Simulating the big blow

Simulating the big blow SCIENTISTS are trying to simulate the generation of hot poisonous gases from the mouth of a volcano in order to minimise the vast destruction they cause. And some scientists posit that volcanic gases, particularly sulphur dioxide, can also help predict eruptions.

The most ambitious and sophisticated model so far is located at the Gruppo Nazionale per la Volcanologia in Pisa, Italy. The model, based on data from Vesuvius -- which persistently blows its stack -- simulates the generation of a gas cloud and how it rolls down the sides of the volcano (Nature, Vol 367, No 6463).

Forewarned, in this case, is saved. This model can predict the intensity of the blast in the first minute of the eruption, providing planners with invaluable information. This knowledge can be used to design low-cost, aerodynamic shelters that can withstand the ferocity of the hot, lethal gases.

While the Italian scientists are investigating what happens in the wake of a volcanic eruption, others are trying to foresee the complex sequence of events. Groups headed by geologist T P Fischer of the Arizona State University, USA, have related sulphur dioxide emissions from Galeras volcano in Colombia with siesmicity.

Galeras erupted massively in January 1993, killing several scientists. But Fischer and his colleagues concentrated on the subsequent larger eruption in March. The observations suggest that a decrease in sulphur dioxide emissions leads to a greater likelihood of a volcanic eruption. Decreasing pre-eruption emissions imply a build-up of pressure within the volcano, as fractures through which gases escape gradually clench and close, plugged with clay and other mineral deposits. This increase in pressure leads to increased seismic activity.

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