On 13 July, PHIVLOCS reported that several days of elevated seismicity at Bulusan continued. During the previous 24 hours, 13 volcanic earthquakes were recorded by the local network. GPS and leveling surveys determined that the volcano was slightly inflated. Alert Level 0 and the 4-km restricted zone, the Permanent Danger Zone (PDZ), were maintained due to the possibility of sudden and hazardous steam-driven or phreatic eruptions.

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)