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/).

We report Akutan non-eruptive seismic activity after our mid-1996 report (BGVN 21:06) through December 2010. AVO (Alaska Volcano Observatory) reporting emphasized seismicity in 2000, 2007, 2008, 2009, and 2010, including seismicity during 2007 triggered by an M 8.2 earthquake in the Kurile islands.

Background. Akutan Island is home to indigenous people located in several coastal villages, and the base of a large fish processing facility. The island resides in the Aleutian arc, a string of islands projecting ~2,000 km into the Bering Sea from the Alaskan Peninsula (figure 2).

Figure 2. Akutan, an island ~32 km by ~20 km, lies on the E Aleutian arc in the Bering Sea near the coast of Alaska. Courtesy of Neal and McGimsey (1996), revised by GVP.

Akutan Island (figure 3) has a vegetated coast line dotted with spectacular bridges and caves created by the erosion of numerous lava tubes. Waythomas and others (1998) presented a map showing that much of the coastline is susceptible to rockfall avalanches and points out that these may trigger local tsunamis. The authors also analyzed the likely path of lava flows.

Figure 3. Akutan Island and its volcanic features, including fumaroles, hot springs, and a new steaming area. A cindercone resides in the NE quadrant of the generally circular caldera. The fumarole field, shown in red, is down slope on the E flank of the summit. The Trident seafood plant, shown as a yellow star, lays along the E coast. Courtesy of AVO, revised by GVP.

A 2 km diameter caldera atop the 1,303 m high volcano is breached to the NW, and elsewhere encircled by crater walls 60 to 365 m high. The caldera contains a ~200 m high cinder cone, and a small lake. Fumeroles lay along the summit flank toward the E (Miller and others, 1998). The cinder cone has been the site of all historical eruptive activity (Richter and others, 1998; Waythomas and others, 1998).

The village of Akatan ( figure 4), ~ 13 km E of the volcano, hosts the Trident seafood plant, the largest such plant in North America, employing up to 900 seasonal workers (McGimsey, 2011). Akutan villagers and seafood plant employees fled the island during the 1996 seismic events (Li and others, 2000). The cited references provide many details omitted here.

Figure 4. Akutan coastal image with seafood plant in foreground adjacent to Akutan village. Image courtesy of AVO, created by Helena Buurman.

According to Diefenbach and others (2009), Akutan has been the most active of the volcanoes monitored by AVO, having over 20 eruptions since 1790; more than any other Alaskan volcano.

A 2009 report by AVO noted that 11 eruptions occurred at Akutan during 1980-1992, many lasting several months (table 5). The most recent eruption started in December 2009 but the eruption's end was not clearly constrained (table 5). A seismic swarm took place in 1996, an episode without a corresponding eruption.

Table 5. Akutan eruptions tabulated from January 1980 to 2009. Courtesy of Diefenbach and others (2009).

From 1980 to 2009, Alaskan eruptions made up to 77% of the total reported in the United States (Diefenbach and others, 2009). Note that, even though during 1980-2009 Akutan erupted more times than other US volcanoes, this distinction is only one of many that can be used for comparisons. For example, in the course of that interval and the 11 recorded eruptions at Akutan, it clearly emitted less material and the eruptive intervals spanned much less time than eruptions at either Kilauea or Mt. St. Helens.

1996 seismicity. In March 1996, two strong earthquake swarms struck the island, causing minor damage and prompting some residents and dozens of plant employees to leave the island. The seismicity, reported in BGVN 21:06, was probably the result of a magmatic intrusion (Lu and others, 2000). They stated the following:

"In March 1996 an intense swarm of volcano-tectonic earthquakes (~3,000 felt by local residents, M max = 5.1, cumulative moment of 2.7 × 10¹⁸ N m) beneath Akutan Island in the Aleutian volcanic arc, Alaska, produced extensive ground cracks but no eruption of Akutan volcano. Synthetic aperture radar interferograms that span the time of the swarm reveal complex island-wide deformation: the western part of the island including Akutan volcano moved upward, while the eastern part moved downward. The axis of the deformation approximately aligns with new ground cracks on the western part of the island and with Holocene normal faults that were reactivated during the swarm on the eastern part of the island. The axis is also roughly parallel to the direction of greatest compressional stress in the region. No ground movements greater than 2.83 cm were observed outside the volcano's summit caldera for periods of 4 years before or 2 years after the swarm. We modeled the deformation primarily as the emplacement of a shallow, E-W trending, north dipping dike plus inflation of a deep, Mogi-type [spherical] magma body beneath the volcano. The pattern of subsidence on the eastern part of the island is poorly constrained. It might have been produced by extensional tectonic strain that both reactivated preexisting faults on the eastern part of the island and facilitated magma movement beneath the western part. Alternatively, magma intrusion beneath the volcano might have been the cause of extension and subsidence in the eastern part of the island."

The 11 March 1996 swarm involved more than 80 earthquakes of M 3.0 or greater with the largest measuring M 5.2. The 13 March swarm involved more than 120 events of M 3.0 or greater with the largest measuring M 5.3 (Waythomas and others, 1998).

As a result, new ground cracks developed ( figure 5) and Waythomas and others (1998) described them as follows: "Numerous fresh, linear ground cracks were discovered in three areas on Akutan Island during field studies in the summer of 1996. Ground breaks and cracks likely formed during the strong seismic swarms in March. The ground cracks extend discontinuously from the NE side of the island near Lava Point to the island's SE side [figure 5].

"The most extensive ground cracks are between Lava Point and the volcano summit [ figure 6]. In this area, the cracks are confined to a zone 300 to 500 m wide and 3 km long. Vertical displacement of the ground surface along individual cracks is 30 to 80 cm. The ground cracks probably formed as magma moved toward the surface between the two most recently active vents on the volcano. Ground cracks on the SE side of the island occur on known faults, indicating that they probably formed in response to motion along these preexisting structures. No ground cracks were found at the head of Akutan Harbor even though this was an area where numerous earthquakes occurred from March through July, 1996."

Figure 5. Location of ground cracks and seismometers on Akutan, as published in 1998. Three sets of ground cracks, shown as black lines, presumably formed during the March 1996 earthquake swarm. The most extensive breaks occurred on the NW flank of the volcano near Lava Point with the other two shorter sets to the SE in line with the first. On the map, the green triangles locate seven monitoring stations, one at the summit, and others spread throughout the island as well as one at the village. Courtesy of AVO, Waythomas and others (1998), annotated by GVP.

Figure 6. Ground breaks like this were found at Akutan in a zone about 300-500 m wide and ~ 3,000 m long on the NW flank of the volcano. Surface deposits offset by the cracks consist of course tephra and colluvium. The backpack in the lower left delineates scale (distant figures removed for clarity). Courtesy of AVO, Waythomas and others (1998).

A permanent seismic network was installed during the summer of 1996 which currently consists of seven short-period stations and five broadband stations (figure 5).

Akutan seismicity, 2000 to 2010. According to AVO annual reports covering the interval 1997-2011, noteworthy seismicity occurred during the years 2000, 2007, 2008, 2009, and 2010.

On 19 January 2000, five earthquakes occurred in less than 30 minutes with epicenters 10-11 km E of the summit at hypocentral depths of ~5-6 km. This was the same region as the March 1996 volcanic swarm.

Akutan was one of several Alaska volcanoes with behavioral anomalies triggered by the M 8.2 earthquake generated in the Kurile Islands on 12 January 2007 at 0423 UTC (McGimsey, 2011). Seismologists located four of the seven largest triggered M 0.0-0.5 earthquakes at Akutan and found their depths in the range from +0.86 to -2.17 km (figure 7). The locations fell along the trend of intense seismicity and ground breakage that occurred in March 1996 at Akutan (Neal and others, 1997; Waythomas and others, 1998; Lu and others, 2005). The AVO Akutan seismic network recorded the triggered seismicity.

Figure 7. Epicenters at Akutan triggered by the 13 January 2007, M 8.2 Kurile Islands earthquake (the event occurred at 0423 UTC, 12 January 2007). The four largest events (red dots) lie along the same trend (blue line) as that of intense seismicity with accompanied ground breakage that occurred during dike intrusion in March 1996 (Waythomas and others, 1998). Open triangles mark locations of seismic stations. Plot of earthquake locations by John Power. Courtesy of AVO, McGimsey and others (2011).

In early October 2007, AVO remote sensors detected signs of renewed inflation of the W flank during the previous month using GPS time series. This inflation was in the same area that inflated during the 1996 seismic crisis. A few days later, on 8 October 2007, the manager of the Trident seafood processing plant called to alert AVO of strong steaming near Hot Springs Bay (figure 8) at a spot significantly up slope from established hot springs in the valley. This plume location was considered "new" by local observers. The established lower-valley thermal springs rarely emit a concentrated, vertically rising steam plume and most earlier reports of steaming arose from the prominent fumarole field located at the 460 m elevation of the E flank at the headwaters of Hot Springs Bay valley. This is also the area of maximum deflation following the 1996 seismic swarms. No unusual seismic activity was noted for the period of W-flank inflation or the location of this steaming episode (McGimsey and others, 2011).

Figure 8. Midway up Akutan's Hot Springs Bay valley on the E flank of Akutan from a point well upslope of the previously active hot springs area, a steam column rises from a new site. AVO photo taken 8 October 2007 by David Abbasian.

In 2008, over 100 seismic events were recorded. During the next two years, Akutan seismic events decreased to about half that number. During 2010 low frequency earthquakes doubled compared to 2009 (Table 6).

Table 6. Akutan seismic activity for 2008-2010 compiled from AVO/USGS annual reports. Total earthquakes (in the second column) summed those in the Volcano-tectonic and Low frequency columns. '--' indicates data not reported. Courtesy of AVO.

According to AVO, Akutan seismic events during the years 2009 and 2010 were temporally spread roughly throughout the months except for a tight cluster of M 2 earthquakes reported at depths of between ~5 km to ~10 km during the first weeks of January 2010. The majority of earthquakes in 2010 were located within ~5 km of the crater along a N-trending line spanning 10 km. In 2009 the spread was longer, over 20 km.

References. Diefenbach, A.K., Guffanti, M., and Ewert, J.W., 2009, Chronology and references of volcanic eruptions and selected unrest in the United States, 1980-2008: U.S. Geological Survey Open-File Report 2009-1118, 85 p. [http://pubs.usgs.gov/of/2009/1118/].

Dixon, J.P., Stihler, S.D., Power, J.A., and Searcy, C.K., 2010, Catalog of Earthquake Hypocenters at Alaskan Volcanoes: January 1 through December 31, 2009: U.S. Geological Survey Data Series 531.

