Along this stretch of coastline Portland Stone protects the softer Purbeck Limestone behind it, all it takes is a crack to be exploited by the immense power of the waves. Over many years this crack will be weakened and expand, eventually forming a cave.
Over a long period of time this cave will go back to the softer clays behind the hard limestone walls, once the waves reach this point they can rapidly erode away at the clay creating the familiar bowl shape of Lulworth Cove. The Portland and Purbeck Limestone at the mouth of the Cove would have collapsed into the sea, forming the bay that is we know today. The wave action form the sea cut into the area greensand, however this is where the erosion is slowed down and brought almost to a stop by the chalk. It is likely that this is as far as the cove will evolve as the power of the waves is going to be significantly reduced, minimising the effect it will have on the chalk.
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Chesil Beach
Fleet Lagoon
The Isle of Portland
Christchurch Harbour
Bournemouth and Barton-on-Sea