The Philippine Institute of Volcanology and Seismology (Phivolcs) reported on Sunday an increase in seismic activity at Bulusan Volcano in Sorsogon.
In an advisory, Phivolcs said Bulusan recorded a total of 72 volcanic quakes since 11 October. It added that the earthquakes are linked to rock fracturing occurring at depths of less than 10 kilometers beneath the northern sector of the volcano.
Degassing activity was also observed, with sulfur dioxide emissions recorded at around 31 tonnes per day on 9 October—below the baseline of 200 tonnes.
Phivolcs noted that these parameters indicate shallow hydrothermal activity beneath the volcano or the movement of hot fluids and steam below its surface.
Bulusan Volcano remains under Alert Level 1, signifying low-level unrest. Phivolcs reminded local governments and the public that entry into the four-kilometer Permanent Danger Zone is strictly prohibited and urged residents to stay alert within the two-kilometer Extended Danger Zone, particularly on the southeast sector.
The agency also advised those living near the volcano to take precautions against possible pyroclastic density currents, rockfalls, ashfall, avalanches, and ballistic projectiles.
Aircraft are cautioned to avoid flying close to the summit of the volcano due to potential ash emissions.