The Philippine Institute of Volcanology and Seismology (Phivolcs) has reported a surge in seismic activity at Bulusan and Kanlaon volcanoes over the past few days, based on advisories issued on Monday, May 12.

Phivolcs said Bulusan Volcano recorded 309 volcanic earthquakes since midnight on May 8. 

Of these, 287 were classified as volcano-tectonic earthquakes, linked to rock fracturing at depths of less than four kilometers beneath the volcano’s southeastern flank. 

The remaining 22 were low-frequency volcanic earthquakes, associated with fluid movement beneath the surface. 

Weak to moderate degassing from active vents was observed when weather conditions allowed visibility.

“These changes in parameters may indicate shallow hydrothermal activity of Bulusan Volcano,” Phivolcs said.

Alert Level 1 remains in effect over Bulusan Volcano (low-level unrest) due to increased risk of phreatic or steam-driven eruptions.

Entry into the four-kilometer permanent danger zone is strictly prohibited.

Meanwhile, heightened caution is advised within the two-kilometer extended danger zone (EDZ) due to potential hazards such as pyroclastic density currents, rockfalls, and ashfall.

‘Moderately explosive eruption’ possible at Kanlaon

At Kanlaon Volcano, Phivolcs said 72 volcanic earthquakes were recorded between 12 a.m. and 12 p.m. on May 12, with magnitudes ranging from 0.3 to 3.1. 

It noted that 135 earthquakes have been recorded since May 11, including several strong volcano-tectonic events, which indicate that rock fracturing is likely being driven by rising magma or gas.

Phivolcs also observed that sulfur dioxide emissions from Kanlaon were measured at 554 tonnes per day on May 11. 

Although emissions have declined over the past year, from an average of 4,144 tons per day in June 2024 to 2,114 tons per day since April 2025, the decline may indicate a blockage of volcanic gas, potentially causing pressure buildup that may lead to a moderately explosive eruption.

Kanlaon remains under Alert Level 3 (magmatic unrest), which indicates an increased likelihood of short-lived but potentially explosive eruptions.

Phivolcs reiterated the need for evacuation within the six-kilometer danger zone around the summit crater.

The agency also urged residents to stay alert to hazards, such as pyroclastic density currents, ballistic projectiles, rockfalls, and ashfall.