A MASSIVE volcanic crater lake in Mount Pinatubo in the Philippines is threatening to collapse, putting thousands of people at risk from an avalanche of water and volcanic debris.
An Oxfam research team, led by Kelvin Rodolfo and Rosalito Alonso, said: 'Two things are for certain, the lake water level is rising and the Maraunot notch [a geological fault in the crater] will eventually be breached. '
The aid agency first warned the Philippines authorities of the danger in May after commissioning a geological survey of the crater inside the 1,445m high mountain. The team measured the distance between the water level and the lowest part of the crater rim at 8. 3m on May 26.
A month later the level had risen 2m, according to geologists from the Philippine Institute of Volcanology & Seismology (Phivolcs).
Once breached, it is feared the crater could release as much as 60Mm 3of water. This would be bulked up with mud, ash and volcanic debris (a lahar). Depending on the slope, rate of release and prevailing weather conditions, this could generate an avalanche of up to 300Mm 3. More than 46,000 people live in towns and villages in the foothills of the mountain.
Draining the lake began last month after Philippine engineers blasted a 1m wide channel 2m below water level into the crater's summit to release the flow.
The water is being channelled into a 70m long emergency spillway designed to take about 10% of the estimated 250Mm 3of water in the crater lake on to the flood plain and out to the South China Sea.
But problems with the channel excavation have meant water levels have continued to rise, with outflow of 0. 33m 3/s being outstripped by an estimated rainwater inflow of 0. 65m 3/s. The level has risen by 80mm since draining began.
'The breaching did not go as planned because of faults in the design of the trench and channel, ' said an Oxfam spokesman. 'It has not drained enough for the government to say that the danger is over. '
Work is now under way to widen the channel.
This view is disputed by Phivolcs director Raymundo Punongbayan.
'The danger has now passed. Everyone has returned to their homes, but we continue to monitor the crater and are standing by to order an evacuation should it be necessary, ' he said.