Sakurajima is a highly active stratovolcano situated in the Aira caldera in southern Kyushu, Japan. Common volcanism for this recent eruptive episode since March 2017 includes frequent explosions, ash plumes, and scattered ejecta. Much of this activity has been focused in the Minamidake crater since 1955; the Showa crater on the E flank has had intermittent activity since 2006. This report updates activity during July through December 2019 with the primary source information from monthly reports by the Japan Meteorological Agency (JMA) and various satellite data.

During July to December 2019, explosive eruptions and ash plumes were reported multiple times per week by JMA. November was the most active, with 137 eruptive events, seven of which were explosive while August was the least active with no eruptive events recorded (table 22). Ash plumes rose between 800 m to 5.5 km above the crater rim during this reporting period. Large blocks of incandescent ejecta traveled as far as 1.7 km from the Minamidake crater during explosions in September through December. The Kagoshima Regional Meteorological Observatory (11 km WSW) reported monthly amounts of ashfall during each month, with a high of 143 g/m² during October. Occasionally at night throughout this reporting period, crater incandescence was observed with a highly sensitive surveillance camera. All explosive activity originated from the Minamidake crater; the adjacent Showa crater produced mild thermal anomalies and gas-and-steam plumes.

Table 22. Monthly summary of eruptive events recorded at Sakurajima's Minamidake crater in the Aira caldera, July through December 2019. The number of events that were explosive in nature are in parentheses. No events were recorded at the Showa crater during this time. Ashfall is measured at the Kagoshima Local Meteorological Observatory (KLMO), 10 km W of Showa crater. Data courtesy of JMA (July to December 2019 monthly reports).

An explosion that occurred at 1044 on 4 July 2019 produced an ash plume that rose up to 3.2 km above the Minamidake crater rim and ejected material 1.1 km from the vent. Field surveys conducted on 17 and 23 July measured SO₂ emissions that were 1,200-1,800 tons/day. Additional explosions between 19-22 July generated smaller plumes that rose to 1.5 km above the crater and ejected material 1.1 km away. On 28 July explosions at 1725 and 1754 produced ash plumes 3.5-3.8 km above the crater rim, which resulted in ashfall in areas N and E of Sakurajima (figure 86), including Kirishima City (20 km NE), Kagoshima Prefecture (30 km SE), Yusui Town (40 km N), and parts of the Kumamoto Prefecture (140 km NE).

Figure 86. Photo of the Sakurajima explosion at 1725 on 28 July 2019 resulting in an ash plume rising 3.8 km above the crater (left). An on-site field survey on 29 July observed ashfall on roads and vegetation on the N side of the island (right). Photo by Moto Higashi-gun (left), courtesy of JMA (July 2019 report).

The month of August 2019 showed the least activity and consisted of mainly small eruptive events occurring up to 800 m above the crater; summit incandescence was observed with a highly sensitive surveillance camera. SO₂ emissions were measured on 8 and 13 August with 1,000-2,000 tons/day, which was slightly greater than the previous month. An extensometer at the Arimura Observation Tunnel and an inclinometer at the Amida River recorded slight inflation on 29 August, but continuous GNSS (Global Navigation Satellite System) observations showed no significant changes.

In September 2019 there were 32 eruptive events recorded, of which 11 were explosions, more than the previous two months. Seismicity also increased during this month. An extensometer and inclinometer recorded inflation at the Minamidake crater on 9 September, which stopped after the eruptive events. On 16 September, an eruption at 0746 produced an ash plume that rose 2.8 km above the crater rim and drifted SW; a series of eruptive events followed from 0830-1110 (figure 87). Explosions on 18 and 20 September produced ash plumes that rose 3.4 km above the crater rim and ejecting material as far as 1.7 km from the summit crater on the 18th and 700 m on the 20th. Field surveys measured an increased amount of SO₂ emissions ranging from 1,100 to 2,300 tons/day during September.

Figure 87. Webcam image of an ash plume rising 2.8 km from the Minamidake crater at Sakurajima on 16 September 2019. Courtesy of Weathernews Inc.

Seismicity, SO₂ emissions, and the number of eruptions continued to increase in October 2019, 41 of which were explosive. Field surveys conducted on 1, 11, and 15 October reported that SO₂ emissions were 2,000-2,800 tons/day. An explosion at 0050 on 12 October produced an ash plume that traveled 1.7 km from the Minamidake crater. Explosions between 16 and 19 October produced an ash plume that rose up to 3 km above the crater rim (figure 88). The Japan Maritime Self-Defense Force 1st Air group observed gas-and-steam plumes rising from both the Minamidake and Showa craters on 25 October. The inflation reported from 16 September began to slow in late October.

Figure 88. Photos taken from the E side of Sakurajima showing gas-and-steam emissions with some amount of ash rising from the volcano on 16 October 2019 after an explosion around 1200 that day (top). At night, summit incandescence is observed (bottom). Courtesy of Bradley Pitcher, Vanderbilt University.

November 2019 was the most active month during this reporting period with increased seismicity, SO₂ emissions, and 137 eruptive events, 77 of which were explosive. GNSS observations indicated that inflation began to slow during this month. On 8 November, an explosion at 1724 produced an ash plume up to a maximum of 5.5 km above the crater rim and drifted E. This explosion ejected large blocks as far as 500-800 m away from the crater (figure 89). The last time plumes rose above 5 km from the vents occurred on 26 July 2016 at the Showa crater and on 7 October 2000 at the Minamidake crater. Field surveys on 8, 21, and 29 November measured increased SO₂ emissions ranging from 2,600 to 3,600 tons/day. Eruptions between 13-19 November produced ash plumes that rose up to 3.6 km above the crater and ejected large blocks up 1.7 km away. An onsite survey on 29 November used infrared thermal imaging equipment to observe incandescence and geothermal areas near the Showa crater and the SE flank of Minamidake (figure 90).

Figure 89. Photos of an ash plume rising 5.5 km above Sakurajima on 8 November 2019 and drifting E. Photo by Moto Higashi-gun (top left), courtesy of JMA (November 2019 report) and the Geoscientific Network of Chile.

Figure 90. Webcam image of nighttime incandescence and gas-and-steam emissions with some amount of ash at Sakurajima on 29 November 2019. Courtesy of JMA (November 2019 report).

Volcanism, which included seismicity, SO₂ emissions, and eruptive events, decreased during December 2019. Explosions during 4-10 December produced ash plumes that rose up to 2.6 km above the crater rim and ejected material up to 1.7 km away. Field surveys conducted on 6, 16, and 23 December measured SO₂ emissions around 1,000-3,000 tons/day. On 24 December, an explosion produced an ash plume that rose to 3.3 km above the crater rim, this high for this month.

Sentinel-2 natural color satellite imagery showed dense ash plumes in late August 2019, early November, and through December (figure 91). These plumes drifted in different directions and rose to a maximum 5.5 km above the crater rim on 8 November.

Figure 91. Natural color Sentinel-2 satellite images of Sakurajima within the Aira caldera from late August through December 2019 showed dense ash plumes rising from the Minamidake crater. Courtesy of Sentinel Hub Playground.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent thermal anomalies beginning in mid-August to early September 2019 after a nearly two-month hiatus (figure 92). Activity increased by early November and continued through December. Three Sentinel-2 thermal satellite images between late July and early October showed distinct thermal hotspots within the Minamidake crater, in addition to faint gas-and-steam emissions in July and September (figure 93).

Figure 92. Thermal anomalies at Sakurajima during January-December 2019 as recorded by the MIROVA system (Log Radiative Power) started up in mid-August to early September after a two-month break and continued through December. Courtesy of MIROVA.

Figure 93. Sentinel-2 thermal satellite images showing small thermal anomalies and gas-and-steam emissions (left and middle) at Sakurajima within the Minamidake crater between late July and early October 2019. All images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.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); Weathernews Inc. (Twitter: @wni_jp, https://twitter.com/wni_jp, URL: https://weathernews.jp/s/topics/201608/210085/, photo posted at https://twitter.com/wni_jp/status/1173382407216652289); Bradley Pitcher, Vanderbilt University, Nashville. TN, USA (URL: https://bradpitcher.weebly.com/, Twitter: @TieDyeSciGuy, photo posted at https://twitter.com/TieDyeSciGuy/status/1185191225101471744); Geoscientific Network of Chile (Twitter: @RedGeoChile, https://twitter.com/RedGeoChile, Facebook: https://www.facebook.com/RedGeoChile/, photo posted at https://twitter.com/RedGeoChile/status/1192921768186515456).

Suwanosejima, located south of Japan in the northern Ryukyu Islands, is an active andesitic stratovolcano that has had continuous activity since October 2004, typically producing ash plumes and Strombolian explosions. Much of this activity is focused within the Otake crater. This report updates information during July through December 2019 using monthly reports from the Japan Meteorological Agency (JMA), the Tokyo Volcanic Ash Advisory Center (VAAC), and various satellite data.

White gas-and-steam plumes rose from Suwanosejima on 26 July 2019, 30-31 August, 1-6, 10, and 20-27 September, reaching a maximum altitude of 2.4 km on 10 September, according to Tokyo VAAC advisories. Intermittent gray-white plumes were observed rising from the summit during October through December (figure 40).

Figure 40. Surveillance camera images of white gas-and-steam emissions rising from Suwanosejima on 10 December 2019 (left) and up to 1.8 km above the crater rim on 28 December (right). At night, summit incandescence was also observed on 10 December. Courtesy of JMA.

An explosion that occurred at 2331 on 1 August 2019 ejected material 400 m from the crater while other eruptions on 3-6 and 26 August produced ash plumes that rose up to a maximum altitude of 2.1 km and drifted generally NW according to the Tokyo VAAC report. JMA reported eruptions and summit incandescence in September accompanied by white gas-and-steam plumes, but no explosions were noted. Eruptions on 19 and 29 October produced ash plumes that rose 300 and 800 m above the crater rim, resulting in ashfall in Toshima (4 km SW), according to the Toshima Village Office, Suwanosejima Branch Office. Another eruption on 30 October produced a similar gray-white plume rising 800 m above the crater rim but did not result in ashfall. Similar activity continued in November with eruptions on 5-7 and 13-15 November producing grayish-white plumes rising 900 m and 1.5 km above the crater rim and frequent crater incandescence. Ashfall was reported in Toshima Village on 19 and 20 November; the 20 November eruption ejected material 200 m from the Otake crater.

Field surveys on 14 and 18 December using an infrared thermal imaging system to the E of Suwanose Island showed hotspots around the Otake crater, on the N slope of the crater, and on the upper part of the E coastline. GNSS (Global Navigation Satellite Systems) observations on 15 and 17 December showed a slight change in the baseline length. After 2122 on 25-26 and 31 December, 23 eruptions, nine of which were explosive were reported, producing gray-white plumes that rose 800-1,800 m above the crater rim and ejected material up to 600 m from the Otake crater. JMA reported volcanic tremors occurred intermittently throughout this reporting period.

Incandescence at the summit crater was occasionally visible at night during July through December 2019, as recorded by webcam images and reported by JMA (figure 41). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed weak thermal anomalies that occurred dominantly in November with little to no activity recorded between July and October (figure 42). Two Sentinel-2 thermal satellite images in early November and late December showed thermal hotspots within the summit crater (figure 43).

Figure 41. Surveillance camera image of summit incandescence at Suwanosejima on 31 October 2019. Courtesy of JMA.

Figure 42. Weak thermal anomalies at Suwanosejima during January-December 2019 as recorded by the MIROVA system (Log Radiative Power) dominantly occurred in mid-March, late May to mid-June, and November, with two hotspots detected in late September and late December. Courtesy of MIROVA.

Figure 43. Sentinel-2 thermal satellite images showing small thermal anomalies (bright yellow-orange) within the Otake crater at Suwanosejima on 8 November 2019 (left) and faintly on 23 December 2019 behind clouds (right). Both images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit of the volcano is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

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

Whakaari/White Island has been New Zealand's most active volcano since 1976. Located 48 km offshore, the volcano is a popular tourism destination with tours leaving the town of Whakatane with approximately 17,500 people visiting the island in 2018. Ten lives were lost in 1914 when part of the crater wall collapsed, impacting sulfur miners. More recently, a brief explosion at 1411 on 9 December 2019 produced an ash plume and pyroclastic surge that impacted the entire crater area. With 47 people on the island at the time, the death toll stood at 21 on 3 February 2019. At that time more patients were still in hospitals within New Zealand or their home countries.

The island is the summit of a large underwater volcano, with around 70% of the edifice below the ocean and rising around 900 m above sea level (figure 70). A broad crater opens to the ocean to the SE, with steep crater walls and an active Main Crater area to the NW rear of the crater floor (figure 71). Although the island is privately owned, GeoNet continuously monitors activity both remotely and with visits to the volcano. This Bulletin covers activity from May 2017 through December 2019 and is based on reports by GeoNet, the New Zealand Civil Defence Bay of Plenty Emergency Management Group, satellite data, and footage taken by visitors to the island.

Figure 70. The top of the Whakaari/White Island edifice forms the island in the Bay of Plenty area, New Zealand, while 70% of the volcano is below sea level. Courtesy of GeoNet.

Figure 71. This photo from 2004 shows the Main Crater area of Whakaari/White Island with the vent area indicated. The crater is an amphitheater shape with the crater floor distance between the vent and the ocean entry being about 700 m. The sediment plume begins at the area where tour boats dock at the island. Photo by Karen Britten, graphic by Danielle Charlton at University of Auckland; courtesy of GeoNet (11 December 2019 report).

