page_title: Geology of Somerset
section_title: Coastline
hierarchical_section_title: Geology of Somerset / Coastline
caption_attribution_description: Steep Holm
context_page_description: Somerset is a rural county in the southwest of England, covering 4,171 square kilometres. It is bounded on the north-west by the Bristol Channel, on the north by Bristol and Gloucestershire, on the north-east by Wiltshire, on the south-east by Dorset, and on the south west and west by Devon. It has broad central plains with several ranges of low hills. The landscape divides into four main geological sections from the Silurian through the Devonian and Carboniferous to the Permian which influence the landscape, together with water-related features.
  The low-lying areas of the North Somerset Levels and Somerset Levels have been subject to thousands of years of flooding and man's attempts to control the flow of water. In the north of the county the Limestone of the Mendip Hills dominates the landscape, while in the south the Blackdown and Quantock Hills rise out of the levels. The highest areas are on Exmoor. The wide variety of landscapes has led to several areas being designated as Sites of Special Scientific Interest for geological reasons, and support a range of flora and fauna as can be seen from the List of Sites of Special Scientific Interest in Somerset.
context_section_description: In prehistoric times the coastline of Somerset was very different from the present one, the sea level at the last glacial maximum being several hundred feet lower than today so that the Bristol Channel was almost non-existent. The Bristol Channel has one of the largest tidal ranges in the world, up to 12 metres (39 ft) at Burnham-on-Sea for example, behind only the Bay of Fundy and Ungava Bay in Canada. Normal high tide may be enhanced by between 3 metres (10 ft) and 4 metres (13 ft) during storm surges. This feature has meant that large areas of the county have been liable to flooding by the sea. Thus the present coastline is partly due to a belt of marine clay at the coast and partly due to seawalls built to reclaim areas previously flooded at high tide. The coastline contains exposures of Devonian sediments and tectonics west of Minehead adjoining the classic exposures of Mesozoic sediments and structural features which extend eastward to the Parrett estuary forming cliffs along the coastline near Clevedon and near Minehead, with low sandhills near Burnham-on-Sea. There are sandy beaches mainly at Burnham-on-Sea, Brean and Weston-super-Mare. There are also storm ridges, salt marsh, and sand dunes.
caption: Steep Holm
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