******************************************************* SI/USGS Weekly Volcanic Activity Report 24-30 September 2008 ******************************************************* Sally Kuhn Sennert - Weekly Report Editor kuhns@xxxxxx URL: http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Garbuna Group, New Britain (SW Pacific) | Piton de la Fournaise, Reunion Island | Sangay, Ecuador Ongoing Activity: | Akan, Hokkaido (Japan) | Arenal, Costa Rica | Chaitén, Southern Chile | Dukono, Halmahera (Indonesia) | Fuego, Guatemala | Karymsky, Eastern Kamchatka | Kilauea, Hawaii (USA) | Rabaul, New Britain (SW Pacific) | Santa María, Guatemala | Shiveluch, Central Kamchatka (Russia) | Soufrière Hills, Montserrat | Suwanose-jima, Ryukyu Islands (Japan) | Turrialba, Costa Rica | Ubinas, Perú The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazards Program. Updated by 2300 UTC every Wednesday, notices of volcanic activity posted on these pages are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth's volcanoes erupting during the week, but rather a summary of activity at volcanoes that meet criteria discussed in detail in the "Criteria and Disclaimers" section. Carefully reviewed, detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism Network. Note: Many news agencies do not archive the articles they post on the Internet, and therefore the links to some sources may not be active. To obtain information about the cited articles that are no longer available on the Internet contact the source. New Activity/Unrest GARBUNA GROUP New Britain (SW Pacific) 5.45°S, 150.03°E; summit elev. 564 m RVO reported that ash emissions from Garbuna started on 23 September and continued through 1 October. Ash plumes rose to an approximate altitude of 1.6 km (5,200 ft) a.s.l. and drifted NW. Geologic Summary. The basaltic-to-dacitic Garbuna volcano group consists of three volcanic peaks, Krummel, Garbuna, and Welcker. They are located along a 7-km N-S line above a shield-like foundation at the southern end of the Willaumez Peninsula. The central and lower peaks of the centrally located 564-m-high Garbuna volcano contain a large vegetation-free area that is probably the most extensive thermal field in Papua New Guinea. A prominent lava dome and blocky lava flow in the center of thermal area have resisted destruction by thermal activity, and may be of Holocene age. Krummel volcano at the S end of the group contains a summit crater, breached to the NW. The highest peak of the Garbuna group is 1,005-m-high Welcker volcano, which has fed blocky lava flows that extend to the eastern coast of the peninsula. Source: Herman Patia and Steve Saunders, Rabaul Volcano Observatory (RVO) PITON DE LA FOURNAISE Reunion Island 21.231°S, 55.713°E; summit elev. 2632 m OVPDLF reported that during 24-30 September, lava flows from Piton de la Fournaise continued to pond at the bottom of Dolomieu crater. The lava flows issued from a fissure about halfway up the W wall of the crater. Based on air photos acquired on 25 September, the lava flow was an estimated 180 m long by 100 m wide and about 30 m deep. The erupted volume was about 300,000 cubic meters. On 26 September, lava fountaining from the fissure was no longer visible, but bubbling lava in the cone was noted. Geologic Summary. Massive Piton de la Fournaise shield volcano on the island of Réunion is one of the world's most active volcanoes. Most historical eruptions have originated from the summit and flanks of a 400-m-high lava shield, Dolomieu, that has grown within the youngest of three large calderas. This depression is 8 km wide and is breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows within the caldera, have been documented since the 17th century. The volcano is monitored by the Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris. Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) http://ovpf.univ-reunion.fr/ SANGAY Ecuador 2.002°S, 78.341°W; summit elev. 5230 m Based on analysis of satellite imagery, information from the Guayaquil MWO, and pilot reports, the Washington VAAC reported that a minor ash plume rose from Sangay on 24 September and drifted WNW. Geologic Summary. The isolated Sangay volcano, located E of the Andean crest, is the southernmost of Ecuador's volcanoes, and its most active. It has been in frequent eruption for the past several centuries. The steep-sided, 5,230-m-high glacier-covered volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the E, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. Sangay towers above the tropical jungle on the E side; on the other sides flat