REYKJAVIK Ash from a massive plume of smoke from an eruption of Iceland's most active volcano could spread south to parts of Europe next week, but experts on Sunday still hoped the impact on air travel would be limited.
The eruption at Grimsvotn has so far hit only Iceland, where the civil aviation authority said the prospects for re-opening the main international airport on Monday were not good.
A thick cloud of ash blocked out the daylight at towns and villages at the foot of the glacier where the volcano lies and covered cars and buildings.
The eruption was much stronger than the one at a volcano further south last year which closed European airspace and halted transatlantic flights, due to worries particles could get into engines and cause accidents.
Iceland's meteorological office said the plume from Grimsvotn, which last exploded in 2004, had fallen to 10 to 15 km in height from a peak of 25 km (16 miles).
Europe's air traffic control organization warned on its website of a possible spread.
"Ash cloud is expected to reach North Scotland on Tuesday 24th May. If volcanic emissions continue with same intensity, cloud might reach west French airspace and north Spain on Thursday 26th May," it said in a traffic bulletin.
Others said the impact on air travel this time would be more limited as winds were more favorable, the content of the plume was heavier therefore less likely to spread and authorities now had a higher tolerance for ash levels.
"It could lead to some disruption, but only for a very limited time and only over a very limited area," said University of Iceland Professor of Geophysics Magnus Tumi Gudmundsson.
"We see some signs that the power is declining a bit, but it is still quite powerful," Gudmundsson said, adding that the eruption was the most violent at the volcano since 1873.
Icelandair, the main airline on the island, stopped flights on Sunday and said on its website the halt could continue on Monday. It said 6,000 passengers had been affected by cancellations so far.
BLACK AS NIGHT
Gudmundsson said the wind direction was different this year, meaning the ash was falling mainly around Iceland. "But also very importantly the rules that apply today and the models are very different. The tolerance is much higher," he said.
Dave Mcgarvie, volcanologist at Britain's Open University, agreed. He said any ash which reached Britain would be less than last year and added that experience gained since the 2010 eruption would lead to less disruption.
In emailed comments, he said "minor re-routing" should enable aircraft to avoid zones where ash is concentrated.
The new eruption at Grimsvotn, which last exploded in 2004, sent up a huge bubbling mass of ash and smoke, which seeped above the clouds high over the North Atlantic island.
Grimsvotn lies under the Vatnajokull glacier in southeast Iceland, the largest glacier in Europe.
Areas to the south of glacier have been covered in thick layers of ash and the sun was blocked out for several hours.
"It was like night is during the winter," said Benedikt Larusson, speaking in the town of Kirkjubaejarklaustur.
"Now it is a little bit better. Now I can see about 100 metres, but before it was about 1 meter."
(Writing by Patrick Lannin in Stockholm; Additional reporting by Tim Hepher in Paris, Kate Kelland in London, Christopher Le Coq in Brussels, Ingolfur Juliusson in Iceland; Editing by Andrew Heavens)