Ash billows from the Eyjafjoell volcano on May 8, 2010 in Hvolsvoellur, Iceland. 
Ash billows from the Eyjafjoell volcano on May 8, 2010 in Hvolsvoellur, Iceland.  - 
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One of Iceland’s many volcanoes has “stirred."

After more than a century of quiescence, Bardarbunga – in the interior of country – has shown some ominous signs of seismic unrest. Some 300 mini earthquakes have been recorded in the vicinity, and molten lava has reached the summit and is now melting the ice cap. The Icelandic authorities have evacuated the area and warned that if there is an eruption, it could be big enough to disrupt air travel over Europe.

The warning has raised some painful memories. The Eyjafjallajokull eruption in April 2010 caused the largest and longest closure of European airspace since World War II; grounding thousands of flights, stranding millions of passengers and costing the airlines more than $2 billion dollars.

But there are good reasons for believing that history isn’t about to repeat itself.

For one thing, there’s been a change in the civil aviation flight rules. In 2010, if there was any ash in the sky, you were forbidden to fly.

But today that’s considered far too restrictive. The rule has been relaxed because weather forecasters with advanced radar are now much better at tracking ash clouds and steering planes away from them. And it is understood that planes can fly safely through lower densities of ash.

“The restrictive flight rules have gone,” says Dave McGarvie, a volcanologist at the Open University in Edinburgh. “With the knowledge and experience we gained from 2010, we now have a much better idea of how to deal with airborne ash. If Bandarbunga does erupt, it will not cause anything like the scale of disruption as Eyjafjallajokull. Absolutely nothing like it.”

That does not mean volcanoes no longer pose a threat to aviation.

“Because a jet sucks in huge amounts of air, if that air contains a lot of ash it will – over a period – accumulate and damage the engine,” explains Colin Brown of the Institution of Mechanical Engineers in London. “If all the engines are affected in that way, the aircraft is going to come down."

Under the current rules, aircraft must not fly if there is more than 4 milligrams of ash in a cubic meter of air in its flight path; the equivalent of a teaspoonful of material in an Olympic size swimming pool. Not as trifling an amount of ash as it seems, says Colin Brown.

“Aircraft engines suck in an Olympic size swimming pool of air every second, so if you’re in that kind of ash cloud, you could end up with about a kilogram coming into the engine once every four minutes. Fly for four or eight minutes and you suddenly have one or two kilos of rock inside your engine. That’s not something any of us would want to contemplate," he says.

Nevertheless, to reassure nervous flyers, it’s worth pointing out that volcanic ash has never, in the entire history of aviation, actually caused a fatal aircraft crash.


CORRECTION: An earlier version of this story misspelled Bardarbunga. The text has been corrected.