Authorities race against time to prevent Pinatubo lake collapse

BOTOLAN, Zambales — Some 130 families have abandoned their homes on the western slope of Mt. Pinatubo here while at least 20 Aeta workers braced for a virtual race against time amid estimates that the volcano’s crater lake has been rising at 1.24 meters a month.

Scientist Jaime Sincioco of the Philippine Institute of Volcanology and Seismology (Phivolcs), however, said yesterday there is no cause for panic.

He disclosed findings that underneath the soft portion of the crater rim’s lowest point facing the Maraunot River, the solid material is expected to withstand lake pressure.

"The soft material at the Maraunot notch is not a landslide deposit. Underneath it is welded material which had solidified some 2,500 years ago," Sincioco said.

The workers are supposed to scrape off the soft portion to give way to a controlled overflow of the lake down the slopes.

Still, Sincioco stressed the need for residents to be alert as the lake level was observed to be only 4.5 meters below the Maraunot notch.

The lake has reached 13.5 meters of the 18-meter thick top layer of the Maraunot notch, he said.

In a study, Phivolcs said that "if the lake water overtops and headward erosion occurs, a breach depth of 10 to 20 meters on the notch may release lake water volume between 28 and 55 million cubic meters."

It added that "a worst-case scenario is for this released water to bulk up or incorporate more sediments as it flows downslope to form lahar."

Sincioco said the flow will likely bury only the upper channels of the Maraunot and Balin-Baquero rivers before reaching the Bucao River in the Botolan valley leading to the South China Sea.

"It’s a long 15 kilometer stretch through the Maraunot River which drains into the 12-kilometer Balin-Baquero River before reaching the Bucao River downstream in Botolan," Sincioco said.

He added that the river system will likely be adequate to hold the volume of water that will flow from the Maraunot notch.

The Department of Public Works and Highways (DPWH) is set to carry out Phivolcs’ proposal to artificially breach the Maraunot notch by scraping off its soft top layer.

Sincioco quoted Botolan officials as saying that 130 families, mostly Aetas, have left their homes in Barangays Villar, Burgos and Ugik on the slopes of Mt. Pinatubo.

As of yesterday, at least 20 local workers, with picks and shovels, were still awaiting instructions on how to reach the Maraunot notch so they can start work.