By: Bennie A. Recebido
SORSOGON PROVINCE, May 4 – Philippine Institute of Volcanology and Seismology (Phivolcs) has finally lowered the alert level status of Mt. Bulusan from Alert level 1 or abnormal to Alert Level 0 or normal. This means that no eruption is foreseen in the immediate future.
Phivolcs Bulusan Volcano Observatory resident volcanologist Crispulo Diolata said that the lowering of the alert level status as stated in Bulusan Volcano Bulletin dated April 24, 2012, was due the overall decline of the monitoring parameters after the volcano’s last phreatic (steam-driven) eruption on May 13, 2011 as supported by the following observations:
(1) The frequency of volcanic earthquake occurrences has declined to baseline levels (0-2 events/day), indicating quiescence in the magmatic or hydrothermal system. Short-lived swarms (9-21 events/day) on 25 May, 10 August, 11 September and December of 2011, and 22 January of 2012, have been ascribed to crustal readjustments in the volcanic edifice after the May 2011 phreatic eruption.
(2) Results of precise leveling at both Inlagadian line on the north-northeastern slope and Mapaso line on the south-southeastern slope indicate that the volcano edifice has deflated since late November 2011. This suggests that no substantial pressure source in the subsurface, which could potentially trigger another eruption, can be detected.
(3) Steaming activity from the crater and known thermal vents has been frequently weak or wispy compared to the more moderate steam emissions during periods of unrest.
He also said that the bulletin issued on April 24, 2012 will be the last bulletin to be issued for Bulusan Volcano until new developments in monitoring parameters occur.
Meanwhile, in the light of the declaration, Diolata still remind the public to avoid entry into the 4-kilometer Permanent Danger Zone (PDZ) due to the perennial threat of sudden phreatic eruptions and rockfalls on the upper slopes. Furthermore, people living in valleys and along active river channels are cautioned to remain vigilant against sediment-laden streamflows and lahars in the event of heavy and prolonged rainfall.