Coastal Processes (AQA GCSE Geography)

Revision Note

Jacque Cartwright

Written by: Jacque Cartwright

Reviewed by: Bridgette Barrett

Wave Types & Characteristics

  • The coast can be defined as:

The meeting point between land and sea

  • Coastal processes are divided into two parts:

    • Marine processes: Offshore (water-based)

    • Terrestrial processes: Onshore (land-based)

  • These processes are further divided into:

    • Wave action

    • Erosion

    • Transportation

    • Weathering

    • Mass movement

  • These processes produce the distinctive landforms found around our coastlines 

Examiner Tip

When you are asked to describe the formation of a landform, you must refer to the physical processes involved in its formation.  

You must also use the correct terminology and show your understanding of each of the processes involved. 

Wave action

  • Waves are marine processes that erode, transport and deposit material

  • Waves are formed as winds blow over the surface of the sea 

  • The height and strength of a wave are dependent on 3 factors:

    • The fetch 

    • The amount of time the wind blows

    • The strength of the wind

  • The greater the strength, time and fetch of the wind, the larger the wave

  • As a wave enters the shallow water of the coast, friction from the seabed causes the wave to lean forward and eventually crest and break onto the beach 

  • The movement of water up the beach is called the swash, and the return movement is the backwash

  • There are two types of waves:

    • Destructive waves erode the beach

    • Constructive waves are beach builders

Comparison of Wave Type

 

Constructive Wave

Destructive Wave

Swash

Strong

Weak

Backwash

Weak

Strong

Wavelength

Long with low height

Short with high height

Frequency

Low (6–8 per minute)

High (10–12 per minute)

Type of beach

Sandy: depositional 

Shingle: erosional

Diagram compares two wave types: constructive with a strong swash and weak backwash, building beaches; destructive with a strong backwash, eroding beaches.
Wave type characteristics.

Worked Example

Identify which statement below best describes the characteristics of a destructive wave?

 

A

 long wavelength and weak backwash

 

B

 short wavelength and weak backwash

 

C

 short wavelength and strong backwash

 

D

 long wavelength and strong backwash

[1 mark]

Answer:

  • The answer is C [1]:

    • A destructive wave has a short wavelength, high frequency rate, steep wave gradient and a strong backwash 

Weathering

  • Weathering is best defined as:

The break-down of rock in-situ

  • Weathering does not involve the movement of the material; this is what makes it different from erosion

  • Sub-aerial weathering describes coastal processes that are not linked to the action of the sea

  • It includes freeze-thaw weathering (mechanical) and chemical weathering

  • Weathering weakens cliffs and makes them more vulnerable to erosion

  • Mechanical weathering physically breaks up rock

    • Freeze-thaw or frost shattering is where:

      •  Water gets into cracks and joints in the rock

      •  When the water freezes, it expands and the cracks open a little wider

      • When the water thaws, the crack contracts, releasing pressure on the crack

      •  Over time, repeated freezing and thawing widens the crack until pieces of rock split off the rock face, whilst big boulders are broken into smaller rocks and gravel

  • When a chemical process breaks down rocks, chemical weathering occurs.

    • Rainwater is slightly acidic through absorbing carbon dioxide from the atmosphere

    • This reacts with minerals in the rock, creating new material

    • Rock-type affects the rate of weathering; e.g. limestone chemically weathers faster than granite

    • The warmer the temperature, the faster the chemical reaction

  • When living things wear away rocks, this is known as biological weathering

    • Trees and other plants can grow within the cracks in a rock formation

      • As the roots grow bigger, they push open cracks in the rocks, making them wider and deeper

      • Over time, the growing tree eventually prizes the rock apart

    • Burrowing animals, such as rabbits, disturb the ground above the burrow, which puts pressure on any cracks, eventually leading to pieces falling off the rock

Mass Movement

  • Mass movement is:

The downhill movement of material under the influence of gravity

  • Heavy rain can also make cliffs more unstable and increase the likelihood of mass movement through throughflow and runoff

  • It includes landslides, slumping and rockfalls

  • The following factors determine the type of movement:

    • Angle of slope (the steeper the slope, the faster the movement)

    • Nature of regolith

    • Amount and type of vegetation

    • Water

    • Type and structure of rock

    • Human activity

    • Climate

  • Soil Creep:

    • Common in humid climes with the movement of less than 1 cm per year 

    • Soil expands when it freezes, gets wet or is heated up in the sun

    • As the soil expands, it lifts at right angles to the slope

    • When the soil shrinks, it falls straight back down

    • Soil creep takes a long time because the soil moves only a millimetre to a few centimetres at a time

  • Flow:

    • Occurs on slopes between 5° and 15° with speeds between 1 and 15 km per year

    • Usually happens after the soil has become saturated with a flow of water across the surface

    • Vegetation is flattened and carried away with the soil

  • Slide:

    • A movement of material 'en masse' which remains together until hitting the bottom of a slope

  • Fall:

    • Slopes are steep and movement is rapid

    • Caused by a number of reasons:

      • Extreme weathering: Freeze-thaw action can loosen rocks that become unstable and collapse

      • Rainfall: Too much rain will soften the surface, leading to the collapse of the slope

      • Earthquakes can dislodge unstable rocks 

      • Hot weather can dry out soil, causing it to shrink and allowing rocks to fall

  • Slump:

    • Usually found on weaker rock types (i.e. clay) that become saturated and heavy

    • This is common at the coast and is also known as rotational slip

    • It involves a large area of land moving down the slope in one piece

    • Because of the way it slumps, it leaves behind a curved indented surface

Diagram of types of mass movement: fall (rock fragments), slide (rock blocks), flow (saturated soil), and slump (soil slumping on a curved surface).
Major mass movement examples

Worked Example

Outline two ways that sub-aerial processes can affect the shape of a cliff

[4 marks] 

  • There will be 2 marks available for each point

  • 1 mark for the processes

  • 1 mark for the explanation

  • Remember that there are three sub-aerial processes that you can use to answer this question

    • Freeze-thaw, chemical and biological

  • You need to explain how each process works and then link that to how it would change the shape of a cliff

Answer:

  1. One subaerial process is freeze-thaw weathering [1], where temperatures need to go above and below freezing 0°C. Any water trapped in cracks of a rock freezes and expands, exerting pressure on the crack. When temperatures rise, water melts, pressure is released and the crack contracts. Repeated cycles eventually break the rock apart. Therefore, there will be more freeze-thaw occurring in winter than in summer, resulting in more weathering of the cliff face [1]. As a result, the cliff is weaker and the waves can erode it more easily [1].

  2. Chemical weathering [1] is another sub-aerial process and the rock type will decide how quickly the rock will dissolve. Rainwater and seawater are both slightly acidic. Less resistant rock, such as limestone, will react with the acid in the water faster than granite. Therefore, a cliff made of softer, less resistant rock will weather faster than a cliff made of harder, more resistant rock [1]

Erosion

  • Destructive waves are responsible for the majority of erosion that happens along a coast

  • They carve the coastline in three main ways:

    • Hydraulic Power/Action 

    • Attrition

    • Abrasion 

  • There is also a fourth way that waves erode along the coast and that is by corrosion 

Examiner Tip

Make sure you know the difference between the four types of erosion, particularly between abrasion (corrasion) and attrition. So many students confuse these two terms.

A tip for you is to think of abrasion as rubbing with sandpaper or maybe you have grazed your knees or elbows when you fell off your bike/skateboard?  Those grazes were abrasions on your knees, elbows, etc. 

Transportation

  • Material in the sea arrives from many sources:

    • Eroded from cliffs

    • Transported by longshore drift along the coastline

    • Brought inland from offshore by constructive waves

    • Carried to the coastline by a river

  • Once in the water, the material is moved in different ways:

    • Traction 

    • Saltation

    • Suspension

    • Solution 

Longshore drift

  • It is the main process of deposition and transportation along the coast 

  • Waves approach the beach at an angle due to the prevailing wind

  • As the waves break, the swash carries material up the beach at the same angle

  • As the swash dies away, the backwash carries the material down the beach at right angles (90°) 

  • The process repeats, transporting material along the beach in a zig-zag movement

Diagram showing longshore drift. The prevailing wind direction drives waves at an angle to the beach. Swash moves material up; backwash moves it down, creating zig-zag motion.
The process of longshore drift

Worked Example

Describe and explain the process of longshore drift

[4 marks] 

  • Identify the command words and link to the key term 

  • Command words are 'describe and explain'—say what you see and why

  • Your focus is on 'longshore drift'—what is it?

Answer:

  • Longshore drift is the process where the waves transport material [1], such as sand, along the beach in the direction of the prevailing wind [1]. The swash moves material up the beach at an angle [1] as the waves approach in a similar direction to the wind. The material then moves back down the beach at 90° due to gravity [1]. This is the backwash. This movement continues along the beach in a zig-zag motion [1] in the direction of the prevailing wind 

Examiner Tip

When describing a feature, make sure you are clear on the correct sequence/stage.  Use annotated sketches or diagrams to help you explain the steps. 

Deposition

  • Deposition will happen when transported material is dropped from the seawater

  • This occurs when the velocity (speed) of the water flow slows down

  • This means there is not enough force to hold/suspend the material in the water anymore, and it is dropped onto the ground

  • Beaches are formed of sediment deposited in bays

  • Saltmarshes and mudflats are formed in sheltered estuaries, usually behind spits

Worked Example

Study Figure 9, a photograph taken along the stretch of coastline.

White chalk cliffs with horizontal red and brown layers, crumbling into a rocky beach below. A cloudy sky overhead with a few people walking in the distance.

Suggest one type of mass movement that is affecting these cliffs.

[1 Mark]

Answer: 

  • Remember the question asks about mass movement and not weathering; therefore, your answer should be one of the following:

    • Rock fall [1]

    • Slumping [1]

    • Landslip [1]

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Jacque Cartwright

Author: Jacque Cartwright

Expertise: Geography Content Creator

Jacque graduated from the Open University with a BSc in Environmental Science and Geography before doing her PGCE with the University of St David’s, Swansea. Teaching is her passion and has taught across a wide range of specifications – GCSE/IGCSE and IB but particularly loves teaching the A-level Geography. For the past 5 years Jacque has been teaching online for international schools, and she knows what is needed to get the top scores on those pesky geography exams.

Bridgette Barrett

Author: Bridgette Barrett

Expertise: Geography Lead

After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.