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).

Recent activity at Yasur, which has been erupting since July 1774, includes frequent Strombolian explosions, along with ash and gas plumes from several vents in the summit crater (BGVN 44:02, 45:03). This report summarizes activity during March through August 2020, using information from monthly bulletins of the Vanuatu Meteorology and Geo-Hazards Department (VMGD) and various satellite data. The volcano has remained on Alert Level 2 (major unrest state, on a scale of 0-5), where it has been since 18 October 2016, according to VMGD.

During the current reporting period, VMGD reported that explosive activity continued at an elevated level, with ongoing ash and gas emissions (figure 71). Some of the more intense explosions ejected bombs outside the summit crater. During 2-3, 13, and 17 March, 2-3 April, and 19 July, the Wellington Volcanic Ash Advisory Center (VAAC) identified low-level ash plumes that reached an altitude of 1.5 km and drifted in multiple directions; the ash plume during 2-3 April resulted in ashfall on the SSW part of the island. On 19 May an ash plume rose to a maximum altitude of 2.1 km and drifted SE.

Figure 71. Webcam photos of ash emissions from Yasur on 18 March (left)and gas-and-steam emissions on 2 April (right) 2020. Courtesy of VMGD.

During the reporting period, the MODVOLC thermal algorithm using MODIS satellite data detected a total of 55 thermal hotspots during three days in April, nine days in May, six days in June and August, and four days in July. A maximum of four pixels were recorded on a single day during 26 May, 6 June, and 20 July. The MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data detected numerous hotspots from 16 September 2019 through August 2020, with a slight increase in power and frequency during May (figure 72). Satellite images from Sentinel-2 detected a strong thermal anomaly within the summit crater on 10 May, accompanied by ash and gas emissions (figure 73).

Figure 72. Persistent low to moderate thermal activity at Yasur occurred from the summit area from 16 September 2019 through August 2020, as shown in this MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 73. Sentinel-2 images of Yasur on 10 May 2020 showing a strong thermal anomaly from the summit crater (left) and a gas emission that appears to contain some ash (right). The thermal anomaly in the S vent area was stronger than in the N vent, an observation also noted in March and April 2019 (BGVN 44:06). The volcano was usually obscured by clouds during March through August. The left image is in false color (bands 12, 11, 4) rendering, the right image is in natural color (bands 4, 3, 2) rendering; courtesy of Sentinel Hub Playground.

High-resolution satellite sensors commonly recorded moderate sulfur dioxide levels drifting in multiple directions from the volcano. High sulfur dioxide levels were also occasionally observed, especially during March (figure 74).

Figure 74. High-density SO2 emissions streaming from Yasur during 8 (left) and 13 (middle) March and 21 April (right) 2020, were observed using the TROPOMI imaging spectrometer on the Sentinel-5P satellite. The plume drifted W on 8 March and E on both 13 March and 21 April. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://vaac.metservice.com/index.html); Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/).

Historical eruptions at Chile's Villarrica, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. An intermittently active lava lake at the summit has been the source of Strombolian activity, incandescent ejecta, and thermal anomalies for several decades; the current eruption has been ongoing since December 2014. Continuing activity during February-August 2020 is covered in this report, with information provided by the Southern Andes Volcano Observatory (Observatorio Volcanológico de Los Andes del Sur, OVDAS), part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN), and Projecto Observación Villarrica Internet (POVI), part of the Fundacion Volcanes de Chile, a private research group that studies volcanoes across Chile. Sentinel satellite imagery also provided valuable data.

Intermittent incandescence was observed at the summit throughout February-August 2020, which was reflected in the MIROVA thermal anomaly data for the period (figure 92). Continuous steam and gas emissions with occasional ash plumes rose 100-520 m above the summit. Every clear satellite image of Villarrica from February -August 2020 showed either a strong thermal anomaly within the summit crater or a dense cloud within the crater that prevented the heat signal from being measured. Sentinel-2 captured on average twelve images of Villarrica each month (figure 93). Larger explosions on 25 July and 7 August produced ejecta and ash emissions.

Figure 92. Thermal anomaly data for Villarrica from 13 October 2019 through August 2020 showed intermittent periods of activity. Incandescence was intermittently reported from the summit and satellite imagery showed a persistent hot spot inside the summit crater throughout the period. Courtesy of MIROVA.

Figure 93. Examples of strong thermal anomalies inside the summit crater of Villarrica each month from March-August 2020 are shown with dates on the image. Sentinel-2 satellite imagery with Atmospheric penetration rendering (bands 12, 11, 8A) showed thermal anomalies at the summit in all clear satellite images during the period. Courtesy of Sentinel Hub Playground.

Primarily white gas emissions rose up to 400 m above the summit during the first half of February 2020 and to 320 m during the second half. Incandescence was observed on clear nights. Incandescent ejecta was captured in the POVI webcam on 7 February (figure 94). Sentinel-2 satellite imagery showed bright thermal anomalies at the summit on 5, 8, 10, 13, 18, 20, 23, 25, and 28 February, nine of the eleven days that images were taken; the other days were cloudy.

Figure 94. Incandescent ejecta at the summit of Villarrica was captured in the POVI webcam late on 7 February 2020. Time sequence runs from top to bottom, then left to right. Courtesy of POVI.

Villarrica remained at Alert Level Yellow (on a four-level Green-Yellow-Orange-Red scale) in March 2020. Plumes of gas rose 350 m above the crater during the first half of March. The POVI webcam captured incandescent ejecta on 1 March (figure 95). SERNAGEOMIN reported continuous white emissions and incandescence at night when the weather permitted. During the second half of March emissions rose 300 m above the crater; they were mostly white but occasionally gray and drifted N, S, and SE. Nighttime incandescence could be observed from communities that were tens of kilometers away on multiple occasions (figure 96). Sentinel-2 satellite imagery showed bright thermal anomalies at the summit on 1, 3, 4, 6, 9, 11, 14, 16, 19, 26, 29, and 31 March, twelve of the fourteen days images were taken. The other days were cloudy.

Figure 95. Incandescent ejecta rose from the summit of Villarrica in the early morning of 1 March 2020. Courtesy of POVI.

Figure 96. Nighttime incandescence was observed on 24 March 2020 tens of kilometers away from Villarrica. Courtesy of Luis Orlando.

During the first half of April 2020 plumes of gas rose 300 m above the crater, mostly as continuous degassing of steam. Incandescence continued to be seen on clear nights throughout the month. Steam plumes rose 150 m high during the second half of the month. A series of Strombolian explosions on 28-29 April ejected material up to 30 m above the crater rim (figure 97). Sentinel-2 satellite imagery showed bright thermal anomalies at the summit on 3, 8, 10, 13, 20, and 30 April, six of the twelve days images were taken; other days were cloudy.

Figure 97. A series of Strombolian explosions on 28-29 April 2020 at Villarrica ejected material up to 30 m above the crater rim. Courtesy of POVI.

Daily plumes of steam rose 160 m above the summit crater during the first half of May 2020; incandescence was visible on clear nights throughout the month. During 5-7 May webcams captured episodes of dark gray emissions with minor ash that, according to SERNAGEOMIN, was related to collapses of the interior crater walls. Plumes rose as high as 360 m above the crater during the second half of May. The continuous degassing was gray and white with periodic ash emissions. Pyroclastic deposits were noted in a radius of 50 m around the crater rim associated with minor explosive activity from the lava lake. The POVI infrared camera captured a strong thermal signal rising from the summit on 29 May (figure 98), although no visual incandescence was reported. Residents of Coñaripe (17 km SSW) could see steam plumes at the snow-covered summit on 31 May (figure 99). Sentinel-2 satellite imagery showed bright thermal anomalies at the summit on 5, 13, 20, 23, 25 and 30 May, six of the twelve days images were taken. The other days were cloudy.

Figure 98. The POVI infrared camera captured a strong thermal signal rising from the summit of Villarrica on 29 May 2020; no visual incandescence was noted. Courtesy of POVI.

Figure 99. Residents of Coñaripe (17 km SSW) could see steam plumes at the snow-covered summit of Villarrica on 31 May 2020. Courtesy of Laura Angarita.

For most of the first half of June, white steam emissions rose as high as 480 m above the crater rim. A few times, emissions were gray, attributed to ash emissions from collapses of the inner wall of the crater by SERNAGEOMIN. Incandescence was visible on clear nights throughout the month. Vertical inflation of 1.5 cm was noted during the first half of June. Skies were cloudy for much of the second half of June; webcams only captured images of the summit on 21 and 27 June with 100-m-high steam plumes. Sentinel-2 satellite imagery showed bright thermal anomalies at the summit on 4, 7, and 14 June, three of the twelve days images were taken. The other days were cloudy.

Atmospheric clouds prevented most observations of the summit during the first half of July (figure 100); during brief periods it was possible to detect incandescence and emissions rising to 320 m above the crater. Continuous degassing was observed during the second half of July; the highest plume rose to 360 m above the crater on 23 July. On 25 July, monitoring stations in the vicinity of Villarrica registered a large-period (LP) seismic event associated with a moderate explosion at the crater. It was accompanied by a 14.7 Pa infrasound signal measured 1 km away. Meteorological conditions did not permit views of any surface activity that day, but a clear view of the summit on 28 July showed dark tephra on the snow around the summit crater (figure 101). Sentinel-2 satellite imagery showed bright thermal anomalies at the summit on 2 and 29 July, two of the twelve days images were taken. The other days were either cloudy or had steam obscuring the summit crater.

Figure 100. Although a multi-layer cap cloud formed over the summit of Villarrica on 15 July 2020, steam emissions could be seen close to the summit drifting down the slope. Cap clouds form when a stable airstream rises to pass over a peak and cools, condensing moisture into clouds. Photograph by Sebastián Campos, courtesy of Geography Fans.

Figure 101. Dark tephra appeared near the summit of Villarrica on 28 July 2020; an explosion had been measured seismically on 25 July but clouds obscured visual observations. Image taken from Coñaripe, courtesy of Laura Angarita.

An explosion on 7 August at 1522 local time (1922 UTC) produced an LP seismic signal and a 10 Pa infrasound signal. Webcams were able to capture an image of the explosion which produced a dense plume of steam and ash that rose 370 m above the summit and drifted SE (figure 102). The highest plumes in the first half of August reached 520 m above the summit on 7 August. Sporadic emissions near the summit level were reported by the Buenos Aires VAAC the following day but were not observed in satellite imagery. When weather permitted during the second half of the month, continuous degassing to 200 m above the crater was visible on the webcams. SERNAGEOMIN participated in a webinar on 20 August 2020 discussing safety at Villarrica and showed an image of the summit crater taken during an overflight on 19 August (figure 103). Sentinel-2 satellite imagery showed bright thermal anomalies at the summit on 6, 21, and 31 August, three of the thirteen days images were taken. The other days were cloudy.

Figure 102. An explosion at Villarrica on 7 August 2020 at 1522 local time (1922 UTC) produced an LP seismic signal and 10 Pa infrasound signal. Webcams were able to capture an image of the explosion which produced a dense plume of steam and ash that rose 370 m above the summit and drifted SE Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, volcan Villarrica, 7 de Agosto de 2020, 16:15 Hora local).

Figure 103. SERNAGEOMIN participated in a webinar on 20 August 2020 discussing safety at Villarrica and showed an image of the summit crater taken during an overflight on 19 August. Courtesy of Turismo Integral.

Geologic Background. Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Information Contacts: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Proyecto Observación Villarrica Internet (POVI), (URL: http://www.povi.cl/, https://twitter.com/povi_cl/status/1237541250825248768); Luis Orlando (URL: https://twitter.com/valepizzas/status/1242657625495539712); Laura Angarita (URL: https://twitter.com/AngaritaV/status/1267275374947377152, https://twitter.com/AngaritaV/status/1288086614422573057); Geography Fans (URL: https://twitter.com/Geografia_Afic/status/1284520850499092480); Turismo Integral (URL: https://turismointegral.net/expertos-entregan-recomendaciones-por-actividad-registrada-en-volcan-villarrica/).

Stromboli, located in northeastern-most part of the Aeolian Islands, is composed of two active summit vents: the Northern (N) Crater and the Central-South (CS) Crater that are situated at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano. The current eruption period began in 1934, continuing to the present with volcanism characterized by consistent Strombolian explosions in both summit craters, ash plumes, pyroclastic flows, and occasional lava flows (BGVN 45:08). This report updates activity consisting of dominantly Strombolian explosions and ash plumes from May to August 2020 with information primarily from daily and weekly reports by Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) and various satellite data.

Activity was consistent during this reporting period. Explosion rates ranged from 1-23 events per hour and were of variable intensity, producing material that typically rose from less than 80 to over 300 m above the crater. One ash plume on 19 July rose 1 km above the crater and high energy ballistics were ejected 500 m above the crater during the week of 20-26 July (table 9). Strombolian explosions were often accompanied by gas-and-steam emissions and spattering that has occasionally resulted in material deposited on the slopes of the Sciara del Fuoco. According to INGV, the average SO₂ emissions measured 250-300 tons/day.

Table 9. Summary of activity at Stromboli during May-August 2020. Low-intensity activity indicates ejecta rising less than 80 m, medium-intensity is ejecta rising less than 150 m, and high-intensity is ejecta rising over 200 m above the vent. Data courtesy of INGV.

Explosive activity was relatively consistent during May 2020 and was mainly produced in 3-4 eruptive vents in the N crater and at least two eruptive vents in the CS crater. As a result of some explosions fallout covered the slopes of the Sciara del Fuoco. Explosion rates varied from 1-17 per hour in the N crater and 1-8 per hour in the CS crater; ejected material rose 80-250 m above the craters.

During June, explosions originated from 2-3 eruptive vents in the N crater and at least 2-3 localized vents in the CS crater. The Strombolian explosions ejected material 80-200 m above the craters, some of which fell back onto the Sciara (figure 182). Explosion rates varied from 5-14 per hour in the N crater and 2-9 per hour in the CS crater. Spattering was typically observed in the CS crater.

Figure 182. An explosion at Stromboli produced gas-and-steam and ash emissions on 18 June 2020 was observed in the CS crater in the Sciara del Fuoco. Courtesy of INGV (Rep. No. 26/2020, Stromboli, Bollettino Settimanale, 15/06/2020 - 21/06/2020, data emissione 23/06/2020).

Ongoing explosive activity continued into July, originating from 2-3 eruptive vents in the N crater and 3-4 eruptive vents in the CS crater. Explosions varied from 3-12 per hour in the N crater and 1-11 per hour in the CS crater; ejected lapilli and bombs rose 80-1,000 m above the craters (figure 183). On 19 July a high-energy explosion between 0500 and 0504 produced an ash plume containing ejecta more than 50 cm that rose to a maximum of 1 km above the crater, with fallout reaching the Pizzo sopra la Fossa and resulting in ashfall on the Sciara and the towns of Liscione and Roccette. During the week of 20-26 July explosions in the E portion of the volcano ejected ballistics 500 m above the crater; the size and shape of these varied between slag bombs to clasts greater than 50 cm.

Figure 183. Webcam (left column) and thermal (right column) images of explosive activity at Stromboli on 29 July (top row) and 2 August (bottom row) 2020 originated from the N and CS craters, producing spatter and ash plumes. Courtesy of INGV (Rep. No. 32/2020, Stromboli, Bollettino Settimanale, 27/07/2020 - 02/08/2020, data emissione 04/08/2020).

Strombolian activity accompanied by discontinuous spattering continued during August. Total daily explosions varied from 3-23 per hour ejecting material that up to 200-250 m above the craters. During the first half of the month the explosions were low-intensity and consisted of fine material. On 13 August the intensity of the explosions increased, producing an ash plume that rose 300 m above the crater drifting SE and resulting in a significant amount of ashfall on the Sciara. During the week of 17-23, explosions in the N1 crater ejected material 200 m above the crater while explosions in the CS crater ejected material 250 m above the crater, predominantly during 22 August in the S2 crater (figure 184).

Figure 184. Images of gas-and-steam and ash plumes rising from the N2 (left), S2 (middle), and CS craters (right) at Stromboli on 22 August 2020. Courtesy of INGV (Rep. No. 35/2020, Stromboli, Bollettino Settimanale, 17/08/2020 - 23/08/2020, data emissione 25/08/2020).

Moderate thermal activity was relatively consistent from October 2019 through mid-April 2020; during May-August thermal activity became less frequent and anomalies were lower in power based on the MIROVA Log Radiative Power graph using MODIS infrared satellite information (figure 185). Though there were no detected MODVOLC thermal alerts during this reporting period, many thermal hotspots were observed in Sentinel-2 thermal satellite imagery in both summit craters (figure 186).

Figure 185. Low to moderate thermal activity at Stromboli occurred frequently from 16 September to mid-April 2020 as shown in the MIROVA graph (Log Radiative Power). During May-August thermal activity decreased and was less frequent compared to the previous months. Courtesy of MIROVA.

Figure 186. Weak thermal anomalies (bright yellow-orange) at Stromboli were observed in thermal satellite imagery from both of the summit vents throughout May-August 2020. Images with atmospheric penetration (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); 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).

A new eruption began on 27 November 2005 when vapor plumes and ash columns were observed originating from Lake Voui, a crater lake at the summit of Aoba (figure 13). The volcano is also referred to locally as Manaro or Lombenben. Prior to this activity, the most recent reported volcanism consisted of phreatic explosions from the lake during March 1995 (BGVN 20:01, 20:02, and 20:08). Bathymetry conducted by ORSTOM in 1996 showed that the vent feeding gases and magma into Lake Voui had a depth of about 150 m and a diameter of about 50 m. The volume of water in the lake (1 x 2 km) totals some 40 million cubic meters, with a mean pH of 1.8. Lake Voui and the Manaro Ngoro summit explosion craters and cones formed ~ 420 years ago (figure 14). Lake Manaro was formed by the accumulation of water in a low-lying area of the Manaro summit caldera.

Figure 13. Map showing the location of volcanoes, including Aoba, in Vanuatu. Open triangles indicate submarine volcanoes. Modified from a map by IRD.

