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).

Explosive activity . . . continued with five explosions in November . . . . The explosions caused no damage. An explosion on 1 November at 0234 produced a large air shock and an incandescent column that was 500 m high for 10 seconds. Lightning was seen in the eruption cloud. The highest November ash cloud rose 1,000 m above the summit, accompanying an explosion at 1211 on the 10th. The month's ashfall at KLMO was only 12 g/m².

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

Information Contacts: JMA; AP; UPI.

Lidar stations in Germany, Japan, and Hawaii detected no apparent new stratospheric aerosol layers, and no recent large explosive eruptions have been reported. Substantially increased backscattering was measured between 17 and 22 km altitude at Mauna Loa, Hawaii on 1 November. Despite some instrument problems that night, the increased aerosols appeared real, but the profile did not have the characteristics of material from a new eruption.

Figure 63. Lidar data from various locations, showing altitudes of aerosol layers during September-November 1988. Note that some layers have multiple peaks. Backscattering ratios from Fukouka, Japan, are for the Nd-YAG wavelength of 1.06 µm; all others are for the ruby wavelength of 0.69 µm. Integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from 16-33 km at Mauna Loa and from the tropopause to 30 km at Hampton, Virginia. Altitudes of maximum backscattering ratios and coefficients are shown for each layer at Mauna Loa. Some upper and lower limits of layers at Mauna Loa were not clearly evident and are therefore not reported.

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

Information Contacts: Thomas DeFoor, Mauna Loa Observatory, P.O. Box 275, Hilo, HI 96720 USA; Motowo Fujiwara, Physics Department, Fukuoka University, Jonan-ku, Fukuoka 814-01, Japan; Horst Jäger, Fraunhofer-Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, West Germany.

"Seismic activity continued at a steady low level until 7 November when a swarm of 1,500 small explosion-type earthquakes were recorded. Visual reports were obtained of red material sliding or rolling down the E slopes of the volcano on the 6th and pale brown dust/vapour rising from the same area on the 7th. Seismic activity then returned to a normal level with 15 rockfall-related tremor events/day, indicating continued slow steady extrusion of lava from the summit crater. Seismic telemetry to Rabaul stopped on the 14th. Records continued to be obtained at Panguna until the nearby Mt. Kupara repeater station, containing RVO telemetry equipment, was destroyed on 2 December."

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

Information Contacts: I. Itikarai and P. Lowenstein, RVO.

Seismicity increased toward the end of November. A total of 188 events were recorded by the seismometer 1.8 km NNW of the summit, up sharply from the background level of ~20/month (figure 1).

Figure 1. Monthly number of recorded earthquakes at Bandai, 1965-88. Courtesy of JMA.

Geologic Background. One of Japan's most noted volcanoes, Bandaisan rises above the north shore of Lake Inawashiro. This complex is formed of several overlapping andesitic stratovolcanoes, the largest of which is Obandai. Kobandai volcano, which collapsed in 1888, was formed about 50,000 years ago. Obandai volcano was constructed within a horseshoe-shaped caldera that formed about 40,000 years when an older volcano collapsed, forming the Okinajima debris avalanche, which traveled to the SW and was accompanied by a plinian explosive eruption. The last magmatic eruption took place more than 25,000 years ago, but four major phreatic eruptions have occurred during the past 5000 years, two of them in historical time, in 806 and 1888. Seen from the south, Bandaisan presents a conical profile, but much of the north side of the volcano is missing as a result of the collapse of Ko-Bandai volcano during the 1888 eruption, in which a debris avalanche buried several villages and formed several large lakes.

Information Contacts: JMA; AP; UPI.

Fumarolic activity in the summit crater remained at the same level. Steaming ground was observed in many parts of the crater, but well-formed fumaroles were not evident. The intensity of steam release increases when atmospheric pressure drops and after precipitation. Tiatia's last reported activity ejected a 1-1.5-km-high white steam column in February 1982.

Geologic Background. Chachadake, also known as Tiatia, consists of a beautifully symmetrical cone that rises above the broad rim of an erosionally furrowed, 2.1 x 2.4 km wide caldera. The edifice occupies the NE tip of Kunashir Island and morphologically resembles Mount Vesuvius. The pristine-looking conical central cone, mostly formed by basaltic to basaltic-andesite strombolian eruptions, rises 400 m above the floor of the caldera and contains a 400 x 250 m wide crater with two explosion vents separated by a linear septum. Fresh lava flows cover much of the SW caldera floor and have overflowed the rim, extending to the foot of the older somma, which formed during the late Pleistocene or early Holocene. A lava flow from a flank cone on the northern caldera rim reached the Sea of Okhotsk. A major explosive eruption in 1973 followed an initial historical eruption in 1812.

