PHIVOLCS Warns of Possible Phreatic Eruptions at Bulusan Volcano

On May 20, 2026, the Philippine Institute of Volcanology and Seismology, or PHIVOLCS, warned of possible phreatic eruptions after increased seismic activity and ground swelling were recorded around the volcano. The advisory was issued after 442 volcano-tectonic earthquakes linked to rock fracturing have been monitored by the Bulusan Volcano Network since May 18 this year.

PHIVOLCS said 55 of the recorded earthquakes were located less than five kilometers beneath the volcano, indicating movement below the edifice. Weak to moderate degassing activity and inflation on the volcano’s northern and upper western slopes were also observed through continuous monitoring.

They explained that these volcanic parameters may indicate slow pressurization caused by shallow hydrothermal or tectonic processes beneath the volcano. Because of this, sudden steam-driven or phreatic eruptions may occur at any of Bulusan’s summit vents.

Alert Level 1 or low-level unrest remains in effect over Bulusan Volcano. Local government units were advised to prohibit entry within the four-kilometer Permanent Danger Zone and stay alert in the two-kilometer Extended Danger Zone due to possible hazards such as ashfall, rockfalls, avalanches, and pyroclastic density currents.

Communities living west and downwind of the volcano were also urged to prepare for possible ashfall, especially vulnerable residents, including children, elderly individuals, and pregnant women. Pilots were likewise advised to avoid flying near the summit because volcanic ash can be hazardous to aircraft.

PHIVOLCS assured the public that it continues to closely monitor the condition of Bulusan Volcano and will immediately report any new developments. The agency also reminded residents to remain vigilant and follow safety measures, as volcanic activity may still increase in the coming days.