Figure 14. Digital image of Aoba created by combing shading and color coding of topographic height. The shading indicates direction of the slopes; NW slopes appear bright, while SE slopes appear dark. Color coding shows height, with green at the lower elevations, rising through yellow and tan, to white at the highest elevations. The flattened-looking summit shows that the newest crater is actually nested within older, larger craters. Elevation data used in this image were acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on 11 February 2000. Annotations added by Smithsonian editors. Courtesy of NASA.

Starting on 3 December a team of volcanologists from the Vanuatu Department of Geology, Mines, and Water Resources (DGMWR), the French Institut de recherche pour le développement (IRD), the New Zealand Institute of Geological & Nuclear Sciences (GNS), and New Zealand's Massey University began collaborating on observations and monitoring. The amplitude of tremor recorded by DGMWR instruments from 30 November to 3 December was lower than during the March 1995 activity.

Scientists who visited the lake on 4 and 5 December (figures 15 and 16) observed a similar style of eruptive activity on both days, but some individual explosions appeared larger on the 5th. It was not possible to reach the lake to collect a water sample. There appeared to be two active vents, side by side, in the lake. One was producing eruptions of mud, rocks, and water, and the other appeared to be the source of the large continuous steam plume rising above the crater; the plume did not contain ash. There were no reports of ash falling on the island since the start of the eruptions the previous week. The team estimated that the cone being built in the lake, at an estimated height of more than 20 m on the 4th, was about 70% complete around the active vents, and grew 5-10% higher between 4 and 5 December. Continuous tremor was recorded during this time, and the level of eruptive and seismic activity seemed to be fairly stable.

Figure 15. Photograph showing a telephoto view of an explosive eruption from Lake Voui at Aoba, 4 December 2005. View is approximately towards the east from the crater rim. Courtesy of Philipson Bani, IRD.

Figure 16. Photograph showing an explosive eruption from Lake Voui at Aoba on 4 December 2005. View is approximately toward the E from the crater rim. A large steam plume can be seen rising above the darker zone containing pyroclastic material. Three small islands formed prior to this eruption can also be distinguished, with the active vent area closest to the western-most island. Courtesy of Philipson Bani, IRD.

Cloud cover and rain prevented a visit to the lake on 6 and 7 December. Earthquake recorders from the GNS were installed at the Provincial Centre at Saratamata, the Longana Peoples Centre (Lovonda village), and at Tahamamavi ("place of warm sea") (figure 17). On 7 December, a final recorder from the IRD was installed near Nduidui on the SW side of the island. Over 6-7 December continuous moderate-level volcanic tremor was recorded, with no significant change in its level; there was no other significant seismic activity.

Figure 17. Hazard map of Aoba, showing risk areas, infrastructure, and settlements. See Cronin and others (2004) for additional details. Map produced by the United Nations, OCHA-ROAP Information Management Unit, 2 December 2005.

On 8 December, the group noted that small-scale eruptions continued in Lake Voui, building a volcanic cone in the lake and producing a tall (2.4-3.0 km) steam-and-gas plume. Afternoon observations showed the cone growing taller and surrounding three sides of the active vents. However, the cone was not complete on its E side, allowing lake water to react with the rising magma. Though the resulting explosions became further apart and slightly larger, the total energy involved appeared similar to 4-5 December. There continued to be two active vents, one producing the small explosions, and the second the steam and gas emissions. Seismic recorders continued to record volcanic tremor, but very few local earthquakes. No volcanic ash was present in the plume. The eruption had no immediate effect beyond Lake Voui. The Volcanic Alert Level remained at Level 2. The level of seismic activity seemed to be stable. No other significant seismic activity was recorded.

While departing by air on the evening of 8 December, the group clearly saw the active vents (figure 18). The cone had grown to the W, joining and partly burying one of the old islands. All eruptions occurred from inside the cone. The largest individual eruptions threw material 150-200 m above the lake. There was also a gas-and-steam vent present within the cone, W of the other vent. The level of the lake appeared unchanged.

Figure 18. Aerial photograph showing a steam plume rising from Lake Voui at Aoba, 8 December 2005. Courtesy of Forces Armées en Nouvelle Calédonie (FANC).

On 10 December, the small-scale volcanic eruption continued from active vents within the summit crater lake (Lake Voui). Molten material entered the crater lake and reacted with the water to produce small explosive eruptions and a plume of steam and gas. The eruption built a cone around the active vents, enclosing them on three sides, forming an island about 200 m across and 50-60 m high. There were two vents, one erupting water, rocks and mud, and the other producing a tall column of steam and gas. The eruption had little effect outside the crater lake (minor ashfall occurred only in the first three days of the eruption). Five days of seismic recordings show a moderate level of seismic activity (mostly volcanic tremor).No change was noted in the level of Lake Voui, and there was also no evidence of ground uplift or fractures near the lake.

Sulfur dioxide measurements. SO₂ data collected using a DOAS spectrometer on the Islander planes of Unity Air Lines (3 December) and Air Vanuatu (5 December). On 3 December the flux was 32.6-33.6 kg/s (~ 2,900 metric tons/day). By 5 December the flux had decreased about 25%, to 24.7-26.4 kg/s (~ 2,300 metric tons/day). SO₂ was clearly detected by the OMI (ozone monitoring instrument) sensor on the NASA Aura satellite (figure 19). One measurement of the volcanic gas output on 10 December showed a moderate level of sulfur dioxide (SO₂) gas (about 2,000 t/d) from the active vents.

Figure 19. SO2 data from the Ozone Monitoring Instrument (OMI) on the Aura satellite, 5 December 2005. Courtesy of NASA, the KNMI MOI Science Team, and Simon Carn, University of Maryland-Baltimore County.

Lake temperatures. A monitoring station for continuous measurements of water temperature at Lake Voui was installed in October 1998. The station used a satellite ARGOS transmission system and recorded the last heating episode of 2001 (figure 20), but failed after three years due to the harsh acid environment. ASTER thermal infrared images can also be used for monitoring lake surface temperatures, and Aoba has a freshwater lake (Manaro Lakua) which can be used to remove the seasonal/diurnal variations in atmospheric temperatures. Unfortunately, the top of the volcano is frequently covered by clouds and few ASTER images are exploitable. The most recent ASTER image clearly showing both lakes was collected on 9 July 2005. Difference in temperatures between lake Voui and Lakua was 4.0°C, slightly above background values during 2002-2003. Maximum background temperatures measured with ASTER during the September 2002-October 2005 were at 26.3°C. The last ASTER images before the eruption, on 5 October 2005, showed no unusual temperatures at Lake Voui.

Figure 20. Temperature data from Lake Voui at Aoba, October 1998-December 2005, from in-situ measurements, ASTER satellite imagery, and MODIS satellite data. Delta T represents the thermal anomaly calculated as the temperature differences between the two lakes. The figure includes the first post-eruption ASTER data (24 December 2005). ARGOS data from Michel Halbwachs (Université de Savoie) and Michel Lardy (IRD). Courtesy of Alain Bernard.

MODIS satellites have a more frequent coverage than ASTER but their spatial resolution is only 1 km. The surface area of Lake Voui (2.1 km²) is too small for an accurate measurement of lake temperature, but MODIS can detect rough temperature changes or an increased thermal anomaly. The MODIS pixel footprint is about 1 km along track and 2 km across track, so the measured temperatures are a mixed signal corresponding to the lake and some signal from the adjacent tropical forest (much colder than the lake at night at this elevation). MODIS SST imagery showed a strong thermal anomaly on 21 November 2005 (figure 20). Approximate lake temperatures, likely a minimum, were 30.4°C on 20 November and 29.5°C (Terra)/ 31.4°C (Aqua) on 21 November. On 25 November the temperature jumped to about 42°C.

Reference. Cronin, S.J., Gaylord, D.R., Charley, D., Alloway, B.V., Wallez, S., and Esau, J.W., 2004, Participatory methods of incorporating scientific with traditional knowledge for volcanic hazard management on Ambae Island, Vanuatu: Bulletin of Volcanology, v. 66, p. 652-668. (URL: http://www.proventionconsortium.org/files/tools_CRA/CS/Vanuatu.pdf)

Geologic Background. The island of Ambae, also known as Aoba, is a massive 2,500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Information Contacts: Esline Garaebiti, Douglas Charley, Morris Harrison, and Sandrine Wallez, Department of Geology, Mines, and Water Resources (DGMWR), Port-Vila, Vanuatu; Michel Lardy, Philipson Bani, Jean-Lambert Join, and Claude Robin, Institut de recherche pour le développement (IRD), BP A5, 98 848 Nouméa CEDEX, New Caledonia (URL: http://www.suds-en-ligne.ird.fr/fr/volcan/vanu_eng/aoba1.htm); Brad Scott and Steve Sherburn, Institute of Geological & Nuclear Sciences (GNS), Wairakei Research Center, Taupo, New Zealand; Shane Cronin, Institute of Natural Resources, Massey University, Palmerston, New Zealand; Alain Bernard, IAVCEI Commission on Volcanic Lakes, Université Libre de Bruxelles, Brussels, Belgium (URL: http://www.ulb.ac.be/sciences/cvl/aoba/Ambae1.html); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/); United Nations, Office for the Coordination of Humanitarian Affairs (OCHA), Regional Office for Asia and the Pacific.

