Report on Bulusan (Philippines) — 17 February-23 February 2016
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 17 February-23 February 2016
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2016. Report on Bulusan (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 17 February-23 February 2016. 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 1701 on 22 February explosions at Bulusan generated a steam-and-ash plume that rose 500 m above the WNW fissure vent. The event was accompanied by a high-frequency earthquake followed by low-frequency earthquakes that lasted 4 minutes and 21 seconds. Rumbling sounds were heard in Puting Sapa, Juban, and Bolos, Irosin, and minor amounts of ash fell in barangays Puting Sapa, Sagkayon, and Caladgao in Juban, and barangay Bolos in Irosin. The report noted that no volcanic earthquakes were recorded prior to the eruption, though increased seismicity had been detected during 20-21 February. 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.