Bagana volcano is found in a remote portion of central Bougainville Island in Papua New Guinea. The most recent eruptive phase that began in early 2000 has produced ash plumes and thermal anomalies (BGVN 44:06, 50:01). Activity has remained low between January-July 2019 with rare thermal anomalies and occasional steam plumes. This reporting period updates information for June-November 2019 and includes thermal anomalies and intermittent gas-and-steam emissions. Thermal data and satellite imagery are the primary sources of information for this report.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed an increased number of thermal anomalies within 5 km from the summit beginning in late July-early August (figure 38). Two Sentinel-2 thermal satellite images showed faint, roughly linear thermal anomalies, indicative of lava flows trending EW and NS on 7 July 2019 and 6 August, respectively (figure 39). Weak thermal hotspots were briefly detected in late September-early October after a short hiatus in September. No thermal anomalies were recorded in Sentinel-2 past August due to cloud cover; however, gas-and-steam emissions were visible on 7 July and in September (figures 39, 40, and 41).

Figure 38. Thermal anomalies near the crater summit at Bagana during February-November 2019 as recorded by the MIROVA system (Log Radiative Power) increased in frequency and power in early August. A small cluster was detected in early October after a brief pause in activity in early September. Courtesy of MIROVA.

Figure 39. Sentinel-2 thermal satellite imagery showing small thermal anomalies at Bagana between July-August 2019. Left: A very faint thermal anomaly and a gas-and-steam plume is seen on 7 July 2019. Right: Two small thermal anomalies are faintly seen on 6 August 2019. Both Sentinel-2 satellite images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 40. A gas-and-steam plume rising from the summit of Bagana on 18 September 2019. Courtesy of Brendan McCormick Kilbride (University of Manchester).

The Deep Carbon Observatory (DCO) scientific team partnered with the Rabaul Volcano Observatory and the Bougainville Disaster Office to observe activity at Bagana and collect gas data using drone technology during two weeks of field work in mid-September 2019. For this field work, the major focus was to understand the composition of the volcanic gas emitted at Bagana and measure the concentration of these gases. Since Bagana is remote and difficult to climb, research about its gas emissions has been limited. The recent advancements in drone technology has allowed for new data collection at the summit of Bagana (figure 41). Most of the emissions consisted of water vapor, according to Brendan McCormick Kilbride, one of the volcanologists on this trip. During 14-19 September there was consistently a strong gas-and-steam plume from Bagana (figure 42).

Figure 41. Degassing plumes seen from drone footage 100 m above the summit of Bagana. Top: Zoomed out view of the summit of Bagana degassing. Bottom: Closer perspective of the gases emitted from Bagana. Courtesy of Kieran Wood (University of Bristol) and the Bristol Flight Laboratory.

Figure 42. Photos of gas-and-steam plumes rising from Bagana between 14-19 September 2019. Courtesy of Brendan McCormick Kilbride (University of Manchester).

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: 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); Brendan McCormick Kilbride, University of Manchester, Manchester M13 9PL, United Kingdom (URL: https://www.research.manchester.ac.uk/portal/brendan.mccormickkilbride.html, Twitter: https://twitter.com/BrendanVolc); Kieran Wood, University of Bristol, Bristol BS8 1QU, United Kingdom (URL: http://www.bristol.ac.uk/engineering/people/kieran-t-wood/index.html, Twitter: https://twitter.com/DrKieranWood, video posted at https://www.youtube.com/watch?v=A7Hx645v0eU); University of Bristol Flight Laboratory, Bristol BS8 1QU, United Kingdom (Twitter: https://twitter.com/UOBFlightLab).

Kerinci, located in Sumatra, Indonesia, is a highly active volcano characterized by explosive eruptions with ash plumes and gas-and-steam emissions. The most recent eruptive episode began in April 2018 and included intermittent explosions with ash plumes. Volcanism continued from June-November 2019 with ongoing intermittent gas-and-steam and ash plumes. The primary source of information for this report comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and MAGMA Indonesia.

Brown- to gray-colored ash clouds drifting in different directions were reported by PVMBG, the Darwin VAAC, and MAGMA Indonesia between June and early November 2019. Ground observations, satellite imagery, and weather models were used to monitor the plume, which ranged from 4.3 to 4.9 km altitude, or about 500-1,100 m above the summit. On 7 June 2019 at 0604 a gray ash emission rose 800 m above the summit, drifting E, according to a ground observer. An ash plume on 12 July rose to 4 km altitude and drifted SW, as determined by satellite imagery and weather models. An eruption produced a gray ash cloud on 31 July that rose to 4.6 km altitude and drifted NE and E, according to PVMBG and the Darwin VAAC (figure 17). Another ash cloud rose up to 4.3 km altitude on 3 August. On 2 September a possible ash plume rose to a maximum altitude of 4.9 km and drifted WSW, according to the Darwin VAAC advisory.

Figure 17. A gray ash plume at Kerinci rose roughly 800 m above the summit on 31 July 2019 and drifted NE and E. Courtesy of MAGMA Indonesia.

Brown ash emissions rose to 4.4 km altitude at 1253 on 6 October, drifting WSW. Similar plumes reached 4.6 km altitude twice on 30 October and moved NE, SE, and E at 0614 and WSW at 1721, based on ground observations. On 1-2 November, ground observers saw brown ash emissions rising up to 4.3 km drifting ESE. Between 3 and 5 November the brown ash plumes rose 100-500 m above the summit, according to PVMBG.

Gas emissions continued to be observed through November, as reported by PVMBG and identified in satellite imagery (figure 18). Seismicity that included volcanic earthquakes also continued between June and early November, when the frequency decreased.

Figure 18. Sentinel-2 thermal satellite imagery showing a typical white gas-and-steam plume at Kerinci on 9 August 2019. Sentinel-2 satellite image with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

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/); 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/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The long-term activity at Bezymianny has been dominated by almost continuous thermal anomalies, moderate gas-steam emissions, dome growth, lava flows, and an occasional ash explosion (BGVN 44:06). The volcano is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT. Throughout the reporting period of June to November 2019, the Aviation Colour Code remained Yellow (second lowest of four levels).

According to KVERT weekly reports, lava dome growth continued in June through mid-July 2019. Thereafter the reports did not mention dome growth, but indicated that moderate gas-and-steam emissions (figure 32) continued through November. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, based on analysis of MODIS data, detected hotspots within 5 km of the summit almost every day. KVERT also reported a thermal anomaly over the volcano almost daily, except when it was obscured by clouds. Infrared satellite imagery often showed thermal anomalies generated by lava flows or dome growth (figure 33).

Figure 32. Photo of Bezymianny showing fumarolic activity on 4 July 2019. Photo by O. Girina (IVS FEB RAS, KVERT); courtesy of KVERT.

Figure 33. Typical infrared satellite images of Bezymianny showing thermal anomalies in the summit crater, including a lava flow to the WNW. Top: 21 August 2019 with SWIR filter (bands 12, 8A, 4). Bottom: 17 September 2019 with Atmospheric Penetration filter (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

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

Information Contacts: 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/); 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).

Mayon, located in the Philippines, is a highly active stratovolcano with recorded historical eruptions dating back to 1616. The most recent eruptive episode began in early January 2018 that consisted of phreatic explosions, steam-and-ash plumes, lava fountaining, and pyroclastic flows (BGVN 43:04). The previous report noted small but distinct thermal anomalies, gas-and-steam plumes, and slight inflation (BGVN 44:05) that continued to occur from May into mid-October 2019. This report includes information based on daily bulletins from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and Sentinel-2 satellite imagery.

Between May and October 2019, white gas-and-steam plumes rose to a maximum altitude of 800 m on 17 May. PHIVOLCS reported that faint summit incandescence was frequently observed at night from May-July and Sentinel-2 thermal satellite imagery showed weaker thermal anomalies in September and October (figure 49); the last anomaly was identified on 12 October. Average SO₂ emissions as measured by PHIVOLCS generally varied between 469-774 tons/day; the high value of the period was on 25 July, with 1,171 tons/day. Small SO₂ plumes were detected by the TROPOMI satellite instrument a few times during May-September 2019 (figure 50).

Figure 49. Sentinel-2 thermal satellite imagery of Mayon between May-October 2019. Small thermal anomalies were recorded in satellite imagery from the summit and some white gas-and-steam plumes are visible. Top left: 30 May 2019. Top right: 9 June 2019. Bottom left: 22 September 2019. Bottom right: 12 October 2019. Sentinel-2 satellite images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 50. Small SO2 plumes rising from Mayon during May-September 2019 recorded in DU (Dobson Units). Top left: 28 May 2019. Top right: 26 July 2019. Bottom left: 16 August 2019. Bottom right: 23 September 2019. Courtesy of NASA Goddard Space Flight Center.

Continuous GPS data has shown slight inflation since June 2018, corroborated by precise leveling data taken on 9-17 April, 16-25 July, and 23-30 October 2019. Elevated seismicity and occasional rockfall events were detected by the seismic monitoring network from PHIVOLCS from May to July; recorded activity decreased in August. Activity reported by PHIVOLCS in September-October 2019 consisted of frequent gas-and-steam emissions, two volcanic earthquakes, and no summit incandescence.

Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://SO₂.gsfc.nasa.gov/).

Merapi is an active volcano north of the city of Yogyakarta (figure 79) that has a recent history of dome growth and collapse, resulting in block-and-ash flows that killed over 400 in 2010, while an estimated 10,000-20,000 lives were saved by evacuations. The edifice contains an active dome at the summit, above the Gendol drainage down the SE flank (figure 80). The current eruption episode began in May 2018 and dome growth was observed from 11 August 2018-onwards. This Bulletin summarizes activity during April through September 2019 and is based on information from Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG, the Center for Research and Development of Geological Disaster Technology, a branch of PVMBG), Sutopo of Badan Nasional Penanggulangan Bencana (BNPB), MAGMA Indonesia, along with observations by Øystein Lund Andersen and Brett Carr of the Lamont-Doherty Earth Observatory.

Figure 79. Merapi volcano is located north of Yogyakarta in Central Java. Photo courtesy of Øystein Lund Andersen.

Figure 80. A view of the Gendol drainage where avalanches and block-and-ash flows are channeled from the active Merapi lava dome. The Gendol drainage is approximately 400 m wide at the summit. Courtesy of Brett Carr, Lamont-Doherty Earth Observatory.

At the beginning of April the rate of dome growth was relatively low, with little morphological change since January, but the overall activity of Merapi was considered high. Magma extrusion above the upper Gendol drainage resulted in rockfalls and block-and-ash flows out to 1.5 km from the dome, which were incandescent and visible at night. Five block-and-ash flows were recorded on 24 April, reaching as far as 1.2 km down the Gendol drainage. The volume of the dome was calculated to be 466,000 m3 on 9 April, a slight decrease from the previous week. Weak gas plumes reached a maximum of 500 m above the dome throughout April.

Six block-and-ash flows were generated on 5 May, lasting up to 77 seconds. Throughout May there were no significant changes to the dome morphology but the volume had decreased to 458,000 by 4 May according to drome imagery analysis. Lava extrusion continued above the Gendol drainage, producing rockfalls and small block-and-ash flows out to 1.2 km (figure 81). Gas plumes were observed to reach 400 m above the top of the crater.

Figure 81. An avalanche from the Merapi summit dome on 17 May 2019. The incandescent blocks traveled down to 850 m away from the dome. Courtesy of Sutopo, BNPB.

There were a total of 72 avalanches and block-and-ash flows from 29 January to 1 June, with an average distance of 1 km and a maximum of 2 km down the Gendol drainage. Photographs taken by Øystein Lund Andersen show the morphological change to the lava dome due to the collapse of rock and extruding lava down the Gendol drainage (figures 82 and 83). Block-and-ash flows were recorded on 17 and 20 June to a distance of 1.2 km, and a webcam image showed an incandescent flow on 26 June (figure 84). Throughout June gas plumes reached a maximum of 250 m above the top of the crater

Figure 82. The development of the Merapi summit dome from 2 June 2018 to 17 June 2019. Courtesy of Øystein Lund Andersen.

Figure 83. Photos taken of the Merapi summit lava dome in June 2019. Top: This nighttime time-lapse photograph shows incandescence at the south-facing side of the dome on the 16 June. Middle: A closeup of a small rockfall from the dome on 17 June. Bottom: A gas plume accompanying a small rockfall on 17 June. Courtesy of Øystein Lund Andersen.

Figure 84. Blocks from an incandescent rockfall off the Merapi dome reached out to 1 km down the Gendol drainage on 26 June 2019. Courtesy of MAGMA Indonesia.

