SI/USGS Weekly Volcanic Activity Report 13-19 August 2008 Sally Kuhn Sennert - Weekly Report Editor kuhns@xxxxxx URL: http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Asama, Honshu (Japan) | Bezymianny, Central Kamchatka (Russia) | Kasatochi, Andreanof Islands | Piton de la Fournaise, Reunion Island | Soufrière Hills, Montserrat Ongoing Activity: | Batu Tara, Komba Island (Indonesia) | Chaitén, Southern Chile | Chikurachki, Paramushir Island | Cleveland, Chuginadak Island | Colima, México | Dukono, Halmahera (Indonesia) | Karymsky, Eastern Kamchatka | Kilauea, Hawaii (USA) | Krakatau, Indonesia | Llaima, Central Chile | Manam, Northeast of New Guinea (SW Pacific) | Masaya, Nicaragua | Okmok, Fox Islands | Rabaul, New Britain (SW Pacific) | Shiveluch, Central Kamchatka (Russia) | 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 ASAMA Honshu (Japan) 36.403°N, 138.526°E; summit elev. 2568 m Based on information from JMA, the Tokyo VAAC reported that on 14 August an eruption plume from Asama rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted S. Geologic Summary. Asama, Honshu's most active volcano, is located at the junction of the Izu-Marianas and NE Japan arcs and has an historical record dating back at least to the 11th century. The modern cone of Maekake-yama is situated E of the horseshoe-shaped remnant of an older andesitic volcano, Kurofu-yama, which was destroyed by a late-Pleistocene landslide about 20,000 years before present (BP). Growth of a dacitic and rhyolitic lava cone was accompanied by pumiceous pyroclastic flows, the largest of which occurred about 14,000-11,000 years BP, and by growth of the Ko-Asama-yama lava dome on the E flank. Maekake-yama is probably only a few thousand years old, but has had several major Plinian eruptions, the last two of which occurred in 1108 and 1783 AD. Source: Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html BEZYMIANNY Central Kamchatka (Russia) 55.978°N, 160.587°E; summit elev. 2882 m Based on observations of satellite imagery, KVERT reported that a thermal anomaly detected over Bezymianny's lava dome was strong during 9-14 August. Seismic activity was slightly above background levels during 10-14 August, possibly indicating that hot avalanches occurred. The Level of Concern Color Code remained at Orange. Based on observations of satellite imagery and information from KEMSD, the Tokyo VAAC reported that on 19 August, an eruption plume rose to an altitude of 7.9 km (26,000 ft) a.s.l. and drifted W. Geologic Summary. Prior to its noted 1955-56 eruption, Bezymianny volcano had been considered extinct. Three periods of intensified activity have occurred during the past 3,000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. That eruption, similar to the 1980 event at Mount St. Helens, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater. Sources: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php, Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html KASATOCHI Andreanof Islands 52.177°N, 175.508°W; summit elev. 314 m AVO reported that during 13-19 August seismic activity from Kasatochi was detected by stations on Great Sitkin, about 40 km W. Clouds prevented satellite image observations. On 17 August, the smell of sulfur was reported in the town of Adak. The Volcano Alert Level remained at Watch and the Aviation Color Code at Orange. Geologic Summary. Located at the northern end of a shallow submarine ridge trending perpendicular to the Aleutian arc, Kasatochi is small 2.7 x 3.3 km wide island volcano with a dramatic 750-m-wide summit crater lake. The summit of Kasatochi reaches only 314 m above sea level, and the lake surface lies less than about 60 m above the sea. A lava dome is located on the NW flank at about 150 m elevation. The asymmetrical island is steeper on the northern side than the southern, and the volcano's crater lies north of the center of the island. Reports of activity from the heavily eroded Koniuji volcano to the east probably refer to eruptions from Kasatochi. A lava flow may have been emplaced during the first historical eruption in 1760. Source: Alaska Volcano Observatory (AVO) http://www.avo.alaska.edu/ PITON DE LA FOURNAISE Reunion Island 21.231°S, 55.713°E; summit elev. 2632 m A small seismic crisis beneath the summit of Piton de la Fournaise lasted a little more than two and a half hours on 15 August. Deformation was also detected at the top of Dolomieu and, coupled with the increase in seismicity, prompted OVPDLF to raise the Alert level to 1. Public access to the summit was prohibited. On 18 August, the Alert Level was lowered because seismicity had decreased and deformation was no longer detected. Geologic Summary. Massive Piton de la Fournaise shield volcano on the island of Réunion is one of the world's most active volcanoes. Most historical eruptions have originated from the summit and flanks of a 400-m-high lava shield, Dolomieu, that has grown within the youngest of three large calderas. This depression is 8 km wide and is breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows within the caldera, have been documented since the 17th century. The volcano is monitored by the Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris. Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) http://ovpf.univ-reunion.fr/ SOUFRIERE HILLS Montserrat 16.72°N, 62.18°W; summit elev. 915 m MVO reported that new lava extrusion from Soufrière Hills started from the W side of the lava dome sometime between the 28 July lava-dome collapse event and 8 August, when a new channel of fresh rockfall material was seen below Gages Wall. Cloud cover often prevented visual observations. During 8-15 August, seismicity and the rate of lava extrusion were generally low and sulfur dioxide emissions were elevated. On 14 August the W side of the dome was visible and the explosion crater that was generated on 28 July was almost completely filled with new lava. Lava spilled over the lower and W side of the crater and generated rockfalls below Gages Wall that were observed and heard from St. George's Hill. During 14-15 August, the scent of volcanic gases was noticeable at times in inhabited areas of Montserrat. The Hazard Level was 3. 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. Source: Montserrat Volcano Observatory (MVO) http://www.mvo.ms/ Ongoing Activity BATU TARA Komba Island (Indonesia) 7.792°S, 123.579°E; summit elev. 748 m Based on analysis of satellite imagery, the Darwin VAAC reported that during 14-17 August ash plumes from Batu Tara rose to an altitude of 1.5 km (5,000 ft) a.s.l. and drifted W. Geologic Summary. The small isolated island of Batu Tara in the Flores Sea about 50 km north of Lembata (formerly Lomblen) Island contains a scarp on the eastern side similar to the Sciara del Fuoco of Italy's Stromboli volcano. Vegetation covers the flanks of Batu Tara to within 50 m of the 748-m-high summit. Batu Tara lies north of the main volcanic arc and is noted for its potassic leucite-bearing basanitic and tephritic rocks. The first historical eruption from Batu Tara, during 1847-52, produced explosions and a lava flow. Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html CHAITEN Southern Chile 42.833°S, 72.646°W; summit elev. 1122 m SERNAGEOMIN reported that continuous emissions of gas-and-ash plumes from Chaitén were observed on 13 August, after three days of bad weather prevented visual observations. Plumes rose to an altitude of 2 km (6,600 ft) a.s.l., but later that day rose to greater altitudes of 6-7 km (19,700-23,000 ft) a.s.l. The increased activity did not correspond to any significant variation in seismicity. Plumes were emitted from two areas on the E and S flanks and were different colors; the area on the E flank produced steam plumes with minor ash content and the area on the S flank emitted darker ash plumes. The plumes drifted SW and caused ashfall in Chaitén town for several hours. The ash accumulation was 1.5 cm thick. Based on web camera views, SIGMET reports, analysis of satellite imagery, and information from the Puerto Montt Flight Information Region (FIR), the Buenos Aires VAAC reported that during 16 and 18-19 August ash plumes rose to altitudes of 1.4-2.4 km (4,500-8,000 ft) a.s.l. and drifted NE, E, and SE. Geologic Summary. Chaitén is a small, glacier-free caldera with a Holocene lava dome located 10 km NE of the town of Chaitén on the Gulf of Corcovado. A pyroclastic-surge and pumice deposit considered to originate from the eruption that formed the elliptical 2.5 x 4 km wide summit caldera was dated at about 9400 years ago. A rhyolitic, 962-m-high obsidian lava dome occupies much of the caldera floor. Obsidian cobbles from this dome found in the Blanco River are the source of prehistorical artifacts from archaeological sites along the Pacific coast as far as 400 km away from the volcano to the north and south. The caldera is breached on the SW side by a river that drains to the bay of Chaitén, and the high point on its southern rim reaches 1122 m. Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN) http://www.sernageomin.cl/index.php, Buenos Aires Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html CHIKURACHKI Paramushir Island 50.325°N, 155.458°E; summit elev. 1816 m KVERT reported that clouds prevented satellite image views of Chikurachki during 8-15 August. The level of seismicity was unknown because Chikurachki lacks dedicated seismic instruments. The Level of Concern Color Code remained at Orange. Geologic Summary. Chikurachki, the highest volcano on Paramushir Island in the northern Kurils, is actually a relatively small cone constructed on a high Pleistocene volcanic edifice. Oxidzed scoria deposits covering the upper part of the young cone give it a distinctive red color. Lava flows from 1816-m-high Chikurachki reached the sea and form capes on the NW coast; several young lava flows also emerge from beneath the scoria blanket on the eastern flank. The more erosionally modified Tatarinov group of six volcanic centers is located immediately to the S of Chikurachki. Tephrochronology gives evidence of only one eruption in historical time from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php CLEVELAND Chuginadak Island 52.825°N, 169.944°W; summit elev. 1730 m AVO reported that cloud cover prevented satellite observations of Cleveland during 13-18 August. The Volcano Alert Level remained at Watch and the Aviation Color Code at Orange. Geologic Summary. Symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited dumbbell-shaped Chuginadak Island in the east-central Aleutians. The 1,730-m-high stratovolcano is the highest of the Islands of Four Mountains group and is one of the most active in the Aleutians. Numerous large lava flows descend its flanks. It is possible that some 18th to 19th century eruptions attributed to Carlisle (a volcano located across the Carlisle Pass Strait to the NW) should be ascribed to Cleveland. In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions from Mt. Cleveland have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks. Source: Alaska Volcano Observatory (AVO) http://www.avo.alaska.edu/ COLIMA México 19.514°N, 103.62°W; summit elev. 3850 m Although visual observations were intermittent due to cloud cover during 13-18 August, gray and white plumes from Colima were observed and rose to altitudes of 4-4.7 km (13,100-15,400 ft) a.s.l. and drifted SW, W, and N. Geologic Summary. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4,320 m high point of the complex) on the N and the historically active Volcán de Colima on the S. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the S, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth. Source: Gobierno del Estado de Colima http://www.colima-estado.gob.mx/2006/seguridad/indvolcan.php DUKONO Halmahera (Indonesia) 1.68°N, 127.88°E; summit elev. 1335 m Based on analysis of satellite imagery, the Darwin VAAC reported that on 19 August an ash plume from Dukono rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted W. Geologic Summary. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the N-flank cone of Gunung Mamuya. Dukono is a complex volcano presenting a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of Dukono's summit crater complex, contains a 700 x 570 m crater that has also been active during historical time. Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html KARYMSKY Eastern Kamchatka 54.05°N, 159.45°E; summit elev. 1536 m KVERT reported that seismic activity at Karymsky was at background levels on 9 and 13 August and slightly above background levels on the other days during 8-15 August. Based on interpretations of seismic data, possible ash plumes rose to an altitude of 3.1 km (10,200 ft) a.s.l. on 8, 10, 11, and 14 August. Analysis of satellite imagery revealed a thermal anomaly in the crater on 11 August; clouds inhibited views on other days. The Level of Concern Color Code remained at Orange. Based on analysis of satellite imagery and information from KEMSD, the Tokyo VAAC reported that on 14 August an eruption plume rose to an altitude of 2.7 km (9,000 ft) a.s.l. 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 (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php, Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html KILAUEA Hawaii (USA) 19.421°N, 155.287°W; summit elev. 1222 m HVO reported that during 13-19 August, lava flowed SE through a lava tube system from underneath Kilauea's Thanksgiving Eve Breakout (TEB) and rootless shield complex to the Waikupanaha ocean entry. Incandescence was noted from the rootless shield complex during 13-15 August. Earthquakes were in various locations along the Koa'e fault system, S and W of the caldera, beneath the summit, along the S-flank faults, and along the E and SW rift zones. Beneath Halema'uma'u crater, around 40 small earthquakes per day (background is 20-40) also occurred but were too small to be located more precisely. The vent in Halema'uma'u crater continued to produce a predominantly white plume with minor ash content that drifted mainly SW. The plume was occasionally tinged brown. Night-time incandescence was intermintently seen at the base of the plume, and rock impacts and rushing sounds were heard in the vicinity of the crater. 