******************************************************************* GVP/USGS Weekly Volcanic Activity Report 31 October-6 November 2007 http://www.volcano.si.edu/reports/usgs/ ******************************************************************* New Activity/Unrest: | Kelut, Indonesia | Krakatau, Indonesia | Ol Doinyo Lengai, Tanzania Ongoing Activity: | Bezymianny, Russia | Chikurachki, Russia | Colima, México | Galeras, Colombia | Jebel at Tair, Yemen | Karymsky, Russia | Kilauea, USA | Rabaul, Papua New Guinea | Semeru, Indonesia | Shiveluch, Russia | Soufrière Hills, Montserrat | St. Helens, USA | Tungurahua, Ecuador | Ubinas, Perú New Activity/Unrest KELUT Java, Indonesia 7.93°S, 112.31°E; summit elev. 1,731 m CVGHM reported that a series of earthquakes from Kelut during 24-31 October were dominated by shallow events and tremor. Seismicity intensified during 2-3 November, and then decreased on 4 November. On 2 November the temperature of the crater lake was 50 degrees Celsius, the highest temperature recorded. On 4 November, white plumes rose to an altitude of 2 km (6,600 ft) a.s.l. and drifted N. Observations of video footage from a closed-circuit television camera revealed that a black mass protruded from the lake and was likely the cause of the plumes. The Alert Level remained at 4 (on a scale of 1-4). Geologic Summary. The relatively inconspicuous 1,731-m-high Kelut stratovolcano contains a summit crater lake that has been the source of some of Indonesia's most deadly eruptions. A cluster of summit lava domes cut by numerous craters has given the summit a very irregular profile. More than 30 eruptions have been recorded from Gunung Kelut since 1000 AD. The ejection of water from the crater lake during Kelut's typically short, but violent eruptions has created pyroclastic flows and lahars that have caused widespread fatalities and destruction. After more than 5,000 people were killed during the 1919 eruption, an ambitious engineering project sought to drain the crater lake. This initial effort lowered the lake by more than 50 m, but the 1951 eruption deepened the crater by 70 m, leaving 50 million cubic meters of water after repair of the damaged drainage tunnels. After more than 200 people were killed in the 1966 eruption, a new deeper tunnel was constructed, lowering the lake's volume to only about 1 million cubic meters prior to the 1990 eruption. Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/ Kelut Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0603-28= KRAKATAU Indonesia 6.10°S, 105.43°E; summit elev. 813 m According to a news article, "red-hot lava flares" from Anak Krakatau rose 500-700 m above the S crater on 6 November. Multiple ash clouds were also observed. Geologic Summary. The renowned Krakatau volcano lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 AD, resulted in a 7-km-wide caldera. Remnants of this volcano formed Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan volcanoes, and left only a remnant of Rakata volcano. The post-collapse cone of Anak Krakatau (Child of Krakatau), constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan, has been the site of frequent eruptions since 1927. Source: Bernama http://www.bernama.com/bernama/v3/news_lite.php?id=294649 Krakatau Information from the Global Volcanism Program http://www.vsi.esdm.go.id/portal/html/index.php OL DOINYO LENGAI Tanzania, eastern Africa 2.751°S, 35.902°E; summit elev. 2,890 m According to Frederick Belton's Ol Doinyo Lengai website, the owner of a camp on the S shore of Lake Natron reported that ash eruptions continued "daily" and some "lava eruptions" were observed at night. Based on pilot observations, the Toulouse VAAC reported an eruption on 6 November. Geologic Summary. The symmetrical Ol Doinyo Lengai stratovolcano is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent volcano, known as "The Mountain of God," rises abruptly above the broad plain S of Lake Natron. The cone-building stage of the volcano ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatite and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra eruptions and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater. Petrologists first observed the eruption of carbonatitic lava flows in the 1960s. Subsequent more frequent visits have documented long-term lava effusion in the summit crater that would not have been seen from the foot of the volcano. Sources: Toulouse Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/FR/messages.html, Frederick Belton's Ol Doinyo Lengai website http://www.mtsu.edu/~fbelton/lengai.html Ol Doinyo Lengai Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0202-12= Ongoing Activity BEZYMIANNY Kamchatka Peninsula, Russia 55.98°N, 160.59°E; summit elev. 2,882 m Based on seismic interpretation, KVERT reported that a series of explosions or collapses from lava flow fronts at Bezymianny occurred on 5 November. Two avalanches and an ash plume were also detected. Observations of satellite imagery revealed a thermal anomaly over the lava dome. The level of Concern Color Code remained at Yellow <http://www.avo.alaska.edu/color_codes.php>. 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: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/updates.shtml Bezymianny Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1000-25= CHIKURACHKI Kuril Islands, Russia 50.325°N, 155.458°E; summit elev. 1,816 m KVERT reported that clouds obscured satellite views of Chikurachki during 26 October-2 November. The Level of Concern Color Code remained at 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. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/updates.shtml Chikurachki Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0900-036= COLIMA Western México 19.514°N, 103.62°W; summit elev. 3,850 m During 31 October-1 November, vapor-and-ash plumes from Colima rose to an altitude of 4.5 km (14,800 ft) a.s.l. Based on reports from the Mexico City MWO, the Washington VAAC reported that an ash plume from Colima drifted N on 1 November. 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 Centre (VAAC) 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= GALERAS Colombia 1.22°N, 77.37°W; summit elev. 4,276 m Based on visual observations during clear weather, INGEOMINAS reported that steam-and-ash plumes from Galeras rose to a maximum altitude of 5.7 km (18,700 ft) a.s.l. during 29 October-4 November. The Alert Level remained at 3 (changes in the behavior of volcanic activity have been noted) on a scale of 4-1. 