Information Contacts: G. Steinberg, Yuzhno-Sakhalinsk.

Deformation and a brief seismic swarm preceded a new fissure eruption on 14 December. Lava production from the fissure eruption that began 31 August had stopped on 12 September. Strong degassing continued until early October. Between September and mid-December, the permanent telemetered EDM (5-minute period) recorded 5 cm expansion of the summit crater, associated with fissure extension measured by strainmeters. Radial tiltmeters detected no significant changes. Seismicity remained weak until 12 November, when 25 minutes of low-energy summit seismicity was recorded, without associated deformation. Since then, discrete shallow events had increased in the summit area.

On 14 December at 0830, a seismic crisis began that included both shallow and deeper events in the summit area. Deformation indicated northward magma migration between 0850 and 0910. The seismic crisis continued until 1220, when low-frequency tremor appeared on the summit seismic station (SFR). At 1306 [but see 13:12], an eruptive fissure opened in the N part of the Enclos Caldera, ~400 m E of the August 1985 crater. Three main NNE-trending, en-echelon fissures developed between 1,900 and 2,050 m elevation, and at 1400 a fissure opened just above them.

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: H. Delorme, P. Nerbusson, D. Vandamme, J. Delmond, and P. Taochi, OVPDLF; P. Bachelery, Univ de la Réunion; J. Dubois, J-L. Cheminée, A. Hirn, J. LePine; P. Blum, and J. Zlotnicki, IPGP.

On 5 November at 1130, ~1/3 of the 400-450 x 60 m lava bench collapsed, and numerous smaller bench collapses were detected seismically throughout November. A large littoral cone that formed on 28 November produced 1-5-cm flakes of volcanic glass.

On 10 November, a series of surface outbreaks near the top of the fault scarp at ~350 m elevation fed lava that flowed into the Royal Gardens subdivision but caused no threat to remaining structures. By 14 November, the flow was barely moving. Two weeks later, an outbreak occurred at 180 m elevation, flowed E of the subdivision, and stagnated days later at ~100 m elevation. The Kupaianaha lava pond level remained stable at 25-30 m below the rim through November. During overflights on the 3rd and the 28th, low fountaining (~5-10 m high) was observed in Pu`u `O`o crater, covering as much as ½ of its floor with lava. Irregular tremor . . . near Pu`u `O`o had ended 4 November and typical low-level tremor resumed. Most upper East rift zone events were deeper than 5 km except along the rift axis where events were generally more shallow. Seismicity was steady beneath Kiluaea's S flank, but episodic swarms of intermediate-depth (5-13 km), long-period earthquakes were measured beneath the summit.

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

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

"Activity returned to a low level in November. Weak-moderate amounts of white vapour with occasional grey [ash] were emitted from Crater 2. Weak rumbling noises occasionally were heard on the 4th. Ashfall was observed on the 11th. Two Vulcanian explosions, on the 18th and 27th, were accompanied by ash columns that rose a few hundred meters. Crater 3 was inactive throughout the month. Seismicity remained low and only 9 explosion earthquakes were recorded."

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: I. Itikarai and P. Lowenstein, RVO.

Between 30 June at 2000 and early the next morning, a new cone (T8) had formed and emitted a large lava flow (F6) that reached the N and E crater wall (figure 10). On the afternoon of 26 July, a party visiting the crater noted lava in the E part of T4/T7, bubbling actively at some depth below the vent's edge. A new cone (T9) had formed a few meters from T5, and lava could be heard moving within the vent. The top of T8 had collapsed somewhat and no lava was visible inside. About five small flows, radiating from a source between T4/T7 and T8, were still warm and black and had probably formed within the last few hours. One flow had moved S and partly entered T1's overhang. Another flow had almost reached T2. No changes were observed on the crater walls or rim.

Figure 10. View from halfway up Ol Doinyo Lengai's E crater wall, looking SW in the early morning of 1 July 1988. The crater floor is 200-240 m across. Tracing of a slide taken by C. Nyamweru.

