Jurassic Limestone Cliffs

August 25, 2006


Provided and copyright: Philip Dawson
Summary author: Philip Dawson

The 200-205 million years old, Jurassic limestone cliffs shown above, reaching heights of 180 ft (55 m), make up a 14 mile (22 km) stretch of shoreline known as the Glamorgan of the Heritage Coast. These cliffs are punctuated by old glacial river valleys and hanging valleys, which send torrents of water plummeting over the clifftop during wet spells. They're also rich in marine fossils that have been readily exposed by erosion.

This coastline lies on the northern flank of the Bristol Channel, which has the second-highest tidal range in the world. For around two hours on either side of each high tide, these cliffs are buffeted by the fast-flowing waters of the Bristol Channel. Frequent winter storms hasten the erosion process. Rock-falls are often observed as the soft shale in between the limestone strata is washed away by waves and attacked by salt sea-spray, wind and rain, leaving the limestone blocks hanging precariously until they fall to the beach, either singly or sometimes as a major landslide. The large rounded boulders, which form the storm beach at the foot of the cliff, bear testament to many hundreds of thousands of years of erosion and smoothing of the boulders by the sea against the wave-cut rock platform that was left behind by the retreating cliffs.

There's a theory that as recently as the 15th century, seismic activity off the south coast of Ireland caused a large tsunami to rush up the narrowing Bristol Channel, rapidly changing the coastline and inundating the lower-lying areas on both the Welsh and English sides of the channel. Photo taken on July 27, 2006.

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