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Last Updated: Wednesday, 18 August, 2004, 10:58 GMT 11:58 UK
Huge waves eroding British coast
Wave, PA
The waves are increasing in size and frequency
Storm waves over 20m high are getting bigger, more frequent and eroding Britain's Atlantic coast, experts say.

The waves rip huge boulders from cliff faces and sweep them up to 50m inland in exposed areas such as Shetland, Orkney and the Western Isles.

This process creates piles of boulders tucked away inland behind cliffs.

The study shows these are not deposited by tsunamis (tidal waves generated by volcanic eruptions or earthquakes) as had been thought, but by storm waves.

Dr James Hansom, a geologist the University of Glasgow, told delegates at the International Geographical Union congress in the Scottish city that the erosion was expected to accelerate because sea levels were rising and the coastline was sinking.

The distance these large boulders are being moved is spectacular
Dr James Hansom, University of Glasgow
"The distance these large boulders are being moved is spectacular. They are being ripped from cliffs up to 35m above sea level and thrown about to form boulder beaches," said Dr Hansom.

"The boulder ridges were formed in recent times and there are no records of recent tsunamis.

"Because sea levels are continuing to rise and larger waves are hitting the cliffs, the rate of modification of the coastline and creation of these boulder ridges is increasing."

Boulder tossing

These boulder beaches occur only in exposed, remote areas where the sea is deep because the waves become smaller in shallower depths.

Research has shown that as many as 100 giant waves might hit the coast of Britain every year - large enough to overtop cliffs 20m high. At least one wave a year is being recorded at higher than 24m.

The average wave height during winter is said to have increased 15% between 1985 and 1995 in the area to the west of Shetland.

Data also suggests that global sea levels have increased by 1mm per year over the past century.

Previous research in Australia and the Caribbean suggested similar effects there were caused by tsunamis.

But the last known tsunami in the North Atlantic occurred 4,900 years ago while the Lisbon earthquake of 1755 produced only slight waves in Scotland.

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