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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

Sheveluch (Russia) Renewed activity with lava dome growth and ash explosions starting in late December 2018

Mayon (Philippines) Intermittent ash emissions; persistent summit incandescence, October 2018-April 2019

Tinakula (Solomon Islands) Thermal anomalies in satellite data December 2018-June 2019; ship visit January 2019

Piton de la Fournaise (France) Eruptive episodes in February-March and June 2019; multiple fissures and lava flows

Heard (Australia) Thermal hotspots continue during October 2018-March 2019 at the summit and on the upper flanks

Semeru (Indonesia) Decreased activity after October 2018

Dukono (Indonesia) Numerous ash explosions from October 2018 through March 2019

Rincon de la Vieja (Costa Rica) Occasional weak phreatic explosions continue through February 2019

Turrialba (Costa Rica) Frequent passive ash emissions continue through February 2019

San Cristobal (Nicaragua) Weak ash explosions in January and March 2019

Semisopochnoi (United States) Minor ash explosions during September and October 2018

Asosan (Japan) Multiple brief ash emission events during April and May 2019; minor ashfall in adjacent villages



Sheveluch (Russia) — May 2019 Citation iconCite this Report

Sheveluch

Russia

56.653°N, 161.36°E; summit elev. 3283 m

All times are local (unless otherwise noted)


Renewed activity with lava dome growth and ash explosions starting in late December 2018

Volcanism at Sheveluch has been ongoing for the past 20 years. Previous activity consisted of pyroclastic flows, explosions, moderate gas-and-steam emissions, and lava dome growth, according to the Kamchatka Volcanic Eruptions Response Team (KVERT). Between May 2018 and mid-December 2018 activity levels were low, with intermittent low-power thermal anomalies and gas-and-steam emissions. Activity increased in the second half of December 2018, remaining high through at least April 2019.

Activity intensified beginning in late December through April 2019, which included increased and more frequent thermal anomalies, according to KVERT and the MIROVA system (figure 50). On 30 December 2018, video data from KVERT showed explosions producing an ash cloud that rose up to 11 km altitude and drifted 244 km WSW and 35 km NE. Eruptive activity included incandescent lava flows and hot avalanches. The ash cloud that drifted WSW resulted in ashfall over Klyuchi Village (50 km SW) and Kozyrevsk (100 km SW).

Figure (see Caption) Figure 50. Thermal anomalies at Sheveluch increased in late December 2018, as seen on this MIROVA Log Radiative Power graph for the year ending 5 April 2019. The elevated thermal activity continued through March 2019. Courtesy of MIROVA.

Beginning in early January and going through April 2019, the lava dome at the northern part of the volcano continued to grow, extruding incandescent, viscous lava blocks (figure 51). Throughout these months, KVERT reported that satellite imagery and video data showed strong fumarolic activity, as well as strong gas-and-steam plumes containing some amount of ash; gas-and-steam plumes rose as high as 7 km. According to the KVERT Daily Reports on 3 and 4 January 2019, a gas-and-steam plume containing ash drifted NE up to about 600 and 400 km, respectively. Gas-and-steam plumes noted in the KVERT Daily Report, Weekly Releases, and Volcano Observatory Notice for Aviation (VONA), drifted 50-263 km in different directions. On 9 November 2018, the KVERT Daily Report recorded an ash plume drifting 461 km E from the volcano and on 26 December 2018, the KVERT Weekly Information Release recorded an ash cloud drifting 300 km NW. The KVERT Weekly Information Release reported that on 10 April 2019 an ash cloud drifted up to 1,300 km SE.

Figure (see Caption) Figure 51. Incandescent avalanches from the lava dome and an ash plume can be seen in this photo of Sheveluch on 22 February 2019. Photo by Yu. Demyanchuk; courtesy of the Institute of Volcanology and Seismology FEB RAS, KVERT.

Thermal anomalies based on MODIS satellite instruments analyzed using the MODVOLC algorithm were frequent beginning on 28 December 2018. In just three days in late December (28-31 December 2018) there were 34 thermal alerts. Hotspots were detected 21-27 days each month between January-April 2019. A majority of these hotspot pixels occurred within the summit crater.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).


Mayon (Philippines) — May 2019 Citation iconCite this Report

Mayon

Philippines

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

All times are local (unless otherwise noted)


Intermittent ash emissions; persistent summit incandescence, October 2018-April 2019

Steep-sloped and symmetrical Mayon has recorded historical eruptions back to 1616 that range from Strombolian fountaining to basaltic and andesitic flows, as well as large ash plumes, and devastating pyroclastic flows and lahars. A phreatic explosion with an ash plume in mid-January 2018 began the latest eruptive episode which included the growth of a lava dome with pyroclastic flows down the flanks and lava fountaining (BGVN 43:04). Activity tapered off during March; occasional ash emissions continued through August 2018. Minor ash emissions and summit incandescence were intermittent from October 2018-April 2019, the period covered in this report. Information is provided primarily by the Philippine Institute of Volcanology and Seismology (PHIVOLCS).

Pyroclastic density currents were reported in early November 2018; ash plumes were produced from phreatic events a few times during both November and December 2018. Emissions produced SO2 anomalies during January-March 2019; a series of events in early March generated several small ash plumes. Satellite images showing a thermal anomaly at the summit were recorded multiple times each month from October 2018-April 2019 (figure 44).

Figure (see Caption) Figure 44. Small but distinct persistent thermal anomalies were recorded in satellite imagery from the summit of Mayon during October 2018-April 2019. Top left: 12 October 2018. Top right: 26 November 2018. Middle left: 11 December 2018. Middle right: 30 January 2019. Bottom left: 14 February 2019. Bottom right: 25 April 2019. All images are using the "Atmospheric penetration" filter (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Very little activity was reported at Mayon during October 2018. Steam plumes rose daily from 250-750 m above the summit before drifting with the prevailing winds and dissipating. Incandescence was observed at the summit most nights during the month, and seismicity remained low with only a few earthquakes reported. Leveling data obtained during 30 August-3 September indicated significant short-term deflation of the volcano relative to 17-24 July 2018. New leveling data obtained on 22-31 October indicated inflation of the SE quadrant and short-term deflation on the N flank relative to the 30 August-3 September data. The volcano remained inflated compared with 2010 baseline data. Electronic tilt data showed pronounced inflation of the mid-slopes beginning 25 June 2018.

Activity increased during November 2018. In addition to steam plumes rising to 750 m and an incandescent glow at the summit most nights, pyroclastic density currents and ash plumes were reported. The seismic monitoring network recorded pyroclastic density currents on 5 and 6 November. On 8 November around noontime, a small, short-lived brownish ash plume, associated with degassing, drifted WSW from the summit. A seismic event on the morning of 11 November was associated with a short-lived fountaining event that produced a brownish-gray ash plume that drifted SW. Another similar plume was reported on the morning of 12 November, also drifting SW before dissipating. Two phreatic events were observed on the morning of 26 November. They produced grayish to grayish-white ash plumes that rose 300-500 m above the summit before drifting SW. The following morning, another event produced a grayish ash plume 500 m above the summit that drifted SW. On 30 November a 1-minute-long ash emission event produced a grayish white plume that also drifted SW.

Steam plume emissions and incandescence at night continued at Mayon during December 2018. The seismic network recorded a four-minute-long event shortly after noon on 9 December that produced a grayish-brown ash plume which drifted W. Precise leveling data obtained on 8-13 December 2018 indicated a slight inflation of the volcano relative to 22-31 October 2018. A 30-second-long ash emission event in the afternoon on 18 December produced a brownish ash plume. Two phreatic events were observed on the morning of 27 December. They produced grayish to grayish-white ash plumes that rose 600 and 200 m above the summit, before drifting SW (figure 45).

Figure (see Caption) Figure 45. Ash plumes rose a few hundred m from the summit of Mayon on 27 December 2018. Courtesy of Twitter users "k i t" (left) and "georgianne" (right).

Very little surface activity except for white steam-laden plumes that crept downslope and drifted NW or SW was noted during January 2019. Incandescence at the summit, visible with the naked eye, became more frequent during February 2019, along with continued steam plumes. Precise leveling data obtained on 25 January-3 February 2019 indicated a slight deflation relative to 8-13 December 2018. However, continuous GPS and electronic tilt data showed inflation of the mid-slopes since June 2018. Small SO2 plumes were detected by the TROPOMI satellite instrument a few times during January-March 2019 (figure 46).

Figure (see Caption) Figure 46. Emissions of SO2 that exceeded 2 DU (Dobson Units) occurred a few times at Mayon during January-March 2019. Top left: 25 January. Top right: 16 February. Lower left: 4 March. Lower right: 15 March. Courtesy of NASA Goddard Space Flight Center.

Steam plumes rose 250-500 m above the summit and drifted generally W in early March 2019; incandescence continued daily at the summit. Phreatic events occurred on 7 and 8 March, producing ash plumes that rose 500 and 300 m from the summit before drifting SW (figure 47). Three more phreatic events occurred on the afternoon of 12 March; they produced light brown to grayish ash plumes that rose 500, 1,000, and 500 m, respectively, and drifted SW. Six phreatic events occurred throughout the day on 13 March, producing ash plumes that rose 200-700 m above the summit and drifted W. A single explosion the next day produced a 500-m-tall ash plume. The Tokyo VAAC reported an ash plume visible for several hours in satellite imagery drifting W at 3.7 km altitude on 13 March (UTC). An increase in the daily number of rockfall events from 1-2 per day to 5-10 per day was noted during the second half of March. Precise leveling data obtained on 20-26 March 2019 indicated a slight inflation relative to 25 January-3 February 2019.

Figure (see Caption) Figure 47. A small ash emission at Mayon was reported by PHIVOLCS on 8 March 3019; the plume rose 300 m from the summit and drifted SW. Courtesy of PHOVOLCS.

Steam plumes drifted SW or NW throughout April, rising 200-400 m from the summit. Incandescence could be observed at night for the first half of the month. Leveling data obtained during 9-17 April 2019 indicated a slight inflation relative to 20-26 March 2019. Seismicity remained low during the month with only occasional volcanic earthquakes and rockfall events. Lenticular clouds around the summit were observed (figure 48), but these are an unusual meteorological occurrence caused by weather conditions not related to volcanic activity.

Figure (see Caption) Figure 48. A double lenticular cloud surrounded the summit of Mayon early in the morning on 23 April 2019 and was captured by a local observer; it was not related to volcanic activity. Courtesy of Twitter user Ivan.

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/); 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/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Twitter user "Ivan", Naga City, Philippines (URL: https://twitter.com/ivanxlcsn); Twitter user "k i t", Legazpi City, Philippines (URL: https://twitter.com/jddmgc); Twitter user "georgianne", Costa Leona, Philippines (URL: https://twitter.com/xolovesgia_).


Tinakula (Solomon Islands) — July 2019 Citation iconCite this Report

Tinakula

Solomon Islands

10.386°S, 165.804°E; summit elev. 796 m

All times are local (unless otherwise noted)


Thermal anomalies in satellite data December 2018-June 2019; ship visit January 2019

Remote Tinakula lies 100 km NE of the Solomon Trench at the N end of the Santa Cruz Islands, which are part of the country of the Solomon Islands located 400 km to the W. It has been uninhabited since an eruption with lava flows and ash explosions in 1971 when the small population was evacuated (CSLP 87-71). The nearest communities live on Te Motu (Trevanion) Island (about 30 km S), Nupani (40 km N), and the Reef Islands (60 km E); residents occasionally report noises from explosions at Tinakula. Ashfall from larger explosions has historically reached these islands. The most recent eruptive episode was a large ash explosion and substantial SO2 plume during 21-26 October 2017; satellite imagery suggested that a flow of some type traveled down the scarp on the W flank. Renewed thermal activity that was recognized in satellite imagery beginning in December 2018 continued intermittently through June 2019 and is covered in this report. Satellite imagery and thermal data are the primary sources of information for this volcano. It is occasionally visited by members of the National Disaster Management Office (NDMO) of the Solomon Islands Government, tourists, and research vessels who are able to capture ground-based information.

Satellite images from December 2018 to February 2019 show thermal anomalies at the summit vent. Excellent ship-based photographs of the island on 24-25 January 2019 provided by a crewmember from the R/V Petrel identify numerous volcanic features and show a steam-and-gas plume at the vent. Satellite images from April and May 2019 show thermal anomalies at both the summit vent and along the W flank scarp suggesting flow activity during that time.

A stream of incandescence on the NW flank of Tinakula in a Sentinel 2 satellite image on 24 October 2017 confirmed that some type of high-temperature flow accompanied the explosions and eruptive activity of 21-25 October 2017 (BGVN 43:02). Satellite imagery during most of 2018 recorded steam plumes drifting in several directions from the summit, but no thermal activity (figure 24). There was no further evidence of activity in satellite visible or thermal data until almost exactly one year later when the MIROVA project recorded two thermal alerts in the third week of October 2018 (figure 25). Satellite images from that week were cloudy and did not confirm any surface activity.

Figure (see Caption) Figure 24. Sentinel-2 satellite imagery of Tinakula provides valuable information about activity at this remote volcano in the South Pacific. A large explosion with ash plumes and flows occurred during 21-26 October 2017. Top left: a strong E-W linear thermal anomaly suggesting a flow event from the summit was evident on the NW flank on 24 October 2017. Top right: a small steam plume rose from the summit vent on a cloudless 11 February 2018. Bottom left: a dense steam plume drifted SE from the summit vent on 4 September 2018. Bottom right: clouds and dense steam obscure the summit on 24 October 2018, about the same time that MIROVA reported a thermal anomaly. Top left image uses bands 12, 11, 8A, others use 12, 4, 2. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 25. The MIROVA project recorded the first thermal anomaly in a year from Tinakula during the third week of October 2018. Courtesy of MIROVA.

The first satellite imagery confirming renewed thermal activity appeared on 8 December 2018, around the same time as a small MIROVA anomaly. After that, several images during January and February 2019 confirmed moderately strong thermal activity at the summit (figure 26). Whether the anomalies were the result of active lava effusion or strong incandescent gases from the summit vent is uncertain.

Figure (see Caption) Figure 26. Thermal anomalies at the summit vent of Tinakula were recorded six times between early December 2018 and early February 2019 with Sentinel-2 satellite images. Top row: 8 December 2018 and 2 January 2019. Middle row: 12 (anomaly is just below date) and 27 January 2019. Bottom row: 1 and 6 February 2019. All images are bands 12, 4, 2. Courtesy of Sentinel Hub Playground.

Visual confirmation of activity at Tinakula is rare, but the research vessel R/V Petrel sailed past the volcano on 24 and 25 January 2019 and a crewmember provided detailed images of the W flank and vent area. The summit vent is located at the top of a W facing scarp, and steam is frequently observed rising from the vent (figures 27). Recent flows and volcaniclastic deposits were visible in the ravine on the W flank (figures 28 and 29). Fresh-looking lava was also visible near the summit vent on top of older deposits (figure 30). Eroded volcaniclastic deposits near the base of the scarp on the W flank were visible on top of older veined and layered volcanic rocks (figure 31). Crewmembers on the vessel R/V Petrel could clearly see an incandescent glow from the summit crater at night (figure 32).

Figure (see Caption) Figure 27. A view from the SW of the W flank of Tinakula on 24-25 January 2019. The summit vent is at the top of a W facing scarp, the steam plume drifted E. Used with permission from Paul G Allen's Vulcan Inc.
Figure (see Caption) Figure 28. The W flank of Tinakula as seen from the W on 24-25 January 2019. The steam plume drifted E. Recent flows and volcaniclastic deposits appeared dark in the steep ravine on the W face (left side). Used with permission from Paul G Allen's Vulcan Inc.
Figure (see Caption) Figure 29. Steam and gas rose from the summit vent at Tinakula on 24-25 January 2019. Recent lava deposits are visible in front of the plume and in the ravine on the left (the W flank). Used with permission from Paul G Allen's Vulcan Inc.
Figure (see Caption) Figure 30. The edge of the summit vent of Tinakula on 24-25 January 2019 had recent lava on older deposits; steam and gas is rising from the vent in the background. Used with permission from Paul G Allen's Vulcan Inc.
Figure (see Caption) Figure 31. The W flank of Tinakula on 24-25 January 2019. Eroded volcaniclastic deposits overlie older veined and layered volcanic rocks. Used with permission from Paul G Allen's Vulcan Inc.
Figure (see Caption) Figure 32. Incandescence was clearly visible from the summit vent at Tinakula on 24-25 January 2019. Used with permission from Paul G Allen's Vulcan Inc.

During April and May 2019, both the MIROVA project and MODVOLC measured a number of thermal anomalies (figure 33) using MODIS satellite data. MODVOLC alerts were issued on 4 and 20 April, and 11, 18, and 27 May. Sentinel-2 satellite images during the period confirmed that a flow on the W flank was a likely source of the thermal energy in addition to the summit vent (figure 34). Thermal anomalies appeared again at the end of June in MIROVA data, but no satellite images showed anomalies at that time.

Figure (see Caption) Figure 33. The number and intensity of MIROVA thermal anomalies increased at Tinakula during April and May 2019. After a short pause, they returned at the end of June. Courtesy of MIROVA.
Figure (see Caption) Figure 34. Sentinel-2 satellite images captured thermal anomalies at the summit and on the W flank of Tinakula during April and May 2019 suggesting the presence of an incandescent flow down the W scarp. Top row: 7 and 22 April 2019 (bands 12, 8, 4). Bottom row: 27 April and 12 May 2019 (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Geologic Background. The small 3.5-km-wide island of Tinakula is the exposed summit of a massive stratovolcano at the NW end of the Santa Cruz islands. Similar to Stromboli, it has a breached summit crater that extends from the summit to below sea level. Landslides enlarged this scarp in 1965, creating an embayment on the NW coast. The satellitic cone of Mendana is located on the SE side. The dominantly andesitic volcano has frequently been observed in eruption since the era of Spanish exploration began in 1595. In about 1840, an explosive eruption apparently produced pyroclastic flows that swept all sides of the island, killing its inhabitants. Frequent historical eruptions have originated from a cone constructed within the large breached crater. These have left the upper flanks and the steep apron of lava flows and volcaniclastic debris within the breach unvegetated.

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/); 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); Vulcan Inc. (URL: https://www.vulcan.com/), additional details about the R/V Petrel (URL: https://www.paulallen.com/).


Piton de la Fournaise (France) — July 2019 Citation iconCite this Report

Piton de la Fournaise

France

21.244°S, 55.708°E; summit elev. 2632 m

All times are local (unless otherwise noted)


Eruptive episodes in February-March and June 2019; multiple fissures and lava flows

Short pulses of intermittent eruptive activity have characterized Piton de la Fournaise, the large basaltic shield volcano on La Réunion Island in the western Indian Ocean, for several thousand years. For the last 20 years, frequent effusive basaltic eruptions have occurred on average twice per year. The activity is characterized by lava fountains and lava flows, and occasional explosive eruptions that shower blocks over the summit area and produce ash plumes. Almost all of the recent activity has occurred within the Enclos Fouqué caldera, although past eruptions in 1977, 1986, and 1998 have occurred at vents outside of the caldera. Four separate eruptive episodes were reported during 2018; from 3-4 April, 27 April-1 June, 13 July, and 15 September-1 November (BGVN 43:12, 43:09). Two episodes from 2019 during February-March and June are covered in this report, with information provided primarily by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) as well as satellite instruments.

Piton de la Fournaise experienced two eruptions during November 2018-June 2019. The first lasted from 18 February to 10 March 2019, and the second episode was 11-13 June. The episode in February-March started consisted of multiple fissures opening on the E flank of the Dolomieu crater on 18 February with lava flows that traveled several hundred meters. After a brief pause, one new fissure opened nearby on 19 February and produced up to 3 million m3 of lava in a little over four days. Although the flow rate then declined, the eruption continued until 10 March. During the last three days, 7-10 March, two new fissures opened nearby and produced large volumes of lava, bringing the total eruptive volume to about 14.5 million m3. After little activity during April and May, a small eruption occurred on the SSE outer slope of Dolomieu crater that lasted for about 48 hours on 11-13 June; multiple small flows traveled about 1,000 m down the steep flank before ceasing. The MIROVA thermal anomaly graph of log radiative power clearly showed the abruptness of the beginning and ends of the last three eruptive episodes at Piton de la Fournaise from August 2018 through June 2019 (figure 165).

Figure (see Caption) Figure 165. The MIROVA graph of thermal energy from Piton de la Fournaise from 30 July 2018 through June 2019 shows the last three eruptive episodes at the volcano. From 15 September through 1 November 2018 fissures and flows were active on the SW flank of Dolomieu crater near Rivals crater (BGVN 43:12). Fissures opened on the E flank of the crater on 18 February 2019, and after a brief pause resumed on 19 February at the foot of Piton Madoré. Lava flows remained active until 10 March 2019. A short episode of lava effusion occurred on 11-12 June 2019 on the SSE outer slope of Dolomieu crater. Courtesy of MIROVA.

Activity during November 2018-March 2019. Following the end of the 15 September-1 November 2018 eruption, seismic activity immediately below the summit remained low (with only 20 shallow and two deep earthquakes during November). The inflationary signal recorded since the beginning of September stopped, and the OVPF deformation networks did not record any significant deformation. There were 35 shallow earthquakes (0-2 km depth) below the summit crater during December, and one deep earthquake. Only 12 shallow earthquakes and one deep earthquake (greater than 2 km below the surface) were reported in January.

OVPF reported an increase in CO2 concentrations beginning in December 2018, and noted the beginning of inflation on 13 February 2019. A seismic swarm of 379 earthquakes accompanied by minor but rapid deformation (less than 1 cm) was reported on 16 February 2019. A new seismic swarm of 208 earthquakes began early on 18 February with a much larger ground deformation (10 cm of elongation of the summit zone). A volcanic tremor indicative of the arrival of magma near the surface began at 0948 that morning. Webcams indicated that eruptive fissures had opened in the NE part of the Enclos Fouqué caldera. The onset of the eruption was marked by a sudden drop in CO2 flux which then stabilized. The eruptive sites were confirmed visually around 1130. Three fissures with actively flowing lava opened on the E flank of Dolomieu Crater; the fountains of lava were less than 30 m high. The front of the longest flow had reached 1,900 m elevation after one hour. The eruption lasted a little over 12 hours and was over by 2200 that evening; it covered about 150-200 m of the hiking trail to the summit.

Seismicity remained high after the event ended, and at 1500 on 19 February 2019 another seismic swarm of 511 deep earthquakes located under the E flank at about 2.5 km depth occurred. It was not accompanied by a significant amount of deformation. At 1710 tremor signals appeared on the observatory seismographs and the first gas plumes and lava ejection were observed at 1750 and 1912, respectively. During an overflight the next day (20 February), OVPF team members observed the new eruptive site at an elevation of 1,800 m at the foot of Piton Madoré. One fissure and one fountain were active at 0620 on 20 February and the flow front was at 1,300 m elevation (figure 166). During the night of 20-21 February the flow front crossed over the "Grandes Pentes" area in the eastern half of the Enclos Fouque (figure 167).

Figure (see Caption) Figure 166. The eruption which began on 19 February 2019 on the E flank of Dolomieu crater at Piton de la Fournaise produced a lava fountain and flow which traveled down at least 500 m of elevation by the next morning when this photo was taken at 0620 local time. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du mercredi 20 février 2019 à 11h00, Heure locale).
Figure (see Caption) Figure 167. The active fissure at Piton de la Fournaise was producing lava fountains and an active flow during the evening of 20 February 2019. Overnight the flow crossed over the "Grandes Pentes" area of the caldera. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du jeudi 21 février 2019 à 14H00, Heure locale).

OVPF reported on 22 February 2019 that 22 shallow earthquakes had been reported since the eruption began on 19 February. Surface flow rates estimated from satellite data, via the HOTVOLC system (OPGC - University of Auvergne), were between 2.5 and 15 m3/s. The quantity of lava emitted between 19 and 22 February was between 1 and 3 million m3. OVPF observed the growth of an eruptive cone that was filled with a small lava lake producing ejecta during a morning overflight on 22 February. A channelized flow moved downstream from the cone and split into two lobes about 1 km from (and 200 m below) the cone (figure 168). The split in the flow occurred near the Guyanin crater. The N flowing lobe, about 50 m wide, had an actively flowing front located at 1,320 m elevation; the incandescent flow was travelling over a recent flow (likely from the previous night). The S-flowing lobe spread to 200 m wide and split into two tongues 300 m SE of Guyanin crater.

Figure (see Caption) Figure 168. During an overflight on the morning of 22 February 2019 scientists from OVPF observed a growing spatter cone with a small lava lake at Piton de la Fournaise. A channelized flow moved downstream from the fissure and split into two flows. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 22 février 2019 à 13h30, Heure locale).

Incandescent ejecta from the cone was captured in a webcam image overnight on 22-23 February 2019 (figure 169). The rate of advance of the flow slowed significantly by 24 February, but the intensity of the eruptive tremor remained relatively constant. Mapping of the lava flow on 28 February carried out by the OI2 platform (OPGC - University Clermont Auvergne) from satellite data confirmed the slow progress of the flow after 24 February (300 m in 5 days) (figure 170). The flow front was located at 1,200 m elevation, and only the N arm was active; the lava had traveled about 2.2 km from the vent by 28 February.

Figure (see Caption) Figure 169. Incandescent ejecta from the eruptive cone at Piton de la Fournaise was captured in the webcam in the early hours of 23 February 2019. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du samedi 23 février 2019 à 13h30, Heure locale).
Figure (see Caption) Figure 170. Contours of the lava flows at Piton de la Fournaise from 18-28 February 2019 were determined from satellite data by the OI2 platform (Université Clermont Auvergne), dated 18 (red) and 19 (blue) February (top image); 20 (green), 21 (red), 22 (blue), 27 (turquoise), and 28 (pink) February (bottom image). Courtesy of and copyright by OVPF/IPGP. Top: Bulletin d'activité du vendredi 22 février 2019 à 13h30 (Heure locale); bottom: Bulletin d'activité du jeudi 28 février 2019 à 16h30 (Heure locale).

Between 28 February and 1 March 2019 a third lobe of lava appeared flowing NE from the vent on the N side of the new flow area; it split into two lobes sometime on 1 March. Very little new lava was recorded on the other lobes. By 4 March the flow rate estimated by satellite data was about 7.5 m3/s. During a site visit on the morning of 5 March OVPF scientists sampled the N lobe of the flow and bombs and tephra near the cone, and acquired infrared and visible images. They noted the continued growth of the cone which still had an open vent at the summit and a base 100 m in diameter. It was 25 m high with a 50-m-wide eruptive vent at the top (figure 171). High-temperature gas emissions and strong Strombolian activity issued from the vent. Steam emissions were present around the base of the cone, suggesting the presence of lava tunnels. A single lobe of lava flowed N from the cone.

Figure (see Caption) Figure 171. The eruptive cone at Piton de la Fournaise on 5 March 2019 had a 100-m-diameter base, 25 m of vertical height, and 50-m-wide vent at the summit. Courtesy of and copyright by OVPF/IPGP, (Bulletin d'activité du mardi 5 mars 2019 à 17h30, Heure locale).

A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré was first observed on the morning of 6 March (figure 172); OVPF concluded that it had opened late on 5 March. A small cone was forming and a new flow traveled N from the main eruptive site. At least six new emission points were noted the following morning (7 March) around the Piton Madoré. Poor weather prevented confirmation by aerial reconnaissance that day, but in a site visit on 8 March OVPF scientists determined that the new fissure from 5 March remained active; a small cone about 10 m high had two flow lobes on the W and N sides (figure 173). A fissure that opened on 7 March was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March with two 50-m-high lava fountains (figure 174). Samples collected by OVPF indicated that the vents of 5 and 7 March produced lava of different compositions.

Figure (see Caption) Figure 172. A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré at Piton de la Fournaise was first observed on the morning of 6 March 2019; OVPF concluded that it had opened late on 5 March. A small cone was forming on the flank of an old one and a new flow traveled N from the main eruptive site. Courtesy of OVPF/IPGP, copyright by Helicopter Coral (Bulletin d'activité du jeudi 7 mars 2019 à 15h00 Heure locale).
Figure (see Caption) Figure 173. The 5 March 2019 fissure at Piton de la Fournaise on the NW flank of Piton Madoré still had two active flow lobes emerging from it and heading N and W on 8 March 2019. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).
Figure (see Caption) Figure 174. A fissure that opened on 7 March 2019 at Piton de la Fournaise was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March 2019 with two 50-m-high lava fountains. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

There was a strong increase in the eruptive tremor intensity on 7 March, related to the opening of the two new fissures on 5 and 7 March (figure 175). As a result, the surface flow estimates made from satellite data increased significantly to high values greater than 50 m3/s, with the average values on 7-8 March of around 20-25 m3/s. The increased flow rates resulted in the flows traveling much greater distances. By the morning of 9 March the active flow had reached 650-700 m above sea level. The flow front had traveled about 1 km in 24 hours. Strong seismicity had been increasing under the summit zone for the previous 48 hours. After a phase of very strong surface activity observed overnight on 9-10 March that included lava fountains 50-100 m high (figure 176), surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. OVPF noted that sudden increases in seismicity and flow rates near the end of an eruption have occurred at about half of the eruptions at Piton de la Fournaise in recent years. Lava volumes emitted on the surface between 18 February and 10 March 2019 were estimated at about 14.5 million m3 (figure 177).

Figure (see Caption) Figure 175. An infrared view of the eruptive site on the E flank of Dolomieu crater at Piton de la Fournaise on 8 March 2019 clearly showed the original fissure from 19 February (bottom right of center), the fissure on Piton Madore that opened on 5 March (right) and the fissures that opened on 7 March (upper, right of center). The combined activity produced significant thermal and seismic activity at the volcano. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 8 mars 2019 à 17h00, Heure locale).
Figure (see Caption) Figure 176. Lava fountains 50-100 m high were the result of very strong surface activity observed overnight on 9-10 March 2019 at Piton de la Fournaise. Surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. Photo taken on 9 March 2019 around midnight from the RN2. Courtesy of OVPF/IPGP, copyright by A. Finizola LGSR/IPGP (Bulletin d'activité du dimanche 10 mars 2019 à 19h30 Heure locale).
Figure (see Caption) Figure 177. A sudden increase in the flow rate at the end of the 18 February-10 March 2019 eruption at Piton de la Fournaise was recorded by researchers at the Université Clermont Auvergne. OVPF noted this was typical of about half of the eruptions at Piton de la Fournaise. Courtesy of OVPF/IPGP, copyright by HOTVOLC, Université Clermont Auvergne (OVPF Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

Significant SO2 plumes were captured by the TROPOMI instrument on the Sentinel 5-P satellite throughout the 18 February-10 March eruption (figure 178). After the surface eruption ceased, shallow seismicity continued at a lower rate of about 12 earthquakes per day. The end of the eruption (7-10 March) was accompanied by a marked deflation, interpreted by OVPF as the rapid emptying of the magma reservoir. Following the end of the eruption, inflation resumed for the rest of March but then ceased. Seismicity continued at a lower level during April with an average of six shallow earthquakes per day.

Figure (see Caption) Figure 178. Multiple days of high DU value SO2 plumes were recorded by the TROPOMI instrument on the Sentinel 5-P satellite during the 18 February-10 March 2019 eruption at Piton de la Fournaise. Top row: during 18, 21, and 22 February SO2 plumes drifted SE. Middle row: during 23, 24, and 25 February the wind direction changed from SE through S to SW and left a curling trail of SO2. Bottom row: 5, 7, and 8 March showed an increase in SO2 emissions that corresponded with increased seismicity and lava flow output before the eruption ceased.

