The ongoing eruption at Sheveluch continued during May-October 2020, characterized by lava dome growth, strong fumarolic activity, and several explosions that generated plumes of resuspended ash. Activity waned between November 2019 and April 2020 (BGVN 45:05), and this less intense level of activity continued during the reporting period (table 15). The volcano is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT). The Aviation Color Code remained at Orange (the second highest level on a four-color scale) throughout.

Notable explosions took place on 13 June, 28 June, 2 August, 24 August, and 7-9 October 2020 (table 15), sending ash plumes more than 1 km above the summit that drifted to distances of between 75 and 310 km. Some of the plumes were described by KVERT as being composed of re-suspended ash. On 28 September a large dacitic block of lava, a “whaleback” dome, was first seen being extruded from the eastern part of the larger lava dome in the summit crater (figure 55); it was given the name “Dolphin” by KVERT.

Table 15. Explosions, ash plumes, and extrusive activity at Sheveluch during May-October 2020. Dates and times are UTC, not local. VONA is Volcano Observatory Notice for Aviation. Data courtesy of KVERT and the Tokyo Volcanic Ash Advisory Center (VAAC).

Figure 55. Photo of the Sheveluch summit showing the new lava block (referred to as “Dolphin”) being extruded in eastern part the lava dome on 28 September 2020. Photo by Yu. Demyanchuk; courtesy of IVS FEB RAS, KVERT.

According to KVERT, a thermal anomaly was identified from the lava dome in the summit crater (figure 56) in satellite images every day during the reporting period, except for several days in August and September when weather clouds obscured the view. During the reporting period, thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, recorded hotspots from 2-13 days per month; after June, the number of days with hotspots gradually diminished every month. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected frequent anomalies. NASA recorded high levels of sulfur dioxide above or near Sheveluch during several scattered days in May and June by the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Copernicus Sentinel-5 Precursor satellite, but very little drift was observed.

Figure 56. Photo showing typical fumarolic activity from the lava dome at Sheveluch on 18 September 2020. Photo by Yu. Demyanchuk; courtesy of IVS FEB RAS, KVERT.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); 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/); 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/).

Erta Ale is an active basaltic volcano in Ethiopia, containing multiple active pit craters in the summit and southeastern caldera. Volcanism has been characterized by lava flows and large lava flow fields since 2017. This report describes continued thermal activity in the summit caldera during May through September 2020 using information from various satellite data.

Volcanism at Erta Ale was relatively low from May to early August 2020. Across all satellite data, thermal anomalies were identified for a total of 2 days in May, 7 days in June, 4 days in July, 11 days in August, and 15 days in September. Beginning in early June and into 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 after a brief hiatus from early January 2020 (figure 99). By mid-August, a small pulse of thermal activity was detected by the MIROVA (Middle Infrared Observation of Volcanic Activity) system. Many of these thermal anomalies were seen in Sentinel-2 thermal satellite imagery on clear weather days from June to September.

Figure 99. A small cluster of thermal anomalies were detected in the summit area of Erta Ale (red dots) during June-September 2020 as recorded by the Sentinel-2 MODIS Thermal Volcanic Activity data (bands 12, 11, 8A). Courtesy of MIROVA.

On 12 June a minor thermal anomaly was observed in the S pit crater; a larger anomaly was detected on 17 June in the summit caldera where there had been a previous lava lake (figure 100). In mid-August, satellite data showed thermal anomalies in both the N and S pit craters, but by 5 September only the N crater showed elevated temperatures (figure 101). The thermal activity in the N summit caldera persisted through September, based on satellite data from NASA VIIRS and Sentinel Hub Playground.

Figure 100. Sentinel-2 thermal satellite imagery of Erta Ale on 17 June 2020 showing a strong thermal anomaly in the summit caldera. Sentinel-2 satellite image with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 101. Sentinel-2 thermal satellite imagery of Erta Ale showing thermal anomalies in the N and S pit craters on 21 (top left), 26 (top right), and 31 (bottom left) August 2020. On 5 September (bottom right) only the anomaly in the N crater remained. Sentinel-2 satellite image with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. Erta Ale is an isolated basaltic shield that is the most active volcano in Ethiopia. The broad, 50-km-wide edifice rises more than 600 m from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The volcano contains a 0.7 x 1.6 km, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera is renowned for one, or sometimes two long-term lava lakes that have been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.

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

Merapi, located just north of the city of Yogyakarta, Indonesia, is a highly active stratovolcano; the current eruption began in May 2018. Volcanism has recently been characterized by lava dome growth and collapse, small block-and-ash flows, explosions, ash plumes, ashfall, and pyroclastic flows (BGVN 44:10 and 45:04). Activity has recently consisted of three large eruptions in April and June, producing dense gray ash plumes and ashfall in June. Dominantly, white gas-and-steam emissions have been reported during April-September 2020. The primary reporting source of activity comes from Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG, the Center for Research and Development of Geological Disaster Technology, a branch of PVMBG), the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), and the Darwin Volcanic Ash Advisory Centre (VAAC).

Activity at Merapi dominantly consisted of frequent white gas-and-steam emissions that generally rose 20-600 m above the crater (figure 95). On 2 April an eruption occurred at 1510, producing a gray ash plume that rose 3 km above the crater, and accompanied by white gas-and-steam emissions up to 600 m above the crater. A second explosion on 10 April at 0910 generated a gray ash plume rising 3 km above the crater and drifting NW, accompanied by white gas-and-steam emissions rising 300 m above the crater (figure 96). Activity over the next six weeks consisted primarily of gas-and-steam emissions.

Figure 95. Gas-and-steam emissions were frequently observed rising from Merapi as seen on 3 April (left) and 4 August (right) 2020. Courtesy of BPPTKG.

Figure 96. Webcam image showed an ash plume rising 3 km above the crater of Merapi at 0917 on 10 April 2020. Courtesy of BPPTKG and MAGMA Indonesia.

On 8 June PVMBG reported an increase in seismicity. Aerial photos from 13 June taken using drones were used to measure the lava dome, which had decreased in volume to 200,000 m³, compared to measurements from 19 February 2020 (291,000 m³). On 21 June two explosions were recorded at 0913 and 0927; the first explosion lasted less than six minutes while the second was less than two minutes. A dense, gray ash plume reached 6 km above the crater drifting S, W, and SW according to the Darwin VAAC notice and CCTV station (figure 97), which resulted in ashfall in the districts of Magelang, Kulonprogo, and as far as the Girimulyo District (45 km). During 21-22 June the gas-and-steam emissions rose to a maximum height of 6 km above the crater. The morphology of the summit crater had slightly changed by 22 June. Based on photos from the Ngepos Post, about 19,000 m³ of material had been removed from the SW part of the summit, likely near or as part of the crater rim. On 11 and 26 July new measurements of the lava dome were taken, measuring 200,000 m³ on both days, based on aerial photos using drones. Gas-and-steam emissions continued through September.

Figure 97. Webcam image showed an ash plume rising 6 km above the crater of Merapi at 0915 on 21 June 2020. Courtesy of BPPTKG.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

Information Contacts: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Center for Research and Development of Geological Disaster Technology (URL: http://merapi.bgl.esdm.go.id/, Twitter: @BPPTKG); 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/).

Semeru in eastern Java, Indonesia, has been erupting almost continuously since 1967 and is characterized by ash plumes, pyroclastic flows, lava flows and lava avalanches down drainages on the SE flanks. The Alert Level has remained at 2 (on a scale of 1-4) since May 2012, and the public reminded to stay outside of the general 1-km radius from the summit and 4 km on the SSE flank. This report updates volcanic activity from March to August 2020, using primary information from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data.

Activity at Semeru consisted of dominantly dense white-gray ash plumes rising 100-600 m above the crater, incandescent material that was ejected 10-50 m high and descended 300-2,000 from the summit crater, and lava flows measuring 500-1,000 m long. Two pyroclastic flows were also observed, extending 2.3 km from the summit crater in March and 2 km on 17 April.

During 1-2 March gray ash plumes rose 200-500 m above the crater, accompanied by incandescent material that was ejected 10-50 m above the Jonggring-Seloko Crater. Lava flows reaching 500-1,000 m long traveled down the Kembar, Bang, and Kobokan drainages on the S flank. During 4-10 March ash plumes up to 200 m high were interspersed with 100-m-high white gas-and-steam plumes. At the end of a 750-m-long lava flow on the S flank, a pyroclastic flow that lasted 9 minutes traveled as far as 2.3 km. During 25-31 March incandescent material found at the end of the lava flow descended 700-950 m from the summit crater (figure 42).

Figure 42. Sentinel-2 thermal satellite imagery showed lava avalanches descending the SSE flank on 26 March 2020. Images using short-wave infrared (SWIR, bands 12, 8A, 4) rendering; courtesy of Sentinel Hub Playground.

Incandescent material continued to be observed in April, rising 10-50 m above the Jonggring-Seloko Crater. Some incandescent material descended from the ends of lava flows as far as 700-2,000 m from the summit crater. Dense white-gray ash plumes rose 100-600 m above the crater drifting N, SE, and SW. During 15-21 April incandescent lava flows traveled 500-1,000 m down the Kembar, Bang, and Kobokan drainages on the S flank. On 17 April at 0608 a pyroclastic flow was observed on the S flank in the Bang drainage measuring 2 km (figure 43). During 22-28 April lava blocks traveled 300 m from the end of lava flows in the Kembar drainage.

Figure 43. A pyroclastic flow at Semeru on 17 April 2020 moving down the S flank toward Besuk Bang. Photo has been color corrected. Courtesy of PVMBG.

Similar activity continued in May, with incandescent material from lava flows in the Kembar and Kobokan drainages descending a maximum distance of 2 km during 29 April-12 May, and 200-1,200 m in the Kembar drainage during 13-27 May, accompanied by dense white-gray ash plumes rising 100-500 m above the crater drifting in different directions. White gas-and-steam plumes rose 300 m above the crater on 26-27 May. Dense white-to-gray ash plumes were visible most days during June, rising 100-500 m above the crater and drifting in various directions. During 3-9 June incandescent material from lava flows descended 200-1,600 m in the Kembar drainage.

