Report on Bulusan (Philippines) — 17 May-23 May 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 17 May-23 May 2023
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2023. Report on Bulusan (Philippines) (Sennert, S, ed.). Weekly Volcanic Activity Report, 17 May-23 May 2023. Smithsonian Institution and US Geological Survey.
12.769°N, 124.056°E; summit elev. 1535 m
All times are local (unless otherwise noted)
In a special advisory, PHIVOLCS reported that from 0500 on 21 May to 1600 on 22 May the seismic network at Bulusan recorded a total of 37 volcanic earthquakes. Out of those, 34 were volcano-tectonic earthquakes associated with rock fracturing and three were low-frequency volcanic earthquakes associated with movement of volcanic gas. Minor steam emissions from an active vent on the SE flank were occasionally visible. Ground deformation data from electronic tiltmeter stations continued to record short-term inflation of the SE flanks, first detected in December 2022. The Alert Level remained at 0 (the lowest level on a scale of 0-5) and PHIVOLCS reminded the public 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.