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.

Ol Doinyo Lengai, located near the southern end of the East African Rift in Tanzania, is a stratovolcano known for its unique low-temperature carbonatitic lava. Frequent eruptions have been recorded since the late 19th century. Activity primarily occurs in the crater offset to the N about 100 m below the summit where hornitos (small cones) and pit craters produce lava flows and spattering. Lava began overflowing various flanks of the crater in 1993. The eruption transitioned to significant explosive activity in September 2007, which formed a new pyroclastic cone inside the crater. Repeated ash emissions reached altitudes greater than 10 km during March 2008. By mid-April 2008 explosive activity had decreased. In September new hornitos with small lava flows formed on the crater floor. The most recent eruptive period began in April 2017 and has been characterized by spattering confined to the crater, effusive activity in the summit crater, and multiple lava flows (BGVN 44:09). Effusive activity continued in the summit crater during this reporting period from September 2019 through August 2020, based on data and images from satellite information.

Throughout September 2019 to August 2020, evidence for repeated small lava flows was recorded in thermal data and satellite imagery. A total of seven low-level pulses of thermal activity were detected within 5 km from the summit in MIROVA data during September 2019 (1), February (2), March (2), and August (2) 2020 (figure 207). Sentinel-2 satellite imagery also provided evidence of multiple lava flows within the summit crater throughout the reporting period. On clear weather days, intermittent thermal anomalies were observed in thermal satellite imagery within the summit crater; new lava flows were detected due to the change in shape, volume, and location of the hotspot (figure 208). During a majority of the reporting period, the thermal anomaly dominantly appeared in the center of the crater, though occasionally it would also migrate to the SE wall, as seen on 3 February, the E wall on 12 July, or the NE wall on 31 August. In Natural Color rendering, fresh lava flows appear black within the crater that quickly cools to a white-brown color. These satellite images showed the migration of new lava flows between February, March, and June (figure 209). The flow on 8 February occurs in the center and along the W wall of the crater; the flow on 9 March is slightly thinner and is observed in the center and along the E wall of the crater; finally, the flow on 17 June is located in the center and along the N wall of the crater.

Figure 207. Seven low-level pulses of thermal activity within 5 km of the summit of Ol Doinyo Lengai were recorded in the MIROVA thermal data between September 2019 to August 2020; one in early September 2019, two in February, two in March, and two in August 2020. Courtesy of MIROVA.

Figure 208. Sentinel-2 thermal satellite images of Ol Doinyo Lengai from November 2019 to August 2020 show intermittent thermal anomalies (bright yellow-orange) within the summit crater. The location of these anomalies occasionally changes, indicating new lava flows. Images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 209. Sentinel-2 satellite images of new lava flows within the summit crater at Ol Doinyo Lengai during 8 February (left), 9 March (middle), and 17 June (right) 2020. Lava flows appear black in the center of the crater that changes in volume and location from February to June. Images with “Natural Color” (bands 4, 3, 2) rendering; courtesy of Sentinel Hub Playground.

During August, multiple lava flows were detected in Sentinel-2 satellite imagery. On relatively clear days, lava flows were visible in the middle of the summit crater, occasionally branching out to one side of the crater (figure 210). On 6 August, a thin lava flow branched to the E flank, which became thicker by 11 August. On 16 and 21 August, the lava remained mostly in the center of the crater. A large pulse of fresh lava occurred on 31 August, extending to the NW and SE sides of the crater.

Figure 210. Sentinel-2 images of multiple new lava flows at Ol Doinyo Lengai during August 2020. When visible in the first half of August, dark lava is concentrated in the center and E side of the crater; by the end of August the lava flows had reached the NW side of the crater. Images with “Natural Color” (bands 4, 3, 2) rendering; courtesy of Sentinel Hub Playground.

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

Information Contacts: 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).

[The following was originally included within the Masaya report, not as a stand-alone report about Apoyo.]

July 2000 seismicity near Masaya and Laguna de Apoyo. During July 2000 there were over 300 earthquakes near Laguna de Apoyo (Apoyo volcano) and Masaya. The earthquakes, determined to be of tectonic rather than volcanic origin, caused surficial damage at both volcanoes.

At 1329 on 6 July a small M 2 earthquake occurred near the N rim of Laguna de Apoyo that was followed at 1330 by a M 5.4 earthquake (figure 1). It was located ~32 km SE of Managua, at 11.96°N, 86.02°E, with a focal depth less than 1 km (figure 2). The earthquake was felt in most of Nicaragua and was most strongly felt in the cities of Managua (Modified Mercalli V-VI) and Masaya (VI), and in the region near Laguna de Apoyo (maximum intensity of VII or VIII). The earthquake caused numerous landslides down the volcano's crater walls and surface faulting was observed. In towns located in the epicentral zone, trees and electric lines fell and many houses were partially or totally destroyed. About 70 people were injured and four children were killed by collapsing walls or roofs of homes. At Masaya volcano, ~8 km from the epicenter, there were minor collapses of Santiago crater's walls. No change in degassing was observed at the volcano.

Figure 1. Seismogram showing the M 2 and M 5.4 earthquakes near the Masaya volcano station on 6 July 2000. Courtesy of INETER.

Figure 2. Epicenters near Masaya for the M 5.4 earthquake on 6 July, and the M 4.8 earthquake on 25 July 2000 (stars). The aftershocks from these earthquakes are also shown (small circles). Courtesy of INETER.

Immediately after the earthquake there were many smaller, shallow earthquakes in a zone that includes the area between Masaya, Laguna de Apoyo, and W of Granada (figure 2). In the epicentral zone property was destroyed, cracks opened in the ground, landslides occurred, and trees fell. Several landslides occurred at the edges and steep walls of Laguna de Apoyo. A large number of earthquakes continued until 10 July (figure 3 and table 1). The number of earthquakes then diminished until 1554 on 25 July when a M 4.8 earthquake took place, initiating a series of smaller earthquakes that lasted until about 27 July.

Figure 3. Graph showing the number of earthquakes in the Masaya region between 4 and 30 July 2000. Courtesy of INETER.

Table 1. A summary of earthquakes in vicinity of Masaya and Laguna de Apoyo in early July 2000. Courtesy of INETER.

The July earthquakes were the most destructive seismic events since the 1972 Managua earthquake. The epicentral zone of the July 2000 earthquakes correlates with the same active zones of past earthquakes, which are caused by fault movement between the Cocos and Caribbean plates.

Geologic Background. The scenic 7-km-wide, lake-filled Apoyo caldera is a large silicic volcanic center immediately SE of Masaya caldera. The surface of Laguna de Apoyo lies only 78 m above sea level; the steep caldera walls rise about 100 m to the eastern rim and up to 500 m to the western rim. An early shield volcano constructed of basaltic-to-andesitic lava flows and small rhyodacitic lava domes collapsed following two major dacitic explosive eruptions. The caldera-forming eruptions have been radiocarbon dated between about 21,000-25,000 years before present. Post-caldera ring-fracture eruptions of uncertain age produced lava flows below the scalloped caldera rim. The slightly arcuate, N-S-trending La Joya fracture system that cuts the eastern flank of the caldera only 2 km east of the caldera rim is a younger regional fissure system structurally unrelated to Apoyo caldera.

Information Contacts: Wilfried Strauch and Virginia Tenorio, Dirección General de Geofísica, Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado 1761, Managua, Nicaragua (URL: http://www.ineter.gob.ni/).

During January to July 2000 Arenal's outbursts generally remained low but included frequent pyroclastic explosions, gas emissions, and avalanches. In late August explosions spawned a pyroclastic flow that injured three people several kilometers from the crater; two later died. Three days later a small airplane crashed into the volcano.

In January through parts of June crater C continued its usual activities, consisting of a constant gas emission, sporadic Strombolian eruptions, and occasional incandescent avalanches. Crater D exhibited fumarolic activity. The lava continued to flow variously toward the NNE, E, SE flanks. The NE and SE flank were continually affected by acid rain and pyroclastic material that contributed to the destruction of the vegetation on these flanks, resulting in major erosion that created small avalanches on the rivers Calle de Arenas, Manolo, Guillermina, and Agua Caliente.

The EDM network (established along the subradial lines) continued to show an average annual contraction of 7-10 ppm. The dry inclinometers ("dry tilt") showed variations in the radial component, deflation at ~5 µrad per year.

During the last half of April and throughout May eruptive activity increased, but few ash columns rose to ~500 m over crater C. The columns of ash were carried by the predominating winds toward the NW and SE flank causing both acid rain and ash fall. In May a narrow channel of lava began to flow toward the NNE flank. It later widened into a fan burning vegetation on the N and NE flanks.

From April to May the seismometer detected an increase in both number of eruptions and the hours of tremor. On 16 May two MR 3 earthquakes were recorded and located on the flanks of the volcano at 2 and 5 km from the summit. These earthquakes were reported to be felt in La Fortuna, 6.5 km NE of the volcano.

Eruptive activity remained low in June; few eruption clouds rose more than 500 m over crater C. In July crater C continued with the emission of gases, lava flows, sporadic Strombolian eruptions, and occasional pyroclastic flows. The eruptive activity increased in July with respect to June, although the number of eruptions, their intensity, and the quantity of pyroclastic material ejected remained low.

In August Arenal became more active and underwent a series of explosions. One began at 0945 on 23 August; mutiple pyroclastic flows came down the volcano's NE side (figure 89) as a series of pulses. Pulses occurred at 0955, 0956, and 0958. The most important pulse occurred at 1001 and continued for six minutes. Two more pulses followed at 1008 and 1012. For the next two hours activity returned to normal, but at 1323 a new series of explosions began. At 1336 a pyroclastic flow began and lasted for ten minutes. Various pulses descended the NNE flank. Normal low-level activity resumed 19 hours after the afternoon explosions.

Figure 89. A map of Arenal and vicinity showing the distribution of deposits from the 23 August pyroclastic flows (N-directed swath of dark-gray color). The light gray shows the lava field formed by past eruptions. Courtesy of Rafael Barquero (OSIVAM).

News reports. One of the pyroclastic flows on 23 August engulfed a Costa Rican tour guide and two tourists from the United States. OVSICORI-UNA stated that the victims were burnt by the front of the flow ~2.3 km from the crater. According to a local volcanologist, the flow was traveling at 80 km/hour at that point.

The three victims were sent to San José to be treated for their burns and injuries. On the night of 23 August the tour guide died in the hospital. An 8-year-old girl from Massachusetts died on 6 September as a result of her burns.

The National Emergency Commission (NEC) ordered evacuations of the tourist centers of Los Lagos, the Tabacón hot springs and resort, Hotel Montaña del Fuego, Arenal Lodge, and other areas. The NEC and Red Cross workers evacuated 600 tourists and residents and closed the route around the volcano to Tilarán. On 24 August the volcano returned to its normal behavior. The 23 August explosive eruptions were believed to be the strongest since the deadly 1968 eruption.

On 26 August a ten-passenger airplane crashed into the NE flank ~200 m below the summit. All of the occupants died. The cause of the crash is unknown at this point and no further details are available.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Oficina de Sismología y Vulcanología del Arenal y Miravalles (OSIVAM), Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San José, Costa Rica; The Tico Times (URL: http://www.ticotimes.net/); La Nacion (URL: http://www.nacion.co.cr/).

During 14 February to 4 March 2000 an eruption occurred at Piton de la Fournaise that was briefly mentioned in a previous report (BGVN 25:01) and is discussed here in more detail. After 4 March through May, there was no volcanic activity and seismicity was low with 1-2 events per month. On 23 June volcanism recommenced with an eruption that lasted more than a month.

Eruption of 14 February 2000. Three and a half months after its previous eruption (BGVN 24:09), Piton de la Fournaise erupted on 14 February. Throughout January, seismicity was well above normal levels until the beginning of February when a relative lull in seismicity lasted for two weeks (figure 50). At 2314 on 13 February a seismic crisis began that lasted 64 minutes. A total of 261 earthquakes occurred with magnitudes up to 1.9. The deepest events were localized at sea level, just below Dolomieu summit crater (figure 51).

Figure 50. Seismic events at Piton de la Fournaise during December 1999- February 2000 shown as a series of five day averages. Heightened activity occurred through January, and a relative lull in activity occurred two weeks prior to the eruption on 14 February. Seismic information was not available for the beginning of the eruption (February 14-24). Courtesy of OVPDLF.

Figure 51. Map of the N flank of Piton de la Fournaise showing the lava flows from the 14 February 2000 eruption (black), fissure vents (white lines within the flow), and the major features associated with the flow. Note Dolomieu summit crater at lower edge of the map. Courtesy of OVPDLF.

On 13 February, three minutes after the beginning of the seismic crisis, the first significant variations in deformation were recorded at 2317 and 2320, on radial and tangential components, respectively, by the "Dolomieu Sud" tiltmeter station. After initial deformation was observed, tiltmeter and extensometer stations at "Soufriere," "Bory," "Tunnel Catherine," and "Flanc Est" (figure 52) registered variations, with up to 270 µrad recorded for the "Soufriere tiltmeter" radial component. The intrusion of magma caused inflation under the summit crater. The inflation center started S of Dolomieu summit crater, migrated below Dolomieu, and then traveled to the N flank of the volcano where several vents opened (figure 53). At 0018 on 14 February, tremors registered at all of the seismic stations marking the beginning of the eruption.

Figure 52. Map showing the location of radon, deformation, magnetic, and seismic stations on Piton de la Fournaise in February 2000. Courtesy of OVPDLF.

Figure 53. During the 14 February 2000 eruption at Piton de la Fournaise the center of inflation migrated. The incenter of inflation was calculated on 5-minute intervals and plotted on this sketch map. The center of inflation was estimted based on the shift of deformation vectors over time. Courtesy of OVPDLF.

Inclement weather produced by cylone Eline passing 200 km N of Reunion inhibited visual observations for several days. After that, scientists found that several en echelon fissures were localized on the N flank starting at 2,490 m elevation (white lines within black lava flows, figure 53). An aa flow inundated the "Puy Mi-Côte" crater, passed to the W and E of the crater, and continued in the direction of "Piton Partage." Both vents were inactive at the time of observation. Eruptive activity was concentrated on a vent 300 m E of Puy Mi-Côte, where stable 20- to 30-m-high fountains were observed from a new crater, whose rim grew to 20 m high at that time. A second, much smaller crater was active about 100 m above the main crater. A large aa lava flow and meter-sized blocks descended in the direction of "Piton Kapor" (site of the 1998 eruption), then joined the first lava flow and followed the "rempart Fouqué" to the E. This lava flow terminated about 4 km away at 1,950 m altitude near "Nez Coupé de Saint Rose." Beginning on 24 February a large number of small pahoehoe lava flows were observed. For several hours on 4 March a large number of gas-piston events were observed and then at 1800 tremor stopped, marking the end of the eruption.

Retrospective analysis revealed that the initial aa lava flow represented most of the erupted material. The lava was particularly irregular with scoria that ranged in size from tens of centimeters to meter-sized blocks. Pahoehoe flows from the 24 February phase of the eruption partly covered the aa lava that was emitted earlier. The entire lava flow covered an area of about 1.3 x 10⁶ m² and comprised a total volume of about 4 x 10⁶ m³ of aphyric basalt. The main new crater was called "Piton Célimène" (figure 53).

