Describe and explain how marine and sub aerial processes have formed the sequence of landforms at Stairhole, Lulworth Cove and Warbarrow bay.

However before we look at the process which have sculpted the coastline we must first analyse the rock type on which these processes have been working in order to fully comprehend what is happening. Hard Purbeck stone was once the front line of defence against the sea however little now remains. The little that does remain has protected the land sufficiently behind it creating headlands. Also found here are Portland limestone which due to it’s massive lithology is also very resistant. The steep angle of dip away from the sea also gives the sea a wall like quality. However behind the Purbeck and Portland softer Wealden Clay and Chalk can be found.

The first feature in question Stairhole, has been created by a breach of the outer Portland limestone. This has created a series of notches and caves.

Once these caves have been created a weakness is formed and so as with all matter concerning erosion it is exploited. The caves are enlarged and this leads to an arch been created as the base is removed. This is the process that has formed Durdle door. Arches eventually become stacks and there are removed completely.

This breach increased the amount of hydraulic action created by the waves on the now exposed rock. In the case of Lulworth the rock gets less resistant as you move inland. Wealden sands and clays lie behind the Purbeck and Greensand behind the Wealden. As a result when a weakness is found it is exploited more and more by the hydraulic wave action. The bases of these rock slopes are removed destabilising the cliff and increasing the rate of erosion.

It is important to remember the sea is not the only factor and sub aerial processes are also at work. This is particularly evident once the softer clay is reached. It is easily washed away by the sea. Equally the rain does equal damage cutting channels through the soft clays. Slump and slides can clearly be seen visibly. It is this varied lithology with the softer, less erosion resistant rocks behind that can be accounted for features such as Lulworth Cove. A weakness has simply been exploited, this may have been because the Portland was very thin or contained a number of joints. These joints created by the folding of the limestone are then exploited. Lulworth cove is simply a weakness that has been exploited and enlarged. The same can be said about Worbarrow bay. The only difference been several bays have been created until they have been eroded into one.

Once a bay has been created there is less erosion however. This is due to the headlands creating wave refraction and in doing so slowing the incoming waves. This in turn reduces hydraulic action.