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Bulletin of the Global Volcanism Network

All reports of volcanic activity published by the Smithsonian since 1968 are available through a monthly table of contents or by searching for a specific volcano. Until 1975, reports were issued for individual volcanoes as information became available; these have been organized by month for convenience. Later publications were done in a monthly newsletter format. Links go to the profile page for each volcano with the Bulletin tab open.

Information is preliminary at time of publication and subject to change.


Recently Published Bulletin Reports

Nyiragongo (DR Congo) Lava lake persists during June-November 2019

Ebeko (Russia) Frequent moderate explosions, ash plumes, and ashfall continue through November 2019

Nevado del Ruiz (Colombia) Intermittent ash plumes with significant gas and steam emissions during January 2016-December 2017

Sabancaya (Peru) Explosions, ash and SO2 plumes, thermal anomalies, and lava dome growth during June-November 2019

Karangetang (Indonesia) Lava flows, strong thermal anomalies, gas-and-steam emissions, and ash plumes during May-November 2019

Ulawun (Papua New Guinea) New vent, lava fountaining, lava flow, and ash plumes in late September-October 2019

Nyamuragira (DR Congo) Strong thermal anomalies and fumaroles within the summit crater during June-November 2019

Bagana (Papua New Guinea) Intermittent gas-and-steam emissions and thermal anomalies during June-November 2019

Kerinci (Indonesia) Intermittent gas-and-steam and ash plumes during June-early November 2019

Bezymianny (Russia) Lava dome growth, ongoing thermal anomalies, moderate gas-steam emissions, June-November 2019

Mayon (Philippines) Gas-and-steam plumes and summit incandescence during May-October 2019

Merapi (Indonesia) Low-volume dome growth continues during April-September 2019 with rockfalls and small block-and-ash flows



Nyiragongo (DR Congo) — December 2019 Citation iconCite this Report

Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)


Lava lake persists during June-November 2019

Nyiragongo is a stratovolcano with a 1.2 km-wide summit crater containing an active lava lake that has been present since at least 1971. It is located the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo, part of the western branch of the East African Rift System. Typical volcanism includes strong and frequent thermal anomalies, primarily due to the lava lake, incandescence, gas-and-steam plumes, and seismicity. This report updates activity during June through November 2019 with the primary source information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

In the July 2019 monthly report, OVG stated that the lava lake level had dropped during the month, with incandescence only visible at night (figure 68). In addition, the small eruptive cone within the crater, which has been active since 2014, decreased in activity during this timeframe. A MONUSCO (United Nations Stabilization Mission in the Democratic Republic of the Congo) helicopter overflight took photos of the lava lake and observed that the level had begun to rise on 27 July. Seismicity was relatively moderate throughout this reporting period; however, on 9-16 July and 21 August strong seismic swarms were recorded.

Figure (see Caption) Figure 68. Webcam images of Nyiragongo on 20 July 2019 where incandescence is not visible during the day (left) but is observed at night (right). Incandescence is accompanied by gas-and-steam emissions. Courtesy of OVG.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data continued to show frequent and strong thermal anomalies within 5 km of the crater summit through November 2019 (figure 69). Similarly, the MODVOLC algorithm reported almost daily thermal hotspots (more than 600) within the summit crater between June 2019 through November. These data are corroborated with Sentinel-2 thermal satellite imagery and a photo from OVG on 19 December 2019 showing the active lava lake (figures 70 and 71).

Figure (see Caption) Figure 69. Thermal anomalies at Nyiragongo from 3 January through November 2019 as recorded by the MIROVA system (Log Radiative Power) were frequent and strong. Courtesy of MIROVA.
Figure (see Caption) Figure 70. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) showed ongoing thermal activity (bright yellow-orange) at Nyiragongo during June through November 2019. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 71. Photo of the active lava lake in the summit crater at Nyiragongo on 19 December 2019. Incandescence is accompanied by a gas-and-steam plume. Courtesy of OVG via Charles Balagizi.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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); Charles Balagizi (Twitter: @CharlesBalagizi, https://twitter.com/CharlesBalagizi).


Ebeko (Russia) — December 2019 Citation iconCite this Report

Ebeko

Russia

50.686°N, 156.014°E; summit elev. 1103 m

All times are local (unless otherwise noted)


Frequent moderate explosions, ash plumes, and ashfall continue through November 2019

Activity at Ebeko includes frequent explosions that have generated ash plumes reaching altitudes of 1.5-6 km over the last several years, with the higher altitudes occurring since mid-2018 (BGVN 43:03, 43:06, 43:12, 44:07). Ash frequently falls in Severo-Kurilsk (7 km ESE), which is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT). This activity continued during June through November 2019; the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Explosive activity during December 2018 through November 2019 often sent ash plumes to altitudes between 2.2 to 4.5 km, or heights of 1.1 to 3.4 km above the crater (table 8). Eruptions since 1967 have originated from the northern crater of the summit area (figure 20). Webcams occasionally captured ash explosions, as seen on 27 July 2019(figure 21). KVERT often reported the presence of thermal anomalies; particularly on 23 September 2019, a Sentinel-2 thermal satellite image showed a strong thermal signature at the crater summit accompanied by an ash plume (figure 22). Ashfall is relatively frequent in Severo-Kurilsk (7 km ESE) and can drift in different direction based on the wind pattern, which can be seen in satellite imagery on 30 October 2019 deposited NE and SE from the crater(figure 23).

Table 8. Summary of activity at Ebeko, December 2018-November 2019. S-K is Severo-Kurilsk (7 km ESE of the volcano). TA is thermal anomaly in satellite images. Data courtesy of KVERT.

Date Plume Altitude (km) Plume Distance Plume Directions Other Observations
30 Nov-07 Dec 2018 3.6 -- E Explosions. Ashfall in S-K on 1, 4 Dec.
07-14 Dec 2018 3.5 -- E Explosions.
25 Jan-01 Feb 2019 2.3 -- -- Explosions. Ashfall in S-K on 27 Jan.
02-08 Feb 2019 2.3 -- -- Explosions. Ashfall in S-K on 4 Feb.
08-15 Feb 2019 2.5 -- -- Explosions. Ashfall in S-K on 11 Feb.
15-22 Feb 2019 3.6 -- -- Explosions.
22-26 Feb 2019 2.5 -- -- Explosions. Ashfall in S-K on 23-26 Feb.
01-02, 05 Mar 2019 -- -- -- Explosions. Ashfall in S-K on 1, 5 Mar.
08-10 Mar 2019 4 30 km ENE Explosions. Ashfall in S-K on 9-10 Mar.
15-19, 21 Mar 2019 4.5 -- -- Explosions. Ashfall in S-K on 15-16, 21 Mar.
22, 24-25, 27-28 Mar 2019 4.2 -- -- Explosions. Ashfall in S-K on 24-25, 27 Mar.
29-31 Mar, 01, 04 Apr 2019 3.2 -- -- Explosions. Ashfall in S-K on 31 Mar. TA on 31 Mar.
09 Apr 2019 2.2 -- -- Explosions.
12-15 Apr 2019 3.2 -- -- Explosions. TA on 13 Apr.
21-22, 24 Apr 2019 -- -- -- Explosions.
26 Apr-03 May 2019 3 -- -- Explosions.
04, 06-07 May 2019 3.5 -- -- Explosions. TA on 6 May.
12-13 May 2019 2.5 -- -- Explosions. TA 12-13 May.
16-20 May 2019 2.5 -- -- Explosions. TA on 16-17 May.
25-28 May 2019 3 -- -- Explosions. TA on 27-28 May.
03 Jun 2019 3 -- E Explosions.
12 Jun 2019 -- -- -- TA.
14-15 Jun 2019 2.5 -- NW, NE Explosions.
21-28 Jun 2019 -- -- -- TA on 23 June.
28 Jun-05 Jul 2019 4.5 -- Multiple Explosions. TA on 29 Jun, 1 Jul.
05-12 Jul 2019 3.5 -- S Explosions. TA on 11 Jul.
15-16 Jul 2019 2 -- S, SE Explosions. TA on 13-16, 18 Jul.
20-26 Jul 2019 4 -- Multiple Explosions. TA on 18, 20, 25 Jul
25-26, 29 Jul, 01 Aug 2019 2.5 -- Multiple Explosions.
02, 04 Aug 2019 3 -- SE Explosions. TA on 2, 4 Aug.
10-16 Aug 2019 3 -- SE Explosions. TA on 10, 12 Aug.
17-23 Aug 2019 3 -- SE Explosions. TA on 16 Aug.
23, 27-28 Aug 2019 3 -- E Explosions. TA on 23 Aug.
30-31 Aug, 03-05 Sep 2019 3 -- E, SE Explosions on 30 Aug, 3-5 Sep. TA on 30-31 Aug.
07-13 Sep 2019 3 -- S, SE, N Explosions. Ashfall in S-K on 6 Sep. TA on 8 Sep.
13-15, 18 Sep 2019 2.5 -- E Explosions. TA on 15 Sep.
22-23 Sep 2019 3 -- E, NE Explosions. Ashfall in S-K.
27 Sep-04 Oct 2019 4 -- SE, E, NE Explosions.
07-08, 10 Oct 2019 2.5 -- E, NE Explosions. Ashfall in S-K on 4-5 Oct. Weak TA on 8 Oct.
11-18 Oct 2019 4 -- NE Explosions. Ashfall in S-K on 15 Oct. Weak TA on 12 Oct.
18, 20-21, 23 Oct 2019 3 -- N, E, SE Explosions. Weak TA on 20 Oct.
25-26, 29-30 Oct 2019 2.5 -- E, NE Explosions. Weak TA on 29 Oct.
02-06 Nov 2019 3 -- N, E, SE Explosions.
11-12, 14 Nov 2019 3 -- E, NE Explosions.
15-17, 20 Nov 2019 3 -- SE, NE Explosions.
22-23, 28 Nov 2019 2.5 -- SE, E Explosions. Ashfall in S-K on 23 Nov.
Figure (see Caption) Figure 20. Satellite image showing the summit crater complex at Ebeko, July 2019. Monthly mosaic image for July 2019, copyright 2019 Planet Labs, Inc.
Figure (see Caption) Figure 21. Webcam photo of an explosion and ash plume at Ebeko on 27 July 2019. Videodata by IMGG FEB RAS and KB GS RAS (color adjusted and cropped); courtesy of Institute of Volcanology and Seismology FEB RAS, KVERT.
Figure (see Caption) Figure 22. Satellite images showing an ash explosion from Ebeko on 23 September 2019. Top image is in natural color (bands 4, 3, 2). Bottom image is using "Atmospheric Penetration" rendering (bands 12, 11, 8A) to show a thermal anomaly in the northern crater visible around the rising plume. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 23. A satellite image of Ebeko from Sentinel-2 (LC1 natural color, bands 4, 3, 2) on 30 October 2019 showing previous ashfall deposits on the snow going in multiple directions. Courtesy of Sentinel Hub Playground.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data detected four low-power thermal anomalies during the second half of July, and one each in the months of June, August, and October; no activity was recorded in September or November MODVOLC thermal alerts observed only one thermal anomaly between June through November 2019.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); 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/).


Nevado del Ruiz (Colombia) — December 2019 Citation iconCite this Report

Nevado del Ruiz

Colombia

4.892°N, 75.324°W; summit elev. 5279 m

All times are local (unless otherwise noted)


Intermittent ash plumes with significant gas and steam emissions during January 2016-December 2017

Nevado del Ruiz is a glaciated volcano in Colombia (figure 86). It is known for the 13 November 1985 eruption that produced an ash plume and associated pyroclastic flows onto the glacier, triggering a lahar that approximately 25,000 people in the towns of Armero (46 km west) and Chinchiná (34 km east). Since 1985 activity has intermittently occurred at the Arenas crater. The eruption that began on 18 November 2014 included ash plumes dominantly dispersed to the NW of Arenas crater (BGVN 42:06). This bulletin summarizes activity during January 2016 through December 2017 and is based on reports by Servicio Geologico Colombiano and Observatorio Vulcanológico y Sismológico de Manizales, Washington Volcanic Ash Advisory Center (VAAC) notices, and satellite data.

Figure (see Caption) Figure 86. A satellite image of Nevado del Ruiz showing the location of the active Arenas crater. September 2019 Monthly Mosaic image copyright Planet Labs 2019.

Activity during 2016. Throughout January 2016 ash and steam plumes were observed reaching up to a few kilometers. Significant water vapor and volcanic gases, especially SO2, were detected throughout the month. Thermal anomalies were detected in the crater on the 27th and 31st. Significant water vapor and volcanic gas plumes, in particular SO2, were frequently detected by the SCAN DOAS (Differential Optical Absorption Spectroscopy) station and satellite data (figure 87). A M3.2 earthquake was felt in the area on 18 January. Similar activity continued through February with notable ash plumes up to 1 km, and a M3.6 earthquake was felt on the 6th. Ash and gas-and-steam plumes were reported throughout March with a maximum of 3.5 km on the 31st (figure 88). Significant water vapor and gas plumes continued from the Arenas crater throughout the month, and a thermal anomaly was noted on the 28th. An increase in seismicity was reported on the 29th.

Figure (see Caption) Figure 87. Examples of SO2 plumes from Nevado del Ruiz detected by the Aura/OMI instrument on 10, 26, and 31 January 2019. Courtesy of Goddard Space Flight Center.
Figure (see Caption) Figure 88. Ash plumes at Nevado del Ruiz during March. Webcam images courtesy of Servicio Geologico Colombiano, various 2016 reports.

The activity continued into April with a M 3.0 earthquake felt by nearby inhabitants on the 8th, an increase in seismicity reported in the week of 12-18, and another significant increase on the 28th with earthquakes felt around Manizales. Thermal anomalies were noted during 12-18 April with the largest on the 16th. Ash plumes continued through the month as well as significant steam-and-gas plumes. Ashfall was reported in Murillo on the 29th.

The elevated activity continued through May with significant steam plumes up to 1.7 km above the crater during the week of 10-16. Thermal anomalies were reported on the 11th and 12th. Steam, gas, and ash plumes reached 2.5 km above the crater and dispersed to the W and NW. Ashfall was reported in La Florida on the 20th (figure 89) and multiple ash plumes on the 22nd reached 2.5 km and resulted in the closure of the La Nubia airport in Manizales. Ash and gas-and-steam emission continued during June (figure 90).

Figure (see Caption) Figure 89. Ash plumes at Nevado del Ruiz on 17, 18, and 20 May 2016 with fine ash deposited on a car in La Florida, Manizales on the 20th. Webcams located in the NE Guali sector of the volcano, courtesy of Servicio Geologico Colombiano 20 May 2016 report.
Figure (see Caption) Figure 90. Examples of gas-and-steam and ash plumes at Nevado del Ruiz during June and July 2016. Courtesy of Servicio Geologico Colombiano (7 July 2016 report).

Similar activity was reported in July with gas-and-steam and ash plumes often dispersing to the NW and W. Ashfall was reported to the NW on 16 July (figure 91). Drumbeat seismicity was detected on 13, 15, 16, and 17 July, with two hours on the 16th being the longest duration episode do far. Drumbeat seismicity was noted by SGC as indicating dome growth. Significant water vapor and gas emissions continued through August. Ash plumes were reported through the month with plumes up to 1.3 km above the crater on 28 and 2.3 km on 29. Similar activity was reported through September as well as a thermal anomaly and ash deposition apparent in satellite data (figure 92). Drumbeat seismicity was noted again on the 17th.

Figure (see Caption) Figure 91. The location of ashfall resulting from an explosion at Nevado del Ruiz on 16 July 2016 and a sample of the ash under a microscope. The ash is composed of lithics, plagioclase and pyroxene crystals, and minor volcanic glass. Courtesy of Servicio Geologico Colombiano (16 July 2016 report).
Figure (see Caption) Figure 92. This Sentinel-2 thermal infrared satellite image shows elevated temperatures in the Nevado del Ruiz Arenas crater (yellow and orange) on 16 September 2016. Ash deposits are also visible to the NW of the crater. In this image blue is snow and ice. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

During the week of 4-10 October it was noted that activity consisting of regular ash plumes had been ongoing for 22 months. Ash plumes continued with reported plumes reaching 2.5 above the crater throughout October (figure 93), accompanied by significant steam and water vapor emissions. A M 4.4 earthquake was felt nearby on the 7th. Similar activity continued through November and December 2016 with plumes consisting of gas and steam, and sometimes ash reaching 2 km above the crater.

Figure (see Caption) Figure 93. An ash plume rising above Nevado del Ruiz on 27 October 2016. Courtesy of Servicio Geologico Colombiano.

Activity during 2017. Significant steam and gas emissions, especially SO2, continued into early 2017. Ash plumes detected through seismicity were confirmed in webcam images and through local reports; the plumes reached a maximum height of 2.5 km above the volcano on the 6th (figure 94). Drumbeat seismicity was recorded during 3-9, and on 22 January. Inflation was detected early in the month and several thermal anomalies were noted.

Intermittent deformation continued into February. Significant steam-and-gas emissions continued with intermittent ash plumes reaching 1.5-2 km above the volcano. Thermal anomalies were noted throughout the month and there was a significant increase in seismicity during 23-26 February.

Figure (see Caption) Figure 94. Ash plumes at Nevado del Ruiz on 6 January 2017. Courtesy of Servicio Geologico Colombiano.

Thermal anomalies continued to be detected through March. Ash plumes continued to be observed and recorded in seismicity and maximum heights of 2 km above the volcano were noted. Deflation continued after the intermittent inflation the previous month. On 10-11 April a period of short-duration and very low-energy drumbeat seismicity was recorded. Significant gas and steam emission continued through April with intermittent ash plumes reaching 1.5 km above the volcano. Thermal anomalies were detected early in the month.

Unrest continued through May with elevated seismicity, significant steam-and-gas emissions, and ash plumes reaching 1.7 km above the crater. Five episodes of drumbeat seismicity were recorded on 29 May and intermittent deformation continued. There were no available reports for June and July.

Variable seismicity was recorded during August and deflation was measured in the first week. Gas-and-steam plumes were observed rising to 850 m above the crater on the 3rd, and 450 m later in the month. A thermal anomaly was noted on the 14th. There were no available reports for September through December.

On 18 December 2017 the Washington VAAC issued an advisory for an ash plume to 6 km that was moving west and dispersing. The plume was described as a "thin veil of volcanic ash and gasses" that was seen in visible satellite imagery, NOAA/CIMSS, and supported by webcam imagery.

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

Information Contacts: Servicio Geologico Colombiano (SGC), Diagonal 53 No. 34-53 - Bogotá D.C., Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html); Observatorio Vulcanológico y Sismológico de Manizales (URL: https://www.facebook.com/ovsmanizales); 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); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Sabancaya (Peru) — December 2019 Citation iconCite this Report

Sabancaya

Peru

15.787°S, 71.857°W; summit elev. 5960 m

All times are local (unless otherwise noted)


Explosions, ash and SO2 plumes, thermal anomalies, and lava dome growth during June-November 2019

Sabancaya is an andesitic stratovolcano located in Peru. The most recent eruptive episode began in early November 2016, which is characterized by gas-and-steam and ash emissions, seismicity, and explosive events (BGVN 44:06). The ash plumes are dispersed by wind with a typical radius of 30 km, which occasionally results in ashfall. Current volcanism includes high seismicity, gas-and-steam emissions, ash and SO2 plumes, numerous thermal anomalies, and explosive events. This report updates information from June through November 2019 using information primarily from the Instituto Geofisico del Peru (IGP) and Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico) (OVI-INGEMMET).

Table 5. Summary of eruptive activity at Sabancaya during June-November 2019 based on IGP weekly reports, the Buenos Aires VAAC advisories, the HIGP MODVOLC hotspot monitoring algorithm, and Sentinel-5P/TROPOMI satellite data.

