********************************************************* GVP/USGS Weekly Volcanic Activity Report 15-21 Feb. 2006 ********************************************************* From: Gari Mayberry <mayberry@xxxxxxxxxxxxxx> GVP/USGS Weekly Volcanic Activity Report 15-21 February 2006 http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Mayon, Philippines | Miyake-jima, Japan Ongoing Activity: | Aoba, Vanuatu | Augustine, USA | Galeras, Colombia | Guagua Pichincha, Ecuador | Karymsky, Russia | Kilauea, USA | Rabaul, Papua New Guinea | Santa María, Guatemala | Soufrière Hills, Montserrat | St. Helens, USA | Tungurahua, Ecuador New Activity/Unrest MAYON southeastern Luzon, Philippines 13.257°N, 123.685°E; summit elev. 2,462 m; All times are local (= UTC + 8 hours) A minor explosion at Mayon on 21 February at 0941 produced an ash plume that rose to ~500 m above the volcano's crater (or 9,700 ft a.s.l.) and drifted SW. Ash was deposited on the upper slopes of the volcano. The ash emission was accompanied by a small explosion-type earthquake, recorded only by seismographs around the volcano. Prior to the explosion, an increase in seismicity was recorded at the volcano. Between 1545 on 20 February and 0520 on 21 February, there were 147 low- frequency volcanic earthquakes recorded, considerably above the five or fewer events per day that are normally recorded. Some minor rockfalls were indicated and probably resulted from detachment of lava blocks from the summit. Steaming was observed. No incandescence was visible at the crater due to clouds obscuring the volcano. Mayon remained at Alert Level 2, with a 6-km-radius Permanent Danger Zone in effect. PHIVOLCS expects similar ash explosions in the coming days as magma intrudes the summit area and releases volcanic gases. Background. The beautifully symmetrical Mayon volcano, which rises to 2,462 m above the Albay Gulf, is the Philippines' most active volcano. The structurally simple volcano has steep upper slopes that average 35-40° and is capped by a small summit crater. The historical eruptions of this basaltic- andesitic volcano date back to 1616 and range from Strombolian to basaltic Plinian. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. Mayon's most violent eruption, in 1814, killed more than 1,200 people and devastated several towns. Eruptions that began in February 2000 led PHIVOLCS to recommend on 23 February the evacuation of people within a radius of 7 km from the summit in the SE and within a 6 km radius for the rest of the volcano. Source: Philippine Institute of Volcanology and Seismology http://www.phivolcs.dost.gov.ph/ Mayon Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0703-03= MIYAKE-JIMA Izu Islands, Japan 34.08EN, 139.53EE; summit elev. 815 m According to a news report, a minor eruption at Miyake-jima on 17 February consisted of small ash emissions. Residents of the island were warned that there could be gas emissions and mudslides. The Geological Survey of Japan, AIST website reported that the sulfur-dioxide flux at Miyake-jima averaged about 2,000-5,000 tons per day in January. Background. The circular, 8-km-wide island of Miyake-jima forms a low-angle stratovolcano with a 3-km-wide summit caldera partially filled by the summit cone Oyama (many reports call the volcano Oyama). Parasitic craters and vents dot the volcano, including maars near the coast and radially oriented fissure vents. Frequent historical eruptions have originated at vents ranging from the summit to sea level, causing much damage. The previous eruption of Miyake-jima occurred in 1983; it forced ~4,000 residents to evacuate the island. There were no injuries or fatalities reported then, but basaltic lava flows destroyed 80% of the W-flank town of Ako and reached the sea on the SW coast. Sources: Geological Survey of Japan, AIST http://staff.aist.go.jp/a.tomiya/miyakeE.html, Associated Press http://news.yahoo.com/s/ap/20060219/ap_on_re_as/japan_volcano_1 Miyake-jima Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0804-04= Ongoing Activity AOBA Vanuatu 15.40°S, 167.83°E; summit elev. 1,496 m A news article reported on 16 February that the 5,000 people who evacuated their homes after increased activity began at Aoba on 27 November 2005 returned home after Department of Geology and Mines officials reduced the threat level from 2 to 1. Background. Aoba is a massive 2,500 cu km basaltic shield volcano that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW- trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes is located at the summit of the Hawaiian-style shield volcano within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. Post-caldera explosive eruptions formed the summit craters of Lake Voui (also spelled Vui) and Lake Manaro Ngoru about 360 years ago. A tuff cone was constructed within Lake Voui about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast. Source: Radio New Zealand International News http://www.rnzi.com/pages/news.php?op=read&id=22272 Aoba Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0507-03= AUGUSTINE SW Alaska, USA 59.363°N, 153.43°W; summit elev. 1,252 m During 15-19 February, AVO seismometers at Augustine recorded occasional rockfalls and small pyroclastic-flow signals indicative of minor collapses of the volcano's lava dome. During the previous week, the number of these events declined, suggesting that the rate of lava effusion may have slowed. Clear satellite views of the volcano on 16 February showed a thermal anomaly in the summit crater area. On the 19th, the web camera showed a light dusting of ash on the ENE flank of the volcano. AVO stated that during the report period a plume composed of variable amounts of gas, steam, and small amounts of ash was probably being emitted intermittently from Augustine's summit. They warned that occasional very localized ash clouds and light ashfall will be produced by collapses from the lava dome. 