Just the natural action of the waves against the cliffs, but that is too simple for the globull folks to understand or accept. Go further south along the channel coast of England and the harbor entrance at Hastings that existed in 1066 and for several hundred years before that was silted over by a series of storms a couple of hundred years after William the Conqueror landed there, thus making modern day folks, with no sense of history or geology, wonder why he chose to land on a strip of beach with no harbor. The ancient harbor is now the marsh lands to the west current coast line/closed harbor entrance.
Interesting, thanks!