Philippine crater lake begins to drain

BOTOLAN, Philippines (CNN) -- In an operation considered one of the largest of its kind, the draining of a volcanic lake in the Philippines has begun.

After a slow start, water was by early afternoon streaming through a canal dug on the west bank of the crater lake.

The 75-meter-long canal has been constructed to reduce the threat of a deluge on a town of 40,000 residents below the Mount Pinatubo volcano in Zambales province, northwest of Manila.

Villagers had been evacuated for fear the volcano wall could collapse during the operation, sending a torrent of water thundering down the mountainside.

EXTRA INFORMATION Pinatubo: The fear of crater lake     RESOURCES Watch it explode!: Anatomy of a volcano   • Educational resource: Riverdeep's Interactive volcano lab   Provided by: CountryWatch.com     AUDIO Dr Raymondo Punongbayan from the Institute of Seismology 2.63 MB / 2 mins 5 secs WAV sound    CNN.com Asia More news from our Asia edition

But the initial outcome has proved far less dramatic, with little more than harmless streams of muddy brown water barely wetting the ankles of workers in the channel.

Philippine Institute of Volcanology and Seismology (Phivolcs) director Raymundo Punongbayan said the emergency spillway dug by government workers and local Aeta tribesmen did not slope as steeply as planned.

"The gradient apparently is not correct for the drain canal," he said. "The gradient is so low that the flow is almost static."

Flow increased

A squad of soldiers and policemen were immediately called in to help deepen the canal and by late afternoon had managed to increase the outpouring to a slow but steady stream.

Scientists decided to drain the massive lake after its waters rose to critical levels following weeks of monsoon rains, threatening to cause a dangerous overflow.

Thousands of villagers fled to emergency shelters in adjacent towns Wednesday, but hundreds of families living in the center Botolan, a coastal town facing the South China Sea, refused to go, saying looters might break into their homes.

The draining aimed to release about a tenth of the estimated 250 million cubic metres of water in the crater lake and direct it through river channels and out into the South China Sea.

This would minimize the risk of an overflow in which torrents of water could sweep up tonnes of volcanic ash and boulders deposited on the slopes of the 1,445-meter (4,667-foot) high volcano and hurl them at Botolan, scientists said.