Activity in July had decreased slightly and consisted of primarily dense white-gray ash plumes that ranged from 200-500 m above the crater and drifted W, SW, N, and S. Weather conditions often prevented visual observations. On 7 July an ash plume at 0633 rose 400 m drifting W. Similar ash activity was observed in August rising 200-500 m above the crater. On 14 and 16 August a Darwin VAAC advisory stated that white-gray ash plumes rose 300-400 m above the crater, drifting W and WSW; on 16 August a thermal anomaly was observed in satellite imagery. MAGMA Indonesia reported ash plumes were visible during 19-31 August and rose 200-400 m above the crater, drifting S and SW.

Hotspots were recorded by MODVOLC on 11, 6, and 7 days during March, April, and May, respectively, with as many as four pixels in March. Thermal activity decreased to a single hotspot in July and none in August. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system recorded numerous thermal anomalies at the volcano during March-July; a lower number was recorded during August (figure 44). The NASA Global Sulfur Dioxide page showed high levels of sulfur dioxide above or near Semeru on 18, 24-25, and 29-31 March, and 9 April.

Figure 44. Thermal anomalies at Semeru detected during March-June 2020. Courtesy of MIROVA.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia (Multiplatform Application for Geohazard Mitigation and Assessment in Indonesia), PVMBG, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); 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).

Kavachi is an active submarine volcano in the SW Pacific, located in the Solomon Islands south of Gatokae and Vangunu islands. Volcanism has been characterized by phreatomagmatic explosions that ejected steam, ash, and incandescent bombs. The previous report described discolored water plumes extending from a single point during early 2018 and April 2020 (BGVN 45:05); similar activity was recorded for this current reporting period covering May through September 2020 and primarily using satellite data.

Activity at Kavachi is most frequently observed through satellite images and typically consists of discolored submarine plumes. On 2 September 2020 a slight yellow discoloration in the water was observed extending E from a specific point (figure 22). Similar faint plumes continued to be recorded on 5, 7, 12, and 17 September, each of which seemed to be drifting generally E from a point source above the summit where previous activity has occurred. On 7 September the discolored plume was accompanied by white degassing and possibly agitated water on the surface at the origin point (figure 22).

Figure 22. Sentinel-2 satellite images of a discolored plume (light yellow) at Kavachi beginning on 2 September (top left) and continuing through 17 September 2020 (bottom right). The light blue circle on the 7 September image highlights the surface degassing and source of the discolored water plume. The white arrow on the bottom right image is pointing to the faint discolored plume. Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

Information Contacts: Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Krakatau, located in the Sunda Strait between Indonesia’s Java and Sumatra Islands, experienced a major caldera collapse around 535 CE, forming a 7-km-wide caldera ringed by three islands. Presently, the caldera is underwater, except for three surrounding islands (Verlaten, Lang, and Rakata) and the active Anak Krakatau that was constructed within the 1883 caldera and has been the site of frequent eruptions since 1927. On 22 December 2018, a large explosion and flank collapse destroyed most of the 338-m-high island of Anak Krakatau (Child of Krakatau) and generated a deadly tsunami (BGVN 44:03). A larger explosion in December 2019 produced the beginnings of a new cone above the surface of crater lake (BGVN 45:02). The previous report (BGVN 45:06) described activity that included Strombolian explosions, ash plumes, and crater incandescence. This report updates information from June through September 2020 using information primarily from Indonesian Center for Volcanology and Geological Hazard Mitigation, also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and satellite data.

A VONA notice from PVMBG reported that the last eruptive event at Krakatau was reported on 17 April 2020, though the eruptive column was not observed. Activity after that was relatively low through September 2020, primarily intermittent diffuse white gas-and-steam emissions, according to PVMBG. No activity was reported during June-August, except for minor seismicity. During 11-13, 16, and 18 September, the CCTV Lava93 webcam showed intermittent white gas-and-steam emissions rising 25-50 m above the crater.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) graph of MODIS thermal anomaly data showed intermittent hotspots within 5 km of the crater from May through September (figure 113). Some of these thermal hotspots were also detected in Suomi NPP/VIIRS sensor data. Sentinel-2 thermal satellite imagery showed faint thermal anomalies in the crater during June; no thermal activity was detected after June (figure 114).

Figure 113. Intermittent thermal activity at Anak Krakatau from 13 October 2019-September 2020 shown on a MIROVA Low Radiative Power graph. The power of the thermal anomalies decreased after activity in April but continued intermittently through September. Courtesy of MIROVA.

Figure 114. Sentinel-2 thermal satellite images showing a faint thermal anomaly in the crater during 1 (left) and 11 (right) June 2020. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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

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

A massive stratovolcano in easternmost Java, Raung has over sixty recorded eruptions dating back to the late 16th Century. Explosions with ash plumes, Strombolian activity, and lava flows from a cinder cone within the 2-km-wide summit crater have been the most common activity. Visual reports of activity have often come from commercial airline flights that pass near the summit; Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) has installed webcams to monitor activity in recent years. An eruption in 2015 produced a large volume of lava within the summit crater and formed a new pyroclastic cone in the same location as the previous one. Confirmation and details of eruptions in 2012, 2013, and 2014-2015 are covered in this report with information provided by PVMBG, the Darwin Volcanic Ash Advisory Center (VAAC), several sources of satellite data, and visitors to the volcano.

Newly available visual and satellite information confirm eruptions at Raung during October 2012-January 2013, June-July 2013, and extend the beginning of the 2015 eruption back to November 2014. The 2015 eruption was the largest in several decades; Strombolian activity was reported for many months and fresh lava flows covered the crater floor. Raung was quiet after the 2015 eruption ended in August of that year until July 2020.

Eruption during October 2012-January 2013. A MODVOLC thermal alert appeared inside the summit crater of Raung on 14 October 2012, followed by another four alerts on 16 October. Multiple daily alerts were reported on many days through 8 November, most within the main crater. Single alerts appeared on 29 November and 1 December 2012 (figure 9). PVMBG raised the Alert Level on 17 October from 1 to 2 due to increased seismicity and raised it further to Level 3 on 22 October. A local news report by Aris Yanto indicted that a minor Strombolian eruption occurred inside the crater on 19 October. Strombolian activity was also observed inside the inner crater on 5 November 2012 by visitors (figure 10); they reported loud rumbling sounds that could be heard up to 15 km from the crater.

Figure 9. Thermal activity at Raung during October and November 2012 included multiple days of multi-pixel anomalies, with almost all activity concentrated within the summit crater. Strombolian activity was observed on 5 November. Image shows all pixels from 23 September-1 December 2012. Courtesy of MODVOLC.

Figure 10. Strombolian activity was observed inside the inner crater of Raung on 5 November 2012 by visitors. They reported loud rumbling sounds that could be heard up to 15 km from the crater. Photo by Galih, courtesy of Volcano Discovery.

The Darwin VAAC issued an advisory of an eruption plume to 9.1 km altitude reported at 0237 UTC on 8 November 2012. In a second advisory about two hours later they noted that an ash plume was not visible in satellite imagery. A press article released by the Center for Volcanology and Geological Hazard Mitigation (PVMBG) indicated that gray ash plumes were observed on 6 January 2013 that rose 300 m above the summit crater rim. Incandescence was observed around the crater and thundering explosions were heard by nearby residents.

Eruption during June-July 2013. Two MODVOLC thermal alerts were measured inside the summit crater on 29 June 2013. A photo taken on 21 July showed minor Strombolian activity at the inner crater (figure 11). A weak SO₂ anomaly was detected in the vicinity of Raung by the OMI instrument on the Aura satellite on 27 July. Thermal alerts were recorded on 29 and 31 July. When Google Earth imageryrom 14 March 2011 created by Maxar Technologies is compared with imagery from 29 July 2013 captured by Landsat/Copernicus, dark tephra is filling the inner crater in the 2013 image; it was not present in 2011 (figure 12).

Figure 11. Strombolian activity was observed inside the inner crater at the summit of Raung on 21 July 2013. Photo by Agus Kurniawan, courtesy of Volcano Discovery.

Figure 12. Satellite imagery from Google Earth showing the eroded pyroclastic cone inside the summit crater of Raung on 14 March 2011 (left) and 29 July 2013 (right). Dark tephra deposits filling the inner crater in the 2013 image were not present in 2011. The crater of the pyroclastic cone is 200 m wide; N is to the top of the images. Courtesy of Google Earth.

Eruption during November 2014-August 2015. Information about this eruption was previously reported (BGVN 41:12), but additional details are provided here. Landsat-8 imagery from 28 October 2014 indicated clear skies and little activity within the summit crater. Local observers reported steam plumes beginning in mid-November (figure 13). MODVOLC thermal alerts within the summit crater were issued on 28 and 30 November, and then 15 alerts were issued on seven days in December. Thermal Landsat-8 imagery from cloudy days on 29 November and 15 December indicated an anomaly over the area of the pyroclastic cone inside the summit crater (figure 14).

Figure 13. Local observers reported steam plumes at Raung beginning in mid-November 2014; this one was photographed on 17 November 2014. Courtesy of Volcano Discovery.

Figure 14. Satellite evidence of new eruptive activity at Raung first appeared on 29 November 2014. The true color-pansharpened Landsat-8 image of Raung from 28 October 2014 (left) shows the summit crater and an eroded pyroclastic cone with its own crater (the inner crater) with no apparent activity. Although dense meteoric clouds on 29 November (center) and 15 December 2014 (right) blocked true color imagery, thermal imagery indicated a thermal anomaly from the center of the pyroclastic cone on both dates. Courtesy of Sentinel Hub Playground.

