********************************************** GVP/USGS Weekly Volcanic Activity Report 25 April-1 May 2007 http://www.volcano.si.edu/reports/usgs/ ********************************************** New Activity/Unrest: | Bezymianny, Russia | Lopevi, Vanuatu | Piton de la Fournaise, Reunion Island Ongoing Activity: | Ambrym, Vanuatu | Batu Tara, Indonesia | Chikurachki, Russia | Colima, México | Karymsky, Russia | Kilauea, USA | Kliuchevskoi, Russia | Manam, Papua New Guinea | Masaya, Nicaragua | Rabaul, Papua New Guinea | Reventador, Ecuador | Santa María, Guatemala | Shiveluch, Russia | Soufrière Hills, Montserrat | St. Helens, USA | Talang, Indonesia | Tungurahua, Ecuador | Ubinas, Perú | Ulawun, Papua New Guinea New Activity/Unrest BEZYMIANNY Kamchatka Peninsula, Russia 55.98°N, 160.59°E; summit elev. 2,882 m Based on pilot reports, satellite imagery, and observations from the Petropavlovsk-Kamchatsky Flight Information Region (FIR), the Tokyo VAAC reported that on 29 April an ash plume from Bezymianny rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted W. Geologic Summary. Prior to its noted 1955-56 eruption, Bezymianny volcano had been considered extinct. The modern Bezymianny volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral volcano that was built between about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of Mount St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater. Source: Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html Bezymianny Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1000-25= LOPEVI Central Islands, Vanuatu 16.507°S, 168.346°E; summit elev. 1,413 m Based on a pilot report, the Wellington VAAC reported that an ash plume from Lopevi covered the vent on 25 April. The altitude of the plume was not reported. Geologic Summary. The small 7-km-wide conical island of Lopevi is one of Vanuatu's most active volcanoes. A small summit crater containing a cinder cone is breached to the NW and tops an older cone that is rimmed by the remnant of a larger crater. The basaltic-to-andesitic volcano has been active during historical time at both summit and flank vents, primarily on the NW and SE sides, producing moderate explosive eruptions and lava flows that reached the coast. Historical eruptions at the 1,413-m-high volcano date back to the mid- 19th century. The island was evacuated following eruptions in 1939 and 1960. The latter eruption, from a NW-flank fissure vent, produced a pyroclastic flow that swept to the sea and a lava flow that formed a new peninsula on the western coast. Source: Wellington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html Lopevi Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0507-05= PITON DE LA FOURNAISE Réunion Island, Indian Ocean 21.23°S, 55.71°E; summit elev. 2,631 m OVPDLF reported that the eruption of Piton de la Fournaise continued during 25- 30 April. Lava flows on the Grand Brûlé set fire to vegetation on 25 April. Tremor remained very low in intensity. Geologic Summary. The massive Piton de la Fournaise shield volcano on the island of Réunion is one of the world's most active volcanoes. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest of three large calderas. This latter caldera is 8 km wide and is breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows within the caldera, have been documented since the 17th century. Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) http://ovpf.univ-reunion.fr/ Piton de la Fournaise Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0303-02= Ongoing Activity AMBRYM Ambrym Island, Vanuatu 16.25°S, 168.12°E; summit elev. 1,334 m The Wellington VAAC reported that an ash plume from Ambrym was visible on satellite imagery on 1 May. The altitude and direction of the plume were not reported. Geologic Summary. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides arc. A thick, almost exclusively pyroclastic sequence, initially dacitic, then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major plinian eruption with dacitic pyroclastic flows about 1900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the caldera floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations. Source: Wellington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html Ambrym Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0507-04= BATU TARA Lesser Sunda Islands, Indonesia 7.792°S, 123.579°E; summit elev. 748 m Based on a pilot report, the Darwin VAAC reported that on 27 April a plume from Batu Tara rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted W. Geologic Summary. The small isolated island of Batu Tara in the Flores Sea about 50 km north of 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 only known historical eruption from Batu Tara, during 1847-52, produced explosions and a lava flow. Source: Darwin Volcanic Ash Advisory Center http://www.bom.gov.au/info/vaac/advisories.shtml Batu Tara Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0604-26= CHIKURACHKI Kuril Islands, Russia 50.325°N, 155.458°E; summit elev. 1,816 m KVERT reported that no eruptive activity from Chikurachki was noted visually or on satellite imagery during 20-27 April. The Level of Concern Color Code was lowered to yellow <http://www.avo.alaska.edu/color_codes.php>. Geologic Summary. Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is actually a relatively small cone constructed on a high Pleistocene volcanic edifice. Oxidized scoria deposits covering the upper part of the young cone give it a distinctive red color. Lava flows from 1,816-m- high Chikurachki reached the sea and form capes on the NW coast; several young lava flows also emerge from beneath the scoria blanket on the eastern flank. The more erosionally modified Tatarinov group of six volcanic centers is located immediately to the S of Chikurachki. Tephrochronology gives evidence of only one eruption in historical time from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/updates.shtml COLIMA Western México 19.514°N, 103.62°W; summit elev. 3,850 m Based on satellite imagery, the Washington VAAC reported that ash plumes from Colima drifted NW on 26 April. On 28 and 30 April, incandescent material was ejected 100 m above the summit. Geologic Summary. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward- younging volcanoes, Nevado de Colima (the 4,320 m high point of the complex) on the N and the historically active Volcán de Colima on the S. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5- km-wide caldera, breached to the S, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth. Sources: Gobierno del Estado de Colima http://www.colima- estado.gob.mx/2006/seguridad/indvolcan.php, Washington Volcanic Ash Advisory Center http://www.ssd.noaa.gov/VAAC/messages.html Colima Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1401-04= KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m Seismic activity at Karymsky was above background levels during 20-27 April. Based on seismic interpretation, satellite imagery, and visual observation, ash plumes rose to altitudes of 4-4.5 km (13,100-14,800 ft) a.s.l. on 21 April and drifted SE. 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 During 25 April-1 May, lava from Kilauea continued to flow SE across a lava delta into the ocean at the Kamokuna entry, but lava was not seen entering the ocean at East Lae'apuki. Incandescence was visible from several vents in the Pu'u 'O'o crater and minimally visible from breakouts on the Pulama pali. On 28 April, a gas plume rose from an unidentified location above the pali. Earthquake activity was scattered at the summit, upper E rift zone, and S-flank areas. Tremor remained at moderate levels. 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- KLIUCHEVSKOI Kamchatka Peninsula, Russia 56.06°N, 160.64°E; summit elev. 4,835 m During 20-27 April, KVERT reported that Strombolian activity occurred at Kliuchevskoi, based on observations and video data. Seismic activity continued above background levels and a thermal anomaly in the crater was detected on satellite imagery. Mudflows and lava flows continued to advance on the NW flank. Phreatic activity and ash plumes from lava-flow fronts were noted. Gas- and-steam plumes containing ash rose to altitudes of 7.2 km (23,600 ft) a.s.l. and were visible on satellite imagery drifting E and SE. Based on satellite imagery and information from KVERT, the Tokyo VAAC reported that ash plumes rose to an altitude of 5.2 (17,000 ft) a.s.l. and drifted E during 25-26 April. The Level of Concern Color Code remained at Orange <http://www.avo.alaska.edu/color_codes.php>. 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= MANAM offshore New Guinea, Papua New Guinea 4.10°S, 145.06°E; summit elev. 1,807 m Based on satellite imagery and information from Rabaul Volcano Observatory, the Darwin VAAC reported diffuse plumes from Manam during 25-26 April. 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 (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html Manam Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0501-02= MASAYA Nicaragua 11.984°N, 86.161°W; summit elev. 635 m The Washington VAAC reported a steam plume from Masaya, visible on satellite imagery and a web camera, drifted WSW on 26 April. 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 fracture system 4 km in diameter. 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: Washington VAAC http://www.ssd.noaa.gov/VAAC/messages.html Masaya Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1404-10= RABAUL New Britain Island, Papua New Guinea 4.271°S, 152.203°E; summit elev. 688 m Based on information from RVO, the Darwin VAAC reported that explosions occasionally occurred from Rabaul on 26 April. Diffuse steam-and-ash plumes were visible on satellite imagery and rose to a few hundred meters. RVO reported that on 29 April, ash plumes rose to 2.7 km (8,900 ft) a.s.l. and drifted W. Ashfall was reported from areas downwind and occasional roaring noises were heard. Incandescence was observed at night during 25-29 April. 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 Rabaul Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0502-14= REVENTADOR Ecuador 0.078°S, 77.656°W, summit elev. 3,562 m On 27 April, a steam plume from Reventador rose to an altitude of 3.7 km (12,000 ft) a.s.l. Later that night, incandescent material was ejected from the crater. On 30 April, a steam plume was observed on satellite imagery drifting NW. Based on the Guayaquil MWO and satellite imagery, the Washington VAAC reported that an ash plume rose to an altitude of 3.7 km (12,000 ft) and drifted NW. Visual observations were hindered during 25 April-1 May due to inclement weather. 