*********************************************** GVP/USGS Weekly Volcanic Activity Report 23-29 May 2007 http://www.volcano.si.edu/reports/usgs/ *********************************************** New Activity/Unrest: | Bulusan, Philippines | Kliuchevskoi, Russia | Llaima, Chile | Ritter Island, Papua New Guinea Ongoing Activity: | Bagana, Papua New Guinea | Fuego, Guatemala | Karymsky, Russia | Kilauea, USA | Lascar, Chile | Manam, Papua New Guinea | Merapi, Indonesia | Reventador, Ecuador | Sakura-jima, Japan | Sangay, Ecuador | Semeru, Indonesia | Shiveluch, Russia | Soufrière Hills, Montserrat | St. Helens, USA | Tungurahua, Ecuador | Ubinas, Perú New Activity/Unrest BULUSAN Luzon, Philippines 12.770°N, 124.05°E; summit elev. 1,565 m According to news articles, scientists from PHIVOLCS conducted an aerial investigation of Bulusan and discovered lahar deposits and three steaming fissures. Lahars were previously reported from the municipalities of Irosin and Juban on 22 May. Scientists also observed steam plumes that rose to altitudes of 1.6-1.7 km (5,200-5,600 ft) a.s.l. and drifted NW and NE. PHIVOLCS reported that the S flank inflated 3 mm. Geologic Summary. Luzon's southernmost volcano, Bulusan, was constructed within the 11-km-diameter dacitic Irosin caldera, which was formed more than 36,000 years ago. A broad, flat moat is located below the prominent SW caldera rim; the NE rim is buried by the andesitic Bulusan complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit of Bulusan volcano is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded at Bulusan since the mid-19th century. Sources: GMA News http://www.gmanews.tv/story/43639/Phivolcs-finds-lahar- deposits-at-Bulusan-UK-issues-travel-alert\, The Philippine Star http://www.abs-cbnnews.com/storypage.aspx?StoryId=78507 Bulusan Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0703-01= KLIUCHEVSKOI Kamchatka Peninsula, Russia 56.06°N, 160.64°E; summit elev. 4,835 m KVERT reported that during 18-25 May, seismic activity at Kliuchevskoi continued above background levels and a thermal anomaly in the crater was detected on satellite imagery. On 18 May, ashfall was reported from the town of Klyuchi, about 30 km to the NE. According to video data and visual observations, Vulcanian activity at the summit crater and phreatic bursts on the NW flank of the volcano were observed during 22-24 May. Ash plumes rose to 5-8 km (16,000-25,600 ft) a.s.l. and drifted SE. Plumes were visible on satellite imagery drifting N, NE, and SE during the reporting period. Clouds inhibited observation on other days. The Level of Concern Color Code remained at Red <http://www.avo.alaska.edu/color_codes.php>. Based on satellite image observations and information from KVERT, the Tokyo VAAC reported that ash emissions produced possible plumes on 26 May to an altitude of 6.4 km (21,000 ft) a.s.l. and on 27 May to an altitude of 10.1 km (33,000 ft) a.s.l. Plumes drifted E, S, SW, and W. Ash plumes were also observed on satellite imagery during 28-29 May drifting S, SW, and W. Geologic Summary. Kliuchevskoi is Kamchatka's highest and most active volcano. Since its origin about 7,000 years ago, the beautifully symmetrical, 4,835-m- high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. More than 100 flank eruptions have occurred during the past 3,000 years, mostly on the NE and SE flanks of the conical volcano between 500 m and 3,600 m elevation. The morphology of its 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included major explosive and effusive eruptions from flank craters. Sources: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/updates.shtml, Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html Kliuchevskoi Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1000-26= LLAIMA central Chile 38.69°S, 71.73°W; summit elev. 3,125 m Based on a Significant Meteorological Information (SIGMET) advisory and satellite image observations, the Buenos Aires VAAC reported that ash plumes from Llaima rose to altitudes of 3-4.3 km (10,000-14,000 ft) a.s.l. on 26 May. The plumes were visible on satellite imagery drifting E. On 28 May, a pilot reported that an ash plume rose to 5.5-6.7 km (18,000-22,000 ft) a.s.l. and drifted E. Geologic Summary. Llaima, one of Chile's largest and most active volcanoes, contains two 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 cubic kilometers. 