Bulusan volcano back to normal alert level —PHIVOLCS

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) on Wednesday lowered the alert level of Bulusan volcano in Sorsogon from Alert Level 1 or low-level of unrest to Alert Level 0 or normal level.

PHIVOLCS said this was after the volcano returned to normalcy following a “general decline” in monitoring parameters.

The agency said volcanic earthquakes recorded by the Bulusan Volcano Network (BVN) have declined to baseline levels (0-5 earthquakes/day) since the first week of December 2022.

“Most of these have occurred at a shallow depth of less than 10 kilometers beneath the edifice. This decline indicates that rock-fracturing processes within the volcano associated with shallow hydrothermal activity has diminished,” it said.

PHIVOLCS said the data from continuous GPS measurements and tilt monitoring indicate short-term deflation of the general southern edifice of Bulusan since August 2022.

“Moreover, long-term GPS data suggests that ground deformation is primarily driven by tectonic processes rather than pressurization from subsurface volcanic sources,” it said.

The agency said the sulfur dioxide emission or SO2 flux from the Bulusan summit based on campaign gas spectrometry has averaged only 274 tonnes/day since Alert Level 1 was raised on October 12, 2022.

“Volcanic gas input from the shallow hydrothermal system has generally remained within baseline level. On the other hand, most monitored springs have been exhibiting overall slight increases in acidity and decreases in temperatures and diffuse carbon dioxide or CO2, but generally do not indicate input from deep magma sources,” it added.

It said that the degassing activity from the active vents on the Bulusan summit has been characterized by very weak to weak emission of steam-laden plumes since the second week of November 2022.

PHIVOLCS, however, reminded that that entry into the four kilometer radius Permanent Danger Zone (PDZ) , 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, rockfall, and landslide.

Civil aviation authorities and pilots were also advised to avoid flying close to the volcano's summit as ash from any sudden phreatic eruption can be hazardous to aircraft.

“People living within valleys and along river/stream channels should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall,” PHIVOLCS said.

“DOST-PHIVOLCS is closely monitoring Bulusan Volcano's condition and any new development will be relayed to all concerned,” it added.—Richa Noriega/LDF, GMA Integrated News