Eruption of 23 June 2000. Beginning in June, long-term deformation was observed at several stations near the volcano. Since the beginning of the month up to 0.1 mm of inflation took place at the "Soufrière" extensometer (figure 52). Starting on 12 June clear inflation of up to 70 µrad was observed at the "Dolomieu Sud" tiltmeter. After 20 June inflation of up to 20 µrad was observed at the "Château Fort" tiltmeter. The Château Fort extensometer showed variations in opening, shear, and vertical movement components.

Seismicity increased during 9-14 June with twelve deep earthquakes ~6 km below the W flank. During 15-21 June seismicity drastically increased with 2, 2, 4, 10, 29, 69, and 101 earthquakes recorded on successive days (figure 54). All of these earthquakes occurred below Dolomieu summit crater, with focal depths between sea level and 1 km above sea level. They had magnitudes up to 1.8 that increased with the number of earthquakes recorded. During the same time period, five deep earthquakes also occurred.

Figure 54. The number of daily seismic events recorded at two seismic stations at Piton de la Fournaise during 1 June through 6 July 2000. Courtesy of OVPDLF.

During 0600-0640 on 22 June, following 50 seismic events, there was a small seismic crisis that consisted of 36 low-energy seismic events. For 36 hours after the seismic crisis only very low-energy earthquakes occurred. At 1650 on 23 June another seismic crisis took place (figure 54). It consisted of about 300 earthquakes, including some greater than M 2 and possibly as high as M 2.5. Some of the earthquakes were recorded at the seismic station in Cilaos, more than 30 km from the volcano.

During the seismic crisis one shallow earthquake was centered under the E flank of the volcano. Around this time the observatory's tiltmeter network showed uplift of the central part of the volcano to over 200 µrad. The inferred effect of an intrusion was first localized under the summit region, then shifted to the SE. At 1800 eruption tremor began, and tremor localization suggested the eruption site was on the SE flank between "Signal de l' Enclose" and "Château Fort" craters between 1.9 and 2.2 km elevation. Figure 55 shows these named locations and the actual fissure vent and extent of lava flows.

Figure 55. Map and image composite of the 23 June 2000 lava flows on the E flank of Piton de la Fournaise. Courtesy of OVPDLF.

According to the observatory staff, the 23 June eruption began with the formation of a short-lived, 500-m-long, SE-trending fissure on the SE flank at an elevation of ~2,100 m (figure 55). A second, 200-m-long, ESE trending vent also formed on the SE flank at ~1,800 m. About eight lava fountains initially rose up to 50 m above the second vent. In addition, a 300-m-long aa lava flow traveled down the "Grandes Pentes" to an elevation of 580 m. About two days after the eruption began, the intensity of the lava fountains decreased, and the crater rim reached a height of 10-15 m.

Within 24 hours after the onset of the eruption, tremor rapidly decreased to less than 10% of the initial value. Unlike typical eruptions at Piton de la Fournaise, seismicity under the central crater continued for the first five days of the eruption. During 24-28 June there were 26, 22, 17, 17 and six seismic events, respectively, up to M 2.5. Similar seismic events occurred during eruptions in 1986, 1988, and 1998; in two cases they preceded the formation of new vents. However, no new vents formed during 24-28 June. After 29 June no seismic events were recorded, and starting on 27 June there was an increase in tremors that remained around initial levels and lasted three weeks. Throughout most of the eruption there was a lava lake in the eruption crater and several meter-sized lava flows emerged at its base reaching up to 300-400 m below the crater. Lava samples were collected during the eruption, and a lava temperature of 1,160°C was measured several times using a thermocouple.

On 30 July the eruption stopped after 37 days of activity. The initial flow was entirely aa lava, while the later outspreading lava flows were aa and pahoehoe lava. The entire lava flow covered an area of ~3 x 10² m² and comprised a total volume of ~1 x 10⁷ m³. The final crater was 26 m high and was named "Piton Pârvédi."

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: Thomas Staudacher, Nicolas Villeneuve, Jean Louis Cheminée, Kei Aki, Jean Battaglia, Philippe Catherine, Valérie Ferrazzini, and Philippe Kowalski, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, Institut National des Sciences de l'Univers, 14 RN3 - Km 27, 97418 La Plaine des Cafres, Réunion, France (URL: http://www.ipgp.fr/fr/ovpf/observatoire-volcanologique-piton-de-fournaise).

This report covers April through June 2000. Activity remained at a low level in April. From visual observation reports received only up to 9 April, Crater 2 periodically gently released moderate to thick ash clouds. However, on 5 and 9 April, the ash clouds were released more forcefully and with rumbling sounds. These ash clouds rose 1-2 km above the summit before being blown SE. Crater 3 released light white vapor throughout the month.

Visual observations were next reported after 16 June. Crater 2 produced thick, white ash clouds in moderate volume. On 23 and 24 June, these clouds were accompanied by blue vapor. On 16 and 18 June, rumbling noises were heard. Crater 3 was inactive in June with the exception of a weak trail of thin white vapor escaping on 16 June.

The seismograph remained non-operational throughout the entire reporting period.

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower E flank of the extinct Talawe volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the N and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: I. Itikarai, D. Lolok, K. Mulina, and F. Taranu, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

This report covers April-June 2000. Inflation that began in January 2000 (BGVN 25:03) peaked in early April. By mid-April the water-tube tiltmeter 4 km SW of the summit detected a 2.5 µrad decrease in tilt. By the end of April the tilt had recovered 1.5 µrad. Emissions from both the summit craters, Main and Southern, consisted of gentle releases of light to moderate volumes of white vapor. Seismicity remained low with the number of events ranging from 500 to 1,200 events a day. Seismic amplitude measurements were steady at background levels.

During May, Manam continued to produce varying amounts of white vapor from both craters. Rabaul Volcanic Observatory (RVO) characterized the seismicity as normal. Tiltmeter readings showed no particular trend.

Throughout June, Main Crater released light to moderate volumes of white vapor. However, during 3-4 June, Southern crater increased in activity.

At 1235 on 3 June, an explosive eruption produced thick, dark ash clouds and produced fine-ash and scoria deposits at Yassa village, W of the summit. The ash clouds reached an altitude of 1-1.2 km. The initial explosion was followed by light to moderate release of ash. At 0004 on 4 June, booming sounds lasting 1-2 minutes were accompanied by the ejection of glowing lava fragments. These fragments fell in the SW valley and had free fall times (FFT) of 5-10 s. Some weak to low fluctuating night time glows were visible during the intervals between lava fragment ejections. Prior to and after the events of 3-4 June, Southern crater produced light amounts of white vapor.

Although there were no water-tiltmeter readings after 19 June, the values taken 4 km S of the crater showed an inflation of 10 µrad from 1-19 June. Since December 1999, there has been an overall inflation of 16 µrad. There were no seismic readings during 1-10 June. Low-level seismicity the remainder of the month had counts ranging from 600-1,360 a day. Seismic amplitude measurements were relatively steady at normal background levels.

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

Information Contacts: I. Itikarai, D. Lolok, K. Mulina, and F. Taranu, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

Since the last report on Masaya, of continued degassing and marked gravity decreases (BGVN 24:04), there have been sporadic reports about its activity, which are summarized below prior to discussion of a nearby M 5.4 earthquake on 6 July 2000.

