Bulusan cools local climate

By P. JULIAN

IT was yet another spectacular show from Mt. Bulusan, with columns of ash, gas and smoke rising thickly 5 kilometers up the Bicol skyline before drifting west-southwest and northwest.
Close the doors, cover your face against possible ashfalls and watch those rivers for lahar, but Bulusan Volcano does not pose an immediate danger, the Philippine Institute of Volcanoly and Seismology (PHIVOLCS) said.
Four craters dot Bulusan’s rim with Blackbird Lake on top the largest at 20 meters wide and 15 m deep. Part of the Bicol Volcanic Chain, Bulusan has erupted 16 times, the latest in March-June 2006.
Several towns surround the 15-km base of the 1.559-kilometer high volcano in Sorsogon province in Bicol, 70 km southeast of Mayon Volcano and about 250 km from Manila.
The low sulphur content of gas coming out of Bulusan Volcano indicates it is not a magmatic eruption, said PHIVOLCS chief Rene Solidum. A magmatic eruption can expel large debris and large amounts of lava.
“It appears from the low sulphur content coming out that magma is not anywhere the crater,” he said. “In that sense, Bulusan does not pose an immediate danger because we base our alert levels on magma movement underneath the volcano.”
According to PHIVOLCS, Bulusan Volcano continues to be in a state of unrest as evidenced by swarms of small to moderate sized earthquakes and the ash explosion last July 31.
The current Alert Level 1 for Bulusan means “No eruption is imminent.”
Alert Level 1 remains in effect over the volcano and the public is prohibited from entering the 4-kilometer radius Permanent Danger Zone because the area is at risk from sudden steam and ash explosions.
Residents near rivers and streams around the volcano should also be on alert against life-threatening lahars during heavy rains that might remobilize ash and loose deposits from the upper slopes.
The latest ash explosion occurred last July 31, PHIVOLCS reported. The explosion was accompanied by rumbling sounds that lasted for about 20 minutes. The eruption column reached a maximum height of 5 km.
Initial field reports indicated that light ashfalls fell in Cogon, Gulang-gulang, Puting Sapa, Bolos, Monbon and Gabao in Irosin and Sangkayon and Buraburan in Juban.
The explosion of ash somehow cooled the local climate, bringing rains, Solidum said, noting it was a small help to the surrounding fields that are reeling from the dry climate that now bedevils Luzon.
“The cold temperature and the high heat of the ash that nucleated into raindrops brought rainfall,” Solidum pointed out.
The ashfall event was not dangerous per se, he said, but warned nearby residents to close doors and cover their faces against ash falls that when inhaled could be detrimental to health.
They should also clean and wash down surroundings heavily draped by ashfall as it may damage farms and vegetation.
Lahar could possibly flow downslope as has happened last year in Bulusan but currently the small volume is confined to river channels. “Local governments should monitor surrounding rivers,” Solidum warned.
Lahar is composed of volcanic ash and debris deposited around the volcano after the materials has cooled and has become water logged.
Observations of past Bulusan eruptions show that volcanic hazards usually consist of hot blasts and hot avalanche as well as lava flows. A 4-kilometer Permanent Danger Zone and a 4-10 km. buffer area (Probable Danger Zone) had been established around the summit.
The PHIVOLCS observation post is located in Cabid-an, Sorsogon City. It monitors ground movements and deformation, hotspring temprature as well as steaming activity and other visually observed phenomena.
Commonly observed signs that a volcano is about to erupt include an increase in the frequency of volcanic quakes with rumbling sounds and occurrence of volcanic tremors. Due to increased ash content, steam coming out of the craters increase and change in color from white to gray.
A crater glow may indicate the presence of magma at or near the crater. The ground swells and tilts and may fissure due to magma intrusion.
Landslides and rockfalls may occur. Vegetation around the volcano's upper slopes may dry up. The temperature of hot springs may increase, with noticeable variation in their chemical content. Springs and well around the volcano may dry up as well.
Hotsprings around Bulusan are found in San Benon, Mapaso, San Vicente and Masacrot.
The Philippines has 22 active volcanoes, from Mt. Babuyan in Cagayan up north to Taal volcano near Metro Manila to Mt. But Dajo in Sulu. Some 27 volcanoes – from Mt. Apo in Davao City to Tumatangas in Jolo – are listed as potentially active. InterNews&Features