November 2014 through 2 February 2015. The results of GNSS (Global Navigation Satellite Systems) measurements suggested a slight inflation across Kusasenri, another cone located W of Nakadake, during February. In late April, ashfall was reported in areas to the SE and NE. A large-amplitude tremor that lasted for 5 minutes was recorded on 3 May. During a field survey on 5 May, JMA scientists observed that the S side of one of the pits (named the 141st pit) in the Nakadake crater had collapsed. On 26 May, an ash plume at 2.1 km altitude was reported 37 km NE of Kumamoto airport (about 25 km W of Asosan). This was the last ash plume reported until 28 June.

Activity during June-October 2015. A field survey by JMA personnel on 10 June noted a lake in part of the 141st pit. Thermal infrared measurements indicated temperatures of up to 80°C in the lake, which had not been observed since 8 July 2014; the lake had disappeared by 29 June. An ash plume was reported by the Tokyo VAAC drifting SW at 1.5 km altitude on 28 June.

Tremor amplitude began decreasing by mid-July, but the number of isolated tremors remained large. Steam plumes and a crater lake were again observed at the 141st pit in late July and August, and temperatures remained high (80-90°C) at the lake. A high-temperature fumarole (around 600°C) was observed SW of the 141st pit on 31 July and again during August. A small eruption was reported on 8 August by JMA with grayish plumes rising 600 m above the crater rim and minor ashfall reported on the S side of the crater. The Tokyo VAAC reported minor ash plumes on 3 and 10-11 September.

A series of new larger explosions began early on 14 September 2015 local time. JMA raised the Alert level from 2 (Do not approach the crater) to 3 (Do not approach the volcano) (on a scale of 1-5) the same day. The ash plumes were reported by JMA at 2,000 m above the crater rim drifting NW. A pyroclastic flow and ejecta impacted the immediate area around the crater. Aerial observation later that day noted discoloration extending 1.3 km SE and 1 km NE from the Nakadake crater as a result of the pyroclastic flow. Ashfall was also observed in areas to the W of the crater from northern Kumamoto Prefecture (including Tamana (50 km NW), Kumamoto City (40 km W), and Yamaga (40 km NW)) to Fukuoka Prefecture (more than 30 k NW). According to a news article in The Japan Times, about 30 tourists in the immediate area were evacuated, and some flights were either canceled or re-routed from Kumamoto Airport, 20 km W. Areas within 4 km of the craters were closed. The Tokyo VAAC reported the plume from the 14 September explosion at 3.7 km altitude drifting NW. During an overflight the following week, scientists observed evidence for pyroclastic flows as far as 3 km SE from the crater. Scientists from Kumamoto University estimated that about 40,000 tons of ash were ejected on 14 September.

Ash plumes were reported daily by the Tokyo VAAC until 23 October 2015, when several small explosions sent plumes up to 1.6 km above the crater rim. A field survey that day noted bombs scattered over the W and NW flank of the crater. After this, only steam plumes to 300 m above the rim were reported from Nakadake during November, leading JMA to lower the Alert level to 2 on 24 November.

Activity during December 2015-May 2016. A small explosion occurred on 7 December 2015. A field survey later that day revealed minor ashfall on the SW side of Nakadake crater. Visual confirmation of emissions associated with a relatively large-amplitude tremor on 25 December was obscured by clouds. During a 7 January 2016 survey, staff from JMA and the Aso Volcanological Laboratory observed fresh ejecta up to 0.5 m in diameter as far as 100 m SW of the crater rim, inferring that it resulted from the 25 December explosion.

The next reported ash eruptions took place on 17-18 February 2016. A field survey on 17 February revealed ashfall in Takamori (7 km SSE). Another survey on 18 February noted lapilli along the SW crater wall from the 17 February explosion. After the 18 February explosion, lapilli were observed 400 m NW of the crater and ashfall was noted in Aso City (10 km NE). Two MODVOLC thermal alerts on 28 February were located about 2 km NE of the active crater and likely unrelated to volcanic activity.

An explosion early in the morning on 4 March 2016 sent a milky-white plume to 1 km above the crater rim. A field survey later in the day confirmed slight ashfall on the E side of the crater. Small explosions were reported by JMA on 16 and 30 April. The Tokyo VAAC issued advisories, but ash was not detected in satellite imagery. The Tokyo VAAC issued no further advisories until 7 October 2016, although JMA noted a small explosion on 1 May with gray-white 'smoke' rising to 300 m above the crater. This was the last reported explosion by JMA until 7 October 2016. Seismic tremor amplitudes decreased after 15 May. During July through September, JMA noted that most of the crater floor was filled with hot water, and seismicity was low and intermittent.

Activity during October 2016-March 2017. After an explosion late in the day on 7 October 2016 and another one in the early hours of 8 October, JMA raised the Alert Level to 3. The Tokyo VAAC reported a large ash plume rising to 11.9 km altitude early on 8 October, and drifting NE. During an overflight on 8 October and a field survey on 12 October, significant ash deposits were observed (figures 39 and 40). They extended as far as 1.6 km on the NW flank and 1 km on the SE flank; ash was also abundant on the NE flank.

Figure 39. View to the N of ash deposits around the Nakadake crater at Asosan after a large explosion on 8 October 2016. Photo by Kyodo/via Reuters.

Figure 40. Area on the SW side of Asosan's Nakadake crater covered with ash by the explosion on 8 Oct 2016. Note the six bunkers on the left side of the crater in figure 39. They correspond to the bunkers in this image. Photo: JMA. Courtesy of Volcano Discovery.

Ashfall 3 cm thick was reported at the Aso City police station 6 km NE of Nakadake crater in Kumamoto Prefecture (figure 41). Ashfall was also confirmed in Oita (50 km NE), Ehime (across the Inland Sea, 150 km NE), and Kagawa (300 km NE) prefectures. According to news articles (Reuters), ashfall was reported as far away as 320 km. Kyoto University Volcano Research Center estimated the amount of ash ejected on 8 October to be around 50-60,000 tons. Samples analyzed by the National Institute of Advanced Industrial Science and Technology (AIST) and the National Research Institute for Earth Science and Disaster Prevention (NIED) revealed a 10% juvenile magma component, and that the explosions were possibly phreatomagmatic. Inflation was recorded near the crater up until 8 October, after which it remained steady.

Figure 41. Cars are covered with volcanic ash from Asosan in Aso City, about 10 km NE of Nakadake crater in Kumamoto prefecture on 8 October 2016. Photo credit: Kyodo/via REUTERS.

On 12 November 2016, JMA observed incandescence at night at Nakadake crater for the first time since 26 April 2015. While SO₂ emissions were reported as continuous after the 8 October explosion, the volcano was otherwise quiet and JMA lowered the Alert Level to 2 on 20 December 2016. There was no change of activity during January 2017, and thus the Alert Level was lowered to 1 on 7 February 2017. Field surveys during February noted that 80% of the bottom of Nakadake was filled with hot water. JMA reported no further activity through the end of March 2017.

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

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); The Japan Times (URL: http://www.japantimes.co.jp/news/2015/09/14/national/mount-aso-erupts-belching-black-plume/#.WRBxXlXyuJD); Reuters (URL: http://www.reuters.com/article/us-japan-volcano-idUSKCN12804E?il=0).

Italy's Mount Etna on the island of Sicily has recorded eruptions for the past 3,500 years. Lava flows, and explosive eruptions with ash plumes and lava fountains, commonly occur from its four major summit crater areas, the North East Crater, the Voragine-Bocca Nuova complex, the South East Crater (formed in 1978), and the newest, the New South East Crater (formed in 2011). The Etna Observatory, which provides weekly reports and special updates on activity, is run by the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV). This report uses information from INGV to provide a brief summary of the major events during 2011-2014, and a detailed summary of events between January 2015 and March 2016. Major eruptions took place during 28 December 2014-2 January 2015, 31 January-2 February 2015, 11-16 May 2015, and 3-7 December 2015.

Summary of 2011-2014 activity. Most of the 44 eruptive episodes at Etna reported by INGV between 12 January 2011 and 2 December 2013 occurred at the New South Crater (NSEC) (figure 154) at the SE edge of the summit crater area. These eruptive events generally lasted for less than an hour and were characterized by sustained lava fountains accompanied by dense ash emissions and ejected pyroclastic material. Eruptive episodes occurred at Bocca Nuova (BN) in July 2011, July-August and October 2012, and January-February 2013. In addition, two weeks of intense Strombolian activity took place at Voragine (VOR) between late February and mid-March 2013. After an episode on 27 April 2013, Etna was quiet for six months until a large explosion on 26 October 2013 sent pyroclastic material several kilometers above the summit and caused a brief closure at the Catania airport. Two other episodes at NSEC during the middle and end of December 2013 were characterized by strong Strombolian activity, but without sustained lava fountains and fewer ash emissions.

Figure 154. DEM (Digital Elevation Model) of the summit crater area at Etna, August 2007, updated with GPS measurements at NSEC in January 2014, and annotated by INGV. The white hatched lines outline the crater rims. BN = Bocca Nuova; VOR = Voragine; NEC = North East Crater; SEC = South East Crater; NSEC = New South East Crater. Courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 6 January 2015, No. 2).

During 2014, major activity was characterized by four events: 1) modest Strombolian activity and lava flows from the NSEC between 21 January and around 7 April; 2) intense Strombolian activity at NSEC accompanied by a lava flow to the SE during 14-18 June; 3) strong Strombolian explosions and lava flows from several vents between NSEC and the E flank of the North East Crater (NEC) between 5 July and 10 August; and 4) intense Strombolian activity at NSEC accompanied by a lava flow during 10-15 August. Weak explosive activity was also reported from NSEC during the second week of October.

Summary of December 2014-March 2016 activity. Activity from NSEC during 28-29 December 2014 created two major lava flows and an ash plume. During 31 January-2 February 2015 NSEC produced a new lava flow and several ash plumes. A minor ash emission from the BN crater took place on 12 April 2015. A large Strombolian eruption began at NSEC during the night of 11-12 May 2015, followed by a lava flow down the E flank on 13 May. Activity continued until 16 May. Minor ash emissions were reported from the NEC on 20 May, and again during 16, 18, and 19 July 2015.

The VOR crater released minor ash emissions on 20 and 24 August 2015, and again on 18 September. Small amounts of ash were also observed in a plume from NEC on 4 October. This was followed the next week by sporadic ash emissions from VOR which grew into persistent Strombolian explosions by the end of October and continued into mid-November. Strombolian activity at a new crater on the E flank of NSEC began on 25 November; ash emissions began there on 2 December 2015.

A major lava fountaining event from VOR began on 3 December 2015 which generated an ash plume that dispersed ash 70 km NE. This was followed by a 7-km-high (over 10 km altitude) ash plume the next day that sent ash to the E. Three more lava-fountain episodes took place at VOR over the next two days. After this the activity decreased at VOR but increased at NSEC with a 3.5-km-long lava flow on 6 December, followed by ash emissions and Strombolian activity. Sporadic ash emissions continued from VOR, NSEC, and NEC during December 2015-March 2016.

Activity during December 2014-February 2015. After four and a half months of relative quiet, with only minor ash emissions during 7-16 October 2014, the NSEC began a new eruptive episode on 28 December 2014 (BGVN 40:02). This was the 45th major episode at Etna since January 2011, according to INGV, and was characterized by lava fountains, lava flows in two different directions from a NE-SW trending fissure that crossed the NSEC (see figure 152, BGVN 40:02), and a tephra plume that drifted to the E. INGV calculated a volume of lava from the 28-29 December event, based on a lava thickness of 1.5-2 m, of about 3 x 10⁶ m³. Coarse ash and lapilli as large as 4-5 cm were reported in Fornazzo (9 km E), and mostly coarse ash and fine lapilli were deposited in Giarre (15 km E). Fine ash was also reported in Linguaglossa 17 km NE.

Explosive activity at NSEC resumed on 2 January 2015 with dense continuous ash emissions lasting until the next day that dispersed SW (figure 155). During the night of 1-2 January, INGV also observed new Strombolian activity from VOR for the first time in two years. During the next week, incandescent pyroclastic material rose up to 150 m above the crater rim and occasionally fell outside the crater onto the W and SW flanks; this was accompanied by minor ash emissions rising a few hundred meters. MODVOLC thermal alerts were issued nine times between 5 and 10 January. Strombolian and ash plume activity resumed at the NEC on 14 January for a few days (figure 156), but clouds obscured the summit area for most of the rest of the month. Intense degassing and minor ash was seen during clear weather through 31 January.

Figure 155. Dense ash cloud from the New Southeast Crater (NSEC) at Etna that dispersed to the SW on 2 January 2015. A) taken from the webcam at La Montagnola (EMOV) 3 km S of the summit, and B) from the town of Tremestieri Etneo, 20 km S of Etna. Photo by Boris Behncke; courtesy of INGV (Il Parossismo dell'Etna del 28 Dicembre 2014 e la Susseguente Attivita al Crateri Sommitale, INGV).

Figure 156. The summit area of Etna on 14 January 2015, observed from a Coast Guard AW139 helicopter. Minor gray ash was emitting from the Northeast Crater (NEC) and the Voragine (VOR). Dense steam plumes are visible coming from Bocca Nuova (BN) and the fumarolic vents at Southeast (SEC) and NSEC. Photo by Marco Neri; courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 20 January 2015, No. 4).

A sudden increase in volcanic tremor amplitude in the early morning of 31 January 2015 indicated a new ash emission from the summit which was obscured from view by clouds. Later in the morning, fine ash fell over the snow in Rifugio Citelle (6 km NE). Strombolian activity was observed, along with a new lava flow moving to the SW, from the NSEC the next day. Sixteen MODVOLC thermal alerts were issued during 1-2 February while the lava flow was active. A field survey on 2 February determined that the lava front had stopped at 1,950 m elevation near the Monte Scavo area on the SW flank (figure 157). An ash emission occurred at NSEC in the early morning of 2 February; only persistent degassing was observed from the summit craters for the remainder of February.

Figure 157. The 1 February 2015 lava flow at Etna observed on 2 February from the base of the S flank of the New Southeast Crater (NSEC). BN = Bocca Nuova, SEC = South East Crater. The NSEC is at the top right of photo. Courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 10 February 2015, No. 7).

Activity during March-September 2015. Degassing continued from the summit craters through March 2015 as viewed during limited clear weather. A high-temperature fumarole was observed in an infrared camera image on the E edge of NSEC on 29 March. The next ash emission occurred on 12 April from Bocca Nuova; it produced a plume a few tens of meters high that drifted SE, leaving fallout of fine reddish ash on the snow covering the western wall of the Bove Valley above 2,000 m elevation. A second smaller emission later in the day quickly dissipated.

A visit to the summit on 29 April 2015 confirmed persistent degassing from the craters. INGV scientists noted that the narrow septum separating the BN and VOR craters was much lower in height and broken through at the base, compared with earlier visits (figure 158). A small brownish-red ash plume on 1 May rose from BN; it likely resulted from a collapse inside the NW crater wall.

Figure 158. A view from the SE rim looking into the Bocca Nuova (BN) crater at Etna on 29 April 2015. In the foreground (a) is the SE pit crater which is blocked with debris, and in the background (b), the NW pit crater is degassing. The red arrow indicates the portion of the septum (setto) between Bocca Nuova (BN) and Voragine (VOR) that has collapsed. Courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 5 May 2015, No. 19).

A Strombolian eruption began during the night of 11-12 May 2015 from the central part of NSEC. By midnight, the activity was strong enough to send tephra out of the crater and onto the flanks. A new lava flow appeared from a fracture just below the rim on the NE side early on 13 May; it generally followed the path of the 28 December 2014 flow to the NE. This was followed by increased ash emissions later in the day. The lava flow continued to advance NE during 14 May, into the Valle del Leone, and crossed near Monte Rittmann, flowing rapidly down the steep slope connecting the Valle del Leone with the Valle del Bove, headed towards Monte Simone (figure 159). By the end of the day it had traveled 3.5 km and was at 2,000 m elevation.

Figure 159. Early morning on 14 May 2015 reveals the lava flow on the NE flank of Etna from a fissure on the E flank. Photo by Emanuela/Volcano Discovery Italia; courtesy of Volcano Discovery.