This report mentions a series of noteworthy events during mid-January through late December 2005. On 11 January 2005 an explosive eruption was inferred from seismic data; it was thought to have produced an ash column to 8-10 km altitude (BGVN 30:03). Seismic activity returned to background levels following this eruption and the Concern Color Code was lowered from Orange to Yellow on 14 January and remained at Yellow until the end of November 2005.

On 6-7 May 2005, weak gas-and-steam plumes were observed, but clouds frequently obscured the volcano. Thermal anomalies at the dome were detected in satellite imagery on 6-8, 10, and 12 May.

On 30 November, KVERT reported that seismicity at Bezymianny had increased during the previous two weeks. Seismic signals indicated that hot avalanches from the lava dome had begun on 29 November and the intensity of the thermal anomaly at the dome had increased. Strong fumarolic activity was captured on video of 29 November.

An explosive eruption began on 30 November at 2400 according to seismic data. Ash plumes were subsequently seen in satellite imagery extending SW at an altitude of about 6 km. The Concern Color Code was raised to Orange.

After the eruption on 30 November, seismic activity at the volcano decreased to background levels. On 2 December the Concern Color Code was reduced from Orange to Yellow. On 9 December, KVERT reported that based on past experience with Bezymianny, a viscous lava flow was probably active at the summit lava dome and there were no indications that an explosive eruption was imminent.

A gas-steam plume was visible on 9-11 December and fumarolic activity at the lava dome continued through December. Thermal anomalies were registered at the dome on 9, 17, 21, 24-25, and 27-29 December.

Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Information Contacts: Olga Girina, Kamchatka Volcanic Eruptions Response Team (KVERT), a cooperative program of the Institute of Volcanic Geology and Geochemistry, Far East Division, Russian Academy of Sciences, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia, the Kamchatka Experimental and Methodical Seismological Department (KEMSD), GS RAS (Russia), and the Alaska Volcano Observatory (USA); Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), the Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and the Alaska Division of Geological and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

Increased seismicity and ground deformation from late June 2004 through 9 August preceded the third eruption of 2004, which started on 13 August (BGVN 29:12). During that eruption ~ 750 m of National Road 2 was overrun by lava. Eruptive activity ceased on the morning of 7 September 2004 (BGVN 29:12). Eruptions occurred again during February and October-December 2005.

Eruption during February 2005. A new period of heightened seismicity began on 17 February 2005 around 1300, consisting of about 100 seismic events within 90 minutes. After that, the number of events decreased, but recommenced at 1638 with several hundred events. Strong deformation was recorded at the same time by tiltmeters and the extensometer network. Eruption tremor began around 2035, becoming strong at 2050. The eruption site seemed to be situated close to Nez Coupé de Sainte Rose (on the N side of the volcano), and lava flows were observed in the Grand Brûlé area.

After a period of relative quiet on 19 February, eruption tremor increased to high levels again on 21 February. Two eruption sites were active: the principal vent at 1,600-m elevation above the Plaine des Osmondes, and a vent at about 1,200-m elevation in the Plaine des Osmondes. The principal vent released a volcanic plume and several pahoehoe lava flows, but no lava fountains were visible. The second vent also released a very fluid pahoehoe lava flow. The flows covered a large area within the Plaine des Osmondes, and smaller lava flows traveled to about 600-m elevation in the Grand Brûlé.

On 24 February, shallow seismicity began beneath Dolomieu crater. It increased over time and by 26 February, several hundreds of seismic events up to M 3 occurred. According to the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), these events may have indicated formation of a new pit crater within Dolomieu crater. On 24 February, visible signs of activity stopped within the Plaine des Osmondes, while eruption tremor slowly increased.

On the evening of 25 February, a lava flow from Plaine des Osmondes traveled down the Grandes Pentes, cutting the National Road on its way to the sea. The lava flow covered a distance of ~ 5 km in about 2 hours. At the same time, seismicity increased on the NE rift zone above Bois Blanc, and a new vent opened within the Trou de Sable on the N border of the caldera at 450-m elevation. This vents lava flow stopped about 100 m from the National Road.

Eruptions during October-December 2005. Another eruption started on 4 October 2005 at 1426 after 4 months of almost continuous inflation and increased seismicity. The eruption was immediately preceded by a 56-minute-long sequence of seismicity and strong summit inflation. A low-intensity eruption at Dolomieu crater produced pahoehoe lava flows that covered a small area of the western part of the crater.

Immediately after the end of the 4 October eruption at Dolomieu crater, the permanent GPS network and extensometer network continued to show strong surface deformation, which was a precursor for a new eruptive event. On 29 November 2005 at 0559 a seismic crisis began, and at 0625 tremor indicated the beginning of an eruption. A vent opened in the western part of Dolomieu crater and another vent opened on the N flank. Very little projected volcanic material was visible. A large, fast-moving lava flow traveled down the N flank in the direction of Piton Kapor. Inclement weather prohibited further observations. The Toulouse VAAC reported that ash from the eruption was not visible on satellite imagery.

Following the 29 November eruption, further summit inflation was recorded by the permanent GPS network. On 26 December at 1444 a seismic crisis started beneath Dolomieu crater. Within the next 2 hours seismic activity shifted to the NE, towards Nez Coupé de Sainte Rose. A first fissure opened at 1715 at the NE base of Piton de la Fournaise; at 2200 eruptive fissures opened in the caldera wall about 500 m E of Nez Coupé de Sainte Rose and lava flowed into the Plaine des Osmondes. By 28 December, eruptive activity was almost constant. An aa-type lava flow crossed the Grandes Brûlé and reached a point 3 km upslope from the national road.

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, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 RN3 le 27 ème km, F-97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr/ovpf/observatoire-volcanologique-piton-de-fournaise); Toulouse Volcanic Ash Advisory Center (VAAC), Météo-France, 42 Avenue G. Coriolis, 31057 Toulouse Cedex, France (URL: http://www.meteo.fr/vaac/).

Notice of Fukutoku-Okanoba unrest in 2005 first came to Bulletin editors from Olivier Hyvernaud, information that was amplified by the Japanese Meteorological Agency (JMA) Volcanic Activity Reports of July and October 2005. The JMA reports contain information from the Japanese Marine Defense Forces as well as the Marine Security and Safety Agency and the Tokyo Institute of Technology. In addition, a Japan Coast Guard website (see URL below) contains a more extensive (and yet untranslated) table on recent events at Fukutoku-Okanoba, which includes photos and videos of the July eruption. That table clearly illustrates activity both earlier and later than the 2-3 July eruption, and several other details not discussed here, including the observation of numerous large and steaming blocks floating on the ocean surface at mid-day on 3 July. Bulletin editors hope to decipher this table and include more details in a later report.

The last five Bulletin reports discussing or mentioning Fukutoku-Okanoba appeared in BGVN 22:01, 24:11, 24:12, 25:05, and 28:06 (1997-2003). Note that the last four cases were considered ambiguous and grouped along with reports under the heading "Acoustic signals in 1999-2000 from unknown source, Volcano Islands, Japan" and only the first case was listed under the volcano name). A 3-d view of the volcano and its setting appears as figure 5.

Figure 5. Fukutoku-Okanoba and vicinity shown in a 3-dimensional diagram, with shading (or color) representing various elevation ranges (see key above); vertical exaggeration is considerable but was not stated. The inset contains an index map showing the Volcano islands along the Bonin trench. The diagram represents data from 1999 and views the region from the SE. Fukutoku-Okanoba is a submarine vent ~ 5 km N of the island (Minami-Iwo-jima). Copyrighted image courtesy of the Japan Coast Guard.

JMA reported that at about 1745 on 2 July 2005, a white plume was witnessed at Fukutoku-Okanoba. During an investigation at 1900 that same day, a white plume reached ~ 1 km above the sea surface. A photo taken from considerable distance was included in the JMA report, showing the plume, but the image's limited contrast has led to its exclusion here. In addition to the plume, other evidence for an eruption included debris on the sea surface. When seen on 2 July, the debris covered an area approximately 100 m wide and 300 m long.

JMA noted that 3 July aerial observations suggested that compared to the previous day, eruptive vigor and the height of the white plume had decreased. The key observation then was a zone of discolored seawater (figure 6).

Figure 6. An aerial view of Fukutoku-Okanoba taken on 3 July 2005 as seen from the NE. Debris and discoloration extend from the arrow. Courtesy of the Maritime Security and Safety Agency.

JMA's report of 4 and 5 July aerial investigations noted the lack of a white vapor plume over the sea. In other words, the 2-3 July eruption had calmed, but fresh debris and seawater discoloration were still present. After that, aerial investigations on 15, 17, 20, and 21 July, again disclosed seawater discoloration, but not the presence of floating debris.

The Maritime Security and Safety Agency conducted an underwater topographical survey on 20-22 July 2005, the result of which was the discovery of two craters caused by the recent eruption. The results suggested that the topography just S of those craters was newly raised.

According to a 3 October aerial observer, the ocean surface near Fukutoku-Okanoba, then displayed a pale, blue-white discoloration, interpreted as indicative of volcanism. The area of discoloration extended ~ 300 m in length to the E and was ~ 50 m wide (N-S) at its widest point. However, in the surrounding area they saw no floating debris or plumes containing ash or steam. On 27 October, an aerial observation could not confirm the seawater discoloration.

