The Philippine Institute of Volcanology and Seismology (Phivolcs) on Sunday, Oct. 12, reported increased seismic activity at Bulusan Volcano in Sorsogon after recording 72 volcanic earthquakes since midnight of Oct. 11.

Phivolcs said the recorded volcano-tectonic earthquakes were associated with rock fracturing, occurring at depths of less than 10 kilometers beneath the northern sector of the volcano.

It added that degassing activity from the active vents has ranged from “very weak to weak” in the past days.

Meanwhile, sulfur dioxide emission averaged 31 tons per day as of Oct. 9, which is still below the baseline of 200 tons per day.

“These parameters indicate shallow hydrothermal activity beneath the volcano,” Phivolcs said.

Despite the increased activity, Alert Level 1 (low-level unrest) remains in effect over Bulusan Volcano.

However, Phivolcs warned that steam-driven or phreatic eruptions from the crater or active vents could occur suddenly and without warning.

It reminded local government units and the public to strictly prohibit entry into the four-kilometer permanent danger zone and to remain vigilant within the two-kilometer extended danger one on the southeast sector due to possible volcanic hazards, such as pyroclastic density currents, rockfall, ashfall, and ballistic projectiles.

Communities affected by ashfall are advised to take necessary precautions, including wearing protective masks or using wet cloths to prevent ash inhalation, particularly for vulnerable individuals such as the elderly, people with respiratory or heart diseases, pregnant women, and infants.

Phivolcs also advised civil aviation authorities to warn pilots against flying close to Bulusan’s summit as ash from a sudden phreatic eruption could be hazardous to aircraft.

Meanwhile, residents in valleys and along river channels, especially on the western slopes of the volcano, were urged to stay alert for possible sediment-laden streamflows and lahars in case heavy and prolonged rainfall occurs during or after an eruption.