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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

Tengger Caldera (Indonesia) Ash emissions on 19 and 28 July 2019; lahar on the SW flank of Bromo

Unnamed (Tonga) Submarine eruption in early August creates pumice rafts that drifted west to Fiji

Popocatepetl (Mexico) Frequent explosions continue during March-August 2019

Semeru (Indonesia) Intermittent activity continues during March-August 2019; ash plumes and thermal anomalies

Saunders (United Kingdom) Intermittent activity most months, October 2018-June 2019; photographs during February and May 2019

Pacaya (Guatemala) Lava flows and Strombolian explosions continued during February-July 2019

Colima (Mexico) Renewed volcanism after two years of quiet; explosion on 11 May 2019

Masaya (Nicaragua) Lava lake activity declined during March-July 2019

Rincon de la Vieja (Costa Rica) Occasional weak phreatic explosions during March-July 2019

Aira (Japan) Explosions with ejecta and ash plumes continue weekly during January-June 2019

Agung (Indonesia) Continued explosions with ash plumes and incandescent ejecta, February-May 2019

Kerinci (Indonesia) Intermittent explosions with ash plumes, February-May 2019



Tengger Caldera (Indonesia) — August 2019 Citation iconCite this Report

Tengger Caldera

Indonesia

7.942°S, 112.95°E; summit elev. 2329 m

All times are local (unless otherwise noted)


Ash emissions on 19 and 28 July 2019; lahar on the SW flank of Bromo

The Mount Bromo pyroclastic cone within the Tengger Caldera erupts frequently, typically producing gas-and-steam plumes, ash plumes, and explosions (BGVN 44:05). Information compiled for the reporting period of May-July 2019 is from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC).

The eruptive activity at Tengger Caldera that began in mid-February continued through late July 2019, including white-and-brown ash plumes, ash emissions, and tremors. During the months of May through June 2019, white plumes rose between 50 to 600 m above the summit. Satellite imagery captured a small gas-and-steam plume from Bromo on 5 June (figure 18). Low-frequency tremors were recorded by a seismograph from May through July 2019.

Figure (see Caption) Figure 18. Sentinel-2 satellite image showing a small gas-and-steam plume rising from the Bromo cone (center) in the Tengger Caldera on 5 June 2019. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

According to PVMBG and a Volcano Observatory Notice for Aviation (VONA), an ash eruption occurred on 19 July 2019; however, no ash column was observed due to weather conditions. A seismograph recorded five earthquakes and three shallow volcanic tremors the same day. In addition, rainfall triggered a lahar on the SW flank of Bromo.

On 28 July the Darwin VAAC reported that ash plumes originating from Bromo rose to a maximum altitude of about 3.9 km and drifted NW from the summit, based on webcam images and pilot reports. PVMBG reported that lower altitude ash plumes (2.4 km) on the same day were also recorded by webcam images, satellite imagery (Himawari-8), and weather models.

Geologic Background. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

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/).


Unnamed (Tonga) — November 2019 Citation iconCite this Report

Unnamed

Tonga

18.325°S, 174.365°W; summit elev. -40 m

All times are local (unless otherwise noted)


Submarine eruption in early August creates pumice rafts that drifted west to Fiji

Large areas of floating pumice, termed rafts, were encountered by sailors in the northern Tonga region approximately 80 km NW of Vava'u starting around 9 August 2019; the pumice reached the western islands of Fiji by 9 October (figure 7). Pumice rafts are floating masses of individual clasts ranging from millimeters to meters in diameter. The pumice clasts form when silicic magma is degassing, forming bubbles as it rises to the surface, which then rapidly cools to form solid rock. The isolated vesicles formed by the bubbles provide buoyancy to the rock and in turn, the entire pumice raft. These rafts are spread and carried by currents across the ocean; rafts originating in the Tonga area can eventually reach Australia. This report summarizes the pumice raft eruption from early August 2019 using witness accounts and satellite images (acquisition dates are given in UTC). Pending further research, the presumed source is the unnamed Tongan seamount (volcano number 243091) about 45 km NW of Vava'u, the origin of an earlier pumice raft produced during an eruption in 2001.

Figure (see Caption) Figure 7. The path of the pumice from the unnamed Tongan seamount from 9 August to 9 October 2019 based on eye-witness accounts and satellite data discussed below, as well as additional Aqua/MODIS satellite images from NASA Worldview. Blue Marble MODIS/NASA Earth Observatory base map courtesy of NASA Worldview.

The first sighting of pumice was around 1430 on 9 August NW of Vava'u in Tonga (18° 22.068' S, 174° 50.800' W), when Shannon Lenz and Tom Whitehead on board SV Finely Finished initially encountered isolated rocks and smaller streaks of pumice clasts. The area covered by rock increasing to a raft with an estimated thickness of at least 15 cm that extended to the horizon in different directions, and which took 6-8 hours to cross (figure 8). There was no sulfur smell and the sound was described as a "cement mixer, especially below deck." There was also no plume or incandescence observed. Their video, posted to YouTube on 17 August, showed a thin surface layer of cohesive interconnected irregular streaks of pumice with the ocean surface still visible between them. Later footage showed a continuous, undulating mass of pumice entirely covering the ocean surface. Larger clasts are visible scattered throughout the raft. The pumice raft was visible in satellite imagery on this day NW of Late Island (figure 9). By 11 August the raft had evolved into a largely linear feature with smaller rafts to the SW (figure 10). Approximately four hours later, about 15 km to the WSW, Rachel Mackie encountered the pumice. Initially the pumice was "ribbons several hundred meters long and up to 20m wide. It was quite fine and like a slick across the surface of the water." By 2130 they were surrounded by the pumice, and around 25 km away the smell of sulfur was noted.

Figure (see Caption) Figure 8. The pumice raft from the unnamed Tongan seamount on 9 August 2019 taken by Shannon Lenz and Tom Whitehead on board SV Finely Finished. The photos show the pumice raft extending to the horizon in different directions. Scattered larger clasts protrude from the relatively smooth surface that entirely obscures the ocean surface. Courtesy of Shannon Lenz and Tom Whitehead via noonsite.
Figure (see Caption) Figure 9. The pumice raft from the unnamed Tongan seamount on 9 August 2019 (UTC) can be seen NW of Late Island of Tonga in this Aqua/MODIS satellite image. The dashed white line encompasses the visible pumice. The location of the pumice in this image is shown in figure 7. Courtesy of NASA WorldView.
Figure (see Caption) Figure 10. The Sentinel-2 satellite first imaged the pumice from the unnamed Tongan seamount on 11 August 2019 (UTC). This image indicates the pumice distribution with the main raft towards the W and the easternmost area of pumice approximately 45 km away. The eastern tip of the pumice area is located approximately 30 km WNW of Lake islands in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Michael and Larissa Hoult aboard the catamaran ROAM encountered the raft on 15 August (figure 11). They initially saw isolated clasts ranging from marble to tennis ball size (15-70 mm) at 18° 46′S, 174° 55'W. At around 0700 UTC (1900 local time) they noted the smell of sulfur at 18° 55′S, 175° 21′W, and by 0800 UTC they were immersed in the raft with visible clasts ranging from marble to basketball (25 cm) sizes. At this point the raft was entirely obscuring the ocean surface. On 16 and 21 August the pumice continued to disperse and drift NW (figures 12 and 13). On 20 August Scott Bryan calculated an average drift rate of around 13 km/day, with the pumice on this date about 164 km W of the unnamed seamount.

Figure (see Caption) Figure 11. Images of pumice from the unnamed Tongan seamount encountered by Michael and Larissa Hoult aboard the catamaran Roam on 15 August. Left: Larissa takes photographs with scale of pumice clasts; top right: a closeup of a pumice clast showing the vesicle network preserving the degassing structures of the magma; bottom left: Michael holding several larger pumice clasts. The location of their encounter with the pumice is shown in figure 7. Courtesy of SailSurfROAM.
Figure (see Caption) Figure 12. The pumice from the unnamed Tongan seamount (volcano number 243091) on 16 August 2019 UTC. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 13. On 21 August 2019 (UTC) the pumice from the unnamed Tongan seamount (volcano number 243091) had drifted at least 120 km WNW of Late Island in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

An online article published by Brad Scott at GeoNet on 9 September reported the preliminary size of the raft to be 60 km2, significantly smaller than the 2012 Havre seamount pumice raft that was 400 km2. Satellite identification of pumice-covered areas by GNS scientists showed the material moving SSW through 14 August (figure 14).

Figure (see Caption) Figure 14. A compilation of mapped pumice raft extents from 9 August (red line) through to 14 August (dark blue) from Suomi NPP, Terra, Aqua, and Sentinel-2 satellite images. The progression of the pumice raft is towards the SW. Courtesy of Salman Ashraf, GNS Science.

On 5 September the Maritime Safety Authority of Fiji (MSAF) issued a notice to mariners stating that the pumice was sighted in the vicinity of Lakeba, Oneata, and Aiwa Islands and was moving to the W. On 6 September a Planet Labs satellite image shows pumice encompassing the Fijian island of Lakeba over 450 km W of the Tongan islands (figure 15). The pumice entered the lagoon within the barrier reef and drifted around the island to continue towards the W. The pumice was imaged by the Landsat 8 satellite on 26 September as it moved through the Fijian islands, approximately 760 km away from its source (figure 16). The pumice is segmented into numerous smaller rafts of varying sizes that stretch over at least 140 km. On 12 September the Fiji Sun reported that the pumice had reached some of the Lau islands and was thick enough near the shore for people to stand on it.

Figure (see Caption) Figure 15. Planet Labs satellite images show Lakeba Island to the E of the larger Viti Levu Island in the Fiji archipelago. The top image shows the island on 7 July 2019 prior to the pumice raft from the unnamed Tongan seamount. The bottom image shows pumice on the sea surface almost entirely encompassing the island on 6 September. The location of the pumice in this image is shown in figure 7. Courtesy of Planet Labs.
Figure (see Caption) Figure 16. Landsat 8 satellite images show the visible extent of the unnamed seamount pumice on 26 September 2019 (UTC), up to approximately 760 km from the Tongan islands. The pumice seen here extends over a distance of 140 km. The top image shows the locations of the other three images in the white boxes, with a, b, and c indicating the locations. White arrows point to examples of the light brown pumice rafts in these images, seen through light cloud cover. The island in the lower right is Koro Island, the island to the lower left is Viti Levu, and the island to the top right is Vanua Levu. The location of the pumice in this image is shown in figure 7. Landsat 8 true color-pansharpened satellite images courtesy of Sentinel Hub.

Pumice had reached the Yasawa islands in western Fiji by 29 September and was beginning to fill the eastern bays (figure 17). By 9 October bays had been filled out to 500-600 m from the shore, and pumice had also passed through the islands to continue towards the W (figure 18). At this point the pumice beyond the islands had broken up into linear segments that continued towards the NW.

Figure (see Caption) Figure 17. These Sentinel-2 satellite images show the pumice from the unnamed Tongan seamount drifting towards the Yasawa islands of Fiji. The 24 September 2019 (UTC) image shows the beaches without the pumice, the 29 September image shows pumice drifting westward towards the islands, and the 9 October image shows the bays partly filled with pumice out to a maximum of 500-600 m from the shore. These islands are approximately 850 km from the Tongan islands. The Yasawa islands coastline impacted by the pumice shown in these images stretches approximately 48 km. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.
Figure (see Caption) Figure 18. This Sentinel-2 satellite image acquired on 9 October 2019 (UTC) shows expanses of pumice from the unnamed Tongan seamount that passed through the Yasawa islands of Fiji and was continuing NWW, seen in the center of the image. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Geologic Background. A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about 35 km S of Fonualei and 60 km NE of Late volcano. The site of the eruption is along a NNE-SSW-trending submarine plateau with an approximate bathymetric depth of 300 m. T-phase waves were recorded on 27-28 September 2001, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the E.

Information Contacts: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Salman Ashraf, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Brad Scott, New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Scott Bryan, School of Earth, Environmental & Biological Sciences, Science and Engineering Faculty, Queensland University of Technology, R Block Level 2, 204, Gardens Point (URL: https://staff.qut.edu.au/staff/scott.bryan); Shannon Lenz and Tom Whitehead, SV Finely Finished (URL: https://www.noonsite.com/news/south-pacific-tonga-to-fiji-navigation-alert-dangerous-slick-of-volcanic-rubble/, YouTube: https://www.youtube.com/watch?v=PEsHLSFFQhQ); Michael and Larissa Hoult, Sail Surf ROAM (URL: https://www.facebook.com/sailsurfroam/); Rachel Mackie, OLIVE (URL: http://www.oliveocean.com/, https://www.facebook.com/rachel.mackie.718); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Fiji Sun (URL: https://fijisun.com.fj/2019/09/12/pumice-menace-hits-parts-of-lau-group/).


Popocatepetl (Mexico) — September 2019 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Frequent explosions continue during March-August 2019

The current eruptive period of Popocatépetl began on 9 January 2005 and it has since been producing frequent explosions accompanied by ash plumes, gas emissions, and ballistic ejecta that can impact several kilometers away from the crater, as well as dome growth and destruction. This activity continued through March-August 2019 with an increase in volcano alert level during 28 March-6 May. This report summarizes activity during this period and is based on information from Centro Nacional de Prevención de Desastres (CENAPRED), Universidad Nacional Autónoma de México (UNAM), and various webcam and remote sensing data.

An overflight on 28 February confirmed that dome 82, which was first observed on 14 February, was still present and was 200 m in diameter. During March there were 3,291 observed low-intensity emissions, and 33 larger explosions that produced ash plumes to a maximum height of 5 km, accompanied by near-continuous emission of water vapor and volcanic gases. Explosions ejected blocks that fell on the flanks out to 1.2-2 km on 1, 10, 13, 17, 26, 27, and 29 March. The events on the 17th and 27th resulted in vegetation fires. Frequent sulfur dioxide (SO2) plumes were detected by TropOMI (figure 130). An overflight on 7 March showed intense degassing and an ash plume at 1142, preventing visibility into the crater (figure 131). On 13 March Strombolian activity was observed for approximately 15 minutes at 0500, accompanied by incandescent ejecta that deposited mainly on the ESE flank.

An overflight on 15 March was taken by CENAPRED and UNAM personnel to observe changes to the crater after explosions on the 13th and 14th. They reported that dome 82 had been destroyed and the crater maintained its previous dimensions of 300 m in diameter and 130 m deep. An explosion on the 27th ejected incandescent rocks out to 2 km from the crater and produced a 3-km-high ash plume that dispersed to the NE. Ashfall was reported in Santa Cruz, Atlixco, San Pedro, San Andrés, Santa Isabel Cholula, San Pedro Benito Juárez, and in the municipalities of Puebla, Hueyapan, Tetela del Volcán, and Morelos.

On 28 March an explosion at 0650 generated a 2.5-km-high ash plume and ejecta out to 1 km from the crater, and a 130-minute-long event produced gas and ah plumes (figure 132). On this day the volcano alert level was increased from Yellow Phase 2 to Yellow Phase 3. On the 29th an ash plume rose to 3 km and was accompanied by ejecta that reached 2 km away from the crater. Later that day a 20-minute-long event produced ash and gas. During a surveillance flight on 30 March a view into the crater showed no dome present, and the crater size had increased to 350 m in width and 250-300 m in depth after recent explosions (figure 131). On this day Strombolian activity was also observed lasting for 14 minutes, producing an ash plume to 800 m and ejecta out to 300 m from the crater. Incandescence at the crater was often seen during nighttime throughout the month.

Figure (see Caption) Figure 130. Significant SO2 plumes at Popocatépetl detected by the TROPOMI instrument on the Sentinel-5P satellite during 3-11 March 2019. SO2 plumes are frequently observed and these images show examples of plume drift directions on 3 March 2019 (top left), 6 March 2019 (top right), 7 March 2019 (bottom left), and 11 March 2019 (bottom right). Date, time, and measurements are provided at the top of each image. Courtesy of NASA Goddard Flight Center.
Figure (see Caption) Figure 131. Activity at Popocatépetl and views of the crater during surveillance flights in March 2019. The top images show an ash plume (left) and a gas-and-steam plume (right) on 7 March. On 30 March (bottom left and right) no lava dome was observed in the crater, which was measured to be 350 m in diameter and 250-300 m deep. Courtesy of CENAPRED and Geophysics Institute of UNAM.
Figure (see Caption) Figure 132. Explosive activity at Popocatépetl on 28 March 2019 producing ash plumes (top and bottom left) and ejecting incandescent ejecta out to 2 km from the crater at 1948. Courtesy of Carlos Sanchez/AFP (top), CENAPRED (bottom left and right), and Webcams de Mexico (bottom left).

There was a decrease in events during the next two months with 1,119 recorded low-intensity emissions and no larger ash explosions throughout April, followed by 1,210 low-intensity emissions and seven larger ash explosions through May (figure 133). Water vapor and volcanic gas emissions were frequently observed through this time and incandescence was observed some nights. A surveillance overflight on 26 April noted no new dome within the crater. On 6 May the alert level was lowered back to Yellow Phase 2. Another overflight on 9 May showed no change in the crater. An explosion at 1910 on 22 May produced an ash plume to 3.5 km above the crater with ashfall reported in Ozumba, Temamatla, Atlautla, Cocotitlán, Ayapango, Ecatzingo, Tenango del Aire and Tepetlixpa.

Figure (see Caption) Figure 133. Graph showing the number of daily ash explosions and low-intensity emissions at Popocatépetl during March-August 2019. There was a decrease in the number of events during April and March, with an increase from March onwards. Data courtesy of CENAPRED.

