************************************************************ SI/USGS Weekly Volcanic Activity Report 6-12 August 2008 ************************************************************ Sally Kuhn Sennert - Weekly Report Editor kuhns@xxxxxx URL: http://www.volcano.si.edu/reports/usgs/ New Activity/Unrest: | Asama, Japan | Bezymianny, Russia | Kasatochi, Aleutian Islands (USA) | Kliuchevskoi, Russia | Mayon, Philippines Ongoing Activity: | Anatahan, Mariana Islands (Central Pacific) | Batu Tara, Komba Island (Indonesia) | Chaitén, Southern Chile | Chikurachki, Paramushir Island | Cleveland, Chuginadak Island | Karymsky, Eastern Kamchatka | Kilauea, Hawaii (USA) | Krakatau, Indonesia | Okmok, Fox Islands | Piton de la Fournaise, Reunion Island | Rabaul, New Britain (SW Pacific) | Reventador, Ecuador | Sakura-jima, Kyushu | Semeru, Eastern Java (Indonesia) | Shiveluch, Central Kamchatka (Russia) | Soufrière Hills, Montserrat | Suwanose-jima, Ryukyu Islands (Japan) | Tungurahua, Ecuador 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 36.40°N, 138.53°E; summit elev. 2,560 m; All times are local (= UTC +9 hours) Based on information from JMA, the Tokyo VAAC reported that on 10 and 11 August eruption plumes from Asama rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted SE and S, respectively. 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 grew in area and intensified during 9-11 August. Based on interpretations of seismic data, four hot avalanches occurred on 10 August and nine occurred on 11 August. On 12 August, the level of Concern Color Code was raised to Orange. 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. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php KASATOCHI Aleutian Islands, USA 52.177°N, 175.508°W; summit elev. 314 m On 6 August, AVO raised the Volcano Alert Level for Kasatochi to Advisory and the Aviation Color Code to Yellow based on increased seismicity detected that day by instruments in the area and by field crews on the island the previous few days. Kasatochi lacks dedicated seismometers and is monitored by neighboring networks. On 7 August, earthquake activity continued; events as large as M 5.6 were detected. Crews reported rockfalls, ground shaking lasting 5-10 minutes, and a strong sulfur smell. Periods of volcanic tremor prompted AVO to raise the Volcano Alert Level to Watch and the Aviation Color Code to Orange. Later that day, an ash plume at an altitude of at least 10.7 km (35,000 ft) a.s.l. was detected on satellite imagery drifting SSW. The Volcano Alert Level was raised to Warning and the Aviation Color Code was raised to Red. Reports from a marine vessel in the area indicated ashfall and tephra up to pebble size, spectacular lightning, and total darkness for a little over 2 hours. Three major explosive eruptions produced ash plumes that rose to an altitude of 13.7 km (45,000 ft) a.s.l. Ash emissions became continuous on 8 August following the last explosive event; an ash plume drifted for more than 950 km in a counterclockwise spiral at altitudes of about 9.1-13.7 km (30,000-45,000 ft) a.s.l. Seismicity decreased, although remained elevated, and ash emissions became less frequent. During 8-9 August, seismicity decreased to a level undetectable by stations on Great Sitkin, about 40 km W. On 9 August ash plumes were detected on satellite imagery early in the day; clouds prevented views during the rest of the day. The Volcano Alert Level was lowered to Watch and the Aviation Color Code to Orange. The ash plume from the third eruption on 7 August was seen on satellite imagery 1,850 km ESE of the volcano and was elongated NE-SW over 1,200 km. According to news articles, flights from Alaska to several west coast cities were cancelled on 10 and 11 August. During 10-12 August, AVO reported that seismicity remained low, but detectable by the network on Great Sitkin. Sources: Alaska Volcano Observatory (AVO) http://www.avo.alaska.edu/, The Seattle Times Company http://seattletimes.nwsource.com/html/localnews/2008105636_webalaska11m.html 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. KLIUCHEVSKOI Kamchatka Peninsula, Russia 56.06°N, 160.64°E; summit elev. 4,835 m KVERT reported that seismic activity at Kliuchevskoi had slowly increased since June and was slightly above background levels during 1-8 August. Observations of satellite imagery revealed that the size and intensity of a thermal anomaly in the crater increased. On 8 August, the level of Concern Color Code was raised to Yellow. Geologic Summary. Kliuchevskoi is Kamchatka's highest and most active volcano. Since its origin about 7,000 years ago, the beautifully symmetrical, 4,835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. More than 100 flank eruptions, mostly on the NE and SE flanks of the conical volcano between 500 m and 3,600 m elevation, have occurred during the past 3,000 years. The morphology of its 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included major explosive and effusive events from flank craters. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php MAYON southeastern Luzon, Philippines 13.257°N, 123.685°E On 10 August, a mild explosion from Mayon produced an ash plume to an altitude of 2.7 km (8,900 ft) a.s.l. and drifted ENE. PHIVOLCS reported that during the previous few weeks seismic activity had increased slightly and incandescence at the crater had intensified. The Alert Level remained at 1. The 7-km Extended Danger Zone (EDZ) on the SE flank and the 6-km Permanent Danger Zone (PDZ) in all other areas remained in effect. 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 (PHIVOLCS) http://www.phivolcs.dost.gov.ph/ Ongoing Activity ANATAHAN Mariana Islands (Central Pacific) 16.35°N, 145.67°E; summit elev. 790 m During 7-8 August, small sulfur dioxide plumes from Anatahan were visible on satellite imagery. On 8 August, seismicity decreased significantly. During 8-9 August, steam plumes with small amounts of ash rose to an altitude of 1.8 km (6,000 ft) a.s.l. On 12 August, the Volcanic Alert Level was lowered to Advisory and the Aviation Color Code to Yellow. Geologic Summary. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of large stratovolcano with a 2.3 x 5 km, E-W-trending compound summit caldera. The larger western caldera is 2.3 x 3 km wide, and its western rim forms the island's 790-m high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. Sparseness of vegetation on the most recent lava flows on Anatahan had indicated that they were of Holocene age, but the first historical eruption of Anatahan did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera. Source: Emergency Management Office of the Commonwealth of the Mariana Islands and the US Geological Survey Hawaiian Volcano Observatory http://volcano.wr.usgs.gov/cnmistatus.php BATU TARA Komba Island (Indonesia) 7.792°S, 123.579°E; summit elev. 748 m Based on a pilot report and observations of satellite imagery, the Darwin VAAC reported that during 6-8 and 10-11 August ash plumes from Batu Tara rose to an altitude of 1.5 km (5,000 ft) a.s.l. and drifted W and NW. 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 Based on web camera views, SIGMET reports, observations of satellite imagery, and information from the Puerto Montt Flight Information Region (FIR), the Buenos Aires VAAC reported that during 7-8 August ash plumes from Chaitén rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted E and NE. 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. Source: 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 Based on observations of satellite imagery, KVERT reported that eruptive activity from Chikurachki continued during 1-8 August. Ash plumes drifted more than 60 km SE, W, and N during 1-3 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 On 6 August, AVO reported that the thermal anomalies noted at Cleveland's summit and on the W, S, and SE flanks had decreased in intensity since first noted on 21 July, indicating that the lava flows slowed or stopped. The Volcanic Alert Level was lowered to Advisory and the Aviation Color Code to Yellow. During 7-10 August, a weak thermal anomaly at the summit was intermittently visible when not obscured by clouds and drifting ash from the eruption of Kasatochi (about 400 km WSW). On 11 August, thermal anomalies on satellite imagery indicated that lava flowed down the flanks. The Volcano Alert Level was raised to Watch and the Aviation Color Code to Orange. On 12 August, an ash plume rose to an altitude of 7.6 km (25,000 ft) a.s.l. and drifted 100 km SW. 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/ KARYMSKY Eastern Kamchatka 54.05°N, 159.45°E; summit elev. 1536 m KVERT reported that seismic activity at Karymsky was above background levels during 1-8 August and possibly indicated that explosions produced ash plumes to an altitude of 3.1 km (10,200 ft) a.s.l. Observations of satellite imagery revealed a thermal anomaly in the crater on 2 August; clouds inhibited views on other days. 