Coastal Processes (Cambridge International IGCSE Geography)

Specification link

This page covers sections 2.1.1 and 2.1.2 of the CIE IGCSE Geography specification.

• 2.1.1- Coastal erosion: hydraulic action, corrosion, corrasion, attrition, transportation, deposition, and longshore drift.
• 2.1.2- Types of waves: constructive and destructive and wave refraction.

Coastal processes

Spec point — Coastal erosion: hydraulic action, corrosion, corrasion, attrition; transportation; deposition; longshore drift.

• The coast is the area where land and sea meet

• Coastal processes are divided into two parts:

  • Marine processes: offshore (water-based)
  • Terrestrial processes: onshore (land-based)

• These processes are further divided into:

  • Erosion
  • Transportation
  • Deposition by wave action

• Together with the local geology, these processes produce distinctive landforms around the coastline

  • A coastline made up of softer rocks such as sands and clays will be easily eroded by destructive waves to form low, flat landscapes such as bays and beaches
  • Coastlines of more resistant, harder rock will take longer to erode and produce rugged landscapes such as headlands

Marine erosion

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

• They cut into the coastline in four ways:

  • Hydraulic action is the sheer force of the waves hitting the coast

  • Attrition occurs when material carried in the waves bumps against each other and becomes smaller and smoother

    • This does not erode the coast but forms the sand and shingle

  • Corrosion, also known as solution, occurs because seawater is slightly acidic and gradually dissolves material. Some types of coastal rock such as limestone and chalk, are particularly prone to corrosion

  • Abrasion, also known as corrasion, occurs when waves pick up material and hurl it at the cliffs

Exam Hint Please ensure you understand the distinction between the four types of erosion, especially between abrasion (corrosion) and attrition. Many students confuse these two terms.

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

Marine transportation

• The sea transports sediment that it gets from erosion in the same way rivers do

• 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

• In the water, material is moved through:

  • Traction when large, heavy material is dragged along the sea floor
  • Saltation occurs when smaller material bounces along the sea floor
  • Suspension is the fine material held in the seawater
  • Solution is dissolved material carried in the seawater

Longshore drift (LSD)

• Longshore drift (LSD) is the main process of 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

Illustration showing the process of longshore drift

• Beach sediment is carried farther down the coast on coasts where longshore drift is one way; if it is blocked, sediment cannot move, and the area farther down the coast is deprived of sediment. This results in two problems:

  • Smaller beaches are less attractive to tourists, causing a loss of income
  • Removes natural coastal protection

Worked Example Describe and explain the process of longshore drift

[4 Marks]

Solution

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

Marking guidance

• The answer above is just one example of a response to this question
• The commands are to describe and explain and answers should detail the steps and reasons for longshore drift
• The focus must be on the process of 'longshore drift' and what it does

Exam Hint

• You can gain full marks using well-annotated diagrams to support your answer. Just as you like having a visual prompt, it helps the examiner to see that you do know the answer. Occasionally a diagram is easier than actually writing it all out.
• Longshore drift does not produce landforms; it is the process of transportation that supplies the sediment for the process of deposition (which does form features).

Marine Deposition

• The waves carry sand or shingle as they travel

  • Swash carries sediment onto the shore
  • Backwash carries sediment away

• The largest material is deposited along the upper reach of the swash when a constructive wave carries sediment up the beach

• The backwash loses water and energy as it travels because of the sand's porosity, resulting in smaller and smaller deposits.

• When a constructive wave carries sediment up the beach, the largest material is deposited along the upper reach of the swash

• During a storm, large shingle is thrown above the usual high tide level to form a ridge at the top of the beach called a berm

The action of the waves deposits sediment onto a beach

Wave types

Spec point — Types of waves: constructive and destructive and wave refraction.

• Waves are marine processes

  • They erode, transport and deposit material

• Waves are formed by winds blowing over the surface of the sea

• The height and strength of a wave are dependent on three 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 approaches the coast, it enters shallower water; 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

Types of waves

• There are two types of waves:

  • Destructive waves erode the beach
  • Constructive waves are beach builders

Constructive waves

• Constructive waves, also known as beach builders, have the following characteristics:

  • a long wavelength with low height
  • a low-frequency wave rate of 6-8 per minute
  • a shallow wave gradient
  • low energy
  • a stronger swash that carries material up onto the beach and deposits a gently sloping, sandy beach

Destructive waves

• Destructive waves erode the beach and have:

  • a steep wave gradient
  • a short wavelength with high height
  • a high-frequency wave rate of 10-12 per minute
  • high energy
  • a strong, abrasive backwash that drags material out to sea and forms steep, shingle beaches

Diagram showing constructive and destructive waves

Wave refraction

• Coastlines have different-depths of water and reflect waves
• The depths vary because headlands and bays have formed over time
• As waves travel into shallower water near the beach, they slow down
• This makes the wave bend or refract to fit the shape of the shoreline
• When waves are refracted, the energy is focused on the headland
• This cause more erosion to the headland than bays, where sediment is deposited

Wave refraction at a headland

Exam Hint Make sure you are familiar with how waves form and their different characteristics. You may have to identify the type of wave from a list of characteristics, such as wavelength, height, and the strength of swash and backwash.

Worked Example **Which statement below best describes the characteristics of a destructive wave? [1]

** A. **Long wavelength and weak backwash

** B. **Short wavelength and weak backwash

C. Short wavelength and strong backwash

** D. long wavelength and strong backwash

Final answer: Answer

• The correct answer is C

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

• The alternative answers are incorrect because:

  • A is a constructive wave
  • B and D are neither constructive nor destructive