Last April, a volcanic eruption in Iceland sent a cloud of ash billowing towards Europe. That ash was potentially hazardous for aircraft, and authorities decided to ground all flights — inconveniencing tens of thousands of travelers — rather than risk an accident. A new study suggests that this was the right decision.

Susan Stipp, a professor of nanotechnology at the University of Copenhagen, was one of the people whose plans were frustrated by the volcanic cloud. She had colleagues who needed to get home to Denmark, and samples were delayed en route from Scotland.

Stipp wondered if officials had acted wisely in closing the airspace over Europe, and because she studies tiny particles like the ones in volcanic ash, she was in a position to find out.

“I called my friend and colleague Siggi Gislason in Iceland, and we agreed to get some ash and see if we could do something,” Stipp said.

Gislason and some of his colleagues from the University of Iceland drove from Reykjavik to the foot of the volcano and collected some ash. When planes started flying again, they sent the samples to Stipp in Denmark, where Stipp analyzed them.

One thing became clear at once — closing the airspace was the right decision.

Stipp said there were several reasons the ash particles from the Iceland volcano were so dangerous. First, they were particularly fine grained.

“Those fine particles are extremely sharp compared to typical ash, which is usually somewhat more rounded,” Stipp said.

They were also extremely hard, making them abrasive to airplane wings, bodies and windows. That abrasion can make it impossible to see out the cockpit window.

Finally, due to their small size, the particles were able to rise high in the atmosphere and spread great distances, where they posed a particular threat to jet engines.

“If they’re tiny particles they can melt quickly,” Stipp said. “Then they condense on the cooler parts of the engine, and cause them to fail.”

Obviously, this research, which appears in the current issue of the journal PNAS, comes long after decisions about air travel had been made. But Stipp says this kind of analysis could help authorities make informed decisions the next time a plume of ash intersects a busy airline travel corridor. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.