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

Information Contacts: C. Nyamweru, Kenyatta Univ.

. . . seismicity remained above background levels in early December, with ~3-4 shallow events recorded weekly by the temporary seismic net installed after the swarm began. Hypocenters were at ~5-10 km depth, almost directly below or slightly W of Mt. Liamuiga, and magnitudes were generally in the 1.5-2 range. The shocks continued to have impulsive P and S wave arrivals typical of both A-type volcanic events and tectonic earthquakes. No tremor has been recorded. Persons familiar with the volcano report that hot springs within the crater remain unchanged.

Geologic Background. Mount Liamuiga volcano, comprising the NW end of St. Kitts Island, contains a steep-walled, 1-km-wide summit crater, which contained a shallow lake until 1959. Two lava domes are located on the upper W flank, and intrusion of a 3rd dome, Brimstone Hill, on the lower SW flank uplifted a Pleistocene limestone block. Liamuiga, sometimes referred to as Mount Misery, is the youngest of three NW-migrating volcanic centers on St. Kitts. Its most recent major eruptions less than 2000 years ago produced pyroclastic flows and mudflows whose deposits underlie populated coastal areas. Reports of possible historical eruptions in 1692 and 1843 are considered uncertain. An earthquake swarm from late 1988 to early 1989 caused small landslides in the summit crater; another earthquake swarm took place in 1999-2000. Active fumaroles are found in the summit crater.

Information Contacts: J. Shepherd, UWI.

One of Long Valley caldera's more significant earthquake swarms of the last several years occurred 20-22 November (figure 4). Of the 393 recorded events (to M 2.0), most were located in the E moat of the caldera (near the E margin of the resurgent dome) with minor activity in the S moat (figure 5). The swarm trended N-S at depths of about 6 km. As the number of events/hour decreased, average magnitude increased. First order levelling surveys were completed across the epicentral area in 1986; about two weeks before the swarm; and the day after it began. The data suggested slight uplift of the area W of the epicentral zone relative to the E side, consistent with normal faulting, but the measured changes were within error limits (figure 6).

Figure 4. Number of events/hour measured at Long Valley caldera on station CNOC, 10 km from most epicenters (detection threshold about M 0). Courtesy of Stephen McNutt.

Figure 5. Epicenters of the 20-22 November Long Valley caldera earthquake swarm. Courtesy of John Estrem.

Figure 6. Preseismic (1986-88) and coseismic (1988-88) elevation changes across the epicentral area of the 20 November swarm at Long Valley caldera. Courtesy of John Estrem.

Further Reference. Langbein, J., 1989, Deformation of the Long Valley Caldera, Eastern California, from mid-1983 to mid-1988; Measurements Using a Two-Color Geodimeter; Journal of Geophysical Research, v. 94, p. 3833-3849.

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

Information Contacts: S. McNutt, California Division of Mines and Geology, Sacramento; D. Hill, John Estrem, and James Savage, USGS Menlo Park.

. . . . The number of shallow volcanic earthquakes began to increase sharply on 20 July. Based on seismic and visual data, VSI anticipated that an eruption would begin within two weeks, and the 15,000 residents of Makian Island were evacuated to Moti Island, ~6 km to the N.

On 28 July, 521 seismic events were recorded, and tremor began . . . at 2200. The eruption started the next morning at 1112 with a continuous thunderous explosion that was clearly heard on Moti Island. A dark ash cloud reached 8-10 km height. On 30 July at 1006, an explosion was followed by nuées ardentes that advanced E (along the Ng. Powate valley) and N (Ng. Para valley). Originating from ~1,200 m asl, the nuées ardentes descended to 250 m altitude, and some finally reached the sea. A series of smaller explosions began on 31 July and continued until 6 August, feeding ash columns that decreased from 6 to 1-2 km above the crater.

As of the first week in December, white fume was still rising weakly from the crater. Seismicity continued to decrease, with 17 tectonic and 14 volcanic earthquakes recorded 1-7 December.

Geologic Background. Makian volcano forms a 10-km-wide island near the southern end of a chain of volcanic islands off the west coast of Halmahera and has been the source of infrequent, but violent eruptions that have devastated villages on the island. The large 1.5-km-wide summit crater, containing a small lake on the NE side, gives the peak a flat-topped profile. Two prominent valleys extend to the coast from the summit crater on the north and east sides. Four parasitic cones are found on the western flanks. Eruption have been recorded since about 1550; major eruptions in 1646, 1760-61, 1861-62, 1890, and 1988 caused extensive damage and many fatalities.

