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).

The eruption from the S flank of Mt. Cameroon that began on 28 March was followed by the opening of a second set of fissures opening on 30 March, sending a voluminous aa flow towards the ocean that continued throughout the first two weeks of April (BGVN 24:03 and 24:04). On 11 April the flow front was 150-200 m wide and 30 m thick and progressing at a rate of several m/hour; lava production ended on 14 April. A notice on 5 June from Henri Hogbe Nlend, the Minister of Scientific and Technical Research (Ministre de la Recherche Scientifique et Technique, MINREST), said abnormal and repeated high-amplitude seismic events were recorded on the night of 30 May by seismographs in Ekona. This was the first time since the end of the eruption that such events have been registered.

On July 11 the head of the Scientific Committee monitoring Mt. Cameroon, Samuel Ayongue, was quoted in The Post, a weekly newspaper, as being "...worried about the tremors going on now because they have increased in intensity and frequency." According to Ayongue, the tremors were being caused by magma refilling spaces created during the eruption. It was difficult to locate the earthquakes because of inadequate seismic equipment.

The Assistant Director of the Institute for Mining and Geological Research (IRGM) at Ekona, Richard Ubangoh, disclosed on 13 October that during 4-6 October, 54 seismic events ("earth tremors") were recorded. A notice to the Minister of Scientific and Technical Research confirmed earlier reports of frequent felt earthquakes by residents living on the foot of Mt. Cameroon. A source at MINREST, quoting the notice for Isaha'a Boh, stated that the events "... were not serious [enough] to cause any damage or immediate threat." The Assistant Director regretted that "... the equipment in use presently, are quite old and cannot provide reliable results." While waiting for 10 new seismographs from Europe in the next six months Ubangoh stated that provisional equipment would be installed at the foot of the mountain in the next three months.

Geologic Background. Mount Cameroon, one of Africa's largest volcanoes, rises above the coast of west Cameroon. The massive steep-sided volcano of dominantly basaltic-to-trachybasaltic composition forms a volcanic horst constructed above a basement of Precambrian metamorphic rocks covered with Cretaceous to Quaternary sediments. More than 100 small cinder cones, often fissure-controlled parallel to the long axis of the 1400 km3 edifice, occur on the flanks and surrounding lowlands. A large satellitic peak, Etinde (also known as Little Cameroon), is located on the S flank near the coast. Historical activity was first observed in the 5th century BCE by the Carthaginian navigator Hannon. During historical time, moderate explosive and effusive eruptions have occurred from both summit and flank vents. A 1922 SW-flank eruption produced a lava flow that reached the Atlantic coast, and a lava flow from a 1999 south-flank eruption stopped only 200 m from the sea. Explosive activity from two vents on the upper SE flank was reported in May 2000.

Information Contacts: Isaha'a Boh Cameroon, Media Research and Strengthening Institute, P.O. Box 731, Yaounde, Cameroon.

The information for this report was compiled by Boris Behncke at the Dipartimento di Scienze Geologiche, University of Catania (DSGUC), and posted on his internet web site. The compilation was based on personal visits to the summit, observations from Catania, and other sources cited in the text. Additional information was provided by Jean-Claude Tanguy (DSGUC), mostly about the activity during September.

Mild eruptive activity resumed at Etna's summit craters (figure 80) in early June, and gradually increased through late August before culminating with a powerful eruptive episode from the Voragine on 4 September. During the same period, lava continued to flow from fissures at the base of Southeast Crater (SEC), and occasional phases of mild lava spattering built hornitos and spatter cones at the eruptive vents.

Figure 80. Sketch map of the summit craters of Etna, based on fieldwork between 7 September and 1 October 1999 by Behncke and others. Courtesy of Boris Behncke.

Activity during June 1999. During early June, lava emission from the 4 February fissure on the SE base of SEC continued at a low rate. Lava issued from ephemeral vents and flowed for a few hundred meters towards the W face of the Valle del Bove (VdB).

The following information regarding activity from 30 May to 2 June was provided by John Guest (University College London, UK) and Angus Duncan (University of Luton, UK). Several explosions were heard from the summit craters on 30 May. On 1 June a brief bright red glow was seen over Bocca Nuova (BN). The active lava pile in the vent area at the foot of SEC on 2 June had increased in thickness since 30 May. Fresh lava now partly buried the 'old' tumulus of altered lava blocks, but a new tumulus had formed a few meters downflow. On 3 June Sandro Privitera (IGGUC) observed three emissions of reddish gray ash to more than 500 m above the crater.

On 4 June the two main sites of activity were generally the same as on 19 May (BGVN 24:05): an effusive vent ~25 m below the hornitos at the upper end of the fissure that became active on 4 February, and a cluster of vents at about 2,600 m elevation on the W slope of the VdB. The upper site had shifted ~30-40 m upslope. During the 16 days between the two visits, the site of lava emission had shifted frequently, sending lava flows in various directions. By 4 June lava flows had covered most traces of the tumulus collapse depression formed on 12 May. It appeared that the effusion rate had remained nearly constant for about 2 months (at ~1 m³/s). About 25-30 x 10⁶ m³ of lava had accumulated since 4 February on the western VdB rim and the slope below.

A brief visit on 10 June by Behncke and Francesca Ghisetti (DSGUC) revealed that the output of lava from the 4 February fissure had increased. The active vents were ~10-20 m below the hornitos at the upper end of the fissure. One vigorous vent was on the fissure, but lava also issued from within and on the margins of recent flows on the SW side of the lava field. A flow down the N side of the lava field appeared to have spilled over the rim of VdB. One vent continued to emit lava on the western VdB slope.

Weak explosive activity at the 4 February fissure resumed in mid-June, accompanied by an increase in the lava output. According to Giuseppe Scarpinati (L'Association Européenne Volcanologique, LAVE), an intermittent glow in the eruption area was visible from Acireale (SE of Etna) on the evening of 16 June. This glow was also clearly visible from Catania on the following evenings, and lava was seen extending from the glow area.

By the afternoon of 19 June one large and several smaller hornitos had grown on a large lava shield, ~50-80 m below the cluster of hornitos built during February-March 1999. Two lava rivers extended a few hundred meters in the direction of the VdB. The effusion rate had increased to 2-3 m³/s (it had been less than or equal to 1 m³/s during the previous month), and the volume of lava emitted since 4 February exceeded 30 x 10⁶ m³.

Between 19 and 23 June there was a notable decrease in activity at the eruptive fissure. After a visit on 26-27 June, Scarpinati reported that variable emission of lava from the 4 February fissure continued. Scarpinati also noted that the Voragine produced explosions, but made no direct observations.

On the evening of 29 June Behncke noted that the 4 February fissure had one eruptive site that produced mild lava spattering and two lava flows. Spattering from three closely spaced vents threw blobs of lava up to 3 m away. A partially drained lava tube containing incandescent but stagnant lava was seen 50 m downslope from the vents. The output was estimated at 1-3 m³/s. The SW ("diaframma") vent in the Voragine produced loud explosions every 2-10 minutes that ejected incandescent bombs above the vent.

Activity during July 1999. Another summit visit by Behncke on 1 July benefitted from perfect viewing conditions and very little wind. The generally flat floor of NEC had changed little since 5 October 1998, but now contained a large pit emitting a high-pressure gas plume charged with SO₂. There were periods lasting a few minutes when the noise level increased notably, and the plume became much denser; one time it contained brownish ash. BN had its usual two large eruptive centers, one in its NW part and the other at the base of its SE rim. While the latter periodically emitted plumes of grayish-brown ash, the former was the site of alternating ash emission and magmatic degassing.

The Voragine, according to a guide, had intensified its activity on 26 May. On the morning of 1 July explosions occurred at the SW vent every 1-10 minutes. Explosions at the SW vent started with a noise followed by large bombs that rose tens of meters above the vent, and sometimes even tens of meters above the crater rim itself, and then by a brownish ash plume. A few fresh vesicular bombs were found on the outer SW slope of the Voragine.

Claude Grandpey (LAVE) visited the eruptive fissure on 2 July and observed vigorous lava emission. The next day, lava emission had decreased. Activity was intense at the SW vent of the Voragine, with explosions ejecting bombs outside the crater on the northern side. Many bombs also fell into BN. The central vent in the Voragine had periodic gas and ash emissions. In the BN, noisy activity occurred in the SE vents (which during the 1 July visit only emitted ash), while the NW vent was relatively quiet.

The summit area was visited on 6 and 7 July by Behncke, Peter Ippach, and Eduard Harms (German Volcano Museum, Mayen, Germany). During the first of these two visits there was strong gas emission from the central pit of the NEC, and every 10-45 minutes there were explosive ejections of rocks and ash emissions. In the Voragine, explosive activity at the SW vent had decreased, and only one explosion was observed during two hours. However, the central vent was the site of Strombolian eruptions every 1-10 minutes. Incandescent bombs were ejected but only in one case rose as high as the rim of the vent, which was estimated to be at least 35-40 m deep and had a pit about 5 m wide in its floor. Recently ejected bombs up to 1.5 m long littered most of the Voragine floor.