Activity during May-June 2019. OVPF reported slight inflation near the summit beginning in early May, and an increase in CO2 concentration in the soil near Plaine des Cafres and Plaine des Palmistes. Strong shallow seismicity reappeared on 27 May 2019 and recurred on 30 and 31 May. Two small seismic swarms were measured on 31 May in the early morning. A new seismic swarm beginning at 0603 on 11 June accompanied by rapid deformation suggested a new eruption was imminent. A tremor near the summit area was first noted at 0635 local time; the webcams indicated a plume of gas, but poor visibility prevented evidence of fresh lava. Around 0930 that morning OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at elevations ranging from 2480 to 2025 m (figure 179). The flow fronts were not visible due to weather. Lava fountains under 30 m in height and lava flows were present in the three lowest fissures. The flows traveled rapidly down the steep flank of the crater (figure 180).

Figure (see Caption) Figure 179. Around 0930 on the morning of 11 June 2019 OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at Piton de la Fournaise at elevations ranging from 2480 to 2025 m. Courtesy of and copyright by OVPF-IPGP and Imazpress (Bulletin d'activité du mardi 11 juin 2019 à 11h00).
Figure (see Caption) Figure 180. Thermal imaging of the 11-12 June 2019 eruptive site at Piton de la Fournaise showed multiple streams of lava traveling rapidly down the steep flank from several fissures on 11 June 2019. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 11h00).

The intensity of the eruptive tremor decreased throughout the day, and by 1530 only the lowest elevation fissure was still active (figure 181). The next afternoon (12 June) images in the OVPF webcam located in Piton des Cascades indicated the flow front was at about 1,200-1,300 m elevation. Seismographs indicated that the eruption stopped around 1200 on 13 June. Poor weather obscured visibility of the flow activity. Seismic activity decreased following the eruption, but appeared to increase again beginning on 21 June, with 10 events detected on 30 June. SO2 plumes were recorded in satellite data on 11 and 12 June 2019.

Figure (see Caption) Figure 181. The intensity of the eruptive activity at Piton de la Fournaise on 11 June 2019 decreased throughout the day, and by 1530 only the lowest elevation fissure was still active. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 17h45 Heure locale).

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

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).


Heard (Australia) — April 2019 Citation iconCite this Report

Heard

Australia

53.106°S, 73.513°E; summit elev. 2745 m

All times are local (unless otherwise noted)


Thermal hotspots continue during October 2018-March 2019 at the summit and on the upper flanks

Heard Island, in the Southern Indian Ocean, includes the large Big Ben stratovolcano and the smaller, apparently inactive, Mt. Dixon. Because of the island's remoteness, satellites are the primary monitoring tool. Big Ben has been active intermittently since 1910, and was active during October 2017-September 2018 (BGVN 43:10). Activity continued during October 2018-March 2019.

Satellite photos using Sentinel Hub showed hotspots every month between October 2018 and March 2019. Because the area was frequently covered by a heavy cloud layer, most of the hotspot signals were partially obscured. Though thermal anomalies are usually seen at summit vents, on 18 October 2018 an anomaly was present about 300 m down the E flank. Similarly, on 1 January 2019, a weak anomaly beginning about 200 m down the NW flank was about 300 m long (figure 40).

The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected three hotspots, two in October and one in early November 2018, all of low radiative power. There were no MODVOLC alert pixels during this period.

Figure (see Caption) Figure 40. Sentinel-2 L1C image of Heard Island's Big Ben volcano on 1 January 2019 one summit hotspot and an elongated thermal anomaly to the NW. Scale bar (bottom right) is 200 m. The photo was taken in atmospheric penetration view (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

Geologic Background. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon volcano lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben volcano because of its extensive ice cover. The historically active Mawson Peak forms the island's 2745-m high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported in historical time at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Information Contacts: Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).


Semeru (Indonesia) — April 2019 Citation iconCite this Report

Semeru

Indonesia

8.108°S, 112.922°E; summit elev. 3657 m

All times are local (unless otherwise noted)


Decreased activity after October 2018

The ongoing eruption at Semeru has been characterized by numerous ash explosions and thermal anomalies, but activity apparently diminished in 2018 (BGVN 43:01 and 43:09); this decreased activity continued through at least February 2019. The current report summarizes activity from 24 August 2018 to 28 February 2019.

The Indonesian volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), reported ongoing daily seismicity, dominated by explosion earthquakes and emission-related events from late November through February (figure 35). Ash plumes resulting in aviation advisories by the Darwin Volcanic Ash Advisory Centre (VAAC) were reported on 4, 6-7, and 19 September, and 12 October 2018. The next significant ash plume reported by the VAAC wasn't until 24 February 2019 (table 23).

Figure (see Caption) Figure 35. Seismicity recorded at Semeru during 28 November 2018-26 February 2019. Plot shows explosion earthquakes ('Letusan'), emission-related events ('Hembusan'), felt earthquakes ('Gempa Terasa'), local tectonic events ('Tektonic Lokal'), and distant tectonic events ('Tektonic Jauh'). Courtesy of PVMBG and MAGMA Indonesia.

Table 23. Summary of ash plumes at Semeru during 25 August 2018 through February 2019. The summit is at 3,657 m elevation. Data courtesy of Darwin VAAC.

Date Plume altitude (km) Plume drift Remarks
04 Sep 2018 4.3 W --
06-07 Sep 2018 4.3 SW --
19 Sep 2018 4 SSW Possible ash-and-steam plume.
12 Oct 2018 4.5 W Discrete eruption.
24 Feb 2019 4.3 W Discrete volcanic ash eruption.

Thermal anomalies using MODIS satellite instruments processed by the MODVOLC algorithm were only recorded on 26, 28, and 30 August 2018, and 22 and 31 October 2018. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected numerous hotspots within 5 km of the volcano during August and early September, with a significant decrease in frequency through October (figure 36); only a few scattered hotspots were recorded from November 2018 through February 2019.

Figure (see Caption) Figure 36. MIROVA plot of thermal anomalies (Log Radiative Power) at Semeru during July 2018-February 2019. Courtesy of MIROVA.

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

Information Contacts: 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/).


Dukono (Indonesia) — April 2019 Citation iconCite this Report

Dukono

Indonesia

1.693°N, 127.894°E; summit elev. 1229 m

All times are local (unless otherwise noted)


Numerous ash explosions from October 2018 through March 2019

The eruption at Dukono that began in 1933 has showered the area with ash from frequent explosions (BGVN 43:04, 43:12). The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM), is responsible for monitoring this volcano.

This long-term pattern of intermittent ash explosions continued during October 2018-March 2019, with ash plumes rising to between 1.5 and 2.7 km altitude, or about 300-1,500 m above the summit (table 19). Although meteorological clouds often obscured views, satellite imagery captured typical ash plumes on 28 September 2018 (figure 10) and 5 February 2019 (figure 11). Instruments aboard NASA satellites (TROPOMI and OMPS) detected high levels of sulfur dioxide near or directly above the volcano on multiple days during January-March 2019. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to remain outside of the 2-km exclusion zone.

Table 19. Monthly summary of reported ash plumes from Dukono for October 2018-March 2019. The direction of drift for the ash plume through each month was highly variable. Data courtesy of the Darwin VAAC and PVMBG.

Month Plume Altitude (km) Notable Plume Drift
Oct 2018 1.5-2.1 --
Nov 2018 1.5-2.1 --
Dec 2018 1.5-2.4 --
Jan 2019 1.8-2.1 --
Feb 2019 1.8-2.7 --
Mar 2019 1.5-2.4 --
Figure (see Caption) Figure 10. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 28 September 2018 with the plume blowing towards the NE. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 11. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 5 February 2019, with the plume blowing SW. Courtesy of Sentinel Hub Playground.

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

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/); 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).


Rincon de la Vieja (Costa Rica) — April 2019 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)


Occasional weak phreatic explosions continue through February 2019

Intermittent small phreatic explosions from the acid lake of Rincón de la Vieja's active crater has most recently occurred since 2011 (BGVN 42:08, 43:03, and 43:09). This activity continued through at least February 2019. The volcano is monitored by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), and the information below comes from its weekly bulletins between 18 August 2018 and 28 February 2019. Weather conditions often prevented webcam views and estimates of plume heights. The volcano was in Activity Level 3 throughout the reporting period (volcano erupting, steady state).

According to OVSICORI-UNA, two distinct, 2-minute-long explosions occurred on 31 August 2018 beginning at 0434 and 1305. Several hours after the eruption tremor became continuous but low-frequency long-period (LP) earthquakes ceased. OVSICORI-UNA reported a gas emission late on 7 September. An unconfirmed small phreatic explosion occurred on 11 September at 0634, and another on 17 September at 1014. The seismic record showed continuous background tremor and very sporadic LP earthquakes.

Intermittent background tremor was recorded during the first half of October, along with a few emissions and phreatic explosions. Deformation measurements during October showed a contraction between the N and S of the volcano, with subsidence. On 17 October there was another phreatic explosion, and thereafter tremor disappeared and seismicity decreased. On 23 and 27 October seismic stations signaled additional possible phreatic explosions.

OVSICORI-UNA reported that a series of explosions began at 1945 on 4 November and consisted of at least three 2-minute-long episodes. The next day at 1511 a plume of water vapor and diffuse gas, recorded by a webcam and visible to residents to the N, rose about 100 m above the crater rim and drifted W. On 9 November a 2-minute-long explosion began at 1703. Another explosion on 27 November at 0237 produced a plume of water vapor and gas that rose 600 m above the crater rim and drifted SW. A short 1-minute explosion began at 1054 on 3 December.

Based on OVSICORI-UNA weekly bulletins, activity remained stable in January 2019 with small-amplitude phreatic explosions on 11, 12, and 14 January. More energetic phreatomagmatic explosions on 17 and 20 January produced lahars. Several small-amplitude explosions were detected at the end of the month. During January, a few LPs, no VTs, and intermittent tremor were recorded.

OVSICORI-UNA reported that two small-scale explosions occurred on 1 February, along with possible events at 1906 and 1950 on 5 February and at 0120 on 6 February. An event at 0000 on 6 February was also recorded; the report noted that poor weather conditions prevented visual observations of the crater. On 16 and 17 February strong degassing was observed. No LPs were recorded, but two significant VTs were detected on 17 and 22 February near or under the crater.

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: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).


Turrialba (Costa Rica) — April 2019 Citation iconCite this Report

Turrialba

Costa Rica

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

All times are local (unless otherwise noted)


Frequent passive ash emissions continue through February 2019

This report summarizes activity at Turrialba during September 2018-February 2019. During this period there was similar activity as described earlier in 2018 (BGVN 43:09), with occasional ash explosions and numerous, sometimes continuous, periods of gas-and-ash emissions (table 8). Data were provided by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA).

Table 8. Ash emissions at Turrialba, September 2018-February 2019. Cloudy weather sometimes obscured observations. Maximum plume height is above the crater rim. Information courtesy of OVSICORI-UNA.

Date Time Max plume height Plume drift Remarks
27 Aug-05 Sep 2018 -- 100 m SW, W Continuous gas-and-ash emissions.
06 Sep 2018 -- -- -- Mostly gas, punctuated by small sporadic ash plumes.
10 Sep 2018 1210 300 m NW --
01-13 Sep 2018 -- -- -- Continuous gas-and-ash emissions.
17-18 Sep 2018 -- 300 m SW, NW --
27 Sep 2018 0915 200 m NW --
30 Sep-01 Oct 2018 -- 500 m NW, NE --
03 Oct 2018 -- -- -- Incandescence.
08 Oct 2018 0800 500 m N --
10-16 Oct 2018 -- 1,000 m Various Intermittent emissions; some explosions, including an energetic one on 14 Oct at 1712. Clouds prevented estimate of plume height.
17-23 Oct 2018 -- 200-500 m E, NW, SW Periodic gas-and-ash emissions. Frequent Strombolian events since 5 Oct.
25-30 Oct 2018 -- -- -- Periodic ash emissions when weather conditions allowed observations.
26 Oct 2018 0134 500 m NE Ashfall in neighborhoods of Coronado (San José, 35 km WSW) and San Isidro de Heredia (Heredia, 38 km W).
29 Oct 2018 0231 500 m NW --
30 Oct 2018 1406 500 m W --
24 Oct-01 Nov 2018 -- 500 m -- Continuous emissions.
01-06 Nov 2018 0530-0640 500 m SW --
02 Nov 2018 1523, 1703 500 m -- --
03 Nov 2018 0109 500 m -- Short (2-3 minutes) duration events. Ashfall reported in Coronado.
05 Nov 2018 0620 600 m NW --
06-11 Nov 2018 -- 500 m -- Low-level, continuous gas-and-ash emissions occasionally punctuated by energetic explosions that sent plumes as high as 500 m and caused ashfall in several areas downwind, including Cascajal de Coronado, Desamparados (35 km WSW), San Antonio, Guadalupe (32 km WSW), Sabanilla, San Pedro Montes de Oca, Moravia (31 km WSW), Heredia, and Coronado (San José, 35 km WSW). Weather prevented observations on 12 Nov.
13-19 Nov 2018 -- -- -- Periodic, passive ash emissions visible in webcam images or during cloudy conditions inferred from the seismic data.
22 Nov 2018 0710 100 m W --
23 Nov 2018 -- -- -- Frequent pulses of ash.
23-25 Nov 2018 -- 500 m -- Occasional Strombolian explosions ejected lava bombs deposited near the crater; residents of Cascajal de Coronado reported hearing several booming sounds.
26-27 Nov 2018 -- -- -- Passive emissions with small quantities of ash visible. Minor ashfall in San Jose (Cascajal de Coronado and Dulce Nombre), San Pedro Montes de Oca, and neighborhoods of Heredia.
28 Nov-03 Dec 2018 -- 500 m N, NW, SW Ashfall in Santo Domingo (36 km WSW) on 2 Dec.
05 Dec 2018 -- -- -- Minor emission.
06 Dec 2018 -- -- S Emission.
08 Dec 2018 0749 500 m NW --
09 Dec 2018 -- 1,000 m -- Ashfall in areas of Valle Central.
10 Dec 2018 -- -- -- Emissions periodically observed during periods of clear viewing. Ashfall in Moravia (31 km WSW) and Santa Ana, and residents of Heredia noted a sulfur odor.
11-12 Dec 2018 -- 500 m NW, SW The Tico Times stated some flights were delayed at San Jose airport, 67 km away.
13 Dec 2018 -- -- -- Pulsing ash emissions; ashfall in Guadalupe (32 km WSW) and Valle Central.
14-16 Dec 2018 -- -- W, SW Emissions with diffuse amounts of ash.
05-06 Jan 2019 0815 -- -- Increased after midnight on 6 Jan.
28 Jan-04 Feb 2019 -- -- -- Minor, sporadic ash emissions rose to low heights during most days.
01 Feb 2019 0640 1,500 m NW --
08 Feb 2019 0540 200 m -- Sporadic ash emissions for more than one hour.
11 Feb 2019 -- -- -- Very small ash emission.
13-15 Feb 2019 200-300 m NW, W, SW Almost continuous gas emissions with minor ash content.
15 Feb 2019 1330 1,000 m W --
18 Feb 2019 1310 500 m W --
21 Feb 2019 -- 300 m NW Frequent ash pulses.
22-24 Feb 2019 -- 300 m NW, SW Frequent ash emissions of variable intensity and duration. On 22 Feb ash fell in Santa Cruz (31 km WSW) and Santa Ana, and a sulfur odor was evident in Moravia.
28 Feb 2019 1050 500 m SW Ash pulses.

According to OVSICORI-UNA's annual summary for 2018, a slow decline in activity occurred after the volcano reached its highest emission rate during 2016. Activity during 2018 was consistent with an open system, generating frequent passive ash emissions. The volcano emitted ash on 58% of the days during the year. Some explosions were large enough to eject ballistics more than 400 m around the crater. Typical activity can be seen in a photo from 11 September 2018 (figure 50) and satellite imagery on 7 November 2018 (figure 51).

