PHIVOLCS issued a special advisory for Bulusan on 7 October, noting that 29 volcanic earthquakes were recorded from 0500 on 6 October until the time the report was issued at 1500 on 7 October. Minor white steam emissions rose from vents in the crater and from NW vents. Data from continuous GPS and radial tilt measurements indicated short-term inflation on the S flanks since April 2022. The inflation and increased seismicity were likely caused by shallow hydrothermal processes. The Alert Level remained at 0 (on a scale of 0-5) and PHIVOLCS reminded the public not to enter the 4-km-radius Permanent Danger Zone (PDZ) nor the 2 km Extended Danger Zone (EDZ) on the SE flank.

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.

Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)