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© ReutersLava and ash explode out of the caldera of Iceland's Eyjafjallajokull volcano
The ash first emitted by Icelandic volcano Eyjafjallajökull when it erupted one year ago has been assessed as dangerous to airplanes and the resulting airport closures as justified, a study by earth scientist Sigurdur R. Gíslason of the University of Iceland says.

He studied the eruption with Susan Stipp from the University of Copenhagen and their findings indicate that any future eruption should be treated the same way until any ash clouds can be proven safe for aircraft.

"We demonstrated the ash had very fine particles and was carried long distances by air currents," Gíslason said.

"If (the ash from the earliest days of the eruption) had hit airplanes it would have sandblasted them so that windows could have become non-see-through."

Also, "The chemical composition - and the crystal the ash was made of - would have melted in the engines of airplanes and then solidified in the engines' colder parts, so it could have shut down the engines".

The study's conclusions have been published in the journal of the American National Academy of Sciences, (PNAS).