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By TIM McDONALD Associated Press Writer
SALEM, Montserrat
(AP)--Scientists have learned a lot from the Soufriere Hills volcano
in the five years it has been erupting, destroying life and property--lessons
they hope will save lives in the future.
``This is
one of the best-studied eruptions ever,'' said Peter Dunkley,
acting director of the Montserrat Volcano Observatory, which monitors
the activity of the volcano on the southern half of this once-lush,
Caribbean island southeast of Puerto Rico.
One of the
most notable discoveries is a new type of pyroclastic flow, the
frightening and destructive phenomenon that is a high-density
mix of hot, dry rock fragments and superheated volcanic gases.
Pyroclastic
flows are the result of explosive eruptions of molten or solid
rock fragments, or both. They can also result, as at the Soufriere
Hills volcano, in what's technically called a ``stratovolcano''
during non-explosive eruptions of lava when parts of the volcano's
dome, or the sides of the entire dome itself, collapse down a
steep slope.
The rocks
and gases inside a pyroclastic flow can range from 392 to 1,292
degrees Fahrenheit, meaning they destroy everything in their path,
causing wood, vegetation and houses to burst into flame.
At night,
from a safe distance, glowing pyroclastic flows can be seen careening
down the slopes of the Soufriere Hills volcano like tumbling fire.
Pyroclastic flows generally consist of a base or ``basal'' flow
of dense fragments that move along the ground at speeds up to
200 mph--usually following natural declivities like rivers or
valleys--and a top layer of turbulent ash clouds that rise above
the basal flow, usually called surges.
Volcanologists
monitoring the Montserrat volcano, one of seven on the island,
were startled to discover a new type of flow, one that is potentially
more lethal, borne from such surges.
``What happened
on at least two occasions is that the surge condensed, (meaning)
the ash suddenly dropped out of the cloud, to form a new flow,''
said Gill Norton, director of the observatory. ``This flow would
be predominantly fine-grained so it behaves very much like a fluid
... It flowed like a river to a much greater distance than the
surge would have done.
``It does
stay close to the bottom of a river valley though, which is better
news, but it can go further than would be expected. So it is a
new hazard which extends the distance to which pyroclastic flows
can normally go, and therefore it increases the hazard at a greater
distance.''
Also, there
have been numerous scientific papers from both the observatory
and visiting volcanologists on the subject of dome growth and
its relation to volcanic activity. Scientists have learned dome
growth is sometimes cyclic, Norton said, related to periodic pressurization,
and that the rate of dome growth has a direct relation to the
``explosivity'' potential.
Higher rates
mean explosions are more likely. However, in studying periods
of repose, they've also found that an absence of dome growth doesn't
necessarily mean no activity, and that the cooling and ``degassing''
of magma in the dome can lead to very hazardous activity months
after dome growth has stopped.
``We have
to wait at least two years, and probably more, after dome growth
has ceased before we can be sure an eruption is over,'' Norton
said.
The Montserrat
volcano is only one of many being studied by scientists. The Smithsonian
Institution's Global Volcanism Program gives preliminary reports
of dangerous volcanoes, and a Web site called Volcano World tracks
92 of the world's active volcanoes, including the legendary Indonesian
volcano Krakatoa, which exploded in earthquakes last spring.
The goal,
of course, is to better understand volcanoes so scientists can
more accurately predict dangerous activity and avoid catastrophes
like the 1902 eruption of Martinique's Mount Pelee, another Caribbean
stratovolcano.
That volcano
awakened scientists to the existence of pyroclastic flows and
started a line of research that is still continuing. The eruption
killed 29,000 people, the most casualties from any volcano this
century.
The sole survivor
was a prisoner in an underground jail cell.
Montserrat's
volcano is valuable to volcanic research because it is both typical
and atypical. It is a typical stratovolcano in many respects,
but what is not typical is that it does not seem to be losing
energy, scientists say.
Most volcanoes
reach a peak relatively early in their activity cycles and then
gradually decline. The Montserrat volcano shows no signs of slowing
down and, indeed, the latest of the weekly updates the observatory
issues shows the continuation of a long trend _ elevated and dangerous
activity.
``Things are
the same as ever--we're just expecting something to happen soon,''
Dunkley said.
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