San Miguel, locally known as Chaparrastique, is a stratovolcano located in El Salvador. Recent activity has consisted of occasional small ash explosions and ash emissions. Infrequent gas-and-steam and ash emissions were observed during this reporting period of June 2018-March 2020. The primary source of information for this report comes from El Salvador's Servicio Nacional de Estudios Territoriales (SNET) and special reports from the Ministero de Medio Ambiente y Recursos Naturales (MARN) in addition to various satellite data.

Based on Sentinel-2 satellite imagery and analyses of infrared MODIS data, volcanism at San Miguel from June 2018 to mid-February was relatively low, consisting of occasional gas-and-steam emissions. During 2019, a weak thermal anomaly in the summit crater was registered in thermal satellite imagery (figure 27). This thermal anomaly persisted during a majority of the year but was not visible after September 2019; faint gas-and-steam emissions could sometimes be seen rising from the summit crater.

Figure 27. Sentinel-2 satellite imagery of a faint but consistent thermal anomaly at San Miguel during 2019. Images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Volcanism was prominent beginning on 13-20 February 2020 when SO₂ emissions exceeded 620 tons/day (typical low SO₂ values are less than 400 tons/day). During 20-21 February the amplitude of microearthquakes increased and minor emissions of gas-and-steam and SO₂ were visible within the crater (figure 28). According to SNET and special reports from MARN, on 22 February at 1055 an ash cloud was visible rising 400 m above the crater rim (figure 29), resulting in minor ashfall in Piedra Azul (5 km SW). That same day RSAM values peaked at 550 units as recorded by the VSM station on the upper N flank, which is above normal values of about 150. Seismicity increased the day after the eruptive activity. Minor gas-and-steam emissions continued to rise 400 m above the crater rim during 23-24 February; the RSAM values fell to 33-97 units. Activity in March was relatively low; some seismicity, including small magnitude earthquakes, occurred during the month in addition to SO₂ emissions ranging from 517 to 808 tons/day.

Figure 28. Minor gas-and-steam emissions rising from the crater at San Miguel on 21 February 2020. Courtesy of Ministero de Medio Ambiente y Recursos Naturales (MARN).

Figure 29. Gas-and-steam and ash emissions rising from the crater at San Miguel on 22 February 2020. Courtesy of Ministero de Medio Ambiente y Recursos Naturales (MARN).

Geologic Background. The symmetrical cone of San Miguel volcano, one of the most active in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. The unvegetated summit rises above slopes draped with coffee plantations. A broad, deep crater complex that has been frequently modified by historical eruptions (recorded since the early 16th century) caps the truncated summit, also known locally as Chaparrastique. Radial fissures on the flanks of the basaltic-andesitic volcano have fed a series of historical lava flows, including several erupted during the 17th-19th centuries that reached beyond the base of the volcano on the N, NE, and SE sides. The SE-flank flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. The location of flank vents has migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.

Information Contacts: Servicio Nacional de Estudios Territoriales (SNET), Ministero de Medio Ambiente y Recursos Naturales (MARN), Km. 5½ Carretera a Nueva San Salvador, Avenida las Mercedes, San Salvador, El Salvador (URL: http://www.snet.gob.sv/ver/vulcanologia); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Cleveland is a stratovolcano located in the western portion of Chuginadak Island, a remote island part of the east central Aleutians. Common volcanism has included small lava flows, explosions, and ash clouds. Intermittent lava dome growth, small ash explosions, and thermal anomalies have characterized more recent activity (BGVN 44:02). For this reporting period during February 2019-January 2020, activity largely consisted of gas-and-steam emissions and intermittent thermal anomalies within the summit crater. The primary source of information comes from the Alaska Volcano Observatory (AVO) and various satellite data.

Low levels of unrest occurred intermittently throughout this reporting period with gas-and-steam emissions and thermal anomalies as the dominant type of activity (figures 30 and 31). An explosion on 9 January 2019 was followed by lava dome growth observed during 12-16 January. Suomi NPP/VIIRS sensor data showed two hotspots on 8 and 14 February 2019, though there was no evidence of lava within the summit crater at that time. According to satellite imagery from AVO, the lava dome was slowly subsiding during February into early March. Elevated surface temperatures were detected on 17 and 24 March in conjunction with degassing; another gas-and-steam plume was observed rising from the summit on 30 March. Thermal anomalies were again seen on 15 and 28 April using Suomi NPP/VIIRS sensor data. Intermittent gas-and-steam emissions continued as the number of detected thermal anomalies slightly increased during the next month, occurring on 1, 7, 15, 18, and 23 May. A gas-and-steam plume was observed on 9 May.

Figure 30. The MIROVA graph of thermal activity (log radiative power) at Cleveland during 4 February 2019 through January 2020 shows increased thermal anomalies between mid-April to late November 2019. Courtesy of MIROVA.

Figure 31. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed intermittent thermal signatures occurring in the summit crater during March 2019 through October 2019. Some gas-and-steam plumes were observed accompanying the thermal anomaly, as seen on 17 March 2019 and 8 May 2019. Courtesy of Sentinel Hub Playground.

There were 10 thermal anomalies observed in June, and 11 each in July and August. Typical mild degassing was visible when photographed on 9 August (figure 32). On 14 August, seismicity increased, which included a swarm of a dozen local earthquakes. The lava dome emplaced in January was clearly visible in satellite imagery (figure 33). The number of thermal anomalies decreased the next month, occurring on 10, 21, and 25 September. During this month, a gas-and-steam plume was observed in a webcam image on 6, 8, 20, and 25 September. On 3-6, 10, and 21 October elevated surface temperatures were recorded as well as small gas-and-steam plumes on 4, 7, 13, and 20-25 October.

Figure 32. Photograph of Cleveland showing mild degassing from the summit vent taken on 9 August 2019. Photo by Max Kaufman; courtesy of AVO/USGS.

Figure 33. Satellite image of Cleveland showing faint gas-and-steam emissions rising from the summit crater. High-resolution image taken on 17 August 2019 showing the lava dome from January 2019 inside the crater (dark ring). Image created by Hannah Dietterich; courtesy of AVO/USGS and DigitalGlobe.

Four thermal anomalies were detected on 3, 6, and 8-9 November. According to a VONA report from AVO on 8 November, satellite data suggested possible slow lava effusion in the summit crater; however, by the 15th no evidence of eruptive activity had been seen in any data sources. Another thermal anomaly was observed on 14 January 2020. Gas-and-steam emissions observed in webcam images continued intermittently.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows intermittent weak thermal anomalies within 5 km of the crater summit during mid-April through November 2019 with a larger cluster of activity in early June, late July and early October (figure 30). Thermal satellite imagery from Sentinel-2 also detected weak thermal anomalies within the summit crater throughout the reporting period, occasionally accompanied by gas-and-steam plumes (figure 31).

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

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/).

Ambrym is an active volcanic island in the Vanuatu archipelago consisting of a 12 km-wide summit caldera. Benbow and Marum are two currently active craters within the caldera that have produced lava lakes, explosions, lava flows, ash, and gas emissions, in addition to fissure eruptions. More recently, a submarine fissure eruption in December 2018 produced lava fountains and lava flows, which resulted in the drainage of the active lava lakes in both the Benbow and Marum craters (BGVN 44:01). This report updates information from January 2019 through March 2020, including the submarine pumice eruption during December 2018 using information from the Vanuatu Meteorology and Geohazards Department (VMGD) and research by Shreve et al. (2019).

Activity on 14 December 2018 consisted of thermal anomalies located in the lava lake that disappeared over a 12-hour time period; a helicopter flight on 16 December confirmed the drainage of the summit lava lakes as well as a partial collapse of the Benbow and Marum craters (figure 49). During 14-15 December, a lava flow (figure 49), accompanied by lava fountaining, was observed originating from the SE flank of Marum, producing SO2 and ash emissions. A Mw 5.6 earthquake on 15 December at 2021 marked the beginning of a dike intrusion into the SE rift zone as well as a sharp increase in seismicity (Shreve et al., 2019). This intrusion extended more than 30 km from within the caldera to beyond the east coast, with a total volume of 419-532 x 106 m3 of magma. More than 2 m of coastal uplift was observed along the SE coast due to the asymmetry of the dike from December, resulting in onshore fractures.

Figure 49. Sentinel-2 thermal satellite images of Ambrym before the December 2018 eruption (left), and during the eruption (right). Before the eruption, the thermal signatures within both summit craters were strong and after the eruption, the thermal signatures were no longer detected. A lava flow was observed during the eruption on 15 December. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

Shreve et al. (2019) state that although the dike almost reached the surface, magma did not erupt from the onshore fractures; only minor gas emissions were detected until 17 December. An abrupt decrease in the seismic moment release on 17 December at 1600 marked the end of the dike propagation (figure 50). InSAR-derived models suggested an offshore eruption (Shreve et al., 2019). This was confirmed on 18-19 December when basaltic pumice, indicating a subaqueous eruption, was collected on the beach near Pamal and Ulei. Though the depth and exact location of the fissure has not been mapped, the nature of the basaltic pumice would suggest it was a relatively shallow offshore eruption, according to Shreve et al. (2019).

Figure 50. Geographical timeline summary of the December 2018 eruptive events at Ambrym. The lava lake level began to drop on 14 December, with fissure-fed lava flows during 14-15 December. After an earthquake on 15 December, a dike was detected, causing coastal uplift as it moved E. As the dike continued to propagate upwards, faulting was observed, though magma did not breach the surface. Eventually a submarine fissure eruption was confirmed offshore on 18-19 December. Image modified from Shreve et al. (2019).

In the weeks following the dike emplacement, there was more than 2 m of subsidence measured at both summit craters identified using ALOS-2 and Sentinel-1 InSAR data. After 22 December, no additional large-scale deformation was observed, though a localized discontinuity (less than 12 cm) measured across the fractures along the SE coast in addition to seismicity suggested a continuation of the distal submarine eruption into late 2019. Additional pumice was observed on 3 February 2019 near Pamal village, suggesting possible ongoing activity. These surveys also noted that no gas-and-steam emissions, lava flows, or volcanic gases were emitted from the recently active cracks and faults on the SE cost of Ambrym.

During February-October 2019, onshore activity at Ambrym declined to low levels of unrest, according to VMGD. The only activity within the summit caldera consisted of gas-and-steam emissions, with no evidence of the previous lava lakes (figure 51). Intermittent seismicity and gas-and-steam emissions continued to be observed at Ambrym and offshore of the SE coast. Mével et al. (2019) installed three Trillium Compact 120s posthole seismometers in the S and E part of Ambrym from 25 May to 5 June 2019. They found that there were multiple seismic events, including a Deep-Long Period event and mixed up/down first motions at two stations near the tip of the dike intrusion and offshore of Pamal at depths of 15-20 km below sea level. Based on a preliminary analysis of these data, Mével et al. (2019) interpreted the observations as indicative of ongoing volcanic seismicity in the region of the offshore dike intrusion and eruption.

Figure 51. Aerial photograph of Ambrym on 12 August 2019 showing gas-and-steam emissions rising from the summit caldera. Courtesy of VMGD.

Seismicity was no longer reported from 10 October 2019 through March 2020. Thermal anomalies were not detected in satellite data except for one in late April and one in early September 2019, according to MODIS thermal infrared data analyzed by the MIROVA system. The most recent report from VMGD was issued on 27 March 2020, which noted low-level unrest consisting of dominantly gas-and-steam emissions.

References:

Shreve T, Grandin R, Boichu M, Garaebiti E, Moussallam Y, Ballu V, Delgado F, Leclerc F, Vallée M, Henriot N, Cevuard S, Tari D, Lebellegard P, Pelletier B, 2019. From prodigious volcanic degassing to caldera subsidence and quiescence at Ambrym (Vanuatu): the influence of regional tectonics. Sci. Rep. 9, 18868. https://doi.org/10.1038/s41598-019-55141-7.

Mével H, Roman D, Brothelande E, Shimizu K, William R, Cevuard S, Garaebiti E, 2019. The CAVA (Carnegie Ambrym Volcano Analysis) Project - a Multidisciplinary Characterization of the Structure and Dynamics of Ambrym Volcano, Vanuatu. American Geophysical Union, Fall 2019 Meeting, Abstract and Poster V43C-0201.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Most of the large edifice of Copahue lies high in the central Chilean Andes, but the active 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 began with phreatic explosions and ash emissions on 2 August 2019 that continued until mid-November 2019. This report summarizes activity from November 2019 through February 2020 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.

MIROVA data indicated a few weak thermal anomalies during mid-October to mid-November 2019. Multiple continuous ash emissions were reported daily until mid-November when activity declined significantly. By mid-December the lake inside El Agrio crater had reappeared and occasional steam plumes were the only reported surface activity at Copahue through February 2020.

The Buenos Aires VAAC and SERNAGEOMIN both reported continuous ash emissions during 1-9 November 2019 that were visible in the webcam. Satellite imagery recorded the plumes drifting generally E or NE at 3.0-4.3 km altitude (figure 49). Most of the emissions on 10 November were steam (figure 50). The last pulse of ash emissions occurred on 12 November with an ash plume visible moving SE at 3 km altitude in satellite imagery and a strong thermal anomaly (figure 51). The following day emissions were primarily steam and gas. SERNAGEOMIN noted the ash emissions rising around 800 m above El Agrio crater and also reported incandescence visible during most nights through mid-November. During the second half of November the constant degassing was primarily water vapor with occasional nighttime incandescence. Steam plumes rose 450 m above the crater on 27 November.

Figure 49. Continuous ash emissions at Copahue during 1-9 November 2019 were visible in Sentinel-2 satellite imagery on 2 and 7 November 2019 drifting NE. Natural color rendering uses bands 4,3, and 2. Courtesy of Sentinel Hub Playground.

Figure 50. Most of the emissions from Copahue on 10 November 2019 were steam. Left image courtesy of Valentina Sepulveda, taken from Caviahue, Argentina. Right image courtesy of Sentinel Hub Playground, natural color rendering using bands 4, 3, and 2.

Figure 51. A strong thermal anomaly and an ash plume at Copahue were visible in Sentinel-2 satellite imagery on 12 November 2019. Courtesy of Sentinel Hub Playground, Atmospheric penetration rendering bands 12, 11, and 8A.

Nighttime incandescence was last observed in the SERNAGEOMIN webcam on 1 December; SERNAGEOMIN lowered the alert level from Yellow to Green on 15 December 2019. Throughout December degassing consisted mainly of minor steam plumes (figure 52), the highest plume rose to 300 m above the crater on 18 December, and minor SO₂ plumes persisted through the 21st (figure 53),. By mid-December the El Agrio crater lake was returning and satellite images clearly showed the increase in size of the lake through February (figure 54). The only surface activity reported during January and February 2020 was occasional white steam plumes rising near El Agrio crater.

Figure 52. Small wisps of steam were the only emissions from Copahue on 3 December 2019. Courtesy of Valentina Sepulveda, taken from Caviahue, Argentina.

Figure 53. Small plumes of SO2 were recorded at Copahue during November and December 2019. Top row: 7, 9, and 30 November. Bottom row: 1, 20, and 21 December. Courtesy of Global Sulfur Dioxide Monitoring Page, NASA.

Figure 54. The lake within El Agrio crater reappeared between 5 and 12 December 2019 and continued to grow in size through the end of January 2020. Top row (left to right): There was no lake inside the crater on 5 December 2019, only a small steam plume rising from the vent. The first water was visible on 12 December and was slightly larger a few days later on 17 December. Bottom row (left to right): the lake was significantly larger on 4 January 2020 filling an embayment close to the steam vent. Fingers of water filled in areas of the crater as the water level rose on 24 and 29 January. Courtesy of Sentinel Hub Playground.

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/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Valentina Sepulveda, Hotel Caviahue, Caviahue, Argentina (URL: https://twitter.com/valecaviahue, Twitter:@valecaviahue).

After 40 years of dormancy, Japan’s Nishinoshima volcano, located about 1,000 km S of Tokyo in the Ogasawara Arc, erupted above sea level in November 2013. Lava flows were active through November 2015, emerging from a central pyroclastic cone. A new eruption in mid-2017 continued the growth of the island with ash plumes, ejecta, and lava flows. A short eruptive event in July 2018 produced a new lava flow and vent on the side of the pyroclastic cone. The next eruption of ash plumes, incandescent ejecta, and lava flows, covered in this report, began in early December 2019 and was ongoing through February 2020. Information is provided primarily from the Japan Meteorological Agency (JMA) monthly reports.

Nishinoshima remained quiet after a short eruptive event in July 2018 until MODVOLC thermal alerts appeared on 5 December 2019. Multiple near-daily alerts continued through February 2020. The intermittent low-level thermal anomalies seen in the MIROVA data beginning in May and June 2019 may reflect areas with increased temperatures and fumarolic activity reported by the Japan Coast Guard during overflights in June and July. The significant increase in thermal anomalies in the MIROVA data on 5 December correlates with the beginning of extrusive and explosive activity (figure 63). Eruptive activity included ash emissions, incandescent ejecta, and numerous lava flows from multiple vents that flowed into the sea down several flanks, significantly enlarging the island.

Figure 63. The MIROVA graph of thermal energy from Nishinoshima from 13 April 2019 through February 2020 shows low-level thermal activity beginning in mid-2019; there were reports of increased temperatures and fumarolic activity during that time. Eruptive activity including ash emissions, incandescent ejecta, and numerous lava flows began on 5 December 2019 and was ongoing through February 2020. Courtesy of MIROVA.

