Iceland has closed its two main airports in preparation for a more powerful volcano after an eruption at the weekend shot lava high into the sky. Transatlantic flights have been re-routed to avoid the risk of ash blocking visibility and destroying engines following the eruption of Eyjafjallajokull volcano, which lies 120km southeast of Reykjavik.

Around 500 people have been evacuated from the local area.

It was initially feared that the volcano had erupted directly underneath the Eyjafjallajokull glacier, which could have led to glacial melt, flooding and mudslides. However experts now believe the volcano blew in between Eyjafjallajokull and the larger Myrdalsjoekull glacier.

But now the even greater danger is that the small volcano is only the start and that it will spark the far more powerful volcano of Katla beneath Myrdalsjoekull.

“That has to be on the table at the moment,” Dave McGarvie, senior lecturer at the Volcano Dynamics Group of the Open University, told The Times. “And it is a much nastier piece of work.”

“Eyjafjallajokull has blown three times in the past thousand years,” Dr McGarvie told The Times, “in 920AD, in 1612 and between 1821 and 1823. Each time it set off Katla.” The likelihood of Katla blowing could become clear “in a few weeks or a few months”, he said.

Iceland is built on a volcanic rock on the Atlantic’s mid-oceanic ridge. The island’s worst eruption in modern times was in 1783, when the Laki volcano erupted. The lava shot to heights of 1.4 kilometres and more than 120 million tonnes of sulphur dioxide was released into the atmosphere. A quarter of the island’s population died in the resulting famine.