Analysis of drone images taken on 4 July gave an updated dome volume of 475,000 m3, a slight increase but with little change in the morphology (figure 85). Block-and-ash flows traveled 1.1 km down the Gendol drainage on 1 July, 1 km on the 13th, and 1.1 km on the 14th, some of which were seen at night as incandescent blocks fell from the dome (figure 86). During the week of 19-25 July there were four recorded block-and-ash flows reaching 1.1 km, and flows traveled out to around 1 km on the 24th, 27th, and 31st. The morphology of the dome continued to be relatively stable due to the extruding lava falling into the Gendol drainage. Gas plumes reached 300 m above the top of the crater during July.

Figure 85. The Merapi dome on 30 July 2019 producing a weak plume. Courtesy of MAGMA Indonesia.

Figure 86. Incandescent rocks from the hot lava dome at the summit of Merapi form rockfalls down the Gendol drainage on 14 July 2019. Courtesy of Øystein Lund Andersen.

During the week of 5-11 August the dome volume was calculated to be 461,000 m3, a slight decrease from the week before with little morphological changes due to the continued lava extrusion collapsing into the Gendol drainage. There were five block-and-ash flows reaching a maximum of 1.2 km during 2-8 August. Two flows were observed on the 13th and 14th reaching 950 m, out to 1.9 km on the 20th and 22nd, and to 550 m on the 24th. There were 16 observed flows that reached 500-1,000 m on 25-27 August, with an additional flow out to 2 km at 1807 on the 27th (figure 87). Gas plumes reached a maximum of 350 m through the month.

Figure 87. An incandescent rockfall from the Merapi dome that reached 2 km down the Gendol drainage on 27 August 2019. Courtesy of BPPTKG.

Brett Carr was conducting field work at Merapi during 12-26 September. During this time the lava extrusion was low (below 1 m3 per second). He observed small rockfalls with blocks a couple of meters in size, traveling about 50-200 m down the drainage every hour or so, producing small plumes as they descended and resulting in incandescence on the dome at night. Small dome collapse events produced block-and-ash flows down the drainage once or twice per day (figure 88) and slightly larger flows just over 1 km long a couple of times per week.

Figure 88. A rockfall on the Merapi dome, towards the Gendol drainage at 0551 on 20 September 2019. Courtesy of Brett Carr, Lamont-Doherty Earth Observatory.

The dome volume was 468,000 m3 by 19 September, a slight increase from the previous calculation but again with little morphological change. Two block-and-ash flows were observed out to 600 m on 9 September and seven occurred on the 9th out to 500-1,100 m. Two occurred on the 14th down to 750-900 m, three occurred on 17, 20, and 21 September to a maximum distance of 1.2 km, and three more out to 1.5 km through the 26th. A VONA (Volcano Observatory Notice for Aviation) was issued on the 22nd due to a small explosion producing an ash plume up to approximately 3.8 km altitude (about 800 m above the summit) and minor ashfall to 15 km SW. This was followed by a block-and-ash flow reaching as far as 1.2 km and lasting for 125 seconds (figure 89). Preceding the explosion there was an increase in temperature at several locations on the dome. Weak gas plumes were observed up to 100 m above the crater throughout the month.

Figure 89. An explosion at Merapi on 22 September 2019 was followed by a block-and-ash flow that reached 1.2 km down the Gendol drainage. Courtesy of BPPTKG.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Information Contacts: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Center for Research and Development of Geological Disaster Technology (URL: http://merapi.bgl.esdm.go.id/, Twitter: @BPPTKG); Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/, Twitter: https://twitter.com/BNPB_Indonesia); Øystein Lund Andersen? (Twitter: @OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN); Brett Carr, Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY, USA (URL: https://www.ldeo.columbia.edu/user/bcarr).

Manam is a frequently active volcano forming an island approximately 10 km wide, located 13 km north of the main island of Papua New Guinea. At the summit are the Main Crater and South Crater, with four valleys down the NE, SE, SW, and NW flanks (figure 57). Recent activity has occurred at both summit craters and has included gas and ash plumes, lava flows, and pyroclastic flows. Activity in December 2018 prompted the evacuation of nearby villages and the last reported activity for 2018 was ashfall on 8 December. Activity from January through September 2019 summarized below is based on information from the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), the University of Hawai'i's MODVOLC thermal alert system, Sentinel-5P/TROPOMI and NASA Aqua/AIRS SO₂ data, MIROVA thermal data, Sentinel-2 satellite images, and observations by visiting scientists. A significant eruption in June resulted in evacuations, airport closure, and damage to local crops and infrastructure.

Figure 57. A PlanetScope image of Manam showing the two active craters with a plume emanating from the South Crater and the four valleys at the summit on 29 August 2019. Image copyright 2019 Planet Labs, Inc.

Activity during January-May 2019. Several explosive eruptions occurred during January 2019 according to Darwin VAAC reports, including an ash plume that rose to around 15 km and dispersed to the W on the 7th. RVO reported that an increase in seismic activity triggered the warning system shortly before the eruption commenced (figure 58). Small explosions were observed through to the next day with ongoing activity from the Main Crater and a lava flow in the NE valley observed from around 0400. Intermittent explosions ejected scoria after 0600, depositing ejecta up to 2 cm in diameter in two villages on the SE side of the island. Incandescence at both summit craters and hot deposits at the terminus of the NE valley are visible in Sentinel-2 TIR data acquired on the 10th (figure 59).

Figure 58. Real-Time Seismic-Amplitude Measurement graph representing seismicity at Manam over 7-9 January 2019, showing the increase during the 7-8 January event. Courtesy of RVO.

Figure 59. Sentinel-2 thermal infrared (TIR) imagery shows incandescence in the two Manam summit craters and at the terminus of the NE valley near the shoreline on 10 January 2019. Courtesy of Sentinel-Hub Playground.

Another explosion generated an ash plume to around 15 km on the 11th that dispersed to the SW. An explosive eruption occurred around 4 pm on the 23rd with the Darwin VAAC reporting an ash plume to around 16.5 km altitude, dispersing to the E. Activity continued into the following day, with satellites detecting SO₂ plumes on both 23 and 24 January (figure 60). Activity declined by February with one ash plume reported up to 4.9 km altitude on 15 February.

Figure 60. SO2 plumes originating from Manam detected by NASA Aqua/AIRS (top) on 23 January 2019 and by Sentinel-5P/TROPOMI on 24 January (bottom). Images courtesy of Simon Carn, Michigan Technological University.

Ash plumes rose up to 3 km between 1 and 5 March, and dispersed to the SE, ESE, and E. During 5-6 March the plumes moved E, and the events were accompanied by elevated seismicity and significant thermal anomalies detected in satellite data. During 19-22 March explosions produced ash plumes up to 4.6 km altitude, which dispersed to the E and SE. Simon Carn of the Michigan Technological University noted a plume in Aqua/AIRS data at around 15 km altitude at 0400 UTC on 23 January with approximately 13 kt measured, similar to other recent eruptions. Additional ash plumes were detected on 29 March, reaching 2.4-3 km and drifting to the E, NE, and N. Multiple SO₂ plumes were detected throughout April (figure 61).

Figure 61. Examples of elevated SO2 (sulfur dioxide) emissions from Manam during April 2019, on 9 April (top left), 21 April (top right), 22 April (bottom left), 28 April (bottom right). Courtesy of the NASA Space Goddard Flight Center.

During 19-28 May the Deep Carbon Observatory ABOVE (Aerial-based Observations of Volcanic Emissions) scientific team observed activity at Manam and collected gas data using drone technology. They recorded degassing from the South Crater and Main Crater (figure 63 and 64), which was also detected in Sentinel-5P/TROPOMI data (figure 65). Later in the day the plumes rose vertically up to 3-4 km above sea level and appeared stronger due to condensation. Incandescence was observed each night at the South Crater (figure 66). The Darwin VAAC reported an ash plume on 10 May, reaching 5.5 km altitude and drifting to the NE. Smaller plumes up to 2.4 km were noted on the 11th.

Figure 62. Degassing plumes from the South Crater of Manam, seen from Baliau village on the northern coast on 24 May 2019. Courtesy of Emma Liu, University College London.

Figure 63. A strong gas-and-steam plume from Manam was observed moving tens of kilometers downwind on 19 May 2019, viewed here form the SSW at dusk. Photo courtesy of Julian Rüdiger, Johannes Gutenberg University Mainz.

Figure 64. Sentinel-5P/TROPOMI SO2 data acquired on 22 May 2019 during the field observations of the Deep Carbon Observatory ABOVE team. Image courtesy of Simon Carn, Michigan Technological University.

Figure 65. Incandescence at the South Crater of Manam was visible during 19-21 May 2019 from the Baliau village on the northern coast of the island. Photos courtesy of Tobias Fischer, University of New Mexico (top) and Matthew Wordell (bottom).

Activity during June 2019. Ash plumes rose to 4.3 km and drifted SW on 7-8 June, and up to 3-3.7 km and towards the E and NE on 18 June. Sentinel-2 thermal satellite data show hot material around the Main Crater on 24 June (figure 66). On 27 June RVO reported that RSAM (Real-time Seismic Amplitude Measurement, a measure of seismic activity through time) increased from 540 to over 1,400 in 30 minutes. "Thundering noise" was noted by locals at around 0100 on the 28th. An ash plume drifting SW was visible in satellite images acquired after 0620, coinciding with reported sightings by nearby residents (figure 67). The Darwin VAAC noted that by 0910 the ash plume had reached 15.2 km altitude and was drifting SW. When seen in satellite imagery at 1700 that day the large ash plume had detached and remained visible extending SW. There were 267 lightning strokes detected within 75 km during the event (figure 68) and pyroclastic flows were generated down the NE and W flanks. At 0745 on 29 June an ash plume reached up to 4.8 km.

Villages including Dugulava, Yassa, Budua, Madauri, Waia, Dangale, and Bokure were impacted by ashfall and approximately 3,775 people had evacuated to care centers. Homes and crops were reportedly damaged due to falling ash and scoria. Flights through Madang airport were also disrupted due to the ash until they resumed on the 30th. The Office of the Resident Coordinator in Papua New Guinea reported that as many as 455 homes and gardens were destroyed. Humanitarian resources were strained due to another significant eruption at nearby Ulawun that began on 26 June.

Figure 66. Sentinel-2 thermal satellite data show hot material around the Main Crater and a plume dispersing SE through light cloud cover on 24 June 2019. Courtesy of Sentinel Hub Playground.

Figure 67. Himawari-8 satellite image showing the ash plume rising above Manam and drifting SW at 0840 on 28 June. Satellite image courtesy of NCIT ScienceCloud.

Figure 68. There were 267 lightning strokes detected within 75 km of Manam between 0729 on 27 June and 0100 on 29 June 2019. Sixty of these occurred within the final two hours of this observation period, reflecting increased activity. Red dots are cloud to ground lightning strokes and black dots are in-cloud strokes. Courtesy of Chris Vagasky, Vaisala Inc.

Activity during July-September 2019. Activity was reduced through July and September. The Darwin VAAC reported an ash plume to approximately 6 km altitude on 6 July that drifted W and NW, another plume that day to 3.7 km that drifted N, and a plume on the 21st that rose to 4.3 km and drifted SW and W. Diffuse plumes rose to 2.4-2.7 km and drifted towards the W on 29 September. Thermal anomalies in the South Crater persisted through September.

Fresh deposits from recent events are visible in satellite deposits, notably in the NE after the January activity (figure 69). Satellite TIR data reflected elevated activity with increased energy detected in March and June-July in MODVOLC and MIROVA data (figure 70).

Figure 69. Sentinel-2 thermal infrared images acquired on 12 October 2018, 20 May 2019, and 12 September 2019 show the eruption deposits that accumulated during this time. A thermal anomaly is visible in the South Crater in the May and September images. Courtesy of Sentinel Hub Playground.

Figure 70. MIROVA log radiative power plot of MODIS thermal infrared at Manam during February through September 2019. Increases in activity were detected in March and June-July. Courtesy of MIROVA.

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: 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; 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); 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/); Office of the Resident Coordinator, United Nations, Port Moresby, National Capital District, Papua New Guinea (URL: https://papuanewguinea.un.org/en/about/about-the-resident-coordinator-office, https://reliefweb.int/report/papua-new-guinea/papua-new-guinea-volcanic-activity-office-resident-coordinator-flash-2); Himawari-8 Real-time Web, developed by the NICT Science Cloud project in NICT (National Institute of Information and Communications Technology), Japan, in collaboration with JMA (Japan Meteorological Agency) and CEReS (Center of Environmental Remote Sensing, Chiba University) (URL: https://himawari8.nict.go.jp/); Simon Carn, Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA (URL: http://www.volcarno.com/, Twitter: @simoncarn); Chris Vagasky, Vaisala Inc., Louisville, Colorado, USA (URL: https://www.vaisala.com/en?type=1, Twitter: @COweatherman, URL: https://twitter.com/COweatherman); Emma Liu, University College London Earth Sciences, London WC1E 6BS (URL: https://www.ucl.ac.uk/earth-sciences/people/academic/dr-emma-liu); Matthew Wordell, Boise, ID, USA (URL: https://www.matthhew.com/biocontact); Julian Rüdiger, Johannes Gutenberg University Mainz, Saarstr. 21, 55122 Mainz, Germany (URL: https://www.uni-mainz.de/).

