© UnknownHorses commutes to an other pasture south of Iceland's Eyjafjoell volcano

Many more of Iceland's volcanoes seem to be stirring

Iceland could be at the start of a surge in volcanic activity that may produce more eruptions.

The Icelandic eruption that has caused misery for air travellers could be part of a surge in volcanic activity that will affect the whole of Europe for decades, scientists have warned.

They have reconstructed a timeline of 205 eruptions in Iceland, spanning the past 1,100 years, and found that they occur in regular cycles - with the relatively quiet phase that dominated the past five decades now coming to an end.

At least three other big Icelandic volcanoes are building towards an eruption, according to Thor Thordarson, a volcanologist at Edinburgh University.

"The frequency of Icelandic eruptions seems to rise and fall in a cycle lasting around 140 years," he said. "In the latter part of the 20th century we were in a low period, but now there is evidence that we could be approaching a peak."

His findings coincide with new warnings that the eruption of Eyjafjallajokull, which has disrupted air traffic across Europe for several weeks, could carry on for many months - and possibly years.

Some geologists have also warned of a serious threat from a fourth volcano, Katla, which lies 15 miles to the east of Eyjafjallajokull. Two of its past three eruptions seemed to be triggered by those of its smaller neighbour and a report issued just before Eyjafjallajokull blew suggested Katla was "close to failure [eruption]".

The three other volcanoes cited by Thordarson as being potentially close to a large eruption are Grimsvotn, Hekla and Askja - all of which are bigger than Eyjafjallajokull.

In the past, they have proved devastating. Hekla alone has erupted about 20 times since AD874, pouring out a total of two cubic miles of lava from a line of fissures that stretches 3Å miles across the mountain.

There was a minor eruption in 2000 and geologists have reported that snow is once again melting on Hekla's summit, suggesting that magma is rising.

Grimsvotn, another highly active volcano, lies under the huge Vatnajokull glacier in Iceland's southeast. An eruption in 1996 saw much of this glacial ice melt, causing a flood that washed away the country's main ring road.

It is linked to the massive Laki fissure volcano whose 1783 eruption ejected so much ash into the atmosphere that it cooled the entire northern hemisphere for nearly three years. The resulting low temperatures caused crop failures and famines that killed 2m people and helped trigger the French Revolution.

Thordarson believes that the behaviour of the volcanoes is linked to movements in the earth's crust which create massive subterranean stresses over wide areas.

As these stresses build up, more volcanoes erupt and as the stress disappears, the volcanoes subside again.

The theory is a controversial one. Gillian Foulger, professor of geophysics at Durham University, suggests that historic clusters of eruptions could well have occurred by chance. She said: "This needs rigorous statistical support."

However, both she and Thordarson agree that Europe needs to take the threat of further Icelandic eruptions more seriously, including improving the monitoring of active volcanoes. Foulger is writing to David Willetts, the new science minister, suggesting Britain could support Iceland in such a project.

She said: "There are about 35 active [big] volcanoes in Iceland and if we put a high quality seismograph and some global positioning equipment on each one we would often be able to tell in advance if an eruption was coming. The cost is tiny compared with the potential economic damage from an unexpected eruption."

The most pressing question for Britain and the rest of Europe is how long the current eruption will continue.

Professor Stephen Sparks, from the earth sciences department at Bristol University, said: "Every volcano has its own personality. This particular volcano has erupted before in 1612 and 1821. When it erupted in 1821 it continued erupting for 15 months so there is no reason why it could not last a similar period of time."

The new rules in place for aviation mean Iceland and Europe can probably cope with Eyjafjallajokull, but an eruption by Katla could cause far bigger problems.

Dr Richard Waller, senior lecturer in physical geography at Keele University, believes the ash cloud could be immense, but for Iceland the biggest problem would be massive flooding.

"Katla has a crater filled with ice more than 2,000ft thick, which will all melt," he said.