Through the month of June there were 2,820 low-intensity emissions and 21 larger ash explosions recorded. Gas emissions were observed throughout the month. Two explosions on 3 June produced ash plumes up to 3.5 and 2.8 km, with ejecta out to 2 km S during the first explosion. On 11 June an explosion produced an ash plume to 1 km above the crater and ballistic ejecta out to 1 km E. Observers on a surveillance overflight on the 12th reported no changes within the crater

Explosions with estimated plume heights of 5 km occurred on the 14th and 15th, with the latter producing ashfall in the municipalities of San Pablo del Monte, Tenancingo, Papantla, San Cosme Mazatencocho, San Luis Teolocholco, Acuamanala, Nativitas, Tepetitla, Santa Apolonia Teacalco, Santa Isabel Tetlatlahuaca, and Huamantla, in the state of Tlaxcala, as well as in Nealtican, San Nicolás de los Ranchos, Calpan, San Pedro Cholula, Juan C. Bonilla, Coronango, Atoyatempan, and Coatzingo, in the state of Puebla.

On 17 June an explosion produced an ash plume that reached 8 km above the crater and dispersed towards the SW. An ash plume rising 2.5 km high was accompanied by incandescent ejecta impacting a short distance from the crater on the 21st, and another ash plume reached 2.5 km on the 22nd. Explosions on 26, 29, and 30 June resulted in ash plumes reaching 1.5 km above the crater and ballistic ejecta impacting on the flanks out to 1 km.

For the month of July there was an increased total of 5,637 recorded low-intensity emissions, and 173 larger ash explosions (figure 134). On 8 July an explosion produced ballistic ejecta out to 1.5 km and an ash plume up to 1 km above the crater. An ash plume up to 2.6 km was produced on the 12th. On 19 July a surveillance overflight observed a new dome (dome 83) with a diameter of 70 m and a thickness of 15 m (figure 135). Explosions on 20 July produced ashfall, and minor explosions that ejected incandescent ballistics onto the slopes. An event on the 24th produced an ash plume that reached 1.2 km, and ash plumes the following day reached 1 km. An overflight on 27 July confirmed that these explosions destroyed dome 83, and the crater dimensions remained the same (figure 136). The following day, ash plumes reached up to 1.6 km above the crater, and up to 2 km on the 29th. Minor ashfall was reported in the municipality of Ozumba on 30 June.

Figure (see Caption) Figure 134. Examples of ash plumes at Popocatépetl on 1 July (top left), 18 July (top right and bottom left), and 30 July (bottom right) 2019. In the night time image taken on 18 July hot rocks are visible on the flank. Webcam images courtesy of CENAPRED and Webcams de Mexico.
Figure (see Caption) Figure 135. A surveillance overflight at Popocatépetl on 19 July 2019 confirmed a new dome, dome number 83, with a width of 70 m and a thickness of 15 m. Courtesy of CENAPRED and Geophysics Institute of UNAM.
Figure (see Caption) Figure 136. Photos of the summit crater of Popocatépetl taken during a surveillance flight on 27 July 2019 confirmed that the 83rd lava dome was destroyed by recent explosions and the crater maintained the same dimensions as previously measured. Courtesy of CENAPRED and Geophysics Institute of UNAM.

Throughout August the number of recorded events was higher than previous months, with 5,091 low-intensity emissions and 204 larger ash explosions (figure 137). Two explosions generated ash plumes and incandescent ejecta on 2 August, the first with a plume up to 1.5 km with ejecta impacting the slopes, and the second with an 800 m plume and ejecta landing back in the crater. Ashfall from the events was reported in in the municipalities of Tenango del Aire, Ayapango and Amecameca. On the 14th ashfall was reported in Juchitepec, Ayapango, and Ozumba. Explosions on 16 August produced ash plumes up to 2 km that dispersed to the WSW. Over the following two days ash plumes reached 1.2 km and resulted in ashfall in Cuernavaca, Tepoztlán, Tlalnepantla, Morelos, Ozumba, and Ecatzingo. Over 30-31 August ash plumes reached between 1-2 km above the crater and ashfall was reported in Amecameca, Atlautla, Ozumba, and Tlalmanalco. Incandescence was sometimes observed at the crater through the month.

Figure (see Caption) Figure 137. Ash plumes at Popocatépetl on 7 August (top) and 26 August 2019 (bottom). Courtesy of CENAPRED and Webcams de Mexico.

The MODVOLC algorithm for MODIS thermal anomalies registered thermal alerts through this period, with 22 in March, three in May, five in July, and one in August. The MIROVA system showed that the frequency of thermal anomalies at Popocatépetl was higher in March, sporadic in April and May, low in June, and had increased again in July and August (figure 138). Elevated temperatures were frequently visible in Sentinel-2 thermal satellite data when clouds and plumes were not covering the crater (figure 139).

Figure (see Caption) Figure 138. Thermal activity at Popocatépetl detected by the MIROVA system showed frequent anomalies in March, intermittent anomalies through April-May, low activity in June, and an increase in July-August 2019. Courtesy of MIROVA.
Figure (see Caption) Figure 139. Sentinel-2 thermal satellite images frequently showed elevated temperatures in the crater of Popocatépetl during March-August 2019, as seen in this representative image from 7 May 2019. Sentinel2- atmospheric penetration (bands 12, 11, 8A) scene courtesy of Sentinel Hub Playground.

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 Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.unam.mx/); Universidad Nacional Autónoma de México (UNAM), University City, 04510 Mexico City, Mexico (URL: https://www.unam.mx/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://SO2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Webcams de Mexico (URL: http://www.webcamsdemexico.com/); Agence France-Presse (URL: http://www.afp.com/).


Semeru (Indonesia) — September 2019 Citation iconCite this Report

Semeru

Indonesia

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

All times are local (unless otherwise noted)


Intermittent activity continues during March-August 2019; ash plumes and thermal anomalies

The ongoing eruption at Semeru weakened in intensity during 2018, with occasional ash plumes and thermal anomalies (BGVN 44:04); this reduced but ongoing level of activity continued through August 2019. The volcano is monitored by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC). The current report summarizes activity from 1 March to 31 August 2019. The Alert Level remained at 2 (on a scale from 1-4); the public was warned to stay 1 km away from the active crater and 4 km away on the SSE flank.

Based on analysis of satellite images, the Darwin VAAC reported that ash plumes rose to an altitude of 4-4.3 km on 19 April, 20 June, 10 July, and 13 July, drifting in various directions. In addition, PVMBG reported that at 0830 on 26 June an explosion produced an ash plume that rose around 600 m above the summit and drifted SW. A news article (Tempo.com) dated 12 August cited PVMBG as stating that the volcano had erupted 17 times since 8 August.

During March-August 2019 thermal anomalies were detected with the MODIS satellite instruments analyzed using the MODVOLC algorithm only on 5 July and 22 August. No explosions were recorded on those two days. Scattered thermal anomalies within 5 km of the volcano were detected by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system, also based on analysis of MODIS data: one at the end of March and 3-6 hotspots over the following months, almost all of low radiative power. Satellite imagery intermittently showed thermal activity in the Jonggring-Seloko crater (figure 37), sometimes with material moving down the SE-flank ravine.

Figure (see Caption) Figure 37. Sentinel-2 satellite images showing the persistent elevated thermal anomaly in the Jonggring-Seloko crater of Semeru were common through August 2019, as seen in this view on 20 July. Hot material could sometimes be identified in the SE-flank ravine. Atmospheric penetration rendering (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Tempo.com (URL: https://www.tempo.com/).


Saunders (United Kingdom) — August 2019 Citation iconCite this Report

Saunders

United Kingdom

57.8°S, 26.483°W; summit elev. 843 m

All times are local (unless otherwise noted)


Intermittent activity most months, October 2018-June 2019; photographs during February and May 2019

Historical observations of eruptive activity from the glacier-covered Mount Michael stratovolcano on Saunders Island in the South Sandwich Islands were not recorded until the early 19th century at this remote site in the southernmost Atlantic Ocean, and remain extremely rare. With the advent of satellite observation technology, indications of more frequent eruptive activity have become apparent. Vapor emission is frequently reported from the summit crater, and AVHRR and MODIS satellite imagery has revealed evidence for lava lake activity in the summit crater (Lachlan-Cope and others, 2001). Limited thermal anomaly data and satellite imagery indicated at least intermittent activity during May 2000-November 2013, and from November 2014 through April 2018 (Gray and others, 2019). Ongoing observations, including photographs from two site visits in February and May 2019 suggest continued activity at the summit during most months through May 2019, the period covered in this report. Information, in addition to on-site photographs, comes from MIROVA thermal anomaly data, NASA SO2 instruments, and Sentinel-2 and Landsat satellite imagery.

Near-constant cloud coverage for much of the year makes satellite data intermittent and creates difficulty in interpreting the ongoing nature of the activity. Gray and others (2019) concluded recently after a detailed study of shortwave and infrared satellite images that there was continued evidence for the previously identified lava lake on Mount Michael since January 1989. MIROVA thermal anomaly data suggest intermittent pulses of thermal energy in September, November, and December 2018, and April 2019 (figure 17). Satellite imagery confirmed some type of activity, either a dense steam plume, evidence of ash, or a thermal anomaly, each month during December 2018-March 2019. Sulfur dioxide anomalies were recorded in January, February, and March 2019. Photographic evidence of fresh ash was captured in February 2019, and images from May 2019 showed dense steam rising from the summit crater.

Figure (see Caption) Figure 17. MIROVA thermal anomaly data from 19 September 2018 through June 2019 showed sporadic, low-level pulses of thermal energy in late September, November, and December 2018, and April 2019. Courtesy of MIROVA.

After satellite imagery and thermal anomaly data in late September 2018 showed evidence for eruptive activity (BGVN 43:10, figure 16), a single thermal anomaly in MIROVA data was recorded in mid-November 2018 (figure 17). A rare, clear Sentinel-2 image on 2 December revealed a dense steam plume over the active summit crater; the steam obscured the presence of any possible thermal anomalies beneath (figure 18).

Figure (see Caption) Figure 18. Sentinel-2 images of Mount Michael on Saunders Island on 2 December 2018 revealed a dense steam plume over the summit crater that was difficult to distinguish from the surrounding snow in Natural Color rendering (bands 4,3,2) (left), but was clearly visible in Atmospheric Penetration rendering (bands 12,11, 8a) (right). Courtesy of Sentinel Hub Playground.

Clear evidence of recent activity appeared on 1 January 2019 with both a thermal anomaly at the summit crater and a streak of ash on the snow (figure 19). Steam was also present within the summit crater. A distinct SO2 anomaly appeared in data from the TROPOMI instrument on 14 January (figure 20).

Figure (see Caption) Figure 19. A thermal anomaly and dense steam were recorded at the summit of Mount Michael on Saunders Island on 1 January 2019 in Sentinel-2 Satellite imagery with Atmospheric Penetration rendering (bands 12, 11, 8a) (left). The same image shown with Natural Color rendering (bands 4,3,2) (right) shows a recent streak of brown particulates drifting SE from the summit crater. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 20. A distinct SO2 plume was recorded drifting NW from Saunders Island by the TROPOMI instrument on the Sentinel 5-P satellite on 14 January 2019. Courtesy of NASA Goddard Space Flight Center.

Multiple sources of satellite data and sea-based visual observation confirmed activity during February 2019. SO2 emissions were recorded with the TROPOMI instrument on 10, 11, 15, and 16 February (figure 21). A Landsat image from 10 February showed a dense steam plume drifting NW from the summit crater, with the dark rim of the summit crater well exposed (figure 22). Sentinel-2 images in natural color and atmospheric penetration renderings identified a dense steam plume drifting S and a thermal anomaly within the summit crater on 15 February (figure 23). An expedition to the South Sandwich Islands between 15 February and 8 March 2019 sponsored by the UK government sailed by Saunders in late February and observed a stream of ash on the NNE flank beneath the cloud cover (figure 24).

Figure (see Caption) Figure 21. Faint but distinct SO2 plumes were recorded drifting away from Saunders Island in various directions on 10, 11, 15, and 16 February 2019. Courtesy of NASA Goddard Space Flight Center.
Figure (see Caption) Figure 22. The dark summit crater of Mount Michael on Saunders Island was visible in Landsat imagery on 10 February 2019. A dense steam plume drifted NW and cast a dark shadow on the underlying cloud cover. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 23. At the summit of Mount Michael on Saunders Island, Sentinel-2 images in Natural Color (bands 4,3,2) (left) and Atmospheric Penetration (bands 12, 11, 8a) (right) renderings identified a dense steam plume drifting S and a thermal anomaly within the summit crater on 15 February 2019. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 24. Recent ash covered the NNE flank of Mount Michael on Saunders Island in late February 2019 when observed by an expedition to the South Sandwich Islands sponsored by the UK government. Courtesy of Chris Darby.

Faint SO2 emissions were recorded twice during March 2019 (figure 25), and a dense steam plume near the summit crater was visible in Landsat imagery on 23 March (figure 26). Two thermal anomalies were captured in the MIROVA data during April 2019 (figure 17).

Figure (see Caption) Figure 25. Faint SO2 plumes were recorded on 1 and 11 March 2019 emerging from Saunders Island. Courtesy of NASA Goddard Space Flight Center.
Figure (see Caption) Figure 26. A dense steam plume drifted E from the summit crater of Mount Michael at Saunders Island on 25 March 2019. Landsat-8 image courtesy of Sentinel Hub Playground.

A volcano-related research project "SSIVOLC" explored the South Sandwich Islands volcanoes during 15 April-31 May 2019. A major aim of SSIVOLC was to collect photogrammetric data of the glacier-covered Mount Michael (Derrien and others, 2019). A number of still images were acquired on 17 and 22 May 2019 showing various features of the island (figures 27-30). The researchers visually observed brief, recurrent, and very weak glow at the summit of Mount Michael after dark on 17 May, which they interpreted as reflecting light from an active lava lake within the summit crater.

Figure (see Caption) Figure 27. The steep slopes of an older eroded crater on the E end of Saunders island in the 'Ashen Hills' shows layers of volcanic deposits dipping away from the open half crater. In the background, steam and gas flow out of the summit crater of Mount Michael and drift down the far slope. Drone image PA-IS-03 taken during 17-22 May 2019, courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.
Figure (see Caption) Figure 28. A dense steam plume drifts away from the summit of Mount Michael on Saunders Island in this drone image taken during 17-22 May 2019. The older summit crater is to the left of the dark patch in the middle of the summit. North is to the right. Image SU-3 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.
Figure (see Caption) Figure 29. This close-up image of the summit of Mount Michael on Saunders Island shows steam plumes billowing from the summit crater, and large crevasses in the glacier covered flank, taken during 17-22 May 2019. The old crater is to the left. Image TL-SU-1 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.
Figure (see Caption) Figure 30. A dense plume of steam rises from the summit crater of Mount Michael on Saunders Island and drifts over mounds of frozen material during 17-22 May 2019. The older crater is to the left, and part of the Ashen Hills is in the foreground. Image TL-SU-2 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

References: Lachlan-Cope T, Smellie J L, Ladkin R, 2001. Discovery of a recurrent lava lake on Saunders Island (South Sandwich Islands) using AVHRR imagery. J. Volcanol. Geotherm. Res., 112: 105-116.

Gray D M, Burton-Johnson A, Fretwell P T, 2019. Evidence for a lava lake on Mt. Michael volcano, Saunders Island (South Sandwich Islands) from Landsat, Sentinel-2 and ASTER satellite imagery. J. Volcanol. Geotherm. Res., 379:60-71. https://doi.org/10.1016/j.volgeores.2019.05.002.

Derrien A, Richter N, Meschede M, Walter T, 2019. Optical DSLR camera- and UAV footage of the remote Mount Michael Volcano, Saunders Island (South Sandwich Islands), acquired in May 2019. GFZ Data Services. http://doi.org/10.5880/GFZ.2.1..2019.003

Geologic Background. Saunders Island is a volcanic structure consisting of a large central edifice intersected by two seamount chains, as shown by bathymetric mapping (Leat et al., 2013). The young constructional Mount Michael stratovolcano dominates the glacier-covered island, while two submarine plateaus, Harpers Bank and Saunders Bank, extend north. The symmetrical Michael has a 500-m-wide summit crater and a remnant of a somma rim to the SE. Tephra layers visible in ice cliffs surrounding the island are evidence of recent eruptions. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a N-flank fissure around the end of the 19th century and beginning of the 20th century. A low ice-free lava platform, Blackstone Plain, is located on the north coast, surrounding a group of former sea stacks. A cluster of parasitic cones on the SE flank, the Ashen Hills, appear to have been modified since 1820 (LeMasurier and Thomson, 1990). Vapor emission is frequently reported from the summit crater. Recent AVHRR and MODIS satellite imagery has revealed evidence for lava lake activity in the summit crater.

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/); 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); Chris Darby (URL: https://twitter.com/ChrisDDarby, image at https://twitter.com/ChrisDDarby/status/1100686838568812544).


Pacaya (Guatemala) — August 2019 Citation iconCite this Report

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)


Lava flows and Strombolian explosions continued during February-July 2019

Pacaya is one of the most active volcanoes in Guatemala, with activity largely consisting of frequent lava flows and Strombolian activity at the Mackenney crater. This report summarizes continued activity during February through July 2019 based on reports by Guatemala's Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) and Sistema de la Coordinadora Nacional para la Reducción de Desastres (CONRED), visiting scientists, and satellite data.