Satellite data. M. Urai (2005) reported that three days after the 2 July 2005 eruption of Fukutoku-Okanoba, satellite remote sensing using ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) observed the discolored seawater and floating materials within 40 km of the submarine volcano. Some of this abstract follows.

"At the most dense discolored seawater area, reflectance of ASTER band 1 is 3% higher [than] the surrounding seawater. The floating materials are similar in ASTER VNIR [Very Near-Infrared Radiometer] reflectance spectra to clouds, however, the floating materials can be separated from clouds using their shape and stereo image features. The extensions of discolored seawater area and floating material detected by ASTER were 6.34 km² and 1.14 km², respectively. It is possible to estimate the scale of [a] submarine eruption using the quantitative data derived from satellite remote sensing."

Distant hydrophones. Robert Dziak and Haru Matsumoto monitor N Pacific volcano seismicity with the National Oceanic and Atmospheric Agency/Pacific Marine Environmental Laboratory (NOAA/PMEL). They initially learned of the eruption via the internet. Regarding the 2 July eruption, Dziak wrote to the Bulletin staff on 22 November 2005. Some of his messages follow.

". . . the [N] Pacific hydrophone array we use recorded seismicity during the Fukutoku-Okanoba eruption near Iwo Jima. I was aware of the eruption at the time [mid 2005] thanks to Haru [Matsumoto; he designed and built the instruments used there to record the T-wave events] forwarding a news image of the discolored water. Despite being only able to roughly locate the seismicity since it is way west of our array, I am pretty sure Fukutoku-Okanoba was the source because the arrival azimuths and timing of the signals were a match. The last earthquake activity we recorded from this area occurred on 25 September [2005] . . .. A few years ago I was contacting you [Smithsonian Institution] about our recording of harmonic tremor from a source in the Volcano Islands. The conclusion I published in JGR [Dziak and Fox, 2002] was that either Fukutoku-Okanoba or Funka-asane ([N] of Iwo Jima) was the probable source because of a history of submarine volcanic activity at both volcanoes. We have still been recording this tremor intermittently over the last few years and another pulse of it occurred during the Fukutoku-Okanoba eruption on July 2, 2005. The last occurrence was on August 22.

According to an Email from Dziak on 23 November 2005, "...I think the tremor is coming from [Fukutoku-Okanoba or Funka-asane]. I was only able to get synchronous data from the French Polynesian seismic net (Hyvernaud). They confirmed the signals but it did not help much with location because they were so far away. My thought is the source of earthquakes and tremor from these submarine volcanoes is at an ocean depth within the sound channel. This allows for very efficient seismic-acoustic coupling and acoustic propagation throughout the Pacific ocean basin."

References. Dziak, R.P., and Fox, C.G., 2002, Evidence of harmonic tremor from a submarine volcano detected across the Pacific Ocean basin: Journal of Geophysical Research, v. 107(B5), p. 2085; doi 10.1029/2001JB0001772085.

Kato, Y., 1988, Gray pumices drifted from Fukutoku-oka-no-ba to the Ryukyu Islands: Bulletin of the Volcanological Society of Japan, Second Series, v. 33, p. 21-30.

Ossaka, J., Mitsuno, C., Shibata, T., Matsuda, T., Hirabayashi, J., Tsuchide, M., Sakurai, M., and Sato, H., 1986, The 1986 submarine eruption of Fukutoku-okanoba, Part 2. Volcanic ejectas: Bull. Vol. Soc. Japan, v. 31, p. 134-135.

Urai, M., 2005, Monitoring submarine volcano with satellite remote sensing: Eos Trans, AGU, v. 86(52), Fall Meet. Suppl., Abstract 611A-1176.

Geologic Background. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the pyramidal island of Minami-Ioto. Water discoloration is frequently observed from the volcano, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.

Information Contacts: Olivier Hyvernaud, Laboratoire de Géophysique, BP 640 Pamatai, Tahiti, French Polynesia; Japanese Meteorological Agency (URL: http://www.jma.go.jp/JMA_HP/jma/indexe.html); Robert Dziak and Haru Matsumoto, NOAA PMEL, Hatfield Marine Science Center, 2115 SE Oregon State University Drive, Newport, OR 97365, USA; Yukio Hayakawa (URL: http://www.hayakawayukio.jp/English.html/); Daily Yomiuri News (URL: http://www.yomiuri.co.jp/); Reuters; Associated Press; Tokyo Institute of Technology, 2-12-1 O-Okayama, Meguro-ku, Tokyo 152-8551, Japan; Japan Coast Guard, Hydrographic and Oceanographic Department (URL: http://www1.kaiho.mlit.go.jp/GIJUTSUKOKUSAI/kaiikiDB/kaiyo24-2.htm); Japan Maritime Security and Safety Agency, Oceanic Information Section (URL: http://www1.kaiho.mlit.go.jp/).

The last eruption at Karthala occurred in April 2005 (BGVN 30:04); this report discusses the second large eruption of the year, on 24-25 November 2005. Karthala is a volcano with a lava lake and well-known for episodic outbursts. This report begins with imagery and maps, discusses satellite images of the 24-25 November ash plume, and then summarizes press and United Nations reports.

Satellite imagery. Elements of Karthala geography appear in figure 11. This and many other figures were produced by a United Nations consortium of public and private organizations, UNOSAT, which provides satellite imagery and geographic information to the humanitarian community. The islands capital, Moroni, lies on the coast directly W of the summit complex.

Figure 11. A shaded relief map portrays the island of Grand Comore, with Karthala's summit complex (the cratered, highest-elevation area) on the S. Courtesy of UNOSAT and their partner organizations.

Perspective on the eruption's impact can be seen on figure 12, containing images from both pre- and post-eruption time frames (13 July 2004 and 5 December 2005). Conspicuous new deposits at distance from the summit area were imaged on 5 December. Some new deposits resided in what appear as channels to the N of the craters, suggesting that freshly deposited tephra may have entered and followed the drainage systems: see channels on figure 12, heading NE. These tentative inferences by Bulletin editors were not discussed in available ground-based reports, so confirmation is lacking. No reports were yet available discussing the morphology or potential hazards of these new deposits.

Figure 12. Karthala portrayed in two images (both with 10-m resolution; bands 321 + IR (RGBI)). Both images are at nearly, though not exactly, the same scales. The image at left is from before the eruption; taken by SPOT4 on 13 July 2004. The image at right is from after the eruption; taken by SPOT5 on 5 December 2005. Both images are partly masked by weather clouds. Large, clearly visible areas of new deposits appear in and around the summit crater area. Courtesy of UNOSAT and partner organizations.

Ash clouds. Charles Holliday (US Air Force Weather Agency, AFWA) assessed the 25 November 2005 Karthala eruption plume using a NASA Terra MODIS image at 1010 local time (0710 UTC; figure 13). He measured the overall E-W extent of eruptive clouds as ~ 150 nautical miles (~ 280 km). The W margin of the brown clouds lie up to 30-50 km W and NW of the volcano. The light-colored clouds were blown SE, and they became far less optically dense towards the E where they extended over the vicinity of reef-fringed Mayotte Island. The image shows light-colored (nearly white) clouds above and centered SE of the visible brown clouds. Holliday interpreted this to represent a brown zone composed of dominantly ash with a higher lighter-colored zone of ash and ice particles. The tallest clouds reached FL 380 ('Flight Level 380,' a height of 38,000 feet or ~ 11.6 km altitude).

Figure 13. An image of the Karthala 25 November 2005 ash plume from NASA Terra MODIS. The image was centered over the Comoros islands, with the islands Mayotte, Anjouan, and Moheli labeled, and Grand Comore under ash clouds but the location of Karthala is indicated. For scale, the distance from Karthala to the S end of Mayotte island is ~240 km. The image shows AFWA interpretations of the ash cloud. Courtesy of Charles Holliday (AFWA).

Fred Prata (CSIRO) processed both MODIS and AIRS images for the 25 November eruption (figures 14 and 15). Both instruments are part of NASA's Earth Observing System: MODIS stands for Moderate Resolution Imaging Spectro-Radiometer (flying onboard the Terra (EOS AM-1) satellite); AIRS stands for Atmospheric Infrared Sounder (which uses a grating spectrometer on the Aqua satellite).

Figure 14. MODIS satellite images of the Karthala eruption plume on 25 November 2005 at 0710 UTC. The top image maps the computed atmospheric mass loading associated with the ash cloud; inset portrays the ash grain-size estimates in the same cloud. The bottom image maps the SO2 burden in the cloud, contoured in Dobson Units; the total mass of SO2 on this image was 2.85 kilotons. For distance scales, 1° of latitude (distance N-S) equates to ~111 km. Courtesy of Fred Prata, CSIRO.

Figure 15. An AIRS image of the Karthala eruption's SO2 content for 25 November at about 2223 UTC. The measured mass total for SO2 was ~2.0 kilotons. Courtesy of Fred Prata, CSIRO.

