Ash from an erupting Icelandic volcano could force the authorities to shut airports and close airspace in Ireland and Britain, in a move which could disrupt many thousands of passengers almost exactly a year since a different Icelandic volcano closed airspace across Europe.
The latest warning is based on five-day weather forecasts but experts said the wind patterns were changeable and could yet sweep the cloud away.
Aviation authorities have said no disruption was expected to European or transatlantic airspace over the next 24 hours.
However, if the eruption continues at the same rate and winds do not change, ash could reach northern Scotland by tomorrow and spread to England, Ireland, France and even Spain by Thursday or Friday, forecasters said.
Grimsvoetn, Iceland’s most active volcano at the heart of its biggest glacier, began erupting late on Saturday, sending a plume of smoke and ash 12miles high.
Irish Weather Online forecaster Peter O’Donnell said today: “Recent eruptions in Iceland may provide a colourful sunset as early as Tuesday due to the strong circulation around storm “Udo” which will bring the first signs of what may turn out to be a more disruptive amount of ash later in the week. Although upper-level winds reverse in direction briefly around Wednesday, which might cut off the supply for a day or two after the initial trace amounts, thereafter it is possible that more significant amounts will arrive as winds return to a more favourable W-NW direction.
By yesterday, the ash had reached the capital Reykjavik, nearly 250m to the west, and all the country’s airspace was closing down.
In April last year, 34 countries shut their airspace after the Eyjafjallajökull volcano erupted due to fears that fine ash particles could cause jet engines to stop.
It was the largest such closure since the Second World War and millions of passengers were affected.
The International Air Transport Association (IATA) estimated that the global airline industry lost £130million a day during the disruption.
Experts and aviation authorities said the impact of the Grimsvoetn eruption should not be as severe and was likely to mainly affect Iceland.
Gunnar Gudmundsson, of Iceland's Meteorological Office, said: “I don’t expect this will have the same effect as Eyjafjoell volcano because the ash is not as fine.”
However, they acknowledged that changing weather patterns could sweep the ash into areas where it would affect other countries.
Einar Kjartansson, a geophysicist at Iceland’s Met Office, warned: “If the eruption lasts for a long time we could be seeing similar effects as seen with Eyjafjallajökull last year.”
He added that “most of the traffic at least to the south of Iceland will probably not be affected” but said: “We don't know what will happen after that.”
The forecast is for winds to clear the ash from Reykjavik and dissipate the problem over the coming days.
Bjorgvin Hardarsson, a farmer in the village of Kirkjubaejarklaustur, close to the latest eruption, described the ash, saying: “It's just black outside, and you can hardly tell it is supposed to be bright daylight.”
A spokesman for Eurocontrol, the European air safety organisation, said: "If volcanic emissions continue with the same intensity, the cloud may reach west French airspace and north Spain on Thursday."
Grimsvoetn, which has erupted nine times between 1922 and 2004, is located in a giant caldera - a collapsed volcanic crater – five miles in diameter near the centre of the Vatnajoekull icefield.
When it last erupted in November 2004, volcanic ash fell as far away as mainland Europe and caused minor disruptions in flights to and from Iceland.
A spokesman for the Civil Aviation Authority said: “It’s early days and we’re keeping an eye on the situation but at the moment the weather patterns are looking pretty favourable.
“It’s the kind of situation that can change very quickly but we’d be very unlucky to be affected again as the winds normally would take this kind of problem away from us.
“The only problem passengers are likely to have is if you’re going to Iceland.”