Forty-one earthquakes rattled Kanlaon Volcano in less than half a day, signaling heightened unrest, the Philippine Institute of Volcanology and Seismology (Phivolcs) said on Sunday, Sept. 14.

In its 10:30 a.m. advisory, the agency said the quakes struck between 11 p.m. Saturday and 10 a.m. Sunday beneath the northwestern flanks of the volcano.

“These events ranged in strength between ML0.8 and ML4.6 and were generated at 0 to 7 kilometers depths beneath the northwestern flanks of the volcanic edifice,” it said.

Phivolcs noted that the strongest quake was felt at Intensity III in La Carlota City and Bacolod City, Negros Occidental, Canlaon City, Negros Oriental, as well as in Bago City, Murcia, and La Castellana, Negros Occidental, “based on social media information.”

It warned that the activity “strongly indicates progressive rock-fracturing beneath the volcano as rising magma or magmatic gas drives a path towards the surface.”

The agency noted that Kanlaon remains under Alert Level 2, which means the volcano is in a state of increased unrest. 

Phivolcs said the quakes could trigger “steam-driven or phreatic eruptions or short-lived weak to moderately explosive eruptions occurring at the summit.”

Residents were reminded to stay out of the 4-kilometer Permanent Danger Zone, while those within 6 kilometers of the crater were told to remain alert.