Government volcanologists said they needed to gather more details and possibly conduct another aerial survey of Bulusan’s summit — the second in a week — before they can assess prospects of a major eruption.
Renato Solidum, director of the Philippine Institute of Seismology and Volcanology (Phivolcs), said Sunday’s explosion — the volcano’s eighth since March — belched ash up to two kilometers into the sky, accompanied by a number of mild tremors.
No one was hurt and the volcano was reported quiet yesterday, officials said.
Local disaster relief official Noel Pura said 344 residents were ferried by military trucks and government vehicles from villages close to the volcano in Juban and Irosin towns to evacuation centers about five kilome—ters away.
Mayor Edwin Hamor of Casiguran town said 541 other villagers living near the slopes of the volcano moved to a high school, but that most of the men stayed behind to guard their homes and farms.
Authorities estimated more than 20,000 people face a possible evacuation in case of a major eruption, and set out plans for erecting tent cities outside a six-kilometer radius of the volcano.
Press Secretary Ignacio Bunye said President Arroyo ordered the National Disaster Coordinating Council yesterday to make sure that the basic needs of the displaced residents are available in the evacuation centers.
"We have to ensure that the affected residents are in the right and secure place until our experts declare that it is safe to go back," he said.
The President visited Juban town last Saturday and was briefed about the situation.
Hamor said rains on Sunday night increased the danger of ash and debris falling from the volcano, prompting the evacuation of residents, who did not resist the move.
Bulusan’s recent ash and gas ejections indicated molten rocks called magma may be moving up within the volcano, but it was not clear whether it would lead to a major eruption, Solidum said.
Local officials have asked Phivolcs to determine which barangays are really situated within the volcano’s permanent danger zone.
"It is now important to define the exact location of these villages or whether the present dwelling areas of the villagers are still safe given the volcano’s latest condition," said volcanologist Ed Laguerta.
He said ash deposits on Bulusan’s slopes pose danger to local folk since heavy rains could wash them down, triggering lahar flows.
In a bulletin, Phivolcs said Bulusan’s explosions this month have become longer and stronger, although it noted the absence of earthquakes and tremors and high sulfur gas emission, which could otherwise indicate large or active magma intrusion.
The volcano’s last major eruption was in 1994.
The Philippines, which has about 22 active volcanoes, is in the Pacific "Ring of Fire," where volcanic activity and earthquakes are common.
In June 1991, Mt. Pinatubo in Zambales exploded in one of the world’s biggest volcanic eruptions in the 20th century. — Cet Dematera, Celso Amo, Paolo Romero, Ding Cervantes and wire reports