With Thursday's failure to breach the canal for the release of some 24 million cubic metres (mcm) of water, government volcanologists and engineers, assisted by 25 soldiers and policemen, began to dig some more around Mt. Pinatubo's crater-lake to deepen the canal's mouth by another metre.

"We want to hasten the flow of water," said Ernesto Corpuz, geologist and head of Phivolcs' (Philippine Institute of Volcanology and Seismology) monitoring and eruption prediction group.

He said the 24 mcm of water needed to be released is about 25 per cent of the lake's 200 mcm of stored water, which has accumulated since Mt. Pinatubo's last eruption 10 years ago.

The government has resorted to trenching to ease the pressure on the crater's wall, whose collapse could send millions of tons of water and lahar crashing onto thousands of residents at the foot of the volcano.

Corpuz said the flow of water has been "sluggish", drawing out 0.11 cubic metres of water per second, through the two-metre wide, four-metre deep and 75-metre long trench on the volcano's Maraunot notch.

He explained that the canal, built on borrowed funds, had not lived up to expectations because a tall slope and huge boulders in the canal's path blocked the water that should have gushed down to the Maraunot River.

Speaking on a two-way radio, Corpuz said the new excavation could be completed late yesterday or early today.

He stressed that at a depth of five metres, the canal is expected to work up a gradual but steady release of water toward the Maraunot and Bucao rivers that drain in the South China Sea.

Corpuz said attempts to airlift 30 more soldiers to the notch to help in the excavation were aborted on Thursday and Friday due to thick clouds and rains over the 1,400-metre volcano.

Dr Raymundo Punongbayan, Phivolcs chief, said there are no more threats of flash floods and lahar flows brought about by the water release. "It was established by the diggings that the rock formations were not as soft as we thought them to be."