Legazpi City (CNN Philippines) — Mount Bulusan, an active volcano in Sorsogon in the Bicol region, spewed a 250-meter-high ash cloud at 9:46 p.m. on Wednesday , according to resident volcanologist Ed Laguerta of the Philippine Institute of Volcanology and Seismology (Phivolcs).
In an eruption notification posted through its Facebook page, the Office of Civil Defense in Bicol said that the ash explosion was generated by an earthquake.
“The explosion event lasted 3.5 minutes based on the seismic records,” Phivolcs reported on its bulletin posted at its website at 8:00 a.m. on Thursday.
At the same time, Phivolcs raised Alert Level 1 over the area, meaning the volcano has started showing abnormal activity.
“This indicates that hydrothermal processes may be underway beneath the volcano that may lead to more steam-driven eruptions,” Phivolcs said in its bulletin.
As defined by Phivolcs, abnormal activity includes “slightly elevated levels of seismic activity, fumarolic activity, drying of vegetation and/or sulfuric stench.”
“Sporadic explosions may also occur,” Phivolcs added.
Fumarolic activity is the emission of hot gases or vapors from holes in the volcano.
Based on an initial assessment on Wednesday, Laguerta said that there were light ashfalls over barangays of Cogon, Tinampo, Monbon and Agasan in the town of Irosin.
Last Friday morning (May 1), a five-minute long ash explosion also occurred at Mount Bulusan.
Phivolcs said that a total of 62 volcanic earthquakes were recorded in the next eight hours after the explosion.
Local government units and the public have been advised not to enter the volcano’s four-kilometer permanent danger zone.
After Mayon’s threat
Mount Bulusan is about 70 km southeast of Mayon Volcano, which is in Albay, and about 250 km southeast of Manila, the capital of the Philippines.
In June 2014, Mayon started showing heightened volcanic activity. By September, Phivolcs had raised Alert Level 3, prompting precautionary evacuation of residents in areas near the volcano.
But by December, with its volcanic activity diminished, Phivolcs lower its warning to Alert Level 2 and evacuees were allowed to return home.
Residents were warned, however, not to venture in the 6-kilometer permanent danger zone.