The 7 July visit to the fissure disclosed continuing activity from two major effusive vents, one located in the area of the hornitos that formed in the past few weeks, while the other lay ~100 m downslope at the end of a lava tube. During four hours of observations, explosion sounds coming from the Voragine (and maybe also from BN) were heard every 5 to 45 minutes.

On 9 and 10 July, Behncke, Ippach, and Harms visited the summit area again, and additional information about the activity on 10-11 July was provided by Scarpinati and Charles Rivière (of Tremblay-en-France, France). Observations were restricted to the area of the 4 February fissure, but Rivière visited the summit craters early on 10 July. At the fissure, three vents were active at the tumulus ~150 m downslope from the uppermost February-March hornitos. Several lava flows were active during 9-10 July, and incandescent lava was seen in many places on the lava field. Lava also issued from several vents along the N margin of the flow-field.

Rivière, who visited the summit craters during the forenoon of 10 July, reported continuous pyroclastic activity deep within the pit of the NEC. In the Voragine, Strombolian activity occurred from the central andSW vents, with bombs at times rising high above the crater rim; Rivière noted that explosions occurred about every two minutes.

Scarpinati and Alain Catté (LAVE) observed the activity from the late afternoon of 10 July through the next morning. Shortly after 1800 on the 10th, the tumulus where the main vent had been emitting lava was seen to "inflate rapidly, and then lava came down on all its sides, forming three lava rivers." On the next morning, none of the vents on the tumulus were active, but a new vent had formed 30 m SE, burying the tourist path to the vent area; lava effusion diminished later that morning. Between 13 and 24 July lava continued to flow from the 4 February fissure, but the amount was relatively small, and short-lived flows extended only a few hundred meters downslope.

On 16 July Grandpey noted clouds of brownish ash from NEC. The Voragine was quiet, but Grandpey learned that the SW vent was active earlier during the week (around 12 or 13 July) with explosions, while lava was visible at the bottom. The NW vent inside BN was quiet, and parts of it had collapsed. Strong explosions heard every few minutes in the SE vent had been audible throughout the night.

Activity was particularly intense in the Voragine on 18 July when Rivière filmed the SW vent. Lava had again risen to ~20 m below the rim, and a small, dome-shaped mound of lava produced numerous small explosions. The mound was partly incandescent and was blown to pieces in some of the larger explosions, then rose again. During the days preceding 24 July, however, Rivière observed a diminution of activity in the Voragine, but there was explosive activity within BN.

The summit craters were visited again on 28 July by Behncke, Carmelo Monaco and Angelita Rigano (DSGUC), and others. Deep within the central pit of the NEC there were near-continuous detonations. Within the BN, explosive activity occurred deep within the two main vents. The SE vent produced near-continuous emissions of brownish ash. The Voragine central vent produced powerful explosions and at times prolonged fountains of incandescent bombs, some of them up to 1 m across. Some of the explosions ejected bombs to ~100 m above the crater rim. Many eruptions were accompanied by high-pitched roaring noises indicating high-pressure gas emission from the top of the magma column in the vent, which had risen by tens of meters since last observed directly by Behncke and others on 6 July. At the 4 February fissure, lava emission continued at a low rate. One area of effusive activity lay on the NE side of a large tumulus ~100 m downslope from the upper hornito cluster. The effusion rate was ~1-2 m³/s, and the volume of lava emitted since 4 February was estimated to exceed 35 x 10⁶ m³.

1 August-3 September 1999. Axel Timm from Germany visited on 15 and 16 August and made the following observations. There was little activity in the BN on 15 August, with quiet degassing at the NW vent, while dilute ash clouds were emitted at intervals of several hours from the SE vent. In the Voragine there was only gas emission from the SW vent, but minor eruptions occurred at intervals of 5-60 minutes from the central vent. Rumbling noises and dense gas emissions came from deep within NEC. Several small lava flows issued from the hornito area at the upper end of the 4 February fissure.

On 16 August the SE vent continued to quietly emit ash to 50-100 m above the vent at intervals of about 30 minutes. Voragine eruptions every 10-30 minutes from the central vent varied from noisy gas emissions to explosions that ejected bombs and scoriae far beyond the rim of the vent.

Grandpey reported that lava effusion from the 4 February fissure decreased notably around 20 August. Activity ceased on 25 August, and no effusive activity occurred thereafter for two days. Grandpey noted that the end of the effusive activity corresponded to a increased activity inside the Voragine. On 24 August he saw explosions from two small vents on the N rim of the SW vent. On 26 August Grandpey observed the central part of the Voragine inflate over a surface ~50 m in diameter, followed by an explosion that disrupted about half of that area, ejecting large pyroclasts. A few minutes later a much stronger explosion sent bombs as far as the center of BN and all over the W slope of the Voragine. Similar explosions followed through the next day. When Grandpey returned on 27 August, a new "cavity" had formed at the center of the Voragine and explosions were occurring near the SW vent.

The cessation of activity from the 4 February fissure on 25 August was followed two days later by the opening of a ~50 m long fissure located 40-50 m N of the hornitos. Mild Strombolian activity occurred during the following days and a small lava flow moved along the rim of the lava field.

4 September 1999 eruption from the Voragine and SEC activity. Scarpinati was observing the effusive activity at the new vents at the SE base of the SEC cone at around 1700 on 4 September and noted a hissing sound at around 1745, which gradually increased until it was "like a jumbo jet taking off." Guides at the Torre del Filosofo hut heard a loud detonation at about 1810, and saw intense red glow above the main summit cone ("the BN was incandescent all over"). Strong continuous incandescence between the Voragine and NEC suggested that lava was flowing down the E side of the main summit cone. At about the same time, Scarpinati saw through a gap in the clouds that gas and ash were rising from the summit area. Shortly afterwards he heard the crashing of impacting blocks and bombs, and retreated to the Piccolo Rifugio at about 2,500 m elevation. The climax of the eruption probably occurred between 1900 and 1930, judging from the audible detonations.

Bad weather during most of 4 September precluded observations, but a relatively clear view from Piano Provenzana (on the N flank, ~6 km from the Voragine) revealed the sudden uprise of a dark, ash-laden column that was bent eastwards. Observers at the Piano delle Concazze, about 2,600 m elevation on the N flank and ~2.5 km from the Voragine, enjoyed a splendid view of the eruption. By the time of their arrival, probably between 1830 and 1900, a huge lava fountain was rising hundreds of meters above the Voragine, and a pitch-black, tephra-laden eruption column rose ~2 km high before being blown E by winds. Large bombs fell onto the upper slopes of the NEC, which continuously emitted a dense brown ash plume, and onto the W side of the fountain. At the climax of the activity, the fountain roared to at least 1,500 m above the Voragine, an unprecedented height in the recent history of Etna.

At 1945 the cloud cover lifted, and the group at Piccolo Rifugio saw "an awesome spectacle of gigantic explosions" occurring at intervals of about 2 minutes, one of which was described by Scarpinati as "the biggest I have ever seen" (he has climbed Etna more than 500 times in the past 35 years), and which showered the main summit cone with meter-sized bombs. Some of this late activity may have come from the BN.

By 2045 all activity on the main summit cone had ended, but explosive activity began from the SEC summit vent consisting of dark "smoke" emissions mixed with incandescent pyroclasts. Ten minutes later the activity became purely Strombolian with 20-25 explosions per minute. Observations from the Piccolo Rifugio continued until about 2200 and were curtailed by bad weather; later that evening lava began to spill from the lower part of the fissure on the SE flank of the SEC cone. Lava supply increased at the vents that had become active on 27 August, and on early 5 September, a lava flow ~1 km long was observed by J.-C. Tanguy and local guides.

Effects of the 4 September 1999 eruptions. Soon after the beginning of the eruption, loud detonations were audible in villages and towns around the volcano. This was followed by a fall of scoriaceous lapilli on the E flank, extending to the coast near the town of Giarre, more than 15 km from the summit (figure 81). Many of the lapilli were walnut-sized, and some, in the area of Fornazzo, were up to 10 cm long (observation by J.-C. Tanguy). Eyewitnesses reported that some of the larger fragments were still hot when falling near the villages of Milo, Fornazzo, and Sant'Alfio, but not hot enough to set vegetation afire. Larger clasts broke windshields and seriously damaged vineyards and fruit gardens. In a narrow sector from the Milo-Fornazzo area towards the coastal strip near Giarre the pyroclastic deposit was several centimeters thick, and traffic was disrupted due to scoriae on roads. On the beach of the Ionian Sea between Riposto and Fondachello, scoriae 5-6 cm in diameter were not rare. Press reports put the damage to agriculture and infrastructure at several tens of billions of Lire (several tens of millions of US $). According to the Catania-based newspaper "La Sicilia," ~1 x 10⁶ m³ of pyroclasts fell on Giarre alone, while the full volume of pyroclasts was given as 5 x 10⁶ m³, a value that fits well with observations by Behncke and others.