Dixon, J.P., Stihler, S.D., Power, J.A., and Searcy, C.K., 2011, Catalog of earthquake hypocenters at Alaskan Volcanoes: January 1 through December 31, 2010: U.S. Geological Survey Data Series 645.

Kent, T., 2011, Hydrothermal Alteration of Open Fractures in Prospective Geothermal Drill Cores, Akutan Island, Alaska, Fall Meeting of the American Geophysical Union, 2011, Abstract ##V13D-2637.

Lu, Z., Wicks Jr., C., Power, J.A., and Dzurisin, D., 2000, Ground deformation associated with the March 1996 earthquake swarm at Akutan volcano, Alaska, revealed by satellite radar interferometry, J. Geophys. Res., 105(B9), 21,483-21,495 (DOI:10.1029/2000JB900200).

Miller, T.P., McGimsey, R.G., Richter, D.H., Riehle, J.R., Nye, C.J., Yount, M.E., and Dumoulin, J.A., 1998, Catalog of the historically active volcanoes of Alaska: U.S. Geological Survey Open-File Report 98-582, 104 p. (Also available at http://www.avo.alaska.edu/downloads/catalog.php.)

McGimsey, R.G., Neal, C.A., Dixon, J.P., Malik, Nataliya, and Chibisova, M., 2011, 2007 Volcanic activity in Alaska, Kamchatka, and the Kurile Islands: Summary of events and response of the Alaska Volcano Observatory: U.S. Geological Survey Scientific Investigations Report 2010-5242, 110 p.

Neal, C.A. and McGimsey, R.G., 1997, 1996 Volcanic Activity In Alaska And Kamchatka: Summary Of Events And Response Of The Alaska Volcano Observatory: U.S. Geological Survey Open-File Report 97-433.

Richter, D.H., Waythomas, C.F., McGimsey, R.G., and Stelling, P.L., 1998, Geologic map of Akutan Island, Alaska: U.S. Geological Survey Open-File Report 98-135, 22 p., 1 plate.

Waythomas, C.F., Power, J.A., Richter, D.H., and McGimsey, R.G., 1998, Preliminary volcano-hazard assessment for Akutan Volcano east-central Aleutian Islands, Alaska: U.S. Geological Survey Open-File Report 98-0360, 36 p., 1 plate.

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: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA, b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys.

Our last Bulletin report (BGVN 35:03) covered eruptive activity through the last eruptive episode, which ended 12 January 2010.

Beginning 14 August and through 10 September 2010, the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) recorded a slow but steady increase in the number and magnitude of earthquakes from Piton de la Fournaise. Inflation of the summit area began in late August. The following report is based on data received from OVPDLF. It discusses eruptions and related behavior as late as 10 December 2010.

On 13 September 2010, localized deformation W of the Dolomieu crater and a small number of landslides in the crater was observed. On 20 September instruments recorded a significant increase in the number of earthquakes located at the W and S of the Dolomieu crater, although their average magnitude was low.

On 24 September, OVPDLF reported the possibility of an impending eruption. During the night, a seismic crisis began with a series of several tens of earthquakes localized under the Dolomieu crater, which was associated with inflation (approximately 3 cm), especially close to the summit. The most significant deformations were measured on the rim and the N and S sides of the volcano, indicating a shallow magma body was distributed directly below the Dolomieu crater. After decreasing on 27 September, seismicity rose again by 29 September. Earthquakes were located at the base of the volcano, and inflation was noted particularly in the E. A significant number of landslides were detected in the crater. The Alert level remained at 1 ("probable or imminent eruption").

Beginning 7 October 2010, there was a steady increase in the number and magnitude of volcano-tectonic (VT) earthquakes. During 10-11 October the summit area inflated 3-7 cm, and an increase in the number of landslides in the crater was detected. The Alert level remained at 1.

Increased seismicity was again recorded on 14 October 2010, with a new seismic crisis of more than several hundred earthquakes. During this phase, significant ground deformation occurred near the summit, which generated numerous rockfalls inside the Dolomieu crater. At 1411, the seismicity moved toward the SE part of the volcano (Château Fort), and at 1910 an eruption began within the Enclos Fouqué, about 1.5 km SE of the Dolomieu crater rim. Lava fountaining occurred from four vents along a fissure. The Alert level was raised to 2 ("eruption in progress in the Fouqué caldera").

Eruptive activity continued on 15-16 October 2010, developing along a fissure. This eruption included low lava fountains and fed a lava flow moving to the ESE. Lava issued from an area close to the old Château Fort crater at the base of the SE flank of Dolomieu crater and remained within the Enclos Fouqué. Four small cones were active along the eruptive fissure; lava fountaining occured from three of them. A lava flow moved slowly about 1.6 km to the E and SE and approached the break in slope at the Grandes pentes. OVPDLF measured lava temperatures of ~1,100°C.

On 17 October 2010 explosions and degassing accompanied lava emissions. These explosions and degassing decreased on 18 October. The volcanic tremor also decreased to one-seventh compared to the beginning of the eruption. The number of VT events remained low (7/day); the strongest event occurred at 2323, a M 1.4 earthquake localized at about 1,600 m depth under the Bory summit crater. The base and the summit of the volcano remained in inflation. Preliminary estimation of the lava volume erupted was 600,000 m³.

During 19-21 October consistent eruptive activity continued, with weak emissions and small lava fountains at the main eruptive vents located along the eruptive fissure. Explosive activity and degassing decreased, and tremor remained stable. Lava flows extended ESE to ~2 km. Gas emissions decreased, but concentrated to the S and W of the fissure.

On 22 October 2010 eruptions continued, located close to the Château Fort area, in the southern portion of the Enclos Fouqué. During 22-26 October lava fountains and gas emissions originated from one vent, and lava traveled ESE. Gas emissions decreased significantly. At this point, only one cone was active and only a few lava fountains were observed. Volcanic tremor was stable. No earthquakes had been reported since the previous day. GPS ground deformation showed a weak deflation under the volcano.

A sudden increase in activity and tremor began on 27 October 2010 and continued on 28 October. On 29 October, observation made during a flight disclosed that a part of summit cone 3 (the only active cone) had collapsed. Some lava ejecta and gas emissions occurred from this cone, which also contained a small active lava pond. Lava from this cone fed a small, slow moving lava flow. This new lava field remained upstream of the cone named Gros Benard. On 31 October, OVPDLF reported that the eruption had ended.

On 9 December 2010, following a seismic crisis and inflation, a new eruption began from an eruptive fissure oriented N-S, just above the Mi-Côte peak, at ~2,500 m elevation, characterized by lava fountaining and two lava flows. Many small landslides occurred in the Dolomieu crater. Later that day lava flows from two fissures on the N flank of Piton de la Fournaise, ~1 km NW of the Dolomieu crater rim, traveled about 1.5 km N and NW. On 10 December 2010, seismicity and deformation measurements indicated that eruption of lava had stopped.

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: Laurent Michon and Patrick Bachélery, Laboratoire GéoSciences Réunion, Institut de Physique du Globe de Paris, Université de La Réunion, CNRS, UMR 7154-Géologie des Systèmes Volcaniques, La Réunion, France; Guillaume Levieux, and Thomas Staudacher, and Valérie Ferrazzini, Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr/ovpf/actualites-ovpf/).

[NOTE: The location shown on the summary page is that for the main summit of Hierro volcano on El Hierro Island. The location of the submarine vent of Hierro that erupted beginning in October 2011 was found to be at latitude 27°37.18' N and longitude 17° 59.58' W.]

In BGVN 36:10 we discussed a submarine eruption of a vent of Hierro volcano that began in early October 2011 S of La Restinga, a town at the southermost tip of El Hierro Island (figure 7). The eruption was preceded by increased seismicity, although this seismicity declined significantly by mid-November 2011 (figures 8 and 9). Based on seismic activity monitored by the Instituto Geográfico Nacional (IGN-National Geographic Institute), authorities for the Canary Islands decided in late March 2012 to shut down the web cameras at La Restinga. Volcanic tremor was still present, although at minimal levels, and some seismicity continued beneath the island. The patch of brown water over the submarine vent (location shown in figure 8) continued to be observed throughout both March and April (figure 10).

Figure 7. Location maps showing the Canary Islands, with volcanoes, and their intra-plate location with respect to plate boundaries. Information on the locations and latest eruptions of the volcanoes is found in table 1. El Hierro Island (and its volcano of the same name) appears on the SW margin of the archipelago. (a) Geographic and geodynamic setting of the NW African continental margin with the Canary Islands; numbers on the Canary Islands show the ages of the oldest surface volcanism, in millions of years before present (Ma). The Canary Islands developed in a geodynamic setting characterized by Jurassic oceanic lithosphere formed during the first stage of opening of the Atlantic at 180-150 Ma and lying close to a passive continental margin on the African plate. The archipelago lies adjacent to a region of intense deformation comprising the Atlas mountains, a part of the Alpine orogenic belt. The intraplate Canary Islands archipelago is within the African plate, bounded by the Azores-Gibralter fault on the north and the mid-Atlantic ridge on the west. (b) Close-up view of the Canary Islands, showing the names of the islands, and the ages of the oldest surface volcanism for each island. Courtesy of Viñuela (2012) and Carracedo and others (2002).

Table 1. Background information on the six main Canary Islands and their volcanoes. Latest eruption dates are from Siebert and others (2010) and Smithsonian's Global Volcanism Program website. The volcano age indicates date of oldest volcanic rocks of each island (Carracedo and others, 2002).

Figure 8. Topographic map of El Hierro Island showing the locations of IGN seismic monitoring stations. A small red triangle offshore of the southernmost tip of the island locates the submarine vent of Hierro that began erupting in October 2011. The pronounced curved form on the N side of the island resulted from lateral collapse; see figure 11b. Courtesy of IGN.

Figure 9. Cumulative energy (in joules) based on daily seismic monitoring at El Hierro island from 18 July 2011 through 19 March 2012. The sharp upturn in the curve occurred ~27 September 2011, leveled out ~9 October 2011, resumed to a sharp upturn on ~29 October 2011 to level out again ~21 November 2011. Since that time, the seismic energy has not increased measureably. Courtesy of IGN.

Figure 10. A natural-color satellite image collected on 10 February 2012 showed the site of the Hierro submarine vent eruption, offshore from the fishing village of La Restinga. Bright aquamarine-colored water indicated high concentrations of volcanic material in the water above the vent, which lies at a water depth of between 200 and 300 m. A patch of turbulent light brown water on the sea surface indicated the area most strongly affected. This image was acquired by the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite. NASA Earth Observatory image prepared by Jesse Allen and Robert Simmon, using EO-1 ALI data.

