Coastal landforms - revision

Waves When waves approach the shore, frictional resistance with the sea bed slows them down at their base. They get taller and their wavelength decreases. The top of the wave overtakes the bottom as the water gets shallower and they break. The energy of waves determines whether they build up or degrade a beach. The former are called constructive waves and the latter destructive waves. Teacher’s note: Constructive waves have a lower height, a longer wavelength, a lower frequency and a greater swash than backwash. Destructive waves have a greater height, a shorter wavelength, a higher frequency and a backwash at least as strong as the swash. Photo: © Stephen Aaron Rees, shutterstock.com What determines whether waves are constructive or destructive? Height Wavelength Frequency Swash/backwash.

Deposition Sediment is deposited where waves and currents slow down or the supply of sediment exceeds the rate of removal. Pebbles are deposited when wave energy is high. Stormy seas are able to carry them and often throw them far up a beach. Photo: © dichohecho. This image is reproduced under the terms of the Creative Commons License. A copy of the license can be read at this address: http://creativecommons.org/licenses/by/2.0/deed.en_GB Smaller particles, like sand, are only deposited when wave energy is low.

How are spits formed?

Complete the picture dragging and dropping the words on the right. Drag and drop exercise.

What is a tombolo? If a spit joins the mainland to an island it is called a tombolo. At Chesil Beach in Dorset, the mainland is joined to the Isle of Portland.

Chesil Beach Study the photograph. Y X Portland Name features X and Y.

What is a bar? If a spit joins one part of the mainland to another it is called a bar. For example, there is a bar at Orford Ness in Devon.

Complete the picture dragging and dropping the words on the right. Drag and drop exercise.

Erosional landforms

Wave-cut platforms Wave-cut platforms are flat areas found at the base of cliffs. What are the stages involved in their formation? Erosion at the base of the cliff creates a wave-cut notch. The cliff material above the notch is undermined. The material becomes unstable and eventually collapses. This repeats and the cliff retreats, leaving a rock platform. Teacher’s note: The photo shows a large wave-cut platform at Southerndown near Bridgend in South Wales. Photo: © Yummifruitbat. This image is reproduced under the terms of the Creative Commons License. A copy of the license can be read at this address: http://creativecommons.org/licenses/by-sa/2.5/

Caves, arches, stacks and stumps Some erosional landforms are created where wave action attacks weak points, such as joints in rocks and bedding planes between bands of rock. The most common types of landforms created in this way are caves, arches, stacks and stumps. Teacher’s note: Durdle Door is a classic example of an arch and the Old Man of Hoy is a famous example of a stack. Photos: Durdle Door © Stu collier, shutterstock.com; Old Man of Hoy © Grinner. This image is reproduced under the terms of the GNU Free Documentation License. A copy of the license can be read at this address: http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License Durdle Door, Dorset Old Man of Hoy, Orkney Do you know what landforms the pictures show?

Cliffs Steep cliffs are often found at the coast in areas where the rocks are more resistant. Erosional processes, such as abrasion and quarrying, attack the base of the cliff. What temporary features are formed by erosion? Wave-cut notches and blow-holes are both temporary features of erosion caused by the sea eroding natural weaknesses in the rock structure – joints, bedding planes and cracks. Photo: © CloudSurfer. This image is reproduced under the terms of the GNU Free Documentation License. A copy of the license can be read at this address: http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License

How much do you know about coasts?

Key Ideas Waves are the result of the wind blowing over the sea. They break as they approach land. Swash and backwash describe the movement of a wave on the beach. Fetch is the distance that the wind has travelled. Sub-aerial processes such as weathering and mass movement occur on the cliff face. Coastal processes of erosion include hydraulic action, attrition, corrosion and solution. Landforms created by erosion include headlands and bays, caves, arches, stacks and stumps. Longshore drift is a method of coastal transport. Landforms created by deposition include beaches, spits, tombolos and bars.