A brief period of activity during 12-21 July 2018 produced explosive activity with blocks and bombs ejected 500 m from a new vent on the E flank of the pyroclastic cone, and a 700-m-long lava flow that stopped about 100 m before reaching the ocean (BGVN 43:09). No further activity was reported during 2018. During overflights on 29 and 31 January, and 7 February 2019, white steam plumes drifted from the E crater margin and inner wall of the pyroclastic cone and discolored waters were present around the island, but no other signs of activity were reported. A survey carried out by the Japan Coast Guard during 7-8 June 2019 reported minor fumarolic activity from the summit crater, and high-temperature areas were noted on the hillsides, measured by infrared thermal imaging equipment. Sulfur dioxide emissions were below the detection limit. In an overflight on 12 July 2019, Coast Guard personnel noted a small white plume rising from the E edge of the summit crater of the pyroclastic cone (figure 64).

Figure 64. The Japan Coast Guard noted a small white plume at the summit of Nishinoshima during an overflight on 12 July 2019, but no other signs of activity. Courtesy of JMA (Volcanic activity monthly report, July 2019).

The white plume was still present during an overflight on 14 August 2019. Greenish yellow areas of water about 500 m wide were distributed around the island, and a plume of green water extended 1.8 km from the NW coast. Similar conditions were observed on 15 October 2019; pale yellow-green discolored water was about 100 m wide and concentrated on the N shore of Nishinoshima. No steam plume from the summit was present during a visit on 19 November 2019, but yellow-white discolored water on the N shore was about 100 m wide and 700 m long. Along the NE and SE coasts, yellow-white water was 100-200 m wide and about 1,000 m long.

A MODVOLC thermal alert appeared at Nishinoshima on 5 December 2019. An eruption was observed by the Japan Coast Guard the following day. A pulsating light gray ash plume rose from the summit crater accompanied by tephra ejected 200 m above the crater rim every few minutes (figure 65). In addition, ash and tephra rose intermittently from a crater on the E flank of the pyroclastic cone, from which lava also flowed down towards the E coast (figure 66). By 1300 on 7 December the lava was flowing into the sea (figure 67).

Figure 65. The eruption observed at Nishinoshima on 6 December 2019 included ash and tephra emissions from the summit vent, and ash, tephra, and a lava flow from the vent on the E flank of the pyroclastic cone. Courtesy of JMA (Volcanic activity monthly report, November 2019).

Figure 66. Thermal infrared imagery revealed incandescent ejecta from the summit crater and lava flowing from the E flank vent at Nishinoshima on 6 December 2019. Courtesy of JMA (Volcanic activity monthly report, November 2019).

Figure 67. By 1300 on 7 December 2019 lava from the E-flank vent at Nishinoshima was flowing into the sea. Courtesy of JMA (Volcanic activity monthly report, November 2019).

Observations by the Japan Coast Guard on 15 December 2019 confirmed that vigorous eruptive activity was ongoing; incandescent ejecta and ash plumes rose 300 m above the summit crater rim (figure 68). A new vent had opened on the N flank of the cone from which lava flowed NW to the sea (figure 69). The lava flow from the E-flank crater also remained active and continued flowing into the sea. The Tokyo VAAC reported an ash emission on 24 December that rose to 1,000 m altitude and drifted S. On 31 December, explosions at the summit continued every few seconds with ash and ejecta rising 300 m high. In addition, lava from the NE flank of the pyroclastic cone flowed NE to the sea (figure 70).

Figure 68. Incandescent ejecta and ash rose 300 m above the summit crater rim at Nishinoshima on 15 December 2019. Courtesy of JMA (Volcanic activity monthly report, December 2019).

Figure 69. Lava from a new vent on the NW flank of Nishinoshima was entering the sea on 15 December 2019, producing vigorous steam plumes. Courtesy of JMA (Volcanic activity monthly report, December 2019).

Figure 70. At Nishinoshima on 31 December 2019 lava flowed down the NE flank of the pyroclastic cone into the sea, and incandescent ejecta rose 300 m above summit. Courtesy of JMA and the Japan Coast Guard (Volcanic activity monthly report, December 2019).

Satellite data from JAXA (Japan Aerospace Exploration Agency) made it possible for JMA to produce maps showing the rapid changes in topography at Nishinoshima resulting from the new lava flows. The new E-flank lava flow was readily seen when comparing imagery from 22 November with 6 December 2019 (figure 71a). An image from 6 December compared with 20 December 2019 shows the flow on the E flank splitting and entering the sea at two locations (figure 71b), the flow on the NW flank traveling briefly N before turning W and forming a large fan into the ocean on the W flank, and a new flow heading NE from the summit area of the pyroclastic cone.

Figure 71. Satellite data from JAXA (Japan Aerospace Exploration Agency) made it possible to produce maps showing the changes in topography at Nishinoshima resulting from the new lava flows (shown in blue). In comparing 22 November with 6 December 2019 (A, left), the new lava flow on the E flank was visible. A new image from 20 December compared with 6 December (B, right) showed the flow on the E flank splitting and entering the sea at two locations, the NW-flank flow building a large fan into the ocean on the W flank, and a new flow heading NE from the summit area of the pyroclastic cone. Courtesy of JMA and the Japan Coast Guard (Volcanic activity monthly report, December 2019).

The Tokyo VAAC reported an ash plume visible in satellite imagery on 15 January 2020 that rose to 1.8 km altitude and drifted SE. The Japan Coast Guard conducted an overflight on 17 January that confirmed the continued eruptions of ash, incandescent ejecta, and lava. Dark gray ash plumes were observed at 1.8 km altitude, with ashfall and tephra concentrated around the pyroclastic cone (figure 72). Plumes of steam were visible where the NE lava flow entered the ocean; the E and NW lava entry areas did not appear active but were still hot. Satellite data from ALOS-2 prepared by JAXA confirmed ongoing activity around the summit vent and on the NE flank, while activity on the W flank had ceased (figure 73). An ash plume was reported by the Tokyo VAAC on 25 January; it rose to 1.5 km altitude and drifted SW for most of the day.

Figure 72. Dense, dark gray ash plumes rose from the summit of Nishinoshima on 17 January 2020. Small plumes of steam from lava-seawater interactions were visible on the NE shore of the island as well (far right). Courtesy of JMA and the Japan Coast Guard (Volcanic activity monthly report, January 2020).

Figure 73. JAXA satellite data from 3 January 2020 (left) showed the growth of a new lava delta on the NE flank of Nishinoshima and minor activity occuring on the W flank compared with the previous image from 20 December 2019. By 17 January 2020 (right), the lava flow activity was concentrated on the NE flank with multiple deltas extending out into the sea. The ‘low correlation areas’ shown in blue represent changes in topography caused by new material from lava flows and ejecta added between the dates shown above the images. Courtesy of JMA (Volcanic activity monthly report, January 2020).

On 3 Feburary 2020 the Tokyo VAAC reported an ash plume visible in satellite imagery that rose to 2.1 km altitude and drifted E. The following day the Japan Coast Guard observed eruptions from the summit crater at five minute intervals that produced grayish white plumes. The plumes rose to 2.7 km altitude (figure 74). Large bombs were scattered around the pyroclastic cone, and the summit crater appeared filled with lava except for the active vent. The lava deltas on the NE flank were only active at the tips of the flows producing a few steam jets where lava entered the sea. The active flows were on the SE flank, and a new 200-m-long lava flow was flowing down the N flank of the pyroclastic cone (figure 75). The lava flowing from the E flank of the pyroclastic cone to the SE into the sea, produced larger jets of steam (figure 76). Yellow-brown discolored water appeared around the island in several places.

Figure 74. Ash emissions at Nishinoshima rose to 2.7 km altitude on 4 February 2020; steam jets from lava entering the ocean were active on the SE flank (far side of the island, right). Courtesy of JMA (Volcanic activity monthly report, February 2020).

Figure 75. The lava deltas on the NE flank of Nishinoshima (bottom center) were much less active on 4 February 2020 than the lava flow and growing delta on the SE flank (left). The newest flow headed N from the summit and was 200 m long (right of center). Courtesy of JMA and the Japan Coast Guard (Volcanic activity monthly report, February 2020).

Figure 76. The most active lava flows at Nishinoshima on 4 February 2020 were on the E flank; significant steam plumes rose in multiple locations along the coast where they entered the sea. Intermittent ash plumes also rose from the summit crater. Courtesy of JMA and Japan Coast Guard (Volcanic activity monthly report, February 2020).

JAXA satellite data confirmed that the flow activity was concentrated on the NE flank and shore during the second half of January 2020, but also recorded the new flow down the SE flank that was observed by the Coast Guard in early February. By mid-February the satellite topographic data indicated the decrease in activity in the NE flank flows, the increased activity on the SE and E flank, and the extension of the flow moving due N to the coast (figure 77). Observations on 17 February 2020 by the Japan Coast Guard revealed eruptions from the summit crater every few seconds, and steam-and-ash plumes rising about 600 m. Vigorous white emissions rose from fractures near the top of the W flank of the pyroclastic cone, but thermal data indicated the area was no hotter than the surrounding area (figure 78). The lava flow on the SE coast still had steam emissions rising from the ocean entry point, but activity was weaker than on 4 February. The newest flow moving due N from the summit produced steam emissions where the flow front entered the ocean.

Figure 77. Constantly changing lava flows at Nishinoshima reshaped the island during late January and February 2020. During the second half of January, flows were active on the NE flank, creating deltas into the sea off the NE coast and also on the SE flank into the sea at the SE coast (left). The ‘low correlation areas’ shown in blue represent changes in topography caused by new material from lava flows and ejecta added between the dates shown above the images. By 14 February (right) activity had slowed on the NE flank and expanded on the SE flank and N flank. Data is from the Land Observing Satellite-2 "Daichi-2" (ALOS-2). Courtesy of JMA and JAXA (Volcanic activity monthly report, February 2020).

Figure 78. Vigorous white emissions rose from fractures near the top of the W flank of the pyroclastic cone at Nishinoshima on 17 February 2020, but thermal data indicated the area was no hotter than the surrounding area. Courtesy of JMA and Japan Coast Guard (Volcanic activity monthly report, February 2020).

Sulfur dioxide plumes from Nishinoshima have been small and infrequent in recent years, but the renewed and increased eruptive activity beginning in December 2019 produced several small SO₂ plumes that were recorded in daily satellite data (figure 79).

Figure 79. Small sulfur dioxide plumes from Nishinoshima were captured by the TROPOMI instrument on the Sentinel 5P satellite a few times during December 2019-February 2020 as the eruptive activity increased. The large red streak in the 3 February 2020 image is SO2 from an eruption of Kuchinoerabujima volcano (Ryukyu Islands) on the same day. Courtesy of NASA Goddard Space Flight Center and Simon Carn.

Geologic Background. The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Another eruption that began offshore in 2013 completely covered the previous exposed surface and enlarged the island again. Water discoloration has been observed on several occasions since. The island is the summit of a massive submarine volcano that has prominent satellitic peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the sea surface 9 km SSE.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Japan Aerospace Exploration Agency-Earth Observation Research Center (JAXA-EORC), 7-44-1 Jindaiji Higashi-machi, Chofu-shi, Tokyo 182-8522, Japan (URL: http://www.eorc.jaxa.jp/); Japan Coast Guard (JCG) Volcano Database, Hydrographic and Oceanographic Department, 3-1-1, Kasumigaseki, Chiyoda-ku, Tokyo 100-8932, Japan (URL: http://www.kaiho.mlit.go.jp/info/kouhou/h29/index.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); 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/); 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).

Krakatau volcano in the Sunda Strait between Indonesia’s Java and Sumatra Islands experienced a major caldera collapse around 535 CE; it formed a 7-km-wide caldera ringed by three islands. Remnants of this volcano joined to create the pre-1883 Krakatau Island which collapsed during the major 1883 eruption. Anak Krakatau (Child of Krakatau), constructed beginning in late 1927 within the 1883 caldera (BGVN 44:03, figure 56), was the site of over 40 eruptive episodes until 22 December 2018 when a large explosion and flank collapse destroyed most of the 338-m-high edifice and generated a deadly tsunami (BGVN 44:03). The near-sea level crater lake inside the remnant of Anak Krakatau was the site of numerous small steam and tephra explosions from February (BGVN 44:08) through November 2019. A larger explosion in December 2019 produced the beginnings of a new cone above the surface of crater lake. Activity from August 2019 through January 2020 is covered in this report with information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, referred to as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG). Aviation reports are provided by the Darwin Volcanic Ash Advisory Center (VAAC), and photographs are from the PVMBG webcam and visitors to the island.

Explosions were reported on more than ten days each month from August to October 2019. They were recorded based on seismicity, but webcam images also showed black tephra and steam being ejected from the crater lake to heights up to 450 m. Activity decreased significantly after the middle of November, although smaller explosions were witnessed by visitors to the island. After a period of relative quiet, a larger series of explosions at the end of December produced ash plumes that rose up to 3 km above the crater; the crater lake was largely filled with tephra after these explosions. Thermal activity persisted throughout the period of August 2019-January 2020. The wattage of Radiative Power increased from August through mid-October, and then decreased through January 2020 (figure 96).

Figure 96. Thermal activity persisted at Anak Krakatau from 20 March 2019-January 2020. The wattage of Radiative Power increased from August through mid-October, and then decreased through January 2020. Courtesy of MIROVA.

Activity during August-November 2019. The new profile of Anak Krakatau rose to about 155 m elevation as of August 2019, almost 100 m less than prior to the December 2018 explosions and flank collapse (figure 97). Smaller explosions continued during August 2019 and were reported by PVMBG in 12 different VONAs (Volcano Observatory Notice to Aviation) on days 1, 3, 6, 17, 19, 22, 23, 25, and 28. Most of the explosions lasted for less than two minutes, according to the seismic data. PVMBG reported steam plumes of 25-50 m height above the sea-level crater on 20 and 21 August. They reported a visible ash cloud on 22 August; it rose to an altitude of 457 m and drifted NNE according to the VONA. In their daily update, they noted that the eruption plume of 250-400 m on 22 August was white, gray, and black. The Darwin VAAC reported that the ash plume was discernable on HIMAWARI-8 satellite imagery for a short period of time. PVMBG noted ten eruptions on 24 August with white, gray, and black ejecta rising 100-300 m. A webcam installed at month’s end provided evidence of diffuse steam plumes rising 25-150 m above the crater during 28-31 August.

Figure 97. Only one tree survived on the once tree-covered spit off the NE end of Sertung Island after the December 2018 tsunami from Anak Krakatau covered it with ash and debris. The elevation of Anak Krakatau (center) was about 155 m on 8 August 2019, almost 100 m less than before the explosions and flank collapse. Panjang Island is on the left, and 746-m-high Rakata, the remnant of the 1883 volcanic island, is behind Anak Krakatau on the right. Courtesy of Amber Madden-Nadeau.

VONAs were issued for explosions on 1-3, 11, 13, 17, 18, 21, 24-27 and 29 September 2019. The explosion on 2 September produced a steam plume that rose 350 m, and dense black ash and ejecta which rose 200 m from the crater and drifted N. Gray and white tephra and steam rose 450 m on 13 and 17 September; ejecta was black and gray and rose 200 m on 21 September (figure 98). During 24-27 and 29 September tephra rose at least 200 m each day; some days it was mostly white with gray, other days it was primarily gray and black. All of the ejecta plumes drifted N. On days without explosions, the webcam recorded steam plumes rising 50-150 m above the crater.

Figure 98. Explosions of steam and dark ejecta were captured by the webcam on Anak Krakatau on 21 (left) and 26 (right) September 2019. Courtesy of MAGMA Indonesia and PVMBG.

Explosions were reported daily during 12-14, 16-20, 25-27, and 29 October (figure 99). PVMBG reported eight explosions on 19 October and seven explosions the next day. Most explosions produced gray and black tephra that rose 200 m from the crater and drifted N. On many of the days an ash plume also rose 350 m from the crater and drifted N. The seismic events that accompanied the explosions varied in duration from 45 to 1,232 seconds (about 20 minutes). The Darwin VAAC reported the 12 October eruption as visible briefly in satellite imagery before dissipating near the volcano. The first of four explosions on 26 October also appeared in visible satellite imagery moving NNW for a short time. The webcam recorded diffuse steam plumes rising 25-150 m above the crater on most days during the month.

Figure 99. A number of explosions at Anak Krakatau were captured by the webcam and visitors near the island during October 2019, shown here on the 12th, 14th, 17th, and 29th. Black and gray ejecta and steam plumes jetted several hundred meters high from the crater lake during the explosions. Webcam images courtesy of PVMBG and MAGMA Indonesia, with 12 October 2019 (top left) via VolcanoYT. Bottom left photo on 17 October courtesy of Christoph Sator.

Five VONAs were issued for explosions during 5-7 November, and one on 13 November 2019. The three explosions on 5 November produced 200-m-high plumes of steam and gray and black ejecta and ash plumes that rose 200, 450, and 550 m respectively; they all drifted N (figure 100). The Darwin VAAC reported ash drifting N in visible imagery for a brief period also. A 350-m-high ash plume accompanied 200-m-high ejecta on 6 November. Tephra rose 150-300 m from the crater during a 43 second explosion on 7 November. The explosion reported by PVMBG on 13 November produced black tephra and white steam 200 m high that drifted N. For the remainder of the month, when not obscured by fog, steam plumes rose daily 25-150 m from the crater.

Figure 100. PVMBG’s KAWAH webcam captured an explosion with steam and dark ejecta from the crater lake at Anak Krakatau on 5 November 2019. Courtesy of PVMBG and MAGMA Indonesia.

A joint expedition with PVMBG and the Earth Observatory of Singapore (EOS) installed geophysical equipment on Anak Krakatau and Rakata during 12 and 13 November 2019 (figure 101). Visitors to the island during 19-23 and 22-24 November recorded the short-lived landscape and continuing small explosions of steam and black tephra from the crater lake (figures 102 and 103).

Figure 101. A joint expedition to Anak Krakatau with PVMBG and the Earth Observatory of Singapore (EOS) installed geophysical equipment on Anak Krakatau and Rakata (background, left) during 12 and 13 November 2019. Images of the crater lake from the same spot (left) in December and January show the changes at the island (figure 108). Monitoring equipment installed near the shore sits over the many layers of ash and tephra that make up the island (right). Courtesy of Anna Perttu.

