A SPECTACULAR volcanic eruption beneath Iceland’s biggest glacier has spewed a column of ash and gas more than seven miles into the air, forcing airlines to divert flights to avoid the blast.

At least ten transatlantic flights have been rerouted south of Iceland to skirt the plume rising from the Gríms- vötn volcano in the east of the island, which began to erupt on Monday and continues to spout noxious fumes and debris.

The cloud of ash has already started to land in Norway, Sweden and Finland, though without causing any damage or health risks.

Meteorologists said it was fortunate that prevailing winds were carrying the column towards Scandinavia rather than south of Iceland, where it would have disrupted the trunk route for flights between Europe and North America.

A change in the wind taking the ash south or west could disrupt up to 50 flights a day, though this is not forecast. Dozens of domestic flights to the north and east of Iceland have been grounded by the ash, which can stop aircraft engines if they attempt to fly through it. The Dutch airline KLM, which operates across the Arctic, has cancelled 59 flights, though fog at Amsterdam’s Schipol airport was also a factor.

The National Air Traffic Control Services said that no flights to or from Britain had been affected. Flight plans are set 12 hours before departure and a spokesman said it had been a simple matter to route them away from the area.

The Grímsvötn volcano, which is buried under 650ft of ice beneath the Vatnajökull ice cap, last erupted in 1998, and although that event caused little damage, eruptions in 1995 and 1993 led to serious flooding. The surrounding region is largely uninhabited, however, and no evacuations have been ordered.

The volcano is a caldera — a large, shallow crater above a “hot spot” of magma (molten rock). The world’s most celebrated caldera is in Yellowstone National Park in the United States, though Grímsvötn is much smaller at five miles wide by 3.7 miles long. The caldera crater is a lake filled with water melted from the glacier by the heat of the magma beneath.

The dramatic blast at 9.50pm GMT on Monday was triggered by a build-up of magma that formed a cone in the caldera, which in turn raised pressure in the lake. Ash and sulphur dioxide spewed high into the atmosphere through a 3,300ft hole in the ice.

As meltwater flows into the lake over the coming days, it is expected to overflow, causing floods to the south.

Bill McGuire, of the Benfield Hazard Research Centre at University College London, said that this eruption was comparatively small. “You’d expect the main ash fall to go only 150km (93 miles) or so, so it isn’t going to have an effect on Britain even if the winds are right.” The same magma system, however, was responsible for the Laki eruption of 1783, among the most serious volcanic blasts to affect this country. A 15-mile fissure pumped out the largest lava flow recorded, covering 200 square miles over seven months. Scientists believe that the eruption may have contributed to more than 10,000 deaths in Britain, as 143 megatonnes of toxic sulphur dioxide were discharged into the atmosphere.

It killed about 9,000 in Iceland — a quarter of the population — mainly as a result of famine as sheep died after eating contaminated grass.

Professor McGuire said: “The Laki fissure was connected to the Grímsvötn caldera, but nothing close to the same scale has happened since. It is still a relatively active caldera, but most of its eruptions are fairly small like this one, even if they do look spectacular.”

CAULDRON OF FIRE

The most serious recent volcanic eruptions were at Mount Pinatubo in the Philippines in 1991, and Mount St Helens in Washington State in 1980

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