Tangkuban is located in the West Bandung and Subang Regencies in the West Java Province and has two main summit craters, Ratu and Upas (figure 3). Recent activity has largely consisted of phreatic explosions and gas-and-steam plumes at the Ratu crater. Prior to July 2019, the most recent activity occurred in 2012-2013, ending with a phreatic eruption on 5 October 2013 (BGVN 40:04). Background activity includes geothermal activity in the Ratu crater consisting of gas and steam emission (figure 4). This area is a tourist destination with infrastructure, and often people, overlooking the active crater. This report summarizes activity during 2014 through September 2019 and is based on official agency reports. Monitoring is the responsibility of Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM).

Figure 3. Map of Tangkuban Parahu showing the Sunda Caldera rim and the Ratu, Upas, and Domas craters. Basemap is the August 2019 mosaic, copyright 2019 Planet Labs, Inc.

Figure 4. Background activity at the Ratu crater of Tangkuban Parahu is shown in these images from 1 May 2012. The top image is an overview of the crater and the bottom four images show typical geothermal activity. Copyrighted photos by Øystein Lund Andersen, used with permission.

The first reported activity in 2014 consisted of gas-and-steam plumes during October-December, prompting PVMBG to increase the alert level from I to II on 31 December 2014. These white plumes reached a maximum of 50 m above the Ratu crater (figure 5) and were accompanied by elevated seismicity and deformation. This prompted the implementation of an exclusion zone with a radius of 1.5 km around the crater. The activity decreased and the alert level was lowered back to I on 8 January 2015. There was no further reported activity from January 2015 through mid-2019.

Figure 5. Changes at the Ratu crater of Tangkuban Parahu during 25 December 2014 to 8 January 2015. Rain water accumulated in the crater in December and intermittent gas-and-steam plumes were observed. Courtesy of PVMBG (8 January 2015 report).

From 27 June 2019 an increase in activity was recorded in seismicity, deformation, gas chemistry, and visual observations. By 24 July the responsible government agencies had communicated that the volcano could erupt at any time. At 1548 on 26 July a phreatic (steam-driven) explosion ejected an ash plume that reached 200 m; a steam-rich plume rose to 600 m above the Ratu crater (figures 6, and 7). People were on the crater rim at the time and videos show a white plume rising from the crater followed by rapid jets of ash and sediment erupting through the first plume. Deposition of eruption material was 5-7 cm thick and concentrated within a 500 m radius from the point between the Rata and Upas craters, and wider deposition occurred within 2 km of the crater (figures 8 and 9). According to seismic data, the eruption lasted around 5 minutes and 30 seconds (figure 10). Videos show several pulses of ash that fell back into the crater, followed by an ash plume moving laterally towards the viewers.

Figure 6. These screenshots are from a video taken from the Ratu crater rim at Tangkuban Parahu on 26 July 2019. Initially there is a white gas-and-steam plume rising from the crater, then a high-velocity black jet of ash and sediment rises through the plume. This video was widely shared across multiple social media platforms, but the original source could not be identified.

Figure 7. The ash plume at Tangkuban Parahu on 26 July 2019. Courtesy of BNPB.

Figure 8. Volcanic ash and lapilli was deposited around the Ratu crater of Tangkuban Parahu during a phreatic eruption on 26 July 2019. Note that the deposits have slumped down the window and are thicker than the actual ashfall. Courtesy of BNPB.

Figure 9. Ash was deposited on buildings that line the Ratu crater at Tangkuban Parahu during a phreatic eruption on 26 July 2019. Photo courtesy of Novrian Arbi/via Reuters.

Figure 10. A seismogram showing the onset of the 26 July 2019 eruption of Tangkuban Parahu and the elevated seismicity following the event. Courtesy of PVMBG via Øystein Lund Andersen.

On 27 July, the day after the eruption, Øystein Lund Andersen observed the volcano using a drone camera, operated from outside the restricted zone. Over a period of two hours the crater produced a small steam plume; ashfall and small blocks from the initial eruption are visible in and around the crater (figure 11). The ashfall is also visible in satellite imagery, which shows that deposition was restricted to the immediate vicinity to the SW of the crater (figure 12).

Figure 11. Photos of the Ratu crater of Tangkuban Parahu on 27 July 2019, the day after a phreatic eruption. A small steam plume continued through the day. Courtesy of Øystein Lund Andersen.

Figure 12. PlanetScope satellite images showing the Ratu crater of Tangkuban Parahu before (17 July 2019) and after (28 July 2019) the explosion that took place on 26 July 2019. Natural color PlanetScope Imagery, copyright 2019 Planet Labs, Inc.

Another eruption occurred at 2046 on 1 August 2019 and lasted around 11 minutes, producing a plume up to 180 m above the vent. Additional explosions occurred at 0043 on 2 August, lasting around 3 minutes according to seismic data, but were not observed. Explosions continued to be recorded at 0145, 0357, and 0406 at the time of the PVMBG report when the last explosion was ongoing, and a photo shows an explosion at 0608 (figure 13). The explosions produced plumes that reached between 20 and 200 m above the vent. Due to elevated activity the Alert Level was increased to II on 2 August. Ash emission continued through the 4th. During 5-11 August events ejecting ash continued to produce plumes up to 80 m, and gas-and-steam plumes up to 200 m above the vent. Ashfall was localized around Ratu crater. The following week, 12-18 August, activity continued with ash and gas-and-steam plumes reaching 100-200 m above the vent. During 19-25 August, similar activity sent ash to 50-180 m, and gas-and-steam plumes to 200 m. A larger phreatic explosion occurred at 0930 on 31 August with an ash plume reaching 300 m, and a gas-and-steam plume reaching 600 m above the vent, depositing ash and sediment around the crater.

Figure 13. A small ash plume below a white gas-and-steam plume erupting from the Ratu crater of Tangkuban Parahu on 2 August 2019 at 0608. Courtesy of PVBMG (2 August 2019 report).

In early September activity consisted of gas-and-steam plumes up to 100-180 m above the vent with some ash plumes observed (figure 14). Two larger explosions occurred at 1657 and 1709 on 7 September with ash reaching 180 m, and gas-and-steam up to 200 m above the vent. Ash and sediment deposited around the crater. Due to strong winds to the SSW, the smell of sulfur was reported around Cimahi City in West Bandung, although there was no detected increase in sulfur emissions. A phreatic explosion on 17 September produced an ash plume to 40 m and a steam plume to 200 m above the crater. Weak gas-and-steam emissions reaching 200 m above the vent continued through to the end of September.

Figure 14. A phreatic explosion at Tangkuban Parahu in the Ratu crater at 0724 on 4 September 2019, lasting nearly one minute. The darker ash plume reached around 100 m above the vent. Courtesy of PVGHM (4 September 2019 report).

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com/tangkuban-prahu/tangkuban-prahu-volcano-west-java-one-day-after-the-26th-july-phreatic-eruption/); Reuters (URL: https://www.reuters.com/news/picture/editors-choice-pictures-idUSRTX71F3E).

After a lull in activity at Sheveluch, levels intensified again in mid-December 2018 and remained high through April 2019, with lava dome growth, strong explosions that produced ash plumes, incandescent lava flows, hot avalanches, numerous thermal anomalies, and strong fumarolic activity (BGVN 44:05). This report summarizes activity between May and October 2019. The volcano is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT).

According to KVERT, explosive activity continued to generate ash plumes during May-October 2019 (table 13). Strong fumarolic activity, incandescence and growth of the lava dome, and hot avalanches accompanied this process. There were also reports of plumes caused by re-suspended ash rather than new explosions. Plumes frequently extended a few hundred kilometers downwind, with the longest ones remaining visible in imagery as much as 1,000-1,400 km away. One of the larger explosions, on 1 October (figure 52), also generated a pyroclastic flow. Some of the stronger explosions sent the plume to an altitude of 10-11 km, or more than 7 km above the summit. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) throughout the reporting period, except for several hours on 6 October when it was raised to Red (the highest level).

Table 13. Explosions and ash plumes at Sheveluch during May-October 2019. Dates and times are UTC, not local. Data courtesy of KVERT.

Figure 52. An explosion of Sheveluch on 1 October 2019. A pyroclastic flow was also reported by KVERT this day. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Numerous thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were observed every month. Consistent with this, the MIROVA (Middle InfraRed Observation of Volcanic Activity) system recorded thermal anomalies almost daily. According to KVERT, a thermal anomaly over Sheveluch was identified in satellite images during the entire reporting period, although cloudy weather sometimes obscured observations.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Short pulses of intermittent eruptive activity have been common at Piton de la Fournaise, the large basaltic shield volcano on La Réunion Island in the western Indian Ocean, for several thousand years. Over the last 20 years effusive basaltic eruptions have occurred on average twice per year. The activity is characterized by lava fountains and lava flows, and occasional explosive eruptions that shower blocks over the summit area and produce ash plumes. Almost all of the recent activity has occurred within the Enclos Fouqué caldera around the flanks of the central cone which has the Dolomieu Crater at its summit, although past eruptions in 1977, 1986, and 1998 have occurred at vents outside the caldera. Two eruptive episodes were reported during January-June 2019; from 18 February to 10 March, and from 11 to 13 June (BGVN 44:07). Three episodes during July-October 2019 are covered in this report, with information provided primarily by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) as well as satellite instruments.

Three brief eruptive episodes took place during July-October 2019. In each case, slow ground inflation in the weeks leading up to the eruption was followed by sudden inflation at the time of the fissure opening and lava flow event. This was followed by a resumption of inflation days or weeks later. The first event took place during 29-30 July and consisted of three fissures opening on the N flank of the Dolomieu cone. It lasted for less than 24 hours, and the maximum flow length was about 730 m. The second event began on 11 August with two fissures opening on the S flank of the Dolomieu cone. The flows traveled downhill almost 3 km; activity ended on 15 August. Two new fissures opened during 25-27 October on the SSE flank of the cone; one was active only briefly while the second created a 3.6-km-long flow that stopped a few hundred meters before the major highway. The sudden surges of thermal energy from the eruptions are clearly visible in the MIROVA thermal data (figure 182). Each of the eruptive episodes was also accompanied by SO₂ emissions that were detected by satellite instruments (figure 183).

Figure 182. Three eruptive events took place at Piton de la Fournaise during July-October 2019 and appear as spikes in thermal activity during 29-30 July, 11-15 August, and 25-27 October. Additional events in late February-early March and mid-June are also visible in this MIROVA graph of thermal energy from 12 December 2018 through October 2019. Courtesy of MIROVA.

Figure 183. Sulfur dioxide emissions were measured from Piton de la Fournaise during each of the eruptive events that occurred in July (top left), August (top right and bottom left), and October (bottom right) 2019. Courtesy of NASA Goddard Space Flight Center.

Activity during July 2019. The last eruption, a series of flows from several fissures on the SSE flank of Dolomieu Crater near the crater rim (at the center of the Enclos Fouqué caldera), lasted from 11 to 13 June 2019 (figure 184). Ground deformation after the eruption indicated renewed inflation of the edifice which had been ongoing since May. OVPF reported an increase in seismicity beginning on 21 June which continued throughout July; the earthquakes were located near the NW rim of the Dolomieu Crater and on its NW flank. Four centimeters of elongation were recorded between two GNSS stations within the Enclos during late June and July prior to the next eruption. The next short-lived eruption took place during 29-30 July, near the location of the seismicity on the NW flank of the Dolomieu cone about 600 m E of the Formica Leo cone. The onset of the eruption was accompanied by rapid ground deformation of about 12-13 cm, recorded at a station that is located west of the Dolomieu Crater (figure 185).

Figure 184. Location maps of lava flows formed during the 11-13 June 2019 (left) and 29-30 July 2019 (right) eruptions at Piton de la Fournaise. Information derived from satellite data via the OI2 platform and aerial photos. Lava flows from June are shown as red polygons and eruptive fissures are shown as white lines. For the July event, the flows are shown in white. Courtesy of OVPF, OI2 and Université Clermont Auvergne (Monthly bulletins of the Piton de la Fournaise Volcanological Observatory, June and July 2019).

Figure 185. Horizontal surface displacements indicating inflation of Piton de la Fournaise of about four centimeters were gradual between 14 June and 28 July 2019 (left). Just prior to and at the onset of the eruption on 29 July, a much greater displacement of about 12 cm occurred, associated with the subsurface ascent of magma (right). Courtesy of OVPF-IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, July 2019).