Nearly continuous activity occurred from December 1975 to September 2000, including the formation of collapse and explosion craters producing ash emissions and explosions that impacted all of the Main Crater area. More recently, it has been in a state of elevated unrest since 2011. Renewed activity commenced with an explosive eruption on 5 August 2012 that was followed by the extrusion of a lava dome and ongoing phreatic explosions and minor ash emissions through March 2013. An ash cone was seen on 4 March 2013, and over the next few months the crater lake reformed. Further significant explosions took place on 20 August and 4, 8, and 11 October 2013. A landslide occurred in November 2015 with material descending into the lake. More recent activity on 27 April 2016 produced a short-lived eruption that deposited material across the crater floor and walls. A short period of ash emission later that year, on 13 September 2016, originated from a vent on the recent lava dome. Explosive eruptions occur with little to no warning.

Since 19 September 2016 the Volcanic Alert Level (VAL) was set to 1 (minor volcanic unrest) (figure 72). During early 2017 background activity in the crater continued, including active fumaroles emitting volcanic gases and steam from the active geothermal system, boiling springs, volcanic tremor, and deformation. By April 2017 a new crater lake had begun to form, the first since the April 2016 explosion when the lake floor was excavated an additional 13 m. Before this, there were areas where water ponded in depressions within the Main Crater but no stable lake.

Figure 72. The New Zealand Volcanic Alert Level system up to date in February 2020. Courtesy of GeoNet.

Activity from mid-2017 through 2018. In July-August 2017 GeoNet scientists carried out the first fieldwork at the crater area since late 2015 to sample the new crater lake and gas emissions. The crater lake was significantly cooler than the past lakes at 20°C, compared to 30-70°C that was typical previously. Chemical analysis of water samples collected in July showed the lowest concentrations of most "volcanic elements" in the lake for the past 10-15 years due to the reduced volcanic gases entering the lake. The acidity remained similar to that of battery acid. Gas emissions from the 2012 dome were 114°C, which were over 450°C in 2012 and 330°C in 2016. Fumarole 0 also had a reduced temperature of 152°C, reduced from over 190°C in late 2016 (figure 73). The observations and measurements indicated a decline in unrest. Further visits in December 2017 noted relatively low-level unrest including 149°C gas emissions from fumarole 0, a small crater lake, and loud gas vents nearby (figures 74 and 75). By 27 November the lake had risen to 10 m below overflow. Analysis of water samples led to an estimate of 75% of the lake water resulting from condensing steam vents below the lake and the rest from rainfall.

Figure 73. A GeoNet scientists conducting field work near Fumarole 0, an accessible gas vent on Whakaari/White Island in August 2017. Courtesy of GeoNet (23 August 2017 report).

Figure 74. GeoNet scientists sample gas emissions from vents on the 2012 Whakaari/White Island dome. The red circle in the left image indicates the location of the scientists. Courtesy of GeoNet (23 August 2017 report).

Figure 75. Active fumaroles and vents in the Main Crater of Whakaari/White Island including Fumarole 0 (top left). The crater lake formed in mid-2017 and gas emissions rise from surrounding vents (right). Courtesy of GeoNet (22 December 2017 report).

Routine fieldwork by GeoNet monitoring teams in early March 2018 showed continued low-level unrest and no apparent changes after a recent nearby earthquake swarm. The most notable change was the increase in the crater lake size, likely a response from recent high rainfall (figure 76). The water remained a relatively cool 27°C. Temperatures continued to decline at the 2012 dome vent (128°C) and Fumarole 0 (138°C). Spring and stream flow had also declined. Deformation was observed towards the Active Crater of 2-5 mm per month and seismicity remained low. The increase in lake level drowned gas vents along the lake shore resulting in geyser-like activity (figure 77). GeoNet warned that a new eruption could occur at any time, often without any useful warning.

In mid-April 2018 visitors reported loud sounds from the crater area as a result of the rising lake level drowning vents on the 2012 dome (in the western side of the crater) and resulting in steam-driven activity. There was no notable change in volcanic activity. The sounds stopped by July 2018 as the geothermal system adjusted to the rising water, up to 17 m below overfill and filling at a rate of about 2,000 m³ per day, rising towards more active vents (figure 78). A gas monitoring flight taken on 12 September showed a steaming lake surrounded by active fumaroles along the crater wall (figure 79).

Figure 76. The increase in the Whakaari/White Island crater lake size in early March 2018 with gas plumes rising from vents on the other side. Courtesy of GeoNet (19 March 2018 report).

Figure 77. The increasing crater lake level at Whakaari/White Island produced geyser-like activity on the lake shore in March 2018. Courtesy of Brad Scott, GeoNet.

Figure 78. Stills taken from a drone video of the Whakaari/White Island Main Crater lake and active vents producing gas emissions. Courtesy of GeoNet.

Figure 79. Photos taken during a gas monitoring flight with GNS Science at Whakaari/White Island show gas and steam emissions, and a steaming crater lake on 12 September 2018. Note the people for scale on the lower-right crater rim in the bottom photograph. Copyright of Ben Clarke, University of Leicester, used with permission.

Activity during April to early December 2019. A GeoNet volcanic alert bulletin in April 2019 reported that steady low-level unrest continued. The level of the lake had been declining since late January and was back down to 13 m below overflow (figure 80). The water temperature had increased to over 60°C due to the fumarole activity below the lake. Fumarole 0 remained steady at around 120-130°C. During May-June a seismic swarm was reported offshore, unrelated to volcanic activity but increasing the risk of landslides within the crater due to the shallow locations.

Figure 80. Planet Labs satellite images from March 2018 to April 2019 show fluctuations in the Whakaari/White Island crater lake level. Image copyright 2019 Planet Labs, Inc.

On 26 June the VAL was raised to level 2 (moderate to heightened volcanic unrest) due to increased SO₂ flux rising to historically high levels. An overflight that day detected 1,886 tons/day, nearly three times the previous values of May 2019, the highest recorded value since 2013, and the second highest since measurements began in 2003. The VAL was subsequently lowered on 1 July due to a reduction in detected SO₂ emissions of 880 tons/day on 28 June and 693 tons/day on 29 June.

GeoNet reported on 26 September that there was an increase in steam-driven activity within the active crater over the past three weeks. This included small geyser-like explosions of mud and steam with material reaching about 10 m above the lake. This was not attributed to an increase in volcanic activity, but to the crater lake level rising since early August.

On 30 October an increase in background activity was reported. An increasing trend in SO₂ gas emissions and volcanic tremor had been ongoing for several months and had reached the highest levels since 2016. This indicated to GeoNet that Whakaari/White Island might be entering a period where eruptive activity was more likely. There were no significant changes in other monitoring parameters at this time and fumarole activity continued (figure 81).

Figure 81. A webcam image taken at 1030 on 30 October 2019 from the crater rim shows the Whakaari/White Island crater lake to the right of the amphitheater-shaped crater and gas-and-steam plumes from active fumaroles. Courtesy of GeoNet.

On 18 November the VAL was raised to level 2 and the Aviation Colour Code was raised to Yellow due to further increase in SO₂ emissions and volcanic tremor. Other monitoring parameters showed no significant changes. On 25 November GeoNet reported that moderate volcanic unrest continued but with no new changes. Gas emissions remained high and gas-driven ejecta regularly jetting material a few meters into the air above fumaroles in the crater lake (figure 82).

Figure 82. A webcam image from the Whakaari/White Island crater rim shows gas-driven ejecta rising above a fumarole within the crater lake on 22 November 2019. Courtesy of GeoNet.

GeoNet reported on 3 December that moderate volcanic unrest continued, with increased but variable explosive gas and steam-driven jetting, with stronger events ejecting mud 20-30 m into the air and depositing mud around the vent area. Gas emissions and volcanic tremor remained elevated and occasional gas smells were reported on the North Island mainland depending on wind direction. The crater lake water level remained unchanged. Monitoring parameters were similar to those observed in 2011-2016 and remained within the expected range for moderate volcanic unrest.

Eruption on 9 December 2019. A short-lived eruption occurred at 1411 on 9 December 2019, generating a steam-and-ash plume to 3.6 km and covering the entire crater floor area with ash. Video taken by tourists on a nearby boat showed an eruption plume composed of a white steam-rich portion, and a black ash-rich ejecta (figure 83). A pyroclastic surge moved laterally across the crater floor and up the inner crater walls. Photos taken soon after the eruption showed sulfur-rich deposits across the crater floor and crater walls, and a helicopter that had been damaged and blown off the landing pad (figure 84). This activity caused the VAL to be raised to 4 (moderate volcanic eruption) and the Aviation Colour Code being raised to Orange.

Figure 83. The beginning of the Whakaari/White Island 9 December 2019 eruption viewed from a boat that left the island about 20-30 minutes prior. Top: the steam-rich eruption plume rising above the volcano and a pyroclastic surge beginning to rise over the crater rim. Bottom: the expanded steam-and-ash plume of the pyroclastic surge that flowed over the crater floor to the ocean. Copyright of Michael Schade, used with permission.

Figure 84. This photo of Whakaari/White Island taken after the 9 December 2019 eruption at around 1424 shows ash and sediment coating the crater floor and walls. The helicopter in this image was blown off the landing pad and damaged during the eruption. Copyright of Michael Schade, used with permission.

A steam plume was visible in a webcam image taken at 1430 from Whakatane, 21 minutes after the explosion (figure 85). Subsequent explosions occurred at 1630 and 1749. Search-and-Rescue teams reached the island after the eruption and noted a very strong sulfur smell that was experienced through respirators. They experienced severe stinging of any exposed skin that came in contact with the gas, and were left with sensitive skin and eyes, and sore throats. Later in the afternoon the gas-and-steam plume continued and a sediment plume was dispersing from the island (figure 86). The VAL was lowered to level 3 (minor volcanic eruption) at 1625 that day; the Aviation Colour Code remained at Orange.

Figure 85. A view of Whakaari/White Island from Whakatane in the North Island of New Zealand. Left: there is no plume visible at 1410 on 9 December 2019, one minute before the eruption. Right: A gas-and-steam plume is visible 21 minutes after the eruption. Courtesy of GeoNet.

Figure 86. A gas-and-steam plume rises from Whakaari/White Island on the afternoon of 9 December 2019 as rescue teams visit the island. A sediment plume in the ocean is dispersing from the island. Courtesy of Auckland Rescue Helicopter Trust.

During or immediately after the eruption an unstable portion of the SW inner crater wall, composed of 1914 landslide material, collapsed and was identified in satellite radar imagery acquired after the eruption. The material slid into the crater lake area and left a 12-m-high scarp. Movement in this area continued into early January.

Activity from late 2019 into early 2020. A significant increase in volcanic tremor began at around 0400 on 11 December (figure 87). The increase was accompanied by vigorous steaming and ejections of mud in several of the new vents. By the afternoon the tremor was at the highest level seen since the 2016 eruption, and monitoring data indicated that shallow magma was driving the increased unrest.

Figure 87. This RSAM (Real-Time Seismic Amplitude) time series plot represents the energy produced at Whakaari/White Island from 11 November to 11 December 2019 with the Volcanic Activity Levels and the 9 December eruption indicated. The plot shows the sharp increase in seismic energy during 11 December. Courtesy of GeoNet (11 December 2019 report).

The VAL was lowered to 2 on the morning of 12 December to reflect moderate to heightened unrest as no further explosive activity had occurred since the event on the 9th. Volcanic tremor was occurring at very high levels by the time a bulletin was released at 1025 that day. Gas emissions increased since 10 January, steam and mud jetting continued, and the situation was interpreted to be highly volatile. The Aviation Colour Code remained at Orange. Risk assessment maps released that day show the high-risk areas as monitoring parameters continued to show an increased likelihood of another eruption (figure 88).

Figure 88. Risk assessment maps of Whakaari/White Island show the increase in high-risk areas from 2 December to 12 December 2019. Courtesy of GeoNet (12 December 2019 report).

The volcanic activity bulletin for 13 December reported that volcanic tremor remained high, but had declined overnight. Vigorous steam and mud jetting continuing at the vent area. Brief ash emission was observed in the evening with ashfall restricted to the vent area. The 14 January bulletin reported that volcanic tremor had declined significantly over night, and nighttime webcam images showed a glow in the vent area due to high heat flow.

Aerial observations on 14 and 15 December revealed steam and gas emissions continuing from at least three open vents within a 100 m² area (figure 89). One vent near the back of the crater area was emitting transparent, high-temperature gas that indicated that magma was near the surface, and produced a glow registered by low-light cameras (figure 90). The gas emissions had a blue tinge that indicated high SO₂ content. The area that once contained the crater lake, 16 m below overflow before the eruption, was filled with debris and small isolated ponds mostly from rainfall, with different colors due to the water reacting with the eruption deposits. The gas-and-steam plume was white near the volcano but changed to a gray-brown color as it cooled and moved downwind due to the gas content (figure 91). On 15 December the tremor remained at low levels (figure 92).

Figure 89. The Main Crater area of Whakaari/White Island showing the active vent area and gas-and-steam emissions on 15 December 2019. Gas emissions were high within the circled area. Before the eruption a few days earlier this area was partially filled by the crater lake. Courtesy of GeoNet (15 December 2019 report).

Figure 90. A low-light nighttime camera at Whakaari/White Island imaged "a glow" at a vent within the active crater area on 13 December 2019. This glow is due to high-temperature gas emissions and light from external sources like the moon. Courtesy of GeoNet (15 December 2019 report).

