Bulusan Volcano on ‘low-level unrest’ after phreatic eruption - Phivolcs

Metro Manila, Philippines - State volcanologists raised the alert status of Bulusan Volcano in Sorsogon to Alert Level 1 after erupting on early Monday morning, April 28.

Alert Level 1 means that “the volcano is currently in a state of low-level unrest with chances of phreatic eruptions succeeding this morning’s event,” the Philippine Institute of Volcanology and Seismology (Phivolcs) said in a bulletin.

Phivolcs warned the public not to enter the four-kilometer radius danger zone.

“[V]igilance in the 2-kilometer Extended Danger Zone (EDZ) on the southeast sector must be exercised due to the possible impacts of volcanic hazards such as PDCs (pyroclastic density currents), ballistic projectiles, rockfall, avalanches and ashfall on these danger areas,” it said.

Phivolcs confirmed reports of ashfall in the villages of Cogon and Bolos in Irosin, and communities of Puting Sapa, Guruyan, Buraburan, and Tulatula Sir in Juban.

In Juban, local authorities shared photos of thick ashfall covering their roads. 

They also advised their residents not to drink water coming from the Juban water system due to possible sulfur exposure of water sources.

The phreatic eruption, or a volcanic eruption driven by stream-driven explosions, started at 4:36 a.m., and ended at 5 a.m. Rumbling sounds were monitored 15 minutes before the eruption.

The 24-minute eruption generated a bent plume that went as high as 4.5 kilometers, drifting west-southwest of the volcano.

Phivolcs said a pyroclastic density current, or a high-speed volcanic flow of fragmented volcanic particles, gas, and ash, descended the southwestern slopes and went down within three kilometers from the summit vent.

In an advisory on April 21, Phivolcs warned of “increased seismic activity” over Mt. Bulusan.

The bureau said a total of 53 volcanic earthquakes were recorded on Sunday.

Phivolcs urged the use of face masks or wet cloths to prevent ash inhalation in communities experiencing ashfall. It also advised people living within valleys and along river/stream channels to be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should another phreatic eruption occur.