********************************************************* GVP/USGS Weekly Volcanic Activity Report 5-11 April 2006 ********************************************************* From: Gari Mayberry <mayberry@xxxxxxxxxxxxxx> GVP/USGS Weekly Volcanic Activity Report 5-11 April 2006 http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Ol Doinyo Lengai, Tanzania | Ubinas, Perú Ongoing Activity: | Augustine, USA | Barren Island, Andaman Islands | Galeras, Colombia | Kilauea, USA | Merapi, Indonesia | Poas, Costa Rica | Raoul Island, New Zealand | Soufrière Hills, Montserrat | St. Helens, USA | Tungurahua, Ecuador | Ulawun, Papua New Guinea | Veniaminof, USA New Activity/Unrest OL DOINYO LENGAI Tanzania, eastern Africa 2.751°S, 35.902°E; summit elev. 2,890 m On Frederick Belton's Ol Doinyo Lengai website, information was compiled about the activity that began around 30 March. According to the site, a bush pilot reported that a lava flow and lava fountains were emitted on the 30th, but there were no ash emissions. A steam plume was visible that may have been mistakenly described as ash in news reports. According to an observer in Tanzania, on 4 April a very large lava flow was visible on the volcano's W flank. The lava flow was over 1 km long and had traveled down the flank of the volcano and into a gorge. There were no signs that the flow was still hot. Photographs revealed that another lava flow may have traveled W of the volcano on 3 or 4 April. On 7 or 8 April, active lava was contained within a new lava lake. Contrary to news reports, a local tour operator stated that there were no evacuations from villages near the volcano. Background. 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. Source: Frederick Belton's Ol Doinyo Lengai website http://www.mtsu.edu/~fbelton/lengai.html Ol Doinyo Lengai Reports from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0202-12= UBINAS Perú 16.355°S, 70.903°W; summit elev. 5,672 m; All times are local (= UTC - 5 hours) Based on information from the Peruvian Volcanologic Observatory, the Buenos Aires VAAC reported that ash emitted from Ubinas reached 6.1-9.1 km (20,000-30,000 ft) a.s.l. on 6 April around 1220. No ash was visible on satellite imagery. The Aviation Color Code for the volcano was at Red, the highest level. At 1900 on the 6th a plume was observed at 6.1-7.3 km (20,000-24,000 ft) a.s.l. and drifting NE. The Aviation Color Code was subsequently reduced to Orange. On 8 April the VAAC received a report that volcanic activity had ceased, so the Aviation Color Code was reduced to Green, the lowest level. On the 9th, a significant meteorological forecast (SIGMET) was issued for an ash cloud at a height of 6.1-7.3 km (20,000-24,000 ft) a.s.l. that was drifting SW. The Aviation Color Code was increased to Red until 11 April. On the 11th volcanic activity reportedly ceased, so the code was again decreased to Green. Background. A small, 1.2-km-wide caldera that cuts the top of Ubinas, Peru's most active volcano, gives it a truncated appearance. Ubinas in 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 http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html Ubina Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1504-02= 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 31 March to 4 April, although it was at lower levels than in previous weeks. The seismic network continued to record signals that were associated with occasional hot block-and-ash flows, rock avalanches, rockfalls, and lava flows. Small and dilute ash clouds resulting from these processes were likely confined to the immediate vicinity of the volcano. Satellite imagery continued to show a thermal anomaly at the volcano's summit. Airborne sulfur-dioxide gas measurements revealed continued magmatic gas emissions. Low-light camera observations indicated that activity was restricted mainly to the summit lava dome. 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- BARREN ISLAND Andaman Islands, Indian Ocean, India 12.29°N, 93.88°E; summit elev. 354 m Based on information from a pilot report and satellite imagery, the Darwin VAAC reported that an ash plume was emitted from Barren Island during 5-6 April. The plume did not rise higher than 4.6 km (15,000 ft) a.s.l. 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 historical eruptions. Source: Darwin Volcanic Ash Advisory Center http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html 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 INGEOMINAS reported that Galeras remained at a critical state during 5-10 April, with a partially solidified lava dome in the main crater. Decreases were observed in various measured parameters at the volcano, including seismicity, deformation, gas emissions, and temperatures. According to INGEOMINAS, most of the explosive eruptions at Galeras in the past 17 years occurred when parameters were at similarly low levels. In addition, the current lava dome has a significantly greater volume than the dome that was destroyed during an eruption in 1992. Also, the volume of magma in the interior of the volcanic system is greater than during 1989-1993. Galeras remained at Alert Level 2 (likely eruption in days or weeks). 