Figure 102.The crater lake at Anak Krakatau during a 19-23 November 2019 visit was the site of continued explosions with jets of steam and tephra that rose as high as 30 m. Courtesy of Andrey Nikiforov and Volcano Discovery, used with permission.

Figure 103. The landscape of Anak Krakatau recorded the rapidly evolving sequence of volcanic events during November 2019. Fresh ash covered recent lava near the shoreline on 22 November 2019 (top left). Large blocks of gray tephra (composed of other tephra fragments) were surrounded by reddish brown smaller fragments in the area between the crater and the ocean on 23 November 2019 (top right). Explosions of steam and black tephra rose tens of meters from the crater lake on 23 November 2019 (bottom). Courtesy of and copyright by Pascal Blondé.

Activity during December 2019-January 2020. Very little activity was recorded for most of December 2019. The webcam captured daily images of diffuse steam plumes rising 25-50 m above the crater which occasionally rose to 150 m. A new explosion on 28 December produced black and gray ejecta 200 m high that drifted N; the explosion was similar to those reported during August-November. A new series of explosions from 30 December 2019 to 1 January 2020 produced ash plumes which rose significantly higher than the previous explosions, reaching 2.4-3.0 km altitude and drifting S, E, and SE according to PVMBG (figure 104). They were initially visible in satellite imagery and reported drifting SW by the Darwin VAAC. By 31 December meteorological clouds prevented observation of the ash plume but a hotspot remained visible for part of that day.

Figure 104.The KAWAH webcam at Anak Krakatau captured this image of incandescent ejecta exploding from the crater lake on 30 December 2019 near the start of a new sequence of large explosions. Courtesy of PVMBG and Alex Bogár.

The explosions on 30 and 31 December 2019 were captured in satellite imagery (figure 105) and appeared to indicate that the crater lake was largely destroyed and filled with tephra from a new growing cone, according to Simon Carn. This was confirmed in both satellite imagery and ground-based photography in early January (figures 106 and 107).

Figure 105. Satellite imagery of the explosions at Anak Krakatau on 30 and 31 December 2019 showed dense steam rising from the crater (left) and a thermal anomaly visible through moderate cloud cover (right). Left image courtesy of Simon Carn, and copyright by Planet Labs, Inc. Right image uses Atmospheric Penetration rendering (bands 12, 11, and 8a) to show the thermal anomaly at the base of the steam plume, courtesy of Sentinel Hub Playground.

Figure 106. Sentinel-2 images of Anak Krakatau before (left, 21 December 2019) and after (right, 13 January 2020) explosions on 30 and 31 December 2019 show the filling in of the crater lake with new volcanic material. Natural color rendering based on bands 4,3, and 2. Courtesy of Sentinel Hub Playground.

Figure 107. The crater lake at Anak Krakatau changed significantly between the first week of December 2019 (left) and 8 January 2020 (right) after explosions on 30 and 31 December 2019. Compare with figure 101, taken from the same location in mid-November 2019. Left image courtesy of Piotr Smieszek. Right image courtesy of Peter Rendezvous.

Steam plumes rose 50-200 m above the crater during the first week of January 2020. An explosion on 7 January produced dense gray ash that rose 200 m from the crater and drifted E. Steam plume heights varied during the second week, with some plumes reaching 300 m above the crater. Multiple explosions on 15 January produced dense, gray and black ejecta that rose 150 m. Fog obscured the crater for most of the second half of the month; for a brief period, diffuse steam plumes were observed 25-1,000 m above the crater.

General Reference: Perttu A, Caudron C, Assink J D, Metz D, Tailpied D, Perttu B, Hibert C, Nurfiani D, Pilger C, Muzli M, Fee D, Andersen O L, Taisne B, 2020, Reconstruction of the 2018 tsunamigenic flank collapse and eruptive activity at Anak Krakatau based on eyewitness reports, seismo-acoustic and satellite observations, Earth and Planetary Science Letters, 541:116268. https://doi.org/10.1016/j.epsl.2020.116268.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Amber Madden-Nadeau, Oxford University (URL: https://www.earth.ox.ac.uk/people/amber-madden-nadeau/, https://twitter.com/AMaddenNadeau/status/1159458288406151169); Anna Perttu, Earth Observatory of Singapore (URL: https://earthobservatory.sg/people/anna-perttu); Simon Carn, Michigan Tech University (URL: https://www.mtu.edu/geo/department/faculty/carn/; https://twitter.com/simoncarn/status/1211793124089044994); VolcanoYT, Indonesia (URL: https://volcanoyt.com/, https://twitter.com/VolcanoYTz/status/1182882409445904386/photo/1; Christoph Sator (URL: https://twitter.com/ChristophSator/status/1184713192670281728/photo/1); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Pascal Blondé, France (URL: https://pascal-blonde.info/portefolio-krakatau/, https://twitter.com/rajo_ameh/status/1199219837265960960); Alex Bogár, Budapest (URL: https://twitter.com/AlexEtna/status/1211396913699991557); Piotr (Piter) Smieszek, Yogyakarta, Java, Indonesia (URL: http://www.lombok.pl/, https://twitter.com/piotr_smieszek/status/1204545970962231296); Peter Rendezvous (URL: https://www.facebook.com/peter.rendezvous ); Wulkany swiata, Poland (URL: http://wulkanyswiata.blogspot.com/, https://twitter.com/Wulkany1/status/1214841708862693376).

Mayotte is a volcanic island in the Comoros archipelago between the eastern coast of Africa and the northern tip of Madagascar. A chain of basaltic volcanism began 10-20 million years ago and migrating W, making up four principal volcanic islands, according to the Institut de Physique du Globe de Paris (IPGP) and Cesca et al. (2020). Before May 2010, only two seismic events had been felt by the nearby community within recent decades. New activity since May 2018 consists of dominantly seismic events and lava effusion. The primary source of information for this report through February 2020 comes from semi-monthly reports from the Réseau de Surveillance Volcanologique et Sismologique de Mayotte (REVOSIMA), a cooperative program between the Institut de Physique du Globe de Paris (IPGP), the Bureau de Recherches Géologiques et Minières (BRGM), and the Observatoire Volcanologique du Piton de la Fournaise (OVPF-IPGP); Lemoine et al. (2019), the Centre National de la Recherche Scientifique (CNRS), and the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER).

Seismicity was the dominant type of activity recorded in association with a new submarine eruption. On 10 May 2018, the first seismic event occurred at 0814, detected by the YTMZ accelerometer from the French RAP Network, according to BRGM and Lemoine et al. (2019). Seismicity continued to increase during 13-15 May 2018, with the strongest recorded event for the Comoros area occurring on 15 May at 1848 and two more events on 20-21 May (figure 1). At the time, no surface effusion were directly observed; however, Global Navigation Satellite System (GNSS) instruments were deployed to monitor any ground motion (Lemoine et al. 2019).

Figure 1. A graph showing the number of daily seismic events greater than M 3.5 occurring offshore of Mayotte from 10 May 2018 through 15 February 2020. Seismicity significantly decreased in July 2018, but continued intermittently through February 2020, with relatively higher seismicity recorded in late August and mid-September 2018. Courtesy of IPGP and REVOSIMA.

Seismicity decreased dramatically after June 2018, with two spikes in August and September (see figure 1). Much of this seismicity occurred offshore 50 km E of Mayotte Island (figure 2). The École Normale Supérieure, the Observatoire Volcanologique du Piton de la Fournaise (OVPF-IPGP), and the REVOSIMA August 2019 bulletin reported that measurements from the GNSS stations and Teria GPS network data indicated eastward surface deformation and subsidence beginning in July 2018. Based on this ground deformation data Lemoine et al. (2019) determined that the eruptive phase began fifty days after the initial seismic events occurred, on 3 July 2018.

Figure 2. Maps of seismic activity offshore near Mayotte during May 2019. Seismic swarms occurred E of Mayotte Island (top) and continued in multiple phases through October 2019. New lava effusions were observed 50 km E of Petite Terre (bottom). Bottom image has been modified with annotations; courtesy of IPGP, BRGM, IFREMER, CNRS, and University of Paris.

Between 2 and 18 May 2019, an oceanographic campaign (MAYOBS 1) discovered a new submarine eruption site 50 km E from the island of Mayotte (figure 2). The director of IPGP, Marc Chaussidon, stated in an interview with Science Magazine that multibeam sonar waves were used to determine the elevation (800 m) and diameter (5 km) of the new submarine cone (figure 3). In addition, this multibeam sonar image showed fluid plumes within the water column rising from the center and flanks of the structure. According to REVOSIMA, these plumes rose to 1 km above the summit of the cone but did not breach the ocean surface. The seafloor image (figure 3) also indicated that as much as 5 km3 of magma erupted onto the seafloor from this new edifice during May 2019, according to Science Magazine.

Figure 3. Seafloor image of the submarine vent offshore of Mayotte created with multibeam sonar from 2 to 18 May 2019. The red line is the outline of the volcanic cone located at approximately 3.5 km depth. The blue-green color rising from the peak of the red outline represents fluid plumes within the water column. Courtesy of IPGP.

On 17 May 2019, a second oceanographic campaign (MAYOBS 2) discovered new lava flows located 5 km S of the new eruptive site. BRGM reported that in June a new lava flow had been identified on the W flank of the cone measuring 150 m thick with an estimated volume of 0.3 km3 (figure 4). According to REVOSIMA, the presence of multiple new lava flows would suggest multiple effusion points. Over a period of 11 months (July 2018-June 2019) the rate of lava effusion was at least 150-200 m3/s; between 18 May to 17 June 2019, 0.2 km3 of lava was produced, and from 17 June to 30 July 2019, 0.3 km3 of lava was produced. The MAYOBS 4 (19 July 2019-4 August 2019) and SHOM (20-21 August 2019) missions revealed a new lava flow formed between 31 July and 20 August to the NW of the eruptive site with a volume of 0.08 km3 and covering 3.25 km2.

Figure 4. Bathymetric map showing the location of the new lava flow on the W flank of the submarine cone offshore to the E of Mayotte Island. The MAYOBS 2 campaign was launched in June 2019 (left) and MAYOBS 4 was launched in late July 2019 (right). Courtesy of BRGM.

During the MAYOBS 4 campaign in late July 2019, scientists dredged the NE flank of the cone for samples and took photographs of the newly erupted lava (figure 5). Two dives found the presence of pillow lavas. When samples were brought up to the surface, they exploded due to the large amount of gas and rapid decompression.

Figure 5. Photographs taken using the submersible interactive camera system (SCAMPI) of newly formed pillow lavas (top) and a vesicular sample (bottom) dredged near the new submarine eruptive site at Mayotte in late July 2019. Courtesy of BRGM.

During April-May 2019 the rate of ground deformation slowed. Deflation was also observed up to 90 km E of Mayotte in late October 2019 and consistently between August 2019 and February 2020. Seismicity continued intermittently through February 2020 offshore E of Mayotte Island, though the number of detected events started to decrease in July 2018 (see figure 1). Though seismicity and deformation continued, the most recent observation of new lava flows occurred during the MAYOBS 4 and SHOM campaigns on 20 August 2019, as reported in REVOSIMA bulletins.

References: Cesca S, Heimann S, Letort J, Razafindrakoto H N T, Dahm T, Cotton F, 2020. Seismic catalogues of the 2018-2019 volcano-seismic crisis offshore Mayotte, Comoro Islands. Nat. Geosci. 13, 87-93. https://doi.org/10.1038/s41561-019-0505-5.

Lemoine A, Bertil D, Roulle A, Briole P, 2019. The volcano-tectonic crisis of 2018 east of Mayotte, Comoros islands. Preprint submitted to EarthArXiv, 28 February 2019. https://doi.org/10.31223/osf.io/d46xj.

Geologic Background. Mayotte, located in the Mozambique Channel between the northern tip of Madagascar and the eastern coast of Africa, consists two main volcanic islands, Grande Terre and Petite Terre, and roughly twenty islets within a barrier-reef lagoon complex (Zinke et al., 2005; Pelleter et al., 2014). Volcanism began roughly 15-10 million years ago (Pelleter et al., 2014; Nougier et al., 1986), and has included basaltic lava flows, nephelinite, tephrite, phonolitic domes, and pyroclastic deposits (Nehlig et al., 2013). Lavas on the NE were active from about 4.7 to 1.4 million years and on the south from about 7.7 to 2.7 million years. Mafic activity resumed on the north from about 2.9 to 1.2 million years and on the south from about 2 to 1.5 million years. Several pumice layers found in cores on the barrier reef-lagoon complex indicate that volcanism likely occurred less than 7,000 years ago (Zinke et al., 2003). More recent activity that began in May 2018 consisted of seismicity and ground deformation occurring offshore E of Mayotte Island (Lemoine et al., 2019). One year later, in May 2019, a new subaqueous edifice and associated lava flows were observed 50 km E of Petite Terre during an oceanographic campaign.

Information Contacts: Réseau de Surveillance Volcanologique et Sismologique de Mayotte (REVOSIMA), a cooperative program of a) Institut de Physique du Globe de Paris (IPGP), b) Bureau de Recherches Géologiques et Minières (BRGM), c) Observatoire Volcanologique du Piton de la Fournaise (OVPF-IPGP); (URL: http://www.ipgp.fr/fr/reseau-de-surveillance-volcanologique-sismologique-de-mayotte); Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); Bureau de Recherches Géologiques et Minières (BRGM), 3 avenue Claude-Guillemin, BP 36009, 45060 Orléans Cedex 2, France (URL: https://www.brgm.fr/); Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), 1625 route de Sainte-Anne, CS 10070, 29280 Plouzané, France (URL: https://wwz.ifremer.fr/); Centre National de la Recherche Scientifique (CNRS), 3 rue Michel-Ange, 75016 Paris, France (URL: http://www.cnrs.fr/); École Normale Supérieure, 45 rue d'Ulm, F-75230 Paris Cedex 05, France (URL: https://www.ens.psl.eu/); Université de Paris, 85 boulevard Saint-Germain, 75006 Paris, France (URL: https://u-paris.fr/en/498-2/); Roland Pease, Science Magazine (URL: https://science.sciencemag.org/, article at https://www.sciencemag.org/news/2019/05/ship-spies-largest-underwater-eruption-ever) published 21 May 2019.

Fernandina is a volcanic island in the Galapagos islands, around 1,000 km W from the coast of mainland Ecuador. It has produced nearly 30 recorded eruptions since 1800, with the most recent events having occurred along radial or circumferential fissures around the summit crater. The most recent previous eruption, starting on 16 June 2018, lasted two days and produced lava flows from a radial fissure on the northern flank. Monitoring and scientific reports come from the Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN).

A report from IG-EPN on 12 January 2020 stated that there had been an increase in seismicity and deformation occurring during the previous weeks. On the day of the report, 11 seismic events had occurred, with the largest magnitude of 4.7 at a depth of 5 km. Shortly before 1810 that day a circumferential fissure formed below the eastern rim of the La Cumbre crater, at about 1.3-1.4 km elevation, and produced lava flows down the flank (figure 39). A rapid-onset seismic swarm reached maximum intensity at 1650 on 12 January (figure 40); a second increase in seismicity indicating the start of the eruption began around 70 minutes later (1800). A hotspot was observed in NOAA / CIMSS data between 1800 and 1810, and a gas plume rising up to 2 km above the fissure dispersed W to NW. The eruption lasted 9 hours, until about 0300 on 13 January.

Figure 39. Lava flows erupting from a circumferential fissure on the eastern flank of Fernandina on 12 January 2020. Photos courtesy of Parque Nacional Galápagos.

Figure 40. Graph showing the Root-Mean-Square (RMS) amplitude of the seismic signals from the FER-1 station at Fernandina on 12-13 January 2020. The graph shows the increase in seismicity leading to the eruption on the 12th (left star), a decrease in the seismicity, and then another increase during the event (right star). Courtesy of S. Hernandez, IG-EPN (Report on 13 January 2020).

A report issued at 1159 local time on 13 January 2020 described a rapid decrease in seismicity, gas emissions, and thermal anomalies, indicating a rapid decline in eruptive activity similar to previous events in 2017 and 2018. An overflight that day confirmed that the eruption had ended, after lava flows had extended around 500 m from the crater and covered an area of 3.8 km² (figures 41 and 42). Seismicity continued on the 14th, with small volcano-tectonic (VT) earthquakes occurring less than 500 m below the surface. Periodic seismicity was recorded through 13-15 January, though there was an increase in seismicity during 17-22 January with deformation also detected (figure 43). No volcanic activity followed, and no additional gas or thermal anomalies were detected.

Figure 41. The lava flow extents at Fernandina of the previous two eruptions (4-7 September 2017 and 16-21 June 2018) and the 12-13 January 2020 eruption as detected by FIRMS thermal anomalies. Thermal data courtesy of NASA; figure prepared by F. Vásconez, IG-EPN (Report on 13 January 2020).

Figure 42. This fissure vent that formed on the E flank of Fernandina on 12 January 2020 produced several lava flows. A weak gas plume was still rising when this photo was taken the next day, but the eruption had ceased. Courtesy of Parque Nacional Galápagos.

Figure 43. Soil displacement map for Fernandina during 10 and 16 January 2020, with the deformation generated by the 12 January eruption shown. Courtesy of IG-EPN (Report on 23 January 2020).

