Report on Bulusan (Philippines) — 5 May-11 May 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
5 May-11 May 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Bulusan (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 5 May-11 May 2021. Smithsonian Institution and US Geological Survey.
12.769°N, 124.056°E; summit elev. 1535 m
All times are local (unless otherwise noted)
PHIVOLCS stated that unrest at Bulusan had increased, noting that 62 volcanic earthquakes were recorded during 7-10 May and 124 were recorded during 10-11 May. Inflation of the upper flanks first recorded on 6 March in tilt data was sustained. GPS data indicated short-term inflation starting in late February, though the long-term pattern since July 2019 showed deflation. The data suggested shallow hydrothermal processes. The Alert Level for Bulusan was raised to 1 on 11 May, reflecting abnormal conditions, and the public was reminded not to enter the 4-km-radius Permanent Danger Zone (PDZ).
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.