Increased seismic activity has been detected in Bulusan Volcano in Sorsogon, with 116 volcanic earthquakes recorded in the past week.

The Philippine Institute of Volcanology and Seismology (Phivolcs) said 110 of the quakes were volcanic-tectonic and associated with rock fracturing beneath the volcano's southern flanks around two to six kilometers in depth.

The rest were low-frequency volcanic earthquakes associated with the movement of volcanic fluids.

Phivolcs said Bulusan remains under Alert Level 1 or a state of low-level unrest.

This means there is an increased chance of steam-driven or phreatic eruptions.

State seismologists said degassing activity as well as swelling of the southwestern and southeastern slopes have been weak since February 2023.

'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.

It said entry into the four-kilometer-radius permanent danger zone should be prohibited. Vigilance should be exercised within the two-kilometer extended danger zone, it added.

Residents along the river or stream channels of the volcano were advised to be wary of possible sediment-laden stream flows and lahar during heavy rainfall.

Bulusan was placed under Alert Level 1 on Oct. 25 last year after Phivolcs observed a sustained series of volcanic earthquakes.

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