Figure 91. A gas-and-steam plume at Whakaari/White Island on 15 December 2019 is white near the crater and changes to a grey-brown color downwind due to the gas content. Courtesy of GeoNet (15 December 2019 report).

Figure 92. The Whakaari/White Island seismic drum plot showing the difference in activity from 12 December (top) to 15 December (bottom). Courtesy of GeoNet (15 December 2019 report).

On 19 December tremor remained low (figure 93) and gas and steam emission continued. Overflight observations confirmed open vents with one producing temperatures over 650°C (figure 94). SO₂ emissions remained high at around 15 kg/s, slightly lower than the 20 kg/s detected on 12 December. Small amounts of ash were produced on 23 and 26 December due to material entering the vents during erosion.

Figure 93. This RSAM (Real-Time Seismic Amplitude) time series plot represents the energy produced at Whakaari/White Island from 1 November to mid-December 2019. The Volcanic Alert Levels and the 9 December eruption are indicated. Courtesy of GeoNet.

Figure 94. A photograph and thermal infrared image of the Whakaari/White Island crater area on 19 December 2019. The thermal imaging registered temperatures up to 650°C at a vent emitting steam and gas. Courtesy of GeoNet.

The Aviation Colour Code was reduced to Yellow on 6 January 2020 and the VAL remained at 2. Strong gas and steam emissions continued from the vent area through early January and the glow persisted in nighttime webcam images. Short-lived episodes of volcanic tremor were recorded between 8-10 January and were accompanied by minor explosions. A 15 January bulletin reported that the temperature at the vent area remained very hot, up to 440°C, and SO₂ emissions were within normal post-eruption levels.

High temperatures were detected within the vent area in Sentinel-2 thermal data on 6 and 16 January (figure 95). Lava extrusion was confirmed within the 9 December vents on 20 January. Airborne SO₂ measurements on that day recorded continued high levels and the vent temperature was over 400°C. Observations on 4 February showed that no new lava extrusion had occurred, and gas fluxes were lower than two weeks ago, but still elevated. The temperatures measured in the crater were 550-570°C and no further changes to the area were observed.

Figure 95. Sentinel-2 thermal infrared satellite images show elevated temperatures in the 9 December 2019 vent area on Whakaari/White Island. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

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

Information Contacts: New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/); GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Bay of Plenty Emergency Management Group Civil Defense, New Zealand (URL: http://www.bopcivildefence.govt.nz/); Auckland Rescue Helicopter Trust, Auckland, New Zealand (URL: https://www.rescuehelicopter.org.nz/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Ben Clarke, The University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom (URL: https://le.ac.uk/geology, Twitter: https://twitter.com/PyroclasticBen); Michael Schade, San Francisco, USA (URL: https://twitter.com/sch).

Barren Island is a remote stratovolcano located east of India in the Andaman Islands. Its most recent eruptive episode began in September 2018 and has included lava flows, explosions, ash plumes, and lava fountaining (BGVN 44:02). This report updates information from February 2019 through January 2020 using various satellite data as a primary source of information.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent thermal anomalies within 5 km of the summit from mid-February 2019 through January 2020 (figure 41). There was a period of relatively low to no discernible activity between May to September 2019. The MODVOLC algorithm for MODIS thermal anomalies in comparison with Sentinel-2 thermal satellite imagery and Suomi NPP/VIIRS sensor data, registered elevated temperatures during late February 2019, early March, sparsely in April, late October, sparsely in November, early December, and intermittently in January 2020 (figure 42). Sentinel-2 thermal satellite imagery shows these thermal hotspots differing in strength from late February to late January 2020 (figure 43). The thermal anomalies in these satellite images are occasionally accompanied by ash plumes (25 February 2019, 23 October 2019, and 21 January 2020) and gas-and-steam emissions (26 April 2019).

Figure 41. Intermittent thermal anomalies at Barren Island for 20 February 2019 through January 2020 occurred dominantly between late March to late April 2019 and late September 2019 through January 2020. Courtesy of MIROVA.

Figure 42. Timeline summary of observed activity at Barren Island from February 2019 through January 2020. For Sentinel-2, MODVOLC, and VIIRS data, the dates indicated are when thermal anomalies were detected. White areas indicated no activity was observed, which may also be due to meteoric clouds. Data courtesy of Darwin VAAC, Sentinel Hub Playground, HIGP, and NASA Worldview using the "Fire and Thermal Anomalies" layer.

Figure 43. Sentinel-2 thermal images show ash plumes, gas-and-steam emissions, and thermal anomalies (bright yellow-orange) at Barren Island during February 2019-January 2020. The strongest thermal signature was observed on 23 October while the weakest one is observed on 26 January. Sentinel-2 False color (bands 12, 11, 4) images courtesy of Sentinel Hub Playground.

The Darwin Volcanic Ash Advisory Center (VAAC) reported ash plumes rising from the summit on 7, 14, and 16 March 2019. The maximum altitude of the ash plume occurred on 7 March, rising 1.8 km altitude, drifting W and NW and 1.2 km altitude, drifting E and ESE, based on observations from Himawari-8. The VAAC reports for 14 and 16 March reported the ash plumes rising 0.9 km and 1.2 km altitude, respectively drifting W and W.

Geologic Background. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

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

Kadovar is an island volcano north of Papua New Guinea and northwest of Manam. The first confirmed historical activity began in January 2018 and resulted in the evacuation of residents from the island. Eruptive activity through 2018 changed the morphology of the SE side of the island and activity continued through 2019 (figure 36). This report summarizes activity from May through December 2019 and is based largely on various satellite data, tourist reports, and Darwin Volcanic Ash Advisory Center (VAAC) reports.

Figure 36. The morphological changes to Kadovar from 2017 to June 2019. Top: the vegetated island has a horseshoe-shaped crater that opens towards the SE; the population of the island was around 600 people at this time. Middle: by May 2018 the eruption was well underway with an active summit crater and an active dome off the east flank. Much of the vegetation has been killed and ashfall covers a lot of the island. Bottom: the bay below the SE flank has filled in with volcanic debris. The E-flank coastal dome is no longer active, but activity continues at the summit. PlanetScope satellite images copyright Planet Labs 2019.

Since this eruptive episode began a large part of the island has been deforested and has undergone erosion (figure 37). Activity in early 2019 included regular gas and steam emissions, ash plumes, and thermal anomalies at the summit (BGVN 44:05). On 15 May an ash plume originated from two vents at the summit area and dispersed to the east. A MODVOLC thermal alert was also issued on this day, and again on 17 May. Elevated temperatures were detected in Sentinel-2 thermal satellite data on 20, 21, and 30 May (figure 38), with accompanying gas-and-steam plumes dispersing to the NNW and NW. On 30 May the area of elevated temperature extended to the SE shoreline, indicating an avalanche of hot material reaching the water.

Figure 37. The southern flank of Kadovar seen here on 13 November 2019 had been deforested by eruptive activity and erosion had produced gullies down the flanks. Copyrighted photo by Chrissie Goldrick, used with permission.

Figure 38. Sentinel-2 thermal satellite images show elevated temperatures at the summit area, and down to the coast in the top image. Gas-and-steam plumes are visible dispersing towards the NW. Sentinel-2 false color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel-Hub Playground.

Throughout June cloud-free Sentinel-2 thermal satellite images showed elevated temperatures at the summit area and extending down the upper SE flank (figure 38). Gas-and-steam plumes were persistent in every Sentinel-2 and NASA Suomi NPP / VIIRS (Visible Infrared Imaging Radiometer Suite) image. MODVOLC thermal alerts were issued on 4 and 9 June. Similar activity continued through July with gas-and-steam emissions visible in every cloud-free satellite image. Thermal anomalies appeared weaker in late-July but remained at the summit area. An ash plume was imaged on 17 July by Landsat 8 with a gas-and-ash plume dispersing to the west (figure 39). Thermal anomalies continued through August with a MODVOLC thermal alert issued on the 14th. Gas emissions also continued and a Volcano Observatory Notice for Aviation (VONA) was issued on the 19th reporting an ash plume to an altitude of 1.5 km and drifting NW.

Figure 39. An ash plume rising above Kadovar and a gas plume dispersing to the NW on 17 July 2019. Truecolor pansharpened Landsat 8 satellite image courtesy of Sentinel Hub Playground.

An elongate area extending from the summit area to the E-flank coastal dome appears lighter in color in a 7 September Sentinel-2 natural color satellite image, and as a higher temperature area in the correlating thermal bands, indicating a hot avalanche deposit. These observations along with the previous avalanche, persistent elevated summit temperatures, and persistent gas and steam emissions from varying vent locations (figure 40) suggests that the summit dome has remained active through 2019.

Figure 40. Sentinel-2 visible and thermal satellite images acquired on 7 September 2019 show fresh deposits down the east flank of Kadovar. They appear as a lighter colored area in visible, and show as a hot area (orange) in thermal data. Sentinel-2 natural color (bands 4, 3, 2) and false color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel-Hub Playground.

Thermal anomalies and emissions continued through to the end of 2019 (figure 41). A tour group witnessed an explosion producing an ash plume at around 1800 on 13 November (figure 42). While the ash plume erupted near-vertically above the island, a more diffuse gas plume rose from multiple vents on the summit dome and dispersed at a lower altitude.

Figure 41. The summit area of Kadovar emitting gas-and-steam plumes in August, September, and November 2019. The plumes are persistent in satellite images throughout May through December and there is variation in the number and locations of the source vents. PlanetScope satellite images copyright Planet Labs 2019.

Figure 42. An ash plume and a lower gas plume rise during an eruption of Kadovar on 13 November 2019. The summit lava dome is visibly degassing to produce the white gas plume. Copyrighted photos by Chrissie Goldrick, used with permission.

While gas plumes were visible throughout May-December 2019 (figure 43), SO₂ plumes were difficult to detect in NASA SO₂ images due to the activity of nearby Manam volcano. The MIROVA thermal detection system shows continued elevated temperatures through to early December, with an increase during May-June (figure 44). Sentinel-2 thermal images showed elevated temperatures through to the end of December but at a lower intensity than previous months.

Figure 43. This photo of the southeast side Kadovar on 13 November 2019 shows a persistent low-level gas plume blowing towards the left and a more vigorous plume is visible near the crater. This is an example of the persistent plume visible in satellite imagery throughout July-December 2019. Copyrighted photo by Chrissie Goldrick, used with permission.

Figure 44. The MIROVA plot of radiative power at Kadovar shows thermal anomalies throughout 2019 with some variations in frequency. Note that while the black lines indicate that the thermal anomalies are greater than 5 km from the vent, the designated summit location is inaccurate so these are actually a the summit crater and on the E flank. Courtesy of MIROVA.

Geologic Background. The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. It is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the andesitic volcano, filling an arcuate landslide scarp open to the south; submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. A period of heightened thermal phenomena took place in 1976. An eruption began in January 2018 that included lava effusion from vents at the summit and at the E coast.

Information Contacts: 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/); Planet Labs, Inc. (URL: https://www.planet.com/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Worldview (URL: https://worldview.earthdata.nasa.gov); Chrissie Goldrick, Australian Geographic, Level 7, 54 Park Street, Sydney, NSW 2000, Australia (URL: https://www.australiangeographic.com.au/).

Nyiragongo is a stratovolcano with a 1.2 km-wide summit crater containing an active lava lake that has been present since at least 1971. It is located the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo, part of the western branch of the East African Rift System. Typical volcanism includes strong and frequent thermal anomalies, primarily due to the lava lake, incandescence, gas-and-steam plumes, and seismicity. This report updates activity during June through November 2019 with the primary source information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

In the July 2019 monthly report, OVG stated that the lava lake level had dropped during the month, with incandescence only visible at night (figure 68). In addition, the small eruptive cone within the crater, which has been active since 2014, decreased in activity during this timeframe. A MONUSCO (United Nations Stabilization Mission in the Democratic Republic of the Congo) helicopter overflight took photos of the lava lake and observed that the level had begun to rise on 27 July. Seismicity was relatively moderate throughout this reporting period; however, on 9-16 July and 21 August strong seismic swarms were recorded.

Figure 68. Webcam images of Nyiragongo on 20 July 2019 where incandescence is not visible during the day (left) but is observed at night (right). Incandescence is accompanied by gas-and-steam emissions. Courtesy of OVG.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data continued to show frequent and strong thermal anomalies within 5 km of the crater summit through November 2019 (figure 69). Similarly, the MODVOLC algorithm reported almost daily thermal hotspots (more than 600) within the summit crater between June 2019 through November. These data are corroborated with Sentinel-2 thermal satellite imagery and a photo from OVG on 19 December 2019 showing the active lava lake (figures 70 and 71).

Figure 69. Thermal anomalies at Nyiragongo from 3 January through November 2019 as recorded by the MIROVA system (Log Radiative Power) were frequent and strong. Courtesy of MIROVA.

Figure 70. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) showed ongoing thermal activity (bright yellow-orange) at Nyiragongo during June through November 2019. Courtesy of Sentinel Hub Playground.

Figure 71. Photo of the active lava lake in the summit crater at Nyiragongo on 19 December 2019. Incandescence is accompanied by a gas-and-steam plume. Courtesy of OVG via Charles Balagizi.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Charles Balagizi (Twitter: @CharlesBalagizi, https://twitter.com/CharlesBalagizi).