Intense Strombolian activity continued the next day at NSEC along with intermittent ash emissions. The lava flow split and flowed down the central part of the Valle del Bove, travelling 4.5 km to just below 1,800 m elevation. During the morning of 15 May a series of strong ash emissions lasting 2-3 minutes each continued from BN for about two hours. By the evening, the lava flow had traveled about 5 km and was at 1,700 m elevation (figure 160). Between 12 and 16 May, MODVOLC issued 103 thermal alerts for Etna.

Figure 160. Images from the Monte Cagliato thermal camera (8.3 km ESE) taken on 14, 15, and 16 May 2015 at Etna show the summit from the E. The 13-16 May lava flow is seen progressively expanding into Valle del Bove until reaching the vicinity of Rocca Musarra and Serracozzo. Courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 19 May 2015, No. 21).

By the morning of 16 May, volcanic tremor had diminished and Strombolian activity had ceased, but magma was still feeding the lava flow until the afternoon, when it tapered off. During the morning of 20 May there were sporadic brown ash emissions from the NEC. After this, variable amounts of degassing continued at the summit craters for a few months, with the NEC being the most active. This period of relative quiet permitted INGV scientists to make several surveys of the summit during July to document the effects of the recent eruptions on the craters (figures 161 and 162).

Figure 161. The vent at the bottom of the Northeast Crater (NEC) at Etna is viewed with both visible (top) and thermal (bottom) images on 2 July 2015. Courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 7 July 2015, No. 28).

Figure 162. Views of the multiple vents at Etna's New Southeast Crater (NSEC) on 8 July 2015 showing changes caused by the 2014 and 2015 activity. Top: Vent on the S side of NSEC formed during the 31 January-2 February 2015 episode, looking SW. Bottom: The NSEC, looking SE at the main crater formed during the 28 December 2014 episode. Inside of this are several vents that were active during the 11-16 May 2015 episode. Photo by B. Behncke; courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 14 July 2015, No. 29).

During a field visit on 16 July 2015, INGV scientists witnessed intense pulsating gas emissions and loud noises at NEC; the gas often contained small amounts of reddish fine-grained ash. Increased gas emissions on 18 and 19 July rose a few hundred meters above the summit and occasionally released appreciable amounts of reddish ash that covered the W flank of the crater. Small puffs with minor ash were intermittent for the next several days. Only degassing from the summit craters was observed until 20 August when minor ash emissions were noted from VOR. The next day increased seismicity was recorded at the summit area, but there were no visible surface effects. Frequent gas emissions that included minor ash were observed at the summit during a visit on 24 August (figures 163 and 164).

Figure 163. Emissions from Etna's summit crater on 24 August 2015. Steam emissions from the Northeast Crater (NEC) viewed from the N edge of the crater (top) and a weak ash emission from the Voragine (bottom), seen from the NW edge of the crater. Photos by B. Behncke; courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 1 September 2015, No. 36).

Figure 164. Activity at the summit craters at Etna on 24 August 2015. Top: The Bocca Nuova seen from its E rim, with vapor emitting from the cone (conetto) that formed during 2011-2013 activity, and darker emissions of gas and small amounts of fine-grained ash from the pit located in the center of the crater floor (pozzo centrale). Bottom: fumarolic activity at the Southeast Crater (SEC) and New Southeast Crater (NSEC), viewed from the E edge of the Voragine. Photos by B. Behncke; courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 1 September 2015, No. 36).

Degassing continued at the summit craters during September. The Montagnola webcam captured a minor ash emission from VOR on 18 September 2015. A glowing fumarole was observed inside the NSEC during a summit visit on 23 September 2015 (figure 165).

Figure 165. A glowing fumarole inside Etna's New Southeast Crater (NSEC) observed on 23 September 2015. Photo by B. Behncke; courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 29 September 2015, No. 40).

Activity during October-November 2015. Small but appreciable amounts of reddish ash which quickly dissipated were contained in a gas plume from NEC on 4 October 2015. Activity the following week (12-18 October) was characterized by sporadic, minor ash emissions from VOR; they were brownish-red, and were ejected during pulsating events that lasted for a few tens of seconds, repeating for as long as a few hours. Explosive activity was witnessed by a field crew at the bottom of VOR on 19 October. Lithic fragments and ashes were ejected in the immediate area of the crater. Activity increased at VOR during the end of October. During an inspection on 27 October, Strombolian explosions every 5-10 minutes sent incandescent pyroclastic material around the crater and produced minor ash emissions. A few bombs fell along the NW crater rim (figure 166).

Figure 166. Activity at Etna's Voragine Crater on 27 October 2015. a) DEM of the summit crater area at Etna (DEM 2012, Aerogeophysical Laboratory - Section 2). The red circle indicates the position of the vent inside Voragine. BN = Bocca Nuova; VOR = Voragine; NEC = Northeast Crater; SEC = Southeast Crater; NSEC = New Southeast Crater. b) The vent on the N side of the Voragine; c) detail of a Strombolian explosion from the vent. Photo by B. Ragonese (Group Guide Etna Nord, 27 October 2015); courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 3 November 2015, No. 45).

On the morning of 2 November, after stormy weather conditions had blocked views of the summit for several days, volcanic ash was observed on the camera lens of the Montagnola (EMOV) webcam that was later washed away by rain. During a 4 November field survey, an ash deposit was discovered within layers of snow that fell between 31 October and 2 November on the upper part of the S flank (figure 167). The source of the ash remains unknown.

Figure 167. Ash deposit at Etna interlayered in the snow that fell between 31 October and 2 November 2015, exposed along the track leading from the cable car station at Torre del Filosofo, at an elevation of approximately 2,800 m. Photo taken on 4 November 2015. Courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 10 November 2015, No. 46).

Modest Strombolian activity continued from the bottom of VOR during November 2015. A single small explosion occurred at the NSEC in the early hours of 8 November. During a 14 November field visit, INGV scientists observed intracrater explosive activity continuing at VOR which included several explosions with abundant ash emissions, interspersed with periods of strong spattering. On the E rim of the crater, several fresh, large (40 cm) clasts of volcanic debris had fallen as far as 12 m from the edge of the rim (figure 168).

Figure 168. Explosive activity at the Voragine crater (VOR) at Etna on 14 November 2015. a and b) volcanic ash explosions; c) an episode of strong spattering of ejecta without ash emissions; d) a recent bomb from the eastern edge of the pit inside the crater. Courtesy of INGV (Bollettino settimanale sul monitoraggio, volcanico, geochimico e sismico del volcano Etna, 17 November 2015, No. 47).

By the third week in November 2015, ash emissions from VOR were more frequent and reached high enough levels to be visible from the webcams on the S slope. Lapilli and bombs rising more than 10 m above the northern edge of VOR were observed on a site visit on 19 November. During 20 and 21 November, a slow and gradual increase in the magnitude of volcanic tremor was noted, but there was no visible change at the summit. Weak Strombolian activity began at NSEC on 25 November and was observed in the Montagnola webcam. This led to the formation of a new "pit crater" located a few tens of meters below the E edge of the NSEC, with a diameter of 15-20 m.

Eruption of 2-8 December 2015. While on a site visit to VOR on 2 December 2015, INGV observed continuing Strombolian explosions with material ejected tens of meters above the crater rim; the cone at the bottom of the crater had continued to grow from the previous week. An explosion at the NSEC pit crater in the afternoon generated minor ash emissions, and Strombolian activity at VOR increased in the evening. A progressive increase in explosive activity began at VOR on 3 December. In the early morning, a lava fountain reached heights well over 1 km (figure 169) above the crater rim.

Figure 169. Eruption from the Voragine crater (VOR) at Etna during the early morning of 3 December 2015. Witnesses reported the lava fountain as over 1 km in height. Photo by Marco Restivo/Demotix/Corbis; courtesy of Erik Klemetti.

An ash plume from this eruption initially drifted NE; ashfall was reported in Linguaglossa (17 km NE), Francavilla di Sicilia (20 km NE), Milazzo, Messina (70 km NE) and Reggio Calabria (70 km NE) (figure 170). Weak and sporadic ash emissions also occurred from the NSEC pit crater. INGV reported this as one of the most intense and among the largest eruptions from Etna in the last twenty years, similar to events on 22 July 1998 and 4 September 1999. After about one hour, activity diminished and returned to less intense Strombolian activity.

Figure 170. The OLI instrument on Landsat 8 collected this natural-color view of the ash plume from Etna on 3 December 2015 drifting SE after initially drifting NE. The close-up image (bottom) reveals abundant fresh ashfall on the NE quadrant of the volcano. Courtesy of NASA Earth Observatory.

The explosive activity at VOR intensified again around 0900 UTC on 4 December, with renewed lava fountains and an ash plume that rose 7-8 km above the summit (10-11 km altitude); this episode lasted until about 1025 UTC (figure 171). Ash emissions continued throughout the day from the NSEC as well. Bombs and lapilli were deposited high on the SW slope above 2,000 m elevation. Ashfall was reported in the Giarre-Zafferana area 17 km E. Strombolian activity continued for much of the day at VOR until 2000 UTC, when the third lava fountain (since 3 December) erupted that lasted for about 90 minutes before subsiding again to less intense Strombolian activity.

Figure 171. Eruption at Etna from the Voragine crater (VOR) in the morning of 4 December 2015, viewed from Cesaro, province of Messina (27 km NW). Copyrighted photo by Giuseppe Famiani, used with permission.

A fourth episode of lava fountaining from VOR took place mid-afternoon on 5 December 2015 and lasted for about 60 minutes. After this, activity decreased (both ash emissions and Strombolian explosions) from VOR, but increased at the NSEC pit crater, which grew due to continuous activity. In the early morning the following day two pyroclastic flows descended a few hundred meters toward the Valle del Bove. Around 1700 UTC, INGV personnel observed two lava flows, fed from the NSEC, headed toward Valle del Bove; one headed E for 3.5 km and reached 2,100 m elevation, and the other advanced ENE a few hundred meters to 2,600-2,700 m elevation. The easternmost vent at NSEC began emitting dark ash plumes on 7 December along with Strombolian activity that evening (figure 172). Activity at NSEC lasted for about 48 hours, ending in the morning of 8 December.

Figure 172. Lava flows and Strombolian activity at Etna on the evening of 7 December 2015 from the new vent on the E side of the New Southeast Crater (NSEC) that formed in late November. Photo by B. Behncke, taken from Piano del Vescovo, on the SE flank. Courtesy of INGV (Etna Update, 8 December 2015).

Activity during December 2015-March 2016. Ash plumes accompanied by sporadic Strombolian activity were ejected from the NEC beginning on 7 December, and lasting intermittently through 14 December. Renewed explosions on 13 December at NSEC produced ash emissions, minor incandescence, and thermal anomalies. MODVOLC reported 84 thermal anomalies at Etna between 2 and 9 December.

INGV scientists observed on a 12 December visit that the BN and VOR craters were essentially joined into a larger, single crater after the early December explosions, similar to the former Central Crater at Etna. VOR was covered with tens of meters of pyroclastic debris. The debris also covered much of the rest of the summit area, including the lava flows from the previous winter. The parking lot of the visitor area, located 0.5-1 km W and NW of VOR, was marked with numerous impact craters several meters in diameter.

Two minor ash emissions occurred at VOR on 19 December. After that, only steam emissions were observed at the summit until 28 December when a new series of ash emissions with minor incandescence were ejected from the vent on the E flank of NSEC. They were sporadic over the next several days and had ceased by 8 January 2016. Trace amounts of ash were again reported from the E flank vent during the last days of January 2016 and on 6 February. During this time, emissions from NEC often contained trace amounts of ash. Modest amounts of brown ash were observed from the NEC in the morning of 9 February.

An explosive event at NEC on 23 February created an ash plume tens of meters high which drifted N and rapidly dissipated. Lightning was observed in the ash cloud. Ashfall was reported in Linguaglossa, Gaggi, and Santa Teresa Riva (40 km NE) from this event. A new emission on 25 February consisted of several pulses of medium-low intensity that produced a very dilute ash plume a few meters above the crater. During March 2016, sporadic ash emissions at NEC accompanied persistent degassing, but there were no reports of ashfall other than in the immediate area of the crater.

Sulfur dioxide data. Numerous images of SO₂ emissions from Etna during this period were captured by the Aura instrument on NASA's OMI satellite. Emissions during the four major eruptive events discussed in this report (28-29 December 2014, 31 January-2 February 2015, 11-16 May 2015, and 2-7 December 2015) were the largest (figure 173).

Figure 173. Sulfur dioxide plume data for Etna during the four major eruptive episodes covered in this report. Clockwise from top left: 29 December 2014, SO2 plume drifts E; 1 February 2015, SO2 plume drifts ENE; 15 May 2015 SO2 plume drifts SW, E and NE; the largest, from 6 December 2015, shows a detached plume drifting NNE and another plume moving NW that is truncated by the row-anomaly shadow. Courtesy of NASA/GSFC.

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/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Erik Klemetti Eruptions Blog, Wired (URL: https://www.wired.com/author/erikvolc/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/).

Volcán de Fuego, one of three active volcanos in Guatemala, has been erupting continuously since 2002. Historical observations of eruptions date back to 1531, and radiocarbon dates are confirmed back to 1580 BCE. These eruptions have resulted in major ashfalls, pyroclastic flows, lava flows, and damaging lahars. A major explosion on 13 September 2012 that caused significant ashfall to the S and SW (figure 30) was described by the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH) as the largest event in the prior 13 years. From September 2012 through June 2014 continuing explosions with ash plumes and ashfall, pyroclastic flows, lahars, and lava flows have impacted much of the region within 20 km of the volcano (BGVN 39:04). This report covers the ongoing activity from June 2014 through mid-December 2015. In addition to regular reports from INSIVUMEH, information comes from the Coordinadora Nacional para la Reducción de Desastres (CONRED), and aviation alerts are provided by the Washington Volcanic Ash Advisory Center (VAAC).

Figure 30. Guatemala's Volcán de Fuego (Volcano of Fire) erupted on the morning of 13 September 2012. According to the Coordinadora Nacional para la Reducción de Desastres (CONRED), the eruption included ash emissions to the W and a 500-m-long lava flow. This natural-color image was acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite. Courtesy of NASA-Earth Observatory.

Fuego was continuously active from June 2014 through December 2015. Ash plumes generally rose to heights of less than 1 km above the summit (4.8 km altitude) and dispersed ash over villages located 10-15 km S, SW, and W virtually every week, and occasionally to the NE and E. The highest plumes rose to 5.75 km in October 2014, 5.8 km in January 2015, and at least 6.1 km in February 2015. The most significant ash eruptions were in February 2015 when air traffic was disrupted in Guatemala City and in November 2015 when ashfall was reported up to 90 km SW. Incandescent ejecta rose 100-300 m above the crater rim on a regular basis, but the strongest events sent tephra and lava fountains as high as 500 m in July 2014, 800 m in August 2014, and 500 m in December 2015. Pyroclastic flows descended several drainages during larger explosive events in February, July, September, and November 2015. Numerous lava flows affected at least five different drainages around Fuego. They were reported during June, July, and August 2014, and February-April, June, and September-November 2015. Lahars during June and September 2014 and June 2015 damaged roadways and filled ravines with meter-sized debris. Table 12 shows the towns and drainages mentioned in the report and their distances and directions from the summit of Fuego, and is posted at the end of this report.

Activity during June-December 2014. Activity at Fuego during June 2014 was dominated by explosions that produced ash plumes which rose between 100 and 800 m above the summit (3.9-4.6 km altitude), and drifted most often generally westward. Minor amounts of ash were reported from explosions on 18-19 June in towns within 15 km of the summit, mainly El Porvenir (8 km ENE), Los Yucales (12 km SW), Santa Sofía (12 km SW), Morelia (10 km SW), Sangre de Cristo (10 km SW), and Panimaché (I and II, ~8 km SW). The Washington VAAC issued three reports of minor volcanic ash from explosions on 18, 20, and 23 June, which dissipated within a few hours.

