Report on Bulusan (Philippines) — 6 May-12 May 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 May-12 May 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Bulusan (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 6 May-12 May 2015. 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 at 2146 on 6 May a phreatic explosion from a vent on the upper NW flank of Bulusan generated an ash plume that rose 250 m before drifting W. Seismic data indicated that the event lasted 3.5 minutes. Traces of ash were reported in Sitio Tulay of Bagsangan Barangay, and in the Cogon, Monbon, and Tinampo Barangays. The Alert Level was raised to 1, indicating abnormal conditions and a 4-km radius Permanent Danger Zone (PDZ). During 8-9 and 11-12 May diffuse white emissions rose from vents on the SW and upper NW flanks.
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.