The Bulusan Volcano was placed under Alert Level 1, indicating low-level unrest, after a sustained increase in seismic activity and ground deformation, the Philippine Institute of Volcanology and Seismology (Phivolcs) reported on Sunday, March 22.

In its 12 noon bulletin, the agency said it raised the alert status from Alert Level 0 (Normal) to Alert Level 1 following a “sustained series of volcanic earthquakes” that began on March 15.

“A total of four hundred seventy-five (475) volcanic earthquakes has been recorded by the Bulusan Volcano Network (BVN),” Phivolcs said.

It noted that most of the recorded events were “weak volcano-tectonic earthquakes that are associated with rock fracturing at shallow depths beneath the volcano edifice,” similar to seismic activity observed prior to Bulusan’s June 2022 and April 2025 eruptions.

Aside from increased seismicity, Phivolcs also reported ground deformation based on monitoring data.

“Ground deformation data from continuous GPS and electronic tilt monitoring indicate inflation or swelling of the western and southeastern flank since the last week of January and first week of March 2026, respectively,” it reported.

“Degassing activity from the active vents when visible has been weak to moderate, consistent with weak volcanic sulfur dioxide or SO2 emission as indicated by below background averages of 91 tonnes/day measured on 17 March 2026,” Phivolcs added.

According to the agency, these combined parameters suggest ongoing subsurface activity.

“Overall, these parameters could indicate that shallow hydrothermal processes beneath the volcano are underway that could lead to steam-driven or phreatic eruptions at any of its summit vents,” it said.

With the alert level raised, Phivolcs warned of an increased likelihood of sudden steam-driven eruptions and reiterated strict safety measures.

“Local government units and the public are hereby reminded that entry into the 4-kilometer radius Permanent Danger Zone (PDZ) should be strictly prohibited and that vigilance in the 2-kilometer Extended Danger Zone (EDZ) on the southeast sector should be exercised,” the agency said.

It warned that hazards may include “pyroclastic density currents or PDCs, ballistic projectiles, rockfall, avalanches and ashfall.”

Phivolcs said communities west of the volcano were also advised to prepare for possible ashfall in case of a phreatic eruption.

As such, the agency also advised civil aviation authorities to instruct pilots to avoid flying close to the volcano’s summit, warning that ash from any sudden phreatic eruption could be hazardous to aircraft.

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