Activity at Ebeko includes frequent explosions that have generated ash plumes reaching altitudes of 1.5-6 km over the last several years, with the higher altitudes occurring since mid-2018 (BGVN 43:03, 43:06, 43:12, 44:07). Ash frequently falls in Severo-Kurilsk (7 km ESE), which is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT). This activity continued during June through November 2019; the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Explosive activity during December 2018 through November 2019 often sent ash plumes to altitudes between 2.2 to 4.5 km, or heights of 1.1 to 3.4 km above the crater (table 8). Eruptions since 1967 have originated from the northern crater of the summit area (figure 20). Webcams occasionally captured ash explosions, as seen on 27 July 2019(figure 21). KVERT often reported the presence of thermal anomalies; particularly on 23 September 2019, a Sentinel-2 thermal satellite image showed a strong thermal signature at the crater summit accompanied by an ash plume (figure 22). Ashfall is relatively frequent in Severo-Kurilsk (7 km ESE) and can drift in different direction based on the wind pattern, which can be seen in satellite imagery on 30 October 2019 deposited NE and SE from the crater(figure 23).

Table 8. Summary of activity at Ebeko, December 2018-November 2019. S-K is Severo-Kurilsk (7 km ESE of the volcano). TA is thermal anomaly in satellite images. Data courtesy of KVERT.

Figure 20. Satellite image showing the summit crater complex at Ebeko, July 2019. Monthly mosaic image for July 2019, copyright 2019 Planet Labs, Inc.

Figure 21. Webcam photo of an explosion and ash plume at Ebeko on 27 July 2019. Videodata by IMGG FEB RAS and KB GS RAS (color adjusted and cropped); courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.

Figure 22. Satellite images showing an ash explosion from Ebeko on 23 September 2019. Top image is in natural color (bands 4, 3, 2). Bottom image is using "Atmospheric Penetration" rendering (bands 12, 11, 8A) to show a thermal anomaly in the northern crater visible around the rising plume. Courtesy of Sentinel Hub Playground.

Figure 23. A satellite image of Ebeko from Sentinel-2 (LC1 natural color, bands 4, 3, 2) on 30 October 2019 showing previous ashfall deposits on the snow going in multiple directions. Courtesy of Sentinel Hub Playground.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data detected four low-power thermal anomalies during the second half of July, and one each in the months of June, August, and October; no activity was recorded in September or November MODVOLC thermal alerts observed only one thermal anomaly between June through November 2019.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion 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/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/).

Nevado del Ruiz is a glaciated volcano in Colombia (figure 86). It is known for the 13 November 1985 eruption that produced an ash plume and associated pyroclastic flows onto the glacier, triggering a lahar that approximately 25,000 people in the towns of Armero (46 km west) and Chinchiná (34 km east). Since 1985 activity has intermittently occurred at the Arenas crater. The eruption that began on 18 November 2014 included ash plumes dominantly dispersed to the NW of Arenas crater (BGVN 42:06). This bulletin summarizes activity during January 2016 through December 2017 and is based on reports by Servicio Geologico Colombiano and Observatorio Vulcanológico y Sismológico de Manizales, Washington Volcanic Ash Advisory Center (VAAC) notices, and satellite data.

Figure 86. A satellite image of Nevado del Ruiz showing the location of the active Arenas crater. September 2019 Monthly Mosaic image copyright Planet Labs 2019.

Activity during 2016. Throughout January 2016 ash and steam plumes were observed reaching up to a few kilometers. Significant water vapor and volcanic gases, especially SO₂, were detected throughout the month. Thermal anomalies were detected in the crater on the 27th and 31st. Significant water vapor and volcanic gas plumes, in particular SO₂, were frequently detected by the SCAN DOAS (Differential Optical Absorption Spectroscopy) station and satellite data (figure 87). A M3.2 earthquake was felt in the area on 18 January. Similar activity continued through February with notable ash plumes up to 1 km, and a M3.6 earthquake was felt on the 6th. Ash and gas-and-steam plumes were reported throughout March with a maximum of 3.5 km on the 31st (figure 88). Significant water vapor and gas plumes continued from the Arenas crater throughout the month, and a thermal anomaly was noted on the 28th. An increase in seismicity was reported on the 29th.

Figure 87. Examples of SO2 plumes from Nevado del Ruiz detected by the Aura/OMI instrument on 10, 26, and 31 January 2019. Courtesy of Goddard Space Flight Center.

Figure 88. Ash plumes at Nevado del Ruiz during March. Webcam images courtesy of Servicio Geologico Colombiano, various 2016 reports.

The activity continued into April with a M 3.0 earthquake felt by nearby inhabitants on the 8th, an increase in seismicity reported in the week of 12-18, and another significant increase on the 28th with earthquakes felt around Manizales. Thermal anomalies were noted during 12-18 April with the largest on the 16th. Ash plumes continued through the month as well as significant steam-and-gas plumes. Ashfall was reported in Murillo on the 29th.

The elevated activity continued through May with significant steam plumes up to 1.7 km above the crater during the week of 10-16. Thermal anomalies were reported on the 11th and 12th. Steam, gas, and ash plumes reached 2.5 km above the crater and dispersed to the W and NW. Ashfall was reported in La Florida on the 20th (figure 89) and multiple ash plumes on the 22nd reached 2.5 km and resulted in the closure of the La Nubia airport in Manizales. Ash and gas-and-steam emission continued during June (figure 90).

Figure 89. Ash plumes at Nevado del Ruiz on 17, 18, and 20 May 2016 with fine ash deposited on a car in La Florida, Manizales on the 20th. Webcams located in the NE Guali sector of the volcano, courtesy of Servicio Geologico Colombiano 20 May 2016 report.

Figure 90. Examples of gas-and-steam and ash plumes at Nevado del Ruiz during June and July 2016. Courtesy of Servicio Geologico Colombiano (7 July 2016 report).

Similar activity was reported in July with gas-and-steam and ash plumes often dispersing to the NW and W. Ashfall was reported to the NW on 16 July (figure 91). Drumbeat seismicity was detected on 13, 15, 16, and 17 July, with two hours on the 16th being the longest duration episode do far. Drumbeat seismicity was noted by SGC as indicating dome growth. Significant water vapor and gas emissions continued through August. Ash plumes were reported through the month with plumes up to 1.3 km above the crater on 28 and 2.3 km on 29. Similar activity was reported through September as well as a thermal anomaly and ash deposition apparent in satellite data (figure 92). Drumbeat seismicity was noted again on the 17th.

Figure 91. The location of ashfall resulting from an explosion at Nevado del Ruiz on 16 July 2016 and a sample of the ash under a microscope. The ash is composed of lithics, plagioclase and pyroxene crystals, and minor volcanic glass. Courtesy of Servicio Geologico Colombiano (16 July 2016 report).

Figure 92. This Sentinel-2 thermal infrared satellite image shows elevated temperatures in the Nevado del Ruiz Arenas crater (yellow and orange) on 16 September 2016. Ash deposits are also visible to the NW of the crater. In this image blue is snow and ice. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

During the week of 4-10 October it was noted that activity consisting of regular ash plumes had been ongoing for 22 months. Ash plumes continued with reported plumes reaching 2.5 above the crater throughout October (figure 93), accompanied by significant steam and water vapor emissions. A M 4.4 earthquake was felt nearby on the 7th. Similar activity continued through November and December 2016 with plumes consisting of gas and steam, and sometimes ash reaching 2 km above the crater.

Figure 93. An ash plume rising above Nevado del Ruiz on 27 October 2016. Courtesy of Servicio Geologico Colombiano.

Activity during 2017. Significant steam and gas emissions, especially SO₂, continued into early 2017. Ash plumes detected through seismicity were confirmed in webcam images and through local reports; the plumes reached a maximum height of 2.5 km above the volcano on the 6th (figure 94). Drumbeat seismicity was recorded during 3-9, and on 22 January. Inflation was detected early in the month and several thermal anomalies were noted.

Intermittent deformation continued into February. Significant steam-and-gas emissions continued with intermittent ash plumes reaching 1.5-2 km above the volcano. Thermal anomalies were noted throughout the month and there was a significant increase in seismicity during 23-26 February.

Figure 94. Ash plumes at Nevado del Ruiz on 6 January 2017. Courtesy of Servicio Geologico Colombiano.

Thermal anomalies continued to be detected through March. Ash plumes continued to be observed and recorded in seismicity and maximum heights of 2 km above the volcano were noted. Deflation continued after the intermittent inflation the previous month. On 10-11 April a period of short-duration and very low-energy drumbeat seismicity was recorded. Significant gas and steam emission continued through April with intermittent ash plumes reaching 1.5 km above the volcano. Thermal anomalies were detected early in the month.

Unrest continued through May with elevated seismicity, significant steam-and-gas emissions, and ash plumes reaching 1.7 km above the crater. Five episodes of drumbeat seismicity were recorded on 29 May and intermittent deformation continued. There were no available reports for June and July.

Variable seismicity was recorded during August and deflation was measured in the first week. Gas-and-steam plumes were observed rising to 850 m above the crater on the 3rd, and 450 m later in the month. A thermal anomaly was noted on the 14th. There were no available reports for September through December.

On 18 December 2017 the Washington VAAC issued an advisory for an ash plume to 6 km that was moving west and dispersing. The plume was described as a "thin veil of volcanic ash and gasses" that was seen in visible satellite imagery, NOAA/CIMSS, and supported by webcam imagery.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: Servicio Geologico Colombiano (SGC), Diagonal 53 No. 34-53 - Bogotá D.C., Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html); Observatorio Vulcanológico y Sismológico de Manizales (URL: https://www.facebook.com/ovsmanizales); 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); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Sabancaya is an andesitic stratovolcano located in Peru. The most recent eruptive episode began in early November 2016, which is characterized by gas-and-steam and ash emissions, seismicity, and explosive events (BGVN 44:06). The ash plumes are dispersed by wind with a typical radius of 30 km, which occasionally results in ashfall. Current volcanism includes high seismicity, gas-and-steam emissions, ash and SO₂ plumes, numerous thermal anomalies, and explosive events. This report updates information from June through November 2019 using information primarily from the Instituto Geofisico del Peru (IGP) and Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico) (OVI-INGEMMET).

Table 5. Summary of eruptive activity at Sabancaya during June-November 2019 based on IGP weekly reports, the Buenos Aires VAAC advisories, the HIGP MODVOLC hotspot monitoring algorithm, and Sentinel-5P/TROPOMI satellite data.

Explosions, ash emissions, thermal signatures, and high concentrations of SO₂ were reported each week during June-November 2019 by IGP, the Buenos Aires Volcanic Ash Advisory Centre (VAAC), HIGP MODVOLC, and Sentinel-2 and Sentinel-5P/TROPOMI satellite data (table 5). Thermal anomalies were visible in the summit crater, even in the presence of meteoric clouds and ash plumes were occasionally visible rising from the summit in clear weather (figure 68). The maximum plume height reached 4.5 km above the crater drifting NW, W, and S the week of 29 July-4 August, according to IGP who used surveillance cameras to visually monitor the plume (figure 69). This ash plume had a radius of 30 km, which resulted in ashfall in Colca (NW) and Huambo (W). On 27 July the SO₂ levels reached a high of 12,814 tons/day, according to INGEMMET. An average of 58 daily explosions occurred in early November, which is the largest average of this reporting period.

Figure 68. Sentinel-2 satellite imagery detected ash plumes, gas-and-steam emissions, and multiple thermal signatures (bright yellow-orange) in the crater at Sabancaya during June-November 2019. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

Figure 69. A webcam image of an ash plume rising from Sabancaya on 1 August 2019 at least 4 km above the crater. Courtesy of IGP.

Seismicity was also particularly high between August and September 2019, according to INGEMMET. On 14 August, roughly 850 earthquakes were detected. There were 280 earthquakes reported on 15 September, located 6 km NE of the crater. Both seismic events were characterized as seismic swarms. Seismicity decreased afterward but continued through the reporting period.

In February 2017, a lava dome was established inside the crater. Since then, it has been growing slowly, filling the N area of the crater and producing thermal anomalies. On 26 October 2019, OVI-INGEMMET conducted a drone overflight and captured video of the lava dome (figure 70). According to IGP, this lava dome is approximately 4.6 million cubic meters with a growth rate of 0.05 m3/s.

Figure 70. Drone images of the lava dome and degassing inside the crater at Sabancaya on 26 (top) and 27 (bottom) October 2019. Courtesy of INGEMMET (Informe Ténico No A6969).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows strong, consistent thermal anomalies occurring all throughout June through November 2019 (figure 71). In conjunction with these thermal anomalies, the October 2019 special issue report by INGEMMET showed new hotspots forming along the crater rim in July 2018 and August 2019 (figure 72).

Figure 71. Thermal anomalies at Sabancaya for 3 January through November 2019 as recorded by the MIROVA system (Log Radiative Power) were frequent, strong, and consistent. Courtesy of MIROVA.

Figure 72. Thermal hotspots on the NW section of the crater at Sabancaya using MIROVA images. These images show the progression of the formation of at least two new hotspots between February 2017 to August 2019. Courtesy of INGEMMET, Informe Técnico No A6969.

Sulfur dioxide emissions also persisted at significant levels from June through November 2019, as detected by Sentinel-5P/TROPOMI satellite data (figure 73). The satellite measurements of the SO₂ emissions exceeded 2 DU (Dobson Units) at least 20 days each month during this time. These SO₂ plumes sometimes occurred for multiple consecutive days (figure 74).

Figure 73. Consistent, large SO2 plumes from Sabancaya were seen in TROPOMI instrument satellite data throughout June-November 2019, many of which drifted in different directions based on the prevailing winds. Courtesy of NASA Goddard Space Flight Center.

