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.

In 1979-1980, an eruption at Chirinkotan included a series of ash explosions and a lava flow (SEAN 05:06). In October and November 1986, airborne observers saw a column of thick gas and ash, and then fumarolic activity (SEAN 12:04). This report discusses events during 2013 through April 2014. The location of Chirinkotan in the Kuril Islands is shown in figure 1.

Figure 1. Map showing location of Chirinkotan. Courtesy of Google Earth.

According to the Sakhalin Volcanic Eruption Response Team (SVERT), gas-and-steam emissions occurred frequently in 2013-2014 (table 1). The Aviation Color Code was Green on 24-25 May 2013, when emissions were first reported, but raised to Yellow during early June 2013, where it has remained through April 2014, the end of this report. The volcano was often obscured by clouds.

According to the U.S. Geological Survey, an M 8.3 earthquake occurred on 24 May 2013 beneath the Sea of Okhotsk, at a point is 656 km N of the volcano. The focal depth of the earthquake was ~ 600 km. The first reported gas-and-steam emission from Chirinkotan, which is in the Sea of Okhotsk, was on 24-25 May, suggesting a possible link between the two events.

Table 1. SVERT-reported dates on which gas-and-steam emissions were observed from 24 May 2013 through 30 April 2014, based on analysis of satellite images. Thermal alerts detected by SVERT and the MODVOLC satellite thermal alert system are also noted.

Geologic Background. The small, mostly unvegetated 3-km-wide island of Chirinkotan occupies the far end of an E-W volcanic chain that extends nearly 50 km W of the central part of the main Kuril Islands arc. It is the emergent summit of a volcano that rises 3000 m from the floor of the Kuril Basin. A small 1-km-wide caldera about 300-400 m deep is open to the SW. Lava flows from a cone within the breached crater reached the shore of the island. Historical eruptions have been recorded since the 18th century. Lava flows were observed by the English fur trader Captain Snow in the 1880s.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT) (URL in English: http://www.imgg.ru/?id_d=659); 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/); and Earthquake Hazards Program, US Geological Survey (URL: http://earthquake.usgs.gov/).

On 6 November 1986, weak fumarolic activity was observed during an aerial survey (SEAN 12:04). The Sakhalin Volcanic Eruption Response Team (SVERT) noted that emissions were again observed in November 2012. This report covers steam-and-gas plumes and emissions and thermal alerts between 20 November 2012 and 30 April 2014.

SVERT's monitoring of Chirpoi is hampered by the lack of surface instruments or seismic network. The volcano is primarily monitored by satellites; cloud cover, however, often prevents space-borne observations. The location of Chirpoi in the Kuril Islands is shown in figure 1.

Figure 1. Map showing location of Chirpoi. Courtesy of Google Earth.

SVERT reported thermal anomalies at a volcano of Chirpoi called Snow, starting on 17 November 2012. Periods of steam-and-gas began on 15 December 2012. This activity continued through at least April 2014, based upon analysis of satellite images (table 1). Cloud cover often obscured views of the volcano.

Table 1. Steam-and-gas plumes and emissions from Snow, a Chirpoi volcano, between 21 November 2012 and 30 April 2014, based on analysis of satellite images. Cloud cover frequently prevented observations. Courtesy of SVERT.

A search of MODVOLC thermal alerts at Chirpoi since 1980 found no such alerts until a they began at Snow on 11 November 2012. Between that date and 24 December 2012, many thermal alerts were reported. According to SVERT, this may have indicated a lava flow on the SE flank. No further alerts were reported until 8 July 2013; between 8 July and October 2013, thermal alerts were issued on six days. The only alerts between November 2013 and 30 April 2014 were on 10 March, 27-28 March, and 14, 16, 18, 21, 27, 29-30 April 2014.

Based on SVERT weekly reports on 12 and 19 November 2012, the Aviation Color Code increased from Green to Yellow between 5 and 19 November 2012, and remained Yellow through at least April 2014. (Green indicates a normal, non-eruptive state; Yellow indicates elevated unrest above background level.)

Geologic Background. Chirpoi, a small island lying between the larger islands of Simushir and Urup, contains a half dozen volcanic edifices constructed within an 8-9 km wide, partially submerged caldera. The southern rim of the caldera is exposed on nearby Brat Chirpoev Island. The symmetrical Cherny volcano, which forms the central cone of the island, erupted twice during the 18th and 19th centuries. The youngest volcano, Snow, originated between 1770 and 1810. It is composed almost entirely of lava flows, many of which have reached the sea on the southern coast. No historical eruptions are known from Brat Chirpoev, but its youthful morphology suggests recent strombolian activity.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT) (URL in English: http://www.imgg.ru/?id_d=659); and 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/).

As reported in BGVN 38:04,18-months of calm at Volcán de Colima was interrupted by a sequence of intermediate-to-small size Vulcanian explosions in January 2013. This sequence of explosions excavated a 250,000 m³ crater in the 2007-2011 lava dome (figure 105).

Figure 105. The new crater at Colima that was formed during the January 2013 explosive sequence. Photo was taken on 31 January 2013 during a flight of Civil Protection of Jalisco State. Courtesy of Colima Volcano Observatory.

Episodes of effusive activity within the new crater were recorded between the explosive events. An infrared image shows fresh magma at the crater base (figure 106).

Figure 106. Thermal image taken during a flight over Colima on 11 January showing the emergence of fresh high temperature lava. Courtesy of Facultad de Ciencias, University of Colima.

Figure 107 summarizes the 2013 activity at Colima, indicating three stages. Those stages were defined based on data from seismic (figure 107, A and B), and video (figure 107C) monitoring. The first stage (St. 1) refers to the sequence of explosions described in (BGVN 38:04). On 15 February and the end of March (St. 2), video observations indicated continued gradual lava dome growth in the new crater. The dome increased in height at the rate of ~1 m/day. As a result, during this interval the maximum elevation of the volcano increased from 3,843 m to 3,874 m. The dome continued to fill the crater through the end of March (figure 108). During April-November 2013 the third stage (St. 3) of significant dome growth stopped.

