MANILA, Philippines — State seismologists on Sunday raised the alert over Bulusan Volcano in Sorsogon province to Level 1, following a sustained series of volcanic earthquakes that began last week.
Teresito Bacolcol, director of the Philippine Institute of Volcanology and Seismology (Phivolcs), said that 475 volcanic earthquakes have been recorded by the Bulusan Volcano Network.
Most of these were weak volcano-tectonic earthquakes associated with rock fracturing at shallow depths beneath the volcano and are similar in general characteristics to seismicity before the June 2022 and April 2025 eruptions, Bacolcol said.
The Phivolcs chief said ground deformation data from continuous GPS (global positioning system) and electronic tilt monitoring indicate inflation, or swelling of the western and southeastern flanks since the last week of January and the first week of March 2026, respectively.
Citing data and analysis, he said degassing activity from the active vents, when visible, has been weak to moderate. This is consistent with weak volcanic sulfur dioxide (SO2) emissions of 91 tons per day, which are considered below background averages.
“Overall, these parameters could indicate that shallow hydrothermal processes are underway beneath the volcano, which could lead to steam-driven or phreatic eruptions at any of its summit vents,” Bacolcol said.
Level 1 means the Sorsogon volcano is in a state of low-level unrest with an increased chance of phreatic eruptions.
Phivolcs reiterated its warning to local government units and the public that the four-kilometer-radius Permanent Danger Zone should be strictly avoided.
“Also, vigilance in the two-kilometer extended danger zone on the southeast sector should be exercised due to the possible impacts of volcanic hazards such as pyroclastic density currents or PDCs, ballistic projectiles, rockfall, avalanches, and ashfall on these danger areas,” Bacolcol said.
