Report on Bulusan (Philippines) — 25 October-31 October 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 October-31 October 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Bulusan (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 25 October-31 October 2006. Smithsonian Institution and US Geological Survey.
12.769°N, 124.056°E; summit elev. 1535 m
All times are local (unless otherwise noted)
PHIVOLCS reported that during 25-26 October, a lahar from Bulusan deposited sediments 15 cm (6 in) thick along a tributary leading to the Gulang-gulang River. According to news articles, the lahar mobilized boulders as large as trucks and caused at least 96 people to evacuate. During 30-31 October, ash explosions generated a light gray ash-and-steam plume that rose to 2.3 km (7,400 ft) a.s.l. and drifted NNE. Later field inspection revealed ashfall (trace to 1 mm) in the N sectors of the volcano, including areas in the municipalities of Casiguran and Gubat.
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.