********************************************************** GVP/USGS Weekly Volcanic Activity Report 22-28 March 2006 ********************************************************** From: Gari Mayberry <mayberry@xxxxxxxxxxxxxx> GVP/USGS Weekly Volcanic Activity Report 22-28 March 2006 http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Galeras, Colombia | Poas, Costa Rica Ongoing Activity: | Anatahan, Mariana Islands | Augustine, USA | Colima, México | Fuego, Guatemala | Karymsky, Russia | Kilauea, USA | Pacaya, Guatemala | Raoul Island, New Zealand | Santa María, Guatemala | Soufrière Hills, Montserrat | St. Helens, USA | Tungurahua, Ecuador | Ulawun, Papua New Guinea | Veniaminof, USA New Activity/Unrest GALERAS Colombia 1.22°N, 77.37°W; summit elev. 4,276 m Due to an increase in tremor at Galeras beginning on the morning of 28 March, INGEOMINAS raised the Alert Level from 3 ("changes in the behavior of volcanic activity have been noted") to 2 ("likely eruption in days or weeks"). On the 28th, energetic signals and tremor began that had been absent during previous weeks. In addition, seismic instruments detected very shallow low-energy hybrid signals, similar to ones recorded during 1991-1993 when dome emplacement occurred on the main crater's floor. Background. 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. Sources: Instituto Colombiano de Geología y Minería http://www.ingeominas.gov.co/tmsingeominas/ModuloPublicacionPortal/PublicacionP ortal.asp, Reuters http://lta.today.reuters.com/news/NewsArticle.aspx? type=domesticNews&storyID=2006-03- 29T170723Z_01_N29300552_RTRIDST_0_LATINOAMERICA-COLOMBIA-VOLCAN-SOL.XML Galeras Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1501-08= POÁS Costa Rica 10.20°N, 84.233°W; summit elev. 2,708 m; All times are local (= UTC - 6 hours) On 24 March around noon, small phreatic eruptions began at Poás. The eruptions originated from the bottom of the volcano's Caliente Lake. Witnesses described a sudden emission of water and sediments S of the lake. Roaring was heard in a nearby tourist area and weak earthquakes were felt. OVSICORI-UNA visited the E side of the volcano on 25 March and confirmed that water, blocks, and sediments from the bottom of the lake had been ejected. Several dozens of impact craters were seen with diameters between 15 and 60 cm, extending E as far as 700 m. Blocks were found that ranged in diameter from a few to 50 cm wide. During 22-27 March, harmonic tremor was recorded. On the 27th, there was a reduction in seismicity and it returned to normal levels. No deformation was measured at the volcano. A news article reported that the area around the volcano was closed to visitors. Poás last erupted in 1994. Background. 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 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. Sources: Observatorio Vulcanológico y Sismológico de Costa Rica , Universidad Nacional (OVSICORI-UNA) http://www.una.ac.cr/ovsi/informes.html, Prensa Latina http://www.plenglish.com/article.asp?ID=%7B6A2CA6B4-66A7-4E7B- 9997-AC0B3F56E90E%7D&language=EN Poás Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1405-04= Ongoing Activity ANATAHAN Mariana Islands, central Pacific Ocean 16.35°N, 145.67°E; summit elev. 788 m; All times are local (= UTC + 10 hours) According to the Air Force Weather Agency (AFWA), on 19 March a hot spot at Anatahan was visible on satellite imagery and vog (volcanic fog) extended 200 km from the island. On 24 March around 1330, seismicity at Anatahan abruptly increased to about twice the background level. The seismicity consisted of low- amplitude tremor and small long-period earthquakes, similar to the seismicity on 17 and 18 March. On the 24th, vog from Anatahan was visible on satellite imagery extending W, then curling N. The plume was estimated to be below 1.2 km (4,000 ft) a.s.l. and no ash or hot spots were visible. Anatahan remained at Alert-level Advisory; Aviation Color Code Yellow (Volcanic activity has increased somewhat, but remains fairly low and is being closely monitored). Background. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of large stratovolcano with a 2.3 x 5 km, E-W-trending compound summit caldera. The larger western caldera is 2.3 x 3 km wide, and its western rim forms the island's 790-m high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern caldera contained a steep-walled inner crater prior to the 2003 eruption whose floor was only 68 m above sea level. Sparseness of vegetation on the most recent lava flows on Anatahan had indicated that they were of Holocene age, but the first historical eruption of Anatahan did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera. Sources: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory http://volcanoes.usgs.gov/updates.html, Washington Volcanic Ash Advisory Center http://www.ssd.noaa.gov/VAAC/messages.html Anatahan Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0804-20= AUGUSTINE SW Alaska, USA 59.363°N, 153.43°W; summit elev. 1,252 m Low-level eruptive activity continued at Augustine during 17-24 March. All available information indicated that the lava dome continued to grow, but the growth rate slowed in comparison to the previous week. Signals from small block-and-ash flows, rock avalanches, rockfalls, and lava flows continued to be recorded by the seismic network though at a decreased rate. Web-camera views showed continued steaming at the summit and occasional small rockfalls. Thermal anomalies continued to be visible on satellite imagery. Low-light camera images showed a decrease in thermal features in the volcano's summit area and on the upper NE flank compared to the previous week. Visual observations during 15-22 March revealed no large-scale dome growth. Decreased SO2 gas emission was measured on 22 March in comparison to 10 and 16 March. However, the level of SO2 emission was comparable to levels in late February and early March, and remained well above background. AVO reported that dome- building eruptive activity will likely continue, perhaps intermittently, over the next several weeks or months. Augustine remained at Concern Color Orange <http://www.avo.alaska.edu/color_codes.php>. Background. Augustine volcano, rising above Kamishak Bay in the southern Cook Inlet about 290 km SW of Anchorage, is the most active volcano of the eastern Aleutian arc. It consists of a complex of overlapping summit lava domes surrounded by an apron of volcaniclastic debris that descends to the sea on all sides. Few lava flows are exposed; the flanks consist mainly of debris- avalanche and pyroclastic-flow deposits formed by repeated collapse and regrowth of the volcano's summit. The latest episode of edifice collapse occurred during Augustine's largest historical eruption in 1883; subsequent dome growth has restored the volcano to a height comparable to that prior to 1883. The oldest dated volcanic rocks on Augustine are more than 40,000 years old. At least 11 large debris avalanches have reached the sea during the past 1800-2000 years, and five major pumiceous tephras have been erupted during this interval. Historical eruptions have typically consisted of explosive activity with emplacement of pumiceous pyroclastic-flow deposits followed by lava dome extrusion with associated block-and-ash flows. Sources: Alaska Volcano Observatory http://www.avo.alaska.edu/activity/avoreport.php?view=update, Anchorage Volcanic Ash Advisory Center http://www.ssd.noaa.gov/VAAC/OTH/AK/messages.html Augustine Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1103-01- COLIMA Western México 19.514°N, 103.62°W; summit elev. ~3,850 m Based on information from the Mexico City MWO, the Washington VAAC reported that there were several emissions from Colima during 26-27 March. The highest rising plume reached 6.1 km (20,000 ft) a.s.l. on the 26th. Background. 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. Source: 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= FUEGO Guatemala 14.47°N, 90.88°W; summit elev. 3,763 m During 22-28 March, several explosions at Fuego ejected incandescent material ~50-75 m high and gas plumes to ~300 m above the volcano (13,300 ft a.s.l.). Short pyroclastic avalanches occurred on the upper flanks. On 28 March, lava flowed ~450 m S and avalanches occurred from the lava-flow fronts. Background. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3,763-m-high Fuego and its twin volcano to the N, Acatenango. Construction of Meseta volcano continued until the late Pleistocene or early Holocene, after which growth of the modern Fuego volcano continued the southward migration of volcanism that began at Acatenango. Frequent vigorous historical eruptions have been recorded at Fuego since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows. The last major explosive eruption from Fuego took place in 1974, producing spectacular pyroclastic flows visible from Antigua. Source: Instituto Nacional de Sismologia, Vulcanologia, Meterologia, e Hidrologia, http://www.insivumeh.gob.gt/geofisica/boletin%20formato.htm Fuego Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1402-09= KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m During 17-24 March, Strombolian activity continued at Karymsky. Several ash plumes were visible on satellite imagery at a height of ~4 km (13,100 ft) a.s.l. and extended SE and E. A thermal anomaly was seen at the volcano during periods of visibility. About 40-450 small earthquakes occurred daily. Karymsky remained at Concern Color Code Orange <http://www.avo.alaska.edu/color_codes.php>. Background. 