************************************************************** SI/USGS Weekly Volcanic Activity Report 22-28 April 2009 ************************************************************** Sally Kuhn Sennert - Weekly Report Editor kuhns@xxxxxx URL: http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Bagana, Bougainville | Ebeko, Paramushir Island | Galeras, Colombia | Pagan, Mariana Islands (Central Pacific) | Reventador, Ecuador | Shiveluch, Central Kamchatka (Russia) | Slamet, Central Java (Indonesia) Ongoing Activity: | Barren Island, Andaman Is | Batu Tara, Komba Island (Indonesia) | Chaitén, Southern Chile | Dukono, Halmahera | Fuego, Guatemala | Karymsky, Eastern Kamchatka | Kerinci, Sumatra (Indonesia) | Kilauea, Hawaii (USA) | Koryaksky, Eastern Kamchatka | Krakatau, Indonesia | Llaima, Central Chile | Pacaya, Guatemala | Rabaul, New Britain | Redoubt, Southwestern Alaska | Sakura-jima, Kyushu | Santa María, Guatemala | Soufrière Hills, Montserrat | Suwanose-jima, Ryukyu Islands (Japan) | Tungurahua, Ecuador 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 BAGANA Bougainville 6.140°S, 155.195°E; summit elev. 1750 m Based on analysis of satellite imagery, the Darwin VAAC reported that on 26 April an ash plume from Bagana rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted 28 km S. Geologic Summary. Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. Bagana is a massive symmetrical lava cone largely constructed by an accumulation of viscous andesitic lava flows. The entire lava cone could have been constructed in about 300 years at its present rate of lava production. Eruptive activity at Bagana is characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50-m-thick with prominent levees that descend the volcano's flanks on all sides. Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html EBEKO Paramushir Island 50.68°N, 156.02°E; summit elev. 1156 m KVERT reported that during 17-24 April observers from Severo-Kurilsk, about 7 km E of Ebeko, observed continued activity. Gas-and-steam plumes with some ash content rose to an altitude of 2 km (6,600 ft) a.s.l. during 17-19 April and drifted 8 km NE. On 22 April, light ash fell in Severo-Kurilsk. The Level of Concern Color Code remained at Yellow. Based on analysis of satellite imagery and information from Yelizovo Airport, the Tokyo VAAC reported that during 25-26 April ash plumes rose to altitudes of 1.2-2.1 km (4,000-7,000 ft) a.s.l. and drifted S, SW, and W. Geologic Summary. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. The eastern part of the southern crater of Ebeko contains strong solfataras and a large boiling spring. The central crater of Ebeko is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters of Ebeko, on the outer flanks of the cone, and in lateral explosion craters. 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 GALERAS Colombia 1.22°N, 77.37°W; summit elev. 4276 m INGEOMINAS reported that on 24 April seismicity from Galeras was similar to that seen prior to previous eruptions. Video camera views of the crater showed decreased gas emissions. The Alert Level was raised to II (Orange; "probable eruption in term of days or weeks"). Later that day, an explosive eruption was detected, prompting INGEOMINAS to raise the Alert Level to I (Red; "imminent eruption or in progress"). Incandescent blocks caused fires on the N flank. An accompanying shock wave was reported by residents up to 25 km away. A second eruption, of greater duration but less energy than the first, was detected about a half an hour later. Incandescence from both eruptions was seen from the city of Pasto (10 km E). An ash plume rose to an altitude of 10.3 km (33,800 ft) a.s.l. Ashfall was reported in areas up to 20 km W, WNW, and NW. According to a news article, populations living near the volcano were ordered to evacuate; about 200 people responded. On 25 April, ash-and-gas plumes rose 1 km above the crater. Thermal anomalies in the crater near the W flank measured 100 degrees Celsius. Ejected rocks had landed 2-3 km from the crater. The Alert Level was lowered to II. 