Information Contacts: VSI.

"Activity continued at a low level during November with weak-moderate white vapour emissions from the two summit craters. Emissions from Southern Crater frequently contained small amounts of grey ash and blue vapour. On the 29th, red glow became sub-continuous and weak incandescent projections were observed. Rumbling noises from the same crater were heard throughout the month. Seismicity remained at a normal inter-eruptive level with a daily average of 1,120 low-frequency events. Tilt measurements indicated 3 µrad of inflation over the month."

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys" channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: I. Itikarai and P. Lowenstein, RVO.

Faint crater glow continued to be observed during nights with good visibility in October and November. Moderate steam emission covered 30-50% of the crater and blue volcanic fumes sometimes moved slowly downslope.

In October and November, 77 high-frequency events, 59 low-frequency events, and 119 harmonic tremor episodes were recorded. Mudflows were detected (by seismographs and by a lahar mapping team) along the SE slopes on 12 and 23 October, and along the SE and SW slopes on 4, 6, 20, and 21 November. The 12 October lahar moved at 2.5 m/s down Basud gully between 2347 and 0141 the next morning. On the 23rd, three lahars with velocities of about 3.2 m/s were triggered by a typhoon. The Basud River was incised by 4 m (near the Lidong-Basud boundary), and a jeep caught by a flow surge along the river was partially buried by debris. Continuous undercutting caused 3-4 m of a cement road to collapse and a house was carried away by a flow. No casualties were reported.

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

Information Contacts: PHIVOLCS.

Small events recorded late November-early December were attributed to freezing phenomena as winter came to N California. On 13 December at 2035, an M 1.9 earthquake, ~0.25 km SW of Medicine Lake glass flow, was recorded. During the next 75 minutes, nine events (M less than 1.9) were detected, followed by seven events on 14 December from 0121 to 0129. Seismicity was shallow (below 1 km) and had a high-frequency character. The 3-component station (LMD) is not currently operating.

Geologic Background. Medicine Lake is a large Pleistocene-to-Holocene, basaltic-to-rhyolitic shield volcano east of the main axis of the Cascade Range. Volcanism, similar in style to that of Newberry volcano in Oregon, began less than one million years ago. A roughly 7 x 12 km caldera truncating the summit contains a lake that gives the volcano its name. A series of young eruptions lasting a few hundred years began about 10,500 years before present (BP) and produced 5 km3 of basaltic lava. Nine Holocene eruptions clustered during three eruptive episodes at about 5000, 3000, and 1000 years ago produced a chemically varied group of basaltic lava flows from flank vents and silicic obsidian flows from vents within the caldera and on the upper flanks. The last eruption produced the massive Glass Mountain obsidian flow on the E flank about 900 years BP. Lava Beds National Monument on the N flank of Medicine Lake shield volcano contains hundreds of lava-tube caves displaying a variety of spectacular lava-flow features, most of which are found in the voluminous Mammoth Crater lava flow, which extends in several lobes up to 24 km from the vent.

Information Contacts: S. Walter, USGS Menlo Park.

Strombolian eruptions accompanied by lava extrusion continued at Pacaya during 1988. The SW flank lava flow observed in February remained active for about 2 months. In March and April lava extrusion began from new vents about 200-400 m below the summit. Lava effusion stopped in May, but resumed 26 May from new vents on the SW flank and continued into June, feeding flows that traveled about 1 km down the W, WSW, SW, SSW, and S flanks. Counts of explosions derived by Otoniel Matías from INSIVUMEH seismic records (figure 3) indicate that explosions increased from a few hundred/day in early June to about 2,000/day in mid-June. Ash fell 2.5 km from the volcano on 11 June. Explosions dropped to a few hundred/day in July and lava effusion stopped from all but one vent. Activity remained low in August, although a SW flank lava flow was emitted on 23 August. A lava flow formed on the NW flank at about 2330 on 6 September, and was active until 18-19 September. When the seismograph resumed operation in mid-September, daily explosion counts ranged from about 1,500 to 2,300. On 20 September a new lava flow began on the S flank at about 2,100 m altitude. Activity increased late September to early October, when some seismic events were felt on Cerro Chino (on the NW somma rim) and rumblings were heard in the S part of Guatemala City. A new lava flow was emitted 4-5 October from a vent at 2,070 m on the SW flank. The daily number of explosions peaked at 3,300 on 5 October, and gradually decreased after 10 October to fewer than 1,000 by 29 October, when lava emission ceased.