Bathymetry and water chemistry. For 4 months following the eruption (a period from 22 October 2011 through 26 February 2012), the Instituto Oceanográfico Español (IOE-Spanish Oceanographic Institute) conducted 12 oceanographic cruise legs (called La Campaña Bimbache-Bimbache Campaign; Bimbache refers to native inhabitants of El Hierro), documenting the submarine morphology and water chemistry changes resulting from the eruption. Reports of these cruises on board the research vessel Ramon Margalef are found on the IEO web site; some highlights follow.

During the 7th leg, 8-12 January 2012, IEO scientists found that the volcano's summit was ~130 m below the water surface, 30 m more since its last survey on 2 December 2011. The diameter of the volcano's base was about 800 m, and its height ~200 m above the ocean floor. The total volume of material emitted since the eruption onset in October 2011 to the date of this cruise leg, calculated by bathymetry compared to 1998, was 145 x 10⁶ m³. This volume included a new eruptive cone and associated lava flows. This new material nearly completely covered the W escarpment of the submarine canyon where the eruption was located. It was also found that a split in the top of the cone recorded in the bathymetric survey of 30 November 2011 no longer existed.

During the 9th leg, 6-8 February 2012, Hierro volcano was found to have grown somewhat more in height. The most significant differences between this and the 7th leg (January 2012) occurred at the top of the cone, including a slight increase in the elevation of its summit, which now reached to ~120 m below the water surface, and the emergence of a secondary cone, ~23 m high, attached to the side of the main cone, with a summit depth of 200 m. The emergence of the secondary cone and the greater mass of material on the volcano flank had caused a flattening of the structure. The slope ranged between 25° and 30° on the N flank, with slopes of up to 35° on the E and W flanks.

The 10th leg, 9-13 February 2012, was dedicated to water sampling. Observers found very high levels of hydrogen sulfide (H₂.S), with a below normal pH, and very high partial pressure of CO₂.

The IEO report of the 11th leg, 23-24 February 2012, notes that the coordinates of the main summit of the new volcano were: latitude 27°37.18' N and longitude 17° 59.58' W.

During a cruise from 5 to 9 April 2012 by researchers from IEO and the University of Las Palmas de Gran Canaria (ULPGC), 19 hydrographic stations were occupied. Data was collected on the physical-chemical properties of the water around the volcano (including temperature, salinity, depth, fluorescence, turbidity, dissolved oxygen, pH, alkalinity, total inorganic carbon, and CO₂ partial pressure). The researchers intend to quantify the environmental impact caused by the volcano 7 months after the beginning of the eruption. The physical-chemical properties of the water column in an area of 500 m radius around the submarine volcanic cone where found to be still significantly affected. At this stage, the degassing of the volcano was fundamentally of CO₂, with complete absence of sulfur compounds.

Remote submarine vessel observations. The University of Las Palmas de Gran Canaria (ULPGC) web site on 16 March 2012 reported initial filming of the submarine vent using the robot submarine vessel Atlantic Explorer. They reported particles of tephra in the mouth of the still-active vent. At a depth of 120 m, hot jets emerged from a vent, forming converging water convection cells reaching upwards to depths of ~40-60 m. From the same depths, some pyroclastic ejecta were seen in the form of large volcanic bombs. The SW flank of the main volcanic vent cone sloped steeply and was the resting place of many large pyroclastics, some of which are similar to the hollow volcanic bombs (lava balloons) that reached the ocean surface during November and December 2011. Marine life had returned to near the vent, and at a depth of ~170 m and under a rain of ash they observed a school of fish (possibly amberjack).

Geologic setting. Carracedo and others (2012a) provided further details on the geologic setting of El Hierro island and the 2011 vent eruption. They state that "As early as 1793, administrative records of El Hierro indicate that a swarm of earthquakes was felt by locals; fearing a greater volcanic catastrophe, the first evacuation plan of an entire island in the history of the Canaries was prepared. The 1793 eruption was probably submarine . . . over the next roughly 215 years the island was seismically quiet. Yet seismic and volcanic activity are expected on this youngest Canary Island due to its being directly above the presumed location of the Canary Island hot spot, a mantle plume that feeds upwelling magma just under the surface, similar to the Hawaiian Islands." Currently, roughly 10,000 people live on the island of El Hierro.

The report continued (references have been removed): "El Hierro, 1.12 million years old, is the youngest of the Canary Islands and rests on a nearly 3,500-m-deep ocean bed (figure 11a). According to stratigraphic data, two eruptions are known to have occurred on El Hierro, one ~4,000 years ago at Tanganasoga volcano complex and one 2,500 ± 70 years ago at Montaña Chamuscada cinder cone (figure 11b). The principal configuration of El Hierro is controlled by a three-armed rift zone system. The last stage of growth of El Hierro started some 158,000 years ago, characterized by volcanism that concentrated mainly at the crests of the three-armed rift system."

Figure 11. El Hierro maps and diagrams to illustrate the setting and context of the 2011 eruption. (a) Location of the submarine vent (red star); image from Masson and others (2002); inset shows the island's location within the Canary Islands archipelago. (b) Simplified geological map of El Hierro, showcasing two recent eruptions. (c) Epicenter distribution migrating southward, 19 July to 8 October 2011 (data from IGN). (d) Hypocenter depths increased during 3 August to 9 October 2011, and then they became shallower (

Carracedo and others (2012a) described the pattern of earthquakes detected by IGN's permanent seismic network. The pattern consisted of an event every few minutes and an average short-period body wave magnitude of about M 1-2. Though the most of these quakes were largely insignificant in terms of seismic hazards, they initially focused N of the island (figure 11c), concentrated within the lower oceanic crust at depths of 8 and 14 km, in agreement with petrological evidence of previous eruptions. The seismic and petrological data are thus in line with a scenario of a magma batch becoming trapped as an intrusion horizon near the base or within the oceanic crust. Shifting seismic foci suggested that magma progressively accumulated and expanded laterally in a southward direction along the southern rift zone, which caused a vertical surface deformation of ~40 mm based on GPS measurements.

The report continues: "Soon after the initial earthquake swarm was observed by the permanent seismometers associated with IGN, efforts were made to mobilize a more complete monitoring seismic and GPS array spaced roughly 2,000 m apart throughout the island. This expanded network, completely installed by September 2011, allowed scientists to follow the progress of the recent activity at El Hierro."

"The new instruments revealed that earthquakes and magma transport remained active but as of the beginning of October 2011 showed no sign of having breached the oceanic crust. Instead, magma continued to move south until, on 9 October, the magma apparently progressed rapidly toward the surface, as indicated by the first-time occurrence of shallow earthquakes (at depths of

"The eruption continued through 15 October, with the appearance of submarine volcanic 'bombs' with cores of white and porous pumice-like material encased in a fine coating of basaltic glass [figure 12; see figure 4 in BGVN 36:10 showing a cross-section view of a bomb]. These bombs are probably xenoliths from pre-island sedimentary rocks that were picked up and heated by the ascending magma, causing them to partially melt and vesiculate." According to Carracedo and others (2012b), "the interiors of these floating rocks are glassy and vesicular (similar to pumice), with frequent mingling between the pumice-like interior and the enveloping basaltic magma. These floating rocks have become known locally as 'restingolites' after the nearby village of La Restinga." Some 'restingolite' samples contain quartz crystals, jasper fragments, gypsum aggregates and carbonate relicts, materials more compatible with sedimentary rocks than with a purely igneous origin for the cores of the floating stones. Figure 13 shows one explanation for the formation these bombs.

Figure 12. Lava fragments ('restingolites') floating on the sea surface about 2 km offshore from La Restinga village on 27 November 2011. At some times a few hundreds of these fragments were present. They arrived at the sea surface at high temperature and, while cooling, they vaporized sea water, suffered intense degassing, and, in some cases broke into small pieces. Courtesy of Alicia Rielo, IGN.

Figure 13. Sketch summarizing the inferred structure of El Hierro Island and the 2011 intrusive and extrusive events. Ascending magma that, according to the distribution of seismic events prior to eruption, moved sub-horizontally from N to S in the oceanic crust and contacted pre-volcanic sedimentary rocks. The floating blocks were attributed to magma-sediment interaction beneath the volcano. These blocks, called 'restingolites', were carried toward the ocean floor during eruption, being melted and vesiculated while immersed in magma. Once erupted onto the ocean floor, they separated from the erupting lava and floated on the sea surface due to their high vesicularity and low density (from Troll and others, 2011). Courtesy of Carracedo and others (2012b).

2012 El Hierro Conference. A conference on the 2011-2012 submarine eruption will take place in the Canary Islands on 10-15 October 2012. The scientific program will cover a broad variety of topics related to volcanic risk management at oceanic island volcanoes and the balance between short-term hazards posed by volcanoes and benefits of volcanism over geologic time.

References. Carracedo, J-C., Perez-Torrado, F-J., Rodriguez-Gonzalez, A., Fernandez-Turiel, J-L., Klügel, A., Troll, V.R., and Wiesmaier, S., 2012a, The ongoing volcanic eruption of El Hierro, Canary Islands, Eos, Transactions, American Geophysical Union, v. 93, no. 9, pp. 89-90.

Carracedo, J.C., Torrado, F.P., González, A.R., Soler, V., Turiel, J.L.F., Troll, V.R., and Wiesmaier, S., 2012b, The 2011 submarine volcanic eruption in El Hierro (Canary Islands), Geology Today, v. 28, issue 2, pp. 53-58.

Carracedo, J.C., 2008, Canarian Volcanoes: La Palma, La Gomera and El Hierro, 213 pp., Editorial Rueda, Madrid.

Carracedo, J.C., Pérez, F.J., Ancochea, E., Meco J., Hernán, F., Cubas C.R., Casillas, R., Rodriguez, E., and Ahijado, A., 2002, Cenozoic volcanism II: The Canary Islands, in: The Geology of Spain, Gibbons, W., and Moreno, T., eds, The Geological Society of London, pp. 439-472.

Carracedo, J.C., Badiola, E.R., Guillou, H.J., de La Nuez, J., and Torrado, F.J.P., 2001, Geology and volcanology of La Palma and El Hierro, western Canaries, Estudios Geológicos, v. 57, no. 5-6, pp. 171-295.

Guillou, H., Carracedo, J.C., Torrado, F.P., and Badiola, E.R., 1996, K-Ar ages and magnetic stratigraphy of a hotspot-induced, fast grown oceanic island: El Hierro, Canary Islands, Journal of Volcanology and Geothermal Research, v. 73, no. 1-2, pp. 141-155.