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: Buenos Aires Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html Llaima Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1507-11= RITTER ISLAND Papua New Guinea 5.52°S, 148.121°E; summit elev. 140 m On 30 May, RVO reported observations of Ritter Island following reports of a possible eruption and ?sea surges? that destroyed homes on 19 May. On the S part of the island, scorched vegetation was observed and dead marine life (mainly reef fish) was seen around the coast line at heights of 4-6 m a.s.l. There was no evidence of fresh volcanic material, but a new landslide scar extended from the upper most part of the island down to sea level. Several more landslide scars were seen on the W wall. The estimated wave surge height resulting from the 19 May event reached 4-10 m, particularly around the S part of the island. Rockfalls continued to produce plumes that could be seen from a distance. Geologic Summary. Prior to 1888, Ritter Island was a steep-sided nearly circular island about 780-m high. Several historical explosive eruptions had been recorded prior to 1888, when large-scale slope failure destroyed the summit of the conical volcano, leaving an arcuate 140-m-high island remnant with a steep W-facing scarp. Devastating tsunamis were produced by the collapse and swept the coast of Papua New Guinea and offshore islands. Two minor post- collapse explosive eruptions, during 1972 and 1974, occurred offshore within the largely submarine 3.5 x 4.5 km breached depression formed by the collapse. Source: Herman Patia, Rabaul Volcano Observatory Ritter Island Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0501-07= Ongoing Activity BAGANA Bougainville Island, Papua New Guinea 6.14°S, 155.19°E; summit elev. 1,750 m Based on satellite image observations and information from RVO, the Darwin VAAC reported that a diffuse ash-and-steam plume rose to an altitude of 3.7 km (12,000 ft) a.s.l. on 22 May and drifted W. Another diffuse plume was visible on satellite imagery to an altitude of 3 km (10,000 ft) a.s.l. on 28 May. 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 Bagana Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0505-02= FUEGO Guatemala 14.47°N, 90.88°W; summit elev. 3,763 m On 25 May, CONRED reported that the Alert Level for Fuego was lowered from Yellow to Green based on recent communication with nearby communities and monitoring by scientists at INSIVUMEH. During 28-29 May, INSIVUMEH reported that the lava flow on the S flank continued to advance and produce incandescent blocks that rolled W into the Taniluyá River valley. Low rumbling noises were heard during 26-27 May and occasionally accompanied pyroclastic explosions. Additional explosions produced plumes to an altitude of 4.1 km (13,500 ft) a.s.l. and expelled incandescent material about 100 m above the crater. Avalanches of blocks were observed on the S and SW flank. Gray plumes drifted S. Steam?and-gas plumes rose to an altitude of 4.6 km (15,100 ft) a.s.l. Geologic Summary. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3,763-m-high Fuego and its twin volcano to the N, Acatenango. Construction of Meseta volcano continued until the late Pleistocene or early Holocene, after which growth of the modern Fuego volcano continued the southward migration of volcanism that began at Acatenango. Frequent vigorous historical eruptions have been recorded at Fuego since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows. The last major explosive eruption from Fuego took place in 1974, producing spectacular pyroclastic flows visible from Antigua. Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/geofisica/boletin% 20formato.htm, Coordinadora Nacional para la Reducción de Desastres (CONRED) http://www.conred.org/boletines/2007/mayo2007/boletin250507a.php Fuego Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1402-09= KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m Seismic activity at Karymsky was slightly above background levels during 18-25 May. A possible ash plume rose to an altitude of 2 km (6,400 ft) a.s.l. on 18 May. The Level of Concern Color Code remained at Orange <http://www.avo.alaska.edu/color_codes.php>. 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/updates.shtml Karymsky Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1000-13= KILAUEA Hawaii, USA 19.43°N, 155.29°W; summit elev. 1,222 m; All times are local (=UTC -10 hours) During 23-29 May, lava from Kilauea flowed SE across a growing lava delta into the ocean at the Poupou entry. By 24 May, lava no longer entered the ocean at the Kamokuna entry. Incandescence was visible from several vents in the Pu'u 'O'o crater and from breakouts above and at the base of the Pulama pali fault scarp. The earthquake swarm that began on 12 May continued S and E of Halema?uma?u, in the upper E rift zone, and at scattered locations in the S flank. On 24 May, HVO recorded a M 4.7 earthquake at 0913, located beneath the upper E rift zone, near Puhimau crater, at a depth of 2 km. A M 4.1 aftershock occurred 20 minutes later and was located 1.5 km farther down-rift, beneath Koko?olau crater. A M 3.9 aftershock occurred at 1051 and was located another 2.5 km down- rift at a depth of 1 km. Since 1998, a few earthquakes with magnitudes greater than 4.0 have occurred at shallow depths beneath the upper E rift zone. 