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. Long-term 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. Source: Instituto Colombiano de Geología y Minería http://www.ingeominas.gov.co/ Galeras Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1501-08= JEBEL AT TAIR Red Sea, Yemen 15.55°N, 41.82°E; summit elev. 244 m Since the beginning of an eruption of Jebel at Tair on 30 September, the MODIS satellite detected thermal anomalies over the island every day through 6 November. Geologic Summary. The basaltic Jebel at Tair volcano rises from a 1200 m depth in the south-central Red Sea, forming an oval-shaped island about 3 km long. Jebel at Tair (one of many variations of the name, including Djebel Teyr, Jabal al Tayr, and Jibbel Tir ) is the northernmost known Holocene volcano in the Red Sea and lies SW of the Farisan Islands. Youthful basaltic pahoehoe lava flows from the steep-sided central vent, Jebel Duchan, cover most of the island. They drape a circular cliff cut by wave erosion of an older edifice and extend beyond it to form a flat coastal plain. Pyroclastic cones are located along the NW and southern coasts, and fumarolic activity occurs from two uneroded scoria cones at the summit. Radial fissures extend from the summit, some of which were the sources of lava flows. The island is of Holocene age, and explosive eruptions were reported in the 18th and 19th centuries. Source: Hawai'i Institute of Geophysics and Planetology (HIGP) Moderate Resolution imaging Spectroradiometer (MODIS) Thermal Alert System, http://modis.higp.hawaii.edu/ Jebel at Tair Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0201-01= KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m KVERT reported that seismic activity at Karymsky was above background levels during 25-28 October and at background levels during 29 October-2 November. Based on seismic interpretation, ash explosions occurred. Cloud cover obscured observations of satellite imagery. The Level of Concern Color Code <http://www.avo.alaska.edu/color_codes.php> remained at Orange. Based on information from KEMSD, the Tokyo VAAC reported that an eruption plume rose to an altitude of 5.2 km (17,000 ft) a.s.l. on 2 November. Ash was not detected on satellite imagery. 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 HVO reported that during 31 October-6 November fissure segment D from Kilauea's 21 July fissure eruption continued to feed an advancing lava flow that frequently overflowed its channel edges. Small breakouts from a lava tube continued to slowly burn a kipuka about 1.2 km N of the main channel's end. An E-traveling lava tube supplied flows that burned into a small kipuka and forested areas. A few small earthquakes were located beneath the summit area, Halema'uma'u crater, and along the E rift zone and S-flank faults during the reporting period. During 3-4 November, an unusually large number of earthquakes were located beneath the S-flank faults. Tremor remained low below the summit and Pu'u 'O'o crater. 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- RABAUL New Britain Island, Papua New Guinea 4.271°S, 152.203°E; summit elev. 688 m RVO reported that white plumes occasionally accompanied by ash plumes from Rabaul caldera's Tavurvur cone rose to altitudes of 1.7-2.7 km (5,600-8,900 ft) a.s.l. during 2-5 November. Plumes drifted N, NW, and W. Ashfall was reported in Rabaul town and surrounding areas. A strong smell of hydrogen-sulfide gas was reported and occasional incandescence at the summit was observed. 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. Source: Herman Patia, Rabaul Volcano Observatory Rabaul Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0502-14= SEMERU Java, Indonesia 8.11°S, 112.92°E; summit elev. 3,676 m Based on reports from CVGHM, the Darwin VAAC reported that an unconfirmed eruption from Semeru was heard from 17 km away on 31 October. An eruption plume 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.ssd.noaa.gov/VAAC/OTH/AU/messages.html 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 was above background levels during 26 October-2 November. Based on seismic interpretation, ash plumes rose to an altitude of 6.8 km (22,300 ft) a.s.l. and small hot avalanches occurred. Observations of video footage indicated that ash and gas-and-steam plumes rose to altitudes of 5-5.3 km (16,400-17,400 ft) a.s.l. on 25, 26, and 31 October, and 1 November. Based on observations of satellite imagery, ash plumes drifted SE during 27-31 October and a thermal anomaly was present in the crater every day during the reporting period. The Level of Concern Color Code remained at Orange <http://www.avo.alaska.edu/color_codes.php>. Based on information from KVERT and KEMSD, the Tokyo VAAC reported that eruption plumes rose to altitudes of 5.2-8.5 km (17,000-28,000 ft) a.s.l. during 4-6 November. 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 MVO reported that during 31 October-5 November the lava dome at Soufrière Hills changed very little, based on limited visual observations due to cloud cover. Seismic activity was very low and low-level rockfall and pyroclastic flow activity continued. The Alert Level remained elevated at 4 (on a scale of 0-5). Geologic Summary. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. English's Crater, a 1-km-wide crater breached widely to the 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 31 October-6 November lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally 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 although visual observations were limited due to cloud cover, ash-and-steam and ash plumes from Tungurahua rose to altitudes of 5.5-8 km (18,000-26,200 ft) a.s.l. during 31 October-6 November. Plumes drifted NNE, N, NW, W, and SW, and occasionally followed explosions. Ashfall was reported from areas downwind every day during the reporting period. On 31 October and 3 November, roars were heard. Incandescence and incandescent blocks at the summit were observed on 1, 2, and 5 November. On 4 November, the road to Baños in the La Pampas sector to the S was temporarily closed due to lahars. 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 Significant Meteorological Information (SIGMET) advisories and observations of satellite imagery, the Buenos Aires VAAC reported that ash plumes from Ubinas rose to altitudes of 5.5-7.6 km (18,000-25,000 ft) a.s.l. during 1 and 3-6 November. Plumes drifted NE and SE. 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. ==============================================================