The late July eruption began around 1200 local time on 29 July 2019 with the opening of three fissures over a distance of about 450 m on the N flank of Dolomieu cone, close to the tourist trail to the summit (figure 186). Lava fountains 20-30 m high were reported. Thermal measurements indicated flow temperatures of about 1,100°C at the base of the lava fountains; samples were collected for analysis (figure 187). Average discharge rates of 11.6 m³s were estimated for the eruption which ended less than 24 hours later, around 0430 on 30 July. The maximum flow length was about 730 m.

Figure 186. Three fissures opened at Piton de la Fournaise on 29 July 2019 and flows traveled 730 m downslope before stopping the next day. The fissures were located on the N flank of Dolomieu cone. Courtesy of OVPF-IPGP, Imaz PressRéunion, and Réunion La 1ère (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, July 2019).

Figure 187. Samples were collected for analysis by OVPF from the 29 July 2019 flow at Piton de la Fournaise. Courtesy of OVPF-IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, July 2019).

Eruption of 11-15 August 2019. During 1-10 August there were 33 shallow volcano-tectonic (VT) earthquakes located under the SE flank of Dolomieu cone; a new eruption began over this area on 11 August (figure 188). Two centimeters of inflation were recorded between the 29-30 July eruption and the 11-15 August event; this was followed by a rapid burst of inflation (tens of centimeters) at the onset of the eruption. Inflation resumed shortly after the eruption ended. The eruption began around 1620 local time on 11 August. Two fissures opened, one at 1,700 m elevation, and one at 1,500 m elevation on the SE flank, about 1,400 m apart (figure 189). Due to the steep slopes in the area, the lava flow quickly reached the "Grande Pentes" area before slowing down at the flatter "Piton Tremblet" area. The farthest traveled flow was cooling at an elevation of about 560 m, about 2 km from the National Road (RN2) on 14 August. The maximum effusion rate was measured at 9 m³/s. The eruption stopped on 15 August 2019 at 2200 local time after more than 6 hours of "piston gas" activity, and a brief pause in flow activity earlier in the day. About 3 million m³of lava were emitted, according to OVPF-IPGP. The flows from the 1,700 m and 1500 m altitude fissures reached maximum lengths of 2.9 and 2.7 km, respectively.

Figure 188. Locations of eruptive fissures that opened on 11 August 2019 on the SE flank of Dolomieu cone at Piton de la Fournaise, and the approximate locations of the associated flows. Courtesy of IVPF-IPGP / OPGC-LMV (Bulletin d'activité du mercredi 14 août 2019 à 15h30, Heure locale).

Figure 189. Lava flows from the Piton de la Fournaise eruption of 11-15 August 2019 emerged from two fissures on the SE flank of Dolomieu cone. The flows were both active on 13 August (left) at around 0930 local time. Visual and thermal images of the lava flows on 14 August at around 2100 local time (center and right) showed them continuing down the steep slope of the cone and spreading out over the shallower area below. Courtesy of OVPF-IPGP, LMV-OPGC (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, August 2019).

Activity during September-October 2019. Very little activity was reported during September 2019. Seismicity remained low with only 32 earthquakes reported during the month, and inflation, which had continued after the 11-15 August eruption, stopped at the beginning of September. Inflation resumed on 11 October. Two seismic swarms were recorded during October 2019. The first, on 21 October (207 events), lasted for about 40 minutes, and did not result in an eruption. The second began on 25 October and consisted of 827 events. It was followed by an eruption during 25-27 October located on the SSE flank of the Dolomieu cone. Deformation followed a similar pattern as it had during and prior to the eruptive events of July and August. Inflation of a few centimeters between 11 and 24 October was followed by rapid inflation of about 10 cm at the onset of the new eruption. Inflation resumed again after this eruption as well.

Two fissures opened during the 25-27 October eruption, one at 1,060 m elevation and one at 990 m. The first fissure was no longer active when viewed during an overflight 2.5 hours after it had opened. The flows moved rapidly until reaching the lower slope areas of the Grand Brule about 1.5-2 km downstream of the "Piton Tremblet" area. On 26 October only one vent was active with fountains 10-20 m high (figure 190). The lava discharge rates during the eruption averaged about 14 m³/s. The eruption ended at 1630 local time on 27 October after one hour of "gas piston" activity (figure 191). A total of about 1.8 million m³ of lava was emitted. The flows from the 990 m elevation site reached a maximum length of 3.6 km, and the lava flow front stopped about 230 m before reaching the RN2 National road (figure 192).

Figure 190. On 25 October 2019 the front of the active flow at Piton de la Fournaise had reached the level of the Piton Tremblet by 1700 local time (left). Image by PGHM (Bulletin d'activité du 25 octobre 2019 à 18h00, Heure locale). The following day, the active vent had lava fountains 10-20 m high (right) (Bulletin d'activité du samedi 26 octobre 2019 à 11h00, Heure locale). Courtesy of OVPF/IPGP.

Figure 191. The eruptive site of the 25-27 October 2019 eruption at Piton de la Fournaise had one flow still active on 27 October with 10-20 m high lava fountains (left). The flow front stopped that day a few hundred meters before the National Road (right). Courtesy of OVPF/IPGP (Bulletin d'activité du dimanche 27 octobre 2019 à 12h00, Heure locale).

Figure 192. The location of the 25-27 October 2019 lava flow at Piton de la Fournaise started at the very base of the SSE flank of Dolomieu cone and traveled 3.6 km E towards the Highway and the coast. Basemap from Google Earth, fissures (red) and flows (in white) derived from aerial photos. Courtesy of OVPF-IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, October 2019).

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: Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris (OVPF-IPGP), 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); 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/).

After a large, deadly explosive and effusive eruption during 1963-64, Indonesia's Mount Agung on Bali remained quiet until a new eruption began in November 2017 (BGVN 43:01). Activity continued throughout 2018 with explosions that produced ash plumes rising multiple kilometers above the summit, and the slow effusion of the lava within the summit crater. Increasingly frequent and intense explosions with ash emissions and incandescent ejecta characterized activity during February through May 2019 (BGVN 44:06). Two more explosions in June 2019 produced significant ash plumes; no further explosive activity occurred through October 2019. Information about Agung comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and multiple sources of satellite data. This report covers the end of the eruption in June and observations through October 2019.

After a large explosion on 31 May 2019, a smaller event occurred on 10 June. Another large explosion with an ash plume that rose to 9.1 km altitude was recorded on 13 June (local time). It drifted hundreds of kilometers before dissipating. No further explosive activity was reported through October 2019, only diffuse white steam plumes rising at most a few hundred meters above the summit. The Alert Level remained at III (of four levels) throughout the period. The record of thermal activity showed an increase during the explosive events of late May and June, but then decreased significantly (figure 57). There was no obvious thermal signature in satellite images that explained the small increase in thermal energy recorded by the MIROVA data at the end of August 2019.

Figure 57. The thermal energy at Agung increased significantly during the explosive events of late May and early June 2019, and then decreased substantially as seen in this MIROVA graph from 23 January through October 2019. There was no obvious satellite thermal signature to explain the brief increase in thermal energy in late August. Courtesy of MIROVA.

On 31 May 2019 a large explosion produced an ash plume that rose more than 2 km above the summit (BGVN 44:06, figure 56). The Darwin VAAC reported that it split into two plumes, one drifted E at 8.2 km and the other ESE at 6.1 km altitude, dissipating after about 20 hours early on 1 June. A small eruption with an ash plume that rose to 3.9 km altitude was reported the next day by the Darwin VAAC. It was detected in the webcam and pilot reports confirmed that it drifted E for a few hours before dissipating. PVMBG reported gray emissions to 300 m above the peak on 1 June and 100 m above the summit on 2 June. By 6 June the emissions were white, rising only 50 m above the summit. For several subsequent days, the summit was covered in fog with no observations of emissions.

On 10 June 2019 an explosion lasting 90 seconds was reported at 1212 local time; PVMBG noted a gray ash plume 1,000 m above the summit (figure 58). The Darwin VAAC confirmed the emission in satellite imagery and by pilot report; it was moving SW at 4.3 km altitude and then drifted S before dissipating by the end of the day. Early on 13 June local time (12 June UTC) a new explosion that was clearly visible in the webcam produced a large ash plume that drifted W and SW (figure 59). The explosion was recorded on the seismogram for almost four minutes and sent incandescent ejecta in all directions up to 700 m from the summit. The first satellite imagery of the plume reported by the Darwin VAAC suggested the altitude to be 9.1 km. A secondary plume was drifting W from the summit at 5.5 km altitude a few hours later. By six hours after the eruption, the 9.1 km altitude plume was about 90 km SSW of the Denpassar airport and the 5.5 km altitude plume was about 110 km W of the airport. By the time the higher altitude plume dissipated after about 14 hours, it had reached 300 km S of the airport. For the remainder of June, only diffuse white steam plumes were reported, rising generally 30-50 m above the summit, with brief pulses to 150-200 m during 27-29 June.

Figure 58. An ash plume rose 1,000 m above the summit of Agung on 10 June 2019. Top image courtesy of Rita Bauer (Volcano Verse), bottom image courtesy of PVMBG (Information on G. Agung Eruption, 10 June 2019).

Figure 59. A large eruption at Agung at 0138 local time on 13 June 2019 sent an ash plume to 9.1 km altitude and incandescent ejecta 700 m in all directions. Courtesy of Jaime S. Sincioco, screenshot from volcano YT webcam.

Although no further surface activity was reported at Agung during July through October 2019, PVMBG kept the Alert Level at III throughout the period. Only steam plumes were reported from the summit usually rising 50 m before dissipating. Steam emissions rose to 150 m a few times each month. Plumes were reported at 300 m above the summit on 6 July and 15 August. No thermal anomalies were visible in Sentinel 2 satellite images during the period.

Geologic Background. Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE caldera rim of neighboring Batur volcano, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Rita Bauer, Volcano Verse (Twitter @wischweg, URL: https://twitter.com/wischweg/status/1137956367258570752); Jamie S. Sincioco, Philippines (Twitter @jaimessincioco, URL: https://twitter.com/jaimessincioco/status/1139109685796020224).

Most of the large edifice of Copahue lies high in the central Chilean Andes, but the active, acidic-lake filled El Agrio crater lies on the Argentinian side of the border at the W edge of the Pliocene Caviahue caldera. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. The most recent eruptive episode with ash plumes lasted from early June 2017 to early December 2018. After 8 months of quiet, renewed phreatic explosions and ash emissions began in August 2019 and were ongoing through October 2019. This report summarizes activity from January through October 2019 and is based on reports issued by Servicio Nacional de Geología y Minería (SERNAGEOMIN) Observatorio Volcanológico de Los Andes del Sur (OVDAS), Buenos Aires Volcanic Ash Advisory Center (VAAC), satellite data, and photographs from nearby residents.

Intermittent steam plumes were reported from the El Agrio crater at the summit during January-July 2019, but no ash emissions were seen. An increase in seismicity and changes in the crater lake level during March led SERNAGEOMIN to increase the Alert Level from Green to Yellow at the beginning of April. Fluctuating tremor signals in the first week of August coincided with satellite imagery that showed the appearance of dark material, possibly ash, on the snow around the summit crater. The first thermal anomaly appeared on 3 September and the first clear ash explosions were recorded on 11 September. Eruptive activity was intermittent through the end of the month; a series of larger explosions beginning on 30 September caused SERNAGEOMIN to raise the Alert Level from Yellow to Orange. A period of more intense explosive activity lasted through the first week of October. The larger explosions then ceased, but during the rest of October there were continuing observations of seismicity, ash emissions, and incandescent ejecta, along with multiple thermal anomalies in the summit area.

Observations during January-April 2019. Copahue remained at Alert Level Yellow with a 1-km exclusion radius during January 2019 after ash emission in December 2018. Ongoing degassing was reported with white plumes from El Agrio crater rising to 355 m (figure 25). The Alert Level was lowered to Green at the end of the month, and the exclusion radius was reduced to 500 m, although intermittent low-level seismicity in the region continued. SERNAGEOMIN reported a M 3.2 earthquake about 10 km NE of the summit, 2 km deep, on 29 January 2019. The acidic lake inside El Agrio crater was quiet at the end of the month (figure 26).

Figure 25. Degassing of steam from Copahue on 10 and 17 (inset) January 2019. Courtesy of OPTIC Neuquén (10 January) and SERNAGEOMIN (17 January).

Figure 26. El Agrio crater at Copahue on 31 January 2019. Courtesy of Valentina Sepulveda, Hotel Caviahue.

