During 11-17 January, PHIVOLCS reported that up to 2 daily volcanic earthquakes at Bulusan were detected by the seismic network. Cloud cover prevented observations of the summit area. An explosion on 18 January was accompanied by a rumbling sound audible in Monbon, a barangay (neighborhood) in the municipality of Irosin, to the S. Cloud cover prevented observations of the crater. Trace amounts of ashfall were observed in Monbon. The Alert Level remained at 1 (on a scale of 0-5).

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)