Figure 107. Plots A-C describe the development of the 2013 eruption at VolcÁn de Colima., showing three stages of development: Stage One (St. 1), involving explosions; Stage Two (St. 2), involving dome growth and extra-crater lava flow; and Stage Three (St. 3), involving lack of measurable dome growth but with ongoing explosions. [A] Daily variations in the number of small explosions and rockfalls identified from a seismometer 4 km from the crater. [B] Variations in the radiated seismic energy of explosive events recorded at a distance of 4 km. The four largest explosions of the St.1 are shown with diamonds. [C] Variations in the maximum elevation of the growing lava dome based on continuous video monitoring. Courtesy of Colima Volcano Observatory.

The February-March lava dome growth was accompanied by an increase in the frequency and energy of the small explosions (figures 107A and 107B). Once the dome filled the crater a small lava flow traveled toward the W (figure 108). Due to the steepness of this flank, much of the fresh material descended as rockfalls, whose frequency increased from April (figure 107A).

Figure 108. The filled crater and the lava flow that was formed during the second stage of activity on Colima's western slope. Photo was taken on 19 April 2013 during a flight of Civil Protection of Jalisco State. Courtesy of Colima Volcano Observatory.

During the third stage, the daily number of small explosions and rockfalls was quite stable. This stage was associated with the occurrence of 14 lahars that began with the rainy season being registered between 11 June and 8 October 2013 descending the flanks of the volcano (figure 109). The largest, lasting around 6 hours, occurred on 16 September 2013, when the Pacific coast was affected by tropical cyclone Manuel.

Figure 109. Block-rich front of the 11 June 2013 lahar recorded along the Montegrande ravine by the lahar monitoring station located 5.8 km S of the crater. Courtesy of Centro de Geociencias, UNAM.

2014. On 21 January 2014 the Washington VAAC first reported scattered ash emissions drifting S at 4.9 km altitude followed by a second and third emission that drifted SSW and S , respectively. Smaller ash emissions were noted throughout the following weeks. For example, Washington VAAC reported that on 7 February a small emission rose and drifted E then SE, followed by a later one the same day that drifted SE.

From data provided by the Mexico Meteorological Watch Office, on 28 February an ash emission drifted 15 km SE at altitudes up to 4.6 km, and the following day, on 1 March, two emissions were reported drifting NNW, followed by three other plumes later the same day.

The Washington VACC continued to report on activity as seen from satellite imaging, noting another emission on 6 March that drifted NE before dissipating and ; an emission on 12 March that drifted 25 km NNE before similarly dissipating; and a 19 March emission, which rose to 4.6 km and drifted E before dissipating 30 km from the source. A separate later plume followed on 22 March and drifted N.

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

Information Contacts: Observatorio Vulcanologico de la Universidad de Colima (Colima Volcanological Observatory), Calle Manuel Payno, 209 Colima, Col., 28045 Mexico (URL: http://www.ucol.mex/volc/); Facultad de Ciencias, Universidad de Colima; and Washington Volcanic Ash Advisory Center (VAAC), NOAA Science Center Room 401, 5200 Auth road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

A large eruption occurred at Cerro Hudson on 8 August 1991 (BGVN 16:07-18:02), which was followed by minor non-eruptive activity that caused sulfurous odors, increased river flows and turbidity, and noise at least through early 1995 (BGVN 20:02). This report describes a minor eruption during 25-26 October 2011. Cerro Hudson is located in Patagonia in the Aysén Region of Chile (figure 1).

Figure 8. Map of Chile (a), the Aysén region in red (b), and a detail marking the region's capital, Coyhaique, and Cerro Hudson (c). Original image courtesy of Wikipedia.

According to the Southern Andes Volcanological Observatory-National Geology and Mining Service (OVDAS-SERNAGEOMIN), seismicity increased during 25-26 October 2011. On 25 October, an M 4.6 volcano-tectonic earthquake occurred at a depth of 19 km, followed by a seismic swarm. More than 100 events, with depths ranging from 15 to 25 km, were recorded through the next day; twelve were M 3, and three were M 4. Most of the earthquakes were volcano-tectonic events with magnitudes below 3.6 and located W of the caldera at depths between 3 and 25 km. The earthquake hypocenters became shallower over time. OVDAS-SERNAGEOMIN did not detect any explosive event or episodes of high intensity harmonic tremor (as reported on 28 October).

During a 24-hour period beginning at 1600 on 27 October, an average of one earthquake per hour was recorded. Most were long-period with magnitudes less than 2.2. On 27 October, an M 3.6 VT earthquake occurred on the SW edge of the crater.

On 26 and 27 October, OVDAS-SERNAGEOMIN and local authorities flew over the caldera and observed three new craters along the SSE edge of the caldera, with approximate diameters of 200, 300, and 500 m. Mostly white plumes rose above the two smaller craters. The largest, southern-most crater emitted a plume with more ash that rose more than 5 km above the crater. Satellite imagery showed a plume drifting 12 km SE. The scientists also observed lahars in the Huemules river, to the W. In response, OVDAS-SERNAGEOMIN raised the Alert Level to 5 (Red), the highest level. According to the Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), 140 people were evacuated from areas within a 45-km radius of the volcano, defined as a high-risk zone. The hazard lay not only with earthquakes and eruption, but also with the possibility of flooding resulting from to glacier melt.

During another overflight on 28 October scientists observed a gas plume with a very low ash content rising 3-4 km above the craters. Seismicity continued to decrease during 28-29 October. Plumes were observed on 29 October (figure 9). Scientists conducting an overflight noted that one ash plume rose 1 km above the craters and drifted 5-8 km NE. They also confirmed that a large lahar descended the volcano and flowed into the drainage system including the Huemules river during the initial phase of the eruption. During another observation flight on 30 October, scientists saw ash plumes rising 0.8 km from two of the three craters.

Figure 9. The three vents at Cerro Hudson observed on 29 October 2011. Dark gray ash can be seen at the base of at least one vent. Courtesy of, and copyrighted by, El Mercurio and SERNAGEOMIN, Chile.

On 31 October, scientists observed gas plumes rising 0.5 km above the craters and drifting SE. Around 31 October, they also noted subsequent minor explosions and ash emissions. On 1 November, scientists observed an explosion and an accompanying ash plume that rose 1.5 km above the active craters.

