LEGAZPI CITY, Nov. 6, 2010 - Sorsogon province's Mt. Bulusan spewed a grayish ash column 600 meters high Saturday, prompting the Philippine Institute of Volcanology and Seismology (Phivolcs) to raise Alert Level 1.
Phivolcs reported observing explosions as thick ash clouds hovered over the volcano's summit.
Seismic instruments recorded a 57-second ash explosion at about 8:11 a.m. Saturday, Phivolcs noted.
In its bulletin, Phivolcs said its seismic instruments already recorded four volcanic earthquakes during the past 24 hours.
Phivolcs field monitoring personnel also reported observing traces of ashes within the six- to 10-kilometer radius around the volcano.
Field investigation showed traces of ashfall in Rangas, Anlog Cogon and Poblacion villages all in Juban town at the foot of Mt. Bulusan.
Phivolcs said abnormalities exhibited by Mt. Bulusan indicate magma is building up in the volcano's vent.
Hydrothermal disturbances like heavy steam emission and ash ejection may take place, Phivolcs warned.
A Phivolcs advisory said ash explosions may continue occurring in the next days or weeks, signifying the volcano's abnormal behavior may intensify.
With Alert Level 1 up, Phivolcs is advising people to keep out of the four-kilometer radius Permanent Danger Zone (PDZ) as sudden hazardous explosions are likely to affect the area.
Residents living beyond this PDZ but are in areas downwind of the crater are likely to be affected by ashfall during explosions.
People near river channels around the volcano are at risk for volcanic mudflow during heavy rain.
Regional Disaster Risk Reduction Management Council (RDRRMC) is coordinating with its provincial counterpart in Sorsogon PDRRMC, Phivolcs, the Army's 9th Infantry Division and Southern Luzon Command (Solcom) for updates on the volcano's status and possible action to be undertaken.
RDRRMC and Phivolcs are monitoring Mt. Bulusan and are considering conducting within the next few days an aerial survey to observe the volcano's activities and to determine its abnormalities.
Authorities concerned reminded PDRRMC Sorsogon about its contingency plan, recognizing the alert level can be raised further.
Mt. Bulusan's full eruption can possibly affect the towns of Juban, Irosin, Casiguran, Gubat, Barcelona and Busulan covering around 70 villages.
Experts describe Mt. Bulusan as Luzon Island's southernmost stratovolcano.
It is found in Bikol region's Sorsogon province, about 70 km southeast of world-famous Mayon Volcano and approximately 250 km southeast of the Philippine capital Manila.
According to experts, Mt. Bulusan is among the Philippines' most active volcanoes.
Mt. Bulusan is inside a caldera formed about 40,000 years ago. It rises 1,565 meters above sea level and has a base diameter of 15 km.
The volcano has four craters and four hot springs.
Crater No. 1 is called Blackbird Lake which is 20 meters in diameter and 15 meters deep.
The oval Crater No. 2 is 60 meters by 3 meters and 15 meters deep.
Crater No. 3 is about 90 meters in diameter and 20 meters deep.
The rim of Crater No. 4 near the northeastern area opened during the 1981 eruption.
A 100-meter fissure five to eight meters wide exists below Crater No. 4.
Mt. Bulusan's hot springs are San Benon Springs, Mapaso Springs, San Vicente Springs and Masacrot Springs.
Volcanoes adjacent to Mt. Bulusan are Mt. Homahan, Mt. Binitacan, Mt. Batuan, Mt. Calungalan, Mt. Calaunan, Mt. Tabon-Tabon, Mt. Juban and Mt. Jormajan.
The volcano erupted 15 times, the latest of which was during the July-October 2007 period. (PNA)