Phivolcs chief: Only eruption can bring down Pinatubo walls

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CITY OF SAN FERNANDO—Only another eruption can cause the collapse of the wall surrounding the lake that formed at the crater of Mt. Pinatubo after its eruptions 20 years ago, the country’s chief volcanologist said on Wednesday.

No major collapse is expected to occur on the wall because the volcano, which gave the world its second strongest eruption in the 20th century, has retreated into slumber, said Dr. Renato Solidum, director of the Philippine Institute of Volcanology and Seismology (Phivolcs).

“There are no signs yet [of an eruption],” Solidum said by telephone.

Mt. Pinatubo’s 1991 blasts, coming more than 600 years after its last eruption, displaced more than 1.3 million people in Pampanga, Tarlac and Zambales. It killed about 1,000 people, damaged billions of pesos worth of structures, and destroyed thousands of hectares of forests, farms and fishponds.

Solidum said Ronaldo Tiotuico, director of the Department of Tourism in Central Luzon, was correct in warning tourists on the dangers from the post-eruption environment of Mt. Pinatubo.

In a travel advisory issued on Monday, Tiotuico said “many other portions of the crater’s inner wall are in danger of collapsing, as indicated by huge cracks and steep slopes. Collapse may be triggered once heavy rain falls within the area.”

Solidum said the collapse of the wall “is a different thing.”

“Since Pinatubo is a volcano, its wall is not [made of] hard [materials]. Rains can trigger landslides on the inner wall. Gravity [can induce landslides] as well,” he said.

The hard rock, he said, is at the center of the crater, which he inspected in 1992 when it was not yet filled with water. The crater‘s rim is 2.9-km wide now.

Water that rains dumped on the crater‘s 2-km wide lake would not cause the wall to collapse. The lake has been “continuously draining” after Aetas and personnel of the Department of Public Works and Highways built in August 2001 a canal on Maraunot, the lowest part of the crater facing Botolan, Zambales, to ease the pressure of a breakout.

More than 40,000 Botolan residents were evacuated then to get them out of harm’s way.

“What is important is for people to watch out for lahar and water during heavy rains,” Solidum said.

Tiotuico said he was not referring to the collapse of the crater lake’s entire wall when he issued the advisory that warned tourists against trekking and doing water activities in Mt. Pinatubo’s crater lake.

“I’m not saying the entire wall of the crater lake will collapse. I was referring to small cracks and possible collapse of some portions of the crater wall due to continuous erosion. The wall is really being eroded, rocks are falling. The erosion is continuous,” he said by telephone on Wednesday.

“The bottom line is [people should] stop trekking when it rains because it is dangerous,” he said.

Tiotuico said the O’Donnel River in Capas, Tarlac, also poses threats to trekkers during the rainy season because heavy rains, especially along the upstream portions of Zambales, will cause flash floods in the area.

The crater lake’s level has dropped by 23 meters after the canal was built in 2001. Aetas reported that the canal, originally a meter wide, expanded to three and five meters.

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