Marie Curie; The Unesco courier: a window ... - unesdoc - Unesco

MENACE OF 'EXTINCT' VOLCANOES (Continued)
Eruption forecasting could be easier
than predicting the weather
tively comprehensible language while
others remain, for the present at least,
indecipherable.
Since we are still at the stage of
conjecture regarding the causes and
consequently the mechanism of
eruptions, these variation which mod;
em techniques make it possible to
measure cannot really be understood
nor, therefore, can their meaning be
interpreted with certainty.
But there is a gradual improvement,
and successful forecasts of impending
activity have several times been made,
the best example being the eruption of
Kilauea in December 1959-January
1960: seismographs had given notice
of the awakening of the volcano nearly
six months before it erupted.
Thanks to their excellent observa¬
tion network on Hawaii and on Kilauea
itself, scientists of the volcanological
observatory were able to determine
the focal depth of the tremors: about
50 kilometres, which is suprising
enough for volcanic seismic effects, the
hypocentre of which is usually localiz¬
ed less than 5 kilometres below the
surface, and still more surprising in
Hawaii where the lower limit of the
earth's crust itself is only 15 kilo¬
metres below sea level.
In the following weeks, the volcano¬
logists noted that the focal depth was
getting less and less and by measur¬
ing the speed of the rise they pro¬
duced an estimate of the time it would
take for this depth to be
reduced to
zero, i.e., when the magma would erupt
at the surface.
As the measurements continued the
coefficient of error due to extrapolation
was reduced.
A network of field seis¬
mographs was brought into service in
addition to the fixed network, allowing
high-precision determination of the
THE CIRCLE
OF FIRE
AROUND THE
NOT SO
PACIFIC
OCEAN
No less than 62 per
cent of the world's
active volcanoes are
located in what is often
called
"the circle of
fire" in the Pacific.
Left, the majestic cone
of Mt. Shishaldin in
Alaska, one of the
79 volcanoes in a chain
co
running through the
Aleutian Islands into
the Alaskan peninsular.
Above, grandiose
firework displays from
active craters in the
Kamchatka
chain
(28 volcanoes).