Month Avg. Daily Explosions by week Max plume Heights (km above crater) Plume drift MODVOLC Alerts Min Days with SO2 over 2 DU
Jun 2019 12, 13, 16, 17 2.6-3.8 30 km S, SW, E, SE, NW, NE 15 20
Jul 2019 23, 22, 16, 13 2.3-3.7 E, SE, S, NE 7 25
Aug 2019 12, 30, 25, 26 2-4.5 30 km NW, W S, NE, SE, SW 7 25
Sep 2019 29, 32, 24, 15 1.5-2.5 S, SE, E, W, NW, SW 14 26
Oct 2019 32, 36, 44, 48, 28 2.5-3.5 S, SE, SW, W 11 25
Nov 2019 58, 50, 47, 17 2-4 W, SW, S, NE, E 13 22

Explosions, ash emissions, thermal signatures, and high concentrations of SO2 were reported each week during June-November 2019 by IGP, the Buenos Aires Volcanic Ash Advisory Centre (VAAC), HIGP MODVOLC, and Sentinel-2 and Sentinel-5P/TROPOMI satellite data (table 5). Thermal anomalies were visible in the summit crater, even in the presence of meteoric clouds and ash plumes were occasionally visible rising from the summit in clear weather (figure 68). The maximum plume height reached 4.5 km above the crater drifting NW, W, and S the week of 29 July-4 August, according to IGP who used surveillance cameras to visually monitor the plume (figure 69). This ash plume had a radius of 30 km, which resulted in ashfall in Colca (NW) and Huambo (W). On 27 July the SO2 levels reached a high of 12,814 tons/day, according to INGEMMET. An average of 58 daily explosions occurred in early November, which is the largest average of this reporting period.

Figure (see Caption) Figure 68. Sentinel-2 satellite imagery detected ash plumes, gas-and-steam emissions, and multiple thermal signatures (bright yellow-orange) in the crater at Sabancaya during June-November 2019. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 69. A webcam image of an ash plume rising from Sabancaya on 1 August 2019 at least 4 km above the crater. Courtesy of IGP.

Seismicity was also particularly high between August and September 2019, according to INGEMMET. On 14 August, roughly 850 earthquakes were detected. There were 280 earthquakes reported on 15 September, located 6 km NE of the crater. Both seismic events were characterized as seismic swarms. Seismicity decreased afterward but continued through the reporting period.

In February 2017, a lava dome was established inside the crater. Since then, it has been growing slowly, filling the N area of the crater and producing thermal anomalies. On 26 October 2019, OVI-INGEMMET conducted a drone overflight and captured video of the lava dome (figure 70). According to IGP, this lava dome is approximately 4.6 million cubic meters with a growth rate of 0.05 m3/s.

Figure (see Caption) Figure 70. Drone images of the lava dome and degassing inside the crater at Sabancaya on 26 (top) and 27 (bottom) October 2019. Courtesy of INGEMMET (Informe Ténico No A6969).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows strong, consistent thermal anomalies occurring all throughout June through November 2019 (figure 71). In conjunction with these thermal anomalies, the October 2019 special issue report by INGEMMET showed new hotspots forming along the crater rim in July 2018 and August 2019 (figure 72).

Figure (see Caption) Figure 71. Thermal anomalies at Sabancaya for 3 January through November 2019 as recorded by the MIROVA system (Log Radiative Power) were frequent, strong, and consistent. Courtesy of MIROVA.
Figure (see Caption) Figure 72. Thermal hotspots on the NW section of the crater at Sabancaya using MIROVA images. These images show the progression of the formation of at least two new hotspots between February 2017 to August 2019. Courtesy of INGEMMET, Informe Técnico No A6969.

Sulfur dioxide emissions also persisted at significant levels from June through November 2019, as detected by Sentinel-5P/TROPOMI satellite data (figure 73). The satellite measurements of the SO2 emissions exceeded 2 DU (Dobson Units) at least 20 days each month during this time. These SO2 plumes sometimes occurred for multiple consecutive days (figure 74).

Figure (see Caption) Figure 73. Consistent, large SO2 plumes from Sabancaya were seen in TROPOMI instrument satellite data throughout June-November 2019, many of which drifted in different directions based on the prevailing winds. Courtesy of NASA Goddard Space Flight Center.
Figure (see Caption) Figure 74. Persistent SO2 plumes from Sabancaya appeared daily during 13-16 September 2019 in the TROPOMI instrument satellite data. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Information Contacts: Instituto Geofisico del Peru (IGP), Calle Badajoz N° 169 Urb. Mayorazgo IV Etapa, Ate, Lima 15012, Perú (URL: https://www.gob.pe/igp); Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa, Peru (URL: http://ovi.ingemmet.gob.pe); 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/); 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/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Karangetang (Indonesia) — December 2019 Citation iconCite this Report

Karangetang

Indonesia

2.781°N, 125.407°E; summit elev. 1797 m

All times are local (unless otherwise noted)


Lava flows, strong thermal anomalies, gas-and-steam emissions, and ash plumes during May-November 2019

Karangetang (also known as Api Siau), located on the island of Siau in the Sitaro Regency, North Sulawesi, Indonesia, has experienced more than 40 recorded eruptions since 1675 in addition to many smaller undocumented eruptions. In early February 2019, a lava flow originated from the N crater (Kawah Dua) traveling NNW and reaching a distance over 3 km. Recent monitoring showed a lava flow from the S crater (Kawah Utama, also considered the "Main Crater") traveling toward the Kahetang and Batuawang River drainages on 15 April 2019. Gas-and-steam emissions, ash plumes, moderate seismicity, and thermal anomalies including lava flow activity define this current reporting period for May through November 2019. The primary source of information for this report comes from daily and weekly reports by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), the Darwin Volcanic Ash Advisory Center (VAAC), and satellite data.

PVMBG reported that white gas-and-steam emissions were visible rising above both craters consistently between May through November 2019 (figures 30 and 31). The maximum altitude for these emissions was 400 m above the Dua Crater on 27 May and 700 m above the Main Crater on 12 June. Throughout the reporting period PVMBG noted that moderate seismicity occurred, which included both shallow and deep volcanic earthquakes.

Figure (see Caption) Figure 30. A Sentinel-2 image of Karangetang showing two active craters producing gas-and-steam emissions with a small amount of ash on 7 August 2019. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 31. Webcam images of gas-and-steam emissions rising from the summit of Karangetang on 14 (top) and 25 (bottom) October 2019. Courtesy of PVMBG via Øystein Lund Andersen.

Activity was relatively low between May and June 2019, consisting mostly of gas-and-steam emissions. On 26-27 May 2019 crater incandescence was observed above the Main Crater; white gas-and-steam emissions were rising from both craters (figures 32 and 33). At 1858 on 20 July, incandescent avalanches of material originating from the Main Crater traveled as far as 1 km W toward the Pangi and Kinali River drainages. By 22 July the incandescent material had traveled another 500 m in the same direction as well as 1 km in the direction of the Nanitu and Beha River drainages. According to a Darwin VAAC report, discreet, intermittent ash eruptions on 30 July resulted in plumes drifting W at 7.6 km altitude and SE at 3 km, as observed in HIMAWARI-8 satellite imagery.

Figure (see Caption) Figure 32. Photograph of summit crater incandescence at Karangetang on 12 May 2019. Courtesy of Dominik Derek.
Figure (see Caption) Figure 33. Photograph of both summit crater incandescence at Karangetang on 12 May 2019 accompanied by gas-and-steam emissions. Courtesy of Dominik Derek.

On 5 August 2019 a minor eruption produced an ash cloud that rose 3 km and drifted E. PVMBG reported in the weekly report for 5-11 August that an incandescent lava flow from the Main Crater was traveling W and SW on the slopes of Karangetang and producing incandescent avalanches (figure 34). During 12 August through 1 September lava continued to effuse from both the Main and Dua craters. Avalanches of material traveled as far as 1.5 km SW toward the Nanitu and Pangi River drainages, 1.4-2 km to the W of Pangi, and 1.8 km down the Sense River drainage. Lava fountaining was observed occurring up to 10 m above the summit on 14-20 August.

Figure (see Caption) Figure 34. Photograph of summit crater incandescence and a lava flow from Karangetang on 7 August 2019. Courtesy of MAGMA Indonesia.

PVMBG reported that during 2-22 September lava continued to effuse from both craters, traveling SW toward the Nanitu, Pangi, and Sense River drainages as far as 1.5 km. On 24 September the lava flow occasionally traveled 0.8-1.5 km toward the West Beha River drainage. The lava flow from the Main Crater continued through at least the end of November, moving SW and W as far as 1.5 km toward the Nanitu, Pangi, and Sense River drainages. In late October and onwards, incandescence from both summit craters was observed at night. The lava flow often traveled as far as 1 km toward the Batang and East Beha River drainage on 12 November, the West Beha River drainage on 15, 22, 24, and 29 November, and the Batang and West Beha River drainages on 25-27 November (figure 35). On 30 November a Strombolian eruption occurred in the Main Crater accompanied by gas-and-steam emissions rising 100 m above the Main Crater and 50 m above the Dua Crater. Lava flows traveled SW and W toward the Nanitu, Sense, and Pangi River drainages as far as 1.5 km, the West Beha and Batang River drainages as far as 1 km, and occasionally the Batu Awang and Kahetang River drainages as far as 2 km. Lava fountaining was reported occurring 10-25 m above the Main Crater and 10 m above the Dua Crater on 6, 8-12, 15, 21-30 November.

Figure (see Caption) Figure 35. Webcam image of gas-and-steam emissions rising from the summit of Karangetang accompanied by incandescence and lava flows at night on 27 November 2019. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed consistent and strong thermal anomalies within 5 km of the summit craters from late July through November 2019 (figure 36). Satellite imagery from Sentinel-2 corroborated this data, showing strong thermal anomalies and lava flows originating from both craters during this same timeframe (figure 37). In addition to these lava flows, satellite imagery also captured intermittent gas-and-steam emissions from May through November (figure 38). MODVOLC thermal alerts registered 165 thermal hotspots near Karangetang's summit between May and November.

Figure (see Caption) Figure 36. Frequent and strong thermal anomalies at Karangetang between 3 January through November 2019 as recorded by the MIROVA system (Log Radiative Power) began in late July and were recorded within 5 km of the summit craters. Courtesy of MIROVA.
Figure (see Caption) Figure 37. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity (bright orange) at Karangetang from July into November 2019. The lava flows traveled dominantly in the W direction from the Main Crater. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 38. Sentinel-2 satellite imagery showing gas-and-steam emissions with a small amount of ash (middle and right) rising from both craters of Karangetang during May through November 2019. Courtesy of Sentinel Hub Playground.

Sentinel-5P/TROPOMI satellite data detected multiple sulfur dioxide plumes between May and November 2019 (figure 39). These emissions occasionally exceeded 2 Dobson Units (DU) and drifted in different directions based on the dominant wind pattern.

Figure (see Caption) Figure 39. SO2 emissions from Karangetang (indicated by the red box) were seen in TROPOMI instrument satellite data during May through November 2019, many of which drifted in different directions based on the prevailing winds. Top left: 27 May 2019. Top middle: 26 July 2019. Top right: 17 August 2019. Bottom left: 27 September 2019. Bottom middle: 3 October 2019. Bottom right: 21 November 2019. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

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.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://SO2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com); Dominik Derek (URL: https://www.facebook.com/07dominikderek/).


Ulawun (Papua New Guinea) — December 2019 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


New vent, lava fountaining, lava flow, and ash plumes in late September-October 2019

Ulawun is a basaltic-to-andesitic stratovolcano located in West New Britain, Papua New Guinea, with typical activity consisting of seismicity, gas-and-steam plumes, and ash emissions. The most recent eruption began in late June 2019 involving ash and gas-and-steam emissions, increased seismicity, and a pyroclastic flow (BGVN 44:09). This report includes volcanism from September to October 2019 with primary source information from the Rabaul Volcano Observatory (RVO) and the Darwin Volcanic Ash Advisory Centre (VAAC).

Activity remained low through 26 September 2019, mainly consisting of variable amounts of gas-and-steam emissions and low seismicity. Between 26 and 29 September RVO reported that the seismicity increased slightly and included low-level volcanic tremors and Real-Time Seismic Amplitude Measurement (RSAM) values in the 200-400 range on 19, 20, and 22 September. On 30 September small volcanic earthquakes began around 1000 and continued to increase in frequency; by 1220, they were characterized as a seismic swarm. The Darwin VAAC advisory noted that an ash plume rose to 4.6-6 km altitude, drifting SW and W, based on ground reports.

On 1 October 2019 the seismicity increased, reaching RSAM values up to 10,000 units between 0130 and 0200, according to RVO. These events preceded an eruption which originated from a new vent that opened on the SW flank at 700 m elevation, about three-quarters of the way down the flank from the summit. The eruption started between 0430 and 0500 and was defined by incandescence and lava fountaining to less than 100 m. In addition to lava fountaining, light- to dark-gray ash plumes were visible rising several kilometers above the vent and drifting NW and W (figure 21). On 2 October, as the lava fountaining continued, ash-and-steam plumes rose to variable heights between 2 and 5.2 km (figures 22 and 23), resulting in ashfall to the W in Navo. Seismicity remained high, with RSAM values passing 12,000. A lava flow also emerged during the night which traveled 1-2 km NW. The main summit crater produced white gas-and-steam emissions, but no incandescence or other signs of activity were observed.

Figure (see Caption) Figure 21. Photographs of incandescence and lava fountaining from Ulawun during 1-2 October 2019. A) Lava fountains along with ash plumes that rose several kilometers above the vent. B) Incandescence and lava fountaining seen from offshore. Courtesy of Christopher Lagisa.
Figure (see Caption) Figure 22. Photographs of an ash plume rising from Ulawun on 1 October 2019. In the right photo, lava fountaining is visible. Courtesy of Christopher Lagisa.
Figure (see Caption) Figure 23. Photograph of lava fountaining and an ash plume rising from Ulawun on 1 October 2019. Courtesy of Joe Metto, WNB Provincial Disaster Office (RVO Report 2019100101).

Ash emissions began to decrease by 3 October 2019; satellite imagery and ground observations showed an ash cloud rising to 3 km altitude and drifting N, according to the Darwin VAAC report. RVO reported that the fissure eruption on the SW flank stopped on 4 October, but gas-and-steam emissions and weak incandescence were still visible. The lava flow slowed, advancing 3-5 m/day, while declining seismicity was reflected in RSAM values fluctuating around 1,000. RVO reported that between 23 and 31 October the main summit crater continued to produce variable amounts of white gas-and-steam emissions (figure 24) and that no incandescence was observed after 5 October. Gas-and-steam emissions were also observed around the new SW vent and along the lava flow. Seismicity remained low until 27-29 October; it increased again and peaked on 30 October, reaching an RSAM value of 1,700 before dropping and fluctuating around 1,200-1,500.

Figure (see Caption) Figure 24. Webcam photo of a gas-and-steam plume rising from Ulawun on 30 October 2019. Courtesy of the Rabaul Volcano Observatory (RVO).

In addition to ash plumes, SO2 plumes were also detected between September and October 2019. Sentinel-5P/TROPOMI data showed SO2 plumes, some of which exceeded 2 Dobson Units (DU) drifting in different directions (figure 25). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed strong, frequent thermal anomalies within 5 km of the summit beginning in early October 2019 and throughout the rest of the month (figure 26). Only one thermal anomaly was detected in early December.

Figure (see Caption) Figure 25. Sentinel-5P/TROPOMI data showing a high concentration of SO2 plumes rising from Ulawun between late September-early October 2019. Top left: 11 September 2019. Top right: 1 October 2019. Bottom left: 2 October 2019. Bottom right: 3 October 2019. Courtesy of the NASA Space Goddard Flight Center.
Figure (see Caption) Figure 26. Frequent and strong thermal anomalies at Ulawun for February through December 2019 as recorded by the MIROVA system (Log Radiative Power) began in early October and continued throughout the month. Courtesy of MIROVA.

Activity in November was relatively low, with only a variable amount of white gas-and-steam emissions visible and low (less than 200 RSAM units) seismicity with sporadic volcanic earthquakes. Between 9-22 December, a webcam showed intermittent white gas-and-steam emissions were observed at the main crater, accompanied by some incandescence at night. Some gas-and-steam emissions were also observed rising from the new SW vent along the lava flow.

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

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://SO2.gsfc.nasa.gov/); Christopher Lagisa, West New Britain Province, Papua New Guinea (URL: https://www.facebook.com/christopher.lagisa, images posted at https://www.facebook.com/christopher.lagisa/posts/730662937360239 and https://www.facebook.com/christopher.lagisa/posts/730215604071639).


Nyamuragira (DR Congo) — December 2019 Citation iconCite this Report

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)


Strong thermal anomalies and fumaroles within the summit crater during June-November 2019

Nyamuragira (also known as Nyamulagira) is a high-potassium basaltic shield volcano located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo. Previous volcanism consisted of the reappearance of a lava lake in the summit crater in mid-April 2018, lava emissions, and high seismicity (BGVN 44:05). Current activity includes strong thermal signatures, continued inner crater wall collapses, and continued moderate seismicity. The primary source of information for this June-November 2019 report comes from the Observatoire Volcanologique de Goma (OVG) and satellite data and imagery from multiple sources.

OVG reported in the July 2019 monthly that the inner crater wall collapses that were observed in May continued to occur. During this month, there was a sharp decrease in the lava lake level, and it is no longer visible. However, the report stated that lava fountaining was visible from a small cone within this crater, though its activity has also decreased since 2014. In late July, a thermal anomaly and fumaroles were observed originating from this cone (figure 85). Seismicity remained moderate throughout this reporting period.

Figure (see Caption) Figure 85. Photograph showing the small active cone within the crater of Nyamuragira in late July 2019. Fumaroles are also observed within the crater originating from the small cone. Courtesy of Sergio Maguna.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows strong, frequent thermal anomalies within 5 km of the summit between June through November (figure 86). The strength of these thermal anomalies noticeably decreases briefly in September. MODVOLC thermal alerts registered 54 thermal hotspots dominantly near the N area of the crater during June through November 2019. Satellite imagery from Sentinel-2 corroborated this data, showing strong thermal anomalies within the summit crater during this same timeframe (figure 87).

Figure (see Caption) Figure 86. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira during 30 January through November 2019 shows strong, frequent thermal anomalies through November with a brief decrease in activity in late April-early May and early September. Courtesy of MIROVA.
Figure (see Caption) Figure 87. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity at Nyamuragira into November 2019. Courtesy of Sentinel Hub Playground.

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sergio Maguna (Facebook: https://www.facebook.com/sergio.maguna.9, images posted at https://www.facebook.com/sergio.maguna.9/posts/1267625096730837).


Bagana (Papua New Guinea) — December 2019 Citation iconCite this Report

Bagana

Papua New Guinea

6.137°S, 155.196°E; summit elev. 1855 m

All times are local (unless otherwise noted)


Intermittent gas-and-steam emissions and thermal anomalies during June-November 2019

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

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

Figure (see Caption) Figure 38. Thermal anomalies near the crater summit at Bagana during February-November 2019 as recorded by the MIROVA system (Log Radiative Power) increased in frequency and power in early August. A small cluster was detected in early October after a brief pause in activity in early September. Courtesy of MIROVA.
Figure (see Caption) Figure 39. Sentinel-2 thermal satellite imagery showing small thermal anomalies at Bagana between July-August 2019. Left: A very faint thermal anomaly and a gas-and-steam plume is seen on 7 July 2019. Right: Two small thermal anomalies are faintly seen on 6 August 2019. Both Sentinel-2 satellite images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 40. A gas-and-steam plume rising from the summit of Bagana on 18 September 2019. Courtesy of Brendan McCormick Kilbride (University of Manchester).