Figure 3. Estimated number of explosions/day at Pacaya, June-October 1988. Explosion events were counted on a vertical section of each day's seismic records from station PCG (on Cerro Chino, 1.5 km NW of MacKenney Crater) then extrapolated to yield 24-hour values. Upward-pointing arrows indicate the appearance of a new lava flow, downward arrows the cessation of feeding for a previously active flow; 2-headed arrows indicate the same observations but for two flows. Courtesy of Otoniel Matías.

During fieldwork 12-26 November on the S side of Pacaya, geologists observed MacKenney Crater during another period of increased activity. On 20 November the active vent was seen from the summit of the 1775 cone. More or less continuous weak Strombolian explosions ejected bombs to a few tens of meters above the crater rim. These were punctuated several times a minute to every few minutes by detonations from stronger explosions that ejected incandescent bombs and blocks to 100-200 m height from a vent at the NW end of MacKenney Crater. Some incandescent blocks rolled 400 vertical meters down the flanks of the cone as far as the moat between MacKenney Crater and the N somma rim. Incandescent ejecta was sometimes visible in daylight from the somma rim in contrast to the less vigorous February activity, and daytime explosions could also be seen from Guatemala City, 25 km NNE.

An area of active fumaroles was located on the N flank about 100 m below the summit. The accumulation of near-vent ejecta in the absence of major explosions since February had considerably narrowed the crater's width and recently raised MacKenney cone to an altitude slightly above that of the 1775 cone, which had formed the highest point on Pacaya at 2552 m. A lava flow originated in early November from a vent high on the SW flank at about the elevation of the saddle between the two summit cones. Lava flowed in several channels to about 2,000 m altitude on the SW flank, and extrusion was continuing on 26 November.

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: Otoniel Matías, Jorge Girón, and Enrique Molina, INSIVUMEH; Jim Vallance, Michigan Tech; Lee Siebert, SI.

"Seismic activity continued to decrease in November with a total of 301 earthquakes. The daily number of events averaged <20 with the highest number (54 events) recorded on the l4th. Four locatable events were detected: on the E side (1) and N of (2) Greet Harbour, and on the W side of Matupit Island (1). Ground deformation rates remained low. Levelling on 3 November showed 12 mm of uplift at the S part of Matupit Island since 20 October. EDM data showed slight expansion (5 microstrain) at Greet Harbour's entrance."

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

Information Contacts: I. Itikarai and P. Lowenstein, RVO.

Energy released in November by high- and low-frequency earthquakes and volcanic tremor remained similar to October values. A tremor episode on 23 November was associated with fumarolic activity and a brief landslide in the canyon of the Río Azufrado, 2 km NE of the crater (figure 21).

Figure 21. Epicenters of high-frequency earthquakes, November 1988, and the position of the Palestina Fault. Courtesy of the Observatorio Vulcanológico de Colombia.

Although the tremor episode lasted only a few minutes, it produced one of the largest displacements of the energy release curve since 1986. A slight increase in seismicity followed for the next few hours. The month's main high-frequency activity was centered parallel to the regional Palestina Fault, occurring in two clusters. Depths were between 0.5 and 6 km. No significant deformation was measured during the month.

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

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.

INSIVUMEH geologist Otoniel Matías reports that the dacite lava flow that extended 3.5 km SSW of the active Caliente vent by February 1988 (13:02) had stagnated there since February, although extrusion was continuing at a reduced rate. Geologists noted continuing small avalanches from the upper portion of the flow on 23 November. The middle portion of the block lava flow (about 1.5 km NNW of Mirador La Florida) was steaming, but remained stagnant. However a new lobe had advanced along the W margin of the flow to about 1.3 km from Caliente vent (figure 6).

Figure 6. Map of Santiaguito Dome, showing the ages of its domes. The 1986-88 flow is emphasized by a shaded pattern; other recent lobes are stippled. Successive positions of the 1986-88 flow are dated, and the approximate November 1988 location of the new lobe is shown. Modified from Rose (1987).