Numerous lahars impacted drainages in June. Las Lajas (SE), Honda (E), and Seca (W) drainages were affected on 1 June, and Las Lajas and El Jute (SE) were impacted the next day. Honda, El Jute, Ceniza (SSW), and Santa Teresa (S) drainages had 1.5-m-diameter blocks in lahars on 5 June, and there were more lahars in Las Lajas and El Jute drainages on 9 June. Incandescent ejecta rose 100-200 m above the crater rim several times, and was responsible for avalanches descending the Taniluyá (SW), Trinidad (S), and Ceniza drainages. A new lava flow reported on 29 June descended the Taniluyá drainage for 150 m and caused avalanches in the nearby Ceniza drainage.

Surges of lava and incandescent avalanches traveled down six drainages (Santa Teresa, Taniluya, Ceniza, Trinidad, Las Lajas, and Honda) during the first half of July 2014, the farthest going 400 m down the Ceniza. MODVOLC thermal alerts possibly related to the lava flows and incandescent material were captured on 1, 2, and 11 July. Pulses of incandescent material rose to 100 m above the rim in early July, but increased to heights up to 500 m above the crater for the second half of the month, causing block avalanches down the flanks. Weak-to-moderate ash-bearing explosions early in the month increased to moderate-to-strong explosions by month's end that sent dark gray ash 400-600 m above the crater. The Washington VAAC reported ash plumes on 8, 11, 18, and 31 July. While no emissions were reported on 11 July, strong winds scattered recent ash as high as 5.5 km altitude (1.8 km above the crater). Ashfall was reported most days in nearby areas, including the Santa Teresa, Taniluya, Ceniza, and Trinidad drainages, and at the Observatory, Morelia, Santa Sophia, Ingenio los Tarros (15 km SW), Panimaché, Yepocapa (9 km NW), and Finca La Conchita.

During August 2014, explosions with incandescent blocks rose 50-400 m above the crater, but explosions as high as 800 m occurred several times. Block avalanches traveled down the flanks into Taniluya, Ceniza, Las Lajas, Trinidad, Honda, and Santa Teresa canyons. Ash plumes rose 300-900 m above the crater and drifted in various directions as far as 15 km before dissipating, numerous times during the month. The Washington VAAC reported a number of discrete ash emissions during 5-8 August, although most were not visible in satellite imagery, and again on 18 August when the highest plume of the month was reported at 5.5 km, or 1.7 km above the crater moving NW. Ashfall was reported in the villages of Yepocapa, Finca La Conchita, Sangre de Cristo, Morelia, and Panimaché I and II, Santa Sofia, Alotenango (8 km ENE), Antigua (18 km NE), San Miguel Dueñas (10 km NE), and around the Observatory. On 30-31 August lava flowed again towards Ceniza Canyon.

On 2 September 2014, INSIVUMEH seismically detected a lahar flowing through the Taniluyá drainage which was measured at a width of 75 m and a height of 2.5 m. The flow cut the road between Santa Lucia Cotzulmaguapa and the communities of Morelia, Santa Sofía, and Panimaché I and II. Lahars were also detected within Río Ceniza and Santa Teresa drainages. Incandescent blocks rose 75-100 m above the crater and weak avalanches were channeled into the Ceniza, Trinidad, Taniluyá, Santa Teresa, Las Lajas, and Honda drainages. Ash plumes rose 500-1,000 m above the summit crater and drifted a few tens of kilometers before dissipating. Fine gray ashfall was reported in communities within 10 km SW and ENE. A lava flow in Ceniza Canyon was 100 m long by 13 September. During 16 September, ashfall was reported in the communities of Alotenango, Antigua, and Ciudad Vieja (13.5 km NE), up to around 20 km NE. Another lahar was detected on 22 September, flowing down the El Jute and Las Lajas drainages on the SE flank carrying volcanic debris, lava blocks, branches, and tree trunks.

This moderate activity continued into early October 2014. Ash plumes that rose to 1,950 m above the summit (5.75 km altitude) were reported by INSIVUMEH during 11-12 October, and plumes to 5.5 km were reported by the Washington VAAC on 28 October. MODVOLC thermal alerts were issued during 5-6-7 October and 23-24 October.

Activity increased again in November 2014. Larger explosions generated block avalanches that descended the drainages on the SE and SW flanks, and ashfall was reported numerous times in the villages within 15 km SW. The Washington VAAC issued 5 series of alerts during 10-11 (drifting NE at 5.2 km), 13 (drifting S), and 17, 23, and 28-29 November (drifting 25 km W at 4.6 to 4.9 km altitude). MODVOLC thermal alerts were also issued on 7 days, including 3 pixels on 25 November.

Heightened activity continued into December 2014 with Special Bulletins issued by INSIVUMEH on 1 and 10 December noting more frequent and intense explosions (as many as 6-8 per hour), and dense gray ash plumes drifting 20 km W and SW depositing fine ash. Lava fountaining was reported on 10 December rising 100-150 m above the crater. The Washington VAAC reported ash plumes on 1-2, 5, 12-15 (S, SE), 27 (NW), and 29-30 (W) December based largely on reports from INSIVUMEH. The plume heights ranged from 4.1 to 4.9 km altitude (300-1,100 m above the crater). There were also MODVOLC thermal alerts on 9 days during December, including three pixels on 6 December.

Activity during 2015. Similar activity continued into January 2015. Ashfall was reported 10-15 km SW from plumes rising 550-950 m above the crater. Incandescent blocks traveled down the SW and SE drainages, generating small fires in vegetated areas. MODVOLC thermal alerts were issued on eight different days during January. The Washington VAAC only issued reports on 9 and 12 January. The 12 January plume was reported as discrete volcanic ash emissions seen in visible satellite imagery fanning out about 16 km W of the summit. The altitude of the plume was noted as 5.8 km, or 2 km above the summit.

A significant Strombolian eruption began on 7 February 2015 that lasted for about 22 hours; pyroclastic flows also descended multiple drainages (figure 31). CONRED reported that ash fell in Guatemala City (about 40 km ENE) and flights were diverted to El Salvador. The communities that reported ashfall from the event are shown in figure 32. The Washington VAAC reported an ash plume visible at about 6.1 km altitude (2.3 km above) and 45 km E of the summit. The next day, the plume was still visible at 5.8 km altitude about 100 km E.

Figure 31. An ash cloud from a pyroclastic flow at Fuego on 7 February 2015 fills the horizon. Courtesy of INSIVUMEH and CONRED.

Figure 32. Communities (in red) that reported ashfall from Fuego on 7 February 2015. Courtesy of CONRED.

On 8 February, although activity had decreased, the seismic network detected 30 explosions per minute. The explosions generated shock waves detected in areas 15 km S and SW. Lava flows up to 2 km long were observed in the El Jute and Trinidad drainages on the SE flanks, reaching vegetated areas and causing fires. Sixteen MODVOLC thermal alert pixels were recorded on 8 February; they continued on 9, 11-13 and 17 February before a 10 day break. INSIVUMEH noted that by 9 February activity levels had subsided with weak to moderate explosions producing ash plumes that rose 550 m above the summit and drifted 8-10 km NW (figure 33).

Figure 33. Ash plumes and incandescence at Fuego on 9 February 2015. Courtesy of twitter user JL@parachico, (https://twitter.com/search?q=Volcan Fuego 2015&src=typd)

More intense activity returned on 16 February with 4-6 ash-bearing explosions per hour. The Washington VAAC reported the plumes at 4.9 km altitude, although INSIVUMEH noted pilot reports of ash at 7-9 km altitude. Ash fell in many villages to the NW, W, S, and SE more than 15 km from the summit. By 19 February, the ash plumes extended up to 150 km S of the summit. Intermittent emissions with dense ash plumes continued to rise from Fuego and disperse through 22 February.

A new effusive episode began on 28 February 2015 when lava fountains rose 300-400 m above the summit. A strong MODVOLC thermal alert signal persisted with multiple pixels through 3 March; afterwards MODVOLC pixels only appeared on six additional days during the month. One lava flow traveled 1.6 km S down the Trinidad drainage and another traveled 600 m W down the Santa Teresa drainage. Ash plumes also rose up to 1.25 km above the crater and drifted 35 km W generating ashfall in communities to the SW. Numerous ash plumes continued intermittently; VAAC reports were issued on 16 days during the month, through 24 March.

Hot spots appeared in satellite data numerous times during April 2015. Incandescent tephra was ejected 150-200 m above the crater. Block avalanches continued from the end of a new 300-m-long lava flow in the Trinidad drainage on 17 April. MODVOLC thermal alert pixels appeared on 12 days through 26 April, with large multi-pixel alerts on 17 and 18 April. According to INSIVUMEH, ash plumes continued rising 650-850 m above the crater and drifting 8-11 km S, SW, and W, but VAAC reports of ash only appeared on 17 and 18 April.

Far fewer MODVOLC thermal alerts were issued during only five different days spanning 5-31 May 2015. The Washington VAAC issued reports of ash plumes on 13, 15, 17, and 18 May. INSIVUMEH noted an increased number and intensity of explosions briefly during 14-15 May; ash plumes rose 450-750 m above the crater and drifted 10-12 km W and SW. They also reported a S-flank lava flow on 18 May. Ashfall was reported in the communities within 10 km SW of the summit. Incandescent material was ejected 150-200 m above the crater, causing block avalanches in drainages on the S and SW.

Strombolian activity again increased during June 2015, ejecting material 300 m above the crater for 30 hours during 4-6 June. Ash plumes rose to around 1 km above the summit and drifted 10-15 km S and SW. During this episode, lava flows traveled 600 and 1,200 m down the Santa Teresa and Trinidad drainages. Two cinder cones within the crater were reported on 6 June. A lahar was detected on 12 June that was 25 m wide and 2-3 m deep, travelling S down the Trinidad drainage carrying abundant volcanic material and blocks 1-2 m in diameter. MODVOLC thermal alerts were captured on 16 days during June. The Washington VAAC reported ash plumes from explosions on 5, 6, and 28 June with altitudes below 4.8 km and ashfall within 10 km in many areas, including La Soledad (11 km N) and Acatenango (12 km NW). During 29-30 June a 300-m-long lava flow was visible in the Las Lajas drainage on the SE flank.

Based on INSIVUMEH notices, CONRED reported that for a 30-hour period during 30 June-1 July 2015 activity at Fuego was at a high level, characterized by explosions, high-temperature pyroclastic flows (that began on 1 July), and ashfall. Ash plumes rose 4.8 km above the crater and drifted 25 km W and NW, producing ashfall in 22 local communities. An SO₂ plume drifting NW was captured by the OMI instrument on the Aura satellite on 1 July (figure 34). The majority of material deposited by pyroclastic flows was located in the Las Lajas drainage where the flow reached 4-5 km in length. People in the La Reunion area near the river bed were evacuated. Nine MODVOLC thermal alert pixels were captured on 1 July, and 10 on 2 July, corroborating the high-temperature pyroclastic flows reported by CONRED. Only single thermal alert pixels were captured after that on 14, 25, and 29 July. The Washington VAAC reports issued on 1, 2, 6, and 14 July included reports of ash emissions to 4.9 km extending up to 55 km SW.

Figure 34. An SO2 plume drifting W from Fuego on 1 July 2015 during a phase of high eruptive activity. Courtesy of NASA GSFC.

Although there were no VAAC reports issued between 14 July and 1 September 2015, the number of MODVOLC thermal alerts increased substantially during August from the previous month, with an especially large multi-pixel signature from 5 through 10 August. INSIVUMEH reported ash plumes rising to 4.2-4.6 m dispersing ash around 12 km in various directions several times during the month, as well as incandescent material rising to 200 m above the crater and sending block avalanches down the drainages on the S and W flanks.

Lava fountains, explosions, pyroclastic flows, and ashfall in surrounding areas picked up again beginning with a strong MODVOLC thermal alert signal on 30 August and lasted through 2 September. By the time activity decreased that day, the remnants of three lava flows were visible in the Santa Teresa, Trinidad and Las Lajas drainages on the S and SE flanks. There were no MODVOLC thermal alerts between 2 and 27 September, and no Washington VAAC reports between 2 and 29 September. During this time, INSIVUMEH reported moderate levels of explosions with ash-bearing plumes rising to 4.5 km altitude and drifting 10-12 km from the summit, dispersing minor amounts of ash to the villages within that radius.

The next pulse of activity began with three MODVOLC thermal alert pixels on 27 September 2015. Lava flows were persistent during October, as reported by INSIVUMEH and evidenced by the number of MODVOLC thermal alert pixels. Multi-pixels days were common between 27 September and 14 October, and again from 23-28 October. INSIVUMEH first reported lava flows on 4 October that were 400 m long in the Santa Teresa drainage and 300 m long in the Trinidad canyon. By 8 October the Trinidad canyon flow was 1.5 km long; the Santa Teresa canyon flow reached 1 km from the crater by 13 October. These flows were fed by Strombolian activity that had increased on 10 October, sending incandescent material 200 m above the crater (figure 35). Lava fountains during 13-14 October produced another lava flow in the Santa Teresa canyon that was 500 m long by 20 October.

Figure 35. Lava flows in the Santa Teresa drainage at Fuego fed by Strombolian activity from the summit vents, 10 October 2015. View is from Yepocapa, 8 km NW. Courtesy of INSIVUMEH (http://www.insivumeh.gob.gt/erupcion_volcan_fuego.html)

A new surge of activity beginning on 21 October through the end of the month generated 200-300 m-high lava fountains that advanced lava flows 1.5 km down the Santa Teresa, Trinidad, and Las Lajas drainages. Ash plumes during October reported by INSIVUMEH rose 450-1,200 m above the crater, dispersing ash to villages 10-12 km S and SW on several occasions; no ash plumes were observed by the Washington VAAC until 26 October when a plume rose to 5.2 km (1.4 km above the summit) and drifted SW.

On 1 November, the Washington VAAC reported discrete ash emissions at 5.2 km altitude drifting SW that dissipated within 50 km early in the day, and a second slightly higher plume later in the day that also dissipated quickly. Most of the rest of the ash plumes at the beginning of November were under 1 km in height above the summit and dispersed ash to communities within 12 km SW. Block avalanches from a 200-m-high fountain of incandescent ejecta traveled down Santa Teresa, Trinidad, and Las Lajas drainages early in the month.

New lava flows were reported in the Las Lajas and El Jute drainages beginning on 9 November 2015. A strong multipixel MODVOLC signal was captured during 7-11 November, including 12 pixels on 9 November. By 10 November the lava flows were 2.5 km long, and incandescent material was ejected 300 m high. Ashfall was reported in Panimache I and II, Morelia, Santa Sofia, El Porvenir, Sangre de Cristo and the municipality of San Pedro Yepocapa. Pyroclastic flows also descended the E flank on 10 November. The Washington VAAC reported an ash plume that morning below 5.2 km altitude drifting WSW at 15 knots. The plume was visible in satellite imagery extending for 110 km to the coast, and possibly out over the ocean to 185 km. By late in the day, ongoing lava flows and rockfalls were causing ash to rise to 6.1 km altitude and the winds were moving the ash out of the valleys around 140 km SW of Fuego. Ashfall was reported from communities as far as 90 km to the west including San Andrés Osuna (12 km SW), El Zapote (10 km S), Siquinala (20 km SW), Santa Lucia Cotzumalguapa (22 km SW), Mazatenango (87 km W), Patulul (30 km W), and Cocales (35 km W).

Strong multi-pixel MODVOLC signatures increased again between 25 November and 2 December and correlate with INSIVUMEH's reporting of large and strong explosions and new lava flows beginning on 29 November. The Washington VAAC reported ongoing emissions to 5.2 km altitude on 25 November which dissipated quickly. INSIVUMEH noted lava fountains rising to 500 m above the crater, feeding four lava flows that traveled 3 km down the Ceniza, Trinidad, Las Lajas, and Santa Teresa drainages on 29 November. A fifth lava flow was seen the next day along with small pyroclastic flows in the Honda drainage on the E flank. A new pulse of ash emissions to 5.5 km began on 30 November extending 45 km SW from the summit and continued through 1 December drifting more to the NW into S Mexico before dissipating.