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

Figure (see Caption) Figure 41. Degassing plumes seen from drone footage 100 m above the summit of Bagana. Top: Zoomed out view of the summit of Bagana degassing. Bottom: Closer perspective of the gases emitted from Bagana. Courtesy of Kieran Wood (University of Bristol) and the Bristol Flight Laboratory.
Figure (see Caption) Figure 42. Photos of gas-and-steam plumes rising from Bagana between 14-19 September 2019. Courtesy of Brendan McCormick Kilbride (University of Manchester).

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

Information Contacts: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Brendan McCormick Kilbride, University of Manchester, Manchester M13 9PL, United Kingdom (URL: https://www.research.manchester.ac.uk/portal/brendan.mccormickkilbride.html, Twitter: https://twitter.com/BrendanVolc); Kieran Wood, University of Bristol, Bristol BS8 1QU, United Kingdom (URL: http://www.bristol.ac.uk/engineering/people/kieran-t-wood/index.html, Twitter: https://twitter.com/DrKieranWood, video posted at https://www.youtube.com/watch?v=A7Hx645v0eU); University of Bristol Flight Laboratory, Bristol BS8 1QU, United Kingdom (Twitter: https://twitter.com/UOBFlightLab).


Kerinci (Indonesia) — December 2019 Citation iconCite this Report

Kerinci

Indonesia

1.697°S, 101.264°E; summit elev. 3800 m

All times are local (unless otherwise noted)


Intermittent gas-and-steam and ash plumes during June-early November 2019

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

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

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

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

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

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

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Bezymianny (Russia) — December 2019 Citation iconCite this Report

Bezymianny

Russia

55.972°N, 160.595°E; summit elev. 2882 m

All times are local (unless otherwise noted)


Lava dome growth, ongoing thermal anomalies, moderate gas-steam emissions, June-November 2019

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

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

Figure (see Caption) Figure 32. Photo of Bezymianny showing fumarolic activity on 4 July 2019. Photo by O. Girina (IVS FEB RAS, KVERT); courtesy of KVERT.
Figure (see Caption) Figure 33. Typical infrared satellite images of Bezymianny showing thermal anomalies in the summit crater, including a lava flow to the WNW. Top: 21 August 2019 with SWIR filter (bands 12, 8A, 4). Bottom: 17 September 2019 with Atmospheric Penetration filter (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Mayon (Philippines) — November 2019 Citation iconCite this Report

Mayon

Philippines

13.257°N, 123.685°E; summit elev. 2462 m

All times are local (unless otherwise noted)


Gas-and-steam plumes and summit incandescence during May-October 2019

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

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

Figure (see Caption) Figure 49. Sentinel-2 thermal satellite imagery of Mayon between May-October 2019. Small thermal anomalies were recorded in satellite imagery from the summit and some white gas-and-steam plumes are visible. Top left: 30 May 2019. Top right: 9 June 2019. Bottom left: 22 September 2019. Bottom right: 12 October 2019. Sentinel-2 satellite images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 50. Small SO2 plumes rising from Mayon during May-September 2019 recorded in DU (Dobson Units). Top left: 28 May 2019. Top right: 26 July 2019. Bottom left: 16 August 2019. Bottom right: 23 September 2019. Courtesy of NASA Goddard Space Flight Center.

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

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

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


Merapi (Indonesia) — October 2019 Citation iconCite this Report

Merapi

Indonesia

7.54°S, 110.446°E; summit elev. 2910 m

All times are local (unless otherwise noted)


Low-volume dome growth continues during April-September 2019 with rockfalls and small block-and-ash flows

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

Figure (see Caption) Figure 79. Merapi volcano is located north of Yogyakarta in Central Java. Photo courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 80. A view of the Gendol drainage where avalanches and block-and-ash flows are channeled from the active Merapi lava dome. The Gendol drainage is approximately 400 m wide at the summit. Courtesy of Brett Carr, Lamont-Doherty Earth Observatory.

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

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

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

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

Figure (see Caption) Figure 82. The development of the Merapi summit dome from 2 June 2018 to 17 June 2019. Courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 83. Photos taken of the Merapi summit lava dome in June 2019. Top: This nighttime time-lapse photograph shows incandescence at the south-facing side of the dome on the 16 June. Middle: A closeup of a small rockfall from the dome on 17 June. Bottom: A gas plume accompanying a small rockfall on 17 June. Courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 84. Blocks from an incandescent rockfall off the Merapi dome reached out to 1 km down the Gendol drainage on 26 June 2019. Courtesy of MAGMA Indonesia.

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

Figure (see Caption) Figure 85. The Merapi dome on 30 July 2019 producing a weak plume. Courtesy of MAGMA Indonesia.
Figure (see Caption) Figure 86. Incandescent rocks from the hot lava dome at the summit of Merapi form rockfalls down the Gendol drainage on 14 July 2019. Courtesy of Øystein Lund Andersen.

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

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

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

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

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

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

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

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

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Bulletin of the Global Volcanism Network - Volume 17, Number 06 (June 1992)

Managing Editor: Lindsay McClelland

Agrigan (United States)

Thermal activity but no seismicity or deformation

Aira (Japan)

Explosions and seismicity less frequent

Alamagan (United States)

Fumarolic activity but no shallow seismicity

Anatahan (United States)

Thermal activity but deformation unchanged

Arenal (Costa Rica)

Lava production and tephra ejection continue

Asosan (Japan)

Explosions follow increased seismicity and heating of crater lake

Asuncion (United States)

Strong steaming

Bogoslof (United States)

Steam and ash emission

Chichon, El (Mexico)

Frequent rockfalls and continued thermal activity

Clark (New Zealand)

New submarine volcano identified; no gas bubbling

Clear Lake (United States)

50 small seismic events triggered by M 7.5 earthquake hundreds of km away

Colima (Mexico)

Rockfalls and thermal activity; large lahar deposit described

Etna (Italy)

Continued flank lava production

Farallon de Pajaros (United States)

Vigorous fuming

Galeras (Colombia)

Strong explosion destroys most of summit lava dome

Guguan (United States)

No gas emission

Irazu (Costa Rica)

Fumarolic activity and seismicity continue

Karangetang (Indonesia)

Some decline in explosive activity, lava production, and seismicity, but glowing rockfalls advance 1.5 km

Kilauea (United States)

Continued east rift lava production

Kozushima (Japan)

Earthquake and aftershocks

Langila (Papua New Guinea)

Strombolian explosions and lava flow

Lascar (Chile)

Satellite data show heat from lava dome

Lassen Volcanic Center (United States)

Seismicity apparently triggered by M 7.5 earthquake hundreds of kilometers away

Lengai, Ol Doinyo (Tanzania)

Lava ejection from small crater-floor vent

Long Valley (United States)

Abrupt increase in seismicity triggered by M 7.5 earthquake hundreds of kilometers away

Manam (Papua New Guinea)

Strong ash ejections; Strombolian explosions; lava and pyroclastic flows

Marapi (Indonesia)

Explosion kills one person and injures five others

Maug Islands (United States)

No activity evident

Medicine Lake (United States)

Seismicity apparently triggered by M 7.5 earthquake hundreds of kilometers away

Nyamuragira (DR Congo)

Continued lava production from fissure vents

Pagan (United States)

Recent small ash eruption; long-period earthquakes and tremor; inflation

Pinatubo (Philippines)

Lava dome extruded into caldera lake; small steam-and-ash ejections; lahars and secondary explosions

Poas (Costa Rica)

Vigorous gas emission in and around crater lake; continued seismicity

Rabaul (Papua New Guinea)

Uplift and seismicity increase slightly

Rincon de la Vieja (Costa Rica)

Continued fumarolic activity

Rumble III (New Zealand)

Gas bubbles detected; summit 140 m below surface

Rumble IV (New Zealand)

Gas bubbles detected; summit 450 m below surface

Rumble V (New Zealand)

New submarine volcano identified; rising gas bubbles

Sarigan (United States)

No activity evident

Shasta (United States)

No seismicity triggered by M 7.5 earthquake hundreds of kilometers away

Spurr (United States)

Details of 27 June eruptive cloud

Stromboli (Italy)

Small explosions and seismicity continue

Tangaroa (New Zealand)

New submarine volcano identified; no gas bubbling

Turrialba (Costa Rica)

Occasional seismicity

Unzendake (Japan)

Continued lava dome growth generates pyroclastic flows



Agrigan (United States) — June 1992 Citation iconCite this Report

Agrigan

United States

18.77°N, 145.67°E; summit elev. 965 m

All times are local (unless otherwise noted)


Thermal activity but no seismicity or deformation

A six-member team of USGS volcanologists visited the Commonwealth of the Northern Mariana Islands 11-27 May 1992 at the request of the CNMI Office of Civil Defense. The team observed all of the islands in the chain N of Saipan, installed a new seismic station at the base of frequently active Pagan, remeasured existing EDM networks, mapped the geology of Alamagan, sampled fumaroles and hot springs, and collected rocks and charcoal for radiocarbon dating. No volcanoes in the chain erupted during the observation period.

Remeasurement of five EDM lines on 15-16 May yielded no significant changes (>1 cm) since the network was established in September 1990. Two seismometers temporarily operated on the caldera floor recorded no local shallow seismicity. The temperature of the boiling spring in the caldera was 98°C, the same as in 1990. The volume of water issuing from the hot spring was less than in 1990, maybe because of seasonal rainfall variations. The highest measured fumarole temperature was 102°C, 4° higher than in 1990, perhaps related to a drop in the water table.

Geologic Background. The highest of the Marianas arc volcanoes, Agrigan contains a 500-m-deep, flat-floored caldera. The elliptical island is 8 km long; its summit is the top of a massive 4000-m-high submarine volcano. Deep radial valleys dissect the flanks of the thickly vegetated stratovolcano. The elongated caldera is 1 x 2 km wide and is breached to the NW, from where a prominent lava flow extends to the coast and forms a lava delta. The caldera floor is surfaced by fresh-looking lava flows and also contains two cones that may have formed during the only historical eruption in 1917. This eruption deposited large blocks and 3 m of ash and lapilli on a village on the SE coast, prompting its evacuation.

Information Contacts: R. Moore, USGS; R. Koyanagi, M. Sako, and F. Trusdell, HVO.


Aira (Japan) — June 1992 Citation iconCite this Report

Aira

Japan

31.593°N, 130.657°E; summit elev. 1117 m

All times are local (unless otherwise noted)


Explosions and seismicity less frequent

Only two explosions occurred . . . in June, causing no damage. The month's highest ash clouds rose 2,000 m on 9 and 18 June. Two 9-hour swarms of volcanic earthquakes were recorded, a relatively low level of seismicity for the volcano.

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

Information Contacts: JMA.


Alamagan (United States) — June 1992 Citation iconCite this Report

Alamagan

United States

17.6°N, 145.83°E; summit elev. 744 m

All times are local (unless otherwise noted)


Fumarolic activity but no shallow seismicity

A six-member team of USGS volcanologists visited the Commonwealth of the Northern Mariana Islands 11-27 May 1992 at the request of the CNMI Office of Civil Defense. The team observed all of the islands in the chain N of Saipan, installed a new seismic station at the base of frequently active Pagan, remeasured existing EDM networks, mapped the geology of Alamagan, sampled fumaroles and hot springs, and collected rocks and charcoal for radiocarbon dating.

[At Alamagan] the team measured a temperature of 72°C at one fumarole. No shallow earthquakes or volcanic tremor have been recorded on the Alamagan seismic station since it was installed in September 1990. Charcoal was collected that should date the youngest and one of the oldest eruptions.

Geologic Background. Alamagan is the emergent summit of a large stratovolcano in the central Mariana Islands with a roughly 350-m-deep summit crater east of the center of the island. The exposed cone is largely Holocene in age. A 1.6 x 1 km graben cuts the SW flank. An extensive basaltic-andesite lava flow has extended the northern coast of the island, and a lava platform also occurs on the S flank. Pyroclastic-flow deposits erupted about 1000 years ago have been dated, but reports of historical eruptions were considered invalid (Moore and Trusdell, 1993).

Information Contacts: R. Moore, USGS; R. Koyanagi, M. Sako, and F. Trusdell, HVO.


Anatahan (United States) — June 1992 Citation iconCite this Report

Anatahan

United States

16.35°N, 145.67°E; summit elev. 790 m

All times are local (unless otherwise noted)


Thermal activity but deformation unchanged

A six-member team of USGS volcanologists visited the Commonwealth of the Northern Mariana Islands 11-27 May 1992 at the request of the CNMI Office of Civil Defense. The team observed all of the islands in the chain N of Saipan, installed a new seismic station at the base of frequently active Pagan, remeasured existing EDM networks, mapped the geology of Alamagan, sampled fumaroles and hot springs, and collected rocks and charcoal for radiocarbon dating. No volcanoes in the chain erupted during the observation period.

Remeasurement of the EDM network on 22 May showed no significant changes, consistent with the lack of shallow seismicity since September 1990. Boiling hot springs on the eastern crater floor and solfataras at the base of the nearby crater wall had maximum temperatures of 98°C.

Geologic Background. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of a large stratovolcano with a 2.3 x 5 km compound summit caldera. The larger western portion of the caldera is 2.3 x 3 km wide, and its western rim forms the island's high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A submarine cone, named NE Anatahan, rises to within 460 m of the sea surface on the NE flank, and numerous other submarine vents are found on the NE-to-SE flanks. Sparseness of vegetation on the most recent lava flows had indicated that they were of Holocene age, but the first historical eruption did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.

Information Contacts: R. Moore, USGS; R. Koyanagi, M. Sako, and F. Trusdell, HVO.


Arenal (Costa Rica) — June 1992 Citation iconCite this Report

Arenal

Costa Rica

10.463°N, 84.703°W; summit elev. 1670 m

All times are local (unless otherwise noted)


Lava production and tephra ejection continue

Lava production, tephra ejection, and fumarolic activity continued through mid-July. Most of the W-flank lava moved down a channel feeding the flow's S lobe, which moved into young forest on the WSW flank, an area that had been affected by the 1968 pyroclastic flows. Since mid-May, the S lobe's front had advanced almost 300 m, reaching 665 m elevation on 10 June and 650 m elevation by the 24th. As it advanced, the lava flow continued to start fires that burned well over a hectare of the surrounding woodland. Between 12 and 22 July, the flow front advanced at an average rate of ~20 m/day, reaching ~2.5 km from the new summit crater (C). The lava supply to the N lobe had dwindled, and its front had halted at 830 m elevation.

Explosions were stronger and more numerous in June than in May. Some caused rumbling that vibrated house windows in La Palma, 4 km N of the volcano. An impact crater 1 m in diameter and 30 cm deep was found at 780 m elevation on the W flank, and large blocks frequently reached slightly >1 km from the new summit crater (C) 12-22 July. Some ash columns rose >1 km above Crater C. The rate of explosions varied; during observations on 12 June, an explosion was heard every hour. Ashfall on the observation point at 780 m elevation, 1.8 km W of the active crater, accumulated more rapidly in the 4 weeks ending 10 June than in the succeeding 2 weeks (see table 5). Vegetation on the NE, E, and SE flanks continues to be affected by acid rain and tephra fall, as it has for more than 20 years. Fumarolic activity occurred from the remnants of the old summit crater (D).

Volcanic seismicity recorded at a station (Fortuna) 4 km E of the active crater averaged 30 events/day, with a maximum of 51 on 18 June (figure 48). Conspicuous tremor episodes occurred on 4, 6, 10, 17, and 30 June. The level of both seismic and pyroclastic activity decreased 12-22 July, as did the number of avalanches from the advancing lava flow front.

Figure (see Caption) Figure 48. Daily number of seismic events recorded at a station (Fortuna) 4 km E of Arenal's active crater, June 1992. Courtesy of the Instituto Costarricense de Electricidad.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI; G. Soto, ICE; M. Fernández, Univ de Costa Rica.


Asosan (Japan) — June 1992 Citation iconCite this Report

Asosan

Japan

32.884°N, 131.104°E; summit elev. 1592 m

All times are local (unless otherwise noted)


Explosions follow increased seismicity and heating of crater lake

Eruptions that occurred from Crater 1 during the night of 30 June-1 July were the first [strong explosions] since . . . December 1990. The daily number of isolated volcanic tremor episodes began to increase in October 1991, and had reached ~100/day by the end of May. Isolated tremor episodes rapidly became more frequent in late June, and the amplitude of continuous tremor also increased through the month.

Ejections of mud and water from the lake in Crater 1 were first noted on 23 April and were sporadically observed later in April and in May. The ejections became more vigorous in late June, increasing in height from 5 m on 24 June to 20 m on the 26th, 50 m on the 29th, and 150 m on the 30th. Surface temperatures of the lake water increased from around 20°C in May 1991 to 78°C in June 1992. Steam plumes also grew to 1,000 m height in late June.

Strong tremor episodes were recorded during the night of 30 June-1 July. During fieldwork at noon on 1 July, the crater was quiet, but many blocks to 0.8 m across had been scattered to 100 m from the crater's NE rim. The eruptions were not seen or heard, but seismic and air-vibration records suggested that they may have occurred at 2349 on 30 June and 0316 on 1 July.

Tremor decreased in early July, but remained at higher levels than in mid-June. Ejections of mud and water to heights of a few tens of meters occurred sporadically through early July, but no additional strong mud/water ejections or eruptions were reported.

Because of the increasing activity, the area within 1 km of the crater was closed to tourists on 24 June, and remained closed as of mid-July.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: JMA.


Asuncion (United States) — June 1992 Citation iconCite this Report

Asuncion

United States

19.671°N, 145.406°E; summit elev. 857 m

All times are local (unless otherwise noted)


Strong steaming

A six-member team of USGS volcanologists visited the Commonwealth of the Northern Mariana Islands 11-27 May 1992 at the request of the CNMI Office of Civil Defense. Vigorous steaming was occurring from several locations in the summit crater [of Asuncion] during observations from a helicopter on 18 May.

Geologic Background. A single large asymmetrical stratovolcano, steeper on the NE side, forms 3-km-wide Asuncion Island. The steep NE flank terminates in high sea cliffs. The gentler SW flanks have low-angle slopes bounded by sea cliffs only a few meters high. The southern flank is cut by a large landslide scar. The southern flanks and western flanks are mantled by ash deposits that may have originated during eruptions in historical time. An explosive eruption in 1906 also produced lava flows that descended about half way down the western and SE flanks, but several other historical eruption reports are of uncertain validity. Few invesitgations have been done on the Cheref and Poyo seamounts, 30 and 50 km SE, respectively.

Information Contacts: R. Moore, USGS; R. Koyanagi, M. Sako, and F. Trusdell, HVO.


Bogoslof (United States) — June 1992 Citation iconCite this Report

Bogoslof

United States

53.93°N, 168.03°W; summit elev. 150 m

All times are local (unless otherwise noted)


Steam and ash emission

A eruption . . . had begun by 6 July, when airplane pilots first reported steam and ash rising through low clouds. Similar activity was seen through the week, when satellite images revealed repeated plumes from Bogoslof. Pilots reported a cloud to ~3 km altitude on 14 July at 1815. Satellite images showed the plume extending roughly 100 km SE, to the S side of Unalaska Island. An image from 16 July at 1140 showed another plume extending ~100 km E to Unalaska. That day, a pilot saw a white plume rising to ~4 km altitude. An episode of vigorous steam and ash ejection began on 20 July at about 1700, and material had reached nearly 8 km asl by 1725, drifting NNE. A dark gray cloud that was ~15 km wide at 3 km altitude was moving NW from the volcano several hours later. Poor weather prevented subsequent observations, but satellite images showed no volcanic plumes rising above weather-cloud tops at ~6 km elevation. There have been no reports of ashfall. Cloudy weather has prevented direct observation of the island . . . .

