PHIVOLCS reported that unrest continued at Bulusan during 15-21 June. Emissions, sometimes voluminous, rose 100-500 m above the summit and drifted NW, WSW, and SW. Daily sulfur dioxide emissions were 660-1,255 tonnes per day. During 0500-2345 on 20 June the seismic network recorded 65 volcanic earthquakes, including one low-frequency volcanic earthquake; most of the events were weak and shallow. The Alert Level remained at 1 (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)