At the beginning of February activity included Strombolian explosions ejecting material up to 5 to 30 m above the Mackenney crater and a degassing plume up to 300 m. Multiple lava flows were observed throughout the month on the N, NW, and W flanks, reaching 350 m from the crater and resulting in avalanches from the flow fronts. Strombolian activity continued with sporadic to continuous explosions ejecting material 5-75 m above the Mackenney crater. Degassing produced plumes up to 300 m above the crater, and incandescence from the crater and lava flows were seen at night. Daniel Sturgess of Bristol University observed activity on the 24th, noting a 70-m-long lava flow with individual blocks from the front of the flow rolling down the flanks (figure 108). He reported that mild Strombolian explosions occurred every 10-20 minutes and ejected blocks, up to approximately 4 m in diameter, as high as 5-30 m above the crater and towards the northern flank.

Figure (see Caption) Figure 108. An active lava flow on the NW flank of Pacaya on 24 February 2019 with incandescence visible in lower light conditions. Courtesy of Daniel Sturgess, University of Bristol.

Similar activity continued through March with multiple lava flows reaching a maximum of 200 m N and NW, and avalanches descending from the flow fronts. Ongoing Strombolian explosions expelled material up to 75 m above the Mackenney crater. Degassing produced a white-blue plume to a maximum of 900 m above the crater (figure 109) and incandescence was noted some nights.

Figure (see Caption) Figure 109. A degassing plume at Pacaya reaching 350 m above the crater and dispersing to the S on 19 March 2019. Courtesy of CONRED.

During April lava flows continued on the N and NW flanks, reaching a maximum length of 300 m, with avalanches forming from the flow fronts. Degassing formed plumes up to 600 m above the crater that dispersed with various wind directions. Strombolian activity continued with explosions ejecting material up to 40 m above the crater. On the 2nd and 3rd weak rumbles were heard at distances of 4-5 km. Similar activity continued through May with lava flows reaching 300 m to the N, degassing producing plumes up to 600 m above the crater, and Strombolian explosions ejecting material up to 15 m above the crater.

Lava flows continued out to 300 m in length to the N and NW during June (figures 110 and 111). Strombolian activity ejected material up to 30 m above the crater and degassing resulted in plumes that reached 300 m. During July there were multiple active lava flows that reached a maximum of 300 m in length on the N and NW flanks (figure 112). Avalanches generated by the collapse of material at the front of the lava flows were accompanied by explosions ejecting material up to 30 m above the crater.

Figure (see Caption) Figure 110. An active lava flow on Pacaya on 9 June 2019 with incandescent blocks rolling down the flank from the flow front. Courtesy of Paul Wallace, University of Liverpool.
Figure (see Caption) Figure 111. Activity at Pacaya on 22 June 2019 with a degassing plume dispersed to the W and a 300-m-long lava flow. Photos by Miguel Morales, courtesy of CONRED.
Figure (see Caption) Figure 112. Two lava flows were active to the N and NW at Pacaya on 20 July 2019. Photos courtesy of CONRED.

During February through July multiple lava flows and crater activity were detected in Sentinel-2 satellite thermal images (figures 113 and 114) and relatively constant thermal energy was detected by the MIROVA system with a slight decrease in the energy and frequency of anomalies during June (figure 115). The thermal anomalies detected by the MODVOLC system for each month from February through July spanned 6-30, with six during June and 30 during April.

Figure (see Caption) Figure 113. Sentinel-2 thermal satellite images of Pacaya show lava flows to the N and NW during February through April 2019. There was a reduction in visible activity in early March. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 114. Sentinel-2 thermal satellite images of Pacaya showing lava flow and hot avalanche activity during June and July 2019. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 115. MIROVA log radiative power plot of MODIS thermal infrared at Pacaya during October 2018 through July 2019. Detected thermal energy is relatively stable with a decrease through June and subsequent increase during July. Courtesy of MIROVA.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php); 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/); Daniel Sturgess, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom (URL: http://www.bristol.ac.uk/earthsciences/); Paul Wallace, Department of Earth, Ocean and Ecological Sciences, University of Liverpool, 4 Brownlow Street, Liverpool L69 3GP, United Kingdom (URL: https://www.liverpool.ac.uk/environmental-sciences/staff/paul-wallace/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Colima (Mexico) — August 2019 Citation iconCite this Report

Colima

Mexico

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

All times are local (unless otherwise noted)


Renewed volcanism after two years of quiet; explosion on 11 May 2019

Frequent historical eruptions at Volcán de Colima date back to the 16th century and include explosive activity, lava flows, and large debris avalanches. The most recent eruptive episode began in January 2013 and continued through March 2017. Previous reports have covered activity involving ash plumes with extensive ashfall, lava flows, lahars, and pyroclastic flows (BGVN 41:01 and 42:08). In late April 2019, increased seismicity related to volcanic activity began again. This report covers activity through July 2019. The primary source of information was the Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima (CUEIV-UdC).

On 11 May 2019, CUEIV-UdC reported an explosion that was recorded by several monitoring stations. A thermal camera located south of Colima captured thermal anomalies associated with the explosion as well as intermittent degassing, which mainly consisted of water vapor (figure 131). A report from the Unidad Estatal de Protección Civil de Colima (UEPCC), and seismic and infrasound network data from CUEIV-UdC, recorded about 60 high-frequency events, 16 landslides, and 14 low-magnitude explosions occurring on the NE side of the crater during 11-24 May. Drone imagery showed fumarolic activity occurring on the inner wall of this crater on 22 May (figure 132).

Figure (see Caption) Figure 131. Gas emissions from Colima during the 11 May 2019 eruption as seen from the Naranjal station. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 17 mayo 2019 no 121).
Figure (see Caption) Figure 132. A drone photo showing fumarolic activity occurring within the NE wall of the crater at Colima on 22 May 2019. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 24 mayo 2019 no 122).

Small explosions and gas-and-steam emissions continued intermittently through mid-July 2019 concentrated on the NE side of the crater. An overflight on 9 July 2019 revealed that subsidence from the consistent activity slightly increased the diameter of the vent; other areas within the crater also showed evidence of subsidence and some collapsed material on the outer W wall (figure 133). During the weeks of 19 and 26 July 2019, monitoring cameras and seismic data recorded eight lahars.

Figure (see Caption) Figure 133. A drone photo of the crater at Colima on 8 July 2019 shows continuing fumarolic activity and evidence of a collapsed wall on the W exterior side. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 12 julio 2019 no 129).

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

Information Contacts: Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima (CUEIV-UdC), Colima, Col. 28045, Mexico; Centro Universitario de Estudios Vulcanologicos y Facultad de Ciencias de la Universidad de Colima, Avenida Universidad 333, Colima, Col. 28045, Mexico (URL: http://portal.ucol.mx/cueiv/); Unidad Estatal de Protección Civil, Colima, Roberto Esperón No. 1170 Col. de los Trabajadores, C.P. 28020, Mexico (URL: http://www.proteccioncivil.col.gob.mx/).


Masaya (Nicaragua) — August 2019 Citation iconCite this Report

Masaya

Nicaragua

11.984°N, 86.161°W; summit elev. 635 m

All times are local (unless otherwise noted)


Lava lake activity declined during March-July 2019

Masaya, in Nicaragua, contains a lava lake found in the Santiago Crater which has remained active since its return in December 2015 (BGVN 41:08). In addition to this lava lake, previous volcanism included explosive eruptions, lava flows, and gas emissions. Activity generally decreased during March-July 2019, including the number and frequency of thermal anomalies, lava lake levels, and gas emissions. The primary source of information for this report comes from the Instituto Nicareguense de Estudios Territoriales (INETER).

On 21 July 2019 a small explosion in the Santiago Crater resulted in some gas emissions and an ash cloud drifting WNW. In addition to the active lava lake (figure 77), monthly reports from INETER noted that thermal activity and gas emissions (figure 78) were decreasing.

Figure (see Caption) Figure 77. Active lava lake visible in the Santiago Crater at Masaya on 27 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).
Figure (see Caption) Figure 78. Gas emissions coming from the Santiago Crater at Masaya on 29 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).

On 15 May and 22 July 2019, INETER scientists used a FLIR SC620 thermal infrared camera to measure temperatures of fumaroles on the Santiago Crater. In May 2019 the temperature of fumaroles had decreased by 48°C since the previous month. Between May and July 2019 fumarole temperatures continued to decline; temperatures ranged from 90° to 136°C (figure 79). Compared to May 2019 these temperatures are 3°C lower. INETER reports that the level of the lava lake has been slowly dropping during this reporting period.

Figure (see Caption) Figure 79. FLIR (forward-looking infrared) and visible images of the Santiago Crater at Masaya showing fumarole temperatures ranging from 90° to 136°C. The scale in the center shows the range of temperatures in the FLIR image. Courtesy of INETER (March 2019 report).

According to MIROVA (Middle InfraRed Observation of Volcanic Activity) data from MODIS satellite instruments, frequent thermal anomalies were recorded from mid-March through early May 2019, with little to no activity from mid-May to July 2019 (figure 80). Sentinel-2 thermal images show high temperatures in the active lava lake on 10 March 2019 (figure 81). Thermal energy detected by the MODVOLC algorithm showed 14 hotspot pixels with the most number of hotspots (7) occurring in March 2019.

Figure (see Caption) Figure 80. Thermal anomalies were relatively constant at Masaya from early September 2018 through early May 2019 and then abruptly decreased until mid-June 2019 as recorded by MIROVA. Courtesy of MIROVA.
Figure (see Caption) Figure 81. Sentinel-2 thermal satellite image showing a detected heat signature from the active lava lake at Masaya on 10 March 2019. The lava lake is visible (bright yellow-orange). Approximate diameter of the crater containing the lava lake is 500 m. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The twin volcanoes of Nindirí and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals cause health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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); Sheila DeForest (URL: https://www.facebook.com/sheila.deforest).


Rincon de la Vieja (Costa Rica) — August 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 during March-July 2019

The acid lake of Rincón de la Vieja's active crater has generated intermittent weak phreatic explosions regularly since 2011, continuing during the past year through at least August 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 4 March and 2 September 2019. Clouds often prevented webcam and satellite views. The current report describes activity from March through July 2019.

OVSICORI-UNA reported that weak events occurred on 19 March at 1851 and on 29 March 2019 at 2043. A two-minute-long phreatic explosion on 1 April at 0802 produced a plume that rose 600 m above the crater rim. Continuous emissions were visible during 3-4 April, rising 200 m above the crater rim. On 3 April, at 1437, a small explosion was detected. An explosion on 10 April at 0617 produced a gas-and-steam plume that rose 1 km above the crater rim and drifted SE. On 12 April at 0643, a plume rose 500 m. Another event took place at 0700 on 13 April, although poor weather conditions prevented visual observations. On 14 April, OVSICORI-UNA noted that aerial photographs showed a milky-gray acid lake at a relatively low water level with convection cells of several tens meters of diameter in the center and eastern parts of the lake.

According to an OVSICORI-UNA bulletin, a small phreatic explosion occurred on 1 May. Another explosion on 11 May at 0720 produced a white gas-and-steam plume that rose 600 m above the crater rim. Phreatic explosions were recorded on 14 May at 1703 and on 17 May at 0357, though dense fog prevented visual confirmation of both events with webcams. On 15 May a local observer noted a diffuse plume of steam and gas, material rising from the crater, and photographed milky-gray deposits on the N part of the crater rim ejected from the event the day before. A major explosion occurred on 24 May.

OVSICORI-UNA recorded a significant phreatic 10-minute-long explosion that began on 11 June at 0343, but plumes were not visible due to weather conditions. No further phreatic events were reported in July.

Seismic activity was very low during the reporting period, and there was no significant deformation. Short tremors were frequent toward the end of April, but were only periodic in May and June; tremor almost disappeared in July. A few long-period earthquakes were recorded, and volcano-tectonic earthquakes were even less frequent.

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/, https://www.facebook.com/OVSICORI/).


Aira (Japan) — July 2019 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Explosions with ejecta and ash plumes continue weekly during January-June 2019

Sakurajima rises from Kagoshima Bay, which fills the Aira Caldera near the southern tip of Japan's Kyushu Island. Frequent explosive and occasional effusive activity has been ongoing for centuries. The Minamidake summit cone has been the location of persistent activity since 1955; the Showa crater on its E flank has also been intermittently active since 2006. Numerous explosions and ash-bearing emissions have been occurring each month at either Minamidake or Showa crater since the latest eruptive episode began in late March 2017. This report covers ongoing activity from January through June 2019; the Japan Meteorological Agency (JMA) provides regular reports on activity, and the Tokyo VAAC (Volcanic Ash Advisory Center) issues tens of reports each month about the frequent ash plumes.

From January to June 2019, ash plumes and explosions were usually reported multiple times each week. The quietest month was June with only five eruptive events; the most active was March with 29 (table 21). Ash plumes rose from a few hundred meters to 3,500 m above the summit during the period. Large blocks of incandescent ejecta traveled as far as 1,700 m from the Minamidake crater during explosions in February and April. All the activity originated in the Minamidake crater; the adjacent Showa crater only had a mild thermal anomaly and fumarole throughout the period. Satellite imagery identified thermal anomalies inside the Minamidake crater several times each month.

Table 21. Monthly summary of eruptive events recorded at Sakurajima's Minamidake crater in Aira caldera, January-June 2019. The number of events that were explosive in nature are in parentheses. No events were recorded at the Showa crater during this time. Data courtesy of JMA (January to June 2019 monthly reports).

Month Ash emissions (explosive) Max. plume height above crater Max. ejecta distance from crater
Jan 2019 8 (6) 2.1 km 1.1 km
Feb 2019 15 (11) 2.3 km 1.7 km
Mar 2019 29 (12) 3.5 km 1.3 km
Apr 2019 10 (5) 2.2 km 1.7 km
May 2019 15 (9) 2.9 km 1.3 km
Jun 2019 5 (2) 2.2 km 1.3 km

There were eight eruptive events reported by JMA during January 2019 at the Minamidake summit crater of Sakurajima. They occurred on 3, 6, 7, 9, 17, and 19 January (figure 76). Ash plume heights ranged from 600 to 2,100 m above the summit. The largest explosion, on 9 January, generated an ash plume that rose 2,100 m above the summit crater and drifted E. In addition, incandescent ejecta was sent 800-1,100 m from the summit. Incandescence was visible at the summit on most clear nights. During an overflight on 18 January no significant changes were noted at the crater (figure 77). Infrared thermal imaging done on 29 January indicated a weak thermal anomaly in the vicinity of the Showa crater on the SE side of Minamidake crater. The Kagoshima Regional Meteorological Observatory (KRMO) (11 km WSW) recorded ashfall there during four days of the month. Satellite imagery indicated thermal anomalies inside Minamidake on 7 and 27 January (figure 77).

Figure (see Caption) Figure 76. Incandescent ejecta and ash emissions characterized activity from Sakurajima volcano at Aira during January 2019. Left: A webcam image showed incandescent ejecta on the flanks on 9 January 2019, courtesy of JMA (Explanation of volcanic activity in Sakurajima, January 2019). Right: An ash plume rose hundreds of meters above the summit, likely also on 9 January, posted on 10 January 2019, courtesy of Mike Day.
Figure (see Caption) Figure 77. The summit of Sakurajima consists of the larger Minamidake crater and the smaller Showa crater on the E flank. Left: The Minamidake crater at the summit of Sakurajima volcano at Aira on 18 January 2019 seen in an overflight courtesy of JMA (Explanation of volcanic activity in Sakurajima, March 2019). Right: Two areas of thermal anomaly were visible in Sentinel-2 satellite imagery on 27 January 2019. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

Activity increased during February 2019, with 15 eruptive events reported on days 1, 3, 7, 8, 10, 13, 14, 17, 22, 24, and 27. Ash plume heights ranged from 600-2,300 m above the summit, and ejecta was reported 300 to 1,700 m from the crater in various events (figure 78). KRMO reported two days of ashfall during February. Satellite imagery identified thermal anomalies at the crater on 6 and 26 February, and ash plumes on 21 and 26 February (figure 79).

Figure (see Caption) Figure 78. An explosion from Sakurajima at Aira on 7 February 2019 sent ejecta up to 1,700 m from the Minamidake summit crater. Courtesy of JMA (Explanation of volcanic activity in Sakurajima, February 2019).
Figure (see Caption) Figure 79. Thermal anomalies and ash emissions were captured in Sentinel-2 satellite imagery on 6, 21, and 26 February 2019 originating from Sakurajima volcano at Aira. Top: Thermal anomalies within the summit crater were visible underneath steam and ash plumes on 6 and 26 February (closeup of bottom right photo). Bottom: Ash emissions on 21 and 26 February drifted SE from the volcano. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

The number of eruptive events continued to increase during March 2019; there were 29 events reported on numerous days (figures 80 and 81). An explosion on 14 March produced an ash plume that rose 3,500 m above the summit and drifted E. It also produced ejecta that landed 800-1,100 m from the crater. During an overflight on 26 March a fumarole was the only activity in Showa crater. KRMO reported 14 days of ashfall during the month. Satellite imagery identified an ash plume on 13 March and a thermal anomaly on 18 March (figure 82).

Figure (see Caption) Figure 80. A large ash emission from Sakurajima volcano at Aira was photographed by a tourist on the W flank and posted on 1 March 2019. Courtesy of Kratü.
Figure (see Caption) Figure 81. An ash plume from Sakurajima volcano at Aira on 18 March 2019 produced enough ashfall to disrupt the trains in the nearby city of Kagoshima according to the photographer. Image taken from about 20 km away. Courtesy of Tim Board.
Figure (see Caption) Figure 82. An ash plume drifted SE from the summit of Sakurajima volcano at Aira on 13 March (left) and a thermal anomaly was visible inside the Minamidake crater on 18 March 2019 (right). "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

A decline in activity to only ten eruptive events on days 7, 13, 17, 22, and 25 was reported by JMA for April 2019. An explosion on 7 April sent ejecta up to 1,700 m from the crater. Another explosion on 13 April produced an ash plume that rose 2,200 m above the summit. Most of the eruptive events at Sakurajima last for less than 30 minutes; on 22 April two events lasted for almost an hour each producing ash plumes that rose 1,400 m above the summit. Ashfall at KRMO was reported during seven days in April. Two distinct thermal anomalies were visible inside the Minamidake crater on both 12 and 27 April (figure 83).