Geologic Background. Bogoslof is the emergent summit of a submarine volcano that lies 40 km north of the main Aleutian arc. It rises 1500 m above the Bering Sea floor. Repeated construction and destruction of lava domes at different locations during historical time has greatly modified the appearance of this "Jack-in-the-Box" volcano and has introduced a confusing nomenclature applied during frequent visits of exploring expeditions. The present triangular-shaped, 0.75 x 2 km island consists of remnants of lava domes emplaced from 1796 to 1992. Castle Rock (Old Bogoslof) is a steep-sided pinnacle that is a remnant of a spine from the 1796 eruption. Fire Island (New Bogoslof), a small island located about 600 m NW of Bogoslof Island, is a remnant of a lava dome that was formed in 1883.

Information Contacts: AVO; SAB.


El Chichon (Mexico) — June 1992 Citation iconCite this Report

El Chichon

Mexico

17.36°N, 93.228°W; summit elev. 1150 m

All times are local (unless otherwise noted)


Frequent rockfalls and continued thermal activity

The following, from José Luís Macías, Arturo Macías, Jean-Christophe Komorowski, Claus Siebe, and Robert Tilling, describes observations during fieldwork 18 April-21 May 1992, ten years after the major 1982 eruption.

Geology. We made several visits to the crater. The very significant erosion that has occurred in the last 10 years allowed us to descend relatively easily into the crater through its SE wall, where the rim's altitude is 1,060 m. The crater floor is at 900 m elevation.

The only changes that we noticed during our visits were caused by frequent rockfalls from the crater walls. Between the first and second visits, on 19 April and 3 May, new crater-floor rockfall deposits had originated from the SE crater wall. Recently exhumed fault planes veneered by secondary mineralization in the crater wall were also quite common. On the SE part of the rim, a fracture system 90 m long, 6-9 cm wide at its SE end, and 0.2-8 cm wide at the NE end, trended N 65°E, and was associated with mild fumarolic activity. The fracture cuts through bedded domal talus breccia mapped by Rose and others (1984) and might evolve to produce rockfalls in the near future. Several other curviplanar slump fractures encompass apparent areas of several hundred square meters on the crater wall. Thus, more vigorous rockfall activity might be expected, particularly during the coming rainy season or periods of heightened regional seismic activity.

People living near the volcano reported an eruption in late March or early April that produced light ashfall near the volcano, and was accompanied by loud, thunder-like noises. We think that the ashfall most likely was dust produced during large rockfalls from the crater walls, and the noise was the sound of the rockfalls. Eruption-like dust clouds produced by rockfall activity have been described at Kilauea by Tilling (1974) and Tilling and others (1975).

To try to reduce local alarm, J.L. Macías and J.-C. Komorowski described the current activity and their interpretations of it during an informal conference on 19 May with residents of Chapultenango (11 km ESE of the crater), local authorities, and a group of elementary school teachers. Rumors in El Volcán (5 km E of the crater) that the volcano would erupt on its 10th anniversary caused many women and children to leave their homes.

Crater lake. Temperature and acidity of the crater lake were measured three times at two different sites (table 2). Lake temperature had increased from 28.6°C in 1986 to more than 40° in May 1992, nearing the 42° of October 1983 and February 1984. The pH values of 1.8 and 1.9 measured in 1983 and 1984, respectively, were similar to the April 1992 value. Although no heavy rainfall occurred between 18 April and 8 May, brief rains were common at night and may have diluted the lake with meteoric water, raising its pH. Water samples collected on the lake's N shore are being studied by M.A. Armienta and S. de la Cruz-Reyna at the Instituto de Geofísica, UNAM.

Table 2. Temperature and acidity of the crater lake at El Chichón, measured at sites on the SE and N shores.

Date Site Temperature pH
18 Apr 1992 SE shore 32.4°C 1.87
18 Apr 1992 N shore 36.9°C 1.87
08 May 1992 SE shore 32.1°C 2.15
08 May 1992 N shore 40.1°C 2.23
18 May 1992 SE shore -- --
18 May 1992 N shore 40.2°C 2.31

Fumarolic activity. Gas emission from the crater fed a low-altitude plume visible on clear days. Fumarolic activity was observed throughout the crater but was much more extensive and vigorous in its NNE sector (steaming ground zone of Casadevall and others, 1984). Almost all of the fumaroles showed a steady, audible release of overpressured gas, except for one just N of the crater lake, where frequent noise changes showed that output was distinctly discontinuous. At times, vapor formed only within about 1 m above this vent, suggesting that the gas is initially superheated. All of the fumaroles produced sublimates, primarily native sulfur. A high-temperature fumarole NE of the crater lake contains molten orange sulfur within the orifice of a 1-m-high feature otherwise covered with needle-like amorphous yellow sulfur. Numerous mildly steaming areas were found in the NW and NE parts of the crater, and small fumaroles were active several tens of meters above the crater floor along the path descending from the SE crater wall. Relict portions of altered brecciated trachyandesite described by Rose and others (1984) as remnants of the pre-1982 dome and shown on the map of Casadevall and others (1984) as "altered areas" are still actively steaming.

A few fumaroles on the NE side of the crater are characterized by vigorous geyser activity, sending a constant flux of boiling water to 2-3 m height. In the same area, several boiling springs about 2-3 m above the present crater-lake surface produce boiling streams with a significant discharge into the lake, 50 m away. A similar situation was evident near a boiling mud pit in the NW part of the crater. These boiling streams are sites of mineral precipitation, and active red, brown, and green algae growth. Ferns and grasses have returned to some of these hydrothermal areas. Ponds 1 m in diameter on the NW side of the lake contained vigorously boiling mud (rising <1 m) and water.

The crater lake, which had recovered to November 1982 levels by November 1990, was turquoise-blue and had at least two large zones of intense surface effervescence as described by Casadevall and others (1984).

Although an acrid smell was noted at active hydrothermal areas, H2S concentrations must have decreased below the 2-6 ppm that forced geologists to take special precautions in 1983 and to leave the crater in 1984. During several 4-hour periods in the crater, we never needed gas masks, even in the most active areas.

Other observations. In the Río Magdalena near Xochimilco (8 km NW of the crater), vegetation has made a strong comeback on pyroclastic-flow deposits, which are now covered by tall grasses and acacia trees up to 2 m high with trunks several centimeters in diameter. In all other areas within 2-3 km of the crater, the 1982 deposits are covered only by moss, lichen, and tall grass. Where pyroclastic flows and surges did not surmount topographic barriers or deposited only a thin veneer of material, vegetation is much more lush, with trees, ferns, and other broad-leafed tropical plants. Trees that were charred but not totally blown down >5 km away have begun to grow again from their stumps. The river that now passes through El Volcán was formed after the pyroclastic flows changed the former drainage pattern. An abundant, rusty colored precipitate (Fe oxides) was sampled for analysis.

Future work. More extensive field observations within the crater are planned for November or December. We will measure temperature and pH, and sample sites of hydrothermal activity. An attempt will be made to overfly the crater with a COSPEC, to bring portable seismometers into the crater and somma flanks, and to make bathymetric measurements.

References. Casadevall, T., de la Cruz-Reyna, S., Rose, W., Bagley, S., Finnegan, D., and Zoller, W., 1984, Crater lake and post-eruption hydrothermal activity, El Chichón Volcano, México: Journal of Volcanology and Geothermal Research, v. 23, p. 169-191.

Rose, W., Bornhorst, T., Halsor, S., Capaul, W., Plumley, P., de la Cruz-Reyna, S., Mena, M., and Mota, R., 1984, Volcán el Chichón, México: pre-1982 S-rich eruptive activity: Journal of Volcanology and Geothermal Research, v. 23, p. 147-167.

Tilling, R., 1974, Rockfall activity in pit craters, Kilauea Volcano, Hawaii: Proceedings of the Symposium on "Andean and Antarctic Volcanology Problems", IAVCEI, Santiago, Chile, September 1974, p. 518-528.

Tilling, R., Koyanagi, R., and Holcomb, R., 1975, Rockfall seismicity-correlation with field observations, Makaopuhi Crater, Kilauea Volcano, Hawaii: Journal of Research, U.S. Geological Survey, v. 3, p. 345-361.

Geologic Background. El Chichón is a small, but powerful trachyandesitic tuff cone and lava dome complex that occupies an isolated part of the Chiapas region in SE México far from other Holocene volcanoes. Prior to 1982, this relatively unknown volcano was heavily forested and of no greater height than adjacent nonvolcanic peaks. The largest dome, the former summit of the volcano, was constructed within a 1.6 x 2 km summit crater created about 220,000 years ago. Two other large craters are located on the SW and SE flanks; a lava dome fills the SW crater, and an older dome is located on the NW flank. More than ten large explosive eruptions have occurred since the mid-Holocene. The powerful 1982 explosive eruptions of high-sulfur, anhydrite-bearing magma destroyed the summit lava dome and were accompanied by pyroclastic flows and surges that devastated an area extending about 8 km around the volcano. The eruptions created a new 1-km-wide, 300-m-deep crater that now contains an acidic crater lake.

Information Contacts: José Luís Macías V. and Michael Sheridan, State Univ of New York, Buffalo, NY; Jean-Christophe Komorowski and Claus Siebe, Instituto de Geofísica, UNAM; Robert Tilling, USGS.


Clark (New Zealand) — June 1992 Citation iconCite this Report

Clark

New Zealand

36.446°S, 177.839°E; summit elev. -860 m

All times are local (unless otherwise noted)


New submarine volcano identified; no gas bubbling

Three previously unknown submarine arc stratovolcanoes have been identified at the S end of the Kermadec Ridge: Rumble V (36.140°S, 178.195°E, summit 700 m below sea level); Tangaroa (36.318°S, 178.031°E, summit 1,350 m below sea level); and Clark (36.423°S, 177.845°E, summit 1,150 m below sea level) (figure 1). All three have basal diameters of 16-18 km and rise from the seafloor at ~2,300 m depth. The first evidence of the volcanoes was from GLORIA side-scan mapping of the southern Havre Trough-Kermadec Ridge region in 1988 (Wright, 1990). Later investigations, including a photographic and rock-dredge study during the 3-week Rapuhia cruise (early 1992), confirmed previous interpretations. Side-scan and photographic data show a complex terrain of lava flows and talus fans on the flanks of all three volcanoes, with the most pristine-looking morphology at Rumble V. During the 1992 cruise, gas bubbles were detected acoustically, rising from the crests of Rumble III, IV, and V. No gas bubbling was evident from Tangaroa or Clark. Bathymetric surveys indicated that the summits of the shallowest volcanoes, Rumble III and IV, were at ~140 and 450 m, respectively, below the sea surface.

Figure (see Caption) Figure 1. Sketch map of New Zealand's North Island and the southern Kermadec Ridge area, with locations of young volcanoes. Courtesy of Ian Wright.

Reference. Wright, I.C., 1990, Bay of Plenty-Southern Havre Trough physiography, 1:400,000: New Zealand Oceanographic Institute Chart, Miscellaneous Series no. 68.

Geologic Background. Clark submarine volcano lies near the southern end of the Southern Kermadec arc. This basaltic and dacitic stratovolcano consists of a basal substrate of massive lava flows, pillow lavas, and pillow tubes overlain by volcaniclastic sediments. Craters occupy the complex crest of the volcano. Clark is the southernmost volcano of the submarine chain that displays hydrothermal activity. Diffuse hydrothermal venting and sulfide chimneys were observed near the summit of Clark volcano during a New Zealand-American NOAA Vents Program expedition in 2006.

Information Contacts: I. Wright, New Zealand Oceanographic Institute, National Institute of Water and Atmospheric Research, Wellington.


Clear Lake (United States) — June 1992 Citation iconCite this Report

Clear Lake

United States

38.97°N, 122.77°W; summit elev. 1439 m

All times are local (unless otherwise noted)


50 small seismic events triggered by M 7.5 earthquake hundreds of km away

Southern California's largest earthquake since 1952, M 7.5 on 28 June, appeared to trigger seismicity at several volcanic centers in California. It was centered roughly 200 km E of Los Angeles. In the following, David Hill describes post-earthquake activity at Long Valley caldera, and Stephen Walter discusses the USGS's seismic network, and the changes it detected at Lassen, Shasta, Medicine Lake, and the Geysers.

In recent years, the USGS northern California seismic network has relied upon Real-Time Processors (RTPs) to detect, record, and locate earthquakes. However, a film recorder (develocorder) collects data from 18 stations in volcanic areas, primarily to detect long-period earthquakes missed by RTPs. The film recorders proved useful in counting the post-M 7.5 earthquakes, most of which were too small to trigger the RTPs.

The film record was scanned for the 24 hours after the M 7.5 earthquake, noting the average coda duration for each identified event. Some events may have been missed because of seismogram saturation by the M 7.5 earthquake. Marked increases in microseismicity were observed at Lassen Peak, Medicine Lake caldera, and the Geysers (table 1). No earthquakes were observed at Shasta, but the lack of operating stations on the volcano limited the capability to observe small events.

Table 1. Number of earthquakes at northern California volcanic centers during 24-hour periods following major earthquakes on 25 April (40.37°N, 124.32°W; M 7.0) and 28 June (34.18°N, 116.47°W; M 7.5) 1992. Events with coda durations less than or equal to 10 seconds and greater than 10 seconds are tallied separately. Earthquakes were identified from film records of seismograms from nearby stations. Courtesy of Stephen Walter.

Volcanic center Lassen Lassen Shasta Shasta Medicine Lake Medicine Lake Geysers Geysers
Codas (seconds) 0-10 11+ 0-10 11+ 0-10 11+ 0-10 11+
25 Apr 1992 0 0 0 1 0 0 7 2
28 Jun 1992 8 14 1 5 12 0 46 4

Film was also scanned for the 24 hours following the M 7.0 earthquake at 40.37°N, 124.32°W (near Cape Mendocino) on 25 April. Although smaller than the 28 June earthquake, its epicenter was only 20-25% as far from the volcanoes. Furthermore, both the 25 April main shock and a M 6.5 aftershock were felt at the volcanic centers, but no felt reports were received from these areas after the 28 June earthquake. Only the Geysers showed any possible triggered events after the 25 April shock. However, background seismicity at the Geysers is higher than at the other centers, and is influenced by fluid injection and withdrawal associated with intensive geothermal development.

Geysers geothermal area report. Film records showed 50 small events in the 24 hours following the M 7.5 earthquake, 46 of which had coda durations

Geologic Background. The late-Pliocene to early Holocene Clear Lake volcanic field in the northern Coast Ranges, contains lava dome complexes, cinder cones, and maars of basaltic-to-rhyolitic composition. The westernmost site of Quaternary volcanism in California, the Clear Lake field is located far to the west of the Cascade Range in a complex geologic setting within the San Andreas transform fault system. Mount Konocti, a composite dacitic lava dome on the south shore of Clear Lake, is the largest volcanic feature. Volcanism has been largely non-explosive, with only one major airfall tuff and no ash flows. The latest eruptive activity, forming maars and cinder cones along the shores of Clear Lake, continued until about 10,000 years ago. A large silicic magma chamber provides the heat source for the Geysers, the world's largest producing geothermal field.

Information Contacts: Stephen Walter and David Hill, MS 977, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 USA.


Colima (Mexico) — June 1992 Citation iconCite this Report

Colima

Mexico

19.514°N, 103.62°W; summit elev. 3850 m

All times are local (unless otherwise noted)


Rockfalls and thermal activity; large lahar deposit described

The following . . . covers activity between 10 April and 30 June 1992, and describes the 25 June 1991 lahar deposits.

Seismicity and rockfall activity. After a brief seismic crisis 4-10 March, activity at Colima remained near background levels. Starting 10 April, seismicity became more frequent. Nine B-type earthquakes were detected by the Red Sismológica de Colima (RESCO) and up to 60 events were recorded 10-20 May at the SW-flank Yerbabuena station (figure 17). Subsequent seismic activity remained near background, with only four B-type earthquakes recorded by RESCO 20-31 May, and three between 1 and 20 June. Seismic activity increased slightly 21-30 June, when 22 B-type earthquakes were recorded and the number of associated seismically detected rockfalls reached 55. Other rockfalls were also noted, probably associated with small diurnal changes in the volcano's hydrothermally altered summit region, which might be related to changes in rock temperature and surface water content. Extraordinary out-of-season precipitation in January, related to the El Niño/Southern Oscillation event of 1991-92, exceeded 700% of the monthly mean of the past 30 years and must have saturated the volcano's upper porous regions.

Figure (see Caption) Figure 17. Sketch map of the summit area and SW flank of Colima, showing major canyons and recent volcanic deposits. Modified from Rodríguez-Elizarrarás, and others, 1991.

Current thermal activity. Fumarolic activity has been steady, with an impressive white plume that can rise several hundred meters above the summit before dissipating. This represents the systematic release of meteoric water accumulated in the upper part of the volcano, not an increase in the magmatic component of the fumarolic activity. Further avalanching of the most precarious hydrothermally altered regions of the summit area is expected during the rainy season, which has just started.

25 June 1991 lahar deposit. Block-and-ash flows emplaced about 1 x 106 m3 of loose pyroclastic debris in the upper Barranca El Cordobán during collapse of the crater dome and rim on 16-17 April 1991, just before the 1991 lava flow began to move down the SW flank (figure 17) (Rodríguez-Elizarrarás and others, 1991). Despite heavy rains in May-September 1991, geologists from the CICT reported that most of the pyroclastic deposits had been washed away without producing sizeable mudflows (Rodríguez-Elizarrarás, and others, 1991). Nevertheless, on 28 March 1992, S. de la Cruz-Reyna and CICT geologists observed a significant laharic mass-flow deposit near El Jabalí, which was studied 5-7 June by J.-C. Komorowski and CICT geologists. A more thorough field and laboratory investigation of this deposit is in progress.

The lahar reached the settlements of La Becerrera and San Antonio, ~12 km SW of the summit (figure 17). Unequivocal non-reworked lahar material was seen at 1,280 m elevation, ~500 m above the confluence of the barrancas El Zarco and El Cordobán. The total thickness was 2 m with a channel width of 30 m. Deposits from this lahar have been identified up to ~1,900 m above sea level, at the bottom of a 20-30-m vertical lava wall in the barranca El Cordobán. The barranca's slope flattens drastically after the lava wall, so deposition probably began below this point. The most distant block-and-ash flow deposits in this barranca reached down to 2,100 m elevation. Upstream, the barranca was significantly eroded by water and debris from a maximum elevation of 2,600 m. Although there is no clear evidence of lahar deposits at San Antonio and La Becerrera, one person reported that the water crossing on the San Antonio-Laguna Verde road was obstructed for two days by lahar material, until machines cleared the debris. Such occurrences are frequent in the rainy season, because several large barrancas draining the upper slopes join there to form a channel 30 m wide.

We estimate the total lahar path at 9.9 km. Based on several measurements at different sites, the lahar deposit averages 25 m wide and 2 m thick. Maximum width was 38 m and maximum thickness 2.9 m at 1,640 m elevation (star on figure 17). Volume was estimated at approximately 0.5 x 106 m3, or about 50% of the material estimated to have been emplaced by the 16-17 April 1991 pyroclastic activity. Field evidence and testimony (see below) unequivocally show that all of the lahar deposit was emplaced during one event. April 1992 field studies of barrancas at higher altitude revealed tremendous erosion since April 1991, leaving ravines incised deeply (to 15 m) into the pre-1991 pyroclastic deposits. A significant volume of loose 1991 debris remains on the mountain, ready to be incorporated into lahars during the rainy season.

Preliminary field investigations showed that the lahar deposit is characterized by a very flat surface, with suspended lava blocks to 1-2 m in maximum dimension protruding through the surface, and abundant pumiceous clasts from eroded 1913 deposits. The deposit is massive, non-stratified, non-graded, poorly sorted, and matrix supported. Its typical massive lowermost zone (0.6 m thick), locally well-sorted, has a concentration of blocks (to 0.5 m size) and wood fragments at the base, a prominent clast-supported medial zone (0.7 m thick) with imbricated sub-rounded boulders (to 0.3 m), and an uppermost massive unit (0.8 m) with a tendency toward reverse grading of lithic cobbles, supported in a sandy matrix. The deposit is typically semi-indurated. Inter-unit contacts are sharply defined in several places, most likely reflecting shear between rheologically different portions of the mass flow. Given the large suspended blocks, the very flat surface, the constant thickness over 9 km of travel distance, the presence of marginal levees, and overturned logs that came to rest vertically, the mass flow clearly had a significant yield strength. However, it must have been relatively swift, as it was able to flow around topographic barriers in the channel, and in some places to leave an elevated deposit on the outside wall when it rounded a sharp curve.

