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【Vocanic Ash Cloud】+08
Page last updated at 15:22 GMT, Monday, 19 April 2010 16:22 UK
【BBC News】
Volcano cloud as it happens: 19 April
A massive cloud of volcanic dust has covered vast areas of northern Europe after the Eyjafjallajoekull volcano erupted in Iceland on 14 April. See below for details on the extent of the dust cloud and for projections of its future spread.
How the cloud has spread？
Expected path of cloud
The cloud appears on the satellite images (left) as black, pink and then red as sporadic eruptions launch ash into the atmosphere where it mixes with different thicknesses of ice clouds.
Nasa's satellite imagery shows the cloud's huge length
By Victoria Gill
Science reporter, BBC News
Aviation authorities have now extended restrictions on UK airspace until 0100 BST on Tuesday.
According to the UK's Met Office, the eruption of the Eyjafjallajoekull volcano in Iceland is "weakening", but weather patterns, for the time being, continue to blow volcanic ash towards the UK.
"We will continue to offer advice to Nats (the UK's air traffic control authority) about the spread of any residual ash," the Met Office said on its website.
"Assuming the volcanic activity continues to weaken, we can expect ash clearance across the UK and we will be looking for the earliest opportunity that this might happen."
And according to current European regulations, no matter how low the concentration, aviation authorities will not reinstate normal control over airspace as long as the ash cloud remains.
A spokesperson from from Nats told BBC News that there was "no threshold" for concentrations at which volcanic ash was acceptable.
The dust is simply too dangerous for jet engines to risk commercial flights encountering it, said Nats. If volcanic ash particles are ingested into a jet engine, they accumulate and clog the engine with molten glass, which can cause the engine to shut down.
Because of this, the International Civil Aviation Organization (ICAO) has recommended implementing a no-fly zone if volcanic ash is detectable in airspace. (ICAO operates the International Airways Volcano Watch system).
Whether to open or close airspace is a decision for national aviation authorities, but all European nations abide by these safety recommendations.
Aviation consultant, Chris Yates explained: "The ICAO regulation that has prompted this widespread grounding is from experience gained from over 80 incidents between 1980 and 2000 [as well as] computer modelling and best 'guestimate'."
But the current paralysis of UK and European air traffic is unprecedented, so the regulations may have to be changed in order to get things moving.
"The airline industry...are clearly making the argument that we are being over cautious in grounding all flights," said Mr Yates.
"Whilst it remains possible to find clear air up above us this doesn't necessarily mean that there are no pockets of high concentrations of ash at the various flight levels. I would suggest it's better to err on the side of caution."
But the European Commission has now intervened to organise a meeting on Friday between technical and safety experts to find out if there are other options, such as setting up a fly zone that would allow carriers to navigate around the plume.
But policy-makers have stressed that any decision must be based on a scientific assessment of where and when it is safe to fly.
Measuring the cloud
From the UK, the Met office is using satellite imaging and lidar (a type of radar) measurements from the ground, as well as consulting satellite images, to measure the cloud and forecast its movement.
Scientists are now "cautiously optimistic" that the volcanic ash could finally be on the wane.
According to webcam images captured early on Friday morning there has been a change in the character of the eruption at Eyjafjallajoekull.
Dr David Rothery, a volcano researcher from the UK's Open University explained that ash was still being produced, but was "dispersing downwind at the altitude of the summit (about 1600 m)".
"There was no high ash column rising above the vent. If this situation persists, then the high altitude ash cloud will be starved of fresh ash, and will eventually disperse," he said.
He said that this was probably because meltwater from the ice-cap was no longer able to leak into the volcano. This meltwater generated steam that has been the main driving force for the explosive nature of the eruption, which initially caused the plume of ash to be ejected up to 11km into the atmosphere.
"There is no guarantee that the situation will not revert to what was happening Thursday-Sunday, but there are grounds for cautious optimism."
But Dr Dave McGarvie, a volcanologist at the Open University pointed out that a decrease in the volcano's activity now might not mean the end of the eruption all together.
"During the 1821-23 eruption there were periods [of weeks to months] when the eruption died down and then started again," he said.
He added that the UK had in fact been "very fortunate" to avoid this situation for so long and that future eruptions in Iceland, which has 22 volcanoes that are considered active, could also have an impact on the UK.
"It was inevitable that this would happen, as Iceland has an eruption every 5 years or so," he said.
"It just so happens that those that have erupted in the past 60 years have not affected us to this extent. But there are plenty of volcanoes that can erupt in a similar (or larger) fashion to Eyjafjallajokull."
For the time being, aviation authorities await a guarantee that skies are clear of ash or for news that a more immediate solution has been arrived at.
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