On 2 November, OVDAS-SERNAGEOMIN reported that the Alert Level for Cerro Hudson had been lowered to 4 (Yellow), noting that the eruption that began on 26 October had ceased. ONEMI reported that the 140 evacuees were permitted to return home. Analysis of ash deposited on the edge of the crater during the eruption indicated the presence of juvenile basalt. During 1-6 November between 16 and 110 earthquakes per day were recorded, and satellite images showed drifting plumes daily.

According to OVDAS-SERNAGEOMIN, satellite imagery and an area web camera showed no plumes during 7-15 November. Seismic activity decreased significantly, reaching no more than four earthquakes per hour.

The NASA Earth Observatory photographed Cerro Hudson on 17 November 2011 (figure 10) and weeks later (figure 11).

Figure 10. Image of Cerro Hudson taken in natural color on 17 November 2011 by the Advanced Land Imager (ALI) on NASA's Earth Observing-1 (EO-1) satellite. The image shows extensive fresh ash on the snowy surface. The apparent vent rests on the image's left-center, at the apex of the darkest funnel-shaped area. Courtesy of NASA Earth Observatory (Image by Jesse Allen; caption by Michon Scott).

Figure 11. This post-eruptive image of Cerro Hudson, taken two weeks after figure 10, shows the volcano covered with snow. The label "apparent vent site" sits directly above the oval shaped vent site, a spot at left located below the gap between the words "apparent" and "vent" (also see previous figure). Courtesy of NASA Earth Observatory.

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

Information Contacts: SERNAGEOMIN (Southern Andes Volcanological Observatory-National Geology and Mining Service), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), Beaucheff 1637 / 1671, Santiago, Chile (URL: http://www.onemi.cl/); and El Mercurio (URL: http://www.elmercurio.cl/).

Our last report on activity at Karthala, located in the Comoros Islands, covered elevated seismicity and a subsequent eruption in January 2007 (BGVN 32:01). The volcano was then quiet until May 2012.

U.S. Embassy Comoros Officer, Michael Zorick informed us that residents on Karthala's W flank, in the villages of Mde and Mkazi (each ~12 km from the summit), reported observing intensified red glow toward the volcano summit during the night of 9-10 May 2012. He further indicated that there was no perceptible seismic activity.

A search for thermal alerts on the MODVOLC website revealed an absence of alerts after those associated with the 2007 eruption.

Geologic Background. The southernmost and largest of the two shield volcanoes forming Grand Comore Island (also known as Ngazidja Island), Karthala contains a 3 x 4 km summit caldera generated by repeated collapse. Elongated rift zones extend to the NNW and SE from the summit of the Hawaiian-style basaltic shield, which has an asymmetrical profile that is steeper to the S. The lower SE rift zone forms the Massif du Badjini, a peninsula at the SE tip of the island. Historical eruptions have modified the morphology of the compound, irregular summit caldera. More than twenty eruptions have been recorded since the 19th century from the summit caldera and vents on the N and S flanks. Many lava flows have reached the sea on both sides of the island. An 1860 lava flow from the summit caldera traveled ~13 km to the NW, reaching the W coast to the N of the capital city of Moroni.

Information Contacts: Michael P. Zorick, Comoros Officer, Embassy of the United States of America, Antananarivo, Madagascar; and 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/).

This is the first Bulletin report for Mauna Kea, the tallest volcano on the Island of Hawai`i (figures 1, 2, and 3). Although the most recent eruption occurred ~4,500 years ago, this volcano has the potential to reawaken. This report presents early observations by Western explorers; discussions from Hawaiian Volcano Observatory (HVO) scientists focusing on the potential for future eruptions; seismicity during 2000-2013; and a recent report by HVO scientists highlighting drastic changes at an alpine lake, Lake Waiau.

Figure 1. Mauna Kea is one of five volcanoes comprising the Island of Hawai`i, the others being Kohala, Hualalai, Mauna Loa, and Kilauea. The archipelago of Hawai`i includes the eight islands: Ni`ihau, Kaua`i, O`ahu, Moloka`i, Lana`i, Maui, Kaho`olawe, and Hawai`i (from W-to-E). Courtesy of Holt and others (2006) and Google Earth.

Figure 2. This view of Mauna Kea is from the Keaukaha area, the S edge of Hilo Bay. Seasonal snowfall covers the summit area which is also dotted with cinder cones. The highest point, indicated with the arrow, is located at the highest point on the rim of the cinder cone Pu`u Wekiu. The small white points to the right of the arrow are several of the astronomical telescopes belonging to the Mauna Kea Observatories, part of the University of Hawai`i's Institute for Astronomy. Photo by Valerie Veriato Victorine; courtesy of Hawaii News Now.

Figure 3. An aerial view of Mauna Kea's summit and S flank was acquired in 1995 from a NASA C-130 aircraft. The Mauna Kea Access Road reaches the summit after numerous switchbacks that cross through fields of cinder cones (note the gray line above the propeller) on the S flank. This view is approximately centered on the cinder cone Pu`u Kole, which is one of the features remaining from the Holocene Laupahoehoe eruption. A forest reserve boundary encloses the upper flanks of Mauna Kea and appears in this photo as a line that makes a sharp corner as it includes the lower edge of Pu`u Kole. Courtesy of Scott Rowland (University of Hawaii at Manoa).

Eruptive style and activity status. Mauna Kea is presently considered a volcano exhibiting quiescence that has, according to the known geologic record, an extensive history of lapsed activity. Between 6,000 and 4,000 years ago, eruptions occurred at at least seven separate vents. The record indicates that compared with Mauna Loa, which erupted every few years to few tens of years, and Hualalai, which erupted every few hundred years, Mauna Kea has exhibited long breaks in activity (USGS, 2002).

Based on the occurrence of 12 eruptions within a 10,000 year period, Mauna Kea's recurrence interval is ~1,000 years (Geohazards Consultants International, Inc., 2000). According to the Mauna Kea Science Reserve Master Plan released by the Geohazards Consultants International, Inc. in March 2000:

"Mauna Kea's post-glacial eruptions have been episodic rather than periodic, however, with a particular concentration of eruptive activity between 4,400-5,600 years ago. The 1,000 year recurrence interval of the past 10,000 years does not thus indicate that an eruption is 'overdue', but does reinforce the likelihood that eruptions will occur sporadically in the future."