Small to moderate vertical explosions from the Caliente vent have continued. The number of explosions, as determined from field observations and seismic records from stations 5 km NNW and 2.6 km S of Santiaguito, has been tabulated by Matías since June (figure 7). Daily explosion totals during June ranged from 5 to 22. Activity decreased steadily through most of July, but increased again August-October, reaching a peak of 28 explosions on 19 October. Larger explosions produced steam and ash columns that rose 1-2 km above Caliente vent; secondary explosions to 400-1,000 m height occurred at roughly similar rates. The number of small block-and-ash avalanches from the active lava flow ranged from about 100 to 250/day in June and dropped to around 50-150/day in July, paralleling the drop in explosion frequency. From August through October the daily number of avalanches ranged from about 100 to over 300.

Figure 7. Number of daily explosions (bottom) and an extrapolation of the number of daily avalanche events (top) recorded by seismic stations near Santiaguito, June-October 1988. Field observations of eruptive phenomena were correlated with records from a portable seismograph to identify their seismic signatures. Courtesy of Otoniel Matías.

The sediment load from Santiaguito has continued to impact downslope river drainages, but the effects of the 1988 rainy season were relatively mild compared to past years. The El Palmar area was observed in November to be essentially unchanged from February, as the Río Nimá II remained contained within perched levees above the town. However, downstream lahars destroyed the supports of an important foot suspension bridge across the Río Samalá below San Felipe, about 14 km SSW of Santiaguito (figure 8); reconstruction of this bridge was continuing in November. The Carretera Internacional del Pacífico (CA2) below Santa Cruz Muluá was closed briefly in late August and around 4-5 September as floods deposited sand and gravel over a 150-m section of the highway. The Río Samalá was again diverted by rainy season lahars into the Río Ixpatz drainage, innundating portions of the Finca San José La Granja (about 5 km S of the sharp bend in route CA2). This diversion of river courses into parallel drainages has occured each year since 1983. The annual construction of barriers to return the Samalá to its normal course had not been completed in November. The Samalá also partially diverted the Río Muluá to the east.

Figure 8. Sketch map of rivers and towns S of Santiaguito, modified from a February 1988 sketch by William Rose. Locations of drainages are approximate. Arrows mark the location of the diversion of the Río Samalá into the Río Ixpatz and the former confluence of Ríos Nimá I and II near El Palmar. Points 1 and 2 indicate the damaged bridge below San Felipe and the flooded segment of route CA2.

Geologic Background. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing W towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Information Contacts: Otoniel Matías and Enrique Molina, INSIVUMEH; Jim Vallance, Michigan Tech; Lee Siebert, SI.

During an October visit to the crater, activity remained at previous levels. Fumaroles were concentrated in five groups with gas temperatures ranging from 98 to 108°C. Gas was released under pressure in four of the five groups, to 2-6 m height.

Geologic Background. The Sashiusudake (also known as Baransky) volcanic complex along the Pacific coast in the central part of Iturup Island consists of an eroded Pleistocene volcano that is capped by a Holocene stratovolcano. A young summit lava dome is cut by a NW-trending chain of small explosion craters. A group of flank cones farther to the NW with a similar NW-SE orientation is partially surrounded by lava flows from the central crater of the andesitic-dacitic volcano. Lava flows from descended 4-5 km SE to reach the Pacific Ocean along a broad front. The only historical eruption occurred in 1951, when local inhabitants reported weak explosive activity at the summit. Strong solfataric activity continues from the summit and several flank craters, and the SW flank geothermal field contains hot springs and geysers. A small hydrothermal explosion took place in 1992 at an exploratory well in the SW-flank geothermal field.

Information Contacts: G. Steinberg, Yuzhno-Sakhalinsk.

Geologists visited Stromboli in October and November. Surface temperatures associated with Strombolian and fumarolic activity were studied for comparison with remotely sensed data. Temperatures were recorded using a Minolta Cyclops 33 radiometer operating at [8-14 mm] wavelength.

Craters 1, 3, and 4 were estimated to be 45 m deep; the floor of Crater 2 was not seen. Crater 1 contained three active vents (figure 2). On 26 and 27 October, a circular pit ([vent 1-1]) 1 m in diameter contained lava that glowed bright orange in daylight. Infrequent incandescent scoria and gas eruptions from vent [1-1] closely followed activity in [vent 1-2], a rubbly surface ~3 m away. At 10-30-minute intervals, [1-2] was ruptured by violent emission of blue incandescent gases (visible only after dark) followed by glowing scoria ejection. Ejecta from [1-1] and [1-2] usually fell within the crater, but on one occasion fell several meters beyond the S rim. A 2-m-diameter glowing vent ([1-3]) almost continuously ejected spatter to 50 m height. The maximum brightness temperature for the lava surface in vent [1-3] was 835°C, although readings sometimes fell as low as 240°C (when taken through dense fumes that frequently accumulated within the crater).

