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GVP/USGS Weekly Volcanic Activity Report
20-26 September 2006
http://www.volcano.si.edu/reports/usgs/
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New Activity/Unrest: | Dempo, Indonesia | Floating Pumice, Fiji | Fourpeaked, USA | Poás, Costa Rica | Simbo, Solomon Islands
Ongoing Activity: | Barren Island, India | Karymsky, Russia | Kilauea, USA | Mayon, Philippines | Sakura-jima, Japan | Semeru, Indonesia | Soufrière Hills, Montserrat | St. Helens, USA | Suwanose-jima, Japan | Tungurahua, Ecuador | Ubinas, Perú
The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the US Geological Survey's Volcano Hazards Program. Updated by 2300 UTC every Wednesday, notices of volcanic activity posted on these pages are preliminary and subject to change as events are studied in more detail. This is not a comprehensive list of all of Earth's volcanoes erupting during the week, but rather a summary of activity at volcanoes that meet criteria discussed in detail in the "Criteria and Disclaimers" section. Carefully reviewed, detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism Network.
Note: Many news agencies do not archive the articles they post on the Internet, and therefore the links to some sources may not be active. To obtain information about the cited articles that are no longer available on the Internet contact the source.
New Activity/Unrest
DEMPO Sumatra, Indonesia 4.03°S, 103.41°E; summit elev. 3,173 m
Increased seismicity at Dempo resulted in an elevation of the hazard status to Alert Level 2.
Geologic Summary. Dempo is a prominent 3173-m-high stratovolcano that rises above the Pasumah Plain of SE Sumatra. Remnants of 7 craters are found at or near the summit, with volcanism migrating to the WNW with time. The historically active summit crater of Gunung Dempo contains a 400-m-wide lake, located at the NW end of the crater complex. Historical eruptions have been restricted to small-to-moderate explosive activity that produced ashfall near the volcano.
Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM)
FLOATING PUMICE Lau Islands, Fiji (unknown source)
Reports have been received of large pumice rafts in the Fiji Islands. On 16 September observers aboard the M/V National Geographic Endeavour noted almost continuous rows of pumice that day as they traveled about 90 km east-southeast to Vatoa Island, where the pumice was present on the beaches. Large rafts of pumice were also passing through the northern Lau Group around Naitauba Island on 19 September. The source of the pumice is unknown at this time.
Geologic Summary. Pumice rafts drifted to the Fiji area in 1979 and 1984 from submarine eruptions at Metis Shoal and Home Reef, both in the Tonga Islands roughly 350 km ENE. The active volcanoes of Tonga are 700-800 km E to SE from Fiji, and Monowai Seamount (Kermadec Islands) is ~1,100 km SE of Suva. Pumice from past eruptions in Tonga has typically traveled W to NW, with some material also moving SW.
Sources: David Cothran, M/V National Geographic Endeavour; David Forsythe, Naitauba Island, Fiji
FOURPEAKED Alaska Peninsula, USA 58.770°N, 153.672°W; summit elev. 2,105 m
On the evening of 17 September the Alaska Volcano Observatory (AVO) received several reports of two discrete plumes rising from the Cape Douglas area, about 320 km SW of Anchorage. Retrospective analysis of data from the NEXRAD Doppler radar in King Salmon showed an unusual cloud starting at 1200 that day. The maximum cloud height determined by radar during the first hour of the event was 6 km (20,000 ft) a.s.l. The radar return from the cloud continued until at least 2145. A cloud of sulfur dioxide gas was observed by colleagues at the University of Maryland Baltimore County over the Cape Douglas/Fourpeaked region at 1500 using data collected by the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite. On this basis all of the clouds were inferred to be volcanic in origin. Although satellite data did not detect ash during this event, AVO received reports of a trace of ashfall at Nonvianuk Lake outlet (110 km WNW) and near Homer (150 km NE).
Both fixed-wing and helicopter overflights in the Cape Douglas area 20 September confirmed the source of volcanic activity to be Fourpeaked volcano. AVO raised the Level of Concern Color Code from "Not Assigned" to YELLOW on 20 September. Fourpeaked and Douglas volcanoes are not monitored seismically. A 23 September observation flight conducted in relatively good weather permitted the first look at the summit since the event of 17 September. Observers saw a linear series of vents running N from the summit for about 1 km. Most of these vents were vigorously emitting steam and other volcanic gases. Gas measurements indicated abundant quantities of sulfur dioxide, hydrogen sulfide, and carbon dioxide.
