**************************************************** GVP/USGS Weekly Volcanic Activity Report 4-10 April 2007 http://www.volcano.si.edu/reports/usgs/ **************************************************** New Activity/Unrest: | Batu Tara, Indonesia | Chikurachki, Russia | Etna, Italy | Piton de la Fournaise, Reunion Island | Reventador, Ecuador | Tungurahua, Ecuador Ongoing Activity: | Bulusan, Philippines | Karangetang, Indonesia | Karymsky, Russia | Kilauea, USA | Kliuchevskoi, Russia | Pacaya, Guatemala | Rabaul, Papua New Guinea | Shiveluch, Russia | Soufrière Hills, Montserrat | St. Helens, USA | Ubinas, Perú New Activity/Unrest BATU TARA Lesser Sunda Islands, Indonesia 7.792°S, 123.579°E; summit elev. 748 m CVGHM reported that observations of Batu Tara from 30 March indicated that the E side of the volcano was most impacted by recent activity. Plant life on the E side was affected by hot ashfall and incandescent rockslides and cooled lava flows were observed at the E foot of the volcano. Steam and occasional ash plumes rose from the area where hot material interacted with the sea. White plumes rose from the summit to an altitude of approximately 1.7 km (5,600 ft) a.s.l. and drifted E. Based on satellite imagery and information from CVGHM, the Darwin VAAC reported that diffuse plumes rose to altitudes of 1.5 km (5,000 ft) a.s.l. and drifted W and NW during 4-10 April. On 5 April, plumes rose to 3 km (10,000 ft) a.s.l. Based on satellite imagery and analysis from USGS, CVGHM reported that on 5 April, a lava flow on the E flank created a central levee with debris "fans" on either side, comprised of lava flows and blocky material. The delta-like shape spanned about 450 m across. 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. Sources: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http:// portal.vsi.esdm.go.id/joomla/, 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 Based on satellite imagery, KVERT reported that an ash plume from Chikurachki drifted 200 km NE on 4 April. On 5 April, the Tokyo VAAC reported that a possible eruption plume to an altitude of 4.3 km (14,000 ft) a.s.l. was seen on satellite imagery drifting N. Explosive activity continued on 9 April. On 10 April, KVERT set the Level of Concern Color Code to Orange <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. Sources: Kamchatkan Volcanic Eruption Response Team (KVERT) via the Volcano Listserv http://www.volcano.si.edu/reports/volclist/, 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 Chikurachki Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0900-36= ETNA Sicily, Italy 37.73°N, 15.00°E; summit elev. 3,315 m In the morning of 29 March, an increase in volcanic tremor at Etna was accompanied by lava fountaining and an ash plume that drifted NE. Three fissures opened and produced lava flows. The first two fissures produced lava flows from vents located on the SE flank of Bocca Nuova and in the saddle between Bocca Nuova and Southeast Crater (SEC), in the same location of the October-November 2006 events. The two flows merged down slope and traveled less than 1 km S, halting at the rim of Cratere del Piano. The third fissure opened at the E base of SEC, and the lava flow spread within the upper Valle del Bove. The flows stopped by early afternoon. Ash and lapilli fallout occurred in a narrow zone between SEC, Rifugio Citelli and Giardini Naxos, on the NE flank of the volcano. Geologic Summary. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BC. Historical lava flows cover much of the surface of this massive basaltic stratovolcano, the highest and most voluminous in Italy. Two styles of eruptive activity typically occur at Etna. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more of the three prominent summit craters, the Central Crater, NE Crater, and SE Crater. Flank eruptions, typically with higher effusion rates, occur less frequently and originate from fissures that open progressively downward from near the summit. A period of more intense intermittent explosive eruptions from Etna's summit craters began in 1995. The active volcano is monitored by the Instituto Nazionale di Geofisica e Volcanologia (INGV) in Catania. Source: Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania http://www.ct.ingv.it/, Etna Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0101-06= PITON DE LA FOURNAISE Réunion Island, Indian Ocean 21.23°S, 55.71°E; summit elev. 2,631 m; All times are local (= UTC + 4 hours) OVPDLF reported that on 30 March at 2300, a 9-hour eruption from the SE flank of Piton de la Fournaise produced a small lava flow. On 2 April, a fissure that opened on the S-part of Grand Brûlé also produced a lava flow that reached the sea later that day. The flow velocity was estimated at 100 