Process zones on a cliff face. Abrasion of the base of the cliff and platform and the cutting of a notch. Washing ands smoothing of the mid-section by wave water. Weathering of the upper cliff by salt and other subaerial processes. Till cap.
Cliffs and platforms at Tantallon
Stack with basal notch near Thorntonloch, the whimsically named Standalane Stane.
Cliffs east of North Berwick, partly protected by a raised beach
Definition: steep to vertical or overhanging rock slope at the coast, free of soil and regolith
The existence of a cliff face in a slope profile is probably very short-lived. Marine action plays a dual role in the cliff process. The obvious role is in cliff erosion, undercutting the slope base and thus forming debris both directly and indirectly due to mass failure of the over-lying rock. Less obvious is the removal of debris by a variety of marine processes including longshore drift.
Cliff formation and erosion can relate directly to the formation of a notch at the base of the cliff. The development of the cliff notch through time is important as it controls both the rate of cliff recession and the form of the shore platform left behind. Experiments have shown that breaking waves are much more effective than broken waves at notch cutting. When cliffs plunge into deep water, waves are reflected and very little other erosion takes place. When waves break some distance offshore, owing to a low beach or shore platform angle, erosion occurs slowly. Cliffs whose base has a relatively narrow steep beach are more likely to experience the maximum erosive forces of breaking waves.
When the shore platform is relatively mature, theoretically only very short steep waves are capable of progressing to the cliff face without breaking. When such abnormal waves do occur, they can cause accelerated cliff erosion. Cliff erosion is therefore dependent on a critical height of wave such that waves lower than this critical height merely removes the loose debris. Waves larger than the critical height occur more and more infrequently until the effect on cliff erosion becomes so rare as to be negligible.
This continued erosion of the coastal slope and the subsequent removal of the debris by near shore currents cause the shoreline to retreat to form a sub-horizontal wave-cut or shore platform.
The advance of cliff erosion is mediated by rock structure to create distinctive cliff morphologies. This provides a family of spectacular landforms, with headlands, bays and geos, often with caves, gloups or blowholes, plus arches and sea stacks in every stage of development and destruction. The process starts with wave-induced erosion of the rocks along fracture lines at the base of the cliff and initiates a small opening following the weakness. Cave enlargement proceeds by hydraulic action of the waves enhanced by the pneumatic action of entrapped air and the abrasive action of sand and pebbles.
Sea-level change during the Quaternary has meant that cliff development in many areas has had a stop-start history such that it is difficult to decide whether a given cliff is a product of present-day processes or whether it is a fossil feature relating to previous sea levels. The cliffs east of North Berwick certainly seem to have had a complex history related to multiple sea levels.