This pattern of activity might also imply that the next eruption of Mauna Kea could be followed by others at much shorter intervals, representing a potential clustering of events in the given time interval (Jim Kauahikaua, personal communication, 30 May 2014).

Mauna Kea's most recent eruption occurred ~4,500 years ago, generating both lava flows and cinder cones. This activity is considered characteristic of a volcanic system that had evolved past the shield-building stage to the post-shield stage (Hoover and Fodor, 1997). The above-stated age determinations were made based on radiocarbon dating of charcoal collected within the Humu`ula soil (Porter, 1971; Wolfe and others, 1997); this soil lies directly beneath the S flank lava flows of Pu`ukole and Pu`u Loa Loa (figure 4).

Figure 4. (Index map) The Island of Hawai`i encompasses five volcanic centers. Note Hilo Bay (HB), the location where the photo in figure 2 was taken. The shaded box shows the area of the main map. (Main Map) Holocene cinder cones and lava flows are located on Mauna Kea's lower S flank, the lower extent of which have been covered by Mauna Loa lava flows. The two sets of isopachs indicate tephra units vented from the cinder cones Pu`ukole and Pu`u Loa Loa. State Highway 200 (the Saddle Road) is indicated in red, located at the lower margin. The point marked as Hale Pohaku is the location of the Visitor Information Station and the Onizuka Center for International Astronomy. Map modified from Porter (1971).

The designations of shield-building and post-shield stages come from a system of structural development that represents the current understanding of Hawaiian volcanism. Significant cinder cone eruptions are a hallmark of the post-shield stage as well as: "(1) the absence of a summit caldera and elongated fissure vents that radiate across its summit; (2) steeper and more irregular topography (for example, the upper flanks of Mauna Kea are twice as steep as those of Mauna Loa; [figure 5]); and (3) different chemical compositions of the lava" (Clague and Dalrymple, 1987; USGS, 2002).

Figure 5.Two profile photos of Mauna Kea (top) and Mauna Loa (bottom). Mauna Kea (top) displays an irregular profile due to the abundance of steep-sided cinder cones formed by hawaiite, a less fluid and more explosive lava composition compared with the tholeiitic basalt that characterizes shield-stage volcanism. Mauna Loa (bottom) exhibits the classic, shield-stage morphology that results due to numerous tholeiitic basalt eruptions (and known to be particularly voluminous). This morphology is relatively smooth and shallow compared with Mauna Kea. USGS photos taken by Taeko Jane Takahashi in 1991 with caption details from Wright and others (1992b).

Gravity model. Investigations by Kauahikaua and others (2000) determined a three-dimensional gravity model for the Island of Hawai`i distinguished the five volcanic centers comprising the island: Kohala, Mauna Kea, Hualalai, Mauna Loa, and Kilauea (figure 6). The base data for that map came from more than 3,300 gravity measurements made above sea level. Positive gravity anomalies define gravitationally dense zones caused by intrusions and cumulates beneath the summit and known rift zones of each of the five volcanoes composing the island. Figure 6 maps the 3-dimensional structure as modeled from the gravity data and expresses the gravity anomalies in terms of elevation from the overlying ground surface.

Figure 6. The Island of Hawai`i, including Mauna Kea, in a map showing the distance from the ground surface to the modeled upper surface of dense volcanic cores. Near the center of the island, the edifice of Mauna Kea appears covered with alkali basalt vents (gray diamonds). The contour interval represents 1 km. The authors plot known vents and other features such as slumps in order to compare them to the model. The subaerial features were taken from Wolfe and Morris (1996) and the submarine geologic features, from Holcomb (1996). Rift zones are marked by linear distributions of vents; alternative locations for the summit of Mahukona volcano are shown by "a" and "b." Modified from Kauahikaua and others, 2000.

"Mauna Kea has an elliptical-shaped core, slightly elongated east-west, with a broad, linear feature trending southeast. This linear feature may be a buried rift zone of Mauna Kea, although no surface expressions of those rift zones have been mapped (Kauahikaua and others, 2000)."

The submarine feature known as the Hilo Ridge was also included in the density study with data contributed by GLORIA (a side-scan sonar) as well as satellites ERS-1, Geosat, and Seasat. Prior to this investigation, the Hilo Ridge had been attributed to Mauna Kea as its possible rift zone; however, the authors determined a stronger connection with Kohala due to multiple factors including the strongly NW-trending linear zone that extends ~80 km from the modelled core of Kohala.

Early European observations. An early survey of Hawai`i was conducted by Archibald Menzies, a botanist who accompanied Captain George Vancouver during the cruises of 1792-1794. Menzies successfully ascended Mauna Loa in February 1794 (a team from Captain Cook's crew had unsuccessfully attempted the summit in 1779; see figure 7). Menzies estimated the heights of Mauna Loa and Mauna Kea to within 31 m of the currently accepted value, "a remarkable surveying feat for that time" (Wright and others, 1992b).

Figure 7. This map of the Hawaiian Islands has been cropped and centered on the area of the Big Island. Mauna Kea and other major landmarks were annotated with the early spelling conventions. According to Wright and others, 1992b, "This was the first map of the island of Hawai`i, made in 1779 by Henry Roberts, a member of Captain Cook's crew. Four volcanoes are shown, and only the two largest ones are named. Kilauea is conspicuously absent from this map and from a similar one made following Vancouver's voyages of 1792-1794. Neither Cook nor Vancouver visited the eastern side of Hawai`i or saw any volcanic activity." Modified from Wright and others (1992b) and Fitzpatrick (1986).

The first petrologist to study Mauna Kea, R.A. Daly, determined not only that Mauna Kea's upper flanks were dominated by lava flows more rich in silica (he called them "andesite" although current classifications label them "hawaiite"), but also that the edifice had been modified by glaciers (Wolfe and others, 1997; Daly, 1911). Stearns and Macdonald (1946) and Washington (1923) expanded the knowledge base of Mauna Kea's geochemistry, and Gregory and Wentworth (1937) established that the glacial features from the most recent glacial episode (40,000 to 13,000 years ago) were interspersed with primary volcanic material. Wolfe and others (1997) determined that "eruptive activity of Mauna Kea was partly contemporaneous with that at Kohala, Hualalai, and Mauna Loa, and the volcano boundaries are undoubtedly complex."

