PINATUBO, the Philippine volcano that erupted ten years ago killing hundreds
of people, may be about to wreak havoc of a different kind among the people
living in its shadow. What鈥檚 more, the authorities are doing little about
it.
Since the last eruption, the volcano鈥檚 crater has been filling with rainwater
and the water is now only a few metres from the rim. If heavy rains continue the
rim could be breached, and a wave of water and volcanic debris sweep through
towns and villages below, say geologists.
Kelvin Rodolfo, an expert on Mount Pinatubo from the University of Illinois
in Chicago, and Rosalito Alonso, head of geology research with the British aid
charity Oxfam, have been trying in vain to persuade the Philippine authorities
to prepare for such a flood. 鈥淲e can鈥檛 ignore the fact that we have several
hundred million cubic metres of water sitting up there, and a town down here,鈥�
says Alonso. 鈥淪omebody has got to say something,鈥� says Rodolfo.
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Pinatubo鈥檚 1991 eruption was one of the most violent of the 20th century.
Hundreds of thousands had to flee their homes as huge swathes of the Philippines
were turned into a grey desert.
Since then, many local people have returned to their homes. Few, however,
know about the crater lake which now holds around 250 million cubic metres of
water. With a local annual rainfall of more than 3.5 metres and the funnel
effect of the crater, the water level has been rising by up to 10 metres each
year.
This year has been particularly wet, and since the rainy season began in June
the water level has been rising by up to a metre each week. The last time
Rodolfo and Alonso flew over the lake in a military helicopter, they estimated
that the water was only 4 metres from the lowest point of the crater wall, a
v-shaped cleft called the Maraunot notch.
The geologists predict that when the water reaches the notch it will spill
over the edge into the Maraunot river. Once the water starts to spill, they fear
the crater wall could give way.
Chris Newhall of the University of Washington in Seattle led a field trip to
Pinatubo in May. His group found that at least the top 10 metres of crater wall
is made of volcanic 鈥渂reccia鈥濃�攁ngular fragments of sand and rock deposited
by the last eruption. If water starts running over the top, Newhall says, the
breccia will crumble. 鈥淲hen the water reaches the top it could begin eroding
downward until it hits rock that is solid,鈥� he says.
Rodolfo and Alonso estimate that if the notch eroded down 10 metres, 30
million cubic metres of water would spill out. The water would probably mix with
loose volcanic sediment on the way, hugely increasing its volume and creating a
cement-like mixture knows as a 鈥渓ahar鈥�. Rodolfo has seen fast-flowing lahars in
action before. 鈥淚t is a horrendous sight鈥攈orrifying and exceedingly
产别补耻迟颈蹿耻濒.鈥�
After hearing about Newhall鈥檚 work, and realising that nothing was being
done, Lan Mercado, Oxfam鈥檚 representative in the Philippines, asked Rodolfo and
Alonso to identify the risks to local people. There are two hamlets built on the
riverbanks and at the bottom of the slopes is the town of Botolan, with 48,000
inhabitants.
At the rate the water is rising, the geologists estimate that the crater wall
could give way in less than a month, letting a lahar plough straight through
Botolan. 鈥淭he town would have less than 2 hours鈥� warning. There is no plan. We
want people to know about it and be prepared,鈥� says Alonso.
National authorities have been slow to respond to Oxfam鈥檚 warnings. Last
month, Rey Punongbayan, director of the Philippines Volcanology and Seismology
Agency commissioned a report into the lake by Masao Chida, an engineer from the
Japanese consultancy firm Nippon Koei. Chida visited the crater by helicopter
and concluded that there was little likelihood of a serious breach. 鈥淲e will
just watch what happens this rainy season,鈥� says Florente Soriquez of the
Department of Public Works and Highways.
Engineering solutions to the threat include reinforcing the notch, or boring
a tunnel into the crater to drain the lake. But the government says it is too
late for such action now the rainy season has started. Rodolfo and Alonso
believe this complacency could be disastrous and are now working with Oxfam to
reach local agencies and people directly.
They are urging people to find safe buildings, arrange shelter and supplies,
and monitor the rivers for rising water levels. Oxfam鈥檚 actions have alarmed the
government. Oxfam 鈥渟hould not announce their findings in public鈥�, says
Punongbayan. 鈥淚t may make people nervous.鈥� But Mercado counters: 鈥淚t鈥檚 raining
cats and dogs out here and the crater is filling up fast.鈥�
