MOUNT Bulusan in Sorsogon spewed a one-kilometer high ash plume after it erupted again on Wednesday, according to Philippine Institute of Volcanology and Seismology (Phivolcs).

Phivolcs said the phreatic explosion occurred at 4:58 a.m. and lasted for about nine minutes.

"The event was recorded as an explosion-type earthquake," it added.

According to Sorsogon Provincial Disaster Risk Reduction Management Office (PDRRMO), around 0.3 millimeter (mm) to 0.5 mm of ash fell in the villages of Dangkalan, Bulusan Proper, San Rafael, Sabang and Mabuhay.

In a report, PDRRMO said classes in all levels in Barangay Bulusan Proper was cancelled due to the volcanic eruption.

Authorities urged the residents in the affected areas to wear facemasks or use wet cloth to cover their nose to avoid breathing the ash.

Evacuation of the affected population is not yet necessary, it said.

According to Phivolcs, the latest eruption of Mount Bulusan was the second since Monday morning. It has recorded 28 volcanic earthquakes round Mount Bulusan in the past 24 hours.

"While these eruption sources are within the Four-Kilometer Radius Permanent Danger Zone or PDZ wherein habitation is strictly prohibited due to a permanently high degree of hazards, the southeast vents bring about increased concern," the Phivolcs said.

Mount Bulusan remained under Alert Level 1 since its first eruption, which means "hydrothermal processes are ongoing beneath the volcano that may lead to more steam-driven eruptions."

Phivolcs said the areas of Barangay Mapaso, Irosin, and San Roque are in danger of possible volcanic hazard of impacting large ballistic injecta.

It said Barangays Patag and Irosin are also at risk of small-volume but hazardous pyroclastic density currents that can potentially be generated by stronger steam-driven or phreatic eruptions and travel down the Malunoy and Mapaso Rivers. (Sunnex)