Sudden increase in volcanic earthquakes triggers Alert Level 1 for Bulusan volcano, Philippines

bulusan volcano philippines

On October 25, 2023, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) raised the alert status of Bulusan Volcano from Alert Level 0 to Alert Level 1 due to a period of low-level unrest that began on October 14, 2023. This includes a series of 121 volcanic earthquakes and signs of ground deformation.

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) announced an alert status change for Bulusan Volcano, moving it from Alert Level 0 to Alert Level 1. The decision follows a series of 121 volcanic earthquakes recorded since October 14, 2023. Among these, 37 were volcano-tectonic earthquakes associated with rock fracturing at depths ranging from 1 to 9 km (0.6 – 5.6 miles) beneath the volcano’s northwestern and southeastern slopes.

Ground deformation data revealed swelling of the southern flank since February 2023 and of the northeastern flank starting September 2023. These observations indicate hydrothermal activity possibly driven by deep-seated magma degassing beneath the volcano. Additionally, heightened levels of volcanic carbon dioxide (CO2) were detected from June to August 2023, along with increased spring temperatures since February 2023.

In light of these developments, local government units and the public are urged to avoid a 4 km (2.5 miles) radius Permanent Danger Zone (PDZ) around the volcano. Extra caution is advised within the 2 km (1.2 miles) Extended Danger Zone (EDZ) in the southeast sector due to the risk of sudden and hazardous phreatic eruptions. Civil aviation authorities have also been advised to prevent aircraft from flying near the volcano’s summit.

Residents living near valleys and along river/stream channels, particularly in the southeast, southwest, and northwest sectors, should remain vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall following a phreatic eruption.

The last eruption at this volcano started on June 5 and ended on June 12, 2023 (VEI 3). Many moderate explosive eruptions have been recorded since the mid-19th century.


1 Bulusan volcano advisory – PHIVOLCS – October 25, 2023

Featured image credit: USGS/Chris Newhall


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