Friday, January 20, 2012

COASTAL PROCESSES: Depositional landforms

Along a coastline you find features created by deposition. These include beaches, spits and tombolos.

Beaches are a common feature of a coastline. Beaches are made up of eroded material that has been transported from elsewhere and deposited by the sea. Constructive waves help to build up beaches. The material found on a beach (ie sand or shingle) depends on the geology of the area and wave energy. A cross-section of a beach is called a beach profile. The shingle ridges often found towards the back of a beach are called berms.

The material found on a beach varies in size and type as you move further away from the shoreline. The smallest material is deposited near the water and larger material is found nearer to the cliffs at the back of the beach. Large material is deposited at the back of the beach in times of high energy, for example during a storm. Most waves break near the shoreline, so sediment near the water is more effectively broken down by attrition. Sandy beaches have gently sloping profiles and shingle and pebble beaches are steeper.

A beach showing berms

A pebble beach with a steep profile

Spits are also created by deposition. 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 longshore drift. An example of a spit is Spurn Head, found along the Holderness coast in Humberside.

The development of Spurn Head

  1. Longshore drift moves material along the coastline.
  2. A spit forms when the material is deposited.
  3. Over time, the spit grows and develops a hook if wind direction changes further out.
  4. Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats orsalt marshes form.

A tombolo is a spit connecting an island to the mainland. An example of a tombolo is Chesil Beach, which connects the Isle of Portland to the mainland of the Dorset coast. Chesil Beach stretches for 18 miles. Lagoons have formed behind the stretch of beach material.

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