Steam plumes occasionally rose to 180 m above the crater during February 2019. A swarm of 117 volcano-tectonic (VT) seismic events on 22-23 February 2019 was located about 14 km NE of the volcano, with the largest events around a M 3.5. Steam plumes rose to about 280 m above the crater during March. SERNAGEOMIN noted an increase in seismicity during the month, and a decrease in the lake level within El Agrio crater. This led them to increase the Alert Level to Yellow (second on a four-level scale) at the beginning of April. Emissions remained minimal during April (figure 27); an 80 m high steam plume was reported on 4 April. The lake level continued to fall, based on satellite imagery, and a M 3.1 earthquake was reported on 29 April located about 10 km NE of the summit about 10 km deep.

Figure 27. Clear skies revealed no activity from the summit of Copahue on 7 or April 2019. The volcano was quiet throughout the month, although the Alert Level remained at Yellow. Image taken near Caviahue, 10 km E in Argentina. Courtesy of Valentina Sepulveda, Hotel Caviahue.

Observations during May-July 2019. Sporadic episodes of low-altitude steam plume degassing were noted during May 2019, but otherwise very little surface activity was reported (figure 28). On 13 May, a steam plume reached 160 m above the crater rim, and on 28 May, the tallest plume rose 200 m above the crater. Hybrid-type earthquakes were recorded early in the month, followed by a slow increase in the amplitude of the tremor signal. Seismicity increased slightly during the second half of the month with activity concentrated closer to the summit crater. A weak SO₂ plume was recorded by satellite instruments on 23 May. The level of the lake began increasing during the second half of the month.

Figure 28. No surface activity was visible at Copahue on 5 May 2019, but seismicity increased slowly during the month. Image taken near Caviahue. Courtesy of Valentina Sepulveda, Hotel Caviahue.

SERNAGEOMIN reported tremor signals with fluctuating amplitude throughout June 2019. Repeated episodes of low-altitude white degassing occurred around the El Agrio crater. On 7 June, a 300 m plume was observed above the crater; the level of the crater lake was variable. On 17 June a 400-m-tall white plume was observed above the crater. Seismicity, although low, increased during the second half of the month. Multiple episodes of low-altitude white degassing occurred around the active crater all during July 2019 (figure 29). On 9 July a plume rose about 450 m above the crater. On 16 July a white plume rose 250 m above the crater. SENAGEOMIN noted a rise in the rate of seismicity during the first half of the month; the tremor signal continued with fluctuating amplitude. Satellite instruments detected small SO₂ plumes on 4 and 9 July (figure 30).

Figure 29. A steam plume rose a few hundred meters above the summit of Copahue on 23 July 2019. Courtesy of Valentina Sepulveda, Hotel Caviahue.

Figure 30. The TROPOMI instrument on the Sentinel-5P satellite detected small SO2 plumes at Copahue on 4 and 9 July 2019. Courtesy of NASA Goddard Space Flight Center.

Activity during August-October 2019. Sentinel-2 satellite imagery from 2, 4, 7, and 9 August suggested the ejection of particulate material (figure 31), with dark streaks in the snow extending a few hundred meters E and SE from the crater. Images from the community of Caviahue on 3 and 4 August show distinct discoloration of the snow around the E side of the summit crater (figures 32 and 33). Small but discernible SO₂ plumes were detected by satellite instruments on 2, 3, 16, 19, 30, and 31 August. Fluctuating tremor signals continued during August with several episodes of low-altitude white degassing from the El Agrio crater; a white plume on 5 August rose 380 m above the crater. The lake level continued to drop and the Alert Level remained at Yellow.

Figure 31. Sentinel 2 satellite imagery of Copahue from late July and early August 2019 show fresh dark material deposited over the fresh winter snow, suggesting recent ejecta from the El Agrio crater. Top left: The summit was covered with fresh snow on 25 July 2019. Top right: A dark streak extends E then N from the El Agrio crater on 2 August. Bottom left: A streak of dark material trends SE from the crater over the snow on 4 August. Bottom Right: On 7 August a different streak extends E from the crater while fresh snow has covered the earlier streak. Courtesy of Sentinel Hub Playground.

Figure 32. At sunset on 3 August 2019, darker material was visible on the snow on the E side of the summit of Copahue; a dense steam plume rose from El Agrio crater. Courtesy of Valentina Sepulveda, Hotel Caviahue.

Figure 33. Particulates covered the fresh snow near the summit of Copahue on 4 August 2019, as seen from the community of Caviahue, about 10 km E. A steam plume rose from El Agrio crater. Courtesy of Valentina Sepulveda, Hotel Caviahue.

Distinct SO₂ plumes were again captured by satellite instruments on 1, 3, and 5-7 September 2019 (figure 34). The first thermal signature in nine months also appeared in Sentinel-2 satellite imagery on 3 September (figure 35). Midday on 9 September, seismometers recorded an increase in the amplitude of a continuous tremor. High clouds prevented clear views of the crater and no ash emissions were observed. Beginning on 11 September, low-energy long-period (LP) events were associated with infrasound signals and low-energy explosions that produced small ash plumes. The largest explosion produced a plume 250 m above the crater. Incandescence and high-temperature ejecta were observed around the emission point. The ash drifted ESE about 3 km. Ten explosions were reported between 11 and 12 September, associated with low-intensity acoustic signals and ash emissions. Plumes reached 430 m above the crater rim on 12 September. Ash deposits on the snow were visible in in Sentinel-2 images on 11 and 13 September, extending about 6 km E from El Agrio crater (figure 35). Images from the ground on 12 September indicated fresh ash on the E flank (figure 36).

Figure 34. Small but distinct SO2 plumes from Copahue were measured by the TROPOMI instrument on the Sentinel 5P satellite on 1 and 3 September 2019, and additionally on 5-7 September. Courtesy of NASA Goddard Space Center.

Figure 35. Sentinel-2 satellite images indicated thermal activity and ash emissions at Copahue on 3, 11, and 13 September 2019. Left: The first thermal anomaly in nine months appeared on 3 September. Middle: An ash streak trended E across the snow from El Agrio crater on 11 September. On 13 September, the streak was a wider cone that extended ESE for about 6 km. Courtesy of Sentinel Hub Playground.

Figure 36. Ash deposits coated snow on the E flank of Copahue on 12 September 2019, while a steam plume drifted SE from the crater, as seen from the community of Caviahue about 10 km E in Argentina. Courtesy of Valentina Sepulveda, Hotel Caviahue.

Although fresh snow had covered any ash deposits by 16 September 2019 (figure 37), small thermal anomalies appeared in Sentinel-2 imagery on 16 and 21 September. SO₂ plumes were measured by satellite instruments on 21 and 25 September. Photos from Caviahue on 25 September showed ash on the E flank and a steam-and-ash plume drifting NE (figure 38). Ashfall on the snow was visible in satellite imagery on 26 September, and covered a larger area on 28 September; there was also a substantial thermal anomaly that day (figure 39).

Figure 37. Fresh snow had covered over recent ash emissions at Copahue by 16 September 2019; thermal anomalies were detected in satellite data from the summit crater the same day. Courtesy of Valentina Sepulveda, Hotel Caviahue.

Figure 38. On a clear 25 September 2019 fresh ash covered snow on the E flank of Copahue, and an ash and steam plume was drifting NE from the El Agrio crater. The mountains are reflected in Lago Caviahue located about 12 km E in Argentina. Courtesy of Valentina Sepulveda, Hotel Caviahue.

Figure 39. Sentinel-2 imagery of Copahue on 28 September showed ashfall in a large area around the summit and a small ash plume (left); a substantial thermal anomaly was also visible within the El Agrio crater (right). Courtesy of Sentinel Hub Playground.

During the late afternoon of 30 September, three high-energy LP earthquakes were reported located 5.8 km NE of the El Agrio crater. They were accompanied by abundant lower energy earthquakes in the same area. The VT earthquakes were equivalent to a M 3.5. Inhabitants of Caviahue (12 km E) reported feeling several of the events; atmospheric conditions prevented observation of the summit. This sudden increase in seismicity prompted SERNGEOMIN to raise the Alert Level to Orange and increase the radius of the area of potential impact to 5 km. Seismicity (VT, LP and tremor earthquakes) continued at a high rate into 1 October. Argentina's geologic hazards and mining agency, Servicio Geologico Minero Argentino (SEGEMAR) also issued a notice of the increased warning level on 30 September (figure 40).

Figure 40. A dense steam plume rises from the active crater at Copahue in this image looking due E towards Caviahue and Lago Caviahue, 12 km E. The rim of the Caviahue caldera is in the distance. Argentina's SEGEMAR posted this photograph (undated) with their notice of the increase in warning level on 30 September 2019. Courtesy of SEGEMAR.

Cameras near the volcano detected ash plumes associated with explosions around the crater at 0945 on 1 October 2019 which continued throughout the first week of the month. Satellite imagery showed streaks of dark ash over snow trending SE and E and from the summit on 1 and 8 October (figure 41). Five separate explosions were recorded during 1-2 October. Persistent degassing was accompanied by episodes of ash emissions and incandescence at night. Seismicity continued during 2-3 October, but poor weather mostly obscured visual evidence of activity; a few pulses of white and gray emissions were observed. Seismic events were located 5-7 km NE at a depths of 0.7-1.7 km, and continued for several days. Clearer skies on 4 October revealed steam plumes and pulses of ash rising from El Agrio crater. Incandescence was visible at night. A ground-based image showed ash covering the E flank and an ash plume drifting NE down the flank (figure 42). The Buenos Aires VAAC reported weak ash emissions on 4 October moving NE at 3.4 km altitude. The webcam showed continuous ash emission from the summit during 4-5 October.

Figure 41. Sentinel-2 satellite imagery of Copahue showed dark streaks trending SE and E from the summit in early October. On 1 October 2019 (left) there was a narrow streak of ash to the SE and a steam plume drifting the same direction. On 8 Octobe0r (right), a wide cone of ashfall covered the E flank, and a plume of gray ash drifted NE over the edge of the deposit. Courtesy of Sentinel Hub Playground.

Figure 42. Gray ash covered areas of Copahue's E flank on 4 October 2019 and an ash plume drifted NE down the flank. Image from Caviahue, about 10 km E. Courtesy of Valentina Sepulveda, Hotel Caviahue.

White steam plumes with pulses of ash and incandescence at night were observed on 5 and 6 October. Seismic activity decreased on 6 October. The following day, SERNAGEOMIN lowered the Alert Level to Yellow and reduced the restricted zone to 1,000 m around the summit crater. While seismicity had decreased, ash emissions continued from low-level pulsating explosions which produced ash plumes that drifted E (figure 43). They observed that the total area to that date affected by ashfall was about 24.5 km², extending up to 5 km W and 6 km E from the summit. They also noted that a pyroclastic cone about 130 m across had appeared inside the crater. Ash emissions and explosions with incandescent ejecta continued during the second week of October (figure 44). A change in wind direction created a several-kilometer-long streak of ash trending SW from the summit by 13 October; a strong thermal anomaly that day indicated continued activity (figure 45). SO₂ plumes were recorded by satellite instruments on 1, 3, 4, and 13 October.

Figure 43. Ash and steam drifted E from the summit of Copahue on 7 October 2019, the day that SERNAGEOMIN lowered the Alert Level from Orange to Yellow. Courtesy of SEGEMAR.

Figure 44. Incandescent ejecta was visible at the summit of Copahue overnight on 11 October 2019 in the image from a local webcam. Courtesy of Culture Volcan.

Figure 45. A new dark streak of ash on snow trended SW from the El Agrio crater at Cophahue on 13 October 2019. The strong thermal anomaly the same day indicated the level of eruptive activity was still high. Natural color image based on bands 4,3, and 2; Atmospheric penetration rendering based on bands 12, 11, and 8a. Courtesy of Sentinel Hub Playground.

Seismicity continued for the rest of October, but no explosions were recorded. Sulfur dioxide emissions were recorded by satellite instruments on 18, 22, 23, and 30 October (figure 46). When weather permitted, constant degassing with episodes of ash emissions from the crater were visible during the day and incandescence appeared at night. Satellite imagery on 18, 23, and 28 October showed substantial ash plumes drifting in different directions from the summit. A large area around the summit crater was covered with dark ash on 18 and 23 October. Fresh snowfall had covered most of the area by 28 October, and the narrow dark streak trending SE underneath the ongoing ash plume was the only surface covered with material (figure 47). Distinct thermal anomalies appeared in satellite images on 16, 18, 23, and 31 October. A number of thermal alerts were recorded by the MIROVA system as well during the second half of the month.

Figure 46. The TROPOMI instrument on the Sentinel-5P satellite recorded SO2 emissions from Copahue on 18, 22, 23, and 30 October 2019. Satellite imagery on also showed ash plumes on 18 and 23 October. Courtesy of NASA Goddard Space Flight Center.