In January 2015 the MODVOLC system identified 25 thermal anomalies in MODIS data, with a peak of eight alerts on 8 January. Visitors to the summit crater on 6 January witnessed explosions from the inner crater approximately every 40 minutes that produced gas and small amounts of ash and tephra. They reported lava flowing continuously from the inner crater onto the larger crater floor, and incandescent activity was seen at night (figure 15). Landsat-8 images from 16 January showed a strong thermal anomaly covering an area of fresh lava (figure 16).

Figure 15. Visitors to the summit crater of Raung on 6 January 2015 witnessed explosions from the inner crater approximately every 40 minutes that produced abundant gas and small amounts of ash and tephra. Lava was flowing continuously from the inner crater onto the larger crater floor, and incandescent activity was observed at night. Photos by Sofya Klimova, courtesy of Volcano Discovery.

Figure 16. On a clear 16 January 2015, Landsat-8 satellite imagery revealed fresh lava flows NW of the pyroclastic cone within the summit crater at Raung. A strong thermal anomaly matches up with the dark material, suggesting that it flowed NW from within the pyroclastic cone. Left image is true color-pansharpened rendering, right image is thermal rendering. Courtesy of Sentinel Hub Playground.

Satellite images were obscured by meteoric clouds during February 2015, but PVMBG reported gray and brown plumes rising 300 m multiple times and incandescence and rumbling on 14 February. Visitors to the summit crater during the second half of February reported Strombolian activity with lava fountains from the inner crater, at times as frequently as every 15 minutes (figure 17). Loud explosions and rumbling were heard 10-15 km away. MODVOLC thermal alerts stopped on 25 February and did not reappear until late June.

Figure 17. A report issued on 25 February 2015 from visitors to the summit of Ruang noted large Strombolian explosions with incandescent ejecta and lava flowing across the crater floor. The fresh lava on the crater floor covered a noticeably larger area than that shown in early January (figure 15). Photo by Andi, courtesy of Volcano Discovery.

PVMBG raised the Alert Level to 2 in mid-March 2015. Weak thermal anomalies located inside and NW of the pyroclastic cone were present in satellite imagery on 21 March. PVMBG reported gray and brown emissions during March, April, and May rising as high as 300 m above the crater. Landsat imagery from 22 April showed a small emission inside the pyroclastic cone, and on 8 May showed a clearer view of the fresh black lava NW and SW of the pyroclastic cone (figure 18).

Figure 18. Fresh lava was visible in Landsat-8 satellite imagery in April and May 2015 at Raung. A small emission was present inside the pyroclastic cone at the summit of Raung on 22 April 2015 (left). Fresh dark material is also evident in the SW quadrant of the summit crater that was not visible on 16 January 2015. A clear view on 8 May 2015 also shows the extent of the fresh black material around the pyroclastic cone (right). The summit crater is 2 km wide. Courtesy of Sentinel Hub Playground.

Nine MODVOLC thermal alerts appeared inside the summit crater on 21 June 2015 after no alerts since late February, suggesting an increase in activity. The Darwin VAAC issued the first ash advisory for 2015 on 24 June noting an aviation report of recent ash. The following day the Ujung Pandang Meteorological Weather Office (MWO) reported an ash emission drifting W at 3.7 km altitude. The same day, 25 June, Landsat-8 imagery clearly showed a new lava flow on the W side of the crater and a strong thermal anomaly. The thermal data showed a point source of heat widening SW from the center of the crater and a second point source of heat that appeared to be inside the pyroclastic cone. A small ash plume was visible over the cone (figure 19). Strombolian activity and ash plumes were reported by BNPB and PVMBG in the following days. On 26 June the Darwin VAAC noted the hotspot had remained visible in infrared imagery for several days. PVMBG reported an ash emission to 3 km altitude on 29 June.

Figure 19. A new lava flow and strong thermal anomaly appeared inside the summit crater of Raung on 25 June 2015 in Landsat-8 imagery. The new flow was visible on the W side of the crater. The darker area extending SW from the rising ash plume is a shadow. The thermal data showed a point source of heat widening SW from the center of the crater and spreading out in the SW quadrant and a second point source of heat on the flank of the pyroclastic cone. Left image is True color-pansharpened rendering, and right image is thermal rendering. Courtesy of Sentinel Hub Playground.

Activity increased significantly during July 2015 (BGVN 41:12). Ash plumes rose as high as 6.7 km altitude and drifted hundreds of kilometers in multiple directions, forcing multiple shutdowns at airports on Bali and Lombok, as well as Banyuwangi and Jember in East Java. The Darwin VAAC issued 152 ash advisories during the month. Ashfall was reported up to 20 km W during July and 20-40 km SE during early August. Visitors to the summit in early July observed a new pyroclastic cone growing inside the inner crater from incandescent ejecta and dense ash emissions (figure 20). Landsat-8 imagery from 11 July showed a dense ash plume drifting SE, fresh black lava covering the 2-km-wide summit caldera floor, and a very strong thermal anomaly most intense at the center near the pyroclastic cone and cooler around the inner edges of the crater (figure 21). On 12 July, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured a view of an ash-and-gas plume drifting hundreds of kilometers SE from Raung (figure 22).

Figure 20. A new pyroclastic cone was growing inside the inner crater at the summit of Raung when photographed by Aris Yanto in early July 2015. Courtesy of Volcano Discovery.

Figure 21. Landsat-8 imagery of Raung during July 2015 indicated dense ash emissions and a large thermal anomaly caused by fresh lava. On 11 July a dense ash plume drifted SE and a strong thermal anomaly was centered inside the summit crater. The 2-km-wide crater floor was covered with fresh lava (compare with 25 June image in figure 19). Courtesy of Sentinel Hub Playground.

Figure 22. On 12 July 2015 the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured a natural-color view of a plume of ash and volcanic gases drifting hundreds of kilometers SE from Raung. Courtesy of NASA Earth Observatory.

A satellite image on 20 July showed fresh incandescent lava covering the floor of the summit crater and a dense ash plume drifting N from the summit (figure 23). Incandescent ejecta emerged from two vents on the new pyroclastic cone inside the inner crater on 26 July (figure 24). On 27 July a dense ash plume was visible again in satellite imagery drifting NW and the hottest part of the thermal anomaly was in the SE quadrant of the crater (figure 25). Substantial SO₂ plumes were recorded by the OMI instrument on the Aura satellite during July and early August 2015 (figure 26).

Figure 23. A satellite image of the summit of Raung on 20 July 2015 showed fresh, incandescent lava covering the floor of the summit crater and a dense ash plume drifting N from the summit. Thermal activity on the NE flank was likely the result of incandescent ejecta from the crater causing a fire. Image created by DigitalGlobe, captured by WorldView3, courtesy of Volcano Discovery.

Figure 24. Incandescent ejecta emerged from two vents on the new pyroclastic cone growing inside the inner crater of Raung on 26 July 2015. Photo by Vianney Tricou, used with permission, courtesy of Volcano Discovery.

Figure 25. Landsat-8 imagery of Raung during July 2015 indicated dense ash emissions and large thermal anomalies from fresh lava. The 2-km-wide crater floor was fully covered with fresh lava by 11 July. On 27 July the dense ash plume was drifting NW and the highest heat was concentrated in the SE quadrant of the crater. Courtesy of Sentinel Hub Playground.

Figure 26. Substantial plumes of sulfur dioxide from Raung were measured by the OMI instrument on the AURA satellite during July and August 2015. The first plumes were measured in mid-June; they intensified during the second half of July and the first week of August, but had decreased by mid-August. Wind directions were highly variable throughout the period. The date is recorded above each image. Courtesy of NASA Global Sulfur Dioxide Page.

Significant ash emissions continued into early August 2015 with numerous flight cancellations. The Darwin VAAC reported ash plumes rising to 5.2 km altitude and extending as far as 750 km SE during the first two weeks in August (figure 27). Satellite imagery indicated a small ash plume drifting W from the center of the crater on 12 August and weak thermal anomalies along the E and S rim of the floor of the crater (figure 28). The summit crater was covered with fresh lava on 14 August when viewed by visitors, and ash emissions rose a few hundred meters above the crater rim from a vent in the SW side of the pyroclastic cone (figure 29). The visitors observed pulsating ash emissions rising from the SW vent on the large double-crater new cinder cone. The larger vent to the NE was almost entirely inactive except for two small, weakly effusive vents on its inner walls.

Figure 27. A dense ash plume drifted many kilometers S from Raung on 2 August 2015 in this view from nearly 100 km W. Incandescence at the summit indicated ongoing activity from the major 2015 eruption. In the foreground is Lamongan volcano whose last known eruption occurred in 1898. Courtesy of Øystein Lund Andersen, used with permission.

Figure 28. Landsat-8 satellite imagery of Raung indicated a small ash plume drifting W from the center of the crater on 12 August 2015. Courtesy of Sentinel Hub Playground.

Figure 29. The summit crater of Raung on 14 August 2015 was filled with fresh lava from an eruption that began in November 2014. Ash emissions from a vent in the side of the newly grown pyroclastic cone within the crater rose a few hundred meters above the crater rim. Courtesy of Volcano Discovery.

The lengthy sequence of multiple daily VAAC reports that began in late June ended on 16 August 2015 with reports becoming more intermittent and ash plume heights rising to only 3.7-3.9 km altitude. Multiple discontinuous eruptions to 3.9 km altitude were reported on 18 August. The plumes extended about 100 km NW. The last report of an ash plume was from an airline on 22 August noting a low-level plume 50 km NW. Two MODVOLC alerts were issued that day. By 28 August only a very small steam plume was present at the center of the crater; the southern half of the edge of the crater floor still had small thermal anomalies (figure 30). The last single MODVOLC thermal alerts were on 29 August and 7 September. The Alert Level was lowered to 2 on 24 August 2015, and further lowered to 1 on 20 October 2016.

