PHIVOLCS reported that during 7-9 May the seismic network at Bulusan recorded a total of 17 volcanic earthquakes at depths of 0-5.2 km beneath the E flank. Six of the earthquakes were tornillo-type events associated with gas movement and the other 11 events were volcano-tectonic earthquakes associated with rock fracturing. Diffuse white steam plumes rose from the active vents in the summit crater. The Alert Level was lowered to 0 (the lowest level on a scale of 0-5) on 18 January and remained unchanged. 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.

Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)