Emergent coasts

Where the sea is receding from the land, the margin of the water meets a gentle slope that was originally the sea bottom. Waves tend to break a long way out because the water is shallow for a considerable distance from the shore. In the line of wavebreak the sea-bed becomes churned up, and loosened material may be thrown ahead of the breaking waves. This sometimes leads to the formation

Emergent Coastlines

Figure 8.10 Stages of evolution of a submerged coast. (a) Early phase - flooded valleys, erosion of headlands and deposition of sand and silt within the inlets. (b) Intermediate phase headlands cut back further, lengthening the cliff line and exposing the bays to stronger wave action. Beach material becomes coarser and less stable. (c) Mature phase -promontories eliminated and cliffs virtually continuous.

Figure 8.10 Stages of evolution of a submerged coast. (a) Early phase - flooded valleys, erosion of headlands and deposition of sand and silt within the inlets. (b) Intermediate phase headlands cut back further, lengthening the cliff line and exposing the bays to stronger wave action. Beach material becomes coarser and less stable. (c) Mature phase -promontories eliminated and cliffs virtually continuous.

of ridges or bars of sand or gravel, known as offshore bars. These are often of transient duration, their shape and position changing from tide to tide, but occasionally the process is cumulative so that a bar is eventually built up above sea level. It may then become stabilized and consolidated by plant growth along its crest. The seaward side of the bar is now the new coastline. The lagoon between the earlier shore line and the newly formed bar becomes silted up, forming an area of salt marsh which may later become converted into sand dunes, and finally into ordinary soil.

If sea level continues to fall, this sequence may be repeated several times. Once the sea level becomes constant over a long period, wave erosion is likely to encroach gradually upon the land, leading at length to the formation of cliffs and the development of a mature coastline.

Due probably to a rise of sea level since the last glaciation, much of the coast of the British Isles is the submergent type in various stages of evolution. However, there are signs of old cliffs and beaches, some now many feet above sea level and far behind the present coastline, in several places, for example, parts of Sussex and Devon, Norfolk and some areas of Scotland.

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