Coastal Landforms

Sub-aerial Processes

The interaction of the land, sea, weather/climate and human activity produces a variety of different coastal landforms. These landforms are broadly divided into those that result from coastal erosion and those due to coastal deposition.

Erosional Features

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By far the most common coastal landforms are the alterations of headlands and bays which give many coastlines their irregular appearance. Destructive waves clearly play an important role in their formation. The nature of the coastal rocks also plays a part. The direction in which rocks occurs in relation to the coastline affects the resulting landforms. Coasts where the rock outcrops run parallel to the sea are called concordant coasts and often produce straighter coastlines. Coasts where the rocks outcrop at right angles to the sea are called discordant coasts and often produce headline and bays. Outcrops of more resistant rock that are able to withstand the destructive waves better protrude as headlands. The image below shows a discordant coast with out crops of chalk and limestone forming the headlands, whilst Stud-land Bay and Swanage Bay have been cut into soft clays and sands.

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The image above shows the features of most cliff they are as follows:

  • Wave-cut Platform
  • Wave-cut Notch
  • Mass Movement
  • Cliff Retreated
  • Cliff Foot
  • Cliff Face

Most headlands are defined by cliffs. where these cliffs rise steeply from the sea, repeated breaking of destructive waves lead to them being undercut at the base. A wave-cut notch is formed. Undercutting weakens the rock above the notch and it eventually collapses. Thus the cliff face retreats but its steep face is maintained. The retreat of the cliff leads to the formation of a gently sloping wave-cut platform at the base.

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Erosional features of headlands are as follows:

  • Crevices/nocks
  • Caves
  • Arches
  • Stacks
  • Stumps

These features form on the sides of headlands as a result of constant attack on the rocks of the headlands by destructive waves. Any points of weakness in the headland’s rocks, such as faults or joints are attacked, particularly by hydraulic action and abrasion. This likely to lead to the opening up of a cave. If the cave is enlarged and extends back through to the other side of the headland, possibly meeting another cave, an arch is formed. Continued erosion by the sea widens the arch. As the sea undercuts the pillars of the arch, the roof is weakened and eventually collapses. This leaves a stack separated form the headland. Further erosion at the base of the stack may eventually cause it too to collapse. This will leave a small, flat portion on the original stack as a stump. It may only be visible at low tide.

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An excellent example of these erosional features is Old Harry’s Rocks at the end of the chalk headland separating Swanage bay from Stud-land Bay in southern England.

Depositional Features

Beaches

Beaches are defined as a pebbly or sandy shore, by the sea between high and low-water marks.

Beaches are formed when sub-aerial processes such as rain, wind and climate which break down big rocks to smaller rocks and rounds can round them. All beach are rock in some form or another and are as follows:

Sand

Gravel/Pebbles

Shingle

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Cobblestones

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Spits

A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end. Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in long shore drift. An example of a spit is Spurn Head, found along the Holderness coast in Humberside.

An example of a spit is Hengistbury Head in the United Kingdom in South England Dorset. One serious threat to the future of the Head is erosion of the exposed southern cliff face from wind and rain, as well as erosion caused by the sea primarily through the process of Long Shore Drift.

A comparison of Ordnance Survey maps reveals that 25 metres of cliff was washed away from 1915 to 1962, a process accelerated by the Bournemouth cliff’s concreted promenade and groins, construction of which started in the early 20th century. It is thought that in the last 200 years around 150 metres of land has been lost from the Head.

Sand Bars/Sand Banks/Shoal

Also known as a sandbank or shoal, is a characteristically linear landform completely within or extending into a body of water. It is typically composed of sand, silt, and/or small pebbles.

Tombolo/Mound

A tombolo also known as a mound is an island is attached to the mainland by a narrow piece of land such as a spit or bar. Once attached, the island is then known as a tied island. Several islands tied together by bars which rise above the water level are called a tombolo cluster.

Lagoons

A lagoon is a stretch of salt water separated from the sea by two or more tombolo’s have formed an enclosed area that may eventually fill with sediment.

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