Figure 74. Persistent SO2 plumes from Sabancaya appeared daily during 13-16 September 2019 in the TROPOMI instrument satellite data. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Information Contacts: Instituto Geofisico del Peru (IGP), Calle Badajoz N° 169 Urb. Mayorazgo IV Etapa, Ate, Lima 15012, Perú (URL: https://www.gob.pe/igp); Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa, Peru (URL: http://ovi.ingemmet.gob.pe); 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/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Karangetang (also known as Api Siau), located on the island of Siau in the Sitaro Regency, North Sulawesi, Indonesia, has experienced more than 40 recorded eruptions since 1675 in addition to many smaller undocumented eruptions. In early February 2019, a lava flow originated from the N crater (Kawah Dua) traveling NNW and reaching a distance over 3 km. Recent monitoring showed a lava flow from the S crater (Kawah Utama, also considered the "Main Crater") traveling toward the Kahetang and Batuawang River drainages on 15 April 2019. Gas-and-steam emissions, ash plumes, moderate seismicity, and thermal anomalies including lava flow activity define this current reporting period for May through November 2019. The primary source of information for this report comes from daily and weekly reports by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), the Darwin Volcanic Ash Advisory Center (VAAC), and satellite data.

PVMBG reported that white gas-and-steam emissions were visible rising above both craters consistently between May through November 2019 (figures 30 and 31). The maximum altitude for these emissions was 400 m above the Dua Crater on 27 May and 700 m above the Main Crater on 12 June. Throughout the reporting period PVMBG noted that moderate seismicity occurred, which included both shallow and deep volcanic earthquakes.

Figure 30. A Sentinel-2 image of Karangetang showing two active craters producing gas-and-steam emissions with a small amount of ash on 7 August 2019. Courtesy of Sentinel Hub Playground.

Figure 31. Webcam images of gas-and-steam emissions rising from the summit of Karangetang on 14 (top) and 25 (bottom) October 2019. Courtesy of PVMBG via Øystein Lund Andersen.

Activity was relatively low between May and June 2019, consisting mostly of gas-and-steam emissions. On 26-27 May 2019 crater incandescence was observed above the Main Crater; white gas-and-steam emissions were rising from both craters (figures 32 and 33). At 1858 on 20 July, incandescent avalanches of material originating from the Main Crater traveled as far as 1 km W toward the Pangi and Kinali River drainages. By 22 July the incandescent material had traveled another 500 m in the same direction as well as 1 km in the direction of the Nanitu and Beha River drainages. According to a Darwin VAAC report, discreet, intermittent ash eruptions on 30 July resulted in plumes drifting W at 7.6 km altitude and SE at 3 km, as observed in HIMAWARI-8 satellite imagery.

Figure 32. Photograph of summit crater incandescence at Karangetang on 12 May 2019. Courtesy of Dominik Derek.

Figure 33. Photograph of both summit crater incandescence at Karangetang on 12 May 2019 accompanied by gas-and-steam emissions. Courtesy of Dominik Derek.

On 5 August 2019 a minor eruption produced an ash cloud that rose 3 km and drifted E. PVMBG reported in the weekly report for 5-11 August that an incandescent lava flow from the Main Crater was traveling W and SW on the slopes of Karangetang and producing incandescent avalanches (figure 34). During 12 August through 1 September lava continued to effuse from both the Main and Dua craters. Avalanches of material traveled as far as 1.5 km SW toward the Nanitu and Pangi River drainages, 1.4-2 km to the W of Pangi, and 1.8 km down the Sense River drainage. Lava fountaining was observed occurring up to 10 m above the summit on 14-20 August.

Figure 34. Photograph of summit crater incandescence and a lava flow from Karangetang on 7 August 2019. Courtesy of MAGMA Indonesia.

PVMBG reported that during 2-22 September lava continued to effuse from both craters, traveling SW toward the Nanitu, Pangi, and Sense River drainages as far as 1.5 km. On 24 September the lava flow occasionally traveled 0.8-1.5 km toward the West Beha River drainage. The lava flow from the Main Crater continued through at least the end of November, moving SW and W as far as 1.5 km toward the Nanitu, Pangi, and Sense River drainages. In late October and onwards, incandescence from both summit craters was observed at night. The lava flow often traveled as far as 1 km toward the Batang and East Beha River drainage on 12 November, the West Beha River drainage on 15, 22, 24, and 29 November, and the Batang and West Beha River drainages on 25-27 November (figure 35). On 30 November a Strombolian eruption occurred in the Main Crater accompanied by gas-and-steam emissions rising 100 m above the Main Crater and 50 m above the Dua Crater. Lava flows traveled SW and W toward the Nanitu, Sense, and Pangi River drainages as far as 1.5 km, the West Beha and Batang River drainages as far as 1 km, and occasionally the Batu Awang and Kahetang River drainages as far as 2 km. Lava fountaining was reported occurring 10-25 m above the Main Crater and 10 m above the Dua Crater on 6, 8-12, 15, 21-30 November.

Figure 35. Webcam image of gas-and-steam emissions rising from the summit of Karangetang accompanied by incandescence and lava flows at night on 27 November 2019. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed consistent and strong thermal anomalies within 5 km of the summit craters from late July through November 2019 (figure 36). Satellite imagery from Sentinel-2 corroborated this data, showing strong thermal anomalies and lava flows originating from both craters during this same timeframe (figure 37). In addition to these lava flows, satellite imagery also captured intermittent gas-and-steam emissions from May through November (figure 38). MODVOLC thermal alerts registered 165 thermal hotspots near Karangetang's summit between May and November.

Figure 36. Frequent and strong thermal anomalies at Karangetang between 3 January through November 2019 as recorded by the MIROVA system (Log Radiative Power) began in late July and were recorded within 5 km of the summit craters. Courtesy of MIROVA.

Figure 37. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity (bright orange) at Karangetang from July into November 2019. The lava flows traveled dominantly in the W direction from the Main Crater. Courtesy of Sentinel Hub Playground.

Figure 38. Sentinel-2 satellite imagery showing gas-and-steam emissions with a small amount of ash (middle and right) rising from both craters of Karangetang during May through November 2019. Courtesy of Sentinel Hub Playground.

Sentinel-5P/TROPOMI satellite data detected multiple sulfur dioxide plumes between May and November 2019 (figure 39). These emissions occasionally exceeded 2 Dobson Units (DU) and drifted in different directions based on the dominant wind pattern.

Figure 39. SO2 emissions from Karangetang (indicated by the red box) were seen in TROPOMI instrument satellite data during May through November 2019, many of which drifted in different directions based on the prevailing winds. Top left: 27 May 2019. Top middle: 26 July 2019. Top right: 17 August 2019. Bottom left: 27 September 2019. Bottom middle: 3 October 2019. Bottom right: 21 November 2019. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://SO2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com); Dominik Derek (URL: https://www.facebook.com/07dominikderek/).

Ulawun is a basaltic-to-andesitic stratovolcano located in West New Britain, Papua New Guinea, with typical activity consisting of seismicity, gas-and-steam plumes, and ash emissions. The most recent eruption began in late June 2019 involving ash and gas-and-steam emissions, increased seismicity, and a pyroclastic flow (BGVN 44:09). This report includes volcanism from September to October 2019 with primary source information from the Rabaul Volcano Observatory (RVO) and the Darwin Volcanic Ash Advisory Centre (VAAC).

Activity remained low through 26 September 2019, mainly consisting of variable amounts of gas-and-steam emissions and low seismicity. Between 26 and 29 September RVO reported that the seismicity increased slightly and included low-level volcanic tremors and Real-Time Seismic Amplitude Measurement (RSAM) values in the 200-400 range on 19, 20, and 22 September. On 30 September small volcanic earthquakes began around 1000 and continued to increase in frequency; by 1220, they were characterized as a seismic swarm. The Darwin VAAC advisory noted that an ash plume rose to 4.6-6 km altitude, drifting SW and W, based on ground reports.

On 1 October 2019 the seismicity increased, reaching RSAM values up to 10,000 units between 0130 and 0200, according to RVO. These events preceded an eruption which originated from a new vent that opened on the SW flank at 700 m elevation, about three-quarters of the way down the flank from the summit. The eruption started between 0430 and 0500 and was defined by incandescence and lava fountaining to less than 100 m. In addition to lava fountaining, light- to dark-gray ash plumes were visible rising several kilometers above the vent and drifting NW and W (figure 21). On 2 October, as the lava fountaining continued, ash-and-steam plumes rose to variable heights between 2 and 5.2 km (figures 22 and 23), resulting in ashfall to the W in Navo. Seismicity remained high, with RSAM values passing 12,000. A lava flow also emerged during the night which traveled 1-2 km NW. The main summit crater produced white gas-and-steam emissions, but no incandescence or other signs of activity were observed.

Figure 21. Photographs of incandescence and lava fountaining from Ulawun during 1-2 October 2019. A) Lava fountains along with ash plumes that rose several kilometers above the vent. B) Incandescence and lava fountaining seen from offshore. Courtesy of Christopher Lagisa.

Figure 22. Photographs of an ash plume rising from Ulawun on 1 October 2019. In the right photo, lava fountaining is visible. Courtesy of Christopher Lagisa.

Figure 23. Photograph of lava fountaining and an ash plume rising from Ulawun on 1 October 2019. Courtesy of Joe Metto, WNB Provincial Disaster Office (RVO Report 2019100101).

Ash emissions began to decrease by 3 October 2019; satellite imagery and ground observations showed an ash cloud rising to 3 km altitude and drifting N, according to the Darwin VAAC report. RVO reported that the fissure eruption on the SW flank stopped on 4 October, but gas-and-steam emissions and weak incandescence were still visible. The lava flow slowed, advancing 3-5 m/day, while declining seismicity was reflected in RSAM values fluctuating around 1,000. RVO reported that between 23 and 31 October the main summit crater continued to produce variable amounts of white gas-and-steam emissions (figure 24) and that no incandescence was observed after 5 October. Gas-and-steam emissions were also observed around the new SW vent and along the lava flow. Seismicity remained low until 27-29 October; it increased again and peaked on 30 October, reaching an RSAM value of 1,700 before dropping and fluctuating around 1,200-1,500.

Figure 24. Webcam photo of a gas-and-steam plume rising from Ulawun on 30 October 2019. Courtesy of the Rabaul Volcano Observatory (RVO).

In addition to ash plumes, SO₂ plumes were also detected between September and October 2019. Sentinel-5P/TROPOMI data showed SO₂ plumes, some of which exceeded 2 Dobson Units (DU) drifting in different directions (figure 25). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed strong, frequent thermal anomalies within 5 km of the summit beginning in early October 2019 and throughout the rest of the month (figure 26). Only one thermal anomaly was detected in early December.

Figure 25. Sentinel-5P/TROPOMI data showing a high concentration of SO2 plumes rising from Ulawun between late September-early October 2019. Top left: 11 September 2019. Top right: 1 October 2019. Bottom left: 2 October 2019. Bottom right: 3 October 2019. Courtesy of the NASA Space Goddard Flight Center.

Figure 26. Frequent and strong thermal anomalies at Ulawun for February through December 2019 as recorded by the MIROVA system (Log Radiative Power) began in early October and continued throughout the month. Courtesy of MIROVA.

Activity in November was relatively low, with only a variable amount of white gas-and-steam emissions visible and low (less than 200 RSAM units) seismicity with sporadic volcanic earthquakes. Between 9-22 December, a webcam showed intermittent white gas-and-steam emissions were observed at the main crater, accompanied by some incandescence at night. Some gas-and-steam emissions were also observed rising from the new SW vent along the lava flow.

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

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/); Christopher Lagisa, West New Britain Province, Papua New Guinea (URL: https://www.facebook.com/christopher.lagisa, images posted at https://www.facebook.com/christopher.lagisa/posts/730662937360239 and https://www.facebook.com/christopher.lagisa/posts/730215604071639).

Nyamuragira (also known as Nyamulagira) is a high-potassium basaltic shield volcano located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo. Previous volcanism consisted of the reappearance of a lava lake in the summit crater in mid-April 2018, lava emissions, and high seismicity (BGVN 44:05). Current activity includes strong thermal signatures, continued inner crater wall collapses, and continued moderate seismicity. The primary source of information for this June-November 2019 report comes from the Observatoire Volcanologique de Goma (OVG) and satellite data and imagery from multiple sources.

OVG reported in the July 2019 monthly that the inner crater wall collapses that were observed in May continued to occur. During this month, there was a sharp decrease in the lava lake level, and it is no longer visible. However, the report stated that lava fountaining was visible from a small cone within this crater, though its activity has also decreased since 2014. In late July, a thermal anomaly and fumaroles were observed originating from this cone (figure 85). Seismicity remained moderate throughout this reporting period.

Figure 85. Photograph showing the small active cone within the crater of Nyamuragira in late July 2019. Fumaroles are also observed within the crater originating from the small cone. Courtesy of Sergio Maguna.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows strong, frequent thermal anomalies within 5 km of the summit between June through November (figure 86). The strength of these thermal anomalies noticeably decreases briefly in September. MODVOLC thermal alerts registered 54 thermal hotspots dominantly near the N area of the crater during June through November 2019. Satellite imagery from Sentinel-2 corroborated this data, showing strong thermal anomalies within the summit crater during this same timeframe (figure 87).

Figure 86. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira during 30 January through November 2019 shows strong, frequent thermal anomalies through November with a brief decrease in activity in late April-early May and early September. Courtesy of MIROVA.