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 http://www.kcs.iks.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 22-28 March, lava from Kilauea flowed off of a lava delta into the ocean at the East Lae`apuki entry. Background volcanic tremor was at normal levels at Kilauea's summit. Small, shallow earthquakes continued beneath the summit area and upper east rift zone, often occurring in bursts but, they were less numerous than during the previous week, and much less than a month ago. Volcanic tremor reached moderate levels at Pu`u `O`o. Slight inflation and deflation occurred at the volcano. Background. 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 about 104 km2 of land on the S flank of Kilauea and building more than 200 hectares of new land. Source: US Geological Survey Hawaiian Volcano Observatory http://volcanoes.usgs.gov/update.html 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 During 22-28 March, incandescent volcanic material was ejected tens of meters above Pacaya and lava flows extended ~100 m down the volcano's S flank. On the 28th, a new lava flow was emitted from the SW edge of the active crater. The flow reached ~150 m and avalanches occurred from the lava-flow fronts. Background. 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, Meterologia, e Hidrologia, 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= RAOUL ISLAND Kermadec Islands, New Zealand 29.27°S, 177.92°W; summit elev. 516 m After a 17 March eruption at Green Lake on Raoul Island, no new eruptions occurred and seismicity declined through 24 March. GNS observed the volcano via photographs and video on the afternoon of the 17th, and noted that many new craters had formed in and around Green Lake and that pre-existing 1964 craters had reactivated. The main steam columns were derived from Crater I, Marker Bay, and Crater XI. The eruption blew over mature trees as far as 200 m from the eruption site and deposited dark gray hydrothermal mud and ballistic blocks. An aerial inspection on 21 March revealed that steam discharge from vents had declined significantly owing to a dramatic (6-8 m) rise in Green Lake's water level, and consequent drowning of most of the active vents. There was no evidence of further eruptions after 17 March. There was also no evidence that any activity occurred at the 1964 craters NW of crater gully, but many new craters had formed at the mouth of the gully where hot, bare ground was present. GNS reported that as the hydrothermal system adjusts to the increased fluid pressure, further eruptions remain possible. They recommended that access to the active crater area should be restricted to the margins of the areas affected to date and the Green Lake area should not be entered. According to news reports, the search for a missing person on the island ceased around 22 March. Raoul Island remained at Alert Level 2 (minor eruptive activity). Background. Anvil-shaped Raoul Island, the largest and northernmost of the Kermadec Islands, has been the source of vigorous eruptive activity during the past several thousand years that was dominated by dacitic explosive eruptions. Two Holocene calderas are found at Raoul. The older caldera cuts the center of Raoul Island and is about 2.5 x 3.5 km wide. Denham caldera, formed during a major dacitic explosive eruption about 2,200 years ago, truncated the western side of the island and is 6.5 x 4 km wide. Historical eruptions at Raoul during the 19th and 20th centuries have sometimes occurred simultaneously from both calderas, and have consisted of small-to-moderate phreatic eruptions, some of which formed ephemeral islands in Denham caldera. A 240-m-high unnamed submarine cone, one of several located along a fissure on the lower NNE flank of Raoul Island volcano, has also erupted during historical time. Sources: Institute of Geological & Nuclear Sciences (GNS) http://data.geonet.org.nz/geonews/index.html, GNS http://data.geonet.org.nz/geonews/index.html, Associated Press http://www.latimes.com/news/nationworld/world/wire/sns-ap- south-pacific-volcano,1,33771.story?coll=sns-ap-world-headlines Raoul Island Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0402-03= SANTA MARÍA Guatemala 14.756°N, 91.552°W; summit elev. 3,772 m A large number of weak-to-moderate explosions occurred at Santa María's Santiaguito lava-dome complex during 22-28 March, producing ash plumes that rose to ~1 km above the volcano (15,650 ft a.s.l.). The plumes drifted SW, depositing ash on properties 8-10 km away. On several days, short pyroclastic flows and block-and-ash avalanches descended the SW flank of Caliente Dome. Background. 