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volcano (1)This serves as notice for the lowering of the alert status of Bulusan Volcano from Alert Level 1 (abnormal) to Alert Level 0 (normal).

Since its last phreatic eruption on 5 June 2017, Bulusan Volcano has returned to normalcy following a general decline in monitoring parameters. This is supported by the following observations:

  1. Volcanic Earthquake Activity:  The frequency of volcanic earthquakes has declined to baseline levels (0-3 earthquakes/day) in the last five (5) months, excepting a brief spate of 12 weak, 2-5 kilometers deep volcano-tectonic earthquakes on 8 June 2018. This indicates that rock-fracturing within the volcanic system associated with magmatic and/or hydrothermal activity has diminished.
  2. Ground Deformation: Continuous electronic tilt recorded deflation of Bulusan’s upper slope since June 2018 after a period of significant inflation beginning this year, consistent with continuous Global Positioning Systems data for the same period. In contrast, Precise Leveling or PL data indicated slight inflation of the mid-slopes in the second quarter of 2018 after a period of deflation beginning this year; however, the cumulative change for 2018 based on PL show net deflation of the mid-slopes. The overall ground deformation data indicate that depressurization has occurred, most likely of a shallow hydrothermal source beneath the edifice.
  3. Gas Emission: Sulfur Dioxide emission or SO2 flux from Bulusan based on gas spectrometry has dropped below detection levels since 9 January 2018 following a decreasing trend after its last eruption in June 2017. The relatively low levels of SO2 flux indicate the depletion of volcanic gas supply from an active shallow hydrothermal or deep magmatic source.
  4. Visual Observation of the Summit: Degassing activity from the active vents has significantly diminished, consistent with depletion of a shallow hydrothermal source.

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 to the 4-kilometer radius Permanent Danger Zone (PDZ), particularly near the vents on the south-southeastern slopes, is strictly prohibited 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

This serves as notice for the lowering of the alert status of Bulusan Volcano from Alert Level 1 (abnormal) to Alert Level 0 (normal).

Since its last phreatic eruption on 5 June 2017, Bulusan Volcano has returned to normalcy following a general decline in monitoring parameters. This is supported by the following observations:

  1. Volcanic Earthquake Activity:  The frequency of volcanic earthquakes has declined to baseline levels (0-3 earthquakes/day) in the last five (5) months, excepting a brief spate of 12 weak, 2-5 kilometers deep volcano-tectonic earthquakes on 8 June 2018. This indicates that rock-fracturing within the volcanic system associated with magmatic and/or hydrothermal activity has diminished.
  2. Ground Deformation: Continuous electronic tilt recorded deflation of Bulusan’s upper slope since June 2018 after a period of significant inflation beginning this year, consistent with continuous Global Positioning Systems data for the same period. In contrast, Precise Leveling or PL data indicated slight inflation of the mid-slopes in the second quarter of 2018 after a period of deflation beginning this year; however, the cumulative change for 2018 based on PL show net deflation of the mid-slopes. The overall ground deformation data indicate that depressurization has occurred, most likely of a shallow hydrothermal source beneath the edifice.
  3. Gas Emission: Sulfur Dioxide emission or SO2 flux from Bulusan based on gas spectrometry has dropped below detection levels since 9 January 2018 following a decreasing trend after its last eruption in June 2017. The relatively low levels of SO2 flux indicate the depletion of volcanic gas supply from an active shallow hydrothermal or deep magmatic source.
  4. Visual Observation of the Summit: Degassing activity from the active vents has significantly diminished, consistent with depletion of a shallow hydrothermal source.

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 to the 4-kilometer radius Permanent Danger Zone (PDZ), particularly near the vents on the south-southeastern slopes, is strictly prohibited 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