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 11 August an eruption plume rose to an altitude of 3.4 km (11,000 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 6 and 9-12 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. Occasional explosions and surface lava flows were noted near the ocean entry. A small fountain in a lava pond at the top of one of the rootless shields was observed on 10 August. The sulfur dioxide emission rate at Pu'u 'O'o was 1,700 and 2,400 tonnes per day on 8 and 9 August, respectively; the average background rate is about 2,000 tonnes per day. During the reporting period, Kilauea earthquakes were variously located beneath Halema'uma'u crater, along the Koa'e fault system, SE and W of the caldera, along the S-flank faults, and along the E and SW rift zones. Beneath Halema'uma'u crater, up to 100 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 mainly white plume with minor ash content that drifted SW. The plume was occasionally tinged brown. Night-time incandescence was seen at the base of the plume rock-clattering sounds were heard in the vicinity of the crater. The sulfur dioxide emission rate was high at 900 tonnes per day on 7 August. The pre-2008 background rate was 150-200 tonnes per day. 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, eruptions from Anak Krakatau increased in frequency during 10-11 August. On 12 August, monitoring personnel reported that active lava flows and emissions of thick "smoke" continued but that the frequency of earthquakes and eruptions had declined. 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: Antara News http://www.antara.co.id/en/arc/2008/8/12/anak-krakatau-erupts-120-times-on-monday/ OKMOK Fox Islands 53.43°N, 168.13°W; summit elev. 1073 m AVO scientists observed the eruption of Okmok during a visit to Umnak Island on 2 and 3 August. They saw significant ashfall that had accumulated in the caldera and on the upper flanks, lahars and lahar deltas that formed in drainages from the SE to the NE flank, and continuous ash jets being emitted from three or more vents in the vicinity of Cone D in the NE sector of the caldera. Elevated seismicity was detected during 6-8 August, and declined on 9 August. According to observations of satellite imagery, steam plumes possibly containing ash rose to altitudes below 4.6 km (15,000 ft) a.s.l. during 9-10 August. On 11 August, steam plumes rose to altitudes of less than 6.1 km (20,000 ft) a.s.l. and drifted SE. Ash plumes that rose to around a hundred meters above the crater were reported by an observer in Nikolski (80 km SW). These plumes were not detected on satellite imagery due to cloud cover. On 12 August, a pilot reported an ash plume at an altitude of 4.6 km (15,000 ft) a.s.l. The Volcano Alert Level remained at Watch and the Aviation Color Code remained 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/ PITON DE LA FOURNAISE Réunion Island, Indian Ocean 21.23°S, 55.71°E; summit elev. 2,631 m OVPDLF reported that a small seismic crisis beneath the summit of Piton de la Fournaise lasted about 10 minutes on 4 August. The strongest earthquake was a M 1. Geologic Summary. The 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 Dolomieu, a 400-m-high lava shield that has grown within the youngest of three large calderas. This latter caldera 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. Source: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) http://ovpf.univ-reunion.fr/ RABAUL New Britain (SW Pacific) 4.271°S, 152.203°E; summit elev. 688 m RVO reported that ash plumes from Rabaul caldera's Tavurvur cone continued to be emitted during 4-10 August. Ashfall was reported in areas NW. Occasionally incandescence at the summit was observed and roaring noises were reported. Incandescent lava fragments were ejected along with some of the more forceful ash emissions. Based on observations of satellite imagery and information from RVO, the Darwin VAAC reported that during 11-12 August, low-level ash plumes rose to an altitude of 1.5 km (5,000 ft) a.s.l. and drifted NW. 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 REVENTADOR Ecuador 0.077°S, 77.656°W; summit elev. 3562 m The IG reported that steam-and-gas from Reventador was emitted during 6-8 August. Incandescence from the crater was observed at night on 8 August. Geologic Summary. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well E of the principal volcanic axis. It is a forested stratovolcano that rises above the remote jungles of the western Amazon basin. A 3-km-wide caldera breached to the E was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1,300 m above the caldera floor. Reventador has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. Source: Instituto Geofísico-Escuela Politécnica Nacional (IG) http://www.igepn.edu.ec/ SAKURA-JIMA Kyushu 31.585°N, 130.657°E; summit elev. 1117 m Based on information from JMA, the Tokyo VAAC reported that on 10 August an eruption plume from Sakura-jima rose to an altitude greater than 2.7 km (9,000 ft) a.s.l. and drifted NW. 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 flow 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 (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html SEMERU Eastern Java (Indonesia) 8.108°S, 112.92°E; summit elev. 3676 m Based on information from CVGHM, the Darwin VAAC reported that on 7 August ash plumes from Semeru rose to an altitude of 4.3 km (14,100 ft) a.s.l. and that incandescent material was ejected from the crater. CVGHM indicated that the activity was normal; the Alert Level remained at 2 (on a scale of 1-4). 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: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://portal.vsi.esdm.go.id/joomla/, 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 1-8 August, and possibly indicated that ash plumes from explosions rose to an altitude of 4.6 km (15,100 ft) a.s.l. on 6 August. Observations of satellite imagery revealed a thermal anomaly on the lava dome during 1-3 August. 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. Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php SOUFRIERE HILLS Montserrat 16.72°N, 62.18°W; summit elev. 915 m MVO reported that seismic levels from Soufrière Hills were relatively low during 1-8 August. Sulfur dioxide emissions (tons per day) were significantly higher than emissions prior to the partial lava-dome collapse on 28 July. Unconfirmed reports indicated the presence of an ash plume on 3 August. A small ash cloud was seen on 7 August. Further investigation of the 28 July event revealed that the total amount of material that collapsed from the dome was about 200,000-300,000 cubic meters. Satellite radar images indicated that the vent above Gages wall was enlarged by the explosion to about 150 x 60 meters, elongated E-W. Precautionary access restrictions for areas in and around Belham valley were lifted because evidence suggested that the dome had not been destabilized due to the event. A new Hazard Level System, designed by MVO and Disaster Management Coordination Agency (DMCA) in consultation with the Government of Montserrat and community groups, was implemented on 8 August. The system divides the southern two-thirds of the island into six zones, and includes two Maritime Exclusion Zones. The Hazard Level ranges from 1-5 and is set by the National Disaster Preparedness, Response, and Advisory Committee (NDPRAC) with advice from MVO. The Hazard Level restricts access into each of the zones depending on the number assigned and is unrelated to the Alert Level. The current 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/ SUWANOSE-JIMA Ryukyu Islands (Japan) 29.635°N, 129.716°E; summit elev. 799 m Based on reports from JMA, the Tokyo VAAC reported that on 7 August an eruption plume from Suwanose-jima rose to an altitude of 1.2 km (4,000 ft) a.s.l. 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 east 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, 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: Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html TUNGURAHUA Ecuador 1.467°S, 78.442°W; summit elev. 5023 m The IG reported that during 6-8 August, explosions from Tungurahua were detected by the seismic network. Although clouds mostly prevented visual observations, steam-and-ash plumes were observed; on 6 August, ash plumes rose to an altitude of 5.5 km (18,000 ft) a.s.l. and drifted W. Ashfall was reported in areas to the SW. 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 all originated from 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. Source: Instituto Geofísico-Escuela Politécnica Nacional (IG) http://www.igepn.edu.ec/ +++++++++++++++++++++++++++++++++++++ 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. ==============================================================