Reports of ash-and-steam emissions. Between November 1999 and January 2000 there were several reports from the Washington VAAC of ash-and-steam emissions from Masaya. On 22 November 1999 the VAAC reported that GOES-8 imagery suggested that Masaya may have awakened. Satellite imagery showed activity at or very near Masaya, including a plume of ash or "smoke" moving to the WSW, and a hotspot that was visible for over two hours. At about 1600 the imagery suggested that an explosion may have occurred and by 1615 the resultant plume was at ~800 m (near Masaya's summit), and had been blown WSW.

On 22 December 1999 the Washington VAAC issued an ash advisory stating that a continuous low-level plume was being emitted from Masaya. Volcanic activity was confirmed by INETER who noted that seismic activity was consistent with ash emissions. The cloud was ~2 km in altitude and was blown to the WSW.

On 18 January 2000 the VAAC reported that GOES-8 imagery through 0845 detected a low-level thin ash plume from Masaya's summit. The plume reached an altitude of ~900 m, was blown to the SW, and rapidly dissipated.

Seismic activity during April 1999-March 2000. Seismic activity at the volcano remained low with eight microearthquakes registered for the month. The RSAM (seismic tremor) stayed at ~30 units. During the first two weeks of April the RSAM signal was not obtained due to technical problems in the seismic power station. On 23 April two explosions were detected by RSAM, which were confirmed by observers at the Masaya Volcano National Park. In that case, RSAM began to show a small increase until 0800, and an hour later the two explosions occurred.

May 1999: The number of microearthquakes was 21 for the month. The RSAM stayed at ~24 units. June: The number of microearthquakes was 18 for the month. The RSAM stayed at ~24 units. August: The number of microearthquakes was 47 for the month. The RSAM remained at ~40 units. Constant gas emissions occurred. September: The number of microearthquakes was 87 for the month. The RSAM stayed constant at ~40 units. Constant gas emissions occurred. October: The number of microearthquakes was 22 for the month. The RSAM stayed constant at ~20 units. Constant gas emissions occurred. November: There were 49 microearthquakes for the month. The RSAM stayed constant. Constant gas emissions occurred. December: Twenty one earthquakes were registered for the month. The RSAM stayed constant.

January 2000: Eleven earthquakes were registered for the month. The RSAM stayed constant. At 1145 on 6 January an explosion occurred in Santiago crater. February: Six microearthquakes and the RSAM remained constant. March: There were three microearthquakes for the month. The RSAM was at a similar level as the previous month.

July 2000 seismicity near Masaya and Laguna de Apoyo. During July 2000 there were over 300 earthquakes near Laguna de Apoyo (Apoyo volcano) and Masaya. The earthquakes, determined to be of tectonic rather than volcanic origin, caused surficial damage at both volcanoes.

At 1329 on 6 July a small M 2 earthquake occurred near the N rim of Laguna de Apoyo that was followed at 1330 by a M 5.4 earthquake (figure 10). It was located ~32 km SE of Managua, at 11.96°N, 86.02°E, with a focal depth less than 1 km (figure 11). The earthquake was felt in most of Nicaragua and was most strongly felt in the cities of Managua (Modified Mercalli V-VI) and Masaya (VI), and in the region near Laguna de Apoyo (maximum intensity of VII or VIII). The earthquake caused numerous landslides down the volcano's crater walls and surface faulting was observed. In towns located in the epicentral zone, trees and electric lines fell and many houses were partially or totally destroyed. About 70 people were injured and four children were killed by collapsing walls or roofs of homes. At Masaya volcano, ~8 km from the epicenter, there were minor collapses of Santiago crater's walls. No change in degassing was observed at the volcano.

Figure 10. Seismogram showing the M 2 and M 5.4 earthquakes near the Masaya volcano station on 6 July 2000. Courtesy of INETER.

Figure 11. Epicenters near Masaya for the M 5.4 earthquake on 6 July, and the M 4.8 earthquake on 25 July 2000 (stars). The aftershocks from these earthquakes are also shown (small circles). Courtesy of INETER.

Immediately after the earthquake there were many smaller, shallow earthquakes in a zone that includes the area between Masaya, Laguna de Apoyo, and W of Granada (figure 11). In the epicentral zone property was destroyed, cracks opened in the ground, landslides occurred, and trees fell. Several landslides occurred at the edges and steep walls of Laguna de Apoyo. A large number of earthquakes continued until 10 July (figure 12 and table 2). The number of earthquakes then diminished until 1554 on 25 July when a M 4.8 earthquake took place, initiating a series of smaller earthquakes that lasted until about 27 July.

Figure 12. Graph showing the number of earthquakes in the Masaya region between 4 and 30 July 2000. Courtesy of INETER.

Table 2. A summary of earthquakes in vicinity of Masaya and Laguna de Apoyo in early July 2000. Courtesy of INETER.

The July earthquakes were the most destructive seismic events since the 1972 Managua earthquake. The epicentral zone of the July 2000 earthquakes correlates with the same active zones of past earthquakes, which are caused by fault movement between the Cocos and Caribbean plates.

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

Information Contacts: Wilfried Strauch and Virginia Tenorio, Dirección General de Geofísica, Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado 1761, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); Washington VAAC, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/).

This report covers the period 8 July-31 August 2000, an interval marked by strong outbursts, spectacular plumes, pyroclastic flows, ashfalls, and a remarkable series of concentric crater collapses that followed the initial crater collapse on 8 July 2000 (figures 6 and 7). Striking ash-column photos, some marked with azimuthal angles and calculated plume heights, appear on Japanese-language websites (see below).

Figure 6. An oblique aerial view of Miyake-jima's pre-eruption summit; the sketched-in curve indicates the area of the collapse on 8 July 2000. That area is sub-circular in plan view (figure 7) and has a diameter of ~ 0.9 km. View is looking NNE. Courtesy of Tokyo Metropolitan Islands Promotion Corporation.

Figure 7. Map of Miyake-jima's active summit crater documenting the crater's expansion during July and August 2000. The margins were drawn from aerial photos taken on the specified dates. The progression was thought to be closely linked with summit deflation; this deflation had been detected since the end of June and accelerated on 8 July. Large dots indicate the locations of a series of small migrating vents seen in the crater during 10-26 August. From the website of K. F. Fujita.

Continuous deflation at the summit had been recorded since the end of June. However, on 8 July the deflation accelerated. Following 4 days of earthquake swarms under the summit, at 1841 on 8 July, a small, phreatic explosion sent a cloud to 800 m above the summit (BGVN 25:07). This explosion lasted several minutes. At the same time, a large pit crater formed with a diameter of ~800-1,000 m and a depth of 100-200 m. A small amount of ash was ejected but was not comparable to the volume of the depression. Red ash and cinder deposits from this eruption were estimated to amount to less than 1 x 10⁶ m³. The volume of collapse was estimated at 50 x 10⁶ m³. No scoriae or any other juvenile material was found. The rapid deflation is thought to have formed as the result of "drain-back" of magma that had intruded near the surface. This appears to have been the catalyst for the explosion.

After the 8 July explosion, tiltmeters recorded periods of sudden inflation. Inflations were preceded and accompanied by long-period earthquakes located less than 2 km below the surface. The intervals of inflation and earthquakes were followed by continued steady deflation. This cycle repeated itself approximately every 12 hours from the 8 July eruption to 23 July.

Following a series of foreshocks, at 1601 on 1 July a Mb 6.1 earthquake struck near Kozu-shima Island, NW of Miyake-jima. This was followed on 14 July by a M 5.3 earthquake off the coast of Miyake-jima. At about 0400, shortly after the earthquake, a phreatic eruption occurred. Thick layers of ash were deposited on the N and E parts of the islands. This eruption continued until about 1300 on 15 July. Photographs taken by Asahi News Network (ANN) on the afternoon of 14 July showed that the 8 July crater had expanded to a diameter of 1,000 m and a depth of 400 m. Observers looking at the bottom of the 8 July crater saw small phreatic explosions yielding plumes with convoluted and scrolled shapes (reminiscent of cock's tails); these originated from a new pit crater that was ~100 m in diameter. The volume of ash from this eruption was estimated to be less than 10 x 10⁶ m³. The volume of collapse was estimated at 200 x 10⁶ m³.

