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Smithsonian/USGS Weekly Volcanic Activity Report 27 April-3 May 2011
From: "Kuhn, Sally" <KUHNS@xxxxxx>
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Smithsonian/USGS Weekly Volcanic Activity Report
27 April-3 May 2011
Sally Kuhn Sennert - Weekly Report Editor
URL: http://www.volcano.si.edu/reports/usgs/
New Activity/Unrest: | Bezymianny, Central Kamchatka (Russia) | Gamkonora, Halmahera | Kizimen, Eastern Kamchatka (Russia) | Planchón-Peteroa, Central Chile-Argentina border | Puyehue-Cordón Caulle, Central Chile | Ruapehu, North Island (New Zealand) | Tungurahua, Ecuador
Ongoing Activity: | Batu Tara, Komba Island (Indonesia) | Dukono, Halmahera | Fuego, Guatemala | Karymsky, Eastern Kamchatka (Russia) | Kilauea, Hawaii (USA) | Sakura-jima, Kyushu | Santa María, Guatemala | Shiveluch, Central Kamchatka (Russia) | Suwanose-jima, Ryukyu Islands (Japan) | Tengger Caldera, Eastern Java (Indonesia)
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
BEZYMIANNY Central Kamchatka (Russia) 55.978°N, 160.587°E; summit elev. 2882 m
KVERT reported that during 22-29 April a bright thermal anomaly on Bezymianny was detected in satellite imagery. A gas-and-steam plume that drifted 27 km NW was also detected on 22 April. According to ground-based observations, gas-and-steam activity was noted during 22 and 24-25 April. The Aviation Color Code was lowered to Yellow.
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
GAMKONORA Halmahera 1.38°N, 127.53°E; summit elev. 1635 m
CVGHM reported that during January-April diffuse white plumes from Gamkonora rose 25-100 m above the crater rim. Seismicity increased during 29 April-3 May. On 1 May, white plumes rose 150 m above the crater rim. The next day, white plumes rose 300 m above the crater rim and incandescence from the crater was observed. Residents near the volcano’s base noted a sulfur smell. The Alert level was raised to 2 (on a scale of 1-4).
Geologic Summary. The shifting of eruption centers on Gamkonora, at 1635 m the highest peak of Halmahera, has produced an elongated series of summit craters along a N-S trending rift. Youthful-looking lava flows originate near the cones of Gunung Alon and Popolojo, south of Gamkonora. Since its first recorded eruption in the 16th century, Gamkonora has typically produced small-to-moderate explosive eruptions. Its largest historical eruption, in 1673, was accompanied by tsunamis that inundated villages.
Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://www.vsi.esdm.go.id/
KIZIMEN Eastern Kamchatka (Russia) 55.130°N, 160.32°E; summit elev. 2376 m
Based on analyses of satellite imagery, KVERT reported that during 22-29 April a large bright thermal anomaly was detected over Kizimen daily and ash plumes drifted 135 km in multiple directions. Ground-based observations indicated that gas-and-steam plumes with a small amount of ash rose to an altitude of 3.5 km (11,500 ft) a.s.l. and drifted W during 20-21 April. The Aviation Color Code remained at Orange. On 3 May seismic data indicated a possible series of ash plumes and avalanches. An ash plume may have risen to an altitude of 10 km (33,000 ft) a.s.l. The Aviation Color Code was raised to Red. On 4 May seismicity decreased but remained high. Satellite imagery showed ash plumes at altitudes of 4-6 km (13,100-19,700 ft) a.s.l. The Aviation Color Code was lowered to Orange.
Geologic Summary. Kizimen is an isolated, conical stratovolcano that is morphologically similar to Mount St. Helens prior to its 1980 eruption. The summit of Kizimen consists of overlapping lava domes, and blocky lava flows descend the flanks of the volcano, which is the westernmost of a volcanic chain north of Kronotsky volcano. The 2,376-m-high Kizimen was formed during four eruptive cycles beginning about 12,000 years ago and lasting 2,000-3,500 years. The largest eruptions took place about 10,000 and 8300-8400 years ago, and three periods of longterm lava-dome growth have occurred. The latest eruptive cycle began about 3,000 years ago with a large explosion and was followed by lava-dome growth lasting intermittently about 1,000 years. An explosive eruption about 1,100 years ago produced a lateral blast and created a 1.0 x 0.7 km wide crater breached to the NE, inside which a small lava dome (the fourth at Kizimen) has grown. A single explosive eruption, during 1927-28, has been recorded in historical time.
Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php
PLANCHON-PETEROA Central Chile-Argentina border 35.240°S, 70.570°W; summit elev. 4107 m
SERNAGEOMIN reported that during 1-15 April a camera installed in Romeral, approximately 61 km NW of Planchón-Peteroa, recorded predominantly white vapor plumes that rose at most 600 m. During 16-19, 21 and 25-29 April episodes of ash-plume production changed from discreet plumes to more continuous emissions. Ash plumes during 17-19 and 29 April rose 1.2 km and contained ash- to lapilli-sized particles. During overflights on 26, 27, and 29 April, a geologist noted that the crater geometry and fumarolic activity had changed very little during the previous few months and that ash emissions drifted mainly SW. SERNAGEOMIN stated that because ash-and-gas emissions were becoming almost continuous, the Alert Level was raised to Level 3, Yellow on 29 April. Based on analyses of satellite imagery, SIGMET notices, and ODVAS web camera observations, the Buenos Aires VAAC reported that during 2-3 May gas-and-ash plumes rose to altitudes of 4.6-5.5 km (15,000-18,000 ft) a.s.l. and drifted NE and E.
Geologic Summary. Planchón-Peteroa is an elongated complex volcano along the Chile-Argentina border with several overlapping calderas. Activity began in the Pleistocene with construction of the basaltic-andesite to dacitic Volcán Azufre, followed by formation of basaltic and basaltic-andesite Volcán Planchón, 6 km to the N. About 11,500 years ago, much of Azufre and part of Planchón collapsed, forming the massive Río Teno debris avalanche, which reached Chile's Central Valley. Subsequently, Volcán Planchón II was formed. The youngest volcano, andesitic and basaltic-andesite Volcá Peteroa, consists of scattered vents between Azufre and Planchón. Peteroa has been active into historical time and contains a small steaming crater lake. Historical eruptions from the Planchón-Peteroa complex have been dominantly explosive, although lava flows were erupted in 1837 and 1937.
Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN) http://www.sernageomin.cl/,
Buenos Aires Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AG/messages.html
PUYEHUE-CORDON CAULLE Central Chile 40.590°S, 72.117°W; summit elev. 2236 m
ODVAS-SERNAGEOMIN reported that on 26 April an overflight was conducted in response to recent increased seismicity and nearby residents noting fumarolic activity in the vicinity of Puyehue-Cordón Caulle. Scientists did not observe anything unusual that would indicate increased activity at Puyehue or Cordón Caulle, just typical fumarolic activity. On 27 April a seismic swarm was detected at depths of 4-6 km; a majority of the events were hybrid earthquakes and the largest was M 3.9. Seismicity decreased but was continuing through 29 April. The Alert Level was raised to 3, Yellow.
Geologic Summary. The Puyehue-Cordón Caulle volcanic complex (PCCVC) is a large NW-SE-trending late-Pleistocene to Holocene basaltic-to-rhyolitic transverse volcanic chain SE of Lago Ranco. The 1799-m-high Pleistocene Cordillera Nevada caldera lies at the NW end, separated from Puyehue stratovolcano at the SE end by the Cordón Caulle fissure complex. The Pleistocene Mencheca volcano with Holocene flank cones lies NE of Puyehue. The basaltic-to-rhyolitic Puyehue volcano is the most geochemically diverse of the PCCVC. The flat-topped, 2236-m-high Puyehue volcano was constructed above a 5-km-wide caldera and is capped by a 2.4-km-wide summit caldera of Holocene age. Lava flows and domes of mostly rhyolitic composition are found on the eastern flank of Puyehue. Historical eruptions originally attributed to Puyehue, including major eruptions in 1921-22 and 1960, are now known to be from the Cordón Caulle rift zone. The Cordón Caulle geothermal area, occupying a 6 x 13 km wide volcano-tectonic depression, is the largest active geothermal area of the southern Andes volcanic zone.
Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN) http://www.sernageomin.cl/
RUAPEHU North Island (New Zealand) 39.28°S, 175.57°E; summit elev. 2797 m
On 2 May, GeoNet reported that the temperature of Ruapehu's summit Crater Lake continued to slowly cool and was about 30 degrees Celsius, down from a peak of 41 degrees in March. The lake level remained below the overflow level and no earthquakes had been located within 10 km of the Crater Lake for two weeks. The Aviation Colour Code was lowered to Green and the Volcanic Alert Level remained at 1 (signs of volcano unrest).
Geologic Summary. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes. The 110 cu km volcanic massif is elongated in a NNE-SSW direction and is surrounded by another 100 cu km ring plain of volcaniclastic debris. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flanks have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to river valleys below the volcano.
Source: New Zealand GeoNet Project http://www.geonet.org.nz/
TUNGURAHUA Ecuador 1.467°S, 78.442°W; summit elev. 5023 m
IG reported that, although visual observations of Tungurahua were occasionally limited due to cloud cover during 26 April-3 May, ash plumes were noted daily and rose to altitudes of 7-12 km (23,000-39,400 ft) a.s.l. The plumes drifted in multiple directions. Ashfall was reported daily in areas within 8 km NNE, N, NW, W, and SW. On 27 and 29 April and during 1-3 May ashfall was reported in areas farther away including the Tungurahua Observatory (OVT) in Guadalupe (11 km N), Ambato (31 km NW), Mocha (25 km W), and 40 km WSW. Blocks ejected from the crater rolled down the flanks on most days and explosions periodically caused doors and windows to vibrate. On 29 April tremor intensified and Strombolian activity increased. According to news articles, an IG scientist noted that boulders the size of a truck were ejected from the crater, causing impact craters 10 m wide where they fell on the flanks. About 300 people evacuated.
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.
Sources: Instituto Geofísico-Escuela Politécnica Nacional (IG) http://www.igepn.edu.ec/,
Batangas Today http://www.batangastoday.com/tungurahua-volcano-in-ecuador-erupts-spews-truck-sized-pyroclastic-boulders/12533/
Ongoing Activity
BATU TARA Komba Island (Indonesia) 7.792°S, 123.579°E; summit elev. 748 m
Based on analyses of satellite imagery, the Darwin VAAC reported that during 28 April-3 May ash plumes from Batu Tara rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted 10-130 km N, NW, W, and SW.
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
DUKONO Halmahera 1.68°N, 127.88°E; summit elev. 1335 m
Based on analyses of satellite imagery, the Darwin VAAC reported that during 28 April-2 May ash plumes from Dukono rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted 55-150 km NW, W, and SW.
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
FUEGO Guatemala 14.473°N, 90.880°W; summit elev. 3763 m
INSIVUMEH reported that during 28-29 April explosions from Fuego produced ash plumes that rose 300-600 m above the crater and drifted SW and S. The explosions sometimes produced shock waves. Lava flows traveled 200 m S and block avalanches descended the Ceniza and Santa Teresa drainages. Explosions during 1-2 May produced ash plumes that rose 200 m above the crater.
Geologic Summary. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3,763-m-high Fuego and its twin volcano to the N, Acatenango. Construction of Meseta volcano continued until the late Pleistocene or early Holocene, after which growth of the modern Fuego volcano continued the southward migration of volcanism that began at Acatenango. Frequent vigorous historical eruptions have been recorded at Fuego since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows. The last major explosive eruption from Fuego took place in 1974, producing spectacular pyroclastic flows visible from Antigua.
Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/
KARYMSKY Eastern Kamchatka (Russia) 54.05°N, 159.45°E; summit elev. 1536 m
KVERT reported moderate seismic activity at Karymsky during 22-29 April and a thermal anomaly that was detected daily in satellite imagery. Seismic data indicated that possible ash plumes rose to an altitude of 3.4 km (11,200 ft) a.s.l. Visual observations showed that moderate explosive activity continued. During 22-23 April gas-and-steam plumes detected in satellite imagery drifted 38 km S. The Aviation Color Code remained at Orange.
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.
