(File photo)

MANILA – The Philippine Institute of Volcano and Seismology (Phivolcs) on Wednesday placed the Bulusan Volcano under Alert Level 1 (low level unrest), following the observation of increased volcanic activity and other monitored parameters.

A total of 126 volcanic earthquakes have been recorded since 5 a.m. Tuesday.

"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," Phivolcs said in an advisory issued at 3 p.m.

The volcano also showed increased hydrothermal activity and unrest.

Residents of Sitio Talistison, Barangay Mapaso, Irosin and Barangay San Roque, Bulusan reported sulfurous odor from Oct. 10 to 11.

Phivolcs, however, said very weak to moderate emission of steam-laden plumes have been recorded from the summit crater and northwest vents.

Volcanic carbon dioxide concentrations measured in springs on the southeastern sector of Bulusan have been increasing since July, in conjunction with the increasing spring temperature in monitored hotsprings on the southwestern sector since April.

Short-term inflation of the southern flanks of Bulusan has been observed since April 2022.

"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," Phivolcs said.

Under Alert Level 1, entry into the 4-km. radius permanent danger zone is strictly prohibited, and the public is advised to be vigilant in the 2-km. extended danger zone on the southeast sector due to the increased possibilities of sudden and hazardous phreatic eruptions.

People living within valleys and along river/stream channels, especially on the southeast, southwest and northwest sector of the edifice, are advised to be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should phreatic eruption occur.

Aviation authorities are also advised to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft. (PNA)