MANILA - The Philippine Institute of Volcanology and Seismology (Phivolcs) has recorded increased seismic activity at Bulusan Volcano in Sorsogon.

According to its advisory released Tuesday night, a total of 116 volcanic earthquakes were recorded in the Bulusan Volcano area since December 29, 2023.

Of this number, 110 were volcanic-tectonic earthquakes, and 6 were low frequency volcanic earthquakes.

Phivolcs also said there inflation or swelling of the southwestern and southeastern slopes was recorded since February 2023.

Degassing activity, on the other hand, has been very weak to moderate when the volcano summit has been visible.

“Nonetheless, increased seismic activity and pressurization of the volcano edifice may indicate that hydrothermal processes may be occurring beneath the volcano and may lead to steam-driven eruptions at any of the summit vents,” Phivolcs said.

Alert Level 1 remains hoisted over Bulusan Volcano, which means “it is currently at low-level unrest with increased chances of steam-driven or phreatic eruptions.”

Phivolcs reminded local government units and the public that entry into the 4-kilometer radius Permanent Danger Zone (PDZ) should be prohibited.

“Vigilance in the 2-kilometer Extended Danger Zone (EDZ) on the southeast sector must be exercised due to the possibilities of sudden and hazardous phreatic eruptions,” it added.

Phivolcs also warned people living within valleys and along river/stream channels of “sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall occurring simultaneous with phreatic eruption.”

The Phivolcs uses a 5-level alert system for volcanoes.

Bulusan has been under Alert Level 1 since October, after it was placed under Alert 0 in January 2023.

• Alert Level 1 raised over Bulusan Volcano: Phivolcs