The Philippine Online Chronicles

Mount Bulusan in Sorsogon spewed a three-kilometer-high ash cloud on Monday morning, following an explosion caused by the build-up of steam in the volcano, said the Philippine Institute of Volcanology and Seismology (PHIVOLCS).

"The explosion produced a greyish ash column that rose to a height of about three kilometers above the summit before drifting to the southwest," said disaster committee NDRRMC in a statement.

On Sunday, PHIVOLCS recorded volcanic earthquakes near Bulusan as well as "weak steaming activity drifting to the southwest direction" from the volcano's northwest thermal vents.

"We expected this,” added PHIVOLCS Director Renato Solidum. “We are on Alert Level 1. At this stage, it is possible to have steam-triggered explosions which are not really very strong. People are still advised not to enter the four-kilometer permanent danger zone."

The ash cloud drifted southwest and fell upon the towns of Casiguran and Juban, at the foot of the volcano.  Around 1,000 residents have had to be evacuated from their homes, said Lieutenant Colonel Santiago Enginco, commanding officer of the 49th Infantry Battalion.

Residents have also been evacuated from the town of Irosin, which experienced darkened skies when the volcano spewed the ash column.

Airplanes have also been ordered not to fly over the volcano, said the Civil Aviation Authority of the Philippines (CAAP). CAAP Director General Ramon Gutierrez said that a Notice to Airmen (NOTAM) had been posted on Monday morning warning pilots that the vicinity of Mt. Bulusan is a "no-fly zone" due to the danger of ash getting into plane engines.

Bulusan began showing signs of activity back in November 2010. It has since been under Alert Level 1, meaning no entry is allowed into the four-kilometer radius Permanent Danger Zone (PDZ) due to the risk of sudden steam and ash explosions.