*********************************************************** SI/USGS Weekly Volcanic Activity Report 7-13 May 2008 *********************************************************** Sally Kuhn Sennert - Weekly Report Editor kuhns@xxxxxx URL: http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Avachinsky, Eastern Kamchatka | Chaitén, Southern Chile | Etna, Sicily (Italy) | Gamalama, Halmahera (Indonesia) Ongoing Activity: | Batu Tara, Komba Island (Indonesia) | Cleveland, Chuginadak Island | Colima, México | Egon, Flores Island (Indonesia) | Karymsky, Eastern Kamchatka | Kerinci, Sumatra (Indonesia) | Kilauea, Hawaii (USA) | Manam, Northeast of New Guinea (SW Pacific) | Rabaul, New Britain (SW Pacific) | Sakura-jima, Kyushu (Japan) | Santa María, Guatemala | Shiveluch, Central Kamchatka (Russia) | Soufrière Hills, Montserrat | 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 AVACHINSKY Eastern Kamchatka 53.255°N, 158.830°E; summit elev. 2741 m Based on information from KEMSD, the Tokyo VAAC reported that an eruption plume from Avachinsky rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted S and E on 10 May. Geologic Summary. Avachinsky, one of Kamchatka's most active volcanoes, rises above Petropavlovsk, Kamchatka's largest city. Avachinsky began to form during the middle or late Pleistocene and is flanked to the SE by the parasitic volcano Kozelsky, which has a large crater breached to the NE. Avachinsky has a large horseshoe-shaped caldera, breached to the SW, that was formed when about 30,000-40,000 years ago a major debris avalanche buried an area of about 500 sq km to the S underlying the city of Petropavlovsk. Reconstruction of the volcano took place in two stages, the first of which began about 18,000 years before present (BP), and the second 7,000 years BP. Most eruptive products have been explosive, with pyroclastic flows and hot lahars being directed primarily to the SW by the breached caldera, although relatively short lava flows have been emitted. The frequent historical eruptions of Avachinsky have been similar in style and magnitude to previous Holocene eruptions. Source: Tokyo Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html CHAITEN Southern Chile 42.833°S, 72.646°W; summit elev. 1122 m Based on observations of satellite imagery, SIGMET reports, and pilot reports, the Buenos Aires VAAC reported that during 7-13 May ash plumes from Chaitén were continuously present and during 7-9 May rose to altitudes of 6.1-10.1 km (20,000-33,000 ft) a.s.l. The plumes drifted E and NE. SERNAGEOMIN reported that on 7 May, seismicity from Chaitén increased and a large explosion was registered. On 8 May small pyroclastic flows traveled E and contacted the Rayas River, possibly causing steam plumes. During a break in the cloud cover, the ash-and-gas plume, present since 2 May, was seen rising to an altitude of 15.1 km (50,000 ft) a.s.l. and drifting NE. The W side of the plume was darker and denser. ONEMI (Oficina Nacional de Emergencia - Ministerio del Interior) reported ashfall in multiple areas on 7, 8, and 10 May. On 12 May, the plume rose to an altitude of 8 km (26,200 ft) a.s.l. During an overflight conducted by SERNAGEOMIN, four more plumes of a similar altitude were generated by explosions and drifted NE. Several hectares of burned vegetation, likely from pyroclastic flows or lateral explosions, were noted on the N flank of the dome. Small pyroclastic flows may also have been responsible for completely burned forest to areas in the NE, and on the W and NW dome flanks. A lahar caused the banks of the Chaitén River to overflow about 200 m on each side, damaging about 40 houses and numerous cars that were partially or fully submerged. During an overflight on 13 May, evidence of pyroclastic flows on the N flank was observed. An ash-and-gas plume emitted from the lava dome drifted NE. The Alert Level remained at Red. 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. Two small lakes occupy the caldera floor on the west and north sides of the lava dome. Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN) http://www.sernageomin.cl/, 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 ETNA Sicily (Italy) 37.734°N, 15.004°E; summit elev. 3330 m Based on observations using the summit web camera, INGV-CT reported that a week of Strombolian activity from a depression on the E flank of the South East Crater at the summit of Etna ceased on 28 April. On 1 May, a seismic swarm was detected along the NE rift and degassing from the South East Crater and the North East Crater was noted. On 10 May, an eruption produced ash plumes that drifted N; observations were hindered due to cloud cover, but the ash cloud was detected on satellite imagery. Lava flows advanced about 6.4 km E and covered the W wall of the Valle del Bove. Ashfall was reported in multiple areas during 10-11 May. Geologic Summary. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BC. Historical lava flows cover much of the surface of this massive basaltic stratovolcano, the highest and most voluminous in Italy. Two styles of eruptive activity typically occur at Etna. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more of the three prominent summit craters, the Central Crater, NE Crater, and SE Crater. Flank eruptions, typically with higher effusion rates, occur less frequently and originate from fissures that open progressively downward from near the summit. A period of more intense intermittent explosive eruptions from Etna's summit craters began in 1995. The active volcano is monitored by the Instituto Nazionale di Geofisica e Volcanologia (INGV) in Catania. Source: Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania (INGV-CT) http://www.ct.ingv.it/ GAMALAMA Halmahera (Indonesia) 0.80°N, 127.33°E; summit elev. 1715 m CVGHM raised the Alert Level for Gamalama to 2 (on a scale of 1-4) on 11 May based on seismicity and visual observations during 10-11 May. On 10 May, white to gray plumes rose to an altitude of 1.8 km (5,900 ft) a.s.l. and drifted N. Residents and tourists were not permitted within 2 km of the summit. Geologic Summary. Gamalama (Peak of Ternate) is a near-conical stratovolcano that comprises the entire island of Ternate off the western coast of Halmahera and is one of Indonesia's most active volcanoes. The island of Ternate was a major regional center in the Portuguese and Dutch spice trade for several centuries, which contributed to the thorough documentation of Gamalama's historical activity. Three cones, progressively younger to the N, form the summit of Gamalama, which reaches 1,715 m. Several maars and vents define a rift zone, parallel to the Halmahera island arc, that cuts the volcano. Eruptions, recorded frequently since the 16th century, typically originated from the summit craters, although flank eruptions have occurred in 1763, 1770, 1775, and 1962-63. Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/ Ongoing Activity BATU TARA Komba Island (Indonesia) 7.792°S, 123.579°E; summit elev. 748 m Based on observations of satellite imagery, the Darwin VAAC reported that low-level plumes from Batu Tara rose to an altitude of 1.8 km (6,000 ft) a.s.l. and drifted NW and W during 11-13 May. On 12 and 13 May a thermal anomaly at the summit was noted. Geologic Summary. The small isolated island of Batu Tara in the Flores Sea about 50 km north of Lembata (formerly Lomblen) Island contains a scarp on the eastern side similar to the Sciara del Fuoco of Italy's Stromboli volcano. Vegetation covers the flanks of Batu Tara to within 50 m of the 748-m-high summit. Batu Tara lies north of the main volcanic arc and is noted for its potassic leucite-bearing basanitic and tephritic rocks. The first historical eruption from Batu Tara, during 1847-52, produced explosions and a lava flow. Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html CLEVELAND Chuginadak Island 52.825°N, 169.944°W; summit elev. 1730 m On 9 May, AVO reported that an increasing number of thermal anomalies at Cleveland were visible on satellite imagery during the previous two weeks. A small ash plume rose to an altitude of below 4.6 km (15,000 ft) a.s.l. on 7 May. A ship N of Nikolski (75 km ENE) reported a dusting of ash around the same time. The Volcanic Alert Level remained at Advisory and the Aviation Color Code remained at Yellow. Geologic Summary. Symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited dumbbell-shaped Chuginadak Island in the east-central Aleutians. The 1,730-m-high stratovolcano is the highest of the Islands of Four Mountains group and is one of the most active in the Aleutians. Numerous large lava flows descend its flanks. It is possible that some 18th to 19th century eruptions attributed to Carlisle (a volcano located across the Carlisle Pass Strait to the NW) should be ascribed to Cleveland. In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions from Mt. Cleveland have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks. Source: Alaska Volcano Observatory (AVO) http://www.avo.alaska.edu/ COLIMA México 19.514°N, 103.62°W; summit elev. 3850 m Based on information from Mexico City MWO and observations of satellite imagery, the Washington VAAC reported that a puff of ash and gas drifted NW on 13 May. Geologic Summary. 