Report on Bulusan (Philippines) — 3 November-9 November 2010
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 3 November-9 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, 3 November-9 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)
PHIVOLCS reported an explosion-type earthquake at Bulusan on 6 November coincident with a steam-and-ash plume that rose 600 m above the crater at 0811. Trace amounts of ashfall were reported in multiple areas 6-10 km NW. The Alert Level was raised from 0 to 1 (out of 5), and PHIVOLCS reminded the public not to enter the permanent danger zone, defined as a 4-km radius around the volcano. White steam plumes were observed rising 200 m above the crater before 1400, when cloud cover prevented observations. On 7 November, PHIVOLCS noted that seismic activity had increased during the previous 24 hours. A phreatic explosion on 8 November was produced a brownish-to-light-gray plume that rose 700 m above the crater. Several neighborhoods to the NW, W, and WSW reported ashfall. Steam rose from the crater after the explosion. On 9 November two consecutive ash explosions, accompanied by rumbling sounds, produced ash plumes that rose as high as 1 km above the crater and drifted SW. Ashfall up to 2 mm thick was reported in areas to the SW and WNW.
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.