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Bulletin of the Global Volcanism Network

All reports of volcanic activity published by the Smithsonian since 1968 are available through a monthly table of contents or by searching for a specific volcano. Until 1975, reports were issued for individual volcanoes as information became available; these have been organized by month for convenience. Later publications were done in a monthly newsletter format. Links go to the profile page for each volcano with the Bulletin tab open.

Information is preliminary at time of publication and subject to change.

Recently Published Bulletin Reports

Kavachi (Solomon Islands) Discolored water plumes observed in satellite imagery during early September 2020

Krakatau (Indonesia) Eruption ends in mid-April 2020, but intermittent thermal anomalies continue

Raung (Indonesia) Eruptions confirmed during 2012- 2013; lava fills inner crater in November 2014-August 2015

Klyuchevskoy (Russia) Strombolian activity, gas-and-steam and ash plumes, and a lava flow during June-early July 2020

Fuego (Guatemala) Ongoing explosions, ash plumes, lava flows, and lahars during April-July 2020

Nishinoshima (Japan) Major June-July eruption of lava, ash, and sulfur dioxide; activity declines in August 2020

Turrialba (Costa Rica) New eruptive period on 18 June 2020 consisted of ash eruptions

Etna (Italy) Effusive activity in early April; frequent Strombolian explosions and ash emissions during April-July 2020

Ol Doinyo Lengai (Tanzania) Multiple lava flows within the summit crater; September 2019-August 2020

Yasur (Vanuatu) Ash and gas explosions continue through August 2020

Villarrica (Chile) Continued summit incandescence February-August 2020 with larger explosions in July and August

Stromboli (Italy) Strombolian activity continues at both summit craters during May-August 2020



Kavachi (Solomon Islands) — October 2020 Citation iconCite this Report

Kavachi

Solomon Islands

8.991°S, 157.979°E; summit elev. -20 m

All times are local (unless otherwise noted)


Discolored water plumes observed in satellite imagery during early September 2020

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 (see Caption) 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 (Indonesia) — October 2020 Citation iconCite this Report

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 155 m

All times are local (unless otherwise noted)


Eruption ends in mid-April 2020, but intermittent thermal anomalies continue

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 (see Caption) 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 (see Caption) 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/).


Raung (Indonesia) — September 2020 Citation iconCite this Report

Raung

Indonesia

8.119°S, 114.056°E; summit elev. 3260 m

All times are local (unless otherwise noted)


Eruptions confirmed during 2012- 2013; lava fills inner crater in November 2014-August 2015

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Russia) — September 2020 Citation iconCite this Report

Klyuchevskoy

Russia

56.056°N, 160.642°E; summit elev. 4754 m

All times are local (unless otherwise noted)


Strombolian activity, gas-and-steam and ash plumes, and a lava flow during June-early July 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Guatemala) — September 2020 Citation iconCite this Report

Fuego

Guatemala

14.473°N, 90.88°W; summit elev. 3763 m

All times are local (unless otherwise noted)


Ongoing explosions, ash plumes, lava flows, and lahars during April-July 2020

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.

Month Number of explosions per hour Ash plume heights (km) Ash plume distance (km) and direction Drainages affected by block avalanches Villages reporting ashfall
Apr 2020 5-16 4.3-4.9 km 8-20 km E, NE, SE, W, NW, SW, S, N Taniluyá, Ceniza, Las Lajas, Trinidad, Seca, Honda, and Santa Teresa Morelia, Panimaché I and II, Sangre de Cristo, Santa Sofía, Finca Palo Verde, San Pedro Yepocapa, Las Cruces Quisache, La Rochela, Ceylan, and Osuna
May 2020 4-16 4.3-4.9 km 10-17 km S, SW, W, N, NE, E, SE Trinidad, Taniluyá, Ceniza, Las Lajas, Santa Teresa, Seca, and Honda Panimaché I, La Rochela, Ceilán, Morelia, San Andrés Osuna, Finca Palo Verde, Santa Sofía, Seilán, San Pedro Yepocapa, Alotenango, Ciudad Vieja, San Miguel Dueñas, and Antigua Guatemala
Jun 2020 3-15 4.2-4.9 km 10-25.9 km E, SE, S, N, NE, W, SW, NW Seca, Taniluyá, Ceniza, Trinidad, Las Lajas, Santa Teresa and Honda San Pedro Yepocapa, Sangre de Cristo, Panimaché I and II, Morelia, Finca Palo Verde, El Porvenir, Yucales, Santa Emilia, Santa Sofía
Jul 2020 1-15 4-4.9 km 10-24 km W, NW, SW, S, NE Trinidad, Taniluyá, Ceniza, Honda, Las Lajas, Seca, and Santa Teresa Panimaché I and II, Morelia, Santa Sofía, Finca Palo Verde, Sangre de Cristo, San Pedro Yepocapa, and El Porvenir
Figure (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).


Nishinoshima (Japan) — September 2020 Citation iconCite this Report

Nishinoshima

Japan

27.247°N, 140.874°E; summit elev. 25 m

All times are local (unless otherwise noted)


Major June-July eruption of lava, ash, and sulfur dioxide; activity declines in August 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Costa Rica) — September 2020 Citation iconCite this Report

Turrialba

Costa Rica

10.025°N, 83.767°W; summit elev. 3340 m

All times are local (unless otherwise noted)


New eruptive period on 18 June 2020 consisted of ash eruptions

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 (see Caption) 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 (see Caption) 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 (Italy) — September 2020 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3320 m

All times are local (unless otherwise noted)


Effusive activity in early April; frequent Strombolian explosions and ash emissions during April-July 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Tanzania) — September 2020 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

2.764°S, 35.914°E; summit elev. 2962 m

All times are local (unless otherwise noted)


Multiple lava flows within the summit crater; September 2019-August 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).


Yasur (Vanuatu) — September 2020 Citation iconCite this Report

Yasur

Vanuatu

19.532°S, 169.447°E; summit elev. 361 m

All times are local (unless otherwise noted)


Ash and gas explosions continue through August 2020

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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/).


Villarrica (Chile) — September 2020 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Continued summit incandescence February-August 2020 with larger explosions in July and August

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) Figure 95. Incandescent ejecta rose from the summit of Villarrica in the early morning of 1 March 2020. Courtesy of POVI.
Figure (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Italy) — September 2020 Citation iconCite this Report

Stromboli

Italy

38.789°N, 15.213°E; summit elev. 924 m

All times are local (unless otherwise noted)


Strombolian activity continues at both summit craters during May-August 2020

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.

Month Activity
May 2020 Strombolian activity and degassing continued with some spattering. Explosion rates varied from 1-17 per hour. Ejected material rose 80-150 m above the N crater and 150-250 m above the CS crater. The average SO2 emissions measured 300 tons/day.
Jun 2020 Strombolian activity and degassing continued with spattering. Explosion rates varied from 2-14 per hour. Ejected material rose 80-200 m above the N crater and 150 m above the CS crater. Spattering was primarily focused in the CS crater. The average SO2 emissions measured 300 tons/day.
Jul 2020 Strombolian activity and degassing continued with some spattering. Explosion rates varied from 1-12 per hour. Ejected material rose 80-1,000 m above the N crater. Spattering was primarily focused in the CS crater. The average SO2 emissions measured 300 tons/day.
Aug 2020 Strombolian activity continued with discontinuous spattering. Explosion rates varied from 1-23 per hour. Ejected material rose at least 200 m above the N crater and at least 250 m above the CS crater.

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).

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Scientific Event Alert Network Bulletin - Volume 11, Number 04 (April 1986)

Managing Editor: Lindsay McClelland

Additional Reports (Unknown)

United States: Possible eruption cloud in the Aleutian Islands seen on satellite imagery

Aira (Japan)

Explosions increase in April

Akutan (United States)

Small steam and ash plume

Arenal (Costa Rica)

Continued lava production; avalanches from flow fronts

Atmospheric Effects (1980-1989) (Unknown)

Ruiz aerosols persist, but no Augustine material evident

Augustine (United States)

New lava dome in summit crater; details on pyroclastic flows and seismicity

Bagana (Papua New Guinea)

Strong plumes; glow; debris slides from lava flow

Bezymianny (Russia)

1984-85 eruptions and related pyroclastic deposits

Bulusan (Philippines)

Seismic swarm in summit caldera

Cleveland (United States)

Steam plume with some ash

Dieng Volcanic Complex (Indonesia)

Earthquakes and tremor but no change in thermal activity

Fournaise, Piton de la (France)

Collapse in summit zone

Gorely (Russia)

Steam and ash emissions

Kelimutu (Indonesia)

Gas emission from crater lake; felt earthquake

Kilauea (United States)

Episode 44 included lava production from new vent

Langila (Papua New Guinea)

Ash and incandescent tephra ejected

Lokon-Empung (Indonesia)

More phreatic explosions

Makushin (United States)

Increased steaming from six summit area vents

Manam (Papua New Guinea)