Figure 30. By 28 August 2015 only a very small steam plume was present at the center of the summit crater of Raung, and the southern half of the edge of the crater floor only had weak thermal anomalies from cooling lava. Courtesy of Sentinel Hub Playground.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/);Google Earth (URL: https://www.google.com/earth/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/, https://earthobservatory.nasa.gov/images/86213/eruption-of-raung-volcano); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Aris Yanto (URL: https://www.exploredesa.com/2012/11/mount-raung-produce-of-vulcanic-ash-plume-and-continue-eruption/); DigitalGlobe (URL: https://www.maxar.com/, https://twitter.com/Maxar/status/875449111398547457); Øystein Lund Andersen (URL: https://twitter.com/OysteinVolcano/status/1194879946042142726, http://www.oysteinlundandersen.com).

Klyuchevskoy is a frequently active stratovolcano located in northern Kamchatka. Historical eruptions dating back 3,000 years have included more than 100 flank eruptions with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks. The previous report (BGVN 45:06) described ash plumes, nighttime incandescence, and Strombolian activity. Strombolian activity, ash plumes, and a strong lava flow continued. This report updates activity from June through August 2020 using weekly and daily reports from the Kamchatkan Volcanic Eruption Response Team (KVERT), the Tokyo Volcanic Ash Advisory (VAAC), and satellite data.

Moderate explosive-effusive activity continued in June 2020, with Strombolian explosions, frequent gas-and-steam emissions that contained some amount of ash, and an active lava flow. On 1 June a gas-and-steam plume containing some ash extended up to 465 km SE and E. The lava flow descended the SE flank down the Apakhonchich chute (figure 43). Occasionally, phreatic explosions accompanied the lava flow as it interacted with snow. Intermittent ash plumes, reported throughout the month by KVERT using video and satellite data and the Tokyo VAAC using HIMAWARI-8 imagery, rose to 5.5-6.7 km altitude and drifted in different directions up to 34 km from the volcano. On 12 and 30 June ash plumes rose to a maximum altitude of 6.7 km. On 19 June, 28-30 June, and 1-3 July some collapses were detected alongside the lava flow as it continued to advance down the SE flank.

Figure 43. Gray ash plumes (left) and a lava flow descending the Apakhonchich chute on the SE flank, accompanied by a dark ash plume and Strombolian activity (right) were observed at the summit of Klyuchevskoy on 10 June 2020. Courtesy of E. Saphonova, IVS FEB RAS, KVERT.

During 1-3 July moderate Strombolian activity was observed, accompanied by gas-and-steam emissions containing ash and a continuous lava flow traveling down the Apakhonchich chute on the SE flank. On 1 July a Tokyo VAAC advisory reported an ash plume rising to 6 km altitude and extending SE. On 3 July the activity sharply decreased. KVERT reported there was some residual heat leftover from the lava flow and Strombolian activity that continued to cool through at least 13 July; KVERT also reported frequent gas-and-steam emissions, which contained a small amount of ash through 5 July, rising from the summit crater (figure 44). The weekly KVERT report on 16 July stated that the eruption had ended on 3 July 2020.

Figure 44. Fumarolic activity continued in the summit crater of Klyuchevskoy on 7 July 2020. Courtesy of KSRS ME, Russia, KVERT.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows frequent and strong thermal activity within 5 km of the summit crater from March through June followed by a sharp and sudden decline in early July (figures 45). A total of six weak thermal anomalies were detected between July and August. According to the MODVOLC thermal algorithm, a total of 111 thermal alerts were detected at or near the summit crater from 1 June to 1 July, a majority of which were due to the active lava flow on the SE flank and Strombolian explosions in the crater. Sentinel-2 thermal satellite imagery frequently showed the active lava flow descending the SE flank as a strong thermal anomaly, sometimes even through weather clouds (figure 46). These thermal anomalies were also recorded by the Sentinel-2 MODIS Thermal Volcanic Activity data on a MIROVA graph, showing a strong cluster during June to early July, followed by a sharp decrease and then a hiatus in activity (figure 47).

Figure 45. Thermal activity at Klyuchevskoy was frequent and strong during February through June 2020, according to the MIROVA graph (Log Radiative Power). Activity sharply decreased during July through August with six low-power thermal anomalies. Courtesy of MIROVA.

Figure 46. Sentinel-2 thermal satellite images show the strong and persistent lava flow (bright yellow-orange) originating from the summit crater at Klyuchevskoy from 1 June through 1 July 2020. The lava flow was active in the Apakhonchich chute on the SE flank. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 47. Strong clusters of thermal anomalies were detected in the summit at Klyuchevskoy (red dots) during January through June 2020, as recorded by the Sentinel-2 MODIS Thermal Volcanic Activity data (bands 12, 11, 8A). Activity sharply decreased during July through August with few low-power thermal anomalies. Courtesy of MIROVA.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); 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).

Fuego, located in Guatemala, is a stratovolcano that has been erupting since 2002 with historical eruptions dating back to 1531. Volcanism is characterized by major ashfalls, pyroclastic flows, lava flows, and lahars. The previous report (BGVN 45:04) described recent activity that included multiple ash explosions, block avalanches, and intermittent lava flows. This report updates activity from April through July 2020 that consisted of daily explosions, ash plumes, block avalanches ashfall, intermittent lava flows, and lahars. The primary source of information comes from the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH), the Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

Summary of activity during April-July 2020. Daily activity throughout April-July 2020 was characterized by multiple hourly explosions, ash plumes that rose to a maximum of 4.9 km altitude, incandescent pulses that reached 600 m above the crater, block avalanches into multiple drainages, and ashfall affecting nearby communities (table 21). The highest rate of explosions occurred on 2 and 3 April and 2 May with up to 16 explosions per hour. White degassing occurred frequently during the reporting period, rising to a maximum altitude of 4.5 km and drifting in multiple directions. Intermittent lava flows were observed each month in the Seca (Santa Teresa) and Ceniza drainages (figure 132); the number of flows decreased in June through July, which is represented in the MIROVA analysis of MODIS satellite data, where the strength and frequency of thermal activity slightly decreased (figure 133). Occasional lahars were detected descending several drainages on the W and SE flanks, sometimes carrying tree branches and large blocks up to 1 m in diameter.

Table 21. Activity summary by month for Fuego with information compiled from INSIVUMEH daily reports.

Figure 132. Sentinel-2 thermal satellite images of Fuego between 9 April 2020 and 13 July 2020 showing lava flows (bright yellow-orange) traveling generally S and W from the summit crater. Some lava flows were accompanied by gas emissions (9 April, 9 May, and 24 May 2020). Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 133. Thermal activity at Fuego was persistent and strong from 16 September through late May 2020, according to the MIROVA graph (Log Radiative Power). From early to mid-June activity seemed to stop briefly before resuming again at a lower rate. Courtesy of MIROVA.

Activity during April-May 2020. Activity in April 2020 consisted of 5-16 explosions per hour, generating ash plumes that rose 4.3-4.9 km altitude and drifted 8-20 km in multiple directions. Ashfall was reported in Morelia (9 km SW), Panimaché I and II (8 km SW), Sangre de Cristo (8 km WSW), Santa Sofía (12 km SW), Finca Palo Verde, San Pedro Yepocapa (8 km NW), Las Cruces Quisache (8 km NW), La Rochela, Ceylan, Osuna (12 km SW). The Washington VAAC issued multiple aviation advisories for a total of six days in April. Intermittent white gas-and-steam emissions reached 4.1-4.5 km altitude drifting in multiple directions. Incandescent ejecta was frequently observed rising 75-400 m above the crater; material ejected up to 600 m above the crater on 11 April. These constant explosions produced block avalanches that traveled down the Taniluyá (SW), Ceniza (SSW), Las Lajas (SE), Trinidad (S), Seca (W), Honda, and Santa Teresa (W) drainages. Effusive activity was reported on 6-13 and 15 April from the summit vent, traveling 150-800 m down the Ceniza drainage, accompanied by block avalanches in the front of the flow up to 1 km. Crater incandescence was also observed.

On 19-20 April a new lava flow descended the Ceniza drainage measuring 200-400 long, generating incandescent block avalanches at the front of the flow that moved up to 1 km. On 22 April lahars descended the Honda, Las Lajas, El Juté (SE), Trinidad, Ceniza, Taniluyá, Mineral, and Seca drainages and tributaries in Guacalate, Achiguate, and Pantaleón. During the evening of 23 April the rate of effusive activity increased; observatory staff observed a second lava flow in the Seca drainage was 170 m long and incandescent blocks from the flow traveled up to 600 m. Two lava flows in the Ceniza (130-400 m) and Seca (150-800 m) drainages continued from 23-28 April and had stopped by 30 April. On 30 April weak and moderate explosions produced ash plumes that rose 4.5-4.7 km altitude drifting S and SE, resulting in fine ashfall in Panimaché I, Morelia, Santa Sofía (figure 134).

Figure 134. Photo of a small ash plume rising from Fuego on 30 April 2020. Photo has been slightly color corrected. Courtesy of William Chigna, CONRED.

During May 2020, the rate of explosion remained similar, with 4-16 explosions per hour, which generated gray ash plumes that rose 4.3-4.9 km altitude and drifted 10-17 km generally W and E. Ashfall was observed in Panimaché I, La Rochela, Ceilán, Morelia, San Andrés Osuna, Finca Palo Verde, Santa Sofía, Seilán, San Pedro Yepocapa, Alotenango (8 km ENE), Ciudad Vieja (13.5 km NE), San Miguel Dueñas (10 km NE), and Antigua Guatemala (18 km NE). The Washington VAAC issued volcanic ash advisory notices on six days in May. White gas-and-steam emissions continued, rising 4-4.5 km altitude drifting in multiple directions. Incandescent ejecta rose 100-400 m above the crater, accompanied by some crater incandescence and block avalanches in the Trinidad, Taniluyá, Ceniza, Las Lajas, Santa Teresa, Seca, and Honda drainages that moved up to 1 km and sometimes reached vegetated areas.

