Increase in seismic activity observed in Bulusan volcano — Phivolcs
MANILA, Philippines — State seismologists said there is a significant increase in seismic activity at Bulusan Volcano in Sorsogon.
According to the state seismology agency Phivolcs, the Bulusan Volcano Network recorded a total of 72 volcano-tectonic earthquakes since 12:00 a.m. on Oct. 11, 2025.
These quakes are indicative of rock fracturing and are occurring at shallow depths, specifically less than 10 kilometers beneath the volcano's northern sector.
While Alert Level 1, or low-level unrest, is being maintained over Bulusan Volcano, the agency warned that there are now increased chances of steam-driven or phreatic eruptions occurring suddenly and without warning from the crater and/or its active vents on the summit.
Degassing activity from the active vents has been observed as ranging from very weak to weak.
Sulfur dioxide (SO2) emission was recorded at an average of 31 tonnes per day on October 9, a figure that remains below the baseline of 200 tonnes per day, according to Phivolcs.
State seismologists reminded the local government and the public that entry into the four-kilometer radius Permanent Danger Zone (PDZ) must be strictly prohibited.
The agency also advised residents to exercise vigilance within the two-kilometer extended danger zone (EDZ) on the southeast sector due to hazards such as pyroclastic density currents, ballistic projectiles and ashfall.
Phivolcs further recommended that communities experiencing ashfall use protective gear, such as masks or wet cloths and pay special attention to vulnerable populations.
It also directed civil aviation authorities to instruct pilots to avoid flying near the volcano’s summit and urged residents along valleys and stream channels on the western sectors to remain vigilant against lahars and sediment-laden stream flows during heavy rainfall following an eruption.
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