Bulusan Volcano in Sorsogon had phreatic eruption —PHIVOLCS

Bulusan Volcano in Sorsogon had a phreatic eruption on Monday morning, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said. 

The phreatic eruption occurred at 4:36 a.m. and lasted until 5 a.m., according to PHIVOLCS Director Teresito Bacolcol in an interview on Dobol B TV.

A bent plume rose from the volcano's crater up to 4.5 kilometers, he added. This drifted west to southwest.

BREAKING NEWS: Ayon kay Dr. Teresito Bacolcol, Philippine Institute of Volcanology and Seismology (@phivolcs_dost), phreatic eruption ang naganap sa Bulkang Bulusan kanina mula 4:36 am hanggang 5:00 am. Umabot ang plume height ng 4.5 kilometers. pic.twitter.com/fFMHVLlQ7j

— DZBB Super Radyo (@dzbb) April 27, 2025

According to the United States Geological Survey (USGS) a phreatic eruption is a "steam-driven explosion" that happens when magma heats the ground or surface water.

The intense heat can cause water to boil and flash into steam, which results in an explosion of water, steam, rock and ash.

"The water, once heated, begins to boil or can even flash straight to steam, causing an explosion," USGS said.

During phreatic eruptions, however, no new magma is produced, only fragments of preexisting solid rock from the volcano.

Phreatic eruptions can also often precede, accompany or follow a more traditional volcanic eruption.

In a separate interview on Unang Balita on Monday, Bacolcol explained the nature of phreatic eruption more.

"Phreatic eruptions are steam-driven explosions that happen when water comes into contact with hot volcanic materials, pwedeng hot volcanic rocks or hot volcanic gases," Bacolcol said.

"Ang nangyayari dito, it ejects steam, ash and rock fragments. Wala pong involved dito na panibagong magma," he added.

(What happens here is that steam, ash, and rock fragments are ejected. No new magma is involved.)

Bacolcol said it is possible that the phreatic eruption today may be followed by a similar event in the coming days or weeks.

"'Yung steam-driven eruption kanina may be succeeded by the same similar events in the following days or following weeks," he said.

(The steam-driven eruption earlier today may be succeeded by the same similar events in the following days or following weeks.)

Alert Level 1

PHIVOLCS raised the alert level at Bulusan Volcano on Monday from Alert Level 0 to Alert Level 1.

This "means that the volcano is currently in a state of low-level unrest with chances of phreatic eruptions succeeding this morning’s event," it said in a bulletin.

PHIVOLCS advised the local government units and the public that the permanent danger zone — the four-kilometer radius from the crater — should be kept off limits.

"Vigilance 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, ballistic projectiles, rockfall, avalanches and ashfall on these danger areas," it added.

PHIVOLCS said ashfall occurred in Barangays Cogon and Bolos in Irosin, and Barangays Puting Sapa, Guruyan, Buraburan and Tulatula Sur in Juban.

"Communities that experience ashfall must take all necessary precautions and use protective masks or wet cloth to prevent ash inhalation," PHIVOLCS advised.

"A pyroclastic density current (PDC) or 'uson' descended the southwestern slopes and traveled within three (3) kilometers from the summit vent," it also said.

Flying aircraft close to the volcano is to be avoided since ash from sudden phreatic eruptions may be hazardous, it added.

"Furthermore, people living within valleys and along river/stream channels especially on the southeast, southwest and northwest sector of the edifice should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should phreatic eruption occur," PHIVOLCS said.

It said Bulusan Volcano had 53 volcanic earthquakes on Sunday prior to Monday's eruption.

Local government officials said rumbling sounds were heard approximately 15 minutes before the eruption and these were recorded by infrasound sensors. —KG, GMA Integrated News