Figure (see Caption) Figure 83. Two thermal anomalies were present inside Minamidake crater at the summit of Sakurajima volcano at Aira on 12 (left) and 27 (right) April 2019. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

There were 15 eruptive events during May 2019. An event that lasted for two hours on 12 May produced an ash plume that rose 2,900 m from the summit and drifted NE (figure 84). The Meteorological Observatory reported 14 days with ashfall during the month. Two thermal anomalies were present in satellite imagery in the Minamidake crater on both 17 and 22 May.

Figure (see Caption) Figure 84. An ash plume rose 2,900 m above the summit of Sakurajima at Aira on 12 May 2019 (left); incandescent ejecta went 1,300 m from the summit crater on 13 May. Courtesy of JMA (Explanation of volcanic activity in Sakurajima, May 2019).

During June 2019 five eruptive events were reported, on 11, 13, and 24 June; the event on 11 June lasted for almost two hours, sent ash 2,200 m above the summit, and produced ejecta that landed up to 1,100 m from the crater (figure 85). Five days of ashfall were reported by KRMO.

Figure (see Caption) Figure 85. A large ash plume on 11 June 2019 rose 2,200 m above the summit of Sakurajima volcano at Aira. Courtesy of Aone Wakatsuki.

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

Information Contacts: 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); Mike Day, Minnesota, Twitter (URL: https://twitter.com/MikeDaySMM, photo at https://twitter.com/MikeDaySMM/status/1083489400451989505/photo/1); Kratü, Twitter (URL: https://twitter.com/TalesOfKratue, photo at https://twitter.com/TalesOfKratue/status/1101469595414589441/photo/1); Tim Board, Japan, Twitter (URL: https://twitter.com/Hawkworld_, photo at https://twitter.com/Hawkworld_/status/1107789108754038789); Aone Wakatsuke, Twitter (URL: https://twitter.com/AoneWakatsuki, photo at https://twitter.com/AoneWakatsuki/status/1138420031258210305/photo/3).


Agung (Indonesia) — June 2019 Citation iconCite this Report

Agung

Indonesia

8.343°S, 115.508°E; summit elev. 2997 m

All times are local (unless otherwise noted)


Continued explosions with ash plumes and incandescent ejecta, February-May 2019

After a large, deadly explosive and effusive eruption during 1963-64, Indonesia's Mount Agung on Bali remained quiet until a new eruption began in November 2017 (BGVN 43:01). Lava emerged into the summit crater at the end of November and intermittent ash plumes rose as high as 3 km above the summit through the end of the year. Activity continued throughout 2018 with explosions that produced ash plumes rising multiple kilometers above the summit, and the slow effusion of the lava within the summit crater (BGVN 43:08, 44:02). Information about the ongoing eruptive episode comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and multiple sources of satellite data. This report covers the ongoing eruption from February through May 2019.

Intermittent but increasingly frequent and intense explosions with ash emissions and incandescent ejecta characterized activity at Agung during February through May 2019. During February, explosions were reported three times; events on seven days in March were documented with ash plumes and ashfall in surrounding villages. Five significant events occurred during April; two involved incandescent ejecta that traveled several kilometers from the summit, and ashfall tens of kilometers from the volcano. Most of the five significant events reported in May involved incandescent ejecta and ashfall in adjacent villages; air traffic was disrupted during the 24 May event. Ash plumes in May reached altitudes over 7 km multiple times. Thermal activity increased steadily during the period, according to both the MIROVA project (figure 44) and MODVOLC thermal alert data. MAGMA Indonesia reported at the end of May 2019 that the volume of lava within the summit crater remained at about 25 million m3; satellite information indicated continued thermal activity within the crater. Alert Level III (of four levels) remained in effect throughout the period with a 4 km exclusion radius around the volcano.

Figure (see Caption) Figure 44. Thermal activity at Agung from 4 September 2018 through May 2019 was variable. The increasing frequency and intensity of thermal events was apparent from February-May. Courtesy of MIROVA.

Steam plumes rose 30-300 m high daily during February 2019. The Agung Volcano Observatory (AVO) and PVMBG issued a VONA on 7 February (UTC) reporting an ash plume, although it was not visible due to meteoric cloud cover. Incandescence, however, was observed at the summit from webcams in both Rendang and Karangasem City (16 km SE). The seismic event associated with the explosion lasted for 97 seconds. A similar event on 13 February was also obscured by clouds but produced a seismic event that lasted for 3 minutes and 40 seconds, and ashfall was reported in the village of Bugbug, about 20 km SE. On 22 February a gray ash plume rose 700 m from the summit during a seismic event that lasted for 6 minutes and 20 seconds (figure 45). The Darwin VAAC reported the plume visible in satellite imagery moving W at 4.3 km altitude. It dissipated after a few hours, but a hotspot remained visible about 10 hours later.

Figure (see Caption) Figure 45. An ash plume rose from the summit of Agung on 22 February 2019, viewed from the Besakih temple, 7 km SW of the summit. Courtesy of PunapiBali.

Persistent steam plumes rose 50-500 m from the summit during March 2019. An explosion on 4 March was recorded for just under three minutes and produced ashfall in Besakih (7 km SW); no ash plume was observed due to fog. A short-lived ash plume rose to 3.7 km altitude and drifted SE on 8 March (UTC) 2019. The seismic event lasted for just under 4 minutes. Ash emissions were reported on 15 and 17 March to 4.3 and 3.7 km altitude, respectively, drifting W (figure 46). Ashfall from the 15 March event spread NNW and was reported in the villages of Kubu (6 km N), Tianyar (14 km NNW), Ban, Kadundung, and Sukadana. MAGMA Indonesia noted that two explosions on the morning of 17 March (local time) produced gray plumes; the first sent a plume to 500 m above the summit drifting E and lasted for about 40 seconds, while the second plume a few hours later rose 600 m above the crater and lasted for 1 minute and 16 seconds. On 18 March an ash plume rose 1 km and drifted W and NW. An event on 20 March was measured only seismically by PVMBG because fog prevented observations. An eruption on 28 March produced an ash plume 2 km high that drifted W and NW. The seismic signal for this event lasted for about two and a half minutes. The Darwin VAAC reported the ash plume at 5.5 km altitude, dissipating quickly to the NW. No ash was visible four hours later, but a thermal anomaly remained at the summit (figure 47). Ashfall was reported in nearby villages.

Figure (see Caption) Figure 46. Ash plumes from Agung on 15 (left) and 17 (right) March 2019 resulted in ashfall in communities 10-20 km from the volcano. Courtesy of PVMBG and MAGMA Indonesia (Information on G. Agung Eruption, 15 March 2019 and Gunung Agung Eruption Press Release March 17, 2019).
Figure (see Caption) Figure 47. A thermal anomaly was visible through thick cloud cover at the summit of Agung on 29 March 2019 less than 24 hours after a gray ash plume was reported 2,000 m above the summit. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

The first explosion of April 2019 occurred on the 3rd (UTC); PVMBG reported the dense gray ash plume 2 km above the summit drifting W. A few hours later the Darwin VAAC raised the altitude to 6.1 km based on infrared temperatures in satellite imagery. The seismic signal lasted for three and a half minutes and the explosion was heard at the PGA Post in Rendang (12 km SW). Incandescent material fell within a radius of 2-3 km, mainly on the S flank (figure 48). Ashfall was reported in the villages of Telungbuana, Badeg, Besakih, Pempatan, Teges, and Puregai on the W and S flanks (figure 49). An explosion on 11 April also produced a dense gray ash plume that rose 2 km above the summit and drifted W. A hotspot remained about six hours later after the ash dissipated.

Figure (see Caption) Figure 48. Incandescent ejecta appeared on the flanks of Agung after an eruption on 4 April 2019 (local time) as viewed from the observation post in Rendang (8 km SW). Courtesy of Jamie Sincioco.
Figure (see Caption) Figure 49. Ashfall in a nearby town dusted mustard plants on 4 April 2019 from an explosion at Agung the previous day. Courtesy of Pantau.com (Photo: Antara / Nyoman Hendra).

PVMBG reported an eruption visible in the webcam early on 21 April (local time) that rose to 5.5 km altitude and drifted SW. The ash spread W and S and ash fell around Besakih (7 km SW), Rendang (8 km SW), Klungkung (25 km S), Gianyar (20 km WSW), Bangli (17 km WNW), Tabanan (50 km WSW), and at the Ngurah Rai-Denpasar Airport (60 km SW). About 15 hours later a new explosion produced a dense gray ash plume that rose to 3 km above the summit and produced incandescent ejecta in all directions as far as 3 km away (figure 50). The ash spread to the S and ashfall was reported in Besakih, Rendang, Sebudi (6 km SW), and Selat (12 km SSW). Both of the explosions were heard in Rendang and Batulompeh. The incandescent ejecta from the explosions remained within the 4-km exclusion zone. A satellite image on 23 April showed multiple thermal anomalies within the summit crater (figure 51). A dense gray plume drifted E from Agung on 29 April (30 April local time) at 4.6 km altitude. It was initially reported by ground observers, but was also visible in multispectral satellite imagery for about six hours before dissipating.

Figure (see Caption) Figure 50. An explosion at Agung on 21 April 2019 sent incandescent eject 3,000 m from the summit. Courtesy of MAGMA Indonesia (Gunung Agung Eruption Press Release April 21, 2019).
Figure (see Caption) Figure 51. Multiple thermal anomalies were still present within the summit crater of Agung on 23 April 2019 after two substantial explosions produced ash and incandescent ejecta around the summit two days earlier. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

PVMBG reported an eruption on 3 May 2019 that was recorded on a seismogram with a signal that lasted for about a minute. Satellite imagery reported by the Darwin VAAC showed a growing hotspot and possible ash near the summit at 4.3 km altitude moving NE. A few days later, on 6 May, a gray ash plume rose to 5.2 km altitude and drifted slowly W before dissipating; it was accompanied by a seismic signal that lasted for about two minutes. Explosions on 12 and 18 May produced significant amounts of incandescent ejecta (figure 52). The seismic signal for the 12 May event lasted for about two minutes; no plume was observed due to fog, but incandescent ejecta was visible on the flanks and the explosion was heard at Rendang. The Darwin VAAC reported an ash plume from the explosion on 17 May (18 May local time) at 6.1 km altitude in satellite imagery moving E. They revised the altitude a short while later to 7.6 km based on IR temperature and movement; the plume drifted N, NE, and E in light and variable winds. A few hours after that it was moving NE at 7.6 km altitude and SE at 5.5 km altitude; this lasted for about 12 hours until it dissipated. Ashfall was reported in villages downwind including Cutcut, Tongtongan, Bonyoh (20 km WNW), and Temakung.

Figure (see Caption) Figure 52. Explosions on 12 (left) and 18 (right) May (local time) 2019 produced substantial ejecta on the flanks of Agung visible from a distance of 10 km or more in PVMBG webcams. The ash plume from the 18 May event resulted in ashfall in numerous communities downwind. Courtesy of PVMBG (Information Eruption G. Agung, May 13, 2019, Information Eruption G. Agung, May 18, 2019).

The initial explosion on 18 May was captured by a webcam at a nearby resort and sent incandescent ejecta hundreds of meters down the NE flank within 20 seconds (figure 53). Satellite imagery on 3, 8, 13, and 18 May indicated multiple thermal anomalies growing stronger at the summit. All of the images were captured within 24 hours of an explosive event reported by PVMBG (figure 54).

Figure (see Caption) Figure 53. The 18 May 2019 explosion at Agung produced an ash plume that rose to over 7 km altitude and large bombs of incandescent material that traveled hundreds of meters down the NE flank within the first 20 seconds of the explosion. Images taken from a private webcam located 12 km NE. Courtesy of Volcanoverse, used with permission.
Figure (see Caption) Figure 54. Satellite images from 3, 8, 13, and 18 May 2019 at Agung showed persistent and increasing thermal anomalies within the summit crater. All images were captured within 24 hours of explosions reported by PVMBG. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

PVMBG issued a VONA on 24 May 2019 reporting a new ash emission. They indicated that incandescent fragments were ejected 2.5-3 km in all directions from the summit, and the seismic signal lasted for four and a half minutes (figure 55). A dense gray ash plume was observed from Tulamben on the NE flank rising 2 km above the summit. Satellite imagery indicated that the plume drifted SW and ashfall was reported in the villages of Besakih, Pempatan, Menanga, Sebudi, Muncan, Amerta Bhuana, Nongan, Rendang, and at the Ngurah Rai Airport in Denpassar. Additionally, ashfall was reported in the districts of Tembuku, Bangli, and Susut (20 km SW). The Darwin VAAC reported an ash plume visible in satellite imagery at 4.6 km altitude along with a thermal anomaly and incandescent lava visible in webcam imagery. The remains of the ash plume were about 170 km S of the airport in Denpasar (60 km SW) and had nearly dissipated 18 hours after the event. According to a news article several flights to and from Australia were cancelled or diverted, though the International Gusti Ngurah Rai (IGNR) airport was not closed. On 31 May another large explosion produced the largest ash plume of the report period, rising more than 2 km above the summit (figure 56). The Darwin VAAC reported its altitude as 8.2 km drifting ESE visible in satellite data. It split into two plumes, one drifted E at 8.2 km and the other ESE at 6.1 km altitude, dissipating after about 20 hours.

Figure (see Caption) Figure 55. A large explosion at Agung on 24 May 2019 produced incandescent ejecta that covered all the flanks and dispersed ash to many communities to the SW. Courtesy of PVMBG (Gunung Agung Eruption Press Release 24 May 2019 20:38 WIB, Kasbani, Ir., M.Sc.).
Figure (see Caption) Figure 56. An explosion at Agung on 31 May 2019 sent an ash plume to 8.2 km altitude, the highest for the report period. Courtesy of Sutopo Purwo Nugroho, BNPB.

Geologic Background. Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE caldera rim of neighboring Batur volcano, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

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/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); The Jakarta Post, Mount Agung eruption disrupts Australian flights, (URL: https://www.thejakartapost.com/news/2019/05/25/mount-agung-eruption-disrupts-australian-flights.html); PunapiBali (URL: http://punapibali.com/, Twitter: https://twitter.com/punapibali, image at https://twitter.com/punapibali/status/1098869352588288000/photo/1); Jamie S. Sincioco, Phillipines (URL: Twitter: https://twitter.com/jaimessincioco. Image at https://twitter.com/jaimessincioco/status/1113765842557104130/photo/1); Pantau.com (URL: https://www.pantau.com/berita/erupsi-gunung-agung-sebagian-wilayah-bali-terpapar-hujan-abu?utm_source=dlvr.it&utm_medium=twitter); Volcanoverse (URL: https://www.youtube.com/channel/UCi3T_esus8Sr9I-3W5teVQQ); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN ).


Kerinci (Indonesia) — June 2019 Citation iconCite this Report

Kerinci

Indonesia

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

All times are local (unless otherwise noted)


Intermittent explosions with ash plumes, February-May 2019

Frequently active, Indonesia's Mount Kerinci on Sumatra has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838. Intermittent explosions with ash plumes, usually multiple times per month, have characterized activity since April 2018. Similar activity continued during February-May 2019, the period covered in this report with information provided primarily by the Indonesian volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), MAGMA Indonesia, notices from the Darwin Volcano Ash Advisory Center (Darwin VAAC), and satellite data. PVMBG has maintained an Alert Level II (of 4) at Kerinci for several years.

On 13 February 2019 the Kerinci Volcano Observatory (KVO), part of PVMBG, noted a brownish-white ash emission that was drifting NE about 400 m above the summit. The seismicity during the event was dominated by continuous volcanic tremor. A brown ash emission was reported on 7 March 2019 that rose to 3.9 km altitude and drifted NE. Ash also drifted 1,300 m down the SE flank. Another ash plume the next morning drifted W at 4.5 km altitude, according to KVO. On 10, 11, and 13 March KVO reported brown ash plumes drifting NE from the summit at about 4.0-4.3 km altitude. The Darwin VAAC observed continuous ash emissions in satellite imagery on 15 March drifting W at 4.3 m altitude that dissipated after about 3 hours (figure 10). A gray ash emission was reported on 19 March about 600 m above the summit drifting NE; local news media noted that residents of Kayo Aro reported emissions on both 18 and 19 March (figure 11). An ash emission appeared in satellite imagery on 25 March (figure 10). On 30 March the observatory reported two ash plumes; a brown emission at 0351 UTC and a gray emission at 0746 UTC that both drifted NE at about 4.4 km altitude and dissipated within a few hours. PVMBG reported another gray ash plume the following day at a similar altitude.

Figure (see Caption) Figure 10. Sentinel-2 satellite imagery of Kerinci from 15 (left) and 25 (right) March 2019 showed evidence of ash plumes rising from the summit. Kerinci's summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 11. Dense ash plumes from Kerinci were reported by local news media on 18 and 19 March 2019. Courtesy of Nusana Jambi.

Activity continued during April with a brown ash emission reported on 3 April by several different agencies; the Darwin VAAC and PVMBG daily reports noted that the plume was about 500 m above the summit (4.3 km altitude) drifting NE. KVO observed two brown ash emissions on 13 April (UTC) that rose to 4.2 km altitude and drifted NE. Satellite imagery showed minor ash emissions from the summit on 14 April; steam plumes 100-500 m above the summit characterized activity for the remainder of April (figure 12).

