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Coastal processes

Coastal Landscapes

Types of wave: constructive and destructive.

Learning objectives:• Describe the characteristics of the two wave types.• Explain their impact on beach profiles.

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Waves are produced by wind blowing across the surface of the water.

Why does wave energy vary?

• The energy of a wave depends on:- the velocity of the wind- how long the wind blows- the fetch which is the length of water the wind

blows over.The stronger the wind is, the longer it blows for

and the longer the fetch the larger the waves will be and the more energy they’ll have!

FETCH

Suggest how wave fetch can cause different rates of coastal recession. (3)Fetch: The length of water the wind blows over. Longer distance waves have more energy (1), more power to erode (1), increasing hydraulic action/abrasion (1).

Key words

Swash and backwashWhen waves break, water rushes up the beach due to the energy from the wave. This is called the swash.When the water has lost its energy further up the beach, it runs down again, under gravity. This is called the backwash.

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WAVE TERMINOLOGY

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Wave length is the average distance between successive wave crests.Wave height is the vertical distance between a wave trough and a wave crest.

Destructive waves

http://www.youtube.com/watch?v=7woVTuN8k3c&feature=related

Destructive waves lower the beach gradient in

its lower section

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Constructive waves

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Constructive waves

Differences between the two types of waves

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Compare the characteristics of constructive and destructive waves. (4) Destructive waves have a greater backwash than swash (1) compared to constructive waves due to their higher energy (1) meaning that they can erode beaches (1). Constructive waves have a lower frequency (1) as a result of their longer wavelength (1) Destructive waves are plunging whereas constructive are surging (1). Destructive waves are higher (>1m) compared with constructive (1).

Impact on beach profile

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Constructive waves Destructive waves

Process Sand and shingle moved up the beach = deposition

Most material is carried downward by the backwash= erosion

Impact on beach profile Sediment is being added to the beach which the backwash cannot entirely remove, producing a gentle build-up of beach material. This will increase the gradient of the beach in its lower section.

Due to erosion, beach profile becomes gentler in its lower section.

Revision

Draw diagrams of constructive and destructive waves and label these to contrast the beach profiles and wave height/wave length.

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Types of erosion, weathering and mass movement

Watch: http://www.youtube.com/watch?v=zUh3WeilFN4

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Learning objectivesDefine and explain the different types of weathering, erosion and mass movement.

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Processes of erosion

(i) Hydraulic action: As the water gets into cracks in the rock face, it compresses the air in the cracks; this puts even more pressure on the cracks and pieces of rock may break off.

(ii) Corrasion [abrasion]: sand and pebbles carried within waves are thrown against the cliff face and particles of rocks are broken off.

(iii) Corrosion [solution]: chemical reaction between rocks made of calcium carbonate and salt and other acids in seawater.

(iv) Attrition: as the boulders in the sea continually roll around, they chip away at each, become smaller, smoother and more rounded. Final material: sand.

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Cross-section diagram of a chalk cliff

Tidal rangeCoastal erosion

Weathering and mass movement

Explain how the type of rock (geology) and structure can affect the rate of coastal erosion. (4)Rock type - if the cliffs are made from resistant rock, (1) like granite or limestone and chalk, (1) they will erode more slowly than cliffs made from less resistant rock, (1) such as clay.Rock structure - the rock’s structure can also have an effect on the rate of erosion. Rocks that are well jointed (1) or with many faults, (1) such as limestone and chalk, (1) will erode more quickly (1) as the waves exploit these lines of weakness. (1)

Sub-aerial processes: work on the cliff face

1- Weathering2- Mass movement

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WEATHERING

Weathering is the breaking or the decomposition of rocks in situ.

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Outline of main types of weatheringPhysical weathering: water expands when changed into ice expansion puts pressure on the rock around it fragments of rock break off.Chemical weathering: weak acids in rainwater react with calcium carbonate in rocks rocks break up or dissolve.Biological weathering: plants grow in cracks roots break up rocks may cause cliff collapse.

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Mass movement

Definition: When material moves down a slope due to the pull of gravity.1- Soil creep: very slow movement, very little impact on landform formation.2- Slumping: great impact on clay cliffs

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Soil creep

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1-Gravity pulls the water that is contained in the soil down a slope

2-The soil moves downhill with the water.

3-The slope appears rippled.

4- These ripples are known as terracettes.

Soil creep (the slowest downhill movement of soil

Soil creep

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Soil creep

2- Slumping [rotational slipping]

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Involves a large area of land moving down a slope. Very common on clay cliffs.Clay dries and cracks in summerWhen it rains, water runs into cracksabsorbs by clay which becomessaturated clay slips down.

Slumping

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Outline how mass movement impacts on coastal landforms. (3)Wave action/sea/rain can cause the cliffs to become saturated (1), if made of clay (1).Over time the material in the cliff becomes weakened and subject to gravity (1) cliff material slides down thereby removing material (1). Landslides can cause rapid removal of coastal material / loss of land (1).Soil creep causes slow removal of soil from coastal slopes (1); ridges / ripples are left (1).Slumping causes a downward moment of material (1) this leaves a curved shape (1).