***************************************************** SI/USGS Weekly Volcanic Activity Report 18-24 June 2008 ***************************************************** Sally Kuhn Sennert - Weekly Report Editor kuhns@xxxxxx URL: http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Masaya, Nicaragua | San Cristóbal, Nicaragua | Tungurahua, Ecuador Ongoing Activity: | Batu Tara, Komba Island (Indonesia) | Cerro Azul, Isabela I | Chaitén, Southern Chile | Dukono, Halmahera (Indonesia) | Fuego, Guatemala | Gorely, Southern Kamchatka | Karymsky, Eastern Kamchatka | Kilauea, Hawaii (USA) | Krakatau, Indonesia | Mutnovsky, Southern Kamchatka | Pacaya, Guatemala | Santa María, Guatemala | Shiveluch, Central Kamchatka (Russia) | Soputan, Sulawesi (Indonesia) | Soufrière Hills, Montserrat | 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 MASAYA Nicaragua 11.984°N, 86.161°W; summit elev. 635 m INETER reported that on 18 June, an explosion from Masaya produced an ash-and-gas plume. Local people felt the explosion and reported that the plume was dark in color. Geologic Summary. Masaya is one of Nicaragua's most unusual and most active volcanoes. It is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high that is filled on its NW end by more than a dozen vents erupted along a circular, 4-km-wide fracture system. The twin volcanoes of Nindiri and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters. A major basaltic Plinian tephra was erupted from Masaya about 6,500 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 N caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted several attempts to extract the volcano's molten "gold." Source: Instituto Nicaragüense de Estudios Territoriales (INETER) http://www.ineter.gob.ni/ SAN CRISTOBAL Nicaragua 12.702°N, 87.004°W; summit elev. 1745 m According to news articles, INETER reported that a moderate explosion from San Cristóbal on 22 June was followed by ash-and-gas emissions from the crater. Ashfall was reported in the city of Chinandega (about 15 km SW) and three other nearby communities. Geologic Summary. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1,745-m-high youngest cone, San Cristóbal itself (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km to the west of San Cristóbal; it and the eroded Moyotepe volcano, 4 km to the NE of San Cristóbal, are of Pleistocene age. Volcán Casita contains an elongated summit crater and lies immediately E of San Cristóbal; Casita was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the San Cristóbal complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes. Source: Terra Actualidad http://actualidad.terra.es/ciencia/articulo/san-cristobal-nicaragua-2567619.htm TUNGURAHUA Ecuador 1.467°S, 78.442°W; summit elev. 5023 m IG reported that during 18-19 June, ash-and-steam plumes from Tungurahua rose to altitudes of 6-8 km (19,700-26,200 ft) a.s.l. and drifted W, NW, and N. On 18 June, a small explosion was detected by the seismic network, and sounds of blocks rolling down the flanks, roaring noises, and "cannon shots" were reported. On 19 June, ashfall was reported in areas NW and W; in Cotaló, about 8 km NW, ash deposits measured about 2 mm thick. Incandescent material and blocks were ejected 500 m above the summit. Blocks rolled about 1 km down the flanks and roaring noises were reported. On 20 June, clouds inhibited visual observations of the summit. Lahars descended NW, W, and S drainages. A mudflow that traveled SW towards the Puela river carried blocks up to 80 cm in diameter. On 21 June, two periods of increased seismicity were accompanied by strong ash emissions. The resultant ash plumes rose to altitudes of 8-11 km (26,200-36,100 ft) a.s.l. and drifted W. Intense ashfall was reported in areas within 8 km W and SW of the crater. On 22 June, lahars descended several drainages on the W and S flanks. Steam plumes with small ash content rose to an altitude of 6 km (19,700 ft) a.s.l. and drifted W. Roaring noises vibrated windows in areas to the W. During 23-24 June, seismicity decreased and visual observations were inhibited by clouds. 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/ Ongoing Activity BATU TARA Komba Island (Indonesia) 7.792°S, 123.579°E; summit elev. 748 m Based on observations of satellite imagery and pilot reports, the Darwin VAAC reported that during 19-22 June, low-level ash plumes from Batu Tara rose to an altitude of 1.5 km (5,000 ft) a.s.l. and drifted NW and W. A thermal anomaly was noted on satellite imagery on 20 June. 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 CERRO AZUL Isabela I 0.92°S, 91.408°W; summit elev. 1640 m According to news articles, a bulletin issued from Galápagos National Park indicated that eruptive activity from Cerro Azul decreased considerably during 16-17 June and on 18 June incandescent material was no longer ejected. Geologic Summary. Located at the SW tip of the J-shaped Isabela Island, Cerro Azul contains a steep-walled 4 x 5 km nested summit caldera complex that is one of the smallest diameter, but at 650 m one of the deepest in the Galápagos Islands. The 1640-m-high shield volcano is the second highest of the archipelago. A conspicuous bench occupies the SW and west sides of the caldera, which formed during several episodes of collapse. Youthful lava flows cover much of the caldera floor, which has also contained ephemeral lakes. A prominent tuff cone located at the ENE side of the caldera is evidence of episodic hydrovolcanism at Cerro Azul. Numerous spatter cones dot the western flanks of the volcano. Fresh-looking lava flows, many erupted from circumferential fissures, descend the NE and