Figure (see Caption) Figure 50. Photo of an ash explosion at Turrialba taken on 11 September 2018. Courtesy of Red Sismologica Nacional (RSN: UCR-ICE), Universidad de Costa Rica.
Figure (see Caption) Figure 51. Sentinel-2 satellite image of an ash emission from Turrialba on 7 November 2018, taken in natural color (gamma adjusted). Courtesy of Sentinel Hub Playground.

During January into early February 2019, passive ash emissions continued irregularly and with less intensity and duration. Emissions sometimes lacked ash. In their report of 4 February 2019, OVSICORI-UNA indicated that passive ash emissions were weak and slow. For the rest of February, they characterized ash emissions as frequent, but of low intensity.

Seismic activity. On 1 November 2018 OVSICORI-UNA reported that seismicity remained high, and involved low-amplitude banded volcanic tremor along with long-period (LP) and volcano-tectonic (VT) earthquakes. In late January-early February 2019, OVSICORI-UNA reported that seismicity remained relatively stable, although a small increase was associated with the hydrothermal system. VT earthquakes were absent, and tremors had decreased in both energy and duration. The number of low-frequency LP volcanic earthquakes remained stable, although they had decreasing amplitudes. No explosions were documented, and emissions were weak and had short durations and very dilute ash content.

Thermal anomalies. No thermal anomalies were recorded during the reporting period using MODIS satellite instruments processed by MODVOLC algorithm. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected five scattered hotspots during September-October 2018, none during November-December 2018, and two during January-February 2019. All were within 2 km of the volcano and of low radiative power.

Gas measurements. Significant sulfur dioxide levels near the volcano were recorded by NASA's satellite-borne ozone instruments only on 29 September 2018 (both NPP/OMPS and Aura/OMI instruments) and on 11 February 2019 (Sentinel 5P/TROPOMI instrument). OVSICORI-UNA's gas measuring instruments were compromised in September 2018 through January 2019 due to vandalism. In early February, however, they detected hydrogen sulfide for the first time since 2016.

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

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Red Sismologica Nacional (RSN) a collaboration between a) the Sección de Sismología, Vulcanología y Exploración Geofísica de la Escuela Centroamericana de Geología de la Universidad de Costa Rica (UCR), and b) the Área de Amenazas y Auscultación Sismológica y Volcánica del Instituto Costarricense de Electricidad (ICE), Costa Rica (URL: https://rsn.ucr.ac.cr/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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://hotspot.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/); Costa Rica Star (URL: https://news.co.cr); The Tico Times (URL: https://ticotimes.net).


San Cristobal (Nicaragua) — April 2019 Citation iconCite this Report

San Cristobal

Nicaragua

12.702°N, 87.004°W; summit elev. 1745 m

All times are local (unless otherwise noted)


Weak ash explosions in January and March 2019

San Cristóbal has produced occasional weak explosions since 1999, with intermittent gas-and-ash emissions. The only reported explosion during the first half of 2018 was on 22 April, the first since November 2017 (BGVN 43:03). The current report covers activity between 1 August 2018 and 1 May 2019. The volcano is monitored by the Instituto Nicaragüense de Estudios Territoriales (INETER).

According to INETER, a series of explosions occurred on 9 January 2019 that lasted several hours. INETER stated that one explosion occurred at 1643; the Washington VAAC's first advisory stated that an explosion occurred at 1145 (local time). The weak explosions, which occurred after a period of heightened seismic activity, generated an ash plume that reached 200 m above the edge of the crater and drifted W. The Washington VAAC reported volcanic ash plumes on 10-11 January extending about 92 km SW, and on 24-25 January extending about 185 km WSW. A low-energy explosion was detected by the seismic network at 1550 on 4 March 2019. The event produced a gas-and-ash plume that rose 400 m above the crater rim and drifted SW.

Monitoring data reported by INETER (table 6) showed elevated levels of seismicity during October 2018 through January 2019. Sulfur dioxide was also measured at higher levels in January 2019.

Table 6. Monthly sulfur dioxide measurements and seismicity reported at San Cristóbal during August 2018-March 2019. "Most" indicates that type of seismicity was dominant that month. Data courtesy of INETER.

Month Average SO2 Total earthquakes Degassing-type earthquakes Volcano-tectonic (VT) earthquakes
Aug 2018 461 t/d 6,464 6,147 251
Sep 2018 893 t/d 9,659 9,586 73
Oct 2018 269 t/d 11,698 3,509 8,189
Nov 2018 -- 19,593 19,586 7
Dec 2018 -- 30,901 -- Most
Jan 2019 1,286 t/d 11,504 Most Very few
Feb 2019 695 t/d 3,470 Most Very few
Mar 2019 -- 3,882 Most Very few

Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://webserver2.ineter.gob.ni/vol/dep-vol.html); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).


Semisopochnoi (United States) — February 2019 Citation iconCite this Report

Semisopochnoi

United States

51.93°N, 179.58°E; summit elev. 1221 m

All times are local (unless otherwise noted)


Minor ash explosions during September and October 2018

The remote Semisopochnoi comprises the uninhabited volcanic island of the same name, ~20 km in diameter, in the Rat Islands group of the western Aleutians (figure 1). Plumes had been reported several times in the 18th and 19th centuries, and most recently observed in April 1987 from Sugarloaf Peak (SEAN 12:04). The volcano is dominated by an 8-km diameter caldera that contains a small lake (Fenner Lake) and a number of post-caldera cones and craters. Monitoring is done by the Alaska Volcano Observatory (AVO) using an on-island seismic network along with satellite observations and lightning sensors. An infrasound array on Adak Island, about 200 km E, may detect explosive emissions with a 13 minute delay if atmospheric conditions permit.

On 16 September 2018 increased seismicity was detected at 0831, prompting AVO to raise the Aviation Color Code (ACC) to Yellow and Volcano Alert Level (VAL) to Advisory. Retrospective analysis of satellite data acquired on 10 September revealed small ash deposits on the N flank of Mount Cerberus, possibly associated with two bursts of tremor recorded on 8 September (figure 5). This new information, coupled with intensifying seismicity and a strong tremor signal recorded at 1249 on 17 September, resulted in AVO raising the ACC to Orange and the VAL to Watch. Seismicity remained elevated on 18 September with nearly constant tremor recorded by local sensors. At the same time, no ash emissions were observed in cloudy satellite images and no eruptive activity was recorded on regional pressure sensors at Adak.

Figure (see Caption) Figure 1. Minor ash deposits can be seen on the south and west flanks of the N cone of Mount Cerberus, Semisopochnoi Island, in this ESA Sentinel-2 image from 1200 on 10 September 2018. Also note probable minor steam emissions obscuring the crater of the N cone. Image courtesy of AVO.

During 19-25 September 2018 seismicity remained elevated, alternating between periods of continuous and intermittent bursts of tremor. Tremor bursts at 1319 on 21 September and at 1034 on 22 September produced airwaves detected on a regional infrasound array on Adak Island; no ash emissions were identified above the low cloud deck in satellite data, and the infrasound detections likely reflected an atmospheric change instead of volcanic activity.

Seismicity remained elevated during 3-9 October 2018, with intermittent bursts of tremor. No volcanic activity was detected in infrasound or satellite data. On 11 October satellite data indicated partial erosion of a tephra cone in the crater of Cerberus's N cone. A crater lake about 90 m in diameter filled the vent. The data also suggested that the vent had not erupted since 1 October. Seismicity remained elevated and above background levels. The next day AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory, noting the recent satellite data results and lack of tremor recorded during the previous week. AVO reported that unrest continued during 11-24 October.

An eruptive event began at 2047 on 25 October 2018, identified based on seismic data; strong volcanic tremor lasted about 20 minutes and was followed by 40 minutes of weak tremor pulses. A weak infrasound signal was detected by instruments on Adak Island. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale) and Volcano Alert Level was raised to Watch (the second highest level on a four-level scale). A dense meteorological cloud deck prevented observations below 3 km, but a diffuse cloud was observed in satellite data rising briefly above the cloud deck, though it was unclear if it was related to eruptive activity. Tremor ended after the event, and seismicity returned to low levels.

Small explosions were detected by the seismic network at 2110 and 2246 on 26 October 2018, and 0057 and 0603 on 27 October. No ash clouds were identified in satellite data, but the volcano was obscured by high meteorological clouds. Additional small explosions were detected in seismic and infrasound data during 28-29 October; no ash clouds were observed in partly-cloudy-to-cloudy satellite images.

AVO reported on 31 October 2018 that unrest continued. Two small explosions were detected, one just before 0400 and the other around 1000. Satellite views were obscured by clouds at the time, and no ash clouds were observed. Unrest continued through 1 November, at which time the satellite link and the seismic line failed. On 21 November the ACC was lowered to Yellow and the VAL was lowered to Advisory.

Geologic Background. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is 1221-m-high Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked 774-m-high Mount Cerberus volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. Other post-caldera volcanoes include the symmetrical 855-m-high Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).


Asosan (Japan) — July 2019 Citation iconCite this Report

Asosan

Japan

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

All times are local (unless otherwise noted)


Multiple brief ash emission events during April and May 2019; minor ashfall in adjacent villages

Japan's 24-km-wide Asosan caldera on the island of Kyushu has been active throughout the Holocene. Nakadake has been the most active of 17 central cones within the caldera for 2,000 years. Historical eruptions have been primarily basaltic to basaltic-andesitic ash eruptions, with periodic Strombolian activity, all from Nakadake Crater 1. The most recent major eruptive episode began in late November 2014 and continued through 1 May 2016. Another eruption, with the largest ash plume in 20 years, occurred on 8 October 2016. Asosan remained quiet until renewed activity from Crater 1 began in mid-April 2019; it is covered in this report, through the end of June 2019. The Japan Meteorological Agency (JMA) provides monthly reports of activity; the Tokyo Volcanic Ash Advisory Center (VAAC) issues aviation alerts reporting on possible ash plumes.

Asosan remained quiet during 2017 and 2018 with steam plumes rising a few hundred meters from Crater 1 and low levels of SO2 emissions; a warm acidic lake was present within the crater. Fumarolic activity from two areas on the S and SW wall of the crater rim generated occasional thermal anomalies in satellite data and incandescence at night. A brief period of increased seismicity was reported in mid-March 2019. An increase in seismic amplitude on 14 April 2019 preceded a small explosion on 16 April; it produced an ash plume which rose 200 m above the crater rim and drifted NW. It was followed by additional small explosions on 19 April. A new explosion on 3 May produced minor ashfall in adjacent communities; ash emissions were reported multiple times during May with plumes reaching 1,400 m above the crater rim. No additional ash emissions were reported in June.

Activity during 2017 and 2018. JMA reported that no eruptions occurred during 2017. Amplitudes of volcanic tremor increased somewhat during March but were generally low for the rest of the year. The earthquake hypocenters were mostly located near the active crater at around sea level. SO2 emissions were slightly less than 1,000 tons per day (t/d) from January through April; for the rest of the year they ranged from 600 to 2,500 t/d. The Alert Level had been lowered from 2 to 1 on 7 February 2017 where it remained throughout the year. Steam plumes generally rose no more than 600 m above the active crater rim (figure 42). JMA noted that from January to June they often observed crater incandescence at night with a high-sensitivity surveillance camera; Sentinel-2 satellite images also captured thermal anomalies a few times (figure 43). The green lake inside the crater persisted throughout the year with water temperatures of 50-60°C. Two fumaroles were present with high-temperature gas emissions on the SW and S crater walls. Temperatures at the S crater wall were over 600°C from February to May; they decreased to 320-560°C during the rest of the year (figure 44). Sulfur deposits were visible around the SW crater wall fumarole during July.

Figure (see Caption) Figure 42. Steam plumes that rose around 600 m above Nakadake Crater 1 at Asosan were typical activity throughout 2017. Images taken with JMA webcam on 9 June (top left), 22 August (top right), 12 November (bottom left), and 20 December (bottom right) 2017. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 43. Sentinel-2 images captured thermal anomalies at the S rim of the green lake at Asosan's Nakadake Crater 1 on 16 February (left) and 27 May 2017 (right). JMA reported that incandescence was occasionally visible during the night from January-June from the same area. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 44. High-temperature gas and steam from fumaroles on the S wall of the Nakadake Crater 1 at Asosan on 24 August (top) and 17 November 2017 (bottom) were persistent all year, with temperatures ranging from 300 to over 600°C. The green lake inside the crater persisted throughout the year as well with water temperatures of 50-60°C. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

The Alert Level did not change at Asosan during 2018, and no eruptions were reported. Sulfur dioxide emissions fluctuated between 400 and 1,800 t/d throughout the year. Steam plumes generally rose less than 500 m above the active crater (figure 45); incandescence was observed at night during May-October and sometimes observed in satellite imagery as thermal anomalies (figure 46). The temperature of the green lake inside the crater ranged from 58 to 75°C throughout the year. The thermal anomaly on the S wall of the crater was consistently in the 300-500°C range, and had a high temperature in April of 580°C; in December the high temperature had risen to 738°C (figure 47). A brief increase in the number of isolated tremors occurred during March, with 1,044 reported on 4 March, exceeding the previous maximum of 1,000 on 27 October 2014. Seismicity also increased briefly during June, with more than 400 events reported each day on 8, 18, and 20 June. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1, continued to produce modest steam plumes throughout 2017 and 2018 (figure 48).

Figure (see Caption) Figure 45. Typical steam plumes at Asosan during 2018 rose around 500 m above the Nakadake Crater 1. Images are from 4 March (top left), 22 July (top right), 17 August (lower left), and 13 September 2018 (lower right). Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 46. Nighttime incandescence was reported by JMA during May-October 2018 from the S rim of Nakadake Crater 1 at Asosan; Sentinel-2 satellite images (bands 12, 4, 2) captured thermal anomalies from the same area numerous times during 2018 including on 16 June (top left), 26 July and 19 September (middle row), and 18 and 23 November (bottom row). JMA photographed incandescence at night on 17 July 2018 at the S fumarole area (top right). Courtesy of Sentinel Hub Playground and JMA (Aso volcano Monthly Report for July 2018).
Figure (see Caption) Figure 47. The "Green Tea Pond" inside Nakadake Crater 1 at Asosan had temperatures that ranged from 58 to 75°C during 2018 (top row, 26 March 2018); the thermal anomaly on the S wall of the crater consistently had temperatures measured in the 300-500°C range and the SW fumarole area had somewhat lower temperatures (bottom row, 22 June 2018). Courtesy of JMA (monthly Asosan reports for March, May, and June 2018).
Figure (see Caption) Figure 48. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1 at Asosan, continued to produce modest steam plumes throughout 2017 and 2018. It is shown here on 20 December 2017 (top) and 12 March 2018 (bottom). Courtesy of JMA (December 2017 and March 2018 monthly volcano reports).

Activity during 2019. Steam plumes rose to 800 m above the crater rim during January 2019. Overall activity increased slightly during February; SO2 emissions peaked at 2,200 t/d early in the month; they ranged from 800 to 1,800 t/d for most of the month. The amplitude of volcanic tremor also increased slightly during February. A further increase in tremor amplitude on 11 March 2019 prompted JMA to raise the Alert Level from 1 to 2 the following morning. Volcanic tremor amplitude decreased on 15 March; JMA determined that activity had decreased, and the Alert Level was lowered back to 1 on 29 March 2019. The amount of water in the crater decreased significantly between 27 February and 20 March, exposing part of the crater floor.

The surface temperature of the lake rose during the first part of 2019; it was 78°C in February and 84°C in March. Steam plumes rose to 1,200 m above the crater rim during March and April. SO2 emissions rose to 4,500 t/d on 12 March but dropped to a lower range of 1,300-2,400 for the rest of the month. Another surge in SO2 emissions on 12 April 2019 to 3,600 t/d prompted a special report from JMA the following day. SO2 emissions varied from about 1,700 to 4,100 t/d during the month; values remained high during the second half of the month. JMA noted that the color of the water in the lake inside Nakadake Crater 1 changed from green to gray after 4 April. Fountains of muddy water were periodically observed; they reached 15 m high on 9 April. The temperatures of both the lake (82°C) and around the two fumarole areas (S area about 530°C, SW area about 310°C) remained constant during April and similar to March.

