*********************************************************** SI/USGS Weekly Volcanic Activity Report 18-24 February 2009 *********************************************************** Sally Kuhn Sennert - Weekly Report Editor kuhns@xxxxxx URL: http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Chaitén, Southern Chile | Galeras, Colombia | Redoubt, Southwestern Alaska Ongoing Activity: | Barren Island, Andaman Is | Fuego, Guatemala | Guagua Pichincha, Ecuador | Karymsky, Eastern Kamchatka | Kilauea, Hawaii (USA) | Popocatépetl, México | Rabaul, New Britain | Sakura-jima, Kyushu | Santa María, Guatemala | Shiveluch, Central Kamchatka (Russia) | Soufrière Hills, Montserrat | Suwanose-jima, Ryukyu Islands (Japan) | Tungurahua, Ecuador | 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 CHAITEN Southern Chile 42.833°S, 72.646°W; summit elev. 1122 m SERNAGEOMIN reported that on 19 February a partial lava-dome collapse of the S flank of Chaitén's Domo Nuevo 1 and Domo Nuevo 2 lava-dome complex generated lateral explosions, block-and-ash flows, and pyroclastic flows. A pyroclastic flow traveled S down the Chaitén (Blanco) River valley, stopping within about 5 km of Chaitén town (10 km SW). Ash plumes rose to an altitude of 9.1 km (30,000 ft) a.s.l. and drifted W and SE. Ash fell in Futaleufú (about 65 km ESE), and, according to ONEMI, accumulated to thicknesses of 3-5 mm. Overflights revealed that the tree leaves in a forest near the S flank were burned and steam rose from new deposits in the Chaitén River valley. Ash-and-steam plumes rose to altitudes of 7.1-9.1 km (23,300-30,000 ft) a.s.l. A 500 x 500 m scar from the partial dome collapse was seen on the S flank. Seismicity decreased to pre-collapse levels by the afternoon. The steaming from pyroclastic flow deposits was again seen in the channel and on the shores of the Chaitén River valley during an overflight the next day, but had greatly decreased by 21 February. Using photos taken during 19 and 20 February overflights, scientists estimated that 10 million cubic meters of material was removed from the S flank of the dome complex. According to a news article, about 200 people were living in Chaitén town on 19 February. ONEMI reported that many of those people self-evacuated, but about 46 people remained in the town, refusing to leave. On 23 February, lahars traveled down river valleys and an off-white plume was seen on the web camera rising about 1 km above the lava domes. Based on SIGMET notices, analysis of satellite imagery, and web camera views, the Buenos Aires VAAC reported that during 23-24 February ash plumes rose to altitudes 2.1-3 km (7,000-10,000 ft) a.s.l. and drifted NE and E. 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, Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI) http://www.onemi.cl/, Buenos Aires Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html Patagonia Times http://www.patagoniatimes.cl/index.php/20090224751/News/Health-Science/CHILES-CHAITEN-VOLCANO-STILL-PUFFING-AWAY.html GALERAS Colombia 1.22°N, 77.37°W; summit elev. 4276 m INGEOMINAS reported an explosive eruption from Galeras that began at 0705 on 20 February; the Alert Level was raised from II (Orange; "probable eruption in term of days or weeks") to I (Red; "imminent eruption or in progress"), on a scale of 4-1. The eruption was accompanied by shock waves detected in several local communities and produced sounds heard in Popayán (about 160 km NNE). Observers from areas on the E flank reported two explosions, incandescent blocks ejected above the summit, ash emissions, and sulfur gas odor. An ash plume rose to an altitude of 12.5 km (41,000 ft) a.s.l. and drifted E, W, and N. Ashfall was reported in areas to the W. Gas plumes with a low ash content continued, especially in the afternoon, and rose 700 m above the summit. On 21 February, the Alert Level was lowered to back to II. During 22-24 February, occasional steam plumes rose 500 m above the summit and drifted NNW. Geologic Summary. Galeras, a stratovolcano with a large breached caldera located immediately W of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic Galeras volcanic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Longterm extensive hydrothermal alteration has affected the volcano. This has contributed to large-scale edifice collapse that has occurred on at least three occasions, producing debris avalanches that swept to the W 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. Source: Instituto Colombiano de Geología y Minería (INGEOMINAS) http://www.ingeominas.gov.co// REDOUBT Southwestern Alaska 60.485°N, 152.742°W; summit elev. 3108 m AVO reported that during 18-24 February seismic activity at Redoubt was variable but remained elevated above background levels. Web camera views and satellite imagery showed no unusual activity; steam plumes within the summit crater were seen on the web camera on 23 and 24 February. Geologic Summary. Redoubt is a 3108-m-high glacier-covered stratovolcano with a breached summit crater in Lake Clark National Park about 170 km SW of Anchorage. Next to Mount Spurr, Redoubt has been the most active Holocene volcano in the upper Cook Inlet. Collapse of the summit of Redoubt 10,500-13,000 years ago produced a major debris avalanche that reached Cook Inlet. Holocene activity has included the emplacement of a large debris avalanche and clay-rich lahars that dammed Lake Crescent on the south side and reached Cook Inlet about 3500 years ago. Eruptions during the past few centuries have affected only the Drift River drainage on the north. Historical eruptions have originated from a vent at the north end of the 1.8-km-wide breached summit crater. The 1989-90 eruption of Redoubt had severe economic impact on the Cook Inlet region and affected air traffic far beyond the volcano. Source: Alaska Volcano Observatory (AVO) http://www.avo.alaska.edu/ Ongoing Activity BARREN ISLAND Andaman Is 12.278°N, 93.858°E; summit elev. 354 m Based on analysis of satellite imagery, the Darwin VAAC reported that during 20-21 February ash plumes from Barren Island rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted about 75-90 km WNW, NW, and N. Geologic Summary. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S-trending volcanic arc extending between Sumatra and Burma (Myanmar). The 354-m-high island is the emergent summit of volcano that rises from a depth of about 2,250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the W, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. The morphology of a fresh pyroclastic cone that was constructed in the center of the caldera has varied during the course of historical eruptions. Lava flows fill much of the caldera floor and have reached the sea along the western coast during historical eruptions. Source: Darwin Volcanic Ash Advisory Center (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 analysis of satellite imagery, the Washington VAAC reported that on 18 February ash plumes from Fuego rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted WSW. On 20 and 24 February, INSIVUMEH reported that explosions produced ash plumes that rose to altitudes of 4.1-4.7 km (13,500-15,400 ft) a.s.l. and drifted 6-8 km SW. Some explosions produced rumbling sounds and shock waves. Incandescent material was ejected 150 m above the crater. Incandescent avalanches of blocks traveled down the W and SW flanks. 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 GUAGUA PICHINCHA Ecuador 0.171°S, 78.598°W; summit elev. 4784 m The IG reported four moderate phreatic explosions from Guagua Pichincha were detected by the seismic network during 16-17 February, following a few days of slightly increased seismicity and rainfall. IG recommended that visitors stay out of the caldera. Geologic Summary. Guagua Pichincha rises immediately west of Quito, Ecuador's capital city. The broad volcanic massif is cut by a large horseshoe-shaped summit caldera, ~6 km in diameter and 600 m deep, that was breached to the W during a slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent consisted of explosive activity with pyroclastic flows accompanied by periodic lava dome growth and destruction. A major eruption in 1660 deposited 30 cm of ash in Quito, but most of the many eruptions since the Spanish colonial era have been minor. The latest eruptive period began with phreatic explosions in 1998. Magmatic eruptions first occurred in October 1999, and intermittent eruptions of varying scale since have blanketed Quito and surrounding towns with ash. Source: Instituto Geofísico-Escuela Politécnica Nacional (IG) http://www.igepn.edu.ec/ KARYMSKY Eastern Kamchatka 54.05°N, 159.45°E; summit elev. 1536 m KVERT reported that during 13-20 January seismic data from Karymsky was unavailable and clouds prevented satellite image observations. The Level of Concern Color Code remained at Orange. Based on information from KEMSD and observations of satellite imagery, the Tokyo VAAC reported that during 21-22 February eruptions produced plumes that rose to altitudes of 3-4.3 km (10,000-14,000 ft) a.s.l. 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 18-24 February lava flowed SE from underneath Kilauea's Thanksgiving Eve Breakout (TEB) and rootless shield complex through a lava tube system, reaching the Waikupanaha ocean entry and occasionally producing explosions. On 17 February, four large explosions that accompanied a collapse of the Waikupanaha bench ejected rocks and spatter 275 m inland. Lava also entered the ocean at Waha'ula during 18-20 February, and at a second point further E, named Poupou, starting on 18 February. Incandescence originated from the Prince lobe on 20 February. Thermal anomalies noted on the coastal plain suggested surface flows. The vent in Halema'uma'u crater continued to produce a predominantly white plume that drifted mainly SW; incandescence was intermittently seen from the vent. Small amounts of ejected tephra, including Pele's hair and some spatter, were routinely collected. Geologists utilizing an infrared imager during an overflight on 20 February saw a small, hot degassing vent deep below the vent rim. The sulfur dioxide emission rate at the summit was 1,400, 1,500, 1,300, and 900 tonnes per day on 17, 18, 19, and 20 February, respectively; the 2003-2007 average rate was 140 tonnes per day. 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/ POPOCATEPETL México 19.023°N, 98.622°W; summit elev. 5426 m CENAPRED reported that emissions of steam and gas from Popocatépetl were visible during 18-24 February; the plumes occasionally contained slight amounts of ash. Geologic Summary. Popocatépetl, whose name is the Aztec word for smoking mountain, towers to 5,426 m 70 km SE of Mexico City and is North America's second-highest volcano. Frequent historical eruptions have been recorded since the beginning of the Spanish colonial era. A small eruption on 21 December 1994 ended five decades of quiescence. Since 1996 small lava domes have incrementally been constructed within the summit crater and destroyed by explosive eruptions. Intermittent small-to-moderate gas-and-ash eruptions have continued, occasionally producing ashfall in neighboring towns and villages. Source: Centro Nacional de Prevencion de Desastres (CENAPRED) http://www.cenapred.unam.mx/es/ RABAUL New Britain 4.271°S, 152.203°E; summit elev. 688 m Based on analysis of satellite imagery, the Darwin VAAC reported that during 22-23 February ash plumes from Rabaul caldera's Tavurvur cone rose to altitudes of 1.8-3 km (6,000-10,000 ft) a.s.l. and drifted S, W, and NW. 