Discrete ash emissions to 5.5 km altitude which quickly dissipated were observed in webcam imagery on 9 December 2015. Late the following day, another plume was spotted at the same elevation drifting 37 km NNE. Activity increased during the night of 14-15 December, characterized by an increased number of explosions (4-6 per hour). Ash plumes rose almost 1 km high and drifted 10-15 km NE, E, and SE. Two 800-m-long lava flows were active in the Trinidad and Santa Teresa drainages. Strong multi-pixel MODVOLC alerts appeared daily from 11-18 December. The Washington VAAC observed ongoing emissions on 16 December at 5.2 km altitude; they drifted as far as 280 km SW of Fuego. Lava flows remained active in the Las Lajas, Trinidad, and Santa Teresa drainages. Activity decreased toward the end of the month with modest ash emissions rising less than a kilometer above the summit, and incandescent material rising 150 m above the crater.

Table 12. Towns and drainages around Fuego and their distance and direction from the summit.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.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/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/).

Previously reported activity at Ibu through November 2015 included shallow seismicity, lava dome growth on the N part of the crater, and occasional white-to-gray plumes rising as high as 500 m above the summit (BGVN 40:11). This report, describing activity through early March 2017, is based on information from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and the Darwin Volcanic Ash Advisory Centre (VAAC).

During the reporting period (at least through 22 Aug 2016), the Alert Level remained at 2 (on a scale of 1-4) and the public was warned to stay at least 2 km away from the active crater, and 3.5 km away on the N side. Inclement weather often prevented visual observation.

According to PVMBG reports, similar activity to that previously described in 2013-2015 continued through at least 22 August 2016. Seismicity was dominated by signals indicating surface or near-surface activity, and the lava dome in the N part of the crater continued to grow. Occasional plumes (described variously as white-to-medium gray, gray-to-gray black, and ash) rose to altitudes of 1.5-2.4 km (200-1,100 m above the summit crater).

Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were observed infrequently during the reporting period. Hotspots were observed on seven days in December 2015, but only 1-3 days per month for subsequent months through March 2017. No hotspots were recorded during December 2016 and February 2017. In contrast, the MIROVA detection system recorded numerous anomalies between April 2016 and March 2017 (figure 10), almost all of which were at least 1 km from the volcano and of low power output.

Figure 10. Thermal anomalies recorded at Ibu by the MIROVA system using MODIS infrared satellite data for the year ending 10 March 2017. Courtesy of MIROVA.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); 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/).

Guatemala's Pacaya volcano has a 450-year record of frequent historical observations of activity, in addition to confirmed radiocarbon dating of eruptions over 1,500 years. Its location approximately 30 km S of the capital of Guatemala City makes it both a popular tourist attraction as a National Park, and a hazard to the several million people that live within 50 km. Activity during the last 50 years has been characterized by extensive lava flows, bomb-laden Strombolian explosions, and ash plumes that have dispersed ash to cities and towns across the region.

Major lava flows and Strombolian activity in January and early March 2014 were previously reported (BGVN 42:04). This report describes activity for the remainder of 2014 through 2016. Information was provided by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), the Coordinadora Nacional para la Reducción de Desastres (CONRED) of Guatemala, and the Washington Volcanic Ash Advisory Center (VAAC), which provides air traffic advisories. Satellite imagery and visitors to the volcano also provided evidence of activity.

Ash plumes were intermittent for the remainder of 2014 after the activity of January and March; they were reported on 10 April, 25 and 28 August, during 11-18 November, and on 22 December. Episodes of ash emissions in mid- and late January 2015 and up to 17 February marked the end of this episode. Renewed activity on 8 June 2015 included intermittent ash plumes and incandescence observed at the summit. Ash plumes were intermittent until 22 September but observations of incandescence grew more frequent and intense during the rest of the year. A small intra-crater cone was growing in mid-December 2015 at the center of MacKenney Crater. Strombolian activity from the cone continued throughout 2016. It was most active during June and July, depositing new ejecta on the N and W flanks of the volcano. Although it had quieted down by the end of the year, persistent degassing, steam plumes, and occasional incandescence were still observed. The intra-crater cone had filled much of MacKenney Crater by December 2016.

Activity during April-December 2014. Extensive lava flows in January and early March 2014 affected large areas on both the N and S flanks of Pacaya (BGVN 42:04). The volcano quieted down significantly after the first week in March. A plume with minor ash was observed rising to 2.6 km altitude and drifting approximately 1 km S and SW on 10 April. During the rest of April through late August 2014 only white and blueish-white plumes rose 50-150 m above the summit, and no thermal anomalies were reported.

INSIVUMEH reported on 25 and 28 August 2014 that small bursts of gray ash rose 200-700 m above the summit and drifted S and SW. Otherwise, only plumes of steam and magmatic gases were observed during August through early November. Small bursts with minor amounts of ash were reported again on 11, 16, and 18 November 2014 that rose a few hundred meters above the summit and drifted S and SW. Incandescence was observed at the summit crater on 9 December. Only steam and gas plumes were observed by INSIVUMEH for the rest of December 2014, but the Washington VAAC reported an emission of gases and possible minor ash to 3.4 km altitude (900 m above the summit) on 22 December drifting S for a few hours before dissipating.

Activity during 2015. Renewed seismic activity with numerous small ash emissions was reported in a special bulletin by INSIVUMEH on 14 January 2015. They noted that about 24 weak explosions with ash had occurred in recent days. In another special notice issued on 28 January, they reported that ash emissions originating from MacKenney Crater had drifted 4 km S and SW. They noted as many as 40 ash explosions within the previous 24 hours. Gas plumes were also observed from an area on the S flank.

Weak ash and steam emissions rising a few hundred meters above the summit were also reported on 1 February 2015. MODVOLC showed three thermal alert pixels on the SE flank on 10 February, but they were near an area of agricultural development and likely not be related to volcanism. Only steam emissions were reported by INSIVUMEH until 13 February when a new series of weak explosions sent dark gray ash plumes 500-700 m above the crater; the plumes were observed until 17 February. After this, INSIVUMEH reported only minor seismicity and steam-and-gas plumes through 5 June. Three MODVOLC pixels on 25 March, located on the E flank, were in agriculture areas similar to the February alerts.

Continuing ash explosions every three or four hours indicated renewed activity on 8 June 2015, as reported by INSIVUMEH. The seismic network detected signals consistent with collapse inside the crater along with ash emissions. Plumes with gas and minor ash were reported on 14, 16, and 18 June rising 50 m above the crater. Increased seismicity on 18 June led to noises that were audible 3 km away. For the rest of June and into the first week of July, ash was frequently dispersed around the crater from gas-and-ash plumes, and incandescence was visible on clear nights. Incandescence from MacKenny crater was reported again on 23 August. CONRED also reported that the low-frequency tremors that started in mid-June were continuing in mid-August.

Blue and white plumes, along with minor ash emissions, were observed drifting W of the summit crater on 1 September 2015, and the low-frequency tremors and incandescence continued on clear nights for the rest of the month. Two ash plumes, on 11 and 22 September, rose to 700 and 900 m above the crater. Although only a single MODVOLC thermal alert pixel appeared near the summit on 2 October, numerous observations of incandescence were made by INSIVUMEH during the month. Cloudy weather limited observations of incandescence during November to only the first and last weeks, but observations were nearly continuous during December.

A visit to the summit of Pacaya on 22 December 2015 by Volcano Discovery provided evidence of the activity responsible for the incandescence observed during the previous months (figure 71). During stronger intervals of activity, lava bombs were ejected 150-200 m above the crater rim, but generally fell back within the crater. A few fresh (days-to-weeks-old) bombs were seen near the eastern crater rim. Around the main vent at the bottom of the approximately 100-m-deep crater, a small cone, about 15 m tall, had formed. Bubbles of lava burst into fragments of spatter from the vent, building up the cone (figure 72). A small secondary vent at the eastern side of the cone also showed occasional spattering, mainly during phases of elevated activity at the main vent. Parts of the crater floor were covered by recent lava flows.

Figure 71. A small cinder cone with a vent 2-3 m wide is active on the floor of MacKenney Crater at the summit of Pacaya on 22 December 2015. Courtesy of Volcano Discovery (photo by Tom Pfeiffer).

Figure 72. Lava bubbles inside the cinder cone at Pacaya burst into thousands of glowing fragments on 22 December 2015, building the cinder cone. Courtesy of Volcano Discovery (photo by Tom Pfeiffer).

Activity during 2016. INSIVUMEH reported that during January 2016, Pacaya exhibited activity similar to 2015. Incandescence was visible at night during 20-27 January, and during this time a hot spot was captured at the summit in a Landsat image. A small collapse on the NW side of the inner crater generated a column of gray emissions that rose to 3 km altitude (500 m above the summit) on 20 January. A Landsat image on 12 February again showed incandescence and a steam plume rising 100 m above the crater. Incandescence reappeared on 20 February and persisted for the remainder of the month. Emissions from the main crater were primarily magmatic SO₂ and steam; they generally rose 50-150 m above the crater and drifted N.

Incandescent activity at MacKenney Crater increased during March and April 2016. Landsat images showed incandescence aligned along a NW-SE trending fissure within the crater. MODVOLC thermal alert pixels appeared on 1, 19, and 26 March and again on 10 April; the 10 April thermal alert was readily visible as a hotspot in satellite imagery (figure 73). INSIVUMEH noted that the intra-crater cone continued to grow during March and April. The MIROVA Log Radiative Power data also registered a number of thermal anomalies during March and April (figure 74).

Figure 73. Incandescence at the MacKenney Crater at Pacaya taken with the European Space Agency's Sentinel 2 satellite on 10 April 2016. Image courtesy INSIVUMEH and ESA (Reporte Mensual, Volcan Pacaya, April 2016).

Figure 74. MIROVA Log Radiative Power data for Pacaya for the year ending 28 December 2016. Thermal anomalies within 5 km of the summit were reported a number of times during January-April, and again during June and July. Courtesy of MIROVA.

During May 2016 the intra-crater cone continued to grow, and minor Strombolian activity during the night was observed regularly by INSIVUMEH. Most of the activity occurred on the N flank, with some incandescence on the W flank at the end of the month. Seismicity continued at modest levels with occasional explosions resulting from minor collapses of the crater wall. Strombolian activity increased during June, although the degassing plume did not reach more than 400 m above the crater. The webcam recorded incandescent material accumulating on the NW flank.

Seismic activity during July 2016 remained constant, caused by degassing and Strombolian explosions which were observed during 7-10 July. Material was ejected 75 m above the crater during 23-24 July. Views of Pacaya from the NW and the S during July and August revealed minor fumarolic activity from the summit as well as evidence of the extensive January-March 2014 lava flows (figures 75 and 76). Incandescence continued to be observed at night and in satellite images during July and August, with debris from the Strombolian activity concentrated on the N and NW flanks.

Figure 75. View of Pacaya on 18 July 2016 from La Meseta (the Mesa) on the NW flank showing lava flows from early 2014 and steam emissions from the summit. Courtesy of INSIVUMEH (Reporte Mensual, Volcan Pacaya, July 2016).

Figure 76. View of Pacaya from Los Pocitos, 5 km S of the summit, on 17 August 2016 showing steam plume drifting SW and part of the extensive 2014 lava flow in the foreground. Courtesy of INSIVUMEH (Report Mensual, Volcan Pacaya, August 2016).

By October 2016, observations of incandescence at the summit were less frequent. INSIVUMEH noted that intermittent incandescence continued for the rest of 2016 with new material accumulating within MacKenney Crater. Visitors to the intra-crater cone in early December 2016 noted strong degassing of steam, magmatic gases, and possible ash, but no Strombolian activity. The intra-caldera cone was significantly larger than when observed a year earlier (figure 77).

Figure 77. Intra-crater cone at Pacaya in early December 2016. Courtesy of Volcano Discovery (Image from Mynor Marroquin via @ClimaEnGuate / Twitter).

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php); 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/); European Space Agency (ESA) (URL: http://www.esa.int/ESA); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/).

Although historical records of eruptive activity at Peru's Sabancaya volcano go back to 1750, there have only been a handful documented since the 1980s; activity that began in 1986 was the first recorded in over 200 years. During the last period of substantial ash eruptions between 1990 and 1998 ashfall deposits up to 4 cm thick were reported 8 km E of the volcano. Evidence for minor ash-emitting events was reported in 2000 and 2003. Intermittent seismic unrest and fumarolic emissions characterized activity from late 2012 through 2015. Seismically detected explosions during August 2014 led to releases of SO₂ gases and steam plumes, some as high as 2 km, along with possible minor volcanic ash. Possible minor volcanic ash emissions were also mentioned by Peruvian authorities and pilot reports between September and December 2014 but there were no confirmed reports of ash emissions during this period. A crater inspection during 9-10 July 2015 found trace amounts of ash at the crater that contained crystals of plagioclase, biotite, and amphibole, along with fresh volcanic glass. These were interpreted by the volcanologists to represent minor ash emissions during recent weeks.

Unrest with steam plumes and variable seismicity continued during 2016 until 6 November when continuous ash-bearing explosions began. Activity during 2016 through February 2017 is covered in this report with information from the two Peruvian observatories that monitor the volcano: Instituto Geofisico del Peru - Observatoria Vulcanologico del Sur (IGP-OVS), and Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico) (OVI-INGEMMET). Aviation reports and notices come from the Buenos Aires Volcanic Ash Advisory Center (VAAC), and satellite data is reported from several sources.

Sabancaya maintained a level of seismic and fumarolic unrest through most of 2016, similar to levels recorded in 2014 and 2015, with almost constant water-vapor and SO₂ plumes rising from the crater. Additionally, tectonic (not volcanic) seismicity caused damage and fatalities in nearby villages. An explosion on 27 August 2016 did not produce ash, but new areas of fumarolic activity on the N flank were observed around this time. Hybrid seismic events related to the movement of magma, and SO₂ emissions, increased noticeably during September and October 2016. An explosive eruption with numerous ash plumes began on 6 November 2016. Continuous ash emissions with plume heights exceeding 10 km altitude were recorded several times through February 2017. Thermal anomalies were first measured in satellite data in early November, along with numerous significant SO₂ plumes.

Activity during January-October 2016. Heights of plumes consisting of water vapor and minor magmatic gases generally decreased during January 2016, from 1,800 m to less than 1,200 m by the month's end. Seismic activity was generally low in terms of both numbers of events and magnitude. The daily number of events ranged from 8 to 20, and the largest event, a M 4.0, was registered on 29 January.

Plume heights continued declining in February, from 1,000 m during the first week to 400-800 m by the end of the month. During March, April, and May the heights of steam and SO₂ plumes ranged from 200 to 1,300 m above the crater, and values of SO₂ flux ranged from 600 to 1,500 metric tons per day (t/d). These values increased only slightly in July and August; plumes rose 2,000 m above the crater rim and SO₂ emissions were as high as 2,600 t/d.

Seismicity continued at low levels through late August. Three significant tectonic earthquakes in mid-August were not related to volcanic activity, but the earthquake 25 km NE of Sabancaya on the Ichupampa fault on 14 August caused at least four fatalities, and numerous aftershocks were recorded in the region. A spike in SO₂ emissions at the volcano to 4,030 t/d occurred shortly after the earthquake.

On 27 August 2016 there was a hybrid-type seismic event that IGP-OVS interpreted as an explosion of 72 MJ (Megajoules) of energy. An official statement from the Scientific and Technical Committee for Risk Management (IGP-OVS, OVI-INGEMMET, and others) issued on 6 September noted that "dense gray gases reached 1,000 m above the crater and drifted E." However, no VAAC reports were issued, and ash was not mentioned in the OVI INGEMMET weekly report.

During the last two weeks of August, two large zones of new fumarolic activity were detected in satellite imagery. OVI visited the site on 25 August, and IGP-OVS visited on 1 September 2016. The scientists observed areas of increased fumarolic emissions outside of the crater on the NE and NW flanks of the volcano (figure 19). The first zone was located on the NW flank and extended from the vicinity of the crater down to 5,700 m elevation, while the second area was located on the NE flank at about 5,600 m. Both areas follow a NW-SE trend. The flux of SO₂ increased to values greater than 4,000 t/d at the end of August.

