North Atlantic storms are creating waves over 20 metres (65 feet) high, powerful enough to tear rocks up and throw them as far as 50 metres (yards) inland in places like the Shetland, Orkney and Western islands in Scotland and the Arran islands in Ireland.

These boulders can be up to 50 tonnes and three metres in size -- as big as a van and much heavier, the Guardian and the Daily Telegraph newspapers reported Wednesday.

Previously, scientists believed the boulders hurled inland had been the product of tsunamis, generated by earthquakes or volcano erruptions, yet the last recorded tsunami dates back 4,900 years.

It is estimated that around 100 giant waves smash British coasts every year. At least once a year, waves measuring more than 24 metres are recorded, and on average a 29-metre wave is thought to occur every 100 years.

The research, conducted jointly by the Scottish universities of Glasgow, Saint Andrews and Strathclyde, was revealed by coastal geomorphologist Jim Hansom at the International Geographical Union congress in London on Tuesday.

He said that this erosion phenomenon was recent, and likely to increase in the future due to rising sea levels and sinking coastlines.

The average winter wave west of the Shetland Islands has grown by 15 percent between 1985 and 1995, and the sea level has increased by one millimetre (0.04 inch) per year in the past century, the Daily Telegraph reported.

Hansom told the Guardian: "When I was asked to investigate the reason for hundreds of boulders piled up inland from 20 metre high cliffs, I did not believe that waves could be responsible."

"The boulders were just to big and too heavy," he said. "But now we can show it is occuring and at an ever increasing rate."

TERRA.WIRE