PHIVOLCS reported that the seismic network at Bulusan recorded an explosion-type event that lasted for two minutes on 18 June; dense clouds obscured visual observations of the summit area. A phreatic explosion that occurred at 1455 on 19 June, and lasted for seven minutes, produced a 1.5-km-high grayish ash plume that drifted WSW. A low-level ash cloud on the upper NW flank, possibly from a short pyroclastic flow, was also observed. Minor amounts of ash fell in the neighborhoods of Bacolod, Buraburan, Mapili, Puting Sapa, and Juban. The event was followed by a voluminous gray white emission, which later turned completely white, that rose 250 m and drifted SW. At 1315 on 21 June an event which lasted 111 seconds generated a steam-and-ash plume that rose 150 m and drifted E. Trace amounts of ash fell in San Jose, San Francisco, Bulusan Proper, Sapngan, San Rafael, and Dapdap. The Alert Level remained at 1, indicating abnormal conditions and a 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)