Few people witnessed the lahar. The best testimony came from a farmer (Ramón Aguirre Valencia) who went to Barranca El Cordobán on 26 June 1991 to check his cattle. At 1,600 m altitude, the barranca was filled by a gravel- and boulder-rich deposit with a flat surface. Rocks on the surface were coated with a thin layer of light-colored fine ash. Of the 20 cows killed by the lahar, several could be seen, with horns, heads, and feet protruding from the deposit. Numerous tree trunks several meters long and as much as 30 cm in diameter were also on the lahar's surface. Heavy rains had occurred the previous day, and the lahar apparently began to form after about 2 hours of heavy precipitation, accompanied by loud thunder. The nearest meteorological station (Cofradía de Suchitlán), about 12 km from the lahar's most likely source area, recorded 50 mm of rain on 25 June. By 3 July, a ravine had developed in the new lahar that was as deep (4.6 m) but not as wide as the present channel, which now spans 10.6 m of the 38-m-wide deposit. Five kilometers downstream, the lahar overran and destroyed a 2-m-high stone wall at El Jabalí and clogged the existing channel, but 2 km farther downslope, residents of La Becerrera noticed nothing unusual. Larger sediment flows reported at La Becerrera in January may have been related to breaching of a small earthen dam.

Warnings of future lahar flows and the hazards within Barranca El Cordobán were reiterated to authorities in 1992, as abundant loose material remains from the 1991 eruption and recently exposed 1913 pyroclastic units. The El Jabalí basin is filled with old mass-flow deposits that have traveled down several steep, deeply incised barrancas. On 12 June, CICT organized a meeting that included civil protection authorities to discuss these hazards.

Reference. Rodríguez-Elizarrarás, C., Siebe, C., Komorowski, J.-C., Espindola, J.M., and Saucedo, R., 1991, Field observations of pristine block-and-ash flow deposits emplaced April 16-17, 1991 at Volcán de Colima, México: Journal of Volcanology and Geothermal Research, v. 48, no. 3/4, p. 399-412.

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: Carlos Navarro, Abel Cortés, I. Galindo, José J. Hernández, and Ricardo Saucedo, CICT, Universidad de Colima; Jean-Christophe Komorowski and Claus Siebe, Instituto de Geofísica, UNAM.


Etna (Italy) — June 1992 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3295 m

All times are local (unless otherwise noted)


Continued flank lava production

Lava production continued from the fissure that opened in the W wall of the Valle del Bove on 15 December. Gas emission from 4 vents in the upper part of the fissure (2,215-2,235 m altitude; figure 52) fluctuated daily, probably with changes in weather conditions. However, gas emission has diminished since the eruption's initial months.

Figure (see Caption) Figure 52. Sketch map of the fissure system and the upper part of the lava field at Etna, June 1992. Contour interval, 50 m. Courtesy of Romolo Romano.

No variation was evident in the movement of lava visible through a skylight high in the main channel, at 2,205 m altitude. Lava was also seen flowing through a skylight in lava tubes that formed in June along the channel into which lava was artificially diverted on 27 May (~ 1,980 m elevation) (17:05). From there, lava advanced through a complex series of tubes past the field that had formed in recent months. Lava again reached the surface around 1,800 m altitude from a changing number (generally 3-4) of ephemeral vents at varying locations representing tube bases. Lava flows extruded from these vents have generally been modest, have remained in the center of the lava field, and have not advanced beyond 1,600 m asl. As of the morning of 9 July, only one flow was active within the Valle del Bove, near the center at around 1,670 m altitude, with a fairly well-fed front. The volume of lava produced during ~7 months of eruption is estimated to be around 165 x 106 m3.

Seismic activity during the period was characterized by low energy release. Significant increases were observed 8-9 July, when events of 2-4 Hz were recorded. The most significant perturbations were detected on 8 July at 1554, for 180 seconds, and at 1601 for 130 seconds. Tremor was almost nonexistent, obscured by seismic noise that characterizes periods of low activity at the volcano.

More or less voluminous gas emissions occurred from two vents at the bottom (~100 m from the rim) of the two central craters (Bocca Nuova and La Voragine). Incandescence caused by superheated gases (>1,000°C) from the vent in La Voragine was sometimes visible. Gas also emerged from a vent that has opened in Southeast Crater. Northeast Crater appeared to have been completely obstructed by internal collapse. COSPEC measurements of SO2 flux from the summit crater showed relatively high values of ~ 8,000 t/d.

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: R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania; G. Luongo, OV.


Farallon de Pajaros (United States) — June 1992 Citation iconCite this Report

Farallon de Pajaros

United States

20.546°N, 144.893°E; summit elev. 337 m

All times are local (unless otherwise noted)


Vigorous fuming

When observed from an airplane on 13 May, the volcano continued to fume vigorously, but no active lava was seen.

Geologic Background. The small 2-km-wide island of Farallon de Pajaros (also known as Uracas) is the northernmost and most active volcano of the Mariana Islands. Its relatively frequent historical eruptions dating back to the mid-19th century have caused the andesitic volcano to be referred to as the "Lighthouse of the western Pacific." The symmetrical, sparsely vegetated summit is the central cone within a small caldera cutting an older edifice, remnants of which are seen on the SE and southern sides near the coast. Flank fissures have fed lava flows during historical time that form platforms along the coast. Both summit and flank vents have been active during historical time. Eruptions have also been observed from nearby submarine vents, and Makhahnas seamount, which rises to within 640 m of the sea surface, lies about 10 km to the SW.

Information Contacts: R. Moore, USGS; R. Koyanagi, M. Sako, and F. Trusdell, HVO.


Galeras (Colombia) — June 1992 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Strong explosion destroys most of summit lava dome

An explosion on 16 July, the largest since activity began in 1989, ejected large tephra and may have generated a small pyroclastic flow. Partial collapse of the summit crater's lava dome occurred in June, and minor seismicity had been recorded a few days before the explosion.

June activity. The NW portion of the 1991 lava dome collapsed during June, and explosions and ash emissions occurred from the collapsed area. Las Portillas fumarole, formerly just NW of the dome, was larger after the collapse, and a line of new vents had opened nearby. The fracture on the NW crater wall remained active, and it and Las Portillas appeared to be the highest temperature vents in the crater. Gas columns were generally small, and were dispersed to the N and W. The number and energy release of long-period events (figure 55) and high-frequency earthquakes were low. Ten high-frequency earthquakes occurred in the NW part of the crater, with magnitudes of 0.3-1.7. The amplitude and period of background tremor showed small variations on 15 and 30 June. The maximum rate of SO2 emission measured by COSPEC was ~5,500 t/d.

Figure (see Caption) Figure 55. Daily number of long-period seismic events at Galeras, 1 January 1991-30 June 1992. The first observation of the summit lava dome is marked by an arrow. Courtesy of INGEOMINAS.

Precursory seismicity and tilt. Banded tremor episodes of moderate to high energy occurred 11-12 July, accompanied by a small inflationary tilt event recorded on both instruments near the summit. Between 14 and 16 July, six monochromatic long-period events were recorded, with durations on the order of 80 seconds. On 15 July, there was a small swarm of high-frequency events with magnitudes of 0-0.5.

16 July explosion. The explosion began at 1740 with a strong shock felt in Pasto . . . . More than 90% of the summit lava dome was destroyed as at least 120,000 m3 of blocks were ejected, falling primarily on the E and NE flanks. Blocks 30 cm in diameter fell 2.3 km from the crater, and impact craters to 3.5 m across were found 400 m away. Incandescent blocks started fires 2 km from the crater on the NE flank. The tephra severely damaged a small military facility on the crater rim, and dropped 40-cm blocks on telephone and television facilities near the summit. Roughly 30,000 m3 of ash were dispersed in a narrow band to the W, with the 1-mm isopach extending ~10 km. The dark-gray cauliflower-shaped eruption column reached ~4 km altitude. Reports from observers 10 km WSW of the crater (in Consacá) suggested that small pyroclastic flows may have descended the W flank. A powerful sonic wave generated by the explosion broke windows in Pasto, and reportedly in Consacá.

A seismic signal lasting ~8 minutes accompanied the explosion, saturating instruments for the first 37 seconds. Two distinct signals were recognized, one with a frequency of 1 Hz and a duration magnitude of 3, the other a 1.3-Hz tremor episode that lasted 4 minutes. A high-frequency, M 3.2-3.5 event occurred 26 hours after the explosion, in the S part of the volcano at ~5 km depth.

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: INGEOMINAS-Observatorio Vulcanológico del Sur.


Guguan (United States) — June 1992 Citation iconCite this Report

Guguan

United States

17.307°N, 145.845°E; summit elev. 287 m

All times are local (unless otherwise noted)


No gas emission

A six-member team of USGS volcanologists visited the Commonwealth of the Northern Mariana Islands 11-27 May 1992 at the request of the CNMI Office of Civil Defense. Observations [of Guguan] from an airplane on 13 May and a helicopter on 21 May revealed no gas emission.

Geologic Background. The small island of Guguan, only 2.8 km wide, is composed of an eroded volcano on the south, a caldera with a post-caldera cone, and a northern volcano. The latter has three coalescing cones and a breached summit crater that fed lava flows to the west and NW. The 287-m high point of the island is the south rim of the caldera. Freycinet misidentifed Guguan with Alamagan; reported eruptions in 1819 and 1901 (Catalog of Active Volcanoes of the World) actually refer to solfataric activity on Alamagan (Corwin, 1971). The only known historical eruption of Guguan took place between 1882 and 1884 and produced the northern volcano and lava flows that reached the coast.

Information Contacts: R. Moore, USGS; R. Koyanagi, M. Sako, and F. Trusdell, HVO.


Irazu (Costa Rica) — June 1992 Citation iconCite this Report

Irazu

Costa Rica

9.979°N, 83.852°W; summit elev. 3432 m

All times are local (unless otherwise noted)


Fumarolic activity and seismicity continue

Fumarolic activity continued in the main crater. Its lime-green lake had a mean temperature of 28°C and a minimum pH of 4.9 on 3 June. Fumaroles persisted in the area NE of the lake, with temperatures of 84-90°C. Areas of bubbling to the NE remained vigorous, with strong emission of cold gas, perhaps CO2. Hot bubbling areas were stable at temperatures <=91°C. Fumarolic vents in the sedimentary fan N of the lake were buried by new sedimentation triggered by heavy rains. The resulting zone of steaming ground had surface temperatures of up to 90°C.

Seismicity continued, with 48 events recorded during June at a station (ICR) 2.2 km E of the active crater and 36 low-frequency microseisms registered 5 km WSW of the crater (at station IRZ2). The largest daily earthquake count was 7 on 2 June (at ICR). On 30 June, a M 1.9 event occurred 6.7 km SW of the main crater, at 3 km depth.

Geologic Background. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI; G.J. Soto, ICE; Mario Fernández, Escuela Centroamericana de Geología, Univ de Costa Rica.


Karangetang (Indonesia) — June 1992 Citation iconCite this Report

Karangetang

Indonesia

2.781°N, 125.407°E; summit elev. 1797 m

All times are local (unless otherwise noted)


Some decline in explosive activity, lava production, and seismicity, but glowing rockfalls advance 1.5 km

Activity began to increase in February 1992. Glowing rockfalls on 18 May filled the upper Keting river valley to 4 km from the crater. The volume of the deposit was estimated at 1.2 x 106 m3, ~ 20% of the dome (17:04). Since then, the eruption has fluctuated, but a general decrease in intensity was indicated by declines in the height of the ash plume, the behavior of the glowing lava flow, and the vigor of incandescent tephra ejection. In July, glowing rockfalls advanced down the Keting river to 1,500 m from the crater. The number of volcanic and local tectonic earthquakes decreased in June and July compared to previous months. June-July seismicity was dominated by surface activity, such as explosion earthquakes and rockfalls (figure 2).

Figure (see Caption) Figure 2. Tectonic seismicity (top) and volcanic earthquakes (bottom) at Karangetang, June-July 1992. Courtesy of VSI.

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

Information Contacts: W. Modjo, VSI.


Kilauea (United States) — June 1992 Citation iconCite this Report

Kilauea

United States

19.421°N, 155.287°W; summit elev. 1222 m

All times are local (unless otherwise noted)


Continued east rift lava production

Lava production continued through early July from the E-51 vent . . . (figure 85), but was interrupted by several brief pauses. With each resumption in activity, lava reoccupied tubes on the S flank of the E-51 shield. Flows emerged from the tubes under some pressure, creating small, meter-high dome fountains at their heads. The lava pond at the top of the E-51 shield drained and refilled with changing lava supply, sustaining frequent overflows that did not advance far. Some lava also ponded at the base of the shield before flows advanced S and E. The small lava lake in Pu`u `O`o crater remained active, fluctuating between 38 and 55 m below the crater rim in June. The lake surface rose during pauses in activity at the episode-51 vent and dropped when lava production resumed there. By early July, it had dropped farther, to 65 m below the rim.

Activity resumed on 2 June, after a 3-day pause (17:5), while harmonic tremor began a gradual increase to about twice background levels at 0000. Large flows advanced N along the W flank of Pu`u `O`o cinder cone. These shelly pahoehoe flows formed shallow tubes and stagnated within a few days. The eruption stopped briefly on 5 June, as tremor dropped to near background at 1800, resumed the next day accompanied by a tremor increase at about 0700, and halted again ~24 hours later on the 7th, when lava drained slowly from the pond atop the shield.

Another increase in tremor began early on 9 June, reaching about twice background levels by noon on the 10th. Shallow, long-period microearthquakes (LPC-A, 3-5 Hz) were frequent on 9 June, as were upper east rift events on 9-10 June. Lava started to emerge from the E-51 vent at 1325 on 10 June, re-entering the tube system on the S flank of the E-51 shield. The lava lake in Pu`u `O`o crater had been nearly level with the crater floor when E-51 activity resumed, but had dropped ~9 m by the next day.

A small spatter cone formed 3-11 June over a weak point in the tube on the N flank of the E-51 shield. This tube had fed numerous aa ooze-outs that spread out around the shield's N flank in past months. On 13 June, an aa flow was active on the shield's N flank, appearing to originate from the new spatter cone.

Lava production stopped again on 16 June, the pond at the top of the shield drained, and flows slowed their advance. The eruption restarted during the morning of 21 June, continuing through the end of the month. Pahoehoe flows extended N and SE from the vent. Through 25 June, the shield's pond was full and intermittently overflowing, but by 1 July it had drained to ~15 m depth with a solid crust at the bottom. However, lava continued to ooze into the S-flank tube system and to break out at the base of the shield. Tremor amplitudes gradually declined to near background by 2000 on 29 June, and remained at low levels into early July.

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: T. Mattox and P. Okubo, HVO.


Kozushima (Japan) — June 1992 Citation iconCite this Report

Kozushima

Japan

34.219°N, 139.153°E; summit elev. 572 m

All times are local (unless otherwise noted)


Earthquake and aftershocks

A M 5.2 earthquake, centered in the sea 8 km SW of the volcano at 9 km depth, occurred on 15 June at 1046. Island residents felt the shock at intensity 5 on the JMA scale of 0-7. Data from 30 stations of the Worldwide Standardized Seismic Network yielded magnitudes of 4.9 (mb) and 4.7 (Ms). One person was slightly injured by a rockfall, and wallrock collapse at 10 sites closed 5 roads to traffic. Aftershocks continued until 17 June off the island's SW coast. The event was the second largest since . . . April 1991 (figure 1). No surface anomalies were observed on the island or on the sea-surface nearby.

Geologic Background. A cluster of rhyolitic lava domes and associated pyroclastic deposits form the small 4 x 6 km island of Kozushima in the northern Izu Islands. Kozushima lies along the Zenisu Ridge, one of several en-echelon ridges oriented NE-SW, transverse to the trend of the northern Izu arc. The youngest and largest of the 18 lava domes, 574-m-high Tenjoyama, occupies the central portion of the island. Most of the older domes, some of which are Holocene in age, flank Tenjoyama to the north, although late-Pleistocene domes are also found at the southern end of the island. Only two possible historical eruptions, from the 9th century, are known. A lava flow may have reached the sea during an eruption in 832 CE. Tenjosan lava dome was formed during a major eruption in 838 CE that also produced pyroclastic flows and surges. Earthquake swarms took place during the 20th century.

Information Contacts: JMA; NEIC.


Langila (Papua New Guinea) — June 1992 Citation iconCite this Report

Langila

Papua New Guinea

5.525°S, 148.42°E; summit elev. 1330 m

All times are local (unless otherwise noted)


Strombolian explosions and lava flow

"A new phase of eruptive activity that started on 30 May lasted until 8 June. From 1 to 4 June, both Crater 2 and Crater 3 produced ash-rich Strombolian explosions to 500-700 m height. A new, short lava flow was emplaced on the NW flank of Crater 3. Emissions from Crater 2 became markedly ash-laden 4-7 June, with a plume rising a few kilometers above the crater and ashfalls on coastal areas 10 km NW. After the 7th, only weak to moderate vapour emissions and occasional Vulcanian explosions were noted from Crater 2.

"Activity at Crater 3 also waned after the first week in June, although more progressively. On the night of 7 June, intermittent explosions projected incandescent lava fragments to 250 m above the crater, while on 8 June there was weak steady glow over the crater. Intermittent explosions still occurred daily until the 24th, producing dark convoluting ash clouds that rose a few hundred meters above the crater.

"Seismic monitoring resumed on 11 June and showed only low-level activity throughout the rest of the month."

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

Information Contacts: P. de Saint-Ours, D. Lolok, and C. McKee, RVO.


Lascar (Chile) — June 1992 Citation iconCite this Report

Lascar

Chile

23.37°S, 67.73°W; summit elev. 5592 m

All times are local (unless otherwise noted)


Satellite data show heat from lava dome

"A Landsat TM image recorded the night of 15 April 1992 shows the most intense thermal anomaly of a dataset extending back to December 1984. The thermal signature, in the short-wavelength infrared bands 5 (1.55-1.75 mm) and 7 (2.08-2.35 mm), represents the active lava dome in the central crater. Comparison with the previous image (night of 7 January 1991) shows a marked increase in the anomaly's area (figure 11). In the April 1992 scene, the core of the anomaly occupies an irregular area of ~7 x 6 pixels (equivalent to 210 x 180 m). These dimensions correspond closely with the 180-190 m dome diameter estimated from 20 March airphotos (17:5). The increase in area of the TM anomaly may be explained, at least in part, by the growth of a subsidiary lava dome first sighted on 4 March. The summed thermal radiance from the whole hot spot shows a corresponding increase in the April Landsat image (figure 12).

Figure (see Caption) Figure 11. 15 x 15 pixel maps (equivalent to 450 x 450 m) of the signal recorded in band 7 of the Landsat TM over Lascar at night on 7 January 1991 (left) and 15 April 1992 (right). The vertical axis represents the number between 0 and 255 proportional to the spectral radiance. In each case, several pixels are saturated. Courtesy of C. Oppenheimer.
Figure (see Caption) Figure 12. Summed spectral radiance in bands 5 and 7 for fifteen images acquired over Lascar since December 1984. The dataset includes several processing formats, and images acquired during the day and night. Only pixels with a thermal signal >=10 were included. The total was then converted to spectral radiance using calibration coefficients supplied with the digital data. Arrows mark the explosive eruptions of September 1986 and February 1990 (12:4-5 and 15:2-3). Courtesy of C. Oppenheimer.

