The Philippine Institute of Volcanology and Seismology is closely monitoring the condition of Bulusan Volcano in Sorsogon after a series of volcanic earthquakes were recorded since Saturday midnight.

Phivolcs said 72 volcano-tectonic (VT) earthquakes, which are associated with rock fracturing, were recorded and are occurring at depths of less than 10 kilometers beneath the northern sector of the volcano.

It noted that gas releases ranged from very weak to weak during the past days when the volcano was visible.

Phivolcs said sulfur dioxide emission, measured last Thursday, averaged 31 tonnes a day — well below the baseline of 200 tonnes a day.

“These parameters indicate shallow hydrothermal activity beneath the volcano,” Phivolcs said.

Alert Level 1 is now hoisted over Bulusan Volcano, and local government units were reminded to enforce a prohibition of entry within the 4-kilometer radius Permanent Danger Zone (PDZ).

Phivolcs said there is an increased chance of steam-driven or phreatic eruptions occurring from the crater or its active vents on the summit, which could happen suddenly and without warning.

Residents in the direction of the southeast sector, in the 2-kilometer Extended Danger Zone (EDZ), are also warned of possible impacts of volcanic hazards such as pyroclastic density currents (PDCs), ballistic projectiles, rockfall, avalanches, ashfall, and others in these danger areas.

Phivolcs advised communities that will experience ashfall to take all necessary precautions and use protective masks or wet cloths to prevent ash inhalation, with special attention given to vulnerable persons including the elderly, persons with respiratory or cardiovascular diseases, expectant mothers, and infants.

The agency also urged civil aviation authorities to advise pilots to avoid flying close to the volcano’s summit, as ash from any sudden phreatic eruption can be hazardous to aircraft.