Towards a process-response model for cliffed coasts: the case of north-east Yorkshire

Within the coastal super system there are the two main systems of the cliff and the foreshore and thirdly, but at a lower hierarchical level, the coastline system. The forms of and processes shaping each of these physical features are analysed quantitatively. Instrumented sites have been set up for the measurement of rates of erosion of the shore platform, of other foreshore features, and of the cliff foot over a longer period than has so far been possible. A section of cliff has also been instrumented. An original technique for the analysis of coastline morphology is described. Bays that are fundamentally arcuate, triangular, or rectangular are associated with different extranous factors, the first particularly with a bare cliff foot or a sand or pebble beach, the second with a boulder beach or geological heterogeneity and the third with glacial deposits. The c1iff consists of any combination of the elements termed the sandstone scarp, the bevel, and the marine-activated cliff. The bevel results from protection of the cliff foot by talus cones and boulder beaches. It is concluded that bevelled cliffs are in dynamic equilibrium though relaxation time is long, leading to continuous changes in form. A cliff consisting of the marine-activated element only is probably a steady-state feature and is associated with a bare cliff foot or one which has a sand or pebble beach. The shore platform may include any combination of two elements, the ramp and the plane, the former being steeper than 2.5 degrees and shaped by the corrasion of the overlying debris. The sub-horizonta1ity of the plane is a product of secondary erosive processes - mainly expansion and contraction of the shale due to wetting and drying in tidal and intertidal periods. The resistance of boulder beaches is increased if the boulders become imprisoned. Boulders partly embedded in the shore platform may remain perched when this feature is lowered. In the base of talus cones conglomerate can be formed in less than 200 years. Therefore the nature of the cliff foot is the principal regulator in the coast su~rsystem but superficial deposits undergo erosion so this regulator and the supersystem continuously change. Measurements of erosion rates show that it is incorrect to hypothesise that some of the coastal landforms have been inherited from Pleistocene times.