Report on Bulusan (Philippines) — 15 July-21 July 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 15 July-21 July 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Bulusan (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 15 July-21 July 2015. Smithsonian Institution and US Geological Survey.
12.769°N, 124.056°E; summit elev. 1535 m
All times are local (unless otherwise noted)
PHIVOLCS reported that at 1310 on 17 July an explosion at Bulusan, detected by the seismic network for 11 minutes, generated an ash plume that rose 200 m above the crater and drifted WNW. Ashfall was reported in areas to the N and NE in the Sorsogon Province, including Inlagadian (municipality of Casiguran), Tigkiw, Tugawe, Nazareno, Bugtong, and Rizal (municipality of Gubat), and Fabrica, San Isidro, Sta. Cruz, and San Ramon (municipality of Barcelona). The Alert Level remained at 1, indicating abnormal conditions and a 4-km radius Permanent Danger Zone (PDZ).
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.