Measurements in early August showed that the collapsed crater had enlarged to a diameter of 1.4 km and a depth of 450 m. According to The Japan Times, an eruption on 10 August produced a plume that rose 3 km above the summit and deposited ash over the NE section of the island. Yukio Hayakawa reported that small pyroclastic flows accompanied this event. After 10 August, phreatic explosions occurred intermittently. Figure 7 shows the progressive expansion of the crater associated with the deflation. GPS measurements made at four stations around the summit indicated continued summit deflation, including during the explosion on 18 August.

At 1700 on 18 August, a large phreatic eruption occurred. This was the largest eruption since activity began on 26 June 2000. Yukio Hayakawa reported small pyroclastic flows. According to articles by the Associated Press and Reuters, white clouds rising to 8 km above the summit were encountered by a commercial airline pilot who was in route from Guam to Narita airport in Tokyo. The plane, which was flying over the island of Miyake shortly after the eruption, later landed safely at Narita. Aviation contacts later revealed that while in flight a commercial airliner encountered airborne ash and underwent a dual-engine flame-out, but managed to land safely. The airliner sustained ~$4 million (US dollars) in damage.

Ash fall was reported to be heaviest on the western part of the island, but ash in the NW sector accumulated up to 15 cm thick as far as 3 km from the crater (figure 8). Ballistics, which included basaltic bombs, were ejected at the end of the eruption and were deposited in a uniform, radial pattern around the crater (figure 9). On the W slope of the volcano, 2-m-diameter ballistics destroyed roofs of cowsheds and formed craters in the meadows. To the SE, there were reports of broken car windows and cinders 5 cm in diameter at the airport. It is uncertain whether these ballistics were juvenile material.

Figure 8. Isopach map of ash-fall deposits from Miyake-jima's eruption on 18 August 2000. Courtesy of Joint University Research Group, Geological Survey of Japan.

Figure 9. Isopleth map of ballistics from Miyake-jima's eruption on 18 August 2000. Courtesy of Joint University Research Group, Geological Survey of Japan.

Although several lower plume-height observations and estimates were made, for example by aviators, one based on a photograph of the actively rising ash column indicated that the 18 August plume rose to at least 15 km. Laser radar (lidar) provided additional constraints on the height of airborne volcanic aerosols at distance from the volcano, detecting them on 23 August at 16 and 17.5 km altitude. More details follow.

For the 18 August eruption, lidar data collected by Takashi Shibata established these values at Nagoya, Japan (35°N, 137°E, on S Honshu Island, 290 km SE of the volcano) around 2100 on 23 August: backscatter ratio at 532 nm, 1.1; depolarization ratio at 532 nm, 5%; plume height, 16 km; and plume width, 100 km.

On 23 August the lidar instrument run by Motowo Fujiwara and Kouichi Shiraishi in Fukuoka (33.5°N, 130.4°E, on NW Kyushu Island, 850 km W of the volcano) detected a thin aerosol layer. Their measurement took place over an interval that began at 0013 and extended over the next hour and a half. They detected relatively strong scattering in the lower stratosphere and found these values: peak backscatter ratio at 532 nm, 1.20-1.25; depolarization ratio at 532 nm, 8-15%; layer height, 17.5 km; and layer width, 1 km. The cited height corresponds to the peak (strongest effect) of the layer; this altitude was ~1.7 km above the tropopause observed by Fukuoka Meteorological Observatory at 2100 on 22 August. Fujiwara and Shiraishi suggested aerosols might have come from Miyake-jima, specifically its eruption at 1702 on 18 August. The Meteorological Observatory reported that during the period from 18-21 August the wind direction around the layer height (17-18 km) changed from ENE to SSE (i.e., basically easterly) and its speed changed from 3 to 7 m/s. These easterly winds further suggested that the lidar-detected aerosol layer originated from a Miyake-jima eruption.

Observations made on 20 August by Osamu Oshima of the University of Tokyo revealed 3 small cones with open pits inside the summit crater, multiple mudflows from the crater pits onto the crater floor, and step faults that crossed new ash layers. He interpreted the step faults to indicate continued subsistence of the crater floor.

The Tokyo VAAC reported three small eruptions at Miyake-jima on 28 August. The eruption clouds reached respective heights of about 5.8, 3.8, and 5 km. On 29 August at 0430, Miyake-jima erupted vigorously again; according to the Eruption Committee this was the second-largest outburst of the recent eruptive episode (the most vigorous being the 18 August eruption). There were two pyroclastic flows, one to the NE that extended 5 km to the sea, and one to the SW that extended for 3 km. The pyroclastic flows contained large amounts of HCl, unlike those of 18 August. The eruption was theorized to be the result of either the collapse of an unstable hydrothermal system or contact between magma and meteoric water inside the volcano. Photos of the pyroclastic flows appeared on the internet (see references).

According to an article by the Associated Press and the Japanese news agency Asahi Shimbun, on 29 August all students, teachers, and school officials on Miyake-jima were evacuated to Tokyo, and all remaining residents of the island were ordered to evacuate. Residents who had not yet left the island as of 31 August were being housed in shelters due to the threat of mudslides produced by thick ash and rain.

Geologic Background. The circular, 8-km-wide island of Miyakejima forms a low-angle stratovolcano that rises about 1,100 m from the sea floor in the northern Izu Islands about 200 km SSW of Tokyo. The basaltic volcano is truncated by small summit calderas, one of which, 3.5 km wide, was formed during a major eruption about 2,500 years ago. Parasitic craters and vents, including maars near the coast and radially oriented fissure vents, dot the flanks of the volcano. Frequent historical eruptions have occurred since 1085 CE at vents ranging from the summit to below sea level, causing much damage on this small populated island. After a three-century-long hiatus ending in 1469, activity has been dominated by flank fissure eruptions sometimes accompanied by minor summit eruptions. A 1.6-km-wide summit caldera was slowly formed by subsidence during an eruption in 2000; by October of that year the crater floor had dropped to only 230 m above sea level.

Information Contacts: Miyake-jima Meterological Observatory and Volcanological Division; Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (URL: http://www.jma.go.jp/); Akihiko Tomiya, Geological Survey of Japan, 1-1-3 Higashi, Ibaraki, Tsukuba 305, Japan (URL: https://www.gsj.jp/); Setsuya Nakada, Volcano Research Center, Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-0032, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Takashi Shibata, STEL, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan; Yukio Hayakawa, Faculty of Education, Gunma University, Aramaki, Maebashi 371, Japan (URL: http://www.hayakawayukio.jp/); Motowo Fujiwara and Kouichi Shiraishi, Department of Earth System Science, Fukuoka University, 8-19-1 Nanakuma, Jonann-ku, Fukuoka 814-0180, Japan; U.S. Geological Survey, Reston, VA, USA (URL: http://www.usgs.gov); The Japan Times, 5-4, Shibaura 4-chome, Minato-ku, Tokyo 108-0023 (URL: http://www.japantimes.co.jp/); Asahi Shimbun (URL: http://www.asahi.com/english/english.html); Associated Press; Reuters.

An explosion at Semeru on 27 July 2000 took the lives of two dedicated Volcanological Survey of Indonesia (VSI) staff members, Wildan and Mukti. Asep Wildan was born in Bandung and a graduate of the physics department at the Institute of Technology Bandung. He worked with VSI since 1993, most recently as a geophysicist in VSI's Eastern Java section where he investigated volcano seismology at Semeru and other volcanoes in East Java and Bali. He is survived by his wife and young daughter.

