Report on Bulusan (Philippines) — July 1978
Scientific Event Alert Network Bulletin, vol. 3, no. 7 (July 1978)
Managing Editor: David Squires.
Bulusan (Philippines) Small ash eruption
Please cite this report as:
Global Volcanism Program, 1978. Report on Bulusan (Philippines) (Squires, D., ed.). Scientific Event Alert Network Bulletin, 3:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN197807-273010.
12.769°N, 124.056°E; summit elev. 1535 m
All times are local (unless otherwise noted)
Bulusan ejected a grayish steam and ash cloud for about 30 minutes on 29 July, beginning at 1155. The cloud rose several hundred meters above the crater and deposited 1-7 mm of ash NE of the volcano. The eruption was accompanied by rumbling. Steam emission persisted after the eruption, and as of 3 August, white to dirty white vapor was being continuously emitted to about 100 m above the crater. COMVOL delineated a danger zone within 5 km of the summit, to be evacuated in the event of a major eruption. Bulusan last erupted in December 1933.
Geologic Background. 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; AFP.