Minor vapor and ash emission

Pavlof (United States)

Strong tremor accompanied large 18 April plume

Rabaul (Papua New Guinea)

Strong increase in seismicity

Rincon de la Vieja (Costa Rica)

Tephra and trees down from fall 1985 eruption

Sangeang Api (Indonesia)

Continued small explosions; glow

Semeru (Indonesia)

Normal small Vulcanian explosions continue

Shishaldin (United States)

Increased steam and ash emission

St. Helens (United States)

Steam and ash emissions, then new lobe added to the summit lava dome; first activity since May-June 1985

Tacana (Mexico-Guatemala)

Earthquake swarm then small phreatic eruption

Tangkuban Parahu (Indonesia)

Fumarole temperatures remain high

Wrangell (United States)

Twenty years of increased heat flow; crater ice melts; fumarole temperatures increase; larger plumes



Additional Reports (Unknown) — April 1986 Citation iconCite this Report

Additional Reports

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


United States: Possible eruption cloud in the Aleutian Islands seen on satellite imagery

Polar orbiting weather satellite imagery on 8 May at 0617 showed a distinct very bright plume along the Aleutian chain at 175-180°E. The plume appeared to be below high weather clouds (probably cirrus) and trended in a different direction, moving W to E and fanning out at its distal end. USGS personnel had received no reports of volcanic activity from airplane pilots or other observers. Several volcanoes with historical eruptions are located at the remote W end of the Aleutian Islands, but heavy weather clouds precluded a precise location for the plume's source area.

Geologic Background. Reports of floating pumice from an unknown source, hydroacoustic signals, or possible eruption plumes seen in satellite imagery.

Information Contacts: W. Gould, NOAA/NESDIS; M.E. Yount, USGS Branch of Alaskan Geology, Anchorage.


Aira (Japan) — April 1986 Citation iconCite this Report

Aira

Japan

31.593°N, 130.657°E; summit elev. 1117 m

All times are local (unless otherwise noted)


Explosions increase in April

In April, 55 explosions . . . were recorded. The highest ash cloud, on 25 April, rose 3,200 m above the crater. An air shock from an explosion on 16 April at 0537 broke windows and glass doors 3 km away at the foot of the volcano. Lapilli from an explosion on 23 April at 1207 broke car windshields near the volcano. Typical bursts of microearthquakes occurred on 5, 11, 15, 25, and 26 April.

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Information Contacts: JMA.


Akutan (United States) — April 1986 Citation iconCite this Report

Akutan

United States

54.134°N, 165.986°W; summit elev. 1303 m

All times are local (unless otherwise noted)


Small steam and ash plume

A plume that was mostly steam but contained some ash was ejected on 28 April 1986. Airplane pilots reported that the plume rose to ~2.5 km altitude. Dark ash fell on the snow-covered volcano. Island residents smelled a strong sulfur odor during the following days, but weather clouds obscured the volcano.

Geologic Background. One of the most active volcanoes of the Aleutian arc, Akutan contains 2-km-wide caldera with an active intracaldera cone. An older, largely buried caldera was formed during the late Pleistocene or early Holocene. Two volcanic centers are located on the NW flank. Lava Peak is of Pleistocene age, and a cinder cone lower on the flank produced a lava flow in 1852 that extended the shoreline of the island and forms Lava Point. The 60-365 m deep younger caldera was formed during a major explosive eruption about 1600 years ago and contains at least three lakes. The currently active large cinder cone in the NE part of the caldera has been the source of frequent explosive eruptions with occasional lava effusion that blankets the caldera floor. A lava flow in 1978 traveled through a narrow breach in the north caldera rim almost to the coast. Fumaroles occur at the base of the caldera cinder cone, and hot springs are located NE of the caldera at the head of Hot Springs Bay valley and along the shores of Hot Springs Bay.

Information Contacts: T. Miller, USGS Anchorage.


Arenal (Costa Rica) — April 1986 Citation iconCite this Report

Arenal

Costa Rica

10.463°N, 84.703°W; summit elev. 1670 m

All times are local (unless otherwise noted)


Continued lava production; avalanches from flow fronts

"Arenal remained very active, with emission of lava from Crater C at 1,450 m elevation. Lava advanced towards the N, NW, W, SW, and S, with flow fronts reaching 900 m elevation. Frequent avalanches, from continuous to every 15 minutes or so, occurred from the flow fronts. Sporadic explosions ejected pyroclastic materials, with some blocks and bombs falling at 800 m elevation. Ash was carried by winds, mainly toward the W and SE, to 4 km distance. Gas and vapor emission was continuous."

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

Information Contacts: J. Barquero and E. Fernández, OVSICORI.


Atmospheric Effects (1980-1989) (Unknown) — April 1986 Citation iconCite this Report

Atmospheric Effects (1980-1989)

Unknown

Unknown, Unknown; summit elev. m

All times are local (unless otherwise noted)


Ruiz aerosols persist, but no Augustine material evident

Lidar instruments in Germany, Virginia, and Hawaii continued to detect stratospheric aerosols that were probably from the 13 November 1985 eruption of Ruiz. No new layers from the late March explosive activity of Augustine were apparent as of late April. At Mauna Loa, Hawaii, lidar continued to detect a strong layer at about 21 km altitude, accompanied by a weaker layer at about 27 km on 1 and 22 April (figure 24). High-altitude layers had previously been observed at Mauna Loa two weeks after the Ruiz eruption and in late February. April backscattering ratios at Garmisch-Partenkirchen, West Germany were similar to those of late February. At Hampton, VA, stratospheric layers were centered at about 19-20 km altitude. Enhanced backscattering, perhaps from large forest fires in the eastern United States, continued down into the troposphere.

Figure with caption Figure 24. Lidar data from various locations, showing altitudes of aerosol layers. Note that some layers have multiple peaks. Backscattering ratios are for the ruby wavelength of 0.69 µm. Integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from 16-33 km at Mauna Loa and from the tropopause to 30 km at Hampton. Altitudes of maximum backscattering ratios and coefficients are shown for each layer at Mauna Loa.

Further Reference. DeFoor, T., and Robinson, E., 1987, Stratospheric Lidar Profiles from Mauna Loa Observatory, Winter 1985-1986: GRL, v. 14, p. 618-621.

Geologic Background. The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found here.

Information Contacts: Thomas DeFoor, Mauna Loa Observatory, P.O. Box 275, Hilo, HI 96720 USA; William Fuller, NASA Langley Research Center, Hampton, VA 23665 USA; H. Jäger, Fraunhofer-Institut fur Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-8l00 Garmisch-Partenkirchen, West Germany.


Augustine (United States) — April 1986 Citation iconCite this Report

Augustine

United States

59.363°N, 153.43°W; summit elev. 1252 m

All times are local (unless otherwise noted)


New lava dome in summit crater; details on pyroclastic flows and seismicity

M.E. Yount and T. Miller report that "A USGS overflight of Augustine on 24 April established the presence of new lava dome material in the moat between the remnants of the 1976 dome and the SW rim of the summit crater. Hot blocks were spalling off the NW side of the new dome, avalanching down a gully on the W side of the 1976 dome. Small ash-rich fumaroles were active on the 1976 dome's entire N flank. During the flight, a burst of white vapor that lasted for several minutes appeared from the 1976 dome's NW base. Observers on a night flight 24 April, using US Army night vision goggles, were able to see incandescent material all around the 1976 dome. Although the summit was obscured on 25 April, observers were able to see a blocky flow in the chute on the 1976 dome's E side. On 27 April it was apparent that the lava flow originated from the summit crater, draping the E side of the 1976 dome. Small pyroclastic flows were observed that day on the 1976 dome's NW side. Samples collected on 28 April from the toe of the lava flow are silicic andesite, as are breadcrusted pumiceous material from the pyroclastic flows. By 6 May, the flow had descended to an elevation of ~600 m through the breached N side of the crater. Seismicity indicated that the dome was actively building between approximately 22 April and the late evening of 28 April, when the almost constant tremor abruptly died out." [The onset of dome growth is given by Swanson and Kienle (1988; see Further References in SEAN 11:08) as 23 April].

Juergen Kienle reports that "After the strong explosive activity that began on 27 March and ended with a major explosion on 31 March at 0952, the volcano was visited by helicopter on 19 and 28 April and 6 May. The following are preliminary results from those field investigations.

Pyroclastic flows. "A 19 April Landsat 5 image clearly shows the light-colored pyroclastic flow deposits that were emplaced 27-31 March on the N flank of the volcano, covering an area of 11 km2 (figure 7). March 31 was the only day on which pyroclastic flows entered the sea, 5 km from the vent. A strong odor of Halogen gas (Cl2, possibly F2, Br2) was detected when crossing the still-steaming areas where flows had entered the sea. The flows were strongly inflated on 19 April, almost 3 weeks after emplacement.