Figure 47. Distinct ash plumes and dark ashfall over snow on 18, 23, and 28 October 2019 at Copahue indicated ongoing eruptive activity (top row) through the end of the month. The large area of ash-covered snow visible on 18 and 23 October was covered with fresh snowfall by 28 October when the dense ash plume drifting SE left only a narrow dark trail of ashfall in the fresh snow underneath (right). Strong thermal anomalies were apparent on 18 and 23 October but obscured by dense ash on 28 October (bottom row). Natural color image based on bands 4, 3, and 2; atmospheric penetration rendering based on bands 12, 11, and 8a. Courtesy of Sentinel Hub Playground.

The highest plume noted by SERNAGEOMIN during the second half of the month rose 1,200 m above the crater on 22 October 2019 (figure 48). The Buenos Aires VAAC reported ash emissions from the summit visible in webcams almost every day in October. On 16 October, an ash plume was seen in satellite imagery moving SE at 3.4 km altitude under mostly clear skies; the webcam showed continuous ash emission. A faint plume was barely seen moving S in satellite imagery at 3.4 km altitude on 18 October; the webcam revealed continuous emission of gases and possible dilute volcanic ash. The VAAC reported ash emissions daily from 18-25 October. Drift directions varied from SE, moving to NE on 21-23 October, and back to E and SE the following days. The altitudes ranged from 3.0 to 4.3 km. On 20 October, the plume extended about 80 km SE. The ash appeared as pulses moving NE on 22 and 23 October at 4.3 km altitude. Emissions reappeared in satellite imagery on 28 and 30-31 October, drifting SE and NE at 3.4-3.7 km altitude; incandescence was visible overnight on 30-31 October from the webcam.

Figure 48. A plume of ash and steam from Copahue rose 1,200 m above the summit on 22 October 2019 and drifted NE. It was clearly visible from 25 km SW of the volcano in the El Barco Indigenous community of Alto Biobío, Chile, along with ash-covered snow on the SW flank. Courtesy of EveLyN.

Geologic Background. Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Information Contacts: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); OPTIC Neuquén, Oficina Provincial de Tecnologías de la Información y la Comunicación- Gobierno de la Provincia del Neuquén, Neuquén, Argentina (URL: https://www.neuqueninforma.gob.ar/tag/optic/, Twitter: @OPTIC_Nqn, https://twitter.com/OPTIC_Nqn); 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); Valentina Sepulveda, Hotel Caviahue, Caviahue, Argentina (URL: https://twitter.com/valecaviahue, Twitter:@valecaviahue); Cultur Volcan, Journal d'un volcanophile, (URL: https://laculturevolcan.blogspot.com, Twitter: @CulturVolcan); EveLyn, Twitter: @EveCaCid (URL: https://twitter.com/EveCaCid/status/1186663015271321601).

This report summarizes activity at Turrialba during March-October 2019. Typical activity similar to that reported in late 2018 and early 2019 (BGVN 44:04) included periodic weak ash explosions and numerous emissions containing some ash. However, during this period activity appeared to diminish with time. Data were provided by weekly reports by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA).

According to OVSICORI-UNA, only highly diluted ash emissions were recorded from 22 April to 27 May (note that no reports were available online from the last week of March until 22 April). Weak ash explosions were again noted on 28 July, 4 August, and possibly on 20 October. OVSICORI-UNA reported more explosions or emissions containing ash on 25 and 28 October (table 9).

Table 9. Summary of reported activity at Turrialba, March-October 2019. Cloudy weather sometimes obscured observations. Maximum plume height is above the crater rim. Information courtesy of OVSICORI-UNA.

A report from Red Sismologica Nacional (RSN) about the 28 October ash explosion noted that it occurred at 1501 local time and lasted about 5 minutes. There were no reports of ashfall, but the crater webcam captured the small plume rising from the active vent. Incandescence in the active crater continued to be seen on the monitoring cameras.

Geologic Background. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Red Sismologica Nacional (RSN) a collaboration between a) the Sección de Sismología, Vulcanología y Exploración Geofísica de la Escuela Centroamericana de Geología de la Universidad de Costa Rica (UCR), and b) the Área de Amenazas y Auscultación Sismológica y Volcánica del Instituto Costarricense de Electricidad (ICE), Costa Rica (URL: https://rsn.ucr.ac.cr/).

The number of recorded summit crater explosions declined to six in June, for a 6-month total of 122. A pair of explosions on 16 June deposited the largest amount of ash (2,671 g/m²) since measurements began in 1969 at KLMO . . . . The month's total ash accumulation was 3,541 g/m². The largest previous ash accumulation at the observatory was 2,476 g/m² on 29 July 1985. The 16 June plume was the month's highest (2.6 km). Four June explosions produced air shocks.

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.

Ash and steam have been sporadically ejected from a cinder cone in the summit caldera since 1972. Recent periods of activity include June 1987 and March-June 1988 (table 4). Most of the observed activity is reported by airline pilots. Cloudy weather commonly obscures the view of the summit from the ground.

Table 4. Reports of activity at Akutan, 7 June-2 July 1988, compiled by John Reeder from the following observers: Clint Schoenleber, Terry Reece, Jerry Friz (Mark Air Inc.), Charles Rodehaver, Rick Wilbur, Buddy Burnett, Brian Carricaburu, Nick Sias (Peninsula Airways), Tom Madsen (Aleutian Air Ltd.), Steve Felch (Northern Air Cargo), david and June McGlashan, Charlotte Jones (Akutan village), and a member of the U.S. Coast Guard (USCG). Summit elevation, 1,303 m; all heights reported as meters above the summit. Observers initials in brackets.

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

Information Contacts: J. Reeder, ADGGS.

Apparent small new aerosol layers near the tropopause, perhaps from the May eruption of Banda Api, Indonesia (4.525°S, 129.871°E), were detected by lidar at Mauna Loa, Hawaii and Fukuoka, Japan (figure 57). Very small lower stratospheric layers that looked sharp and fresh were evident on profiles from all three June observations at Mauna Loa (figure 58). The 8 June data showed peaks at 15.9 and 17.7 km altitude; only the peak at 17.7 km was evident on 16 and 21 June. Data from Fukuoka first showed a very thin layer at about 15.4 km altitude (about 1 km below the tropopause) on 5 July, nearly a month after the previous measurement on 10 June. The layer was less than 0.75 km thick, much thinner than the usual cirrus cloud. The next night, a similar layer appeared at the same altitude. Observation with a height resolution of 0.15 km showed it to be thinner than 0.3 km. No cirrus clouds were visible either night. No new layers were detected in late June from Hampton, VA.

Figure 57. Lidar data from various locations, showing altitudes of aerosol layers during March-July 1988. Note that some layers have multiple peaks. Backscattering ratios from Fukouka, Japan, are for the Nd-YAG wavelength of 1.06 µm; all others are for the ruby wavelength of 0.69 µm. Integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from 16-33 km at Mauna Loa and from the tropopause to 30 km at Hampton, Virginia. Altitudes of maximum backscattering ratios and coefficients are shown for each layer at Mauna Loa.

Figure 58. Average monthly lidar profiles from Mauna Loa, Hawaii, December 1987-June 1988. The dotted line superimposed on each profile represents the average 5-22 November 1985 data, before the arrival of Ruiz aerosols.

Figure 59 shows vertically integrated backscattering at Garmisch-Partenkirchen, West Germany, 1982-87. Seasonal variations measured 1983-85 were discussed in Jäger and Carnuth, 1987. The 3 closely spaced higher values in May-June 1987 are from a lower stratospheric layer that may have been caused by strong forest fires in China.

Figure 59. Vertically integrated ruby-wavelength backscattering data from Garmisch-Partenkirchen, West Germany, 1982-1987. Integration was performed from 1 km above the local tropopause to the top of the aerosol layer (at 25-35 km).

Reference. Jäger, H., and Carnuth, W., 1987, The Decay of the El Chichón Stratospheric Perturbation, Observed by Lidar at Northern Midlatitudes; Geophysical Research Letters, v. 14, p. 696-699.

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

Information Contacts: Motowo Fujiwara, Physics Department, Fukuoka University, Jonan-ku, Fukuoka 814-01, Japan; Thomas DeFoor, Mauna Loa Observatory, P. O. Box 275, Hilo, HI 96720 USA; Horst Jäger, Fraunhofer-Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, West Germany; William Fuller and Mary Osborn, NASA Langley Research Center, Hampton, VA 23665 USA.

The violent ash explosions and vigorous lava production that began 9 May had subsided by mid-May (13:05). Activity had been concentrated at two vents on the N flank and at numerous vents on the S flank, along a fissure oriented NNE-SSW. Most of the 9.4 x 10⁶ m³ of lava was produced during the first 12-18 hours of the 9-15 May eruption. The flows in order of decreasing volume are: NW flank (Pasir Besar), N flank (Batu Angus), and the two S-flank flows. A persistent white steam plume rose 50 m above the summit vent during June. Approximately eight A-type and eight B-type earthquakes were recorded daily. VSI installed three additional seismometers, including two on Gunung Api.

Through May, a total of 7,000 residents had remained evacuated. On 13 June, VSI reassessed the volcanic activity and recommended that residents return to neighboring Banda Neira and Lontar islands. The 1,800 residents of Pulau Gunung Api remained evacuated to Ambon, Ceram, and Lontar Islands.

Further Reference. Casadevall, T., Pardyanto, L., Abas, H., and Tulus, 1989, The 1988 eruption of Banda Api volcano, Maluku, Indonesia: Geologi Indonesia, v. 12, n. 1, p. 603-635.

Geologic Background. The small island volcano of Banda Api is the NE-most volcano in the Sunda-Banda arc and has a long period of historical observation because of its key location in the Portuguese and Dutch spice trade. The basaltic-to-rhyodacitic volcano is located in the SW corner of a 7-km-wide mostly submerged caldera that comprises the northernmost of a chain of volcanic islands in the Banda Sea. At least two episodes of caldera formation are thought to have occurred, with the arcuate islands of Lonthor and Neira considered to be remnants of the pre-caldera volcanoes. A conical peak rises to about 600 m at the center of the 3-km-wide Banda Api island. Historical eruptions have been recorded since 1586, mostly consisting of Strombolian eruptions from the summit crater, but larger explosive eruptions have occurred and occasional lava flows have reached the coast.

Information Contacts: VSI.

High levels of seismicity have persisted at Bulusan for the past 2 months. Volcanic earthquakes averaged 70/day with peak numbers of events reported on 26 April and 9 June. Seismic activity has not been as high since 24 February when one large event of Rossi-Forel intensity V and 80 smaller events were recorded at Bulusan (13:2).

On 26 April, 535 high-frequency and 37 low-frequency volcanic earthquakes, and one harmonic tremor episode were recorded by the San Benon Observatory (5.1 km SW of the crater). Three of these large-amplitude events were felt at intensity I (San Benon) and two events at intensity II (Bulusan Lake, 5.9 km SE of the crater). Several strong pulses of seismicity were noted in May and June: 1-11 May, 12-22 May, 25 May-1 June, and 5 June to July. These pulses may be attributed to fracturing within the caldera or within defined faults along the SE caldera rim. Epicentral plots clustered in two areas; one 6 km SE of the crater and the other 3 km NW of the crater. Depths ranged from 3 to 5 km. The seismic network recorded 233 volcanic earthquakes on 9 June. On 16 June, one of the day's 42 recorded volcanic events was felt at intensity I at San Benon, and on 17 June a tectonic earthquake was felt at intensity II at the Bulusan Lake Station.

Steam emission generally was profuse. The latest EDM data (19 June) suggest a slight inflationary trend for Bulusan.

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

Information Contacts: PHIVOLCS.

A group from the Centro de Investigación en Ciencias Básicas (CICBAS), Universidad de Colima, visited the volcano on 24-25 May to test future sites for a local seismic network. Guillermo Castellanos and Raul López measured average temperatures of 118°C adjacent to the main fumaroles. Emissions were dense, light-gray, and toxic. Large rockfall avalanches similar to the one that originated at the base of Colima's lava dome on 2 July 1987 (12:07) have been occurring periodically. Thick sulfur deposits coated the areas around fumaroles and avalanche source areas. Contrary to some public reports, rumbling noises were not heard during the visit.

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: G. Castellanos, R. López, G. Ornelas, J.C. Pérez, C.A. Ramírez, G. Reyes, and H. Tamez, CICBAS, Universidad de Colima.

A series of ash ejections began on 21 June. During the initial outburst from 1725 to 1740, light-grayish steam clouds rose to a maximum height of 300 m above the crater. Traces of ash were noted at the village of Mananawin on the SE slope at 980 m elevation. This event was not recorded by the flank seismic network. Previous ash ejections in April 1987 were similarly not recorded (12:4-5).

Ash ejections ocurred again the next day at 1230 and 1418 and were recorded as small-amplitude (0.5 mm) harmonic tremors with durations not exceeding 2 minutes. The maximum ash cloud height was 600 m above the crater. Sulfur stench was noted by SE flank residents. On 24 June, ash ejections occurred at 1155 and 1455, accompanied by faint rumbling sounds. Ash from the 400-m-high eruption clouds was deposited on the upper SE slopes. No eruption signal was recorded by PHIVOLCS seismic stations.