Figure 19. New areas of fumarolic activity at Sabancaya, August 2016. Top: Two large fumarolic areas photographed on 1 September 2016 that appeared on the flanks during late August. The main zone was located on the NW flank and extended from the vicinity of the crater down to 5,700 m elevation, while the second area was located on the NE flank at about 5,600 m. Courtesy of IGP-OVS (Sabancaya Report 27, 1 September 2016) Bottom: Google Earth image showing location of fumarolic fields. A, B, C, and D are part of the NW flank field and E is the NE flank field. Courtesy of OVI-INGEMMET (Special Report, 1 September 2016).

OVI-INGEMMET reported an increase in the total number of seismic events during September 2016, especially hybrid-type events, along with generally lower plume heights, but increased emissions of SO₂. IGP-OVS noted a swarm of hybrid-type seismic events on 27 September distinct from the distal tectonic-related events of the previous month, and indicative of an increase in volcanic activity. IGP-OVS returned to Sabancaya on 28 September 2016 to gather temperature measurements at the new fumarole areas. A NW-SE trending belt on the NE side of the volcano had temperature readings between 71° and 91°C.

At the beginning of October, water vapor and SO₂ gas plumes rose as high as 2,000 m above the crater, and the SO₂ flux was over 3,000 t/d. Volcanic seismicity increased from 220 earthquakes per day during the first week to 470 during the second week. SO₂ emissions continued to increase and by 22 October were at 7,173 t/d.

From 9 January through 3 November 2016 the Buenos Aires VAAC issued 52 reports with pilot observations of ash. The VAAC was unable to confirm the presence of ash in emissions and instead described only water vapor or magmatic gases recorded via the web camera. There were no MODIS thermal anomalies shown by the MODVOLC or MIROVA systems from January 2014 through October 2016.

Activity during November 2016-February 2017. OVI-INGEMMET reported an eruption beginning at 2040 local time on 6 November 2016 (0140 on 7 November UTC) that started with an explosion and was followed by the continuous emission of low volume ash that rose up to 1,500 m above the crater rim (about 7,500 m altitude) (figure 20).

Figure 20. The beginning of the eruption at Sabancaya, in the province of Caylloma in Arequipa, on 6 November 2016. Courtesy OVI-INGEMMET (Sabancaya 2016 Weekly Report 45).

Several types of volcanic-related seismic events continued to increase in number and intensity during November and December. The eruption exhibited an average of 39 daily explosive events with ash plumes (figures 21, 22, and 23) between 7 November and 15 December. There were 63 explosions on 30 November, and between 5 and 11 December there were 328 explosions.

Figure 21. Ash plume rising over 4,000 m above the summit (5, 967 m elevation) at Sabancaya, 24 November 2016. Courtesy OVI-OVS (2016 Sabancaya Joint OVI-OVS Weekly Report 2, 21-27 November).

Figure 22. Plume heights and compositions at Sabancaya from 28 October through 27 November 2016. Ash emissions began on 6 November, and continued to increase in density and plume height throughout the month. White circles represent water vapor, light gray are ash, dark gray are abundant ash, blue are SO2 gas, and yellow are sulfur aerosols. Courtesy OVI-OVS (2016 Sabancaya Joint OVI-OVS Weekly Report 2, 21-27 November).

Figure 23. NASA Earth Observatory images of ash plumes from Sabancaya on 16 and 19 November 2016. The bright area to the SW in the 16 November image is snow near the peak of Mount Ampato, which is covered with ash in the 19 November image. The 16 November image was acquired by a multispectral imager on the European Space Agency's Sentinel 2 spacecraft. The Operational Land Imager (OLI) on Landsat 8 captured the November 19 image. Courtesy of NASA Earth Observatory.

Ash emissions were continuous from the beginning of the eruption through mid-December, with heights up to 4.5 km (10.5 km altitude) above the crater, according to the Scientific-Technical Committee of government scientists monitoring the eruption. Ashfall several millimeters thick was recorded in areas as far as 40 km away. During the first weeks of the eruption ash fell mainly to the E and NE on the villages of Maca, Achoma, Yanque and Chivay (18-30 km NE). Later in December, ashfall was reported W and NW in the villages of Huambo (28 km W), Cabanaconde (22 km NW), and Pinchollo (18 km N). On 26 December, ashfall was again reported in the villages of Cabanaconde, Pinchollo, and Tapay (25 km NW) to the NW and N, and Lari and Madrigal (20 km NE), Maca, and areas of Achoma to the NE. The seismic energy released from tremors and explosive events continued to increase throughout November into December (figures 24 and 25).

Figure 24. Seismic energy and types of seismic events at Sabancaya, 6 November-8 December 2016. HIB are hybrid-type seismic events, TRE are tremors, EXP are explosions. Black line represents cumulative energy in Megajoules (MJ). Y axis is daily seismic energy on the left and cumulative energy on the right. Stars represent the period of continuous explosions. Courtesy of OVI-OVS (2016 Sabancaya Joint OVI-OVS Weekly Report 4, 5-11 December).

Figure 25. Web camera image of ash-and-steam plume at Sabancaya, 9 December 2016. Courtesy of OVI-OVS (2016 Sabancaya Joint OVI-OVS Weekly Report 4, 5-11 December).

Beginning on 21 December there was a notable increase in seismicity (mainly of hybrid events), in the number (up to 52 per day) and height of plumes, and ash emissions. These changes led the Scientific-Technical Committee to raise the Volcanic Warning Level from Yellow to Orange (2 to 3 on a 4-level scale) on 28 December, warning people to remain more than 12 km from the crater (figures 26 and 27). A small lahar affected the area of Pinchollo (18 km N) on 3 January 2017.

Figure 26. Dense ash cloud at Sabancaya, 26 December 2016. Increasing intensity of seismicity and number of explosions led to an increase in the Volcano Warning Level on 28 December. Courtesy of OVI-OVS (Informe Especial No. 01-2017).

Figure 27. Seismic energy released by Sabancaya between 5 December 2016 and 4 January 2017. Note increasing energy of the explosions in early January. Courtesy of OVI-OVS (Informe Especial No. 01-2017).

Seismicity remained high during January with long-period (LP), tremor, and hybrid-type events all continuing, and an average of 70-76 daily explosions. During the second week in January explosions peaked at an average of 84 per day. This number decreased during early February to around 20 per day but then rose back to over 40 by the end of the month. A significant number of hybrid seismic events occurred during the last week of February.

Gas-and-ash plumes rose to 4.5 km above the crater in early January, dropping back to 2-3 km for the rest of the month, before rising again to 3-4 km (9-10 km altitude) during February. In their Special Report in January 2017, the joint Scientific-Technical committee presented a map showing that ash dispersal had affected communities in nearly every direction 40 km from the summit (figure 28).

Figure 28. Area affected by ashfall (in pink) from Sabancaya as of mid-January 2017. Courtesy of OVI-OVS (Informe Especial No. 01-2017).

Buenos Aires VAAC Reports, November 2016-February 2017. The Buenos Aires VAAC first noted minor amounts of volcanic ash in emissions visible from the volcano webcam on 7 November 2016 (UTC). Ash was not identified in satellite imagery until midday 8 November when it was reported at 7.6 km altitude (about 1.7 km above the summit). Observations of continuous emissions of steam and ash were reported daily, when not obscured by weather, from then through the end of February 2017. Plume heights were commonly 7.6-8.2 km altitude, about 1.7-2.3 km above the summit. Higher plumes were also recorded a number of times during this period, including 10.3 km altitude on 17 and 23 November. The plume was clearly visible in satellite imagery on 24 November, drifting SE at 10.9 km. Plumes on 3 December rose 10 km and drifted SW; they were partially hidden by weather clouds. Pulses of volcanic ash drifting over 35 km SE at 10.6 km altitude were visible on 11 and 12 December. For most of January 2017 the plumes were obscured by weather clouds, but were visible on 6 January at 9.1 km altitude. Higher plumes were more often recorded in February; they rose continuously over 10 km from 4 to 7 February. The highest plume during the period was on 26 February, at 11.9 km, drifting SW.

Thermal anomalies in satellite data. The MIROVA thermal anomaly plot of MODIS data provided independent satellite confirmation of the beginning of the eruption. The first thermal anomaly appeared on 2 November 2016, and values increased in frequency and intensity in the subsequent weeks. Energy values reached moderate levels in early February 2017 (figure 29). The first MODVOLC thermal alert pixel for Sabancaya appeared on 6 January 2017. There were seven MODVOLC alert pixels in January and six in February, suggesting a persistent source of heat during this time.

Figure 29. Log Radiative Power values for Sabancaya between 13 March 2016 and 13 March 2017. The first MIROVA-identified thermal anomaly was on 2 November 2016, and values increased in frequency and intensity after that. Courtesy of MIROVA.

Sulfur dioxide data. Sulfur dioxide plumes from Sabancaya were captured numerous times by the OMI satellite instrument from NASA's Global Sulfur Dioxide Monitoring system between November 2016 and February 2017. They revealed significant SO₂ plumes travelling in all directions away from the summit for distances up to 200 km (figure 30).

Figure 30. SO2 plumes drifting in different directions up to 200 km from Sabancaya captured by the OMI instrument on the Aura satellite. Clockwise from top left: 7 November 2016, first day of ash eruption, plume drifting SW and S towards Arequipa; 16 November 2016, plume drifting NE toward Lake Titicaca; 25 December 2016, plume drifting WSW over the Pacific Ocean; 27 February 2017, large plume drifting S and W, corresponding to an 11.9-km-altitude ash plume reported by Buenos Aires VAAC on 26 February. Courtesy of NASA GSFC.

Geologic Background. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Information Contacts: Observatorio Volcanologico del INGEMMET, (Instituto Geológical Minero y Metalúrgico), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa (URL: http://ovi.ingemmet.gob.pe); Instituto Geofisico del Peru, Observatoria Vulcanologico del Sur (IGP-OVS), Arequipa Regional Office, Urb La Marina B-19, Cayma, Arequipa, Peru (URL: http://ovs.igp.gob.pe/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

With hundreds of eruptive events in the 19th and early 20th centuries, and nearly continuous activity since 1967, Indonesia's Semeru is one of the world's most active volcanos. This activity has included lava flows, Vulcanian and Strombolian explosions, nuées ardentes, lava domes, and mudflows; fatalities and serious injuries occurred in 1981, 1994, 1997, and 2000.

Activity at the volcano is tracked by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, (CVGHM), the Darwin Volcanic Ash Advisor Center (VAAC), and remote sensing satellite data that provides visible imagery and thermal anomaly data. In this report, imagery and data from 2000-2009 is reviewed, along with details of activity from 2009 through March 2017.

Overview of activity since 2000. Strong evidence for continuous eruption at Semeru was gathered by satellite instruments from March 2000 through 2 January 2009. PVMBG reported ash explosions and an active lava dome in the Jonggring Seloko summit crater during early March 2009; after an ash plume on 15 March the gas and ash "gradually disappeared." A single MODVOLC thermal alert pixel was captured on 8 August 2009. PVMBG noted in their March 2010 report that the character of eruptive activity changed in April 2009 from ash-dominated explosions to emissions associated with dome growth. Only intermittent minor emissions were reported until incandescence appeared at the summit on 5 January 2010; strong thermal alert signals indicated continued lava-dome growth through November 2010. After 29 November 2010, there were no reports of unrest until small ash plumes were observed on 13 May 2011. These were followed by reports of pyroclastic flows in June, observations of the growing lava dome in September, and a new lava flow in December 2011.

Pyroclastic flows in January and February 2012 accompanied observations of incandescence and thermal alerts detected by satellite through mid-May. Small ash plumes from the summit area and incandescence at the lava dome were observed on 19 July 2012, but no further activity was noted until June 2013 when thermal alerts reappeared for about a month. An ash plume was reported by the Darwin VAAC in October 2013 and a thermal alert pixel appeared on 29 November 2013. After this, another break in activity occurred until the following spring.

PVMBG reported 22 incidents of emissions that were white to gray during March 2014, and 21 during 1-27 April 2014. They also reported eight explosions during April with white to gray emissions. A new, longer-lasting eruptive episode began with ash plumes, an incandescent lava flow, and rock avalanches that descended from the summit lava dome on 26 April 2014.

Thermal alert pixels reappeared on 5 June 2014 and remained abundant through 30 July 2016. During this time, the lava dome was actively growing and a lava flow slowly advanced down the S-flank Kembar ravine. Ash plume eruptions increased in frequency during 2015, and during 2016 they became large enough to produce aviation advisories from the Darwin VAAC several times. An image of the incandescent lava flow on the S flank in September 2016 and a thermal alert pixel in November 2016 suggested continuing dome growth through the end of the year. An ash plume reported by the Darwin VAAC on 9 January 2017 indicated continuing activity.

Satellite data from 2000-2009. From March 2000 through 2 January 2009, the University of Hawai'i's MODVOLC system recorded numerous thermally elevated pixels captured by the MODIS satellite instrument every single month except for February 2002. Explosive activity, lava avalanches, and pyroclastic flows were the sources of these abundant alerts (see previous BGVN reports). A NASA image from 14 June 2004 available in Google Earth clearly shows an ash plume erupting from Semeru and abundant ash deposited around its flanks (figure 20).

Figure 20. An ash plume rising from Semeru on 14 June 2004. Abundant recent ash deposits surround the summit, and steep ravines that carry pyroclastic flows and lahars are clearly visible. The ash plume is directly over the summit crater, and remnants of an earlier plume have drifted NW to the upper left edge of the image. Courtesy of Google Earth.

Imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite also captured images in 2006 and 2007 that demonstrate the characteristics of ash explosions from Semeru. They commonly occur as discrete puffs at regular intervals and can maintain their integrity for tens of kilometers from the volcano (figure 21).

Figure 21. Two NASA-EO satellite images from MODIS on 15 June 2006 and 3 May 2007 show the often pulsing nature of ash emissions from Semeru. The discrete puffs can maintain their integrity for tens of kilometers from the volcano. Prevailing winds most commonly send ash to the W. Courtesy of NASA-EO.

Activity during January 2009-July 2012. The style of activity changed during 2009. MODVOLC recorded only a single thermal alert pixel on 2 January 2009, and nothing after that until August 2009. PVMBG maintains a four-level Volcano Alert system; Level 1 (Normal) is the lowest, followed by Level II (Alert), Level III (Standby), and Level IV (Beware). They reported that typical activity during Alert Level II ("Alert") conditions were ash eruptions at 20-30 minute intervals with plumes rising 100-400 m from the summit. They noted a loud explosion on 8 February 2009, and another on 6 March that was accompanied by lightning. The 6 March event led PVMBG to increase the Alert Level to III (Standby) in their 6 March 2009 report. This activity was followed a few days later by an ash eruption, reported by the Darwin VAAC, with a plume that rose to 4.6 km altitude. After another ash emission on 15 March that rose 600 m above the crater, ash emissions "gradually disappeared" and seismicity decreased, according to a 17 July 2009 report from PVMBG; the Alert Level was then lowered back to II.

A single MODVOLC thermal alert pixel was recorded on the NW flank on 8 August 2009. In their next report in March 2010, PVMBG noted that from November 2009 through February 2010 visibility was generally poor due to weather, but there were occasional undescribed emissions that rose 50-500 m above the summit. They reported that the pattern of activity between April 2009 and 1 March 2010 changed from being dominated by ash eruptions to regular low-level emissions.

Incandescence from the summit on 5 January 2010 was followed by a MODVOLC thermal alert on 21 January. PVMBG reported a new lava flow on 25 February, which by 28 February had traveled 750 m. Rock avalanches from lava flows were reported during February (BGVN 35:08), September, and November 2010 (BGVN 37:04). Thermal alerts increased in number during April and May, before tapering off and ending on 28 November 2010. In their 4 November report PVMBG kept the Alert Level at II but noted an increase in lava-dome growth at the summit. Ash plumes were also observed by the Darwin VAAC rising to 4.6 km and drifting 75-110 km N and NW during 18-19 November.

No activity was reported between 29 November 2010 and 13 May 2011. Evidence for activity beginning again in May comes from a report by Volcano Discovery of 2-3 small ash eruptions per day during 13- 17 May (figure 22). MODVOLC thermal alert pixels reappeared on 2 June and were also noted on 15 June and 1 July. PVMBG reported eruptions of pyroclastic material on 9, 14, and 17 June. Volcano Discovery reported a growing lava dome on 1 September with 3-4 ash explosions per day during the first two weeks of September. MODVOLC thermal alerts were recorded on 5 and 7 October. PVMBG noted that seismicity had increased beginning on 29 December 2011, which was accompanied by dense white-and-gray plumes rising to 600 m above the Jonggring Seloko crater; a 300-m-long lava flow was also observed that day.

