Report on Bulusan (Philippines) — 9 May-15 May 2007
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
9 May-15 May 2007
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2007. Report on Bulusan (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 9 May-15 May 2007. 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 an explosion from Bulusan on 12 May produced an ash plume that rose to an altitude of 5.6 km (18,400 ft) a.s.l. and drifted WSW and WNW. The activity was accompanied by rumbling sounds and was recorded by the seismic network as an explosion-type earthquake that lasted about 35 minutes. An increase in seismicity was noted during 9-12 May. Ashfall (trace-2 mm thick) was reported in 11 barangays from the municipalities of Irosin and Juban.
Geological Summary. 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.