Figure (see Caption) Figure 7. Landsat-5 image (no. 5077920515) of Augustine on 19 April. Pyroclastic flows erupted 31 March onto the N flank are outlined in black. Points 1 and 2 mark stations where temperature measurements were taken. The distance from the summit to the shore at point 2 is 5.0 km.

"With every step we (Kienle, Miller, Power) took, we sank up to our knees into the still hot fluidized flow tops. Temperatures measured at depths of 5 cm in active fumarole pipes and fissures (which were actively elutriating fines) on the NW and NE flow lobes were 550°C (at location 1) and 339°C (at location 2) (figure 7). Driftwood on the beach was charred; one log was charcoaled, indicating that it had caught on fire. The NW flow lobe had buried a former fresh-water lake and a brackish-water swamp area. In that area we noted several small phreatic explosion craters, about 10 m in diameter.

"Levee-forming pumice blocks were typically up to 50 cm in diameter with rounded edges. There were rare banded pumices and occasional breadcrusted blocks. Individual flow units were about 3-5 m thick. The bulk chemistry of one of the breadcrusted blocks is given in table 3 (sample 4).

Table 3. X-ray fluorescence analyses of Augustine's 1986 eruptive products (normalized to 100% anhydrous) by Christopher Nye. * Total iron expressed as Fe2O3 (FeO = 0.9 x Fe2O3).

Date 28 Mar 1986 31 Mar 1986 31 Mar 1986 (?) 31 Mar 1986 (?) 28 Apr 1986
Sample Ash Ash Bomb Pumice flow Dome fragment
Location Stariski State Park (100 km NE) English Bay (90 km E) near VABM Kamishak N flank --
Collector S. Estes G. Harris J. Kienle J. Kienle T. Miller
 
SiO2 65.46 64.53 61.76 62.15 60.17
Al2O3 16.25 16.59 16.68 16.75 17.05
Fe2O3* 4.62 4.82 5.92 5.75 6.30
CaO 5.66 5.81 6.64 6.50 7.31
Na2O 3.85 3.98 3.69 3.75 3.52
MgO 2.14 2.31 3.50 3.29 3.88
K2O 1.25 1.20 1.00 1.03 0.92
TiO2 0.53 0.52 0.54 0.53 0.57
P2O5 0.14 0.15 0.15 0.14 0.14
MnO 0.09 0.09 0.13 0.12 0.13
LOI 0.36 0.19 0.16 0.13 -0.04
Total 99.75 100.34 100.40 100.05 100.69
 
FeO/MgO 1.94 1.88 1.52 1.57 1.46
CaO/Al2O3 0.35 0.35 0.40 0.39 0.43

"A crude estimate of the 31 March pyroclastic flow volume can be obtained by assuming an average thickness of the flows of 10 m (we estimate about 8 m for the lower half of the pumice plain and in excess of 20 m for the upper part of the flow fan just below "Hells Gate," near the S end of the area outlined in black in figure 7. Using 11 km2 we obtain 0.11 km3 of inflated ejecta.

Seismicity. "Since 4 April, when violent explosive activity subsided, we have not registered explosion earthquakes at seismic station OPT, 28 km N of the volcano. Individual locatable earthquakes are now rarely recorded. Figure 8 shows a count of individual pyroclastic flows (or rock avalanches) 31 March-10 May. The plot thus essentially shows periods of intense dome deformation. Figure 9 shows one of the avalanches that would have been counted, descending the N flank of the volcano to about the 750 m level. It was photographed from our N flank seismic station 2 km from the vent on 19 April at 1411. That station was damaged and a solar panel was incinerated by a hot blast associated with pyroclastic flow activity on 31 March. Parts of the installation protruding above ground (antennas, masts, and solar panel) were pockmarked with dents from flying rock. Fortunately the buried electronics box and batteries were not damaged and the station has continued to operate uninterruptedly up to 10 May. Significant avalanche activity was observed 20 April-10 May, a period of strong dome transformation. Figure 10 is a hypocentral cross section for events occurring 27 March-27 April. The plot shows that most earthquakes occurred in the upper 2 km of the volcano.

Figure (see Caption) Figure 8. Number of pyroclastic flows and rock avalanches recorded at the flank seismic station 3 km from the summit. Counted events had amplitudes larger than 5 mm on that seismometer's record.
Figure (see Caption) Figure 9. Pyroclastic flow, 19 April at 1411, photographed by Juergen Kienle from 3 km N of the summit.
Figure (see Caption) Figure 10. Cross-section showing depths of local earthquakes 27 March-April. Plot by Charlotte Rowe.

"A seismic curiosity: On 28-29 April and 3-6 May, we recorded thousands of small earthquakes with nearly identical wave forms and magnitudes. Scaling of the time interval between events for a 15-minute period showed a periodicity of 12 ± 2 seconds (77 events). Figure 11 is a digital playback for 3 individual events showing their great similarity. The events occur at the central conduit of the volcano at ~750 m elevation (near station AUH). We speculate that they are produced by meltwater contacting the central glowing conduit and flashing the water rhythmically to steam. On 6 May, Tom Miller thought that he could see puffing of the eruption column in spite of the strong winds that drove the plume down to the shore. He also noted that new snow had fallen and was melting.

Figure (see Caption) Figure 11. Three nearly identical wavetrains of rhythmic events recorded on 5 May at a seismic station less than 1 km NW of the summit.

Dome growth. "The 1976 dome was never cleared out in any individual explosion, but was slowly transformed into a new dome by magma intrusions and extrusions starting 31 March. As of 6 May its height was 460 m with a base diameter of 400 m and a volume of about 0.06 km3 (figure 12). Its surface was blocky and spiny. An active vent was located in the SSW corner of the crater, a source of numerous boil-over pyroclastic flows. Slabs of glowing rock frequently spilled off the N face of the dome as seen by Kienle on 28 April.

Figure (see Caption) Figure 12. New dome photographed from the N on 6 May by Juergen Kienle.

Chemistry. Five XRF chemical analyses of 1986 ejecta are listed in table 3. The bulk chemistry shows an interesting trend toward less silicic magma as the eruption proceeded. Ballistic bombs collected on 19 April on the S flank (near Bench Mark Kamishaki sample 3) and a breadcrust block (sample 4) collected from the NE lobe of the pyroclastic flows are believed to have been ejected on 31 March. They are very similar in chemistry, showing about 62% SiO2 content. In contrast, the new dome rock collected on 28 April by Tom Miller shows a more basic bulk chemistry with an SiO2 content of about 60%, suggesting the tapping of deeper levels in the magma chamber (less than 2 km deep, based on the seismic data). The high SiO2 content (64.5% and 65.6%) of the distal tephras from the 28 and 31 March eruptions probably reflect aeolian fractionation.

Summary. The 1986 eruption of Augustine has thus far followed a quite different course from the 1976 eruption, which began with a violent vent-clearing phase, followed by a 14-day repose, in turn followed by intrusion of a new dome. During the present eruption, a vent-clearing phase never occurred. The pre-existing dome was slowly transformed into a new dome. March 31 was the only day of substantial production of highly vesiculated magma, ejected as large blocks on all flanks of the volcano but predominantly as pyroclastic flows down the N flank. There are no sub-plinian pumice fall deposits on the island. A pathway for the vesiculating material was probably eroded out of the pre-existing conduit (the 1976 dome) on 31 March. This open conduit continues to produce occasional small-volume pyroclastic flows and was the source of the peculiar "percolator-like" seismicity described above, as meltwater interacted with new hot conduit rock. The most remarkable feature of the 1986 eruption thus far is how well lithostatic pressure has confined the eruption, which was never particularly violent in spite of the fact that the beginning phase shows clear evidence of phreato-magmatic processes due to the interaction of ground water near sea level with the rising magma. If any of the pre-existing structures (1935 dome, 1964 dome, or 1976 dome) had collapsed catastrophically, the unloading would have very likely produced much more violent activity."

Geologic Background. Augustine volcano, rising above Kamishak Bay in the southern Cook Inlet about 290 km SW of Anchorage, is the most active volcano of the eastern Aleutian arc. It consists of a complex of overlapping summit lava domes surrounded by an apron of volcaniclastic debris that descends to the sea on all sides. Few lava flows are exposed; the flanks consist mainly of debris-avalanche and pyroclastic-flow deposits formed by repeated collapse and regrowth of the summit. The latest episode of edifice collapse occurred during Augustine's largest historical eruption in 1883; subsequent dome growth has restored the volcano to a height comparable to that prior to 1883. The oldest dated volcanic rocks on Augustine are more than 40,000 years old. At least 11 large debris avalanches have reached the sea during the past 1,800-2,000 years, and five major pumiceous tephras have been erupted during this interval. Historical eruptions have typically consisted of explosive activity with emplacement of pumiceous pyroclastic-flow deposits followed by lava dome extrusion with associated block-and-ash flows.