Figure 87. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity at Nyamuragira into November 2019. Courtesy of Sentinel Hub Playground.

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); Sergio Maguna (Facebook: https://www.facebook.com/sergio.maguna.9, images posted at https://www.facebook.com/sergio.maguna.9/posts/1267625096730837).

The summit crater of Minami-dake remained active, with 14 recorded explosions in both January and February. The largest, at 1003 on 11 January and 1659 on 24 February, ejected ash to 3,000 m above the crater rim, but did not cause any damage. Monthly ash accumulation [at KLMO] was 80 g/m² in January and 144 g/m² in February.

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.

Activity was relatively quiet in the first half of January, but increased in the second half of the month. A 21 January explosion ejected blocks to 300 m above the crater rim. Additional explosions occurred at 1645 on 1 February and 1320 on 7 February, the latter continuously ejecting blocks to 300 m above the crater rim. Minor ash emission was observed almost daily, causing ashfalls around the crater. A total of 30 g/m² of ash was deposited in January and 3,167 g/m² in February at AWS. Volcanic tremor amplitude increased from the end of January, but declined toward the end of February.

A pool of water was present in Vent 892 during fieldwork on 15 February. Mud ejection was observed for the first time since September 1989. Vent 892 began to develop in October, and has gradually enlarged to occupy half of the crater floor.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: JMA.

"Mild eruptive activity continued in February. Regular reporting of observations ceased on the 12th but it appears that the more-or-less steady extrusion of viscous blocky lava continued through the month. Frequent rockfalls occurred on the W, S, and E flanks. Glow from the summit area was seen occasionally. Emissions were mostly white vapours, but grey emission clouds were reported on a few days."

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: C. McKee, RVO.

"Strong seismicity took place near Bamus during February. The seismicity started on the 2nd when almost 100 events were recorded (maximum M_L 5.8 [but see 15:3]). In the following days the activity waned, but began to increase on the 8th. Seismicity peaked between the 10th and the 15th, when ~1,400 events were recorded, including three earthquakes of M 5.8-6.0. Activity declined irregularly during the following 10 days, but began increasing again on the 25th. During the second peak of activity, between the 25th and the 28th, ~880 events were recorded including two earthquakes of M 5.0. Activity declined again at the end of the month.

"Inspections of Bamus were carried out on 13 and 16 February. Rockfalls had occurred at many places on the volcano, apparently associated with the seismicity. Temperatures in solfataric areas on the summit tholoid remained low (<15°C) however. A temporary seismograph network, operated in the area between 13 and 16 February, enabled locations of some earthquakes to be calculated. Epicenters were distributed in a 10-km-long NNE-trending zone that included the S flanks of Bamus. Focal depths ranged between 0 and 23 km. The seismicity was continuing in early March and was being monitored primarily by the permanent seismograph at Ulawun Volcano."

Geologic Background. Symmetrical 2248-m-high Bamus volcano, also referred to locally as the South Son, is located SW of Ulawun volcano, known as the Father. These two volcanoes are the highest in the 1000-km-long Bismarck volcanic arc. The andesitic stratovolcano is draped by rainforest and contains a breached summit crater filled with a lava dome. A satellitic cone is located on the southern flank, and a prominent 1.5-km-wide crater with two small adjacent cones is situated halfway up the SE flank. Young pyroclastic-flow deposits are found on the volcano's flanks, and villagers describe an eruption that took place during the late 19th century.

Information Contacts: C. McKee, RVO.

"Geologists from Florida International University and the Universidad de Colima visited the central crater and dome complex on 3 and 7 March. Fumarole temperatures have decreased dramatically in fractures just below the summit dome. The maximum temperature recorded in upper NE flank fractures was 100°C, down from 895°C in December 1985. The plume was much smaller during the 1990 visit, and no new tephra was found in the summit area.

"Temperatures of three fumaroles on the summit lava dome were measured at 3-minute intervals for about 4 days (figure 7). Surface temperatures were monitored simultaneously. The three measured fumaroles, on the SW side of the dome, had the highest temperatures found.

Figure 7. Temperature profiles at three fumaroles (channels 2-4) and surface temperatures (channel 1) on the SW side of Colima's summit lava dome, 3-7 March 1990. Note the differing temperature scales. Courtesy of C. Connor.

"Two fumaroles (channels 3 and 4 on figure 7), located in the same fracture ~ 10 m apart, had a similar temperature range and showed a high degree of cross-correlation. The fracture trended about N70°E and extended for at least 200 m across the summit dome. Its maximum width was ~ 15 cm. The third fumarole (channel 2) was in a different fracture, oriented about E-W and about 6 m from the channel 4 fumarole. Channel 2 data were quite rhythmic, showing minimum temperatures each day about 1200, followed by maximums around 1830. This fumarole had a maximum temperature of 571°C on 5 March at 1827. One of 11 local earthquakes recorded (by CICBAS) during the sampling period occurred the same day at 1826. Channels 1 (surface temperature) and 2 retained relatively high temperatures after this event for the remainder of the sampling period, while channels 3 and 4 remained comparatively steady."

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: C.B. Connor, Florida International University, Miami; J. Piza Espinosa, Universidad de Colima.

After the May 1989 activity, geologists performed aerial and field investigations at the request of local authorities. They forecast that vigorous fumarolic activity and rare weak explosions would continue through August, and this assessment was printed in the regional newspaper Suvorovsky Natisc on 15 June 1989, 4 days before the June eruption. Moderate fumarolic activity continued in June.

Seismic activity in a 100-m-wide zone extending NE across the volcano had increased March-May 1989. According to R.Z. Tarakanov, the earthquakes were at 30 and 60 km depths.

Aerial observations in August revealed a new group of fumaroles in the NNE part of the dome. During their 16 September ascent of the dome, Steinberg and Tkachenko measured gas temperatures of 100-104°C. Deep, narrow, craters had formed at the intersections of en-echelon fissures, and the surface around them was covered by andesitic ash (table 1). It is not yet known if the material was juvenile.

Table 1. Chemical analyses of ash samples collected from fissures in Ivan Grozny's summit dome. Analytical values are volume percent of dry gas. Courtesy of G. Steinberg.

Fumarolic activity was distributed along the summit crater fissure. Before the May explosions, emissions had been observed over the entire cross-section of the crater's fissure and on the E slope of the dome. No fumarolic activity was observed in August on the E outer slope of the dome, only from its uppermost W portion. The floor of the E part of the crater was covered with 30 cm of ash but exhibited no fumarolic activity.

At the request of the local authorities, geologists forecast (and published in the local newspaper Krasny Mayak on 28 September) that the volcano's activity should continue at its present level through February 1990.

Geologic Background. Etorofu-Yakeyama (Ivan Grozny), is located in the center of Iturup Island. It has a 3-3.5 km diameter caldera that is open to the south, where the large extrusive andesitic dome was emplaced. Several other lava domes of Holocene age were constructed to the NE; extrusion of these domes has constricted a former lake in the northern side of the caldera to an extremely sinuous shoreline. Historical eruptions, the first of which took place in 1968, have been restricted to Etorofu-Yakeyama.

Information Contacts: G. Steinberg and R. Bulgakov, Yuzhno-Sakhalinsk.

Both short- and long-period seismic events were recorded in the months preceding the eruption. Most were located below the summit, with some below the volcano's E flank (Grandes Pentes area). Three seismic swarms, each with >25 shocks, occurred in September and October, but no deformation or surface changes were noted. The number of seismic events (figure 21) increased in the days before the eruption, with 32 and 69 shocks recorded on 16 and 17 January respectively, centered below the N flank of Dolomieu Crater (figure 22).

Figure 21. Seismic events at Piton de la Fournaise, 10-20 January 1990.

Figure 22. Epicenter map showing times of located earthquakes (top) and cross-section showing focal depths of the same earthquakes (bottom) during the 17-18 January 1990 pre-eruption seismic crisis at Piton de la Fournaise. 17 January events are labeled in italics, 18 January events in regular type.

The eruptive crisis began at 0322 with a 4-5-minute swarm of 33 events. Seismicity then decreased until 1036, when a new swarm of short-period earthquakes (lasting 2-5 seconds with events ~15 seconds apart) was recorded. Deformation (figure 23) was observed from 1032 until 1052 at the Soufrière and Dolomieu tilt stations (7 and 19 µrads respectively), suggesting inflation centered on Dolomieu Crater. An 11-second shock was detected at 1048, followed by a new swarm recorded by the summit stations. Numerous collapses of the Dolomieu crater rim were observed, especially on the NE rim. From 1052 to 1112 a clear deflation pattern (45 µrads) through Dolomieu Crater was detected by the Soufrière tiltmeters, whereas the Dolomieu tiltmeters (on the S edge of Dolomieu Crater) suggested tilt towards the SW. Events of the second swarm were at first generally centered below Dolomieu's NE flank (1038-1042), then succeeding events moved below the SE flank. All were very shallow, the deepest ~1 km asl.

Figure 23. Deformation data from the continuously recording Soufriere tiltmeter at Piton de la Fournaise, 18 February 1990. Numbers correspond to the following phases of the activity: 1) Seismic swarm; onset of inflation, centered below Dolomieu crater. 2) Beginning of magma injection. 3) Beginning of tremor. 4) Lava output. 5) Beginning of fissure migration towards the N. Deformation values in the text have been corrected for temperature effects.

Tremor appeared at 1112 on summit stations, with discrete shocks continuing until 1120. Maximum tremor intensity occurred at approximately 1124, while Soufrière tiltmeters recorded a 58 µrad tilt toward the NNW, and Dolomieu tiltmeters recorded a >100 µrad tilt toward the NE. These seismic and deformation signals coincided with the opening of an eruptive fissure in Dolomieu Crater, seen at 1124 by geologists making distance measurements in the summit area.

The fissure trended roughly N170°E, feeding vigorous lava fountains ~30 m high, and mainly aa flows that covered roughly 20% of Dolomieu's crater floor. The fissure rapidly propagated S towards Dolomieu's crater rim, then towards Maillard crater (figure 24). Lava fountains also occurred from the fissure extension, and lava emerged from the base of Maillard crater. After reaching Maillard Crater, the fissure progressively migrated NNW within Dolomieu Crater, to near the N crater rim. Fissure migration was accompanied by local SW tilting, recorded by the Soufrière station, whereas no significant motion was detected by Dolomieu tiltmeters. Eruptive spatter cones were aligned along this section of the fissure, which produced strong gas emissions and ejected lava fragments. Tremor remained at a significant level until 1730, then progressively decreased. Another seismic swarm occurred at 0244 before tremor ceased completely at 0630 on 19 January.

Figure 24. Sketch map of the summit area at Piton de la Fournaise, showing the lava flows, main fractures, and the approximate positions of the Soufriere and Dolomieu tilt stations.

During this brief eruption (~17 hours), <1 x 10⁶ m³ of aphyric lava was emitted, with a mean calculated lava output rate of ~14 m³/s. Geologists noted that geodetic measurements could be interpreted in terms of an E-dipping dike injection.

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: J. Toutain and P. Taochy, OVPDLF; P. Bachelery, Univ de la Reunion; J-L. Cheminée, IPGP. Field observations are fromP. Kowalski, A. Mussard, P. Piquemal, and P. Taochy (OVPDLF); P. Mairine, and A. Talibart.

Seismicity was at low-moderate levels in February, although substantial seismic energy was released by high-frequency events. The earthquakes were concentrated 2.5 km W of, and beneath the summit crater at 2.5-5.0 km depths (figures 15 and 16). Ash emissions were associated with spasmodic tremor on 3, 8, and 27 February. SO₂ emissions reached 5,374 t/d on 10 February, the highest value measured since late October.

Figure 15. Epicenters of 92 high-frequency earthquakes at Galeras, February 1990. Courtesy of INGEOMINAS.

Figure 16. E-W cross-section at Galeras, showing focal depths of the 92 high-frequency earthquakes in figure 15. Courtesy of INGEOMINAS.

Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.

Information Contacts: INGEOMINAS, Pasto.

An eruption hiatus [see also Addendum to 15:01] began on 5 February at about 2000, when . . . tremor near Kupaianaha lava pond decreased to about half its previous level. A peak in long-period caldera seismicity of almost 200 events/day had been recorded on 4 February, but the number of these events had fallen to < 20/day by the 7th. By 6 February, the terminus of the 13 January 1990 flow (figure 66) was stagnant, with only minor activity upslope. A rockfall near the ocean entry was recorded . . . at 1319 on 6 February, and background tremor in that area has remained low since then. By the 7th, only 10-20% of the normal lava output at the Poupou ocean entry was flowing into the sea. On the 8th and 9th, only small pahoehoe lobes were active around crusted lava in Kupaianaha lava pond and the Poupou ocean entry was generally stagnant.

