VOLCANO: Smithsonian/USGS Weekly Volcanic Activity Report 30 March-5 April 2011

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Smithsonian/USGS Weekly Volcanic Activity Report 30 March-5 April 2011
From: "Kuhn, Sally" <KUHNS@xxxxxx>
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Smithsonian/USGS Weekly Volcanic Activity Report
30 March-5 April 2011
 
Sally Kuhn Sennert - Weekly Report Editor
kuhns@xxxxxx
URL: http://www.volcano.si.edu/reports/usgs/
 
 
New Activity/Unrest: | Karangetang [Api Siau], Siau I | Kilauea, Hawaii (USA) | Ruapehu, New Zealand
 
Ongoing Activity: | Cleveland, Chuginadak Island | Dukono, Halmahera | Etna, Sicily (Italy) | Fuego, Guatemala | Galeras, Colombia | Karymsky, Eastern Kamchatka (Russia) | Kirishima, Kyushu | Kizimen, Eastern Kamchatka (Russia) | Kliuchevskoi, Central Kamchatka (Russia) | Sakura-jima, Kyushu | Santa María, Guatemala | Shiveluch, Central Kamchatka (Russia) | Soufrière Hills, Montserrat | 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
 
 
KARANGETANG [API SIAU] Siau I 2.78°N, 125.40°E; summit elev. 1784 m
 
CVGHM reported that during 30-31 March incandescence emanated from Karangetang's main crater as well as bluish and white gas plumes. Lava flows originating from the main crater traveled 2 km down the flanks. Incandescent avalanches from the main crater and from the lava-flow fronts traveled up to 1.8 km down the flanks. On 31 March a thunderous sound was accompanied by a gray plume that rose 200 m above the crater. The Alert Level remained at 3 (on a scale of 1-4).
 
Geologic Summary. Karangetang (also known as Api Siau) lies at the northern end of the island of Siau, N of Sulawesi, and contains five summit craters strung along a N-S line. One of Indonesia's most active volcanoes, Karangetang has had more than 40 recorded eruptions since 1675. Twentieth-century eruptions have included frequent explosions, sometimes accompanied by pyroclastic flows and lahars.
 
Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://www.vsi.esdm.go.id/
 
 
KILAUEA Hawaii (USA) 19.421°N, 155.287°W; summit elev. 1222 m
 
HVO reported that the lava lake in the deep pit within Kilauea's Halema'uma'u crater was mostly crusted over during 30 March-5 April. Incandescence was observed through the web camera on 30 March, and lava was visible at times during 31 March and 3-4 April. A gas plume from the vent deposited very small amounts of ash nearby, derived from rockfalls and occasional spatter from the lake. At Pu'u 'O'o crater, the lava lake was fed from a few sources in the center or W portions of the lake. The deepest part of the crater was episodically filled and drained. During 4-5 April the central lava sources produced two or three small lava flows and infrequent spatter.
 
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/
 
 
RUAPEHU New Zealand 39.28°S, 175.57°E; summit elev. 2797 m
 
On 5 April, GeoNet reported that the temperature of Ruapehu's summit Crater Lake had been high for a sustained period and was currently between 38 and 39 degrees Celsius. The highest temperature since unrest began in October 2010 was 41 degrees Celsius, measured on 1 March. The report also noted that during the previous few weeks there was an increase in carbon dioxide gas emissions, increased seismicity, and changes in Crater Lake water chemistry. The unrest prompted GeoNet to raise the Aviation Colour Code although the Volcanic Alert Level remained at 1 (some 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/
 
 
Ongoing Activity
 
 
CLEVELAND Chuginadak Island 52.825°N, 169.944°W; summit elev. 1730 m
 
On 31 March, AVO lowered the Volcano Alert Level and the Aviation Color Code for Cleveland to Unassigned noting that no eruptive activity had been confirmed during the previous few months. Neither significant thermal anomalies nor ash deposits on snow were observed in recent satellite imagery.
 
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/
 
 
DUKONO Halmahera 1.68°N, 127.88°E; summit elev. 1335 m
 
Based on analyses of satellite imagery, the Darwin VAAC reported that on 4 April an ash plume from Dukono rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted 185 km E.
 