Information Contacts: J. Kienle, C. Rowe, J. Power, and L. Gedney, Geophysical Institute, University of Alaska, Fairbanks; C. Nye and J. Davies, Alaska Division of Geological and Geophysical Surveys, Fairbanks; M.E. Yount and Tom Miller, Branch of Alaskan Geology, USGS Anchorage.


Bagana (Papua New Guinea) — April 1986 Citation iconCite this Report

Bagana

Papua New Guinea

6.137°S, 155.196°E; summit elev. 1855 m

All times are local (unless otherwise noted)


Strong plumes; glow; debris slides from lava flow

"Stronger activity continued in April. On most days, strong white to brown emissions from the summit were reported. Weak crater glow was often observed at night, and on one occasion the upper part of the N flank's active lava flow was also observed to be glowing. Occasional debris slides from the flanks of the lava flow produced impressive ash clouds. Seismicity increased from about 20 B-type events/day in early April to about 50-60 events/day at mid-month, staying at that level for the rest of April."

Geologic Background. Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

Information Contacts: P. Lowenstein, RVO.


Bezymianny (Russia) — April 1986 Citation iconCite this Report

Bezymianny

Russia

55.972°N, 160.595°E; summit elev. 2882 m

All times are local (unless otherwise noted)


1984-85 eruptions and related pyroclastic deposits

The following report, on the 1984-85 eruptions, is from G.E. Bogoyavlenskaya, I.T. Kirsanov, P.P. Firstov and O.A. Girina. Observation data obtained by A.I. Malyshev and K.S. Kirishev of the Apakhonchich seismic station region are included in the 1984 eruption report.

". . . The altitude . . . before the 1956 eruption was 3,085 m, and relative altitudes were 700 m to the N and 1,200 m to the S. A poorly developed crater containing a small inner cone was located at the top of the volcano. More than 10 extrusive domes of different ages are located on the S flank of the volcano and near its base. The base of the complex is composed of pyroclastic flow deposits from eruptions that occurred during the past 2,000 years. Young lava flows of the same age are also well-exposed on the S flank of the volcano; older lava flows are exposed on the N flank.

Eruption of 1955-56. "A new cycle of eruptive activity began with the 1955-56 catastrophic eruption and is continuing today. For this eruption, the following stages have been distinguished: 1) A preclimactic stage that consisted of intense seismic activity, Vulcanian explosive activity, and deformation of the summit area. 2) A climactic stage including a directed blast that destroyed the summit and Plinian activity that erupted a large volume of juvenile tephra and pyroclastic flows. 3) A post-climactic stage characterized by growth of an extrusive dome in the crater.

"In April 1956, after the climactic explosion, an extrusive dome began to form in the new [1.7x2.8 km] crater. By July 1956, the dome had grown to a height of 320 m, and the diameter of its base was 600-650 m. Since 1956, activity . . . has been limited to continued growth of the Novy intracrater dome, which is the largest extrusion in recent history at Bezymianny. During the dome growth the character of magma extrusion changed periodically, allowing us to distinguish three stages in the development of intracrater extrusion.

Dome growth and eruptions through 1982. "During the first decade, individual rigid blocks of the dome and occasionally the whole massif squeezed out. This was accompanied by explosive activity. Distinct variations in volume and height of extruding blocks occurred during strong eruptions. Eruptions of different power occurred, as a rule, once or twice a year. The strongest eruptions, which occurred every few years (1961, 1962, 1965), began with a powerful explosive phase, forming pyroclastic flows of 0.01 km3 volume. This was followed by a decrease in activity, but punctuated by numerous glowing avalanches.

"During the second stage, which began in 1965, the extrusion of rigid blocks was joined by plastic lava as small dikes and lava bulges. In 1967 and 1968, rigid extrusion predominated in the northern and then in the central part of the Novy dome summit. Plastic andesite lavas were extruded only along fissures and weakened zones. "The third stage began in 1976. At that time the absolute altitude of the Novy dome was 2,869 m: the height of the dome itself was 800 m and its volume was ~0.367 km3 (Seleznev and others, 1983). Eruptions occurred one or two times a year, the strongest in March 1977, February 1979, and August 1980. Long-lasting eruptions with lava extrusion were observed in 1981-82, twice in 1984, and in 1985.

"Almost every eruption was preceded by volcanic earthquakes and accompanied by volcanic tremor. Eruptions generally began with small explosions and rigid andesitic block extrusions. They were generally accompanied by destruction of the upper active part of the dome and by the formation of glowing avalanches. Eruptive clouds rose to heights of 3-10 km and plumes were traced to distances of 50-100 km. Simultaneously, pyroclastic flows 6-8 km long formed, with volumes of 0.005 to 0.01 km3. In addition to juvenile material (fragments of vesicular andesites and matrix) they generally contained many large blocks and lithic fragments of the dome. These block and ash flows were erosional and by 1980 they had eroded a 50-m-deep trench near the foot of the volcano. The paroxysmal stage of eruptions lasted from several hours to two or three days. During the final stage lava flows reached lengths of 300 to 500 m. The 1981-82 eruption lavas were extruded at small intervals within a period exceeding one year, and covered the E and NE flanks to the foot of the dome.

Eruptions in 1984. "In 1984 Bezymianny erupted twice, in February and October. Fissures that formed at the top of the dome and broke it into blocks were the precursors to the February eruption. On 5 February the first small single earthquakes were recorded, and the first small explosions began. Large earthquakes began on 10 February and were most numerous on 15 February. Earthquakes stopped on 16 February and only weak continuous volcanic tremor was recorded. On 13-15 February rigid andesite blocks began to be squeezed out at the top of the dome, and rockslide avalanches formed. On 16 February slow lava extrusion began. By August a lava carapace had covered the E and NE flanks to the foot of the dome (figure 1).

Figure (see Caption) Figure 1. Oblique airphoto of Bezymianny's summit in August 1984, showing the new lava carapace covering the E and NE flanks of the dome.

"The October 1984 eruption was large. The first local earthquakes were recorded on 24 September, simultaneously with the failure of the dome blocks and with the formation of glowing avalanches. At that same time continuous volcanic tremor began, with amplitudes that reached 5 µm during the periods of the most intense explosive activity.

"A dark gray gas-ash plume appeared above the volcano on 13 October. At a height of ~2 km it was traced 40 km ESE. Beginning from 1100 to 1,500, vertical and inclined explosions occurred every 5-10 minutes. Simultaneously, pyroclastic flows were generated, forming a large deposit near the foot of the volcano. Ash clouds rising above moving pyroclastic flows joined with material ejected from the vent to form an eruptive cloud 6-9 km high. The plume was traced 50-100 km ENE. The explosive eruption continued until 15 October. Seismicity ceased the next day, but the extrusion of rigid blocks at the dome summit continued until the end of October. Wreathing gases of white or occasionally gray color were observed continually over the dome. Glowing avalanches periodically rolled down the flanks.

"The paroxysmal eruption was characterized by a powerful explosive phase. A crater formed at the top of the dome and an erosion trench formed on the E flank, essentially dividing the dome into N and S parts. Two pyroclastic flow tongues formed at the foot of the volcano. The S part of the flow, 6 km long, had an area of 2.7 km2 and a volume of 0.013 km3. Tephra . . . covered an area of ~5,000 km2.

Eruptions in 1985. "The next strong eruption occurred in late June-July 1985 and was preceded by small seismic activity. Geologists saw a paroxysmal stage of this eruption from a distance of 8.5 km (P.P. Firstov, A.I. Malyshev, and M.A. Alidibirov). Bad weather limited visual observations, but seismic and acoustic signals (processed by P.P. Firstov from the Apakhonchich seismic station, 16 km from the volcano), in comparison with visual observations, have allowed some interpretation of eruptive dynamics.

"The active phase began, apparently, on 29 June at 1930 when observers heard a strong roar from the volcano lasting half an hour. Three small pyroclastic flows formed between 1922 and 1941. Deposits of these flows as long as 7-8 km were found the next morning. Then the explosive activity of the volcano sharply increased, and seemed to cause a failure of the E part of the dome. The material from the destroyed part of the dome and juvenile pyroclastic material formed a thick block-ash pyroclastic flow that apparently formed in the period from 0705 to 0715 on 30 June and was deposited at a distance of 10 km. Strong explosive activity continued, accompanied by lightning in the cloud. From 1229 to 1425, 10 small pyroclastic flows formed. At 1425-1430 the longest pyroclastic flow (10-12 km) formed, overlapping deposits of former flows. After that, explosive activity began to decrease. The last small pyroclastic flow formed on 1 July at 1930. Then calm lava flow extrusion began from the new dome crater and continued for several months (figure 2).

Figure (see Caption) Figure 2. Lava flow extruded from the new dome crater at Bezymianny after the June-July 1985 explosions. Lava advances through the crater breach seen (from a higher vantage point) below the dome in figure 1. Photo taken by N. Smelov.

