Bulusan Volcano alert lifted — Phivolcs

MANILA, Philippines — With no more signs of unrest, the alert on Bulusan Volcano in Sorsogon was lifted yesterday.

The Philippine Institute of Volcanology and Seismology (Phivolcs) said the volcano returned to normalcy, citing a general decline in monitoring parameters. 

In a bulletin, the agency said the frequency of volcanic earthquakes has dropped to zero to two since May 17, 2019. This is an indication that rock fracturing within the volcanic system associated with hydrothermal activity has diminished, state seismologists said.

“Precise leveling data indicated slight inflation of the mid-slopes since the second quarter of 2019 after a period of deflation in the beginning of the year while continuous GPS data for the same period recorded apparent deflation of the edifice related to regional tectonic motion,” Phivolcs said.

The agency said overall ground deformation data indicates that there is no pressurization from sub-surface magma, with the deformation observed in the mid-slopes most likely due to seasonal changes within the shallow hydrothermal system.

Sulfur dioxide emission from Bulusan based on gas spectrometry remains below detection levels since 2018, it said.

“The relatively low level of sulphur dioxide flux indicate the depletion of volcanic gas supply from an active shallow hydrothermal or deep magmatic source. Ambient carbon dioxide  concentration is also decreasing in monitored springs around Bulusan Volcano,” Phivolcs said.

It said degassing activity from the active vents has been characterized by ”weak emission of steam-laden plumes consistent with diminished hydrothermal activity.”

Phivolcs said the lowering of the alert level means observational parameters have returned to baseline levels and “no magmatic eruption is foreseen in the immediate future.”

An alert will be raised again if an increase in any or combination of monitoring parameters will be observed.

However,  Phivolcs reminded the public that  entry into the four-kilometer radius permanent danger zone, particularly near the vents on the south-southeastern slopes, should be avoided due to the possibility of sudden and hazardous steam-driven or phreatic eruption, rockfalls and landslides.

Pilots should avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft, it said.