Report on Bulusan (Philippines) — 19 January-25 January 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 19 January-25 January 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Bulusan (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 19 January-25 January 2011. Smithsonian Institution and US Geological Survey.
12.769°N, 124.056°E; summit elev. 1535 m
All times are local (unless otherwise noted)
During 18-19 January, PHIVOLCS reported that 11 volcanic earthquakes at Bulusan were detected by the seismic network. From 20 to 25 January up to five volcanic earthquakes per day were detected. Cloud cover mostly prevented observations of the summit area. Diffuse steam plumes rose from vents on 20 and 22 January. The Alert Level remained at 1 (on a scale of 0-5).
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.