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 of lava flows less than about 1,100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 sq km, destroying nearly 200 houses and adding new coastline to the island. Source: US Geological Survey Hawaiian Volcano Observatory (HVO) http://hvo.wr.usgs.gov/ KRAKATAU Indonesia 6.102°S, 105.423°E; summit elev. 813 m According to a news article, explosions and earthquakes from Anak Krakatau averaged 120 per day approximately during 11-17 August. Monitoring personnel observed active lava flows, ejecting rocks, and emissions of "smoke." Geologic Summary. Renowned Krakatau volcano lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 AD, resulted in a 7-km-wide caldera. Remnants of this volcano formed Verlaten and Lang Islands; subsequently Rakata, Danan and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan volcanoes, and left only a remnant of Rakata volcano. The post-collapse cone of Anak Krakatau (Child of Krakatau), constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan, has been the site of frequent eruptions since 1927. Source: EFE http://www.unionradio.com.ve/Noticias/Noticia.aspx?noticiaid=251217 LLAIMA Central Chile 38.692°S, 71.729°W; summit elev. 3125 m During 8-11 August, SERNAGEOMIN reported that fumarolic activity from the snow-free pyroclastic cones in Llaima's main crater was visible during periods of clear weather; resultant plumes drifted E. A 2-km long strip on the NE flank was black in color (snow-free) due to elevated temperatures. On 13 August, gas-and-ash plumes rose to an altitude of 3.3 km (10,800 ft) a.s.l. and drifted E. Later that day, incandescence from the crater accompanied the gas-and-ash emissions. Geologic Summary. Llaima, one of Chile's largest and most active volcanoes, contains two main historically active craters, one at the summit and the other to the SE. The massive 3,125-m-high, glacier-covered stratovolcano has a volume of 400 cu km. A Holocene edifice built primarily of accumulated lava flows was constructed over an 8-km-wide caldera that formed about 13,200 years ago, following eruption of the 24 cu km Curacautín Ignimbrite. More than 40 scoria cones dot the volcano's flanks. Following the end of an explosive stage about 7,200 years ago, construction of the present edifice began, characterized by Strombolian, Hawaiian, and infrequent subplinian eruptions. Frequent moderate explosive eruptions with occasional lava flows have been recorded since the 17th century. Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN) http://www.sernageomin.cl/index.php MANAM Northeast of New Guinea (SW Pacific) 4.080°S, 145.037°E; summit elev. 1807 m Based on analysis of satellite imagery and information from RVO, the Darwin VAAC reported that low-level ash plumes from Manam rose to an altitude of 1.5 km (5,000 ft) a.s.l. and drifted NW during 16-17 August. Geologic Summary. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys," regularly spaced 90 degrees apart, channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE avalanche valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded at Manam since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas. Source: Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html MASAYA Nicaragua 11.984°N, 86.161°W; summit elev. 635 m Based on analysis of satellite imagery, the Washington VAAC reported that a diffuse steam plume from Masaya drifted WSW on 12 August and a gas plume was detected on 18 August. Both plumes possibly contained ash. Geologic Summary. Masaya is one of Nicaragua's most unusual and most active volcanoes. It is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high that is filled on its NW end by more than a dozen vents erupted along a circular, 4-km-wide fracture system. The twin volcanoes of Nindiri and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters. A major basaltic Plinian tephra was erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. A lava flow from the 1670 eruption overtopped the N caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted several attempts to extract the volcano's molten "gold." Source: Washington Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/messages.html OKMOK Fox Islands 53.43°N, 168.13°W; summit elev. 1073 m AVO reported that on 13 August low-level steam-and-ash plumes from Okmok were visible on satellite imagery drifting SE at altitudes of 3-4.6 km (10,000-15,000 ft) a.s.l. During 14-17 August satellite observations were hindered due to cloud cover; seismic levels fluctuated possibly indicating that steam-and-ash emissions continued. During 18-19 August, ash plumes were seen on satellite imagery at altitudes of 3-4.6 km (5,000-15,000 ft) a.s.l. The Volcano Alert Level remained at Watch and the Aviation Color Code at Orange. Geologic Summary. The broad, basaltic Okmok shield volcano, which forms the NE end of Umnak Island, has a dramatically different profile than most other Aleutian volcanoes. The summit of the low, 35-km-wide volcano is cut by two 10-km-wide calderas formed during eruptions about 8,250 and 2,400 years ago that produced dacitic pyroclastic flows that reached the coast. Numerous satellitic cones and lava domes dot the flanks of the volcano down to the coast. Some of the post-caldera cones show evidence of wave-cut lake terraces; the more recent cones, some of which have been active historically, were formed after the caldera lake disappeared. Hot springs and fumaroles are found within the caldera and at Hot Springs Cone, 20 km to the SW. Historical eruptions have occurred since 1805 from cinder cones within the caldera. Source: Alaska Volcano Observatory (AVO) http://www.avo.alaska.edu/ RABAUL New Britain (SW Pacific) 4.271°S, 152.203°E; summit elev. 688 m Based on analysis of satellite imagery and reports from RVO, the Darwin VAAC reported that during 13-19 August, low-level plumes from Rabaul caldera's Tavurvur cone rose to altitudes of 1.5-2.4 km (5,000-8,000 ft) a.s.l. and drifted WNW and NW. During 16-18 August, RVO reported ashfall in areas downwind. Occasionally incandescence at the summit was observed and roaring noises were heard. Explosions also ejected incandescent lava fragments. Geologic Summary. 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: Ima Itikarai, Rabaul Volcano Observatory (RVO), Darwin Volcanic Ash Advisory Centre (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html SHIVELUCH Central Kamchatka (Russia) 56.653°N, 161.360°E; summit elev. 3283 m KVERT reported that seismic activity at Shiveluch was slightly above background levels during 8-15 August. Analysis of satellite imagery revealed a daily thermal anomaly on the lava dome. Based on information from KEMSD and observations of satellite imagery, the Tokyo VAAC reported that on 15 August an eruption plume rose to an altitude of 4.6 km (15,000 ft) a.s.l. The Level of Concern Color Code remained at Orange. Geologic Summary. The high, isolated massif of Shiveluch volcano (also spelled Sheveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group and forms one of Kamchatka's largest and most active volcanoes. The currently active Molodoy Shiveluch lava-dome complex was constructed during the Holocene within a large breached caldera formed by collapse of the massive late-Pleistocene Strary Shiveluch volcano. At least 60 large eruptions of Shiveluch have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Frequent collapses of lava-dome complexes, most recently in 1964, have produced large debris avalanches whose deposits cover much of the floor of the breached caldera. During the 1990s, intermittent explosive eruptions took place from a new lava dome that began growing in 1980. The largest historical eruptions from Shiveluch occurred in 1854 and 1964. Sources: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php, Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html UBINAS Perú 16.355°S, 70.903°W; summit elev. 5672 m Based on SIGMET reports and pilot observations, the Buenos Aires VAAC reported that on 18 August ash plumes from Ubinas rose to altitudes of 5.5-6.4 km (18,000-21,000 ft) a.s.l. and drifted W. 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 (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html +++++++++++++++++++++++++++++++++++++ Sally Kuhn Sennert SI/USGS Weekly Volcanic Activity Report Editor Global Volcanism Program http://www.volcano.si.edu/reports/usgs/ Smithsonian Institution, National Museum of Natural History Department of Mineral Sciences, MRC-119 Washington, D.C., 20560 Phone: 202.633.1805 Fax: 202.357.2476 ============================================================== 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. ==============================================================
