Report on Bulusan (Philippines) — 17 November-23 November 2010
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 17 November-23 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, 17 November-23 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)
On 16 November, white steam rose from Bulusan's NW vent, but no steaming was observed from the crater and SE vent. Cloud cover prevented observations the next day. On 18 November weak steaming from the crater and known thermal vents produced plumes that drifted downslope to the SW. Cloud cover obscured views of the crater during 19-20 November. An explosion-type earthquake on 21 November was coincident with rumbling sounds and an ash plume that rose 2 km above the crater. Ashfall up to 3 mm thick was reported in multiple areas. According to news reports, about 500 families evacuated and some local roads were impassable. Steam was emitted from the crater and known thermal vents during 22-23 November.
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.