By Connie Calipay
LEGAZPI CITY – The Philippine Institute of Volcanology and Seismology (Phivolcs) on Sunday raised Alert Level 1 (low-level unrest) over Bulusan Volcano in Sorsogon due to weeks of seismic activity.
In an advisory, Phivolcs said the Bulusan Volcano Network recorded a total of 475 volcanic earthquakes since March 15.
Most earthquakes were weak volcano-tectonic events associated with rock fracturing at shallow depths beneath the volcanic edifice, it added.
Phivolcs noted that their general characteristics are similar to the seismicity observed before the June 2022 and April 2025 eruptions.
Ground deformation data from continuous global positioning system and electronic tilt monitoring indicate inflation or swelling of the western and southeastern flanks of Bulusan since the last week of January and the first week of March 2026, respectively.
Phivolcs said degassing activity from the active vents, when visible, has been weak to moderate, consistent with weak volcanic sulfur dioxide emission, as indicated by background averages of 91 tons per day measured on March 17.
Overall, the parameters indicate that shallow hydrothermal processes beneath the volcano are underway and could lead to steam-driven or phreatic eruptions at any of its summit vents.
Phivolcs said the raised alert level means the volcano has increased chances of phreatic eruptions.
Local government units and the public are reminded that entry into the four-kilometer radius permanent danger zone is strictly prohibited.
Vigilance is also advised within the two-kilometer extended danger zone on the southeast sector due to the possible impacts of volcanic hazards such as pyroclastic density currents, ballistic projectiles, rockfall, avalanches and ashfall in these areas.
Communities west of the volcano are urged to prepare for possible ashfall in the event of a phreatic eruption and to pay special attention to vulnerable members of the community, including the elderly, pregnant, infants, and people with pre-existing medical conditions.
Pilots are advised to avoid flying close to the volcano’s summit, as ash from sudden phreatic eruptions can be hazardous to aircraft.
People living in valleys and along river and stream channels, especially in the southeast, southwest, and northwest sectors of the edifice, should remain vigilant against sediment-laden stream flows and lahars during heavy and prolonged rainfall should a phreatic eruption occur. (PNA)