Figure 81. Sketch map showing the distribution of pyroclasts from the 4 September 1999 eruption of the Voragine, based on field work during the week following the eruption. Courtesy of Boris Behncke.

Field investigations were made by Behncke and Werner Keller (Proyecto de Observación Villarrica/Internet) in the area of Milo, Fornazzo, and Giarre on 6-8 September, and during a summit visit on 7 September. Measurements were made of the thickness of the deposit in various locations before heavy rainfall swept part of it away, and when the cleaning of roads was still in an initial stage. During the afternoon of 7 September visibility was hampered by clouds, but the effects of the eruption were striking. The cones of the summit craters were hit by countless bombs up to 5 m in largest dimension and lithic blocks up to 1 m across. Many bombs and some blocks had fragmented upon impact, and others were found up to 10 m outside the craters created by their impact. Projectiles had arrived on both fairly flat and vertical trajectories. Some of the larger bombs were still warm about 60 hours after their emplacement.

On the S flank of the main summit cone the accumulation of juvenile scoriaceous pyroclasts had apparently been so rapid that the deposit began to slide down the steep flank, forming something like a dry debris flow that extended ~500 m down the slope to its base. In its distal portion the flow ended in two distinct lobes ~1 m thick. About 80% of this deposit consisted of juvenile clasts 10-30 cm in diameter whose edges were rounded while sliding down the slope, the other 20% were older, slightly smaller clasts (reddish scoriae and gray lithic blocks).

Brief glimpses through the clouds permitted a view on the Voragine from ~500 m W of the crater rim. The heavy fallout close to the crater almost healed the large scar cut into the S flank of the adjacent NEC cone during the 22 July 1998 Voragine eruption (BGVN 23:11). On the SW crater rim, the rapid accumulation of fluid ejecta formed a lava flow ~300 m wide and 250-300 m long. Two similar fountain-fed flows were emplaced on the E side of the Voragine, the longer of which traveled ~700 m towards the VdB. Guides on the N flank indicated that another fountain-fed lava flow cascaded into the Bocca Nuova.

On the lower E flank the lapilli deposit extended in a narrow strip E towards the coast near Giarre. Five communities (including Milo, Mascali, and Giarre) suffered heavy fallout. Going northwards from Zafferana, on the SE flank, the southern margin of the fall deposit was in the forests between Petrulli (~2 km N of the center of Zafferana) and Milo, where isolated scoriaceous lapilli with 1-3-cm diameters occurred. Closer to Milo (1.5 km farther N) the number of clasts per square meter increased as did their mean diameter, and on the southern margin of the village the deposit became continuous. Most of the deposit consisted of lapilli-size scoriae, with little ash mostly coating leaves and grass. The largest clasts found in the S part of Milo were 7 cm across, and many reached 5 cm. In the N part of Milo, the thickness of the deposit exceeded 5 cm, and many leaves were damaged. In the S part, ~1.5 km from Milo, the deposit was 5-6 cm thick, and the largest clasts were up to 10 cm across. Residents reported that larger clasts fragmented upon impact. Going north, the deposit thinned gradually and ended with a relatively sharp margin ~2 km N of Fornazzo. Downslope, near the town of Giarre, the area of fallout was ~5 km wide in N-S extension, and up to 5 cm thick in its central portion. Most of the deposit here was composed of fragments with diameters of a few millimeters to 3 cm. The N and S margins of the deposit were strikingly sharp, it seemed that only very little fine ash fell beyond the margins of the lapilli deposit.

Comparison with the (relatively poor) descriptions of the fall deposit produced by an eruption from the Voragine on 17 July 1960 allows the conclusion that the 4 September 1999 eruption was less voluminous but similarly violent, and therefore among the largest explosive eruptions at Etna's summit craters during the past 100 years. The 1960 eruption produced ~10 x 10⁶ m³ of pyroclasts, and clasts more than 5 cm in diameter were reported.

The activity at SEC on the evening of 4 September had many minor effects. The most impressive changes since 28 July were the presence of the new lava lobe that had issued from the lower part of the 4 February fissure, and the collapse of part of the E crater rim.

Activity after 4 September 1999. During the week following 4 September activity continued at the summit craters, but observations were hampered by bad weather. Intense explosive activity occurred each day at the BN, and at times bombs were ejected onto the outer slopes of the main summit cone. The Voragine remained active, and vigorous seismicity indicated that the most intense activity occurred between 0100 and 0400 on 9 September. During their summit visit on 7 September, Behncke and Keller reached the area of activity near SEC and saw two small lava flows issuing from vents 15 m below the spatter cone formed after 27 August that extended onto the W slope of the VdB after a few days. Mild Strombolian activity occurred from a new cluster of hornitos near the effusive vents.

During the evening of 11 September Scarpinati observed lava flowing from a vent ~200-250 m farther downslope to the E of the SEC effusive area. The next morning a new double spatter cone ~200-250 m E of the previous cone issued fluid lava, at an estimated rate of at least 1 m³/s, that moved along the margin of the flow-field. The new vents were on terrain not covered by lava during the previous months, and it appeared that this was a true new eruptive fissure.

Mild magmatic explosions were observed by guides every few minutes early on 18 September. On the next day, Rivière observed vigorous lava splashing from the NW cone of BN. Strombolian activity was relatively weak until early the next morning. At 0445, Tanguy observed the eruption from Trecastagni (on the SE flank). Continuous jets of incandescent material illuminated a gas plume rising more than 500 m above the crater rim. A bright glow in the area of the effusive vents at the ESE base of the SEC was noted, and weak incandescence was seen in the area of the Voragine. Tanguy arrived at the Piccolo Rifugio at about 0545, by which time the most energetic phase was over, although some incandescent bombs still rose up to 300 m above the crater rim. The activity had virtually ceased by 0630.

During the early morning hours of 20 September, vigorous lava fountaining occurred at the BN, mostly from the vents in the NW part of the crater where a broad cone had been the site of weak degassing for several weeks; previous reports noted that the area of this cone had remained virtually unchanged even during the 4 September Voragine eruption. The episode covered almost the entire floor of the BN with lava to thicknesses of several meters to tens of meters. A lava tongue invaded the depression that had previously hosted the SE vents, and only an irregularly shaped depression was left at the site of the NW vents. Explosive activity was again observed on the evening of 20 September, and a brief surge of activity occurred on late 21 September, after which BN became silent for about two weeks.

Effusive activity from the vents on the ESE base of the SEC was intense on the morning of 20 September when visited by Tanguy; lava issued from a vent that had opened the previous afternoon near the large spatter cone built after 27 August, and mild spattering occurred from this cone itself. A new vent had also formed at the fissure that had become active on 12 September. Vigorous effusive activity was continuing at the 12 September vents.

During the week following the 20 September eruptive episode at BN, the most persistently active summit crater was NEC, which had Strombolian activity in its central pit. A visit by Behncke on 28 September revealed that NEC cone had received heavy fallout of bombs on 4 September, and the footpath on its W side had vanished under a continuous cover of bombs, some up to 1.5 m in diameter. While the collapse scar on the SW flank of the cone had been largely healed by bomb fallout, a portion of the cone's flank farther to the ESE had collapsed, leaving a similar scar. Activity within the central pit consisted of near-continuous expulsions of dark ash. Good views obtained by Rivière on 25 September showed that the pit continued to a depth of several hundred meters with vertical walls.

On 28 September, good panoramic views of the Voragine from the S rim of NEC revealed that the former SW and central vents had merged into one large ~200-m-wide crater, but it appeared that there were still two eruptive centers. On the SW rim a wide U-shaped gap had formed in the former "diaframma" (septum) through which the floor of BN could be seen. Eruptive activity within the Voragine on 28 September consisted of frequent loud explosions.

Sub-concentric fractures were present on the outer ENE and E rim of the Voragine and on a ridge which now constitutes both the SE flank of the NEC cone and the NE rim of the Voragine. A fountain-fed lava flow that had formed during the 4 September eruption on the W side of the Voragine was up to 150 m wide in its upper part but narrowed to ~30 m in its distal portion where it formed a lobe along the N side of the 22 July 1998 flow; the new lobe, however, was shorter than its predecessor. Two fountain-fed lava flows also formed on the E side of the Voragine. The longer of these flows extended about halfway to the W rim of the Valle del Bove.

Rivière visited SEC on 24 September and reported that discontinuous effusive activity continued from the new vents (first seen by Scarpinati on the morning of 11 September) near the 4 February fissure. Lava flows extended ~1 km and spilled down the W face of the VdB.

Vigorous eruptive activity resumed in the BN on 30 September, ejecting large bombs hundreds of meters beyond the crater rim. At the same time, activity increased at the NEC. On 29-30 September, near-continuous Strombolian activity ejected bombs tens of meters above the crater rim, and larger bursts reached heights of up to 150 m, dropping bombs all over the crater floor and onto the flanks of the NEC cone.

