We have heard a lot about the unpredictability of the ash cloud, but what are the experts’ best guesses as to when it will clear?

Two factors determine the disruption that an eruption will cause to airspace: the composition and height of the dust plume emerging from the volcano, and the regional winds and atmospheric circulation.

Volcanic activity is far harder to predict a few days ahead than the weather. The UK Met Office and World Meteorological Organisation are confident there will be a change at the end of this week in pressure over the North Atlantic. Instead of the current north-westerly drift, which has carried ash from Iceland to Europe, there will be southerly and south-westerly winds next week, which are expected to blow whatever emerges from Eyjafjallajökull volcano towards the Arctic.
Assuming forecasts are right and unrestricted flights resume next week, how likely is it that restrictions will have to be imposed again?

If Eyjafjallajökull continues to spew ash high into the sky, even intermittently, Europe is bound to be affected again. The weather conditions that prevailed over the past week are not unusual and will recur sooner or later.

The big question is what happens to the volcano. And vulcanologists’ answers today are as uncertain as they were when the crisis started.

As the ice around the volcanic vents on Eyjafjallajökull diminishes in the heat, there is less potential for explosive ash-generating interaction between magma (molten rock), ice and meltwater.

But as Professor Bill McGuire of University College London says, “we just don’t know. I would not be surprised, however, to see the eruption last for several months, sending ash clouds our way whenever the wind is in the right direction.”

Iceland is known as one of the most volcanically active places on Earth. Why have its eruptions not affected European aviation before?

Through good luck. “We have been extremely fortunate in the UK and western Europe to have avoided this disruption for so long,” says Dave McGarvie, vulcanologist at the UK Open University. “It was inevitable that this would happen, as Iceland has an eruption every five years or so.”

So there could be worse to come in the future?

There will be worse to come. The current eruption is modest by global or even Icelandic standards.

Iceland’s most active and dangerous volcanoes have been Hekla and Katla. Vulcanologists say Hekla has been “full” and potentially ready to blow for months now. Eruptions of Katla have in the past followed activity at Eyjafjallajökull 27km away, after intervals of months or a few years.

The most damaging eruption since European settlement was that of Laki in 1783, which is estimated to have killed a quarter of the population – and caused a toxic haze across western Europe for months on end.

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