Masson, D.G., Watts, A.B., Gee, M.J.R., Urgeles, R., Mitchell, N.C., Le Bas, T.P., and Canals, M., 2002, Slope failures on the flanks of the western Canary Islands, Earth-Science Reviews, v. 57, no. 1-2, pp. 1-35.

Siebert, L., Simkin, T., and Kimberly, P., 2010, Volcanoes of the World, Third Edition, Smithsonian Institution, Washington, D.C., and University of California Press, Berkeley, 551 pp.

Troll, V.R., Klügel, A., Longpré, M.-A., Burchardt, S., Deegan, F.M., Carracedo, J.C., Wiesmaier, S., Kueppers, U., Dahren, B., Blythe, L.S., Hansteen, T., Freda, C.D., Budd, A., Jolis, E.M., Jonsson, E., Meade, F., Berg, S., Mancini, L., and Polacci, M., 2011, Floating sandstones off El Hierro (Canary Islands, Spain): the peculiar case of the October 2011 eruption. Solid Earth Discussion, v. 3, pp. 975-999.

Viñuela, J.M., 2012, (online) The Canary Islands Hot Spot, www.mantleplumes.org/Canary.html, updated 21 December 2007, accessed 27 March 2012.

Geologic Background. The triangular island of Hierro is the SW-most and least studied of the Canary Islands. The massive shield volcano is truncated by a large NW-facing escarpment formed as a result of gravitational collapse of El Golfo volcano about 130,000 years ago. The steep-sided scarp towers above a low lava platform bordering 12-km-wide El Golfo Bay, and three other large submarine landslide deposits occur to the SW and SE. Three prominent rifts oriented NW, NE, and south at 120 degree angles form prominent topographic ridges. The subaerial portion of the volcano consists of flat-lying Quaternary basaltic and trachybasaltic lava flows and tuffs capped by numerous young cinder cones and lava flows. Holocene cones and flows are found both on the outer flanks and in the El Golfo depression. Hierro contains the greatest concentration of young vents in the Canary Islands. Uncertainty surrounds the report of an historical eruption in 1793.

Information Contacts: Alicia Felpeto Rielo, Instituto Geográfico Nacional (IGN), General Ibáñez de Ibero, 3. 28003, Madrid, España (URL: http://www.ign.es/); Volcano Discovery (URL: http://www.volcanodiscovery.com); Earthquake Report (URL: http://www.earthquake-report.com); University of Las Palmas de Gran Canaria (ULPGC) (URL: http://www.ulpgc.es); Canaries News (URL: http://www.canariesnews.com); Instituto Oceanográfico Español (IEO) (URL: htp://www.ieo.es).

A memorable eruption at Kelut began in August 2007 injecting what became a substantial lava dome in the midst of a crater lake. The process was devoid of large violent steam explosions of the kind often associated with molten lava extruding into a lake. The passively emplaced lava dome evaporated and displaced most or all of the crater lake. Dome extrusion had clearly stopped by April 2008 (BGVN 33:07) or perhaps by May 2008 (De Bélizal and others, 2012). Since then and as late as April 2012, the Center of Volcanology and Geological Hazard Mitigation (CVGHM), has noted ongoing quiet, at times broken by the emergence of diffuse white plumes. Those plume were seen in June 2009 rising 50-150 m above the crater and the new dome was still emitting steam in February 2012. As of 30 March 2012, the Alert Level remained Green, although CVGHM recommended that people not approach the lava dome due to instability of the area and the presence of potentially high temperatures and poisonous gases.

Three short subsections follow. The first discusses uplift at Kelut during 2007-2008 as part of a larger survey of volcanic deformation on Java (Philibosian and Simons, 2011). The next subsection discusses a paper that provides an overview on the unexpectedly tranquil eruption, which, though of substantial size, was one of Kelut's few substantial yet passive eruptions in the historic record (De Bélizal and others, 2012). The authors surveyed residents to assess how they felt about how authorities had managed the crisis. The third subsection below discusses the dome's declining thermal output in early 2008, and presents a photo taken in February 2011 showing the steaming dome's spiny upper surface.

2007-2008 deformation. Philibosian and Simons (2011) discussed satellite-borne (Japanese ALOS) L-band synthetic aperture radar used to conduct a comprehensive survey of volcanic deformation on Java during 2007-2008. For Kelut, the authors found a possible 15 cm line-of-sight change in late 2008, an uplift. The area of uplift was limited to the very top of Kelut and was only a few hundred meters wide. However, the authors state that, given there were only two radar acquisitions after this late 2008 uplift, it was "difficult to judge whether this was permanent, real deformation rather than a short-term atmospheric effect." According to the authors, "the volcano did not exhibit a significant deformation before or during the dome extrusion in our time series" (figure 13).

Figure 13. Time series of Kelut's deformation during October 2006-January 2009 (summing all the time steps and for satellite track 428). The plot shows the 15-cm line-of-sight change consistent with an uplift peaking during late 2008. The period of observed lava dome extrusion (shown in red) corresponded with a minor uplift (under 5 cm along the line of sight). Taken from Philibosian and Simons (2011).

2007 eruption and crisis management revisited. De Bélizal and others (2012) discuss a survey conducted shortly after the end of an evacuation process triggered by Kelut's eruption that started in 2007.

The authors summarized Kelut's unrest that started prior to the extrusions first seen in August by noting that earlier, on 1 November 2007, CVGHM recorded a new peak of seismicity with signals having reached shallow depths beneath the crater floor. The crater lake temperature recorded by a thermal camera increased significantly by 6 November. A steam plume developed, reaching 550 m above the crater lake. A new lava dome extruded through the ~350 m diameter crater lake (BGVN 33:03). Progressively, nearly all the lake water vaporized as the lava dome grew to a diameter of 400 m and a height of 260 m representing a volume of ~35 x 10⁶ m³.

According to De Bélizal and others (2012), "recorded volcanic seismicity decreased shortly after the onset of dome growth. Tiltmeter records also showed the absence of any significant deformation on the flanks of the volcano. These data suggested that the magmatic pressure decreased within the volcano therefore greatly reducing the likelihood of a violent explosion. Thus, on 8 November 2007, Indonesian authorities decided to end the emergency phase. The volcano Alert Level was lowered to Level 3 'Siaga' until 30 November, when it was then lowered to Level 2 'Waspada' until August 2008."

The passively extrusive and unexpectedly non-explosive eruption was the first here in recent historical times. This called for careful monitoring of both the eruptive behavior of the volcano and the stability of a lake-bound dome plugging the vent. Tourism and agriculture ceased on its flanks for many months in anticipation of potential sudden signs of renewed activity.

The article stated that the crisis management team ordered an evacuation, which followed the rise to Alert Level 4 on 16 October 2007 (BGVN 33:03), but it noted that many residents disregarded the order because they did not consider that an eruption was imminent. The authors conducted interviews with members of the crisis management team, and undertook a questionnaire-based survey in the settlement nearest to the crater to determine how residents reacted to the crisis and how they thought authorities managed the crisis. The survey was carried out while Kelut was still under surveillance for fear of an explosive phase. According to the authors, the crisis management team "was well organized and strategic"; however, the results "showed that crisis management was not fully integrated with the way of life of the local communities at risk, and that information, communication and trust were lacking."

Decreasing thermal alerts in 2008 and an early 2011 photo. During November and December 2007, there were numerous days with MODVOLC thermal alerts. This number decreased in January 2008 to only six days that month. After January 2008, thermal alerts had been absent as late as 27 April 2012. The probable cause was the cooling of the dome to the point where the levels of thermal radiation emitted dropped below the threshold values needed to create MODVOLC alerts.

A photo of Kelut taken by Daniel Quinn in early 2011 shows the steaming, rough-surfaced lava dome in the crater (figure 14). The photo only showed a small portion of the entire crater floor, but on the N side of the dome, the crater floor contained a dark brown, muddy-colored patch of water the photographer considered a large puddle. Some 2010 photos on the Picassa website showed a small body of water on the crater floor at that time.

Figure 14. A late January or early February 2011 photo taken of Kelut's new dome from a high spot on the NNW rim. Apparent are both the dome's spiny upper surface, and many areas of the dome still emitting small amounts of steam. The photo appeared on the Picassa website and is used with the permission of the photographer, Daniel Quinn.

According to Daniel Quinn, the photo in figure 14 was taken on the rim at a spot accessed via a small pavilion he passed walking from the car parking area. He took the photo having walked clockwise about as far around the rim as he could travel before reaching vertical cliffs. Pungent odors were absent during his visit.

References. De Bélizal, É., Lavigne, F., Gaillard, J., Grancher, D., Pratomo, I., and Komorowski, J. , 2012. The 2007 eruption of Kelut volcano (East Java, Indonesia): Phenomenology, crisis management and social response, Geomorphology, v. 136, issue 1, p. 165-175.

Philibosian, B., and Simons, M., 2011. A survey of volcanic deformation on Java using ALOS PALSAR interferometric time series, Geochemistry Geophysics Geosystems, v. 12, no. 11, 8 November 2011, Q11004, 20 pp. (DOI:10.1029/2011GC003775).

Geologic Background. The relatively inconspicuous Kelut stratovolcano contains a summit crater lake that has been the source of some of Indonesia's most deadly eruptions. A cluster of summit lava domes cut by numerous craters has given the summit a very irregular profile. Satellitic cones and lava domes are also located low on the E, W, and SSW flanks. Eruptive activity has in general migrated in a clockwise direction around the summit vent complex. More than 30 eruptions have been recorded from Gunung Kelut since 1000 CE. The ejection of water from the crater lake during the typically short but violent eruptions has created pyroclastic flows and lahars that have caused widespread fatalities and destruction. After more than 5000 people were killed during an eruption in 1919, an ambitious engineering project sought to drain the crater lake. This initial effort lowered the lake by more than 50 m, but the 1951 eruption deepened the crater by 70 m, leaving 50 million cubic meters of water after repair of the damaged drainage tunnels. After more than 200 deaths in the 1966 eruption, a new deeper tunnel was constructed, and the lake's volume before the 1990 eruption was only about 1 million cubic meters.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Daniel P. Quinn (URL: http://bubbingtondump.com/).

This report on Long Valley caldera, California, summarizes USGS reports for 2009. The volcano remained non-eruptive. Long Valley Observatory (LVO) is now part of the California Volcano Observatory (CalVO). A tectonic earthquake sequence during 2011 in nearby Hawthorne, Nevada, is also discussed.

Long Valley caldera entered relative quiescence in the spring of 1999 (BGVN 26:07) following unrest that began in 1980 (SEAN 07:05); this relative quiescence continued through 2009.