Geologic Summary. Poorly known Fourpeaked volcano in NE Katmai National Park consists of isolated outcrops surrounded by the Fourpeaked Glacier, which descends eastward almost to the Shelikof Strait. The orientation of lava flows and extensive hydrothermal alteration of rocks near the present summit suggest that it probably marks the vent of Fourpeaked volcano.
Source: Alaska Volcano Observatory
POÁS Costa Rica 10.20°N, 84.233°W; summit elev. 2,708 m; All times are local (= UTC - 6 hours)
On 26 September at least two phreatic eruptions occurred at Poás. One during the night of 25 September reached a height of at least 350 m above the warm acid lake, depositing rock fragments, mud, and water in the southern part of the inner crater and outside the western part of the crater. Material ejected that night reached Trojas de Sarchí, almost 10 km SW. A smaller eruption on the morning of 26 September was limited to the area of the lake, and formed green-yellow semicircular zones of mud and sulfur up to 75 m in diameter.
Geologic Summary. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2,708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Poás eruptions often include geyser-like ejection of crater-lake water.
Source: Red Sismologica Nacional (RSN: UCR-ICE), Universidad de Costa Rica and Instituto Costarricense de Electricidad
SIMBO Solomon Islands 8.292°S, 156.52°E; summit elev. 335 m
Residents on Simbo Island reported feeling seven "earth tremors" on 21 September, and others in recent days. None of the events caused damage. The Solomon Islands Seismology Division does not have monitoring equipment on the island.
Geologic Summary. Simbo is a small island in the Western Solomons with three truncated andesitic volcanic centers. The only known Potassium-Argon date suggests a Pliocene-to-Pleistocene age for the island, although the southern half of the island is thermally active. Fault-related fumarolic areas and hot springs are found near saltwater Lake Ove along the western coast and along the eastern coast near Mount Patukio, which has a steep-walled summit crater. Grover (1955) noted native accounts of the explosive enlargement of the Ngusunu explosion crater along the SW coast of the island one to two generations prior to 1955, probably after a visit by Guppy in 1882. Press reports mentioned an eruption at Simbo in the early 1900s that forced the evacuation of villages beside Lake Ove, immediately adjacent to Ngusunu crater.
Source: Solomon Star
Ongoing Activity
BARREN ISLAND Andaman Islands, Indian Ocean, India 12.29°N, 93.88°E; summit elev. 354 m; All times are local (= UTC + 5 1/2 hours)
Indian Coast Guard officials noted in a news report on 23 September that the continuing eruption at Barren Island was decreasing in intensity. A surveillance report stated that there was less lava but more "smoke" coming from the volcano.
Geologic Summary. 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: The Hindu
KARYMSKY Kamchatka Peninsula, Russia 54.05°N, 159.43°E; summit elev. 1,536 m
Seismic data and satellite observations reported by KVERT indicate that moderate ash eruptions were continuing from Karymsky during 16-22 September. There have been 40-200 weak shallow earthquakes recorded each day. A thermal anomaly over the crater was noted on 18-19 September. Based on visual observations, volcanologists in the area on 19 September estimated ash explosions to have reached altitudes of 2.3 km (7,500 ft) a.s.l. Ash plumes extending 16-40 km SW and SE were noted at satellite images on 18-19 September.
Geologic Summary. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed about 7,600-7,700 radiocarbon years ago. Construction of the Karymsky stratovolcano began about 2,000 years later. The latest eruptive period began about 500 years ago, following a 2,300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been Vulcanian or Vulcanian-Strombolian with moderate explosive activity and occasional lava flows from the summit crater. Most seismicity preceding Karymsky eruptions has originated beneath Akademia Nauk caldera, which is located immediately S of Karymsky volcano and erupted simultaneously with Karymsky in 1996.
Sources: Kamchatkan Volcanic Eruption Response Team
KILAUEA Hawaii, USA 19.43°N, 155.29°W; summit elev. 1,222 m
Throughout 20-26 September Kilauea continued to erupt from the Pu`u `O`o vent on the East Rift Zone. Summit inflation centered in the south part of the caldera also continued. Lava was flowing through the PKK lava tube from its source on the SW flank of Pu`u `O`o to the ocean. About 1 km S of Pu`u `O`o, the Campout flow branches off from the PKK tube. The PKK and Campout systems feed two widely separated ocean entries named East Lae`apuki and East Ka`ili`ili, respectively. Activity during this period included numerous small breakouts from the Campout flow, new skylights along the PKK tube, and variable activity at the ocean entries. At Pu`u `O`o, intermittent lava incandescence reflected on gas plumes was visible from the usual four vents (East Pond, January, South Wall Complex, and Drainhole).