Figure (see Caption) Figure 12. A dilute ash emission rose from the summit of Kerinci on 14 April 2019 (left); only steam emissions were present on a clear 29 April in Sentinel-2 imagery (right). "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Ashfall on the NE and S flanks within 7 km of the volcano was reported on 2 May 2019. According to a news article, at least five villages were affected late on 2 May, including Tanjung Bungo, Sangir, Sangir Tengah, Sungai Rumpun, and Bendung Air (figures 13 and 14). The smell of sulfur was apparent in the villages. Brown ash emissions were observed on 3 and 4 May that rose to 4.6 and 4.1 km altitude and drifted SE. The Darwin VAAC reported an emission on 5 May, based on a pilot report, that rose to 6.7 km altitude and drifted NE for about an hour before dissipating. A brown ash emission on 10 May rose 700 m above the summit and drifted SE. Satellite imagery captured ash emissions from the summit on 14 and 24 May (figure 15). For the remainder of the month, 300-700-m-high dense steam plumes were noted daily until PVMBG reported white and brown plumes on 26 and 27 May rising 500-1,000 m above the summit. Although thermal anomalies were not reported during the period, persistent weak SO2 emissions were identified in TROPOMI instrument satellite data multiple times per month (figure 16).

Figure (see Caption) Figure 13. Ashfall was reported from five villages on the flanks of Kerinci on 2 May 2019. Courtesy of Uzone.
Figure (see Caption) Figure 14. An ash plume at Kerinci rose hundreds of meters on 2 May 2019; ashfall was reported in several nearby villages. Courtesy of Kerinci Time.
Figure (see Caption) Figure 15. Ash emissions from Kerinci were captured in Sentinel-2 satellite imagery on 14 (left) and 24 (right) May 2019. The summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 16. Weak SO2 anomalies from Kerinci emissions were captured by the TROPOMI instrument on the Sentinel-5P satellite multiple times each month from February to May 2019. Courtesy of NASA Goddard Space Flight Center.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); Nuansa Jambi, Informasi Utama Jambi: (URL: https://nuansajambi.com/2019/03/20/gunung-kerinci-semburkan-asap-tebal/); Kerinci Time (URL: https://kerincitime.co.id/gunung-kerinci-semburkan-abu-vulkanik.html); Uzone.id (URL: https://news.uzone.id/gunung-kerinci-erupsi-5-desa-tertutup-abu-tebal).

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Bulletin of the Global Volcanism Network - Volume 19, Number 08 (August 1994)

Managing Editor: Richard Wunderman

Aira (Japan)

Number of eruptions and amount of ashfall increase

Asosan (Japan)

Mud and stone ejections from crater floor

Batur (Indonesia)

Activity declines following 7-11 August eruption

Bezymianny (Russia)

Gas-and-steam plume seen for the first time since February 1994

Colima (Mexico)

Additional details about 21 July explosion; recent deposits described

Galeras (Colombia)

Long-period screw-type seismic events detected

Karangetang (Indonesia)

Description of fumaroles and morphology

Kilauea (United States)

New lava flow advances over a fault scarp; ocean entries remain active

Klyuchevskoy (Russia)

Eruption sends gas-and-ash bursts at least 3 km high; lava fountaining

Langila (Papua New Guinea)

Explosions produce thick eruption columns and light ashfall

Llaima (Chile)

New eruptive episode involves multiple explosive events

Lokon-Empung (Indonesia)

Description of fumaroles in the active crater

Mahawu (Indonesia)

Mudpots, small geysers, and vigorous, noisy fumaroles

Manam (Papua New Guinea)

Ash ejections from Southern Crater up to 1,000 m above the summit

Merapi (Indonesia)

Two new broad-band seismometers detect long-period pulses and tremor

Nyamuragira (DR Congo)

Summit caldera observations

Nyiragongo (DR Congo)

Seismicity associated with June-August activity

Pinatubo (Philippines)

Monsoon rains generate lahars and secondary explosions

Popocatepetl (Mexico)

Seismicity moderate, but distinct plume and very high SO2 flux

Rabaul (Papua New Guinea)

Major eruption sends plume to 18 km and covers Rabaul town with ash

Sheveluch (Russia)

Normal fumarolic activity and seismicity

Soputan (Indonesia)

Lava dome and fumarole descriptions

Ulawun (Papua New Guinea)

Low-frequency seismicity

Unzendake (Japan)

Slow endogenous growth of the lava dome; pyroclastic flows continue



Aira (Japan) — August 1994 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Number of eruptions and amount of ashfall increase

Volcanic activity increased in August . . . with 55 eruptions . . . including 17 explosive ones. No damage was caused. The highest ash plume of the month rose to 3,200 m at 1725 on 24 August. No volcanic swarms were registered, but 861 earthquakes were detected at a station 2.3 km NW of Minamidake crater. Heavy ashfall was observed on 21 August (159 g/m2) at [KLMO]. Total ashfall . . . during August was 425 g/m2.

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

Information Contacts: JMA.


Asosan (Japan) — August 1994 Citation iconCite this Report

Asosan

Japan

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

All times are local (unless otherwise noted)


Mud and stone ejections from crater floor

Activity from Crater 1 was moderate in August. However, at about 0800 on 11 September, intermittent mud ejection from the water-covered crater floor was detected seismically. Tremor registered at a station 800 m W of the crater had an amplitude of 4.8 µm. The seismic station detected similar activity on the evening of 12 September. During the daily crater visit on the morning of 14 September, several tens of stones were found outside the crater rim, within ~300 m of the crater 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: JMA.


Batur (Indonesia) — August 1994 Citation iconCite this Report

Batur

Indonesia

8.242°S, 115.375°E; summit elev. 1717 m

All times are local (unless otherwise noted)


Activity declines following 7-11 August eruption

An . . . eruption . . . on 7 August . . . marked the first significant eruptive activity in 18 years. According to a 12 August Reuters news report, during 7-11 August Batur "spewed glowing ash and smoke more than 600 times." The Reuters report noted that a spokesman for the local governor's office said "the threat of a major volcanic blast on Indonesia's resort island of Bali appeared to lessen on Friday [12 August] after Mount Batur's activity slowed." The news report also quoted Wimpy Tjetjep (VSI): "The probability that there will be a big and destructive eruption is small."

Geologic Background. The historically active Batur is located at the center of two concentric calderas NW of Agung volcano. The outer 10 x 13.5 km wide caldera was formed during eruption of the Bali (or Ubud) Ignimbrite about 29,300 years ago and now contains a caldera lake on its SE side, opposite the satellitic Gunung Abang cone, the topographic high of the complex. The inner 6.4 x 9.4 km wide caldera was formed about 20,150 years ago during eruption of the Gunungkawi Ignimbrite. The SE wall of the inner caldera lies beneath Lake Batur; Batur cone has been constructed within the inner caldera to a height above the outer caldera rim. The Batur stratovolcano has produced vents over much of the inner caldera, but a NE-SW fissure system has localized the Batur I, II, and III craters along the summit ridge. Historical eruptions have been characterized by mild-to-moderate explosive activity sometimes accompanied by lava emission. Basaltic lava flows from both summit and flank vents have reached the caldera floor and the shores of Lake Batur in historical time.

Information Contacts: W. Tjetjep, VSI; Reuters.


Bezymianny (Russia) — August 1994 Citation iconCite this Report

Bezymianny

Russia

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

All times are local (unless otherwise noted)


Gas-and-steam plume seen for the first time since February 1994

Seismicity remained at background levels from mid-July through early September. However, during 7-14 July, a gas-and-steam plume with a small amount of ash was observed rising ~500 m above the extrusive dome. On 11 July the ash-and-steam plume rose to ~3,000 m asl and drifted generally NE. The gas-and-steam plume extended 150 m above dome through 24 July. During the week of 11-18 August a gas-and-steam plume rose ~200 m above the volcano. A small gas-and-steam plume (to 50-70 m above the volcano) continued during the last 2 weeks of August. On 2-8 September, E. Zhdanova (KVERT) observed a viscous lava flow being "squeezed" from the extrusive dome. A gas-and-ash plume reached 1 km above the volcano and extended >40 km from the volcano. The volcano was obscured by clouds during the next week.

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: V. Kirianov, IVGG.


Colima (Mexico) — August 1994 Citation iconCite this Report

Colima

Mexico

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

All times are local (unless otherwise noted)


Additional details about 21 July explosion; recent deposits described

Increased seismicity in July 1994 culminated in a phreatic explosion on 21 July, destroying the 1991 lobe and producing avalanches and ashfall. The following report, from the geology group of the CUICT at the Universidad de Colima, provides additional details about this activity based on observations from La Yerbabuena village (8 km SW of Colima).

Rock avalanches occurred during the two days prior to the explosion at 2020 on 21 July. At La Yerbabuena it was possible to hear about 15 rock avalanches between 2230 and 2330 on 19 July, each lasting for 2-3 minutes. The day before the explosion, 11 rock avalanches with durations of 1-3 minutes were heard within 3.5 hours, but rain and fog hindered observations. On 21 July, two eyewitnesses, located 10 km (rancho El Jabalí) and 8.5 km (rancho La Joya) SSW of the volcano, respectively (figure 20), observed 30 minutes of incandescent rock avalanches down the SW flank just prior to the explosion. Following these avalanches there was a 15-second-long sharp hissing sound, a reddish glow at the summit, and then the explosion. A dark mushroom-shaped column rose above the summit and remained for about 15 minutes before dissipating. The explosion was heard within a radius of 20-35 km S of the volcano (figure 20). Rock avalanches continued throughout the rest of the night.

Figure (see Caption) Figure 20. Map of the area around Colima volcano showing the limit of ashfall (dashed line) from the 21 July 1994 phreatic explosion, and the radius within which the explosion was heard (heavy line). Courtesy of Geology group at CUICT.

Light ashfall began 30 minutes after the explosion and lasted for 90 minutes. An accumulation of 36.6 g of ash was measured during the first hour within a 1 m2 area at La Yerbabuena. Observations of the ash that night using a binocular microscope revealed no juvenile glass. Winds with velocities of 7.5-11.8 m/s at 3,500 m altitude transported ash as far as 35 km W, forming a deposit2 (figure 20). The ashfall caused no adverse effects to people or vegetation because of rainfall during the next few days.

Block-and-ash flows left deposits in the upper part of El Cordobán valley that stopped at 2,700 and 2,325 m elevation in two branches of the valley. Because of these deposits, civil protection authorities were notified of the possibility of lahars farther down the valleys during the current rainy season, similar to those that occurred following the 1991 eruption. Six days after deposition, temperatures at 20 cm depth in pristine block-and-ash-flow deposits were 116-282°C; some blocks yeilded temperatures of 120°C. Gas pipe structures were identified where hot vapor was escaping and forming conical features on the surface of the deposit. The block-and-ash-flow deposits had an average thickness of ~4 m and an estimated total volume of 450,000 m3 (in both branches). A massive ash-cloud surge deposit found on both sides of the El Cordobán valley was 1-2 cm thick and 50-70 m wide; brushwood and small trees were inclined in the direction of the flow, and maguey plants close to the valley rim were scorched. The ash-cloud surge extended ~500 m beyond the block-and-ash flow, and covered surrounding vegetation with 1-3 cm of ash.

A new lahar deposit was discovered at 1,650 m elevation in the Cordobán Valley. It was 80 cm thick and had enlarged the width of the channel by 1.7 m. Two eyewitnesses confirmed that at 1700 on 25 August, following three hours of rainfall, a lahar descended with the sound of rolling rocks. The lahar traveled ~10 km downslope, and covered part of a road at about 1,250 m elevation.

COSPEC flights made on 25 July and 6 August revealed an SO2 flux of 270 metric tons/day, close to the baseline value of 300 tons/day. Seismicity recorded at the Red Sísmica de Colima (RESCO) was low for the first 48 hours after the 21 July explosion, but then increased above the level recorded in the 72 hours before the explosion. A few minor explosions were also detected seismically.

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

Information Contacts: C. Navarro, A. Cortés, R. Saucedo, J-C. Gavilanes, J. Orozco, A. González, and I. Galindo (Director), CUICT-Universidad de Colima; G. Reyes and A. Ramírez, Centro de Investigación en Ciencias Básicas (RESCO-CICBAS), Universidad de Colima.


Galeras (Colombia) — August 1994 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Long-period screw-type seismic events detected

Long-period "screw-type" events, associated with fluid movements, appeared again on 9 August 1994. There were 18 of these events during 9-26 August, with a maximum of 2/day. These events are called "screws" because of the similarity on a seismograph record to the profile of a screw with a fine thread. This type of signal is significant at Galeras because it preceded five of the six eruptions between July 1992 and June 1993. After the 7 June 1993 eruption (18:6), 94 of these signals were recorded in July, August, September, October, and November 1993, and sporadically in January, March, and May 1994, without being followed by an eruption. However, the lack of eruptions following these occurrences does not decrease their importance. These signals, similar to those that preceded the 7 June 1993 eruption, were also the most monochromatic that have been seen, with frequencies of 2.6-3.2 Hz and durations of 20-120 seconds. These events occurred around the volcano at depths of <3 km. Some small-magnitude earthquakes were located NNE of the crater at a depth of 3-8 km; this source has remained active since the last swarm of screw-type signals between November and December 1993.

SO2 flux measurements taken by the mobile COSPEC were low. Deformation equipment indicated no variations; apparent changes at one tiltmeter were due to electronic problems.

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

Information Contacts: INGEOMINAS, Pasto.


Karangetang (Indonesia) — August 1994 Citation iconCite this Report

Karangetang

Indonesia

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

All times are local (unless otherwise noted)


Description of fumaroles and morphology

"During observations at 1145 on 15 July from the SW flank, a white plume rose above the volcano and extended toward the E. Two active lava domes were present on the summit, one in the S, and the other in the NE. Each generated white plumes from its top. Many fumaroles with yellow sulfur deposits covered the S side of the NE dome. A small chaotic-looking lava flow was located near the foot of the NE lava dome. It was possible to hear weak, rhythmic explosions from an area located between the two lava domes behind the summit pass, but no direct observations were possible because of the cover of rising clouds."

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

Information Contacts: H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland.


Kilauea (United States) — August 1994 Citation iconCite this Report

Kilauea

United States

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

All times are local (unless otherwise noted)


New lava flow advances over a fault scarp; ocean entries remain active

"Lava continued to enter the ocean in the W Kamoamoa/Lae Apuki area. Surface flows broke out on the bench, directly behind the littoral cone formed in July. These flows extended the active bench area 300-400 m W and formed a new tube parallel to the shoreline. Lava initially entered the ocean along a 500-m-wide front, but by the end of August entries had consolidated and lava entered the ocean along a 150-m-wide front. Additional breakouts resurfaced much of the older part of the bench early in the month. Small bench collapses and moderate-sized littoral explosions were observed towards mid-month. High surf on 23-24 August deposited sand and debris 50 m inland, along the entire front of the bench. Breakouts immediately behind the active ocean entries covered parts of the new bench and the storm deposit. There were no major bench collapses during the last half of August; material swept in by the storm appeared to support and slow the seaward movement of the bench.

"On 16 August a small pahoehoe flow broke out of the tube at 90 m elevation. A much larger channelized aa and pahoehoe flow broke out at 285 m on 20 August and rapidly advanced below 90 m elevation. The flow was active along its entire length, and by the end of the month fingers of active lava extended below the Paliuli fault scarp.

"The pond in Pu`u `O`o was active throughout August and its surface fluctuated at 79-84 m below the crater rim. Circulation in the pond was sluggish."

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

Information Contacts: T. Mattox, HVO.


Klyuchevskoy (Russia) — August 1994 Citation iconCite this Report

Klyuchevskoy

Russia

56.056°N, 160.642°E; summit elev. 4754 m

All times are local (unless otherwise noted)


Eruption sends gas-and-ash bursts at least 3 km high; lava fountaining

An eruption began on 8 September with lava fountaining and ash plumes that rose to an altitude of at least 8 km on 12 September. Explosive activity increased on 30 September, and on 1 October the ash column rose to >15 km altitude.

During 7-24 July, seismic stations continued to register weak intermediate-depth (10-30 km) earthquakes under the volcano (15-55/day); the duration of volcanic tremor averaged 8-22 hours/day. Weak fumarolic activity from the central crater was observed during the week of 7-14 July. Clouds frequently obscured the volcano through mid-August, but British climbers who visited the summit in early August reported no unusual activity. Seismicity increased from 24 July to 2 August, when 15-149 weak intermediate-depth earthquakes were recorded each day, accompanied by 1-20 hours/day of volcanic tremor. The number of weak intermediate-depth events decreased again during the next three weeks to 8-37 earthquakes/day. Tremor averaged 5-10 hours/day through 11 August, 3-4.5 hours/day the following week, and 5-17 hours/day by 2 September. Weak intermediate-depth earthquakes decreased from 2 to 8 September, averaging only 1-4 events/day. However, volcanic tremor was recorded for an average of 19-22 hours/day. Normal fumarolic activity was observed from the central crater early in September.

Seismic data indicated that an eruption began from the central crater at about 0400 on 8 September. Lava was observed fountaining 200-300 m above the crater from two separate vents. Gas and ash outbursts to 1 km were recorded every 10 minutes. Pilots from American Airlines reported an ash cloud as high as 11 km above sea level around 1445 on 9 September, and at 1010 the next day the cloud was reportedly moving SE at the same altitude.

On 12 September ground observers reported that the eruption sent gas and ash to 1.5 km above the crater. The ash plume reached an estimated 3 km above the 4.7-km-high volcano, to an altitude of ~8 km. The plume extended to the NE for more than 50 km and ashfall was reported in Kliuchi, [30 km NNE]. A 1-km-long lava flow was observed on the SW slope of the volcano; mudflows were also noted. Continuous volcanic tremor was recorded as far as 65 km from the volcano.

