Concerns about aircraft safety during the eruption of an Icelandic volcano in 2010 were well founded, according to a new scientific study.

Ash particles from the early phase of the eruption were small and abundant, posing a potential threat to aircraft flying through the cloud.

Such particles could have melted inside jet engines, potentially causing them to fail mid-flight. The work by an Icelandic-Danish team is published in PNAS journal.

The analysis also reveals that ash particles from early in the eruption were particularly sharp and abrasive. The outpour of ash from Eyjafjallajokull caused the largest closure of European airspace since World War II, with losses estimated at between 1.5bn and 2.5bn euros. Some 10 million travellers were affected by the shutdown. [ bbc ]

The latest research was carried out by researchers at the University of Copenhagen in Denmark and the University of Iceland in Reykjavik.

Senior author Susan Stipp, from Copenhagen University, told BBC News: "I think the really important parts of it are: Number one, the aviation authorities were absolutely right in closing airspace.

"Number two, we have presented a protocol so that, if answers are needed quickly in future, they can be had.

"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 analysed the sizes and structures of ash particles using a variety of techniques, such as atomic force microscopy, scanning electron microscopy and X-ray diffraction.

Ash samples from the early phase of the eruption (L) contained large quantities of fine dust compared with ash from later in the eruption (R)

They compared ash that was ejected in the early, explosive phase of the eruption with ash from a later, more typical eruption of the volcano.

The ash ejected in the early phase was light and powdery. The more typical ash thrown out in the later stages was more granular, with the consistency of dry sand.

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

"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 travelled 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 2,000C. Dr Stipp says the glassy particles in the ash cloud start to soften at about 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 explained.