Geologic Background. Fernandina, the most active of Galápagos volcanoes and the one closest to the Galápagos mantle plume, is a basaltic shield volcano with a deep 5 x 6.5 km summit caldera. The volcano displays the classic "overturned soup bowl" profile of Galápagos shield volcanoes. Its caldera is elongated in a NW-SE direction and formed during several episodes of collapse. Circumferential fissures surround the caldera and were instrumental in growth of the volcano. Reporting has been poor in this uninhabited western end of the archipelago, and even a 1981 eruption was not witnessed at the time. In 1968 the caldera floor dropped 350 m following a major explosive eruption. Subsequent eruptions, mostly from vents located on or near the caldera boundary faults, have produced lava flows inside the caldera as well as those in 1995 that reached the coast from a SW-flank vent. Collapse of a nearly 1 km3 section of the east caldera wall during an eruption in 1988 produced a debris-avalanche deposit that covered much of the caldera floor and absorbed the caldera lake.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Dirección del Parque Nacional Galápagos (DPNG), Isla Santa Cruz, Galápagos, Ecuador (URL: http://www.galapagos.gob.ec/).

Masaya is a basaltic caldera located in Nicaragua and contains the Nindirí, San Pedro, San Juan, and Santiago craters. The currently active Santiago crater hosts a lava lake, which has remained active since December 2015 (BGVN 41:08). The primary source of information for this August 2019-January 2020 report comes from the Instituto Nicareguense de Estudios Territoriales (INETER) and satellite -based imagery and thermal data.

On 16 August, 13 September, and 11 November 2019, INETER took SO2 measurements by making a transect using a mobile DOAS spectrometer that sampled for gases downwind of the volcano. Average values during these months were 2,095 tons/day, 1,416 tons/day, and 1,037 tons/day, respectively. August had the highest SO2 measurements while those during September and November were more typical values.

Satellite imagery showed a constant thermal anomaly in the Santiago crater at the lava lake during August 2019 through January 2020 (figure 82). According to a news report, ash was expelled from Masaya on 15 October 2019, resulting in minor ashfall in Colonia 4 de Mayo (6 km NW). On 21 November thermal measurements were taken at the fumaroles and near the lava lake using a FLIR SC620 thermal camera (figure 83). The temperature measured 287°C, which was 53° cooler than the last time thermal temperatures were taken in May 2019.

Figure 82. Sentinel-2 thermal satellite imagery showed the consistent presence of an active lava lake within the Santiago crater at Masaya during August 2019 through January 2020. Images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 83. Thermal measurements taken at Masaya on 21 November 2019 with a FLIR SC620 thermal camera that recorded a temperature of 287°C. Courtesy of INETER (Boletin Sismos y Volcanes de Nicaragua, Noviembre, 2019).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent low-power thermal anomalies compared to the higher-power ones before May 2019 (figure 84). The thermal anomalies were detected during August 2019 through January 2020 after a brief hiatus from early may to mid-June.

Figure 84. Thermal anomalies occurred intermittently at Masaya during 21 February 2019 through January 2020. Courtesy of MIROVA.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); 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); La Jornada (URL: https://www.lajornadanet.com/, article at https://www.lajornadanet.com/index.php/2019/10/16/volcan-masaya-expulsa-cenizas/#.Xl6f8ahKjct).

Reventador is an andesitic stratovolcano located in the Cordillera Real, Ecuador. Historical eruptions date back to the 16th century, consisting of lava flows and explosive events. The current eruptive activity has been ongoing since 2008 with previous activity including daily explosions with ash emissions, and incandescent block avalanches (BGVN 44:08). This report covers volcanism from August 2019 through January 2020 using information primarily from the Instituto Geofísico (IG-EPN), the Washington Volcano Ash Advisory Center (VAAC), and various infrared satellite data.

During August 2019 to January 2020, IG-EPN reported almost daily explosive eruptions and ash plumes. September had the highest average of explosive eruptions while January 2020 had the lowest (table 11). Ash plumes rose between a maximum of 1.2 to 2.5 km above the crater during this reporting period with the highest plume height recorded in December. The largest amount of SO2 gases produced was during the month of October with 502 tons/day. Frequently at night during this reporting period, crater incandescence was observed and was occasionally accompanied by incandescent block avalanches traveling as far as 900 m downslope from the summit of the volcano.

Table 11. Monthly summary of eruptive events recorded at Reventador from August 2019 through January 2020. Data courtesy of IG-EPN (August to January 2020 daily reports).

During the month of August 2019, between 11 and 45 explosions were recorded every day, frequently accompanied by gas-and-steam and ash emissions (figure 119); plumes rose more than 1 km above the crater on nine days. On 20 August the ash plume rose to a maximum 1.6 km above the crater. Summit incandescence was seen at night beginning on 10 August, continuing frequently throughout the rest of the reporting period. Incandescent block avalanches were reported intermittently beginning that same night through 26 January 2020, ejecting material between 300 to 900 m below the summit and moving on all sides of the volcano.

Figure 119. An ash plume rising from the summit of Reventador on 1 August 2019. Courtesy of Radio La Voz del Santuario.

Throughout most of September 2019 gas-and-steam and ash emissions were observed almost daily, with plumes rising more than 1 km above the crater on 15 days, according to IG-EPN. On 30 September, the ash plume rose to a high of 1.7 km above the crater. Each day, between 18 and 72 explosions were reported, with the latter occurring on 19 September. At night, crater incandescence was commonly observed, sometimes accompanied by incandescent material rolling down every flank.

Elevated seismicity was reported during 8-15 October 2019 and almost daily gas-and-steam and ash emissions were present, ranging up to 1.3 km above the summit. Every day during this month, between 13 and 54 explosions were documented and crater incandescence was commonly observed at night. During November 2019, gas-and-steam and ash emissions rose greater than 1 km above the crater except for 10 days; no emissions were reported on 29 November. Daily explosions ranged up to 42, occasionally accompanied by crater incandescence and incandescent ejecta.

Washington VAAC notices were issued almost daily during December 2019, reporting ash plumes between 4.6 and 6 km altitude throughout the month and drifting in multiple directions. Each day produced 5-52 explosions, many of which were accompanied by incandescent blocks rolling down all sides of the volcano up to 900 m below the summit. IG-EPN reported on 11 December that a gas-and-steam and ash emission column rose to a maximum height of 2.5 km above the crater, drifting SW as was observed by satellite images and reported by the Washington VAAC.

Volcanism in January 2020 was relatively low compared to the other months of this reporting period. Explosions continued on a nearly daily basis early in the month, ranging from 20 to 51. During 5-7 January incandescent material ejected from the summit vent moved as block avalanches downslope and multiple gas-and-steam and ash plumes were produced (figures 120, 121, and 122). After 9 January the number of explosions decreased to 0-16 per day. Ash plumes rose between 4.6 and 5.8 km altitude, according to the Washington VAAC.

Figure 120. Night footage of activity on 5 (top) and 6 (bottom) January 2020 at the summit of Reventador, producing a dense, dark gray ash plume and ejecting incandescent material down multiple sides of the volcano. This activity is not uncommon during this reporting period. Courtesy of Martin Rietze, used with permission.

Figure 121. An explosion at Reventador on 7 January 2020, which produced a dense gray ash plume. Courtesy of Martin Rietze, used with permission.

Figure 122. Night footage of the evolution of an eruption on 7 January 2020 at the summit of Reventador, which produced an ash plume and ejected incandescent material down multiple sides of the volcano. Courtesy of Martin Rietze, used with permission.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed frequent and strong thermal anomalies within 5 km of the summit during 21 February 2019 through January 2020 (figure 123). In comparison, the MODVOLC algorithm reported 24 thermal alerts between August 2019 and January 2020 near the summit. Some thermal anomalies can be seen in Sentinel-2 thermal satellite imagery throughout this reporting period, even with the presence of meteorological clouds (figure 124). These thermal anomalies were accompanied by persistent gas-and-steam and ash plumes.

Figure 123. Thermal anomalies at Reventador persisted during 21 February 2019 through January 2020 as recorded by the MIROVA system (Log Radiative Power). Courtesy of MIROVA.

Figure 124. Sentinel-2 thermal satellite images of Reventador from August 2019 to January 2020 showing a thermal hotspot in the central summit crater summit. In the image on 7 January 2020, the thermal anomaly is accompanied by an ash plume. Courtesy of Sentinel Hub Playground.

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-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Radio La Voz del Santuario (URL: https://www.facebook.com/Radio-La-Voz-del-Santuario-126394484061111/, posted at: https://www.facebook.com/permalink.php?story_fbid=2630739100293291&id=126394484061111); Martin Rietze, Taubenstr. 1, D-82223 Eichenau, Germany (URL: https://mrietze.com/, https://www.youtube.com/channel/UC5LzAA_nyNWEUfpcUFOCpJw/videos).

Pacaya is a highly active basaltic volcano located in Guatemala with volcanism consisting of frequent lava flows and Strombolian explosions originating in the Mackenney crater. The previous report summarizes volcanism that included multiple lava flows, Strombolian activity, avalanches, and gas-and-steam emissions (BGVN 44:08), all of which continue through this reporting period of August 2019 to January 2020. The primary source of information comes from reports by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) in Guatemala and various satellite data.

Strombolian explosions occurred consistently throughout this reporting period. During the month of August 2019, explosions ejected material up to 30 m above the Mackenney crater. These explosions deposited material that contributed to the formation of a small cone on the NW flank of the Mackenney crater. White and occasionally blue gas-and-steam plumes rose up to 600 m above the crater drifting S and W. Multiple incandescent lava flows were observed traveling down the N and NW flanks, measuring up to 400 m long. Small to moderate avalanches were generated at the front of the lava flows, including incandescent blocks that measured up to 1 m in diameter. Occasionally incandescence was observed at night from the Mackenney crater.

In September 2019 seismicity was elevated compared to the previous month, registering a maximum of 8,000 RSAM (Realtime Seismic Amplitude Measurement) units. White and occasionally blue gas-and-steam plumes that rose up to 1 km above the crater drifted generally S as far as 3 km from the crater. Strombolian explosions continued, ejecting material up to 100 m above the crater rim. At night and during the early morning, crater incandescence was observed. Incandescent lava flows traveled as much as 600 m down the N and NW flanks toward the Cerro Chino crater (figure 116). On 21 September two lava flows descended the SW flank. Constant avalanches with incandescent blocks measuring 1 m in diameter occurred from the front of many of these lava flows.

Figure 116. Webcam image of Pacaya on 25 September 2019 showing thermal signatures and the point of emission on the NNW flank at night using Landsat 8 (Nocturnal) imagery (left) and a daytime image showing the location of these lava effusions (right) along with gas-and-steam emissions from the active crater. Courtesy of INSIVUMEH.

Weak explosions continued through October 2019, ejecting material up to 75 m above the crater and building a small cone within the crater. White and occasionally blue gas-and-steam plumes rose 400-800 m above the crater, drifting W and NW and extending up to 4 km from the crater during the week of 26 October-1 November. Lava flows measuring up to 250 m long, originating from the Mackenney crater were descending the N and NW flanks (figure 117). Avalanches carrying large blocks 1 m in diameter commonly occurred at the front of these lava flows.

Figure 117. Photo of lava flows traveling down the flanks of Pacaya taken between 28 September 2019 and 4 October. Courtesy of INSIVUMEH (28 September 2019 to 4 October Weekly Report).

Continuing Strombolian explosions in November 2019 ejected material 15-75 m above the crater, which then contributed to the formation of the new cone. White and occasionally blue gas-and-steam plumes rose 100-600 m above the crater drifting in different directions and extending up to 2 km. Multiple lava flows from the Mackenney crater moving down all sides of the volcano continued, measuring 50-700 m long. Avalanches were generated at the front of the lava flows, often moving blocks as large as 1 m in diameter. The number of lava flows decreased during 2-8 November and the following week of 9-15 November no lava flows were observed, according to INSIVUMEH. During the week of 16-22 November, a small collapse occurred in the Mackenney crater and explosive activity increased during 16, 18, and 20 November, reaching RSAM units of 4,500. At night and early morning in late November crater incandescence was visible. On 24 November two lava flows descended the NW flank toward the Cerro Chino crater, measuring 100 m long.

During December 2019, much of the activity remained the same, with Strombolian explosions originating from two emission points in the Mackenney crater ejecting material 75-100 m above the crater; white and occasionally blue gas-and-steam plumes to 100-300 m above the crater drifted up to 1.5 km downwind to the S and SW. Lava flows descended the S and SW flanks reaching 250-600 m long (figure 118). On 29 December seismicity increased, reaching 5,000 RSAM units.

Figure 118. Lava flows moving to the S and SW at Pacaya on 31 December 2019. Courtesy of INSIVUMEH (28 December 2019 to 3 January 2020 Weekly Report).

Consistent Strombolian activity continued into January 2020 ejecting material 25-100 m above the crater. These explosions deposited material inside the Mackenney crater, contributing to the formation of a small cone. White and occasionally blue fumaroles consisting of mostly water vapor were observed drifting in different directions. At night, summit incandescence and lava flows were visible descending the N, NW, and S flanks with the flow on the NW flank traveling toward the Cerro Chino crater.

During August 2019 through January 2020, multiple lava flows and bright thermal anomalies (yellow-orange) within the crater were seen in Sentinel-2 thermal satellite imagery (figures 119 and 120). In addition, constant strong thermal anomalies were detected by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system during 21 February 2019 through January 2020 within 5 km of the summit (figure 121). A slight decrease in energy was seen from May to June and August to September. Energy increased again between November and December. According to the MODVOLC algorithm, 37 thermal alerts were recorded during August 2019 through January 2020.

Figure 119. Sentinel-2 thermal satellite images of Pacaya showing thermal activity (bright yellow-orange) during August 2019 to November. All images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 120. Sentinel-2 thermal satellite images of Pacaya showing thermal activity (bright yellow-orange) during December 2019 through January 2020. All images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 121. The MIROVA thermal activity graph (log radiative power) at Pacaya during 21 February 2019 to January 2020 shows strong, frequent thermal anomalies through January with a slight decrease in energy between May 2019 to June 2019 and August 2019 to September 2019. Courtesy of MIROVA.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The 19-km-wide submerged Kikai caldera at the N end of Japan’s Ryukyu Islands was the source of one of the world's largest Holocene eruptions about 6,300 years ago, producing large pyroclastic flows and abundant ashfall. During the last century, however, only intermittent minor ash emissions have characterized activity at Satsuma Iwo Jima island, the larger subaerial fragment of the Kikai caldera; several events have included limited ashfall in communities on nearby islands. The most recent event was a single day of explosions on 4 June 2013 that produced ash plumes and minor ashfall on the flank. A minor episode of increased seismicity and fumarolic activity was reported in late March 2018, but no ash emissions were reported. A new single-day event on 2 November 2019 is described here with information provided by the Japan Meteorological Agency (JMA).

JMA reduced the Alert Level to 1 on 27 April 2018 after a brief increase in seismicity during March 2018 (BGVN 45:05); no significant changes in volcanic activity were observed for the rest of the year. Steam plumes rose from the summit crater to heights around 1,000 m; the highest plume rose 1,800 m. Occasional nighttime incandescence was recorded by high-sensitivity surveillance cameras. SO₂ measurements made during site visits in March, April, and May indicated amounts ranging from 300-1,500 tons per day, similar to values from 2017 (400-1,000 tons per day). Infrared imaging devices indicated thermal anomalies from fumarolic activity persisted on the N and W flanks during the three site visits. A field survey of the SW flank on 25 May 2018 confirmed that the crater edge had dropped several meters into the crater since a similar survey in April 2007. Scientists on a 19 December 2018 overflight had observed fumarolic activity.

There were no changes in activity through October 2019. Weak incandescence at night continued to be periodically recorded with the surveillance cameras (figure 9). A brief eruption on 2 November 2019 at 1735 local time produced a gray-white plume that rose slightly over 1,000 m above the Iodake crater rim (figure 10). As a result, JMA raised the Alert Level from 1 to 2. During an overflight the following day, a steam plume rose a few hundred meters above the summit, but no further activity was observed. No clear traces of volcanic ash or other ejecta were found around the summit (figure 11). Infrared imaging also showed no particular changes from previous measurements. Discolored seawater continued to be observed around the base of the island in several locations.

Figure 9. Incandescence at night on 25 October 2019 was observed at Satsuma Iwo Jima (Kikai) with the Iwanogami webcam. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, October 1st year of Reiwa [2019]).

Figure 10. The Iwanogami webcam captured a brief gray-white ash and steam emission rising above the Iodake crater rim on Satsuma Iwo Jima (Kikai) on 2 November 2019 at 1738 local time. The plume rose slightly over 1,000 m before dissipating. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, October 1st year of Reiwa [2019]).

Figure 11. During an overflight of Satsuma Iwo Jima (Kikai) on 3 November 2019 no traces of ash were seen from the previous day’s explosion; only steam plumes rose a few hundred meters above the summit, and discolored water was present in a few places around the shoreline. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, October 1st year of Reiwa [2019]).

For the remainder of November 2019, steam plumes rose up to 1,300 m above the summit, and nighttime incandescence was occasionally observed in the webcam. Seismic activity remained low and there were no additional changes noted through January 2020.

Geologic Background. Kikai is a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. It was the source of one of the world's largest Holocene eruptions about 6,300 years ago when rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake lava dome and Inamuradake scoria cone, as well as submarine lava domes. Historical eruptions have occurred at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km E of Tokara-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Tokara-Iojima.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html).

This is our first Bulletin report on Bardarbunga, a subglacial caldera found within the Barbarbunga volcanic system. This report is divided into two major sections, the first discussing activity between 1986 and 2008 and the second looking at more recent activity from 2014-early 2015.

As background, Bardarbunga, the second highest volcano of Iceland, is one of approximately 30 known Holocene volcanoes or volcano systems in the country. It lies beneath the NW part of the Vatnajokull ice cap. Carrivick and Gertisser (2014) described the volcano as a caldera 700 m deep with a diameter of 11 km, covered by glacial ice ~850 m thick.

1986-2008 activity. In 2010, the Icelandic Meteorological Office (IMO) presented a list of Icelandic volcanic eruptions from 1902-2010 on their website. That list lacks any eruption at the Bardarbunga caldera. Seibert and others (2010) stated that between 1986 and 2008, there were several uncertain cases of eruptions or unrest in the area of Loki-Fögrufjöll (S-SW of Bardarbunga caldera), which they consider a part of the larger Bardarbunga volcanic system (green in figure 1). The eruptive characteristics of these events included regional fissure and subglacial events associated with jökulhlaups (glacier bursts).