Seismicity during 2009 was characterized by a low level of seismicity within the caldera, and a typical higher level of seismicity in the surrounding Sierra Nevada range (figure 41). Three recorded earthquakes were larger than M 3.0, yet none of them occurred within the region of Long Valley caldera as delimited by LVO. The largest earthquakes within Long Valley caldera were an M 2.7 on 9 January in the S moat, and a pair of M 2.3 earthquakes on 10 December that were located beneath the resurgent dome.

Figure 41. Seismicity in the region of Long Valley caldera and the surrounding Seirra Nevada range. The upper red dashed outline indicates volcanic areas associated with Long Valley caldera (including Mammoth Mountain and Inyo Craters), and the red dashed and dotted outline indicates the adjacent Sierra Nevada range. Earthquake epicenters are shown with symbols proportional to earthquake magnitudes, according to the scale at top-right. Modified from USGS-LVO.

Deep seismic swarm at Mammoth Mountain.At Mammoth Mountain, increased seismicity began in late May, and a deep seismic swarm occurred on 29 September. The 29 September seismic swarm included over 50 M ≥0.5 high-frequency earthquakes that occurred at depths of 20-25 km, depths inferred to be in the mafic lower crust (figure 42). The high frequencies of these earthquakes indicated brittle-rock failure similar to shallow earthquakes that typically occur at <10 km depth, and were distinctly different than the long-period earthquakes that occur within the silicic upper crust, at depths of 10-25 km. The increased seismicity at Mammoth Mountain during 2009 produced more earthquakes there than occurred within Long Valley caldera (figures 41, 42, and 43).

Figure 42. Map (left) and cross-section (right) views focusing on Mammoth Mountain seismicity during 2009. Note the two main clusters of earthquakes at ~0-7 km and ~20-25 km depth. Earthquakes are shown by symbols proportional to earthquake magnitude, shown by the scale at left. The line A-A' on the map indicates the plane of projection of the cross-section. The inferred mafic lower crust and silicic upper crust regions are indicated to the right of the cross-section. The cross-section also indicates interpreted brittle and plastic zones and the typical source area for deep, long-period (LP) earthquakes. Modified from USGS-LVO.

Figure 43. Plot of the cumulative number of earthquakes within Long Valley caldera (dashed line) and beneath Mammoth Mountain (solid line, highlighted in orange) during 2009. The 29 September deep earthquake swarm took place within a longer episode of enhanced seismicity at Mammoth Mountain that lasted from mid-2009 through at least the end of the year. Mammoth Mountain's cumulative 2009 seismicity surpassed that at the rest of the Long Valley caldera area. Courtesy of USGS-LVO.

Slow inflation of the caldera's resurgent dome. Deformation trends during 2007-2009 highlighted slow inflation of the resurgent dome. At the end of 2009, the height of the resurgent dome remained ~75 cm higher than prior to the onset of unrest in 1980. Measurements since 2007 indicated horizontal displacement rates of ~5 mm/year, mostly in a pattern radiating away from the resurgent dome (figure 44).

Figure 44. Horizontal displacement rates determined by GPS at different measurement sites in and around Long Valley caldera during the start of 2007 to early 2010, which highlight a trend of expansion away from the resurgent dome. Displacement rate vectors are relative to two reference sites located off the map in the Sierra Nevada range. Ellipses around arrows represent standard 2σ errors on the measurements. Light gray arrows represent insignificant displacement rates. The black dashed outline indicates the extent of Long Valley caldera, the gray dashed outline labeled "inflation source" indicates the resurgent dome, and the gray dashed outline at the SW edge of Long Valley caldera indicates Mammoth Mountain. From S to N, the brown dashed outlines indicate the Inyo Domes, Mono Craters, and Mono Lake islands. Modified from USGS-LVO.

During 2009, soil CO₂ emission measurements revealed variations typical of most previous years. The increase in seismicity at Mammoth Mountain on 29 September did not produce a corresponding increase in CO₂ emissions.

2011 Hawthorne, Nevada, earthquake sequence. In March 2011, an earthquake sequence (mentioned in LVO weekly activity updates) began in Hawthorne, Nevada (~100 km NNE of the center of Long Valley caldera) that, according to Smith and others (2011), initially sparked brief concerns of unrest at Mud Springs volcano (figure 45). Mud Springs volcano is a probable Pleistocene volcano of the Aurora-Bodie volcanic field, Nevada (Wood and Kienle, 1992). The Hawthorne earthquakes did not show volcanic signatures in near-source seismograms (Smith and others, 2011), and the sequence was quickly identified as tectonic in origin.

Figure 45. Mapped epicenters and magnitudes (legend, bottom right) of the 2011 Hawthorne, Nevada, earthquake sequence through 19 May 2011. Hawthorne is ~10 km to the NE of the top right margin of the image. Green triangles mark the locations of three temporary seismometers (TVH1-3) installed during 17-19 April 2011. Mud Springs volcano and its associated lava flows are labeled at the bottom of the image. Modified from the Nevada Seismological Laboratory, University of Nevada, Reno.

According to Smith and others (2011), "An additional concern, as the sequence . . . proceeded, was a clear progression eastward toward the Wassuk Range front fault. The east dipping range bounding fault is capable of M 7+ events, and poses a significant hazard to the community of Hawthorne and local military facilities. The Hawthorne Army Depot is an ordinance storage facility and the nation's storage site for surplus mercury."

Earthquakes of the March 2011 sequence were as strong as M 4.6 (figure 46); the largest earthquakes may have been felt in Bridgeport, CA (~60 km SW of Hawthorne, and ~70 km NNW from the center of Long Valley caldera), according to LVO. The earthquakes occurred along at least two shallow faults, originating at 2-6 km depth (Smith and others, 2011). The earthquake sequence "slowly decreased in intensity through mid-2011" (Smith and others, 2011).

Figure 46. Mapped areas of felt responses to the M 4.6 earthquake that occurred on 16 April 2011 (see scale at bottom). The hypocenter is indicated by the red star (center). This was the strongest earthquake of the 2011 Hawthorne, Nevada earthquake sequence. The red triangle near the bottom of the map shows the location of Long Valley caldera. Modified from the Nevada Seismological Laboratory, University of Nevada, Reno.

References. Smith, K.D., Johnson, C., Davies, J.A., Agbaje, T., Antonijevic, S.K., and Kent, G., 2011. The 2011 Hawthorne, Nevada, Earthquake Sequence; Shallow Normal Faulting. American Geophysical Union, Fall Meeting 2011, Abstract ##S53B-2284.

Wood, C.A. and Kienle, J., 1992. Volcanoes of North America: United States and Canada, Cambridge University Press, 354 p., pgs. 256-262.

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

Information Contacts: Dave Hill, California Volcano Observatory (CalVO), formerly theLong Valley Observatory (LVO), U.S. Geological Survey, Menlo Park, CA (URL: http://volcanoes.usgs.gov/observatories/calvo/); Nevada Seismological Laboratory, Laxalt Mineral Engineering Building, Room 322, University of Nevada-Reno, Reno, NV 89557 (URL: http://www.seismo.unr.edu/).

In this report we present seismicity at Maderas from 1998 through 2011, highlight the 2005 earthquake swarm, describe the "Tomography Under Costa Rica and Nicaragua" (TUCAN) Broadband Seismometer Experiment and the subsequent analysis of an M_w 6.3 event also from 2005, and summarize results from fieldwork conducted in 2009 with new age dates from Kapelancyzk and others (2012).

The 2009 field investigation also characterized two distinct phases of volcanism at Maderas, as recent as the Upper Pleistocene (70.4 ± 6.1 ka before present). Despite this interval without documented eruptions, it is plausible that the volcano could erupt again, but risk of a future eruption from Maderas is considered low (Kapelancyzk, 2011). More likely are hazards associated with non-eruptive processes such as seismically triggered mass wasting and gas emissions. A deadly lahar in 1996 (BGVN 21:09) emphasized that non-eruptive processes still offer considerable hazards and justify efforts to watch for and catalog non-eruptive events.

Maderas and Concepción volcanoes sit at opposite ends of the dumbbell-shaped Ometepe Island (figure 1). The population on the island is estimated at 30,000 however seasonal tourism increases that number during the year. These volcanoes are monitored by the Instituto Nicaragüense de Estudios Territoriales (INETER) with seismic stations and regular field investigations by staff volcanologists.

Figure 1. This map of Central America focuses on Maderas volcano; the inset zooms in on Lake Nicaragua and Ometepe Island. Dashed lines represent the large-scale geologic features, the Nicaraguan depression (ND) to the S and the Median Trough (MT) to the N; triangles represent volcanic centers (Kapelanczyk and others, 2012).

Seismicity. One seismic station is located on Ometepe Island within a network of ~32 stations in Nicaragua. From 1998 to 2011, INETER reported that seismicity was irregular although in most years, they located fewer than four earthquakes (table 1). Earthquakes were frequently M_L < 3.5 (M_L= Local earthquake magnitude) with focal depths ranging between the surface and 179 km.

Table 1. Earthquakes located near Maderas volcano from 1998 through 2011. For each year, the table also lists the range of the earthquakes' local magnitudes (M_L), the range of their focal depths, and their average focal depths. INETER did not comment on earthquakes that were anomalously deep (e.g. 179 km below sea level). Courtesy of INETER.

During 2005, INETER's network registered a total of 2,785 earthquakes throughout Nicaragua; 2,629 of these events were located by seismologists, 78 caused shaking that was strong enough to be reported by local populations, and 406 were located near Maderas volcano. Many of these events were located beneath Lake Nicaragua and S of Maderas volcano (figure 2). According to an interview presented in a La Prensa news article, 71% of the events were attributed to strain release along the subduction zone while 27% were associated with the volcanic chain. INETER reported that a significant number of earthquakes also occurred offshore in the Pacific Ocean with magnitudes greater than 5.0.

Figure 2. (Left) A map of epicenters for the entire year of 2005 plotted for Nicaragua and the surrounding region. (Right) A map of epicenters for the month of September 2005 plotted for the Lake Nicaragua region. On both maps, note the concentration of epicenters around Maderas at the SE portion of Ometepe Island. Courtesy of INETER.

Large regional earthquake. In their monthly bulletins, INETER reported that the earthquake swarm from August through September 2005 included an M_L 5.7 earthquake that occurred on 3 August. The USGS National Earthquake Information Center reported this event as M_s 6.2 (M_s = surface-wave magnitude). This earthquake was located ~15 km S of Maderas volcano (figure 3) and INETER reported that many homes on Ometepe Island were destroyed. Shaking was felt by local residents on the Pacific coast of Nicaragua as well as the interior of the country and in Costa Rica. INETER noted that this was the first time in memory that an event of this magnitude occurred near Maderas. Aftershocks continued for several weeks after the event (La Prensa).