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. Sources: Instituto Colombiano de Geología y Minería (INGEOMINAS) http://www.ingeominas.gov.co//, Colombia Reports http://colombiareports.com/colombia-news/news/3744-galeras-volcano-erupts-again.html PAGAN Mariana Islands (Central Pacific) 18.13°N, 145.80°E; summit elev. 570 m The USGS stated that a crew from a NOAA ship working at Pagan observed continuous steam emissions from the N crater during 21-22 April. Satellite imagery analyzed by the Washington VAAC showed a diffuse plume drifting 15 km W on 23 April. On 28 April, steam emissions had decreased so the Aviation Color Code and the Volcano Alert Level were lowered to “Unassigned.” There are no monitoring instruments on Pagan, thus the levels “Green” or “Normal” do not apply because background activity is not defined. Monitoring is done by satellite and ground observers. Geologic Summary. Pagan Island, the largest and one of the most active of the Marianas Islands volcanoes, consists of two stratovolcanoes connected by a narrow isthmus. Both North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. The 570-m-high Mount Pagan at the NE end of the island rises above the flat floor of the caldera, which probably formed during the early Holocene. South Pagan is a 548-m-high stratovolcano with an elongated summit containing four distinct craters. Almost all of the historical eruptions of Pagan, which date back to the 17th century, have originated from North Pagan volcano. The largest eruption of Pagan during historical time took place in 1981 and prompted the evacuation of the sparsely populated island. Source: Emergency Management Office of the Commonwealth of the Mariana Islands, Office of the Governor, United States Geological Survey Volcano Hazards Program http://volcano.wr.usgs.gov/ REVENTADOR Ecuador 0.077°S, 77.656°W; summit elev. 3562 m The IG reported that seismicity from Reventador decreased to low levels on 26 March, after the seismic network had detected an earthquake swarm the same day. On 23 April, increased seismicity was characterized by long-period events interspersed with bands of spasmodic and harmonic tremor. Observers reported that steam plumes with low ash content rose to altitudes of 5.6-6.6 km (18,400-21,700 ft) a.s.l. and drifted W. Intense noises from the volcano were also reported. A thermal anomaly and a steam plume drifting 26 km WSW were detected on satellite imagery. Geologic Summary. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well E of the principal volcanic axis. It is a forested stratovolcano that rises above the remote jungles of the western Amazon basin. A 3-km-wide caldera breached to the E was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1,300 m above the caldera floor. Reventador has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. Source: Instituto Geofísico-Escuela Politécnica Nacional (IG) http://www.igepn.edu.ec/ 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 17-24 April. Based on interpretations of seismic data, ash plumes likely rose to altitudes of 4.5-5.3 km (14,800-17,400 ft) a.s.l. Analysis of satellite imagery revealed a daily thermal anomaly on the lava dome. According to observers, fumaroles were active during 16-22 and 22 April. A hot avalanche produced an ash plume that rose to an altitude of 4 km (13,100 ft) a.s.l. on 22 April. On 25 April, increased seismicity indicated that an ash plume rose to an altitude of 7.5 km (24,600 ft) a.s.l. On 26 April, seismicity remained at high levels; continuous spasmodic tremor and a series of weak shallow earthquakes occurred. An ash explosion from the lava dome was seen on video camera. Ash emitted from a large fissure on the S flank of the lava dome produced plumes that rose to an altitude of 4 km (13,100 ft) a.s.l. and drifted ESE. The Level of Concern Color Code was raised to Red. The next day, seismicity decreased slightly but remained elevated and gas-and-steam emissions with some ash content emanated from the fissure. Based on video camera views and analysis of satellite imagery, plumes rose to altitudes of 3.5-5 km (11,500-16,400 ft) a.s.l. during 27-28 April and drifted 250 km NE. On 28 April, pyroclastic flows originated from areas near the lava dome. The Level of Concern Color Code was lowered to 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. Intermittent explosive eruptions began in the 1990s 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 SLAMET Central Java (Indonesia) 7.242°S, 109.208°E; summit elev. 3428 m CVGHM reported that seismicity from Slamet increased during 19-23 April. Diffuse white plumes rose about 50 m above the crater on 20 April. During 21-23 April, white and white-to-brownish plumes rose 50-800 m above the crater. On 23 April, the Alert Level was raised to 3 (on a scale of 1-4); people