"Thus, the main events of this eruption are as follows: 1) Moderate explosive activity resulted in destruction and failure of the E part of the complex intracrater dome. A large (0.04 km3) crater formed with an active vent in its upper part. 2) Dome material plus fresh juvenile material formed a thick block and ash pyroclastic flow deposit (with a volume of ~0.01 km3), covering the E foot of the volcano to 8-10 km from the crater. 3) Failure of part of the dome resulted in rapid decompression of the remainder of the dome. Rapid expansion of volcanic gases produced a blast directed to the E that covered an area of 10 km2 and destroyed two volcanologist houses 3.5 km from the crater. Erosion traces on the ruins of the buildings suggest that the ground surge velocity was very high. The temperature, as evidenced by the melting of polyethylene objects, was greater than l50°C. Blast deposits - a layer of stratified sand - had a volume of ~0.001 km3. 4) Continuing explosive activity formed of a series of hot juvenile pyroclastic flows that covered a 3.5 km2 area with a layer 1-5 m thick. The total volume of juvenile pyroclastic material apparently did not exceed 0.01 km3. 5) When the explosive phase of the eruption stopped, calm outpouring of a lava flow began from the newly formed crater.

"Detailed field investigations of the eruption products allowed us to distinguish the following types of pyroclastic deposits: 1) 'Block and ash flow' deposits are the most typical of the eruptions of Bezymianny. They are connected with growth of the intracrater dome, especially during the first two decades, when explosions and extrusion of rigid blocks of the dome occured. During the first stages of the 1984-85 eruption, pyroclastic flows of this type were produced as well. 2) Vesicular (or semi-vesicular) andesite pyroclastic flow deposits are represented by debris of gray vesicular andesites generally of one size (not more than 1-2 m) and by a great amount of fine matrix. The temperature of material at the moment of deposition was ~700°C, and the mean thickness was 2-3 m. The pyroclastic flow deposits represent a complex of separate units. The main pyroclastic flows are distinguished most clearly, each underlain by ground surge deposits associated with the flow, represented by a layer of well-sorted sand 10-12 cm thick. 3) Deposits from ash clouds that rose from pyroclastic flows are represented by stratified and sorted sand at different sites on and around the pyroclastic flow deposits. Gradual transitions from coarse-grained pyroclastic flow deposits to more fine-grained ash cloud deposits were noted. Everywhere these deposits were overlapped by a thin (1-2 cm) layer of pelitic airfall material. Ash cloud deposits were hot; drying and slightly charring the shrubs and grasses on surrounding hills.

"Small amounts of airfall tephra are a characteristic feature of the 1985 eruption. A thin layer of pelitic material which covered the area around the volcano had apparently fallen from the ash cloud that rose from the pyroclastic flows during their movement. The apparent lack of associated airfall beds with some sequences of pyroclastic flows and surges suggests that these might have been formed directly from the crater without the production of an eruption column, with the eruptive material just topping the crater rim (or 'boiling-over') and moving down the outer slopes.

"The chemical composition of dome rocks changed slightly during growth from 59.9% SiO2 in 1956 to 56% SiO2 in 1984-85. Variations in mineral composition were more considerable, from hornblende pyroxene andesites in 1956 to two-pyroxene, well-crystallized, basic andesites in the next ten years. An interesting peculiarity of eruptions during the last 2-3 years is the appearance of tephra more acid (61-62% SiO2) than rocks from either the dome or from pyroclastic flows. Andesites of the dated Novy dome eruptions fall between the curves of tholeiitic and calc-alkaline types, tending to occur close to the latter. In contrast to the rocks from the edifice of the volcano they have a close, slightly differentiated composition. Rocks of the 1984 eruption show a tendency to increase slightly in alkalinity; rocks of the 1985 eruption have a higher Mg content."

Reference. Seleznev, B.V., Dvigalo, V.N., and Gusev, N.A., 1983, Development of Bezymianny volcano according to data on stereophotogrammetric treatment of the aerial survey materials of 1950, 1967, and 1976-1981: Volcanology and Seismology, no. 1, p. 52-64.

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: G. Bogoyavlenskaya, I. Kirsanov, P. Firstov, and O. Girina, IV.


Bulusan (Philippines) — April 1986 Citation iconCite this Report

Bulusan

Philippines

12.769°N, 124.056°E; summit elev. 1535 m

All times are local (unless otherwise noted)


Seismic swarm in summit caldera

A seismic swarm began on 19 April at 2022 and lasted for ~ 10 hours. A total of 229 volcanic earthquakes were recorded by most of the five seismic monitoring stations. The initial phase was characterized by high-frequency volcanic earthquakes, gradually replaced by low-frequency volcanic earthquakes during the peak and latter part of the activity. Three of the events were felt, with epicenters initially located ~ 7.4 km SE (azimuth 134°) of the summit crater, within the caldera.

No other significant change was observed. Steam emission remained weak and hot spring temperatures remained normal. Local seismicity gradually declined to a low level, with only 1 high-frequency volcanic earthquake recorded on 22 April.

The last eruption of Bulusan, in June 1983, was not preceded by an increase in seismicity, but hot spring temperatures had increased several degrees. The April 1981 eruption, however, was preceded by an 8-day earthquake swarm. A seismic swarm following that eruption did not culminate in additional eruptive activity.

Geologic Background. Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.

Information Contacts: PHIVOLCS.


Cleveland (United States) — April 1986 Citation iconCite this Report

Cleveland

United States

52.825°N, 169.944°W; summit elev. 1730 m

All times are local (unless otherwise noted)


Steam plume with some ash

On 28 April, Thomas Madsen (president, Aleutian Air Ltd.) observed an eruption plume emerging from the summit of Mt. Cleveland. He first saw the grayish-white plume at about 1220, from 190 km to the E, estimating that it reached ~2,900 m altitude . . . and extended SW. The plume had definite dark streaks and swirls of ash. Passengers on a Peninsula Airways flight . . . at about 1900 reported that the eruptive activity had declined to minor steam emission.

Geologic Background. The beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Joined to the rest of Chuginadak Island by a low isthmus, Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 it produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

Information Contacts: J. Reeder, ADGGS.


Dieng Volcanic Complex (Indonesia) — April 1986 Citation iconCite this Report

Dieng Volcanic Complex

Indonesia

7.2°S, 109.879°E; summit elev. 2565 m

All times are local (unless otherwise noted)


Earthquakes and tremor but no change in thermal activity

"A widely-felt earthquake occurred near Dieng on 13 April at 0747. Tremor was recorded for up to 10 minutes 14-15 April. Additional small earthquakes were recorded in the following two weeks. No changes were noted in thermal activity."

Geologic Background. The Dieng plateau in the highlands of central Java is renowned both for the variety of its volcanic scenery and as a sacred area housing Java's oldest Hindu temples, dating back to the 9th century CE. The Dieng volcanic complex consists of two or more stratovolcanoes and more than 20 small craters and cones of Pleistocene-to-Holocene age over a 6 x 14 km area. Prahu stratovolcano was truncated by a large Pleistocene caldera, which was subsequently filled by a series of dissected to youthful cones, lava domes, and craters, many containing lakes. Lava flows cover much of the plateau, but have not occurred in historical time, when activity has been restricted to minor phreatic eruptions. Toxic gas emissions are a hazard at several craters and have caused fatalities. The abundant thermal features and high heat flow make Dieng a major geothermal prospect.

Information Contacts: Olas, Suratman, Suparto, Kaswanda, and A. Sudradjat, VSI.


Piton de la Fournaise (France) — April 1986 Citation iconCite this Report

Piton de la Fournaise

France

21.244°S, 55.708°E; summit elev. 2632 m

All times are local (unless otherwise noted)


Collapse in summit zone

After the eruptive episode of late March-early April, seismic events were due primarily to collapse in the summit zone, especially inside Dolomieu Crater and in the walls of its newly formed pit crater. Some deeper events were recorded in the SE part of the Enclos Caldera at depths of 2 km below sea level. The lava that had cascaded into the pit crater 29 March-5 April was originally extruded during the 29 December eruption. Summit tilt stations indicated a continuation of low deflation. The SE flank fissures (~8 km from Dolomieu Crater, near Piton Takamaka) continued to emit vapor for a few days. Fumaroles, some emitting SO2, covered the floor of Dolomieu Crater. Reoccupation of the radial leveling profile (3 km long, from the Enclos Caldera rim to the summit) did not show significant movement since October 1985.

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: H. DeLorme and J-F. DeLarue, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Le Mouel, J-L. Cheminée, A. Hirn, P.A. Blum, and J. Zlotnicki, IPGP.


Gorely (Russia) — April 1986

Gorely

Russia

52.559°N, 158.03°E; summit elev. 1799 m

All times are local (unless otherwise noted)


Steam and ash emissions

The eruption that began in late 1984 continued into 1986, when steam and ash emissions were observed in April.

Reference. Budnikov, V.A., 1988, The eruption of Gorelyi volcano in April 1986: Volcanology and Seismology, no. 4, p. 99-103 (in Russian); v. 10, p. 650-658 (in English).