"An interesting feature of the two most recent TM acquisitions is the persistence of a discrete hot site ~200 m W of the centre of the main anomaly (figure 11). This is very likely the expression of incandescent fumarole vent(s) beyond the steep margin of the extruded lava."

Reference. Oppenheimer, C., Francis, P.W., Rothery, D.A., Carlton, R.W., and Glaze, L.S., Analysis of Volcanic Thermal Features in Infrared Images: Lascar Volcano, Chile, 1984-1992; Journal of Geophysical Research, in press.

Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Information Contacts: C. Oppenheimer, D. Rothery, P. Francis, and R. Carlton, Open Univ.


Lassen Volcanic Center (United States) — June 1992 Citation iconCite this Report

Lassen Volcanic Center

United States

40.492°N, 121.508°W; summit elev. 3187 m

All times are local (unless otherwise noted)


Seismicity apparently triggered by M 7.5 earthquake hundreds of kilometers away

Southern California's largest earthquake since 1952, M 7.5 on 28 June, appeared to trigger seismicity at several volcanic centers in California. It was centered roughly 200 km E of Los Angeles. In the following, David Hill describes post-earthquake activity at Long Valley caldera, and Stephen Walter discusses the USGS's seismic network, and the changes it detected at Lassen, Shasta, Medicine Lake, and the Geysers.

In recent years, the USGS northern California seismic network has relied upon Real-Time Processors (RTPs) to detect, record, and locate earthquakes. However, a film recorder (develocorder) collects data from 18 stations in volcanic areas, primarily to detect long-period earthquakes missed by RTPs. The film recorders proved useful in counting the post-M 7.5 earthquakes, most of which were too small to trigger the RTPs.

The film record was scanned for the 24 hours after the M 7.5 earthquake, noting the average coda duration for each identified event. Some events may have been missed because of seismogram saturation by the M 7.5 earthquake. Marked increases in microseismicity were observed at Lassen Peak, Medicine Lake caldera, and the Geysers (table 1). No earthquakes were observed at Shasta, but the lack of operating stations on the volcano limited the capability to observe small events.

Table 1. Number of earthquakes at northern California volcanic centers during 24-hour periods following major earthquakes on 25 April (40.37°N, 124.32°W; M 7.0) and 28 June (34.18°N, 116.47°W; M 7.5) 1992. Events with coda durations less than or equal to 10 seconds and greater than 10 seconds are tallied separately. Earthquakes were identified from film records of seismograms from nearby stations. Courtesy of Stephen Walter.

Date Lassen Shasta Medicine Lake Geysers
Codas (seconds) <= 10 > 10 <= 10 > 10 <= 10 > 10 <= 10 > 10
25 Apr 1992 0 0 0 1 0 0 7 2
28 Jun 1992 8 14 1 5 12 0 46 4

Film was also scanned for the 24 hours following the M 7.0 earthquake at 40.37°N, 124.32°W (near Cape Mendocino) on 25 April. Although smaller than the 28 June earthquake, its epicenter was only 20-25% as far from the volcanoes. Furthermore, both the 25 April main shock and a M 6.5 aftershock were felt at the volcanic centers, but no felt reports were received from these areas after the 28 June earthquake. Only the Geysers showed any possible triggered events after the 25 April shock. However, background seismicity at the Geysers is higher than at the other centers, and is influenced by fluid injection and withdrawal associated with intensive geothermal development.

Lassen Report. Of the three major Holocene volcanoes in the California Cascades, Lassen (~800 km NNW of the epicenter) had the strongest response to the 28 June earthquake (figure 1). About 10 minutes after the S-wave's arrival and while surface waves were still being recorded, a M 2.8 event occurred south of Lassen Peak. Film records showed 9 more earthquakes in the first hour, and 22 events were identified during the first 24 hours. Although most were M 1 or smaller, at least two and perhaps as many as four were of magnitude greater than or equal to 2. Nine were detected by the RTP system. The best preliminary locations were concentrated ~3 km SW of Lassen Peak at

Figure (see Caption) Figure 1. Seismic events in the Lassen area that were apparently triggered by the M 7.5 southern California earthquake of 28 June 1992 (circles) compared to 1978-90 seismicity in the region (crosses). Squares mark seismic stations. Courtesy of S. Walter.

Geologic Background. The Lassen volcanic center consists of the andesitic Brokeoff stratovolcano SW of Lassen Peak, a dacitic lava dome field, and peripheral small andesitic shield volcanoes and large lava flows, primarily on the Central Plateau NE of Lassen Peak. A series of eruptions from Lassen Peak from 1914 to 1917 marks the most recent eruptive activity in the southern Cascade Range. Activity spanning about 825,000 years began with eruptions of the Rockland caldera complex and was followed beginning about 590,000 years ago by construction of Brokeoff stratovolcano. Beginning about 310,000 years ago activity shifted to the north flank of Brokeoff, where episodic, more silicic eruptions produced the Lassen dome field, a group of 30 dacitic lava domes including Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak. At least 12 eruptive episodes took place during the past 100,000 years, with Lassen Peak being constructed about 27,000 years ago. The Chaos Crags dome complex was constructed about 1100-1000 years ago north of Lassen Peak. The Cinder Cone complex NE of Lassen Peak was erupted in a single episode several hundred years before present and is considered part of the Lassen volcanic center (Clynne et al., 2000). The 1914-1917 eruptions of Lassen Peak began with phreatic eruptions and included emplacement of a small summit lava dome, subplinian explosions, mudflows, and pyroclastic flows.

Information Contacts: Stephen Walter and David Hill, MS 977, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 USA.


Ol Doinyo Lengai (Tanzania) — June 1992 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

2.764°S, 35.914°E; summit elev. 2962 m

All times are local (unless otherwise noted)


Lava ejection from small crater-floor vent

During a previously unreported 26 February climb by David Peterson, Howard Brown, and students from St. Lawrence Univ, activity was continuing from one cone (T20) . . . . Periodic gurgling and rumbling noises from the cone were audible from the crater rim. As Peterson and several students approached the active cone, lava fragments were ejected, one of which struck a student on the leg, causing a small burn. Crater photographs show a small dark vent at the summit of T20, but no dark (fresh) lava was evident on its flanks. However, by . . . 12 March, T20 had extruded a lava flow that covered much of the W part of the crater floor (17:03).

Brown's 26 February photographs show . . . T5/T9 as tall but pale gray, with no fresh, dark patches of lava. T15 was composed of jagged dark-gray pinnacles with medium-brown lower slopes and no sign of fresh lava. T8 and T8A seemed little changed from recent photographs, with slight yellow coloring at T8's summit. T14 appeared to have been surrounded by younger lava, which had turned pale gray to white. Some dark patches were visible around its summit vent. No dark fresh flows were evident on the crater floor.

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

Information Contacts: C. Nyamweru, St. Lawrence Univ; D. Peterson, Arusha; H. Brown, Nairobi, Kenya.


Long Valley (United States) — June 1992 Citation iconCite this Report

Long Valley

United States

37.7°N, 118.87°W; summit elev. 3390 m

All times are local (unless otherwise noted)


Abrupt increase in seismicity triggered by M 7.5 earthquake hundreds of kilometers away

Southern California's largest earthquake since 1952, M 7.5 on 28 June, appeared to trigger seismicity at several volcanic centers in California. It was centered roughly 200 km E of Los Angeles. In the following, David Hill describes post-earthquake activity at Long Valley caldera, and Stephen Walter discusses the USGS's seismic network, and the changes it detected at Lassen, Shasta, Medicine Lake, and the Geysers.

In recent years, the USGS northern California seismic network has relied upon Real-Time Processors (RTPs) to detect, record, and locate earthquakes. However, a film recorder (develocorder) collects data from 18 stations in volcanic areas, primarily to detect long-period earthquakes missed by RTPs. The film recorders proved useful in counting the post-M 7.5 earthquakes, most of which were too small to trigger the RTPs.

The film record was scanned for the 24 hours after the M 7.5 earthquake, noting the average coda duration for each identified event. Some events may have been missed because of seismogram saturation by the M 7.5 earthquake. Marked increases in microseismicity were observed at Lassen Peak, Medicine Lake caldera, and the Geysers. No earthquakes were observed at Shasta, but the lack of operating stations on the volcano limited the capability to observe small events.

Film was also scanned for the 24 hours following the M 7.0 earthquake at 40.37°N, 124.32°W (near Cape Mendocino) on 25 April. Although smaller than the 28 June earthquake, its epicenter was only 20-25% as far from the volcanoes. Furthermore, both the 25 April main shock and a M 6.5 aftershock were felt at the volcanic centers, but no felt reports were received from these areas after the 28 June earthquake. Only the Geysers showed any possible triggered events after the 25 April shock. However, background seismicity at the Geysers is higher than at the other centers, and is influenced by fluid injection and withdrawal associated with intensive geothermal development.

Long Valley Report. Within eight minutes of the major earthquake's origin time, seismic activity within Long Valley caldera (400 km NNW of the epicenter) increased abruptly (figure 15). Of the >260 events located by the RTP system during the next three days, three were of M 3 or greater. The first event within the caldera located by the RTP system was a M 1.4 earthquake at 1207, but develocorder film from caldera stations provides evidence of local earthquakes beginning at least a minute earlier within the strong coda waves from the M 7.5 event. The P-wave travel-time from the epicenter is just over 1 minute, and the S-wave travel-time just under two minutes, so it appears that local earthquake activity began no later than six minutes after the S-wave arrival.

Figure (see Caption) Figure 15. Earthquakes >M 1.5 in the Long Valley area, 25 June-1 July 1992. Larger events are identified by numbered triangular labels beside earthquake symbols: (1) 25 June, 2143 GMT, M 2.4; (2) 28 June, 1214, 1230, 1232, M 2.6, 3.0, 2.5; (3) 29 June, 0103, M 3.1; (4) 29 June, 0537, 0638, M 3.7, 2.3; (5) 29 June, 0758, M 3.4; (6) 29 June, 0834, 0838, 0839, M 2.0, 2.1, 2.0. Courtesy of D. Hill.

Earthquake activity within Long Valley caldera had persisted, but at relatively low levels, through the first half of 1992, averaging

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

Information Contacts: D. Hill, USGS Menlo Park.


Manam (Papua New Guinea) — June 1992 Citation iconCite this Report

Manam

Papua New Guinea

4.08°S, 145.037°E; summit elev. 1807 m

All times are local (unless otherwise noted)


Strong ash ejections; Strombolian explosions; lava and pyroclastic flows

"The eruption . . . ended on 15 June after another paroxysmal phase from Main Crater (on 7 June). Following the paroxysmal phase of 31 May from Southern Crater, the level of activity was moderate in the first days of June. Both craters were emitting white and blue vapours in weak to moderate amounts, with occasional explosions of ash-laden vapour rising a few hundred meters above the craters, weak roaring noises, and weak fluctuating glow at night.

"On the afternoon of 5 June, Southern Crater entered a phase of intermittent Strombolian activity that sprayed incandescent spatter to as much as 300 m above the crater at intervals of 30-40 minutes. At 1600, Main Crater emitted a dark ash column to ~1,000 m above the crater. Strombolian explosions within the crater must have started soon afterwards, as suggested by fluctuating night glow and roaring sounds. On the 6th, the level of activity remained moderate at Southern Crater while it strengthened at Main Crater. The forceful emissions of grey-brown ash from the latter were identified as Strombolian projections at night. From 0025 until about 1830 on 7 June, this crater produced continuous incandescent projections to 600 m above the rim in an ash column that rose 2-3 km. New lava flows were erupted into the NE Valley and followed the path of the previous flows (4-6 May) on the southern side of the valley, down to 110 m asl.

"Pyroclastic flows were also produced, scorching vegetation and some garden areas on the southern side of the NE Valley to about 1 km from Bokure Village. Downwind from the crater, on the NW side of the island, the sustained dark ash cloud overhead, the fall of ash and lapilli, and roaring sounds of the eruption caused some concern to the population.

"This paroxysmal eruption phase ended with loud explosions from 1817 to 1830 on 7 June. In the following days there was hardly any visible activity from either crater, apart from weak-to-moderate vapour emission. However, the seismicity, which had increased dramatically during the eruptive phase of 6-7 June, remained moderately high. On 12 June, occasional dull explosion sounds were heard again from Main Crater with occasional brown ash clouds and incandescent projections at night. This activity lasted until the 14th, becoming more and more intermittent. The last significant event from Main Crater observed in this eruption was a moderately strong Vulcanian explosion at 0800 on 14 June, which projected a convoluting cloud to 2-3 km above the crater. Likewise, Southern Crater was somewhat reactivated 13-15 June, with occasional weak explosions, a fluctuating night glow, and incandescent projections to 250 m above the crater rim. From 16 June onward, the seismicity dropped markedly and neither crater showed further signs of activity apart from weak, fumarolic emission. The Stage 2 volcanic alert that had applied since 13 April was dropped to Stage 1 (i.e. non-threatening, background level) on 25 June.

"This eruption of Manam is among the most significant since 1958, and can be compared with the eruption of 1974 (Palfreyman and Cooke, 1976; Cooke et al., 1976) as it involved both craters, produced pyroclastic flows and lava flows of significant volume, and affected all but one of the main valleys. However, the 1992 eruption appears to have been larger than the 1974 event. A preliminary estimate of the 1992 lava-flow volume is 17 x 106 m3, compared with only 3 x 106 m3 of lava flows in 1974."

References. Cooke, R.J.S., McKee, C.O., Dent, V.F., and Wallace, D.A., 1976, Striking Sequence of Volcanic Eruptions in the Bismarck Volcanic Arc, Papua New Guinea, in 1972-75; in Johnson, R.W, ed., Volcanism in Australasia, Elsevier, p. 149-172.

Palfreyman, W.D. and Cooke, R.J.S., 1976, Eruptive History of Manam Volcano, Papua New Guinea; Ibid., p. 117-131.

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

Information Contacts: P. de Saint-Ours, D. Lolok, and C. McKee, RVO.


Marapi (Indonesia) — June 1992 Citation iconCite this Report

Marapi

Indonesia

0.38°S, 100.474°E; summit elev. 2885 m

All times are local (unless otherwise noted)


Explosion kills one person and injures five others

An explosion on 5 July killed one person and injured five others. Marapi has been erupting since 1987, with explosions typically occurring about once every 1-7 days. Material ejected by the smaller explosions rises 100-800 m, whereas ejecta from larger explosions reach 800-2,000 m above the summit. The recent explosions, which produce ash and lapilli, have originated from Verbeek Crater in the summit complex. Ashfalls have been frequent NW of the volcano in Bukittinggi (roughly 15 km NW of the summit), Sungai Puar (30 km NW), and the Agam district (>30 km NW), depending on wind direction. Fluctuations in Marapi's explosions seem to parallel shallow volcanic earthquakes (figure 2), suggesting that the activity is primarily caused by degassing from a relatively shallow source through an open vent.

Figure (see Caption) Figure 2. Number of explosion, A-, and B-type earthquakes at Marapi, January 1991-June 1992. Courtesy of VSI.

Activity in June began with an explosion on the 1st. Continuous tremor followed, and on 6 June at 0227 another explosion occurred. Repeated explosions then deposited ~0.5 mm of ash on Bukittinggi. On 25 June, witnesses 2 km from the volcano (at the Batu Palano Volcano Observatory) heard a detonation and saw glow. A brownish-black cauliflower-shaped plume rose 1,800 m above the summit. During June, 45 deep and 312 shallow volcanic earthquakes, 108 volcanic tremor episodes, and 2,104 explosion earthquakes were recorded.

The strongest explosion occurred on 5 July at 0912. Bukittinggi and vicinity were covered by 0.5-1.5 mm of ash several hours later, with ash in some areas reaching 2 mm thickness. Ash also extended to Padang, ~10 km SW of the crater. Bombs killed one person, seriously injured three, and caused minor injuries to two others. The victims had climbed to the summit without consultation with the Mt. Marapi Volcano Observatory or local authorities, although a hazard warning had been in effect since 1987.

Geologic Background. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Information Contacts: W. Modjo, VSI.


Maug Islands (United States) — June 1992 Citation iconCite this Report

Maug Islands

United States

20.02°N, 145.22°E; summit elev. 227 m

All times are local (unless otherwise noted)


No activity evident

A six-member team of USGS volcanologists visited the Commonwealth of the Northern Mariana Islands 11-27 May 1992 at the request of the CNMI Office of Civil Defense. Aerial observations [of Maug] on 13 May revealed no signs of steaming or other evidence of recent volcanic activity.

Geologic Background. Three small elongated islands up to 2.3 km long mark the northern, western, and eastern rims of a largely submerged 2.5-km-wide caldera. The highest point of the Maug Islands reaches only 227 m above sea level; the submerged southern notch on the caldera rim lies about 140 m below sea level. The caldera has an average submarine depth of about 200 m and contains a twin-peaked central lava dome that rises to within about 20 m of the sea surface. The Maug Islands form a twin volcanic massif with Supply Reef, about 11 km N. The truncated inner walls of the caldera on all three islands expose lava flows and pyroclastic deposits that are cut by radial dikes; bedded ash deposits overlie the outer flanks of the islands. No eruptions are known since the discovery of the islands by Espinosa in 1522. The presence of poorly developed coral reefs and coral on the central lava dome suggests a long period of general quiescence, although it does not exclude mild eruptions (Corwin, 1971). A 2003 NOAA expedition detected possible evidence of submarine geothermal activity.

Information Contacts: R. Moore, USGS; R. Koyanagi, M. Sako, and F. Trusdell, HVO.


Medicine Lake (United States) — June 1992 Citation iconCite this Report

Medicine Lake

United States

41.611°N, 121.554°W; summit elev. 2412 m

All times are local (unless otherwise noted)


Seismicity apparently triggered by M 7.5 earthquake hundreds of kilometers away

Southern California's largest earthquake since 1952, M 7.5 on 28 June, appeared to trigger seismicity at several volcanic centers in California. It was centered roughly 200 km E of Los Angeles. In the following, David Hill describes post-earthquake activity at Long Valley caldera, and Stephen Walter discusses the USGS's seismic network, and the changes it detected at Lassen, Shasta, Medicine Lake, and the Geysers.

In recent years, the USGS northern California seismic network has relied upon Real-Time Processors (RTPs) to detect, record, and locate earthquakes. However, a film recorder (develocorder) collects data from 18 stations in volcanic areas, primarily to detect long-period earthquakes missed by RTPs. The film recorders proved useful in counting the post-M 7.5 earthquakes, most of which were too small to trigger the RTPs.

The film record was scanned for the 24 hours after the M 7.5 earthquake, noting the average coda duration for each identified event. Some events may have been missed because of seismogram saturation by the M 7.5 earthquake. Marked increases in microseismicity were observed at Lassen Peak, Medicine Lake caldera, and the Geysers (table 1). No earthquakes were observed at Shasta, but the lack of operating stations on the volcano limited the capability to observe small events.

Table 1. Number of earthquakes at northern California volcanic centers during 24-hour periods following major earthquakes on 25 April (40.37°N, 124.32°W; M 7.0) and 28 June (34.18°N, 116.47°W; M 7.5) 1992. Events with coda durations less than or equal to 10 seconds and greater than 10 seconds are tallied separately. Earthquakes were identified from film records of seismograms from nearby stations. Courtesy of Stephen Walter.

Date Lassen Shasta Medicine Lake Geysers
Codas (seconds) <= 10 > 10 <= 10 > 10 <= 10 > 10 <= 10 > 10
25 Apr 1992 0 0 0 1 0 0 7 2
28 Jun 1992 8 14 1 5 12 0 46 4

Film was also scanned for the 24 hours following the M 7.0 earthquake at 40.37°N, 124.32°W (near Cape Mendocino) on 25 April. Although smaller than the 28 June earthquake, its epicenter was only 20-25% as far from the volcanoes. Furthermore, both the 25 April main shock and a M 6.5 aftershock were felt at the volcanic centers, but no felt reports were received from these areas after the 28 June earthquake. Only the Geysers showed any possible triggered events after the 25 April shock. However, background seismicity at the Geysers is higher than at the other centers, and is influenced by fluid injection and withdrawal associated with intensive geothermal development.

