PHIVOLCS reported that unrest continued at Bulusan during 22-28 June. Emissions rose 100-400 m above the summit and drifted NW and W; cloudy weather prevented views of the volcano on 26 June. Sulfur dioxide emissions were 559-751 tonnes per day during 22-26 June. The seismic network recorded 7-65 daily volcanic earthquakes. A small-volume lahar was detected during a thunderstorm, beginning at 1904 on 26 June and lasting for 54 minutes based on seismic and infrasound data. Narrow, channel-confined lahar deposits were seen later along the Calang Creek on the SW flank, in the Cogon barangay. 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)