Geologic Background. Gorely volcano consists of five small overlapping stratovolcanoes constructed along a WNW-ESE line within a large 9 x 13.5 km caldera. The caldera formed about 38,000-40,000 years ago accompanied by the eruption of about 100 km3 of tephra. The massive complex includes 11 summit and 30 flank craters, some of which contain acid or freshwater crater lakes; three major rift zones cut the complex. Another Holocene stratovolcano is located on the SW flank. Activity during the Holocene was characterized by frequent mild-to-moderate explosive eruptions along with a half dozen episodes of major lava extrusion. Early Holocene explosive activity, along with lava flows filled in much of the caldera. Quiescent periods became longer between 6000 and 2000 years ago, after which the activity was mainly explosive. About 600-650 years ago intermittent strong explosions and lava flow effusion accompanied frequent mild eruptions. Historical eruptions have consisted of moderate Vulcanian and phreatic explosions.

Information Contacts:


Kelimutu (Indonesia) — April 1986 Citation iconCite this Report

Kelimutu

Indonesia

8.77°S, 121.82°E; summit elev. 1639 m

All times are local (unless otherwise noted)


Gas emission from crater lake; felt earthquake

". . . signs of unrest from the Tiwu Nua Muri crater . . . consisted of increased gas bubbling from the crater lake beginning on 27 April and a felt earthquake on 28 April."

Geologic Background. Kelimutu is a small, but well-known, Indonesian compound volcano in central Flores Island with three summit crater lakes of varying colors. The western lake, Tiwi Ata Mbupu (Lake of Old People) is commonly blue. Tiwu Nua Muri Kooh Tai (Lake of Young Men and Maidens) and Tiwu Ata Polo (Bewitched, or Enchanted Lake), which share a common crater wall, are commonly colored green and red, respectively, although lake colors periodically vary. Active upwelling, probably fed by subaqueous fumaroles, occurs at the two eastern lakes. The scenic lakes are a popular tourist destination and have been the source of minor phreatic eruptions in historical time. The summit is elongated 2 km in a WNW-ESE direction; the older cones of Kelido (3 km N) and Kelibara (2 km S).

Information Contacts: Olas, Suratman, Suparto, Kaswanda, and A. Sudradjat, VSI.


Kilauea (United States) — April 1986 Citation iconCite this Report

Kilauea

United States

19.421°N, 155.287°W; summit elev. 1222 m

All times are local (unless otherwise noted)


Episode 44 included lava production from new vent

Episode 44 (E-44). After 22 days of repose, E-44 . . . began 11 hours of continuous lava production on 13 April at 2054. Several hours of intermittent low-level lava spillovers from Pu`u `O`o vent had preceded vigorous fountaining, which continued until 14 April at 0756. A small satellite vent that opened 1.2 km N of Pu`u `O`o was first observed on 13 April at 1310. Fountains 5-10 m high fed a pahoehoe lava flow ~1 km long. "

Lava fountains from Pu`u `O`o vent with maximum sustained heights of 280 m were directed to the E, eroding the main channel to form two spillways, one to the NE and another to the SE. Lava flows surrounded HVO's primary observation post on a cinder cone built earlier in the eruption (the "1123 vent"), [1.5] km E of Pu`u `O`o. Lava advanced a maximum of 4.1 km (to the ESE).

By 12 April . . . the summit had recovered all of the deflation recorded during the previous episode. Slow deflation began that day at 1000, and rapid subsidence started on 13 April at 2000, less than an hour before the onset of vigorous fountaining. The summit lost 13.7 µrad of inflation before subsidence ended at 1000 on 14 April, 2 hours after fountaining stopped. Only 2.6 µrad had been regained when the tiltmeter was removed for repairs (figure 43). Strong tremor began 13 April at 2104, remained high until 0754 on the 14th, and then dropped to background level for the rest of the month.

Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Information Contacts: C. Heliker, R. Koyanagi, and M. Sako, HVO.


Langila (Papua New Guinea) — April 1986 Citation iconCite this Report

Langila

Papua New Guinea

5.525°S, 148.42°E; summit elev. 1330 m

All times are local (unless otherwise noted)


Ash and incandescent tephra ejected

"A further increase in activity at Crater 2 occurred in April. Weak to strong emissions of white to grey plumes were observed on most days and fine ashfalls occurred [9] km downwind on 2 and 27 April. Weak to moderate explosions and rumblings were heard on most days. Weak red crater glow was seen on ~30% of the nights and ejections of incandescent lava fragments were occasionally observed. Vulcanian explosions were recorded at rates of 0-3/day, but other higher frequency events and periods of harmonic tremor were also recorded."

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: P. Lowenstein, RVO.


Lokon-Empung (Indonesia) — April 1986 Citation iconCite this Report

Lokon-Empung

Indonesia

1.358°N, 124.792°E; summit elev. 1580 m

All times are local (unless otherwise noted)


More phreatic explosions

"On 5, 7, 12, and 27 April, small explosions were observed from Tompaluan Crater. The maximum height of the explosion clouds was 500 m."

Geologic Background. The twin volcanoes Lokon and Empung, rising about 800 m above the plain of Tondano, are among the most active volcanoes of Sulawesi. Lokon, the higher of the two peaks (whose summits are only 2 km apart), has a flat, craterless top. The morphologically younger Empung volcano to the NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks. Historical eruptions have primarily produced small-to-moderate ash plumes that have occasionally damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred. A ridge extending WNW from Lokon includes Tatawiran and Tetempangan peak, 3 km away.

Information Contacts: Olas, Suratman, Suparto, Kaswanda, and A. Sudradjat, VSI.


Makushin (United States) — April 1986 Citation iconCite this Report

Makushin

United States

53.891°N, 166.923°W; summit elev. 1800 m

All times are local (unless otherwise noted)


Increased steaming from six summit area vents

On 20 December, pilot T. Madsen (Aleutian Air) noticed anomalous amounts of steam rising from six large and closely spaced steam vents just E of the summit. The largest plume was 500-600 m high. No ash was observed in the white plumes. Air temperature at 2,400 m was -6.7°C, warm for that altitude. Steaming remained anomalously vigorous for the next two days before returning to a more normal level. Based on John Reeder's observations . . . since 1979, the summit steam activity is continuous and normally reaches heights of 100 m or slightly less.

Geologic Background. The ice-covered Makushin volcano on northern Unalaska Island west of the town of Dutch Harbor is capped by a 2.5-km-wide caldera. Its broad, dome-like structure contrasts with the steep-sided profiles of most other Aleutian stratovolcanoes. Much of the volcano was formed during the Pleistocene, but the caldera (which formed about 8,000 years ago), Sugarloaf cone on the ENE flank, and a cluster of about a dozen explosion pits and cinder cones at Point Kadin on the WNW flank, are of Holocene age. A broad band of NE-SW-trending satellitic vents cuts across the volcano. The composite Pakushin cone, with multiple summit craters, lies 8 km to the SW. Frequent explosive eruptions have occurred during the past 4,000 years, sometimes accompanied by pyroclastic flows and surges. Geothermal areas are found in the summit caldera and on the SE and E flanks. Small-to-moderate explosive eruptions have been recorded at Makushin since 1786.

Information Contacts: J. Reeder, Alaska Division of Geological and Geophysical Surveys (ADGGS).


Manam (Papua New Guinea) — April 1986 Citation iconCite this Report

Manam

Papua New Guinea

4.08°S, 145.037°E; summit elev. 1807 m

All times are local (unless otherwise noted)


Minor vapor and ash emission

"Activity remained at a low level during April. Southern Crater released weak to moderate emissions containing small amounts of grey or brown ash. Main Crater emissions were usually weak white vapours, occasionally coloured with grey ash. The only audible activity was a low roaring heard on 29 April. No crater glows were seen. Seismicity remained about the same as in March. Daily earthquake totals were ~1,500 at the beginning and end of April, dropping to ~1,100 at mid-month. The amplitudes of these events remained at 1-2 times normal inter-eruptive levels. No significant tilt was recorded."

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

Information Contacts: P. Lowenstein, RVO.


Pavlof (United States) — April 1986 Citation iconCite this Report

Pavlof

United States

55.417°N, 161.894°W; summit elev. 2493 m

All times are local (unless otherwise noted)


Strong tremor accompanied large 18 April plume

No other reports of activity had been received as of early May [but see 11:05], and no information was available about changes that might have occurred to the active crater.

John Taber provided the following information from seismic stations operated by LDGO. "The number of volcanic events increased from a slightly above normal 20 events on 6 April, to 370 events on 11 April and 750 events on 13 April. The rate of seismicity then stayed relatively constant until the main eruption on 18 April. Continuous tremor began at around 1440 and intensified around 1610, when it was visible at stations 100 km away. The strong tremor continued until 1800 then gradually subsided, ending around 2100. The number and duration of volcanic events dropped abruptly after the tremor ended and continued to decrease until background levels were reached by 26 April."

