Bulusan

Geography & Climate

Bulusan is located in Philippines, within the Eastern Philippine Volcanic Arc of the broader Western Pacific Volcanic Regions. Situated at 12.77° N, 124.06° E in the Northern Hemisphere, the volcano lies within a tropical climate zone. With a summit elevation of 1,535 meters above sea level, Bulusan is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Bulusan sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in Philippines near Bulusan, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is andesite / basaltic andesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Bulusan has 20 recorded eruptions in the geological database, spanning from 1894 CE to 2025 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 1981 CE, reaching VEI 3 on the Volcanic Explosivity Index. Notable eruptions include 1981 CE (VEI 3), 1979 CE (VEI 3). With an average interval of roughly 7 years between eruptions over a span of 131 years, this is one of the more frequently active volcanoes in the database. This persistent activity suggests a robust and well-supplied magma system beneath the volcano. With eruptive activity as recently as 2025 CE, Bulusan remains an actively monitored volcano.

Significance

With a maximum recorded VEI of 3, Bulusan has produced eruptions capable of generating pyroclastic flows and significant ash fall in the surrounding area. While not among the largest eruptions globally, VEI 3 events pose serious hazards to local populations and can disrupt regional air travel. Its 20 recorded eruptions make it one of the most prolific volcanoes in our database, reflecting a persistent and well-documented eruptive history that has provided volcanologists with extensive data for understanding eruption patterns and forecasting future activity. Given its recent activity, Bulusan is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference 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.

— Smithsonian Institution, Global Volcanism Program