Punongbayan says: Measures vs Pinatubo crater lake breaching up to DPWH

BOTOLAN, Zambales — The government’s chief volcanologist said yesterday the protection of this province from a "catastrophic breaching" of Mt. Pinatubo’s crater lake now lies in the hands of the Department of Public Works and Highways (DPWH) amid projections that the two-kilometer wide lake could overflow early next year.

"We have already conveyed three alternative measures to the DPWH to prevent the possibility of catastrophic breaching at the lowest point of Mt. Pinatubo’s crater rim facing Zambales," Raymundo Punongbayan, director of the Philippine Institute of Volcanology and Seismology (Phivolcs), told The STAR in a telephone interview.

July Sabit, Phivolcs’ supervising science research specialist, said the crater lake’s clearance from the lowest point or notch of the crater rim facing this town was noted to be only 10 meters as of their latest study.

"Our estimate is that the lake level would reach the lowest point early next year," Sabit said.

Punongbayan has warned that unless proper measures are undertaken, water pressure could trigger the collapse of the crater wall at its lowest point.

Scientists have referred to the lowest point as the Maraunot notch since it leads to the Maraunot River on Pinatubo’s western slopes.

Downstream, the Maraunot River empties into the Marella-Balin Baquero river system. However, a catastrophic breaching at the Maraunot notch could affect wide populated areas in this town.

Punongbayan said Phivolcs has presented to the DPWH three alternative measures that could be done at the Maraunot notch. These include the scrapping of the soft outer layer of the lowest point, the "strengthening" of the site to prevent collapse, or the creation of a tunnel to serve as passageway for the lake’s waters.

"What I understand is that the DPWH has access to available funds from the Japan International Cooperation Agency (JICA) for engineering interventions at the Maraunot notch," he said.

Meanwhile, Punongbayan said Phivolcs might yet revise its lahar hazard map in Central Luzon and lift the lahar-prone classification of many residential areas.

After Pinatubo’s eruption in 1991, Phivolcs came out with a map identifying many areas in the region as threatened by lahar flows.

As a result of the map, banks refused to accept as loan collateral properties covered by the hazard map.

But Punongbayan said lahar threat from Mt. Pinatubo has greatly diminished, although studies on the so-called "cementation" of lahar materials on the volcano’s slopes still have to be finished.

He said that even the half-buried, centuries-old Catholic church in Bacolor, Pampanga can now be converted into a historical and tourist destination.

"Bacolor is now safe from inundation as lahar debris which have accumulated there has elevated the town beyond reach of lahar," he said.