Phivolcs warns of Bulusanactivity; 400 quakes in 2 days

By Rhaydz Barcia

LEGAZPI CITY --- The Philippine Institute of Volcanology and Seismology (Phivolcs) has warned the public, local government units, and disaster officials to remain alert and prepared as Bulusan Volcano showed increasing activity, recording 442 volcano-tectonic earthquakes associated with rock fracturing over the past two days.

In its latest bulletin issued today, Phivolcs said a total of 442 volcano-tectonic earthquakes have been detected by the Bulusan Volcano Network (BVN) since 4:00 p.m. of May 18, 2026. Of these, 55 were located at depths of less than five kilometers beneath the volcano edifice.

Degassing activity from the active vents has been described as very weak to moderate in recent days when the volcano was visible. A low average emission rate of 121 tonnes per day was last measured on April 22, 2026.

“This is a notice of increased seismic activity at Bulusan Volcano,” Phivolcs said in its advisory.

The agency also noted that ground deformation data from continuous GPS monitoring indicate inflation or swelling of the northern and upper western slopes since June 2025 and January 2026, respectively.

“These parameters may indicate slow pressurization of the edifice due to shallow hydrothermal or tectonic processes beneath the volcano that could lead to steam-driven or phreatic eruptions at any of its summit vents,” Phivolcs added.

Alert Level 1 (low-level unrest) remains in effect over Bulusan Volcano. However, Phivolcs emphasized that increased seismicity raises the likelihood of phreatic eruptions from any of its summit vents.

Local government units were advised to strictly prohibit entry into the 4-kilometer Permanent Danger Zone (PDZ) and to exercise vigilance within the 2-kilometer Extended Danger Zone (EDZ) on the southeastern sector due to potential volcanic hazards, including pyroclastic density currents, ballistic projectiles, rockfalls, avalanches, and ashfall.

Communities west and downwind of the volcano were likewise advised to prepare for possible ashfall in the event of a phreatic eruption, with special attention given to vulnerable groups such as the elderly, pregnant women, infants, and persons with medical conditions.

Civil aviation authorities were urged to advise pilots to avoid flying near the volcano’s summit, as ash from sudden phreatic eruptions may pose hazards to aircraft.

Residents living in valleys and along river and stream channels—particularly in western sectors—were also warned to remain vigilant against sediment-laden stream flows and lahars in case of heavy and prolonged rainfall following a possible eruption.

Bulusan Volcano, a stratovolcano in Sorsogon province about 70 kilometers from Mayon Volcano in Albay, remains under Alert Level 1 while Mayon continues its ongoing eruption under Alert Level 3 since January 2026.

Bulusan sits on the northeastern rim of the 11-kilometer-wide Irosin Caldera, formed approximately 35,000 to 40,000 years ago. Its summit area features four craters and several hot springs that are well-known eco-tourism sites.

Among these are Blackbird Lake, the second and third craters of varying sizes, and a fissure associated with Crater 4 that was exposed during the 1981 eruption. The volcanic complex also hosts several geothermal features, including hot springs in Irosin such as Mapaso, San Benon, Masacrot, and San Vicente, known for their mineral-rich waters and tourism value.