The Philippine Institute of Volcanology and Seismology (PHIVOLCS) on Saturday issued an advisory warning of increased seismic activity at Bulusan Volcano in Sorsogon.
According to PHIVOLCS, a total of 72 volcanic earthquakes were recorded by the Bulusan Volcano Network (BVN) since 12:00 a.m. of October 11, 2025. These volcano-tectonic (VT) earthquakes are linked to rock fracturing and occurred at depths of less than 10 kilometers beneath the volcano’s northern sector.
The agency noted that degassing activity from the active vents has ranged from very weak to weak in the past few days when the volcano was visible. The sulfur dioxide (SO₂) emission measured on October 9 averaged 31 tonnes per day, which remains below the baseline level of 200 tonnes per day.
“These parameters indicate shallow hydrothermal activity beneath the volcano,” PHIVOLCS said.
Despite the increase in activity, Alert Level 1 or low-level unrest remains in effect over Bulusan Volcano. However, PHIVOLCS warned that there is an increased chance of sudden steam-driven or phreatic eruptions that may occur without warning.
The public and local government units were reminded that entry into the 4-kilometer Permanent Danger Zone (PDZ) is strictly prohibited, while vigilance within the 2-kilometer Extended Danger Zone (EDZ) on the volcano’s southeast sector must be maintained.
Residents are also advised to take precautions against possible volcanic hazards such as pyroclastic density currents, rockfall, avalanches, ballistic projectiles, and ashfall. Communities that may experience ashfall should wear protective masks or damp cloths to avoid inhalation, especially vulnerable groups such as the elderly, pregnant women, infants, and those with respiratory or heart conditions.
Civil aviation authorities were likewise urged to advise pilots to avoid flying close to the summit, as ash from a sudden phreatic eruption could be hazardous to aircraft.
PHIVOLCS also cautioned communities living in valleys and river channels, especially on the western slopes, to remain alert for sediment-laden streamflows or lahars that could occur during heavy rainfall.