Mukti was born in the city of Banyuwangi on the eastern tip of Java. A high-school graduate, he served with VSI since 1990 in the capacity of volcano observer and was posted at Semeru. He is survived by his mother. Efforts are underway to work with VSI to provide economic assistance for the families of Wildan and Mukti.

Asep Wildan and Mukti made important contributions to VSI's volcano research and monitoring programs, and both had, in the past, generously provided vital assistance to international researchers working at Semeru. They will be greatly missed by their many Indonesian and international friends and colleagues.

Geologic Background. Obituary notices for volcanologists are sometimes written when scientists are killed during an eruption or have had a special relationship with the Global Volcanism Program.

Information Contacts:

This report covers the period form 15 June to 22 August 2000. The highest ash column in this period rose to over 5 km above the summit.

Throughout most of the reporting period, activity remained stable with periodic exhalations of small amplitude and duration. However, two small mudflows were reported: one on 23 June and the other on 24 June. According to CENAPRED, the mudflow on 24 June did not reach any human settlements. No information was available concerning the 23 June mudflow.

On 3 July, two small exhalations generated ash clouds that reached 1 and 2.5 km above the summit and ash fell over the volcano's SW sector. On 4 July, ash from a small exhalation fell in Tetela, a town ~15 km SW of the crater. On 14 July, the volcano erupted and produced an ash cloud that reached 1.6 km in height. According to the Associated Press (AP), the ash from this eruption was blown N and did not significantly impact any populated regions surrounding the volcano.

On 4 August, two closely spaced explosive eruptions occurred. The first at 1251, a moderately large exhalation, lasted 2 minutes. The second one occurred at 1255 and lasted 1.5 minutes. The resulting ash cloud rose to greater than 5 km above the volcano. Ash reportedly fell in nearby communities (Atlautla, San Juan Tehuixtitlan, San Pedro Nexapa, Amecameca, and Tenango).

At 0910 on 10 August, Popocatépetl erupted again. Ash reached to 3.5 km above the volcano. The ash clouds traveled to the W. A second eruption was visible in GOES 8 imagery. It was expected that nearby Mexican states would be coated with a thin layer of ash. At 19:15 on 23 August, a moderate exhalation produced ashfall in the nearby communities of San Pedro Nexapa and Amecameca (~12 km NW and ~16 km NW of the summit, respectively). Throughout the rest of the reporting period there were exhalations of low intensity and short duration that mainly involved gas with small amounts of ash.

Several volcano-tectonic earthquakes, ranging in magnitude from 1.7 to 2.3, occurred during the month of July. The first of these was on 2 July. It was followed by earthquakes on 6, 8, 9, 11, 15, and 23 of July. Three volcano-tectonic earthquakes occurred on 20 July, all under M 2.5. On 1 August, three more tectonic earthquakes were recorded, M 1.9 - 2.7. Other earthquakes occurred on 5 and 10 August; both were less than M 2.

Popocatépetl's volcanic hazard level remained at yellow. CENAPRED recommended that all visitors remain 7 km or more from the crater.

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

Information Contacts: The National Center of the Prevention of Disasters (CENAPRED) (URL: https://www.gob.mx/cenapred/); Discovery.com (URL: http://www.discovery.com); Washington VAAC (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Volcano World (URL: http://volcano.oregonstate.edu).

This report covers the period April-June 2000. During mid-April, the inflationary trend that began in February 2000 tapered off (BGVN 25:03). However, the realtime GPS system, along with electronic and water tilt data, continued to indicate a long-term inflation trend.

Emissions from the 1941 vent were characterized by thin, white vapor throughout the months of April and May. The 1995 vent was free of vapor emissions except for gentle puffs of grey ash-clouds on 5, 14-16, and 28-30 April, and 5 and 30 May. During April, these ash clouds rose several hundred meters above the summit before being blown to the W, NW, and SW. Towards the end of May, the general haze produced began to contain a weak ash component and there was a strong smell of SO₂.

In April, a single high-frequency earthquake was recorded and located NE of the caldera wall. Low-frequency earthquakes continued to occur throughout April and were related to the eruptive activity associated with Tavurvur (figure 35). The number of these earthquakes fluctuated within background levels. There was a significant decrease in the number of trigger counts from 78 in February and 90 in March to 28 in April. The number rose again in May to 64. However, it should be noted that these trigger counts include only events that trigger two or more stations. The count that includes non-triggered events (seismic events that do not trigger more than one station) is much higher. On 15 and 30 April, bands of sub-continuous, 2-3 hour long, non-harmonic tremor were recorded.

Figure 35. Map of Rabaul caldera showing locations of volcanic vents, selected towns, and features (modified from Almond and McKee, 1982).

For most of May, seismic activity was low. The exception was a ~M 4.8 earthquake that occurred at 1649 on 10 May and was centered 30 km NE of Rabaul. This produced several aftershocks; a total of 95 high-frequency triggered events were recorded on this date. Because of the proximity of these events to the established 'NE earthquake zone,' which is associated with ongoing eruptive activity, there was an expectation that higher levels of summit activity would occur at Tavurvur.

In June, 13 high-frequency events were recorded. Most originated NE of the Rabaul caldera. The S-P interval for these events was 1-4 seconds. Earthquakes occurring in this region have apparently been associated with the ongoing eruptive activity that began on 28 November 1995. A total of 185 low-frequency triggered events were recorded in June. Most of these events were related to explosions during two episodes of ashfall, one on 5 June and the other on 28 June. In addition, quasi-monochromatic volcanic tremor with durations ranging from a few minutes to a few hours were recorded during these periods. An increase in low- frequency non-triggered events was noted before each of the two episodes.

The 5 and 28 June episodes were characterized by moderate ashfall that emanated from Tavurvur. The first episode began on 5 June with a Vulcanian eruption that deposited lithic blocks beyond the crater rim. Through 8 June there was moderate-to-heavy ashfall. On 6 June at 1150 a loud explosion occurred at the 1941 vent. This was followed by increased explosive activity until the afternoon of 7 June when explosions occurred at 30-minute intervals. The explosion clouds contained moderate amounts of ash and rose to about 1.0-1.5 km above the summit. These ash clouds were blown such that they deposited ash towards the N, NE, and NW where Rabaul Town is located. By 8 June, the explosions had subsided to occasional emissions of light-to-moderate white vapor. For the following two weeks, the areas to the N, NE, and NW were continuosly blanketed in a thin fog of white vapor from Tavurvur.

At 0527(?) on 28 June, another explosion from the 1941 vent triggered the second period of light-to-moderate ashfall. The explosion was followed immediately by a dark grey ash cloud that rose to 1.5 km above the summit before being blown to the N and NW. Over the next two days, further ash clouds were produced that attained heights of several hundred meters. Discrete explosions, occurring at long intervals, marked the end of this period of activity. The last explosion occurred on 30 June.

Beginning in early May, electronic and wet-tilt measurements showed a downward tilt with a total deflation of ~9.0 µrad throughout May and June. However, an inflation of 4.0 µrad was recorded before the activity of 5-8 June and 5.5 µrad was recorded before the 27-30 June activity.

The low-lying Rabaul caldera forms a sheltered harbor once utilized by New Britain's largest city Rabaul prior to the 1994 eruption, which forced the abandonment of the city. Tavurvur and Vulcan are two eruption centers within the Rabaul caldera complex. These volcanoes have had virtually simultaneous eruptions in 1878, 1937, and 1994.