Figure 3. Map views of initial (left) and double-difference (right) relocated hypocenters. The green and red stars correspond to the Mw 5.3 and 6.3 fore and main shock, respectively (Mw = moment magnitude). The initial hypocenters were cataloged by INETER except for the main shock, which was located separately using TUCAN P and S phase data (horizontal plane 95% confidence ellipse shown). The red inverted triangle represents the INETER catalog location of the main shock. Note that contour intervals are inconsistent with those elsewhere in the literature. Map is modified from French and others (2010).

This major seismic event was also captured by the "Tomography Under Costa Rica and Nicaragua" (TUCAN) Broadband Seismometer Experiment. This array of instruments was in the field from July 2004 to March 2006 (French and others, 2010). Project collaborators conducted a relocation and directivity analysis based on data from 16 of the 48 TUCAN stations. They determined the rupture was on a vertical, N60°E striking main shock plane; a secondary fault, with a strike of N350°E-N355°E, was also activated during the 5 hours following the main event.

The seismic analysis provided important insight into the regional tectonic setting while also characterizing activity that was independent from the coincident volcanism at Concepción Volcano. Just six days prior to the 3 August 2005 M_w 6.3 event, INETER reported high local seismicity and an ash explosion from Concepción (BGVN 30:07). Explosive activity had begun on 28 July but they lacked any other local diagnostic signatures at Maderas or Concepción related to the M_w 6.3 event. French and others (2010) conclude that "the eruption was not triggered at short time scales by stress transfer from slip on this fault. No earthquakes in [the] analysis relocated beneath Concepción either before or after the eruption."

These were also significant findings as they correlate well with the larger interpretation of the region's tectonic setting, supporting the "bookshelf model" (LaFemina and others, 2002). This model addresses the complexities of Nicaragua's deforming tectonic blocks that include clockwise rotation and slip on NE-striking left-lateral faults.

Volcanic history. In 2009, field investigations by Michigan Technological University student Lara Kapelanczyk yielded new age dates and geologic mapping for Maderas. Previous investigators had characterized Maderas as a small-volume (~30 km³) stratovolcano (Carr and others, 2007), lacking historic volcanic activity (Borgia and others, 2000), and having unique structural characteristics variously attributed to gravitational spreading (van Wyk de Vries and Borgia, 1996) and localized faulting (Mathieu and others, 2011).

Geologic mapping and rock sampling during field campaigns in 2009 contributed to new insight about the eruptive history of Maderas as well as the geologic hazards of the area. Geomorphologic characteristics also distinguish Maderas as an older volcanic site compared to its frequently active neighbor, Concepción (figure 4). Satellite remote sensing also distinguishes deep ravines that cut through the edifice of Maderas, features that suggest long-term, uninterrupted erosion. As recent as March 2010 (BGVN 36:10), Concepción has erupted ash and tephra.

Figure 4. A view across Lake Nicaragua in March 2010 toward the twin volcanoes on Ometepe Island, Concepción (left) and Maderas (right). Intermittent ash explosions characterized Concepción's activity in 2010. In this view, a diffuse ash plume covered Concepción's summit and was dissipating at a low altitude, spreading toward the shoreline. Courtesy of Lara Kapelanczyk, Michigan Technological University.

Geochemical data and ⁴⁰Ar/³⁹Ar dating determined that Maderas is an andesitic volcano with lava flows dating from 179.2 ± 16.4 ka to 70.4 ± 6.1 ka. These ages are significant in that, for the first time, quantitative data shows that Maderas has not been active for tens of thousands of years.

Kapelanczyk (2011) concluded that, during its lifespan, edifice construction at Maderas was marked by fault displacements that cross the major sectors of the volcano (figure 5). These major events led to the formation of a central graben and distinguish two phases of activity at Maderas: cone growth with pre-graben lava flows and post-graben lava flows. Pre-graben activity included the formation of a lateral vent and two littoral maars to the NE while post-graben activity included a lateral vent to the NW. Maar structures were also described in this research as well as structural information about the summit crater which includes a small lake, Laguna de Maderas (figure 6).

Figure 5. Geologic map of Maderas volcano (Kapelancyzk and others, 2012). Note the normal faults (heavy black lines) bounding the NNW-trending graben crossing the structure, an extension of the San Ramon fault zone (Funk and others, 2009). Pre- and post-graben lithologies and structures were recognized by Kapelancyzk (2011). Laguna de Maderas appears as the gray area within the summit crater.

Figure 6. View inside of the Maderas summit crater looking SE toward Laguna de Maderas, the summit crater lake. Courtesy of Lara Kapelanczyk, Michigan Technological University.

Based on the new information about Maderas's volcanic history, the risk associated with eruptions is considered low (Kapelanczyk, 2011). However, geophysical monitoring is important due to processes such as occasional, significant earthquakes and the potential for debris flows on the steep flanks.

In 1996 a deadly lahar occurred on the E flank (BGVN 21:09). This event was triggered during a heavy rainstorm and released a significant volume of material, enough to destroy the town of El Corozal and other settlements nearby. Deep, steep-sided ravines have cut through the slopes, especially on the lower NE and SW flanks (figure 7).

Figure 7. This satellite image of Ometepe Island was processed by GVP using near-, mid-infrared, and infrared bands (4,5,7). Water-poor soils appear cyan; brown-to-red areas indicate moist soils; water is black. A small pond is located within the circular crater of Maderas (Laguna de Maderas) and deep erosional features radiate from the summit, distinguishing the relatively older edifice from the neighboring volcano, Concepción. Recent lava flows on Concepción appear black/blue and have distinctive terminal lobes. Landsat acquired this ETM+ image on 27 January 2000 (NASA Landsat Program, 2003).

References. Borgia, A., Delaney, P.T. and Denlinger, R.P., 2000. Spreading volcanoes. Annual Review of Earth and Planetary Sciences, 28, 539-570.

Carr, M.J., Saginor, I., Alvarado, G.E., Bolge, L.L., Lindsay, F.N., Milidakis, K., Turrin, B.D., Feigenson, M.D. and Swisher, C.C., 2007. Element fluxes from the volcanic front of Nicaragua and Costa Rica. Geochemistry, Geophysics, Geosystems (G3), 8, 6.

French, S.W., Warren, L.M., Fischer, K.M., Abers, G.A., Strauch, W., Protti, J.M., and Gonzalez, V., 2010. Constraints on upper plate deformation in the Nicaraguan subduction zone from earthquake relocation and directivity analysis, Geochemistry, Geophysics, Geosystems (G3), 11, 3.

Funk, J., Mann, P., McIntosh, K., and Stephens, J., 2009. Cenozoic tectonics of the Nicaraguan depression, Nicaragua, and Median Trough, El Salvador, based on seismic-reflection profiling and remote-sensing data, GSA Bulletin 121, 11-12, 1491-1521.

Kapelanczyk, L.N., 2011. An eruptive history of Maderas Volcano using new ⁴⁰Ar/³⁹Ar ages and geochemical analyses [Master's thesis]: Houghton, MI, Michigan Technological University, 118 p.

Kapelanczyk, L.N., Rose, W.I., and Jicha, B.R., 2012. An eruptive history of Maderas volcano using new ⁴⁰Ar/³⁹Ar ages and geochemical analyses. Bulletin of Volcanology, In Review.

LaFemina, P.C., Dixon, T.H., and Strauch, W., 2002. Bookshelf faulting in Nicaragua, Geology, 30, 751-754.

Mathieu, L., van Wyk de Vries, B., Pilato, M. and Troll, V.R., 2011. The interaction between volcanoes and strike-slip, transtensional and transpressional fault zones: Analogue models and natural examples. Journal of Structural Geology, 33, 898-906.

NASA Landsat Program, 2003, Landsat ETM+ scene 7dx20000127, SLC-Off, USGS, Sioux Falls, Jan. 27, 2000.

van Wyk de Vries, B. and Borgia, A., 1996. The role of basement in volcano deformation. Geological Society Special Publication, 110, 95-110.

Geologic Background. Volcán Maderas is a roughly conical stratovolcano that forms the SE end of the dumbbell-shaped Ometepe island in Lake Nicaragua. The basaltic-to-trachydacitic edifice is cut by numerous faults and grabens, the largest of which is a NW-SE-oriented graben that cuts the summit and has at least 140 m of vertical displacement. The small Laguna de Maderas lake occupies the bottom of the 800-m-wide summit crater, which is located at the western side of the central graben. The SW side of the edifice has been affected by large-scale slumping. Several pyroclastic cones, some of which may have originated from littoral explosions produced by lava flow entry into Lake Nicaragua, are situated on the lower NE flank down to the level of Lake Nicaragua. The latest period of major growth was considered to have taken place more than 3000 years ago, but later detailed mapping has shown that the most recent dated eruptive activity took place about 70,000 years ago and that it has likely been inactive for tens of thousands of years (Kapelanczyk et al., 2012). A lahar in September 1996 killed six people in an E-flank village, but associated volcanic activity was not confirmed.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); Global Land Cover Facility (URL: http:// http://www.glcf.umiacs.umd.edu/); National Earthquake Information Center (NEIC), US Geological Survey, Geologic Hazards Team Office, Colorado School of Mines, 1711 Illinois St., Golden, CO 80401, USA (URL: https://earthquake.usgs.gov/); La Prensa (URL: http://archivo.laprensa.com.ni).

Until 4 June 2011, the volcanic complex named Puyehue-Cordón Caulle had been quiet since its last major eruption in 1960. This report summarizes an increase in seismicity in early 2011 and the ensuing eruption that began on 4 June 2011. Our previous and only reports on the complex were in March and April 1972, which offered and then dismissed a report of a 1972 eruption (CSLP Cards 1362 and 1371). Information here goes through 2011 but omits some remote sensing observations. The eruption continued through at least April 2012, but in March and again in April 2012 the eruption's diminished vigor resulted in successively lowered alert statuses. During the height of the eruption the vent emitted ash plumes and generated significant ashfall, and flights were cancelled as far away as Australia and New Zealand. Pyroclastic flows occurred, with runout distances up to 10 km.

The Puyehue-Cordón Caulle complex includes Puyehue volcano at the SE end and the Cordillera Nevada caldera at the NW end. The current eruption discussed here vented at a location roughly between these two features, along the same fissure complex that had been active in the 1960 eruption. Available information failed to disclose any other eruptive sites during the reporting interval. Although the eruption continues as this report goes to press in March 2012, the report discusses activity only during 2011. A subsequent report will discuss further details, including satellite data on eruptive plumes, and updates since the end of the 2011 reporting period. This report also contains a table that condenses reporting from the Buenos Aires Volcanic Ash Advisory Center (VAAC).

