April 26, 2011

Airport Closures Justified During Iceland Eruption

A new study finds that the closing of some European airports last year during and after volcanic eruptions in Iceland was the proper thing to do, and may have saved lives.

The eruption of ash from Eyjafjallajokull resulted in the largest closure of European airspace since World War II, with losses estimated at around $2 billion.

Concerns about aircraft safety during the eruptions were well founded, as ash particles from the initial phase of the eruptions were particularly abrasive, posing a possible threat to aircraft flying through the cloud, said the researchers from the University of Copenhagen in Denmark and the University of Iceland in Reykjavik.

Furthermore, these particles were so tiny they could have rapidly melted inside jet engines, potentially causing them to fail during flight.

"I think the really important parts of it are: Number one, the aviation authorities were absolutely right in closing airspace," said senior author Susan Stipp from Copenhagen University during an interview with BBC News.

"Number two, we have presented a protocol so that, if answers are needed quickly in future, they can be had," she said, adding that roughly 10 million passengers were affected by the closures.

"Then the data that are produced can be put into models to determine how far, how high and how wide the ash will spread that will be based more on fact than on guesswork."

The researchers analyzed the size and structure of the ash particles using a number of methods, such as atomic force microscopy, scanning electron microscopy and X-ray diffraction. They compared ash from the initial, explosive phase of the eruption with that from a later, more typical eruption of the volcano.  The ash ejected in the early phase was light and powdery, while the more typical ash emitted in the later stages was more granular, the scientists said.

"The ash that was ejected in the first few days was so fine-grained because it was produced by an explosive eruption," Dr. Stipp said.

"The meltwater from the glacier on top of the volcano ran down into the crater, chilling the magma and then the pressure from underneath caused an explosion. So the particles of ash were very fine-grained and very sharp compared to normal ash."

"The smaller the particles, the slower they come back down again. Normal ash is usually settled as it moves away from the volcano. But because the particles were so small, they traveled a longer distance from the volcano and remained in the area where the airplanes fly for a much longer time."

Modern aircraft engines operate at temperatures of around 3,600 Fahrenheit (2,000 Celcius).  Dr. Stipp says the glassy particles in the ash cloud begin to soften at about 1500 F (800C).

"By 1,000C, they are melted. And because they are so small, they melt faster. It's like when you have a drink with one big ice cube. The ice cube will stay around, but when you crush it, it melts quickly," she said.

The sharp, abrasive qualities of the particles indicate they could have "sandblasted" the bodies and windows of the planes.

"There's no way they could have allowed those aircraft to keep flying when it first happened. That was absolutely the right, safe decision, because no one knew any better," aircraft safety expert Stewart John told BBC News.

However, "the amount of time it took to get going again is debatable," he added.

The report cited a 1982 incident in which a British Airways 747 flew into an ash cloud over Indonesia.  All four engines failed, and the pilot reported that the aircraft's windows were sandblasted.  The pilot was able to restart some of the engines and managed to make an emergency landing with limited visibility through a 2-inch clear area in a side window.

The study was published in the Proceedings of the National of Academy of Sciences.


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