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. Sources: Instituto Geofísico-Escuela Politécnica Nacional http://www.igepn.edu.ec/, Washington 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= SANTA MARÍA Guatemala 14.756°N, 91.552°W; summit elev. 3,772 m INSIVUMEH reported that explosions from Santa María's Santiaguito lava dome complex on 26 April produced ash plumes that rose to altitudes of 4.4-4.8 km (14,400-15,700 ft) a.s.l. and drifted SW. Based on satellite imagery, the Washington VAAC reported that ash plumes and steam-and-ash plumes drifted S and WSW on 26 and 28 April, respectively. On 30 April, INSIVUMEH reported that explosions caused ashfall to the SW. Lava extrusion was low. Geologic Summary. Symmetrical, forest-covered Santa María volcano is one of a chain of large stratovolcanoes that rises dramatically above the Pacific coastal plain of Guatemala. The stratovolcano has a sharp-topped, conical profile that is cut on the SW flank by a large, 1-km-wide crater, which formed during a catastrophic eruption in 1902 and extends from just below the summit to the lower flank. The renowned Plinian eruption of 1902 followed a long repose period and devastated much of SW Guatemala. The large dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four westward-younging vents, accompanied by almost continuous minor explosions and periodic lava extrusion, larger explosions, pyroclastic flows, and lahars. Sources: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/geofisica/boletin% 20formato.htm, Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html Santa María Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1402-03= 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 20-27 April. Based on seismic interpretation, observation, and video data, ash-and-steam plumes possibly rose to altitudes of 6.5-9 km (21,300- 30,000 ft) a.s.l. throughout the reporting period. Plumes were seen on satellite imagery drifting E and SE, and a thermal anomaly was present. Hot avalanches originated from the dome. 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. 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 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 During 25 April-1 May, lava-dome growth at Soufrière Hills continued at a reduced rate. Rockfalls and pyroclastic flows occasionally occurred. On 30 April, two pyroclastic flows were observed to the NE in Tuitt?s Ghaut. 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 and observations from a remote camera showed that during 25 April-1 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. On 27 April, a thermal plume was detected on satellite imagery. 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- TALANG Sumatra, Indonesia 00.98°S, 100.68°E; summit elev. 2,896 m CVGHM lowered the Alert Level at Talang to 2 (on a scale of 1-4) on 27 April. Geologic Summary. Talang, which forms a twin volcano with the extinct Pasar Arbaa volcano, has two crater lakes on its flanks. The largest of these is 1 x 2 km wide Danau Talang. No historical eruptions have occurred from the summit of the volcano, which lacks a crater. All historical eruptions from Gunung Talang volcano have involved small-to-moderate 19th-century explosive activity originating from a series of small craters in a valley on the upper NE flank. Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://www.vsi.esdm.go.id/portal/html/index.php Talang Information from the Global Volcano Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0601-16= TUNGURAHUA Ecuador 1.47°S, 78.44°W; summit elev. 5,023 m IG reported that during 25, 27-29 April, and 1 May, ash plumes from Tungurahua rose to altitudes of 5.8-7.5 km (19,000-24,600 ft) a.s.l. and drifted SW and W. Ashfall was reported in areas to the SW, W, and NW during 25, 29-30 April, and 1 May. On 25 April, muddy water flowed down river valleys to the NW and disrupted the road between Ambato and Baños. The next day, lahars traveled down almost all of the river valleys, but were most concentrated in valleys to the W. Lahars and muddy water flowed down NW and W river valleys on 27 and 30 April. 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 satellite imagery and pilot reports, the Buenos Aires VAAC reported that ash plumes from Ubinas rose to altitudes of 5.5-7 km (18,000-23,000 ft) a.s.l. on 26, 29, and 30 April, and 1 May. Plumes drifted E and SSE. 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= ULAWUN New Britain Island, Papua New Guinea 5.04°S, 151.34°E; summit elev. 2,334 m Based on satellite imagery and information from the Rabaul Volcano Observatory, the Darwin VAAC reported that diffuse plumes from Ulawun drifted N on 28 April. On 1 May, an ash plume rose to an altitude of 4 km (13,000 ft) a.s.l. and drifted W. Geologic Summary. The symmetrical basaltic to andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. Ulawun rises above the N coast of New Britain opposite Bamus volcano. The upper 1,000 m of the 2,334-m-high volcano is unvegetated. A steep- walled valley cuts the NW side of the volcano, and a flank lava-flow complex lies to the S of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater. Source: Darwin Volcanic Ash Advisory Centre http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html Ulawun Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0502-12= ------------------------------------------------------------- ============================================================== 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. ==============================================================