NW flanks of the volcano. Historical eruptions date back only to 1932, but Cerro Azul has been one of the most active Galápagos volcanoes since that time. Source: EFE http://www.soitu.es/soitu/2008/06/18/info/1213821409_069619.html CHAITEN Southern Chile 42.833°S, 72.646°W; summit elev. 1122 m Based on observations during an overflight on 17 June, SERNAGEOMIN reported that ash plumes emitted from the S contact between Chaitén's old and new lava domes rose to an altitude of 2 km (6,600 ft) a.s.l. and drifted N and NW. An explosion temporarily propelled the ash plume to an altitude of 3 km (10,000 ft) a.s.l. and steam plumes rose from several other contact points along the S edge of the lava dome. Rockfalls from the active dome continued to descend the S flank of the old dome to the caldera floor. During 18-21 June, visual observations were inhibited due to inclement weather. During 18-20 June, possible ashfall was reported in Queilén (about 70 km W) and Quellón (about 80 km WSW). Ashfall was reported in Chaitén town (10 km SW) and other areas SE, W, and E. The Alert Level remained at Red. Based on observations of satellite imagery, SIGMET reports, and pilot observations, the Buenos Aires VAAC reported that during 18-24 June ash plumes rose to altitudes of 2.4-4.6 km (8,000-15,000 ft) a.s.l. and drifted approximately NE, E, SE, SW, and W. Thermal anomalies were identified on satellite imagery on 19 and 22 June. 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/, 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 On 19 June, CVGHM reported that during 30 May-12 June, seismicity from Dukono decreased and white plumes at altitudes of 1.4-1.8 km (4,600-5,900 ft) a.s.l. were spotted when clouds did not inhibit observations The Alert Level was decreased to 2 (on a scale of 1-4) on 13 June. Residents and visitors were not permitted within 2 km of the summit. 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: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/ FUEGO Guatemala 14.473°N, 90.880°W; summit elev. 3763 m On 18 June, INSIVUMEH reported that explosions from Fuego produced ash plumes that rose to an altitude of 4.3 km (14,100 ft) a.s.l. and drifted W and SW. Incandescent material was ejected 50 m above the crater. Constant avalanches of blocks descended the W flank and rumbling and degassing noises were reported. On 20 June, a lahar that was hot in areas, descended the Ceniza drainage to the SW, dragging tree branches and blocks 0.5-1 m in diameter. 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. Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/ GORELY Southern Kamchatka 52.558°N, 158.03°E; summit elev. 1829 m KVERT reported that seismic activity in the area of Gorely and Mutnovsky volcanoes decreased during 15-18 June. Moderate fumarolic activity was observed on 17 June; no activity was noted or cloud cover obscured views the other days during 14-20 June. The level of Concern Color Code was lowered to Green on 20 June. Geologic Summary. Gorely volcano, one of the most active in southern Kamchatka, consists of five small overlapping stratovolcanoes constructed along a WNW-ESE line within a large 9 x 13.5 km late-Pleistocene caldera. The massive Gorely complex contains 11 summit and 30 flank craters. During the early Holocene, activity was characterized by frequent mild eruptions with occasional larger explosions and lava flows that filled in the caldera. Quiescent periods became longer between 6,000 and 2,000 years ago, after which the activity was mainly explosive. About 600-650 years ago intermittent strong explosions and lava flow effusion accompanied frequent mild eruptions. Historical eruptions have consisted of vulcanian and phreatic explosions of moderate volume. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php KARYMSKY Eastern Kamchatka 54.05°N, 159.45°E; summit elev. 1536 m KVERT reported that seismic activity at Karymsky was at background levels during 13-20 June but may have indicated weak explosions daily. Observations of satellite imagery revealed a thermal anomaly in the crater on 12 June; clouds obscured views on other days during the reporting period. The Level of Concern Color Code remained at Orange. 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. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php KILAUEA Hawaii (USA) 19.421°N, 155.287°W; summit elev. 1222 m Based on visual observations from HVO crews and web camera views, HVO reported that during 18-24 June, 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. The sulfur dioxide emission rate was 1,400 tonnes per day when measured on 18 June; the average background rate was about 2,000 tonnes per day. During the reporting period, Kilauea summit earthquakes were located beneath Halema'uma'u crater, beneath the summit area, along the Koa'e and S-flank faults, and along the E and SW rift zones. About 100-140 small earthquakes (not located) were detected during 18-21 June. The vent in Halema'uma'u crater continued to produce white plumes with minor ash content that drifted mainly SW. Night-time incandescence was seen at the base of the plume. Seismic tremor was elevated. The sulfur dioxide emission rate was high and fluctuated between 400 and 1,100 tonnes per day when measured during 18-22 June. The background rate is 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/ KRAKATAU Indonesia 6.102°S, 105.423°E; summit elev. 813 m Based on observations of satellite imagery, the Darwin VAAC reported that a low-level ash plume from Anak Krakatau rose to an altitude of 3 km (10,000 ft) a.s.l. on 20 June and drifted NW. Geologic Summary. Renowned Krakatau volcano lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 AD, resulted in a 7-km-wide caldera. Remnants of this volcano formed Verlaten and Lang Islands; subsequently Rakata, Danan and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan volcanoes, and left only a remnant of Rakata volcano. The post-collapse cone of Anak Krakatau (Child of Krakatau), constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan, has been the site of frequent eruptions since 1927. Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html MUTNOVSKY Southern Kamchatka 52.453°N, 158.195°E; summit elev. 2322 m KVERT reported that seismic activity in the area of Gorely and Mutnovsky volcanoes decreased during 15-18 June. Moderate fumarolic activity was observed on 17 June; no activity was noted or cloud cover obscured views the other days during 14-20 June. The level of Concern Color Code was lowered to Green on 20 June. Geologic Summary. Massive Mutnovsky, one of the most active volcanoes of southern Kamchatka, is formed of four coalescing stratovolcanoes of predominately basaltic composition. Multiple summit craters cap the volcanic complex. Growth of Mutnovsky IV, the youngest cone, began during the early Holocene. An intracrater cone was constructed along the northern wall of the 1.3-km-wide summit crater. Abundant flank cinder cones were concentrated on the SW side. Holocene activity was characterized by mild-to-moderate phreatic and phreatomagmatic eruptions from the summit crater. Historical eruptions have been explosive, with lava flows produced only during the 1904 eruption. Geothermal development is planned at Mutnovsky, which has the highest heat capacity of any volcano in the Kuril-Kamchatka arc. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php PACAYA Guatemala 14.381°N, 90.601°W; summit elev. 2552 m During 18-24 June, INSIVUMEH reported that white fumarolic plumes from Pacaya's MacKenney cone drifted S and W. Lava flows traveled 50-100 m NW in the area between MacKenney cone and Cerro Chino crater to the N. Incandescence in the crater was observed at night. Geologic Summary. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. Pacaya is a complex volcano constructed on the southern rim of the 14 x 16 km Pleistocene Amatitlan caldera. A cluster of dacitic lava domes occupies the caldera floor. The Pacaya massif includes the Cerro Grande lava dome and a younger volcano to the SW. Collapse of Pacaya volcano about 1,100 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. During the past several decades, activity at Pacaya has consisted of frequent Strombolian eruptions with intermittent lava flow extrusion on the flanks of MacKenney cone, punctuated by occasional larger explosive eruptions. Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/ SANTA MARIA Guatemala 14.756°N, 91.552°W; summit elev. 3772 m During 19-24 June, INSIVUMEH reported that weak-to-moderate explosions from Santa María's Santiaguito lava dome complex produced ash plumes that rose to altitudes of 2.8-3.3 km (9,200-10,800 ft) a.s.l. and drifted SW and S. An incandescent lava flow accompanied by constant avalanches of blocks descended the SW flank. On 20 June, a lahar traveled S down the Nima I river, carrying blocks up to 1 m in diameter. 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: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/ 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 during 13-20 June. According to video footage and visual observations, moderate fumarolic activity was noted on 13 June. Observations of satellite imagery revealed a thermal anomaly on the lava dome during 12-13 June; clouds obscured views on other days. 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 SOPUTAN Sulawesi (Indonesia) 1.108°N, 124.73°E; summit elev. 1784 m CVGHM reported that the eruption of Soputan during 6-7 June caused part of the crater wall to collapse creating an opening to the W, and the diameter of the crater to increase. Ash plumes generated on 6 June drifted NW, W, SW, and as far as 60 km S. Ash deposits were about 4 cm thick in an area 5 km NW. A nearby coconut plantation reported damage to trees. During 7-18 June, seismicity decreased and white plumes at altitudes at or less than 1.8 km (5,900 ft) a.s.l. were spotted when clouds did not inhibit observations. On 18 June, the Alert Level was decreased to 2 (on a scale of 1-4). Geologic Summary. The small conical volcano of Soputan on the southern rim of the Quaternary Tondano caldera is one of Sulawesi's most active volcanoes. 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. Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/ SOUFRIERE HILLS Montserrat 16.72°N, 62.18°W; summit elev. 915 m MVO reported no evidence of lava-dome growth at Soufrière Hills during 14-20 June. Seismic activity remained low. On 19 June, mild ash venting from the Gages vent (to the W) resulted in an ash plume that rose to an altitude less than 1.2 km (4,000 ft) a.s.l. and drifted E. The E talus slope continued to erode, producing minor rockfalls that descended into the Tar River Valley. The Alert Level remained elevated at 4 (on a scale of 0-5). 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/ UBINAS Perú 16.355°S, 70.903°W; summit elev. 5672 m Based on SIGMET reports, the Buenos Aires VAAC reported that ash plumes from Ubinas rose to altitudes of 5.5-5.8 km (18,000-19,000 ft) a.s.l. on 18 June and altitudes of 5.5-7.6 km (18,000-25,000 ft) a.s.l. on 22 June. The plumes drifted S, SE, and NE and were not observed 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. ==============================================================
