The volume of material removed from the cliff is found by doing a simple calculation using data already collected, see Fig xx.
Volume Removed = Disappearing Cliff x Height Of Cliff
To make sense of the data collected we consider some influencing factors and again compare with other parts of the beach.
Data Presentation
Diagram Of The Composition of The Cliff:
The cliff cross section shows evidence that it is very vulnerable to rotational slip, because its second from top layer consists of a material called Red crag which is very absorbent. The layer below the Red Grag, London Clay, is not at all absorbent.
The water is rejected by the London Clay and acts as a lubricant between the two layers. This allows the Red Grag to slide along the London Clay, causing it to rotate as it falls off the edge. A clear example of this type of mass movement appears at the centre of the beach. There is an upside down pillbox, which probably not long ago was perched on top of the cliff. The material, which it sat on, Red crag, had obviously been exposed to rotation slip causing the pillbox to fall.
This graph illustrates the amount of material removed and the height of the cliff at different points along the beach,
The graph shows that the height of the cliff shadows the amount of material removed. i.e. The higher the cliff the more material removed. The smallest amount of material removed is positioned near the sea wall. Therefore the sea wall and other coastal defences surrounding that part of the cliff are obviously effective in slowing down the rate of erosion.
Diagram showing the workings to find the height of the cliff;
X = height of cliff near pill box
Tan 26 = x x tan 26
59.5
x= 29 metres