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Boris Behncke and Jean-Claude Tanguy, Dipartimento di Scienze Geologiche, Palazzo delle Scienze, Università di Catania, Corso Italia 55, 95129 Catania, Italy.

Less than 2 months after the end of the eruption of July (BGVN 24:09), a new seismic crisis started at 1037 on 28 September. Most of the observed 189 seismic events had magnitudes of less than 1. All were situated above sea level. Only two of them had significantly larger magnitudes of 1.8 and 2.2, at 1042 and 1053, respectively.

An eruption started at 1158 in the W part of Dolomieu crater with a strong whistling noise. Seconds later, a 10-m-diameter, ~50-m-high lava fountain rose from the SW corner of Dolomieu crater. Immediately after that, a fissure formed going NW, followed by the development of small lava fountains and a lava flow. Less than 5 minutes later the fissure measured ~200 m long and was terminated by another lava fountain 20-30 m high. At 1210, the fissure opened on the S flank "en echelon," ~100 m below the crater rim. The two upper fissures measured ~50 m long, followed by a third one ~250 m. The lava flow down the steep S flank extended ~1 km in less than 15 minutes. It continued to the SE on a more gentle slope and reached "Château Fort" crater, 2 km away, within two hours.

Less than 8 hours after the eruption started, activity was limited to some individual points on the upper S flank, while the main lava flow had stagnated. No further activity was observed in the Dolomieu crater. In the night, small fissures on the S flank at 2,150 m elevation produced some small pahoehoe lava flows.

On 8 October, after a significant increase of tremor, steam release was observed in the south "enclos," at 1,900 m altitude, ~4 km away from Dolomieu crater and on the morning of 11 October a new 600-m-long lava flow was observed 500 m to the SE, on the base of crater "Villèlle," close to southern border of the caldera. On 18 October this lava flow measured ~1.5 km. No further activity was observed at this site on 21 October. As of 22 October tremor was still visible, mainly in form of small "gas piston events," centered on the upper fissures on the S flank of Fournaise, where a small cone was formed. The eruption ended following small "gas piston events" on at about 1800 on 23 October. Residual fumarolic plumes, consisting primarily of water vapor, were visible the following week.

Mapping of the lava flow was performed in the first days by use of small hand-held GPS. Early lava flows, in Dolomieu crater and on the S flank are mainly aa lava flows. In the Dolomieu crater, it represents a surface of ~40,000 m² (?) and a volume of <100,000 m³. It partly covered the July lava flow. On the border of the lava flow we could observe fissuring of the ground, up to 3 m deep, due to the weight of the new up to 3-m-high lava flow.

The main lava flow on the S flank represents about 300,000 m² and <1 x 10⁶ m³. Taking into account an emplacement within less than 5 hours, the eruption rate was estimated to be >50 m³/s. The small pahoehoe flow from the fissures at 2,150 m altitude covered less than 5,000 m².

The southern-most lava flow starting at crater Villèlle also was mainly pahoehoe. There were no projections at its point of emission, indicating a highly degassed magma. On 11 October a ~1 m lava flow emerged from a small "well" on the SW base of "Villèlle." The volume of this lava flow is estimated to be under 50,000 m³. All recovered samples were aphyric basalt.

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: Thomas Staudacher, Nicolas Villeneuve, and Jean Louis Cheminée, Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, Institut National des Sciences de l'Univers, 14 RN3 - Km 27, 97418 La Plaine des Cafres, Réunion, France (URL: http://www.ipgp.fr/fr/ovpf/observatoire-volcanologique-piton-de-fournaise).

During July and August 1999, low-intensity seismic activity continued, similar to that of previous months (BGVN 24:07). Fifty-six volcano-tectonic (VT) earthquakes were registered during this period compared to 90 during the previous two months. The depths of these VT events were between 0.35 and 19 km below the summit, and the total energy released was estimated as 4.82 x 1013 ergs. The largest magnitude event, on the morning of 16 July, had a coda magnitude 1.7 and depth of 8 km.

Additionally, 20 long-period events and 10 tremor episodes were recorded with an energy release of 5.38 x 1012 ergs. Dominant frequencies during the tremor episodes were 2.0-4.0 Hz. The tremor event on 23 July had a small amplitude with respect to the long coda, a quasi-monocromatic frequency of ~2.01 Hz, and an energy release of 2.09 x 1012 ergs. Periodic fumarole temperature measurements taken during the two-month period in the active crater registered a range of 130-394°C.

Radon-222 emissions measured in the soil at six stations were not significantly different from values in previous months. As in the May-June period, the greatest emissions occurred at the Sismo2 station (~5 km NE of the summit) attaining a maximum value of 2,297 pCi/l.

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

Information Contacts: Observatorio Vulcanológico y Sismológico de Pasto (OVSP), Carrera 31, 18-07 Parque Infantil, PO Box 1795, Pasto, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).

During a 6-10 September visit by John Seach to the Gaua caldera and the cone of Mt. Garat, of the five craters only Crater A was solfatarically active (figure 1). The W side of the caldera lake was stained yellow by sulfurous mud and emitted a strong SO₂ smell. The water temperature was measured at 30.1°C while that of the lake shore mud was 35.1°C. The Mt. Garat cone was largely denuded of vegetation around the craters. Only on the NE side near Crater E was there any regrowth on top. Moss and grasses had regrown on the flanks of the cone, to within 20 m of the E side of Crater E. Fallen trees were scattered around the rims of all five craters.

Figure 1. Sketch map showing the positions of the five summit craters (A-E) on Mt. Garat within the Gaua caldera (larger solid line), 6-10 September 1999. Courtesy of John Seach.

Hot, whistling ground with a temperature of 97.6°C was located 20 m S of the Mt. Garat summit, located along the W summit crater rim. Fumarole fields were found both inside and outside of the summit crater rim. Another fumarole field with a temperature of 45.3°C was located ~25 m SW of Crater B. Steam was observed venting ~2 km SW of Crater E but was not approached due to its remote location.

The active Crater A is located on the SE side of the Mt. Garat cone. The E crater wall contained solfataras emitting white vapor with a strong SO₂ smell and a temperature of 95.0°C. The solfataras were surrounded by bright yellow deposits, and were active up to the rim of the crater. Solfatara plumes were easily visible from a distance of 5 km on the E shore of the lake. On the SE crater floor, a solfatara constantly vented 102.7°C vapor. Continuous loud high-pressure venting noises originated from along the N and W walls and the W floor of the crater. A pile of blocks coated in yellow deposits rested on the SW floor; mild degassing with a temperature of 99.7°C occurred here. Large blocks 1-2 m in diameter littered the SW wall and floor of the crater. The floor of the crater was split into two levels with the N level being ~5 m below the S level. Large cracks ~3 m deep were present on the S floor. Two 3-m-diameter blocks sat near a brown pond on the low, N-level floor. Rockfalls were heard coming from the E wall. Mild acid rain fell inside the crater, which was mostly filled with white vapor. At times, twin plumes emitting from the crater were visible, rising to a height of 100 m.

Craters B and C are similar in size and depth (figure 2), are denuded of vegetation, contain standing, devastated trees (figure 3), have and flat silty floors with brown ponds. The crater walls contain tuffs, cinders, and scattered blocks. Crater D is the shallowest of the five and has a flat and silty floor containing a shallow brown pond and standing, devastated trees. A 3 m-diameter block was observed on the E wall. Crater E is the smallest crater, ~20 m wide and 20 m deep. It is cone-shaped with blocks and a full cover of vegetation inside.

Figure 2. View towards the NNW of two inactive craters (B in the foreground, C in the background) in the summit area of Mt. Garat within the Gaua caldera, September 1999. The peak on the right is at 682 m elevation. Courtesy of John Seach.

Figure 3. Devastated tree at the NW edge of the Mt. Garat cone within the Gaua caldera, 8 September 1999. Courtesy of John Seach.

Background. The roughly 20-km-diameter Gaua Island, also known as Santa Maria, consists of a basaltic-to-andesitic stratovolcano with a 6 x 9 km summit caldera. Small parasitic vents near the caldera rim fed Pleistocene lava flows that reached the coast on several sides of the island; several littoral cones were formed where these lava flows reached the sea. Quiet collapse that formed the roughly 700-m-deep caldera was followed by extensive ash eruptions. Construction of the historically active cone of Mount Garat (Gharat) and other small cinder cones in the SW part of the caldera has left a crescent-shaped caldera lake named Letas (figure 4). The symmetrical, flat-topped Mount Garat cone is topped by three pit craters.

Figure 4. View of a fumarolic plume rising from a cone on the SE flank of Mt. Garat in the Gaua caldera, September 1999. Lake Letas is in the foreground. Courtesy of John Seach.

