On election day, Kanlaon and Bulusan volcanic earthquakes increase

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Phivolcs on Monday, May 12, reminds residents near Negros Island's Kanlaon Volcano and Sorsogon's Bulusan Volcano not to enter the permanent danger zones

MANILA, Philippines – As Filipinos headed to the polls on Monday, May 12, Kanlaon Volcano in Negros Island and Bulusan Volcano in Sorsogon were both showing “increased seismic activity,” or a high number of volcanic earthquakes.

The Philippine Institute of Volcanology and Seismology (Phivolcs) issued two separate advisories on the volcanoes on election day.

Kanlaon

Phivolcs said it recorded 72 volcanic earthquakes at Kanlaon between 12 am and 12 pm of Monday, ranging from magnitude 0.3 to magnitude 3.1. These earthquakes were 0 to 8 kilometers deep “beneath the northern and northwestern flanks of the volcanic edifice.”

Since 12 am of Sunday, May 11, Kanlaon volcanic earthquakes have reached 135, “including relatively strong volcano-tectonic or VT earthquakes.”

“VTs are generated by rock fracturing processes and the increase in VT activity strongly indicates progressive rock-fracturing beneath the volcano as rising magma or magmatic gas drives a path towards the surface,” Phivolcs explained.

The agency also noted that sulfur dioxide (SO2) emission from Kanlaon averaged only 554 tons per day on Sunday — a worrying drop since this could indicate a blockage of volcanic gas and possible pressurization within the volcano. The pressurization may then lead to a “moderately explosive eruption” at Kanlaon.

The volcano’s average SO2 emission has declined from 4,144 tons per day since June 3, 2024, to 2,114 tons per day since April 1, 2025.

Kanlaon has been under Alert Level 3 since December 9, 2024, when an explosive eruption occurred. This alert level means there is magmatic unrest.

“Currently there are increased chances of short-lived moderately explosive eruptions occurring that could generate life-threatening volcanic hazards,” Phivolcs said.

“It is recommended that communities within a 6-kilometer radius from the summit crater remain evacuated due to the danger of pyroclastic density currents or PDCs, ballistic projectiles, ashfall, rockfall, and other related hazards.”

Bulusan

Meanwhile, there have been 309 volcanic earthquakes at Bulusan since 12 am of Thursday, May 8, with 287 of these VT earthquakes triggered by rock fracturing and 22 low-frequency volcanic earthquakes “associated with movement of fluid.”

Weak to moderate emission of gas was observed in the past days.

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

The volcano has been under Alert Level 1 since April 28, when it last erupted. The eruption was phreatic or steam-driven in nature.

Phivolcs warned the public that more phreatic eruptions might occur since Bulusan is in a state of low-level unrest.

The agency reminded the public not to enter the 4-kilometer-radius permanent danger zone surrounding Bulusan, and called for vigilance in the 2-kilometer extended danger zone in the volcano’s southeast sector.

Bulusan and Kanlaon are among the Philippines’ two dozen active volcanoes. – Rappler.com