ASH CLOUD: Particles likely to remain airborne for up to five days

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Preliminary analysis of ash samples taken from close to the Grimsvotn volcano indicates that the particles do not differ significantly from those collected from the Eyjafjallajokull volcano just over a year ago, and will likely remain airborne for up to five days.

Dr Susan Stipp, co-author of a recent report which concluded that the decision in April 2010 to close much of Europe's airspace following the eruption of Eyjafjallajokull was "well-grounded", said her colleagues in Iceland took samples of the Grimsvotn ash from "as close to the volcano as they could safely go" on the day of the eruption.

Although her colleagues lacked some of the necessary testing equipment, Stipp said their preliminary analysis showed that the particles were "very much the same" as the ash particles emitted by Eyjafjallajokull.

At 20km (12.4mi) high, the initial ash plume from Grimsvotn was double the height of the Eyjafjallajokull plume. "To get up that high [the particles] have to be small," said Stipp, adding that the finest particles "would stay suspended for four to five days" before either dispersing or falling to the ground.

Grimsvotn now appears to have stopped erupting, but if further eruptions do occur they are unlikely to be as explosive. The severity of the initial eruption was caused by meltwater from an ice layer over the volcano entering the crater and interacting with the magma, said Stipp.

The ice layer covering Grimsvotn was thinner than that which covered Eyjafjallajokull, which "suggests that any future eruptions, if there is no ice left, are unlikely to be as explosive, and the ash won't carry as high", she added.

The ash cloud initially disrupted flights across Scotland and northern England, but has since move south and is now disrupting flights over northern Germany.