Kliuchevskoi was obscured by clouds on 13 September, but gas and ash explosions on 14 September rose 600-800 m above the crater with an ash column extending to 2 km above the crater. The ash plume was carried E for at least 50 km. A new lava flow 1.5 km long was observed on 14 September issuing from two NW-flank vents ~200 m below the crater rim. This flow is in addition to the lava flow on the SW flank of the volcano. Lava fountains were again observed extending to 200 m above the crater rim. Continuous volcanic tremor, with a maximum amplitude of 6.3 µm, was recorded at distances of 11 km from the volcano.

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

Information Contacts: V. Kirianov, IVGG; J. Lynch, SAB.


Langila (Papua New Guinea) — August 1994 Citation iconCite this Report

Langila

Papua New Guinea

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

All times are local (unless otherwise noted)


Explosions produce thick eruption columns and light ashfall

"Eruptive activity at Crater 2 continued in August. Except for a quiet period during 1-11 August, on most days thick columns of mushroom-shaped grey-brown ash clouds were released. Light ashfall in coastal areas downwind was reported on 12 and 26 August. One explosion noise was heard on the 12th, and occasional rumbling noises were heard on the 17th and 23rd. Steady weak red glow was seen on 1 and 15 August.

"Crater 3 activity was generally low. Throughout August, Crater 3 produced weak emissions of thin, pale-grey and occasionally blue vapour. After the 26th the volume of blue emissions became moderate. The 30th marked the beginning of occasional moderate to thick emissions of grey-brown ash clouds producing light ash fall on the N and NW sides of the volcano.

"Seismicity was low throughout the month. Daily totals of volcanic earthquakes were between 1 and 5."

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

Information Contacts: I. Itikarai, R. Stewart, and C. McKee, RVO.


Llaima (Chile) — August 1994 Citation iconCite this Report

Llaima

Chile

38.692°S, 71.729°W; summit elev. 3125 m

All times are local (unless otherwise noted)


New eruptive episode involves multiple explosive events

On 25 August 1994 Llaima volcano began a new eruptive episode. Its last eruption started on 17 May, generating an ash column >4 km high, subglacial lava, lahars, and flooding. The subglacial lava left a melted ice channel down the SW side of the volcano. From a point ~5.4 km W of the summit (Las Paraguas) at 0900 and 0915 on 21 August people felt two earthquakes of intensity II and III. On 25 August, beginning at 0900, observers heard explosions from the principal crater, and at 1135 the first ash column became visible.

Between 1630 and 1800 on 26 August, a gas-and-ash cloud rose 350 m above the summit and a portion of the cloud extended along the ice channel. Continuing from 1930 through the night, the eruption increased in intensity, ejecting gases and incandescent tephra up to 500 m above the summit; some tephra fell as far away as the summit's outer flanks. On 27-28 August the volcano was completely cloud covered, preventing direct visual observations. Some sources reported feeling continuous explosion shocks throughout 27 August, and one source felt 3 clear explosion shocks at 5-second intervals on 28 August. These observations suggested continuing eruptions.

Several seismic stations were installed during the crisis; the first began operation at 1458 on 26 August. During its first 21.2 hours of operation station El Trueno, located 18 km WNW of the principal crater (N of Cherquenco village), revealed harmonic tremor with a predominant frequency of 1.1 Hz. It is fitting to emphasize that in this situation the gain of the seismic system was relatively low (66 on a MEQ-800 instrument), and in May higher gains were in use (78 and 84). In essence, the August tremor had higher amplitude than it did in a roughly 6-hour post-effusive period associated with the May eruption. In addition, other high-frequency signals were detected during parts of 26-27 August, which are still under study. In the last 15 hours of this interval the record contains banded tremor predominantly of 1.0 Hz frequency.

A second seismic station began operation at 1046 on 27 August when a portable MEQ-800 (filter 0-5, gain 72) was installed. Station MELI was placed 14.5 km from the principal crater (N of Melipeuco, a town 20 km SSE of the volcano). The instrument detected harmonic tremor of 1.0-1.2 Hz frequency at roughly 4-5 episodes/minute. The tremor signal was thought to arise from magma-water contact in Llaima's magma-laden conduit system. Tremor of the same frequency continued for the first 6 hours of 28 August (0000-0600), but grew in amplitude and frequency range (to 1.5 Hz). Banded tremor appeared, possibly indicating pressurization processes associated with the ascent of a new batch of magma from depth. In the interval 1100 to 1752 on 28 August the seismicity remained roughly constant, although there was a tendency toward increased energy release.

A third station, installed at 1300 on 27 August, was located 1.1 km from Lago Verde, 7 km E from the principal crater. During 1300-1700 this instrument received such strong tremor signal that it had to be set at minimum gain (60). Later, the station was moved farther away, to Pangueco, 10 km from the principal crater.

On 28 August, scientists monitoring the volcano made several "General Recommendations." These included an Orange alert, 72 hours of vigilant watching of the seismic data, warnings to stay away from Llaima's drainages, and to remain attentive for further official instructions.

A new eruptive phase started at midnight on 28 August when a strong explosion produced a gas-and-ash column. The column was observed in Melipeuco beginning at 0300 when the sky cleared. The activity decreased noticeably by 0510 but reactivated so that between 0640 and 0940 puffs of gas-and-ash in the crater reached 100-600 m above the rim. Thereafter they decayed and grew weak though constant. Between 1120 and 1209 pyroclastic emissions reactivated, discharging a continuous column to 1,000 m above the crater with explosions producing dense scrolls every 5 seconds (VEI = 2).

A 4-hour overflight began at 1125 on 29 August. During that interval the plume mainly rose 400-500 m, but sometimes 1,000 m, above the principal crater's rim. Strong winds came from the W, carrying a visible plume at least 80 km toward the Andean passes "Pino Hachado" and "El Arco" along the Argentine border. The plume lay between 3,200 and 4,000 m altitude; vapor appeared to be absent in both the plume and the column suggesting a very magmatic eruption. The source vent was a 100-m-diameter crater in the E side of the principal crater, surrounded by a small spatter-cone covering the crater floor. From mid-day until 1700 erupted material rose 600-1,000 m and the wind continued to carry the plume E. At 1740 the eruptive intensity decreased but at 1818 it increased, again sending ash 600-700 m above the crater. After 1930 frequent intermittent explosions tossed more ejecta onto the spatter cone verifying its mode of the construction.

Seismicity monitored at station MEI captured the 29 August midnight explosion noted above. In the interval from 2200 on 28 August to 0100 on 29 August, the seismic record showed increased tremor amplitude (3-5 mm at a gain setting of 66) at frequencies of 1.1-1.2 Hz. Later, from 0200-0430, tremor frequency remained stationary at 1.1 Hz, amplitude dropped, and intervals of banded tremor prevailed. Further decreases in amplitude occurred later (0841-1909, 29 August), and while the frequency range of the tremor remained approximately stationary, tremor dropped to a level from where it only appeared episodically.

On 28 or 29 August the Emergency Committee met with members of the community to explain Llaima's activity, including a summary of the eruption character and fundamentals to help maintain civil calm and at the same time to convey potential hazards. Civil calm was called for owing to preparedness by the regional government, community groups, Carabineros, firefighters, the Chilean Air Force, and other groups. Hazard status remained at alert-level Orange.

On 30 August the ash eruption intensified; column height oscillated 2-3.7 km above the crater (corresponding to VEI 2). At 1603 the first dense, vapor-rich ejection took place; 38 minutes later an intermediate phase began, with vapor discharge accompanied by increased amounts of ash. The highest ash column during this phase ascended to 1.5 km above the crater. Vapor-rich and ash-rich phases alternated for ~ 3 hours (until 1901). At 2100 venting stopped. On 31 August, vapor discharge became pronounced around 0900 and continued until 1600.

Beginning at 2000 on 30 August and again at 0155 on 31 August, there was continuous tremor in the 0.9-1.0 Hz frequency range followed by ~ 40 minutes of banded tremor of similar frequency. Seismic quiet prevailed during the next 6 hours at stations MELI and PANG. Seismicity also remained low from 31 August until at least 0941 on 2 September.

Figure 7 shows a sketch of the crater seen during a 1 September overflight of Llaima (in a Chilean Air Force aircraft); the flight took place during calm, clear weather and visibility into the principal crater was excellent. The crater's normally snow-and-ice-covered surface was completely blackened by ashfall; about 15 fumaroles remained, yet ash-emissions were absent. A small cone covered most of the crater floor, its 100-m-diameter, funnel-shaped source vent lay adjacent to the SE crater wall (figure 8). On 1 September, the fissure of melting ice created by the 17 May subglacial lava flow still continued to send up a significant vapor plume. Although mostly westerly winds were noted by observers, the weak ash distribution was over a wide arc, ranging from compass bearings 190-310 (figure 9). There were two lobes of heavier deposition, one toward the N, the other ESE.

Because of decreases in both volcanic and seismic activity, around 2 August scientists lowered the hazard status from Orange to Yellow. However, they expressed concern about potential restriction or blockage of the vent by new deposits in the main crater. They were also concerned about the recent shift in seismic character compared to the previous 4 years.

Figure (see Caption) Figure 7. Sketch looking down on Llaima's principal crater at 1500 on 1 September. Courtesy of Hugo Moreno.
Figure (see Caption) Figure 8. Preliminary cross section of Llaima's crater showing estimates of the fill thickness and the funnel-shaped vent from the recent eruption. Courtesy of Hugo Moreno.
Figure (see Caption) Figure 9. Zones of major ash cover from the Llaima eruptions in late-August. The ESE lobe reached about 6 km from the source, the length of the N lobe was unreported. Courtesy of Hugo Moreno.

Geologic Background. Llaima, one of Chile's largest and most active volcanoes, contains two main historically active craters, one at the summit and the other, Pichillaima, to the SE. The massive, dominantly basaltic-to-andesitic, stratovolcano has a volume of 400 km3. A Holocene edifice built primarily of accumulated lava flows was constructed over an 8-km-wide caldera that formed about 13,200 years ago, following the eruption of the 24 km3 Curacautín Ignimbrite. More than 40 scoria cones dot the volcano's flanks. Following the end of an explosive stage about 7200 years ago, construction of the present edifice began, characterized by Strombolian, Hawaiian, and infrequent subplinian eruptions. Frequent moderate explosive eruptions with occasional lava flows have been recorded since the 17th century.

Information Contacts: H. Moreno1, M. Murillo, M. Petit-Breuilh, and P. Peña, SERNAGEOMIN, Temuco. 1Also at Univ de Chile, Santiago.


Lokon-Empung (Indonesia) — August 1994 Citation iconCite this Report

Lokon-Empung

Indonesia

1.358°N, 124.792°E; summit elev. 1580 m

All times are local (unless otherwise noted)


Description of fumaroles in the active crater

"During our visit to the summit zone on 8 July, intense fumaroles escaped from several parts of the Tompaluan crater floor. This fumarolic activity was mainly concentrated in the N where an intracaldera structure was covered by yellow sulfur deposits. Many other fumaroles with sulfur deposits were also located in the S, E, and W parts of the crater. Temperatures measured with an electronic thermometer at the E fumaroles showed a maximum value of 95-96°C. The fumarolic gases were mainly composed of H2O and H2S."

Geologic Background. The twin volcanoes Lokon and Empung, rising about 800 m above the plain of Tondano, are among the most active volcanoes of Sulawesi. Lokon, the higher of the two peaks (whose summits are only 2 km apart), has a flat, craterless top. The morphologically younger Empung volcano to the NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks. Historical eruptions have primarily produced small-to-moderate ash plumes that have occasionally damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred. A ridge extending WNW from Lokon includes Tatawiran and Tetempangan peak, 3 km away.

Information Contacts: H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland.


Mahawu (Indonesia) — August 1994 Citation iconCite this Report

Mahawu

Indonesia

1.352°N, 124.865°E; summit elev. 1299 m

All times are local (unless otherwise noted)


Mudpots, small geysers, and vigorous, noisy fumaroles

Part of the EVS report follows. "During our observations at 1100 on 9 July intense and noisy gas emissions (like a jet engine) occurred near the low NW part of the inner wall of the crater. These gas emissions generated a gray-white plume. This area of the crater was covered by many yellow sulfur deposits. A strong smell of hydrogen sulfide was also noted. An important solfatara zone surrounded the NW, N, NE, and E sides of the green, ~40,000 m3, acidic crater lake. Two small geysers, the one in the N and the other in the NW, were very active (2-3 m height). Several boiling basins and mud pots were active around the lake. It was not possible to get down into the crater without rock climbing equipment, because the crater walls were very steep." EVS observers also proposed that a low part of the S wall had collapsed.

Geologic Background. The elongated Mahawu volcano immediately east of Lokon-Empung volcano is the northernmost of a series of young volcanoes along a SSW-NNE line near the margin of the Quaternary Tondano caldera. Mahawu is capped by a 180-m-wide, 140-m-deep crater that sometimes contains a small crater lake, and has two pyroclastic cones on its N flank. Historical activity has been restricted to occasional small explosive eruptions recorded since 1789. In 1994 fumaroles, mudpots, and small geysers were observed along the shores of a greenish-colored crater lake.

Information Contacts: H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland.


Manam (Papua New Guinea) — August 1994 Citation iconCite this Report

Manam

Papua New Guinea

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

All times are local (unless otherwise noted)


Ash ejections from Southern Crater up to 1,000 m above the summit

"Increased activity at Southern Crater began on 8 August following a week of low-level activity. This change initiated with weak emissions of thick grey ash clouds. On the 9th, the emissions changed to forceful ejections of thick grey-brown ash clouds that caused light ashfall on the NW side of the volcano. Activity subsided after the 11th, but started again on the 18th and continued until 30 August. The thick grey-brown ash columns rose ~400-1,000 m above the summit. Most of the ash ejections were associated with explosion and low roaring and/or rumbling noises. Incandescent lava fragment projections were seen on 23 and 26-30 August.

"Activity from Main Crater consisted of emissions of weak-to-moderate white vapour through August. No noises or night glows were observed. Seismicity remained at low levels throughout the month except for a brief period during 21-29 August when it was moderate. This coincided with the period of thick brown ash cloud emissions and incandescent lava fragment projections. On average, ~1,200 volcanic earthquakes were recorded each day."

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

Information Contacts: I. Itikarai, R. Stewart, and C. McKee, RVO.


Merapi (Indonesia) — August 1994 Citation iconCite this Report

Merapi

Indonesia

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

All times are local (unless otherwise noted)


Two new broad-band seismometers detect long-period pulses and tremor

Two STS2 broad-band seismometers were deployed on 27-29 July by collaborators of the Geophysical Laboratory of GMU and Martin Beisser of GFZ-Potsdam. The researchers investigated signal coherency at different points on the volcano to find suitable sites for a multi-station seismic array that will make permanent records at a 50-Hz sampling rate. The researchers measured Merapi seismicity at a base station located at Klathakan (1.8 km WNW of the summit between 1,200-1,300 m elev), the site of a seismic station for the last eight years. The second station was mobile and GPS-equipped; however, for the following comparisons and discussion the mobile site remained 400 m N of the base station.

Figure 10 shows amplitude data for three components of volcanic shock from the mobile station. The volcanic shock event that began at 1750 and 37 seconds on 27 July is here termed Event A. Figure 11 shows the arriving signals and allows for a visual comparison of the coherency in the vertical component (top two plots), and two orthogonal horizontal components (lower four plots). From visual inspection, the best coherency appeared in the vertical-component data. Some other types of events received appeared to show less coherency between the two sites.

Figure (see Caption) Figure 10. A seismic event on Merapi received at the mobile station showing 3-component amplitude data. The event shown began at 1750 and 37 seconds on 27 July 1994 and is termed "Event A." Courtesy of A. Brodscholl.
Figure (see Caption) Figure 11. The first five seconds of Event A on Merapi (27 July 1994) as received at the broadband base and mobile stations (400-m separation). The records show considerable coherency. Courtesy of A. Brodscholl.

Figure 12 shows three components of a previously undetected tremor type, a tremor preceded by or superimposed on a long-period pulse. On the record, the interval of greatest short-period amplitude came after the pulse's maximum. Examples of this kind of tremor were seen three times in 12 hours. Whether these events are common on Merapi and elsewhere still remains uncertain.

Figure (see Caption) Figure 12. Merapi seismic record from the mobile station showing an example of tremor coming after the maximum of a long-period pulse. These pulses and temporally associated tremors were seen three times in a 12-hour period and were not previously detected. Courtesy of A. Brodscholl.

[The reported low-frequency signal was later found to be caused by instrumental problems not recognized at the time of submission.]

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

Information Contacts: M. Beisser, GFZ-Potsdam, Germany; A. Brodscholl, GMU.


Nyamuragira (DR Congo) — August 1994 Citation iconCite this Report

Nyamuragira

DR Congo

1.408°S, 29.2°E; summit elev. 3058 m

All times are local (unless otherwise noted)


Summit caldera observations

The eruptive activity . . . continued until 27 July, when seismic tremor ended and no more glow was observed. The lava flow moved over the 1971 Rugarama flow and partially filled Lake Magera at the W Precambrian escarpment. Heavy steaming from the unfilled portion of the lake was observed on 23 August during an overflight. Fumarolic activity was also observed along the 1989 fissure (figure 14), and the fresh lava plain in and around the pit crater appeared much larger than before. At the S end of the 1989 fissure a new solfataric area was noticed; a feature not formed during the 1989 or 1991 eruptions. Zairian scientists who visited the crater on 25 August observed ash emission from the 1989 fissure and confirmed that there had been fresh lava extrusion in the central crater. No evidence of lava flows on the S slope of the volcano was observed.

