A voluminous ash-laden cloud rose 2,500-3,000 m above the crater rim on 14 August, then was blown NE by the prevailing wind. The eruption, accompanied by hissing and rumbling sounds, began at 0545 and lasted about 30 minutes. A seismograph 5 km SSE of the crater was saturated by an explosion-type earthquake.

Further Reference. Aguila, L.G., 1978, The 1978 eruptions of Bulusan volcano: The COMVOL Letter, v. 10, nos. 3-4, p. 4-8.

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.

Information Contacts: G. Andal, COMVOL, Quezon City.