By Danielle Tiu
LEGAZPI CITY – Increased seismic activity has prompted the Philippine Institute of Volcanology and Seismology to place Mount Bulusan in Sorsogon under Alert Level 1, signaling low-level unrest.
Phivolcs said its monitoring network recorded 475 volcanic earthquakes since March 15, prompting the agency to raise the volcano’s alert status.
Most of the earthquakes were weak and classified as volcano-tectonic events caused by the breaking of rocks beneath the volcanic structure.
Experts noted that the characteristics of the recent seismic activity resemble those observed prior to Bulusan’s eruptions in June 2022 and April 2025.
Monitoring systems have also detected ground swelling on the volcano’s western and southeastern flanks since late January and early March, suggesting pressure build-up beneath the surface.
Degassing activity from Bulusan’s vents has been weak to moderate when visible. Measurements taken on March 17 indicated sulfur dioxide emissions averaging 91 tons per day.
Phivolcs said these indicators suggest ongoing hydrothermal processes beneath the volcano, which could lead to sudden phreatic or steam-driven eruptions at the summit.
Authorities reiterated that the four-kilometer permanent danger zone around the volcano remains off-limits to the public.
People are also advised to remain cautious within the two-kilometer extended danger zone in the southeast sector because of possible hazards including ashfall, pyroclastic density currents, ballistic fragments, rockfalls, and avalanches.
Communities located west of the volcano should prepare for possible ashfall in the event of an eruption and ensure the safety of vulnerable residents such as seniors, pregnant women, infants, and individuals with health conditions.
Pilots were warned against flying near the volcano’s summit due to the risk of ash clouds affecting aircraft.
Residents living along rivers and valleys around the volcano—especially in the southeast, southwest, and northwest sectors—were also advised to stay alert for lahars and sediment-laden flows during heavy rainfall.
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