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- GALERAS Colombia 1.22°N, 77.37°W; summit elev. 4,276 m During 13-20 February, seismicity continued at Galeras, with an average of about 190 small earthquakes occurring per day. A flux of about 200 metric tons of sulfur dioxide was measured daily. Steam and gas rose to ~1.1 km above the volcano (or ~17,600 ft a.s.l.) on 19 February. Incandescence was visible at parts of the lava dome. The volume of the lava dome in the main crater was approximately 1.5 times larger than when it was first observed on 13 January. Galeras remained at Alert Level 3 ("changes in the behavior of volcanic activity have been noted"). Note: It was incorrectly reported in the 8-14 February Weekly Volcanic Activity Report that on 8 February pyroclastic-flow deposits were found at Galeras. Pyroclastic-fall deposits were observed. 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= GUAGUA PICHINCHA north-central Ecuador 0.17°S, 78.60°W; summit elev. 4,784 m IG reported that seismic activity at Guagua Pichincha during 6-12 February decreased in comparison to the previous week, confirming that a small increase in activity around 5 February was related to brief phreatic activity. No explosions occurred during the report period and low-level volcanic tremor was recorded. Background. Guagua Pichincha rises immediately west of Quito, Ecuador's capital city. The broad volcanic massif is cut by a large horseshoe-shaped summit caldera, ~6 km in diameter and 600 m deep, that was breached to the W during a slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent consisted of explosive activity with pyroclastic flows accompanied by periodic lava dome growth and destruction. A major eruption in 1660 deposited 30 cm of ash in Quito, but most of the many eruptions since the Spanish colonial era have been minor. The latest eruptive period began with phreatic explosions in 1998. Magmatic eruptions first occurred in October 1999, and intermittent eruptions of varying scale since then have blanketed Quito and surrounding towns with ash. Source: Instituto Geofísico-Escuela Politécnica Nacional http://www.igepn.edu.ec/ Guagua Pichincha Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=1502-02= KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m During 10-17 February, a large thermal anomaly was visible at Karymsky's crater and numerous ash plumes were visible on satellite imagery. Karymsky remained at Concern Color Code Orange <http://www.avo.alaska.edu/avo4/updates/color_code.html>. 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 16-20 February, no surface lava flows were visible on Kilauea's Pulama pali fault scarp, which had been the case since 8 February. Several streams of lava poured into the sea from the lava delta at the East Lae`apuki entry. Background volcanic tremor was at normal levels at Kilauea's summit, with shallow earthquakes continuing to occur beneath the summit area and the upper east rift zone. Volcanic tremor reached moderate levels at Pu`u `O`o. 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- RABAUL New Britain Island, Papua New Guinea 4.271°S, 152.203°E; summit elev. 688 m RVO reported that during 30 January to 15 February, Rabaul caldera's Tavurvur cone continued to be relatively quiet. Variable amounts of gas were emitted from an active fumarole at the summit area on the upper part of the W flank. An average sulfur-dioxide flux of 200 metric tons per day was recorded and seismicity was at low levels. According to the Darwin VAAC, ash from Rabaul was visible on satellite imagery at a height of ~3.7 km (12,100 ft) a.s.l. on 17 February. Background. 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. Sources: Rabaul Volcano Observatory, Darwin Volcanic Ash Advisory Center http://www.bom.gov.au/info/vaac/advisories.shtml Rabaul Information from the Global Volcanism Program http://www.volcano.si.edu/world/volcano.cfm?vnum=0502-14= SANTA MARÍA Guatemala 14.756°N, 91.552°W; summit elev. 3,772 m Several explosions occurred at Santa Maria's Santiaguito lava-dome complex during 15-17 February, with ash plumes rising to ~1.5 km above the volcano (or 17,300 ft a.s.l.). Some explosions were accompanied by small pyroclastic flows that traveled SW and NE down Caliente dome. Avalanches of incandescent volcanic material spalled off of active lava-flow fronts. 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 MVO reported that during vigorous ash-and-steam venting at Soufrière Hills on 10 February, a small dark lobe of lava was observed on the western side of the lava dome in the crater. By early on 11 February this lobe had advanced rapidly towards the NE side of the dome and was visible as a steep-sided plateau of lava from inhabited areas around Salem. Photographs from fixed cameras showed continued changes to this lava lobe over the next few days, and the NE margin could be seen glowing at night and shedding rockfalls into the NE part of the crater. The initial growth rate of this lobe was well over 5 cubic meters per second, but the rate declined around 17 February. The new lava lobe began to fill the gap between the lava dome and the northern and western crater walls, raising the possibility that small rockfalls could spill over those areas in coming weeks. The sulfur-dioxide flux averaged 568 metric tons per day. Data from Fourier Transform Infra Red spectrometry measurements indicated an increase in the hydrogen chloride/sulfur dioxide mass ratio in the gas plume from 2.0 in the last reporting period to an average of 2.5 on 13 February. 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 16-20 February, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Gas measurements made on 15 February suggested that the volcanic-gas flux remained unchanged from recent measurements. Observations made on 17 February revealed that the northeastern active part of the new lava dome was developing a steeply inclined jagged spine. At its top, temperatures as high as 580 degrees Celsius were measured using a thermal sensor. 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 Activity began to increase slightly at Tungurahua around 15 February. Several moderate explosions occurred during 15-19 February, with ash plumes rising as high as 3 km above the volcano (or 26,300 ft a.s.l.) on 15 February. Small amounts of ashfall were reported NW of the volcano in Cotaló, Cusúa, Pondoa, Bilbao, and at the Tungurahua Observatory (OVT) on the 18th. Rainfall generated a small mudflow SW of the volcano in the Quebrada Rea sector of Puela on 19 February. 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. ==============================================================