Only solfataric activity was recorded from 1868 to 1962. Beginning in 1962, central crater explosions with frequent associated ash columns were reported nearly every year until 1977. Information after 1977 is scarce, but steam was reported in mid-1980 and ash plumes were reported in July 1981 and April 1982. Increased fumarolic activity was noted and the NW slopes of the cone were denuded of vegetation in July 1991 (BGVN 16:07). Strong fumarolic activity was continuing in July 1996 (BGVN 21:09).

Geologic Background. The roughly 20-km-diameter Gaua Island, also known as Santa Maria, consists of a basaltic-to-andesitic stratovolcano with an 6 x 9 km wide summit caldera. Small parasitic vents near the caldera rim fed Pleistocene lava flows that reached the coast on several sides of the island; several littoral cones were formed where these lava flows reached the sea. Quiet collapse that formed the roughly 700-m-deep caldera was followed by extensive ash eruptions. Construction of the historically active cone of Mount Garat (Gharat) and other small cinder cones in the SW part of the caldera has left a crescent-shaped caldera lake. The symmetrical, flat-topped Mount Garat cone is topped by three pit craters. The onset of eruptive activity from a vent high on the SE flank in 1962 ended a long period of dormancy.

Information Contacts: John Seach, P.O. Box 16, Chatsworth Island, NSW 2469, Australia.

This report chiefly covers the turbulent period of 1 September through 19 October 1999. Histograms available on the Instituto Geofísico's website for the crisis interval through 31 October illustrated that September and October had a striking abundance of both phreatic explosions and earthquakes. The monthly explosion count for October 1999 (53 phreatic explosions) was almost double any other month during the crisis.

Despite the steep increases in explosions and earthquakes during September and October, non-explosive episodes were common during the reporting interval. They were marked with fumarolic emissions rising from a few meters to a few kilometers above the summit vent.

Microscopic inspection of tephra erupted on 30 August led researchers to conclude that the explosions to that point had continued to eject older, non-juvenile material. But John Ewert of the USGS noted that juvenile pumice of dacitic composition began to appear in deposits starting on 26 September. And, the comparatively large 5 and 7 October eruptions both contained similar juvenile pumice.

The intracrater dome, cold at the start of the crisis, began to grow by lava extrusion around 28 September. The volume of material extruded was small,3. The comparatively large eruptions on 5 and 7 October excavated part of the dome and sent pyroclastic flows 4-5 km down the W-flank into the Rio Cristal. Shortly after both events Ewert shot videos of their still-steaming deposits.

Earthquakes. Compared to the earlier stages of the crisis, the number of multiphase, volcano-tectonic, and long-period earthquakes grew sharply during September and October. For all three types, the highest numbers seen during the entire crisis interval (July 1998-October 1999) took place during October when multiphase earthquakes occurred 15,024 times, volcano-tectonic, 1,701 times, and long-period, 15,075 times. Omitting September 1999 and comparing the October 1999 earthquakes to the previous monthly highs during the crisis, one obtains the following: multiphase earthquakes underwent a 7-fold increase; volcano-tectonic earthquakes, a ~10-fold increase; and long-period earthquakes, an impressive ~70-fold increase. It was not just the numbers of events that rose. Seismic amplitudes at stations 7 to 9 km from the summit increased notably during September and October. Many of the earthquakes had depths between the surface and 6 km.

Eruptions. Table 5 provides an overview of some of the interval's larger outbursts. The one on 3 September yielded a reduced displacement (RD) of over 25 cm². The event generated a plume to ~5.5 km altitude, which could be seen from Quito and included four distinct explosions (at 0723, 0726, 0743, and 0751). The plume dispersed after 30 minutes. Ash fall concentrated over the N flank. The next day, aerial observers noted that the 1981 crater had merged with another recent one, leaving a larger, roughly E-W trending crater in the vent area.

Table 5. Noteworthy explosions at Guagua Pichincha during 3 September through 19 October 1999. Cases shown are those where reduced displacements were stated in daily reports, with the exception of 7 October, for which the explosion's RD remained undisclosed. Plume heights were frequently undetermined due to restricted visibility (eg. darkness and clouds). Courtesy of the Instituto de Geofísico.

The 26 September explosion was described as "important." The loud noise accompanying the early morning outburst (at 0315) awakened residents on the SSW flank in Lloa (see maps in BGVN 23:09). Ash fell over some areas; a lahar moved down the W flank Rio Cristal.

Eruption on 5 October. The explosion with the largest reduced displacement disclosed during the reporting interval (36 cm²) happened on 5 October; it was associated with an ash column to over 8 km altitude. The explosion vented on the caldera's W side; observers on the scene saw airborne material move SW and SE. In addition, the next day it was reported that ash thicknesses of 2 and 3 mm were found in central and N Quito as well as the settlement of Nono. Accumulated ash in other sectors (Mindo, Cumbayá, Tumbaco, Conocoto, El Tingo, Pomasqui, and Guayllabamba) reached only minor thicknesses. On the morning of 6 October, technicians visiting monitoring stations found ash-covered solar panels.

The 6 October issue of the newspaper Diario Hoy reported that the 5 October eruption took place at 1409, and that residents in S Quito heard the explosion. They also said that the resulting plume attained a height of 20 km. Diario Hoy further wrote that one hour after the audible sound, the first ash particles descended on N Quito, which became darkened by an enormous gray cloud. In four hours the cloud covered the city in a thick fog-like mantle; Marshal Sucre airport closed at 1730. The paper noted that Quito citizens would find their normal potable water supply intact. The news report added a comment by the mayor that this behavior could persist for months or even years. Although the news report, and other information around this time described the eruption as phreatic, tephra samples indicated the presence of juvenile pumice (mentioned above), indicating that the eruption was at least partly magmatic.

Observers on a flight at around 0800 on 6 October over the S part of the volcano confirmed extensive coverage of ash, but they saw vigorous, 3-km-tall fumarolic plumes-not ash plumes-being emitted. Ash hanging over Quito at that time was therefore assumed to mainly have resulted from earlier deposited ash remobilized by traffic and wind. The 5 October eruption column was captured on NOAA GOES-8 imagery, which can be viewed as a time-lapse animation, revealing some of the dynamics of the ash column (for URL, see discussion below). Portions of the rising column split into components directed E and W, forming what appeared as a dumbbell-shaped bifurcating plume. A plume on 7 October behaved in much the same way. In both cases, analysts attributed the bifurcation to wind shear.

Eruption on 7 October. Another comparatively large explosion took place the morning of 7 October (figure 16). Hugo Yepes, John Ewert, and Dan Miller of the Instituto and USGS accompanied Ecuador's president and members of the media on a flight just after the explosion. The pilot tried to approach the S flank but a curtain of falling ash prevented the occupants from seeing into the caldera. Ash fell over Quito, the Capital. The U.S. National Oceanographic and Atmospheric Administration (NOAA) reported that the plume rose to 16.5 km altitude.

Figure 16. Guagua Pichincha's ascending ash plume at 0730 on 7 October 1999 as shot with a digital camera from the uplands of Quito. Pichincha's summit vent was ~ 11 km W, lying well behind the peak in the foreground. Courtesy of Arden and Debra Burgess.

Regarding the 7 October explosion, the Diario Hoy's headline read "Guagua: A million tons of ash." The article went on to note that the Instituto estimated 1.1 x 10⁶ metric tons of ash lay within 15 km of the summit. Thicknesses of 1-3 mm accumulated in the northern parts of Quito. Ash clean-up proceeded within the city and at the airport. The article went on to caution that in a stronger eruption 5-10 cm of ash might fall on the city.

In similar manner to satellite images of the 5 October plume, those of the 7 October plume showed that it also bifurcated. Figure 17 shows GOES-8 visible imagery available on websites operated by both NOAA and the Cooperative Institute for Meteorological Satellite Studies (CIMSS) at the University of Wisconsin. An initial pre-eruption image was made at 0645 (1145 GMT) (not shown on figure 5); the image a half hour later showed the plume at an early stage. Due to variable wind shear with height, the advecting 7 October plume moved in two directions: the highest portion (~15 km in altitude) drifted W, away from Quito, while a lower portion (~12 km in altitude) drifted E over Quito.

Figure 17. GOES-8 satellite images showing the dynamics of Guagua Pichincha's ascending 7 October plume. All images came from visible wavelengths; they are all similarly oriented and at identical scales although the upper image covers a larger area. The upper image shows the location of Guagua Pichincha (gp) and Quito (Q). Clouds on that image lay over parts of the Pacific Ocean and Ecuador (E), but N-central Ecuador and much of Colombia (C) remained unobscured. The first image (a) was taken directly from the larger one; both were captured at 0715 (1215 GMT). In the first image (a) the plume was compact and circular. The image at 0745 (b) shows the plume beginning to split into components directed W towards the Pacific, and E over Quito. The two components may have differed slightly in reflectivity. By 0815 (c), the plume had become decidedly dumb-bell shaped with the area above the volcano becoming relatively diffuse. The plume continued to spread at 0845 (d), where now the W component had also become diffuse. The eastern plume still sustained a relatively dense white color. These and associated images are displayed as time-lapse animations on NOAA and CIMSS websites (see URLS below). Courtesy of NOAA and CIMSS.