Figure 2. Sketch of active craters at Stromboli, October-November 1988. Courtesy of C. Oppenheimer and D. Rothery.

On 28 October, vent [1-1] had increased in area four-fold but was no longer glowing visibly in daylight. Incandescent scoria, ejected at 5-30-minute intervals, usually fell inside the crater although medium-coarse ash often reached the crater rim. Tephra ejections were usually immediately preceded by brief, rapid, bluish-gray steam emission and a roaring sound. Vent [1-3] was faintly glowing in daylight. Separate activity at former site [1-2] was no longer evident.

When geologists returned 3-6 November, a large volume of dark scoria and agglutinate had accumulated within the crater. Two new incandescent cracks had developed near site [1-1] and sharp cracking noises, like pistol shots, were often heard. Activity was dominated by ~7 explosions/hour at site [1-1]. Two distinct eruption types (ejecting tephra well above the crater rim) were recognized: very brief, violent detonations expelling gases and comminuted scoria; and longer duration (5-10-second) ejections of incandescent, highly vesiculated bombs. Site [1-3] glowed brightly but erupted infrequently.

Crater 2 was inaccessible and could not be observed directly. The crater continuously emitted high volumes of thick white fume. An eruption on 28 October that ejected a brown ash plume may have originated from this crater. A very low inner wall separated craters 3 and 4, and it was difficult to determine the origin of some eruptions. Dirty-brown plumes, attributed to Crater 3, frequently reached a height of 200-300 m above the crater rim. Brief (3-8-second) powerful incandescent bomb ejections at 5-40-minute intervals deposited tephra onto the crater's outer flanks. Infrequent explosions, clearly from Crater 4, obliquely ejected incandescent scoria over the crater's E rim, accompanied by small mushrooming ash columns. On 5 November, two small glowing vents, a few meters apart, were observed on the crater floor.

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5,000 years ago due to a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: C. Oppenheimer and D. Rothery, Open Univ.

Local seismicity was at a high level in November. A seismometer, 4.5 km NW of the three craters active in 1962, recorded 29 events on 15 November, 9 on the 19th, and 10 on the 26th. The month's total increased to 93 from [43] in October. Four shocks were felt, three on 15 November and one on the 27th. Epicenters were estimated to be around crater 62-2. On 22 November, personnel at the JMA Tokachidake Observatory saw a 1,200-m steam plume emerge from crater 62-2, the highest since a 1,400-m plume in June 1981.

Addendum. The press reported that Tokachi began to erupt on 19 December at 2148 [but see 13:12], ejecting incandescent tephra and a plume that rose about 2 km. Ash fell on two cities more than 100 km NE of the volcano. A lahar about 30 m wide flowed 2.5 km downslope. Children within 25 km of the volcano were kept home from school the next day and residents were warned by officials to be ready to evacuate. The eruption had apparently declined, but seismicity was continuing.

Geologic Background. Tokachidake volcano consists of a group of dominantly andesitic stratovolcanoes and lava domes arranged on a NE-SW line above a plateau of welded Pleistocene tuffs in central Hokkaido. Numerous explosion craters and cinder cones are located on the upper flanks of the small stratovolcanoes, with the youngest Holocene centers located at the NW end of the chain. Frequent historical eruptions, consisting mostly of mild-to-moderate phreatic explosions, have been recorded since the mid-19th century. Two larger eruptions occurred in 1926 and 1962. Partial cone collapse of the western flank during the 1926 eruption produced a disastrous debris avalanche and mudflow.

Information Contacts: JMA; AP; UPI.

Fumarolic activity, concentrated at the foot of the lava dome, continued at a constant level. The temperature of the hot lake in the same area had not changed, but varied within the lake from 34 to 84°C. The temperature of the stream that flowed from the lake remained at 30-34°.