A large increase in the amplitude of volcanic tremor early on 14 April 2019 prompted JMA to raise the Alert Level from 1 to 2 later in the day. The epicenters of the earthquakes were very shallow, located within 1 km beneath the crater. A small eruption occurred at 1828 on 16 April at Nakadake Crater 1; it produced a gray and white plume that rose 200 m above the crater rim and was the first eruption since 8 October 2016 (figure 49). Incandescence was observed inside the crater on 3 and 17 April. The amplitude of seismic tremors decreased on 18 April. Three very small eruptions on 19 April produced ash and steam plumes that rose 500 m above the crater rim. During a site visit that day JMA measured a high-temperature area that produced incandescence from the bottom of the crater at night (figure 50).

Figure (see Caption) Figure 49. The first eruption since October 2016 at Nakadake Crater 1 at Asosan on 16 April 2019 sent an ash plume 200 m above the crater rim (top). Incandescent gas appeared on the crater floor the next day (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 50. Three small explosions on 19 April 2019 at Asosan's Nakadake Crater 1 produced small ash emissions that rose 500 m above the crater rim (top). A strong thermal signal also appeared from the bottom of the crater. Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

A new eruption began at 1540 on 3 May that lasted until 0620 on 5 May (figure 51). Initially the ash plume rose 600 m above the crater rim, but a few hours later the volume of ash increased, and the plume reached 2 km above the crater rim for a brief period. Incandescence was visible from the webcam. The Tokyo VAAC reported the ash plume at 3 km altitude drifting SE on 3 May. Later in the day it rose to 3.7 km altitude and drifted SW. During a field survey the following day (4 May) JMA reported a steam and ash plume rising from the center of the active crater. The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (figure 52).

Figure (see Caption) Figure 51. An explosion at Asosan's Nakadake Crater 1 on 3 May 2019 produced an ash plume that reached 2 km above the crater rim (top) and incandescence visible from the webcam (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 52. During a site visit on 4 May 2019, staff from JMA witnessed an ash and steam plume rising from the bottom of Nakadake Crater 1 at Asosan (top). The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (bottom). Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Ash fell on the S flank, and a small amount of ashfall on 4 May was confirmed by evidence on a car windshield in Takamori Town (6 km S), Kumamoto Prefecture (figure 53). Ashfall was also reported in Takamori-machi, Minami Aso village (9 km SW), and part of Yamato-cho (25 km SW), also in the Kumamoto Prefecture. SO2 emissions were measured as high as 4,000 t/d on 4 May. Additional explosions with ash plumes were reported from Asosan on 9, 12-16, 29, and 31 May; the plumes rose from 200 to 1,400 m above the crater rim but were not visible in satellite imagery. The TROPOMI instrument on the Sentinel-5 satellite captured SO2 plumes on 3 and 26 May 2019 (figure 54).

Figure (see Caption) Figure 53. Ashfall was reported on 4 May 2019 in Takamori Town, Kumamoto Prefecture, from the eruption at Asosan's Nakadake Crater 1 on 3 May 2019. Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 54. Plumes of SO2 from Asosan were recorded by the TROPOMI instrument on the Sentinel-5P satellite on 3 (left) and 26 (right) May 2019. Courtesy of NASA Goddard Space Flight Center.

Steam plumes rose to 1,700 m above the crater rim during June 2019 (figure 55). During field visits on 6 and 25 June diffuse ash emissions were observed rising from the center of the active crater, but they did not extend significantly above the crater rim (figure 56). The maximum temperature of the plume was measured at about 340°C with a thermal imaging camera. Almost all of the water in the crater bottom had evaporated since early May; incandescence continued to be observed within the crater at night with the high-resolution webcam (figure 57).

Figure (see Caption) Figure 55. Steam plumes rose to 1,700 m above the crater rim at Asosan's Nakadake Crater 1 on 10 June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 56. Plumes of gas and minor ash were visible at Asosan's Nakadake Crater 1 during site visits by JMA on 6 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).
Figure (see Caption) Figure 57. Incandescent gas was visible from the vent at Asosan's Nakadake Crater 1 on 18 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

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: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); 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/).

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Bulletin of the Global Volcanism Network - Volume 27, Number 10 (October 2002)

Managing Editor: Richard Wunderman

Bezymianny (Russia)

A one-pixel thermal anomaly on 16-17 November 2002

Etna (Italy)

A flank eruption started on 27 October; lava vented at N- and S-flank fissures

Izu-Torishima (Japan)

Mid-August 2002 plumes, larger crater, and discolored water

Lengai, Ol Doinyo (Tanzania)

Lava exits crater at 3 points during January 2001-September 2002

Nyamuragira (DR Congo)

Multi-vent eruption, 25 July-27 September 2002; regional earthquake

Nyiragongo (DR Congo)

New fissure vents and lava fountains; largest regional earthquake in 30 years

Panarea (Italy)

Increased submarine fumarolic activity near Panarea Island

Popocatepetl (Mexico)

Small explosions, earthquakes, and tremor during July-October 2002

Ruang (Indonesia)

Eruption on 25 September 2002 sends ash to at least 5 km

Veniaminof (United States)

Volcanic unrest, uncertain low-level eruptive activity in September 2002



Bezymianny (Russia) — October 2002 Citation iconCite this Report

Bezymianny

Russia

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

All times are local (unless otherwise noted)


A one-pixel thermal anomaly on 16-17 November 2002

The last reported activity at Bezymianny included a 4-km plume and thermal anomalies visible on satellite imagery during December 2001 and January 2002 (BGVN 26:12). No further reports were issued until mid-November 2002.

On 18 November KVERT raised the Concern Color Code at Bezymianny from Green to Yellow after a 1-pixel thermal anomaly was observed on various satellite images on 16 and 17 November. The closest telemetered seismic stations, situated on Kliuchevskoi, 13.5 km from Bezymianny's lava dome, only recorded several shallow seismic events at Bezymianny: 13 in August and September, and 3 in October. High seismic activity at Kliuchevskoi made it difficult to separate Bezymianny's seismic events from Kliuchevskoi's. According to AVHRR satellite images the thermal anomaly had a temperature of 18°C in a background of -30°C.

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: Olga Girina, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709.


Etna (Italy) — October 2002 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


A flank eruption started on 27 October; lava vented at N- and S-flank fissures

At 2225 on 26 October 2002 a swarm of earthquakes was recorded by the seismic network of the National Institute of Geophysics and Volcanology (INGV) in the Catania sector. Three hours after the swarm began, Etna started a new flank eruption. Until 1 November, ~500 shocks registered. The seismic swarm preceded and accompanied explosive activity in the summit area.

A survey at 0400 on 27 October found that two eruptive fissures had opened on Etna's N and S flanks; they were still propagating up- and down-slope when observed. Fire fountains escaped at both fissures.

At that time, lava flows started to pour from the lower part of the N-flank fissure, causing concern on Etna's N flank around Piano Provenzana. At the lower end of this fissure, two major flows spread NE and E. The NE flow stopped on 31 October after having traveled 2 km, behavior congruent with an observed decline in the effusion rate.

The E flow slowed down until 1 November, but it continued moving and crusting over in the middle portion of the flow field until 3 November. Scientists from INGV-CT conducted a helicopter-based aerial survey, using helicopters from the Civil Protection, and deploying a FLIR TM 695 thermal camera. Survey results showed a few sectors of solid crust and suggested the initial formation of a lava tube on this lava flow, which completely stopped on 5 November. The ski station and tourist shops on Piano Provenzana were first destroyed by the earthquakes, and then surrounded by lava flows. The flows also caused fire that engulfed parts of the pine forest. Flow mapping (shown on the INGV website) was limited by both the presence of fire around the flow fronts and ash clouds masking most of the flow field, and only the use of the FLIR TM 695 thermal camera allowed views of the active lava flows.

The N fissure opened between 2,500 and 2,350 m elevation, an area close to the fissure developed in the year 1809. The current N-flank fissure is a few kilometers long and expanded NE following the NE Rift Zone.

A lava flow from the S-flank fissure started ~12 hours after the N one. It spread SW and split in two branches around Monte Nero, following the same path as one of the 2001 lava branches. The S flows stopped on 31 October, having reached a total length of about 2 km. Fire fountains and phreatomagmatic activity decreased in intensity with time and disappeared at the N fissure, but were still continuing on the S fissure.

The S fissure, which opened at 2700 m elevation, traveled N20°W, and occurred a few hundred meters W of the 2001 S-fissure field, between Monte Frumento Supino and Cisternazza (a map appears at the INGV website, see below). Spatter falling around the S-fissure's vents formed two cinder cones at about 2,030 m elevation. Fire fountains from these vents were initially 100-300 m high, producing an ash plume and abundant ashfall on Etna's S flank. In 3 days the city of Catania received ~2.5 kg/m2 of ash due to strong winds from the N. This disrupted the local airport and caused problems with travel.

The high amount of gas released by the summit vents and at the 2,750-m cone (up to 25,000 tons/day), and the continuing explosive activity at the S vent, suggest a long duration for this eruptive event (figure 96).

Figure (see Caption) Figure 96. SO2 released from Etna during January 2001-1 December 2002. Courtesy INGV.

Editor's note: Summaries of Etna activity from recent issues of the Bulletin have been prepared by our staff without the benefit of crafted summaries in English. As such, the contributors found them deficient in clarity of translation. For greater clarity and more technical details consult journal publications and the INGV website.

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: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania, Piazza Roma 2, 95123 Catania (URL: http://www.ct.ingv.it/).


Izu-Torishima (Japan) — October 2002 Citation iconCite this Report

Izu-Torishima

Japan

30.484°N, 140.303°E; summit elev. 394 m

All times are local (unless otherwise noted)


Mid-August 2002 plumes, larger crater, and discolored water

Following ship-based reports of activity at Tori-shima on 11 August 2002, scientists from the Japanese Meterological Agency overflew the area the next day when they observed and photographed ash plumes being erupted from the crater (BGVN 27:07). According to the Japan Coast Guard (via JMA), the activity continued as of 1200 on 14 August; the plume reached ~1.2-1.5 km above sea level on 13 August (figure 3), and ~900 m on 14 August. Emissions were observed from three active areas along the western inner-wall of the summit crater. The crater appeared to have widened. By 21 August, the Japan Coast Guard reported that Izu-Tori-shima no longer "smoked" and only weak steaming was seen in the southern portion of the crater. Faintly discolored sea surface was observed around the island.

Figure (see Caption) Figure 3. Izu-Tori-Shima plume on 13 August 2002. Courtesy Air Force Weather Agency.

Geologic Background. The circular, 2.7-km-wide island of Izu-Torishima in the southern Izu Islands is capped by an unvegetated summit cone formed during an eruption in 1939. Fresh lava flows from this eruption form part of the northern coastline of the basaltic-to-dacitic edifice. The volcano is referred to as Izu-Torishima to distinguish it from the several other Japanese island volcanoes called Torishima ("Bird Island"). The main cone is truncated by a 1.5-km-wide caldera that contains two central cones, of which 394-m-high Ioyama is the highest. Historical eruptions have also occurred from flank vents near the north coast and offshore submarine vents. A 6-8 km wide submarine caldera lies immediately to the north.

Information Contacts: Tomonori Kannno and Hitoshi Yamasato, Japanese Meteorological Agency (JMA), Volcanological Division, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (URL: http://www.jma.go.jp/); Volcano Research Center (VRC), Earthquake Research Institute (ERI), University of Tokyo (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); U.S. Air Force Weather Agency, Offutt AFB, NE 68113-4039, USA.


Ol Doinyo Lengai (Tanzania) — October 2002 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 exits crater at 3 points during January 2001-September 2002

In 2001-2002 the crater at Ol Doinyo Lengai has become filled with lava. The thin lava flows (nearly devoid of silica and extremely low viscosity) have begun to regularly spill over three points on the crater rim, descending hundreds of meters downslope. The crater, whose high ground was once considered suitable for camping, is no longer free from sudden inundation by lava. Activity through December 2000 was reported in BGVN 25:12.

This report chronicles many visits to the volcano between January 2001 and September 2002. Fred Belton compiled reports of multiple field parties during July 2001 and May-September 2002. Other visitors are noted in the text. Jörg Keller and Aoife McGrath contributed some observations, photos, a reference, and lab data on whole-rock chemistry.

Observations during January 2001. Paul Hloben contributed the following report. "We visited Lengai 15-17 January 2001. The place was very wet, and most of the soda coating the crater floor and cones had washed away or was in solution within the crater floor and cones. The entire crater was sandy brown and muddy (except recent lava flows, which were brown or gray and rock-hard). Older cones were just soil-brown in color, like gigantic termite mounds. [In contrast, in dry conditions, older lavas generally look white in color.] At that time only two cones were active . . . one nearest the camp site located at the path leading down the volcano."

"The [T51] cone was too high for lava flows (to escape) or for viewing what was happening inside, but we heard continuous blows every 10-20 seconds. Further on (towards the crater's center) there resided twin partially collapsed cones [newly developed features between T49 and T48, figure 71]. They harbored two active ponds (the lava level was ~1.5 m below the collapsed crust at the adjacent point of access and overview). The ponds were interconnected, with lava and gas surges occurring approximately every 20-30 seconds independently in each pond. The smaller pond (on the N) was ~1-2 m in diameter. The larger pond was about 4-5 m in diameter, but not easy to see due to heat blows that forced us to retreat; we could observe it best during the night as it was glowing."

Figure (see Caption) Figure 71. A sketch map of the crater at Ol Doinyo Lengai reflecting conditions seen up to 9 August 2002. In the rapidly changing landscape of the crater, some of the features may have been short-lived; some labeled features may not have existed at the same times. The lava ponds seen by Hloben in January 2001 are not shown, although some of their locations may coincide with later features. The inset shows lava flows active during 4-9 August 2002 (areas with a vertical striped pattern in the crater's W and central sectors). Chris Weber provided the base map; Fred Belton compiled field observations by multiple workers and made revisions on this base map.

Comparison of field maps indicates that the larger of the two adjacent ponds stood in an area later identified as T55 (figure 71). Apparently fresh flows had recently cooled and stopped. They crossed the outflow on the NW crater rim and descended hundreds of meters down the flanks.

Observations during June 2001. Bob Carson and a group of 18 from Whitman College used the guide services of Burra Ami Gadiye to access the summit on 28 June. Carson's report follows. "We climbed on 28 June 2001 and spent from about 0800 to 1245 in the active southern crater. The crater floor was covered with about twenty steep-sided spatter cones and countless pahoehoe flows (some of the longer flows are aa-like near their toes). Radial cracks on the young surface of the crater floor penetrate the older rocks of the crater rim.

"Spatter cone T40B had been active on 27 June, sending ~10-cm-thick pahoehoe flows ~10 m from the vent; access to moisture was turning the edges of the still-warm black natrocarbonatite flows white. Later a slightly explosive eruption spewed tiny glassy spheres of tephra (1-2 mm in diameter) onto the surface of the 27 June pahoehoe flows. Spatter cone T40B sounded like a steam engine for the entire time we were near the volcano's summit. From about 1130 to 1200 on 28 June this cone erupted spatter, throwing blobs of tar-looking lava about 2 m into the air; the blobs landed on the side of the spatter cone making lava stalactites and short pahoehoe flows so that the cone looked like a giant sand castle."