were advised not to climb the summit. According to a news article, a CVGHM volcanologist stated that lava was ejected 600 m high and ash bursts up to 112 times within a 6-hour period were detected. Geologic Summary. Slamet, Java's second highest volcano at 3428 m and one of its most active, has a cluster of about three dozen cinder cones on its lower SE-NE flanks and a single cinder cone on the western flank. Slamet is composed of two overlapping edifices, an older basaltic-andesite to andesitic volcano on the west and a younger basaltic to basaltic-andesite one on the east. Gunung Malang II cinder cone on the upper eastern flank on the younger edifice fed a lava flow that extends 6 km to the east. Four craters occur at the summit of Gunung Slamet, with activity migrating to the SW over time. Historical eruptions, recorded since the 18th century, have originated from a 150-m-deep, 450-m-wide, steep-walled crater at the western part of the summit and have consisted of explosive eruptions generally lasting a few days to a few weeks. Sources: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/, Jakarta Globe http://www.thejakartaglobe.com/home/article/17955.html 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 23-25 April ash plumes from Barren Island rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted 45-65 km NE, E, and SE. 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 BATU TARA Komba Island (Indonesia) 7.792°S, 123.579°E; summit elev. 748 m Based on analysis of satellite imagery, the Darwin VAAC reported that during 24-25 and 28 April ash plumes from Batu Tara rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted up to 110 km in multiple directions. 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 Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.htmlc CHAITEN Southern Chile 42.833°S, 72.646°W; summit elev. 1122 m SERNAGEOMIN reported that gas-and-ash plumes rose 1.5 km from Chaitén's Domo Nuevo 1 and Domo Nuevo 2 lava-dome complex during 15-21 April. Seismicity remained elevated; the largest earthquakes recorded were M 4.5. The Alert Level remained at Red. Based on web camera views, analysis of satellite imagery, and pilot observations, the Buenos Aires VAAC reported that on 25 and 28 April, ash plumes rose to altitudes of 2.1-3 km (7,000-10,000 ft) a.s.l. and drifted NE and N. According to a news article, one of about 70 people who had refused to evacuate Chaitén town (and stayed without basic services) died from hypothermia. 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, Herald Tribune http://www.laht.com/article.asp?ArticleId=333198&CategoryId=14094 DUKONO Halmahera 1.68°N, 127.88°E; summit elev. 1335 m Based on analysis of satellite imagery, the Darwin VAAC reported that on 28 April an ash plume from Dukono rose to an altitude of 4.5 km (14,000 ft) a.s.l. and drifted 150 km E. 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 On 24 and 28 April, INSIVUMEH reported that explosions from Fuego produced ash plumes that rose to altitudes of 4.1-4.8 km (13,500-15,700 ft) a.s.l. and drifted 10 km SW. Some explosions were accompanied by rumbling noises and shock waves detected 5 km away. Avalanches of blocks traveled down the flanks. Fumarolic plumes rose 50-150 m and drifted S, NW, and N. On 28 April, incandescent material was ejected 75-100 m into the air. 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/ KARYMSKY Eastern Kamchatka 54.05°N, 159.45°E; summit elev. 1536 m KVERT reported that fumarolic activity from Karymsky was seen by volcanologists during 17-24 April. Analysis of satellite imagery revealed a thermal anomaly on the volcano on 17 April. 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.insivumeh.gob.gt/ KERINCI Sumatra (Indonesia) 1.697°S, 101.264°E; summit elev. 3800 m CVGHM reported that diffuse white plumes from Kerinci typically rise about 300 m above the crater. On 9 September 2007 the Alert Level was raised to 2 (on a scale of 1-4) because "black smoke" plumes rose 800 m above the crater. The height of the plumes (described as “smoke”) declined, but remained variable, so the Alert Level continued at 2. On 24 March 2008, ash-and-gas plumes rose to 4.3 km (14,100 ft) a.s.l. In early April 2009, increased seismicity was accompanied by ash plumes that rose as high as 600 m above the crater. During 1-20 April, light and dark plumes rose to a maximum of 500 m above the crater. On 19 April, ashfall was reported at a nearby observation post. During 19-20 April, noises indicative of an eruption were heard at the observation post. 