Figure (see Caption) Figure 14. Summit caldera of Nyamuragira, 25 August 1994, showing lava flows from 1989 (black) and 1994 (cross-hatched). Courtesy of N. Zana.

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

Information Contacts: N. Zana, Centre de Recherche en Géophysique, Kinshasa.


Nyiragongo (DR Congo) — August 1994 Citation iconCite this Report

Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)


Seismicity associated with June-August activity

On the night of 22-23 June, glow above the central crater [indicated] a reactivation of the lava lake. A seismic station on the S slope of the volcano recorded a low-frequency microearthquake at 0232 on 23 June that may have coincided with the initial lava outburst; there were no felt earthquakes before this event. Long-period tremors recorded at Katale station ceased ~2 hours after the initial lava outburst. However, tremor activity increased significantly at 2355 later that same day.

A National Park team that visited the summit reported three active vents inside the crater, the northern-most of which had formed a small scoria cone. On 1 July, four lava fountains were active. Intense lava emission was accompanied by increasing tremor amplitude recorded at local seismic stations. Continuous activity lasted until about 17 July, but decreased notably after 4 July. Additional episodes of lava lake activity occurred during 13-15 August, 19-21 August, and from about 1920 on 25 August through the 29th. The rate of lava fountaining . . . seemed to be lower than that observed during 1982. Lava fountain heights of 30-40 m were also less than the 80-100 m heights reached in 1982. The level of the fresh lava lake was ~5-10 m below the 1982 lava lake height, and the lake was confined close to the central vent in an area of ~120-150 m.

Renewed lava lake activity was preceded by a general increase in amplitude and frequency of long-period volcanic earthquakes. Volcanic tremor and earthquake swarms were recorded on 5-9 January, 20 January, and 16 May 1994. Records from the S-flank seismic station (Bulengo) indicated increased seismicity in the SW Virunga area; the frequent volcanic tremor and microearthquakes recorded at this station were not recorded at other stations outside the Nyiragongo field. A seismic swarm on 5 January 1993 was dominated by A-type volcanic events with focal depths of <5 km. On 21 November 1990 a M 4.5 earthquake was centered on the S flank. This event, felt in Goma with an intensity of MM V-VI, resulted in cracked walls of several brick houses and the death of one woman caused by a falling concrete platform. There were several aftershocks, and tremor activity was recorded for several days.

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: N. Zana, Centre de Recherche en Géophysique, Kinshasa.


Pinatubo (Philippines) — August 1994 Citation iconCite this Report

Pinatubo

Philippines

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

All times are local (unless otherwise noted)


Monsoon rains generate lahars and secondary explosions

Lahars from the upper slopes of Pinatubo began again in June 1994, induced by monsoon rains. This volcanic hazard has been frequent in the drainages of Pinatubo during every monsoon season following its June 1991 eruption. Tropical cyclones brought continuous rains on the Pinatubo area in June. Lahars developed in the major drainage channels of the O'Donnell (NE), Sacobia (E), Pasig-Potrero (SE), Marella-Santo Tomas (SW), and Bucao (NW) rivers. On the SE flank, the lahar crisis was more dramatic along the Pasig-Potrero River because it had captured the upper reaches of the Sacobia River in October 1993. The following report, from the Philippine Institute of Volcanology and Seismology, summarizes lahar activity during June-August 1994.

The first lahars were noted on 23 June. Other lahars on 10 July caused damage in downstream villages. They passed under Mancatian Bridge 2 and then curved to the left side of the Pasig-Potrero channel towards Bancal, in barangay Maliwalu (figure 31). These lahars resulted in 2-3 m of deposition on the Mancatian area (from the Angeles-Porac Road to ~2 km upstream) and at least 2 m of in-dike deposition, decreasing to 1-m-thick deposits near Bancal.

Figure (see Caption) Figure 31. Pinatubo lahar deposit map along the Pasig-Potrero River between Mancatian and Santa Rita, 3 August 1994. Courtesy of PHIVOLCS.

On 19 July, lahars cut through the Mancatian portion of the left dike and encroached on several houses at and near its outer base (figure 31). Aggradation on the left side of the channel forced the active channel to shift towards the right inner dike, so subsequent lahars (25 July) aggraded the right portion of the diked area. Average aggradation along the Mancatian area was ~3 m. Succeeding lahars (26 and 30-31 July) overtopped and breached the inner right dike ~600 m upstream from the road. The breach allowed the lahars to bury areas outside of the inner dike with 2 m of debris. Downstream, strong lahar flows (even as early as 19 July) breached the left dike at Bancal. The breach, ~100 m wide, allowed the lahars to be delivered as far as barangay San Antonio, Bacolor. The bulk of the lahars that passed through the breach were deposited at barangays Potrero and Cotod. Deposits in these areas were as thick as 4 m, especially very near the dike. Deposits in barangay San Antonio and Duat areas were 20-100 cm thick.

Significant deposition in the Mancatian area along the right side of the channel shifted the active flow back towards the left side of the channel so that by 1 August the lahars were again battering the left dike. The active channel maintained this course as of early September.

The passage of Typhoon Ritang on 6-7 August did not bring much rain over the Pinatubo area. However, the lahars generated filled the Pasig-Potrero River from the Delta 5 watchpoint (figure 32) to barangay Mancatian, and caused additional deposition at the alluvial fan area. In-channel aggradation left only a few meters of freeboard along some of the channel and lahars overflowed at the left bank, near the base of Delta 5. The overflowing lahar buried part of an old fan area between Pasig-Potrero River and Sapang Ebus (Taug River) with 0.2-2.0 m of debris. The overflow started on the afternoon of 6 August. The Typhoon Ritang lahars that were conveyed all the way down to the alluvial fan reaches had observed discharges of 60-300 m3/s upon reaching Mancatian. These laminar lahars further aggraded the Cotod and Potrero area by 50-100 cm.

Figure (see Caption) Figure 32. Pinatubo lahar deposit map between the Pasig-Potrero River and Sapang Ebus, 17 August 1994. Courtesy of PHIVOLCS.

After Typhon Ritang and beginning on 8 August, lahars continuously flowed in the Pasig-Potrero River. These non-streaming hyperconcentrated streamflow lahars had an average discharge of 6 m3/s at Delta 5 and 3 m3/s at Mancatian. It is suspected that these lahars were triggered by the breaching of a lake, because no rainfall was recorded by the Upper Sacobia rain gage during 8-16 August. Lahars with the same characteristics were observed in 1991 and 1992 during the release of water from lakes formed on the pyroclastic-flow field by the damming of tributaries with lahar and secondary pyroclastic-flow deposits.

On 16 August, shortly after a large secondary explosion and possibly a secondary pyroclastic flow on the Sacobia pyroclastic-flow field, lahars in the Pasig-Potrero River suddenly ceased and the river became dry. Debris from the secondary pyroclastic flow might have temporarily dammed the river because continuous lahars resumed on 20 August. Aerial surveys on 19 and 30 August revealed several lakes, the biggest of which was in the same location as the 1992 lake. A breach on the outer left dike ~500 m downstream of the Angeles-Porac road allowed these continuous non-rainfall lahars to be delivered and deposited at the alluvial fan area outside of the dike. The accumulation of sediment caused extensive damage outside of the left dike from Barangay Manibaug-Pasig down to Barangay San Antonio in Bacolor, Pampanga.

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

Information Contacts: R. Arboleda and M. Matinez, PHIVOLCS.


Popocatepetl (Mexico) — August 1994 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Seismicity moderate, but distinct plume and very high SO2 flux

As usual, seismicity during July and August consisted primarily of B-type events (figure 3). During these two months, B-type events were recorded more frequently than during much of January-March and less frequently than during much of May. Type-A, -AB, and -B seismic events at Popocatépetl were defined in 19:1.

Guillermo González-Pomposo and Carlos Valdés-González noted that when B-type seismicity increased in July and August, A- and AB-type seismicity declined. Both A- and AB-type seismicity remained at 0-1 events/day for July-August, except for two days when one or the other type reached 2 events/day. Overall, during July type-A events took place 4 times, type-B events 150 times, and type-AB events 6 times. During August type-A events took place 5 times, type-B events 165 times, and type-AB events 6 times.

In contrast with the moderate levels of seismicity seen in July and August, early July ultraviolet absorption correlation spectrometry (COSPEC) measurements made by ASU and UNAM researchers indicated a prodigious SO2 flux: a minimum of 575 metric tons/day (t/d) and an estimated "true flux" of 2,700-3,500 t/d. Their report on the 5,420-m-high volcano follows.

"We were able to make a driven traverse [using an automobile] of the plume of Popocatépetl on 1 July, 1994. The data showed an SO2 flux of 575 t/d, if a standard wind velocity of 1 m/s was assumed; this must be considered as the absolute minimum. Our best estimate of the true wind velocity was based on the National Airport measurements at 5 km above sea level (on 2 July) of 5 m/s. Therefore, our best estimate of the true flux was 2,900 t/d. An estimate of the uncertainty in this flux is complicated by measurements made on 2 July using the Trimble GPS (Global Positioning System) instrument on board the chartered aircraft. One aircraft traverse, at the crater level, suggested a wind velocity of ~30 m/s. So, we are reporting what seems to be a minimum realistic SO2 flux.

"At ~0900 on 1 July, the sky was relatively clear and the plume was visibly blowing to the SW. It appeared to rise a few hundred meters above the crater, before being blown by the wind. The white, cloudy plume remained visible for tens of kilometers, perhaps a hundred kilometers. By the time we were on the road that passes around the W margin of the base of Popocatépetl and Iztaccíhuatl, the cloud cover became sufficient to block any certain view of the plume. At 1700 in the afternoon, however, we were in the saddle between Popocatépetl and Iztaccíhuatl and had another very clear view of the plume. Its appearance then was similar to the way it had looked before, suggesting approximate stability for intervals of hours and days. Using the standard approach (Stoiber and others, 1983), we mounted the COSPEC on the passenger seat of the van, with the telescope looking vertically, and drove at roughly constant velocity (~30-40 km/hr). The traverse was more than 40 km in total length, with its center being at a point approximately straight W of the volcano's crater. Good maps facilitated geometrical corrections to allow for portions of the traverse not normal to the plume's axis.

"The airplane traverses made on 2 July used a plane flown by Sergio Zambrano who used his on-board GPS instrument to minimize all of the usual uncertainties concerning location, aircraft velocity, length of traverse, and angle between the traverse and the plume axis. However, the one measurement that we did not recognize adequately while airborne was the ability to realistically estimate wind velocity at the elevation of the plume, as it was dispersed. The five traverses gave extremely repeatable graphs [on the strip chart records] and the estimated flux was 3,100 ± 400 t/d (using the 5 m/s wind velocity measurement from the National Airport). Because we failed to recognize the possibility of using the GPS instrument for measuring the wind velocity we cannot accept the one [~30 km/hr] measurement as well constrained. If it were true, then the SO2 flux was enormous.

"Our measurements of SO2, by two different COSPEC methods on two different days, were remarkably similar. The plume looked very homogeneous, when we were able to see it on these two days. The increase in SO2 flux since measured by T. Fisher and others by aircraft on 1 February 1994 (1,200 ± 400 t/d) is very difficult to escape [19:1]. An increased gas flux is also consistent with the visual impression of H. Delgado upon climbing to the crater rim in August, that the gas emissions were greater with more loud sounds from the fumaroles within the crater."

Although the reported SO2 flux is strikingly large for a volcano not in eruption, it is too small to confirm with the satellite-borne TOMS, which detects masses of SO2 greater than about 5 kilotons (Bluth and others, 1992). Popocatépetl looms over the México and Puebla valleys, potentially threatening over 20 million people.

References. Bluth, G.J.S., Doiron, S.D., Schnetzler, C.C., Krueger, A.J., and Walter, L.S., 1992, Global tracking of the SO2 clouds from the June, 1991 Mount Pinatubo eruptions: Geophysical Research Letters, v. 19, no. 2, p. 151-154.

Stoiber, R.E., Malinconico, Jr., L.L., and Williams, S.N., 1983, Use of the correlation spectrometer at volcanoes, in Forecasting Volcanic Events, H. Tazieff and J.C. Sabroux (eds.): Elsevier, New York, p. 425-444.

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: Departamento de Sismología y Volcanología, Instituto de Geofísica, UNAM; Stanley N. Williams and Tobias Fisher, Arizona State Univ, USA; Claus Siebe and Hugo Delgado, Instituto de Geofísica, UNAM, Circuito Exterior. 1 Also at Benemérita Univ Autónoma de Puebla, México.


Rabaul (Papua New Guinea) — August 1994 Citation iconCite this Report

Rabaul

Papua New Guinea

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

All times are local (unless otherwise noted)


Major eruption sends plume to 18 km and covers Rabaul town with ash

Vulcan and Tavurvur, two vents on opposite sides of Rabaul Caldera (figures 15 and 12), erupted on the morning of 19 September and sent ash as high as 18 km asl. This caldera forms a sheltered harbor whose N end is occupied by Rabaul, New Britain's largest city. The report of August seismicity was sent from RVO on 9 September. Satellite interpretations are courtesy of NOAA, with TOMS data from the NASA Goddard Space Flight Center. Although communication with Rabaul was cut off for many days, RVO reports were received for 23 and 27 September. Information based on reports from local and international news services is noted, and may not be accurate.

Figure (see Caption) Figure 15. NW tip of the Gazelle Peninsula, New Britain Island, papua New Guinea, showing the road network (dashed lines), towns (dots), and volcanic centers (triangles). Modified from McKee and others, 1985.
Figure (see Caption) Figure 12. Map of the Rabaul Caldera showing recently active volcanic vents and extinct composite cones (modified from Almond and McKee, 1982). [copy from 18:03]

August seismicity. The total number of detected events for August was 448 . . . . The month was quiet until 25-28 August when 227 earthquakes were detected, with more than half of them on the 26th. Unusually for Rabaul, these earthquakes tended to be discrete events not occurring in swarms. Only 34 of the August events were located, 25 of them during 25-28 August. Most located earthquakes were along the ring fault near Tavurvur, or offshore to the S and SW; 17 hypocenters had location errors ofL 2.6, but none of the earthquakes were felt. On 28 August, the caldera network recorded what appeared to be a low-frequency earthquake. Signals with a dominant frequency of ~1 Hz recorded on some of the inner network stations were very complicated with no clear phase arrivals or onsets. These signals probably originated close to the Matupit Island seismometer. No seismicity was recorded after 29 August.

Seismic precursors, 18-19 September. RVO reported that at 0300 on 18 September, a M 5.1 earthquake occurred beneath the harbor. An aftershock sequence from this event merged into an intensifying swarm of high-frequency (A-type) earthquakes. Peak intensity of this swarm occurred around 2400 that night with ~2 felt events/minute, but then tapered off slightly toward morning. By 0600 on 19 September the eruption had begun. Thus, only 27 hours of unusual seismicity preceded the eruption. Inspection of the seismograms since the onset of the eruption revealed several long-period events in the 12 hours prior to the M 5.1 earthquake.

Initial eruptive activity, 19 September. Tavurvur began erupting around 0600 on 19 September, followed by an explosion from Vulcan ~1-1.5 hours later. RVO volcanologist Patrice de Saint-Ours was quoted in press reports that day as stating that the pattern of eruptions was very similar to 1937, and that the vents were no longer visible from the observatory because of the ash cloud, estimated by ground observers to be >3 km high. Most press reports described thick mushroom-shaped pulses of ash rising from the vents, hot ash falling near the vents, and loud explosion noises. Aerial video footage showed vigorous, thick, light-brown ash columns, and the surface of the harbor covered with ash and floating pumice. Other press reports on 19 September stated that Rabaul town was covered with 20-25 cm of ash, and that thunderstorms mixed rain with the ash, forming a heavy mud that damaged buildings and vegetation. The press reports also described columns of gray ash rising thousands of meters into the air, ejecta as large as trucks, and "black muddy rain." Ash fell across New Britain and New Ireland.

A pilot report received at Port Moresby at 1034 placed the top of the volcanic ash cloud between 15 and 18 km altitude. A later pilot report noted the presence of drifting ash ~185 km SW of Rabaul well above 6 km altitude. GMS satellite imagery as late as 2132 on 19 September revealed an obvious plume fanning out to the S through WNW. The W part of the plume was tracking W and WNW at ~110 km/hour, and had moved across central Papua New Guinea; plume height was estimated to be 21-30 km, well into the stratosphere. The S part of the plume, at an altitude of 12-18 km, had begun to move SE at ~55 km/hour around an upper tropospheric ridge. A satellite infrared image taken a few hours earlier, at 1800 on the 19th (figure 16), showed similar plume morphology. Initial estimates of plume height during the first two days of activity were between 18 and 30 km. Space Shuttle astronauts who observed and photographed the plume (figure 17) estimated its height as at least 18 km based on altitudes of storm clouds in the area.

Figure (see Caption) Figure 16. Infrared satellite image of the ash plume from Rabaul, 1800 on 19 September 1994, about 12 hours after the start of the eruption. Courtesy of George Stephens, NOAA/NESDIS.
Figure (see Caption) Figure 17. Photograph of plumes from Rabaul taken by Space Shuttle astronauts roughly 24 hours after the start of the 19 September 1994 eruption. Oblique view is to the SW. The cloud-covered island in the foreground is New Ireland, and the papua New Guinea mainland is in the distance. The eruption column rose to 18 km where it flattened out and was blown W in a fan-shaped plume. A layer of yellow-brown ash was blown towards the N by lower level winds. NASA photograph STS064-116-064, courtesy of Cindy Evans.