Prata used the MODIS image to estimate the 25 November eruption's mass loading. This resulted in an estimate of fine ash amounting to 83 kilotons (kt) in the grain-size ranges indicated. Analysis of SO₂ from the MODIS data for 0710 on the 25th yielded 2.85 kt.

Prata also downloaded and processed the AIRS data available from 25 November but found only one good image (figure 12). Prata commented that the reason for the shortage of AIRS data stems from a compromise in instrument design, whereby when acquiring images at low latitudes, polar-orbiting satellites frequently lack sufficient overlap in their scanners to obtain full coverage. The one available satisfactory AIRS image, ~ 13 hours later than the MODIS image, showed a different plume configuration that included two separate zones of SO₂ concentration rather than one. The mass of the SO₂ measured by the AIRS instrument for the 25th was 2.0 kilotons. This value about the same as Prata obtained in a MODIS retrieval for the same 25 November eruption. In addition, the zones of elevated concentrations on both images stood in roughly the same place—except for the blob near 11°S detected by AIRS and not by MODIS.

Regarding his analysis of the 25 November Karthala eruption, Prata goes on to say that "assuming my fine ash loading of 83 kt is right and (big assumption now) this represents ~ 1% of the total erupted mass, then the volume of erupted ash would be ~ 0.006 km³. This suggests a VEI ~ 2. If the 1% estimate is robust (I've seen this quoted in Bill Rose's work) then the fine ash estimates from remote sensing may be quite helpful [in] assessing the 'size' of an eruption. Coupled with cloud-height estimates we may be moving towards some nice tools for volcanologists."

Prata further commented that he had hoped to image an algal bloom in the ocean where the Karthala ash had fallen. Recent work on ocean chemistry and biology (Boyd and others, 2000) point to iron enrichment as a means of ocean fertilization. As briefly discussed on the NASA Earth Observatory website, Anatahan plumes had recently been suggested to have triggered such blooms; however, with available remote-sensing data Prata was unable to confirm that the Karthala eruption triggered such a plume.

UN and related reports. The following appeared in a 28 November 2005 report of the United Nations Office for the Coordination of Humanitarian Affairs.

"The Karthala Volcano forms most of the landmass of Grande Comore (also called Ngazidja), the main island of the Union of the Comoros. The volcano is one of the largest volcanoes in activity in the world. Over the last two hundred years, it has erupted every eleven years on average. In April 2005, a volcanic eruption projected ashes and volcanic debris on the eastern part of the island, affecting as many as 40,000 people.

"[Karthala] had an eruption for the second time this year in the night of . . . 24 November, spilling ashes and smoke over the southeastern and southwestern parts of Grande Comore Island, and the Comoros capital, Moroni.

"During Friday 25, the projections of ashes and smoke receded. However, seismographic data collected by the Karthala Volcano Observatory has shown that the seismic activity is continuing. According to the observatory, a lava lake is in formation in the crater, as of yet confined within the crater. According to the local authorities, approximately 2,000 people fled from their villages in the region of Bambao in the central part of the island, and sought refuge in less exposed areas, such as Mitsamiouli, Mboudé, and Oichili."

"Concerns exist regarding the availability of potable water in the areas exposed to smoke and ashes. Preliminary results from the assessment indicate that as many as 118,000 persons living in 75 villages may be affected by the contamination of water tanks. A further assessment of the water tanks is underway to ascertain the exact scope of the needs. Concerns also exist regarding the impact of the pollution by volcanic debris on agriculture and livestock."

A 28 November news report by Agence France-Presse (AFP) also noted some of the above details, but added some new points. They said that the eruption had the effect of " . . .killing at least one infant, infiltrating homes, shops and offices and contaminating water in cisterns during the height of the dry season. 'We have two problems with water: one, we are in the dry season and two, the reserves in many private cisterns are now polluted,' minister of state for defense Abdu Madi Mari told AFP."

"He said cistern water supplies for about 120,000 residents mainly from rural villages near the volcano had been contaminated by the ash, which has also raised fears of respiratory ailments."

"Authorities on Grand Comore, the largest of the three semi-autonomous islands in the Comoros, had appealed for international assistance to help in distributing potable water to those in need, Mari said."

The AFP news report stated the eruption sent only "about 500 villagers fleeing from their homes in the shadow of the mountain." and said that despite continued tremor reported by the observatory, "almost all have now returned."

In a 9 December report the World Food Program estimated that the 24 November Karthala eruption affected 245,000 people. They briefly mentioned the issue of potentially contaminated drinking water but noted that, although minor eruptions continued, abundant rain in the weeks that followed helped reduce the potential water and air contamination problems. As noted above, no reports were found discussing problems from ash-choked drainages (lahars).

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

Information Contacts: UNOSAT, United Nations Institute for Training and Research (UNITAR), Palais des Nations, CH - 1211 Geneva 10, Switzerland (URL: https://unitar.org/unosat/); Charles Holliday, U.S. Air Force Weather Agency (AFWA)/XOGM, Offutt Air Force Base, NE 68113, USA; Fred Prata, CSIRO Marine and Atmospheric Research, 107-121 Station Street, PMB 1, Aspendale, Victoria 3195, Australia; NASA Earth Observatory, NASA Goddard Space Flight Center, Code 900, Greenbelt, MD 20771, USA (URL: http://earthobservatory.nasa.gov/); MODIS Rapid Response Team, Goddard Space Flight Center, Code 923, Greenbelt, MD 20771, USA; Agence France-Presse (AFP); United Nations, Office for the Coordination of Humanitarian Affairs (OCHA) and the World Food Program (WFP) (URL: https://reliefweb.int/, http://www.wfp.org/).

From December 2004 to June 2005 frequent explosions and plumes were detected at Karymsky (BGVN 30:06). In June 2005, the alert level was briefly lowered from Orange to Yellow because of a decrease in seismic and volcanic activity, but it was raised to Orange again on 23 June because of ash and gas plumes which rose to 3 km above the crater.

Karymsky remained at Concern Color Code Orange and seismicity remained above background levels throughout August-December 2005.

Throughout July 2005 ash-and-gas plumes frequently may have risen to 1-3 km above the crater. During 8-15 July, 450-600 shallow earthquakes occurred daily. On 11 July, an ash-and-gas plume extended about 11 km SE. During 15-22 July, 350-700 shallow earthquakes occurred daily. On 22 July, a weak thermal anomaly and a short E-drifting ash-and-gas plume were visible on satellite imagery.

Seismic activity during August indicated frequent possible ash-and-gas plumes up to 4 km altitude. A MODIS satellite thermal anomaly was registered on 2 August. On 22 August, three ash plumes reached heights around 3-4 km altitude and extended ~ 130 km E. An ash plume was visible at an altitude of ~ 5.8 km on 27 August.

Small ash and gas plumes continued to be emitted in September. A thermal anomaly was visible at the volcano on satellite imagery on 15 September.

Visual observations on 17 October revealed that the lava dome in the volcano's crater had been partially destroyed. Based on seismic data, three ash-and-gas plumes may have risen to 2.5-4 km altitude during 14-16 October. Five ash-and-gas plumes may have reached heights of 2.5-3.5 km altitude on several days during the last week of October 2005. A thermal anomaly at the volcano was visible on satellite imagery.

The lava dome inside the volcano's crater continued to grow during November 2005. Based on seismic data, three gas plumes containing some ash possibly rose 3-3.8 km altitude during 29-31 October and 1 November. Ash plumes were visible on satellite imagery extending NE on 31 October and 2 November. During 4-11 November five gas-and-steam plumes with some ash may have reached heights of 3-3.5 km altitude.

No seismic data were available after 10 November. A thermal anomaly was visible at the volcano on 15 and 17 November. According to seismic data, many weak shallow earthquakes and possible gas-steam plumes with some amount of ash up to 2.5 km altitude were registered on 20-23 November. A thermal anomaly was noted over the volcano during the last week of November and the first week of December. According to satellite data from Russia and USA, ash clouds moving to the SE from the volcano were noted on 6-7 December.

After 3 December the availability of seismic data became very erratic. A thermal anomaly was registered on 9-11 December and 14-15 December. According to satellite data, ash plumes and clouds were noted on 9 and on 10 December, moving SW and SE, and SE and E, respectively.

During the third week of December, many weak shallow earthquakes and possibly ten ash plumes up to 3.6 km altitude were registered. According to Kamchatka Volcanic Eruptions Response Team (KVERT) volcanologists who work near Karymsky, ash explosions rose up to 2.5-3 km altitude on 17-21 December 2005, and extended WSW and ENE. A thermal anomaly was registered over the volcano on 15-21 December. Seismicity indicated that ash explosions from the summit crater continued.

Many weak shallow earthquakes were registered during the last week of December. Ash plumes rose up to 2.5-4 km altitude on 24 December and 26-27 December and extended mainly E and SE from the volcano, and occasionally SW. According to KVERT volcanologists, a new cone approximately 60-80 m in diameter was formed at the summit of Karymsky volcano. A small lava dome 20-30 m in diameter was seen in the cone's crater. According to satellite data from the USA and Russia, a thermal anomaly was registered over the volcano all week.