Renewed activity was signaled by a sharp increase in summit microearthquakes on 9 February at 0900-1000 that continued for 8 hours, with >150 events registered on the Kilauea caldera station (NPT). From 1400 to 1500 the number of earthquakes in the upper and middle East rift zone rose significantly, remaining high until seismicity decreased to moderate levels at 2200. Strong glow from Pu`u `O`o was observed that night, and by the next morning, vigorous surface activity had resumed. Active lava had returned to Pu`u `O`o, the level of Kupaianaha had risen to 20 m below the rim, and lava had reoccupied the tube system as far as 560 m (1,850 ft) elevation. A surface lava breakout at 590 m (1,950 ft) elevation fed a flow that contained ~1/3 of the lava output from Kupaianaha pond. Lava flowed into the Royal Gardens subdivision (along Queen St.), destroying two houses and narrowly missing several others. By the end of the month, its terminus had stagnated, but small breakouts continued above the fault scarp at ~180 m (600 ft) elevation. Another major surface flow emerged from the tube at the 560 m elevation and split into three lobes. The main (Quarry) lobe flowed along the E side of of the 1988 Quarry flow (figure 66), entered the ocean on the 20th at 2340, and built a 500 x 100 m bench by the end of the month. The second (Roberts) entered the ocean on the 23rd at 0500, ~600 m SW of the main lobe's entry, building a small bench. To the E, the third, low-volume lobe (Keone) flowed through grassland, and by the end of the month was < 1 km from houses and a highway near the town of Kalapana. All lobes remained active by the end of February.

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 and P. Okubo, HVO.

Volcanic tremor began at about 1445 on 27 January and continued through 1 February. The largest amplitude was about 0.2 µm. A field survey on 2 February found no new ash deposition around the crater. Water discoloration in Yugama crater lake was observed as usual.

Volcanic tremor resumed at 0019 on 12 February and continued until 0417 the next day. Additional tremor episodes occurred on 18 and 24 February. Amplitudes of 1.3 µm on 18 January and 1.1 µm on 24 February were the highest recorded since the last eruption in 1982-83. The number of discrete volcanic earthquakes also increased between 17 February and 7 March.

Geologic Background. The Kusatsu-Shiranesan complex, located immediately north of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid-Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the E, S, and SW flanks. The latest eruptive stage began about 14,000 years ago. Historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.

Information Contacts: JMA

"Moderate vapour and ash emissions continued at Crater 2. Ashfalls were mainly in uninhabited areas SE of the volcano, but on one occasion there was a fine ashfall ~10 km to the NW. Weak red crater glow was often seen at night. Seismicity was generally at a low level. Vulcanian explosion earthquakes were occasionally 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 eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north 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 of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: C. McKee, RVO.

An explosive episode on 20 February at 1545 ejected an eruption column that contained large amounts of water vapor and some tephra. Gentle winds during the activity allowed a large plume to develop, reaching ~8 km above the crater (almost 14 km altitude; figure 4). The activity appeared to be phreatomagmatic (but see comment by González-Ferrán below), consisted of only a single pulse [but see 15:03], and lasted for ~5 minutes. Near-summit winds shifted the plume slightly southward, then high-altitude winds carried away the upper part of the plume to the south. The plume had completely dispersed 30 minutes after the eruption. No felt pre-eruption seismicity was reported. Sounds from the explosion were reported to ~150 km from the volcano. Eruption-related noises were heard 40 km SW of the volcano (by Stephen Foot) at 1547, and windows rattled at Toconao, 32 km NW. As of 16 March, no new major eruptions have been reported, and the volcano has continued to show its normal fumarolic activity.

Figure 4. Sketch of Lascar and its 20 February 1990 eruption column by O. González-Ferrán, based on a photo taken by policeman Raul Orellana from Toconao (32 km NW of the volcano) 3 minutes after the onset of the explosion.

With the support of the Chilean Air force, Oscar González-Ferrán carried out an aerial and ground investigation between 22 and 26 February. During aerial reconnaissance on 24 February between about 0800 and 0900, an active lava dome remained in the crater. Numerous incandescent radial and concentric fractures were visible on the dome, and strong gas emission was occurring. Fieldwork on 24 and 25 February between Tumbre (N of the volcano) and Laguna de la Legia to ~5,400 m altitude on the SE flank, revealed that numerous blocks from the dacitic lava dome had been ballistically ejected to distances of as much as 5 km (figure 5). The blocks ranged from 0.5 to 1.5 m³ and formed impact craters as much as 4 m across and 1 m deep. Sotero Armella, president of the Residents' Council of the town of Talabre (11 km NW of Lascar) noted that large ballistic tephra had not been ejected this far during the 1986 and 1988 activity.

Figure 5. Oblique aerial view by O. González-Ferrán, looking W at the Lascar complex and the area to the N and W. Vapor rises from the active crater. Ballistic blocks from the dacitic lava dome were found at sites marked "B".

Stephen Foot conducted additional fieldwork on 11 March. On the SSE flank, he found bombs within 4 km of the crater and lapilli at greater distances. Bombs had formed craters up to 4 m wide and 1.5 m deep. Three types of bombs were sampled: dark, dense, glassy, crystal-rich, possibly dacitic material; light gray pumiceous fragments; and less abundant white, dense, crystal-rich, mafic-poor, weakly aligned tephra that may not have been juvenile. The tephra were found both intact and shattered, showing breadcrust texture and cooling fractures. No evidence of new tephra was found on the W flank, 16 km from the crater.

González-Ferrán noted that analyses of vertical airphotos, video, and field reconnaissance suggest that: 1) the rate of extrusion of the dacitic lava dome has increased; 2) the weakest sector of the volcano is its NW wall, so the hazard from a possible lateral explosion is greatest in that direction; and 3) the 20 February explosion was primarily from magmatic degassing rather than phreatomagmatic activity, given the long drought that has affected the area. He added that the village of Talabre (population 76, 40 of whom are children), relocated at its present site on 25 April 1985, is in the direction of highest estimated risk.

Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Information Contacts: O. González-Ferrán, Univ de Chile; S. Foot, MINSAL Ltd., Santiago; J. Gerneck, Chile Hunt Oil, Toconao; M. Gardeweg, SERNAGEOMIN, Santiago.

Seismicity has continued a systematic increase along the S margin of the resurgent dome. Swarms occurred on 4 and 14 Febuary, the latter containing >100 located events, one reaching M 3. Another swarm on 27-28 February contained several of M >2, and on 3 March more than 200 shocks were recorded, the largest at M 2.8. In the two weeks following the 3 March swarm, seismic activity remained relatively quiet, with a few days having as many as ten recorded events. Depths remained between 8 and <3 km. The 2-color geodimeter system has continued to detect enhanced strain rates of ~5 microstrain/year since September. On the SW rim of the caldera, Mammoth Mountain was generally quiet, although a series of events occurred there on 6 March, the largest reaching M 1.7.

Geologic Background. The large 17 x 32 km Long Valley caldera east of the central Sierra Nevada Range formed as a result of the voluminous Bishop Tuff eruption about 760,000 years ago. Resurgent doming in the central part of the caldera occurred shortly afterwards, followed by rhyolitic eruptions from the caldera moat and the eruption of rhyodacite from outer ring fracture vents, ending about 50,000 years ago. During early resurgent doming the caldera was filled with a large lake that left strandlines on the caldera walls and the resurgent dome island; the lake eventually drained through the Owens River Gorge. The caldera remains thermally active, with many hot springs and fumaroles, and has had significant deformation, seismicity, and other unrest in recent years. The late-Pleistocene to Holocene Inyo Craters cut the NW topographic rim of the caldera, and along with Mammoth Mountain on the SW topographic rim, are west of the structural caldera and are chemically and tectonically distinct from the Long Valley magmatic system.

Information Contacts: D. Hill, USGS Menlo Park.

"Activity remained at a low level in February. Emissions from both summit craters consisted of white vapours in weak to moderate amounts. Weak, deep rumbling noises from Southern Crater were heard occasionally between 18 and 24 February. There were no sightings of summit crater glow. Seismicity remained low. Daily volcanic earthquake totals ranged between 1,000 and 1,100, and amplitudes were small. A progressive inflationary tilt of ~2 µrad accumulated during February."

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 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche 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 historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical 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: C. McKee, RVO.

Activity had been limited to degassing from fumaroles since the March 1989 eruption. Moderate steam emissions and a rumbling noise were noted during a summit climb on 29 November. Deep rumbling noises and a weak red glow within the crater were reported by nearby residents at the beginning of January, and geologists observed gas bursts and Strombolian spattering during 4 January fieldwork. Observation trips on 27 January and 4 February revealed a growing cone on the floor of MacKenney Crater, with intermittent explosive activity that occurred every 2-5 minutes.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: A. MacKenney, Guatemala City.

February activity was characterized by intermittent geyser-type phreatic eruptions from the center of the hot crater lake, reaching maximum heights of 2-3 m. Sulfur emissions from a vent in the NE part of the lake coated the crater wall, coloring it light yellow. The crater lake has been enriched in sediments transported by surface erosion. As evaporation has exceeded input from precipitation, the level of the lake has continued to fall.

Seismicity increased slightly in February. A total of 9,460 events were recorded the first 27 days of the month, a mean of 350/day. Most of the events were B-type, with some A-type shocks and brief tremor episodes.

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: Mario Fernández and Hector Flores, Univ de Costa Rica.

"A further decline in activity was evident in February. The total number of caldera earthquakes recorded in February was 161. Daily earthquake totals ranged between 0 and 17. The earthquakes occurred on the NE and NW-SW parts of the caldera seismic zone. The strongest was an M_L 3.1 event from the SW part of the zone on the 28th. Levelling measurements on the Rabaul Town-Matupit Island line carried out on 20 February indicated little or no change since the previous measurements (9 January)."

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: C. McKee, RVO.

Strong explosions separated by periods of lava dome growth continued into March (table 1). Frequent seismicity, centered on Redoubt from the surface to about 10 km depth, has continued since mid-December (figure 6). Information about the 15 and 21 February explosive episodes supplements the initial reports in 15:01.

Table 1. Strong explosive episodes and periods of lava extrusion during Redoubt's 1989-90 eruption, modified extensively from the original table with data from Brantley (1990). See Alaska Volcano Observatory, 1990, for a more detailed tabular summary of activity through January.

Figure 6. Epicenter map top and depth vs. time plot bottom, of earthquakes recorded near Redoubt by AVO, 12 December 1989-11 March 1990. Squares on the epicenter map mark positions of seismic stations. Station RDN, a few kilometers N of the summit, is obscured by numerous earthquake symbols. Courtesy of John Power, AVO.

Explosive episode, 15 February; deposits and morphologic changes. Fieldwork after the episode revealed changes in the vent area, and pyroclastic flow, surge, and lahar deposits. The explosion had removed about 75% of the dome, leaving only a steep remnant of its W portion. The concentrically fissured icewall S of the vent appeared unchanged and remained steep. Steam from vigorous fumaroles obscured the vent area and the north gorge, a steep gully that had been cut into the upper Drift Glacier. Heavy ashfall had occurred over a broad area of the NNW to W flanks within 5-6 km from the vent, and airfall tephra was also evident to 6-8 km S and 20 km E to ENE of the vent. On the NNW flank, snow avalanches or slush flows moved across snow-covered glaciers and into gullies W of those affected by earlier explosions. A sheet flood of slush flows traveled NE and E from the summit, entering the Drift River from a small valley (E of Drift Glacier) also unaffected by previous explosions. A pyroclastic surge had spread N across the Drift Glacier to the crest of a steep ridge 750-900 m above the glacier's toe. The deposit near the ridge crest, 1-8 mm thick, was dominated by sand-sized andesite fragments with occasional pebble-sized grains. In a creek valley NE of the ridge, the deposit was coarser (very angular, coarse sand-sized andesite grains) and thicker (4-8 mm). The deposit also included willow branches to 8 cm in diameter and 1.5 m long, slightly scorched and thrust as much as 1 m into the snow. The surge was diverted eastward by the ridge, depositing dark material against another ridge 4-5 km to the NE, in a zone from about 450 to 850 m altitude. The base of this zone was about 300 m above the valley floor. The surge destabilized snow on steep sides of S- and SW-facing valleys, triggering snow avalanches (some ash-rich) and slush flows.

Drift Glacier was mantled by a deposit of poorly sorted, massive, pebbly, medium sand-sized, pyroclastic flow material. The deposit ranged from a few centimeters thick on slopes to considerably more on flat areas, and appeared to be concentrated on the E half of the glacier. Portions of the deposit that were more than 20 cm thick were loose, easily fluidized, and hot (230°C at 20 cm depth measured at one site 9 hours after the eruption). Flooding had wet the top 10-15 cm of the deposit in gullies. The glacier itself was much more deeply gullied than it had been after the 8 January explosion, with many large ice blocks partially detached from the glacier surface.

The pyroclastic flow(s) and surge fed a mixed flood of water and pyroclastic debris that caused considerable erosion of the glacier and the banks of the Drift River (W of the glacier's Piedmont Lobe). Most of the debris was sand-sized, but included clasts (some juvenile) up to 1 m in diameter, plus clear ice from Drift Glacier and large amounts of snow from the glacier and valley. Hot andesitic dome rocks were found as much as 37 km from the dome (30 km from the glacier). The flow was apparently very water-rich for its entire length, which extended 33-35 km from the glacier to the oil facility at the mouth of the Drift River. Heights of overtopped banks suggested that the flow was 5 m or more deep in the gully on the E side of the glacier and was still 1-2 m deep in the lower valley. A zone of snow blocks 1-8 m wide marked flow margins.

Flow characteristics were detailed from field evidence. The W portion of the flow moved as much as 15-20 m up a valley moraine, and energy calculations suggested a minimum velocity of 60-70 km/hour. About halfway down the valley, flow speed had apparently slowed to less than 30 km/hour, while evidence of splashing against the valley wall indicated considerable turbulence. Although the flow filled most portions of the valley from wall to wall, islands were left in wider sections, suggesting a maximum discharge less than that on 2 January. Below the canyon mouth, some of the peak flow followed the old Drift River channel, but most went into Rust Slough, a relatively low-capacity stream. Muddy water from Rust Slough entered the oil facility roughly 4 hours after the onset of the eruptive episode, flooding a larger area than on 2 January, but caused no major damage. Some water seeped through (but did not flow over) the southernmost tank's containment dike, and did no apparent damage.