Source: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/index_eng.php
KILAUEA Hawaii (USA) 19.421°N, 155.287°W; summit elev. 1222 m
During 27 April-3 May, HVO reported that the level of Kilauea's summit lava lake fluctuated but remained mostly stable deep in the vent inset within the E wall of Halema'uma'u Crater. A gas plume from the vent drifted SW and deposited very small amounts of ash nearby. At Pu'u 'O'o crater, lava from one or two vent sources continued to fill in a new lava lake in the center of the crater floor. Lava overflowed the edges of the lake, constructing a perched lava lake. During 30 April-1 May the overflows filled the entire crater floor before receding back within the boundaries of the perched lava lake.
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/
SAKURA-JIMA Kyushu 31.585°N, 130.657°E; summit elev. 1117 m
Based on information from JMA, the Tokyo VAAC reported that during 27-30 April and 2-3 May explosions from Sakura-jima produced plumes that rose to altitudes of 1.8-2.7 km (6,000-9,000 ft) a.s.l. and drifted N, NE, E, SE, and S. On 29 April and 2 May, pilots observed ash plumes that rose to altitudes of 1.8-2.7 km (6,000-9,000 ft) a.s.l. and drifted S and SE.
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
SANTA MARIA Guatemala 14.756°N, 91.552°W; summit elev. 3772 m
INSIVUMEH reported that during 28-29 April explosions from Santa María's Santiaguito lava dome complex produced ash plumes that rose 600-800 m above the crater and drifted S, SW, and W. Block avalanches descended the flanks of Caliente dome. At night pyroclastic flows traveled down the Rio Nima I and Rio Nima II drainages.
Geologic Summary. Symmetrical, forest-covered Santa María volcano is one of a chain of large stratovolcanoes that rises dramatically above the Pacific coastal plain of Guatemala. The stratovolcano has a sharp-topped, conical profile that is cut on the SW flank by a large, 1-km-wide crater, which formed during a catastrophic eruption in 1902 and extends from just below the summit to the lower flank. The renowned Plinian eruption of 1902 followed a long repose period and devastated much of SW Guatemala. The large dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four westward-younging vents, accompanied by almost continuous minor explosions and periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.
Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) http://www.insivumeh.gob.gt/
SHIVELUCH Central Kamchatka (Russia) 56.653°N, 161.360°E; summit elev. 3283 m
KVERT reported that during 22-29 April seismic data at Shiveluch indicated that possible ash plumes rose to an altitude of 6.7 km (22,000 ft) a.s.l. Satellite imagery showed a thermal anomaly daily on the lava dome. According to ground-based observations during 22 and 25-27 April ash plumes rose to an altitude of 7.5 km (24,600 ft) a.s.l. and drifted N and SE. Satellite imagery showed ash plumes drifting 153 km N on 22 April and as far as 400 km SE during 23-24 and 27 April. KVERT noted that the Aviation Color Code remained at Orange. Based on information from KEMSD, the Tokyo VAAC reported that on 1 May an eruption produced a plume that rose to an altitude of 6.1 km (20,000 ft) a.s.l.
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. Intermittent explosive eruptions began in the 1990s 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
SUWANOSE-JIMA Ryukyu Islands (Japan) 29.635°N, 129.716°E; summit elev. 799 m
Based on information from JMA, the Tokyo VAAC reported explosions from Suwanose-jima on 3 May. Details of a possible resulting plume were not reported.
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
TENGGER CALDERA Eastern Java (Indonesia) 7.942°S, 112.95°E; summit elev. 2329 m
Based on analyses of satellite imagery, the Darwin VAAC reported that on 27 April an ash plume from Tengger Caldera's Bromo cone rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted about 75 km WSW. On 2 May an ash plume rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted about 75 km N.
Geologic Summary. The 16-km-wide Tengger caldera in eastern Java is located at the northern end of a volcanic massif extending from Semeru volcano. The massive Tengger volcanic complex consists of five overlapping stratovolcanoes, each truncated by a caldera. The most recent is the 9 x 10 km wide Sandsea caldera, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most frequently visited and most active volcanoes. More than 50 mild-to-moderate explosive eruptions have occurred since 1804.
Source: Darwin Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/AU/messages.html
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