Another ash ejection occurred at 1105 on 27 June, accompanied by an explosion-type earthquake that had a maximum double amplitude of 4.0 mm and lasted for 1 minute. As observed from the Canlaon Volcano Observatory (8.7 km SE of the crater), the cloud rose 500 m above the crater and deposited ash along the SW upper slopes. Background seismicity varied from 5 to 18 events/day following the first outburst. Steam emission between ash ejections covered 20-50% of the crater's area.

Since the ash eruption of April 1987, slight inflation of the SE flank and moderate seismicity have occurred (12:4-5).

Further Reference. Sincioco, J., 1988, The 1988 Eruptive Activity of Canlaon Volcano; Phivolcs Observer, v. 4, no. 3, p. 3.

Geologic Background. Kanlaon volcano (also spelled Canlaon), the most active of the central Philippines, forms the highest point on the island of Negros. The massive andesitic stratovolcano is dotted with fissure-controlled pyroclastic cones and craters, many of which are filled by lakes. The largest debris avalanche known in the Philippines traveled 33 km SW from Kanlaon. The summit contains a 2-km-wide, elongated northern caldera with a crater lake and a smaller, but higher, historically active vent, Lugud crater, to the south. Historical eruptions, recorded since 1866, have typically consisted of phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano.

Information Contacts: PHIVOLCS.

Lava flows . . . continued to enter the ocean along two fronts E of Kupapau Point. The W flow front had two active areas ~200 m apart. At the W end of a 100-m-wide front, minor littoral explosions built a small ephemeral cone that sometimes grew to 1-2 m high by 4 m in diameter, and added pyroclastic material to a growing black sand beach 100 m to the W. Divers observed development of underwater tube systems that extended as much as a few hundred meters from the coast. Flows from the other front sporadically entered the ocean nearly a kilometer to the E. Surface activity upslope along the two lava tube systems was minimal. The lava pond level remained several meters below the rim all month.

Low-level tremor continued . . . near Kupaianaha and Pu`u `O`o. Amplitude varied according to the pattern of lava movement and ranged from frequent tremor variations, minutes apart during gas-piston activity, to relatively steady tremor sustained for hours to days. Some collapse events at Pu`u `O`o were also recorded. The number of microearthquakes was about average in the summit region and East rift zone. Of more than 1,000 earthquakes located . . . in June, 23 registered at M 2.5-5.1. The largest (M 5.1) was centered above the S flank of Kilauea at a depth of 10 km on 7 June.

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 R. Koyanagi, HVO.

"Activity remained at a low level during June. Crater 2 occasionally produced weak to moderate white-grey emissions. Low rumbling noises were heard on 4, 12, 15, 19, and 27 June. Weak night glow was seen above this crater 14-19 June. Crater 3 remained virtually inactive with only weak white vapour emissions on 17 June."

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: P. de Saint-Ours and P. Lowenstein, RVO.

A recurring pattern of recharge of small lava lakes followed by either overflow or drainage through nearby vents was observed by Maurice and Katia Krafft, C. Nyamweru, Jörg Keller (Albert Ludwigs Univ, Freiburg), and the Peterson brothers (Arusha) 24 June-1 July. The visit was timed to coincide with the full moon (29 June) so that tidal effects, if any, would be maximized. The following was compiled by M. Krafft.

24 June: When geologists reached the summit at 1700, small lava lakes were active in vents T4 and T7. Black, bubbling lava filled T7 to within 0.5 m of its rim. A steep spatter cone, 3 m high, partially covered the T4 lava lake and ejected spatter 1-2 m high. Hot lava fields, N of T7, were probably erupted hours [earlier]. At 1800, the T7 lava lake overflowed E through two spillways, each 1 m wide. Overflows were 1-1.5 m wide and 20-40 cm deep with speeds of 1-5 m/s. The lava flowed in surges. Estimated viscosity was very low, similar to a fluid mudflow and less viscous than the most fluid basaltic lava flow. Temperatures repeatedly measured with thermocouples and galvanometers ranged from a maximum of 544°C for the hottest orange-colored lake lava, to a minimum of 495°C at flow fronts. Pahoehoe and aa lava flowed E and SE around T5. Four hours of overflow formed a new lava field 100 m long and 10-40 m wide. At night, the red lava lake became orange when hotter pulses of magma surged to the surface. Lava continuously overflowed from T4 to T7 until the T4 lake level decreased 3 m and the current reversed to flow from T7 to T4. The T4 spatter cone collapsed, split, and was destroyed.

25 June: At 1200, a new single-spillway overflow from T7, half the volume of the previous day's overflow, traveled NE and E until it stopped at 1400. The level of the T7 lava decreased 2 m. Small overflows developed but stopped during the night. Small spatter cones (20-50 cm) formed on T7's NE flank and emitted a small lava tongue.

26 June: At 1100, the toe of the N lobe was still squeezing out droplets of fluid lava. A bubbling lava lake in T5 was at the same level as the T7 and T4 lakes, suggesting that a tube system joined these lakes. During the day, the T7 lake level decreased 2.5 m. No more overflows occurred.

27 June: At 0830, the T7 lake was full. At 0930, lava was emitted from two 50-cm-high spatter cones that formed on T7's SSW slope and traveled 20 m SW at 2-4 m/s. The flow was 0.5 m wide at the outlet vent and some small lava tubes formed.

At 1800 the level of the T7 lake dropped below that of the outlet vent and the 100 m-long flows stopped. The remains of the T4 spatter cone collapsed into the T4 lake. The T4 and T7 lakes coalesced under a chilled lava bridge.

28 June: Lava was 1 m below the rim of T4 and T7. At about 0400, two new T7 overflows developed on the E rim of the lake and traveled NE and S. A row of small spatter cones (tens of centimeters high) formed on T7's SE slope and emitted small lava tongues. Spatter cone construction progressed towards the T7 lava lake; lake level decreased until it reached vent level.

29 June: At 1600, the flow of lava stopped. The SW lava field was 110 m long, 30 m wide, and 30 cm thick. T7 ejected lava 2-3 m high every 2-3 seconds. T5 became quiet.

30 June: The T7 and T4 lake levels decreased. At 1949 violent gas emission and spattering (4-5 m) occurred 30 m ESE on T7's slope. Big, fluid, red lava flows were emitted from the spatter cone and traveled E towards T5. The spatter cone grew 3 m in 1 hour. At 2330, the lava covered 10% of the crater bottom.

1 July: The 7-m-high spatter cone was continuing to emit lava lumps when the team left . . . . The T4/T7 lava lake level had dropped 4 m.

The lava flows, black when active, had whitish edges 24 hours after they stopped advancing, and their surface was entirely whitish after 48 hours of cooling. Gas temperatures ranged from 78 to 504°C. In hand sample, 1-3-mm nyerereite [Na2Ca(CO3)2] phenocrysts were visible. Fresh lava, gas, and sublimate samples were collected and will be analyzed by J. Keller. Mapping will be done by C. Nyamweru. All phases of the eruption were documented on 16 mm film.

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

Information Contacts: M. Krafft, Cernay, France.

"Activity remained at a low level during June. Both Southern and Main Craters released white vapours at weak to moderate rates. Emissions from Southern Crater were occasionally ash-bearing and were accompanied by thin blue vapours on 3 and 10 June. Deep rumbling noises from Southern Crater were heard on 3 June and from 17 June to the month's end. No night glow was observed, and no significant tilt changes were recorded."

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 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: P. de Saint-Ours and P. Lowenstein, RVO.

Single explosions ejected ash-laden eruption columns to 1 km above the vent on 7 and 8 July [see also 13:7].

Geologic Background. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2000 m above the Bukittinggi plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Information Contacts: VSI.

Strong explosions in April ejected acidic sulfur-rich mud onto the crater rim. Laboratory studies of the sulfurous droplets showed that they were liquid when they fell, and had melting points between 112 and 120°C. According to park guards, there have not been large eruptions like those of April and May for some time.

When geologists visited the volcano on 30 June, geyser-like phreatic activity was continuing, ejecting muddy plumes every 2-3 minutes. Plume heights were predominantly less than 15 m, with maximum observed heights of 80 m. There were frequent sequences of continuous plumes lasting 45 seconds. Most of the plumes were pine-tree shaped but some showed a broad cauliflower form. The strongest explosions originated dispersive seismic signals, without an initial explosive phase.

Since mid-April, three new sites of convective bubbling had formed (C, D, and E on figure 3). From these, bubbles with sediment were intermittently ejected, and on occasion, small mud plumes. The most intense activity was from site E. The level of the hot lake continued to descend, revealing a wide littoral crescent formed by terraces of precipitated sediment. These sediments were thixotropic, making measurements of lake level and temperature difficult. Fractures on the E edge of the lake had openings of up to 25 cm, and facilitated rockfalls into the lake.

Figure 3. Map by Gerardo Soto of the crater at Poás on 30 June 1988, showing the remnant of the 1953-55 [dome] and hot lake. Point A marks the source of the primary mud plumes, and B-E the sites of convective bubbling and secondary plume production.

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: G. Soto, UCR.

"Microseismicity showed a further increase in June with a monthly total of 238 events. All were of small magnitude (M_L <1.5) but occurred in swarms, with the highest output on 1 June (23 events) and 26-27 June (62 events). Locatable events were grouped on the NW to NE portion of the . . . caldera seismic zone (Vulcan, Beehives, Greet Harbour) at depths of 1-4 km. All measured parameters of ground deformation (EDM, tilt, levelling, and tide gauges) showed neither inflationary nor deflationary trends."

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

Information Contacts: P. de Saint-Ours and P. Lowenstein, RVO.

Since the eruption began in December, lava dome height has increased 150 m, and the N lava flow volume has grown by 2.5-3.0 x 10⁶ m³. The growth of the dome and flow slowed in June. Rockfall avalanches detected on the seismometer decreased . . . to an average of 40-50/day in June.

Geologic Background. A new lava dome, named Anak Ranakah (Child of Ranakah) was formed in 1987 in an area without previous historical eruptions at the base of the large older lava dome of Gunung Ranakah. An arcuate group of lava domes extending westward from Gunung Ranakah occurs on the outer flanks of the poorly known Poco Leok caldera on western Flores Island. Pocok Mandosawa lava dome, at 2350 m the highest point on the island of Flores, lies west of Anak Ranakah.

Information Contacts: VSI.

The occasional minor phreatic activity . . . continued through late May, then stopped as Crater Lake cooled substantially. Since the observed 12 April activity, small eruptions occurred around mid-day on 16 April, and steam clouds were observed above Crater Lake at 1000 on 19 April and 0956-0958 on 3 May. Low-amplitude 2-Hz tremor was observed daily 12 April-2 May. Geologists visited the crater 3 May, 1 June, and 21-22 June. On 3 May, total heat flow remained elevated at 290 MW (compared to 120 MW on 25 January). Crater Lake temperature was 36.5°C, a decrease of 2.3° since the last visit 12 April. Distinct convection cells with yellow-green slicks were present above several of the N vents.

A volcanic earthquake recorded at 0515 on 29 April was preceded by 1 hour of seismic quiet. Low-amplitude 2-Hz tremor with a number of small discrete earthquakes continued through May. From 24 May until 0800 on 26 May, there were 50-100 small high-frequency tectonic events that ceased when strong 2-Hz tremor began. Tremor persisted until 31 May. By 1 June, Crater Lake temperature had dropped 11° to 25.5°C, equivalent to a surface heat flow of 160 MW. Weak upwelling cells with yellow slicks were seen in the lake's N end. Minor phreatic eruptions had occurred between 21 and 28 May, possibly associated with the 24-26 May seismicity. By the 21-22 June visits, phreatic activity that began 20 March had ended. Crater Lake temperature was 22.5°C, down 3° since 1 June. No central vent upwelling occurred and N vent convection had weakened. Since early June only minor tremor had been recorded and no volcanic earthquakes were detected.

Cumulative 3-year extension of a crater EDM line totaled 28 mm. Monthly surveys indicated that this inflation accumulated from a series of four short-lived inflationary-deflationary pulses (October 1985, January & November 1986, and August 1987) associated with significant Crater Lake heating episodes that culminated in minor phreatic eruptions. Negligible deformation recorded by outer stations suggests no lasting deep magmatic movements since early 1976.

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: I. Nairn and B. Scott, NZGS Rotorua; P. Otway, NZGS Wairakei.

Several small brief ash emissions occurred daily during June, all associated with increased harmonic tremor. Ash fell to the W, usually <10 km from the vent. High-frequency earthquakes increased to 2,362 in June, while low-frequency events decreased to 1,758. A significant high-frequency swarm (273 events) occurred on 15 June (figure 13). There were 212 shallow events in June and daily energy release tended to increase, continuing a trend that began in late 1987 (figure 14). Average SO₂ content was 1,700 t/d (measured by COSPEC), a decrease from May's average of 2,435 t/d. Deformation measurements showed no significant changes.