Observations during July 2001. A visit by Fred Belton, Roberto Carniel, Marco Fulle, Andrew Locock, and four others during 23-30 July 2001 revealed that most of the previous year's morphologic changes occurred in the NW third of the crater. For example, T51 was 12 m tall, twice the previous year's height. T51B represented a new spatter cone just SE of T51, that contained a low rim overhanging a pit crater. Another new cone (T53) stood ~40 m NW of T40, but was inactive. Comprising a ~4 m tall rounded cone, T53 contained a hooded cave feeding a solidified open lava lake and lava channels that had flowed N. T40 had grown several meters toward the W. T40C, also new, was a white-to-gray 5-m-tall cone just SW of T40. T49B was white with a rounded summit, standing ~6 m tall. T49C was a broad cone of about the same height; it was first noted by C. Weber in October 2000. The new feature T49D was slightly lower than T49B and had vertical sides ringed with shallow grooves. T49E, probably the newest vent, formed an oval, 15 x 6 m low-rimmed crater just below the N flank of T49C.

On 23 July, T49E contained a frothy lava lake that drained N through a lava channel and frequently overflowed its E rim. By 0630 on 24 July the lava lake's surface had completely crusted over. During the day T49E inflated as lava entered and pushed up its solid surface. Early on 25 July the lake's solid surface had been lifted nearly 1 m above its position of the previous evening. It made continuous cracking and popping noises, and small rocks fell from its rim as it became increasingly engorged with lava. Cracks abruptly opened in its NW side and released copious flows of fluid lava. The filling/draining cycle was repeated twice more that day and several times on 26 July. The most interesting event occurred at 1710 on 25 July when a 3 m section of T49E's side collapsed, releasing a sudden flood of fluid lava that swept large blocks up to 9 m from their original positions (figure 72).

Figure (see Caption) Figure 72. On 25 July 2001 Lengai's ~ 2-m tall, spatter cone T49E underwent a flank collapse over a ~ 3-m-wide sector. This NE-looking photo captured the scene at a late stage of the failure. Lava can be seen escaping the cone through fractures in its disintegrating wall. The entire wall collapsed outward immediately after the photo was made. The volume of material involved in the collapse (both cooled rock wall and molten lava that swept away T49E's side) was on the order of 15-25 m3. Fred Belton, who took this picture, was standing on T49C. Standing on the crater floor just beyond T49E is Roby Carniel, who ran to safety as the failure took place. Courtesy of F. Belton.

During 27-28 July 2001 an eruption occurred that far exceeded the volume and duration of typical lava eruptions. Estimates of lava output were 5 m3/s during the greatest outflow and no less than 1 m3/s at anytime during the first 30 hours of the eruption. At 0630 on 27 July, pencil-wide streams of light gray, comparitively transparent lava flowed from T49E. T49E's lava output increased at 1113, and T49C erupted from its summit vent. At 1430 lava from those vents reached the NW crater rim overflow. Then, T49C ceased erupting, while T49D began to emit spatter from a small hole in its N side and T49B began to overflow from its summit vent. T49B developed a large dome fountain and T49D began ejecting a narrow fan of spatter at a 30° angle.

At 1510 the previously solid surface of T49E abruptly released fountains 1-2 m high, and T49C began erupting clots of spatter every 10 seconds. Thus, four vents were erupting simultaneously. Highly fluid lava flowed in meter-wide channels toward the NW, E, and S. Lava crossed the NW crater rim overflow and cascaded hundreds of meters down the NW flank of Lengai. Lava did not cross the E rim of Lengai because it flowed into a fissure in the crater floor ~25 m NW of the E rim overflow, at a rate of ~1 m3/s. About 1 hour later a vent opened on the E flank of Lengai ~12 m below the rim overflow area and released torrents of lava that flowed far down the flank and started brush fires. Destruction of a seismic station (established 4 m E of the fissure by Joshua Jones, Univ. of Washington) was narrowly averted thanks to the fissure's absorption of the lava flow and Carniel and Locock moving the equipment to a more secure location on the crater rim.

After sunset, spectacular orange fountains played steadily from T49B and T49D. Jets of incandescent gas appeared as flames 1-2 m high above the vent of T49C. By 0600 on 28 July the lava fountain from T49B was diminished but T49D continued to feed a large lava channel toward the E. Width of the channel exceeded 1 m, and depth of the fluid lava within it varied in the range 0.5-1 m. During all of 28 July lava flowed hundreds of meters down a gully on Lengai's E flank after emerging from the channel and the crater-floor fissure, both of which had been enlarged by thermal erosion. During the afternoon, the vigor of T49D's activity gradually diminished and its lava became increasingly frothy. Early on 29 July the eruption ceased and there was no further activity before observers left at 0715 on 30 July. J. Jones revisited the crater on 31 July and 6 August 2001 but saw no activity or fresh lava flows.

Observations during February-September 2002. During 3-7 February 2002, several members of the Societe de Volcanologie Geneve observed lava flows and strong fountains from the T49 complex and reported a new overflow of lava on the W crater rim (Bessard, 2002).

Aoife McGrath climbed the volcano on 26 May 2002 and reported continual small-scale eruptions at T49B. A new spatter cone had formed ~30 m SW of T49B and, according to mountain guide Burra Ami Gadiye, was about 4 months old.

During 18-22 June 2002, Christoph Weber, Jurgis Klaudius, and a film team observed the crater (figures 73 and 74). Fresh lava had flowed 120 m W from T49B and several recent 20-80 m flows originated from T46. Fresh lava was also seen on T37B, and fresh lapilli covered T48, a feature that was audibly active at depth. A new vent, designated T54, was visible between T46 and the W-rim overflow. It was an open solidified lava pond with a 40 m overflow to the W, which covered flows that had passed over the W rim in February 2002. Since August 2001, the diameter of the T49 complex had greatly increased, and there were more and hotter (>125°C) fumaroles in the crater. During this visit, spatter cones T49D, T51B, and T52C were no longer visible.

Figure (see Caption) Figure 73. N-looking view labeling key features in the central-western crater of Ol Doinyo Lengai, as photographed on an 18-22 June 2002 crater visit. Courtesy of Chris Weber and Jurgis Klaudius.
Figure (see Caption) Figure 74. View of Ol Doinyo Lengai's entire crater as seen from the summit region (looking N) during 18-22 June 2002. Courtesy of Chris Weber and Jurgis Klaudius.

During a five-hour period on 18 June lava spattered up to 3 m above the top of T49B (figure 75) and produced a 50-m lava flow to the NE. On 19 June spattering from T49B occurred several times until 1615, after which no further activity was seen through 22 June. On 22 June the team witnessed a ~10 m3 section of the crater wall in an area below the summit collapse into the crater. On each day there were 2-3 discrete tremors of about 1-cm amplitude, accompanied by gunshot sounds. They were distinctly different events from the continuous tremors caused by subsurface lava movement.

Figure (see Caption) Figure 75. A lone photographer with a tripod photographs Ol Doinyo Lengai's vent T49B as it emits spatter in June 2002. The zone of airborne spatter is not visible on the photograph. A fresh lava flows passes close to the photograher. Courtesy of Christoph Weber.

During the first half of July 2002 Jörg Keller was working near Lengai. He noted that until his departure on 14 July, a number of visitors returning from the summit reported either no activity or slight spattering from two cones.

During 4-9 August 2002, Fred Belton, Sven Dahlgren, Jeff Brown, and seven others observed four new spatter cones that had formed between 22 June and 4 August. One of these new cones was T55. Inactive when visited, T55 formed a white cone under 2 m tall containing a wide crater. T56, black and active, was ~7 m tall including a distinctive thin spire rising ~2 m above the summit. T57, ~4 m tall, was partly black but inactive. T57B stood ~7 m tall and was covered by fresh black lava. T54, documented by Weber on 21 June, had disappeared. Older cones such as T37B, T49B, and T49C had grown significantly since 2001 and towered above the N half of the crater rim.

Throughout the visit, T57B ejected clots of lava, expelled loud gas puffs, and produced thick clinkery aa flows. T56 spattered intermittently, T48 erupted pahoehoe lava from vents near its NW base, and T44 and T46 also produced spatter and a few short flows.

At around noon on 4 August a new vent, T49F, abruptly opened in rough, steaming ground near the W base of T49B. The eruption began with noisy ejection of spherical lapilli to a height of ~7 m and fluid lava to a height of 1 m. Throughout the day, the vent erupted at intervals of 1-2 hours, ejecting clouds of lapilli and forming aa lava flows that moved slowly W and NW to the crater rim area. Around 0200 on 5 August T49F eruptions dramatically increased in height and volume. Fountains played to at least 15 m and produced a flood of fluid pahoehoe that flowed W with great speed, destroying a supply camp. Similar eruptions continued for the next 28 hours, at first about two hours apart with gradually lengthening periods of repose between eruptions.

A typical T49F eruption consisted of lava first flowing or spattering from the low, open vent, then the abrupt onset of violent fountains that played for 2-4 minutes to a height of 10-15 m at a ~60° angle toward the W, and finally a decrease in fountain height and the draining of lava back into the vent. The final draining accompanied loud noises that to J. Brown sounded like "sheet metal being bent." By the afternoon of 5 August the site of the supply camp was under at least 1 m of thick pahoehoe slabs. The area just W of the vent was more than ankle deep in 2-8-mm-diameter spherical lapilli. Three vigorous fountaining episodes at T49F the night of 5 August started brush fires along the W crater rim. After dawn on 6 August, T49F's activity gradually waned, completely stopping by evening.

On 7 and 8 August T49F was completely inactive, thin pahoehoe lava flowed from T48, and T57B produced meter-thick clinkery aa flows. In the central crater there was an exceptionally strong smell of sulfur that at times made breathing uncomfortable, continuous low-pitched audible vibrations, and frequent hard bumps and tremors underfoot, especially near T57B and T56.

At about 2300 on 8 August a fissure ~12 m in length opened between T52B and T56 and began erupting a curtain of fire 6-8 m high with nearly continuous violent explosions. After midnight observers began to see an elongated spatter cone containing an extremely vigorous lava lake, whose surface rose ~0.3 m/hour. The new cone (T58) gradually merged with the flanks of T52B and T56. By 0830, T58 was over 2 m tall and its lava lake measured ~5 x 9 m. Lava bubbles over 2 m in diameter burst every 1-3 seconds and the activity showed no sign of abating when observers left at 0830 on 9 August. A photo from 17 August by Jean Bahr documented that T58 had grown to ~10 m in height and had a wide circular summit vent.

On 26 September 2002, Celia Nyamweru and twenty St. Lawrence University students visited the crater during 0630-0830. Lava spattered from T55 at 10-20 second intervals. Highly fluid pahoehoe lava emerged from the lower N slope of T49 and moved across other recent flows, probably from the previous night, which had passed between T40 and T40C and partially surrounded T53. Lava had accumulated against the N wall of the crater rim (then only 5 m high) and was heard flowing into a crack in the wall. The visitors could not see where the lava was going, but the next morning (27 September) as they were leaving the area by road a grass fire (started by lava?) was visible on the cone's upper NW slope. A local Maasai woman said that she had heard a loud noise from the volcano in the night. However, no activity was visible from the lowland N of Lengai.

Nyamweru's team observed one big crack, with steam, sulfur fumes, and black and yellow staining, running NW across the NW crater floor near T53. Other cracks on the NE floor were up to 30 or 40 cm wide and ran into cracks in the crater wall that were not steaming. The cones T26, T27, and T30 were still visible at the base of the S crater wall, surrounded by younger but deeply weathered lavas. The rim of T30 was less than 3 m above the lava surface, but its circular pit was still very well defined. In the NE segment of the crater floor a big blocky flow, brown and crumbly, bordered the NE wall for a considerable distance. It may have originated from T57 or T57B. Many cones from all parts of the crater were gently emitting steam, including T51, T45, T37, T30, and T47. The SE crater floor was very heavily weathered, with no sign of any fresh lava. There were a couple of patches of ground (each a shallow depression about 50 m2) that seemed to be the sites of former standing water. The depressions were floored with very fine pale brown clay/mud, which showed some fine layers and some areas with polygonal cracks. This seemed to be 'sediment' washed off the weathered lava by rain.

The most striking features of the topography were the extent to which the central crater floor has been built up. Except for the big wall to the S that rises to the summit, the topographic expression of the outer crater wall has diminished considerably (table 3). This impression was reinforced on 27 September when at a point about 10 km E of Lengai, they could look back and see the tops of several spatter cones showing above the eastern crater wall.

Table 3. Lava escaped Ol Doinyo Lengai's summit crater at three spots on the rim descending over the NW, E, and W sides. Visitors to the summit recorded these widths at each of the crater outlets. Courtesy of C. Nyamweru and F. Belton.

Date Location Overflow width (m)
30 Jul 2001 NW rim 106
30 Jul 2001 E rim 33
26 Sep 2002 NW rim 135
26 Sep 2002 E rim 39
26 Sep 2002 W rim 12

Jörg Keller provided photographs showing the evolution of the crater from 1988 through the present, emphasizing the progressive upward growth of the crater floor (figure 76). The sequence shows how the volcano has reached a critical stage where extremely fluid lavas can pour down the flanks.

Figure (see Caption) Figure 76. A suite of photographs showing Lengai's crater evolution, 1988-2002. The photographs were taken from the same position with respect to the summit (looking toward the N). Courtesy Jörg Keller and Jurgis Klaudius.

Whole-rock chemistry. Lengai's lavas have been analyzed by several techniques. High-precision XRF (x-ray fluorescence) analyses (table 4) were cross-checked and confirmed with ICP and ICP-MS (inductively coupled plasma and inductively coupled plasma mass spectrometer) instruments. The geochemistry of these lavas are of interest because of their unusual low-silica natrocarbonatite compositions.

Table 4. Natrocarbonatite compositions at Ol Doinyo Lengai for lavas erupted in 1988, 1995, and 2000. Analyses were by XRF. * From Keller and Krafft, 1990. Courtesy of Jürg Keller and Aoife McGrath.

Sample OL 102* OL 122 OL 148
Eruption Date 1988 1995 2000
SiO2 0.16 0.53 0.24
TiO2 0.02 0.02 0.02
Al2O3 b.d. 0.13 0.01
Fe2O3t 0.28 0.91 0.37
MnO 0.38 0.39 0.46
MgO 0.38 0.39 0.46
CaO 14.02 16.25 14.61
SrO 1.42 1.4 1.42
BaO 1.6 1.25 1.71
Na2O 32.22 32.22 32.64
K2O 8.38 7.52 8.41
P2O5 0.85 0.93 0.72
CO2 31.55 32.7 30.9
Cl 3.4 3.16 4.53
SO3 3.72 2.23 2.35
F 2.5 2.57 3.47
H2O 0.56 0.01 0.01
- O = F, Cl -1.82 -1.91 -2.48
Total 99.62 100.7 99.85

Safety warnings. Deep radial cracks in the crater floor present a serious risk to visitors walking in the crater of Ol Doinyo Lengai, especially at night. Some of the cracks may be hidden by thin lava flows. Protective eyeglasses should be worn near any type of activity. In 2001 an observer without glasses was hit in one eye by spatter and escaped serious injury because his eye was closed at the moment of impact. He sustained second-degree burns on both eyelids.

Camping inside the active N crater has become much more dangerous due to increased crater floor steepness that allows lava from the central spatter cones to reach the crater rim very quickly. Around 0200 on 5 August 2002, fluid pahoehoe lava from the T49F vent destroyed a supply camp and injured Paul Mongi, a Tanzanian guide. One of Belton's websites gives credit to guides like Mongi, who have aided numerous visitors. (Mongi has recovered from second-degree burns on one foot, sustained when lava ignited his sleeping bag.) Lava invaded the camp in spite of a small ridge separating the camp from the crater floor. No location in the active crater is safe from lava flows. Sudden outbreaks of explosive lava fountains are also a serious risk. On 8 August 2002 two observers walked across the site of the T58 fissure eruption little more than an hour before the activity began. Contributors recommended that camps be set up in the inactive S crater, a 15 minute walk away.

References. Keller, J., and Krafft, M., 1990, Effusive natrocarbonatite activity of Oldoinyo Lengai, June 1988, Bulletin of Volcanology, v. 52, no. 8, p. 629-645.

Bessard, Yves, 2002, Ol Doinyo Lengai: Société de Volcanologie-Geneve (SVG), no. 22 (April 2002), p. 2-10 (URL: http://www.volcans.ch/).