Figure 1. Map of Iceland that highlights the Bardarbunga volcanic system (shaded in green), which is 190 km long (NE-SW) and up to 25 km wide (NW-SE). The main Bardarbunga volcano, a subglacial caldera, is represented by the letter 'B' on the map. This map, showing all of Iceland was part of a more detailed map of the Bardarbunga volcanic system. Iceland's capital, Reykjavik, and other towns are also highlighted on the map. Taken from Larsen and others (2014).

The associated jökulhlaups from 1986-2008 originated from the East and West Loki cauldrons found along the Loki Ridge of the Loki-Fögrufjöll system (figure 2). The cauldrons are located ~15 km SW of the center of the Bardarbunga caldera. Other terms for the Loki cauldrons include the East and West Skaftárketill cauldrons; the Eastern and Western Skaftá cauldrons; and the Eastern and Western cauldrons.

Figure 2. Two maps showing the location of East and West Loki cauldrons on the Vatnajokull glacier surface. The Loki cauldrons are found along the Loki Ridge of the Loki-Fögrufjöll system, located SW of Bardarbunga volcano and are within the larger Bardarbunga volcanic system. (Top) The Loki cauldrons are labeled as the Eastern and Western Skaftá cauldrons. (Bottom) The cauldrons are labelled the Eastern and Western cauldrons and the Skatfá river is highlighted. Both maps highlight the inferred subglacial water route (black and green lines) of melt water that is eventually discharged during a jökulhlaup. The jökulhlaups that originate from the Loki cauldrons empty into the Skatfá river. Top map after being taken from Marteinsson and others (2013) was slightly edited and the bottom map was taken from Einarsson (2009).

The Loki cauldrons are depressions formed in the Vatnajokull glacier surface by two underlying, subglacial geothermal areas (Einarsson, 2009). The geothermal areas melt the glacier's base and melt water collects forming subglacial lakes. As the lakes grow, the ice above them flattens. Eventually, the melt water escapes from the subglacial lakes in a jökulhlaup. The water of the jökulhlaup then travels ~40 km subglacially to flood the Skatfá river (Einarsson, 2009). Once the subglacial lake has emptied, the overlying ice collapses and the cauldrons can be seen again in the glacier surface (Einarsson, 2009).

Table 1 presents the dates of uncertain cases of eruption within the Bardarbunga volcanic system. The source of the jökulhlaups associated with these uncertain eruptions consistently originated from the East or West Loki cauldron or both.

Table 1. Table condensing Bardarbunga's uncertain cases of eruptive history during 1986-2008. The uncertain cases all reside in the area of Loki-Fögrufjöll. The table also show the source of the jökulhlaup associated with each of the cases. None of these uncertain cases occurred at the Bardarbunga caldera. Data in this table summarizes written communication with Páll Einarsson in 2008.

Two examples of uncertain eruptions at the East Loki cauldron follow. They occurred in November 1986 and August 1991. For the 1986 case, Björnsson and Einarsson (1990) stated, "There is a seismic indication that a small eruption occurred in 1986 during a Skaftá jökulhlaup from beneath the easternmost ice cauldron [figure 2]. The flood in Skaftá began on November 29, and on November 30 and the following day short bursts of continuous tremor were recorded on seismographs around Vatnajokull. . ..It is likely that the pressure release associated with the jökulhlaup triggered a short eruption that did not reach the surface of the glacier."

For the 1991 case, Björnsson and Einarsson (1990) reported that "Bursts of tremor were recorded on seismographs near Vatnajokull on Aug. 12, 1991, during a jökulhlaup in Skaftá. The course of events is similar to that of Nov. 30, 1986, and suggests that a small and short-lived eruption may have occurred beneath the Eastern Loki cauldron."

Based on the communication between Einarsson and GVP, the other cases in table 1 followed a similar pattern. For each of those events, the occurrence of a jökulhlaup was followed by either an eruption tremor or bursts of eruption tremor, which suggested the possibility of a small, subglacial eruption at East or West Loki.

Confirmed 1996 eruptions. There are two confirmed eruptions at Bardarbunga, both within a few weeks of each other in 1996 (1 and 2 below).

(1) Einarsson and others (1997) discuss the complex interplay of events that occurred during 29 September through 7 November 1996, which involved seismicity, dikes, jökulhlaups, and various eruptions at Bardarbunga, Grímsvötn and Gjálp (fissure between the two calderas). Einarsson and others (1997) start with this introduction: "A volcanic eruption beneath the Vatnajokull ice cap in central Iceland . . . began on September 30, 1996, along a 7-km-long fissure between the volcanoes Bardarbunga and Grímsvötn. The eruption continued for 13 days . . .."

They further note ". . . a minor subglacial eruption occurred on the southeast rim of the Bardarbunga caldera, 6-7 km to the north. Two small depressions formed in the ice surface there." Regarding this, Páll Einarsson added this comment in a 2015 email: "The small subglacial eruptions at the Bárðarbunga caldera rim, mentioned in our paper, are a separate event [from the one a few weeks later mentioned in (2) below]. They are evidenced by sinkholes in the glacier that were discovered late and the timing of these events is not known. Most likely the sinkholes were initiated during the Gjálp eruption, i.e. between September 30 and October 13."

(2) According to the Institute of Earth Sciences of the University of Iceland (IES, posting date uncertain), a small eruption took place at Bardarbunga in 1996. They wrote the following: "A small eruption started in Bardarbunga around 1300 hrs on November 6th. The eruption lasted for about 20 to 30 min. According to seismograms at the Meteorological office, the eruption was initiated by some intrusive activity. The intrusive activity is based on recorded eruption tremor picked up [by] the seismometers. Eruption column reached about 4 km in to the air. Relation between pressure decrease due to the flooding [has] been suggested as the main cause of the eruption." This eruption came a day after a jökulhlaup was released from the Grímsvötn caldera (BGVN 21:09 and 23:11, and IES (posting date uncertain). We have not found a clear description of where in the caldera the eruption took place on 6 November 1996.

In regards to the confirmed eruption of 6 November, Einarsson's email made these remarks: "Keep in mind that Bárðarbunga is very remote and observations of the activity are difficult and very dependent on weather conditions. The webpage of our institute describes a small explosive event that happened on Nov. 6 at the end of the large jökulhlaup, when the meltwater from the large Gjálp eruption was flushed down to the coast. Most of us think now that this was a phreatic reaction of the still hot edifice to the sudden pressure release when the caldera lake of Grímsvötn was emptied, i.e. not due to a fresh injection of magma. But observations were scarce and there may be other opinions on this."

2014-early 2015 activity. This section of the Bulletin report primarily summarizes events from 16 August 2014, when seismic activity began, into mid-January 2015. The eruption was still ongoing at that time.

Bardarbunga is monitored by a seismic network, an extensive GPS network, and various sensors such as webcams and infrared cameras. Monitoring and analyses at Bardarbunga is conducted by a group of collaborators that include the IMO, the Institute of Earth Sciences (IES) at the University of Iceland, and the National Commissioner of Police, and the Department of Civil Protection and Emergency Management.

Gudmundsson and others (2014) and IMO describe dike emplacement (without apparent breaching the ground surface) associated with a seismic swarm that began at the caldera and migrated tens of kilometers with branches to the N and NE during 16-31 August 2014. On 29 August 2014, two days before the swarm ended, an eruption was first documented at the surface at a flank vent devoid of ice cover ~45 km NE of the caldera.

Figures 3 and 4 help explain the location of volcanoes in Iceland and Bardarbunga lava that progressed northward as a dike and ultimately erupted in the Holuhraun vent.

Figure 3. IMO map of Iceland showing key Holocene volcano locations. Bardarbunga (yellow triangle) is located on the NW part of the 14,000 km2 Vatnajokull ice cap (continental glacier). Although seismicity and dike injection began at Bardarbunga, intrusive processes seemingly prevailed until dikes had propagated to Holuhraun (tip of arrow designated with "H", location approximate). Holuhraun sits ~45 km NE of the caldera. Courtesy of Iceland Met Office.

Figure 4. A map reflecting Bardarbunga's lava that erupted in the Holuhraun vent area between 29 August 2014 and about 15 January 2015 (shaded lens-shaped zone between the glacier and Askja volcano). The map shows the N margin of the Vatnajokull ice cap but Bardarbunga caldera lies 17 km off the map to lower left. The site of the eruptive fissure is in the vicinity of the orange bull's eye. Dyngjujokull glacier is an outlet glacier that forms a N-trending lobe streaming N and outward from the much larger Vatnajokull glacier. Note the E end of the new flow field following the drainage system (the Jökulsá á Fjöllum river) Image published online by the Icelandic Met Office (IMO) on 15 January 2015 (based, in part, on a NASA Landsat 8 image).

The NE-trending dike reached an area outboard of the Vatnajokull ice cap at the Holuhraun volcanic field (figure 4), where the first clear eruption began on 29 August 2014. The fissure vent area was 4.5 km from the ice margin of the outlet glacier Dyngjujökull. The venting took place along an old fissure, and came out along an N-trending zone 600 m long. According to Gudmundsson and others (2014), that eruption was moderate and effusive.

Holuhraun is sometimes discussed in the context of Askja volcano (figure 4), which lies just to the N. Holuhraun is sometimes considered as peripheral vent system for Askja (Ialongo and others, 2015).

Figure 5 indicates the location of earthquakes during the first 16 days of dike emplacement (where days 1-16 correspond to 16-31 August 2014). Gudmundsson and others (2014) comment that "During this time, the dike generated some 17,000 earthquakes, more than produced in Iceland as a whole over a normal year." The venting to the surface at Holuhraun took place on 29 August 2014 and became strong by 31 August. In the early hours of the 29 August, the onset consisted of a minor, four-hour long, fissure eruption. The pattern on figure 5, depicting a 45-km-long dike injection along the rift system passing through Bardarbunga, testifies to the importance and utility of the seismograph in monitoring shallow magmatism leading to eruption.

Figure 5. For the Bardarbunga eruption, earthquake locations during the first 16 days of the dike emplacement (16-31 August 2014). The word 'Dike' is located approximately where the fissure eruptions have taken place (at a volcanic field called Holuhraun). The white area is the Vatnajokull ice cap (including the associated Dyngjujokull outlet glacier; figure 4). Earthquake magnitudes are indicated in the lower right portion of the map. Taken from Gudmundsson and others (2014), based on preliminary data from IMO.

According to IMO, seismic activity associated with Bardarbunga had gradually increased during the last seven years, although it temporarily diminished during the Grimsvotn eruption in May 2011. Vatnajokull GPS stations showed both upward and outward movements since early June 2014, and on 16 August 2014, the number of earthquakes significantly increased, with more than 300 earthquakes detected under the NW part of Vatnajokull ice cap (figure 5). As a result, the Aviation Color Code was increased to Yellow, the third level from the highest on a five color scale (Gray, Green, Yellow, Orange, and Red). On 18 August, IMO reported one earthquake swarm to the E and another swarm to the N of Bardarbunga. An M 4 earthquake occurred, the strongest in the region since 1996. By 18 August, 2,600 earthquakes had been detected at the volcano; earthquake locations from the E and N swarms had been migrating NE. In the evening of 18 August, earthquakes diminished in the N swarm. That same day the Aviation Color Code was raised to Orange.

According to IMO, GPS and seismic data during 20-26 August suggested that a NE-trending intrusive dike had increased from 25 to 40 km in length. During 22-26 August, several earthquakes in the 4.7-5.7 magnitude range had been detected at or near the volcano. These values were among the largest detected in the first few weeks of the swarm (Gudmundsson and others, 2014). The Aviation Color Code, chiefly Orange during this reporting interval, rose to the highest level, Red, several times during late August and September.

On 23 August seismic tremor indicated what IMO initially suggested was a small lava eruption at beneath the Dyngjujokull glacier (which is 150-400 m thick in this region). An overflight the next day found no evidence for an eruption.

On 27 August an overflight showed a 4- to 6-km-long row of cauldrons 10-15 m in diameter S of Bardarbunga.

Beginning on 31 August, lava erupted along a 1.5 km long fissure. During 1-2 September a white steam-and-gas plume rose to an altitude of 4.5 km and drifted 60 km NNE and ENE. Lava flowed N and lava fountains rose tens of meters. The number of earthquakes decreased from 500 earthquakes on 1 September to 300 earthquakes on 2 September. During the middle of September, seismicity persisted mainly around the caldera and the Dyngjujokull glacier.

On 2 September the lava had covered 4.2 km2 and was 4.5 km from the glacier's edge. By 3 September, the lava flow advanced ENE and covered 7.2 km2. The following day, the lava flow had an aerial extent of 10.8 km2. During 3-9 September, IMO observers noted ongoing lava effusion, high gas emissions, and elevated seismicity from the Holuhraun lava field. Ash production was almost negligible.

On 5 September, two new eruptive fissures were observed S of the main eruption site. These sites were less effusive and were located ~2 km from the edge of Dyngjujokull glacier (see this small shaded area in figure 2). The eruption also continued from the original fissure and generated a ~460 m high steam plume. Eventually, a row of craters formed along the eruptive fissure, the largest one was named Baugur crater.

The fissure eruption continued during 6-7 September, and the lava effusion rate was 100-200 m3/sec on 7 September (figures 6 and 7). Activity from the S fissures was less than that of the N fissure, which had been active since the beginning of the eruption. The advancing lava flow reached the W main branch of the Jökulsá á Fjöllum river (figure 4), which is fed by the icecap and exits the icecap ENE of the volcano. No explosive activity due to lava and river water interaction was observed, but steam rose from the area.

Figure 6. Lava fountaining, lava flows, and plumes emerging from Holuhraun on 6 September 2014, as viewed by NASA's Landsat 8. Much of the flow was in lava rivers on the surface during September. Courtesy of NASA Earth Observatory.

Figure 7. Aerial view Bardarbunga fissure eruptions taken on 4 September 2014. The fissure venting these eruptions is in Holuhraun lava field. Courtesy of Peter Hartree (peter@reykjavikcoworking.is).

During 8-9 September, activity was no longer detected from the southernmost fissure. Lava continued to advance and interact with the Jökulsá á Fjöllum river. The extent of the lava flow reached 19 km2 and gas emissions remained high.

During 10-16 September, lava flows continued to advance at a consistent rate toward the E and W. A report on 22 September noted that the total volume of the erupted lava was 0.4-0.6 km3 and the flow rate was 250-350 m3/sec. By 30 September, the lava field was 46 km2, and the main flow had entered the river bed of Jökulsá á Fjöllum and continued to follow the river's course. Steam rose from the river where the lava was in contact with water but no explosive activity occurred.

Although reporting noted a lack of tall mobile ash plumes blown towards Europe and causing air traffic delays, the plumes remained lower and more local causing widespread air quality problems in Iceland. IMO reported continued gas emissions that included elevated SO2 emissions during 10-16 September and issued warnings to the public in the municipality of Fjarðarbyggð (180 km ENE of Bardarbunga) on 13 September. These emissions persisted through at least November.

During 17-23 September, chemical analysis and geophysical modeling indicated that the source of the magma was at a depth of more than 10 km. On 21 September, field scientists estimated that about 90% of the SO2 from the eruption originated at the active craters and the rest rose from the lava field. Dead birds were also found around the eruption site.

Seismic activity at the N part of the dike and around the vents declined in October 2014, although the lava field continued to grow and lava production continued at the same output. On 5 October, a new lava front emerged at the S edge of the main lava flow and advanced E.

On 18 October, an M 5.4 earthquake struck in the N part of Bardarbunga caldera, one of the biggest earthquakes since the start of the eruption. The growing lava field at Holuhraun was 66 km2 by 31 October. By late October, the fissure's main vent (Baugur crater) had constructed a local topographic high that stood 80 m higher than the local landscape.

In November, eruption-associated seismicity remained strong although an IMO report on the 19th suggested that the number of large, M~5 events seemed to be decreasing. FLIR thermal images of the craters on 18 November showed that by then the most intense area of thermal convection was at a crater in the N part of the eruption site. On 20 November, observers characterized the eruption in the crater as pulsating explosions every 10-15 minutes, followed by a gush of lava down the main channel with splashing on either side. During 25-26 November, the activity was characterized as pulsating, with lava surging from the vent for 2-3 minutes at intervals of about 5-10 minutes. The upper parts of the lava channel developed a sinuous appearance owing to a series of bulges in the channel's margins.

On 12 November, IMO indicated that it monitored gas releases from Holuhraun using DOAS and FTIR instruments to estimate the fluxes of SO2 and other gases in the volcanic cloud. In the first month and a half of the eruption, the average flux was 400 kg/s (~35,000 metric tons per day, t/d) with peaks up to 1300 kg/s (~112,000 t/d). The IMO calculated that, assuming a constant release of gas through 12 November, the eruption had injected into the atmosphere an amount of SO2 in the range 3.5–11.2 Mega tons, Mt (depending on whether the computed from the average or the peak flux).

On 27 November, observers indicated that a plume rose 3.1 km above the sandy plain. A thermal image from 1 December showed several changes to the lava field. In just over 24 hours there was a new lava extrusion at the NE margin that had traveled 450 m. A new flow traveled N in an area just W of the lava lake. One or more new flows also developed S of the lava lake. The lava field from this eruption was just over 75 km2.

In early December, data also showed a decline in the eruption's intensity, although seismic activity remained strong. By 9 December, the lava field at Holuhraun had covered just over 76 km2, making its aerial extent the second largest in Iceland (but still considerably smaller than the largest historical field created by the Laki fissure eruption of 1783-1784). By 18 January 2015, the lava covered an area of 85 km2. A NASA photo of the lava flow is shown in figure 8. The vent area contained a lava lake, a large mass of highly radiant (molten, red-colored) lava.