Medicine Lake Report. Twelve events were detected in the Medicine Lake area (~900 km NNW of the epicenter) in the 30 minutes after the M 7.5 earthquake. All had coda durations less than or equal to 10 seconds. The lack of any S-P separation indicated that they were centered very close to the single seismic station, near the center of the caldera. All known historical seismicity had occurred in the central caldera as part of a mainshock/aftershock sequence during the fall and winter of 1988-89.

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

Information Contacts: S. Walter and D. Hill, USGS Menlo Park.


Nyamuragira (DR Congo) — June 1992 Citation iconCite this Report

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)


Continued lava production from fissure vents

Vigorous lava production continued through June . . . . The eruption has built 23 cinder cones along a 2.5-km zone that trends generally NE, ~15 km NE of Nyamuragira caldera and 5 km ENE of the 1957 Kitsimbanyi vent (figure 12 and table 1). The eruption's early phases produced substantial lava flows, but since 20 November activity has been characterized by vigorous ejection of bombs, lava fragments, and ash, with lava flows of only limited extent.

Figure (see Caption) Figure 12. Schematic map of cones built by the 1991-92 eruption of Nyamuragira, in a zone ~15 km NE of the caldera. Vent 20, shown in black, opened on 14 July, and remained active in August 1992. Courtesy of N. Zana.

Table 1. Sequence of activity at Nyamuragira's 1991-92 eruption vents. Locations are shown on figure 12. Some small, short-lived vents removed by subsequent lava flows are not listed.

Cone First Activity Comments
1 24 Sep 1991 Named Mikombe.
2 24 Oct 1991 --
3 25 Oct 1991 Through 3 Feb 1992.
4a, b 07 Nov 1991 --
5a, b, c 08 Nov 1991 On 24 November 1991 only cone 5 was active.
6 10 Nov 1991 --
7 11 Nov 1991 --
8 23 Dec 1991 --
9 06 Feb 1992 --
10a, b 26 Feb 1992 --
11 08 Mar 1992 --
12 10 Mar 1992 --
13 12 Mar 1992 --
14 16 Mar 1992 Still active in May.
15 08 May 1992 --
16a, b 10 May 1992 Cones 14-17 still active through the end of May.
16b 10 May 1992 --
17 11 May 1992 --
18 24 May 1992 --
19 05 Jul 1992 Cones 19-21 still intermittently active through August 1992.
20 14 Jul 1992 --
21 19 Jul 1992 --

From 20 September until 5 February, activity was confined to a N32-34°E fissure (cones 1-8). The most persistent activity at a single vent, 25 October-3 February, has made Cone 3 the largest of the eruption, rising ~80 m above the surrounding lava plain. Three new cones developed in February, nos. 9 (6 February), 10a and 10b (26 February). In March, activity resumed at the S end of the fissure along a branch that trended E from the initial vent, successively building cones 11, 12, and 14. Vent 13, 1 km to the N, erupted during the same period.

In early May, activity moved to the N end of the fissure, as a NE branch developed and formed vents 15-17. These vents remained active at the end of May, as did no. 14 at the S end of the fissure, producing intermittent lava fountains. Vent 18, near the middle of the fissure, began to erupt at about 1100 on 24 May. By 8 June it had grown to ~25 m height and its lava flows had extended ~3 km N, eroding away cones 10a and 10b. Activity at the new vent was preceded by an increase in microtremor amplitude recorded at a seismic station (Katale) 12 km E. Amplitude increased significantly from 8 June, indicating movement of new magma from a deeper source. As of 1 July, there was no indication that the eruption was nearing its end. Lava production remained vigorous, with high lava fountains, and strong emission of bombs and other tephra.

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: N. Zana, CRSN, Bukavu.


Pagan (United States) — June 1992 Citation iconCite this Report

Pagan

United States

18.13°N, 145.8°E; summit elev. 570 m

All times are local (unless otherwise noted)


Recent small ash eruption; long-period earthquakes and tremor; inflation

A six-member team of USGS volcanologists visited the Commonwealth of the Northern Mariana Islands 11-27 May 1992 at the request of the CNMI Office of Civil Defense. The team observed all of the islands in the chain N of Saipan, installed a new seismic station at the base of frequently active Pagan, remeasured existing EDM networks, mapped the geology of Alamagan, sampled fumaroles and hot springs, and collected rocks and charcoal for radiocarbon dating. No volcanoes in the chain erupted during the observation period.

Reports from brief visits to Pagan indicate that the most recent small ash eruption occurred on 13 April. Continuing seismicity was dominated by short bursts of long-period earthquakes and volcanic tremor. The highest measured steam temperature was 76°C; solfataras that are probably hotter are inaccessible deep within the crater. Episodic fuming, marked by periods of relatively high SO2 outgassing followed by quiescence, was observed continuously 13-21 May. EDM lines from the coast to reflectors on the flanks had shortened by as much as 11.3 cm since September 1990. These lines had shown no significant changes between 1983 and 1990, a period characterized by frequent small ash eruptions following the large Plinian eruption of 15 May 1981 (Banks and others, 1984). After the first remeasurement on 17 May, no large changes in line lengths were detected during the next 3 days.

The team collected three charcoal samples on Pagan. Two of the units to be dated are relatively old, and their ages should help to constrain the age of the caldera.

South Pagan . . . has several steaming fumaroles, but no temperatures were measured. No shallow earthquake swarms have been recorded since the installation of the seismic station in 1990.

Reference. Banks, N.G., Koyanagi, R.Y., Sinton, J.M., and Honma, K.T., 1984, The eruption of Mount Pagan volcano, Mariana Islands, 15 May 1981: JVGR, v. 22, p. 225-269.

Geologic Background. Pagan Island, the largest and one of the most active of the Mariana Islands volcanoes, consists of two stratovolcanoes connected by a narrow isthmus. Both North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. The 570-m-high Mount Pagan at the NE end of the island rises above the flat floor of the northern caldera, which may have formed less than 1000 years ago. South Pagan is a 548-m-high stratovolcano with an elongated summit containing four distinct craters. Almost all of the historical eruptions of Pagan, which date back to the 17th century, have originated from North Pagan volcano. The largest eruption of Pagan during historical time took place in 1981 and prompted the evacuation of the sparsely populated island.

Information Contacts: R. Moore, USGS; R. Koyanagi, M. Sako, and F. Trusdell, HVO.


Pinatubo (Philippines) — June 1992 Citation iconCite this Report

Pinatubo

Philippines

15.13°N, 120.35°E; summit elev. 1486 m

All times are local (unless otherwise noted)


Lava dome extruded into caldera lake; small steam-and-ash ejections; lahars and secondary explosions

Increased seismicity preceded the emergence of a lava dome into the center of the caldera lake. Moderate steam-and-ash emission was associated with the lava extrusion.

Long-period earthquakes and tremor began to be recorded on 6 July. An aerial survey during the morning of 7 July showed no visible change in steaming from crater vents, although the caldera lake was convecting and somewhat muddier than normal. A small island was reported in the caldera lake early on 9 July. An overflight that day at 1500 revealed a mud cone about 100 m in diameter near the center of the lake, protruding about 5 m above the lake surface. Small phreatic explosions to about 100 m height occurred near the side of the island. PHIVOLCS raised the official alert level to 3, indicating the possibility of an eruption within weeks. The announcement described possible activity as quiet extrusion of a lava dome or moderately explosive phreatomagmatic eruptions. A danger zone of 10-km radius was being enforced.

The cone had reportedly reached 200-300 m in diameter by 12 July. A lava dome 100-150 m in diameter was visible near the center of the island during an aerial survey on 14 July at 0900-1000. The island had grown to around 250-300 m across and was 8-10 m above lake level. A continuous dirty white steam column that included some ash was emerging from the dome and drifting SW during the overflight. Ashfall was reported on two towns ~30 km SW of the summit (San Marcelino and Castillejos) at about 0600 and 1300. The alert level was raised to 5 (eruption in progress).

On the flanks of the volcano, monsoon rains triggered secondary explosions and lahars that forced the evacuation of thousands of people living along rivers. Two people were reported killed by lahars on 12 July. The Department of Social Welfare said that about 70,000 people remained in evacuation centers and resettlement sites in the aftermath of the June 1991 eruption.

Geologic Background. Prior to 1991 Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located 100 km NW of Manila with no records of historical eruptions. The 1991 eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2.5-km-wide summit caldera whose floor is now covered by a lake. Caldera formation lowered the height of the summit by more than 300 m. Although the eruption caused hundreds of fatalities and major damage with severe social and economic impact, successful monitoring efforts greatly reduced the number of fatalities. Widespread lahars that redistributed products of the 1991 eruption have continued to cause severe disruption. Previous major eruptive periods, interrupted by lengthy quiescent periods, have produced pyroclastic flows and lahars that were even more extensive than in 1991.

Information Contacts: PHIVOLCS; UPI; Reuters; AP.


Poas (Costa Rica) — June 1992 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Vigorous gas emission in and around crater lake; continued seismicity

Water level in the crater lake had dropped at least 3 m since April, shrinking it substantially by early June (figure 41). Its color was lime green to sky blue, and the temperature in accessible areas reached 85.8°C. Numerous cones and miniature mud volcanoes were visible within the lake. The nine main fumaroles emitted water vapor with yellowish and bluish gases (sulfur and SO2). Bluish gases and orange flames, probably caused by combustion of sulfur, emerged from the northernmost fumarole. The fumaroles to the SE occurred among collapsed sulfur-and-mud cones, as in the past 3 years.

Figure (see Caption) Figure 41. Sketch map of the crater at Poás, 10 June 1992. Courtesy of the Instituto Costarricense de Electricidad.

As the rainy season began, fumaroles exposed by the shrinkage of the crater lake were covered by water. The resulting continuous phreatic activity produced plumes 1-2 m high. As the lake rose, it cooled to 64-73°C, with a pH of 1.1. Weak fumarolic activity continued on the 1953-55 dome, with a maximum measured temperature of 89°C and a condensate pH of 4.4.

A daily average of 200 low-frequency events and 24 A-B-type (medium-frequency) events were recorded 2.7 km SW of the summit (by station POA2) in June (figure 42). Highest seismicity was on 2 June.

Figure (see Caption) Figure 42. Daily number of seismic events recorded at a station (POA2) 2.7 km SW of the summit of Poás, June 1992. Courtesy of the Univ Nacional.

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSCIORI; G. Soto, ICE; M. Fernández, UCR.


Rabaul (Papua New Guinea) — June 1992 Citation iconCite this Report

Rabaul

Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)


Uplift and seismicity increase slightly

"Seismic activity . . . has shown a slight increase over the last 2 months (June: 410 caldera earthquakes, May: 425) compared with activity over the last 2.5 years (100-300 events/month). Less than 1% of the recorded earthquakes in June could be located. Most were from the NW part of the caldera seismic zone. Similarly, levelling measurements showed a slight uplift of the central part of the caldera during the last two months (20 mm, 11 May-4 June; and an additional 13 mm by 8 July)."

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

Information Contacts: P. de Saint-Ours, D. Lolok, and C. McKee, RVO.


Rincon de la Vieja (Costa Rica) — June 1992 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

10.83°N, 85.324°W; summit elev. 1916 m

All times are local (unless otherwise noted)


Continued fumarolic activity

Fumarolic activity continued through June in the active crater, where it had fed a plume more than 100 m high during May fieldwork. Chemical analyses of water collected 13 May showed pH values of less than 3 in two of the three N-flank rivers sampled, and some enhancement in sulfate and chloride concentrations (table 2). A seismographic station 5 km SW of the crater (RIN3) registered seven low-frequency earthquakes in June.

Table 2. Chemistry of water collected 13 May 1992 from three rivers on the N flank of Rincón de la Vieja. Data courtesy of the Univ. de Costa Rica.

River pH Cl- (ppm) SO4-2 (ppm)
Pénjamo 2.9 1.5 392
Blanco 5.8 2.1 122
Azul 2.4 10.0 384

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of 1916-m-high Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A plinian eruption producing the 0.25 km3 Río Blanca tephra about 3500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI; G. Soto, ICE; Mario Fernández, Univ. de Costa Rica.


Rumble III (New Zealand) — June 1992 Citation iconCite this Report

Rumble III

New Zealand

35.745°S, 178.478°E; summit elev. -220 m

All times are local (unless otherwise noted)


Gas bubbles detected; summit 140 m below surface

Three previously unknown submarine arc stratovolcanoes have been identified at the S end of the Kermadec Ridge: Rumble V (36.140°S, 178.195°E, summit 700 m below sea level); Tangaroa (36.318°S, 178.031°E, summit 1,350 m below sea level); and Clark (36.423°S, 177.845°E, summit 1,150 m below sea level) (figure 1). All three have basal diameters of 16-18 km and rise from the seafloor at ~2,300 m depth. The first evidence of the volcanoes was from GLORIA side-scan mapping of the southern Havre Trough-Kermadec Ridge region in 1988 (Wright, 1990). Later investigations, including a photographic and rock-dredge study during the 3-week Rapuhia cruise (early 1992), confirmed previous interpretations. Side-scan and photographic data show a complex terrain of lava flows and talus fans on the flanks of all three volcanoes, with the most pristine-looking morphology at Rumble V. During the 1992 cruise, gas bubbles were detected acoustically, rising from the crests of Rumble III, IV, and V. No gas bubbling was evident from Tangaroa or Clark. Bathymetric surveys indicated that the summits of the shallowest volcanoes, Rumble III and IV, were at ~140 and 450 m, respectively, below the sea surface.

Figure (see Caption) Figure 1. Sketch map of New Zealand's North Island and the southern Kermadec Ridge area, with locations of young volcanoes. Courtesy of Ian Wright.

Reference. Wright, I.C., 1990, Bay of Plenty-Southern Havre Trough physiography, 1:400,000: New Zealand Oceanographic Institute Chart, Miscellaneous Series no. 68.

Geologic Background. The Rumble III seamount, the largest of the Rumbles group of submarine volcanoes along the South Kermadec Ridge, rises 2300 m from the sea floor to within about 200 m of the sea surface. Collapse of the edifice produced a horseshoe-shaped caldera breached to the west and a large debris-avalanche deposit. Fresh-looking andesitic rocks have been dredged from the summit and basaltic lava from its flanks. Rumble III has been the source of several submarine eruptions detected by hydrophone signals.

Information Contacts: I. Wright, New Zealand Oceanographic Institute, National Institute of Water and Atmospheric Research, Wellington.


Rumble IV (New Zealand) — June 1992 Citation iconCite this Report

Rumble IV

New Zealand

36.13°S, 178.05°E; summit elev. -500 m

All times are local (unless otherwise noted)


Gas bubbles detected; summit 450 m below surface

Three previously unknown submarine arc stratovolcanoes have been identified at the S end of the Kermadec Ridge: Rumble V (36.140°S, 178.195°E, summit 700 m below sea level); Tangaroa (36.318°S, 178.031°E, summit 1,350 m below sea level); and Clark (36.423°S, 177.845°E, summit 1,150 m below sea level) (figure 1). All three have basal diameters of 16-18 km and rise from the seafloor at ~2,300 m depth. The first evidence of the volcanoes was from GLORIA side-scan mapping of the southern Havre Trough-Kermadec Ridge region in 1988 (Wright, 1990). Later investigations, including a photographic and rock-dredge study during the 3-week Rapuhia cruise (early 1992), confirmed previous interpretations. Side-scan and photographic data show a complex terrain of lava flows and talus fans on the flanks of all three volcanoes, with the most pristine-looking morphology at Rumble V. During the 1992 cruise, gas bubbles were detected acoustically, rising from the crests of Rumble III, IV, and V. No gas bubbling was evident from Tangaroa or Clark. Bathymetric surveys indicated that the summits of the shallowest volcanoes, Rumble III and IV, were at ~140 and 450 m, respectively, below the sea surface.

Figure (see Caption) Figure 1. Sketch map of New Zealand's North Island and the southern Kermadec Ridge area, with locations of young volcanoes. Courtesy of Ian Wright.

Reference. Wright, I.C., 1990, Bay of Plenty-Southern Havre Trough physiography, 1:400,000: New Zealand Oceanographic Institute Chart, Miscellaneous Series no. 68.

Geologic Background. The submarine volcano Rumble IV was thought to have been active from April to December 1966, based on hydrophone signals (Kibblewhite, 1967), but later evidence indicates that the hydrophone array had been damaged and that the signals originated from Rumble III (Hall, 1985). Fresh, glassy andesitic lava was dredged from the summit in 1992 during a New Zealand Oceanographic Institute cruise, and gas bubbles were acoustically detected rising from Rumble IV.

Information Contacts: I. Wright, New Zealand Oceanographic Institute, National Institute of Water and Atmospheric Research, Wellington.


Rumble V (New Zealand) — June 1992 Citation iconCite this Report

Rumble V

New Zealand

36.142°S, 178.196°E; summit elev. -400 m

All times are local (unless otherwise noted)


New submarine volcano identified; rising gas bubbles

Three previously unknown submarine arc stratovolcanoes have been identified at the S end of the Kermadec Ridge: Rumble V (36.140°S, 178.195°E, summit 700 m below sea level); Tangaroa (36.318°S, 178.031°E, summit 1,350 m below sea level); and Clark (36.423°S, 177.845°E, summit 1,150 m below sea level) (figure 1). All three have basal diameters of 16-18 km and rise from the seafloor at ~2,300 m depth. The first evidence of the volcanoes was from GLORIA side-scan mapping of the southern Havre Trough-Kermadec Ridge region in 1988 (Wright, 1990). Later investigations, including a photographic and rock-dredge study during the 3-week Rapuhia cruise (early 1992), confirmed previous interpretations. Side-scan and photographic data show a complex terrain of lava flows and talus fans on the flanks of all three volcanoes, with the most pristine-looking morphology at Rumble V. During the 1992 cruise, gas bubbles were detected acoustically, rising from the crests of Rumble III, IV, and V. No gas bubbling was evident from Tangaroa or Clark. Bathymetric surveys indicated that the summits of the shallowest volcanoes, Rumble III and IV, were at ~140 and 450 m, respectively, below the sea surface.

Figure (see Caption) Figure 1. Sketch map of New Zealand's North Island and the southern Kermadec Ridge area, with locations of young volcanoes. Courtesy of Ian Wright.

Reference. Wright, I.C., 1990, Bay of Plenty-Southern Havre Trough physiography, 1:400,000: New Zealand Oceanographic Institute Chart, Miscellaneous Series no. 68.

Geologic Background. A previously unknown submarine volcano, Rumble V was discovered in 1992 at the southernmost of a group of seamounts on the southern Kermadec Ridge, known as the Rumbles. It rises more than 2,000 m to nearly 400 m below the sea surface and shows a pristine morphology. Andesitic and basaltic-andesite rocks have been dredged from Rumble V, which lies 17 km ESE of Rumble IV. A large plume of gas bubbles was acoustically detected rising from the summit of Rumble V in 1992, and subsequent expeditions detected evidence of vigorous hydrothermal activity.

Information Contacts: I. Wright, New Zealand Oceanographic Institute, National Institute of Water and Atmospheric Research, Wellington.


Sarigan (United States) — June 1992 Citation iconCite this Report

Sarigan

United States

16.708°N, 145.78°E; summit elev. 538 m

All times are local (unless otherwise noted)


No activity evident

A six-member team of USGS volcanologists visited the Commonwealth of the Northern Mariana Islands 11-27 May 1992 at the request of the CNMI Office of Civil Defense. Gas emission [from Sarigan] was not evident during overflights in an airplane on 13 May and a helicopter on 21 May.