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. Source: Instituto Nacional de Sismologia, Vulcanologia, Meterologia, e Hidrologia, http://www.insivumeh.gob.gt/geofisica/boletin%20formato.htm Santa María Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1402-03= SOUFRIÈRE HILLS Montserrat, West Indies 16.72°N, 62.18°W; summit elev. 1,052 m Observations of Soufrière Hills during 17-24 March revealed that lava-dome growth was focused in the summit area and towards the E and NE. The N side of the lava dome showed little change. Rockfalls and pyroclastic flows were restricted to the Tar River Valley and they were particularly numerous on 19- 20 March. The largest pyroclastic flows traveled as far as 2 km down Tar River Valley. There was an increase in gas emission during the report period. The sulfur-dioxide flux averaged 1,034 metric tons per day, with high gas emissions occurring on days of elevated pyroclastic-flow activity. The hydrogen chloride to sulfur dioxide ratio was 2.8 on 22 March. The ground- deformation network continued to indicate deflation across the volcano. Background. 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. Sources: Montserrat Volcano Observatory http://www.mvo.ms/, Washington Volcanic Ash Advisory Center http://www.ssd.noaa.gov/VAAC/messages.html 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 Growth of the new lava dome inside the crater of Mount St. Helens continued during 22-28 March, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Very small periodic earthquakes occurred every few minutes that were punctuated by occasional larger events. The GPS (Global Positioning System) network on the volcano continued to show spine motion on the active lava dome of ~1 m per day. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange. Background. 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: USGS 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 During 22-27 March, small-to-moderate explosions occurred at Tungurahua that consisted of gas, steam, and small amounts of ash. Plumes rose as high as ~1 km above the volcano (19,750 ft a.s.l.) on several days. An explosion on 26 March was accompanied by incandescent blocks that rolled down the volcano's NW flank. Background. 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. Sources: Instituto Geofisico-Escuela Poltecnica Nacional http://www.igepn.edu.ec/vulcanologia/tungurahua/actividad/informet.htm, Washington Volcanic Ash Advisory Center http://www.ssd.noaa.gov/VAAC/messages.html Tungurahua Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-08= ULAWUN New Britain Island, Papua New Guinea 5.04°S, 151.34°E; summit elev. 2,334 m Based on a pilot report, the Darwin VAAC reported that ash from Ulawun was visible at a height of ~3 km (10,000 ft) a.s.l. Ash was not visible on satellite imagery due to meteorological clouds around the volcano. Background. 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 Center 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= VENIAMINOF Alaska Peninsula, USA 56.17°N, 159.38°W; summit elev. 2,507 m Web-camera images of Veniaminof on 24 March showed a steam-and-ash plume drifting from the summit cone at a height less than 2.3 km (7,600 ft) a.s.l. This level of activity was similar to activity on 23 March, but higher than activity on 21 and 22 March when a very diffuse steam-and-ash plume was confined to the summit caldera. The flow of seismic data from Veniaminof stopped on the evening of 21 March due to technical problems. Veniaminof remained at Concern Color Code Yellow <http://www.avo.alaska.edu/color_codes.php>. Background. Massive Veniaminof volcano, one of the highest and largest volcanoes on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3,700 years ago. The caldera rim is up to 520 m high on the N, is deeply notched on the W by Cone Glacier, and is covered by an ice sheet on the S. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which reaches an elevation of 2,156 m and rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface. Source: Alaska Volcano Observatory http://www.avo.alaska.edu/avo4/updates/updates.htm Veniaminof Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1102-07- ============================================================== 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. ==============================================================