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

Information Contacts: Ima Itikarai, David Lolok, Herman Patia, and Steve Saunders, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

Semeru has been undergoing nearly constant eruptive activity since 1967. Volcanological Survey of Indonesia (VSI) reports through mid-September 1999 (BGVN 24:09) and earlier described seismicity (including seismically detected pyroclastic flows) and ongoing eruptive outbursts. Accessible Darwin VAAC reports since 3 June 1998 help to characterize the long-term eruptive patterns (table 3). VSI reports are not available for September 1999 through January 2000.

Table 3. A summary of aviation reports (Volcanic Ash Advisories) describing Semeru's plumes during 3 June 1998-21 August 2000. The first two columns describe the time and date when a report was issued. Time entries with commas signify that multiple reports were generated with similar comments. Where available, the time of the observations appear with the comment. Dash marks indicate lack of mention in report. Note that for plume heights, Semeru's summit lies at 3,676 m above sea level. Information sources include air reports (for example, routed via airlines, AIREPS), pilot reports (PIREPS), Notice to Airmen (NOTAM), satellite data, and reports from ground observations. Source data was provided by the Darwin VAAC.

Activity during February-July 2000. Explosive activity during February 2000 included ash emissions, numerous rockfalls, and a few deep A-type earthquakes (table 4). Plumes of thick white ash were seen to rise up to 400 m above the summit on many occasions. Persistent haze or cloudy weather prevented direct observation throughout most of the month. At night during the week of 8-14 February observers noted a 60-m-high flame. Generally, explosions and rockfalls dominated recorded seismicity.

Table 4. Summary of seismicity at Semeru, 31 January-29 August 2000. * Six days of data, through 15 July. Courtesy of VSI.

Explosions and lava avalanches continued in March. Clouds and haze often obscured the volcano, but sometimes thick white emissions appeared above the summit to a maximum height of 500 m. Visual activity and seismicity appeared to increase in late March-early April.

During 4-10 April explosions and lava avalanches were still continuing and became stronger. Seismicity also increased significantly; tremor earthquakes took place 56 times, with maximum amplitudes of 3-15 mm. One pyroclastic flow traveled 1,500 m down the Besuk Kembar river. Many observations in clear conditions showed that the ash cloud was thick and white, rising 400-600 m above the summit. Emissions continued the following week, and explosions increased. "Red flames" sometimes appeared at the summit during night observations. Similar activity continued throughout April. The number of pyroclastic flows increased in late April, and continued at a typical rate of 2-7 per week for the next few months (table 4). On 30 April at 0743, from a location 15 km NNW of Semeru, a pyroclastic flow was observed travelling 800 m down the SSW flank.

Ashfall occurred at the Semeru Volcano Observatory during the week of 2-8 May, when five pyroclastic flows were recorded. Seismicity decreased again, but "red flame" was still seen at night and plumes rose as high as 600 m through 23 May.

Explosive activity was continuing in the second half of June; observers noted white-gray plumes ~600 m above the summit. Pyroclastic flows that reached maximum distances of ~2.5-3 km were reported on 1-2, 4, 10, and 15 July.

Observations on 2 May 2000. John Seach and Geoff Mackley made observations during a 3-hour summit stay on 2 May 2000. During the climb from Ranu Pani village in the N, ash deposits were observed to cover vegetation at a distance of 10 km from the volcano. The bottom third of the cone was vegetated, and zones of mass-wasting had sliced away 20- m-wide sections of forest. The top two-thirds of the cone consisted of ash, cinders, and blocks up to 1.5 m in diameter. There were areas of deep erosion and the risk of rockfalls posed a hazard to climbers.

The summit area (Mahameru) lay covered by ash and baseball-sized blocks with a density of 50/m². A 20-m-wide, 60-m-deep, W-sloping valley separated Mahameru from the active Jonggring Seloko crater, but they are joined by a ridge. The highest N rim of the crater was approximately 30 m below the summit peak. A 2-m-diameter block was located 15 m below the summit on the wall of the valley.

Between 0725 and 1010, 13 eruptive events were observed. During this interval the N rim of Jonggring could not be approached because of the intermittent rain of blocks falling outside the crater and into the valley 50 m from the crater. Two vents produced short-lived Vulcanian eruptions with variable timing and size. Eruptions commenced with degassing, explosions, or the sound of breaking rock, followed by falling bombs and brown ash emission. The explosions were relatively quiet and not accompanied by groundshaking. Brown ash clouds rose to 600 m above the vent and drifted SE. The plume detached from the summit before the next eruption began. Steam emission occurred between eruptions.

Observations on 14 July 2000. Volcanologists on an International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) field trip in east Java observed eruptions of Semeru from an observation point on the N rim of the Sand Sea caldera at Bromo (figure 10). Eruption plumes became visible just before sunrise. Gray ash-and-steam plumes rose a few hundred meters and drifted out over the ocean. Multiple plumes from earlier eruptions were visible downwind. Eruptions lasted up to 2 minutes, and occurred at intervals of between 5 and 30 minutes during the approximately 2 hours of observations. One explosion event was quickly followed by another explosion, apparently from a second location within the crater. Plumes were frequently seen during the next two days from other points around the volcano.

Figure 10. Photograph taken just after sunrise on 14 July 2000 showing an ash eruption from Semeru (upper right) and a steam plume rising from Bromo (lower left). The cone in the lower right is Batok, another young cone within the Sand Sea caldera of the Bromo-Tengger volcanic complex. Note the extensive ash cover on the upper part of Semeru. View is towards the S. Courtesy of Ed Venzke, Smithsonian Institution.

Explosion on 27 July 2000. At approximately 0706 on the morning of 27 July an explosion resulted in two deaths and injuries to five other volcanologists near the NE rim of the active summit crater Jonggring Seloko (see map in BGVN 17:10). The group consisted of a five-member Semeru evaluation team of the Volcanological Survey of Indonesia (VSI), four local porters, and foreign scientists who had attended the IAVCEI conference in Bali the previous week. The fatalities and injuries were caused by impacts and burns from ballistic clasts. These originated from the second of two closely spaced explosions from separate vents that ejected material out to a few hundred meters. Both fatalities were VSI staff members: Asep Wildan was the team leader, and Mukti was a volcano observer from the Semeru Volcano Observatory. Those injured included Suparno, a VSI volcano observer from the Semeru Volcano Observatory, Amit Mushkin from the Hebrew University in Israel, Mike Ramsey from the University of Pittsburgh, and Lee Siebert and Paul Kimberly from the Smithsonian Institution. Kimberly sustained the most serious injuries among the five survivors, including a broken hand, broken arm, and 3rd-degree burns. Following surgeries in Singapore and burn treatments in the United States, Kimberly was released from the hospital in early September.

Continuing activity through August. Visual observations were hindered by bad weather the first week of August. Activity generally decreased through 22 August. White to light-brown ash clouds rising to about 600 m in height were frequently seen during this period. Seismicity increased again in late August, and on 25 and 27 August three pyroclastic flows were recorded. Thin white-gray ash plumes rose ~600 m.

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

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); 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/); John Seach, P.O. Box 16, Chatsworth Island, NSW 2469, Australia; Ed Venzke, Global Volcanism Program, Smithsonian Institution, Washington DC 20560-0119, USA.

During January-July 2000 Tungurahua volcano experienced continuous but relatively mild activity with occasional lava fountaining. There were periods (hours to days) of relative calm during June and July.

The volcano continues to generate a variety of seismic events, most events being the long-period (LP) type. Two episodes of volcano-tectonic (VT) events were observed; one between late January and early March, and one less intense event between early May and mid-June. Epicenters for these events were across the top of the volcano's cone with focal depths at 3-13 km. Hybrid events, whose waveforms consist of a short, higher-frequency onset followed by lower-frequency, larger-amplitude signals, were most abundant in January and February (~50 events/week), partially coinciding with the greater VT activity. Subsequently these events diminished to 1-2 events/week, except for a brief swarm in early April.