Eruptive activity, 20-23 September. Video of the eruption, taken from a helicopter about 1.5 days after its start, showed massive, gray-to-black ash columns billowing vigorously from Vulcan and Tavurvur. The maximum height of the cloud was reported by the press to be ~20 km, with blocks as big as cars falling into the harbor. Black ash appeared to be falling over a wide area and scenes from Rabaul town showed buildings and vegetation blanketed by ash.

Night winds on 19 September, which were generally blowing NNE-NE (taking the ash over New Ireland), changed direction at dawn on the 20th and started blowing N-NNW, and as the afternoon progressed the winds became more westerly. By 1532 on 20 September the plume had narrowed compared to previous GMS satellite images and the core was moving WSW at ~55 km/hour at an altitude of ~12 km. As night fell on 20 September the cloud had reached the main island of Papua New Guinea between Lae and Milne Bay; residents in the town of Lae, 600 km away, reported ashfall.

On 21 September, witnesses said huge mushroom clouds of dense, black smoke and debris continued to rise high above Tavurvur and Vulcan. Much of the falling ash combined with rain, turning to a heavy mud mixture that demolished some houses and destroyed coconut plantations. The airport was buried under debris, many roads were blocked, and the harbor was covered with debris and floating pumice.

The plume was still moving WSW at 1832 on 21 September at ~7.5 km altitude, and was visible for up to 90 km SW of the origin. Soon after this time the plume was no longer clearly visible on GMS imagery, indicating that strong explosive activity, which had ejected ash high into the atmosphere almost continuously since about 0600 on 19 September, had declined. Some residents returned to Rabaul town during a brief respite from the falling ash. However, by the morning of 22 September Vulcan was ejecting massive amounts of whitish ash and Tavurvur was emitting dark blackish-gray ash. GMS satellite imagery for 1230 on 22 September revealed a new mid-high level plume that was ~40 km long and moving WSW. The plume was estimated to be at ~7.5 km altitude, and could still be seen at 1530 on GMS infrared images.

A report from RVO for the period from 1500 on 22 September through 0900 the next day indicated that volcanic and seismic activity remained relatively stable. Steady emissions continued from Tavurvur with a dark gray ash-and-vapor cloud rising ~2 km and blowing NE over Rabaul town. Low rumbling sounds accompanied the stronger emissions. At night, incandescent ejecta could be seen falling on the NW flank, but incandescence was rarely visible in the eruptive column due to its high ash content. Intermittent pulses of stronger activity from Vulcan produced jets of a vapor-rich ash at intervals of 5-15 minutes. Collapse of the column generated pyroclastic surges that traveled 2-5 km from the vent, mostly to the NE. Generally there was a low volume of ash in the eruption cloud. The column height was about 1.5 km. At night witnesses saw incandescent ejecta accumulate around the vent at the beginning of each pulse.

An aerial inspection by volcanologists at 1620-1640 on 22 September revealed little morphological change at Tavurvur, with the active vent located on the W side of the 1937 crater. At Vulcan, the only active vent was near sea level on the breached NE-flank crater. Eruptions were Surtseyan, highly explosive, and vapor-rich with low ash content. No great deformation was noted since the start of the eruption. Overall, volcano-seismic activity showed a steady small decline during 20-22 September. During the inspection, visibility over Rabaul was generally very good, but there were occasional ash falls.

On the morning of 27 September, RVO reported that Vulcan was no longer erupting, but an ash plume from Tavurvur was still present, and there was an ashy haze over Rabaul town. Seismicity had decreased to about the detection limit using the RSAM averaging method. The observatory reported ~40 mm of fine powdery ash at their location, and ~50 cm of ash at the airport, with the ash-fall layer thickening rapidly towards Matupit Island. The press initially reported up to a meter of ash in Rabaul town, but later estimates were consistently around 75 cm for most areas. No accurate mapping of the ashfall has been completed. Press reports on 25 September estimated that 25% of the buildings in the greater Rabaul area had been completely destroyed, and that another 50% had significant structural damage. Preliminary damage assessments reported on 27 September by the UNDHA indicated that 40% of the buildings in the area had been seriously damaged.

Satellite-based SO2 data. The Meteor-3 satellite overflew the eruption plume . . . at 1538 on 19 September. Preliminary results from the TOMS instrument showed SO2 column amounts no higher than background and a slight column ozone increase in the region that was most likely due to the presence of SO2. Another pass at 1520 on 20 September showed an SO2 plume of ~45,000 km2, with an SO2 mass estimated at a maximum of 80 kilotons (kt) ± 50%. At 1503 the next day, preliminary results showed that the estimated size of the SO2 plume was 50,000 km2, with an SO2 mass estimated at 70 kt ± 50%. The SO2 detected on 21 September had probably been produced since the overflight on the previous day because the small tropospheric plume noted at that time would have either dispersed or been chemically converted within 24 hours. Preliminary data from the overflight at 1430 on 23 September showed an estimated size of at least 40,000 km2 for the SO2 plume, with an estimated SO2 mass of 35 kt ± 50%. By 1410 on 24 September, SO2 column amounts were no higher than background levels in the vicinity of the volcano.

Evacuations and official response. On the night of 18-19 September, during the period of strong continuous seismicity, an estimated 30,000 people evacuated from Rabaul town and surrounding villages. Apparently, most of the people left before the eruptions began, but evacuations by road and sea to the towns of Kokopo (20 km SE) and Kerevat (~25 km SW), continued on 19 September. The airport closed just as Tavurvur began erupting. Evacuees went to missions and townships along the Gazelle Peninsula, where they were housed in camps, schools, church halls, and hospitals. Authorities were preparing to provide food and shelter for up to 70,000 people.

Ships rescued thousands of villagers off beaches near Rabaul town on 20 September. Press reports indicated that although Rabaul town was totally evacuated, there were small villages in the surrounding hills where people were trapped and taking shelter in schools and churches. As of 21 September, 45,000 people had been displaced, of whom 25,000 were located in Kokopo and the remainder at Kerevat and nearby mission and government stations. By 23 September, the UNDHA reported that a total of 53,000 people had been displaced. The only reported casualties were one boy killed when he was hit by a truck during the evacuation, and one man struck by lightning.

Following the declaration of a state of emergency in Rabaul, the Prime Minister of Papua New Guinea made a helicopter inspection on the afternoon of 19 September. NOTAMs issued from the Port Moresby Flight Information Region on 19-20 September advised pilots to exercise caution and informed them that the airspace within a 110 km radius of the Rabaul airport was closed to all air traffic unless authorized by emergency management officials. A NOTAM on the 22nd advised aircraft to avoid an abnormally colored cloud, especially yellow-brown or grayish layers. It further stated that the ash particles could contaminate engine oil and cause engine deterioration within hours. The duty manager of Air Niugini (national airline of Papua New Guinea) said all flights to and from New Britain and New Ireland provinces had been suspended. Relief flights were using an abandoned airstrip at Tokua (~20 km SE of Rabaul), which had received no ashfall.

Looting in Rabaul town was reported during both the evacuation and on 21 September, when military forces were brought in to help local police. News reports frequently mentioned looting by residents who had not evacuated or by non-residents going into the evacuated area. By the evening of 21 September, the army had sealed off all outlying roads and only allowed entry by authorized personnel.

At the request of the Papua New Guinea government, the USGS Volcano Disaster Assistance Program sent three volcanologists to Rabaul on 28 September. They took telemetered seismic stations with a PC-based data acquisition and analysis system, several telemetered tiltmeters, and other deformation-monitoring instrumentation. This equipment was requested because RVO was unable to locate earthquakes with only three seismic stations remaining in operation. The other stations were incapacitated by tsunamis, vandalism, or heavy ashfall.

References. Almond, R.A., and McKee, C.O., 1982, Location of volcano-tectonic earthquakes within the Rabaul Caldera: Geological Survey of Papua New Guinea report 82/19.

McKee, C.O., Johnson, R.W., Lowenstein, P.L., Riley, S.J., Blong, R.J., de Saint-Ours, P., and Talai, B., 1985, Rabaul caldera, Papua New Guinea: volcanic hazards, surveillance, and eruption contingency planning: Journal of Volcanology and Geothermal Research, v. 23, p. 195-237.

Mori, J., McKee, C., Itikarai, I., Lowenstein, P., de Saint-Ours, P., and Talai, B., 1989, Earthquakes of the Rabaul Seismo-Deformational Crisis September 1983 to July 1985: Seismicity on a caldera ring fault: IAVCEI Proceedings in Volcanology 1, J.H. Latter (ed.), Volcanic Hazards: Assessment and Monitoring, p. 429-462.

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

Information Contacts: C. McKee, R. Stewart, and I. Itikarai, RVO; J. Lynch, SAB; G. Stephens, NOAA/NESDIS; I. Sprod, GSFC; C. Evans, NASA-SSEOP; G. Wheller, Volcanex International Pty Ltd, Tasmania; Kevin Vang, Macquarie Univ, Sydney; ICAO; UNDHA; AP; UPI; Reuters; Papua New Guinea Post-Courier.


Sheveluch (Russia) — August 1994 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Normal fumarolic activity and seismicity

Weak shallow seismic activity (1-4 events/day) continued to be registered beneath the volcano throughout July and August. Average duration of volcanic tremor was less than 30 minutes/day. The gas-and-steam plume (up to 500 m above the extrusive dome) observed during 7-14 July was blown E for about 30 km. Clouds frequently prevented observations in July and early August. Normal fumarolic activity was observed above the extrusive dome during mid-August. In late August and early September a gas-and-steam plume was observed up to ~3 km above the extrusive dome. Shallow seismicity remained at normal levels (1-5 events/day) through 12 September, with an average of 0.3 hours of tremor/day.

A strong eruption in April 1993 has been followed by a plume visible during clear weather (18:4-8 & 10-12, and 19:1-4 & 6). Prior to that eruption, the most recent explosive activity was in April 1991 (16:3). The largest historical eruptions from Shiveluch occurred in 1854 and 1964.

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: V. Kirianov, IVGG.


Soputan (Indonesia) — August 1994 Citation iconCite this Report

Soputan

Indonesia

1.112°N, 124.737°E; summit elev. 1785 m

All times are local (unless otherwise noted)


Lava dome and fumarole descriptions

The EVS mounted an expedition to visit N Sulawesi volcanoes in July. They found that the morphology of Soputan's lava dome suggested continued endogenous growth. Some other parts of their Soputan report follow.

"Many fumaroles rose in different parts of the dome, mainly in its central part and in the space between the dome's foot and the crater wall. The summit area of the dome was strewn with chaotic blocks covered by white and yellow sulfur deposits. Two other fumarolic fields were located on the SW and W parts of the lava dome. Temperature measurements showed a maximum of 140°C; gases mainly consisted of H2S, SO2, and CO2."

Geologic Background. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano is located SW of Riendengan-Sempu, which some workers have included with Soputan and Manimporok (3.5 km ESE) as a volcanic complex. It was constructed at the southern end of a SSW-NNE trending line of vents. During historical time the locus of eruptions has included both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Information Contacts: H. Gaudru, C. Pittet, M. Auber, C. Bopp, and O. Saudan, EVS, Switzerland.


Ulawun (Papua New Guinea) — August 1994 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


Low-frequency seismicity

"Seismic activity in August continued the pattern of previous months, with mainly sub-continuous low-frequency tremor and occasional larger low-frequency earthquakes. No high-frequency earthquakes were recorded."

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

Information Contacts: I. Itikarai, R. Stewart, and C. McKee, RVO.


Unzendake (Japan) — August 1994 Citation iconCite this Report

Unzendake

Japan

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

All times are local (unless otherwise noted)


Slow endogenous growth of the lava dome; pyroclastic flows continue

The lava dome grew endogenously SE to SW during mid- to late-August. The S ridge on the dome top 0moved S by ~1 m/day and rose vertically by ~0.5 m/day; the central ridge decreased in height. Crest-line measurements from 3.5 km SE of the dome confirmed the endogenous growth. EDM measurements by the JMA in cooperation with the GSJ were hampered by poor weather conditions and volcanic ash. The eruption (magmatic extrusion) rate remained at a low level. The GSJ calculated the average eruption rate from early-April to mid-July as 60,000 m3/day, based on aerial photographs. This value is similar to those for February-April, although no values for the calculation error were given.

The N and S parts of the presently growing dome had no room for talus deposition (figure 75). Therefore, the advancing dome easily triggered rockfalls in both directions that moved straight downward as pyroclastic flows. Most parts of lobe 13 collapsed during 15-29 August, generating pyroclastic flows to the SW, S, and SE, which reached the Akamatsu valley. Pyroclastic flows detected seismically at a station ~1 km WSW of the dome totaled 264 during August. Real-time monitoring of pyroclastic flows is also conducted at the UWS using four sets of visible and thermal-infrared video cameras. In late August, JMA recorded the second largest daily number of pyroclastic flows since 20 May 1991, based on signals registered at the seismic station SW of the dome. This large number of events reflected smaller distances between pyroclastic flow routes and the seismic station than was previously the case.

Figure (see Caption) Figure 75. Sketch map of the lava dome at Unzen, late August 1994. Solid dome rock is shown as black. Arrows indicate the main direction of pyroclastic flows and rockfalls. Solid and dashed lines represent slope dip directions of new and old talus deposits, respectively. Volcanic gas emission points are shown by "f" symbols. Courtesy of S. Nakada, Kyushu Univ.

On the nights of 15 and 16 August, pyroclastic flows descended SE ~400 m through a deep gully, which developed during rainy seasons at the S margin of the Akamatsu valley floor. Field inspection on 24 August showed that the 15-16 products were block-and-ash-flow deposits consisting of multiple layers each ~2 m thick. The deposits included still-hot lava blocks up to 3 m across in an ash matrix, and were covered with an ashfall layer ~10 cm thick. No associated surge deposits were evident. Gently sloped depressions ~2 m across, indicating underlying fumarolic pipes, were found on the surface of the 15-16 August deposits. The depression surfaces were reddish to yellowish brown, and lava pebbles (3. Density has increased roughly with time during this eruption (1.8 to 2.5 g/cm3); there has been a roughly negative correlation between density of lava blocks and eruption rate. The SiO2 contents of new samples were 64.7-65.1 wt.%, remaining roughly constant with previous lavas (63.5-65.5%). These results indicate that the vesicularity (porosity) of lava blocks probably decreased with time.

Pyroclastic flows moving SW passed through a gully in the S slope of the dome, crossed the Akamatsu valley floor, and came against the N wall of Mt. Iwatoko, generating frequent ash clouds. A pyroclastic flow late on 27 August traveled 2.0 km SE and produced a signal that lasted for almost 30 minutes, the longest duration since pyroclastic flows began in May 1991. Many pyroclastic flows in the last 10 days of the month had long durations, but all were considered to be triggered by small-scale collapses. On 29 August, pyroclastic flows again moved SE through the gully in the Akamatsu valley; the horizontal travel distance was ~3 km from the source. The volume of the largest pyroclastic-flow deposits during this period was estimated to be ~100,000 m3.

Microearthquakes beneath the lava dome were registered at a rate of ~50/day during the first half of August, and gradually increased in number later in the month. On 28 August, 474 earthquakes were detected at a seismic station 3.6 km SW of the dome. In total, 7,306 earthquakes were registered during August.

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

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

Atmospheric Effects

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

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

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements

Additional Reports

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

Kermadec Islands


Floating Pumice (Kermadec Islands)

1986 Submarine Explosion


Tonga Islands


Floating Pumice (Tonga)


Fiji Islands


Floating Pumice (Fiji)


Andaman Islands


False Report of Andaman Islands Eruptions


Sangihe Islands


1968 Northern Celebes Earthquake


Southeast Asia


Pumice Raft (South China Sea)

Land Subsidence near Ham Rong


Ryukyu Islands and Kyushu


Pumice Rafts (Ryukyu Islands)


Izu, Volcano, and Mariana Islands


Acoustic Signals in 1996 from Unknown Source

Acoustic Signals in 1999-2000 from Unknown Source


Kuril Islands


Possible 1988 Eruption Plume


Aleutian Islands


Possible 1986 Eruption Plume


Mexico


False Report of New Volcano


Nicaragua


Apoyo


Colombia


La Lorenza Mud Volcano


Pacific Ocean (Chilean Islands)


False Report of Submarine Volcanism


Central Chile and Argentina


Estero de Parraguirre


West Indies


Mid-Cayman Spreading Center


Atlantic Ocean (northern)


Northern Reykjanes Ridge


Azores


Azores-Gibraltar Fracture Zone


Antarctica and South Sandwich Islands


Jun Jaegyu

East Scotia Ridge


Additional Reports (database)

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

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

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

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

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

UFO adherent claims new volcano in Sea of Marmara

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

Fumaroles and minor seismicity since October 2002

12/2005 (BGVN 30:12) Elgon

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



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

False Report of Mount Pinokis Eruption

Philippines

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

All times are local (unless otherwise noted)


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

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

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

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

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

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

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

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

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

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


False Report of Somalia Eruption (Somalia) — December 1997

False Report of Somalia Eruption

Somalia

3.25°N, 41.667°E; summit elev. 500 m

All times are local (unless otherwise noted)


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

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

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

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

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


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

False Report of Sea of Marmara Eruption

Turkey

40.683°N, 29.1°E; summit elev. 0 m

All times are local (unless otherwise noted)


UFO adherent claims new volcano in Sea of Marmara

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Information Contacts: Erol Erkmen, Tuvpo Project Alp.


Har-Togoo (Mongolia) — May 2003

Har-Togoo

Mongolia

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

All times are local (unless otherwise noted)


Fumaroles and minor seismicity since October 2002

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


Elgon (Uganda) — December 2005

Elgon

Uganda

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

All times are local (unless otherwise noted)


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

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

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

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

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

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

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

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