Figure 8. NASA image of the Bardarbunga eruption venting at Holuhraun on 3 January 2015, as captured by the Operational Land Imager on Landsat 8. According to the NASA caption, the false-color images combine shortwave infrared, near infrared, and red light. The dark area represents newly-formed basalt associated with the 2014-2015 eruption. The plume of steam and sulfur dioxide appears white, while fresh lava is bright orange. Courtesy of NASA Earth Observatory.

According to the IMO, the ongoing eruption's very gas-rich emissions had affected the entire country. IMO stated that "we have to go 150 years back to find an event (Trölladyngja) that had a comparable impact on Iceland and its inhabitants, in terms of environmental and health issues."

Radar measurements of the flow field during a surveillance flight on 30 December 2014 provided preliminary evidence that lava thickness averaged ~10 m in the eastern part, ~12 m in the center, and at least 14 m in the western part. IMO indicated that the preliminary estimate of the lava volume was 1.1 km3. (A later estimate in 2015 took the volume to 1.4 km3, roughly 10% of the Laki fissure eruption.)

IMO reported that during 31 December-6 January fresh lava flowed N and also to the E where in part it transited through a closed channel (shallow lava tube). During 7-20 January 2015, IMO noted that the lava field expanded along its N and NE margins. Seismicity remained strong and local air pollution from gas emissions persisted. IMO said that on the days10 and 15 January the lava field covered 84.1 and 84.3 km2, respectively.

Figure 9 shows the eruption on 21 January 2015.

Figure 9. Photo taking on 21 January 2015 showing the Bardarbunga' eruption site at Holuhraun, including fissure vent, crater, lava flow, and plumes. The margins of the flow field are distinct in the distance, owing to snow cover. The main body of the flow field lies off the photo's margin to the right. Courtesy of IMO (Morten S. Riishuus).

Subsidence. The caldera had been subsiding during the reporting period. The subsidence at Bardarbunga caldera was visible on the ice surface and was interpreted as reflecting deformation of the caldera itself. The depression developed in a roughly bowl-shape area that, as of 20 January 2015, was about 80 km2 in area with a volume exceeding 1.5 km3.

Figure 10 shows the chronology of subsidence levels between 5 September 2014 and 30 December 2014. The subsidence in the center of the caldera was about 60 m by 20 January 2015, a value determined by comparing the ice surface elevation with that elevation at the same location before the beginning of the collapse. Gudmundsson states that the assumption is that the ice surface lies more or less passively on top of the bedrock in the caldera. As of 20 January, no evidence of major ice melting had been observed; however, increased geothermal activity on the caldera rims has resulted in ice depressions over the hot spots. Other ice depressions on the Dyngjujokull glacier were also observed, suggesting that small, short sub-glacial eruptions may have occurred there. According to Gunnar Gudmundsson, there was no evidence of a subglacial eruption within the caldera.

Figure 10. Topographic profiles plotted along a line across Bardarbunga's caldera for 5 September-30 December 2014. The N-trending profile crosses the E-central caldera (see inset on middle panel). The ice surface (top of light blue area) was constrained by lidar in 2011. The y-axis terms hys (m) and metrar refer to elevation and subsidence (both in meters). Subsidence (colored lines) was measured by a GPS station on the glacier surface in the caldera's center and by radar altimetry from aircraft. The bottom profile shows the overall picture with the caldera's surface and the 30 December 2014 profile (maximum subsidence). Courtesy of the Institute of Earth Sciences, University of Iceland (Magnus Gudmundsson and Thordis Hognadottir).

During early December, IMO reported that the Scientific Advisory Board of the Icelandic Civil Protection had reviewed data from the beginning of the eruption to 3 December. They acknowledged that the subsidence rate had decreased during that time, dropping from highs of up to 80 cm/day down to 25 cm/day, with most of the subsidence concentrated at the caldera center.

References. Björnsson, H. and Einarsson, P., 1990, Volcanoes beneath Vatnajokull, Iceland: Evidence from radio echo-sounding, earthquakes and j kulhlaups, Jökull, no. 40, pp 147-168 (URL: http://jardvis.hi.is/sites/jardvis.hi.is/files/Pdf_skjol/Bardarbunga_greinar/bjornsson_and_einarsson_1990.pdf )

Carrivick, J and Gertisser, R, 2014, Bardabunga: eruption develops in Iceland, Geology Today, v. 30, Issue 6, pp. 205-206, November/December 2014, John Wiley & Sons Ltd.

Einarsson, P., B. Brandsdóttir, M. T. Gudmundsson, H. Björnsson, K. Grínvold, and F. Sigmundsson, 1997, Center of the Iceland hotspot experiences volcanic unrest, Eos Trans. AGU, 78(35),369–375, doi:10.1029/97EO00237.

Einarsson, B., 2009, Jökulhlaups in Skaftá: A study of a jökulhlaup from the Western Skaftá cauldron in the Vatnajokull ice cap, Iceland, Thesis for Master of Science in Geophysics degree, School of Engineering and Natural Sciences, Faculty of Sciences, University of Iceland, (URL: https://notendur.hi.is//~mtg/nemritg/BE-MS_2009.pdf)

Gudmundsson, A, Lecoeur, N, Mohajeri, N, and Thordarson, T, 2014, Dike emplacement at Bardarbunga, Iceland, induces unusual stress changes, caldera deformation, and earthquakes. Bulletin of Volcanology, vol. 76, no. 10, pp. 1-7.

Hartley, M. E., and Thordarson, T., 2013, The 1874–1876 volcano-tectonic episode at Askja, North Iceland: Lateral flow revisited. Geochemistry, Geophysics, Geosystems, vol. 14, no. 7, pp. 2286-2309.

Ialongo, I., Hakkarainen, J., Kivi, R., Anttila, P., Krotkov, N. A., Yang, K., & Tamminen, J., 2015, Validation of satellite SO2 observations in northern Finland during the Icelandic Holuhraun fissure eruption. Atmospheric Measurement Techniques Discussions, vol. 8, no. 1, pp. 599-621.

IES, uncertain publication date, The Gjálp eruption in Vatnajokull 30/9 - 13/10 1996, Institute of Earth Sciences (IES), University of Iceland, Accessed on 31 March 2015 (URL: http://earthice.hi.is/gjalp_eruption_vatnajokull_309_1310_1996) .

Larsen, G. and Gudmundsson, M. T., 2014, Volcanic system: Bárðarbunga system, pre-publication extract from the Catalogue of Icelandic Volcanoes, Accessed on 4 April 2015, (URL: http://blog.snaefell.de/images/Bardarbunga_kafli20140825.pdf).

Icelandic Meteorological Office, 2010, List of recent volcanic eruptions in Iceland, Accessed on 31 March 2015 (URL: http://en.vedur.is/earthquakes-and-volcanism/articles/nr/1874).

Marteinsson, V.T., Rúnarsson, Á., Stefánsson, A., Thorsteinsson, T., Jóhannesson, T., Magnússon, S.H., Reynisson, E., Einarsson, B., Wade, N., Morrison, H., and Gaidos, E., 2013, Microbial communities in the subglacial waters of the Vatnajokull ice cap, Iceland, The ISME Journal, vol. 7, pp. 427–437, doi:10.1038/ismej.2012.97, (URL: http://www.nature.com/ismej/journal/v7/n2/full/ismej201297a.html ).

Seibert, L., Simkin, T., and Kimberly, P., 2010, Volcanoes of the World (Third Edition), pp. 204-205, University of Cailfornia Press, ISBN 978-0-520-26877-7.

Geologic Background. The large central volcano of Bárðarbunga lies beneath the NW part of the Vatnajökull icecap, NW of Grímsvötn volcano, and contains a subglacial 700-m-deep caldera. Related fissure systems include the Veidivötn and Trollagigar fissures, which extend about 100 km SW to near Torfajökull volcano and 50 km NE to near Askja volcano, respectively. Voluminous fissure eruptions, including one at Thjorsarhraun, which produced the largest known Holocene lava flow on Earth with a volume of more than 21 km3, have occurred throughout the Holocene into historical time from the Veidivötn fissure system. The last major eruption of Veidivötn, in 1477, also produced a large tephra deposit. The subglacial Loki-Fögrufjöll volcanic system to the SW is also part of the Bárðarbunga volcanic system and contains two subglacial ridges extending from the largely subglacial Hamarinn central volcano; the Loki ridge trends to the NE and the Fögrufjöll ridge to the SW. Jökulhlaups (glacier-outburst floods) from eruptions at Bárðarbunga potentially affect drainages in all directions.

Information Contacts: Icelandic Met Office (IMO) (URL: http://en.vedur.is/); London Volcanic Ash Advisory Centre (URL: http://www.metoffice.gov.uk/aviation/vaac/); Institute of Earth Sciences (IES), University of Iceland (URL: http://earthice.hi.is); Pall Einarsson, IES, University of Iceland; Gunnar Gudmundsson, IMO; Magnus Tumi Gudmundsson, IES, University of Iceland (URL: http://earthice.hi.is); National Commissioner of Police, Department of Civil Protection and Emergency Management (URL: http://avd.is/en/):NASA Earth Observatory (URL: http://earthobservatory.nasa.gov).

During mid-2013 to early 2015, Klyuchevskoy had two strong eruptive pulses with an intervening lull. The first pulse occurred 15 August-20 December 2013 (~3 months of eruption). Ash plumes and related eruptive activity halted during 2014 until about January 2015 (12 months pause). The second pulse occurred very late December 2014 or very early January 2015 through at least 24 March 2015 (~3 months of eruption).

We start by discussing the latter portion of the first pulse, covering the interval 15 November to 20 December 2013. That time period was missing from our earlier reporting, which ended with our last report (BGVN 38:07) summarizing eruptions during October 2012 through 14 November 2013.

In a later subsection labeled "2015," we discuss the second of the two eruptive pulses. The Global Volcanism Program requires an eruptive repose of three or more months before an eruption is considered to be over; thus, at the time of this writing (6 April 2015), it is too early to tell whether 24 March will hold true as the end date for the later pulse.

We base this report on the reporting interval from the Kamchatkan Volcanic Eruption Response Team (KVERT). Table 15 in BGVN 38:07 delineates the Aviation Color Code (a four-step code from a low of Green, advancing from Yellow to Orange, and ultimately to a high of Red). Klyuchevskoy is also spelled alternatively Kliuchevskoi, Klyuchevskaya Sopka, and Klyuchevskaya.

Late 2013 activity (and lull during 2014). KVERT documented that eruptions were common during 15 August 2013-20 December 2013 (continuing for about 5 weeks beyond our last Bulletin report).

Figure 16 shows a photo taken on 16 November 2014 (UTC) by an astronaut aboard the International Space Station. This low angle image highlights some interesting plume dynamics–whereby the dark material at left branches off from a lighter colored plume trending farther to the right (heading ESE)). A NASA Earth Observatory article (posted in 2 December 2013) commented: "The plume—likely a combination of steam, volcanic gases, and ash—stretched to the [ESE] due to prevailing winds. The dark region to the [NNW] is likely a product of shadows and of ash settling out. Several other volcanoes are visible in the image, including Ushkovsky, Tolbachik, Zimina, and Udina. To the [SSW] of Klyuchevskoy lies Bezymianny Volcano, which appears to be emitting a small steam plume (at image center)."

Figure 16. A NE-looking photo taken from space at an oblique angle accentuating topography and showing the Klyuchevskoy eruption of 16 November 2013 (UTC). The image was taken when the ISS was located over a spot on Earth more than 1,500 km to the SW. The scene also labels additional volcanoes in the region (see text). Note N arrow at bottom left. This image and associated labels and interpretation came from the NASA Earth Observatory website (Photo identifier: ISS038-E-5515). Photo credits: Expedition 38 crew; with additional credit to the ISS National Lab and to original captioning information by William L. Stefanov, Jacobs Technology/ESCG, NASA Johnson Space Center, Houston, Texas.

During the reporting interval, KVERT issued multiple reports of a type called a VONA (Volcano Observatory Notices for Aviation), and they provide a record of eruptive activity at Klyuchevskoy. A VONA issued at 0242 on 17 November 2013 indicated that web camera assessments revealed strombolian eruptions with strong gas and steam; an ash plume rose to 7 km altitude and blew 160 km E. The four-step Aviation Color Code (low to high, Green, Yellow, Orange, and Red) rose to Orange. The VONA issued the next day at 0246 on the 18th (UTC) indicated significant decrease in eruptive activity, including a lack of ash plume during the last several hours, but with cautions that aerosols with ash were still possible at low altitudes.

Two VONAs were issued on 19 November 2013; the first at 0248 (UTC) raised the Aviation Color Code from Yellow to Red. This VONA noted that based on seismic data strong ash explosions had resumed at 0216 UTC on the 19th. Visual data showed ash plumes up to 10-12 km altitude extending unstated distances SE.

The VONA for 2341 on the 19th reported a lowered Color Code, to Orange, in response to lowered ash plumes (at 5-5.5 km altitude) during the previous several hours. The plumes blew unstated distances N and NE.

2014. The VONAs for December 2013 and into early January 2014 mentioned some still robust plumes, but the eruption ended on 20 December. A 3 December 2013 VONA indicated that an explosive eruption had seemingly stopped on 19 November, but this was ruled out by a 6 December VONA that again raised the Color Code to Red associated with strong ash plumes up to 5.5-6.0 km altitude and extending over 212 km NE of the volcano.

More information about the 3 December 2013 eruption came out in the 12 December WIR (emphasis added and plume length converted to kilometers): "Seismicity of the volcano increased on December 06, and began to decrease on December 10. Video data showed ash plumes rose up to [5-6 km altitude] on December 06-10. Satellite data showed a very weak thermal anomaly over the volcano summit; ash plumes extended about [1020 km in] the different directions [from] the volcano: to the [E] on December 06-08, to the [NW] on December 09-10, and to the [E and SE] on December 10-11 [2013]." This 1020 km long ash plume was among the longest documented during the reporting interval.

On 7 December a VONA announced the Color Code had dropped to Orange although explosive eruption continued. Video and satellite data revealed a 5.5-km-altitude, NE-directed plume of unstated length. Also, volcanic tremor remained at the previous level (0.7-1.0 mcm/s) and shallow volcanic earthquakes registered.

VONAs issued on 26 December 2013 and 2 January 2014 stated the eruption had ended. The later report noted the eruption end date of 20 December 2014.

No further VONAs were issued for Klyuchevskoy during the remainder of 2014.

2015. Late in 2014, KVERT reported that both the abundance and the magnitude of shallow volcanic earthquakes began to increase during 19-20 December 2014 and again on 31 December 2014; tremor became constant. The volcano was cloaked in clouds during 31 December 2014 to 1 January 2015, but KVERT judged that a strombolian eruption probably began on 1 January 2015, which is consistent with a satellite thermal anomaly. On 2 January 2015, the Aviation Color Code rose from Green (normal) to Yellow (which is a sign of elevated unrest). During the course of January 2015 the volcano resumed frequent eruptive activity and that month KVERT issued ~15 VONAs for Klyuchevskoy. The eruption stopped on 24 March 2015 and any later events after 6 April 2015 extend beyond the current reporting period.

Besides the VONAs, KVERT also creates Weekly Information Releases (hereafter WIRs). The WIR issued on 8 January 2015 stated that both strombolian explosive eruptions of the volcano and associated incandescence continued. Lava bombs rose up to 200-300 m above the crater and ash plumes to ~5 km altitude. Seismic activity of the volcano continued to increase. The magnitude of tremor increased from 3 to 13 x10-5 m/sec. (Note that KVERT reported tremor in units reflecting the velocity of the seismic sensor. They state these units as "mcm/s," 'milli-centimeters per second', which are equivalent to 10-5 m/sec, the means of expression used in this report.) Video data on the 4th and 7th revealed strong gas-steam emissions. Clouds obscured the volcano during other days of the week. Satellite infrared data showed a bright thermal anomaly over the volcano all week.

KVERT's 16 January WIR noted clear visibility of the summit area where bombs were ejected 200-300 m above the summit crater. Strombolian and vulcanian eruptions produced a series of ash plumes that rose to 5-8 km altitude (table 16). The Aviation Color Code increased to Orange.

Figure 17 shows a strombolian eruption at the summit on 19 January 2015. The KVERT caption reported that at this time two centers of strombolian activity and lava flows could be observed at the summit crater. About a week before, video images suggested a new lava flow had started to discharge downslope, and by mid-January through March, lava flows were regularly indicated in KVERT reports (two were seen on the NW slope on 15 March).

The lava flows led to phreatic explosions at the lava flow front. These produced gas-and-steam clouds with minor amounts of ash that during 27-28 January rose to an altitude of 7-8 km. Ashfall was reported in nearby (table 16). Consistent with the lava flows and the spatter from strombolian eruptions, satellite images consistently showed thermal anomalies over the volcano.

Figure 17. Photo of Klyuchevskoy taken during strombolian emissions on 19 Jan 2015. Strombolian activity with bombs rose to heights of 200-300 m and were common around this time (see table 16). Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

On 15 February, a series of explosions generated ash plumes that rose to an altitude of 8 km, prompting KVERT to raise briefly the Aviation Color Code to Red. Later that day, it was lowered to Orange. During the second half of February, bombs were ejected 150 m above the crater, rather than up to ~300 m, as earlier. Towards the end of February they were no longer reported although that may have been due to lack of visibility or the spatter and bombs may have decreased in size to the point where such emissions became difficult to observe.

On 9 March, the magnitude of seismic tremor significantly decreased. Only moderate emissions of steam and gas were observed, and a thermal anomaly over the summit disappeared. The Aviation Color Code was lowered to Yellow. On 10 March, seismic tremor significantly increased again, prompting KVERT to raise the Aviation Color Code to Orange. Video images showed moderate gas-and-steam activity, while satellite images detected a gas-and-steam plume with small amounts of ash. During 10-17 March, a weak thermal anomaly was detected occasionally over the summit. The eruption continued through the middle of March, but the energy of the explosions decreased significantly, prompting KVERT to lower the Aviation Color Code to Yellow on 25 March.