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: Fred Belton, Developmental Studies, Middle Tennessee State University, Murfreesboro, TN 37132, USA (URL: http://oldoinyolengai.pbworks.com/); Paul Hloben, P.O. Box 71860, Bryanston 2021, South Africa; Bob Carson, Department of Geology, Whitman College, Walla Walla, WA 99362, USA; Burra Ami Gadiye, c/o Sengo Safari Tours, P.O. Box 207, Arusha, Tanzania, Africa; Roberto Carniel, Dip. Georisorse e Territorio, Universita' di Udine Via Cotonificio, 114-33100 Udine, Italy (URL: http://www.swisseduc.ch/stromboli/); Sven Dahlgren, Fylkeshuset, Svend Foynsgt 9, 3126 Tonsberg, Norway; Marco Fulle, Osservatorio Astronomico, Via Tiepolo 11, I-34131 Trieste, Italy (URL: http://www.swisseduc.ch/stromboli/); Jörg Keller, Universitaet Freiburg, Albertstr. 23b, D-79104 Freiburg, Germany; Aoife McGrath, Senior Exploration Geologist, Geita Gold Mine, P.O. Box 532, Geita, Mwanza, Tanzania; Jurgis Klaudius, Institut für Mineralogie, Petrologie und Geochemie, Albertstr. 23 B, 79104 Freiburg, Germany; Andrew Locock, Dept. of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA; Celia Nyamweru, Dept. of Anthropology, St. Lawerence University, Canton, NY 13617, USA (URL: http://blogs.stlawu.edu/lengai/); Joshua Jones, Department of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; Jean M. Bahr, University of Wisconsin-Madison, Dept. of Geology & Geophysics, 411 Weeks Hall, 1215 W Dayton St. Madison, WI 53706, USA (URL: http://geoscience.wisc.edu/geoscience/people/faculty/jean-bahr/); Christoph Weber, Volcano Expeditions International, Muehlweg 11, 74199 Untergruppenbach, Germany (URL: http://www.Vulkanexpeditionen.de/).


Nyamuragira (DR Congo) — October 2002 Citation iconCite this Report

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)


Multi-vent eruption, 25 July-27 September 2002; regional earthquake

An eruption began at Nyamuragira on 25 July 2002 (BGVN 27:07). Flights on 1 and 3 August confirmed that the eruption was continuing at a high rate, but another look on 27 September showed that the eruption had ceased. An unusually large earthquake (Mw 6.1-6.2) and its aftershock (Mw 5.5) struck the region on 24 October 2002.

During 6-8 August a team composed of scientists from the Goma Volcano Observatory (GVO) (Kaseraka Mahinda and François Lukaya) and a UN-OCHA consultant volcanologist (Jacques Durieux) made a survey trip to the active eruption site of Nyamuragira. The team landed by helicopter in the summit caldera, reached the eruption site by foot, and spent 24 hours on the scene.

The team saw the eruption at 0330 on 25 July with lava venting at 3 different fractures, or fracture systems. One fracture was open in the central caldera, and lava flows had covered a major part of the floor and partially filled the pit crater (Crater B). Another fracture was active on the S flank, with lava fountains and one lava flow traveling towards the SW. This fracture was active during the first hours of the eruption only.

N-flank fractures had opened and extended for ~2 km, reaching from the crater rim (2,959 m) down to an elevation of ~2,540 m. At the beginning of the activity, lava fountains appeared along the fractures and spatter accumulated around them. Numerous lava flows (pahoehoe and aa) were emitted from several points of the fracture system. Both the fountaining and the presence of multiple fissure vents followed Nyamuragira's usual eruptive pattern.

On 6 August only the lower part of the fracture was active; a cone (several hundreds meters long, ~70 m high) contained three very active lava fountains ejecting scoria to an altitude of ~100 m. From a breach in the lowest part of the cone (on the S), very fast moving lava flowed NE. At that time the lava extrusion rate was ~3 x 106 m3 per day, a typical value at this volcano. The activity of fountaining and lava emission regained some intensity at the beginning of the night but dropped dramatically during the early morning of 7 August. At that time, only one weak lava fountain remained active in the new crater. Decreasing tremor registered across GVO's seismic network, and low tremor prevailed on the morning of 8 August.

An overflight on 27 September confirmed the end of this eruptive episode when observers failed to see any still-active lava flow and the eruptive cones displayed only fumaroles. At that time, however, weak tremor still consistently registered, with slightly less at Nyamuragira (Katale station) than at Nyiragongo (Rusayo station). Nyamuragira also was the scene of a greater number of high frequency (HF) and long-period (LP) earthquakes.

A large tectonic earthquake (Mw 6.1-6.2; mb 5.8; Ms 6.3), one of the two largest in at least 30 years, occurred on 24 October. A second large-magnitude event (Mw 5.5) occurred about an hour later. For further details on these events, see the text and tables in the section "Regional seismicity" within the report on Nyiragongo in this Bulletin.

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: Kasereka Mahinda and François Lukaya, Goma Volcano Observatory, Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Jacques Durieux, Resident Volcanologist, United Nations Office for the Coordination of Humanitarian Affairs (OCHA), United Nations, New York, NY 10017 USA (URL: https://reliefweb.int/).


Nyiragongo (DR Congo) — October 2002 Citation iconCite this Report

Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)


New fissure vents and lava fountains; largest regional earthquake in 30 years

An expedition visited the summit of Nyiragongo during 17-18 May 2002 to look for possible extrusive activity (BGVN 27:05). During the visit, a small lava fountain was observed on the floor of the crater.

A team ascended to the summit by foot during 16-17 July 2002. As they climbed the team first observed a gray-black plume at 2,700 m elevation, and began to clearly smell SO2 at 3,100 m. From the crater rim (3,425 m) the inner crater was only partially visible because of dense fog and the dark plume. Sounds of molten lava (fountains and spatters) falling on rocks were heard. Despite the extremely poor visibility, it was possible, around 0600, to witness some lava fountaining. The height was estimated as 100 m above the crater floor. During the night, a continuous and strong ashfall affected the upper part of the volcano. On the morning of 17 July the ashfall had ended and only a white plume exited the crater. It was clear that the lower and central part of the crater was extremely active and the presence of a new lava lake was suspected.

On 20 July, the Goma Volcano Observatory (GVO) reported that during the previous weeks, episodes of tremor (some lasting for 23 hours per day) were recorded on several seismic stations around the volcano. Because of poor atmospheric conditions, no helicopter flights were organized. From very limited views through clouds, a white to gray plume was suspected to rise above the crater.

A series of Nyiragongo crater observations were made in September and October of 2002. During 29-30 September the level of the bottom of the crater was stable and occupied by accumulated debris. The crater also contained several vents, the largest of which continued to eject gases at very high pressure. The red coloration of the plume at night was attributed by the GVO to Strombolian explosions and combustion of gases. Burned plants were seen on the crater's E side. An 8 October flight found the crater to be entirely filled by visible vapor as a result of magma degassing. An 11 October flight revealed a new crack at the top of Nyiragongo (at 01°36.840' S and 029°14.505' E), trending in an E-W direction. Scientists conducted gas measurements on 12 October on the ground at Kibunga (Binza); the sampled gases lacked indications of deep origin.

Dario Tedesco indicated that during the two nights preceding a large earthquake on 24 October (see "Regional seismicity" below), incandescence was visible above Nyiragongo's crater from Goma. Witnesses also reported that around this time they saw projections of incandescent lava rising above the crater's confines (perhaps signifying a particularly intense episode of lava fountaining).

Regional seismicity. During 29 September-5 October, GVO noted a slight decrease in high-frequency (HF) and a strong increase in long-period (LP) seismicity compared to mid-August. Specifically, a total of 260 HF and 1,024 LP earthquakes occurred during the week (compared to 290 HF and 287 LP events during 18-24 August). Volcanic tremor was registered at all seismic stations (except in Lwiro), consistent with the eruption at Nyamuragira and a gas plume at Nyiragongo. The tremor was slightly less significant at Nyamuragira (Katale station) than at Nyiragongo (Rusayo station). The spatial distribution of the epicenters revealed that the LP earthquakes were mostly located in the vicinity of Nyamuragira. In contrast, HF epicenters were dispersed, occurring both in the N, at Virunga and Masisi, and in the S, at Lake Kivu. Located magmatic and HF earthquakes tended to be distributed to the E of Nyamuragira and Nyiragongo, at depths of 5-15 km. Tremor, practically constant in amplitude, duration (several hours per day), and temporal distribution, registered at Katale and Rusayo stations. The tremor was taken to indicate great activity at Nyamuragira and Nyiragongo. At each volcano, there was a negative correlation between the abundance of tremor and presence of LP swarms.

During 6-12 October, GVO noted a total of 342 HF and 996 LP earthquakes. Magmatic and HF earthquakes at Nyamuragira and Nyiragongo yielded hypocenters at 5-20 km depths. Other observations of seismicity were similar to the previous week.

A tectonic earthquake was felt in Goma and surrounding areas on 8 October 2002. The region had been the scene of an unusual number of recent earthquakes (table 4). The U.S. Geological Survey's National Earthquake Information Center (NEIC) catalog for 2002 included an anomalously large swarm of tectonic earthquakes in the area, including many events over M 4 during January 2002. Epicenters in the January swarm were commonly within 50 km, and in one case 6 km, of Nyiragongo. The 8 October earthquake mentioned above is absent from table 4, perhaps because of insufficient magnitude or depth.

Table 4. A list containing all earthquakes of M 2 or greater within 200 km of Nyiragongo during 1 January 2002-26 November 2002. Data courtesy of US Geological Survey, National Earthquake Information Center (NEIC) catalog of historical and preliminary data; Bruce Presgrave (NEIC) first noted the anomalously large number of earthquakes in January 2002. Magnitudes include mb, Ms, Mw, and Mn; all are computed magnitudes (where available). Moment magnitude (Mw) is a preferred magnitude scale for large earthquakes; it is in common use, computed from a long-period body- and mantle-wave moment tensor-inversion method. Surface-wave magnitude (Ms) is computed from the vertical component of surface waves of 20-second period; Ms does not increase beyond magnitude 8, and thus indicates smaller values than some other magnitude scales for large earthquakes (not a big factor here). Body-wave magnitude (mb) is computed using short-period P waves; for large natural earthquakes it is generally less uniform and reliable than the moment magnitude. The Mn magnitude, sometimes labeled MbLg, is computed from the vertical component of 1-second Lg seismic-waves (short-period surface waves).

Date Coordinates (decimal degrees) mb Ms Other magnitude Radial distance (km)
04 Jan 2002 0.136°S, 29.758°E 4.8 4.5 -- 162
17 Jan 2002 1.629°S, 29.152°E 4.3 -- 4.30 Mn 16
17 Jan 2002 1.684°S, 29.077°E 4.7 -- 4.90 Mn 26
18 Jan 2002 1.578°S, 29.031°E 4.2 -- 4.70 Mn 25
18 Jan 2002 1.780°S, 29.076°E 4.3 -- 4.70 Mn 34
18 Jan 2002 1.662°S, 28.866°E 4.2 -- -- 45
19 Jan 2002 1.761°S, 28.969°E 3.9 -- 4.40 Mn 41
19 Jan 2002 1.931°S, 29.579°E 4.6 -- 4.70 Mn 58
19 Jan 2002 1.879°S, 29.059°E 4.2 -- 4.40 Mn 44
20 Jan 2002 1.681°S, 28.981°E 4.9 4.6 5.20 Mn 34
20 Jan 2002 1.641°S, 29.042°E 3.9 -- 4.40 Mn 26
20 Jan 2002 1.599°S, 29.050°E 4.2 -- 4.60 Mn 23
20 Jan 2002 1.726°S, 29.168°E 3.8 -- 4.20 Mn 24
21 Jan 2002 1.726°S, 28.854°E 4.6 -- 4.90 Mn 49
21 Jan 2002 1.505°S, 28.941°E 4.2 -- 4.50 Mn 34
21 Jan 2002 1.776°S, 29.041°E 4.9 4.5 5.10 Mn 36
21 Jan 2002 1.903°S, 29.117°E 4.7 -- 5.10 Mn 44
22 Jan 2002 1.787°S, 28.971°E 4.0 -- 4.30 Mn 42
22 Jan 2002 1.746°S, 29.095°E 3.9 -- 4.50 Mn 30
22 Jan 2002 1.515°S, 28.993°E 4.9 4.7 5.20 Mn 28
22 Jan 2002 1.551°S, 28.995°E 4.4 -- 4.70 Mn 28
22 Jan 2002 1.461°S, 29.249°E 4.2 -- 4.60 Mn 6
30 Jan 2002 1.633°S, 28.886°E -- -- 4.60 Mn 42
11 Feb 2002 1.386°S, 29.010°E 4.4 -- -- 30
09 Sep 2002 2.567°S, 28.867°E 4.5 -- -- 123
24 Oct 2002 1.899°S, 28.904°E 5.8 6.3 6.10-6.20 Mw 56
24 Oct 2002 1.988°S, 28.875°E 5.3 5.5 5.50 Mw 66

A violent earthquake (Mw 6.1-6.2), one of the two largest in at least 30 years in this area, occurred at 0808 on 24 October (table 4). GVO reported that it was felt in surrounding areas, including Rutshuru, Goma, Bukavu, Butare, Kigali, and Bujumbura. GVO's seven operating seismic stations (Lwiro, Goma, Kunene, Katale, Kubumba, Rusayo, and Bulengo) recorded the earthquake but the high amplitude of the signals caused saturations, thwarting attempts to use local data to obtain rapid, meaningful solutions for seismic parameters. A second large-magnitude event (Mw 5.5) occurred about an hour later. Both earthquakes struck SW of Nyiragongo, at distances of 56 and 66 km (tables 4 and 5).

Table 5. A list containing earthquakes of M 5 or greater located within 300 km of Nyiragongo during 1 January 1973-26 November 2002. Earthquake depths were typically ~10-33 km. Data courtesy of US Geological Survey, National Earthquake Information Center (NEIC) catalog of historical and preliminary data. See the previous table caption for a discussion of the magnitude types.

Date Coordinates (decimal degrees) mb Ms Other magnitude Radial distance (km)
21 Nov 1973 3.607°S, 28.186°E 5.1 -- -- 258
25 Apr 1974 0.995°N, 30.091°E 5.0 -- -- 292
06 Jan 1977 2.509°S, 28.702°E 5.3 -- -- 124
14 Apr 1977 2.456°S, 28.940°E 5.2 -- -- 108
29 Dec 1977 0.013°S, 29.683°E 4.8 5.4 -- 175
29 Jan 1978 3.929°S, 29.350°E 5.3 -- -- 266
25 Oct 1979 3.412°S, 29.070°E 5.2 -- -- 209
09 Jan 1980 3.445°S, 27.442°E 5.0 4.6 -- 292
21 May 1981 2.698°S, 28.661°E 5.0 -- -- 145
20 Jul 1981 2.709°S, 28.461°E 5.0 4.0 -- 157
09 Jan 1982 1.671°S, 28.338°E 5.0 -- -- 102
03 Jul 1982 3.737°S, 28.951°E 5.2 -- -- 246
04 Jul 1982 3.778°S, 28.917°E 5.0 -- -- 251
15 Jan 1983 0.513°N, 30.199°E 5.2 4.1 -- 247
24 Sep 1983 1.563°S, 28.381°E 5.2 -- -- 96
04 Sep 1990 0.479°S, 29.085°E 5.0 5.0 -- 116
18 Sep 1990 4.060°S, 29.483°E 5.0 4.3 -- 281
05 Feb 1994 0.593°S, 30.037°E 5.8 6.0 6.20 Mw 249
29 Apr 1995 1.315°S, 28.605°E 5.1 4.9 -- 75
24 Mar 1996 0.565°N, 30.169°E 5.0 -- 5.40 Mw 251
02 Mar 2000 2.582°S, 27.826°E 5.4 4.5 -- 196
02 Mar 2000 2.371°S, 28.026°E 5.0 4.1 -- 165
29 Jun 2001 0.292°N, 29.972°E 5.0 4.4 5.30 Mw 215
20 Jan 2002 1.681°S, 28.981°E 4.9 4.6 -- 34
21 Jan 2002 1.776°S, 29.041°E 4.9 4.5 5.10 Mn 36
21 Jan 2002 1.903°S, 29.117°E 4.7 -- 5.10 Mn 44
22 Jan 2002 1.515°S, 28.993°E 4.9 4.7 5.20 Mn 28
24 Oct 2002 1.899°S, 28.904°E 5.8 6.3 6.10-6.20 Mw 56
24 Oct 2002 1.988°S, 28.875°E 5.3 5.5 5.50 Mw 66

Soon after the earthquakes, a GVO team measured the temperature and composition of gas released from fractures on the S flank of Nyiragongo and along the N shore of Lake Kivu. No significant changes were found with respect to the measurements taken in the previous days.