plains of ash from the volcano have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The more or less constant eruptive activity has caused frequent changes to the morphology of the summit crater complex. Source: Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html Ongoing Activity AKAN Hokkaido (Japan) 43.384°N, 144.013°E; summit elev. 1499 m Seismic tremor from the Akan volcanic complex that lasted for four minutes on 29 September prompted JMA to raise the Alert Level from 1 to 2 (using a 1-5 scale). The number of earthquakes had increased since 26 September. A white plume rose less than 100 m above the Me-Akan volcano group. Geologic Summary. Akan is a 13 x 24 km, elongated caldera that formed more than 31,500 years ago immediately SW of Kutcharo caldera. Growth of four post-caldera stratovolcanoes, three at the SW end of the caldera and the other at the NE side, has restricted the size of the caldera lake. The 1-km-wide Nakamachineshiri crater was formed during a major pumice-and-scoria eruption about 13,500 years ago. Of the Holocene volcanoes of the Akan volcanic complex, only the Me-Akan group, E of Lake Akan, has been historically active, producing mild phreatic eruptions since the beginning of the 19th century. Me-Akan is composed of 9 overlapping cones. The main cone of Me-Akan proper has a triple crater at its summit. Historical eruptions at Me-Akan have consisted of minor phreatic explosions, but four major magmatic eruptions including pyroclastic flows have occurred during the Holocene. Source: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/indexe.html ARENAL Costa Rica 10.463°N, 84.703°W; summit elev. 1670 m OVSICORI-UNA reported that changes in morphology and the health of vegetation at Arenal were documented during approximately 14-20 September. Fine ashfall produced at the summit by an active lava flow impacted and burned vegetation along the upper and lower E and NE flanks. The impact on the vegetation was more severe near the summit. By mid September, additional material moving down the SW flank had filled the 6 June collapse scar and built an 800-m-high levee. Occasional incandescent blocks roll down the top of the levee. Material accumulated on both sides of the levee and at the distal end, creating a 200-m-wide fan. A mass of material also accumulated at the SW edge of the summit, causing blocks to occasionally roll down the N flank. Geologic Summary. Conical Volcan Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1,657-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. The earliest known eruptions of Arenal took place about 7,000 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. Arenal's most recent eruptive period began with a major explosive eruption in 1968. Continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows has occurred since then from vents at the summit and on the upper western flank. Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA) http://www.ovsicori.una.ac.cr/ CHAITEN Southern Chile 42.833°S, 72.646°W; summit elev. 1122 m Based on web camera views and analysis of satellite imagery, the Buenos Aires VAAC reported that during 25-30 September continuous ash plumes rose to altitudes of 2.1-2.7 km (7,000-9,000 ft) a.s.l. and drifted E, ESE, and SE. A thermal anomaly over the lava dome was detected by satellite imagery during 25-27 September. On 26 September, SERNAGEOMIN reported that Chaitén continued to produce two gas-and-ash plumes that rose to altitudes of 2.6-3.1 km (8,500-10,200 ft) a.s.l. and drifted NE. Geologic Summary. Chaitén is a small, glacier-free caldera with a Holocene lava dome located 10 km NE of the town of Chaitén on the Gulf of Corcovado. A pyroclastic-surge and pumice deposit considered to originate from the eruption that formed the elliptical 2.5 x 4 km wide summit caldera was dated at about 9400 years ago. A rhyolitic, 962-m-high obsidian lava dome occupies much of the caldera floor. Obsidian cobbles from this dome found in the Blanco River are the source of prehistorical artifacts from archaeological sites along the Pacific coast as far as 400 km away from the volcano to the north and south. The caldera is breached on the SW side by a river that drains to the bay of Chaitén, and the high point on its southern rim reaches 1122 m. Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN) http://www.sernageomin.cl/index.php, Buenos Aires Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html DUKONO Halmahera (Indonesia) 1.68°N, 127.88°E; summit elev. 1335 m Based on analysis of satellite imagery, the Darwin VAAC reported that on 24 September a low-level ash plume from Dukono rose to an altitude of 1.8 km (6,000 ft) a.s.l. and drifted NE. Geologic Summary. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the N-flank cone of Gunung Mamuya. Dukono is a complex volcano presenting a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of Dukono's summit crater complex, contains a 700 x 570 m crater that has also been active during historical time. Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html FUEGO Guatemala 14.473°N, 90.880°W; summit elev. 3763 m Based on information from the Tegucigalpa MWO, the Washington VAAC reported that on 18 September a possible ash plume from Fuego rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted SSW. INSIVUMEH reported on 24 September that a lava flow traveled 300 m W towards the Seca ravine. Avalanches were generated from the lava flow front. Explosions generated ash plumes that rose to an altitude of 4.1 km (13,500 ft) a.s.l. and drifted W. Geologic Summary. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3,763-m-high Fuego and its twin volcano to the N, Acatenango. Construction of Meseta volcano continued until the late Pleistocene or early Holocene, after which growth of the modern Fuego volcano continued the southward migration of volcanism that began at Acatenango. Frequent vigorous historical eruptions have been recorded at Fuego since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows. The last major explosive eruption from Fuego took place in 1974, producing spectacular pyroclastic flows visible from Antigua. Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/, Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html KARYMSKY Eastern Kamchatka 54.05°N, 159.45°E; summit elev. 1536 m KVERT reported that seismic activity at Karymsky was above background levels during 19-26 September. Possible daily explosions may have generated ash plumes to an altitude of 3.8 km (12,500 ft) a.s.l. Analysis of satellite imagery revealed a thermal anomaly in the crater on 18 and 23 September. The Level of Concern Color Code remained at Orange. Based on analysis of satellite imagery and information from KEMSD, the Tokyo VAAC reported that eruptions generated plumes to altitudes of 3-3.4 km (10,000-11,000 ft) a.s.l. on 24 and 28 September. Geologic Summary. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed about 7,600-7,700 radiocarbon years ago. Construction of the Karymsky stratovolcano began about 2,000 years later. The latest eruptive period began about 500 years ago, following a 2,300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been Vulcanian or Vulcanian-Strombolian with moderate explosive activity and occasional lava flows from the summit crater. Most seismicity preceding Karymsky eruptions has originated beneath Akademia Nauk caldera, which is located immediately S of Karymsky volcano and erupted simultaneously with Karymsky in 1996. Sources: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php, Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html KILAUEA Hawaii (USA) 19.421°N, 155.287°W; summit elev. 1222 m HVO reported that during 24-30 September, lava flowed SE through a tube system from underneath Kilauea's Thanksgiving Eve Breakout (TEB) and rootless shield complex, reaching the ocean entry. Explosions at the ocean entry were noted on 25 and 27 September. During the reporting period, Kilauea earthquakes were variously located beneath and to the S of the caldera, along the SW rift zone, and along the S-flank faults. Beneath Halema'uma'u crater, 40-100 small earthquakes per day (background is 20-40) also occurred but were too small to be located more precisely. The vent in Halema'uma'u crater continued to produce a predominantly white plume with minor tephra content that drifted mainly SW. Weak night-time incandescence was intermittently seen at the base of the plume. The plume was occasionally tinged brown in association with small local earthquakes. During an overflight on 26 September, HVO geologists estimated that the surface of the lava pond was about 120-140 m below the crater floor, about 20-40 m lower than the previous pond surface observed on 5 September. Geologic Summary. Kilauea, one of five coalescing volcanoes that comprise the island of Hawaii, is one of the world's most active volcanoes. Eruptions at Kilauea originate primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the caldera to the sea. About 90% of the surface of Kilauea is formed of lava flows less than about 1,100 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 sq km, destroying nearly 200 houses and adding