2.5 million truckloads of volcanic debrisloosened by ‘Reming,’ says volcanologist

11 December 2006

LEGAZPI CITY—AN ESTIMATED 10 million cubic meters or around 2.5 million truckloads of volcanic debris were loosened by Supertyphoon “Reming,” a volcanologist yesterday said.

The loosened debris caused lahar flows on high risk areas around Mayon volcano and buried homes that left more than 1,200 villagers, listed as dead or missing.

Ed Laguerta, senior science research specialist of the Philippine Institute of Volcanology and Seismology-Bicol (Phivolcs-Bicol), said two teams of geologists started measuring the amount of volcanic debris along the three main river channels that merge along the Yawa River and lead into the Albay gulf.

The geologists conducted an aerial survey and took photos of the areas covered by the lahar and were about to measure the thickness of the debris deposits through ground routing.

“It will take a week or two to complete all these procedures and the 10 million cubic meters could still increase,” Laguerta said.

He added that the results of the measurement will serve as significant inputs to disaster officials studying the permanent relocation of residents living in lahar-prone areas.

It will also benefit the Department of Public Works and Highways if it would plan to create dikes or do other engineering intervention.

Laguerta said the people residing near river channels should be prioritized in the relocation although, ideally, all those in lahar-prone areas should be relocated as far as “total safety” is concerned.

He said Phivolcs would also be comparing river channels before and after the lahar to determine significant changes in its future paths.

After studying the present lahar flow, Phivolcs will also measure how many “collapsible materials” are left on the slopes, which could possibly turn into lahar when loosened by a heavy volume of rainfall.

Laguerta explained that the recent “quiet eruption” of Mt. Mayon served to prevent rather than trigger the lahar that encroached on low-lying areas at the height of “Reming” on Nov. 30.

During the latest eruption, an estimated 80 million cubic meters of lava or hardened magma was ejected from the crater, Phivolcs records showed.

“The lava flow is hardened magma, which could not be loosened by water. It actually blocked quite a good quantity of lahar that could have added to those which buried houses at the low-lying areas during “Reming,” he said.

Lahar consists of a sufficient volume of rainfall mixed with sand, boulders and ash that were shed off from the main chunks of lava during the eruption.

He said the speed of lahar varies depending on the topography and the composition of debris and amount of rainfall.

“Lahar also does not have barriers. It will keep flowing for as long as there are low-lying areas to encroach on. The end point of lahar would turn out to be the foot of mountainous slopes,” he said.

“Lahar flow from the foot of Mt. Mayon at the height of ‘Reming’ was the first such experience in the history of Albay, preceded perhaps in terms of destruction only by the 1814 eruption that buried Cagsawa Church in Daraga, Albay,” observed Laguerta. Ephraim Aguilar, Inquirer Southern Luzon