The Philippine Institute of Volcanology and Seismology (Phivolcs) has monitored an increase in activity of Bulusan Volcano in Sorsogon.

In an advisory on Thursday, March 18, Phivolcs said the Bulusan Volcano Network recorded 20 volcanic earthquakes in the last 30 hours, which included one “tornillo” and three low frequency events.

The state seismology bureau also measured a “steady inflation” of the upper slopes of the edifice that began on March 6.

It said that ground deformation data also indicated a “short-term” slight inflation since February, “while the long-term trend from July 2020 denotes that the edifice is still deflated.”

“Only very weak to weak emission of white steam-laden plumes could be observed at the southeast vents presently,” Phivolcs said.

“The increased seismic activity and short-term ground deformation are likely caused by shallow hydrothermal processes beneath the edifice,” it added.

Considering these observations, Phivolcs said Bulusan Volcano remains under Alert Level 0 or “normal,” but it noted that the alert level may change should the current activity persist.

“Since hydrothermal processes are underway beneath the volcano, there are increased chances of steam-driven or phreatic eruptions from the active vents,” the agency said.

State seismologists said that entry into the four-kilometer radius permanent danger zones should be prohibited.

Those within the volcano’s extended danger zone should also exercise vigilance due to the increased possibilities of sudden and hazardous phreatic eruptions.

Phivolcs said pilots should avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft.

“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 event of heavy and prolonged rainfall,” it added.