MANILA – The Philippine Institute of Volcanology and Seismology (Phivolcs) on Monday afternoon raised Alert Level 1 or an “abnormal” status over Bulusan Volcano in Sorsogon province.
In a bulletin issued 4 p.m., Phivolcs said 53 volcanic earthquakes, including 43 low frequency events associated with weak and shallow hydrothermal or magmatic gas activity within the edifice, were recorded since July 3.
Volcanic earthquakes are caused by movements or eruptions of magma from the volcano, compared to tectonic quakes which are caused by fault movements.
“The increased seismicity could be succeeded by steam-driven or phreatic eruptions at the summit crater or from flank vents on the upper to middle slopes, despite the absence of visible degassing or steaming from the active vent this year,” Phivolcs added.
Ground deformation data from continuous GPS measurements also indicate a short-term inflation of the edifice since late February.
“These parameters indicate that volcanic processes are underway beneath the edifice that may be caused by deep-seated degassing or hydrothermal activity or magmatic intrusion,” it said.
On Sunday, Phivolcs also issued an advisory regarding volcanic activities observed in Bulusan.
It maintained, however, that it was still under alert level 0 (normal) as of Sunday.
Seismicity, ground deformation and sulfur dioxide were within background levels, and there were no other anomalous parameters, according to Phivolcs director Renato Solidum, Jr.
He, however, reiterated that even at quiescence, phreatic or steam-driven explosions can occur.
Meanwhile, Phivolcs reiterated that entry into the four-kilometer radius Permanent Danger Zone is prohibited.
“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. Furthermore, people living within valleys and along river or stream channels, especially on the southeast, southwest and northwest sector of the edifice, should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall,” it said.
Bulusan Volcano was under Alert Level 0 from January 25 to July 5.
It was previously under Alert Level 1 for eight months, from May 5, 2019 to Jan. 24, 2020.