In an advisory, Phivolcs said Bulusan Volcano generated 29 volcanic earthquakes. Sulfur dioxide emission was 279 tons on September 29.
Weak to moderate emission of white steam-laden plumes could be observed at the crater while very weak emission of the white-steam laden plumes could be observed at northwest vents.
Phivolcs said the increased seismic activity and short-term ground deformation are likely caused by shallow hydrothermal processes beneath the edifice.
"Since hydrothermal processes are underway beneath the volcano, there are increased chances of steam-driven or phreatic eruptions from its active vents," it said.
Local government units and the public are reminded that entry into the 4-km. radius permanent danger zone should be prohibited.
Aviation authorities must advise pilots to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft.
Phivolcs also advised people living within valleys and along the river/stream channels, especially on the southeast, southwest, and northwest sector of the edifice, to be vigilant against sediment-laden stream flows and lahars during heavy and prolonged rainfall. (PNA)