SORSOGON — The Philippine Institute of Volcanology and Seismology (Phivolcs) is keeping a close watch on Mount Bulusan after recording a noticeable uptick in volcanic activity since Saturday midnight.

According to Phivolcs, 72 volcano-tectonic earthquakes — or small quakes caused by rock fracturing beneath the surface — were detected less than 10 kilometers deep under the northern part of the volcano.

The agency also observed weak gas emissions over the past few days when the volcano’s summit was visible.

Meanwhile, sulfur dioxide emissions measured last Thursday averaged 31 tonnes per day, well below the baseline of 200 tonnes per day.

“These parameters indicate shallow hydrothermal activity beneath the volcano,” Phivolcs said in its latest bulletin.

With these findings, Alert Level 1 remains raised over Bulusan, meaning it is currently in an abnormal state. Local government units have been reminded to strictly prohibit entry within the four-kilometer Permanent Danger Zone (PDZ).

Phivolcs also warned that steam-driven or phreatic eruptions may occur suddenly and without warning. Residents in the southeastern sector within the two-kilometer Extended Danger Zone are urged to stay alert for possible volcanic hazards such as pyroclastic density currents (PDCs), ballistic projectiles, rockfalls and ashfall.

Communities that may experience ashfall are advised to take precautions — wear masks or use wet cloths to cover their nose and mouth — especially for elderly people, those with respiratory or heart conditions, pregnant women and infants.

Phivolcs also asked civil aviation authorities to remind pilots to avoid flying near the volcano’s summit, as ash from a sudden eruption can pose serious risks to aircraft.