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, which closed its international airspace. 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 is much stronger than at a volcano further south last year which closed European airspace for six days.
Airlines were told on Sunday during a conference call with weather experts and officials responsible for European airspace to brace for a possible further spread of ash later in the week.
"There is the potential for some ash to be effective in northern Scotland and the northern North Sea by midday on the 24th," a UK weather official tracking the cloud told airlines.
"After that, as long as the volcano continues to erupt at the same intensity, there are concerns that ash could become effective further into the UK and western France and northern Spain by the 26th or 27th (Thursday and Friday)," he added.
Others said the impact on air travel this time was set to be more limited as winds were more favourable, the content of the plume was heavier and less likely to spread and authorities now had a higher tolerance for ash levels, they said.
"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.
Iceland's meteorological office said the plume had fallen to 10 to 15 km in height from a maximum of 25 km (16 miles).
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, has 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 for several hours the sun was blocked out.
"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 metre."
(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 Alison Williams)