The Philippine Institute of Volcanology and Seismology (Phivolcs) has raised the alert status of Bulusan Volcano in Sorsogon from Alert Level 0 (normal) to Alert Level 1 (low-level unrest) following a phreatic or steam-driven eruption early Monday morning, April 28.

The eruption occurred at 4:36 a.m., and lasted for 24 minutes, based on seismic and infrasound monitoring data.

The steam-driven explosion from the summit crater produced a plume about 4,500 meters above the volcano before drifting west to southwest.

Ashfall was reported in several barangays, including Cogon and Bolos in Irosin, and Puting Sapa, Guruyan, Buraburan, and Tulatula Sur in Juban.

A pyroclastic density current (PDC), locally known as “uson,” was also observed descending the southwestern slopes, traveling up to three kilometers from the summit.

Phivolcs said that before the eruption, 53 volcanic earthquakes had been recorded over the past 24 hours.

Rumbling sounds were heard about 15 minutes before the explosion and were detected by infrasound sensors.

With the raised alert level, Phivolcs warned that the volcano is experiencing low-level unrest and that further phreatic eruptions are possible.

Entry into the four-kilometer permanent danger zone is strictly prohibited.

Meanwhile, caution is advised in the two-kilometer extended danger zone on the southeast flank due to risks of ashfall, PDCs, rockfall, and other volcanic hazards.

Residents are urged to wear face masks or wet cloths to avoid inhaling volcanic ash.

Civil aviation authorities are also advised to remind pilots to avoid flying near the volcano’s summit due to potential ash hazards.

Phivolcs further warned communities near rivers and stream channels, especially on the southeast, southwest, and northwest sectors of the volcano, to stay alert for possible lahars or sediment-laden flows during heavy rainfall.