THE Philippine Institute of Volcanology and Seismology (Phivolcs) yesterday lowered the alert status of Bulusan Volcano in Sorsogon to Level 0 (normal) from Level 1 (low-level unrest) due to a decrease in volcanic activities.
“Bulusan Volcano has returned to normalcy following a decline in monitoring parameters,” it said.
Alert Level 1 was raised in October last year.
Phivolcs said Level 0 “means that monitoring parameters have returned to baseline or background levels and no magmatic eruption is foreseen in the immediate future.”
The status will be brought back to Alert Level 1 “in the event of a renewed increase in any one or combination of the above monitoring parameters.”
Phivolcs said Bulusan’s volcanic earthquake activity declined to the baseline levels — or 0 to 5 per day — since the third week of August.
On ground deformation, Phivolcs said, “Data from continuous GPS (global positioning system) and electronic tilt measurements tracked an unsteady inflation of the southern and northeastern flank of the Bulusan between December 2022 and September 2023.”
“While shallow hydrothermal processes beneath the edifice may have contributed to this, ground deformation was more likely driven by recent tectonic movement along the Masbate segment of the PFZ (Philippine Fault System),” it added.
Phivolcs also said Bulusan’s sulfur dioxide emission has been low — at an average of 76 tons a day — since the volcano was placed under Alert Level 1 on October 25 last year.
“Moreover, most monitored springs have exhibited decreases in acidity, temperature and diffuse carbon dioxide,” Phivolcs said.
“These parameters indicate that input from the shallow hydrothermal system has remained within background levels and that there has been no input from deep magma sources,” it added.
It said degassing activity from the summit vents “has remained in the background levels and has produced only very weak to moderate plumes since September 2023.”
Phivolcs reminded local government units and the public that entry into the four-kilometer permanent danger zone should be avoided, particularly near the volcano’s south-southeastern slopes “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,” Phivolcs also said.
It also advised people living within the valleys and along river and stream channels to remain vigilant against sediment-laden stream flows and lahar during heavy and prolonged rainfall.