Precursory seismicity. The Southern Andes Volcanological Observatory-National Geology and Mining Service (SERNAGEOMIN) reported that on 26 April 2011 an overflight of the volcano was conducted in response to recent increased seismicity and observations of fumarolic activity by nearby residents. Scientists confirmed fumarolic activity, but did not observe any other unusual activity.

On 27 April a seismic swarm (with about 140 events under M_L 3.0) was detected at depths of 4-6 km below the complex. Most were hybrid earthquakes, the largest being M 3.9. Lower levels of seismicity continued through 29 April. That day the Alert Level was raised to Yellow (on a scale from Green to Yellow to Red).

According to SERNAGEOMIN, between 2000 on 2 June and 1959 on 3 June 2011, about 1,450 earthquakes occurred at Puyehue-Cordón Caulle (~60 earthquakes/hour, on average). More than 130 earthquakes occurred with magnitudes greater than 2.0. The earthquakes were mostly hybrid and long-period, and located in the SE sector of the Cordón Caulle rift zone at depths of 2-5 km. A flight over the volcano revelaed no significant changes. Area residents reported feeling earthquakes during the evening of 3 June through the morning of 4 June.

For a six-hour period on 4 June, seismicity increased to an average of 230 earthquakes/hour, with hypocenter depths of 1-4 km. About 12 events were of magnitudes greater than 4.0, and 50 events were of magnitudes greater than 3.0. As a result of the increased seismicity, the Alert Level was raised from Yellow to Red on 4 June.

Eruption. On 4 June 2011, an explosion from Cordón Caulle produced a set of plumes, including an ash plume described as 5 km wide and with its top at ~12 km altitude. Portions of the plume bifurcated; at ~5 km altitude a part of the plume drifted S, and at ~10 km altitude parts drifted W and E. A news account (Agency France-Presse) around this time, quoting a government official, said the eruption would lead to the evacuation of 4,270 residents.

According to the Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI), SERNAGEOMIN had noted the presence of pyroclastic flow deposits, but not lava. Residents reported a strong sulfur odor and significant ash and pumice fall. According to the BBC, the number of evacuees rose to 3,500-4,000 during the next several days.

According to SERNAGEOMIN, the eruption from the Cordón Caulle rift zone, although somewhat diminished, continued on 5 June. At least five pyroclastic flows were generated from partial collapses of the eruptive column and traveled N in the Nilahue River drainage. These pyroclastic flows extended up to 10 km from the vent.

Figures 1-3 show scenes of the volcano from various perspectives, including a natural color January 2012 image from space.

Figure 1. Puyehue-Cordón Caulle's eruption seen in a long-exposure photo taken during 4-6 June 2011. The photo depicts molten material discharging over a wide area near the eruption column's base. Above the glowing, molten material there grew a substantial, rapidly rising ash plume. Much of the scene is lit by numerous bolts of lightning. Courtesy of Daniel Basualto, European Pressphoto Agency.

Figure 2. A long-exposure photograph of the eruption at the Puyehue-Cordón Caulle complex taken on 5 June 2011. The complex scene shows a wide eruption column aglow with prominent lightning strikes branching across its surface. The long exposure is evidenced by the long star trails (with stars forming streaks due to the Earth's rotation) and the superimposition of many distinct bolts of lightning. Courtesy of Franscisco Negroni, Agencia Uno/European Pressphoto Agency.

Figure 3. Satellite photo acquired on 26 January 2012 of the Puyehue-Cordón Caulle area. The natural color image was taken by the Advanced Land Imager aboard the Earth Observing (EO-1) satellite. The emissions, which blow in a narrow band toward the SE, can clearly be observed emanating from the Cordón Caulle fissure complex and not from the Puyehue volcano itself. According to a NASA Earth Observatory report, after 8 months of ceaseless activity, the landscape around the Puyehue-Cordón Caulle complex was covered in ash. The light-colored ash appears most clearly on the rocky, alpine slopes surrounding the active vent and the Puyehue caldera. Within the caldera, the ash appears slightly darker, possibly because it may be resting on wet snow that is melting and ponding during the South American summer. NASA also noted that evergreen forests on the E side of the volcano complex have been damaged by months of nearly continuous ashfall, and are now an unhealthy brown, while forests to the W had only received intermittent coatings of ash and appeared relatively healthy. Courtesy of NASA (Robert Simmon, Mike Carlowicz, and Jesse Allen).

Eruptive plumes were dense, oftentimes continuous, and extended E over Argentina and then the Atlantic Ocean (table 1). Ashfall reached up to about 15 cm thick in Argentina and adjacent parts of Chile (figures 4-6). Numerous flights were cancelled as far away as Australia and New Zealand, and many airports were forced to close temporarily (see section below).

Table 1. The Puyehue-Cordón Caulle ash plume altitudes and drift distances and directions documented by aviation authorities between 4 June 2011 and 3 January 2012. A plume on any particular date may be a continuation of a plume on the previous day(s). All maximum plume heights are stated in altitudes (a.s.l.). '-' indicates data not reported. Cloud cover often prevented video camera and satellite observations. Data from the Buenos Aires Volcanic Ash Advisory Center (VAAC) and SERNAGEOMIN.

Figure 4. Photograph published on 6 June 2011 of workers using earth-moving equipment to remove the ash that fell 100 km SE of the Puyehue-Cordón Caulle in San Carlos de Bariloche, Argentina. As discussed in a subsection below, the ash led to the cancellation of numerous public activities, and flights were suspended. Courtesy of Alfredo Leiva, Associated Press.

Figure 5. Photograph of an Air Austral jet stranded at the airport at San Carlos de Beriloche, Argentina, on 7 June 2011 after being covered with ash that blew over the Andes from the Puyehue-Cordón Caulle complex. Courtesy of Alfredo Leiva, Associated Press.

Figure 6. A member of the media walks along a road covered with ash from the Puyehue-Cordón Caulle complex that crossed Cardenal Samoré pass, a major linkage along the border between Argentina and Chile. Courtesy of Ivan Alvarado, Reuters.

According to news accounts (BBC, MailOnline, Merco Press), the Nilahue river, which runs off the N slopes of the volcano, became clogged with ash and overflowed its banks. The press reports said that the river water was steaming, having been locally heated up to 45°C by hot volcanic material, and more than four million salmon and other fish died.

During 4-5 June, ashfall several centimeters thick was reported in San Carlos de Bariloche, Argentina (about 100 km SE of the volcano) and in surrounding areas (figures 4-6). ONEMI reported that the Cardenal Samoré mountain pass border crossing between Argentina and Chile had temporarily closed on 4 June due to poor visibility caused by the heavy ashfall. According to a press report (EMOL), the road crossing the border was covered with ash that locally reached 10-15 cm thick. According to MailOnline and Boston.com, ash covered Lake Nahuel Huapi, Argentina's largest lake, which lies in the eastern foothills of the Andes. Videos documenting the eruption are abundant on the YouTube website (a search there using "Puyehue volcano" brings up over 400 hits. See several examples in the Reference list below).

By 9 June 2011, pumice and vitreous tephra had accumulated in many area lakes and rivers, darkening the color or their waters (figure 7).

Figure 7. Photo of ash-clogged Nilahue River (Chile) with steam hanging above the river. Courtesy of Reuters.

A government observation flight on 11 June revealed that the vent was located at the head of the Nilahue River's basin, a spot immediately N of the 1960 eruption fissure. Observers found that abundant amounts of ash had accumulated around the vent, as well as to the E and SW.

Scientists aboard an observation flight on 13 June reported that the eruption formed a cone located in the center of a crater ~300 to ~400 m in diameter. Gas-and-steam plumes rose from two or three locations along the same fissure as the eruptive vent. Scientists watching a strong ash emission saw the lower part of the ash column collapse. Dark gray ash plumes that rose to an altitude of ~11 km. Instrumental records around that time registered pulses of tremor. At other points on 13 June, plume heights oscillated.

On 20 June, a news article (Agency France-Presse) reported that authorities had ended the evacuation, enabling residents to return home.

SERNAGEOMIN personnel along with regional authorities flew over the Puyehue-Cordón Caulle complex on 20 June. They observed a viscous lava flow, confirming speculation of magma ascent based on seismic data from the previous few days. A 50-m-wide lava flow had traveled 200 m NW and 100 m NE from the point of emission, filling a depression. A white plume with a gray base rose 3-4 km above the crater. Devastated vegetation from pyroclastic flows was observed near the Nilahue and Abutment rivers. Pulses of tremor were detected by the seismic network.

Plumes continued through at least the end of 2011. Although there were no new aerial observations, the seismic signals indicated that the lava flow remained active. Ashfall was periodically reported in areas downwind, including on 22 June in Riñinahue (5-10 mm of ash), Llifen, Futrono, and Curarrehue, and on 25 June in Riñinahue, Pucón, and Melipeuco (in the region of Araucanía).

Decline in seismicity. By the end of June, seismic activity had decreased further. During July through at least 31 December 2011, the eruption continued at a low level. Numerous plumes (mostly white, but sometimes containing ash) were noted during this period, often rising as high as 2.5 km above the crater (4.7 km altitude) and occasionally higher. Cloudy weather often prevented satellite and camera observations. Some of the ash plumes dropped ash in nearby communities, and some ash plumes extended for hundreds of kilometers, continuing to disrupt air traffic. Occasional incandescence and lava flows were noted.

During 18-19 August 2011, a period of harmonic tremor lasted about 25 minutes and may have indicated lava emission. Incandescence was observed at night. An observation flight on 19 August showed that solidified lava had filled up a depression around the cliffs of the Cordón Caulle area; no active lava flows were noted.

On 30 October 2011 seismicity indicated a possible minor lava effusion. Ashfall was reported in Río Bueno (80 km WNW).

During the night of 11-12 November 2011, crater incandescence and small explosions were observed. Satellite imagery showed ash plumes drifting 90 km NE on 11 November and 400 km SE on 12 November. Ash fell in areas on the border of Chile and Argentina, and at Paso Samore on 12 November. As of 31 December 2011, the Alert Level remained at Red.

Disruption of airline traffic. Based upon a review of news accounts on the Internet, the massive ash plumes resulting from the eruption caused major delays and cancellations of air traffic worldwide. Between 4-14 June, numerous flights were cancelled or disrupted in Paraguay, Chile, southern Argentina, Uruguay, and Brazil. News accounts (Reuters, CBS News, Global Media Post) reported that the two major airports serving Buenos Aires, Argentina, and the international airport in Montevideo, Uruguay, closed for several days as did many airports in southern Argentina, including those in Patagonia. One of the worst hit airports serves the ski resort city of San Carlos de Bariloche, Argentina. On 9 June alone, workers removed about 15,000 tons of volcanic ash (600 truckloads) from the airport's main runway.

