BRITISH AID workers fear a massive crater lake inside a volcanic mountain in the Philippines is threatening to collapse.
This is despite efforts by Filipino engineers to relieve excess water pressure on the crater's rim.
The warning comes from UK aid agency Oxfam, which first alerted the Philippines authorities to the danger in May after commissioning a geological survey of the crater inside the 1,445m high Mount Pinatubo.
At least 46,000 people living in the foothills are at risk from a potential avalanche of up to 300M. m 3of 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 team measured the distance between the water level and the lowest part of the crater rim at 8.3m on 26 May.
A month later the level had risen 2m, according to geologists from the Philippine Institute of Volcanology & Seismology (Phivolcs).
Once breached, the geological research team fears the crater could release as much as 60M. m 3of water. This would bulk up with mud, ash and volcanic debris, called lahar.
Draining Mount Pinatubo's crater lake began last month after engineers blasted a channel 1m wide and 2m below water level into the summit.
The flow is released into a 70m long emergency spillway designed to take about 10% of the 250M. m of water held in the crater lake on to the flood plain and out into the South China Sea.
But problems with the excavation have meant that water levels have continued to rise, with the current outflow of 0.33m 3/sbeing outstripped by an estimated rainwater inflow at 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 the danger is over.'
This view is disputed by Phivolcs director Raymundo Punongbayan: 'The danger has passed, but we continue to monitor the crater and are standing by to order an evacuation should it be necessary.'