Geologic Background. The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing Strombolian to Vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption took place in 1911, at the end of a 5-year-long eruptive episode, when a fissure opened on the N flank, ejecting large blocks and issuing lava flows.

Information Contacts: J. Taber, LDGO.


Rabaul (Papua New Guinea) — April 1986 Citation iconCite this Report

Rabaul

Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)


Strong increase in seismicity

"Seismicity increased markedly in April, when 1,769 events were recorded, almost an order of magnitude greater [than] March. It is the highest monthly total since March 1985 (2,042). This increase was not caused by seismic crises but by fairly consistently higher daily earthquake counts. The strongest event was a ML 2.7 earthquake on 13 April.

"Another unusual feature of Rabaul's April seismicity was the average duration of the events, which increased progressively during the second half of the month. A considerable number of events were located near the centre of the caldera, rather than on the caldera fault zone; many events were shallow. The earthquakes were previously concentrated at depths of 1-3 km, but in April ~30% of located events were <1 km deep.

"Measurements of ground deformation indicated a slight resurgence of inflation in the Matupit Island-Greet Harbour area. Tilt stations in that area showed maximum changes of ~10-12 µrad for the month. The largest horizontal distance changes, ~10-15 microstrain, were across the mouth of Greet Harbour. Levelling measurements showed that the SE part of Matupit Island was elevated 16 mm between 11 April and 7 May.

"At the end of April there was no indication whether the rate of seismic and ground deformation activity was likely to increase or subside. The change in the pattern of seismicity may be significant."

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

Information Contacts: P. Lowenstein, RVO.


Rincon de la Vieja (Costa Rica) — April 1986 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

10.83°N, 85.324°W; summit elev. 1916 m

All times are local (unless otherwise noted)


Tephra and trees down from fall 1985 eruption

The following reports are from the Observatorio Vulcanológico y Sismologico de Costa Rica (OVSICORI). "After several attempts to climb to the summit of Rincón de la Vieja were turned back by bad weather, we reached the active crater on 19 April with W. Melson of the Smithsonian Institution. During this visit, we were able to confirm that there had been a recent eruption, since we encountered recently erupted material and a devastated area, both SE of the crater.

"At the time of our previous ascent, in August 1985, this tephra had not been deposited. In a photograph taken 25 November 1985 by E. Valverde, it is possible to observe white tephra. In addition, the seismic station at the base of the volcano registered an increase in activity (harmonic tremor and A- and B-type events) between September and November, suggesting that the eruption occurred during that time.

"A fan-shaped area of about 0.25 km3 was affected. The ejecta reached a maximum distance of 500 m SE of the active crater. The erupted material is secondary, including ash, sand, and blocks as much as 20 cm across. On one rock, an ash deposit 6 cm thick was observed. The effect of the eruption on rain forest vegetation was marked about 500 m SE of the crater (in the E bank of the Quebrada Azufrosa) where trees had been knocked down in a radial pattern by the activity. This pattern is unusual in that the fallen trees appeared to radiate from a point near their center, not from the crater. In addition, various plant species in this area were affected by the acid in the pyroclastics and the associated water.

"On 19 April there was a strong and constant emission of gas that affected breathing because of its acidity, and made it difficult to observe the lake in the active crater."

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: J. Barquero and E. Fernández Soto, OVSICORI.


Sangeang Api (Indonesia) — April 1986 Citation iconCite this Report

Sangeang Api

Indonesia

8.2°S, 119.07°E; summit elev. 1912 m

All times are local (unless otherwise noted)


Continued small explosions; glow

". . . Activity consisted of small explosions with eruption clouds reaching <1 km above the crater. Persistent glow has been observed above the summit crater during the night, suggesting the presence of lava within the crater and in the 1985 lava channel which drains W from the crater."

Geologic Background. Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, Doro Api and Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent eruptions have been recorded since 1512, most of them during in the 20th century.

Information Contacts: Olas, Suratman, Suparto, Kaswanda, and A. Sudradjat, VSI.


Semeru (Indonesia) — April 1986 Citation iconCite this Report

Semeru

Indonesia

8.108°S, 112.922°E; summit elev. 3657 m

All times are local (unless otherwise noted)


Normal small Vulcanian explosions continue

"Semeru continued to have several small Vulcanian explosions/hour during April. The maximum height of the eruption clouds was ~1 km above the summit. This represents the normal state of activity at Semeru."

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

Information Contacts: Olas, Suratman, Suparto, Kaswanda, and A. Sudradjat, VSI.


Shishaldin (United States) — April 1986 Citation iconCite this Report

Shishaldin

United States

54.756°N, 163.97°W; summit elev. 2857 m

All times are local (unless otherwise noted)


Increased steam and ash emission

Anomalously large steam plumes with traces of ash have been noted for the past several months at Shishaldin by airline pilots and passengers. Diffuse ash layers extended from the volcano on 19 and 28 March, and steam and ash emission was seen on 6-7 May. Activity was less intense the next day, and had declined to minor steaming by 10 and 13 May. [See also 11:05].

Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Information Contacts: J. Reeder, ADGGS.


St. Helens (United States) — April 1986 Citation iconCite this Report

St. Helens

United States

46.2°N, 122.18°W; summit elev. 2549 m

All times are local (unless otherwise noted)


Steam and ash emissions, then new lobe added to the summit lava dome; first activity since May-June 1985

The gas-and-ash emission event of 16 April (SEAN 11:03) marked the beginning of increased seismicity and deformation that culminated in the extrusion of a new lobe on top of the lava dome on 8 or 9 May.

Approximately 50 gas-and-ash emissions occurred in the 3 weeks following the onset of activity, emitting plumes to as much as 6 km altitude. On 19 April at 1950, 50-kg blocks were expelled to > 1 km from the vent; some were thrown over the S rim of the crater. Two small mudflows were generated, which were confined to the crater. A new crater 50-75 m N-S, 20-30 m E-W, and 20 m deep was formed on the top of the dome, and the gas sensor, strainmeter, and tiltmeter that were on top of the dome were destroyed. Between 18 and 20 April the tiltmeter on the N side of the dome registered 1,500 µrads of inflation and a line on the crater floor N of the dome shortened 2 cm.

The last of the unusually deep (3-8 km) earthquakes that began on 29 January (SEAN 11:03) was recorded on 13 April. Seismicity remained at background levels for ~10 days following the 16 April emission, with the exception of 20-23 April, when a slight increase was recorded. On 27 April, activity began to increase again. Shallow events increased rapidly on 5 and 6 May. By 7 May, earthquake activity reached high levels (figure 30), prompting the USGS to issue a Volcano Advisory Notice, forecasting a magmatic event within the next few weeks. Seismicity and tilt increased greatly overnight, so the Advisory was revised on 8 May to predict an event within the next few days.

Figure (see Caption) Figure 30. Seismic strain release at Mt. St. Helens, 2 April-13 May. The dashed line represents surface events, the solid line earthquakes, and the dotted line total E energy release. Courtesy of C. Jonientz-Trisler.

In the morning of 8 May, discrete earthquake activity was almost continuous. Larger events with magnitudes of 2.5-3.0 were recorded every few tens of minutes. The tiltmeter on the N flank of the dome went off scale [see also SEAN 11:05], and one on the crater floor 280 m N of the dome registered as much as 85 µrads/hour of inflationary tilt until it leveled off at about 1500 (figure 31). At about that time, high-frequency earthquakes also decreased, and low-frequency events, commonly associated with lava extrusions, became dominant. Field crews in the crater that day measured 7 cm of contraction along a 66-m line on the N crater floor, suggesting that the crater floor was thrusting away from the dome. USGS geophysicists noted that the change in tilt direction and decrease in seismicity probably occurred when magma intruding the dome gained easy access to the summit area and stopped deforming the NE flank. During the mid-afternoon, the first successful gas flight since the onset of gas emission episodes in mid-April measured an SO2 emission rate of 700 t/d, an order of magnitude above rates measured in recent months.

Figure (see Caption) Figure 31. Tilt and seismicity at Mt. St. Helens, 14 April-14 May. Tilt plots are from single-axis bubble tiltmeters on the dome's N flank (Ruby, top) and on the crater floor near the N base of the dome (Sauna, middle). Both measure tilt radial to the dome; increasing values correspond to tilt outward from the dome or down to the N. Seismic amplitudes (bottom) are from the Garden. Seismic station, 700 m N of the center of the dome.

At approximately 1950, another major gas-and-ash emission occurred, ejecting juvenile tephra to the E and SE of the crater. Accompanying the event was a large rockfall from the new lobe. The rockfall moved down the N talus chute, destroying the tiltmeter on the N flank of the dome, and generated a hot surge that moved 600-800 m from the base of the dome. Meltwater generated by the slide and surge caused a water and/or mudflow 1 m deep that tripped flood gauge wires just N of the crater. Gauges downstream did not detect the flow. Scientists flying over the volcano that night saw a glow on top of the lava dome.

