The violent winter storms that rocked the UK last year had the power to physically shake cliffs to a degree in excess of anything recorded previously, according to marine scientists.
A team at Plymouth University used seismometers, laser scanners and video cameras to evaluate the impact of the massive waves - some up to eight metres high - that struck the cliffs in Porthleven, West Cornwall, during January and February.
They found that the level of shaking was of an order of magnitude greater than ever previously recorded. Words: PA
The researchers also recorded 1,350 cubic metres of cliff face being eroded along a 300-metre stretch of coastline in just two weeks - a cliff retreat rate more than 100 times greater than the long-term average.
PhD student Claire Earlie, from the university's school of marine science and engineering, said: "Coastal cliff erosion from storm waves is observed worldwide but the processes are notoriously difficult to measure during extreme storm wave conditions when most erosion normally occurs, limiting our understanding of cliff processes.
"Over January and February 2014, during the most energetic Atlantic storm period since at least 1950, with deep water significant wave heights of six to eight metres, cliff-top ground motions showed vertical ground displacements in excess of 50 to 100 microns, an order of magnitude larger than observations made previously anywhere in the world."
Using seismometers on loan from the Scripps institution of oceanography at the University of California, Miss Earlie and the team embedded the instruments seven metres from the cliff's edge.
Within two weeks, they were just five metres from the edge such had been the rate of erosion.
Terrestrial laser scanner surveys conducted from the beach also revealed a cliff face volume loss two orders of magnitude larger than the long-term erosion rate.
Professor Paul Russell, who helped to supervise the project, said: "The results imply that erosion of coastal cliffs exposed to extreme storm waves is highly episodic and that long-term rates of cliff erosion will depend on the frequency and severity of extreme storm wave impacts."
Professor Gerd Masselink, who led the research, added: "Our coastline acts as a natural barrier to the sea, but what we've seen right across south west of England is unprecedented damage and change, from huge amounts of sand being stripped from beaches to rapid erosion of cliffs.
"These figures will help to explain some of the invisible forces being brought to bear on our coastal structures, and highlight the risk of sudden cliff damage."
The paper, Coastal Cliff Ground Motions And Response To Extreme Storm Waves, is published in the academic journal Geophysical Research Letters.