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 by lava flows less than about 1,100 years old; 70% of the volcano's surface is younger than 600 years. The latest Kilauea eruption began in January 1983 along the E rift zone. This long-term ongoing eruption from Pu'u 'O'o-Kupaianaha has produced lava flows that have traveled 11-12 km from the vents to the sea, paving broad areas on the S flank of Kilauea and adding new land beyond the former coastline. Source: US Geological Survey Hawaiian Volcano Observatory http://volcano.wr.usgs.gov/hvostatus.php Kilauea information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1302-01- LASCAR northern Chile 23.37°S, 67.73°W; summit elev. 5,592 m Based on a Significant Meteorological Information (SIGMET) advisory and satellite image observations, the Buenos Aires VAAC reported that an ash plume from Lascar rose to an altitude of 9.1 km (30,000 ft) a.s.l. on 23 May and drifted SSE. Geologic Summary. Lascar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters and lies 5 km W of an older, higher stratovolcano, Volcán Aguas Calientes. Lascar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption of Lascar took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9,000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to- moderate explosive eruptions have been recorded from Lascar in historical time since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away from the volcano. The largest historical eruption of Lascar took place in 1993 and produced pyroclastic flows that extended up to 8.5 km NW of the summit. Source: Buenos Aires Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html Lascar Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1505-10= MANAM offshore New Guinea, Papua New Guinea 4.10°S, 145.06°E; summit elev. 1,807 m Based on satellite image observations and information from RVO, the Darwin VAAC reported that diffuse plumes from Manam rose to an altitude of 3 km (10,000 ft) a.s.l. on 23 May and drifted SW and W. Geologic Summary. The 10-km-wide island of Manam is one of Papua New Guinea's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1,807-m-high 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. Five satellitic centers are located near the island's shoreline. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during the past century into the SE avalanche valley. Frequent historical eruptions have been recorded since 1616. Source: Darwin Volcanic Ash Advisory Centre http://www.bom.gov.au/products/IDD41300.shtml Manam Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0501-02= MERAPI central Java, Indonesia 7.542°S, 110.442°E; summit elev. 2,947 m According to a news article, ?hot clouds? and incandescent material from Merapi traveled a distance of 1 km SE down the Gendol River on 23 May. People in the nearby village of Muntilan, about 16 km W, reported ?hot clouds? and ashfall. Geologic Summary. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately N of the major city of Yogyakarta. The steep-sided modern Merapi edifice, its upper part unvegetated due to frequent eruptive activity, was constructed to the SW of an arcuate scarp cutting the eroded older Batulawang volcano. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated and inhabited lands on the volcano's western-to-southern flanks and caused many fatalities during historical time. The volcano is the object of extensive monitoring efforts by the Merapi Volcano Observatory. Source: Antara News http://www.antara.co.id/en/arc/2007/5/23/mount-merapi-emits- hot-clouds-anew/ Merapi Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0603-25= REVENTADOR Ecuador 0.078°S, 77.656°W, summit elev. 3,562 m Based on information from IG, the Washington VAAC reported that an ash plume from Reventador rose to an altitude of 3.7 km (12,000 ft) a.s.l. on 18 May and drifted NW. Ash was not observed 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: Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html Reventador Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-01= SAKURA-JIMA Kyushu, Japan 31.58°N, 130.67°E; summit elev. 1,117 m Based on information from JMA and a pilot report, the Tokyo VAAC reported that ash plumes from Sakura-jima rose to altitudes of 1.8-2.1 km (6,000-7,000 ft) a.s.l. during 23-24 and 26-28 May. Plumes drifted E and SE and rose straight up. 