During midmorning on 9 May, moderate- to high-frequency events stopped, low-frequency events decreased and rockfalls began to dominate the seismic record for the next 24 hours. On 10 May, moderate- to high-frequency events resumed, but overall seismicity dropped to moderate levels and by 13 May levels were only slightly elevated.

On 14 May, field crews were able to reach the crater to confirm the extrusion of a new lobe on top of the dome. The new lobe was 250-300 m wide (E-W), 275-300 m long (N-S), and > 40 m thick in places, covering the E one quarter to one third of the September 1984 lobe. A broad area of the dome's summit was heavily fissured, with many hot radial cracks low on the S flank of the dome, indicating that intrusive growth had also taken place. Monitoring is limited to the N side of the crater because of snow cover, precluding estimates of dome volume change. The maximum deformation measured between 8 and 14 May was 1.9 m along a line from the N-crater floor to a point on the N flank of the dome. Lines were remeasured after 1 hour and showed no additional change.

The April-May activity was the first since the dome building episode in May-June 1985 (SEAN 10:05), the longest quiet period since eruptive activity began in 1980.

Geologic Background. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fujisan of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2,200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older edifice, but few lava flows extended beyond the base of the volcano. The modern edifice consists of basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers.

Information Contacts: D. Swanson, E. Endo, D. Dzurisin, and K. McGee, CVO; C. Jonientz-Trisler, University of Washington.


Tacana (Mexico-Guatemala) — April 1986 Citation iconCite this Report

Tacana

Mexico-Guatemala

15.132°N, 92.109°W; summit elev. 4064 m

All times are local (unless otherwise noted)


Earthquake swarm then small phreatic eruption

A series of shallow earthquakes, many strong enough to be felt near the volcano, began in mid-December and continued through April.

The following is from Servando de la Cruz Reyna. "A volcanic earthquake swarm started in Tacaná volcano on 7 May at 1500. Earthquakes occurred at an average rate of 1/minute, accompanied by thunder-like noises that continued for 23 hours. On 8 May near noon, a moderate phreatic explosion opened a [20-m-diameter] vent that ejected a small amount of fine ash, partially destroying vegetation in an area 200 x 100 m. The vent is located on the upper NE flank (right on the México/Guatemala border) at about 3,800 m altitude [see also 11:09]. The seismic activity continued unchanged through 9 May, then started decreasing on 10 May to a rate of about one earthquake every 5 minutes that has persisted through 11 May. A white plume some 300 m high continued to be emitted as of 11 May. H2S has been qualitatively detected in the plume. No deformation changes have been detected on a bubble tiltmeter located about 1/3 of the way up the S flank. Dry tiltmeter measurements and radon counting are underway. The intensity of the swarm motivated the issuance of an orange alert at three levels (10, 15, and 20 km radius) effective on May 8." Press sources reported that 17,000 people, mostly residents of flank villages, had left their homes.

Geologic Background. Tacaná is a 4064-m-high composite stratovolcano that straddles the México/Guatemala border at the NW end of the Central American volcanic belt. The volcano rises 1800 m above deeply dissected plutonic and metamorphic terrain. Three large calderas breached to the south, and the elongated summit region is dominated by a series of lava domes intruded along a NE-SW trend. Volcanism has migrated to the SW, and a small adventive lava dome is located in the crater of the youngest volcano, San Antonio, on the upper SW flank. Viscous lava flow complexes are found on the north and south flanks, and lobate lahar deposits fill many valleys. Radial drainages on the Guatemalan side are deflected by surrounding mountains into the Pacific coastal plain on the SW side of the volcano. Historical activity has been restricted to mild phreatic eruptions, but more powerful explosive activity, including the production of pyroclastic flows, has occurred as recently as about 1950 years ago.

Information Contacts: S. de la Cruz Reyna, M. Mena, N. Segovia, L. Gonzalez, E. Ramos, A. González, V.H. Espindola, A. Nava, J.M. Espindola, Z. Jimenez, and M.A. Armienta, UNAM, México D.F.; E. Sánchez, INSIVUMEH; AP.


Tangkuban Parahu (Indonesia) — April 1986 Citation iconCite this Report

Tangkuban Parahu

Indonesia

6.77°S, 107.6°E; summit elev. 2084 m

All times are local (unless otherwise noted)


Fumarole temperatures remain high

Fumarole temperatures at Kawah Baru crater remained elevated, reaching 161°C during April, but no additional seismic tremor was observed during the month.

Geologic Background. Gunung Tangkuban Parahu is a broad shield-like stratovolcano overlooking Indonesia's former capital city of Bandung. The volcano was constructed within the 6 x 8 km Pleistocene Sunda caldera, which formed about 190,000 years ago. The volcano's low profile is the subject of legends referring to the mountain of the "upturned boat." The Sunda caldera rim forms a prominent ridge on the western side; elsewhere the rim is largely buried by deposits of the current volcano. The dominantly small phreatic eruptions recorded since the 19th century have originated from several nested craters within an elliptical 1 x 1.5 km summit depression.

Information Contacts: Olas, Suratman, Suparto, Kaswanda, and A. Sudradjat, VSI.


Wrangell (United States) — April 1986 Citation iconCite this Report

Wrangell

United States

62.006°N, 144.017°W; summit elev. 4278 m

All times are local (unless otherwise noted)


Twenty years of increased heat flow; crater ice melts; fumarole temperatures increase; larger plumes

University of Alaska geologists have documented a major long-term increase in heat flux at Mt. Wrangell, an andesitic shield volcano with a summit caldera 6 km long, 4 km wide, and 1 km deep. Heat flux from a crater on the N side of the summit caldera rim has increased by an order of magnitude since the great earthquake of 1964 (magnitude 8.3) centered ~250 km to the SW. Annual aerial photogrammetric surveys and digital cross sections demonstrate that since 1965 about 85% of the 4.4 x 107 m3 of ice in the north crater (figure 1) has melted; all melting at that altitude is caused by volcanic heat. Fumaroles remained at the boiling point (86°C at 600 mb pressure) from 1961 through the late 1970's, but some superheating may have begun by 1980, and in 1982 superheating was evident as vapor rose 1 m above the vents before condensing. In 1985, a temperature of l92°C was measured at the edge of one fumarole. The fumarole gases were dominantly water, but the SO2 content of the dry fraction was 28% in 1982 and 35% in 1985; most of the remaining gas was CO2 (gases were collected by Roman Motyka and Matthew Sturm, 1982, Matthew Sturm and Daniel Solie, 1985; analyses by W. Evans, USGS, and Roman Motyka).

Figure (see Caption) Figure 1. E-W cross-section of Wrangell's N crater, showing changes in the ice volume of the crater between 1957 and 1983; after Benson and Motyka (1978) and Benson and others (1984).

During April 1986, nearby residents reported occasional plumes rising as much as 1 km above the summit, with several observations of large plumes the last week of the month. On 30 April, the plume was estimated to be 1 km high and 300 m wide. Geologists plan overflights to monitor the activity.

References. Benson, C., and Follett, A., 1986, Application of photogrammetry to the study of volcano-glacier interactions on Mt. Wrangell, Alaska: Photogrammetric Engineering and Remote Sensing, v. 52, no. 6, p. 813-827.

Benson, C., and Motyka, R., 1978, Glacier-volcano interactions on Mt. Wrangell, Alaska: Annual Report, Geophysical Institute, University of Alaska, 1977-78, p. 1-25.

Benson, C., Sturm, M., and others, 1984, Glacier-volcano interactions, Mt. Wrangell, Alaska: Annual Report, Geophysical Institute, University of Alaska, 1983-84, p. 102-104.

Geologic Background. With a diameter of 30 km at 2000 m elevation, Mount Wrangell is one of the world's largest continental-margin volcanoes. The massive andesitic shield volcano has produced fluid lava flows as long as 58 km and contains an ice-filled caldera 4-6 km in diameter and 1 km deep, located within an ancestral 15-km-wide caldera. Most of the edifice was constructed during eruptions between about 600,000 and 200,000 years ago. Formation of the summit caldera followed sometime between about 200,000 and 50,000 years ago. Three post-caldera craters are located at the broad summit, along the northern and western caldera rim. A steep-sided flank cinder cone, Mount Zanetti, is located 6 km NW of the summit. The westernmost cone has been the source of infrequent historical eruptions beginning in the 18th century. Increased heat flux in recent years has melted large volumes of ice in the northern crater.

Information Contacts: Carl S. Benson, Geophysical Institute, Univ of Alaska, Fairbanks; Roman Motyka, Alaska Dept of Natural Resources, Juneau.

Atmospheric Effects

The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found in this section.

Atmospheric Effects (1980-1989)  Atmospheric Effects (1995-2001)

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements  Obituaries

Misc Reports

Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false. All of these types of additional reports are listed below by subject.

Additional Reports  False Reports