LEGAZPI CITY: Mount Bulusan in Sorsogon continued to show signs of restiveness as it caused at least five volcanic earthquakes, including an explosion-type one, during the past 24-hour observation period, the Philippine Institute of Volcanology and Seismology (Phivolcs) said Saturday.
The volcano has also been exhibiting a slight inflation of its edifice since May this year, indicating that steam-driven pressure could be building up beneath the volcano’s vent, Phivolcs resident volcanologist Ed Laguerta said.
Laguerta explained that when hydrothermal processes continue to develop beneath the volcano, it may lead to steam-driven eruptions.
Aside from volcanic quakes and the bulging of the edifice, Phivolcs instruments recorded during the past 24-hour monitoring period that the volcano expelled weak-to-moderate white steam plumes that rose up to 150 meters and drifted towards the north-northwest portion of the volcano.
On Friday, it spewed a two-kilometer high grayish ash plume that drifted northwest and fell on the villages of Anog, Juban and Mabini in Casiguran.
Traces of volcanic ash were observed in barangays Casay, Poblacion, Escuala, Inlagadian, San Antonio and San Juan, all in Casiguran town and barangays Aroroy, Juban proper, Puting Sapa and Rangas in Juban town.
In a previous interview, Laguerta said that as a standard practice, the collected volcanic ash would be tested on whether its contains magma fragments.
“If the test finds that it contains ‘juvenile magma fragments,’ this would mean that magma is building up and this may be a precursor to a much stronger eruption,” he said.
Alert Level 1 remains in effect, and the Phivolcs has warned the villagers not to venture into the four-kilometer Permanent Danger Zone because of sudden phreatic explosions.
Civil aviation authorities were likewise told to advise pilots to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft.