Volcanic activity in Indonesia throughout September 2012

List in order of event's date:
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KRAKATAU
6.102°S, 105.423°E; summit elev. 813 m

According to NASA's Earth Observatory, a satellite image of Krakatau acquired on 4 September showed fresh lava flows descending the SE flank of Anak Krakatau, extending the shoreline by about 100 m.

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: NASA Earth Observatory

Lava flow as seen on Sept 3, 2012, image source: Ndeso Adventure

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TANGKUBANPARAHU 
Western Java, 6.77°S, 107.60°E; summit elev. 2084 m

CVGHM reported that seismicity at Tangkubanparahu had increased significantly on 13 August, then again on 23 August; seismicity fluctuated and remained elevated through 6 September. Earthquakes were located 0.5-4 km beneath Ratu Crater and in an area W at depths of 4-12 km. Soil temperatures at Ratu Crater showed an increasing trend on 31 August, but had gradually declined by 5 September. Sulfur dioxide gas emissions were high in an area NW of the crater, causing CVGHM to remind visitors not to approach the crater within a 1.5-km radius. Based on seismicity, visual observations, gas measurements, and crater lake water temperatures through 7 September, the Alert Level remained at 2 (on a scale of 1-4).

Geologic Summary. Tangkubanparahu is a broad shield-like stratovolcano overlooking Indonesia's former capital city of Bandung that was constructed within the 6 x 8 km Pleistocene Sunda caldera. The volcano's low profile is the subject of legends referring to the mountain of the "upturned boat." The rim of Sunda caldera forms a prominent ridge on the western side; elsewhere the caldera rim is largely buried by deposits of Tangkubanparahu volcano. The dominantly small phreatic historical eruptions recorded since the 19th century have originated from several nested craters within an elliptical 1 x 1.5 km summit depression. Tangkubanparahu last erupted in September 1983, when ash rose up to 150 m above the rim of Kawah Ratu.

Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM)
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BATU TARA 
Komba Island,  7.792°S, 123.579°E; summit elev. 748 m

Based on analyses of satellite imagery, the Darwin Volcanic Ash Advisory Centre (VAAC) reported that during 5-11 August ash plumes from Batu Tara rose to an altitude of 2.1 km (7,000 ft) a.s.l. and drifted 55-75 km W, WNW, 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) ftp://ftp.bom.gov.au/anon/gen/vaac
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GAMKONORA 
Halmahera, 1.38°N, 127.53°E; summit elev. 1635 m

CVGHM reported that on 7 September the Alert Level for Gamkonora was lowered from 3 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)
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SIRUNG 
Pantar Island, 8.508°S, 124.13°E; summit elev. 862 m

CVGHM reported that on 7 September the Alert Level for Sirung was lowered from 2 to 1 (on a scale of 1-4).

Geologic Summary. Sirung volcano is located at the NE end of a 14-km-long line of volcanic centers that form a peninsula at the southern end of Pantar Island. The low, 862-m-high volcano is truncated by a 2-km-wide caldera whose floor often contains one or more small lakes. Much of the volcano is constructed of basaltic lava flows, and the Gunung Sirung lava dome forms the high point on the caldera's western rim. A number of phreatic eruptions have occurred from vents within the caldera during the 20th century.

Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM)
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LOKON-EMPUNG
Sulawesi 1.358°N, 124.792°E; summit elev. 1580 m

According to the Darwin VAAC, ground-based observers reported that on 21 September an ash plume from Lokon-Empung rose to an altitude of 3 km (10,000 ft) a.s.l. Ash was not identified in satellite imagery.

Geologic Summary. The twin volcanoes Lokon and Empung, rising about 800 m above the plain of Tondano, are among the most active volcanoes of Sulawesi. Lokon, the higher of the two peaks (whose summits are only 2.2 km apart) has a flat, craterless top. The morphologically younger Empung volcano has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks. Historical eruptions have primarily produced small-to-moderate ash plumes that have occasionally damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred.

Source: Darwin Volcanic Ash Advisory Centre (VAAC) ftp://ftp.bom.gov.au/anon/gen/vaac/
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SOPUTAN 
Sulawesi 1.108°N, 124.73°E; summit elev. 1784 m

Based on information from the US Air Force Weather Agency (AFWA), the Support to Aviation Control Service (SACS), and CVGHM, the Darwin VAAC reported that an ash plume from Soputan rose to an altitude of 9.1 km (30,000 ft) a.s.l. on 19 September. Later that day an ash plume rose to an altitude of 2.4 km (8,000 ft) a.s.l.

Geologic Summary. The small conical volcano of Soputan on the southern rim of the Quaternary Tondano caldera is one of Sulawesi's most active volcanoes. During historical time the locus of eruptions has included both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Source: Darwin Volcanic Ash Advisory Centre (VAAC) ftp://ftp.bom.gov.au/anon/gen/vaac/
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TANGKUBANPARAHU 
Western Java, 6.77°S, 107.60°E; summit elev. 2084 m

CVGHM reported that during 23 August-21 September shallow volcanic earthquakes continued to be recorded at Tangkubanparahu but were less frequent. Other types of seismic signals also decreased. Based on seismicity, visual observations, deformation data, gas measurements, and soil and crater lake water temperatures, the Alert Level was lowered to 1 (on a scale of 1-4) on 21 September.

Geologic Summary. Tangkubanparahu is a broad shield-like stratovolcano overlooking Indonesia's former capital city of Bandung that was constructed within the 6 x 8 km Pleistocene Sunda caldera. The volcano's low profile is the subject of legends referring to the mountain of the "upturned boat." The rim of Sunda caldera forms a prominent ridge on the western side; elsewhere the caldera rim is largely buried by deposits of Tangkubanparahu volcano. The dominantly small phreatic historical eruptions recorded since the 19th century have originated from several nested craters within an elliptical 1 x 1.5 km summit depression. Tangkubanparahu last erupted in September 1983, when ash rose up to 150 m above the rim of Kawah Ratu.

Source: Center of Volcanology and Geological Hazard Mitigation (CVGHM)
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BATU TARA 
Komba Island, 7.792°S, 123.579°E; summit elev. 748 m

Based on analyses of satellite imagery, the Darwin Volcanic Ash Advisory Centre (VAAC) reported that on 25 September an ash plume from Batu Tara rose to an altitude of 2.4 km (8,000 ft) a.s.l. and drifted 28 km 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) ftp://ftp.bom.gov.au/anon/gen/vaac/