During 8-11 May a new 400 m long lava flow was detected in the Ceniza drainage, accompanied by constant crater incandescence and block avalanches traveling up to 1 km, according to INSIVUMEH. On 8 and 17 May moderate to strong lahars descended the Santa Teresa and Mineral drainages on the W flank and on 21 May they descended the Las Lajas drainage on the E flank and the Ceniza drainage on the SW flank. During 20-24 May a 100-400 m long lava flow was reported in the Ceniza drainage alongside degassing and avalanches moving up to 1 km and during 25-26 May a 150 m long lava flow was reported in the Seca drainage.

Activity during June-July 2020. The rate of explosions in June 2020 decreased slightly to 3-15 per hour, generating gray ash plumes that rose 4.2-4.9 km altitude and drifted 10-26 km in multiple directions (figure 135). As a result, intermittent ashfall was reported in San Pedro Yepocapa, Sangre de Cristo, Panimaché I and II, Morelia, Finca Palo Verde, El Porvenir (8 km ENE), Yucales (12 km SW), Santa Emilia, Santa Sofia, according to INSIVUMEH. VAAC advisories were published on eight days in June. Degassing persisted in the summit crater that rose 4.1-4.5 km altitude extending in different directions. Crater incandescence was observed occasionally, as well as incandescent pulses that rose 100-300 m above the crater. Block avalanches were observed descending the Seca, Taniluyá, Ceniza, Trinidad, Las Lajas, Santa Teresa, and Honda drainages, which could sometimes carry blocks up to 1 km in diameter.

On 2 June at 1050 a weak to moderate lahar was observed in the Las Lajas drainage on the SE flank. On 5 June, more lahars were detected in the Seca and Mineral drainages on the W flanks. A new lava flow was detected on 12 June, traveling 250 m down the Seca drainage on the NW flank, and accompanied by constant summit crater incandescence and gas emissions. The flow continued into 14 June, lengthening up to 300 m long. On 24 June weak and moderate explosions produced ash plumes that rose 4.3-4.7 km altitude drifting W and SW (figure 135). On 29 June at 1300 a weak lahar was reported in the Seca, Santa Teresa, and Mineral drainages on the W flank.

Figure 135. Examples of small ash plumes at Fuego on 15 (left) and 24 (right) June 2020. Courtesy of William Chigna, CONRED.

Daily explosions and ash plumes continued through July 2020, with 1-15 explosions per hour and producing consistent ash plumes 4-4.9 km altitude drifting generally W for 10-24 km. These explosions resulted in block avalanches that descended the Trinidad, Taniluyá, Ceniza, Honda, Las Lajas, Seca, and Santa Teresa drainages. The number of white gas emissions decrease slightly compared to previous months and 4-4.4 km altitude. VAAC advisories were distributed on twenty different days in July. Incandescent ejecta was observed rising 100-350 m above the crater. Occasional ashfall was observed in Panimaché I and II, Morelia, Santa Sofía, Finca Palo Verde, Sangre de Cristo, San Pedro Yepocapa, and El Porvenir, according to INSIVUMEH.

On 4 July in the early morning, a lava flow began in the Seca drainage, which also produced some fine ash particles that drifted W. The lava flow continued into 5 July, measuring 150 m long. On the same day, weak to moderate lahars traveled only 20 m, carrying tree branches and blocks measuring 30 cm to 1 m. On 14, 24, and 29 July more lahars were generated in the Las Lajas drainages on the former date and both the Las Lajas and El Jute drainages on the two latter dates.

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/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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); William Chigna, CONRED (URL: https://twitter.com/william_chigna).

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 through November 2015 and returned during mid-2017, continuing the growth of the island with ash plumes, ejecta, and lava flows. A short eruptive event in July 2018 produced a small lava flow and vent on the side of the pyroclastic cone. The next eruption of ash plumes, incandescent ejecta, and lava flows began in early December 2019, resulting in significant growth of the island. This report covers the ongoing activity from March-August 2020 when activity decreased. Information is provided primarily from Japan Meteorological Agency (JMA) monthly reports and the Japan Coast Guard (JCG), which makes regular overflights to make observations.

Renewed eruptive activity that began on 5 December 2019 continued during March-August 2020 but appeared to wane by the end of August. Major lava flows covered all sides of the island, with higher levels of activity during late June and early July. Ash emissions increased significantly during June and produced dense black ash plumes that rose up to 6 km altitude in early July. Explosive activity produced lightning and incandescent jets that rose 200 m and large bombs that fell to the base of the pyroclastic cone. Lava flow activity diminished at the end of July. Ash emissions decreased throughout August and appeared to cease after 27 August 2020. The MIROVA plot clearly reflects the high levels of thermal activity between December 2019 and August 2020 (figure 80); this event was reported by JMA as the largest eruption recorded to date. Sulfur dioxide emissions were very high during late June through early August, producing emissions that drifted across much of the western Pacific region.

Figure 80. The MIROVA plot of thermal activity at Nishinoshima from 14 October 2019 through August 2020 indicates the high levels between early December 2019 and late July 2020 that resulted from the eruption of numerous lava flows on all flanks of the pyroclastic cone, significantly enlarging the island. Courtesy of MIROVA.

The Japan Coast Guard (JCG) conducted overflights of Nishinoshima on 9 and 15 March 2020 (figure 81). During both visits they observed eruptive activity from the summit crater, including ash emissions that rose to an altitude of approximately 1,000 m and lava flowing down the N and SE flanks (figure 82). Large ejecta was scattered around the base of the pyroclastic cone. The lava flowing north had reached the coast and was producing vigorous steam as it entered the water on 9 March; whitish gas emissions were visible on the N flank of the cone at the source of the lava flow (figure 83). On 9 March yellow-green discolored water was noted off the NE shore. The lava flow on the SE coast produced a small amount of steam at the ocean entry point and a strong signal in thermal imagery on 15 March (figure 84). Multiple daily MODVOLC thermal alerts were issued during 1-10, 17-24, and 27-30 March. Landsat-8 visual and thermal imagery on 30 March 2020 confirmed that thermal anomalies on the N and SE flanks of the volcano continued.

Figure 81. The Japan Coast Guard conducted an overflight of Nishinoshima on 9 March 2020 and observed ash emissions rising 1,000 m above the summit and lava flowing into the ocean off the N flank of the island. Courtesy of Japan Coast Guard (JCG) and JMA.

Figure 82. Lava flows at Nishinoshima during February and March 2020 were concentrated on the N and SE flanks. The areas in blue indicate topographical changes due to lava flows and pyroclastic deposits from the previous measurement. The growth of the SE-flank flow decreased during March while the N-flank flow rate increased significantly. Left image shows changes between 14 and 28 February and right image shows the differences between 28 February and 13 March. The correlated image analysis uses ALOS-2 / PALSAR-2 and is carried out with the cooperation of JAXA through the activities of the Satellite Analysis Group of the Volcano Eruption Prediction Liaison Committee. The software was developed by the Japan National Research Institute for Earth Science and Disaster Prevention and uses the technical data C1-No 478 of the Geospatial Information Authority of Japan. Courtesy of JAXA and JMA (Volcanic activity commentary material on Nishinoshima, March 2020).

Figure 83. Vigorous steam emissions on the N flank of Nishinoshima on 9 March 2020 were caused by the active flow on the N flank. Whitish steam and gas midway up the flank indicated the outlet of the flow. Ash emissions rose from the summit crater and drifted E. Courtesy of Japan Coast Guard and JMA.

Figure 84. Infrared imagery from 15 March 2020 at Nishinoshima showed the incandescent lava flow on the SE flank (foreground), blocks of ejecta scattered around the summit and flanks of the pyroclastic cone, and the active N-flank flow (left). Courtesy of Japan Coast Guard and JMA.

Ash emissions were not observed at Nishinoshima during JCG overflights on 6, 16, and 19 April 2020, but gas-and-steam emissions were noted from the summit crater, and a yellow discoloration interpreted by JMA to be sulfur precipitation was observed near the top of the pyroclastic cone. The summit crater was larger than during previous visits. Steam plumes seen each of those days on the N and NE coasts suggested active ocean entry of lava flows (figure 85). A lava flow was observed emerging from the E flank of the cone and entering the ocean on the E coast on 19 and 29 April (figure 86). During the overflight on 29 April observers noted lava flowing southward from a vent on the E flank of the pyroclastic cone. A narrow, brown, ash plume was visible on 29 April at the summit crater rising to an altitude of about 1,500 m. Thermal observations indicated continued flow activity throughout the month. Multiple daily MODVOLC thermal alerts were recorded during 2-6, 10-11, 17-23, and 28-30 April. Significant growth of the pyroclastic cone occurred between early February and late April 2020 (figure 87).

Figure 85. Multiple entry points of lava flowed into the ocean producing jets of steam along the N flank of Nishinoshima on 6 April 2020. Courtesy of JCG and JMA.

Figure 86. Lava flowed down the E flank of Nishinoshima from a vent below the summit on 19 April 2020. The ocean entry produced a vigorous steam plume (left). Courtesy of JCG.

Figure 87. The pyroclastic cone at Nishinoshima grew significantly in size between 4 February (left), 9 March (middle), and 19 April 2020 (right). View is to the E. Courtesy of JMA and JCG.

Infrared satellite imagery from 17 May 2020 showed a strong thermal anomaly at the summit and hot spots on the NW flank indicative of flows. Visible imagery confirmed emissions at the summit and steam plumes on the NW flank (figure 88). Gray ash plumes rose to about 1,800 m altitude on 18 May during the only overflight of the month made by the Japan Coast Guard. In addition, white gas emissions rose from around the summit area and large blocks of ejecta were scattered around the base of the pyroclastic cone (figure 89). Steam from ocean-entry lava on the N flank was reduced from previous months, but a new flow moving NW into the ocean was generating a steam plume and a strong thermal signature. Multi-pixel thermal alerts were measured by the MODVOLC system on 1-3, 9-10, 13-15, 18, and 26-30 May. Sulfur dioxide emissions had been weak and intermittent from March through early May 2020 but became more persistent during the second half of May. Although modest in size, the plumes were detectible hundreds of kilometers away from the volcano (figure 90).

