Mayon: Killer lahar feared

20 July 2006

By Ephraim Aguilar
PDI Southern Luzon Bureau

LEGAZPI CITY—MT. MAYON’S LAHAR could be much more dangerous than that of Mt. Pinatubo in Zambales, which buried thousands of houses in 1991, due to the presence of big boulders on Mayon, the Philippine Institute of Volcanology and Seismology said yesterday.

Resident volcanologist Eduardo Laguerta said Mayon’s lahar would contain massive boulders which could wreak total havoc on anything on their path while that of Pinatubo only submerged the houses in lahar in the absence of the big boulders.

Aside from pyroclastic flows, lahar is one of the two major hazards of Mt. Mayon eruptions that the Albayanos should brace for, the Phivolcs official said.

Laguerta said that pryoclastic flows in past eruptions usually affect areas within the six-to-seven-kilometer PDZ only.

But he said there had been two occasions when Mt. Mayon’s pyroclastic flows reached beyond the six-kilometer-radius Permanent Danger Zone. One was during the 1814 eruption and the other, in 1897 when the pryoclastic flows even reached the sea in the Sto. Domingo, Albay area.

“What we have to invest upon more money in prevention is lahar since it is a long term and capricious hazard in any volcano. In Pinatubo, for instance, it took around 10 years before it subsided,” Laguerta said.

What is dangerous with lahar, he said, is that even if one were positioned 20 kilometers away from the volcano but were facing a channel in a low-lying area, one can be reached by the gushing lahar—depending on the volume and amount of rainfall.

After simmering down on Tuesday, Mayon again exhibited increased signs of restiveness with 250 tremor episodes monitored in the last 24 hours until 6 a.m. yesterday.

Phivolcs said sulfur dioxide emissions have increased to 2,157 tons per day as lava flows continued in the Bonga Gully, less than three kilometers from the crater.

“Seismic activity apparently resumed to high levels,” suggesting lava extrusion and rock falls, the Phivolcs said in its latest advisory.

“At this stage, Mayon continues its mild eruption with little or no explosions,” Phivolcs said.
Lava fragments were also observed to have reached farther downslope at least about four kilometers from the crater.

Phivolcs, however, assured that all flows and rockfalls were within the six-kilometer-radius PDZ.

Ash falls derived mainly from lava fragments may be experienced in areas beyond the PDZ due to prevailing winds.

“The public, however, is reminded that explosions are still very possible and the probability of life-threatening pyroclastic flows resulting from an explosive eruption remains high,” the Phivolcs warned.

“As time progresses, there is lesser time we have to wait before an explosive eruption occurs,” Laguerta said.

He noted that the parameters and signs observed yesterday in the Mt. Mayon were also observed in its past eruptions and they always led to a major eruption.

Farmers working on the lower slopes of the cone-shaped Mayon were warned yesterday to leave the slopes.

“We are worried about the people who remain in the permanent danger zone. There are livestock in there as well,” said regional disaster coordinating council official Angel Capili. With a report from B. S. Rivera and AFP