The Philippine Institute of Volcanology and Seismology (Phivolcs) on Wednesday, Jan. 18 lowered the alert level of Bulusan Volcano in Sorsogon from Level 1 to 0 as the active volcano has returned to its normal condition.

“This serves as notice for the lowering of the alert status of Bulusan Volcano from Alert Level 1 (low-level unrest) to Alert Level 0 (normal),” Phivolcs said in a bulletin on Wednesday.

Bulusan Volcano’s alert status was raised to Level 1 on Oct. 12, 2022.

In the volcano bulletin, Phivolcs explained that Bulusan Volcano’s observational parameters have “returned to baseline or background levels and no magmatic eruption is foreseen in the immediate future.”

Following a general decline in monitoring parameters, Phivolcs said Bulusan Volcano has “returned to normalcy.”

It noted that the volcanic earthquakes recorded by the Bulusan Volcano Network (BVN) have declined to baseline levels—up to five earthquakes a 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,” Phivolcs said.

Moreover, it pointed out that continuous GPS measurement and tilt monitoring indicated short-term deflation of the general southern edifice of Bulusan Volcano since August 2022, and long-term GPS data suggest that ground deformation is mainly driven by tectonic processes rather than pressure from subsurface volcanic sources.

“Sulfur dioxide emission or SO2 flux from the Bulusan summit based on campaign gas spectrometry has averaged only 274 tons per day since Alert Level 1 was raised on 12 October 2022, with the highest average emission recorded at 462 tons per day on 21 October 2022. Volcanic gas input from the shallow hydrothermal system has generally remained within baseline level,” Phivolcs added.

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

However, Phivolcs noted that in the event of a renewed increase in one or a combination of monitoring parameters, the alert status is likely to be raised to Alert Level 1 again.

Phivolcs reminded the concerned local government units and the public to avoid entering the four-kilometer permanent danger zone, particularly near the vents on the south-southeast slopes.