Report on Bulusan (Philippines) — 21 October-27 October 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 21 October-27 October 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Bulusan (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 21 October-27 October 2020. Smithsonian Institution and US Geological Survey.
12.769°N, 124.056°E; summit elev. 1535 m
All times are local (unless otherwise noted)
On 26 October PHIVOLCS lowered the Alert Level for Bulusan to 0, indicating normal conditions, though warnings remained to not enter the 4-km-radius Permanent Danger Zone (PDZ). The decision was based on monitoring data that showed sulfur dioxide flux remaining below detection levels since 2018, deformation continuing a deflationary trend since May 2019, and the frequency of volcanic earthquakes declining to baseline levels (0-2 earthquakes/day) beginning in late September 2020. Very diffuse white plumes rose from the summit vents.
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.