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 During 22-28 April, HVO reported that lava flowed SE from underneath Kilauea's Thanksgiving Eve Breakout (TEB) and rootless shield complex through a lava tube system, reaching the Waikupanaha and Kupapa'u ocean entries. Occasional explosions occurred from the Waikupanaha ocean entry, and on 22 April small littoral explosions continued to build up a steep-sided cone at the Kupapa'u entry. Surface flows were present on the coastal plain. The vent in Halema'uma'u crater continued to produce a white plume occasionally tinged brown that drifted SW, N, and NE. Poor air quality in nearby communities was sometimes caused by the plume. Incandescence was intermittently seen from the vent, and sounds resembling rushing gas or rockfalls were sometimes heard in the vicinity of the crater. Various amounts of tephra, including Pele's hair, spatter, and ash, were frequently retrieved from collection bins placed near the plume. 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/ KORYAKSKY Eastern Kamchatka 53.320°N, 158.688°E; summit elev. 3456 m During 17-25 April, KVERT reported that seismic activity at Koryaksky was above background levels and weak volcanic tremor was detected. Gas plumes containing a small amount of ash drifted in multiple directions during 17-18 April. On 17 and 18 April, gas-and-ash plumes were also seen on satellite imagery and drifted 100 km NE. On 20 April, a sulfur dioxide plume extended about 15 km from the volcano. During 26-28 April, seismic activity decreased to background levels; tremor was occasionally detected. The Level of Concern Color Code was lowered to Yellow. Geologic Summary. The large symmetrical Koryaksky stratovolcano is the most prominent landmark of the NW-trending Avachinskaya volcano group, which towers above Kamchatka's largest city, Petropavlovsk. Erosion has produced a ribbed surface on the eastern flanks of the 3456-m-high volcano; the youngest lava flows are found on the upper western flank and below SE-flank cinder cones. No strong explosive eruptions have been documented during the Holocene. Extensive Holocene lava fields on the western flank were primarily fed by summit vents; those on the SW flank originated from flank vents. Lahars associated with a period of lava effusion from south- and SW-flank fissure vents about 3900-3500 years ago reached Avacha Bay. Only a few moderate explosive eruptions have occurred during historical time. Koryaksky's first historical eruption, in 1895, also produced a lava flow. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php KRAKATAU Indonesia 6.102°S, 105.423°E; summit elev. 813 m According to a news article on 29 April, some residents on western Java (Lampung) near Krakatau have evacuated due to their observations of increased volcanic activity during the previous week. Observers reported loud blasts, lava flows, and ash plumes that rose 200-800 m above the Anak Krakatau crater. Pilots had also reported seeing ash plumes. A volcanologist from CVGHM stated that the activity did not merit an increase in the Alert level. The Alert Level remained at 2 (on a scale of 1-4). 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. Sources: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/, Jakarta Post http://www.thejakartapost.com/news/2009/04/21/lampung-residents-told-not-panic-mt-anak-krakatau-spews-ash.html LLAIMA Central Chile 38.692°S, 71.729°W; summit elev. 3125 m SERNAGEOMIN reported that on 24 April ash plumes originating from an area about 700 m down the E flank of Llaima rose 500 m and drifted E. Steam emissions that accompanied the ash plumes indicated that the point of activity came from underneath the glacier. The activity lasted about 1.5 hours. The Volcano Alert Level remained at Yellow. Geologic Summary. Llaima, one of Chile's largest and most active volcanoes, contains two main historically active craters, one at the summit and the other to the SE. The massive 3,125-m-high, glacier-covered stratovolcano has a volume of 400 cu km. A Holocene edifice built primarily of accumulated lava flows was constructed over an 8-km-wide caldera that formed about 13,200 years ago, following eruption of the 24 cu km Curacautín Ignimbrite. More than 40 scoria cones dot the volcano's flanks. Following the end of an explosive stage about 7,200 years ago, construction of the present edifice began, characterized by Strombolian, Hawaiian, and infrequent subplinian eruptions. Frequent moderate explosive eruptions with occasional lava flows have been recorded since the 17th century. Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN) http://www.sernageomin.cl/index.php PACAYA Guatemala 14.381°N, 90.601°W; summit elev. 2552 m On 24 and 28 April, INSIVUMEH reported gas emissions from Pacaya's MacKenney cone; occasional ash explosions ejected tephra 15-25 m high. The seismic network detected tremor and explosions. A small spatter cone being built in the S part of the crater was 4 m high. Rumbling noises were heard 3-5 km away and degassing produced sounds resembled airplane engines. Lava flows traveled 50-400 m down the SW flank and fumarolic plumes drifted S. 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/ RABAUL New Britain 4.271°S, 152.203°E; summit elev. 688 m RVO reported that during 18-25 April white and gray plumes from Rabaul caldera's Tavurvur cone rose 0.5-1.5 km above the crater. Plumes drifted E and SE. Incandescence from the summit crater was seen at night and occasional roaring noises were reported. Ashfall was reported in Kokopo, about 20 km SE, and surrounding areas. Based on analysis of satellite imagery, the Darwin VAAC reported that on 27 and 28 April ash plumes rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted 55 km S and 35 km SW. 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: Herman Patia, Rabaul Volcano Observatory (RVO), Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html REDOUBT Southwestern Alaska 60.485°N, 152.742°W; summit elev. 3108 m AVO reported that during 22-28 April seismicity from Redoubt remained above background levels, indicating ongoing growth of the lava dome in the summit crater. On 22 April, the web camera showed steam-and-gas plumes that may have occasionally contained small amounts of ash rising from the lava dome. Views during 23-28 April were prevented by meteorological clouds. Pilots reported sulfur odors to the NE on 22 April and to the S on 28 April. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange. 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/ SAKURA-JIMA Kyushu 31.585°N, 130.657°E; summit elev. 1117 m On 24 April, JMA lowered the Alert Level for Sakura-jima from 3 to 2 (on a scale of 1-5). No large eruptions occurred after 11 April, seismicity was low, and deformation was not detected. 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: Japan Meteorological Agency (JMA) http://www.jma.go.jp/jma/indexe.html SANTA MARIA Guatemala 14.756°N, 91.552°W; summit elev. 3772 m INSIVUMEH reported that during 24-28 April explosions from Santa María's Santiaguito lava dome complex produced ash plumes that drifted 5-8 km WSW. Gas plumes rose 25-75 m above Caliente dome. The number of explosions had decreased during the previous few weeks. 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/ SOUFRIERE HILLS Montserrat 16.72°N, 62.18°W; summit elev. 915 m MVO reported that during 17-24 April activity from the Soufrière Hills lava dome was at a low level. On 24 April, a small pyroclastic flow traveled E down the Tar River Valley. 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 The Tokyo VAAC reported that a pilot saw an ash plume from Suwanose-jima on 22 April. JMA reported that an eruption the next day produced ash plumes to altitudes of 1.2-1.5 km (4,000-5,000 ft) a.s.l. and drifted E and S. On 27 April, an explosion was reported but details of a possible resultant ash plume were not. On 28 April, explosions produced plumes that rose to altitudes of 1.5-1.8 km (5,000-6,000 ft) a.s.l. and drifted E. 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 TUNGURAHUA Ecuador 1.467°S, 78.442°W; summit elev. 5023 m The IG reported that during 22-28 April steam-and-gas plumes occasionally containing ash rose from Tungurahua to an altitude of 6.5 km (21,300 ft) a.s.l. and drifted SW and W. Roaring noises were reported. Ashfall was noted in areas to the SW on 21 April. During 21-22 April, incandescence from the crater was seen; incandescent blocks ejected from the crater on 22 April rolled down the flanks. On 25 April, a lahar descended the Patacocha drainage. 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/ +++++++++++++++++++++++++++++++++++++ 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. ==============================================================