Figure 88. Landsat-8 satellite imagery of Nishinoshima from 17 May 2020 confirmed continued eruptive activity. Visible imagery showed emissions at the summit and steam plumes on the NW flank (left) and infrared imagery showed a strong thermal anomaly at the summit and anomalies on the NW flank indicative of lava flows (right). Courtesy of Sentinel Hub Playground.

Figure 89. Lava continued to enter the ocean at Nishinoshima during May 2020. A new lava flow on the NW flank produced a strong steam plume at an ocean entry (left) on 18 May 2020. In addition to a light gray plume of gas and ash, steaming blocks of ejecta were visible on the flanks of the pyroclastic cone. The strong thermal signature of the NW-flank flow in infrared imagery that same day showed multiple new lobes flowing to the ocean (right). Courtesy of JCG and JMA.

Figure 90. Small but distinct SO2 emissions from Nishinoshima were recorded by the TROPOMI instrument on the Sentinel-5P satellite during the second half of May 2020. The plumes drifted tens to hundreds of kilometers away from the volcano in multiple directions as the wind directions changed. Nishinoshima is about 1,000 kilometers S of Tokyo. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Activity increased significantly during June 2020. Satellite imagery from 2 June revealed two intense thermal anomalies at the summit indicating a new crater, and lava flows active on the NW and NE flanks, all showing gas or steam emissions (figure 91). Dense brown and gray ash emissions were observed rising from the summit crater during JCG overflights on 7 and 15 June (figure 92). Plumes reached at least 1,500 m altitude, and ejecta reached the base of the pyroclastic cone. Between 5 and 19 June the lava flow on the WNW coast slowed significantly, while the flows to the N and E became significantly more active (figure 93). The Tokyo VAAC reported the first ash plume since mid-February on 12 June rose to 2.1 km and drifted NE. On 14 June they reported an ash plume extending E at 2.7 km altitude. Dense emissions continued to drift N and E at 2.1-2.7 km altitude until the last week of the month. The JCG overflight on 19 June observed darker ash emissions than two weeks earlier that drifted at least 180 km NE (figure 94) and incandescent tephra that exploded from the enlarged summit area where three overlapping craters trending E-W had formed.

Figure 91. Landsat-8 satellite imagery on 2 June 2020 confirmed ongoing activity at Nishinoshima. Lava produced ocean-entry steam on the NE coast; a weak plume on the NW coast suggested reduced activity in that area (left). In addition, a dense steam plume drifted E from the summit, while a fainter plume adjacent to it also drifted E. The infrared image (right) indicated two intense anomalies at the summit, and weaker anomalies from lava flows on the NW and NE flanks. Courtesy of Sentinel Hub Playground.

Figure 92. Lava flows at Nishinoshima entered the ocean on the N and NE coasts (left) on 7 June 2020, and dense, gray ash emissions rose to at least 1,500 m altitude. Courtesy of JCG.

Figure 93. The lava flow on the WNW coast of Nishinoshima slowed significantly in early June 2020, while the flows to the N and E covered large areas of those flanks between 5 and 19 June. The areas in blue indicate topographical changes due to lava flows and pyroclastic deposits from the previous measurement. Left image shows the differences between 22 May and 5 June and right image shows changes between 5 and 19 June. The correlated image analysis uses ALOS-2 / PALSAR-2 and is carried out with the cooperation of JAXA through the activities of the Satellite Analysis Group of the Volcano Eruption Prediction Liaison Committee. The software was developed by the National Research Institute for Earth Science and Disaster Prevention and uses the technical data C1-No 478 of the Geospatial Information Authority of Japan. Courtesy of JAXA and JMA (Volcanic activity commentary material on Nishinoshima, June 2020).

Figure 94. Ash emissions and explosive activity at Nishinoshima increased significantly during the second half of June. Dense black ash rose to 2.4 km altitude and drifted at least 180 km to the NE on 19 June 2020. Vigorous white steam plumes rose from the ocean on the E flank where a lava flow entered the ocean. Courtesy of JCG.

The Tokyo VAAC reported ash emissions that rose to 4.6 km altitude and drifted NE on 25 June. For the remainder of the month they rose to 2.7-3.9 km altitude and drifted N and NE. By the time of the JCG overflight on 29 June, the new crater that had opened on the SW flank had merged with the summit crater (figure 95). Dense black ash emissions rose to 3.4 km altitude and drifted NE, lava flowed down the SW flank into the ocean producing violent steam explosions, and incandescent tephra was scattered at least 200 m from the base of the pyroclastic cone from ongoing explosive activity (figure 96). Multiple layers of recent flow activity were visible along the SW coast (figure 97). Yellow-green discolored water encircled the entire island with a width of 1,000 m.

Figure 95. The new crater on the SW flank of Nishinoshima had merged with the summit crater by 29 June 2020. Courtesy of JCG and JMA.

Figure 96. Dense black ash emissions rose to 3.4 km altitude and drifted NE from the summit of Nishinoshima on 29 June 2020. Lava flowed down the SW flank into the ocean producing steam explosions, and incandescent tephra was scattered at least 200 m from the base of the pyroclastic cone from ongoing explosive activity at the summit (inset). Courtesy of JCG.

Figure 97. Different textures of lava flows were visible along the SW flank of Nishinoshima on 29 June 2020. The active flow appeared dark brown and blocky, and produced steam explosions at the ocean entry site (right). Slightly older, brownish-red lava (center) still produced steam along the coastline. Courtesy of JCG.

MODVOLC thermal alerts reached their highest levels of the period during June 2020 with multi-pixel alerts recorded on most days of the month. Sulfur dioxide emissions increased steadily throughout June to the highest levels recorded for Nishinoshima; by the end of the month plumes of SO₂ were drifting thousands of kilometers across the Pacific Ocean and being captured in complex atmospheric circulation currents (figure 98).

Figure 98. Sulfur dioxide emissions at Nishinoshima increased noticeably during the second half of June 2020 as measured by the TROPOMI instrument on the Sentinel-5P satellite. Atmospheric circulation currents produced long-lived plumes that drifted thousands of kilometers from the volcano. Nishinoshima is 1,000 km S of Tokyo. Courtesy of NASA Sulfur Dioxide Monitoring Page.

By early July 2020, satellite data indicated that the NE quadrant of the island was covered with ash, and a large amount of new lava had flowed down the SW flank, creating fans extending into the ocean (figure 99). The Tokyo VAAC reported ash emissions that rose to 3.7-4.9 km altitude and drifted N during 1-6 July. The altitude increased to 6.1 km during 8 and 9 July, and ranged from 4.6-6.1 km during 10-14 July while the drift direction changed to NE. The marine meteorological observation ship "Ryofu Maru" reported on 11 July that dense black ash was continuously erupting from the summit crater and drifting W at 1,700 m altitude or higher. They observed large volcanic blocks scattered around the base of the pyroclastic cone, and ash falling from the drifting plume. During the night of 11 July incandescent lava and volcanic lightning rose to about 200 m above the crater rim (figure 100).

Figure 99. By early July 2020, satellite data from Nishinoshima indicated that the NE quadrant of the island was covered with ash, and a large amount of new lava had flowed down the SW flank creating fans extending into the ocean. The areas in blue indicate topographical changes due to lava flows and pyroclastic deposits from the previous measurement. Left image shows differences between 5 and 19 June and the right image shows changes between 19 June and 3 July that included abundant ashfall on the NE flank. The correlated image analysis uses ALOS-2 / PALSAR-2 and is carried out with the cooperation of JAXA through the activities of the Satellite Analysis Group of the Volcano Eruption Prediction Liaison Committee. The software was developed by the National Research Institute for Earth Science and Disaster Prevention and uses the technical data C1-No 478 of the Geospatial Information Authority of Japan. Courtesy of JAXA and JMA (Volcanic activity commentary material on Nishinoshima, June 2020).

Figure 100. High levels of activity were observed at Nishinoshima by crew members aboard the marine meteorological observation ship "Ryofu Maru” on 11 July 2020. Abundant ash emissions filled the sky and tephra fell out of the ash cloud for several kilometers downwind (left, seen from 6 km NE). Incandescent explosions rose as much as 200 m into the night sky (right, seen from 4 km E). Courtesy of JMA.

During 16-26 July 2020 the Tokyo VAAC reported ash emissions at 3.7-5.2 km altitude that drifted primarily N and NE. The vessel "Keifu Maru" passed Nishinoshima on 20 July and crewmembers observed continuing emissions from the summit of dense, black ash. JCG observed an ash plume rising to at least 2.7 km altitude during their overflight of 20 July. A large dome of fresh lava was visible on the SW flank of the island (figure 101). Lower ash emissions from 2.4-3.7 km altitude were reported by the Tokyo VAAC during 27-29 July, but the altitude increased to 5.5-5.8 km during the last two days of the month. During an overflight on 30 July by the National Research Institute for Earth Science and Disaster Prevention, dark and light gray ash emissions rose to 3.0 km altitude, but no flowing lava or large bombs were observed. They also noted thick deposits of brownish-gray ash on the N side of the island (figure 102).

Figure 101. JCG observed an ash plume at Nishinoshima rising to at least 2.7 km altitude during their overflight of 20 July 2020. A large dome of fresh lava was visible on the SW flank of the island. Courtesy of JCG.

Figure 102. Ash emissions changed from dark to light gray on 30 July 2020 at Nishinoshima as seen during an overflight by the National Research Institute for Earth Science and Disaster Prevention. Thick brownish-gray ash was deposited over the lava on the N side of the island. Courtesy of JMA (Information on volcanic activity in Nishinoshima, July 2020).