Figure 22. A view to the south of Semeru on the morning of 13 May 2011 from the Bromo-Tennger volcanic complex located 18 km N. The Bromo cone to the left is also producing an emission; Batok is in the middle foreground. Courtesy of Andi Rosati/Volcano Discovery.

Dense gray-white plumes rose 600 m and preceded an explosion on 6 January 2012; the explosion was followed by summit incandescence. Repeated observations of incandescent material flowing up to 400 m SE toward the Besuk Kembar drainage were made during the rest of January. On 2 February, just after midnight, a pyroclastic flow traveled 300 m from the Jongring Seloko crater, and by mid-morning it had traveled farther, to 2.5 km from the crater. This led PVMBG to raise the Alert Level to III that day, prohibiting people from an area on the SE slopes within 4 km of the crater (BGVN 37:04).

Numerous MODVOLC thermal alert pixels were recorded between 30 January and 21 April 2012, and a final pixel recorded on 9 May 2012. PVMBG noted that several pyroclastic flows had occurred during February, and incandescence at the summit was common through the end of March. During April, white plumes rose 500 m above the summit, seismicity decreased, and no incandescence was observed. Based on this, PVMBG lowered the Alert Level to II on 2 May 2012. A Google Earth image of the volcano taken a few weeks later on 21 May 2012 shows a clear view of the summit crater with the lava dome visible (figure 23). Volcano Discovery reported that on an expedition during 18-19 July they observed slow lava dome growth, with an incandescent area at the SW part of the dome producing small to moderate ash explosions. There were no reports of ash plumes from the Darwin VAAC during 2012.

Figure 23. DigitalGlobe satellite image of Semeru captured on 21 May 2012 with a clear view of the lava dome inside the Jonggring Seloko summit crater. Slow moving lava flows from the dome traveled down the ravine on the S flank. Courtesy of Google Earth.

Activity during June 2013-December 2015. After the 19 July 2012 update from Volcano Discovery, there was no evidence for activity at Semeru until a MODVOLC thermal alert pixel appeared on 4 June 2013, followed by four more in June and one on 7 July. No reports were issued by PVMBG during 2013. The Darwin VAAC issued a report on 18 October 2013 that a low-level ash plume had been observed, but was not visible on satellite imagery. A single MODVOLC pixel was recorded on 29 November.

The volcano was quiet again from 29 November 2013 until April 2014. PVMBG reported white-and-gray plumes drifting W from the summit 22 times during March 2014, and 21 times during April, at heights between 100 and 400 m from the summit. They also reported eight explosions during April with gray-to-white emissions rising 300-500 m and drifting W. Incandescent material was reported on 26 and 27 April, with rock avalanches sliding 300 m S from the summit. Strong multi-pixel MODVOLC alerts were recorded beginning on 5 June 2014 and continued for the rest of the year, although there were no further reports from PVMBG or the Darwin VAAC. The thermal anomalies were likely due to the growth of the lava dome. Volcano Discovery reported a lava flow from the dome in July 2014, noting that it extended a few hundred meters down Kembar ravine on the S flank in early September, when they also observed Strombolian activity in the summit crater (figure 24). They reported in November 2014 that the lava dome had a diameter of 100-200 m, and Strombolian activity ejected bombs up to 100 m above the vent (figure 25).

Figure 24. Strombolian activity in the summit crater at Semeru in mid-September 2014. Courtesy of Andi/Volcano Discovery.

Figure 25. The active lava dome at Semeru in late November 2014. Courtesy of Andi/Volcano Discovery.

Multiple MODVOLC thermal alert pixels were recorded every month during 2015. Although the volcano was very active during January-March 2015, PVMBG did not raise the Alert Level. Steam plumes rising 200-300 m above the crater were reported almost daily; explosions with gray-white plumes rising to heights of 200-500 m happened several times a week. In January, incandescent material traveled as far as 300 m down the Kembar ravine. In early March a trace amount of ash was deposited at a monitoring post near the summit after one explosion. During April 2015, ash plumes rose 200-600 m above the crater 68 times according to PVMBG; minor ashfall was reported on the flanks, and explosions were heard 30 times.

Activity increased further in May 2015, with ash plumes reported 122 times, rising 200-500 m above the summit and drifting W, NW, and SW. Incandescent rock avalanches descended as far as 1 km in the Kembar ravine. During June and July, ash emissions continued at the rate of a few per day, rising to 500 m above the summit (figure 26).

Figure 26. Ash emission at Semeru on 11 June 2015. Courtesy of Aris Yanto and Volcano Discovery.

During August 2015 ash events were reported 47 times, with plumes rising 100-600 m above the summit and drifting S. Rock avalanches were reported twice travelling 500 m down the S flank. By September, explosions with white-and-gray plumes had decreased to 45 for the month. They caused the plumes to rise 100-500 m above the summit and drift W and N. Thirty-two explosions occurred during October producing gray-to-white plumes that rose 200-500 m and drifted W. Incandescent material was observed nine times in November and traveled as far as 500 m down the S flank. Also in November, Volcano Discovery reported continuous degassing and minor explosions from the lava dome (figure 27). Strombolian activity was observed five times in December by PVMBG. Dense gray-to-white ash plumes occurred eight times during November and 20 times in December, rising 100-500 m and drifting W.

Figure 27. Active vent on the lava dome inside Semeru's summit crater in early November 2015. Courtesy of Andi/ Volcano Discovery.

Activity during 2016-March 2017. Twenty-one ash explosions were reported in January 2016, with low-level plumes rising to 500 m and drifting E, N, and W. Although activity during 2016 began similarly to 2015, the character of the eruption changed during February. Beginning in mid-February, larger ash plumes triggered a series of VAAC reports, the first in many years. Multiple MODVOLC thermal alert pixels were also captured through the end of July 2016, with another one on 24 August and 19 November, suggesting continued growth of the lava dome and intermittent lava.

The Darwin VAAC reported ash plumes five times in 2016, on 13 February, 17 April (UTC), 25 and 27 May, and 10 June. The 13 February plume rose 7.9 km (4.3 km above the summit) and drifted 45 km NE. A local news source, Tempo Nasional, also reported a pyroclastic flow the same day that traveled 4-5 km down the S and SE flanks (figure 28).

Figure 28. Pyroclastic flow from Semeru on 13 February 2016. Courtesy of David P, Tempo Nasional.

The 18 April 2016 ash plume rose to 4.3 km altitude and drifted 40 km NE. Plumes on 25 and 27 May also rose to 4.3 km but drifted 25-40 km SW. On 10 June another plume rose 3.7 km and drifted 25 km SW. Volcano Discovery observed mild Strombolian activity from the crater on 26 July, and noted that the lava flow in the southern ravine was inactive. On another visit in late September the lava flow was incandescent 1,500 m down the ravine (figure 29). The MODVOLC thermal alert pixel from 19 November suggested that the lava dome remained active.

Figure 29. The incandescent lava flow in the ravine on the S slope of Semeru on 25 September 2016. View looking north. Courtesy of Aravind P./VolcanoDiscovery.

A report from the Darwin VAAC on 9 January 2017 noted that an ash plume rose 3.9 km altitude that drifted N. A decrease in thermal activity is clear in the MIROVA thermal anomaly data for late March 2016 through late March 2017. Volcanic Radiative Power (VRP) values during April through June 2016 were in the Moderate range; they decreased in intensity (and frequency) to the Low range between July and December, and decreased again in both intensity and frequency after December 2016 (figure 30).

Figure 30. MIROVA thermal anomaly data for Semeru between 22 March 2016 and 22 March 2017. Volcanic Radiative Power (VRP) values during April through June 2016 were abundant and in the Moderate intensity range of 107-108 Watts; they decreased in intensity (and frequency) to slightly below 107 W between July and December, and decreased again in both intensity and frequency after December 2016. Courtesy of MIROVA.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); 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/); Volcano Discovery, https://www.volcanodiscovery.com; 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/); Tempo Nasional, https://nasional.tempo.co, https://nasional.tempo.co/read/news/2016/02/14/058744712/ini-yang-jadi-penyebab-guguran-awan-panas-di-gunung-semeru.

Abundant ash emissions, Strombolian activity, pyroclastic flows, lahars, and a few lava flows have all been documented at Tungurahua, which lies in the center of Ecuador. Historic observations are recorded back to 1557, and radiocarbon dates are as old as 7750 BCE. Prior to renewed activity in 1999, the last major eruption had occurred during 1916-1918. Since 1999, there have been numerous eruptive episodes, but only a few with breaks in activity longer than three months. Our last bulletin report (BGVN 40:03) covered the first part of the eruption that began on 22 November 2010. This report details activity from November 2011 through December of 2014. Tungurahua is monitored by the Observatorio del Volcán Tungurahua (OVT) of the Instituto Geofísico (IG) of Ecuador, and aviation alerts are reported by the Washington Volcanic Ash Advisory Center (VAAC).

Summary of November 2010-December 2014 activity. After a period of quiescence from 29 July through 21 November 2010, a new eruption began with a series of ash explosions and Strombolian activity on 22 November. Explosions continued through 25 December 2010 (BGVN 40:03), and emissions containing ash continued through 2 January 2011. A new eruption with tremor and ash emissions began on 20 April 2011; explosions with substantial ash plumes occurred on 22 April. Strombolian activity was frequent, and ashfall affected numerous communities within 10 km for the next five weeks. This episode ended with explosions and ash plumes on 21 May (BGVN 40:03), followed by ashfall reported to the SW through 26 May 2011. After damaging lahars at the end of May, Tungurahua was quiet until November 2011.

Volcanic activity between November 2011 and December 2014 occurred in eight discrete episodes (table 19). The length of these episodes ranged from 3 weeks to 9 months, and the lengths of the breaks between them lasted from 4 weeks to 3 months. Ash plumes rising several kilometers above the 5-km-high summit and ashfall in communities tens of kilometers from the volcano characterized each episode. Strombolian activity also sent incandescent blocks down the flanks hundreds of meters, pyroclastic flows traveled several kilometers down the ravines, and lahars during the wet seasons flooded drainages and frequently damaged roadways. A lava flow several hundred meters long descended the upper W flank in April 2014.

Table 19. Episodes of activity at Tungurahua, November 2011 through December 2014. These episodes are based on reported activity as described in this report, and may not correspond to current or previous "Eruptive Episodes" identified by IG.

Hundreds of ash plumes were emitted over this time period. Nine times, the ash plumes were recorded at altitudes over 10 km (more than 5 km above the summit) (table 20), with the highest on 4 April 2014 rising to 15.2 km altitude (50,000 ft).

Table 20. Ash plumes over 10 km altitude recorded at Tungurahua between November 2011 and December 2014.

Activity during May 2011-September 2012. After loud explosions and ash emissions on 21 May 2011, constant rains at the end of May caused lahars and muddy water to descend the ravines of Tungurahua (BGVN 40:03). Ashfall was reported on 26 May, although cloud cover prevented observations of plumes. No further ash emissions or thermal anomalies were confirmed for six months. The Washington VAAC issued a volcanic ash advisory on 7 October based on a report from IG, and two additional reports on 24 October and 9 November from pilot reports. They noted that no ash was visible in satellite imagery at the time of those reports; on 9 November a revised statement from IG stated that no ash emissions had occurred since June.

A new eruption began on 27 November 2011, when three large explosions generated pyroclastic flows and caused ashfall within 10 km in several communities. Ashfall was reported in El Manzano (8 km SW), Bilbao (8 km W), Pailitas (8 km W), Cotaló (8 km NW), and Cusúa (8 km NW) (figure 62). The first Washington VAAC reports after these explosions noted an ash plume at 10.7 km altitude (5.7 km above the summit crater) drifting WNW and extending about 100 km from the summit.

Figure 62. Isopach map of ashfall accumulation around Tungurahua on 27 November 2011. Courtesy of IG (Resumen Mensual, Actividad del Volcan Tungurahua, November 2011).

During the next three weeks, nearly constant ash emissions with plumes as high as 11 km altitude (3 December) deposited ashfall in numerous communities. In addition to those communities mentioned above, Choglontús (13 WSW), Chacauco (17 km NW), Cahuají 8 km SW), Baños (9 km N), and Vazcún also received ashfall during this period. Many residents in Cusúa, Juive (8 km NNW), Palitahua (6 km SSW), and El Manzano evacuated voluntarily. Strombolian activity sent large incandescent blocks 500 m above the crater and 1,000 m down the flanks (figure 63), and pyroclastic flows traveled as far as 2 km down the flanks (BGVN 40:03). MODVOLC thermal alerts were issued on 1 and 4 December. Substantial plumes of SO₂ were recorded by NASA's Global Sulfur Dioxide Monitoring system between 28 November and 8 December (figure 64).

Figure 63. Strombolian activity at Tungurahua sometime between 27 and 30 November 2011. Incandescent blocks reached 500 m above the crater, and traveled up to 1,000 m down the flanks. Courtesy of IG; photo by J. Bustillos, IG-EPN (Resumen Mensual, Actividad del Volcan Tungurahua, November 2011).

Figure 64. Plumes of SO2 at Tungurahua between 28 November and 5 December 2011. The plumes dispersed in multiple directions and were detected as far as 300 km from the volcano. Clockwise from top left: 28 November, 1 December, 3 December, and 5 December. Gas plumes were detected through 8 December 2011. Courtesy of NASA GSFC (Goddard Space Flight Center).

Another major explosion on 22 December sent ash plumes to 12.2 km (7.2 km above the summit), according to the Washington VAAC. Emissions continued through 28 December. Ashfall from explosions near the end of December accumulated to a depth of 2-4 mm in villages to the SW. After two weeks of quiet, with only steam plumes emitting from the summit, a series of explosions between 12 and 15 January 2012 caused ashfall in communities up to 10 km SW. Ash plumes reported by IG rose to 7 km altitude; weather clouds often prevented satellite observations. Three lahars occurred during this time; one descended the Achupashal drainage on the NW flank carrying blocks up to 1 m in diameter, and the other two descended the Juive and Pondoa drainiages farther N on the NW flank, carrying blocks 10-20 cm in diameter. Another lahar on 21 January traveled down the Pampas drainage.

A large explosion on 4 February 2012, with an ash plume reported by the Washington VAAC at 12.2 km altitude, caused lapilli and ash to fall in communities as far away as Cevallos (23 km NW). Ongoing emissions were reported five hours later; the ash cloud was observed 250 km NE near the Ecuador-Colombia border. A pyroclastic flow also descended the Achupashal drainage, and incandescent blocks traveled 1 km down the flanks. Ash plumes during 17-18 February were reported by IG to rise to 6 km altitude, although weather clouds obscured satellite images. From 23 February to 13 March, numerous ash plumes caused ashfall in most communities NW and SW of the volcano, as far as Choglontus (13 km WSW). The Washington VAAC and IG both reported plumes as high as 8.5 km altitude (3.5 km above the summit crater) drifting W and SW during this time. Strombolian activity ejected material 500 m above the crater and onto the W and NW flanks on 24 February, and another pyroclastic flow was observed in the Achupashal drainage on 4 March. Lahars descended the Chacauco (NW) and Mapayacu (SW) drainages on 11 March.

After a short break, explosions were again detected on 19 March 2012. During brief periods when the crater was visible, observers noted incandescence and a few blocks rolling 200 m down the flank. A single MODVOLC thermal alert pixel was recorded on 20 March. IG and the Washington VAAC reported numerous ash plumes between 20 and 29 March, although weather clouds and precipitation made observations difficult for much of the month. Ashfall was reported in the villages within 10 km in most directions. Heavy rain during 24-25 March generated lahars in the Pampas area to the S and caused flooding in the Puela (8 km SW), Palitahua, and Ulba (10 km NNE) sectors. Additional lahars on 1 April descended the Pingullo and Achupashal (NW) drainages, carrying material 30 cm in diameter and causing a temporary road closure.