Other processed views and animations of the 7 October plume dynamics were also available on the web. Scott Bachmeier at CIMSS posted an image prepared from GOES infrared (IR) data. He used a difference or "split window" technique that enhances the ash plume. Radiation escaping from a body can be described in terms of emissivity (emissive power). The emissivity of silicate particles within an ash plume varies with wavelength. This image processed the wavelengths 10.7 and 12.0 micrometers, which led to brightness temperature differences of 1-5 Kelvin. The IR difference product shows the ash plume very well initially; but later, the plume became thinner, losing its identity on the IR difference product images.

The eastern portion of the 7 October ash plume was tracked for a longer time on the GOES 6.7 micrometer IR ("water vapor") channel. Due to the generally dry middle and upper troposphere over northern South America that day, the water vapor content in the higher plume created a discernible contrast that drifted eastward across Ecuador toward Colombia and Perú.

John Ewert took videos of the plume's dynamics, as seen from the ground. From that perspective the ascending plume appeared to have a strong rotational component. He also noted that these plumes' behaviors were hard to forecast from available wind data.

Background. On September 27, the Mayor of Quito closed schools and raised the alert from yellow to orange signifying a possible eruption within days (BGVN 24:08). About a week later the character of the alerts was revised to become more local in scope. For example, on the W flank, small settlements incorporating about 60 families along the Rio Cristal were evacuated and the status there stood at the highest level, red. The SSW flank city of Lloa remained at orange alert; and in Quito, it returned to yellow where it remained throughout the reporting period, including during times of ashfall.

During early October, the U.S. State Department issued these statements: "Geological experts conclude that the city of Quito is protected from possible lava flows, avalanches, and lateral explosions by the bulk of Pichincha Mountain, which stands between the city and the volcano crater. Parts of Quito could be affected by secondary mud flows caused by heavy rains that usually accompany an eruption. The entire city could also be affected by slight to significant ash falls and resulting disruptions of water, power, communications, and transportation. According to geological experts, lava flows, ash falls, avalanches, and lateral explosions would almost certainly head W and SW from the volcano, in the direction of three small communities, Lloa, Mindo, and Nono, popular destinations for birdwatchers. Travelers should avoid these towns."

In addition to Guagua Pichincha, a second volcanic crisis has developed at Tungurahua. Volcanological and geophysical colleagues from multiple countries have participated, or continue to collaborate in instrumenting and monitoring these crises. In the midst of these events Ecuador's economy has undergone a serious downturn with the currency recently declining in value by more than 50%.

Geologic Background. Guagua Pichincha and the older Pleistocene Rucu Pichincha stratovolcanoes form a broad volcanic massif that rises immediately to the W of Ecuador's capital city, Quito. A lava dome is located at the head of a 6-km-wide breached caldera that formed during a late-Pleistocene slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent in the breached caldera consisted of explosive activity with pyroclastic flows accompanied by periodic growth and destruction of the central lava dome. One of Ecuador's most active volcanoes, it is the site of many minor eruptions since the beginning of the Spanish era. The largest historical eruption took place in 1660, when ash fell over a 1000 km radius, accumulating to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primarily to then W, and affected agricultural activity, causing great economic losses.

Information Contacts: Instituto Geofísico (URL: http://www.igepn.edu.ec/); John Ewert, Volcano Disaster Assistance Team (VDAP), United States Geologic Survey (USGS), Cascades Volcano Observatory, 5400 MacArthur Blvd., Vancouver, WA 98661 USA (URL: https://volcanoes.usgs.gov/observatories/cvo/); Diario Hoy ("Hoy Digital,", URL: http://www.hoy.com.ec/); Arden and Debra Burgess, Centro Aereo 1Q1702, P.O. Box 02-5268, Miami, FL 33102-5268 USA; NOAA/NESDIS Operational Significant Event Imagery Support Team, E/SP22, 5200 Auth Road, Camp Springs, MD 20746-4304 USA (URL: https://www.nnvl.noaa.gov/); Scott Bachmeier, Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin, 1225 West Dayton St., Madison, WI 53706 USA (URL: http://cimss.ssec.wisc.edu/).

Seismicity at Ijen increased starting in early April, when volcanic B-type events rose from 15 during the week ending on 5 April to 41 events during 6-12 April. Tremor during April and May had amplitudes of 0.5-2 mm. The number of B-type events remained high (more than 34/week) for most of the period through mid-June. Seismicity then gradually declined through mid-July, after which the weekly number of B-type events remained stable at an average of 9/week. During the period of 18 May through the week ending on 21 June a "white ash plume" rose 50-100 m. Recorded tremor had an amplitude of 0.5-3 mm.

Two phreatic eruptions occurred at the Sibanteng location inside the active crater lake at 0510 on 28 June. An accompanying detonation was heard at the sulfur mining site 2 km from the summit and volcanic tremor was recorded with an amplitude of 0.5-1 mm. The following week, 6-12 July, yellow-gray sulfur emissions were observed from the crater and a loud "whizz" noise was heard. The crater lake's water was brownish-white and had sulfur agglutinate floating on the surface. Measurements on 8 July showed that the hotspring temperature was 48°C, air temperature at the crater lake was 15°C, the lakewater temperature was 40°C, and the sulfur gas temperature was 207-221°C. Thick haze prevented observations from 13 July through 23 August, but B-type events and continuous tremor was recorded. When J.M. Bardintzeff visited, on 17 August 1999, the solfatara was strongly active and the crater filled with gas. The acid lake was a pale-green color.

Conductivity determinations were made of acid lake waters sampled on 7 December 1998 (BGVN 23:11) by Bardintzeff, Marlin, and Barsuglia. Conductivity in the middle of the lake was 146 mS/cm. Near the S side it was 140 and only 98-120 mS/cm near the hot sub-lacustrine spring. A small affluent in the S side, was (from its source to the lake) 39-27°C, with a pH of 1.6, and conductivity of 17 mS/cm. In the Banyupahit River, 3 km from the dam, conductivity was 138 mS/cm. On 10 December 1998 conductivity in the middle of the lake was 181 mS/cm.

Geologic Background. The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Picturesque Kawah Ijen is the world's largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor, and tourists are drawn to its waterfalls, hot springs, and volcanic scenery.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); J.M. Bardintzeff; C. Marlin, and F. Barsuglia, Sciences de la Terre, bat 504, Universite Paris-Sud, 91405 Orsay cedex, France.

In the early morning of 18 July, a small jökulhlaup (sudden glacier-outburst flood) lasting less than 24 hours, occurred in "Jökulsá á Sólheimasandi," one of the rivers draining from the Mýrdalsjökull icecap (figure 2) towards the S. Inspection of the icecap revealed that a new ice cauldron, ~2 km wide, and 50 m deep, had formed just above the origin of the Sólheimajökull outlet glacier. The jökulhlaup was preceded on 17 July by a 20-minute-long burst of modest volcanic tremor (reported by P. Einarsson). Intrusion of magma at a low level within the subglacial Katla volcano or even a small subglacial eruption may have occurred, possibly associated with pulse of CO₂ which could have caused boiling in geothermal areas under the icecap.

Figure 2. Topographic map of the Mýrdalsjökull icecap over Katla volcano showing tilt stations. Courtesy of the Nordisk Vulkvanologisk Institut.

From 18 July until mid-August, ten new ice cauldrons formed along the W, S, and E borders of the Mýrdalsjökull caldera (figure 3), signifying increased geothermal activity along a large part of the caldera rim. Changes on the icecap surface have been reported for some of the earlier eruptions of Katla, and the current activity could be a possible long-term precursor to a new eruption. A flight over the area on 9 September by Reynir Ragnarsson at Vík, revealed that the ice cauldrons did not develop much after mid-August.

Figure 3. One of the new ice cauldrons on Mýrdalsjökull, July-August 1999. Photo by Freysteinn Sigmundsson.

Geologic Background. Katla volcano, located near the southern end of Iceland's eastern volcanic zone, is hidden beneath the Myrdalsjökull icecap. The subglacial basaltic-to-rhyolitic volcano is one of Iceland's most active and is a frequent producer of damaging jökulhlaups, or glacier-outburst floods. A large 10 x 14 km subglacial caldera with a long axis in a NW-SE direction is up to 750 m deep. Its high point reaches 1380 m, and three major outlet glaciers have breached its rim. Although most historical eruptions have taken place from fissures inside the caldera, the Eldgjá fissure system, which extends about 60 km to the NE from the current ice margin towards Grímsvötn volcano, has been the source of major Holocene eruptions. An eruption from the Eldgjá fissure system about 934 CE produced a voluminous lava flow of about 18 km3, one of the world's largest known Holocene lava flows. Katla has been the source of frequent subglacial basaltic explosive eruptions that have been among the largest tephra-producers in Iceland during historical time and has also produced numerous dacitic explosive eruptions during the Holocene.