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Olga Girina, Kamchatka Volcanic Eruptions Response Team (KVERT), a cooperative program of the Institute of Volcanic Geology and Geochemistry, Far East Division, Russian Academy of Sciences, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia, the Kamchatka Experimental and Methodical Seismological Department (KEMSD), GS RAS (Russia), and the Alaska Volcano Observatory (USA); Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), the Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and the Alaska Division of Geological and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; Tokyo Volcanic Ash Advisory Center (VAAC) (URL: https://ds.data.jma.go.jp/svd/vaac/data/).

This report concerns Garbuna volcano's first historically witnessed eruption. That occurred in mid-October 2005 after a felt earthquake. This report contains a section by members of the Rabaul Volcano Observatory (RVO) and another by Rodger Wilson, a NOAA meteorologist , who made an unofficial visit in November.

Setting. Garbuna is part of the 23 x 15 km Krummel-Garbuna-Welcker complex (a volcanic field with these major topographic highs located in S-to-N progression; figure 1). The field resides at the S end of New Britain island's Willaumez (Talasea) peninsula, a narrow projection jutting well N from the island's W-central region. The peninsula and some local reefs and islands are known for volcanoes and hydrothermal features (including, from N to S, Dakataua caldera and its large lake, Bola stratovolcano, Garua Harbour volcanic field, and the Garbuna complex). In addition to young volcanics found at the complex's three summit (ridge) centers and their associated domes and craters, there have been prior flank and eccentric eruptions, most notably Numundo Maar. The complex's products are mostly high-SiO₂ andesites to high-SiO₂ dacites with more mafic eruptives from Krummel and Numundo Maar. (McKee and others, 2005). Only 5-6 km to the E and W of the volcanic field are some inhabited and intensively cultivated strips along the coast.

Figure 1. Photograph of Garbuna taken on 19 October 2005 from the SSE. View is northward along the Krummel-Garbuna-Welcker ridge, across the general area of Garbuna with Welcker on skyline; Krummel is behind the camera. The two fuming vents can be seen on the periphery of an old lava dome. The bare geothermal nature of the area is apparent. The incised cone to the left is what locals refer to as Mount Garbuna. Photo by Steve Saunders provided courtesy of RVO.

Garbuna and Welcker volcanoes were thought to have had a latest significant/datable eruption at ~ 1,800 BP. Garbuna in particular was very geothermally active, with the central area containing 4 km² of fumaroles, solfataras, hot and bubbling mud and water springs, and patches of hot ground. Conspicuous from the barren, sulfurous and geothermally altered, clay-rich areas was a timber-covered but undated lava dome (or alternately, a short, thick lava flow to the S, a feature sometimes described as a coulée). This dome shows little geothermal alteration, appears very youthful, and is not obviously mantled by the regional tephras from Witori or Dakataua, all features suggesting a comparatively young age. The low cone hosting the dome stands ~ 500-600 m in diameter.

Events surrounding the eruption. The RVO team reported this section and noted that the complex was not instrumentally monitored. A single, locally felt earthquake occurred around midday on 16 October 2005. Jet-like noises were noticed about 2342 that night, rumbling noises started soon after, and at about midnight ash emissions began. The eruption continued and by morning pale to dark gray ash clouds were being driven forcefully into the sky. By 1000 a 3-4-km-high eruption column was visible; the main plume drifted NW with a thin veil of falling material below it. The eruption began to wane between midnight and the morning of 18 October, reducing to slow pale-gray emissions, with only white vapor by the end of the day. A second vent opened quietly during the night of the 18-19 October, with two white vapor plumes visible at dawn on the 19th.

Aerial inspections on 19, 20, and 26 October showed the two vents situated in the central low area of Garbuna, historically an area of high geothermal activity. Both vents are located on or close to the edge of the youthful lava dome mentioned above. The center of the dome is at 05° 26' 48" S, 150° 01' 36" E, with the active vents aligned SW-NE at across a NW sector of the old cone. Both active vents are 60-75 m in diameter and emitted low to moderate amounts of white fume, the southerly plume being more voluminous. On the first two visits fume billowed out gently.

The SW vent seems to have been the source of the initial October emissions. Before the 19th a small incomplete cone had formed around it. Within a kilometer of this vent several ten's of centimeters of ash/mud had been deposited, which thinned very rapidly away from the vent. Old records did not indicate the existence of the SW vent or other conspicuous feature prior to the onset of this eruption.

The second, or NE, vent became active on the night of 18-19 October. Photographs from 1996 showed that prior to the eruption this vent was a small, wooded, funnel-shaped pit, with some evidence of instability on its western side and visible un-vegetated scars.

Although ashfall was reported to the NW, images of the eruption at first light on the 17th showed the fallout to resemble rain rather than dry ash. Vegetation damaged by the fallout had brown blotches rather than uniform discoloration, leading to the conclusion that the initial column was made up primarily of acidic water and mud.

It appears that the NE vent is predominantly a collapse feature, surrounded by a small apron of brownish-gray mud, with a jagged edge and bright red/yellow walls. Following a locally felt earthquake, summit observations on the 20th showed that the NE vent had increased ~ 10-20 m by concentric collapse since the previous day and was 50-60 m deeper. At this time it contained a boiling mud lake ~ 60-70 m below the rim.

Observations on the 26th showed the ash cone around the SW vent had all but disappeared as it had increased in size by collapse. The resulting pit was irregular in shape. Quite vigorous steam emissions occurred and some ash was visibly mixed with the fume and dropping out as fine droplets of dilute mud. Impact craters from projectiles were evident around the vent, especially to the SW. Near the vent these small projectiles were visible and block-like. Up to 500-600 m to the SW small impact craters could still be seen but the projectiles themselves were not apparent.

Close study of the old dome, on whose periphery the vents have opened, suggests that it has undergone little or no movement during the onset of this eruption. Foliage-stripped trees are mainly up-right, and no fresh cracks or heaved boulders are evident. Thermal imagery also showed no hot cracks in the dome, suggesting that the eruption was not preceded by intense surface deformation, and that the vents are now enlarging by concentric collapse.

A large area of grass N of the vents gave the impression of having been flattened in a uniform direction. Trees and shrubs, although stripped of leaves, did not show this flattening. This may suggest that floods of water were responsible for the flattened grass, rather than blast effects. To the S, flooding is also suggested by the apparently recent incising of the valley floor (headwaters of the Garu-Haella sulfur stream). The edge of the jungle also shows undercutting with trees having fallen toward the vents.

Since the start of the eruption changes in the amount of discharge, along with unusual discoloration and dying fish were seen in the streams draining from Garbuna. On 26 October, aerial observers followed one of the Garu thermal streams from the Plantation-Garu village road on its ascent to the summit. At higher elevations the stream's water level dropped markedly, until within a few kilometers of the summit, it dried out completely. The stream was not blocked or dammed, and the falling levels of streams and drying of springs appeared to be related to the drying of the summit, or fracturing, allowing water to percolate into the mountain rather than flow off the geothermally produced clay-rich area. At first light on the morning of 29 October, the watercourse commonly known as the Walindi river was milky white with a blue tinge. It was odorless, of normal temperature, and tasted simply of clayey water with no bitterness. This is the first recorded case of one of the eastern drainage systems exhibiting this behavior, although it is common in the W and SW regions.

A few locally felt earthquakes and sulfur odors were reported from areas not traditionally affected by the complex's sulfatara emissions. On several occasions explosions or booming noises from the Garbuna area were heard at Garu Plantation.

Two seismic stations were installed on 18 October. A 3-component digital recorder was located at Garu Plantation ~ 5.5 km SW of the active vents. An analog recorder was installed at Sisi near Walindi, ~ 5.6 km E of the vents. Notable seismicity was recorded on 20, 21, and 22 October. On the 20th a ML ~ 2.5 local volcano-tectonic earthquake was felt, which was followed by a dozen smaller VT earthquakes between 1300 and 1500. Starting about 0500 on 21 October many very small (ML < 0.5) VT earthquakes began to occur. These events continued throughout 21 October and ceased about 1600 on 22 October. Random VT earthquakes numbering 1-4 per day were recorded on 23, 25, and 28 October. Other volcano-related earthquakes recorded included some small low-frequency earthquakes on 22 October by the Sisi station. Continuous tremor was recorded immediately when a new telemetered seismometer was installed about 0.9 km NE of the active vents. At the end of the month the tremors were continuing.

The West New Britain Provincial Disaster Committee has ensured a smooth civic response to this unforeseen event with public education and preparations for a possible evacuation being well advanced.

Observations during mid-November 2005. Rodger Wilson submitted the following report of his visit to Garbuna with John Seach.

"We climbed Garbuna the first time on 14 November. We smelled H₂S(?) from at least three locations at lower elevations along the trek. Wind at the time was to the NE, so I don't believe we were sensing the summit gas plume. Also, there was an area that I jokingly referred to as, 'The Valley of Death,' where we all (four) felt nauseated (on both climbs at the same location, both coming and going), but did not detect any odor of gas. On the second climb, we found an immature parrot on the ground at the (SE?) edge of this area (we removed him from that area, and he seemed fine afterward). Again, we were unable to get a GPS fix there, but it occurs along a (NW to SE-running?) depression just prior to a steeper climb to the summit.

