The Philippine Institute of Volcanology and Seismology (Phivolcs) on Wednesday afternoon, Oct. 12 placed Bulusan Volcano in Sorsogon under Alert Level 1 due to “low-level unrest.”

In a bulletin issued at 3 p.m., Wednesday, Phivolcs said 126 weak and shallow volcanic earthquakes were recorded since 5 a.m. on Tuesday, Oct. 11.

“Most of these events occurred in the northwestern sector and the summit area of Bulusan and are attributed to rock-fracturing processes within the edifice,” it said.

“In addition to these earthquakes, several monitored parameters indicate increased hydrothermal activity and overall unrest,” it said.

According to Phivolcs, the ground deformation data from continuous GPS measurements and radial tilt indicate a short-term inflation of the southern flanks of Bulusan Volcano since April 2022.

“Moreover, a pronounced and ongoing inflationary trend that began in late September 2022 was detected by most of the electronic tilt stations on the southwestern and southern slopes. This current inflation cycle signifies ongoing pressurization of the shallow hydrothermal system,” it said.

Phivolcs also observed that the volcanic carbon dioxide concentrations measured monthly in springs on the southeastern sector of Bulusan Volcano have been increasing since July 2022, with increasing spring temperature since April 2022 in monitored hot springs on the southwestern sector.

It said residents at Sitio Talistison, Brgy. Mapaso in Irosin and Brgy. San Roque in Bulusan reported a “sulfurous odor” on Oct. 10 to 11.

However, Phivolcs pointed out that “only very weak to moderate emission of steam-laden plumes is transpiring at the summit crater and northwest vents.”

“Phivolcs is now raising the alert status from Alert Level 0 to Alert Level 1, which means that the volcano is currently in a state of low-level unrest,” it said.

Phivolcs reminded local government units and the public that entry into the four-kilometer radius permanent danger zone is strictly prohibited.

It added that vigilance in the two-kilometer extended danger zone on the southeast sector must be exercised because of the increased possibilities of sudden and hazardous phreatic eruptions.