Page last updated at 14:48 GMT, Thursday, 22 April 2010 15:48 UK

Iceland and the UK: Ancient volcanic connections

Dr Kathryn Goodenough
British Geological Survey

Island of Rum
Rum, an island off Scotland's west coast, exposes the core of an ancient volcano

The eruption of the Icelandic volcano that has caused so much disruption in the UK and Europe is really nothing unusual.

For hundreds of thousands of years, periodic eruption of Icelandic volcanoes has produced ash that has been carried over the British Isles.

This ash settles down into peat bogs and lakes, where it forms consistent layers. Nowadays, geologists and geographers find the ash incredibly useful, because each ash layer can be analysed and linked to a known eruption, allowing us to work out the age of the surrounding peat or lake sediments.

This way of working even has its own name - tephrochronology.

Because the peat and mud contain evidence of climatic changes in the past - for instance, tiny pollen grains that indicate the type of vegetation growing in an area - these past volcanic eruptions in Iceland are actually a vital tool for understanding how the climate in the British Isles has changed over time.

Ancient divide

A scientist investigating layering in rocks formed in an ancient magma chamber on the Isle of Rum.
Layering in rocks on the island of Rum formed in an ancient magma chamber

Going even further back in time, Iceland and the British Isles are linked in another, more dramatic way.

Sixty million years ago, America and Europe were joined together - the North Atlantic Ocean simply didn't exist. Then, volcanoes began to erupt in the middle of that huge supercontinent.

This volcanic activity was caused by a mantle plume - a great upwelling of hot magma from deep within the Earth.

Slowly, the American and European continents began to be forced apart, as magma upwelled between them, and a new ocean - the North Atlantic - began to form.

And we can see dramatic evidence of the upwelling in the form of the Giant's Causeway in Northern Ireland.

That ocean is ever widening, as magma rises to the surface along a chain of sub-sea volcanoes, known as the Mid-Atlantic Ridge. But in Iceland, this sub-sea volcanism interacts with the hot mantle plume, creating the incredibly volcanic island that we know today.

And what of the ancient volcanoes, which formed sixty million years ago when the mantle plume first reached the Earth's surface?

Well, their remains are perfectly preserved in the British Isles today - they form the islands of Rum, Skye, Mull and Arran in Scotland, Lundy Island in England, and the Mourne Mountains of Northern Ireland.

These ancient volcanoes have been eroded away over the millions of years since they ceased to be active, so that now we can see the cold remains of the magma chambers - the furnaces of the volcano.

Giants Causeway in Northern Ireland
The Giant's Causeway was formed by volcanic eruptions

Geologists and volcanologists study these ancient British volcanoes, and they provide vital information about what might be happening at depth beneath active Icelandic volcanoes.



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