cubic meters per second, a value not seen at Réunion Island within the last 20 or 30 years. Lava fountaining to 100 m was observed at the point of emission during 4-6 April. On 6 April, very liquid and fast-moving lava reached a higher velocity than on 2 April in the main channel and a'a' flows covered a broad area. Explosions and fragmentation of rock were observed at the point were the lava flows met the sea. Fine-grained particles and Pele's Hair were observed 10-20 km away and millimeter-sized grains of basalt were found within 5 km. Intense seismic activity was observed beneath the summit. Based on aerial photographs on 7 April, an area of 1000 x 700 m of Dolomieu crater collapsed to an estimated depth of 300 m on the N side and 10 m on the NW edge; the estimated collapse volume was 50 million cubic meters. On 7 and 8 April, seismicity and the intensity of lava fountaining decreased. On 10 April, tremor decreased in frequency and two lava flows were observed, one reaching the sea. 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. Sources: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) http://ovpf.univ-reunion.fr/, Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) via the Volcano Listserv http://www.volcano.si.edu/reports/volclist/ Piton de la Fournaise Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0303-02= REVENTADOR Ecuador 0.078°S, 77.656°W, summit elev. 3,562 m Incandescent blocks ejected from the summit of Reventador that subsequently rolled down the S flanks were observed at night during 3-4 April. Satellite imagery revealed ash plumes drifting W and a large thermal anomaly over the crater. On 4 April, a plume rose to an altitude of 4.6 km (15,100 ft) a.s.l. Crater incandescence was observed on 4 and 6 April and "cannon shots" were heard on 6 April. Ash-and-steam emissions were observed during 8-9 April. Steam emissions from the flanks on 8 April possibly originated from a lava flow. 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 Geofisico-Escuela Poltecnica Nacional http://www.igepn.edu.ec/ Reventador Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-01= TUNGURAHUA Ecuador 1.47°S, 78.44°W; summit elev. 5,023 m IG reported that during 3-5 April, ash plumes from Tungurahua rose to altitudes of 8-9 km (26,200-29,500 ft) a.s.l. and drifted NW and W. Ashfall was reported at areas to the SW on 4 April. On 3 April, blocks rolled 800 m down the W flank; noises indicating rolling blocks were heard on 5 and 6 April. Lahars descended the W flank on 6 April. During 6-8 April, ash plumes, occasionally accompanied by roaring noises and "cannon shots," rose to altitudes of 7-10.5 km (23,000-34,400 ft) a.s.l. and drifted mainly W and NW. Ashfall was reported from areas about 8 km NW and SW from the summit on 6 April. On 9 April, ashfall was reported from areas 8 km W. On 10 April an explosion occurred. Incandescence was seen at the summit and blocks rolled about 100 m down the flanks. Clouds occasionally inhibited visual observations during the reporting period. 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= Ongoing Activity BULUSAN Luzon, Philippines 12.770°N, 124.05°E; summit elev. 1,565 m According to news articles, eruptions from Bulusan on 8 April produced ash plumes that rose to altitudes of 3.1-6.6 km (10,200-21,700 ft) a.s.l. 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. Source: GMA News http://www.gmanews.tv/story/37377/Easter-Sunday-alert-Bulusan-Volcano- explodes-Taal-stirs-up Bulusan Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0703-01= KARANGETANG [Api Siau] Siau Island, Indonesia 2.47°N, 125.29°E; summit elev. 1,784 m Based on satellite imagery and analysis from USGS, CVGHM reported that sometime between mid-March and 6 April, the lava dome in the northern of three craters at Karangetang collapsed and was replaced by a new dome. The new dome was about 40 m in diameter. Material from the old dome was not evident. Geologic Summary. Karangetang (also known as Api Siau) lies at the northern end of the island of Siau, N of Sulawesi. The 1,784-m-high stratovolcano contains five summit craters along a N-S line. One of Indonesia's most active volcanoes, Karangetang has had more than 40 recorded eruptions since 1675. Twentieth-century eruptions have included frequent explosions, sometimes accompanied by pyroclastic flows and lahars. Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/ joomla/, Karangetang Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0607-02= KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m Seismic activity at Karymsky was above background levels during 4-10 April, with 100-250 shallow earthquakes occurring daily. Ash plumes may have reached altitudes of 4.5 km (14,800 ft) a.s.l. during the reporting period. Based on satellite imagery and information from the Petropavlovsk-Kamchatsky Flight Information Region (FIR), AVO, pilot reports, and KEMSD, the Tokyo VAAC reported that eruption plumes rose to altitudes of 3.4-7.6 km (11,000-25,000 ft) a.s.l. on 5, 9, and 10 April. Plumes drifted SE and E on 9 and 10 April, respectively. A thermal anomaly in the crater was detected on satellite imagery during 4-5 and 7-10 April. 