Events of classical LP waveform were frequent, varying from ~400 events/week in January, ~600 in February, ~400 in March, ~600 in April, ~500 in May, and ~400 in June. A sharp increase to ~950 events/week was observed in July. Some of the LP events (3.7-4.0 Hz) were located tentatively at depths of 7-10 km below the crater. However, the great majority of LP events (1.5-3.3 Hz) were 3-7 km deep. They were often associated with explosion clouds or forceful emissions of ash-and-steam within 1-3 seconds of the seismic onset, suggesting a high-level origin.

Explosions, recognized principally by their impulsive onset, were more frequent during January and February (~80-90 events/week), but in subsequent months dropped to ~20-30 events/week, with many accompanied by a sonic boom. Reduced displacement values for the explosions typically were 5-10 cm², and occasionally 12-18 cm².

Low-frequency tremor with spectral frequencies between 0.5-1.6 Hz, but monochromatic at times, were observed in April and May, but only sporadically in June and July. During the period from the 2nd week of April through the 2nd week of May, the low-frequency episode coincided with lava fountaining in the summit crater. The fountains, comprised of the continuous ejection of incandescent material 100-500 m into the air, lasted hours; sustained roaring and surf-like noises heard 12 km away.

The constant glow of incandescent material in the crater, which was observed frequently in late 1999, was seen only occasionally during August, possibly due to unfavorable weather conditions. Better viewing conditions in late June and July confirmed that incandescent lava still remained in the crater or immediately below it.

The emissions have consisted of a permanent, grayish-white to light-gray column of steam with varying amounts of fine-grained ash that commonly rise less than 1 km above the crater. Explosions or strong emissions have consisted of blocks being thrown hundreds of meters into the air and by the formation of Vulcanian-like eruption clouds that are medium-to-dark gray in color and sometimes with a mushroom shape. The clouds have reached as high as 5 km above the summit. Primarily, easterly winds have carried the very fine ash to the W and WSW, but occasionally anywhere in the azimuthal arc between NW and SW. Both national and international flights reported the ash plume. The ash deposits were several centimeters thick on the lower W flank of the cone, but only several millimeters in the agriculturally important lands farther W.

Ballistic blocks were vesicular, black, glassy andesite containing phenocrysts of olivine, plagioclase, augite, and hypersthene, in a glassy matrix with 10-20% microlites. More recent samples had fewer olivines and larger augites. Chemical analyses of these blocks as well as collected ash gave the following typical values: SiO₂ ~58.5%, K₂O ~1.72%, MgO ~3.9%, Ni ~33 ppm, and Cr ~65 ppm.

COSPEC monitoring since November was hindered by heavy cloud cover. Following the consistently high SO₂ flux values of 6,000-8,000 metric tons/day (t/d) during September-October 1999, values decreased to an average of 3,000-4,000 t/d in November-December 1999. Values then rose to ~8,000 t/d in January and subsequently dropped to an average of ~1,000-2,000 t/d in June and July 2000. An exception to this trend was an increase to ~4,000 t/d observed in April-May, 2000, which coincided with the lava fountaining episode. In general, higher SO₂ values seem to be associated with greater tremor activity.

Monthly water analyses of hot springs at both the N and S bases of the edifice have not shown any variation in temperature, pH, conductivity, nor in the concentrations of SO₄, Cl^-, Na+, CO₃^--, Ca⁺⁺, Mg⁺⁺, and K⁺, since chemical monitoring began in 1992 and since the activity on Tungurahua began in July 1999.

Lahars coincided with the rainy season and became frequent in October and November 1999; they rapidly cut the main highway at every stream crossing along the western half of the cone (the area of greatest ash fall). Occasional rains from December to June generated flows of debris. The main highway to Baños and to the Amazon Basin was frequently blocked for hours due to lahar deposits.

In general, the activity appeared to be subsiding. However, during the 1916-18 eruptive period the volcano experienced 1.5 years of little activity between major eruptions. An orange alert is still in effect. In the past, Tungurahua typically generated both Merapi- and St. Vincent-like nuées ardentes. The W sector of Baños (17,000 inhabitants) lies at the mouth of a canyon that starts near the summit of the volcano, 9 km away and 3,000 m above the town.

Following the evacuation of Baños on 17 October 1999, the town remained abandoned until late December (BGVN 25:01). As of August 2000, about 80% of the population had returned and tourism has re-established itself.

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

Information Contacts: Geophysical Institute (Instituto Geofísico), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador.

This report covers the period from April to June 2000. There were no unusual reports from Ulawun in April. Throughout May, moderate to thick white vapor was emitted. Emissions in June consisted of thin white vapor. However, on 5 and 7 June, the emissions were thick white vapor. Seismic activity for June was at a moderate level.

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: I. Itikarai, D. Lolok, K. Mulina, and F. Taranu, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

This report covers June and July 2000. On 18 April 2000, the Institute of Geological and Nuclear Sciences (IGNS) increased the alert level from 1 to 2 (level 5 being the most severe) following minor eruptive activity that began on 7 March 2000 and included elevated seismicity and higher than normal SO₂ gas flux (BGVN 25:03).

The IGNS reported that for the week ending 16 June 2000, the active MH vent continued to emit an ash plume. This plume sometimes extended as far as 60 km downwind and deposited ash as far as 15 km away. Up to several centimeters of ash were deposited on White Island. Until 16 June, seismic activity was significantly less than in May.

Field observations on 12 July indicated little change in activity since April. Furthermore, no direct relationship between seismic activity during this time and the eruptive activity could be determined. The ash continued to be vented to an altitude of 800-1,000 m. By 19 July, strong NE winds had periodically blown the ash plume towards the mainland, resulting in minor ash deposition there. Ashfall at Turango airport led to landing and departure restrictions. Air traffic was also disrupted around the Bay of Plenty.

On 22 July IGNS staff noticed an increase in activity compared to previous observations. A yellowish-brown gas and an ash plume extending to a height of 1500 m were blown to the E and SE. This continued to disrupt air traffic and deposit ash on the mainland. In fact, the IGNS staff were unable to land due to ash accumulation at the landing site. However, they noted that yellowish-brown ash now covered the island with thicknesses ranging from several mm to several cm. They saw no evidence of ballistic bombs or evidence that the eruptive style had changed from the previous months. However, they did note that the height of the MH vent had decreased from its previous location above the acid lake to a height level with the lake.

On Thursday 27 July between 1700 and 2200, a period of strong seismic activity was recorded. Visual and satellite observations were not possible due to poor weather conditions. A tour operator arriving at the island the morning of 28 July, confirmed that there had been an eruption. IGNS staff arrived 29 July and discovered that a large explosive eruption formed a new crater 120 x 150 m wide in the site formerly occupied by a warm acidic lake in the 1978-90 Crater Complex. The eruption deposited as much as 30 cm of ash and pyroclastic material, including juvenile pumice blocks, over the eastern part of the island. This was the largest eruption at White Island in about 20 years; deposits from this eruption were found in areas frequently visited by tourists. The IGNS advised all visitors that similar eruptions pose serious risks to anyone on the island.

Observations on 31 July found the MH vent, which had enlarged to ~50 m, spewing a dark ash cloud while a reddish-brown ash cloud rose from the new 27 July vent. The plumes combined and rose as high as 1-1.2 km above the vents. After this event, activity returned to the level typical since April: minor eruptions that produced plumes of gas, steam, and volcanic ash.

Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Information Contacts: Brent Alloway, Brad Scott, and Steven Sherburn, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).