Geologic Summary. Kilauea, one of five coalescing volcanoes that comprise the island of Hawaii, is one of the world's most active volcanoes. Eruptions at Kilauea originate primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the caldera to the sea. About 90% of the surface of Kilauea is formed by lava flows less than about 1,100 years old; 70% of the volcano's surface is younger than 600 years. The latest Kilauea eruption began in January 1983 along the E rift zone. This long-term ongoing eruption from Pu`u `O`o-Kupaianaha has produced lava flows that have traveled 11-12 km from the vents to the sea, paving broad areas on the S flank of Kilauea and adding new land beyond the former coastline.
Source: US Geological Survey Hawaiian Volcano Observatory
MAYON southeastern Luzon, Philippines 13.257°N, 123.685°E
Surface activity at Mayon consisted of incandescent lava fragments rolling down the slopes and glow coming from the summit crater. Moderate white steam emissions continued from the summit. The number of daily volcanic earthquakes was low during 20-24 September, with 1-3 events per day. On the 25th there were 14 earthquakes recorded. There were also 114 tremor episodes that day, also a high for the week ending on 26 September. Sulfur dioxide flux remained above normal, between 1,200 and 2,200 metric tons/day.
Geologic Summary. 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 2000 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
SAKURA-JIMA Kyushu, Japan 31.58°N 130.67°E; summit elev. 1,117 m
Based on information from JMA, the Tokyo VAAC reported eruptions at Sakura-jima on 20 and 21 September. A plume from the second eruption rose to 2.4 km (8,000 ft) a.s.l.
Geologic Summary. Sakura-jima, one of Japan's most active volcanoes, is a post-caldera cone of the Aira caldera at the northern half of Kagoshima Bay. Eruption of the voluminous Ito pyroclastic flows was associated with the formation of the 17 x 23-km-wide Aira caldera about 22,000 years ago. The construction of Sakura-jima began about 13,000 years ago and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kita-dake summit cone ended about 4,850 years ago, after which eruptions took place at Minami-dake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.
Source: Tokyo Volcanic Ash Advisory Center
SEMERU Java, Indonesia 8.11°S, 112.92°E; summit elev. 3,676 m
Based on satellite imagery, the Darwin VAAC issued multiple aviation ash advisories for Semeru during 20-21 September. Plumes were initially reported to be near 11 km (36,000 ft) a.s.l. and drifting SW. The later reports noted a plume at 4.9 km (16,000 ft) a.s.l. extending about 90 km W.
Geologic Summary. Semeru is the highest volcano on Java and one of its most active. The symmetrical stratovolcano rises abruptly to 3,676 m above coastal plains to the S and lies at the southern end of a volcanic massif extending N to the Tengger caldera. Semeru has been in almost continuous eruption since 1967. Frequent small-to-moderate Vulcanian eruptions have accompanied intermittent lava dome extrusion, and periodic pyroclastic flows and lahars have damaged villages below the volcano. A major secondary lahar on 14 May 1981 caused more than 250 deaths and damaged 16 villages.
Source: Darwin Volcanic Ash Advisory Centre
SOUFRIÈRE HILLS Montserrat, West Indies 16.72°N, 62.18°W; summit elev. 1,052 m
MVO reported that during 15-22 September the lava dome at Soufrière Hills continued to grow at a moderate rate, slower than earlier in the month. Growth appears to have occurred predominantly in the summit area and on the S and E sides of the dome. The vent situated in the Gages Wall is still active, with minor explosive activity seen during an observation flight on 19 September. An intense 30-minute episode of volcanic tremor on 19 September was accompanied by rockfall activity that caused minor pyroclastic flows down the N and NE flanks of the lava dome. On 22 September the volume of the dome was about 80 million cubic meters. Seismicity was dominated by rockfalls with a significant drop in earthquake activity relative to the previous reporting period. The alert level was reduced to 3 (on a scale of 0-5) on 21 September. Aviation ash advisories during this period noted continuous ash emissions.