Persistent ash emissions rising to 8 km altitude and higher began again on 9 April 2012, and occurred with few breaks until mid-June when they became more intermittent. Ashfall was commonly reported from villages within 10 km during this period. A large plume on 11 April was reported by the Washington VAAC at over 10 km altitude drifting NE and SE (figure 65); rice-sized tephra fell in Pillate (7 km W) on 22 April. Ashfall covered houses and pastures in Bilbao and Pillate on 6 May. Several plumes in early June (3, 5, 10, 11, 13) resulted in ashfall, with noise and vibrations noted, within 10 km. IG staff witnessed an ash emission on 4 June (during an overflight) that rose about 1 km above the crater and drifted E (figure 66). Numerous lahars descended drainages on the W and SW flanks in late April, and again down the W flank on 16 May. On 7 June a lahar caused a temporary closure of the Baños-Penipe highway. Smaller lahars were reported in the same area on 24 June.

Figure 65. A large ash plume at Tungurahua that rose to 10.7 km altitude on 11 April 2012 was seen using the OVT webcam located near Guadalupe, 13 km N of the crater. Two block-and-ash flows are also visible, caused by the rolling of large blocks down the flank that disperse newly fallen ash as they descend the drainage. Courtesy of IG (Informe semanal No. 15-Volcan Tungurahua, 9-15 April 2012).

Figure 66. Ash emissions and snow on the summit at Tungurahua on 4 June 2012 were observed during an IG overflight. The plume rose about 1 km and drifted E. Courtesy of IG; photo by P. Ramon OVT/IG (Informe semanal No. 23 – Volcan Tungurahua, 4-10 June 2012).

After an explosion on 27 June 2012 generated an ash plume that rose to 3 km above the crater, only small intermittent explosions with ash plumes occurred during July; steam-and-gas plumes rising up to 1 km above the summit were more common (figure 67). Incandescence at the summit and small explosions were noted on 25 July, and a few days later muddy waters carried blocks 50 cm in diameter down several S and W flank drainages. Surface and seismic activity increased noticeably during the last week of July.

Figure 67. Fresh ash covers the snow on 7 July 2012 at Tungurahua, probably from an explosion on 5 July. View is to the south. Courtesy of OVT/IG; photo by P. Ramón OVT/IG, (Informe semanal No. 27 – Volcan Tungurahua, 2-8 July 2012).

Explosions on 5 August 2012 rattled windows in nearby areas and produced sounds resembling gunshots. A plume rose 3 km above the crater and drifted W. Several periods of continuous ash emissions occurred during the rest of the month; ashfall was reported in villages within 10 km many times. Incandescent blocks that were ejected 100 m above the crater fell 500 m down the flanks on 12-13 August. Activity significantly increased with strong explosions on 17 August. The next day, five small pyroclastic flows descended the NW and NE flanks, stopping 2.5 km from the crater. Numerous explosions continued on 19 and 20 August, with steam-and-ash plumes rising 1.5-2 km above the summit and drifting W and SW. Ash fell in communities farther to the NW than in previous months, including in Igualata (20 km W), El Santuario, Hualpamba, Cevallos (23 km NW), Quero (20 km NW), Mocha (25 km WNW), Santa Anita, and Tisaleo (29 km NW). IG scientists determined that an approximate volume of 400-500,000 cubic meters of ash was deposited within 15 km of the volcano between 10 and 20 August. The maximum deposit thicknesses were 3 mm in Yuibug, 2 mm in Pillate, 1.5 mm in Choglontús and Chontapamba, 1 mm in Cahuají, and 0.5 mm in Puela (figure 68).

Figure 68. Isopach map of ashfall accumulation around Tungurahua during 10-20 August 2012. Courtesy of IG (Boletín Especial del Volcán Tungurahua No. 4, 25 Aug 2012).

An overflight on 20 August revealed an 80-m-wide inner crater. On 21 August, 16 large explosions caused windows to rattle. Strong "cannon shots" were heard in areas as far away as Ambato (31 km NW) and Riobamba (30 km S), although noises had decreased in intensity and duration compared to the previous few days. Ash plumes rose as high as 9.7 km altitude and drifted W, and a pyroclastic flow traveled 2.5 km down the NW flank that day. MODVOLC thermal alert pixels appeared during 16-23 August. Explosions and ash plumes rising up to 4 km above the crater continued for the rest of August, along with ejected incandescent tephra and ashfall in nearby communities. IG reported that the intensity of seismic tremor and emissions decreased beginning on 21 August.

NASA's Global Sulfur Dioxide Monitoring system captured SO₂ plumes during 13-21 August, and again from 31 August to 3 September. An explosion on 3 September produced an ash plume that rose 300 m above the crater; two MODVOLC thermal alerts also appeared that day. A final ash plume was reported by IG on 4 September rising to 6.7 km altitude (1.7 km above the summit), but dense cloud cover prevented satellite observation. No more ash plumes were reported until 14 December 2012.

Activity during December 2012-January 2013. A major rainfall event on 1 December generated a large lahar that descended the Vazcún drainage on the N flank, causing an evacuation of people at the El Salado resort (8 km N) before the 6-m-deep lahar that carried 3-m-diameter blocks reached the area. An increase in seismicity beginning on 12 December preceded a large explosion on 14 December. The explosion created an ash plume, identified in satellite imagery by the Washington VAAC, that rose to 7.9 km altitude. The leading edge of the 10-km-wide, detached plume was 15 km SE of the summit. Pyroclastic flows traveled down the SW flank. A smaller ash plume the next day caused a trace of ashfall in Runtún (6 km NNE).

Three large explosions on 16 December 2012 ejected incandescent blocks and expelled an ash plume, containing lightning, that rose to 12.2 km altitude (7.2 km above the summit) (figure 69). The soundwaves from the explosion reportedly broke the windows of the church of Cusúa. The Washington VAAC identified the plume in satellite imagery extending up to 140 km NW, and 110 km NE at a lower altitude of 7.9 km. Ashfall was reported up to 31 km NW from Tungurahua, in Cotaló (8 km NW), Pondoa (8 km N), Runtún, and Pillate (8 km W). More specifically, coarse-grained ash fell in Baños (9 km N), Vascún, and Ulba (NNE), and medium-to-fine-grained ash fell in Palitahua (S), Choglontús (SW), El Manzano (8 km SW), Capil, Guadalupe Observatory (13 km N), Cevallos (23 km NW), Tisaleo (29 km NW), Ambato (31 km NW), Patate (NW), Píllaro, Pelileo (8 km N), Salcedo, and Pujilí, Latacunga, Rio Verde, Agoyán, and Palora.

Figure 69. Ash plume and pyroclastic flows from explosions at Tungurahua at 0553 on 16 December 2012. View to the south from the OVT webcam, located near Guadalupe, about 13 km N of the crater. Courtesy of IG; photo by V. Valverde (IG-OVT) (Informe Especial del Volcán Tungurahua No. 10, 16 December 2012).

Explosions and ashfall continued on 17 December; a dense ash plume was observed drifting over 200 km NE at an altitude of 7 km. A seven-pixel MODVOLC thermal alert also appeared. Substantial SO₂ plumes were recorded by the OMI satellite instrument between 16 and 29 December. Two pyroclastic flows traveled 3-4 km down the flanks and burned vegetation on 18 December. Explosions shook structures, were often heard by local residents, and generated ashfall in the neighboring communities for several days. The following week, ash plumes decreased in frequency and density, but explosions of incandescent blocks increased. During 21-24 December Strombolian explosions appeared at night; they peaked at over 500 m above the crater, sending blocks more than one kilometer down the W and NW flanks. On the night of 23 December, observers noted intermittent lava fountains rising to 500 m. Another MODVOLC thermal alert pixel was recorded on 24 December. After this, seismicity decreased significantly; the Washington VAAC last reported emissions on 30 December.

Trace amounts of ashfall were reported by IG on 6 and 10 January 2013 in Choglontús (SW) and El Manzano (8 km SW), after small explosions on those days. Explosions, but no ash, were recorded on 21 January; in the evening of 24 January, a column of steam and gas with very low ash content rose less than 1 km and drifted W and SW after reported explosions. The lookout at Palitahua reported black ashfall the following morning. After this, Tungurahua was quiet until the end of February 2013.

Activity during March 2013. IG reported increased seismicity on 28 February 2013. Explosions occurred, and ash emissions rose a few hundred meters above the crater the next day. Ashfall was reported in areas on the SW flank including Choglontús and El Manzano. Multiple VAAC reports were issued daily from 1 to 18 March. Ash plume heights were generally 1-1.5 km above the summit crater (6-6.5 km altitude), but were reported 4 km above the crater on 17 March. Several times during March, IG reported incandescent blocks rolling as far as 500 m down the flanks, and repeated ashfall in communities within 15 km (figure 70). Deformation measurements suggested that a small magma body was rising beneath the NW flank. An SO₂ plume first appeared in the OMI satellite data on 2 March, and was visible daily until 12 March. From 10 to 15 March, MODVOLC recorded 15 thermal alert pixels. Pyroclastic flows occurred on 15 and 17 March; lava fountains rose 200-300 m above the crater on 17 March. A notable decline in seismicity began on 21 March, and a low-ash-content plume that rose 1 km above the crater on 24 March was the last ash emission until the end of April.

Figure 70. Observations of volcanic activity at Tungurahua on 16 March 2013. Top: Detail of an ash column around 1800 local time. Bottom: Strombolian activity a short time later. Courtesy of IG; photos by P. Mothes OVT/IGEPN (Informe Especial del Volcán Tungurahua No.7, 16 March 2013).

Activity during April-May 2013. The webcam confirmed the minor emission of volcanic ash on 24 April 2013; the Washington VAAC reported an ash plume at 6.7 km altitude extending 50 km WNW from the summit on the same day. A series of large explosions began on 27 April. During the next week, these explosions sent steam-and-ash plumes up to 4.7 km above the summit (9.7 km altitude) which drifted at least 100 km SW and W. Ash plumes reported daily by the Washington VAAC rose 1-3 km above the summit until 15 May, and ash fell in communities across the region up to 30 km away in many directions. Lahars traveled down drainages on the S, N, and NW flanks on 4 May. A pyroclastic flow traveled 2 km down the NW flank on 5 May, and Strombolian activity was visible on most nights. During 9-10 May, lava fountains rose 700 m above the crater. MODVOLC thermal alert pixels appeared on 1, 10, 12, and 13 May. An SO₂ plume was recorded in the OMI satellite data on 29 and 30 April, and again from 5 to 12 May. After a slight amount of ash was reported in Choglontus (SW) on 15 May, there were no more reports of ash plumes for two months.

Activity during July-August 2013. IG reported increased seismicity on 13 July 2012 in advance of two large explosions on the morning of 14 July; the first was heard in areas as far away as Guayaquil (about 180 km SW). The Washington VAAC reported the plume from these explosions at 13.7 km altitude (8.7 km above the summit) around midday. They noted that satellite imagery showed a dense ash plume expanding in all directions from the summit, but moving generally N and W. Significant amounts of tephra fell in areas near the volcano including Bilbao (4-cm-diameter), Chacauco (5-cm-diameter), Cotaló, Cahuají, Choglontus, El Manzano, Puela, and Penipe (15 km SW). Thinner deposits were reported in towns including Pelileo, Ambato, Cevallos, Colta (45 km SW), Guanujo (65 km WSW), and Guaranda (65 km WSW), and in the cantons of Guano (30 km SW), Valencia, Empalme, Buena Fé, and areas in the province of Manabi (180 km NW).

Several significant pyroclastic flows also descended drainages on the NW flanks, including the Achupashal and Juive Grande drainages, during the explosions of 14 July. The pyroclastic flows at Juive Grande reached a distance of 6.3 km and stopped a kilometer above the road (figure 71). The temperature measured in the deposit with a thermal camera the next day was 95°C. In the Achupashal stream, the pyroclastic flows reached 6.5 km and crossed the Chambo River. The temperature measured in this deposit was 65°C. According to USA Today, over 200 people were evacuated from Cusua, Chacauco, and Juive.

Figure 71. Pyroclastic flow deposit from Tungurahua in the Juive Grande ravine, 14 July 2013. Courtesy of IG; photo by P. Mothes, IG-EPN (Informe Especial del Volcán Tungurahua No. 15, 16 July 2013).

Volcanic ash advisories were issued daily by the Washington VAAC until 1 August 2013. IG reported that on 19 July the geodetic monitoring system indicated an inflationary trend on the N flank and deflation SW of the volcano, a continuing indication of the presence of a magma body about 2 km below the crater. Ash fell in communities up to 30 km away several times during the period, including after large plumes that rose to 9.6 and 9.9 km altitude on 21 and 24 July. Minor amounts of ash were reported in the Guaranda, Salinas, and Guanujo (65 km WSW) areas after explosions on 26 July, one of which also generated a small pyroclastic flow. Strombolian activity occurred throughout the period, with activity including incandescent blocks rolling up to 500 m down the flanks several times. The OMI instrument captured SO₂ plumes from 15 July through 2 August. MODVOLC thermal alerts were issued on 27 and 29 July. Seismic and explosive activity decreased during the first week in August. An ash plume on 8 August that rose 2 km above the summit and drifted W caused minor ashfall in Choglontus (SW). Trace ashfall was reported in Choglontús and El Manzano on 23 August.

Activity during October-November 2013. Activity resumed in early October 2013 with increased seismicity, Strombolian activity, ash plumes, and pyroclastic flows. A small explosion on 6 October produced ashfall in nearby areas. A larger high-level ash plume on 11 October was observed by the Washington VAAC rising to 8.5 km altitude; ashfall spread to nearby towns. Pyroclastic flows were reported on 14 October. Daily VAAC reports that began on 11 October continued through 30 October, followed by reports on 3, 7, and 9 November. The near-continuous ash emissions during this time generally rose 2-4 km above the crater, and deposited ash in communities within 30 km. Daily SO₂ plumes were captured by OMI between 7 and 22 October, and eight MODVOLC thermal alerts appeared between 19 and 24 October. The last reports of ashfall during this episode were on 12 November when plumes rose 1.5 km from the summit and drifted W, with ashfall reported in El Manzano.

Activity during January-May 2014. The community of Pungal, 40 km SSW of Tungurahua, received ashfall on 30 January from a series of explosions that began after two and a half months of quiet. The Washington VAAC reported the ash plume visible at 8.2 km altitude extending 11 km ESE from the summit. A swarm of VT earthquakes on 1 February was followed by two explosions that generated ash plumes to 2-4 km above the summit, and pyroclastic flows that traveled 500 m down the NE and NW flanks. These explosions were followed a few minutes later by a larger explosion that produced an ash plume reported by IG that rose more than 8 km above the summit (figure 72).

Figure 72. Two sequences of images from the OVT webcam, located near Guadalupe, about 13 km N of the crater, of the large explosions and ash emissions at Tungurahua that began at 2239 on 1 February 2014. Pyroclastic flows descended ravines on the NW and NE flanks. The images on the left record thermal activity during the explosions, while the images on the right record the visual activity. Courtesy of IG (Informe No. 728, Sintesis semanal del estado del Volcán Tungurahua, 28 Jan-4 Feb 2014).

Based on reports from IG, satellite images, pilot observations, web-camera images, and the Guayaquil MWO, the Washington VAAC reported that the ash plume from the 1 February explosions rose to an estimated altitude of 13.7 km, and drifted S at high altitudes and SW at lower altitudes. IG noted that pyroclastic flows traveled 7-8 km, reaching the base of the volcano and crossing over the Achupashal Baños- Penipe highway. Continuous ash-and-gas emissions followed; ash fell in multiple areas and total darkness was reported in Chacauco (NW). Explosions continued every minute and vibrated structures in local towns. Pyroclastic flows descended the SW, W, NW, and NE flanks, but stopped short of towns and infrastructure. Ash emissions were sustained through the rest of the evening, and Strombolian explosions ejected incandescent blocks 800 m above the crater that fell and rolled 500 m down the flanks.

