Alert Level Bulletin

18 Agosto 2021


18 August 2021

08:00 AM


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).


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 earthquake activity declined to the baseline level of 2-3 earthquakes/day between 1 July 2021 and 17 August 2021, during which a total of only 109 weak events were recorded. This indicates that rock fracturing within the volcanic system associated with shallow hydrothermal activity has diminished.
  2. Ground Deformation: Data from continuous GPS measurements indicated short-term inflation of the Bulusan edifice since July 2020, but measured horizontal changes nonetheless indicate that ground deformation has been driven by tectonic processes rather than pressurization from subsurface magma.
  3. Gas Emission: Sulfur dioxide emission or SO2 flux from active vents on Bulusan measured by gas spectrometry remained below detection levels since 6 May 2021. The last significant emission was recorded at 48 tonnes/day on 20 May 2021, which is well within the baseline level. Ambient carbon dioxide or CO2 concentrations in most monitored springs have weakened since April 2021 consistent with weak contributions from the shallow hydrothermal system or from deep magma degassing.
  4. Surface Activity:  When present, emission of steam plumes from the active vents on the upper Bulusan edifice has been very weak to weak, consistent with diminished hydrothermal activity.


In view of the above, PHIVOLCS-DOST is now lowering the alert status of Bulusan Volcano from Alert Level 1 to Alert Level 0.  This means that observational parameters have returned to baseline 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 public is reminded to avoid entry into the 4-km Permanent Danger Zone or PDZ due to perennial hazards of rockfalls, avalanches and sudden steam-driven or phreatic eruption from any of the active vents which may occur without warning. Furthermore, people living in valleys and active river channels are cautioned to remain vigilant against sediment-laden streamflows and floods in the event of prolonged and heavy rainfall. PHIVOLCS-DOST is closely monitoring Bulusan’s activity and any new development will be immediately communicated to all concerned.


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