********************************************************************* GVP/USGS Weekly Volcanic Activity Report 5-11 September 2007 http://www.volcano.si.edu/reports/usgs/ ********************************************************************* New Activity/Unrest: | Chikurachki, Russia | Kerinci, Indonesia | Ol Doinyo Lengai, Tanzania | Pavlof, USA Ongoing Activity: | Arenal, Costa Rica | Cleveland, USA | Karymsky, Russia | Kilauea, USA | Pacaya, Guatemala | Poás, Costa Rica | Rabaul, Papua New Guinea | Sangay, Ecuador | Shiveluch, Russia | Soufrière Hills, Montserrat | St. Helens, USA | Tungurahua, Ecuador | Turrialba, Costa Rica | Ubinas, Perú New Activity/Unrest CHIKURACHKI Kuril Islands, Russia 50.325°N, 155.458°E; summit elev. 1,816 m Based on ground and aerial observations, KVERT reported that explosions from Chikurachki produced ash plumes that rose to an altitude of 3.2 km (9,800 ft) a.s.l. during 31 August-7 September. Ash plumes were visible on satellite imagery drifting NE on 31 August and 1 September, and S and SE on 3 September. 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= KERINCI Sumatra, Indonesia 1.69°S, 101.27°E; summit elev. 3,805 m CVGHM reported that the Alert Status of Kerinci was raised on 9 September from 1 to 2 (on a scale of 1-4). Geologic Summary. The summit of 3,800-m-high Kerinci, Indonesia's highest volcano, contains a deep 600-m-wide crater often partially filled by a small crater lake. The massive 13 x 25 km wide volcano towers 2,400-3,300 m above surrounding plains. Kerinci is elongated in a N-S direction and is capped by an unvegetated young summit cone constructed NE of an older crater remnant. One of Sumatra's most active volcanoes, Gunung Kerinci has produced a series of moderate explosive eruptions during the 19th and 20th centuries. Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/ Kerinci Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0601-17= OL DOINYO LENGAI Tanzania, eastern Africa 2.751°S, 35.902°E; summit elev. 2,890 m An eruption of Ol Doinyo Lengai on 4 September produced an ash plume that was reported by a pilot and visible on satellite imagery. Ashfall lasted about 12 hours in the village of Engare Sero, about 18 km N. Dark areas on the NW, W, and E flanks that were noticeable on satellite imagery from 4 September were possibly due to recent lava flows and burned vegetation or both. An ash plume was also visible, drifting SSW. Multiple thermal anomalies at and around the summit were present on satellite imagery since 21 August 2007, and on the flanks on 31 August and 1 September. 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: Frank Moeckel, Matthieu Kervyn, Mercator and Ortelius Research Center for Eruption Dynamics, Ghent University, Greg Vaughan, JPL, Thomas M. Holden, Nature Discovery, Fred Belton, The Guardian Ol Doinyo Lengai Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0202-12= PAVLOF Alaska, USA 55.42°N, 161.887°W; summit elev. 2,519 m Seismic activity at Pavlof fluctuated, but generally remained elevated during 5-11 September. Seismicity was characterized by volcanic tremor, and signals interpreted as frequent explosions and debris flows. During the reporting period, satellite imagery revealed strong thermal anomalies at the summit. On 8 September, a possible steam plume was visible on satellite imagery and a pilot reported that a steam-and-ash plume drifted from the summit. The Volcanic Alert Level remained at Watch and the Aviation Color Code remained at Orange <http://www.avo.alaska.edu/color_codes.php>. Geologic Summary. The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavolf, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing strombolian to vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption of Pavlof took place in 1911, at the end of a 5-year-long eruptive episode; a fissure opened on the northern flank of the volcano, ejecting large blocks and issuing lava flows. Source: Alaska Volcano Observatory http://www.avo.alaska.edu/ Pavlof Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1102-03- Ongoing Activity ARENAL Costa Rica 10.46°N, 84.70°W; summit elev. 1,657 m In August, activity originating from Arenal's Crater C consisted of gas emissions, sporadic Strombolian eruptions, lava flows traveling down the SW and S flanks, and occasional avalanches from lava-flow fronts. Volcanic activity was at relatively low levels and few eruptions occurred. Blocks from the lava-flow fronts periodically reached vegetation and started small fires. Acid rain and small amounts of ejected pyroclastic material affected the NE and SE flanks. Eruptions produced ash plumes that rose about 2.2 km (7,100 ft) a.s.l. Pyroclastic cones on the NE and SW flanks continued to grow. Small avalanches of volcanic material traveled down several ravines. Crater D showed only fumarolic activity. Geologic Summary. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1,657-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. The earliest known eruptions of Arenal took place about 7,000 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. Arenal's most recent eruptive period began with a major explosive eruption in 1968. Continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows has occurred since then from vents at the summit and on the upper western flank. Source: Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) http://www.ovsicori.una.ac.cr/ Arenal Information from the Global Volcanism Program http://www.volcano.si.edu/gvp/world/volcano.cfm?vnum=1405-033 CLEVELAND Aleutian Islands, USA 52.82°N, 169.95°W; summit elev. 1,730 m AVO lowered the Volcanic Alert Level for Cleveland from Watch to Advisory and the Aviation Color Code from Orange to Yellow <http://www.avo.alaska.edu/color_codes.php> on 6 September. AVO noted that since late July, ash and gas plumes were absent in satellite imagery and no reports of activity were received. Clouds obscured satellite and web camera views during 5-11 September. Geologic Summary. The symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited dumbbell-shaped Chuginadak Island in the east-central Aleutians. The 1,730-m-high stratovolcano is the highest of the Islands of Four Mountains group and is one of the most active in the Aleutians. Numerous large lava flows descend its flanks. It is possible that some 18th to 19th century eruptions attributed to Carlisle (a volcano located across the Carlisle Pass Strait to the NW) should be ascribed to Cleveland. In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions from Mt. Cleveland have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks. Source: Alaska Volcano Observatory http://www.avo.alaska.edu/ Cleveland Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1101-24- KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m Seismic activity at Karymsky was above background levels during 31 August-7 September. Based on seismic interpretation, ash plumes may have risen to altitudes of 5.5-6 km (18,000-19,700 ft) a.s.l. Observations of satellite imagery revealed that a thermal anomaly was present in the crater during the reporting period. Ash plumes were also present and drifted NE on 31 August, and SE and NW during 1-3 September. The Level of Concern Color Code remained at Orange <http://www.avo.alaska.edu/color_codes.php>. Based on information from KEMSD, pilot reports, and observations in the Petropavlovsk-Kamchatsky Flight Information Region (FIR), the Tokyo VAAC reported that ash plumes rose to altitudes of 3-7.3 km (10,000-24,000 ft) a.s.l. during 5-10 September. Ash was not identified 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 5-11 September fissure segment D from Kilauea's 21 July fissure eruption continued to feed an advancing 'a'a lava flow that frequently overflowed its channel edges. Several of the lava flows that branched from the main channel continued to advance. A section of the lava flow's channel collapsed during 6-7 September, and several new lava flows branched away and advanced less than 1 km. On 8 September, the level of the lava in the channel was about 3-8 m below the previous level before the channel was breached. On 9 September, the channel was again full and overflowing. On 11 September, a breakout occurred at the fissure vent of segment D, sending a small lava flow to the S. A few small earthquakes were located beneath Halema'uma'u crater, the S flank, and the SW rift zone during the reporting period. 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- PACAYA southern Guatemala 14.38°N, 90.60°W; summit elev. 2,552 m On 7 September, INSIVUMEH reported that lava flows on the W flank of Pacaya's MacKenney cone were about 150 m in length. During the week prior, fumaroles in the crater produced white and blue plumes that drifted S and SW. Incandescence was observed from the summit. 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: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/geofisica/boletin%20formato.htm Pacaya Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1402-11= POÁS Costa Rica 10.20°N, 84.233°W; summit elev. 2,708 m OVSICORI-UNA reported that during August, Laguna Caliente, a summit lake of Poás, was greenish-gray in color, exhibited convection cells in the lake's center, and contained dark gray floating particles. Subaqueous fumaroles at the center of the lake released gases that spread and covered the entire surface of the lake. The level of the lake had dropped 59 cm with respect to its level in July, and it had a temperature of 58 degrees Celsius. Fumarolic activity from a pyroclastic cone produced gas plumes that rose 400 m above the floor of the crater. Points of gas discharge were noted from the N and NW crater walls, the terrace, and the NE edge of the crater. Fumaroles in contact with the lake and the NE wall produced sulfur particles that floated in the lake. Emissions from the SE and NE crater walls were very low in volume. Geologic Summary. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2,708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Poás eruptions often include geyser-like ejection of crater-lake water. Source: Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA) http://www.ovsicori.una.ac.cr/ Poás Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1405-04= RABAUL New Britain Island, Papua New Guinea 4.271°S, 152.203°E; summit elev. 688 m RVO reported that ash plumes from Rabaul caldera's Tavurvur cone rose to an altitude less than 1 km (3,300 ft) a.s.l. and drifted W on 3 September. Ashfall was reported from areas downwind. During 4-10 September, white vapor plumes rose to altitudes less than 2 km (6,600 ft) a.s.l. and drifted WNW. On 8 and 9 September, the smell of hydrogen-sulfide gas coincided with a blue tinge in the vapor plumes. During the reporting period, emissions were accompanied by roaring noises and observers saw incandescence at the summit. 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 and Steve Saunders, Rabaul Volcano Observatory Rabaul Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0502-14= SANGAY Ecuador 2.03°S, 78.34°W; summit elev. 5,188 m The Washington VAAC reported that ash plumes from Sangay were observed by pilots during 8-9 September. Ash was not detected on satellite imagery. 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= 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 31 August-7 September. Based on seismic interpretation during this interval, avalanches and ash plumes that rose to an altitude of 5.7 km (18,700 ft) a.s.l. Visual observation and video data indicated that ash plumes rose to an altitude of 4.5 km (14,800 ft) a.s.l. on 1 September and drifted SE. Gas-and-steam plumes were noted on the other days. Observations of satellite imagery revealed a thermal anomaly present in the crater during the reporting period. The Level of Concern Color Code remained at Orange <http://www.avo.alaska.edu/color_codes.php>. Based on information reported from KEMSD, the Tokyo VAAC reported that an eruption plume rose to an altitude of 4.9 km (16,000 ft) a.s.l. on 9 September. Ash was not identified on satellite imagery. 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 3-11 September the lava dome at Soufrière Hills changed very little, based on visual observations. Seismic activity was very low and low-level rockfall 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 5-11 September lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. 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 ash plumes from Tungurahua rose to altitudes of 5.3-8 km (17,400-26,200 ft) a.s.l. during 5-6 and 9-10 September. A few explosions occurred on 7 September, in one case associated with incandescent blocks rolling down the flanks. On 8 September, a steam plume rose to an altitude of 6 km (19,700 ft) a.s.l. and drifted W. During 9-10 September, incandescent blocks rolled about 100 m down the flanks. On 10 September, ashfall was reported in areas to the SW. 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= TURRIALBA Costa Rica 10.025°N, 83.767°W; summit elev. 3,340 m OVSICORI-UNA reported that fumarolic activity and gas discharge in and to the W of Turrialba's central crater continued throughout August. New points of gas discharge, small landslides, and accelerated vegetation die-off were noted from various locations within and around the crater. Fumaroles were active in almost all directions in the central crater; many exhibited sulfur deposits and those in the S, SE, and SW reached a temperature of 91 degrees C. Fumaroles at the bottom of the W crater reached 176 degrees C on 16 August. Small sulfur flows from a few of the fumaroles descended about 2 m from the emission point. Steam plumes from fumaroles on the W wall rose to an altitude of 3.8 km (12,500 ft) a.s.l. New fumaroles appeared on the SW flank and N and NW of the central crater. Some of the fumaroles corresponded to two widening cracks, to the SW and NW of the W crater. Vegetation affected from gas and steam discharge and sulfur deposits were noted. People living on the N flank and from areas to the NW and W reported constant gas emissions from cracks in an area of about 20 by 50 meters, NW of the W crater. Geologic Summary. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive 3340-m-high Turrialba is exceeded in height only by Irazú, covers an area of 500 sq km, and is one of Costa Rica's most voluminous volcanoes. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m wide summit depression that is breached to the NE. Most activity at Turrialba originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred at Turrialba during the past 3500 years. Turrialba has been quiescent since a series of explosive eruptions during the 19th century that were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters. Source: Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) http://www.ovsicori.una.ac.cr/ Turrialba Information from the Global Volcanism Program http://www.volcano.si.edu/gvp/world/volcano.cfm?vnum=1405-07= UBINAS Perú 16.355°S, 70.903°W; summit elev. 5,672 m Based on observations of satellite imagery and a pilot report, the Buenos Aires VAAC reported that an eruption plume from Ubinas rose to altitudes of 5.5-7.6 km (18,000-25,000 ft) a.s.l. and drifted SE on 11 September. 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. ==============================================================
