MANILA, Philippines — State seismologists at Phivolcs have lowered Bulusan Volcano's status due to its declining volcanic activity in recent months, signifying no volcanic unrest.
In Tuesday’s bulletin, November 12, Phivolcs announced that “Bulusan Volcano has returned to normalcy following a general decline in monitoring parameters.”
Bulusan Volcano had been on Alert Level 1, indicating low-level unrest, since Oct. 25, 2023. After more than a year, Phivolcs has downgraded it to Alert Level 0.
State seismologists observed that volcanic earthquakes have dropped to “baseline levels” since the third week of August 2024, meaning there are at most five earthquakes per day.
Phivolcs said the reduced tectonic stresses from the 6.6-magnitude earthquake on Aug. 18, 2020 near the Masbate segment of the Philippine Fault Zone (PFZ) may have led to the decrease in volcanic earthquakes.
Meanwhile, sulfur dioxide emissions from Bulusan Volcano's summit vents are reported to be low, averaging just 76 tonnes per day. Phivolcs added that the volcano’s springs have shown decreases in acidity, temperature and diffuse carbon dioxide levels.
“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,” the Tuesday bulletin read.
Degassing activity has also been maintaining background levels, producing very weak to moderate plumes since September 2023.
When will a new alert be raised? Phivolcs said that Alert Level 1 will only be issued if there is a “renewed increase” in volcanic earthquakes, emissions and degassing activity.
Local government units are still advised to restrict entry within the 4-kilometer radius of the Permanent Danger Zone, located near the vents on Bulusan Volcano’s south-southeastern slopes.
Phivolcs also cautioned that hazards like steam-driven phreatic eruptions, rockfalls and landslides remain possible.
Residents along the volcano's valleys and river channels should stay vigilant, as sediment-laden streams and lahars could still occur during prolonged rainfall.
Phivolcs said its Tuesday bulletin will be the last for Bulusan Volcano until further changes are observed.