The Philippine Institute of Volcanology and Seismology (Phivolcs) on Tuesday evening, May 11, raised the status of Mt. Bulusan to Alert Level 1 as the active volcano in Sorsogon manifested a "low-level unrest."
Phivolcs said Bulusan Volcano's monitoring network has recorded a total of 124 earthquakes since May 8, 2021.
It warned that the volcano's increased seismicity "could be followed by steam-driven or phreatic eruptions at the summit crater or from flank vents on the upper to middle slopes."
Phivolcs also observed sustained inflation of the upper slopes that began on March 6, 2021, consistent with short-term inflation of the edifice measured by continuous GPS monitoring since February 2021.
"These parameters indicate that volcanic processes are underway beneath the edifice that are likely caused by shallow hydrothermal activity," it said.
From a normal status (Alert Level 0), Phivolcs said "abnormal" status (Alert Level 1) now prevails over Bulusan Volcano.
It advised the local government units and the public to prevent from entering the four-kilometer radius permanent danger zone and remain vigilant when entering the two-kilometer extended danger zone "due to the increased possibilities of sudden and hazardous phreatic eruptions."
"Civil aviation authorities must also advise pilots to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft," Phivolcs said.
Moreover, people living within valleys and along river/stream channels especially on the southeast, southwest, and northwest sector of the edifice were asked to stay vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should a phreatic eruption occur.