THOUSANDS of people living on the slopes of Mount Pinatubo in the Philippines
may still be in danger after a botched attempt to drain the lake at its summit
last week. Government officials claimed on Saturday that the risk of the lake
bursting through the crater wall had been averted and local people got the
all-clear to return home. But aid agencies are not convinced the worst is
over.
British charity Oxfam warned in July about the rising level of the lake and
the possibility that millions of tonnes of water and volcanic debris could spew
out onto the town of Botolan below
(快猫短视频, 28 July, p 4). The
Philippine Institute of Volcanology and Seismology (PHIVOLCS) insisted the risk
was minimal.
But several weeks ago, when the water was just centimetres from the crater
rim, the agency brought in geologist Chris Newhall of the University of
Washington in Seattle. With so little time, he felt the only option was to
breach the lake wall deliberately.
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He proposed digging a channel to release a small amount of water, in the hope
that this would erode the sides of the channel, enlarging it and increasing the
flow until the lake was safely drained. It was a desperate strategy. 鈥淥nce that
happens, you have no control over it,鈥� says Lan Mercado, Oxfam鈥檚 representative
in the Philippines. But by choosing the time of the flood, people in the town
below could be evacuated.
Around 100 workers dug a channel with picks and shovels, while 40,000 people
left Botolan for temporary camps. The workers completed their task on 7
September. But nothing happened. 鈥淚t wasn鈥檛 done properly,鈥� says Matt Grainger
of Oxfam UK. 鈥淧arts of the channel were sloping uphill.鈥�
Last Saturday, army engineers dug the trench wider and deeper. Water is now
flowing out of the lake but at only 0.25 cubic metres per second, while rain is
still filling it up at 2 cubic metres per second.
The runaway breach idea didn鈥檛 work because the crater wall turned out to be
too solid. This means that the crater is less likely to suffer a catastrophic
breach. But Kelvin Rodolfo of the University of Illinois in Chicago, who first
raised the alarm about the lake, advises caution. 鈥淭he rock may only resist up
to a certain threshold. The rain could still produce a discharge strong enough
to initiate a runaway breach.鈥�
Rodolfo says the authorities have squandered a vital opportunity. 鈥淲hat鈥檚 the
likelihood these people will be willing to evacuate a second time?鈥� 鈥淲e were
able to remove the short-term risk,鈥� counters PHIVOLCS director Ray Punongbayan,
and that may buy some valuable time. 鈥淲e are now looking at whether siphoning is
an option,鈥� Mercado says.