As of 2 April 2015, KVERT reported that moderate activity continued, with strong fumarole activity. As previously mentioned, KVERT described the explosive eruption as ended on 24 March (table 16).

Table 16. Plume characteristics at Klyuchevskoy during 10 January to 2 April 2015 (UTC). -- means not reported, Bhgt stands for the height above the crater to which bombs were thrown (in meters). Data do not include low-rising emissions. KVERTs satellite-based assessment of the ash content in plumes was generally determined by methods discussed by Ellrod (2012) and Ackerman and others (undated) and references therein. The table was assembled largely from KVERT VONAs and their Weekly Information Releases (WIRs).

References: Gary Ellrod, 2012, Remote Sensing of Volcanic Ash, National Weather Association (URL: http://www.nwas.org/committees/rs/volcano/ash.htm).

Ackerman, S., Lettvin, E, Mooney, M, Emerson, N, Lindstrom, S, Whittaker, T., Avila, L, Kohrs, R, and Bellon, B., undated, Satellite applications for geoscience education [online course; Facilitating the use of satellite observations in G6-12 Earth Science Education] University of Wisconsin and University of Washington (URL: https://cimss.ssec.wisc.edu/sage/geology/lesson3/concepts.html).

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: Kamchatka Volcanic Eruption Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/); Kamchatka Branch, Geophysical Service, Russian Academy of Sciences (KB GS RAS) (URL: http://www.krsc.ru/english/network.htm); NASA Earth Observatory (URL: http://earthobservatory.NASA.gov/); and William L. Stefanov, Jacobs Technology/ESCG, NASA Johnson Space Center, Houston, Texas.

This report details activity and monitoring at Merapi from 13 June 2011 through December 2014.

The last major eruption at Merapi was in 2010 as discussed in the previous two reports. As noted in BGVN 36:01 (covering 26 October 2010 to January 2011), Merapi began to erupt on 26 October 2010 and continued erupting throughout the interval, causing ~400 fatalities. BGVN 36:05 (26 October 2010 to 12 June 2011) further discussed this eruption detailing new dome growth and how lahars damaged infrastructure.

During the current reporting interval (13 June 2011 through December 2014), Merapi erupted regularly amid elevated seismicity. This report chiefly derives from three sources: (1) Balai Penyelidikan dan Pengembangan Teknologi Kegunungapian (BPPTK), (2) Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG; here referenced as CVGHM which stands for Center for Volcanology and Geological Hazard Mitigation), and (3) the Darwin Volcanic Ash Advisory Center (VAAC).

Activity during 2011.The hazard status for Merapi from 13 June 2011 onwards was Alert, Level II (on a scale of I–IV), before it decreased during 12–18 September 2011 and remained at Normal, Level I. Several minor avalanches occurred, with noted incidents on 2, 4, 6, 7, 14, and 25 July; 2, 7, and 15 August; and 4 and 8 September. Merapi also released several plumes, most of which consisted of white, thin or thin-to-thick clouds that rose to a maximum of only a few hundred meters above the summit (table 21).

Table 21. From 13 June to 31 December 2011, the plumes released by Merapi were generally described as thin or thin-to-thick and white in color. The only exception was apparent puffing associated with the plume on 10 July 2011, which lasted ~3 hours. Courtesy of BPPTK weekly reports from 2011.

The non-tremor seismicity at Merapi in 2011 (figure 54) was categorized into four types of earthquakes, each of which had different patterns on the time-series plots. The seismicity was also described in terms of Real-time Seismic Amplitude Measurement (RSAM), (not shown here). In 2011, avalanche earthquakes and multiphase earthquakes dominated the record.

Figure 54. Number of earthquakes ("Jumlah Kejadian" in Indonesian) recorded at Merapi for 2011 with shallow volcanic (VB, green), deep volcanic (VA, red), avalanche ("Guguran," purple), and multiphase (MP, orange) earthquakes. The terms shallow and deep were not quantified. Note that the y-axis scales vary such that the most numerous earthquakes were MP and avalanche, and the least numerous were VB and VA. Courtesy of BPPTK (taken from their 2–8 January 2012 weekly report).

A key means of measuring changes in linear length at Merapi consisted of surveys employing Electronic Distance Measurement (EDM) instruments (figure 55). The instruments computed the distance from several reflectors positioned on Merapi's slopes to fixed points at surrounding observatory posts. Figure 56 (below) provides the location of the posts and reflectors mentioned. Length changes were generally in the range of a few centimeters.

Figure 55. EDM linear length at Merapi in 2011, based on the distances from specified reflectors to various fixed locations. "Jarak" signifies distance (in meters). (A) 1 July to 30 December, recorded by Post Babadan. (B) 1 July to 9 December, recorded by Post Kaliurang. (C) 1 July to 5 December, recorded by Post Jrakah. The EDM linear lengths between the Post and both reflectors were broadly similar. (D) 1 July to 5 December, recorded by Post Selo. Courtesy of BPPTK (26 December 2011–1 January 2012 report).

Figure 56. Images highlighting the locations of Merapi's observation posts (left) and reflectors (right). The right image is a zoomed-in version of the summit area (approximate red rectangle on the left image). To provide scales, the distance (in the image at left) from the summit to Kantor BPPTKG is ~30 km and the distance (in the image at right) from Jrakah 1 to Deles 3 is ~300 m. Courtesy of BPPTK (page titled Aktivitas Merapi), image captioned by Bulletin editors.

Activity during 2012. A thin, white plume rose to a maximum of 150 m above the crater at 1910 on 6 January, and storms and heavy clouds covered Merapi's summit. On 9 January at an unstated time, a photo from CCTV Deles (discussed by BPPTK) showed Merapi amid clear weather with a white billowing cloud rising from the crater area. A few days later, at 1835 on 15 January, Merapi ejected a thin, white plume, rising to a maximum of 100 m above the summit, heading W.

Thin, white plumes were also observed above the crater to 50 m, heading E on 1 February at 1720; to 500 m at 1745 on 11 February; and to 400 m at 1800 on 13 February.

During 30 July to 5 August 2012, BPPTK referred to thick, white plumes drifting from the volcano. One plume reached a maximum of 600 m above the crater at an unstated date around this time.

For the intervals in 2012 discussed above, the hazard status remained constantly at Normal (I). Furthermore, during 2012, the BPPTK recorded the seismicity (figure 57) and the EDM linear length (figure 58).

Figure 57. Number of earthquakes ("Jumlah Kejadian" in Indonesian) at Merapi for 2012 with low-high frequency (LHF, pink), shallow volcanic (VB, green), deep volcanic (VA, red), avalanche ("Guguran," purple), and multiphase (MP, orange) earthquakes. The numbers/peaks for each type of earthquake did not follow the same pattern. Note that the numbered scales on the left side vary. Courtesy of BPPTK (28 January–3 February 2013 report).

Figure 58. Merapi's EDM linear length in 2012, based on the distances from reflectors to various fixed locations. "Jarak" signifies distance (in meters). The measurements were recorded by Selo, Jrakah, Kaliurang, and Babadan stations (top to bottom). The sudden shift in the trend and the words "Setting ulang alat" (red words on the topmost graph) refer to technicians resetting the scale at that time (the instrument remained stable). Courtesy of BPPTK (28 January–3 February 2013 report).

Activity during 2013. A thick plume blew W and reached a maximum of 450 m above the crater at 1750 on 3 February. The hazard status was at Normal (I).

On 22 July at 0415, BPPTK observed an ash eruption with brown-to-black color, reaching 1 km above the crater. A roar was heard within a radius of 6–7 km around Merapi, and ash fell to the SE, S, and SW. The hazard status remained at Normal (I); the Aviation Color Code was at Orange. According to a news article (Yahya, 2013), the eruption caused hundreds to temporarily evacuate; they returned to their homes later the same day.

On 29 October 2013, BPPTK observed a white, thin-to-thick plume that reached 150 m above the summit, heading W.

On 18 November 2013, Merapi erupted. A news article in the Jakarta Post discussed the event extensively quoting BPPTK staff (Muryanto and Ayuningtyas, 2013). The article said that the eruption began at 0453 LT forming a plume that rose to 2 km above the crater. Ash fell until about 1000 that day, with noticeable amounts found up to 60 km to the E. The news report also noted that ~600 families "in Kalitengah Lor, Kalitengah Kidul and Srune hamlets, and in Glagaharjo village, Sleman regency, Yogyakarta, had immediately gathered to be evacuated" and that "villagers in Turgo village, Turi district, Sleman, located on the western flank of Mount Merapi, also fled their homes, [returning] a few hours later as the situation returned to normal." The eruption followed an M 4.7 tectonic earthquake detected in Ciamis, West Java earlier that day and was more powerful than a previous eruption on 22 July 2013 (Muryanto and Ayuningtyas, 2013).

Based on a Darwin VAAC report at 2025 LT on the same day (18 Nov), the eruption formed a plume that reached ~12.2 km altitude. The Aviation Color Code was increased to Red. By 2104 on the 18th, VAAC satellite analysis no longer detected the high altitude volcanic plume, but the VAAC reported a lower plume at ~4.6 km altitude. At 0300 on 19 November, the low level plume had extended to ~46 km E. However, by 0735, the plume had completely dissipated, and the Aviation Color Code returned to Orange.

BPPTK noted the seismicity (figure 59), the EDM linear length (figure 60), and the tilt (figure 61). In 2013, seismicity was dominated by avalanche earthquakes (figure 59). The only major change in linear length was the distance to Kaliurang 2 which had a gradual upward trend for most of the year, before a comparatively rapid downward trend in mid-October (figure 60). The two tiltmeter records showed broad consistency, with mild increases in the middle to late part of the year that reverted near to the original tilt (figure 61). The temperature graph had a broad peak in August 2013 that could account for some of the increase in tilt, but the BPPTK report did not discuss this in any detail. (For the location of the tiltmeter stations mentioned, see figure 62.)

Figure 59. Number of earthquakes ("Jumlah Kejadian" in Indonesian) in 2013 at Merapi for low-to-high frequency (LHF, pink), deep volcanic (VA, red), shallow volcanic (VB, green), multiphase (MP, orange), and avalanche ("Guguran," purple) earthquakes. Y-axis scales vary. Courtesy of BPPTK (17–23 January 2014 report).

Figure 60. Merapi EDM linear length recorded during 2013, based on the distances from reflectors to various fixed locations. "Jarak" signifies distance (in meters). The measurements were recorded using reflectors Selo 1, Jrakah 1, Kaliurang 2, and Babadan 1 (top to bottom). Courtesy of BPPTK (25–31 October 2013 report).

Figure 61. Tilt recorded at Merapi's station Plawangan. Y-axis units for the upper two tilt plots are microradians (arbitrary values). "Sumbu X" refers to tilt along a line running E-W and "Sumbu Y" to tilt along a line running N-S. The bottom plot is "Suhu" or temperature in degrees Celsius, which CVGHM noted may have a strong impact on the tilt measurements. Courtesy of BPPTK (17–23 January 2014 report).

Figure 62. The location of the tiltmeter stations. To provide a scale, the distance from Klatakan Analog to Pusunglondon is ~0.9 km. Courtesy of BPPTK (Aktivitas Merapi).

Activity during 2014. BPPTK noted that on 17 January at 1615, a white plume rose to 50 m above the summit, heading E.

At 1854 LT on 10 March 2014, Merapi erupted forming an ash plume that blew W. The event was captured on an automated closed-circuit video (CCTV Pasarbubar) and was followed by two more blasts within a minute (the first at 1855). At 1908, BPPTK noted a volcanic earthquake (with a maximum amplitude of 20 cm). Another video monitor (CCTV Bubar) recorded brown eruptive columns that rose straight up, reaching up to ~1.5 km above the summit. During 1925 to 1930, the eruption gradually stopped. Around this time, ash fell on several villages including Umbulharjo, Kepuharjo, Sidorejo, and Balerante, areas located ~6–7 km to the S of Merapi.

During 14-20 March 2014, thick gas plumes rose to ~600 m above the summit. On 17 March, the BPPTK recorded one such event at 0530.

On 27 March 2014, an eruption lasted from 1312 to 1316 LT. The VAAC detected volcanic ash to ~9.8 km altitude, using multi-spectral MTSAT-2 imagery, and the Aviation Color Code was raised to Red. A pilot reported that the "large ash cloud [was] moving NW." Darwin VAAC received a SACS SO2 alert at 2150 for the plume, and atmospheric SO2 gas was detected SE of Merapi. By 2232, the volcanic ash appeared to be dissipating; the advisory was terminated at 0830 on 28 March.

The 27 March eruption was the subject of a Jakarta Post news article by Muryanto and Ayuningtyas (2014), who indicated that ash fell in the Kemalang and Balerante Klaten regency and that it was 1 mm thick in some areas. The article also noted an M 5.4 tectonic earthquake that struck ~115 km SE of Malang regency, East Java on 23 March. The ash discharge had apparently been occurring regularly since the 2010 eruption but authorities had not taken this as a sign of an escalation in activity, and they urged locals to remain calm. However, according to the article, Sukiman, a resident of the nearby Deles district, said villagers responded to half an hour of ash falling by hitting "kentongan [bamboo drums] to warn others of the danger."

On 15 April, BPPTK reported that a thick white plume rose to a maximum of 300 m above the summit.

Several tectonic earthquakes occurred in April 2014. On 18 April at 2033, BPPTK recorded tectonic earthquakes 151 km SW of Merapi at a depth of 10 km. On 19 April, four more tectonic earthquakes occurred between 0800 and 2000, and an earthquake lasting 20 minutes was recorded at 0421 from a station on the peak of Merapi. On 20 April from 0426 to 0440, rumbling could be heard within a radius of 8 km around the volcano.

The BPPTK reported that on 20 April at 1600, an ash plume traveled W towards the village of Sewukan, amid foggy conditions. The associated eruption was followed by a widely heard roar and a later thin-to-thick plume rose to 400 m above the summit at 1800. The activity ultimately led to ashfall in Sewukan and in sectors to the SE, S, and SW, up to 15 km away from Merapi's summit.

The ash from this eruption was also detected by Darwin VAAC, who stated that the ash plume rose to ~10.7 km and extended ~260 km W to NW. The ash was difficult to distinguish from meteorological clouds, and at 1004 LT on 21 April, the VAAC terminated the advisory. In a news article, Minggu (2014) added further details on the eruption omitted here.

The BPPTK conducted a field expedition on 22 April to Merapi's crater. The expedition found that the eruption on 20 April had changed the summit crater morphology (figure 63). The slit that cut through the lava dome trending NE had widened by 70 m to the W, and reddish material that the team judged as indicative of oxidation was visible around the center of the lava dome. They also found new eruptive products along the crater's W side and evidence of new growth at the lava dome.

Figure 63. Field observations made on 22 April 2014 of Merapi's crater, assessing the aftermath of the 20 April eruption. (Top) View through the NW slit in the dome's crater. The crater wall appears in the background. (Bottom) Blowup of region depicted by base of red arrow. A wall in the summit crater area shifted W by ~70 m. New deposits were found in the area on the far side of the yellow dashed line. Courtesy of BPPTK (18–24 April 2014 report), image re-captioned in English by Bulletin editors.

The BPPTK reported that monitoring outposts heard as many as 47 thumping sounds between 25 April and 1 May 2014, 20 sounds between 2 and 8 May, and 22 sounds between 9 and 15 May. On 25 April at 0740, a white, fumarolic plume rose to a maximum of 450 m above the summit, heading W, and the hazard status was raised to Alert (II). White, thin-to-thick plumes rose above the summit to 650 m on 2 May at 0700; to 350 m on 12 May at 0606; to 450 m on 22 May at 1924; to 300 m, heading W, on 27 May at 1854; and to 400 m on 31 May at 2010. The hazard status was lowered to Normal (I) during 21–27 May.

On 4 July 2014 at 1754, BPPTK observed thin-to-thick white plumes rising to 450 m above the summit.

On 10 September at 2008, thin, white plumes rose to 200 m above the summit, according to BPPTK.

During 10 to 16 October, Merapi released a thin white plume to ~200 m above the summit. The Darwin VAAC noted that small rock avalanches extended for ~1 km.

For 2014, BPPTK noted the seismicity (figure 64), EDM linear length (figure 65), and tilt (figure 66).

Figure 64. Number of earthquakes ("Jumlah Kejadian" in Indonesian) registered at Merapi for 2014. Note that the y-axis scales vary. (Top) Chart covers from January to September 2014 and consists of earthquakes: volcano-tectonic (TEK), low frequency (LF), low-to-high frequency (LHF), volcanic (VUL), multiphase (MP), and avalanche (GGR). (Bottom) Chart covers from October to December 2014 and consists of tremors (VT) and earthquakes: multiphase (MP), rock fall signals (RF), and tectonic (TT). Courtesy of BPPTK (5–11 September 2014 and 20–26 March 2015 reports).

Figure 65. Merapi EDM linear length in 2014, based on the distances from reflectors to Post Kaliurang. "Jarak" signifies distance (in meters). The top chart covers from January to September and the bottom from October to December. (Date format for bottom is day/month/year.) Courtesy of BPPTK (5-11 September 2014 and 20–26 March 2015 reports).

Figure 66. Tilt registered at Merapi in 2014 (y-axis/microradians with arbitrary values). (Top) January to September 2014, based on recordings made at stations Plawangan (left) and Babadan (right). "Sumbu X" portrays tilt along an E-W direction and "Sumbu Y", tilt along a N-S direction. The last plot ("Suhu") in each of these two cases shows the temperature in degrees Celsius. (Bottom) October to December, based on recordings made by station Klatakan Analog. The red line represents (tangential) tilt in an E-W direction ("Sudut B-T"). The blue line represents (radial) tilt in a N-S direction ("S-U"). The sudden changes in the red and blue lines were caused by repositioning. Courtesy of BPPTK (5–11 September 2014 and 20–26 March 2015 reports).

