Eruptions could continue for months

THE eruption beneath the Eyjafjallajoekull glacier in south-western Iceland began on 20 March, when it forced about 500 people in the sparsely populated area to leave their homes.

This was the first time the volcano had erupted since 1823, but experts have warned activity could go on for months.

Although the eruption is small in relative terms, the location, close to a very busy airspace, and the fact it is beneath an icecap, have produced a great deal of ash. The glacial ice causes the molten rock to cool very quickly, pulverising into tiny glass-like fragments.

The fine volcanic ash is then lifted into the sky by enormous steam plumes, created by vast quantities of melted ice. The high temperatures mean the gas expands and rises, as it is less dense than the surrounding air. When it reaches neutral buoyancy, it is blown by the wind, with the fine ash remaining airborne.

Dr Matthew Roberts, a British glaciologist, said: "It's the interaction of the molten rock, the magma and the glacial ice which is causing the magma to cool very quickly and to be pulverised into tiny fragments of rock. And these updrafts of fine volcanic ash are being lifted into the sky by the enormous steam plumes that have been created by the vast quantities of ice that's been melted."

The ash has been moving at a height of about 30,000ft, and it is impossible to predict when the eruptions might cease.

"There is really no way to know that," said Dr Pall Einarsson, a geophysicist of the Institute of Earth Sciences at the University of Iceland.

"We have quite good measurements to know what's going on. We can see where the stresses are changing due to earthquakes, and so on. But how it will develop is a very difficult thing to say.

"The activity is quite variable; it goes up and down a bit," he added. "But on the whole the vigour of the eruption seems very little changed."

Einarsson said, for now, the question was unanswerable.