According to news accounts (Sydney Morning Herald, Agency France-Presse, Stuff, Australian Associated Press), by the middle of June, the ash plume that had been drifting mostly E since the beginning of the eruption had reached Australia and New Zealand. This caused flight disruptions and airport closures in Australia.

By the third week in June, according to the Associated Press, plumes from the eruption had circumnavigated the globe, arrived in the W part of Chile (in Coyhaique, 550 km S of the volcano), and again caused the cancellation of domestic flights. During the last week of June, numerous flights in and around Argentina and Chile were again cancelled, as well as some flights in Uruguay. According to Stuff, Associated Press, and South Africa To, ash from the second circumnavigation of the ash plume again disrupted flights at Capetown and Port Elizabeth, South Africa, as well as in Australia.

During the first two weeks of July, numerous flights in and around Argentina and Uruguay were cancelled and some airports remained closed. According to Merco, the first private plane landed around 17 July at the airport in Bariloche, Argentina, since the airport had closed on 4 June. On 17 September, the first commercial flights resumed at Bariloche.

Ash clouds remained a problem for months after the eruption. According to news articles, several domestic and international flights in Argentina, Brazil, Chile and Uruguay were cancelled on 16 October due to re-suspended ash kicked up by high winds in the region. Flights resumed the next day. According to the Agency France-Presse, airborne ash again disrupted or cancelled flights in Uruguay and Argentina on 22 and 26 November.

References (sample of videos available on Youtube):

1. !!Rock, ash fill overflowing river in Chile (Cordon Caulle)!!; MSNBC.com, uploaded by ThisisMotherNature on 10 June 2011. URL: http://www.youtube.com/watch?v=Mw3132MPfvE [Lahar scenes; MSNBC newscast in English]

2. Chile Volcano Erupts (Breathtaking Raw Video) 4th June 2011; (original author uncertain), uploaded by horrificStorms on 14 June 2011. URL: http://www.youtube.com/watch?feature=fvwp&NR=1&v=ZIq0tlYVb9U [Umbrella cloud forms above rising ash plume, seen from the ground; a yet-unidentified newscast]

3. Dormant Puyehue volcano in Chile erupts after lying dormant for decades; SkyNews, 2011, uploaded by TruthTube451 on 5 June 2011. URL: http://www.youtube.com/watch?NR=1&feature=endscreen&v=xhANgMJdvsk Source: SkyNews (URL: http://news.sky.com) [Newscast showing rising plumes, ashfall, and scenes of mitigation efforts]

4. Buzo intentando nadar en el lago Nahuel Huapi, el cuál se encuentra cubierto por una gruesa capa de cenizas volcánicas emitidas por volcán Puyehue. Uploaded by SonyOficial on 14 June 2011. URL: http://www.youtube.com/watch?v=4_cXUVZJxP8&feature=fvsr [An amusing attempt to enter Nahuel Huapi Lake to scuba dive beneath a thick mat of floating tephra. This video exceeded 1 million views on 16 November 2011.]

Geologic Background. The Puyehue-Cordón Caulle volcanic complex (PCCVC) is a large NW-SE-trending late-Pleistocene to Holocene basaltic-to-rhyolitic transverse volcanic chain SE of Lago Ranco. The 1799-m-high Pleistocene Cordillera Nevada caldera lies at the NW end, separated from Puyehue stratovolcano at the SE end by the Cordón Caulle fissure complex. The Pleistocene Mencheca volcano with Holocene flank cones lies NE of Puyehue. The basaltic-to-rhyolitic Puyehue volcano is the most geochemically diverse of the PCCVC. The flat-topped, 2236-m-high volcano was constructed above a 5-km-wide caldera and is capped by a 2.4-km-wide Holocene summit caldera. Lava flows and domes of mostly rhyolitic composition are found on the E flank. Historical eruptions originally attributed to Puyehue, including major eruptions in 1921-22 and 1960, are now known to be from the Cordón Caulle rift zone. The Cordón Caulle geothermal area, occupying a 6 x 13 km wide volcano-tectonic depression, is the largest active geothermal area of the southern Andes volcanic zone.

Information Contacts: Southern Andes Volcanological Observatory-National Geology and Mining Service (SERNAGEOMIN), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/productos.php); Robert Simmon, Mike Carlowicz, and Jesse Allen, NASA Earth Observatory (URL: http://earthobservatory.nasa.gov); Agency France-Presse (URL: http://www.afp.com/afpcom/en/); Associated Press (URL: http://www.ap.org/); Australian Associated Press (AAP) (URL: http://aap.com.au/); BBC News (URL: http://www.bbc.co.uk/); Big Pond News (URL: http://bigpondnews.com); Boston.com (URL: http://www.boston.com); CBS News (URL: https://www.cbsnews.com/); EMOL (URL: http://www.emol.com/); europaPress (URL: http://www.europapress.es); European Pressphoto Agency (URL: http://wn.com/european_pressphoto_agency); Flight Global (URL: http://www.flightglobal.com); Global Media Post (URL: http://www.globalmediapost.com; La Mañana Neuquén (URL: http://www.lmneuquen.com.ar/); Mail Online (URL: http://www.dailymail.com.uk); MercoPress (URL: http://en.mercopress.com); Reuters (URL: http://www.reuters.com); Sky News (URL: news.sky.com); Stuff (URL: http://www.stuff.co.nz); South Africa To (URL: http://www.southafrica.to); Sydney Morning Herald (URL: http://news.smh.com.au/); The Telegraph (URL: http://bigpondnews.com).

Reventador discharged a series of small eruptions and lava flows during 2007-2009 (BGVN 33:04; 33:08; 34:03; and 34:09). Our last report (BGVN 34:09) discussed events through 26 October 2009. Since then seismicity generally remained moderate to low through at least April 2012, and ash emissions accompanying lava-dome growth intermittently occurred. Much of this report stems from work by the Instituto Geofísico-Escuela Politécnica Nacional (IG). The andesitic volcano contains a 4-km summit caldera that opens to form a large U-shaped scarp that funnels material SE (see map in BGVN 28:06). A VEI 4 eruption on 3 November 2002 (BGVN 27:11) occurred unexpectedly after a 26-year repose.

During this reporting interval, October 2009-April 2012, small plumes with occasional ash emissions accompanied dome growth (table 5). In August 2011, the top of the growing lava dome first reached the same height as the highest part of the rim. MODVOLC thermal alerts, which are satellite based using the MODIS instrument, were absent during 2011, possibly due to masking effects of cloud cover. The two tallest plumes noted in table 5 rose to approximately 7 km altitude. In addition, as discussed below in text, pyroclastic flows were also seen during the reporting interval. Lahars were common, including one that destroyed a bridge over a river on the SE flank on 25 May 2010.

Table 5. Summary of behavior and plumes at Reventador between mid-October 2009 and 18 April 2012. Some aspects of the October 2009 activity were previously reported (BGVN 34:09). Cloud cover frequently prevented observations of the volcano, and minor plumes may not have been recorded or were omitted. Heights above crater were converted to altitude by adding the summit elevation of 3.6 km. '-' indicates data not reported. Data provided by the Instituto Geofísico-Escuela Politécnica Nacional (IG), the Guayaquil Meteorolgical Watch Office (MWO) in Ecuador, and the Washington Volcanic Ash Advisory Center (VAAC).

On 20 April 2010, IG scientists flying over Reventador saw an explosion that generated a pyroclastic flow. It traveled ~200 m down the S flank. Recent deposits from earlier pyroclastic flows were also seen on the same flank. Steam-and-gas emissions also continued. On 8 May 2010, IG noted a small lahar inside the caldera.

On 25 May a destructive lahar took place that was detected for 90 minutes by the seismic network. It traveled down the SE flank and destroyed a bridge over the Marker River, ~8 km SE of the summit area. The loss of the bridge disrupted travel along Route E45 between Baeza (~34 km SSW) to Lago Agrio (also called Nueva Loja, ~121 NE).

On 28 September 2010, IG recorded three seismic episodes from Reventador. Cloud cover prevented observations during the first episode. The second seismic episode was accompanied by a steam plume containing a small amount of ash that rose 400-500 m above the crater. The third episode occurred in conjunction with a steam-and-ash plume that rose 2 km above the crater. Ash fell on the flanks.

In May 2011, seismicity began to increase and became more pronounced by early July.

During an overflight on 14 July 2011, IG scientists noted that the lava dome at the top of the 2008 cone had continued to grow (figures 37 and 38). The dome had reached the same height, or higher, as the highest part of the crater rim formed during 2002 (figures 37 and 38). Intense fumarolic activity produced continuous plumes.

Figure 37. Annotated photo of Reventador taken looking NW on 14 July 2011. The green lines trace the topographic margin of the summit caldera initially formed in the sudden 2002 eruption. The conical structure outlined in orange is a scoria or tephra cone (which includes some lavas) and spills out of the breach toward the viewer. The red line outlines the dome, initially seen in 2004, that grew substantially in 2011. Courtesy of J. Bustillos/Instituto Geofísico-Escuela Politécnica Nacional.

Figure 38. Thermal image of Reventador crater for comparison with the visual image (figure 37), also taken 14 July 2011. The measured temperature of the growing dome was ~150°C. Courtesy of S. Vallejo/Instituto Geofísico-Escuela Politécnica Nacional.

During 3-9 August cloud cover prevented observations of the lava dome, but the seismic network detected long-period and explosion-type earthquakes.

During a field trip on 6-7 January 2012, IG staff observed constant emissions of gas and steam that originated from the growing lava dome. At this point in time the dome had broadened and stood a few ten's of meters above the crater rim.

During 10-13 February 2012, IG detected new activity, including a thermal anomaly, an ash plume, and crater incandescence. This elevated activity continued during 15-21 February. Incandescence near the summit was again observed during 25-26 March but seismicity decreased around this time.

In accordance with these other observations, occasional MODVOLC thermal alerts were posted. Between 1 November 2009-1 April 2012, there were 12 days with MODVOLC thermal alerts. No thermal alerts were detected in 2011. As of 26 April 2012, six days in 2012 had thermal alerts (10, 13, 22, 26 February, 18 March, and 26 April).

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Information Contacts: Instituto Geofísico-Escuela Politécnica Nacional (IG), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Guayaquil Meteorological Watch Office (MWO); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); 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/).

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/).