Information Contacts: Rósa Ólafsdóttir, Guðrún Sverrisdóttir, Freysteinn Sigmundsson, Erik Sturkell, and Níels Óskarsson, Nordisk Vulkvanologisk Institut, Grenásvegur 50, 108 Reyjavík, Iceland (URL: http://nordvulk.hi.is); Helgi Björnsson, Páll Einarsson, and Magnús Tumi Guðmundsson, Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland (URL: http://www.raunvis.hi.is/); Ármann Höskuldsson, South Iceland Institute of Natural History, Strandvegur 50, 900 Vestmannaeyjar, Iceland (URL: https://www.nattsud.is/).

Early on the morning of 12 September monitoring instruments detected a swarm of small earthquakes and volcanic tremor on the east rift zone, and a sharp deflation (tilt) of the summit area and parts of the east rift zone. A pause in on-going eruptive activity also occurred. These effects were interpreted as due to a new intrusion of magma. Apparently, magma moved from both the summit area and from near Pu`u `O`o into the upper rift zone, forming a dike in the area between Pauahi Crater and Mauna Ulu.

Figure 142 shows the seismic record for part of 11-12 September. After tremor associated with the seismic swarm ceased, another pause in episode 55 of the Pu`u `O`o-Kupaianaha eruption began at 0131 on 12 September. This change was thought to be due to the above-mentioned intrusion.

Figure 142. Part of the 11-12 September seismogram for station STC near Pu`u `O`o at Kilauea. There is a time difference of 15 minutes between each horizontal line and 1 minute between each small tic. Volcanic tremor was normal before the seismic swarm of 12 September but absent afterward. This absence of tremor was due to a pause in eruptive activity during the time of the swarm. Courtesy of the Hawaiian Volcano Observatory.

The onset of seismic activity and tilting on 12 September was abrupt and simultaneous to within the one-minute resolution of the tilt data. Strong tilt commenced early on 12 September, as indicated by the vertical line on figure 143, where tilt for a station was toward the caldera. A swarm of small earthquakes along the upper rift zone accompanied the ground deformation. The downward tilt (figure 143) suggested that magma was moving away from and out of the summit reservoir. Data from two other tiltmeters on the E rift zone (E of Pauahi Crater and just uprift from Pu`u `O`o) indicated that the magma was moving into the rift zone. The reversal of summit tilt about 4-6 hours later suggests that when the intrusion stopped, magma once again moved into the summit reservoir. An inspection of the ground above the intrusion on 12 September did not reveal new ground cracks, which indicated that the intrusion remained 1-2 km below the surface. On the other hand, leveling across the zone of intrusion on 14 September showed elevation changes indicative of a dike, but its size and depth remained to be calculated. It was estimated that 3-5 million cubic meters intruded into the rift zone.

Figure 143. Kilauea tiltmeter record for early September 1999 at Uwekahuna (tilt along an azimuth of N50W). Courtesy of Hawaiian Volcano Observatory.

About eight hours after the start of the intrusion, the active lava bench on the S coast of Kilauea began collapsing into the sea. Several small collapses were observed by scientists on 12 September. The lava bench began to collapse during 0800-0915 on 12 September and this process continued for most of the day (figure 144). By the evening of 13 September, about 2 x 10⁴ m² of the S coast had been removed. The discharge of lava into the sea stopped completely in the afternoon of 13 September.

Figure 144. W-looking view of the lava bench on the S coast of Kilauea as it appeared on 9 September (left) and at about noon on 12 September 1999 (right). Photo courtesy of J. Kauahikaua.

Background. Kilauea is one of five coalescing volcanoes that comprise the island of Hawaii. Historically its eruptions have originated primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the caldera to the sea. The latest Kilauea eruption began in January 1983 along the east rift zone. The eruption's early phases, or episodes, occurred along a portion of the rift zone that extends from Napau Crater on the uprift (toward the summit) end to ~8 km E on the downrift end (toward the sea). Mike Garcia has compiled a tabular summary of the episodes, now available on the web.

Activity eventually centered on the area and crater that were later named Pu`u `O`o. Between July 1986 and January 1992, the Kupaianaha lava lake was active ~3 km NE (downrift) of Pu`u `O`o. It was during this period that the town of Kalapana and most of the 181 homes lost were destroyed. In December 1991, one month before the shutdown of Kupaianaha, eruptive activity returned to Pu`u `O`o. More than 1 km³ of lava was erupted from January 1983 through January 1997.

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: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii Volcanoes National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/); Mike Garcia, Hawaii Center for Volcanology, University of Hawaii, Dept. of Geology & Geophysics, 2525 Correa Rd., Honolulu, HI 96822 USA (URL: http://www.soest.hawaii.edu/GG/HCV/puuoo-episodes.html)

Low-level activity continued throughout most of July, August, September, and into the first week of October, with only small-to-moderate exhalations and some light gas and steam emissions. Generally, fumarolic activity was low, but clouds frequently obstructed visibility. The hazard status remained Yellow and the radius of restricted access remained at 5 km. A M 7.4 earthquake in the state of Oaxaca on 30 September did not affect the volcano.

Low-magnitude microseismic and/or tectonic events occurred occasionally. Type-A earthquake events were recorded at the following times: M 2.2 at 0141 on 14 July (preceded by a type-A microseism); M 3.3 at 2053 on 15 July; M 2.1 at 2336 on 23 July (followed by a small tectonic type-A event on 25 July); a small-magnitude event at 1638 on 29 August; and two events at 2008 and 2148 on 1 September of M 2.2 and 2.5, respectively.

Several low-magnitude tectono-volcanic earthquakes were also detected as follows: M 2.7 at 0654 on 28 July; two events at 2029 on 29 July with M 2.0 and 2.6, respectively; a M 2.5 event at 1431 on 6 September at a depth of 7.9 km from the summit and 5 km S of the crater; M 3.2 at 2047 on 8 September with its hypocenter at 7.1 km below the summit and 6 km S of the crater; and another M 3.2 event at 0834 on 27 September at a depth of 5.3 km under the summit and 6 km SSE of the crater.

Moderate exhalations starting in late August continued through September and into the first week of October. At 0920 on 27 August two small ash emissions caused light ashfall over several towns on the W flank. Another emission on 1 September caused minor ashfall. A larger event with a duration of two minutes occurred at 2205 on 5 September, causing light ashfall over several towns. At 0757 on 20 September a small exhalation ejected a plume 1 km above the summit before dispersing to the W. Two moderate exhalations occurred at 0916 and 0949 on 29 September, both lasting about 2 minutes, with ash falling W of the volcano about an hour later.

Volcanic activity during the first week of October, subsequent to a M 7.4 earthquake in the state of Oaxaca on 30 September and a number of aftershocks, remained similar to recent months. At 1101 on 3 October, a moderately large exhalation lasted for more than 15 minutes; the ash column rose to 4 km above the crater and ash fell on several towns to the SW.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Servando De la Cruz-Reyna1, 2, Roberto Quaas1, 2; Carlos Valdés G.², and Alicia Martinez Bringas1.1-Centro Nacional de Prevencion de Desastres (CENAPRED), Delfin Madrigal 665, Col. Pedregal de Santo Domingo, Coyoacán, 04360, México D.F. (URL: https://www.gob.mx/cenapred/); 2-Instituto de Geofisica, UNAM, Coyoacán 04510, México D.F., México.

The activity at Jonggring Seloko Crater in mid-September 1999 was very similar to that observed in the last recent years at the volcano. It consisted of short-lived non-sustained Vulcanian explosions producing 300-1,000-m-high ash plumes.

On 17 September there were 17 explosions witnessed during day-time hours. The time interval between two successive explosions ranged from 1 to 71 minutes, with an average of one explosion every 36 minutes. The next day 25 explosions were witnessed with 1 to 75 minutes between explosions and an average of one explosion every 32 minutes. These consistent statistics suggest that the present level of activity is lower than that observed in July 1996 and 1997 (BGVN 22:08). Of the 18 explosions closely witnessed, only two were capable of sending ballistic blocks higher than the N crater rim. All ballistic material felt back into the crater. However, the presence of fresh impact structures on the northern pyroclastic rampart of Jonggring Seloko Crater indicated that it is still occasionally showered by pyroclastic blocks.

The morphology of the crater floor changed considerably after the 1994 and 1995 eruptions. In mid-1996 and 1997 the bottom of Jonggring Seloko Crater was too deep to be visible from the NE crater rim. Observations on 18 September 1999 showed that the floor of the crater had risen several tens of meters and about 2/3 of the crater floor could be clearly seen. No evidence of lava or dome extrusion could be observed because of a thick carapace of pyroclastic ejecta and scree. The floor consists of an irregular platform. The southern part of the platform showed evidence of a recent subsidence event (scalloped normal faulting of ~10 m). The platform contained three principal active vents covered by their own ejecta. The central vent was partly surrounded by a small pyroclastic crescent.

