Sorsogon: An increase in seismic activity was observed in Bulusan Volcano in Sorsogon province, the Philippine Institute of Volcanology and Seismology (Phivolcs) said. Ninety-four volcanic earthquakes were recorded since 3 a.m., the seismology agency said in an advisory late Monday.

According to Philippines News Agency, of the 94 earthquakes, a majority were weak and shallow volcano-tectonic earthquakes produced by rock fracturing, while four were low-frequency volcanic earthquakes produced by the movement of fluids. Phivolcs reported that these volcanic earthquakes were generated within 20 km deep beneath the Bulusan edifice, with nearly half being shallow events. Meanwhile, the degassing activity at the summit crater and active vents has been very weak to moderate during the same period.

Phivolcs stated that the slight increase in volcanic earthquake activity could be caused by hydrothermal activity, potentially leading to short-term pressurization of the edifice. Although Alert Level 0 (normal) is maintained over Bulusan Volcano, there are chances of steam-driven or phreatic eruptions from the crater and/or its active vents on the summit that could occur suddenly and without warning.

Local government units and the public are advised to refrain from venturing into the 4-km radius permanent danger zone, particularly near the vents on the south-southeastern slopes, due to the possible threat of sudden volcanic hazards, such as rockfall, landslide, ballistic projectiles, and small pyroclastic density currents. Aviation authorities should 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.