HVO Volcano Watch article highlights a Mauna Kea forecast. The potential for a future eruption from Mauna Kea was addressed in a Volcano Watch article posted in June 2000 by then Scientist-in-Charge, Don Swanson, from the Hawaiian Volcano Observatory (HVO) (Swanson, 2000ab). The article addresses not only eruption frequency but also trends in eruption style, the potential response of the telescope installation at Mauna Kea's summit, and a general forecast for a likely scenario in the future.

"The next eruption of Mauna Kea."

"Mauna Kea's peaceful appearance is misleading. The volcano is not dead. It erupted many times between 60,000 and 4,000 years ago, and some periods of quiet during that time apparently lasted longer than 4,000 years. Given that record, future eruptions seem almost certain.

"Before the next one, we should have ample warning provided by our current seismic and geodetic monitoring systems. A number of earthquakes occur beneath Mauna Kea each year, and you can bet that we pay close attention to them. However, they all appear to be associated with tectonic faulting rather than movement of magma.

"The telescopes on top of the volcano may be the first to indicate that something is amiss. The coordinates used for tracking their observations will begin to drift unexpectedly as the volcano is swelling. In a sense, the telescopes will serve as very expensive tiltmeters.

"We cannot now say when the next eruption will take place, except that it is unlikely to be in the next several months, given the current lack of any precursory signs. Whether the timing is years, centuries, or millennia is entirely unclear.

"But we can say something about the probable nature of the next eruption, because we know what the most recent ones were like, thanks to recently published research by Ed Wolfe [see Wolfe and others, 1997], former staff member of HVO, and colleagues.

"The next eruption could take place anywhere on the upper flanks of the volcano. As Mauna Kea evolved from its early shield stage (equivalent to Kilauea and Mauna Loa today) to its present postshield stage, the volcano lost its rift zones. Consequently, the postshield eruptions are not concentrated along narrow zones but instead are scattered across the mountain. [See figure 6.]

"For example, the most recent eruptive period, 6,000-4,000 years ago, involved eight vents on the south flank of the volcano between Kala`i`eha cone (near Humu`ula) and Pu`ukole (east of Hale Pohaku). During this same period, eruptions took place on the northeast flank at Pu`u Lehu and Pu`u Kanakaleonui. Lava from Pu`u Kanakaleonui flowed more than 20 km (12 miles) northeastward, entering the sea to form Laupahoehoe Point.

"The next eruption will likely produce a lava flow, because each eruption in the past 60,000 years has done so. The longest flows will reach 15-25 km (9-15 miles) downslope. Most of each flow will be `a`a, but pahoehoe may form near vents.

"A prominent cinder cone will probably be constructed at each vent. The cinder cones responsible for the "bumpy" appearance of Mauna Kea's surface formed during the 60,000-4,000-year interval. The cones mentioned by name above, and several others, were built during the latest eruptive period 6,000-4,000 years ago. The next eruption will likely produce a similar cone.

"Cinder cones form at vents that are point sources, not elongate fissures. All activity is concentrated at one place, so that fountaining and spattering build a high cone rather than a long rampart. Past eruptions-and hence future ones--probably lasted months to several years, providing enough time to construct a substantial cone. Those eruptions spread voluminous ash deposits far beyond the cinder cones themselves, and the next eruption will probably do so, too.

"Possibly, however, there will not be enough spattering to build a lasting cone. Such an eruption happened about 1 km (0.6 miles) southeast of Hale Pohaku, when a vent put out a moderate volume of lava without building a spatter or cinder cone.

"The next eruption of Mauna Kea is unlikely to occur in our lifetimes, but it could. There is no reason to fear such an eruption. It would not threaten human life, provided due care were taken, though it could prove devastating to property and infrastructure, particularly if a lava flow traveled to the Hamakua coast or the Waimea area."

Mauna Kea's seismicity. HVO has monitored and maintained the record of seismicity for the entire region of Hawai`i. The seismicity detected beneath Mauna Kea has been characterized as "infrequent and sparse." Notable seismicity occurred in 1994, 2001, and 2011, when earthquakes were large enough to be felt by the general public. Island-wide instrumentation allowed excellent location data for the local seismicity (figure 8).

Figure 8. The seismic network that monitors Mauna Kea and the other volcanoes of Hawai`i spans six islands. This map appeared in the USGS Fact Sheet released in 2011.

HVO reported that, several times each year, earthquakes from Mauna Kea cause shaking that is noted by local populations - especially the operators of the Mauna Kea astronomical observatory, who rely on stable instrumentation in order to make precise observations. Reports of felt earthquakes from Mauna Kea correlated with magnitude 2.1-4.9 earthquakes during 1973-2012.

Elevated seismicity during October-December 2011 resulted in 30 felt earthquakes. Approximately 570 people reported the M 4.5 earthquake that occurred on 20 October 2011 and also 10 of the aftershocks that followed (figure 9). HVO reported that, like many of Mauna Kea's earthquakes, these earthquakes were "most likely caused by structural adjustments within the Earth's crust due to the heavy load of Mauna Kea." With an estimated volume of >30,000 km³, Mauna Kea rises ~10,000 m above the seafloor, causing stress to accumulate from the mass of the volcano (Lockwood and Hazlett, 2010).

Figure 9. This map includes the located seismicity from Mauna Kea's seismic sequence between 19 October and 31 December 2011. Within 10 km of the summit, an M 4.5 earthquake (20 October 2011) and aftershocks occurred. Courtesy of HVO.

Earthquake swarms at Mauna Kea. HVO reported that earthquake swarms occasionally occur at Mauna Kea. On 23 February 2001, a swarm of ~15 events was detected within a 21-hour period. These earthquakes were mainly located ~15 km S of Pa`auilo (~3 km NW of Kuka`iau, figure 10), at a depth of 8-11 km.

Figure 10. Geographic features of Mauna Kea included in this map are discussed in this text. Topographic contours are from U.S. Geological Survey, Hawaii County, Sheets 1 and 2, 1980; 4,000-m contour omitted. The following abbreviations are included: ag, the aqueduct gulch; HS, Hopukani Springs; HSS, Humu`ula Sheep Station; LS, Liloe Spring; WS, Waihu Spring. Map modified from Wolfe and others (1997).

