Ernesto Corpus, chief of the volcano monitoring division of the Philippine Institute of Volcanology and Seismology (Phivolcs), said magma intrusion toward the crater is now highly possible.
This, as sulfur dioxide emission was measured at 949 tons in the past 24-hour observation period, way above the previous level of 500 tons per day. A short-duration harmonic tremor was also recorded last Wednesday.
"The sulfur dioxide emission rate of the volcanic plum was… considerably above the normal level. This could possibly indicate influx of new magma which will lead to more energetic activity," Phivolcs said in a bulletin.
During a meeting of the provincial disaster coordinating council yesterday, Noel Pura, the agency’s action officer, said the worst scenario is expected when the Phivolcs raises Bulusan’s alert level from two to three.
According to the council, Bulusan’s eruption would affect six barangays in Bulusan town, 13 in Barcelona, 10 in Casiguran, 22 in Juban, eight in Irosin, and three in Gubat.
Sixty-three evacuation centers, mostly schools, have been identified. At least 190 government and private vehicles, mostly trucks, are on standby for the evacuation.
Corpus said the harmonic tremor recorded last Wednesday confirms magma movement toward the crater.
"But whether how fast (the magma) is and will it continue to be pushed toward the surface are still very premature to tell based on this short harmonic tremor," he told The STAR.
Meanwhile, Corpus expressed dismay over the loss of the agency’s sensitive instrument that monitored harmonic tremors on Bulusan’s upper slope in Barangay Cogon, Irosin town.
"Because of this, we are having difficulty in detecting this kind of tremor that indicates magma movement inside the volcano," he said.
President Arroyo is expected to visit Juban town tomorrow to have a first-hand briefing on the situation.
In a related development, Phivolcs said Kanlaon Volcano in Negros Occidental continued to emit ash during the past 24-hour observation period.
"The steam emissions reached heights of up to two kilometers with an initial drift toward the southwest before clouds obscured the summit," it said.
Phivolcs said at least six barangays in Kanlaon City experienced ashfalls from 4:30 to 6:30 p.m. last Thursday. — With Sheila Crisostomo