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
 
 
ETNA Sicily (Italy) 37.734°N, 15.004°E; summit elev. 3330 m
 
Based on a NOTAM, the Toulouse VAAC reported that on 3 April ash from Etna rose to an altitude between 2.4-3.4 km (8,000-11,000 ft) a.s.l. Ash was not identified in satellite imagery.
 
Geologic Summary. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BC. Historical lava flows cover much of the surface of this massive basaltic stratovolcano, the highest and most voluminous in Italy. Two styles of eruptive activity typically occur at Etna. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more of the three prominent summit craters, the Central Crater, NE Crater, and SE Crater. Flank eruptions, typically with higher effusion rates, occur less frequently and originate from fissures that open progressively downward from near the summit. A period of more intense intermittent explosive eruptions from Etna's summit craters began in 1995. The active volcano is monitored by the Instituto Nazionale di Geofisica e Volcanologia (INGV) in Catania.
 
Source: Toulouse Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/FR/messages.html
 
 
FUEGO Guatemala 14.473°N, 90.880°W; summit elev. 3763 m
 
INSIVUMEH reported that during 30-31 March and 4-5 April explosions from Fuego produced ash plumes that rose 200-700 m above the crater and drifted W, SW, and S. Lava flows traveled almost 200 m SW down the Ceniza drainage and produced block avalanches from lava-flow fronts. Crater incandescence was observed at night.
 
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.ssd.noaa.gov/VAAC/messages.html
 
 
GALERAS Colombia 1.22°N, 77.37°W; summit elev. 4276 m
 
INGEOMINAS reported that on 31 March and 1 April emissions from Galeras were characterized by gas-and-steam plumes with low ash content. On 1 April a M 2.3 earthquake occurred 3 km E of the crater at a depth of 6 km and was felt by nearby residents. During an overflight on 2 April scientists noted a sulfur gas odor and observed that gas emissions rose from multiple areas of the active cone. During 30 March-5 April, sulfur dioxide gas values were between 50 and 2,000 tons per day, the latter value was considered high for Galeras. The Alert Level remained at III (Yellow; "changes in the behavior of volcanic activity").
 
Geologic Summary. Galeras, a stratovolcano with a large breached caldera located immediately W of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic Galeras volcanic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Longterm extensive hydrothermal alteration has affected the volcano. This has contributed to large-scale edifice collapse that has occurred on at least three occasions, producing debris avalanches that swept to the W and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.
 
Source: Instituto Colombiano de Geología y Minería (INGEOMINAS) http://www.ingeominas.gov.co//
 
 
KARYMSKY Eastern Kamchatka (Russia) 54.05°N, 159.45°E; summit elev. 1536 m
 
KVERT reported moderate seismic activity at Karymsky during 25 March-1 April. Seismic data indicated that possible ash plumes rose to an altitude of 5 km (16,400 ft) a.s.l. A thermal anomaly was detected daily in satellite imagery. Ash and gas-and-steam plumes drifted 55 km in multiple directions during 25, 27, and 29-30 March. 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/updates.php
 
 
KIRISHIMA Kyushu 31.931°N, 130.864°E; summit elev. 1700 m
 
Based on notifications from JMA and pilot observations, the Tokyo VAAC reported that during 3-4 April ash plumes from Kirishima's Shinmoe-dake (Shinmoe peak) rose to altitudes of 4.6-6.1 km (15,000-20,000 ft) a.s.l. and drifted E.
 
Geologic Summary. Kirishima is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene volcano group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located, 1,700-m-high Karakuni-dake being the highest. Onami-ike and Mi-ike, the two largest maars, are located SW of Karakuni-dake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Mi-ike to Ohachi, and at Shinmoe-dake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.
 
Source: Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html
 
 
KIZIMEN Eastern Kamchatka (Russia) 55.130°N, 160.32°E; summit elev. 2376 m
 
KVERT reported that during 25 March-1 April seismicity from Kizimen was high, with many shallow volcanic earthquakes and volcanic tremor continuing to be detected. Satellite images showed a large bright thermal anomaly daily on the volcano. Ash and gas-and-steam plumes drifted multiple directions as far as 464 km. The Aviation Color Code remained at Orange.
 
Based on analyses of satellite imagery, the Tokyo VAAC reported that a possible eruption on 1 April produced a plume that rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted E. Subsequent images that day and during 2-3 April showed continuing ash emissions. Another possible eruption on 6 April produced a plume that rose to an altitude of 3.7 km (12,000 ft) a.s.l.
 