Background. Several detailed maps of Merapi have been published by various sources. Handisantono and others (2002) contains a topographic hazard map of Merapi. The map includes the location of several villages mentioned in this report, as wells as rivers and other geological landmarks. BNPB also published a map of Merapi (figure 67). The map highlights the location of the W/SW/S-flank drainage systems, which have the potential to funnel lahars to local infrastructure such as bridges and into inhabited areas.

Figure 67. A section of a map of Merapi detailing lahars and related drainage systems (blue lines). The bounding color areas around the lahars represent associated hazard zones with risk levels ranging from yellow to red (least risk to most). Portions of concentric red, orange, and yellow circles mark the radial distance from Merapi's summit in kilometers. Courtesy of BNPB (date unknown).

A detailed analysis of Merapi's history and periods of activity is documented by CVGHM (2014). The ongoing magmatism and volcanism at Merapi are considered consistent with documented copper, zinc, and lead enrichment as well as zonation there (Nadeau and others, 2013).

References.

Badan Nasional Penanggulangan Bencana (BNPB), date unknown, Peta Zonasi Ancaman Banjir Laha Dingin, Relief Web (URL: http://reliefweb.int/sites/reliefweb.int/files/resources/E0676C85D7612CE1852578340054FD68-map.pdf) [accessed in April 2015]

CVGHM, 2014, G. Merapi, Jawa Tengah, 03 June 2014, Center for Volcanology and Geological Hazard Mitigation (URL: http://www.vsi.esdm.go.id/index.php/gunungapi/data-dasar-gunungapi/542-g-merapi) [accessed in April 2015]

Hadisantono, R.D., Andreastuti, M.CH.S.D., Abdurachman, E.K., Sayudi, D.S., Nurnusanto, I., Martono, A., Sumpena, A.D., Muzani, M., 2002, Peta Kawasan Rawan Bencana Gunungapi Merapi, Jawa Tengah Dan Daerah Istimewa Yogayakarta (Volcanic Hazard Map of Merapi Volcano, Central Java and Yogyakarta Special Province), Center for Volcanology and Geological Hazard Mitigation (URL: http://www.vsi.esdm.go.id/galeri/index.php/Peta-Kawasan-Rawan-Bencana-Gunungapi-01/Wilayah-Jawa/KRB-G_-Merapi) [accessed in April 2015]

Minggu, 2014, Mt. Merapi rumbles spewing volcanic material to nearby areas, 20 April 2014, Antara News (URL: http://www.antaranews.com/en/news/93713/mt-merapi-rumbles-spewing-volcanic-material-to-nearby-areas) [accessed in April 2015]

Muryanto, B., Ayuningtyas, K., 2013, Hundreds of villagers flee Mount Merapi eruptions, 19 November 2013, The Jakarta Post (URL: www.thejakartapost.com/news/2013/11/19/hundreds-villagers-flee-mount-merapi-eruptions.html) [accessed in April 2015]

Muryanto, B., Ayuningtyas, K., 2014, Mount Merapi spews sulfuric gas, ash, 11 March 2014, The Jakarta Post (URL: www.thejakartapost.com/news/2014/03/11/mt-merapi-spews-sulfuric-gas-ash.html) [accessed in April 2015]

Nadeau, O., Stix, J., Williams-Jones, A.E., 2013, The behavior of Cu, Zn and Pb during magmatic–hydrothermal activity at Merapi volcano, Indonesia, 29 March 2013, Chemical Geology Volume 342 (URL: www.sciencedirect.com/science/article/pii/S0009254113000466)

Yahya, A., 2013, Mount Merapi Status Remains Normal Despite Weak Eruptions, 22 July 2013, Bernama (URL: http://www.bernama.com/bernama/v7/ge/newsgeneral.php?id=965338) [accessed in April 2015]

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 Kegunungapian (BPPTK), Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) (URL: http://merapi.bgl.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC) (URL: http://www.bom.gov.au/info/vaac/); and Center for Volcanology and Geological Hazard Mitigation (CVGHM, Pusat Vulkanologi dan Mitigasi Bencana Geologi), Badan Geologi, Kementerian Energi dan Sumber Daya Mineral (ESDM), Yogyakarta 55166, Indonesia (URL: http://www.vsi.esdm.go.id/).

On the basis of ash-plume reports from the aviation community around the time of this reporting, Sinabung ranked as the most active volcano in Indonesia, the world's fourth-most populated country. The volcano is located in the Karo Regency of N Sumatra (figure 19). The latest eruption began mid-September 2013; activity through April 2014 was reported in BGVN 39:01. This report describes the continuing volcanic activity from May 2014 through October 2014, primarily drawn from reports issued by the Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) and reports from the Darwin Volcanic Ash Advisory Centre (VAAC). During this reporting interval, many photographs of Sinabung emerged online, some with outstanding information content, but far too numerous to either catalog or feature here.

Figure 19. Sinabung is located in Karo Regency on the island of Sumatra in the Indonesian archipelago. Sinabung resides NE of the closest margin of Toba caldera, the largest volcano of this type known on Earth. The elongate caldera contains a lake 100 km long. The central portion of the lake is occupied by a prominent island (a classic resurgent dome). Taken from Darwin VAAC.

The Darwin VAAC describes their jurisdiction as covering ~150 active volcanoes located in the South Pacific region from the Philippines to the Solomon Islands, including Indonesia. They issued 1,511 Volcanic Ash Advisories (VAAs) during the 12-month period, 1 July 2013 to 30 June 2014 (their fiscal year 13/14; Darwin VAAC, 2014). During the next 7-month interval (ending 31 January 2015) the VAAC issued 742 reports (Darwin VAAC, 2015). These VAAs are part of their mission to create materials for warning and guidance to the aviation community, including aviation meteorologists, air traffic control offices, and airlines (e.g. dispatchers and pilots).

One way to assess the production of noteworthy ash plumes at volcanoes is to consider the number of VAAs issued, an assessment found in their Management Reports (Darwin VAAC, 2014; 2015). The Darwin VAAC issued Management Reports that both cover and extend beyond (i.e., both earlier and later than) this reporting interval (May to October 2014). Specifically, their reports cover 1 July 2013-30 June 2014 and 1 July 2014-31 January 2015. In both those intervals the largest number of VAAs issued for any single volcano in their region went to Sinabung. In the earlier interval this consisted of 537 out of 1,511 total regional reports; in the later interval, 321 out of 742 total regional reports.

The table in the section "Data compilation" at the bottom of this report also highlights a case at 12:32 UTC on 22 May 2014 of a rapidly growing cloud around Sinabung plausibly associated with an eruption there. The cloud reached ~15.2 km altitude and was initially assessed as eruptive and ash bearing. At the time forecasters felt there was sufficient evidence the cloud contained ash to warrant an advisory. A more detailed assessment made later determined the cloud to probably have been a cumulonimbus cloud (abbreviated Cb; a towering vertical dense cloud often associated with thunderstorms and atmospheric instability). The case illustrates the challenge of creating VAAs rapidly with limited information and time for analysis, balanced against the desire for high accuracy (with low rates of false positives and false negatives). Darwin VAAC (2015) also described the region as one with "...moist tropical convection that makes remote sensing difficult for much of the year."

During the reporting interval, Sinabung was the scene of both lava flows and vigorous dome-building eruptions that discharged significant ash plumes and pyroclastic flows (PFs). Lava flows constructed a several kilometer long tongue or lobe of lava on the flank to the S-SE. These events accompanied elevated seismicity.

During the reporting interval the Aviation Colour Code (ACC) issued by the VAAC was generally Orange; however, during the week of 15-21 October, the ACC was Red.

The ACC is a four-color scale used to inform the needs of the aviation community. The four colors denoting increasing risk are Green, Yellow, Orange, and Red. According to the World Organization of Volcano Observatories' website, Orange connotes "Volcano is exhibiting heightened unrest with increased likelihood of eruption." Red connotes "Eruption is forecast to be imminent with significant emission of ash into the atmosphere likely."

The CVGHM uses a separate volcanic hazard status code to warn people in the region. The Darwin VAAC Weekly report issued for 29 October-4 November 2014 gave this overview of the eruption and the variation in CVGHM's volcanic hazard status: "On 14 September 2013, a new eruptive phase began. By mid-October the volcano was degassing almost daily with small phreatic eruptions. Seismic and visual activity continued to build into November. After nine powerful explosions in a 24 hour period, the Centre for Volcanology and Geological Hazard Mitigation (CVGHM) raised the Alert level to Level IV on 24 November 2013, the highest volcano rating. The status was decreased to Alert Level III on 8 April 2014."

During this reporting interval, lava flows advanced in the sector S- SE from the summit (figure 20). In accord with that lobe or tongue of lava, incandescent zones were at various times noted in different parts of the flows. As reported by CVGHM, avalanches from the front of the advancing lava flows occurred often. Scientists associated this process with a distinct seismic signal called an avalanche earthquake. CVGHM repeatedly warned residents that the lava flows and their associated avalanches could threaten areas to the S and SE within 5 km of the summit. Measurements of the length of this flow are included in the table at the bottom of this report. A previous map with clearer labels of the earlier flows appears as figure 16 in BGVN 39:01.

Figure 20. Annotated photo showing the S-SE flank of Sinabung covered by an advancing lava flow (often referred to as lava tongue, 'lidah lava' in Indonesian). On 6 September 2014, the day of this photo, the lava flow was reported as measuring 2.915 km long from distal end to the vent area at or adjacent the summit lava dome. Although the upper slopes on the E (right) side are too cloudy to see, CVGHM had recorded the locations of the various dated flow margins there. Note the area on the upper flanks where some lava branched off the main lobe to create a series of small finger-shaped areas trending more to the W. Courtesy of CVGHM.

Seismicity at Sinabung included avalanche earthquakes, low-frequency earthquakes, tectonic earthquakes, volcanic earthquakes and ongoing tremor. Totals and measured averages of these seismic events are included when available (see table at bottom). CVGHM reported that the dominating seismic signals, avalanche earthquakes and intervals of constant tremor, were associated with the instability of the growing lava dome and lava flows.

During this reporting interval, numerous eruptions took place, often generating ash plumes and in some cases pyroclastic flow. During the eruptions, some ash plumes were detected by satellite imagery. Ground-based observations were also important. For example, CVGHM often detected Sinabung eruptions, PFs, and plumes via webcam. Darwin VAAC also benefited from the CVGHM webcam data in several of their VAAs. The VAAC has also begun to use social media to both dispense and retrieve operationally relevant information (Darwin VAAC, 2015). This has aided VAAC forecaster's understanding of, for example, whether residents have noticed ashfall during times when ash is not discernable due to meteorological clouds (Darwin VAAC, 2015).

During May and October 2014, PFs had runout distances up to 4.5 km and ash plumes rose up to 5.2 km altitude. White or slightly discolored plumes were the most common type reported by CVGHM. These plumes sometimes rose to as high as on the order of 1 km over the summit.

Figure 21 is a map of Sinabung and towns surrounding the volcano.

Figure 21. Relief map of Sinabung volcano and surrounding towns, some of which are named in reporting. The base map was made prior to the current eruption and the lava tongue descending the S-SE flank is not shown. For scale, the distance is ~3 km from the summit area N to the closest (S) margin of Kawar lake. Map found online at Pixshark.com and edited by Bulletin editors.

Photographs. The following are photos documenting events at Sinabung during this reporting interval. Ancillary information pertaining to each photo can be found in a table at the bottom of this report.

Figure 22. Photo of a pyroclastic flow (PF) descending Sinabung on 14 August 2014. Two PFs occurred that day, at 0728 UTC and 0750 UTC. The time that this photo was captured is unknown. Photographer unknown; photo posted on Facebook by CVGHM and taken from the 13-19 August 2014 Darwin VAAC weekly activity report.

Figure 23. A pyroclastic flow (PF) captured at 0940 UTC on 2 September 2014. This PF traveled 1.5 km to the SE. Taken from the 27 August-2 September 2014 Darwin VAAC weekly activity report.

Figure 24. Sinabung in a low-light photo allegedly taken at 1444 UTC on 7 September 2014, which would make it about 46 minutes after Darwin VAAC reported an eruption. The ash plume rose 2 km above the summit and blew S. A rivulet of red glowing material descends an area of the flank. Bulletin editors interpret the rivulet as a lava flow (or possibly a glowing avalanche or both) traveling down the lava tongue on the S-SE flank. Copyrighted photo taken by Endro Lewa, posted on Facebook by CVGHM, and taken from the 3-9 September 2014 Darwin VAAC weekly activity report.

Figure 25. Eruption at Sinabung on 8 October 2014. This time and the location of this photo were unstated. Photo by the news agency AFP and taken from the 8-14 October 2014 Darwin VAAC weekly activity report.

Figure 26. (A) Ground-based photo of a Sinabung eruption column looking approximately NE on 19 October 2014. Photo was captured at 0731 UTC. The eruption column is obscured by weather clouds but is visible again above them in a small area. Photo was taken by Ricky Febriand, posted on Facebook by CVGHM, and taken from the 15-21 October 2014 Darwin VAAC weekly activity report. B. Aerial photo of Sinabung's eruption column on 20 October 2014. Photo was captured at 0736 UTC. Height of eruption column and position photo was taken are unknown. Photo taken by Ricky Febriand, posted on Facebook by CVGHM and taken from the 15-21 October 2014 Darwin VAAC weekly activity report.

Data compilation. Table 4 summarizes activity at Sinabung from May-October 2014. Data sources include reporting by CVGHM (often the original source), the Darwin VAAC (their Volcanic Ash Advisories (VAAs), Weekly Activity Reports; and other reports), the Indonesian National Agency for Disaster Management (Badan Nacional Penanggulangan Bencana-BNPB), occasional news articles; and the Smithsonian-USGS Weekly Volcanic Activity Reports.

Table 4. A synthesis of Sinabung's reported activity from May-October 2014. The bulk of this table came from CVGHM and Darwin VAAC reporting unless otherwise stated. Dates and times are in some cases ambiguous as to local time (LT) or UTC (LT = UTC + 7). Abbreviations: pyroclastic flow, PF; Aviation Color Code, ACC; earthquake(s), EQ(s); maximum amplitude, max. amp.; and altitude, alt.

References. Associated Press, 2014, Volcano in Western Indonesia erupts again, accessed on 28 September 2014, (URL: http://abcnews.go.com/International/wireStory/volcano-western-indonesia-erupts-25720623 )

Darwin VAAC, (6 August) 2014, VAAC Darwin Management Report [discussing 1 July 2013 to the 30 June 2014], International Civil Aviation Organization (ICAO); Eighteenth Meeting of the Meteorology Sub-Group (Met Sg/18) Of Apanpirg; ICAO Regional Sub-Office, Beijing, China; 18–21 August 2014 [Agenda Item 7.4: Research, development and implementation issues in the MET field, [7.4] Advisories and warnings, MET SG/18 - IP/17; Agenda Item 7.4; 6 August 2014; (Presented by Australia)]; 5 pp. (URL: http://www.icao.int/APAC/Meetings/2014 METSG18/IP17_AUS AI.7.4 - VAAC Darwin Management.pdf )

Darwin VAAC, (18 February) 2015, Darwin VAAC Management Report [discussing 1 July 2014-31 January 2015], International Civil Aviation Organization (ICAO), Fifth Meeting of Meteorological Hazards Task Force (MET/H TF/5), Seoul, Republic of Korea, 18 March 2015 [Thirteenth Meeting of the Asia/Pacific Regional Opmet Bulletin Exchange Working Group (Robex Wg/13), ROBEX WG/13 & MET/H TF/5 – WP/C6; Agenda Item (conjoint session) 2 (Presented by Australia)] (URL: http://www.icao.int/APAC/Meetings/2015 ROBEXWG13/WP-C6 - AI.2 - AUS - Darwin VAAC Management Report.pdf )

Indonesian National Agency for Disaster Management (Badan Nacional Penanggulangan Bencana-BNPB), 2014, Four time Sinabung, Normal Community Activity, accessed on 6 October 2014, (URL: http://bnpb.go.id/berita/2211/empat-kali-sinabung-meletus-masyarakat-beraktivitas-normal)

The Jakarta Post/Asia News Network, 2014, Mount Sinabung erupts again, accessed on 6 October 2014, (URL: http://news.asiaone.com/news/asia/mount-sinabung-erupts-again)

Okezone.com, 2014, accessed on 28 September 2014, (URL: http://news.okezone.com/read/2014/10/01/340/1046715/hujan-abu-gunung-sinabung-guyur-karo-petani-menderita )

Pixshark.com, accessed on 7 April 2015 (URL: http://pixshark.com/peta-gunung-sinabung.htm)

World Organizations of Volcano Observatories (WOVO), Aviation Colour Codes, accessed on 8 April 2015, (URL: http://www.wovo.org/aviation-colour-codes.html)

Xinhua News Agency, 2014, 2nd LD Writethru: Mount Sinabung in Indonesia erupts, triggering massive evacuation, accessed on 29 June 2014, (URL: http://www.globalpost.com/article/6190943/2014/06/29/2nd-ld-writethru-mount-sinabung-indonesia-erupts-triggering-massive)

Xinhua News Agency, 2014, Mount Sinabung erupts in Sumatra, Indonesia, accessed on 28 September 2014, (URL: http://english.cntv.cn/2014/09/24/ARTI1411549583755731.shtml).

Geologic Background. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Information Contacts: Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) (also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi-PVMBG), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Indonesian National Agency for Disaster Management (Badan Nacional Penanggulangan Bencana-BNPB), Gedung Graha 55 Jl. Tanah Abang II No. 57, 10120, Jakarta Pusat (URL: http://www.bnpb.go.id/); and 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/).

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/).