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 4,320 m high point of the complex) on the N and the historically active Volcán de Colima on the S. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the S, 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. Source: Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html EGON Flores Island (Indonesia) 8.67°S, 122.45°E; summit elev. 1703 m CVGHM reported that plume altitudes and seismicity from Egon decreased during 25 April-10 May. On 12 May, small steam plumes were visible. The Alert Level was lowered from 3 to 2 (on a scale of 1-4). Geologic Summary. Gunung Egon volcano sits astride the narrow waist of eastern Flores Island. The barren, sparsely vegetated summit region has a 350-m-wide, 200-m-deep crater that sometimes contains a lake. Other small crater lakes occur on the flanks of the 1,703-m-high volcano. A lava dome forms the southern 1,671-m-high summit. Reports of historical eruptive activity are inconclusive. A column of "smoke" was often observed above the summit during 1888-1891 and in 1892. Strong "smoke" emission in 1907 reported by Sapper (1917) was considered by the Catalog of Active Volcanoes of the World (Neumann van Padang, 1951) to be an historical eruption, but Kemmerling (1929) noted that this was likely confused with an eruption on the same date and time from Lewotobi Lakilaki volcano. Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/ KARYMSKY Eastern Kamchatka 54.05°N, 159.45°E; summit elev. 1536 m KVERT reported that seismic activity at Karymsky was slightly above background levels on 3 and 7 May and at background levels the other days during 2-9 May; gas-and-ash explosions may have occurred on 3 and 7 May. Based on pilot observations, an ash plume rose to an altitude of about 5 km (16,400 ft) a.s.l. on 6 May. The Level of Concern Color Code remained at Orange. Based on information from KEMSD and KVERT, pilot reports, observations of satellite imagery, the Tokyo VAAC reported that ash plumes rose to altitudes of 4.6 km (15,000 ft) a.s.l. and 3.4 km (11,000 ft) a.s.l. on 9 and 13 May, respectively. 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 KERINCI Sumatra (Indonesia) 1.697°S, 101.264°E; summit elev. 3800 m CVGHM reported that seismic and surface activity from Kerinci increased during 10-11 May. White plumes rose to altitudes of 4.3-4.5 km (14,100-14,800 ft) a.s.l. and drifted E. On 11 May, a gray plume was possibly spotted. The Alert Status remained at 2 (on a scale of 1-4). Residents and visitors were advised not to enter an area within 1 km of the summit. Geologic Summary. The summit of 3800-m-high Kerinci, Indonesia's highest volcano, contains a deep 600-m-wide crater often partially filled by a small crater lake. The massive 13 x 25 km wide volcano towers 2,400-3,300 m above surrounding plains. Kerinci is elongated in a N-S direction and is capped by an unvegetated young summit cone constructed NE of an older crater remnant. One of Sumatra's most active volcanoes, Gunung Kerinci has produced a series of moderate explosive eruptions during the 19th and 20th centuries. Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/ KILAUEA Hawaii (USA) 19.421°N, 155.287°W; summit elev. 1222 m Based on observations during helicopter overflights, visual observations from HVO and National Park Service (NPS) crews, and web camera views, HVO reported that during 7-13 May lava flowed SE through a lava tube system underneath Kilauea's Thanksgiving Eve Breakout (TEB) and rootless shield complex to the Waikupanaha ocean entry. Incandescence was occasionally noted from the TEB vent area. During 10-13 May, spatter at the Waikupanaha ocean entry was propelled 20-30 m high and built a littoral cone. During the reporting period, Kilauea summit earthquakes were located beneath the Halema'uma'u crater, N of the summit, along the S-flank faults, and along the SW and E rift zones. The eruption from the vent in Halema'uma'u Crater continued to produce white plumes with minor ash content that drifted mainly SW. During most nights incandescence was seen at the base of the plume. Seismic tremor was elevated. During 11-12 May, the summit tiltmeter network recorded the tenth 'deflation-inflation' (DI) tilt event since the emergence of the new vent in Halema`uma`u Crater and the seventeenth so far in 2008.The sulfur dioxide emission rate was high and fluctuated between 590 and 1,100 tonnes per day during 6-12 May. The background rate was 150-200 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/ MANAM Northeast of New Guinea (SW Pacific) 4.080°S, 145.037°E; summit elev. 1807 m Based on observations of satellite imagery and information from RVO, the Darwin VAAC reported that during 11-12 May low-level plumes from Manam rose to an altitude 3 km (10,000 ft) a.s.l. and drifted SE. Geologic Summary. 