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Science & Technology

Waiting for the mud

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Jul 15, 1996 | From the print edition
Mexican vulcanologists are trying to track the path that destructive mudslides, the fallout of an impending volcanic eruption, might take

-- (Credit: Shri Krishan)WHEN Mt Vesuvius erupted in Italy, the
town of Pompeii vanished. All that was
left behind were crusts of dried lava. For
long, scientists have held that it is the
run-off streams of lava from volcanic
eruptions that kills thousands of people,
sweeping away entire civilisations. But
recent reports have put forth an entirely
new explanation.

Scientists have come to the conclusion that it is the mudslides from the
volcanic eruption, which follow days,
sometimes even months later - and
not the molten lava and gases - that are
responsible for such scales of destruction. Scientists are now faced with the
task of predicting the path of these
mudslides.

Volcanic eruptions, like that of Mt
St Helena (1980), can have the energy of
several hundred atomic bombs, propelling many cubic kilometres of debris
into the upper atmosphere. Then, with
the first rains, millioiis of tonnes of
loose ash are washed into the waters of
rivers. Mudslides from the eruption of
Columbia's Nevada del Ruiz in 1985
killed 25,000 people overnight.

The giant sleeping volcano, Popocateped (popularly referred to as Popo)
in Mexico is now under study. Till one
year ago, Popo was taken for granted,
but the crater is now sending off ominous smoke signals. The lives of millions living in the towns and cities nearby will be in danger once the eruption
takes place. Scientists are thus working
overtime to know the path the mudslides might take. They have little time...
it could be only months away.

Mexican vulcanologists are using
new, powerful computer simulations
that have been devised to predict exactly
which way the mudflows will head, so
that the authorities are able to evacuate
only those towns which will be in immediate danger. Evacuating all the millions
who live around the volcano will lead to
mass panic.

The studies by Jos-Luis Macias and
his team were done by starting a simulated mudflow at any height of the volcano and then running it and following
it through, keeping a track on how far it
could travel. He concluded that not only
the small towns around Popo will be
hit, but the mudflows might reach as far
as the cities of Puebla and Cholula -
over 40 km away. Two million lives
will be at stake.

New discoveries about the history of
Popo's activity back up Macias' model
with alarming accuracy. Excavations in
Cholula, a city doomed in Macias'
simulation, hold the key. Or rather, it is
the great pyramid of Cholula, the largest
in the world, now half-buried and
topped with a Spanish church, which
does. Excavations have been going on
here to discover the secrets of the
volcano's violent past, and also what
happened to those who built the
pyramid. It was in this region that the
Olemic people, one of the most
advanced civilisations
in the world at the
time, had built their
empire in 300 BC.
For 900 years,
Cholula prospered
and became increasingly important. Then
it vanished.

Recent research
by Macias and his
team is providing a
vital clue which came
from searching the
huge mudflows that
foll6wed Popo's last great eruption.
Embedded in its deposits they found
objects they could use to date the
evept. They found pieces of pottery
imbedded in the matrix of these
deposits. They also found a piece of
charcoal and dated it. And from this
they know that a series of mudslides
descended on the city about 1,200 years
ago. They believe that that is how the
Cholula civilisation was destroyed in
the 8th century.

Despite such convincing results,
a lot depends on how seriously the
politicians take scientific predictions,
particularly if the next great eruption is
only months away. The decision taken
by the authorities will be gigantic, and
they need a lot of convincing. If Macias'
model is right, Cholula will be destroyed
again, along with the nearby city of
Puebla and a number of other neighbouring towns. The vulcanologists want
these places evacuated immediately
after an eruption and now they believe
have enough evidence to convince
the authorities.

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