Lake Waiau recedes. The cinder cone Pu`uwaiau, located within 2 km of the summit, has contained a freshwater lake that was considered permanent by Wolfe and others (1997) (figures 11 and 12). Lake Waiau has likely persisted due to the once-glassy cinders and bombs that have weathered to smectite with zeolites within the void spaces. These alteration products may serve as a weak cement between the pyroclasts and reduce the permeability of the cinder cone's base. Sporadic winter storms have provided most, if not all, of the water captured in this considerably arid region (Patrick and Delparte, 2014). Contributions from permafrost were also proposed by Woodcock (1980), but the presence of permafrost has not been confirmed near Lake Waiau.

Figure 11. An aerial view of Mauna Kea's summit was acquired in 1995 from a NASA C-130 aircraft. The highest cinder cone, Pu`u Wekiu, is centered in this view with several astronomical telescopes in view on the left-hand side. The small oval Lake Waiau is on upper the right-hand side of this photo. Courtesy of Scott Rowland (School of Ocean and Earth Science and Technology, University of Hawaii at Manoa).

Figure 12. This aerial photo includes Mauna Kea's Pu`uwaiau where Lake Waiau is indicated with the yellow arrow. The view is approximately SW. A large cinder cone, Pu`uhaukea, is in the foreground. A dark lava flow from Mauna Loa is in the far distance. Courtesy of Richard Wainscoat (Institute for Astronomy, University of Hawai`i).

Patrick and Delparte (2014) reported that the lake size before 2010 was 5,000-7,000 m² with a depth of ~3 m, but recently, the size has been decreasing rapidly. In the recent past, the lake was known to overflow through the Pohakuloa Gulch when water levels exceeded the rim (as recently as February 2002) (Ehlmann and others, 2005).

Researchers have determined that Lake Waiau is sensitive to precipitation levels (Woodcock, 1980) and that ongoing drought conditions could be driving the lake's change (Patrick and Delparte, 2014). Based on the National Drought Mitigation Center's data, since 2008, and notably in March 2010, precipitation has been sparse at the summit of Mauna Kea.

In December 2013, scientists visited the lake and observed an unprecedented sight (figure 13). Lake Waiau measured a mere 115 m² and was roughly 10-20 cm deep (Patrick and Delparte, 2014). While the lake size was known to fluctuate over time, this dramatic reduction has caused concern, given the possibility of losing a specialized ecosystem as well as a prominent feature of Hawaiian ethnogeography. Mauna Kea's summit is considered "one of the most sacred spots in the Hawaiian Islands. Archaeological sites near the summit attest to its prolonged spiritual importance...(Patrick and Delparte, 2014)."

Figure 13. The rapid drop in Mauna Kea's Lake Waiau water level began in 2010. Prior to 2010, the lake area was typically 5,000-7,000 m2, with the maximum size outlined in yellow in the top left image (depth was ~3 m). By late 2013, the lake was just 100-200 m2 in area. Photographs courtesy of Office of Mauna Kea Management and modified from Patrick and Delparte (2014)..

USGS scientists at HVO as well as collaborators, including Idaho State University, continued to study the conditions at Lake Waiau after the significant survey was conducted in December 2013. As of May 2014, strong winter rains had partially restored the lake, providing stronger evidence that the multi-year shrinkage was due to the ongoing drought as opposed to changes in the volcanic system.

A note regarding the name Mauna Kea. The popular translation of the Hawaiian name Mauna Kea is frequently "White Mountain," however, significant discussions have focused on the source of the name. There has been growing consensus that Mauna Kea is a shortened form of Mauna a Wakea, which refers to the sky father Wakea.

According to testaments presented in the Final Environmental Impact Statement of the Federal Highway Administration Project No. A-AD-6(1) which included potential cultural impacts on the island by expanding State Routes 190 and 200, "The mountain is the sacred child of Wakea, and it is the source for the land. The mountains and land were genealogically connected to native Hawaiians through the original ancestor, Wakea [sky father] and Papa [earth mother]."

Ethnographic research conducted prior to 1999 and released in the impact statement concluded that the summit area of Mauna Kea was eligible for the National Register of Historic Places due to traditional cultural property.

A note regarding Hawaiian names and nomenclature. As previously noted in other Bulletin reports, according to Runyon (2006), "The U.S. Board on Geographic Names (BGN) is responsible for establishing and maintaining uniform geographical name usage throughout all departments and agencies of the United States government. As such, the Board collects and promulgates every name that is considered official for Federal use. The official vehicle for promulgating these names and their locative attributes is the Geographic Names Information System (GNIS).

"Until the 1990's, it was also Federal policy to omit most diacritics and writing marks from placenames on Federal maps and documents. The few exceptions included the Spanish tilde and the French accent marks, but otherwise the special characters found in indigenous names were always dropped. In more recent years, however, the BGN has amended its policy to permit the inclusion of such marks, thus more accurately reflecting the true representation of the native language. An example of this has been the addition of the glottal stop (okina) and macron (kahako) to placenames of Hawaiian origin, which prior to 1995 had always been omitted. The BGN staff, under the direction and guidance of the Hawaii State Geographic Names Authority, has been restoring systemically these marks to each Hawaiian name listed in GNIS."

GVP will strive to conform to GNIS nomenclature. It remains a technological challenge, but a goal.

References: Clague, D.A., and Dalrymple, G.B., 1987, The Hawaiian-Emperor volcanic chain. Part I. Geologic evolution, chap. 1 of Decker, R.W, Wright, T.L., and Stauffer, PH., eds., Volcanism in Hawaii: U.S. Geological Survey Professional Paper 1350, v. 1, p. 5-54.

Daly, R.A., 1911, Magmatic differentiation in Hawaii: Journal of Geology, v. 19, no. 4, p. 289-316.

Federal Highway Administration, 1999, Final Environmental Impact Statement Part 1: Hawaii State Route 200, Mamalahoa Highway (SR 190) to Milepost 6 Saddle Road, County of Hawai`i, State of Hawai`i, FHWA Project No. A-AD-6(1).