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: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html SAKURA-JIMA Kyushu 31.585°N, 130.657°E; summit elev. 1117 m JMA lowered the Alert Level for Sakura-jima from 3 to 2 (on a scale of 1-5) on 19 February because deformation was absent, seismicity was low, and no eruptions occurred after 5 February. Based on information from JMA, the Tokyo VAAC reported that on 22 February an explosion produced a plume that rose to an altitude of 2.7 km (9,000 ft) a.s.l. and drifted N. Geologic Summary. Sakura-jima, one of Japan's most active volcanoes, is a post-caldera cone of the Aira caldera at the northern half of Kagoshima Bay. Eruption of the voluminous Ito pyroclastic flow was associated with the formation of the 17 x 23-km-wide Aira caldera about 22,000 years ago. The construction of Sakura-jima began about 13,000 years ago and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kita-dake summit cone ended about 4,850 years ago, after which eruptions took place at Minami-dake. 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. Sources: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/indexe.html, Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html SANTA MARIA Guatemala 14.756°N, 91.552°W; summit elev. 3772 m Based on analysis of satellite imagery, the Washington VAAC reported that on 18 February a dense ash plume from Santa María's Santiaguito lava dome complex drifted W. On 20 February, INSIVUMEH reported that an explosion produced an ash plume that rose to an altitude of 3.2 km (10,500 ft) a.s.l. and drifted E. On 24 February, an explosion produced a white plume that rose 500 m above the summit and drifted SW. Incandescence was seen SW of Caliente dome. 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 at background levels during 13-20 February. Based on interpretations of seismic data, ash plumes likely rose to an altitude of 4.6 km (15,100 ft) a.s.l. Lava flows continued to be active on the S and N flanks. Fumarolic activity was seen during 12-13 and 19 February. Analysis of satellite imagery revealed a daily thermal anomaly on the lava dome and an ash plume that drifted 31 km NW on 17 February. The Level of Concern Color Code remained at Orange. Based on information from KEMSD and analysis of satellite imagery, the Tokyo VAAC reported that an eruption on 18 February produced a plume that rose to an altitude of 4.9 km (16,000 ft) a.s.l. 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, Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html SOUFRIERE HILLS Montserrat 16.72°N, 62.18°W; summit elev. 915 m MVO reported that during 13-20 February activity from the Soufrière Hills lava dome was at a low level. Four rockfalls were detected and seismicity had increased slightly compared to previous weeks. On 16 February, heavy rainfall triggered a small pyroclastic flow on the N side of the lava dome and a substantial lahar NW in the Belham River. A thermal camera showed a large amount of steaming in the Dyer's area (NW) during this period, and occasionally for a few days after. The Hazard Level was lowered to 3 on 19 February. 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 JMA reported that Suwanose-jima erupted explosively on 18 February; a colored plume rose 400 m above the crater and drifted E. Two explosive eruptions occurred the next day. Based on information from JMA, the Tokyo VAAC reported explosions on 20 and 21 February. Details of possible resultant ash plumes were not reported. 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. Sources: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/indexe.html, Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html TUNGURAHUA Ecuador 1.467°S, 78.442°W; summit elev. 5023 m The IG reported that, although cloud cover occasionally prevented visual observation during 18-24 February, ash plumes from Tungurahua were seen and rose to altitudes of 6-8 km (19,700-26,200 ft) a.s.l. The plumes drifted mainly W and NW. Ashfall was reported almost daily and was noted in areas to the SW, W, and NW. Blocks were often seen or heard rolling down the flanks, and roaring or explosion noises were noted. On 18 February, incandescence in the crater was seen and a lahar traveled down a drainage to the W. Strombolian activity at the summit was observed during 19-20 and 22-23 February. Geologic Summary. The steep-sided Tungurahua stratovolcano towers more than 3 km above its northern base. It sits ~140 km S of Quito, Ecuador's capital city, and is one of Ecuador's most active volcanoes. Historical eruptions have all originated from the summit crater. They have been accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. The last major eruption took place from 1916 to 1918, although minor activity continued until 1925. The latest eruption began in October 1999 and prompted temporary evacuation of the town of Baños on the N side of the volcano. Source: Instituto Geofísico-Escuela Politécnica Nacional (IG) http://www.igepn.edu.ec/ UBINAS Perú 16.355°S, 70.903°W; summit elev. 5672 m Based on a SIGMET notice and a pilot observation, the Buenos Aires VAAC reported that on 23 February an ash plume from Ubinas rose to altitudes of 6.2-7.6 km (20,500-25,000 ft) a.s.l. and drifted S. Ash was not seen on satellite imagery. 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. ==============================================================