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.
 
Sources: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/updates.php,
Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html
 
 
KLIUCHEVSKOI Central Kamchatka (Russia) 56.057°N, 160.638°E; summit elev. 4835 m
 
Based on analyses of satellite imagery, the Tokyo VAAC reported that a possible eruption from Kliuchevskoi on 30 March produced a plume that rose to an altitude of 5.2 km (17,000 ft) a.s.l. and drifted E. Subsequent images that day showed continuing ash emissions that later dissipated. The Aviation Color Code remained at Green.
 
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.
 
Sources: Kamchatkan Volcanic Eruption Response Team (KVERT) http://www.kscnet.ru/ivs/kvert/updates.php,
Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html
 
 
SAKURA-JIMA Kyushu 31.585°N, 130.657°E; summit elev. 1117 m
 
Based on information from JMA, the Tokyo VAAC reported that during 1 and 3-5 April explosions from Sakura-jima produced plumes that rose to altitudes of 1.5-4 km (5,000-13,000 ft) a.s.l. and occasionally drifted E. A video of activity from 4 April showed incandescence emanating from the crater and a few explosions that ejected incandescent material onto the flanks. On 5 April, a pilot observed an ash plume that rose to an altitude of 2.7 km (9,000 ft) a.s.l.
 
Geologic Summary. Sakura-jima, one of Japan's most active volcanoes, is a post-caldera cone of the Aira caldera at the northern half of Kagoshima Bay. Eruption of the voluminous Ito pyroclastic 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.
 
Sources: Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html,
Volcano Sakura-jima http://volcanosakurajima.web.fc2.com/
 
 
SANTA MARIA Guatemala 14.756°N, 91.552°W; summit elev. 3772 m
 
INSIVUMEH reported that on 28 March explosions from Santa María's Santiaguito lava dome complex produced ash plumes that rose 300-800 m above Caliente dome and drifted NNE, depositing fine ash in Quetzaltenango (10 km NNE). During 30-31 March and 4-5 April explosions produced ash plumes that rose 400-700 m above the dome and drifted S; ashfall was reported in nearby areas downwind. Avalanches descended the SW and E flanks.
 
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.ssd.noaa.gov/VAAC/messages.html
 
 
SHIVELUCH Central Kamchatka (Russia) 56.653°N, 161.360°E; summit elev. 3283 m
 
KVERT reported that during 25 March-1 April seismic data at Shiveluch indicated that possible ash plumes rose to an altitude of 3.7 km (12,100 ft) a.s.l. A thermal anomaly on the lava dome was observed in satellite imagery during 25-29 March, and ash plumes drifted 57 km SE on 26 March. Ground-based observers noted that ash-and-gas plumes rose to an altitude of 5.5 km (18,000 ft) a.s.l. during 25-30 March.
 
Based on information from KEMSD and analyses of satellite imagery, the Tokyo VAAC reported that on 5 April an eruption produced a plume that rose to an altitude of 7.6 km (23,000 ft) a.s.l. and drifted N. A possible eruption detected in satellite imagery the next day produced a plume that rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted NE.
 
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/updates.php,
Tokyo Volcanic Ash Advisory Center (VAAC) http://www.ssd.noaa.gov/VAAC/OTH/JP/messages.html
 
 
SOUFRIERE HILLS Montserrat 16.72°N, 62.18°W; summit elev. 915 m
 
MVO reported that during 25 March-1 April activity at the Soufrière Hills lava dome was at a low level. A swarm of 36 earthquakes occurred within an hour on 28 March, the largest volcano-tectonic swarm since February 2010. The Hazard Level remained at 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/
 
 
TENGGER CALDERA Eastern Java (Indonesia) 7.942°S, 112.95°E; summit elev. 2329 m
 
CVGHM reported that during 29 March-4 April brownish-gray ash plumes from Tengger Caldera's Bromo cone rose 400-800 m above the crater and drifted N, E, and NE. Ash fell at the Bromo observation post. Incandescence emanated from the crater and incandescent material was periodically ejected above the crater. Roaring of varying intensity was heard. The Alert Level remained at 3 (on a scale of 1-4). Residents and tourists were not permitted within a 2-km radius of the active crater.
 
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: Center of Volcanology and Geological Hazard Mitigation (CVGHM) http://www.vsi.esdm.go.id/
 
 
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