Ehlmann, B.L., Arvidson, R.E., Jolliff, B.L., Johnson, S.S., Ebel, B., Lovenduski, N., Morris, J.D., Beyers, J.A., Snider, N.O., and Criss, R.E., 2005. Hydrologic and isotopic modeling of Alpine Lake Waiau, Mauna Kea, Hawai`i. University of Hawaii Press, p. 1-15.

Fitzpatrick, G.L, 1986. The early mapping of Hawaii. Honolulu: Editions Limited, vol. 1, 160 pp.

Geohazards Consultants International, Inc., Mauna Kea Science Reserve Master Plan, Volcano, HI, March 2000, 22 p.

Gregory, H.E., and Wentworth, C.K., 1937, General features and glacial geology of Mauna Kea, Hawaii: Geological Society of America Bulletin, v. 48, no. 12, p. 1719-1742.

Holt, Rinehart, and Winston (2006), Hawaii. Retrieved from http://go.hrw.com/atlas/norm_htm/hawaii.htm.

Hoover, S.R. and Fodor, R.V., 1997, Magma-reservoir crystallization processes: small-scale dikes in cumulate gabbros, Mauna Kea Volcano, Hawaii, Bulletin of Volcanology, 59, p. 186-197.

Kauahikaua, J., Hildenbrand, T., & Webring, M., 2000. Deep magmatic structures of Hawaiian volcanoes, imaged by three-dimensional gravity models. Geology, 28, 10, p. 883.

Lockwood, J.P., and Hazlett, R.W., 2010. Volcanoes: Global Perspectives, Wiley-Blackwell, Hoboken, NJ, ix, 539 p.

Okubo, P.G. and Nakata, J.S., 2011, Earthquakes in Hawai`i-An Underappreciated but Serious Hazard, Fact Sheet 2011-3013, USGS Fact Sheet, September 2011. (http://pubs.usgs.gov/fs/2011/3013/)

Patrick, M. R. and Delparte, D., 2014, Tracking Dramatic Changes at Hawaii's Only Alpine Lake: EOS (Transactions, American Geophysical Union), Vol. 95, No. 14, p. 117-118.

Porter, S.C., 1971, Holocene Eruptions of Mauna Kea Volcano, Hawaii, Science, Vol. 172 no. 3981 p. 375-377.

Stearns, H.T., and Macdonald, G.A., 1946, Geology and ground-water resources of the Island of Hawaii: Hawaii Division of Hydrography Bulletin 9, 363 p.

Swanson, D.A., (June 2000a). The next eruption of Mauna Kea. Volcano Watch. Retrieved from http://hvo.wr.usgs.gov/volcanowatch/archive/2000/00_06_01.html.

Swanson, D.A., 2000b, Don't be fooled by seemingly peaceful Mauna Kea Volcano--it could erupt again: Hawaii Tribune-Herald, June 4, p. 2.

USGS-HVO (May 2002). Mauna Kea Hawai`i's Tallest Volcano. Other Volcanoes. Retrieved from http://hvo.wr.usgs.gov/volcanoes/maunakea/.

Washington, H.S., 1923, Petrology of the Hawaiian Islands; I, Kohala and Mauna Kea, Hawaii: American Journal of Science, ser. 5, v. 5, no. 30, p. 465-502.

Wolfe, E.W., Wise, W.S., and Dalrymple, G.B., 1997, The geology and petrology of Mauna Kea volcano, Hawaii: a study of postshield volcanism. U.S. Geological Survey Professional Paper 1557, Washington, D.C.: U.S. G.P.O.

Woodcock, A., 1980. Hawaiian alpine lake level, rainfall trends, and spring flow, Pacific Science, 34, p. 195–209.

Wright, T.L., Chu, J.Y., Esposo, J., Heliker, C., Hodge, J., Lockwood, J.P., and Vogt, S.M., 1992a, Map showing lava-flow hazard zones, island of Hawaii: U.S. Geological Survey Miscellaneous Field Studies Map MF-2193, scale 1:250,000.

Wright, T.L., Takahashi, T.J., and Griggs, J.D., 1992b, Hawai`i Volcano Watch: A Pictorial History, 1779-1991, University of Hawaii Press, Honolulu, 162 p.

Geologic Background. Mauna Kea, Hawaii's highest volcano, reaches 4205 m, only 35 m above its neighbor, Mauna Loa. In contrast to Mauna Loa, Mauna Kea lacks a summit caldera and is capped by a profusion of cinder cones and pyroclastic deposits. It's rift zones are less pronounced than on neighboring volcanoes, and the eruption of voluminous, late-stage pyroclastic material has buried much of the early basaltic shield volcano, creating a steeper and more irregular profile. This transition took place about 200,000 to 250,000 years ago, and much of Mauna Kea, whose Hawaiian name means "White Mountain," was constructed during the Pleistocene. Its age and high altitude make it the only Hawaiian volcano with glacial moraines. A road that reaches a cluster of astronomical observatories on the summit also provides access to seasonal tropical skiing. The latest eruptions produced a series of cinder cones and lava flows from vents on the northern and southern flanks during the early- to mid-Holocene.

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai`i National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/); Richard Wainscoat, University of Hawaii at Manoa, Institute for Astronomy (URL: http://www.ifa.hawaii.edu/, http://www.ifa.hawaii.edu/images/aerial-tour-95/); Scott Rowland, University of Hawaii at Manoa, School of Ocean and Earth Science and Technology (URL: http://www.soest.hawaii.edu/); and Hawaii News Now (URL: http://www.hawaiinewsnow.com/).

Our last Bulletin report covered seismicity and explosions at San Cristóbal through 31 December 2012 (BGVN 38:01).

2013. The Instituto Nicaragüense de Estudios Territoriales (INETER) reported that on 7 June 2013 seven explosions at San Cristóbal, that ejected gas and ash, were detected by the seismic station located on the W flank. The explosions occurred at 0615, 0645, 0653, 0911, 1137, 1139, and 1143, and were observed by civil defense and INETER staff. The largest explosion, at 1139, generated a plume that rose 100 m. Sulfur dioxide (SO₂) emissions, which had been low, increased. A report later that afternoon stated that gas-and-ash explosions decreased, but RSAM values almost tripled to between 80 and 100 units due to increased tremor. INETER noted that tremor is frequently detected at San Cristóbal, and for the public not to be alarmed. A small mud flow, producing no damage, occurred at 1710.

