Iceland and the British Isles: the volcanic connections

The mountainous island of Rum, off the west coast of Scotland, exposes the eroded core of an ancient volcano that formed nearly 60 million years ago, as the North Atlantic Ocean began to open. Volcanologists study the rocks here to gain insight into similar eruptions on Iceland today.

In 2010 and 2011, ash from Eyjafjallajökull and Grímsvötn volcanoes in Iceland caused major disruption to our lives in Britain. But this eruption 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.

The Island of Rum viewed in GeoVisionary. (NEXTMap Britain elevation data from Intermap Technologies).

Nowadays, geologists and geographers find the ash incredibly useful, because each ash layer can be analysed and linked to a known eruption — thus 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 geological time.

Sub-sea volcanoes known as the Mid-Atlantic Ridge

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. That ocean is ever widening, as magma rises to the surface along a chain of sub-sea volcanoes, known as the Mid-Atlantic Ridge.

For further information download our factsheet on Plate Tectonics.

This diagram shows how volcanoes developed between Europe and North America 60 million years ago, as magma from deep in the Earth moved upwards and was erupted at the surface. Volcanism has continued ever since along a structure called the Mid-Atlantic Ridge, creating new ocean floor and pushing the continents steadily apart at a rate of a few millimetres a year. In Iceland, this steady volcanism has interacted with a hot mantle plume to create the volcanic island we see today. (Image: © Elizabeth Pickett

Britain's ancient volcanoes

Dr Dougal Jerram investigating layering in rocks formed in an ancient magma chamber on the Isle of Rum. This is one of the best examples of a cold, eroded magma chamber anywhere in the world, and provides vital clues to understand the processes occurring beneath Iceland today.

In Iceland, however, 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 60 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.

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

Further information

Contact Dr Kathryn Goodenough for further information on Britain's ancient volcanoes.