********************************************************** GVP/USGS Weekly Volcanic Activity Report 15-21 March 2006 ********************************************************** From: Gari Mayberry <mayberry@xxxxxxxxxxxxxx> GVP/USGS Weekly Volcanic Activity Report 15-21 March 2006 http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Akan, Japan | Anatahan, Mariana Islands | Bulusan, Philippines | Merapi, Indonesia | Raoul Island, New Zealand Ongoing Activity: | Augustine, USA | Barren Island, Andaman Islands | Galeras, Colombia | Kilauea, USA | Soufrière Hills, Montserrat | St. Helens, USA | Tungurahua, Ecuador New Activity/Unrest AKAN Hokkaido, Japan 43.384°N, 144.013°E; summit elev. 1,499 m; All times are local (= UTC + 9 hours) A very small eruption occurred at Me-Akan (also called Meakan-dake, which means Meakan Peak) of the Akan volcanic complex on 21 March. Tremor began around 0628, the eruption apparently began around 0637, and an alert was issued by JMA at 0643. The eruption occurred from the volcano's NE flank. Ash was deposited on snow as far as 10 km SE of the volcano. The volcano is in a remote area and no populated areas were threatened. Me-Akan last erupted in 1998. Background. Akan is a 13 x 24 km, elongated caldera that formed more than 31,500 years ago immediately SW of Kutcharo caldera. Growth of four post- caldera stratovolcanoes, three at the SW end of the caldera and the other at the NE side, has restricted the size of the caldera lake. The 1-km-wide Nakamachineshiri crater was formed during a major pumice-and-scoria eruption about 13,500 years ago. Of the Holocene volcanoes of the Akan volcanic complex, only the Me-Akan group, E of Lake Akan, has been historically active, producing mild phreatic eruptions since the beginning of the 19th century. Me- Akan is composed of 9 overlapping cones. The main cone of Me-Akan proper has a triple crater at its summit. Historical eruptions at Me-Akan have consisted of minor phreatic explosions, but four major magmatic eruptions including pyroclastic flows have occurred during the Holocene. Sources: Gunma University, Reuters http://asia.news.yahoo.com/060321/3/2hp07.html Akan Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0805-07= ANATAHAN Mariana Islands, central Pacific Ocean 16.35°N, 145.67°E; summit elev. 788 m; All times are local (= UTC + 10 hours) During January and February, thin gas plumes from Anatahan were occasionally visible on satellite imagery, but became continuous and slightly more dense during 26 February to 19 March. On 17 March around 2200, seismicity abruptly increased by a factor of nearly two and continued at that level for 2 hours. On the 18th around 1400, seismicity again abruptly increased by a factor of nearly two and continued at that level for about 8 hours before returning to the baseline level prior to 17 March. The increased seismicity consisted of small (M 0-1) long-period earthquakes occurring approximately every minute or so, sometimes reaching two per minute. A total of about 600 such events were detected during 17 and 18 March. Volcanic Ash Advisories were issued by the Washington VAAC, but were cancelled when the plume was determined to contain gas and only insignificant amounts of ash. The Alert Level was raised from Normal; Aviation Color Code Green, to Advisory; Aviation Color Code Yellow around 20 March. 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= BULUSAN Luzon, Philippines 12.770°N, 124.05°E; summit elev. 1,565 m; All times are local (= UTC + 8 hours) On 21 March at 1058, a modest ash explosion occurred at Bulusan's summit crater. The phreatic explosion produced an ash cloud that rose ~1.5 km above the volcano (or 10,050 ft a.s.l.). Based on interpretations of seismic data, the event lasted ~20 minutes. It was accompanied by lightning and rumbling sounds. Ash drifted N, W, and SW of the volcano, and ~1 hour after the explosion light ash fell (producing ~5-mm-thick deposits) in Barangays (neighborhoods) Cogon, Tinampo, Gulang-Gulang, and Bolos in the town of Irosin. Ash also fell in Barangays Puting Sapa and Bura-Buran of Juban town, and other neighboring barangays under the municipalities of Irosin and Juban, Sorsogon. Three explosion-type earthquakes were also recorded on the 21st, at 1130, 1132, and 1137, but the accompanying eruptive events were not observed because the summit was obscured. PHIVOLCS reported that the ash explosions were more-or-less typical of activity at Bulusan during its restive period and they expect more explosions to occur. Bulusan was at Alert Level 1, with a Permanent Danger Zone of 4 kilometers around the summit. Background. 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: Philippine Institute of Volcanology and Seismology http://www.phivolcs.dost.gov.ph/ Bulusan Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0703-01= MERAPI central Java, Indonesia 7.542°S, 110.442°E; summit elev. 2,947 m Increased seismicity at Merapi led CVGHM to raise the Alert Level from 1 to 2 (on a scale of 1-4) around 20 March. According to a news articles, small earthquakes were recorded at the volcano on 19 March and more than 200 were recorded during the week. Around 10,000 residents near the volcano were warned to prepare for possible evacuations if activity escalates. Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately N of the major city of Yogyakarta. The steep-sided modern Merapi edifice, its upper part unvegetated due to frequent eruptive activity, was constructed to the SW of an arcuate scarp cutting the eroded older Batulawang volcano. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated and inhabited lands on the volcano's western-to-southern flanks and caused many fatalities during historical time. The volcano is the object of extensive monitoring efforts by the Merapi Volcano Observatory of the Volcanological Survey of Indonesia. Sources: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://www.vsi.esdm.go.id/portal/html/index.php, Agence France-Presse http://news.yahoo.com/s/afp/20060320/sc_afp/indonesiavolcano_060320194019 Merapi Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0603-25= RAOUL ISLAND Kermadec Islands, New Zealand 29.27°S, 177.92°W; summit elev. 516 m; All times are local (= UTC + 12 hours) An eruption began in the Green Lake area of Raoul Island volcano on 17 March around 0821. Based on interpretations of seismic data, the eruption appeared to have lasted for 30 minutes, with the most intense activity lasting 5-10 minutes. The eruption consisted of the ejection of mud and rocks, and a steam plume. A strong sequence of earthquakes began during the evening of the 12th that declined in number and size a few days before the 17th. According to GNS, the eruption appeared to have occurred with no immediate warning. New Zealand Department of Conservation officials evacuated a dozen staff on the island. News articles reported that one person remained missing on the island as of 22 March. The last eruption from the Green Lake area occurred during November 1964-April 1965. 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, Wellington Volcanic Ash Advisory Center http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html, Associated Press http://www.washingtonpost.com/wp- dyn/content/article/2006/03/17/AR2006031700340.html Raoul Island Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0402-03= Ongoing Activity AUGUSTINE SW Alaska, USA 59.363°N, 153.43°W; summit elev. 1,252 m Low-level eruptive activity continued at Augustine during 10-17 March. The seismicity changed from periods of prolonged volcanic tremor and closely spaced discreet earthquakes to episodic short-duration events. This change indicated that steady effusion of lava and dome growth gave way to activity characterized by slower effusion of lava and intermittent block-and-ash-flows, rock avalanches, and rockfalls originating from the summit lava dome. Observers saw numerous hot avalanches and prolonged periods of incandescence in the summit area and on the upper NE flank on several evenings. Satellite images showed that thermal anomalies persisted. Observations made during overflights of the volcano indicated that two lava flows on the N and NE flanks continued to advance slowly. Occasional collapses of the lava-flow fronts shed hot blocks and produced minor ash emissions. Photographs indicated that the new lava dome was about 70 m higher than the level of the lava dome formed in 1986. Augustine remained at Concern Color Code 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- BARREN ISLAND Andaman Islands, Indian Ocean, India 12.29°N, 93.88°E; summit elev. 354 m According to a news article, a team of scientists that visited Barren Island around 12 March found that the volcano was still very active and the height of the volcanic cone had increased by 50 m since eruptive activity began in May 2005. In addition, lava flows covered the NW side of the island. Background. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S-trending volcanic arc extending between Sumatra and Burma (Myanmar). The 354-m-high island is the emergent summit of a volcano that rises from a depth of about 2,250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the W, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and - surge deposits. The morphology of a fresh pyroclastic cone that was constructed in the center of the caldera has varied during the course of historical eruptions. Lava flows fill much of the caldera floor and have reached the sea along the western coast during eruptions in the 19th century and more recently in 1991 and 1995. Source: Indo-Asian News Service http://www.dailyindia.com/show/8974.php/No_fear_from_Barren_Island_volcano:_exp erts Barren Island Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0600-01= GALERAS Colombia 1.22°N, 77.37°W; summit elev. 4,276 m During 13-20 March, seismicity at Galeras decreased in comparison to previous weeks and deformation was measured at the volcano. Plumes of mainly steam, gas, and small amounts of ash were emitted from the volcano and rose to a maximum height of 1.2 km above the volcano (or 18,000 ft a.s.l.). Galeras remained at Alert Level 3 ("changes in the behavior of volcanic activity have been noted"). 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. Source: Instituto Colombiano de Geología y Minería http://www.ingeominas.gov.co/tmsingeominas/ModuloPublicacionPortal/PublicacionP ortal.asp Galeras Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1501-08= KILAUEA Hawaii, USA 19.43°N, 155.29°W; summit elev. 1,222 m During 15-22 March, lava flowed off of a lava delta into the ocean at the East Lae`apuki entry and surface lava flows were occasionally visible. Background volcanic tremor was at normal levels at Kilauea's summit, with shallow earthquakes continuing to occur beneath the summit area and the upper E rift zone. 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- SOUFRIÈRE HILLS Montserrat, West Indies 16.72°N, 62.18°W; summit elev. 1,052 m Cloudy conditions during 10-17 March limited visual observations of Soufrière Hills, however, lava-dome growth continued to be focused towards the E, NE, and NW as was evidenced by the production of large numbers of rockfalls and small pyroclastic flows. The ground deformation network showed a continuing trend of line shortening across the volcano. The sulfur-dioxide flux averaged 480 metric tons per day. The hydrogen chloride to sulphur dioxide ratio ranged between 1.1. and 2.1. 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 15-21 March, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Monitoring instruments showed no significant change in patterns of earthquake activity or deformation. Very small periodic earthquakes occurred every few minutes that were punctuated by occasional larger (< M 3) events. The active lava dome continued to build towards the W at about 1 m per day, consistent with the trend established over the previous few weeks. 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 16-20 March, small-to-moderate explosions occurred at Tungurahua that consisted of gas, steam, and small amounts of ash. Plumes rose to a height of ~3 km above the volcano (or 26,300 ft a.s.l.). 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= ============================================================== 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. ==============================================================