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 Sakura-jima Information from the Global Volcanism Program http://www.volcano.si.edu/gvp/world/volcano.cfm?vnum=0802-08= SANGAY Ecuador 2.03°S, 78.34°W; summit elev. 5,188 m Based on pilot observations, the Washington VAAC reported that an ash plume from Sangay rose to an altitude of 7.3 km (24,000 ft) a.s.l. on 24 May. Geologic Summary. The isolated Sangay volcano, located E of the Andean crest, is the southernmost of Ecuador's volcanoes, and its most active. It has been in frequent eruption for the past several centuries. The steep-sided, 5,230-m-high glacier-covered volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the E, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. Sangay towers above the tropical jungle on the E side; on the other sides flat plains of ash from the volcano have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The more or less constant eruptive activity has caused frequent changes to the morphology of the summit crater complex. Source: Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html Sangay Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-09= SEMERU Java, Indonesia 8.11°S, 112.92°E; summit elev. 3,676 m Based on a pilot report and information from CVGHM, the Darwin VAAC reported diffuse ash plumes from Semeru at an altitude of 4.6 (15,000 ft) a.s.l. on 25 May. The plumes drifted W. Ash was not detected on satellite imagery. Geologic Summary. Semeru is the highest volcano on Java and one of its most active. The symmetrical stratovolcano rises abruptly to 3,676 m above coastal plains to the S and lies at the southern end of a volcanic massif extending N to the Tengger caldera. Semeru has been in almost continuous eruption since 1967. Frequent small-to-moderate Vulcanian eruptions have accompanied intermittent lava dome extrusion, and periodic pyroclastic flows and lahars have damaged villages below the volcano. A major secondary lahar on 14 May 1981 caused more than 250 deaths and damaged 16 villages. Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.bom.gov.au/info/vaac/advisories.shtml Semeru Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0603-30= SHIVELUCH Kamchatka Peninsula, Russia 56.653°N, 161.360°E; summit elev. 3,283 m KVERT reported that seismic activity at Shiveluch continued above background levels during 18-25 May. Based on seismic interpretation, ash plumes possibly rose to altitudes of 4-8 km (13,100-26,200 ft) a.s.l. throughout the reporting period. Plumes were visible on satellite imagery drifting N, NE, and NW during 17-19 May. A large thermal anomaly was also visible on satellite imagery. The Level of Concern Color Code remained at Orange <http://www.avo.alaska.edu/color_codes.php>. 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 horseshoe-shaped 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/updates.shtml Shiveluch Information from the Global Volcanism Program http://www.volcano.si.edu/gvp/world/volcano.cfm?vnum=1000-27= SOUFRIÈRE HILLS Montserrat, West Indies 16.72°N, 62.18°W; summit elev. 1,052 m Based on visual observations, MVO reported that during 18-25 May lava-dome growth at Soufrière Hills likely ceased and the overall structure of the dome changed very little. Seismic activity was very low. The Alert Level remained 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 east, was formed during an eruption about 4000 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 http://www.mvo.ms/ Soufrière Hills Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1600-05= ST. HELENS Washington, USA 46.20°N, 122.18°W; summit elev. 2,549 m Data from deformation-monitoring instruments indicated that during 23-29 May lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations. Geologic Summary. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago, and has been the most active volcano in the Cascade Range during the Holocene. The modern edifice was constructed during the last 2,200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the N flank, and were witnessed by early settlers. Source: US Geological Survey Cascades Volcano Observatory http://vulcan.wr.usgs.gov/Volcanoes/MSH/CurrentActivity/framework.html St. Helens Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1201-05- TUNGURAHUA Ecuador 1.47°S, 78.44°W; summit elev. 5,023 m IG reported that during 23-29 May, steam and steam-and-ash plumes intermittently visible from Tungurahua rose to altitudes of 6-8 km (19,700- 26,200 ft) a.s.l. and drifted NW and W. Ashfall was reported from areas SW on 25 May, W and SW on 26 and 29 May, and NW on 27 May. 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 been restricted to 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 Poltécnica Nacional http://www.igepn.edu.ec/ Tungurahua Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-08= UBINAS Perú 16.355°S, 70.903°W; summit elev. 5,672 m Based on pilot reports, observations from satellite imagery, and Significant Meteorological Information (SIGMET) advisories, the Buenos Aires VAAC reported that during 22-28 May ash plumes from Ubinas rose to altitudes of 5.5-7.3 km (18,000-24,000 ft) a.s.l. Plumes drifted NE, E, and ESE. 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 Ubinas Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1504-02= +++++++++++++++++++++++++++++++++++++ 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. ==============================================================