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. 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 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 4-10 April, lava from Kilauea continued to flow across a lava delta into the ocean at the Kamokuna entry. Lava was not seen entering the ocean at the East Lae'apuki entry. Incandescence was intermittently visible from several breakouts on the Pulama pali and from several vents in Pu'u 'O'o's crater. Earthquake activity was scattered at the summit and S-flank areas. 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 Seismic activity at Kliuchevskoi continued at above background levels during 4-10 April. A gas-and-steam plume with a small amount of ash rose to an altitude of 5.3 km (17,400 ft) a.s.l. and drifted W and SW during 4-8 April. Strombolian activity was seen at the crater during 4-9 April. Based on observations and video data, lava was observed flowing down the NW flank on 9 April. A thermal anomaly in the crater was detected on satellite imagery during 2-10 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. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/ updates.shtml Kliuchevskoi Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1000-26= PACAYA southern Guatemala 14.38°N, 90.60°W; summit elev. 2,552 m The Washington VAAC reported that an ash plume from Pacaya was visible on satellite imagery drifting SSE on 6 April. 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 Amatitlán 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: Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/ messages.html Pacaya Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1402-11= RABAUL New Britain Island, Papua New Guinea 4.271°S, 152.203°E; summit elev. 688 m RVO reported that during 3-10 April, Rabaul caldera's Tavurvur cone emitted steam and steam-and-ash plumes that rose to 0.8-2.7 km (2,600-8,900 ft) a.s.l. and drifted W, NW, N, NE, and E. Occasional weak roaring noises occasionally accompanied the emissions. On 3 April, explosions shook buildings in Rabaul town. Based on reports from RVO and satellite imagery, the Darwin VAAC reported that ash plumes rose to an altitude of 3 km (10,000 ft) a.s.l. during 8-9 April. Incandescent material was ejected from the crater during 9-10 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: Steve Saunders and Herman Patia, Rabaul Volcano Observatory, Darwin Volcanic Ash Advisory Center http://www.bom.gov.au/info/vaac/advisories.shtml Rabaul Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0502-14= SHIVELUCH Kamchatka Peninsula, Russia 56.653°N, 161.360°E; summit elev. 3,283 m Seismic activity at Shiveluch continued above background levels during 4-10 April. Based on seismic interpretation, observation, and video data, ash-and-steam plumes rose to altitudes of 4.5-5 km (14,800-16,400 ft) a.s.l. throughout the reporting period. Plumes drifted N on 6 April. A large thermal anomaly was visible on satellite imagery during 1-10 April. 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 During 30 March-9 April, lava-dome growth at Soufrière Hills remained reduced or had possibly ceased. Small, intermittent pyroclastic flows originating from the E-facing shear lobe occurred in the Tar River Valley. Fumarolic activity was observed around the SE and NW regions of a collapse scar at the head of Tyres Ghaut, and to the W, above Gages Valley. Incandescent rockfalls from the E side of the dome were seen at night during 5-9 April. 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 4-10 April lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. The clear weather allowed for views of the sometimes steaming dome from remote cameras. 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- UBINAS Perú 16.355°S, 70.903°W; summit elev. 5,672 m Based on pilot reports and a significant meteorological notice (SIGMET), the Buenos Aires VAAC reported that ash plumes from Ubinas rose to 5.5-7 km (18,000-23,000 ft) a.s.l. during 5 and 7-9 April. Plumes drifted E, SE, S, and SW. 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 <http://www.volcano.si.edu/reports/usgs/> ++++++++++++++++++++++++++++++++++++++++++ ============================================================== 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. ==============================================================
