The Philippine Institute of Volcanology and Seismology (PHIVOLCS) on Wednesday, Oct. 25 raised Alert Level 1 over Mt. Bulusan or Bulusan Volcano in the province of Sorsogon, indicating a low level of unrest.
In an advisory issued at 3 PM, PHIVOLCS said that Bulusan Volcano "entered a period of low-level unrest with a sustained series of volcanic earthquakes that began" on Oct. 14.
The state seismologist said the number of volcanic earthquakes recorded reached up to 121.
"Of these, thirty-seven (37) were volcano-tectonic earthquakes that are associated with rock fracturing processes at depths of 1 to 9 kilometers beneath the northwestern and southeastern slopes of the volcano edifice," it added.
According to PHIVOLCS, Mt. Bulusan's southern flank has been inflated or swollen since February 2023 while its northeastern flank experienced the same since September 2023.
The state seismologist said it has also monitored "a notable increase of volcanic carbon dioxide (CO2) concentrations from June to August 2023 and spring temperature since February 2023."
With these developments, PHIVOLCS advised local government units and the residents living nearby to refrain from entering into the Bulusan Volcano's four-kilometer radius Permanent Danger Zone (PDZ).
It added that those who are situated in the two-kilometer Extended Danger Zone (EDZ) "in the southeast sector must be exercised due to increased possibilities of sudden and hazardous phreatic eruptions from the summit crater and/or lateral vents."
Civil aviation authorities, meanwhile, are directed to advise pilots "to avoid flying close to the volcano’s summit as the ash from any sudden eruption could be hazardous to aircraft."
"Furthermore, people living within the valleys and along rivers/stream channels, especially on the southeast, southwest, and northwest sectors of the edifice should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should a phreatic eruption occur," the state seismologist said.