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/PublicacionPortal.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 5-11 April, lava from Kilauea continued to flow 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 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- MERAPI central Java, Indonesia 7.542°S, 110.442°E; summit elev. 2,947 m According to a news article, authorities banned mountain climbing on 10 April at Merapi due to increased activity. There were reports that the amount of tremor had increased and that lava was seen flowing near Pasar Bubar village, ~350 m from the volcano's crater. 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. Source: Deutsche Presse-Agentur http://news.monstersandcritics.com/asiapacific/article_1154303.php/Indonesia_bans_climbers_as_Javas_Mount_Merapi_volcano_heats_up Merapi Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0603-25= POÁS Costa Rica 10.20°N, 84.233°W; summit elev. 2,708 m On 1 April, clear weather allowed OVSICORI-UNA staff to visit Poás for the first time since explosions occurred during 24-26 March. They confirmed that Laguna Caliente at the volcano's summit had widened, and that sediments and blocks from the lake's bottom and surrounding walls were ejected during the explosions. The lava dome's (or pyroclastic cone's) N wall was greatly fractured and a 40 x 7 x 8 m segment of the wall was gone. In addition, a 40 x 4 x 6 m chunk of the SE wall of the lake was missing and must have been destroyed during the explosions. They also found that the lake was light gray due to large quantities of suspended sediments, had a temperature of 54 degrees Celsius, had a pH of 0.63, and the lake level had decreased in comparison to the level before the explosions. 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, 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.una.ac.cr/ovsi/informes.html Poás Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1405-04= RAOUL ISLAND Kermadec Islands, New Zealand 29.27°S, 177.92°W; summit elev. 516 m Seismicity continued to decline at Raoul Island through 7 April. In addition, Green Lake's water level began to recede, ending the water-level increase that had occurred in response to the 17 March eruption. 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. Source: Institute of Geological & Nuclear Sciences (GNS) http://data.geonet.org.nz/geonews/index.html Raoul Island Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0402-03= SOUFRIÈRE HILLS Montserrat, West Indies 16.72°N, 62.18°W; summit elev. 1,052 m; All times are local (= UTC - 4 hours) Low extrusion rates occurred at Soufrière Hills' lava dome at the beginning of the interval 31 March to 7 April. Continued lava-dome growth was focused E, with a lava lobe growing in that direction and the majority of rockfalls and pyroclastic flows occurring in the SE to NE sector. Photographs taken on 6 April clearly showed slightly elevated extrusion rates with lobe development on the E side of the dome. One moderate-sized pyroclastic flow occurred around 1030 on 2 April, resulting in minor ashfall to the W of the island. During the report period, the sulfur-dioxide flux averaged 578 metric tons per day. The hydrogen chloride to sulfur dioxide ratio was 2.3 and 2.6 on 4 and 5 April, respectively. 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 5-10 April, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Small earthquakes occurred once every several minutes, and GPS (global positioning system) data showed that solidified dacite lava continued to extrude slowly. 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; All times are local (= UTC - 5 hours) During 4-10 April, small-to-moderate explosions at Tungurahua consisted of gas, steam, and small amounts of ash. Plumes rose to ~3 km above the volcano (or 26,300 ft a.s.l.) on 9 April. Ash fell in the Baños, Guadalupe, Choglontus, Bilbao, and Manzano sectors. Around 1500 on the 9th, several lahars traveled down gorges mainly on the W side of the volcano, disrupting traffic along the Baños-Penipe highway. 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 A small low-level plume emitted from Ulawun was visible on satellite imagery extending W on 9 April. 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 During 31 March to 7 April, low-altitude ash emissions occurred from Veniaminof and seismicity remained at low levels. On 6 April, a pilot reported an ash plume at a height of ~3 km (10,000 ft) a.s.l. 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. ==============================================================