Damage was reported at Bukavu (fissures in house walls), Lwiro (some houses destroyed, roof of the seismic station collapsed, and walls of laboratories fissured), Mugeri (a church destroyed), Goma (several house walls fissured, and a truck accident killed two people), and Kigali (walls of several houses fissured, and a school wall collapsed, causing panic).

Since earthquakes commonly occur and are expected to occur again in the future in the active rift, GVO recommended an education campaign discussing seismic hazards and response related to Africa's Great Lakes region.

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: Kavotha Kalendi Sadaka, Celestin Kasereka, Jean-Pierre Bajope, Mathieu Yalire, and Paolo Papale, Goma Volcano Observatory, Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Jacques Durieux, Dario Tedesco, and Jack Lockwood, Groupe d'Etude des Volcans Actifs, 6, rue des Razes, 69320 Feyzin, France; Bruce Presgrave, National Earthquake Information Center, P.O. Box 25046, MS 966, Lakewood, CO 80225, USA (URL: https://earthquake.usgs.gov/); United Nations Office for the Coordination of Humanitarian Affairs (OCHA), United Nations, New York, NY 10017, USA (URL: https://reliefweb.int/).


Panarea (Italy) — October 2002 Citation iconCite this Report

Panarea

Italy

38.638°N, 15.064°E; summit elev. 399 m

All times are local (unless otherwise noted)


Increased submarine fumarolic activity near Panarea Island

On 3 November 2002, fishermen reported strong exhalative phenomena in the Lisca Bianca-Bottaro-Lisca Nera area, E of Panarea Island (figure 1). They described boiling seawater, dead fish, and an intense sulfur smell. On 4 November, scientists of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) carried out aerial and sea surveys between Panarea and the Lisca Bianca-Dattilo-Bottaro islets from a Civil Protection helicopter and a Coast Guard boat.

Figure (see Caption) Figure 1. Bathymetric map of the Panarea Island area, showing the area of degassing in November 2002. Modified from Gabbianelli et. al. (1990); courtesy of INGV.

In three distinct areas between Lisca Bianca and Lisca Nera (figure 2), discolored water was visible, accompanied by intense gas bubbling. The first area, located W of Lisca Bianca, had three distinct degassing points in which bubbles with diameters of some meters reached the sea surface. A second area stretched SSE from W of Bottaro; on the sea surface there was only one point where vigorous outbursts of meter-sized bubbles were noted (figure 3). The third and smallest area was just SW of the second one. Water depths in all three areas are shallower than 30 m.

Figure (see Caption) Figure 2. Bathymetric map and location of degassing points on 4 November 2002. Modified from Gabbianelli et. al. (1996); courtesy of INGV.
Figure (see Caption) Figure 3. Aerial photo of the Lisca Bianca-Bottaro-Lisca Nera-Panarea Island area with evident water discoloration phenomena on 4 November 2002. Courtesy of INGV.

During the preliminary survey, INGV scientists recorded thermal images of the sea surface. Direct pH and temperature measurements were carried out at different depths, and seawater samples were collected. Neither temperature measurements nor thermal images identified appreciable thermal anomalies, because water temperatures (22-23°C) near the degassing points were similar to those close to the island's pier. Conversely, pH values were about 5.6-5.7, significantly lower than typical seawater values.

A field survey was also carried out in the Calcara Beach area, where fumarolic activity has been known since the Roman Age. No anomalies were detected in either the fumarolic flux or in the measured temperature (100°C). Finally, field and aerial surveys were performed in order to exclude the occurrence of ground fissuring or other related anomalous phenomena on Panarea Island.

On 5 November the aerial survey highlighted a remarkable decrease in the intensity of exhalation activity and a sharp reduction of the area affected by water discoloration. In particular, gas bubbling was restricted to the area W of Bottaro. Repeated thermal investigations did not find any significant anomaly. Vigorous bubbling and water discoloration further decreased in the following days.

Seismicity. In the early morning on 3 November the INGV seismic station PAN recorded a swarm of microseisms close to Panarea. PAN, in the E part of the island, is equipped with a 1-Hz vertical seismometer. Although isolated micro-events were recorded beginning at 0253 GMT, the most intense phase of the swarm, in terms of number of events, occurred between 0337 and 0500 GMT. During the swarm, geophysicists noted some hundreds of micro-events with average durations of 8 seconds and magnitudes generally less than 1. After the climax, isolated events continued. Overall, there were a few events with magnitudes between 1 and 1.5; it was impossible to locate their hypocenters because they were not detected at stations more distant from the island. According to S-P arrival time differences, the source could lay within a radius of 2-3 km from the island. The spectrum of the events analyzed shows a broad frequency content, with dominant peaks from 5 to 16 Hz.

Background. Panarea, the smallest island of the Aeolian volcanic arc in the Southern Tyrrhenian Sea, is located ~30 km SW of Stromboli. Panarea is a cone-shaped edifice rising from 1,700 m below sea level to 421 m at Punta del Corvo peak. The subaerial portion of the island was built by prevailing effusive activity and emplacement of domes from 149 to 124 Ka (Calanchi et al., 1999). A second stage, during which pyroclastic activity prevailed, occurred between 59 and 13 Ka (Losito, 1989). As of November 2002 the only volcanic activity consists of a broad fumarolic field in a submarine crater, whose rim is inferred by the semicircular distribution of the islets of Dattilo, Lisca Bianca, Bottaro, and Lisca Nera (Gabbianelli et al., 1990, Italiano and Nuccio, 1991). Panarea and the Aeolian Islands are monitored by the Istiuto Nazioanle di Geofisica e Vulcanologias, Sezz. Catania and Palermo.

References. Calanchi, N., Tranne, C.A., Lucchini, F., Rossi, P.L., and Villa, I.M., 1999, Explanatory notes to the geological map (1:10000) of Panarea and Basiluzzo islands (Aeolian arc. Italy): Acta Vulcanologica, v. 11, no. 2, p. 223-243.

Gabbianelli, G., Gillot, P.Y., Lanzafame, G., Romagnoli, C., and Rossi, P.L., 1990, Tectonic and volcanic evolution of Panarea (Aeolian Islands, Italy): Marine Geology, v. 92, p. 313-326.

Gabbianelli, G., Cortecci, G., Capra, A., Giacomelli, L., Pompilio, M., and Rossi, P.L., 1996, Lineamenti geo-vulcanologici ed ambientali del'area craterica sottomarina di Dattilo-Lisca Bianca (Isola di Panarea, Arcipelago Eoliano) in Caratterizzazione ambientale marina del sistema Eolie e dei bacini limitrofi di Cefalù e Gioia (EOCUMM 95) (edited by Faranda, F.M., and Povero, P.): Data Report, p. 455-462.

Italiano, F., and Nuccio, P.M., 1991, Geochemical investigation of submarine volcanic exhalations to the east of Panarea, Aeolian Islands, Italy: Journal of Volcanology and Geothermal Research, v. 46, p. 125-141.

Losito, R., 1989, Stratigrafia, caratteri deposizionali e aree sorgenti dei Tufi Bruni delle Isole Eolie: Unpublished Ph.D. thesis, Bari University, 92 p.

Geologic Background. The mostly submerged Panarea volcanic complex lies about midway between Stromboli and Lipari in the eastern part of the Aeolian Islands. Panarea, the smallest island in the Aeolian Archipelago, lies on the western side of a shallow platform whose shelf margin is at about 130 m depth. A series of small islands breach the surface to form the Central Reefs, the rim of a crater 2 km E of Panarea, whose shallow submerged floor contains Roman ruins. The submerged Secca dei Pesci lava dome lies at the SE end of the platform, and the rhyolitic Basiluzzo lava dome rises 165 m above the surface at the NE end, along a ridge trending towards Stromboli volcano. The complex was constructed in two main stages: an initial effusive activity phase that produced lava domes, and an explosive stage. The youngest subaerial airfall-tephra deposits are dated to about 20,000 years ago; a date of less then 10,000 BP on a lava flow is uncertain. Vigorous hydrothermal activity has continued at fumarolic fields at several locations on the submerged platform; submarine hydrothermal explosions have occurred in historical time.

Information Contacts: Susanna Falsaperla, Luigi Lodato, and Massimo Pompilio, Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Catania (INGV), Piazza Roma, 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/en/).


Popocatepetl (Mexico) — October 2002 Citation iconCite this Report

Popocatepetl

Mexico

19.023°N, 98.622°W; summit elev. 5393 m

All times are local (unless otherwise noted)


Small explosions, earthquakes, and tremor during July-October 2002

During July-October 2002, volcanic activity at Popocatépetl consisted of small-to-moderate, but at times explosive, eruptions of steam, gas, and generally minor amounts of ash. Explosions on 1 and 2 July produced ash plumes that reached 2 km and 700 m above the crater, respectively. Volcano-tectonic (VT) earthquakes (M 1.8-2.9) occurred almost daily. The earthquakes were located mostly to the S and E at depths up to 8 km beneath the crater. Isolated episodes of low-amplitude harmonic tremor were registered, typically for a few hours daily.

The Centro Nacional de Prevencion de Desastres (CENAPRED) reported that during most of July through mid-August, up to 25 small-to-moderate emissions per day were accompanied by steam, gas, and sometimes small amounts of ash. The number of exhalations per day increased during 22-24 July (43, 80, and 55) and 15-17 August (68, 58, and 70). Around 25-45 exhalations occurred per day through the end of August. During September and October, no more than 26 exhalations were registered per day.

Activity reported by CENAPRED in July was probably related to changes in morphology of the intracrater dome (BGVN 27:02 and 27:06). Compared to an aerial photo taken on 29 April (figure 46), an image on 22 May 2002 (figure 47) showed that the dome had diminished in size.

Figure (see Caption) Figure 46. Vertical aerial photo of Popocatépetl taken on 29 April 2002. The top of the image is generally towards the N. Courtesy CENAPRED.
Figure (see Caption) Figure 47. Vertical aerial photo of Popocatépetl taken on 22 May 2002. The photo provided evidence that the dome was diminished in size compared to 29 April 2002 (figure 46). The top of the image is generally towards the NNW. Courtesy CENAPRED.

CENAPRED stated that future activity could consist of isolated minor explosions with emission of incandescent fragments out to short distances from the crater or emissions of variable quantities of ash. The Alert Level remained at 2, and CENAPRED recommended that people avoid the zone extending out to 12 km from the crater, although the road between Santiago Xalitzintla (Puebla) and San Pedro Nexapa (Mexico State), including Paso de Cortés, remained open for controlled traffic.

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

Information Contacts: Centro Nacional de Prevencion de Desastres (CENAPRED), Delfin Madrigal 665, Col. Pedregal de Santo Domingo, Coyoacan, 04360, Mexico D.F. (URL: https://www.gob.mx/cenapred/).


Ruang (Indonesia) — October 2002 Citation iconCite this Report

Ruang

Indonesia

2.3°N, 125.37°E; summit elev. 725 m

All times are local (unless otherwise noted)


Eruption on 25 September 2002 sends ash to at least 5 km

The last reported activity at Ruang occurred when Qantas Airlines pilots observed an eruption around 1600 on 27 June 1996 (BGVN 21:08). A resulting plume moved W and reached an altitude of ~6 km. However, the eruption was not visible in GMS satellite imagery. The last known confirmed eruption at Ruang occurred in 1949.

A drastic increase of seismic events - from 3 to 24 events/day - was observed on 24 September by the Volcanological Survey of Indonesia (VSI). The next day, people near the volcano reported hearing a noise, and ash eruptions began by 0100. By 0300 ash emissions were continuous, and ash began falling around Ruang island and the nearby island of Tagulandang. Observers reported that the sounds accompanying the eruption were weak. By 0400 more than 1,000 people living near the volcano were evacuated to a nearby island. Around 0800, the Alert Level advanced to the highest status (level 4).

The first strong eruption commenced at 1140 on 25 September, producing thick black clouds that rose 3 km. Ten minutes later, a second eruption sent ash clouds rising 5 km. At 1210 the activity subsided enough to observe glowing material on E flank. The specific eruption site has not been firmly established. It has been presumed by VSI that it originated from "Crater II" or "where the 1949 lava originated (E side of summit)." The eruption column was reported from ground-based observations as rising to at least 5 km, and by Darwin VAAC advisories as rising to about 17 km. According to the Darwin VAAC, satellite imagery revealed that the ash cloud drifted westward to Borneo and Sumatra. Satellite images from NOAA showed the plume drifting SW with other components drifting W (figure 1). By 30 September the volcano was quiet with only a thin white plume rising about 100 m. The Alert Level was reduced from 4 to 3 on 30 September 2002.

Figure (see Caption) Figure 1. Satellite imagery on 25 September 2002 showed a large eruption plume from Ruang. The volcano's location is shown by the arrow. The plume appears to branch into SW- and W-drifting components. Courtesy NOAA.

Geologic Background. Ruang volcano, not to be confused with the better known Raung volcano on Java, is the southernmost volcano in the Sangihe Island arc, north of Sulawesi Island. The 4 x 5 km island volcano rises to 725 m across a narrow strait SW of the larger Tagulandang Island. The summit contains a crater partially filled by a lava dome initially emplaced in 1904. Explosive eruptions recorded since 1808 have often been accompanied by lava dome formation and pyroclastic flows that have damaged inhabited areas.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Center (VAAC), Bureau of Meteorology, Northern Territory Regional Office, P.O. Box 735, Darwin, NT 0801 Australia; NOAA/NESDIS Satellite Analysis Branch, Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA.


Veniaminof (United States) — October 2002 Citation iconCite this Report

Veniaminof

United States

56.17°N, 159.38°W; summit elev. 2507 m

All times are local (unless otherwise noted)


Volcanic unrest, uncertain low-level eruptive activity in September 2002

On 10 September 2002 the Alaska Volcano Observatory (AVO) detected 1-minute-long pulses of low-frequency tremor arriving every 2-5 minutes on several seismic stations at Veniaminof. This type of seismicity is indicative of volcanic unrest. Retrospective analysis of seismic data suggested that tremor began as early as 8 September. The overall level of seismicity decreased through late September, but remained above the background level established during the summer of 2002.

On 24 September, residents of Perryville, 35 km S of the volcano, reported and photographed small bursts of steam, possibly containing minor amounts of ash, rising just above the historically active intracaldera cinder cone. Without additional observations, AVO could not determine if this indicated very low-level eruptive activity or vigorous steaming from the cone. On several occasions of relatively clear weather conditions, AVO observed no signs of elevated temperature or ash emission on satellite imagery.

A satellite image recorded on 2 October suggested an apparent gray, diffuse deposit extending across the caldera from the historically active intracaldera cinder cone. This could reflect a small explosion, vigorous steam emission, or redistribution of material on the cone by strong winds. No thermal anomalies were observed on satellite imagery. AVO considered the activity at Veniaminof to be minor, but the exact nature of the unrest remained unknown. Due to the continuing seismicity and reports of unusual steaming, the Concern Color Code remained at Yellow.

Geologic Background. Veniaminof, on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3,700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA, b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

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/).