Page last updated at 15:32 GMT, Friday, 16 April 2010 16:32 UK

Iceland volcano's uncertain timescale

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Aerial video of ash cloud and advice from Volcanologist Dr Hazel Rymer

By Victoria Gill
Science reporter, BBC News

The picture of whether Iceland's volcanic eruption is intensifying or abating remains murky, particularly since the webcam images on Friday were shrouded in cloud.

Scientists are struggling to work out if the eruption itself could continue for days, weeks or even months.

But, as Professor Jon Davidson - an earth scientist from the University of Durham - told BBC News, it was not the eruption per se that caused the problem.

"It's the fact that the prevailing winds are driving the ash plume over the UK," he explained.

And scientists in Iceland reported on Friday morning that the volcano was continuing to generate a tall plume of ash - contributing to the cloud already drifting high in the atmosphere over the UK.

So the cloud that has grounded UK flights appears to be continuing to grow. And the researchers say that could go on for several days.

Dr David Rothery, a volcanologist from the UK's Open University agrees this could happen, but suggests that it is unlikely.

Intense and explosive

"It is usual that an explosive eruption like this has its most intensive point at the start and that it gradually subsides," he told BBC News.

What scientists are trying to find out, he explained, is if the [ongoing] eruption is explosive enough to create a tall column of ash and continue feeding the plume.

It is the explosion that initially forces the ash upward - expanding gas at the eruption site generates thrust. From there, the cloud of dust and gas rises because it is warmer than the surrounding air.

So if the eruption continues to be intense and explosive, giving the ash that initial upward thrust, the plume that has been blown in UK and European airspace could continue to grow.

But according to the most recent reports from the UK Met Office and the Icelandic Met Service, ash is now being released in pulses rather than a continuous plume.

Unpredictable eruption

Professor Davidson said that there was no way to reliably predict how the Eyjafjallajokull volcano will behave.

"This eruption started on 20 March," he said. "So in a sense it's been erupting already for almost a month.

"We will be watching the seismic activity because [from that] we will be able to see the predictions in changes in the behaviour of the volcano that will herald an increase or decrease in its activity."

And currently, there appears to be far less seismic activity in Iceland than in the days running up to Wednesday's eruption. This could mean that the worst is over.

But researchers in Iceland, who have analysed the first sample of ash produced by the volcano, have found that its composition could contribute to the explosiveness of future eruptions.

"The magma is much richer in silicon than the basalt that was previously erupting in the initial stages," explained Dr Mike Burton, senior volcanologist at the Italian National Institute for Geophysics and Volcanology.

We are formulating some forecasts about how long this may last, but that will be very dependent on the eruption from the volcano, so we're working closely with scientists in Iceland
Jim Haywood
Met Office

"This has two important implications. Firstly, the ash produced will be finer, with smaller particles compared with basalt."

Finer ash will rise more easily.

Secondly, he said, "the activity may well be more explosive because of the higher viscosity of the magma."

The more viscous the magma, the less easily gas flows through it. "Therefore it's easier for pressure build up to occur, leading to more violent explosions."

Through Thursday and Friday, the volcano has continued to feed an existing large plume of ash that is moving very slowly eastward at a height of about 30,000ft.

Aviation authorities cannot risk reinstating flights when this plume is within airspace, as the ash could clog jet engines and cause them to fail.

Jim Haywood, a researcher from the Met Office confirmed on Friday that he and his colleagues had detected the plume above the UK.

"It's patchy but it's certainly there, although you won't see it with the naked eye," he said.

"We are formulating some forecasts about how long this may last, but that will be very dependent on the eruption from the volcano, so we're working closely with scientists in Iceland to get the most up to date information about the eruption height and intensity."



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