new coastline to the island. Source: US Geological Survey Hawaiian Volcano Observatory (HVO) http://hvo.wr.usgs.gov/ RABAUL New Britain (SW Pacific) 4.271°S, 152.203°E; summit elev. 688 m RVO reported that ash plumes from Rabaul caldera's Tavurvur cone continued to be emitted during 15-29 September. Plumes drifted in multiple directions. Ashfall was reported in areas downwind, including Rabaul town (3-5 km NW), Namanula Hill (3 km W), and Kokopo (20 km SE). Flights to Tokua airport (20 km SW) were canceled on 24 September due to ashfall. During 28-29 September, ash plumes rose to altitudes of 2.7-3.2 km (8,900-10,500 ft) a.s.l. Continuous incandescence at the summit was observed and roaring noises were heard. Geologic Summary. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor. 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 E, where its floor is flooded by Blanche Bay.Two major Holocene caldera-forming eruptions at Rabaul took place as recently as 3,500 and 1,400 years ago. 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. Source: Herman Patia, Rabaul Volcano Observatory (RVO) SANTA MARIA Guatemala 14.756°N, 91.552°W; summit elev. 3772 m Based on information from the Tegucigalpa MWO, the Washington VAAC reported that on 18 September an ash plume from Caliente dome in Santa María's Santiaguito complex rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted SSW. INSIVUMEH reported on 24 September that explosions produced ash plumes that rose to altitudes of 2.8 km (9,200 ft) a.s.l. and drifted SW. Avalanches of material from the top of the lava dome descended the flank and lava flows traveled SW. Geologic Summary. Symmetrical, forest-covered Santa María volcano is one of a chain of large stratovolcanoes that rises dramatically above the Pacific coastal plain of Guatemala. The stratovolcano has a sharp-topped, conical profile that is cut on the SW flank by a large, 1-km-wide crater, which formed during a catastrophic eruption in 1902 and extends from just below the summit to the lower flank. The renowned Plinian eruption of 1902 followed a long repose period and devastated much of SW Guatemala. The large dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four westward-younging vents, accompanied by almost continuous minor explosions and periodic lava extrusion, larger explosions, pyroclastic flows, and lahars. Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/, Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html SHIVELUCH Central Kamchatka (Russia) 56.653°N, 161.360°E; summit elev. 3283 m KVERT reported that seismic activity at Shiveluch was above background levels during 19-26 September. A large number of hot avalanches may have descended the lava dome and produced ash plumes that rose to an altitude of 3.6 km (11,800 ft) a.s.l. Fumaroles on the lava dome were active on 19 September. Analysis of satellite imagery revealed a daily thermal anomaly on the lava dome. According to a news article, video cameras recorded an eruption that produced an ash plume on 26 September. The ash plume rose to an altitude of 4.5 km (14,800 ft) a.s.l. The Level of Concern Color Code remained at Orange. Geologic Summary. The high, isolated massif of Shiveluch volcano (also spelled Sheveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group and forms one of Kamchatka's largest and most active volcanoes. The currently active Molodoy Shiveluch lava-dome complex was constructed during the Holocene within a large breached caldera formed by collapse of the massive late-Pleistocene Strary Shiveluch volcano. At least 60 large eruptions of Shiveluch have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Frequent collapses of lava-dome complexes, most recently in 1964, have produced large debris avalanches whose deposits cover much of the floor of the breached caldera. During the 1990s, intermittent explosive eruptions took place from a new lava dome that began growing in 1980. The largest historical eruptions from Shiveluch occurred in 1854 and 1964. Sources: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php, Itar-Tass http://www.itar-tass.com/eng/level2.html?NewsID=13111541&PageNum=0 SOUFRIERE HILLS Montserrat 16.72°N, 62.18°W; summit elev. 915 m MVO reported that during 20-26 September, the W side of the Soufrière Hills lava dome continued to grow. Rockfalls were detected by the seismic network. The Hazard Level remained at 3. Geologic Summary. The complex dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. English's Crater, a 1-km-wide crater breached widely to the E, was formed during an eruption about 4,000 years ago in which the summit collapsed, producing a large submarine debris avalanche. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits at Soufrière Hills. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but with the exception of a 17th-century eruption that produced the Castle Peak lava dome, no historical eruptions were recorded on Montserrat until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption. Source: Montserrat Volcano Observatory (MVO) http://www.mvo.ms SUWANOSE-JIMA Ryukyu Islands (Japan) 29.635°N, 129.716°E; summit elev. 799 m Based on reports from JMA, the Tokyo VAAC reported explosions from Suwanose-jima during 25-26 and 28-29 September. Resultant plumes rose to altitudes of 1.5-3 km (5,000-10,000 ft) a.s.l. and drifted NE, E, and SW. Geologic Summary. The 8-km-long, spindle-shaped island of Suwanose-jima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. Only about 50 persons live on the sparsely populated island. The summit of the volcano is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanose-jima, one of Japan's most frequently active volcanoes, was in a state of intermittent Strombolian activity from On-take, the NE summit crater, that began in 1949 and lasted nearly a half century. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, after which the island was uninhabited for about 70 years. The SW crater produced lava flows that reached the western coast in 1813, and lava flows reached the eastern coast of the island in 1884. Source: Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html TURRIALBA Costa Rica 10.025°N, 83.767°W; summit elev. 3340 m OVSICORI-UNA reported that fieldwork on 23 September revealed severely impacted vegetation on Turrialba's flanks and inner caldera in areas only mildly affected during the previous three years of sustained degassing. Vegetation in the S and SE summit areas was severely burned and infrastructure was impacted during August and September. Along the flank, S of the W crater, plants were burned down to the soil. Trees in lower-altitude areas were yellowed and seared due to extreme acidification. Pastures and areas along canyons and depressions were also affected. OVSICORI-UNA recommended that precautions should be taken when carrying out activities in the affected areas. Geologic Summary. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive 3340-m-high Turrialba is exceeded in height only by Irazú, covers an area of 500 sq km, and is one of Costa Rica's most voluminous volcanoes. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m wide summit depression that is breached to the NE. Most activity at Turrialba originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred at Turrialba during the past 3500 years. Turrialba has been quiescent since a series of explosive eruptions during the 19th century that were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters. Source: Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) http://www.ovsicori.una.ac.cr/ UBINAS Perú 16.355°S, 70.903°W; summit elev. 5672 m Based on SIGMET reports, the Buenos Aires VAAC reported that on 30 September ash plumes from Ubinas rose to altitudes of 5.5-8.8 km (18,000-29,000 ft) a.s.l. and drifted SSE. Geologic Summary. A small, 1.2-km-wide caldera that cuts the top of Ubinas, Peru's most active volcano, gives it a truncated appearance. Ubinas is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front of Peru. The upper slopes of the stratovolcano, composed primarily of Pleistocene andesitic lava flows, steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank of Ubinas extend 10 km from the volcano. Widespread Plinian pumice-fall deposits from Ubinas include some of Holocene age. Holocene lava flows are visible on the volcano's flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor explosive eruptions. Source: Buenos Aires Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html +++++++++++++++++++++++++++++++++++++ Sally Kuhn Sennert SI/USGS Weekly Volcanic Activity Report Editor Global Volcanism Program http://www.volcano.si.edu/reports/usgs/ Smithsonian Institution, National Museum of Natural History Department of Mineral Sciences, MRC-119 Washington, D.C., 20560 Phone: 202.633.1805 Fax: 202.357.2476 ============================================================== To unsubscribe from the volcano list, send the message: signoff volcano to: listserv@xxxxxxx, or write to: volcano-request@xxxxxxxx To contribute to the volcano list, send your message to: volcano@xxxxxxxx Please do not send attachments. ==============================================================