Geologic Background. Sarigan volcano forms a 3-km-long, roughly triangular island. A low truncated cone with a 750-m-wide summit crater contains a small ash cone. The youngest eruptions produced two lava domes from vents above and near the south crater rim. Lava flows from each dome reached the coast and extended out to sea, forming irregular shorelines. The northern flow overtopped the crater rim on the north and NW sides. The sparse vegetation on the flows indicates they are of Holocene age (Meijer and Reagan, 1981).

Information Contacts: R. Moore, USGS; R. Koyanagi, M. Sako, and F. Trusdell, HVO.


Shasta (United States) — June 1992 Citation iconCite this Report

Shasta

United States

41.409°N, 122.193°W; summit elev. 4317 m

All times are local (unless otherwise noted)


No seismicity triggered by M 7.5 earthquake hundreds of kilometers away

Southern California's largest earthquake since 1952, M 7.5 on 28 June, appeared to trigger seismicity at several volcanic centers in California. It was centered roughly 200 km E of Los Angeles. In the following, David Hill describes post-earthquake activity at Long Valley caldera, and Stephen Walter discusses the USGS's seismic network, and the changes it detected at Lassen, Shasta, Medicine Lake, and the Geysers.

In recent years, the USGS northern California seismic network has relied upon Real-Time Processors (RTPs) to detect, record, and locate earthquakes. However, a film recorder (develocorder) collects data from 18 stations in volcanic areas, primarily to detect long-period earthquakes missed by RTPs. The film recorders proved useful in counting the post-M 7.5 earthquakes, most of which were too small to trigger the RTPs.

The film record was scanned for the 24 hours after the M 7.5 earthquake, noting the average coda duration for each identified event. Some events may have been missed because of seismogram saturation by the M 7.5 earthquake. Marked increases in microseismicity were observed at Lassen Peak, Medicine Lake caldera, and the Geysers (table 1). No earthquakes were observed at Shasta, but the lack of operating stations on the volcano limited the capability to observe small events.

Table 1. Number of earthquakes at northern California volcanic centers during 24-hour periods following major earthquakes on 25 April (40.37°N, 124.32°W; M 7.0) and 28 June (34.18°N, 116.47°W; M 7.5) 1992. Events with coda durations less than or equal to 10 seconds and greater than 10 seconds are tallied separately. Earthquakes were identified from film records of seismograms from nearby stations. Courtesy of Stephen Walter.

Date Lassen Shasta Medicine Lake Geysers
Codas (seconds) <= 10 > 10 <= 10 > 10 <= 10 > 10 <= 10 > 10
25 Apr 1992 0 0 0 1 0 0 7 2
28 Jun 1992 8 14 1 5 12 0 46 4

Film was also scanned for the 24 hours following the M 7.0 earthquake at 40.37°N, 124.32°W (near Cape Mendocino) on 25 April. Although smaller than the 28 June earthquake, its epicenter was only 20-25% as far from the volcanoes. Furthermore, both the 25 April main shock and a M 6.5 aftershock were felt at the volcanic centers, but no felt reports were received from these areas after the 28 June earthquake. Only the Geysers showed any possible triggered events after the 25 April shock. However, background seismicity at the Geysers is higher than at the other centers, and is influenced by fluid injection and withdrawal associated with intensive geothermal development.

Shasta report. The film record showed no earthquake activity beneath Shasta (~900 km NNW of the epicenter), although telemetry problems limited the ability to detect events below M 2. Of the six earthquakes in the 24 hours following the M 7.5 shock, two were large enough to be recorded by the RTP system. These were centered about 60 km SE of Shasta and about equidistant from Lassen (figure 1). Because the arrival times and S-P sequences of the other four events were similar to those of the two located shocks, it is likely that all had similar epicenters. Occasional M 2 earthquakes have previously occurred in this area, which includes several mapped N-trending normal faults with Quaternary movement. Three days after the M 7.5 earthquake, a M 2.0 shock occurred beneath Shasta's SE flank, followed by a M 2.7 event the next day. Both were centered at about 15 km depth, similar to most earthquakes beneath Shasta in the last decade.

Figure (see Caption) Figure 1. Seismic events in the Shasta/Medicine Lake area that were apparently triggered by the M 7.5 southern California earthquake of 28 June 1992 (circles) compared to 1978-90 seismicity in the region (crosses). Squares mark seismic stations. Courtesy of Stephen Walter.

Geologic Background. The most voluminous of the Cascade volcanoes, northern California's Mount Shasta is a massive compound stratovolcano composed of at least four main edifices constructed over a period of at least 590,000 years. An ancestral edifice was destroyed by one of Earth's largest known Quaternary subaerial debris avalanches, which filled the Shasta River valley NW of the volcano. The Hotlum cone, forming the present summit, the Shastina lava dome complex, and the SW flank Black Butte lava dome, were constructed during the early Holocene. Eruptions from these vents have produced pyroclastic flows and mudflows that affected areas as far as 20 km from the summit. Eruptions from Hotlum cone continued throughout the Holocene.

Information Contacts: Stephen Walter and David Hill, MS 977, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 USA.


Spurr (United States) — June 1992 Citation iconCite this Report

Spurr

United States

61.299°N, 152.251°W; summit elev. 3374 m

All times are local (unless otherwise noted)


Details of 27 June eruptive cloud

Increased seismicity preceded a brief eruption of Spurr that began on 27 June at 0704, producing an eruption cloud that was carried rapidly NNE. Seismic data suggested that the eruption ended at about 1100, after apparent eruptive pulses at 0814 and 0904. By 1049, shortly before feeding of the plume stopped, data from the Nimbus-7 satellite's TOMS showed its leading edge roughly 500 km from the volcano, near Fairbanks (figure 3), with an apparent SO2 content of 35 kilotons. The next day, the cloud was detached from the volcano but still clearly visible on weather satellite imagery, extending in a 2,000-km arc E and SE over NE Alaska and NW Canada (figures 3 and 4). As the plume elongated, SO2 detected by the TOMS instrument increased to a maximum of 185 kilotons on 28 June at 1125, then decreased slightly to 160 kilotons as it started to dissipate on 29 June. The cloud remained visible on both TOMS data and weather satellite imagery for several more days.

Figure (see Caption) Figure 3. Three overlain images of the SO2 cloud from Spurr, as detected by the Total Ozone Mapping Spectrometer on the Nimbus-7 satellite. Values of SO2 in each 50 x 50-km pixel are shown on a relative scale of 0-9, then upward through alphabetic characters with increasing concentration. The cloud slowly dispersed until 3 July, when it could no longer be distinguished above background. Courtesy of Gregg Bluth.
Figure (see Caption) Figure 4. Image from the NOAA 11 polar-orbiting weather satellite on 29 June at about 0600, showing the plume from Spurr over the Beaufort Sea and western Canada. Courtesy of NOAA/NESDIS.

The maximum eruption cloud altitude reported by pilots was about 12 km. However, radar installed on the Kenai Peninsula after the Redoubt eruption, to monitor nearby volcanic activity, measured higher altitudes. At 0803, radar detected a vertical cloud to about 9 km altitude; at 0840, strong returns to 9 km and some material to 14.5 km; at 0950 and 1004, columns to 16 km altitude; and at 1018, to 18 km (figure 5).

Figure (see Caption) Figure 5. One of several radar images of the eruption column from Spurr on 27 June. This image, at 1018, shows echoes from the plume to about 18 km altitude. The instrument, an Enterprise Electronics WSR74C, 5-cm radar, is at Kenai, Alaska, about 80 km away. Vertical scans were used to maximize detection of the vertical cloud; the plume extending downwind is not visible. Courtesy of Joel Curtis and Dale Eubanks.

Because the plume was carried northward, major air routes to Asia that extend along the Aleutian chain from Anchorage were not affected. A Notice to Airmen warned aircraft to avoid the immediate vicinity of the volcano. No routes were officially closed, but airlines avoided using routes N and NW of the volcano (J501, 111, 133, 120, and 122; and V319, 444, and 480) during the eruption. Flights arriving in Anchorage, 120 km E of Spurr, were routed along normal approaches from the south.

Geologic Background. The summit of Mount Spurr, the highest volcano of the Aleutian arc, is a large lava dome constructed at the center of a roughly 5-km-wide horseshoe-shaped caldera open to the south. The volcano lies 130 km W of Anchorage and NE of Chakachamna Lake. The caldera was formed by a late-Pleistocene or early Holocene debris avalanche and associated pyroclastic flows that destroyed an ancestral edifice. The debris avalanche traveled more than 25 km SE, and the resulting deposit contains blocks as large as 100 m in diameter. Several ice-carved post-caldera cones or lava domes lie in the center of the caldera. The youngest vent, Crater Peak, formed at the breached southern end of the caldera and has been the source of about 40 identified Holocene tephra layers. Eruptions from Crater Peak in 1953 and 1992 deposited ash on the city of Anchorage.

Information Contacts: AVO; G. Bluth, NASA GSFC; SAB, NOAA/NESDIS; Joel Curtis and Dale Eubanks, NWS Alaska Region, Anchorage; Darla Gerlach, Air Traffic Division, FAA, Anchorage.


Stromboli (Italy) — June 1992 Citation iconCite this Report

Stromboli

Italy

38.789°N, 15.213°E; summit elev. 924 m

All times are local (unless otherwise noted)


Small explosions and seismicity continue

Fieldwork during the first week in June revealed that eruptive activity was mainly concentrated in craters C1 (vent 1) and C3 (vent 4), which fed black plumes no more than 100 m high. Seismicity remained high in June (figure 26), near the 180 events/day reached in the last third of May. A minimum of 108 events was recorded on 24 June. After declining rapidly about 20 May, tremor energy returned to levels characteristic of the period since November 1991.

Figure (see Caption) Figure 26. Seismicity at Stromboli, June 1992. Open bars show the number of recorded events per day, black bars those with ground velocities exceeding 100 mm/s. The curve represents the each day's average of tremor energies on hourly 60-second samples. Courtesy of M. Riuscetti.

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

Information Contacts: M. Riuscetti, Univ di Udine.


Tangaroa (New Zealand) — June 1992 Citation iconCite this Report

Tangaroa

New Zealand

36.321°S, 178.028°E; summit elev. -600 m

All times are local (unless otherwise noted)


New submarine volcano identified; no gas bubbling

Three previously unknown submarine arc stratovolcanoes have been identified at the S end of the Kermadec Ridge: Rumble V (36.140°S, 178.195°E, summit 700 m below sea level); Tangaroa (36.318°S, 178.031°E, summit 1,350 m below sea level); and Clark (36.423°S, 177.845°E, summit 1,150 m below sea level) (figure 1). All three have basal diameters of 16-18 km and rise from the seafloor at ~2,300 m depth. The first evidence of the volcanoes was from GLORIA side-scan mapping of the southern Havre Trough-Kermadec Ridge region in 1988 (Wright, 1990). Later investigations, including a photographic and rock-dredge study during the 3-week Rapuhia cruise (early 1992), confirmed previous interpretations. Side-scan and photographic data show a complex terrain of lava flows and talus fans on the flanks of all three volcanoes, with the most pristine-looking morphology at Rumble V. During the 1992 cruise, gas bubbles were detected acoustically, rising from the crests of Rumble III, IV, and V. No gas bubbling was evident from Tangaroa or Clark. Bathymetric surveys indicated that the summits of the shallowest volcanoes, Rumble III and IV, were at ~140 and 450 m, respectively, below the sea surface.

Figure (see Caption) Figure 1. Sketch map of New Zealand's North Island and the southern Kermadec Ridge area, with locations of young volcanoes. Courtesy of Ian Wright.

Reference. Wright, I.C., 1990, Bay of Plenty-Southern Havre Trough physiography, 1:400,000: New Zealand Oceanographic Institute Chart, Miscellaneous Series no. 68.

Geologic Background. Tangaroa submarine volcano in the southern Kermadec arc rises to within 600 m of the sea surface. The volcano is elongated in a NW-SE direction and contains smaller cones on its SE to eastern flanks. A larger edifice lies further to the SE. Tangaroa lies between Clark and Rumble V submarine volcanoes near the southern end of the Kermadec arc and is one of more than a half dozen volcanoes in this part of the arc showing evidence for active hydrothermal vent fields.

Information Contacts: I. Wright, New Zealand Oceanographic Institute, National Institute of Water and Atmospheric Research, Wellington.


Turrialba (Costa Rica) — June 1992 Citation iconCite this Report

Turrialba

Costa Rica

10.025°N, 83.767°W; summit elev. 3340 m

All times are local (unless otherwise noted)


Occasional seismicity

A telemetering seismic station (VTU) 0.5 km E of the active crater recorded 17 events in June. The maximum daily number, 4, occurred on 13 June.

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

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI.


Unzendake (Japan) — June 1992 Citation iconCite this Report

Unzendake

Japan

32.761°N, 130.299°E; summit elev. 1483 m

All times are local (unless otherwise noted)


Continued lava dome growth generates pyroclastic flows

Growth of the lava dome continued through early July. Partial collapses of the dome complex frequently generated pyroclastic flows. Dome 7, which had begun to emerge in late March, grew exogenously against dome 6 (figure 43), which was buried and eroded by dome 7's lava blocks. Frequent rockfalls from the front and margins of dome 7 reduced its length (to ~ 200 m) and height (to ~ 50 m). Petal or peel structures, which had always appeared on the dome's surface during periods of rapid lava extrusion, were not evident, perhaps indicating a declining magma supply rate. The cryptodome, including dome 5, grew endogenously, frequently generating small rockfalls that were probably triggered by earthquakes within or beneath the dome complex.

Figure (see Caption) Figure 43. Sketch of the dome complex at the summit of Unzen, 8 July 1992. Courtesy of Setsuya Nakada.

Volcanic gas was emitted continuously from the E part of dome 3, as well as from the depression between domes 3 and 7. The depression divides the cryptodome area into a conical NE section that includes the dome's summit, and a lower SW section with a flat top.

Deposits of the pyroclastic flows that cascade down the SE flank continue to bury the Akamatsu valley. The lowest saddle of the valley's southern cliff remains ~ 10 m high. On 23 June, the ash-cloud surge from a pyroclastic flow struck the saddle, but the main flow did not reach the cliff. The surge toppled brush on the saddle and to ~ 100 m distance, but small cedar trees remained standing. Bark and leaves were not burned, but leaves in the area died. About 10 cm of ash was deposited on the saddle. Thin lead foil, set in a stainless-steel hole to detect the pressure of the ash-cloud surge, was hollowed, and aluminum foil was broken.

Debris flows that have occasionally occurred during the current rainy season eroded pyroclastic flow deposits in the valley. Pyroclastic-flow material was deposited along the valley's N side and in its upper reaches. This deposition pattern, erosion by debris flows, and the declining magma-supply rate delayed the overflow of the lowest part of the saddle by southern-cliff pyroclastic flow deposits. In early July, the Nagasaki prefectural government began to construct a steel fence, 35 m wide and 10 m high, in a stream originating from the saddle, hoping to prevent ash-cloud surges from entering the stream.

JMA reported that the daily number of seismically detected pyroclastic flows ranged from 6 to 21 in June. The total of 373 in June was almost unchanged from previous months. The longest June flow extended 3 km SE from the dome. Most ash clouds generated by the flows rose about 1,000 m, with the highest, to 1,200 m, on 13 and 17 June.

Small earthquakes continued to occur within and beneath the dome complex, at rates of 50-200/day through mid-July. The June total, 3,671 recorded earthquakes, was similar to previous months.

Evacuated areas . . . were somewhat reduced on 11 July, decreasing the number of evacuees from 6,746 to 6,064.

Geologic Background. The massive Unzendake volcanic complex comprises much of the Shimabara Peninsula east of the city of Nagasaki. An E-W graben, 30-40 km long, extends across the peninsula. Three large stratovolcanoes with complex structures, Kinugasa on the north, Fugen-dake at the east-center, and Kusenbu on the south, form topographic highs on the broad peninsula. Fugendake and Mayuyama volcanoes in the east-central portion of the andesitic-to-dacitic volcanic complex have been active during the Holocene. The Mayuyama lava dome complex, located along the eastern coast west of Shimabara City, formed about 4000 years ago and was the source of a devastating 1792 CE debris avalanche and tsunami. Historical eruptive activity has been restricted to the summit and flanks of Fugendake. The latest activity during 1990-95 formed a lava dome at the summit, accompanied by pyroclastic flows that caused fatalities and damaged populated areas near Shimabara City.

Information Contacts: S. Nakada, Kyushu Univ; JMA.

Atmospheric Effects

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

Atmospheric Effects (1980-1989)  Atmospheric Effects (1995-2001)

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements

Additional Reports

Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false. All of these types of additional reports are listed below by subregion and subject.

Kermadec Islands


Floating Pumice (Kermadec Islands)

1986 Submarine Explosion


Tonga Islands


Floating Pumice (Tonga)


Fiji Islands


Floating Pumice (Fiji)


Andaman Islands


False Report of Andaman Islands Eruptions


Sangihe Islands


1968 Northern Celebes Earthquake


Southeast Asia


Pumice Raft (South China Sea)

Land Subsidence near Ham Rong


Ryukyu Islands and Kyushu


Pumice Rafts (Ryukyu Islands)


Izu, Volcano, and Mariana Islands


Acoustic Signals in 1996 from Unknown Source

Acoustic Signals in 1999-2000 from Unknown Source


Kuril Islands


Possible 1988 Eruption Plume


Aleutian Islands


Possible 1986 Eruption Plume


Mexico


False Report of New Volcano


Nicaragua


Apoyo


Colombia


La Lorenza Mud Volcano


Pacific Ocean (Chilean Islands)


False Report of Submarine Volcanism


Central Chile and Argentina


Estero de Parraguirre


West Indies


Mid-Cayman Spreading Center


Atlantic Ocean (northern)


Northern Reykjanes Ridge


Azores


Azores-Gibraltar Fracture Zone


Antarctica and South Sandwich Islands


Jun Jaegyu

East Scotia Ridge


Additional Reports (database)

08/1997 (BGVN 22:08) False Report of Mount Pinokis Eruption

False report of volcanism intended to exclude would-be gold miners

12/1997 (BGVN 22:12) False Report of Somalia Eruption

Press reports of Somalia's first historical eruption were likely in error

11/1999 (BGVN 24:11) False Report of Sea of Marmara Eruption

UFO adherent claims new volcano in Sea of Marmara

05/2003 (BGVN 28:05) Har-Togoo

Fumaroles and minor seismicity since October 2002

12/2005 (BGVN 30:12) Elgon

False report of activity; confusion caused by burning dung in a lava tube



False Report of Mount Pinokis Eruption (Philippines) — August 1997

False Report of Mount Pinokis Eruption

Philippines

7.975°N, 123.23°E; summit elev. 1510 m

All times are local (unless otherwise noted)


False report of volcanism intended to exclude would-be gold miners

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.


False Report of Somalia Eruption (Somalia) — December 1997

False Report of Somalia Eruption

Somalia

3.25°N, 41.667°E; summit elev. 500 m

All times are local (unless otherwise noted)


Press reports of Somalia's first historical eruption were likely in error

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.


False Report of Sea of Marmara Eruption (Turkey) — November 1999

False Report of Sea of Marmara Eruption

Turkey

40.683°N, 29.1°E; summit elev. 0 m

All times are local (unless otherwise noted)


UFO adherent claims new volcano in Sea of Marmara

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.


Har-Togoo (Mongolia) — May 2003

Har-Togoo

Mongolia

48.831°N, 101.626°E; summit elev. 1675 m

All times are local (unless otherwise noted)


Fumaroles and minor seismicity since October 2002

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 (see Caption) 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 (see Caption) 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 (see Caption) 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.


Elgon (Uganda) — December 2005

Elgon

Uganda

1.136°N, 34.559°E; summit elev. 3885 m

All times are local (unless otherwise noted)


False report of activity; confusion caused by burning dung in a lava tube

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/).