2014. INETER reported that seismic tremor increased at 0340 on 17 January; RSAM values increased to 460 units from a baseline of 70 units. Twelve gas emissions were observed between 1259 and 1315, and RSAM climbed to 649 units. A report at 1700 noted that RSAM values decreased to 100 and no additional gas emissions were observed. The next day RSAM values fluctuated between 90 and 190 units.

INETER reported that a gas emission with small amounts of ash rose from San Cristóbal between 0641 and 0850 on 4 February. Although there was no increase noted, the report stated that seismicity decreased to background levels. By the afternoon SO₂ emission values were 2,000-3,000 tons per day, the normal levels, and on 7 February, they were 1,000 tons per day. RSAM fluctuated between 20 and 140 units, which is considered normal.

Based on analysis of satellite images, the Washington VAAC reported that on 11 April a gas plume from San Cristóbal that possibly contained small amounts of ash drifted 20 km W. A thermal anomaly was present in short wave infrared satellite images. Periods of elevated seismicity were also detected.

Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); and Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

Our last report, (BGVN 36:09), covered activity at Stromboli through 11 October 2011, characterized by explosions, spattering, rockslides, and occasional lava flows. Similar activity persisted through February 2013. Stromboli (volcano and island) sits N of Sicily in the Tyrrhenian sea along the N side of the Aeolian archipelago.

Activity during 2011. The activity documented in October 2011 continued into November, December, and January 2012, and was concentrated at the two active vent areas in the northern and southern portions of the crater terrace. The wide array of activity noted above fluctuated. There were, along with frequent episodes of spattering, in particular on 10 December 2011. The spattering episodes occurred in the southern area and did not lead to the formation of any lava flows.

Activity during 2012. Stromboli exhibited two periods of isolated activity early in 2012, discussed next. On 16 February there were two sequences of up to 6 explosion earthquakes of medium-high amplitude, and ~9 Very Long Period (VLP) events per hour.

On 6 March, instruments detected both tremor coupled with a strong explosion and at least three major explosions. The first event, at 0643 UTC, presented a VLP component with amplitude ~10-times higher than the daily average. The last event, at 0645, was also of very high amplitude. The VLP events occurred at a rate of ~12 per hour, at a low level with a single event of high amplitude, corresponding to the first event in the sequence at 0643. The VLP sequence was followed by an increase in tremor lasting ~30 minutes. The tremor amplitude was medium-low with its peak corresponding to the earlier events seen around 0643.

On 22 November 2012, the persistent explosive activity at Stromboli showed a clear increase, with episodes of spattering and low lava fountains from two vents in the northern and central portions of the crater terrace.

Beginning on 23 December 2012, repeated lava overflows from the crater terrace generated small lava flows down the northern and northwestern sectors of the Sciara del Fuoco (see images below), and were accompanied by numerous landslides.

Major lava flows occurred on the evening of 23 December 2012 (to the N), during 25-27 December 2012 (to the NW), and on the morning of 7 January 2013 (to the NW). Lava vented from points just below the rim of the northernmost explosive vent on the crater terrace. During the intervals between the main effusive episodes, lava vented at extremely low, releasing numerous incandescent blocks down the Sciara del Fuoco (the area within the sector collapse). At times, small lava flows advanced for a few tens of meters before disintegrating into blocks, such as on the morning of 10 January 2013 (see the last photo in the sequence below in figure 82).

Figure 82. Frames extracted from video recorded by the visible surveillance camera at 400 m elevation on Stromboli (SQV) during the effusive episodes between 23 December 2012 and 10 January 2013. (Note date format: DD-MM-YY.) The first frame (upper left) shows the sliding of material caused by the emplacement of a lava flow onto unstable material on the slope of the Sciara del Fuoco. Courtesy INGV.

Around this time, in all cases, the effusion of lava was preceded, and often accompanied, by intense explosive activity on the crater terrace.

More insight into behavior at Stromboli during this December 2012-March 2013 eruptive phase can be found in Di Traglia and others (2014). They applied the ground-based InSAR monitoring system at Stromboli volcano, linking changes in displacement and other field-monitored observations to volcanism.

Activity during January-February 2013. A new phase of intermittent effusive activity at Stromboli consisting of small overflows of lava from the crater terrace began on 8 February 2013 and continued with significant fluctuations until the morning of 17 February. During this interval, several episodes of effusive activity occurred, which produced lava flows reaching several tens to a few hundred meters in length in the northern and northwestern sectors of the Sciara del Fuoco.

Spattering from vent N2, which lies at the top of a hornito perched on the NW rim of the crater terrace, continued for a few hours, and then diminished during the late afternoon of 14 February. See Figure 83. Subsequently, effusive activity diminished considerably, producing only very small lava overflows that extended a few tens of meters downslope to the NW. On the morning of 17 February, all effusive activity ceased and mild Strombolian activity resumed.

Figure 83. Frames extracted from video recorded by the thermal monitoring camera at 400 m elevation on Stromboli (SQT), showing effusive activity on 11 February (top) and 14 February 2013 (bottom).

After an interval of 10 days of normal Strombolian activity, Stromboli again produced small lava overflows from the crater terrace from the afternoon of 27 February 2013 through the following night. A second episode of lava overflow started on the evening of 1 March and ceased the next afternoon. Both overflows were fed by continuous spattering from vent N2.

Reference. Di Traglia, F., Intrieri, E., Nolesini, T., Bardi, F., Del Ventisette, C., Ferrigno, F., Frangioni, S., Frodella, W., Gigli, G., Lotti, A., Tacconi Stefanelli, C., Tanteri, L., Leva, D., Casagli, N., 2014, The ground-based InSAR monitoring system at Stromboli volcano: linking changes in displacement rate and intensity of persistent volcanic activity, Bulletin of Volcanology 76:786DOI 10.1007/s00445-013-0786-2.

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

Information Contacts: Boris Behncke and Mauro Coltelli, Istituto Nazionale di Geofisica e Vulcanologia (INGV) Osservatorio Etneo (Catania), 95125 Catania (URL: http://www.ct.ingv.it/).