JMA reported a sharp decrease in the lava eruption rate during July with thermal anomalies decreasing significantly mid-month. Multiple daily MODVOLC thermal alerts were recorded during the first half of the month but were reduced to two or three per day during the last third of July. Throughout July, SO₂ emissions were the highest recorded in modern times for Nishinoshima. High levels of emissions were measured daily, producing streams with high concentrations of SO₂ that were caught up in rotating wind currents and drifted thousands of kilometers across the Pacific Ocean (figure 103).

Figure 103. Complex atmospheric wind patterns carried the largest SO2 plumes recorded from Nishinoshima thousands of kilometers around the western Pacific Ocean during July 2020. Nishinoshima is about 1,000 km S of Tokyo. Top and bottom left images both show 6 July but at different scales. Courtesy of NASA Sulfur Dioxide Monitoring Page.

Thermal activity was greatly reduced during August 2020. Only one or two MODVOLC alerts were issued on 11, 18, 20, 21, 29, and 30 August, and no fresh lava flows were observed. The Tokyo VAAC reported ash emissions daily from 1-20 August. Plume heights were 4.9-5.8 km altitude during 1-4 August after which they dropped to 3.9 km altitude through 15 August. A brief pulse to 4.6 km altitude was recorded on 16 August, but then they dropped to 3.0 km or lower through the end of the month and became intermittent. The last ash emission was reported at 2.7 km altitude drifting W on 27 August.

No eruptive activity was observed during the Japan Coast Guard overflights on 19 and 23 August. High temperatures were measured on the inner wall of the summit crater on 19 August (figure 104). Steam plumes rose from the summit crater to about 2.5 km altitude during both visits (figure 105). Yellow-green discolored water was present on 23 August around the NW and SW coasts. No lava flows were observed, and infrared cameras did not measure any surface thermal anomalies outside of the crater. Very high levels of SO₂ emissions were measured through 12 August when they began to noticeably decrease (figure 106). By the end of the month, only small amounts of SO₂ were measured in satellite data.

Figure 104. A strong thermal anomaly was still present inside the newly enlarged summit crater at Nishinoshima on 19 August 2020. Courtesy of JCG.

Figure 105. Only steam plumes were observed rising from the summit crater of Nishinoshima during the 23 August 2020 overflight by the Japan Coast Guard. Courtesy of JCG.

Figure 106. Sulfur dioxide emissions remained very high at Nishinoshima until 12 August 2020 when they declined sharply. Circulating air currents carried SO2 thousands of kilometers around the western Pacific region. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

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), Hydrographic and Oceanographic Department, 3-1-1, Kasumigaseki, Chiyoda-ku, Tokyo 100-8932, Japan (URL: https://www1.kaiho.mlit.go.jp/GIJUTSUKOKUSAI/kaiikiDB/kaiyo18-e1.htm); 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/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Japan Aerospace Exploration Agency-Earth Observation Research Center (JAXA-EORC), 7-44-1 Jindaiji Higashi-machi, Chofu-shi, Tokyo 182-8522, Japan (URL: http://www.eorc.jaxa.jp/); 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/).

Turrialba is a stratovolcano located in Costa Rica that overlooks the city of Cartago. Three well-defined craters occur at the upper SW end of a broad 800 x 2,200 m summit depression that is breached to the NE. Activity described in the previous report primarily included weak ash explosions and minor ash emissions (BGVN 44:11). This reporting period updates information from November 2019-August 2020; volcanism dominantly consists of ash emissions during June-August, based on information from daily and weekly reports by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA) and satellite data.

Volcanism during November 2019 through mid-June was relatively low, dominated by low SO₂ emissions (100-300 tons/day) and typical low seismic tremors. A single explosion was recorded at 1850 on 7 December 2019, and two gas-and-steam plumes rose 800 m and 300 m above the crater on 25 and 27 December, respectively. An explosion was detected on 29 January 2020 but did not result in any ejecta. An overflight during the week of 10 February measured the depth of the crater (140 m); since the previous measurements made in February 2019 (220 m), the crater has filled with 80 m of debris due to frequent collapses of the NW and SE internal crater walls. Beginning around February and into at least early May 2020 the Sentinel-2 MODIS Thermal Volcanic Activity graph provided by the MIROVA system detected a small cluster of thermal anomalies (figure 52). Some of these anomalies were faintly registered in Sentinel-2 thermal satellite imagery during 10 and 25 April, with a more distinct anomaly occurring on 15 May (figure 53).

Figure 52. A small cluster of thermal anomalies were detected in the summit area of Turrialba (red dots) during February-May 2020 as recorded by the Sentinel-2 MODIS Thermal Volcanic Activity data (bands 12, 11, 8A). Courtesy of MIROVA.

Figure 53. Sentinel-2 thermal satellite imagery detected minor gas-and-steam emissions (left) and a weak thermal anomaly (right) in the summit crater at Turrialba on 11 January and 15 May 2020, respectively. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

On 18 June activity increased, which marked the start of a new eruptive period that produced ash emissions rising 100 m above the crater rim at 1714, 1723, and 1818. The next morning, 19 June, two more events at 1023 and 1039 resulted in ash emissions rising 100 m above the crater. During 23-26 June small ash emissions continued to occur each day, rising no higher than 100 m above the crater. A series of small ash eruptions that rose 100 m above the crater occurred during 28 and 29 June; four events were recorded at 0821, 1348, 1739, and 2303 on 28 June and five more were recorded at 0107, 0232, 0306, 0412, and 0818 on 29 June. The two events at 0107 and 0412 were accompanied by ballistics ejected onto the N wall of the crater, according to OVSICORI-UNA.

Almost daily ash emissions continued during 1-7 July, rising less than 100 m above the crater; no ash emissions were observed on 3 July. On 6 July, gas-and-steam and ash emissions rose hundreds of meters above the crater at 0900, resulting in local ashfall. Passive gas-and-steam emissions with minor amounts of ash were occasionally visible during 9-10 July. On 14 July an eruptive pulse was observed, generating brief incandescence at 2328, which was likely associated with a small ash emission. Dilute ash emissions at 1028 on 16 July preceded an eruption at 1209 that resulted in an ash plume rising 200 m above the crater. Ash emissions of variable densities continued through 20 July rising as high as 200 m above the crater; on 20 July incandescence was observed on the W wall of the crater. An eruptive event at 0946 on 29 July produced an ash plume that rose 200-300 m above the crater rim. During 30-31 July a series of at least ten ash eruptions were detected, rising no higher than 200 m above the crater, each lasting less than ten minutes. Some incandescence was visible on the SW wall of the crater during this time.

On 1 August at 0746 an ash plume rose 500 m above the crater. During 4-5 August a total of 19 minor ash emissions occurred, accompanied by ash plumes that rose no higher than 200 m above the crater. OVSICORI-UNA reported on 21 August that the SW wall of the crater had fractured; some incandescence in the fracture zone had been observed the previous month. Two final eruptions were detected on 22 and 24 August at 1253 and 2023, respectively. The eruption on 24 August resulted in an ash plume that rose to a maximum height of 1 km above the crater.

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

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/, https://www.facebook.com/OVSICORI/); 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, located on the island of Sicily, Italy, is a stratovolcano that has had historical eruptions dating back 3,500 years. Its most recent eruptive period began in September 2013 and has continued through July 2020, characterized by Strombolian explosions, lava flows, 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. Volcanism during this reporting period from April through July 2020 includes frequent Strombolian explosions primarily in the Voragine and NSEC craters, ash emissions, some lava effusions, and gas-and-steam emissions. Information primarily comes 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 April-July 2020. Degassing of variable intensity is typical activity from all summit vents at Etna during the reporting period. Intra-crater Strombolian explosions and ash emissions that rose to a maximum altitude of 5 km on 19 April primarily originated from the Voragine (VOR) and New Southeast Crater (NSEC) craters. At night, summit crater incandescence was occasionally visible in conjunction with explosions and degassing. During 18-19 April small lava flows were observed in the VOR and NSEC craters that descended toward the BN from the VOR Crater and the upper E and S flanks of the NSEC. On 19 April a significant eruptive event began with Strombolian explosions that gradually evolved into lava fountaining activity, ejecting hot material and spatter from the NSEC. Ash plumes that were produced during this event resulted in ashfall to the E of Etna. The flows had stopped by the end of April; activity during May consisted of Strombolian explosions in both the VOR and NSEC craters and intermittent ash plumes rising 4.5 km altitude. On 22 May Strombolian explosions in the NSEC produced multiple ash plumes, which resulted in ashfall to the S. INGV reported that the pit crater at the bottom of BN had widened and was accompanied by degassing. Explosions with intermittent ash emissions continued during June and July and were primarily focused in the VOR and NSEC craters; mild Strombolian activity in the SEC was reported in mid-July.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows multiple episodes of thermal activity throughout the reporting period (figure 296). In early April, the frequency and power of the thermal anomalies began to decrease through mid-June; in July, they had increased in power again but remained less frequent compared to activity in January through March. According to the MODVOLC thermal algorithm, a total of seven alerts were detected in the summit craters during 10 April (1), 17 April (1), 24 April (2), 10 July (1), 13 July (1), and 29 July (1) 2020. These thermal hotspots were typically registered during or after a Strombolian event. Frequent Strombolian activity contributed to distinct SO₂ plumes that drifted in different directions (figure 297).

Figure 296. Multiple episodes of varying thermal activity at Etna from 14 October 2019 through July 2020 were reflected in the MIROVA data (Log Radiative Power). In early April, the frequency and power of the thermal anomalies decreased through mid-June. In July, the thermal anomalies increased in power, but did not increase in frequency. Courtesy of MIROVA.