Geologic Background. Tomariyama, also known as Golovnin, forms the southern end of Kunashir Island, across the Nemuro Strait from Hokkaido. Explosive activity has dominated in the formation of this andesitic-dacitic volcano; no lava flows are exposed. The gently sloping stratovolcano, is truncated by a 4-5 km wide caldera that formed during a series of late-Pleistocene eruptions beginning about 43,00 years ago. Several lava domes were subsequently emplaced on the caldera floor. Topographic highs outside the caldera rim define a series of lava domes extruded along a ring structure or an outer caldera. A 1 x 2.5 km caldera lake on the northern side of the inner caldera drains through a narrow breach in the western caldera wall. Solfataric activity occurs at the northern lake shore and at explosion craters (one of which contains a hot crater lake with reported temperatures from 36-100 degrees C) that cut the caldera-floor lava domes. The only known historical eruption was a minor explosion in 1848.

Information Contacts: G. Steinberg, Yuzhno-Sakhalinsk.

"Ulawun's summit crater was covered by clouds during most of November. When visible, weak-moderate white vapour emissions were observed. Vapour emission intensified during the last week of the month. November's recorded seismicity was mainly characterized by an average of 9 bands of low-amplitude, high-frequency harmonic tremor, each lasting 1-2 hours. The number and size of accompanying B-type events also increased with a maximum of 1,055 recorded on the 19th.

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

Information Contacts: I. Itikarai and P. Lowenstein, RVO.

Geologists visited Vulcano on 25 and 30 October and 1, 7, and 8 November to obtain spatial and temporal surface temperature distributions (figure 5). Fumaroles typically formed linear zones of acid steam discharge. Transects of a zone extending 40 m somewhat radially along the N rim of Gran Cratere were surveyed.

Figure 5. Apparent surface temperature profiles transverse to an elongated fumarolic zone on the N rim of Vulcano's Gran Cratere measured at 0930 (filled circles) and 1230 (open circles) on 8 November. Temperatures were recorded using a Minolta Cyclops 33 radiometer operating at [8-14 µm] wavelength. Each datum is the integrated temperature for the whole field of view of the radiometer, between 2.5 and 4.5 cm in diameter. The later survey shows warming of the downwind side of the zone by hot clouds of condensates blowing across the area. Courtesy of C. Oppenheimer and D. Rothery.

Gas temperatures (recorded by a thermocouple) were stable during the visits. The highest temperature measured was 396°C, although surface temperatures above 300°C were uncommon and highly localized (<0.01 m²) near vents. Because sublimates were unstable above about 150°C, there was a gray sublimate-free belt within 5-40 cm of the vents, flanked on either side first by white ammonium chloride, then yellow sulfur sublimates.

Further Reference. Oppenheimer, C., and Rothery, D., 1991, Infrared monitoring of volcanoes by satellite: J. of the Geological Society, London, v. 148, p. 563-569.

Geologic Background. The word volcano is derived from Vulcano stratovolcano in Italy's Aeolian Islands. Vulcano was constructed during six stages during the past 136,000 years. Two overlapping calderas, the 2.5-km-wide Caldera del Piano on the SE and the 4-km-wide Caldera della Fossa on the NW, were formed at about 100,000 and 24,000-15,000 years ago, respectively, and volcanism has migrated to the north over time. La Fossa cone, active throughout the Holocene and the location of most of the historical eruptions, occupies the 3-km-wide Caldera della Fossa at the NW end of the elongated 3 x 7 km island. The Vulcanello lava platform forms a low, roughly circular peninsula on the northern tip of Vulcano that was formed as an island beginning in 183 BCE and was connected to Vulcano in about 1550 CE. Vulcanello is capped by three pyroclastic cones and was active intermittently until the 16th century. The latest eruption from Vulcano consisted of explosive activity from the Fossa cone from 1898 to 1900.

Information Contacts: C. Oppenheimer and D. Rothery, Open Univ.

When geologists visited ... on 16 November, fine pink/red ash emerged from Hitchhiker vent, and moist acidic tephra fell near 1978 Crater. Since the last visit, on [14] October, up to 10 mm of ash had been deposited near its E rim. A new noisy fumarole (~1 m in diameter) discharged transparent blue vapor from the W edge of 1978 Crater's floor, near the location of the ephemeral vent documented 20 November 1987. Other fumaroles emitted gases at temperatures as high as 681°C. No incandescence was observed.

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

Information Contacts: E.F. Lloyd, NZGS Rotorua.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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