Geologic Summary. The complex dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. English's Crater, a 1-km-wide crater breached widely to the E, was formed during an eruption about 4,000 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, Washington Volcanic Ash Advisory Center
ST. HELENS Washington, USA 46.20°N, 122.18°W; summit elev. 2,549 m
Lava continued to extrude onto the crater floor during 20-26 September with low seismicity, generating occasional rockfalls as talus sloughed off the flanks of the growing dome.
Geologic Summary. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago, and has been the most active volcano in the Cascade Range during the Holocene. The modern edifice was constructed during the last 2,200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the N flank, and were witnessed by early settlers.
Source: US Geological Survey Cascades Volcano Observatory
SUWANOSE-JIMA Ryukyu Islands, Japan 29.53°N, 129.72°E; summit elev. 799 m
On 20 September the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite caught Suwanose-jima in the process of emitting volcanic ash and steam. The volcano's emissions blew N, gradually fanning out over the ocean, with a grayish tinge that distinguished it from nearby white clouds. Aviation ash advisories for this eruption issued by the Tokyo VAAC based on satellite imagery, pilot reports, and JMA, noted that the plume rose to 2.1 km (7,000 ft) a.s.l. and extended about 80 km N.
Geologic Summary. The 8-km-long, spindle-shaped island of Suwanose-jima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. Only about 50 persons live on the sparsely populated island. The summit of the volcano is truncated by a large breached crater extending to the sea on the E flank that was formed by edifice collapse. Suwanose-jima, one of Japan's most frequently active volcanoes, was in a state of intermittent Strombolian activity from On-take (also called Otake), the NE summit crater, that began in 1949 and lasted nearly a half century. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, after which the island was uninhabited for about 70 years. The SW crater produced lava flows that reached the western coast in 1813, and lava flows reached the eastern coast of the island in 1884.
Source: NASA Earth Observatory, Tokyo Volcanic Ash Advisory Center
TUNGURAHUA Ecuador 1.47°S, 78.44°W; summit elev. 5,023 m
During 20-26 September seismicity remained low, as Tungurahua continued to generate ash eruptions. Ash rose 2 km above summit (23,000 ft a.s.l.) on the afternoon of 21 September. Moderate ash emissions occurred again on 22 September. Three more ash emissions on 23 September caused ashfall in Penipe; one plume rose 3 km above the summit (26,000 ft a.s.l.), and another 4 km (29,500 ft a.s.l.). Ash plumes were seen again on 25 September.
Geologic Summary. The steep-sided Tungurahua stratovolcano towers more than 3 km above its northern base. It sits ~140 km S of Quito, Ecuador's capital city, and is one of Ecuador's most active volcanoes. Historical eruptions have been restricted to the summit crater. They have been accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. The last major eruption took place from 1916 to 1918, although minor activity continued until 1925. The latest eruption began in October 1999 and initially prompted temporary evacuation of the entire town of Baños on the N side of the volcano.
Source: Instituto Geofísico-Escuela Politécnica Nacional, Washington Volcanic Ash Advisory Center
UBINAS Perú 16.355°S, 70.903°W; summit elev. 5,672 m
Based on pilot reports, the Buenos Aires VAAC issued aviation ash advisories for Ubinas on 24 and 25 September. The continuous ash emissions were rising as high as 9 km (30,000 ft) a.s.l. and drifting SSE.
Geologic Summary. A small, 1.2-km-wide caldera that cuts the top of Ubinas, Peru's most active volcano, gives it a truncated appearance. Ubinas is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front of Peru. The upper slopes of the stratovolcano, composed primarily of Pleistocene andesitic lava flows, steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank of Ubinas extend 10 km from the volcano. Widespread Plinian pumice-fall deposits from Ubinas include some of Holocene age. Holocene lava flows are visible on the volcano's flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor explosive eruptions.
Source: Buenos Aires Volcanic Ash Advisory Center
Additional Reports of Volcanic Activity by Country
The following websites have frequently updated activity reports on volcanoes in addition to those that meet the criteria for inclusion in the Weekly Volcanic Activity Report. The websites are organized by country and are maintained by various agencies.
Ecuador, Indonesia, Japan, New Zealand, United States and Russia
Ed Venzke - Weekly Report Editor
URL: http://www.volcano.si.edu/reports/usgs/
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