Figure 297. Distinct SO2 plumes from Etna were detected on multiple days during April to July 2020 due to frequent Strombolian explosions, including, 24 April (top left), 9 May (top right), 25 June (bottom left), and 21 July (bottom right) 2020. Captured by the TROPOMI instrument on the Sentinel 5P satellite, courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Activity during April-May 2020. During April, INGV reported Strombolian explosions that produced some ash emissions and intra-crater effusive activity within the Voragine Crater (VOR) and abundant degassing from the New Southeast Crater (NSEC), Northeast Crater (NEC), and from two vents on the cono della sella (saddle cone) that were sometimes accompanied by a modest amount of ash (figure 298). At night, summit crater incandescence was observed in the cono della salla. The Strombolian activity in the VOR built intra-crater scoria cones while lava flows traveled down the S flank of the largest, main cone. On 18 April effusive activity from the main cone in the VOR Crater traveled 30 m toward the Bocca Nuova (BN) Crater; the pit crater at the bottom of the BN crater had widened compared to previous observations. A brief episode of Strombolian explosions that started around 0830 on 19 April in the NSEC gradually evolved into modest lava fountaining activity by 0915, rising to 3 km altitude and ejecting bombs up to 100 m (figure 299). A large spatter deposit was found 50 m from the vent and 3-4 small lava flows were descending the NSEC crater rim; two of these summit lava flows were observed at 1006, confined to the upper E and S flanks of the cone. Around 1030, one or two vents in the cono della sella produced a gas-and-steam and ash plume that rose 5 km altitude and drifted E, resulting in ashfall on the E flank of Etna in the Valle del Bove, as well as between the towns of Zafferana Etnea (10 km SE) and Linguaglossa (17 km NE). At night, flashes of incandescence were visible at the summit. By 1155, the lava fountaining had gradually slowed, stopping completely around 1300. The NEC continued to produce gas-and-steam emissions with some intra-crater explosive activity. During the week of 20-26 April, Strombolian activity in the VOR intra-crater scoria cone ejected pyroclastic material several hundred meters above the crater rim while the lava flows had significantly decreased, though continued to travel on the E flank of the main cone. Weak, intra-crater Strombolian activity with occasional ash emissions and nightly summit incandescence were observed in the NSEC (figure 300). By 30 April there were no longer any active lava flows; the entire flow field had begun cooling. The mass of the SO₂ emissions varied in April from 5,000-15,000 tons per day.

Figure 298. Photos of Strombolian explosions at Etna in the Voragine Crater (top left), strong degassing at the Northeast Crater (NEC) (top right), and incandescent flashes and Strombolian activity in the New Southeast Crater (NSEC) seen from Tremestieri Etneo (bottom row) on 10 April 2020. Photos by Francesco Ciancitto (top row) and Boris Behncke (bottom row), courtesy of INGV.

Figure 299. Strombolian activity at Etna’s “cono della sella” of the NSEC crater on 19 April 2020 included (a-b) lava fountaining that rose 3 km altitude, ejecting bomb-sized material and a spatter deposit captured by the Montagnola (EMOV) thermal camera. (c-d) An eruptive column and increased white gas-and-steam and ash emissions were captured by the Montagnola (EMOV) visible camera and (e-f) were also seen from Tremestieri Etneo captured by Boris Behncke. Courtesy of INGV (Report 17/2020, ETNA, Bollettino Settimanale, 13/04/2020 – 19/04/2020, data emissione 21/04/2020).

Figure 300. Webcam images showing intra-crater explosive activity at Etna in the Voragine (VOR) and New Southeast Crater (NSEC) on 24 April 2020 captured by the (a-b) Montagnola and (c) Monte Cagliato cameras. At night, summit incandescence was visible and accompanied by strong degassing. Courtesy of INGV (Report 18/2020, ETNA, Bollettino Settimanale, 20/04/2020 – 26/04/2020, data emissione 28/04/2020).

Strombolian explosions produced periodic ash emissions and ejected mild, discontinuous incandescent material in the VOR Crater; the coarse material was deposited onto the S flank of BN (figure 301). Pulsating degassing continued from the summit craters, some of which were accompanied by incandescent flashes at night. The Strombolian activity in the cono della sella occasionally produced reddish ash during 3-4 May. During 5 and 8 May, there was an increase in ash emissions at the NSEC that drifted SSE. A strong explosive event in the VOR Crater located E of the main cone produced a significant amount of ash and ejected coarse material, which included blocks and bombs measuring 15-20 cm, that fell on the W edge of the crater, as well as on the S terrace of the BN Crater (figure 302).

Figure 301. Photos of Strombolian explosions and summit incandescence at Etna on 4 May (left) and during the night of 11-12 May. Photos by Gianni Pennisi (left) and Boris Behncke (right, seen from Tremestieri Etneo). Courtesy of INGV.

Figure 302. A photo on 5 May (left) and thermal image on 8 May (right) of Strombolian explosions at Etna in the Voragine Crater accompanied by a dense, gray ash plume. Photo by Daniele Andronico. Courtesy of INGV (Report 20/2020, ETNA, Bollettino Settimanale, 04/05/2020 – 10/05/2020, data emissione 12/05/2020).

On 10 May degassing continued in the NSEC while Strombolian activity fluctuated in both the VOR and NSEC Craters, ejecting ballistics beyond the crater rim; in the latter, some of the blocks fell back in, accumulated on the edge, and rolled down the slopes (figure 303). During the week of 11-17 May, eruptive activity at the VOR Crater was the lowest observed since early March; there were 4-5 weak, low intensity pulses not accompanied by bombs or ashfall in the VOR Crater. Degassing continued in the BN Crater. The crater of the cono della sella had widened further N following collapses due to the Strombolian activity, which exposed the internal wall.

Figure 303. Map of the summit craters of Etna showing the active vents, the area of cooled lava flows (light green), and the location of the widening pit crater in the Bocca Nuova (BN) Crater (light blue circle) updated on 9 May 2020. The base is modified from a 2014 DEM created by Laboratorio di Aerogeofisica-Sezione Roma 2. Black hatch marks indicate the crater rims: BN = Bocca Nuova, with NW BN-1 and SE BN-2; 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 29/2020, ETNA, Bollettino Settimanale, 06/07/2020 – 12/07/2020, data emissione 14/07/2020).

On 18 May an ash plume from the NSEC rose 4.5 km altitude and drifted NE. Strombolian explosions on 22 May at the NSEC produced multiple ash plumes that rose 4.5 km altitude and drifted S and SW (figure 304), depositing a thin layer of ash on the S slope, and resulting in ashfall in Catania (27 km S). Explosions from the VOR Crater had ejected a deposit of large clasts (greater than 30 cm) on the NE flank, between the VOR Crater and NEC on 23 May. INGV reported that the pit crater in the BN continued to widen and degassing was observed in the NSEC, VOR Crater, and NEC. During the week of 25-31 May persistent visible flashes of incandescence at night were observed, which suggested there was intra-crater Strombolian activity in the SEC and NSEC. The mass of the SO₂ plumes varied between 5,000-9,000 tons per day.

Figure 304. Photo of repeated Strombolian activity and ash emissions rising from Etna above the New Southeast Crater (NSEC) on 22 May 2020 seen from Zafferana Etnea on the SE flank at 0955 local time. Photo by Boris Behncke, INGV.

Activity during June-July 2020. During June, moderate intra-crater Strombolian activity with intermittent ash emissions continued in the NSEC and occurred more sporadically in the VOR Crater; at night, incandescence of variable intensity was observed at the summit. During the week of 8-14 June, Strombolian explosions in the cono della sella generated some incandescence and rare jets of incandescent material above the crater rim, though no ash emissions were reported. On the morning of 14 June a sequence of ten small explosions in the VOR Crater ejected incandescent material just above the crater rim and produced small ash emissions. On 25 June an overflight showed the developing pit crater in the center of the BN, accompanied by degassing along the S edge of the wall; degassing continued from the NEC, VOR Crater, SEC, and NSEC (figure 305). The mass of the SO₂ plumes measured 5,000-7,000 tons per day, according to INGV.

Figure 305. Aerial photo of Etna from the NE during an overflight on 25 June 2020 by the Catania Coast Guard (2 Nucleo Aereo della Guardia Costiera di Catania) showing degassing of the summit craters. Photo captured from the Aw139 helicopter by Stefano Branca. Courtesy of INGV (Report 27/2020, ETNA, Bollettino Settimanale, 22/06/2020 – 28/06/2020, data emissione 30/06/2020).

Similar modest, intra-crater Strombolian explosions in the NSEC, sporadic explosions in the VOR Crater, and degassing in the BN, VOR Crater, and NEC persisted into July. On 2 July degassing in the NEC was accompanied by weak intra-crater Strombolian activity. Intermittent weak ash emissions and ejecta from the NSEC and VOR Crater were observed during the month. During the week of 6-12 July INGV reported gas-and-steam emissions continued to rise from the vent in the pit crater at the bottom of BN (figure 306). On 11 July mild Strombolian activity, nighttime incandescence, and degassing was visible in the SEC (figure 307). By 15 July there was a modest increase in activity in the NSEC and VOR Craters, generating ash emissions and ejecting material over the crater rims while the other summit craters were dominantly characterized by degassing. On 31 July an explosion in the NSEC produced an ash plume that rose 4.5 km altitude.

Figure 306. Photos of the bottom of the Bocca Nuova (BN) crater at Etna on 8 July 2020 showing the developing pit crater (left) and degassing. Minor ash emissions were visible in the background at the Voragine Crater (right). Both photos by Daniele Andronico. Courtesy of INGV (Report 29/2020, ETNA, Bollettino Settimanale, 06/07/2020 – 12/07/2020, data emissione 14/07/2020).

Figure 307. Mild Strombolian activity and summit incandescence in the “cono della sella” (saddle vent) at the Southeast crater (SEC) of Etna on 11 July 2020, seen from Piano del Vescovo (left) and Piano Vetore (right). Photo by Boris Behncke, INGV.

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.

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/).