Report on Bulusan (Philippines) — 10 November-16 November 2010
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 10 November-16 November 2010
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2010. Report on Bulusan (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 10 November-16 November 2010. Smithsonian Institution and US Geological Survey.
12.769°N, 124.056°E; summit elev. 1535 m
All times are local (unless otherwise noted)
During 10-11 November, PHIVOLCS reported that 18 volcano tectonic earthquakes from Bulusan were detected by the seismic network. On 11 November white steam plumes rose 150 m above the crater and drifted ENE. During an aerial survey, scientists saw that recent explosions resulted in the joining of two of the 2006-2007 craters into one. They also noted that deposits from an explosion on 9 November did not contain juvenile material. On 12 November an ash explosion produced an ash-and-steam plume that rose 700 m above the crater and drifted SW. Multiple neighborhoods to the W and SW reported light ashfall. Four volcano-tectonic earthquakes were detected during the previous 24 hours. Steam plumes rose to a maximum height of 100 m above the crater. Some steaming was seen during 13-14 November. White steam rose from the NW vent, but no steaming was observed from the crater and SE vent on 14 and 15 November. An explosion late at night on 15 November was followed by ashfall in nearby neighborhoods. Cloud cover prevented observations of the summit area the next morning. The Alert Level remained at 1 (out of 5).
Geologic Background. Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.