Unsteady noisy steam emissions occurred sporadically either from the major vents or from other smaller vents on the crater floor. Larger explosions occurred only from the three principal vents and frequently progressed from the western to the eastern vent during the same explosion event. A moderate explosion at the central vent, observed from the NE crater rim, started with a booming sound followed by the noisy fallback of ballistic material into the crater. Convective uplift of the ash cloud allowed clear observation of the vent area which showed ash geysering silently ~20-40 m above the vent (with "cocktail" projections) for a few tens of seconds. The floor of the crater showed several dark areas, probably corresponding to wet zones, suggesting that water plays an important role in the explosive activity of Jonggring Seloko Crater.

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

Information Contacts: Jean-Luc le Pennec, Institut de Recherche pour le Developpement and Institut de Physique du Globe de Paris. Tour 26, case 109, 4 place Jussieu, 75 252 Paris cedex 05, France; Sandrine Poteaux, 6 Villa Daviel, 75013 Paris, France; Isya N. Dana, Volcanological Survey of Indonesia, Jalan Diponegoro No 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

In mid-September, increasing seismic activity was recorded at the volcano, continuing into the first week of October. As a result of this increased activity, instrumentation for a new deformation network was installed on the W-side of the volcano and 10 new seismic stations were installed on the N-side and at other locations on the volcano. In late September, an inclinometer was installed adjacent to the seismically active area and a Yellow alert was declared, which continued as of 5 October.

Increased seismicity started on 14 September in conjunction with increased gas emissions, with plumes rising up to 3 km above the volcano. On 1 October, a column of vapor and gas rose to a height of 1 km. COSPEC measurements on 2 and 4 October indicated elevated SO₂ fluxes of ~4,300 and ~9,500 tons/day, respectively. Then on the morning of 5 October three explosions at 0721, 0738, and 0743 threw blocks of rock and ash around the crater. The largest in this sequence, at 0738, yielded a reduced displacement of 25 cm² and explosion hypocenters 4-5 km under the crater. During the night of the 4th, seismicity had reduced considerably and the activity that followed appeared to have produced a seal, leading to the subsequent explosions.

One particularly vulnerable town, Baños, was evacuated during the current crisis.

Reference. Hall, M., Robin, C., Beate, B., Mothes, P., Monzier, M., 1999. Tungurahua Volcano, Ecuador: structure, eruptive history and hazards. Journal of Volcanology and Geothermal Research, v. 91, p. 1-21.

Geologic Background. Tungurahua, a steep-sided andesitic-dacitic stratovolcano that towers more than 3 km above its northern base, is one of Ecuador's most active volcanoes. Three major edifices have been sequentially constructed since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II itself collapsed about 3000 years ago and produced a large debris-avalanche deposit and a horseshoe-shaped caldera open to the west, inside which the modern glacier-capped stratovolcano (Tungurahua III) was constructed. Historical eruptions have all originated from the summit crater, accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador.

The following report, from the scientific team at the Observatorio Volcanologico de Los Andes del Sur (OVDAS), is for the period 20 August through 11 October 1999.

Since 22 August, seismic activity at Villarrica has increased from background levels, shown by an increase in the amplitude of harmonic tremor signals registered at station CVVI, located 19 km from the crater. Periods of high-amplitude tremor lasting 2-30 hours occurred, alternating with background-level tremor (banded tremor). Elevated levels of harmonic tremor lasting for hours-days preceded the last eruption in 1984. OVDAS has therefore recommended to local authorities a move to Level 2 (Green) in the "Semaforo" (traffic light) alert scheme adapted for Villarrica. If the harmonic tremor increases further in amplitude or high levels are maintained for longer periods, recommendations will be made to move to Level 3 (Amber). An energetic long-period event on 15 September, the culmination of this period of high-amplitude tremor, is considered to have been associated with a small explosive event in the crater and ash emission.

The level of seismicity rapidly decreased after 15 September to unusually low levels. Magma level in the crater lake however, is inferred to have been high on 25 September from nighttime observations of glow. Observations by local residents suggest that during the early morning of 26 September a second explosion occurred, depositing new ash. This event was not registered by CVVI so is considered to have been less energetic than the first.

On 1 October, OVDAS scientists on a helicopter flight observed that the level of the magma lake was unusually low (~200 m below the crater rim). The incandescent lava was only visible through a small opening (20-30 m) in a solid crust. Ashfall deposits extended ~5 km ESE from the crater. The deposits clearly exhibited two components, that of the Strombolian fountain (proximally) and that of the upper ash plume. A further increase in tremor amplitude and frequency was observed on 3 October. Observations of new ash and projectiles on the crater rim on the 4th suggested that this tremor episode also culminated in a small explosive event.

A new type of seismic signal, apparently strong hybrid earthquakes, was also registered at the VNVI seismic station (4 km from the crater). They have been increasing in number since 1 October (typically 2-3/day) and are not associated with any visible activity. These events do not comprise the normal background activity.

Geologic Background. Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Information Contacts: Gustavo Fuentealba¹, Paola Peña S., and Eliza Calder, Observatorio Volcanologico de Los Andes del Sur (OVDAS), Casilla 23D, Temuco, Chile (URL: http://www.sernageomin.cl/); 1-also at Universidad de La Frontera (UFRO), Departamento Ciencias Fisicas, Universidad de la Frontera, Instituto del Medioambiente, Avda. Francisco Salazar 01145, Casilla 54-D, Temuco, Chile.

A series of earthquake swarms began along the NW edge of Yellowstone National Park on the evening of 13 June 1999. Between 13 and 22 June over 630 earthquakes were recorded in a region ~13 km NE of the town of West Yellowstone, Montana and ~5 km SE of Grayling Creek Junction, Montana. The largest of the earthquakes, M 3.5, occurred at 1038 on 16 June. No residents reported noticing the earthquakes. The activity was located along mapped faults that extend eastward from the S end of 1959 Hebgen Lake rupture (the 7.5 magnitude Hebgen Lake earthquake was the largest in the history of the Intermountain region). Earthquake swarms are common in Yellowstone, but this was the largest since June 1997. That swarm also occurred along the NW edge of the park, the area that historically records the most persistent swarms. The most extensive recorded earthquake swarm occurred ~10 km SE of the June activity over a period of several months in 1985 and 1986.

Seismicity in the Yellowstone region is recorded by 22 University of Utah Seismograph Stations and two Global Positioning System stations. The telemetered surveillance system provides coverage for both earthquakes and ground movement related to volcanic or earthquake activity. The project is conducted cooperatively with the U.S. Geological Survey Volcano Hazards Program and the National Park Service.

As discussed by Robert B. Smith on his web pages at the University of Utah, Yellowstone National Park is located on a hotspot within the North American Plate; its three calderas are the most recent in a string that extends to the SW across Idaho. Dubbed "The Restless Giant" for its geological instability, Yellowstone could one day have another major eruption like the one that formed its youngest caldera 600,000 years ago. Symptoms include numerous earthquakes (most too small to be felt), uplift and subsidence of the ground surface, and persistent hydrothermal activity. The current rates of seismicity, ground deformation, and hydrothermal activity at Yellowstone, although high by most geologic standards, are probably typical of long time periods between eruptions and therefore not a reason for immediate concern. Scientists from the U.S. Geological Survey and the University of Utah are studying the Yellowstone region to assess the potential hazards from future earthquakes and eruptions and to provide warning if the current level of unrest should intensify.

Geologic Background. The Yellowstone Plateau volcanic field developed through three volcanic cycles spanning two million years that included some of the world's largest known eruptions. Eruption of the over 2450 km3 Huckleberry Ridge Tuff about 2.1 million years ago created the more than 75-km-long Island Park caldera. The second cycle concluded with the eruption of the Mesa Falls Tuff around 1.3 million years ago, forming the 16-km-wide Henrys Fork caldera at the western end of the first caldera. Activity subsequently shifted to the present Yellowstone Plateau and culminated 640,000 years ago with the eruption of the over 1000 km3 Lava Creek Tuff and the formation of the present 45 x 85 km caldera. Resurgent doming subsequently occurred at both the NE and SW sides of the caldera and voluminous (1000 km3) intracaldera rhyolitic lava flows were erupted between 150,000 and 70,000 years ago. No magmatic eruptions have occurred since the late Pleistocene, but large hydrothermal eruptions took place near Yellowstone Lake during the Holocene. Yellowstone is presently the site of one of the world's largest hydrothermal systems including Earth's largest concentration of geysers.

Information Contacts: U.S. Geological Survey, Cascades Volcano Observatory, 5400 MacArthur Blvd., Vancouver, WA 98661 USA (URL: https://volcanoes.usgs.gov/observatories/cvo/); Michael Finley, Tom Deutch, and Anne Deutch, National Park Service, P.O. Box 168, Yellowstone, WY 82190 USA (URL: https://www.nps.gov/yell/); Robert B. Smith, Department of Geology and Geophysics, 135 S. 1460 East, Room 702, University of Utah, Salt Lake City, UT 84112 USA.

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/).