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," regularly spaced 90 degrees apart, channel lava flows and pyroclastic avalanches that have sometimes reached the coast. 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 avalanche valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded at Manam 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. Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html RABAUL New Britain (SW Pacific) 4.271°S, 152.203°E; summit elev. 688 m RVO reported that during 7-13 May ash-and-steam plumes from multiple places inside Rabaul caldera's Tavurvur cone rose to an altitude of 2.2 km (7,200 ft) a.s.l. and drifted S. Intermittent roaring and rumbling noises were reported. Incandescent tephra was occasionally visible at night. Based on observations of satellite imagery and reports from RVO, the Darwin VAAC reported that low-level ash plumes rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted SE during 8-9 May. Low-level plumes drifted NE during 10-11 May. 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. Sources: Steve Saunders, Rabaul Volcano Observatory (RVO), Darwin Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html SAKURA-JIMA Kyushu (Japan) 31.585°N, 130.657°E; summit elev. 1117 m Based on information from JMA, the Tokyo VAAC reported that on 8 May an eruption plume from Sakura-jima rose to an altitude of 4 km (13,000 ft) a.s.l. The plume drifted E. 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. Source: 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 observations of satellite imagery, the Washington VAAC reported that ash puffs from Santa María's Santiaguito lava dome complex drifted NW on 13 May. 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. Source: 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 slightly above background levels on 5 May and at background levels the other days during 2-9 May. Based on seismic interpretation, hot avalanches possibly descended the growing lava dome. Video footage and visual observations showed fumarolic activity from the lava dome during 5-6 and 8 May. Observations of satellite imagery revealed that a thermal anomaly was present in the crater during 5-8 May. 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. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php SOUFRIERE HILLS Montserrat 16.72°N, 62.18°W; summit elev. 915 m MVO reported that during 2-9 May the lava dome at Soufrière Hills changed very little, based on measurable parameters. A small pyroclastic flow descended the E flank on 5 May. Light ashfall was reported in the Old Town area about 9 km NW. Ash deposits were also evident in the Corkhill (NW) and St. Georges Hill (N) areas. Heavy rainfall generated lahars. The Alert Level remained elevated at 4 (on a scale of 0-5). Based on information from MVO and observations of satellite imagery, the Washington VAAC reported that an ash plume rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted NW on 13 May. 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/, Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html TUNGURAHUA Ecuador 1.467°S, 78.442°W; summit elev. 5023 m The IG reported that although visual observations were occasionally limited due to cloud cover during 7-13 May, ash and steam plumes from Tungurahua were spotted most days and rose to altitudes of 5-8 km (16,400-26,200 ft) a.s.l. Ashfall was reported in areas within 8 km to the SW, W, N, and NW on 6, 10, and 11 May. On 8 May, muddy waters were reported in areas SW and S and roaring noises were audible. On 11 May, incandescence at the summit was reported along with roaring noises and blocks that rolled 1 km down the flanks. After an explosion on 12 May, windows vibrated, roaring noises were again reported, and rockfalls occurred in an area 8 km S. 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 SIGMET reports and pilot observations, the Buenos Aires VAAC reported that ash plumes from Ubinas rose to altitudes of 5.5-7 km (18,000-23,000 ft) a.s.l. on 9 and 12 May. Plumes drifted E and SE, respectively. 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. ==============================================================
