LEGAZPI CITY -- Mount Bulusan in Sorsogon erupted anew early morning Thursday but scientists described the steam-driven or phreatic eruption that lasted for around 15 minutes as “minor.”

“The explosion today was only of low energy though observed with a long duration,” said Eduardo Laguerta, resident volcanologist of the Philippine Institute of Volcanology and Seismology (Phivolcs).

He said the minor phreatic eruption could not be observed due to thick clouds covering the summit.

Laguerta said if it were a high-intensity eruption, no large volume of thick clouds could cover the ash plume spewed as high as five kilometers above the summit.

Phivolcs in its bulletin Thursday, October 6, said Mt. Bulusan recorded 40 volcanic earthquakes and a short harmonic tremor.

It said rumbling sounds were heard in Barangay San Roque in Bulusan town while ashfalls reached some areas in Gubat, Sorsogon.

Laguerta said the harmonic tremor was not produced by magma building up inside but by the phreatic explosion due to hydrothermal pressure beneath the volcano.

“The harmonic tremor was due to an explosion which is of low intensity and should not be a cause for alarm,” he said.

Phivolcs has advised 188 families or 728 persons in Irosin town in Sorsogon to be cautious against sulfur dioxide (SO2) emissions and volcanic ash spewed by a fissure on the southeast portion of the slopes of Mt. Bulusan for the past seven days.

The Irosin Municipal Disaster Risk Reduction and Management office told villagers of Barangay Mapaso to take precautions against respiratory illnesses that could be triggered by the volcanic ash and SO2 emissions.

Alex Baloloy, Phivolcs volcanologist, said a degassing episode at the fissure, 1.5 kms away from the volcano’s southeast summit, has reactivated.

“This (fissure) emits a low-lying plume with minor amounts of ash and gas creeping downslope that affect residents of Barangay Mapaso,” he said.

Barangay Mapaso is five kilometers away from Irosin town proper or 101 kilometers away from this city.

A Phivolcs advisory said the degassing episode, which has been observed since September 30, sent hundreds of villagers to complain about the foul odor brought about by the strong sulfuric odor emitted by the fissure.

Phivolcs said the fissure could have been reactivated by hydrothermal pressure and rock fracturing beneath the volcano’s vent.

This prompted the Office of Civil Defense (OCD) to send a team of health and environment personnel to determine the extent of hazard posed to the community by the volcanic gas and ash emission.

Alert level 1, indicating abnormal behavior, remains hoisted over Mt. Bulusan. The four-km Permanent Danger Zone remains off limits to residents living near the volcano. Authorities raised the alert level to 1 on Sept. 16. (PNA)