Small pyroclastic flows and dome growth, 15-20 February. A pyroclastic flow moved about halfway down the Drift Glacier's north gorge on 15 February between about 1450 and 1505. Gas jetting had been audible about 30 minutes earlier, and an abrupt 40% increase in stream discharge preceded the pyroclastic flow by about 15 minutes. An overflight on 18 February revealed that a small new lava dome was growing in the previously active vent. Geologists observed another pyroclastic flow, triggered by dome collapse, that moved down the gorge on 20 February at 1338. A dark ash plume rose from the flow to about 3.5-4.5 km altitude, depositing a small amount of ash to the ENE. A similar but larger episode was seen from the Drift River oil facility at about 0600, accompanied by a plume and lightning. Steaming pyroclastic flow deposits in the gorge extended to about 700 m altitude, and fresh ash ENE of the vent, primarily from the early morning episode, lay on snow that had fallen 16-17 February.

Explosive episode, 21 February. An explosion that produced a large steam and ash plume accompanied by thunder and lightning began at 0032 and lasted for about 12 minutes. Ash deposits appeared thick NE of the volcano. Ashfall was reported at Kenai (80 km E), Hope (175 km ENE), and Girdwood (200 km ENE), and significant ashfall at the Drift River oil facility prevented evacuation of its crew. Both the Drift River and Rust Slough were bank-full before the activity began, but much less additional stream flow was generated by this explosive episode than on 15 February and only minor flooding resulted, without reported damage or injuries. The small dome that had been growing in the crater was partially destroyed by the explosion. Some pyroclastic flow deposits were visible on the glacier near the gorge.

Explosive episode, 24 February. Seismic stations near Redoubt began to record a strong signal associated with explosive activity at 0505. Amplitude increased sharply after 45 seconds, saturating instruments 8 km S and 11 km NW of the volcano for 3 1/2 minutes, then gradually decreased for 10-12 minutes. Seismicity had returned to background after 15-20 minutes. A steam and ash column rose to about 9 km altitude, accompanied by thunder and lightning. Heavy weather clouds prevented observations by satellites, but ashfall was reported along a narrow zone extending NE from the volcano. At the Beluga power plant (130 km NE of Redoubt), the main power source for Anchorage, light ashfall began at about 0630 and heavy ashfall 30 minutes later. All but one of its gas turbines were shut down to prevent damage. Ashfall stopped at Beluga by 0935, and was reported farther NE of Redoubt at Alexander (150 km from Redoubt, before 0935), Willow (200 km NE, 0800-0945), Kashwitna (210 km NE, 0930), and Montana (230 km NE, well before midafternoon). Water in Rust Slough, W of the Drift River oil facility, abruptly rose 2/3-1 m at 0915, then stabilized and began to recede after about 15 minutes. A second crest, at 1015, flooded the S half of the oil facility's runway. Helicopter observations suggested that about 30% of the Drift River/Rust Slough channel was occupied during peak flow. Aerial observations revealed that another small lava dome had begun to grow in the active vent after the 24 February explosion.

Explosive episode, 28 February. Seismic data indicated that explosive activity began at 0846, continued at a relatively low level for about 10 minutes, paused, then resumed more vigorously at 0947. During the initial pulse, no ash rose above the tops of weather clouds at 6-8 km altitude. Ash was reported at 11 km altitude within 9 minutes of the onset of the much stronger second pulse. Satellite data showed a cloud about 25 km across extending ENE from Redoubt at 1000, as ashfall was beginning on oil platforms in the Cook Inlet. Light ashfall had begun in the Anchorage area, roughly 170 km ENE of Redoubt, by 1130, and was reported at Talkeetna (about 250 km NE), Fort Richardson (NE of Anchorage), the Prince William Sound area (roughly 300 km E), and the Copper River basin (roughly 450 km NE). By 1400, infrared imagery showed a cloud about 120 km long and 100 km wide moving rapidly ENE, nearly 600 km from the volcano. A seismometer near the Drift River recorded 2 apparent flow events, the first associated with the initial pulse, the second, much larger, with the stronger second pulse. Significant flooding was anticipated for the lower Drift River, but instead, its flow declined somewhat. During field work several days later, deposits from numerous pyroclastic flows were found on the Drift Glacier, some of which may have temporarily blocked the main N flank drainage channel on the glacier. Such blockage, if any, had ended by 4 March.

Explosive episode, 4 March. A large explosive eruption occurred at 2039. An airplane pilot reported that the eruption cloud had reached about 12 km altitude 30 minutes after the onset of the activity. The cloud moved N, and ashfall was reported about 30 km NNE of the volcano. By 2330, infrared imagery from the GOES satellite showed a cloud about 55 km (W-E) x 50 km (N-S) 325 km N of the volcano. Comparison of the satellite-derived cloud temperature with radiosonde temperature profiles from Anchorage 8 1/2 hours earlier suggested an altitude of about 12.5 km for the top of the dense portion of the cloud. Increased water flow, but no flooding, was reported from the Drift River oil facility. [See also 15:3].

Explosive episode, 9 March. An explosion at 0951 ejected an ash-poor plume that reached about 10.5 km altitude, accompanied by lightning. The explosion was slightly larger than those of 21, 24, and 28 February, and 4 March, but significantly smaller than the 15 December, 2 January, and 15 February episodes. At 1108, a satellite image showed a plume about 90 km across (E-W), extending N and W from the volcano (figure 7). Ash fell to the W and NW, as much as 55 km from the volcano (in the Lake Clark Pass area). Flooding occurred in the Drift River, and water flowed into small streams just to the S (Rust Slough and Cannery Creek), but no water penetrated dikes protecting the Drift River oil facility. The activity was preceded by a magnitude 5.5 earthquake centered 82 km below Redoubt. Shallow seismicity remained elevated for 3-4 hours after the explosion, then declined, but remained above background level. By the next day, a small dome was again being extruded from the summit vent, and seismic data indicated continued dome growth through 13 March. [See also 15:3].

Figure 7. Image from the NOAA 10 polar orbiting satellite on 9 March at 1108, showing a bright white plume extending W and N from Redoubt. The plume's longest (E-W) dimension is about 90 km. Courtesy of G. Stephens.

Explosive episode, 14 March. Explosive activity began at 0947, ejecting a plume to 12 km altitude that was also accompanied by lightning. There was little or no ash in the upper portion of the plume. Seismic data suggested that the explosion was slightly more vigorous than on 9 March, but the plumes appeared similar. Most of the ashfall occurred E and NE of the volcano on the W side of Cook Inlet. Traces of ash were reported on the Kenai Peninsula and in the Anchorage area. Satellite data at 1030 showed a plume moving ENE. The satellite-derived temperature of the dense portion of the plume was -40°C, corresponding to an altitude of about 7 km. Moderate flooding occurred in the lower Drift River, and some water was again diverted into Rust Slough and Cannery Creek. Water did not enter the oil facility, where 90,000 gallons of oil had leaked through a defective or open valve on 10 March. The oil had been confined by a containment dike, and most had been cleaned up by the time of the 14 March activity. [See also 15:3].

Geologic Background. Redoubt is a glacier-covered stratovolcano with a breached summit crater in Lake Clark National Park about 170 km SW of Anchorage. Next to Mount Spurr, Redoubt has been the most active Holocene volcano in the upper Cook Inlet. The volcano was constructed beginning about 890,000 years ago over Mesozoic granitic rocks of the Alaska-Aleutian Range batholith. Collapse of the summit 13,000-10,500 years ago produced a major debris avalanche that reached Cook Inlet. Holocene activity has included the emplacement of a large debris avalanche and clay-rich lahars that dammed Lake Crescent on the south side and reached Cook Inlet about 3,500 years ago. Eruptions during the past few centuries have affected only the Drift River drainage on the north. Historical eruptions have originated from a vent at the north end of the 1.8-km-wide breached summit crater. The 1989-90 eruption had severe economic impact on the Cook Inlet region and affected air traffic far beyond the volcano.

Information Contacts: AVO Staff; SAB; UPI; AP; Reuters.

Eruptions and vigorous upwellings continued throughout January, with the latest episodes reported on 23-26 and 31 January. The lake temperature continued to rise, from 27°C on 11 January to 46.7°C on 1 February. No significant changes in lake chemistry, deformation, or seismicity were observed.

During fieldwork on 26 January, the lake was battleship gray and visibly convecting from the central and N vents, which were surrounded by black and yellow slicks, respectively. Water temperature was 42.1°C (at the outflow). Within 4 hours, geologists witnessed five episodes of phreatic activity at the central vent. A 1-2-m updoming of the lake surface occurred at 1232. Two minutes later, a vigorous steam eruption ejected a dark gray, 5-m, superheated steam plume, 4 m in diameter. A 30-minute eruption at 1332 was followed by a small, 25-second, audible upwelling. The largest eruption, at 1519, ejected a 25-m-wide superheated column to ~30 m, cored by black, suspension-laden fluid. The diffuse steam column rose several hundred meters. Water surged onto the lake shore, washing ~3.0 m above the outlet.

Crater Lake appeared similar when next visited on 1 February. One small phreatic episode at about 1153 produced upwelling to ~10 m above the lake surface, followed by a decrease in lake outflow. The maximum temperature measured by thermocouple was 46.7°C (at the outlet).

Seismicity was generally typical of recent Crater Lake heating episodes. Continuous, moderate to strong, 2-Hz and occasional 1-Hz tremor was recorded through early February. Small high-frequency earthquakes sometimes accompanied eruptions but appeared unrelated to the activity. No discrete volcanic earthquakes were recorded.

Geologists noted that characteristics of the current lake heating episode were slightly different from those of the early 1980's. Although the lake has reached its highest temperature since 1982, Mg/Cl ratios have persistently declined, suggesting continuous introduction of HCl into the lake, with little or no exposure of fresh rock to reactive vent fluids. The present low deformation is consistent with an open vent situation and suggests no recent intrusion of magma.

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The 110 km3 dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: B. Christenson, DSIR Wairakei; B. Scott, NZGS Rotorua.

Seismic energy release and the number of earthquakes were at low levels in February. A swarm of low-energy, high-frequency events occurred NW of Arenas crater at 6.5 km depth on 7 February. Pulses of low-energy tremor were also detected. The average measured dry-tilt change in February was only 4 µrad. Variations in electronic tilt (at the Refugio station) were associated with tremor (1.5-2.0 km depth) 14-16 February.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.

"Activity continued at a low level in February. The summit crater emitted white and blue vapours in weak to moderate amounts. An aerial inspection on 13 February showed no change in the configuration of the summit crater or in its activity. Seismicity was very low throughout the month."

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

Information Contacts: C. McKee, RVO.

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

References. Newman, S., 1997, Earthweek, a diary of the planet (week ending 12 September): syndicated newspaper column (URL: http://www.earthweek.com/).

Manila Bulletin, 4 Sept. 1997, Dante's Peak (URL: http://www.mb.com.ph/).

Simkin, T., and Siebert, L., 1994, Volcanoes of the world, 2nd edition: Geoscience Press in association with the Smithsonian Institution Global Volcanism Program, Tucson AZ, 368 p.

Information Contacts: Emmanuel G. Ramos, Deputy Director, Philippine Institute of Volcanology and Seismology, Department of Science and Technology, PHIVOLCS Building, C. P. Garcia Ave., University of the Philippines, Diliman campus, Quezon City, Philippines.

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

Information Contacts: Xinhua News Agency, 5 Sharp Street West, Wanchai, Hong Kong; Giday WoldeGabriel, EES-1/MS D462, Geology-Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545; Ayalaw Yiman, Ethiopian Embassy, 2134 Kalorama Rd. NW, Washington DC 20008.

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

References. Omlin, A, Damm, E., Mienert, J., and Lukas, D., 1999, In-situ detection of methane releases adjacent to gas hydrate fields on the Norwegian margin: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Yalciner, A.C., Borrero, J., Kukano, U., Watts, P., Synolakis, C. E., and Imamura, F., 1999, Field survey of 1999 Izmit tsunami and modeling effort of new tsunami generation mechanism: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Gold, T., 1998, The deep hot biosphere: Springer Verlag, 256 p., ISBN: 0387985468.

Gold, T., 2000, Eye-witness accounts of several major earthquakes (URL: http://www.people.cornell.edu/ pages/tg21/eyewit.html).

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

References. Devyatkin, E.V. and Smelov, S.B., 1979, Position of basalts in sequence of Cenozoic sediments of Mongolia: Izvestiya USSR Academy of Sciences, geological series, no. 1, p. 16-29. (In Russian).

Logatchev, N.A., Devyatkin, E.V., Malaeva, E.M., and others, 1982, Cenozoic deposits of Taryat basin and Chulutu river valley (Central Hangai): Izvestiya USSR Academy of Sciences, geological series, no. 8, p. 76-86. (In Russian).

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Information Contacts: Alexei V. Ivanov, Institute of the Earth Crust SB, Russian Academy of Sciences, Irkutsk, Russia; Bekhtur andM. Ulziibat, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulan-Bator, Mongolia; M. Ganzorig, Institute of Informatics MAS, Ulan-Bator, Mongolia.

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.

Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8, B-9000, Belgium; Chris Newhall, USGS, Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; The Daily Nation (URL: http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL: http://www.visituganda.com/).