Numerous explosions and ashfall continued in subsequent days; on 3 February 2014 an ash plume rose 4 km above the summit and drifted N, reaching Quito (130 km N) as a mist of suspended very fine material that lingered most of the day. The Washington VAAC issued multiple daily reports of ash plumes from 30 January until 23 February. An eight-pixel thermal alert on 2 February was the beginning of a sequence of MODVOLC thermal alerts that included 10 more during February. SO₂ plumes drifting W were captured by the OMI satellite instrument between 7 and 10 February. During 16-18 February, ash plumes again rose to altitudes between 9 and 10 km, dispersing ash to the W and NW. Strombolian activity and loud noises were common during this interval.

Fewer ash plumes were reported during March 2014, at generally lower heights of 1-3 km above the crater; ash fell in communities within 15 km. Only three MODVOLC thermal alerts were recorded: two on 6 March and one on 15 March. On 11 and 21 March rains caused major lahars in the Achupashal drainage which led to traffic disruption on the Baños- Penipe highway. Lahars on 31 March traveled down the Vascún (N) and Mapayacu (SW) drainages, carrying blocks up to 1 m in diameter in the latter drainage.

Explosions and substantial ash plumes increased in April 2014, with multiple daily VAAC reports issued between 2 and 25 April. The largest explosion, on 4 April, lasted five minutes, and generated pyroclastic flows that descended the NW and N flanks. It also caused an ash plume that rose over 10 km above the crater, reported at 15.2 km altitude (50,000 ft) by the Washington VAAC, the highest reported in many years (figure 73). Tephra up to 7 cm in diameter fell in Cusúa and Píllaro.

Figure 73. A major explosion at Tungurahua on 4 April 2014. Top: The first phase of the explosion at the western edge of the crater, the ash plume reaches at least 8 km above the summit (13 km altitude); pyroclastic flows descend the Achupashal, La Pirámide, and Rea or Romero ravines. Middle: the beginning of the second phase, an explosion on the eastern edge of the crater, which produced a dense plume of ash that reached 10 km above the crater; pyroclastic flows descend the Vazcún and Juive ravines. Bottom: Emission column of at least 10 km above the crater (15 km altitude). Courtesy of IG; photos by F. Vásconez, OVT-IG (Informe No. 737, Sintesis semanal del estado de Volcán Tungurahua, 1-8 April 2014).

During 5-11 April, SO₂ plumes drifting W were detected by the OMI satellite instrument. Large lahars descended the Achupashal (NW) and Confesionario drainages (WSW) on 8 April. On 9 April Strombolian activity caused incandescent blocks to roll 3 km down the flanks (figure 74). The next day a lava flow on the upper W flank, in the Mandur drainage, was estimated to be 2 km long, 100 m wide, and 15 m thick (figure 75). This was likely the cause of the six MODVOLC thermal alerts recorded on 11 April.

Figure 74. At 2243 on 9 April 2014 a lava flow emerged from the crater at Tungurahua; the incandescent material covered the NW and W flanks. Courtesy of IG; photo by P. Ramón, OVT/IG (Sintesis semanal del estado de Volcán Tungurahua, 8-15 April 2014).

Figure 75. The lava flow descending an area between Mandur and Hacienda ravines at Tungurahua. Upper image is from late in the day on 10 April 2014, lower image is a few hours later in the early morning of 11 April. Courtesy of IG; photo by P. Ramón, OVT/IG (Sintesis semanal del estado de Volcán Tungurahua, 8-15 April 2014).

A significant explosion on 14 April 2014 produced an infrasound signal that was detected at 150 decibels 5.5 km away. Unconfirmed reports indicated that windows in Chacauco and Cusúa shattered. The shock wave was also detected in other locations, including Ambato and Riobamba (30 km S). Although IG reported an ash plume rising to over 5 km above the crater (10 km altitude), the Washington VAAC only reported the plume to 8.5 km. A lahar in the Achupashal drainage on 15 April affected traffic on the main highway. Repeated ashfall was reported for the rest of the month in communities within 30 km; crater incandescence was often observed at night.

OVT reported a gas-and-ash emission to an estimated 9 km altitude on 8 May 2014. Three explosions on 10 May generated ash emissions that rose an estimated 5 km above the crater, with ashfall reported in the communities to the SW. There were no VAAC reports issued for the 10 May explosions. A small plume on 11 May had minor amounts of ash. After this, there were no further reports of ash until the end of July. Intense rains on 10 and 11 May caused lahars to flow down most drainages, and roads crossing the Chontapamba and Romero gorges were washed out (figure 76).

Figure 76. Photos taken on 12 May of damage from lahars at Tungurahua from rains on 10 and 11 May 2014. Upper: Lahar that descended the Chontapamba ravine washed out the road and trapped a vehicle. Lower: A large lahar descended the Romero ravine and destroyed the highway in two places. Courtesy of IG; photos by P. Ramón, OVT/IG (Informe No. 742, Sintesis semanal del estado del Volcán Tungurahua, 6-13 May 2014).

The episodic nature of the activity at Tungurahua is demonstrated well by the plot of MIROVA thermal anomaly data captured between April 2013 and April 2014 (figure 77). While the whole duration of the episode is seldom recorded due to weather and other factors, each set of anomalies based on MODIS satellite data is within the boundaries of each episode listed in table 19.

Figure 77. MIROVA thermal anomaly data from the year ending on 12 April 2014, showing the episodic nature of activity at Tungurahua. Courtesy of MIROVA, in IG weekly report (Sintesis semanal del estado de Volcán Tungurahua, 8-15 April 2014).

Activity during June-December 2014. Seasonal rains in June and July 2014 generated numerous lahars, some causing major damage to roads. Otherwise, the volcano was largely quiet with only 100-m-high steam plumes rising from the summit crater on clear days, until seismicity increased once again on 27 July. The seismicity was accompanied by a small ash plume that rose 1 km above the crater and drifted NW. This event was the beginning of a lengthy episode of explosions, ash plumes, Strombolian activity, pyroclastic flows, and lahars that lasted through most of December 2014.

Deformation data revealed additional information about the the activity at Tungurahua (figure 78). The inclinometer of the RETU station is located on the NNE flank at an elevation of 4,000 m. During a 14-month period from 1 June 2013 to 1 August 2014 the radial axis inflation and deflation correlated with four significant explosion events. Periods of gradual inflation were followed by sudden deflation that accompanied an explosion. A new series of explosions began shortly after 24 July 2014 when the last deflation on the graph was detected.

Figure 78. Deformation record of the RETU station at Tungurahua. The inclinometer of the RETU station is located on the NNE flank at an elevation of 4,000 m. During a 14-month period from 1 June 2013 to 1 August 2014 the radial axis inflation and deflation correlated with four significant explosion events. Periods of gradual inflation were followed by sudden deflation and an explosion. A new series of explosions began shortly after 24 July 2014 when the last deflation on the graph began. Courtesy of IG-EPN Volcanology (Informe especial del Volcán Tungurahua No. 16, 28 July 2014).

Seismicity increased on 28 July 2014; a small explosion with an ash plume rose 1 km above the crater and drifted NW with ashfall reported in the Chontapamba area. The Washington VAAC issued multiple daily reports of ash plumes between 1 August and 11 September 2014. They were generally reported at 1-4 km above the summit, or to altitudes of 6-9 km. Ashfall was reported a number of times in communities within 30 km. Strombolian activity sent incandescent blocks as high as 1 km above the crater and up to 1.5 km down the flanks (figure 79). Incandescence appeared on most clear nights. Lahars occurred after rainy episodes during 8-9 and 13 August. On 30 and 31 August, near-constant explosions were detected, and pyroclastic flows traveled 1,500 m down the NW flank. The pyroclastic flows surrounded the lava flow from April 2014, in the La Hacienda, Achupashal, and Mandur drainages. Another pyroclastic flow reported on 3 September descended 500 m from the crater. During 10 August and 7 September, 12 MODVOLC thermal alerts were issued. SO₂ plumes reappeared on the OMI satellite instrument on 2 August and were captured daily until 6 September.

Figure 79. Incandescent blocks from Strombolian activity roll down the flank adjacent to snow near the summit of Tungurahua, 7 August 2014. Courtesy of IG; photo by P. Ramón, OVT/IG (Informe No. 755, Sintesis semanal sel estado del Volcán Tugurahua, 5-12 August 2014).

Activity decreased slightly toward the end of September 2014, although intermittent ash plumes were still reported as high as 2.5 km above the crater; ashfall was recorded in communities up to 25 km away, generally to the W. Rains on 12 and 14 September resulted in lahars within the NW drainages of Achupashal and La Pampa. LP seismic events increased slightly at the end of September along with several low-level ash plumes. The last reports of nighttime incandescence were on 27 September.

Emissions with low to moderate ash content were noted most days in early October. Ashfall was reported from a few communities within 30 km on 1, 3, and 6 October. Trace amounts of ashfall appeared on the SW flank the following week. OVT reported emissions with moderate ash content rising 2-3 km above the summit during 19 and 20 October. Plumes rising to 2 km with low ash content were observed on 25 October. During the end of October and the first few days of November, IG observed only water vapor emissions to 500 m above the crater.

Although quieter, Tungurahua was still active through November and December 2014. Trace amounts of ash in the emissions were observed from El Manzano on 3 November. On 7 and 8 November ash-bearing plumes rose less than 300 m and drifted WSW. For the rest of November, only steam plumes rose to 700 m above the crater. Incandescence was visible at the summit in the early morning hours of 21 November, and again on 4 December. Residents in Choglontus reported a steam-and-ash plume drifting S early on 6 December. A significant lahar on the NW flank washed out the Penipe-Banos road in the Achupashal gorge on 7 December. Low ash content was reported in plumes rising to 500 m above the crater each day from 9-15 December, and magmatic gases and steam emissions were persistent (figure 80). Slight incandescence was seen at night on 11 December. On 14 December, a column consisting of re-suspended ash was seen drifting E. For the remainder of December, weak water vapor plumes rose a few hundred meters above the crater; lahars were reported on 25 December.

Figure 80. A minor plume of magmatic gases rose from the summit crater of Tungurahua on 11 December 2014, as seen from the NW. Courtesy of IG; photo by P. Ramón, OVT/IG (Informe No. 773, Sintesis semanal del estado del Volcan Tungurahua, 9-16 December 2014).

Geologic Background. Tungurahua, a steep-sided andesitic-dacitic stratovolcano that towers more than 3 km above its northern base, is one of Ecuador's most active volcanoes. Three major edifices have been sequentially constructed since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II itself collapsed about 3000 years ago and produced a large debris-avalanche deposit and a horseshoe-shaped caldera open to the west, inside which the modern glacier-capped stratovolcano (Tungurahua III) was constructed. Historical eruptions have all originated from the summit crater, accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.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 Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); USA Today (URL: http://www.usatoday.com/story/news/world/2013/07/14/ecuador-volcano-spews-ash/2516393/).

Following a period with frequent eruptions between 1995 and 2001, White Island (officially called Whakaari/White Island) was quiet until 2012, when plumes began rising from the crater lake on 5 August that included ash two days later (BGVN 37:06). Hydrothermal activity was vigorous, generating phreatic explosions and ash emissions through July 2013, followed by larger explosions in August and October (BGVN 39:02). No further eruptive activity was observed until 2016, when brief phreatic explosions took place on 27 April and 13 September. Monitoring by GNS Science is conducted under the GeoNet Project, the official source of geological hazard information in New Zealand. The following information comes from the GeoNet website.

GNS scientists visited in early February 2014 and measured the crater lake temperature of 57°C and that of fumarole F0, on the S part of the crater floor, at 147°C. The lake level was still rising, and had drowned one of the fumaroles on the southern lakeshore, causing occasional geysering in that area. A new Global Positioning System (GPS) station was installed on the crater floor to strengthen the deformation monitoring network. The average SO₂ gas flux remained below 500 metric tons per day; this was lower than the previous few months and may have been partly due to the higher lake level. On 28 August 2014 the GeoNet seismic network detected a sequence of small earthquakes near White Island, the largest event was magnitude 3.3 and located within 5 km of the island. All the quakes were shallow (less than 10 km depth).

Monitoring by plane, ground instruments, and visual observation throughout 2015 indicated that minor volcanic unrest continued. In October 2015, GNS Science volcanologists measured such factors are ground deformation, CO₂ soil gas, fumarole and crater lake temperature, lake level, and SO₂ gas. Seismometers continued to monitor volcanic tremors, and airborne monitoring measured CO₂, SO₂, and H₂S levels. Elevated amounts of CO₂ emitted from one of the large accessible fumaroles was detected on 1 October; temperatures and SO₂ emissions also increased. On 8 October volcanic tremor magnitude strengthened and became banded (the signal disappeared and reappeared every few hours), commonly noted during periods on unrest and eruptive periods.

Over two weeks in mid-April 2016 the lake level dropped by 2 m. Then, on the morning of 27 April, a brief eruption occurred (lasting about 90 minutes) accompanied by moderately elevated seismic activity. The eruption appears to have deposited material over the N side of the crater floor and up onto the N crater wall. The Volcanic Alert Level was raised to 3 (minor volcanic eruption) and the Aviation Colour Code (ACC) changed from Green to Orange. A subsequent lack of activity resulted in a lowering of the Volcanic Alert Level to 2 (moderate to heightened volcanic unrest) that evening. Observers who flew over the volcano the following day saw a dark-green ash covering at least 80% of the crater floor and up the sides of the crater wall on both N and S sides; the deposit was ~5 mm thick at a distance of 500 m from the eruption site (figure 65).

Figure 65. Ash from the White Island eruption on 27 April 2016 covering the monitoring station. Courtesy of GeoNet (Volcanic Alert Bulletin WI 2016/02).

An aerial inspection two days after the eruption revealed a new crater and vent in the NE corner of the 1978/1990 crater complex. Analysis of the deposit showed the ash to be strongly hydrothermally altered old rock; no evidence of new, juvenile lava was found, suggesting that the eruption was likely driven by steam and gas, like the eruptions in 2012 and 2013. The eruption did produce very energetic blasts and surges that broke survey pegs at ground level. The eruption sequence, as reported by GNS, was that the area around Donald Duck Crater collapsed and exploded (figure 66), then the former lake and sediments erupted, resulting in the blast and surge deposits. The lake floor dropped at least 13 m, and there was a collapse of the 1978/90 Crater walls.

Figure 66. Collapsed area in Donald Duck Crater at White Island as a result of the 27 April 2016 eruption. Courtesy of GeoNet (Volcanic Alert Bulletin WI 2016/07).

By 2 May, observations indicated no change in volcanic activity. As a consequence, the ACC was lowered to Yellow, and by 9 May the Volcanic Alert Level was lowered to 1. Although the April activity was a moderate steam and gas eruption, it did result in a new vent and ash deposits.

GeoNet reported that in the morning of 13 September 2016 a vent on the 2012 lava dome had a minor passive ash emission. The Volcanic Alert Level was raised to 3 from 1, and the ACC was changed from Green to Orange. Observations from a visit on 14 September found that the ash emissions had ceased; the Volcanic Alert Level was lowered to 2 and the ACC lowered to Yellow. The Alert Level was lowered to 1 on 19 September. The crater lake water level began to drop on 24 September, and by 26 September the lake was gone.

GNS has been using Unmanned Aerial Vehicles (UAV's; also known as drones), to monitor the volcano. In December 2016 the drone was used to obtain images of the active crater area, resulting in a new Digital Terrain Model (DTM) of the area (figure 67).

Figure 67. Digital Terrain Model of the White Island volcano crater floor as of December 2016. Courtesy of Geonet (Volcanic Alert Bulletin of December 2016).

According to a GeoNet report on 3 April 2017, visits to White Island over the previous 3-4 months confirmed that activity remained at low levels. Activity was confined to the gas-rich vents on the western side of the active crater. Hot, clear gas continued to be emitted. Some water had ponded on the floor of the active crater but no permanent lake had reformed. The seismic and acoustic activity generally remain low, and the SO₂ gas flux was slowly declining (figures 68 and 69).

Figure 68. View of the active crater area of White Island in early 2017. Note the gas vent (center-rear) and ponded rainwater. Courtesy of GeoNet (Volcanic Alert Bulletin WI-2017-01, 3 April 2017).

Figure 69. Close up view of a gas vent in the active vent area of White Island in early 2017. Courtesy of GeoNet (Volcanic Alert Bulletin WI-2017-01, 3 April 2017).

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/).