Bulusan Volcano Bulletin

18 January 2023

07:00 PM

 

This serves as notice for the lowering of the alert status of Bulusan Volcano from Alert Level 1 (Low-Level of Unrest) to Alert Level 0 (Normal).

 

Bulusan Volcano has returned to normalcy following a general decline in monitoring parameters. This is supported by the following observations:

 

1. Volcanic Earthquake Activity:  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.
    
2. Ground Deformation: 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.
    
3. Volcanic Gas and Heat Emission: 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 12 October 2022, with the highest average emission recorded at 462 tonnes/day on 21 October 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.
    
4. Visual Observation of the Summit:  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.

In view of the above, PHIVOLCS-DOST is now lowering the alert status of Bulusan from Alert Level 1 to Alert Level 0.  This means observational parameters have returned to baseline or background levels and no magmatic eruption is foreseen in the immediate future. However, in the event of a renewed increase in any one or combination of the above monitoring parameters, the alert status may step up once again to Alert Level 1.

 

The local government units and the public, however, are reminded that entry into the 4-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 must also advise pilots to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft. Furthermore, 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. DOST-PHIVOLCS is closely monitoring Bulusan Volcano’s condition and any new development will be relayed to all concerned.

 

This will be the last bulletin for Bulusan Volcano until new developments in monitoring parameters occur.

 

DOST-PHIVOLCS