"Just before reaching the clearing at the summit, along a more N-S-running depression, we encountered an area where the trees appeared to have been 'sprayed' horizontally as evidenced by ash being 'plastered' to their N (crater) sides. Bark on many of the larger trees appeared to be at least lightly abraded, but not removed. Numerous smaller trees of approximately 6 cm or less in diameter had been neatly 'clipped' or sharply bent over at just less than 2 m height. There was no evidence of high temperature in connection with the physical damage. Our visit was restricted to along the S edge of the summit, bounded by the hydrothermal area on the W and the two old phreatic craters to the E. This area of damaged trees was, as far as we could see, the only significant damage to the surrounding forest (by a base surge or a cold density current?) in contrast to the more complete devastation suffered by the fewer trees and lower vegetation at the summit. Interestingly, the trees still standing at the summit, appeared to be stripped solely by vertically falling, not horizontally moving, debris.

"We exited the forest at the summit at about 1100, along a N-S bare ridge (old crater rim?), that is clearly visible in aerial photos of the area. Copious fume emanated soundlessly from the two new craters. White fume exited the western crater, with yellow-tinged fume rising from the eastern one. There was a fairly strong smell of H₂S, but not the eye-stinging or choking sensation I've felt with SO₂ at Etna and Stromboli. As we rested there, we noted the water in our bottles was in constant motion and once we made our way to the thermal area, we clearly felt frequent (several per minute) small shocks while we took temperatures at several spots there. The highest temperatures were all at 100°C. During the first couple of hours at the summit, we had two brief bands of rain showers pass overhead, but by about 1330 the rain became sustained and heavy. Run-off in most of the surrounding gullies had increased to several inches deep. We . . . were picking our way back toward the forest when, just as we left the southern edge of the thermal area, we heard a loud roar and witnessed a lahar issue from the gully draining the crater . . ..

"Changes we noted during the second visit 3 days later were [as follows]: a low rumble or rushing noise associated with the summit vents which was heard through most of the journey to the summit, although [they observed] a complete lack of detectable seismicity while at the summit. The interval between "huffs" of fume was shorter, on the order of maybe 4-5 minutes rather than the 8-10 minutes observed during the first visit. Fume leaving the western vent remained white, while ash was clearly visible as it fell over the E flank of the volcano from the eastern plume. That plume also had a more yellow cast as it issued from its source, compared with a few days before.

"We heard low booming rumbles from near Walindi at around 0530 on 17 November and loud roaring the next morning at about 0700 from the same location. The latter was preceded (by as much as 10 minutes) by dogs at our location being agitated and barking, simultaneously with others in the distance.

Reference. McKee, C.O., Patia, H., Kuduon, J., and Torrence, R., 2005, Volcanic Hazard Assessment of the Krummel-Garbuna-Welcker Volcanic Complex, Southern Willaumez Peninsula, WNB, Papua New Guinea: Geological Survey of Papua New Guinea—Report 2005/4.

Geologic Background. The basaltic-to-dacitic Krummel-Garbuna-Welcker Volcanic Complex consists of three volcanic peaks located along a 7-km N-S line above a shield-like foundation at the southern end of the Willaumez Peninsula. The central and lower peaks of the centrally located Garbuna contain a large vegetation-free area that is probably the most extensive thermal field in Papua New Guinea. A prominent lava dome and blocky lava flow in the center of thermal area have resisted destruction by thermal activity, and may be of Holocene age. Krummel volcano at the south end of the group contains a summit crater, breached to the NW. The highest peak of the group is Welcker volcano, which has fed blocky lava flows that extend to the eastern coast of the peninsula. The last major eruption from both it and Garbuna volcanoes took place about 1800 years ago. The first historical eruption took place at Garbuna in October 2005.

Information Contacts: Steve Saunders, Ima Itikarai, and Herman Patia, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; Rodger Wilson, Meteorological Technician, US National Oceanic and Atmospheric Administration (NOAA) and National Weather Service (NWS), WSO, P.O. Box 1685, Valdez, AK 99686, USA.

Rabaul Volcano Observatory (RVO) reported that during 22-28 August 2005, modest eruptive activity was observed at Langila's Crater 2. Occasional forceful emissions of ash produced plumes that rose ~ 1 km above the crater on 22 and 25 August, but reached only several hundred meters after that. The ash plumes drifted N and NW, resulting in fine ashfall in downwind areas, including the town of Kilenge. Seismicity was at low levels, consisting mainly of low-frequency earthquakes. The Darwin Volcanic Ash Advisory Centre (VAAC) reported that a plume was visible on satellite imagery on 30 August extending NNW.

During 12-18 September, Crater 2 continued to forcefully erupt ash at irregular intervals. The resultant ash plumes drifted NW and W. Incandescence and weak projections of volcanic material were visible on the evening of 13 September. There was no activity at Crater 3. Seismicity was at low levels at the volcano, consisting mainly of low-frequency earthquakes.

During 20-23 October, low-level plumes from Langila were occasionally visible on satellite imagery. On 29 October, a plume from Langila was visible on satellite imagery at an altitude of ~ 2.7 km.

During 11-12 November, low-level ash plumes emitted from Langila were visible. The heights of the plumes were not reported.

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: 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); Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; International Federation of Red Cross And Red Crescent Societies (IFRC) (URL: https://reliefweb.int/).

MODVOLC radiant heat-flux data and ASTER high-resolution satellite imagery revealed discharging lava flows that traveled N to the sea where they constructed a lava delta. The large effusive episode described in BGVN 30:09 had ceased, followed by a smaller episode in November. MODVOLC responses were most intense during 14 September to 4 October 2005. Figure 11a shows the radiant heat flux for the volcano since the start of the eruption in October 2001, providing rough idea eruptive intensity. Figure 11b indicates the distance of each alert pixel from the vent, giving insights into the timing of significant effusive episodes.

Figure 11. Plots of MODVOLC data at Belinda volcano on Montagu Island. Courtesy of Matt Patrick, HIGP.

As figure 12b suggests, the September-October 2005 episode was likely the largest effusive episode of the eruption in that it involved the only sustained occurrence of alert pixels (i.e. active lava) more than 2 km from the vent. Following 4 October 2005, a single alert pixel appeared more than 3 km from the vent on 17 November 2005, but subsequent alert pixels were all near-vent. It is not yet clear if this 17 November anomaly represents the start of a substantial additional episode of lava effusion.

An ASTER image collected on 3 November 2005, shows the result from the September-October 2005 effusive episode (visible wavelength image shown in figure 12a). The shortwave infrared anomaly in this image (not shown) is minor compared to the 23 September 2005 image (BGVN 30:09), suggesting that any effusion had dropped to low levels by early November. The 3 November image indicates that a significant lava delta had formed on the N shore of the island during the September-October effusive phase (see arrow in figure 12a). The delta comprises two major lobes, and is approximately 400-500 m in width and length, equating to approximately 0.2 km². An enlarged view of the visible image is provided in figure 12b, where the approximate path of the September-October 2005 lava flow is shown by the dotted arrow. The current coastline is shown by the dotted line, with the lava delta (denoted by solid arrow) clearly jutting out. Note the faint steam wisps extending E from delta's eastern margin. The thermal infrared image (band 14, at 11-micron wavelength) of the island is shown in figure 12c, and clearly indicates the anomalously warm delta.

Figure 12. An ASTER image and enlargement on Montagu Island showing Belinda as it appeared in visible wavelength data on 3 November 2005 (a and b). An ASTER thermal-infrared image was obtained of the island on the same date (c). Courtesy of Matt Patrick, HIGP.

A Royal Air Force overflight on 11 October 2005, captured an oblique photograph of the delta (not shown). The lava flow appears to have steeply cut through thick ice approaching the shore, producing a broad and relatively flat delta that is vigorously steaming from the delta margins in the photograph.

Geologic Background. The largest of the South Sandwich Islands, Montagu consists of a massive shield volcano cut by a 6-km-wide ice-filled summit caldera. The summit of the 10 x 12 km wide island rises about 3000 m from the sea floor between Bristol and Saunders Islands. Around 90% of the island is ice-covered; glaciers extending to the sea typically form vertical ice cliffs. The name Mount Belinda has been applied both to the high point at the southern end of the summit caldera and to the young central cone. Mount Oceanite, an isolated 900-m-high peak with a 270-m-wide summit crater, lies at the SE tip of the island and was the source of lava flows exposed at Mathias Point and Allen Point. There was no record of Holocene or historical eruptive activity until MODIS satellite data, beginning in late 2001, revealed thermal anomalies consistent with lava lake activity that has been persistent since then. Apparent plumes and single anomalous pixels were observed intermittently on AVHRR images during the period March 1995 to February 1998, possibly indicating earlier unconfirmed and more sporadic volcanic activity.

Information Contacts: Matt Patrick, University of Hawaii, Hawaii Institute of Geophysics and Planetology (HIGP) Thermal Alerts Team, 2525 Correa Road, Honolulu, HI 96822 (URL: http://modis.higp.hawaii.edu/); John Smelie, British Antarctic Survey, Natural Environment Research Council, High Cross, Madingly Road, Cambridge CB3 0ET, United Kingdom (URL: https://www.bas.ac.uk/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).