Figure 13. Daily number of recorded seismic events of high (solid line) and low frequency (dashed line), June 1988. Courtesy of the Observatorio Vulcanológico de Colombia.

Figure 14. Cumulative seismic energy release at Ruiz, June 1985-February 1988. The solid line sums high- and low-frequency energy release, indicated by dashed and dotted lines, respectively. Courtesy of the Observatorio Vulcanológico de Colombia.

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: E. Parra, R. Mendez, and F. Muñoz, INGEOMINAS, Manizales.

Sabancaya reportedly began strong fumarolic activity in December 1986 [see also 15:05]. Interviews with area residents indicated that glowing tephra ejections from the crater were visible at night. Seismicity was felt on the flanks but was not noticed at a distance of 15 km.

A summit photograph was taken 10 August 1987, 8 months after initial reports of activity, during a civil defense helicopter reconnaissance in response to requests from residents and local authorities. Light to dense steam emerged from several sources in a moat surrounding the central plug of the middle (of at least three) summit cone. The dome, moat, and surrounding pyroclastic cone were covered with thick ice and snow except in areas adjacent to steam emission.

Geologists observed the volcano 22-24 June 1988.

22 June (Banks, Hall, Salas, Mothes, and Huaman; at 40 km distance with binoculars.) Every 0.5-2 minutes, voluminous steam pulses, some with dark, basal "rooster-tails," rose 0.5-1 km above the summit. A yellowish plume streamed horizontally 10-15 km E. A dark area of several tens to hundreds of square meters was prominent on the NE slope adjacent to the source of the steam emission.

23 June (Hall, Salas, Mothes, and Huaman; at 15 km.) Activity was similar to 22 June with perhaps slightly decreased plume heights. Strong sulfurous fumes were reported by flank inhabitants. Some cattle had died in these areas, either directly from the fumes or after eating contaminated foliage.

24 June (Banks, Lazo, Portillo, Salas, Huaman, and Tejada; from a fixed-wing flight supported by the Fuerza Aérea del Perú in coordination with the Defensa Civil. Observations are preliminary and will be improved by analysis of photographs and geological investigations on the ground.) A continuous annular crack encircled the outer flanks of an old pyroclastic cone. Weak to moderate fumarolic activity emitted vapor along the annular crack and the dome's edges. Frequent steam emissions (every 1-2 minutes) rose 0.3-5 km and originated from a vent in the moat on the SE side of the dome. Emission energy was substantially less than on 22 June. Some ejection events were lightly colored with ash but no "rooster-tail" forms were noted. Initial white steam pulses dissipated 500 m above the crater, but a yellowish plume streamed more than 10 km E. There was ~ 20-50 x 10⁶ m³ of ice and snow on Sabancaya, a substantial decrease since the August 1987 observations. A bare area, devoid of snow and ice, surrounded the annular crack at variable distances averaging 50 m. Snow beyond this bare area was lightly dusted with ash, particularly on the SE side nearest the pulsing steam vent. Fresh sulfur surrounded many of the fumaroles. Several tens of meters in the bare area, S of the summit, were yellow. No crater lake was observed in the moat between the central dome and the surrounding pyroclastic cone. No new lava or bomb craters were observed. Sabancaya appeared to be built on a pile of young, thick, blocky lava flows and domes erupted from a vent on the mid-NE flanks of the larger Ampato volcano (figure 1). No thick pyroclastic deposits were obvious on Sabancaya or Ampato.

Figure 1. Map of Sabancaya and Ampato showing the plateau, drainage system, and villages to the SE. Contour interval, 50 m. From the Chivay sheet (1:100,000), Instituto Geográfico Militar, 1980.

25 June (at 30 km from Aeroperú flight.) Activity was greatly diminished relative to that of 24 June.

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: N. Banks, CVO; M. Hall, Instituto Geofísico, and P. Mothes, Defensa Civil liaison, Quito, Ecuador; M. Lazo, G. Salas Alvarez, and H. Portillo, Univ Nacional de Arequipa; D. Huaman, Instituto Geofísico del Perú, Lima; M. Tejada, Tercera Region Defensa Civil, Arequipa.

Normal Vulcanian activity continued during May and June.

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

Information Contacts: VSI.

Slamet began to erupt ash and incandescent tephra at about 1800 on [12] July. At 0700 the next morning, explosions were occurring once a minute, ejecting incandescent fragments to 500 m above the vent. Ash fell 45 and 85 km NE at Cirebon and Brebes. By 1500, eruptive activity had stopped but heavy fuming continued from one of the active craters, feeding an 800-m plume. The moderate activity was consistent with most of the volcano's 38 eruptions in the past 200 years and no evacuation was ordered.

The eruption was preceded by periods of brief harmonic tremor on 9 July and six hours of increased seimicity including brief tremor episodes on 10 July. A second radio-telemetered seismometer will be installed on the volcano.

Geologic Background. Slamet, Java's second highest volcano at 3428 m and one of its most active, has a cluster of about three dozen cinder cones on its lower SE-NE flanks and a single cinder cone on the western flank. It is composed of two overlapping edifices, an older basaltic-andesite to andesitic volcano on the west and a younger basaltic to basaltic-andesite one on the east. Gunung Malang II cinder cone on the upper E flank on the younger edifice fed a lava flow that extends 6 km E. Four craters occur at the summit of Gunung Slamet, with activity migrating to the SW over time. Historical eruptions, recorded since the 18th century, have originated from a 150-m-deep, 450-m-wide, steep-walled crater at the western part of the summit and have consisted of explosive eruptions generally lasting a few days to a few weeks.

Information Contacts: VSI.

O. González-Ferrán presented additional information about the cause and dynamics of the 29 November 1987 debris flow.

"Tupungatito volcano has been increasing its thermal activity since January 1986 and on 28, 29, and 30 November 1987 registered an increase in local shallow seismic activity. Seismographs of the Chilean and Argentine nets registered some B-type shocks. The seismicity caused 15 rockfalls of different magnitudes within 5-20 km of the historically active craters . . . (N and NW of the ice-filled summit caldera) during that period (figure 2).

Figure 2. Sketch map illustrating the 15 rockfalls documented near Tupungatito in late November (heavy arrows), and tabulating the casualties and damage caused by the 29 November debris flow. Courtesy of O. González-Ferrán.

"One of the shocks occurred at 103340 on the 29th, causing one of the rockfalls, which reached a volume of 17.25 x 10⁶ m³ in the headwaters of the Estero Parraguirre, 17 km from the active crater and the epicentral zone of the seismic activity.

"A mass of sedimentary rocks from the headwaters of the Estero Parraguirre free-fell 1100 m onto the terminal front of a glacier, impacting it with a velocity of ~300 km/hour. Incorporated in the impact was 1.2 x 10⁶ m³ of ice, as well as 11 x 10⁶ m³ of snow along the Estero.

"This generated the avalanche debris flow that discharged into the Río Colorado, temporarily obstructing the flow of the Colorado's waters. Finally, the debris flow reached the Central Hidroeléctrica de Maitenes at 1114 with a velocity of 50-60 km/hour, causing the death of 41 persons and millions of dollars in losses to buildings and machinery along its path. In addition, by damaging the Las Vizcachas plant, it affected the supply of drinking water to nine communes of the city of Santiago (population 4.5 million) for 24 hours.

"The high instability and strong fracturing of the nearly vertical strata of Mesozoic sedimentary rocks in this mountainous region of the Tupungatito area, along with the supersaturation and water pressure generated by snowmelt and the abnormal seasonal temperature increase, facilitated rockfalls and avalanches as a consequence of the local volcano-seismic activity of Tupungatito."

Geologic Background. Tupungatito volcano, the northernmost historically active volcano of the central Chilean Andes, is located along the Chile-Argentina border about 90 km E of Santiago and immediately SW of the Pleistocene Tupungato volcano. Tupungatito consists of a group of 12 Holocene andesitic and basaltic andesite craters and a pyroclastic cone at the NW end of the 4-km-wide, Pleistocene dacitic Nevado Sin Nombre caldera, which is filled by glaciers at its southern end and is breached to the NW. Lava flows from the northernmost vent have traveled down the NW flank breach. Tupungatito has produced frequent mild explosive eruptions during the 19th and 20th centuries.

Information Contacts: O. Gonzalez-Ferrán, Univ de Chile; J. Castrano, Instituto Nacional de Prevención Sísmica, San Juan, Argentina; S. Kunstmann, Empresa Nacional de Electricidad, Santiago; G. Ugarte, Pontificia Univ Católica de Chile, Santiago.

"Low-level activity persisted. Weak to moderate amounts of white vapour continued to be released from the summit crater. The recorded seismicity fluctuated between 1,500 and 300 small B-type events/day (relatively less numerous than during the last two months). The average amplitude of these events built up considerably (up to 8 times the norm) from early May to mid-June before decreasing again to regular non-eruptive levels. Apparent tremors were also recorded for long periods from 6-10, 15-16, and 19-29 June. It is not certain to what extent that signal was caused by the strong seasonal wind.

"An aerial and field inspection was carried out on 6 and 7 June. The interior of the summit crater was mostly obscured by abundant white and blue vapours. Little morphological change was noted compared to the last inspection, in July 1987, apart from the erosion. However, a series of fissures enhanced by fumarolic encrustations were observed to run horizontally, ~100 m below the rim of the internal S wall.

"Dry tilt measurements indicated summit area deflation of up to 55 µrad since the last eruption in November 1985. EDM measurements showed minor contractions of three lines radial to the flanks of the volcano since previously measured in November."

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: P. de Saint-Ours and P. Lowenstein, RVO.

White Island's activity has changed from continuous moderate gas and ash emission to episodic short-duration discrete eruptions. The largest eruption since September 1987 occurred at 1030 on 27 April; it was slightly larger than the 14 March explosion. The phreatomagmatic eruption emitted red ash, lithic blocks, and scoria bombs. A black plume (3.5 km high) was observed >50 km away, from the Bay of Plenty coast. Ash fell into the sea and moderate ash emission continued after the initial explosion.

The eruption followed 9.5 hours of relatively weak microseismicity. Its onset was marked by 2-3 minutes of relatively low-frequency (3-4 Hz) C-type seismicity that increased in frequency (6-7 Hz) and amplitude (60 mm) between 1031 and 1033, then declined to background by 1036. Twenty minutes of low-amplitude tremor followed, with lower frequency (2-3 Hz) than before the eruption. The tremor ceased after two high-amplitude/duration-ratio A-type volcano-tectonic events at 1058 and 1100. Two more volcano-tectonic events occurred at 1254 and 1301. Medium- to high-frequency tremor had dominated seismic records in the two weeks preceding the eruption.

Numerous swarm-like A-type events were recorded 4-6 May. Medium-frequency volcanic tremor was established by 7 May but declined to background by 0200 on 9 May. Small E-type (explosion) earthquakes occurred 7 May at 1821, 8 May at 1257, 12 May at 0357 and 2541, and 13 May at 0722. Tremor reappeared 11 May and dominated records in succeeding weeks.

When geologists visited the volcano on 27 May, impact craters probably produced by the 27 April eruption extended 750 m from Hitchhiker vent to Crater Bay. Numerous ash-covered scoria bombs deposited by the same eruption were found on the crater floor. Post-14 April ejecta at the crater rim consisted of 20 mm of fine pink ash, 25 mm of coarse dark ash, and lithic lapilli. The interior walls of Fumarole 6, 200 m E of Hitchhiker vent, were incandescent. A small eruption 10 m N of Fumarole 6 had ejected lithic blocks as large as 20 cm in size.

A 15 June visit revealed no changes apart from possible minor collapse along the rim of 1978 crater. Fumarole 6 was still incandescent and its temperature had declined only slightly, to 785 from 830°C two months earlier. Hitchhiker vent emitted gas that contained a little ash. A deformation survey measured deflation of the main crater, E and NE of Hitchhiker vent. Rapid local inflation had occurred around Fumarole 6 during its strongest activity.

Since 15 June, White Island seismicity has changed significantly. Tremor became more intermittent until it ceased 18 June. E-type earthquakes occurred at 0205 on 19 June (large), 1308 on 21 June (very small), 1026 on 22 June (medium), and 0705 on 23 June (large). Only the 23 June event was associated with an observed eruption, when pilots Morter and Ford (Air New Zealand) noted a "mushrooming" eruption column rapidly rising to 3.0 km at 0710.

Geologic Background. The uninhabited White Island, also known as Whakaari in the Maori language, 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 summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of eruptions since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced 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.

Information Contacts: I. Nairn, NZGS Rotorua.

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/).