Coastal Erosion and Deposition

Waves, winds, currents, tides, and storms are the major forces on the coastline. The results of these actions and interactions by natural forces on the shoreline and near-shore seabed are coastal processes, which include erosion and deposition. 

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    What factors are involved in coastal erosion and deposition?

    There are several factors involved in coastal erosion and deposition. The main processes are:

    Shaping coastlines

    Waves are the primary drivers in shaping coastlines. Destructive waves (waves that have a stronger backwash) are the most common types of waves that cause erosion . These waves occur during stormy conditions and are characterised by big, strong waves that have high energy. Constructive waves (with a limited backwash) occur during calmer weather, have low energy, and cause deposition rather than erosion. Because of their characteristics, destructive waves can erode the coastlines in several ways:

    • Hydraulic action – air in cracks in the cliff is compressed when waves crash in. The pressure caused by this action breaks off pieces of rocks.
    • Attrition – bits of rock in water smash against each other and break into smaller pieces.
    • Abrasion – bits of rock and sediment transported by the waves, smash and grind against rocks and cliffs, breaking bits off and smoothing the surface.
    • Corrosionsoluble rocks get gradually dissolved by the seawater.

    Coastal formations

    The principle marine processes responsible for shaping the coastline are erosion , transportation , and deposition. Erosion is where the force of waves breaks down the land. Transportation is when waves and tides transfer the broken material somewhere else. Meanwhile, deposition is when waves and tides lose their energy, cease transporting the eroded material, and deposit it. Each coastline has its balance between the processes of erosion, transportation, and deposition.

    Erosional coastal formations include:

    1. Headlands and bays.
    2. Cliffs and wave-cut platforms.
    3. Stacks and stumps.
    4. Shoreline platforms.

    Coastal Erosion and Deposition Stacks and Stumps StudySmarterDuncansby Stacks Image: Bill C CC BY-SA 3.0

    When waves no longer have any energy left to transport the sediment, deposition occurs. What features are formed by the sediment will depend on how and where the sediment is deposited.

    Depositional coastal formations include:

    1. Spits.
    2. Beaches.
    3. Offshore bars and tombolos.
    4. Cuspate forelands.
    5. Salt marshes and estuarine mudflats.
    6. Sand dunes.

    Sediment transportation

    The energy provided by waves, tides, and currents transport the eroded material. There are four main processes involved in sediment transportation:

    • Solution – substance that is dissolved and carried along in the water.
    • Saltation – larger particles are too heavy to be carried, so they are bounced along the sea bed.
    • Suspension – this is where very fine material is carried along in the water.
    • Traction – enormous particles are pushed along the sea bed by the force of the water.

    These processes can transport sediment along the shore; this is known as longshore drift or littoral drift .

    Sediment is moved along the coast in sediment cells. Within each cell, the sediment moves between the beach, cliffs, and the sea through the process of erosion, transportation, and deposition. Any action taken in one place has an impact elsewhere in the cell. Each cell operates between physical barriers that prevent the sediment from moving any further along the coast. There are 11 principal cells along the coastline of England and Wales.

    Sub-aerial processes

    Sub-aerial processes are land-based processes that alter the shape of the coastline. The main sub-aerial processes are weathering and mass movement.

    Weathering

    The gradual breakdown of rocks in situ at or close to the ground surface is known as weathering. This can be divided into three different types - mechanical, chemical and biological.

    Types of Weathering
    Mechanical (physical)Freeze-thaw (frost shattering) Salt weathering (salt crystallisation) Wetting and drying (sea weathering)
    Chemical Carbonation
    BiologicalPlants WaterMicrobes

    Mass movement

    This is the movement of materials downslope at a range of speeds. Water acts as the common lubricant involved in mass movement.

    Types of mass movement are:

    • Soil creep

    • Solifluction

    • Earth and mudflows

    • Rock falls

    • Rock / debris slides

    • Slumps

    Coastal Erosion and Deposition - Key takeaways

    • Constructive and destructive waves are the primary drivers in shaping the coastline.

    • Constructive waves are depositional.

    • Destructive waves are erosive.

    • Destructive waves can erode the coastlines through hydraulic action, corrosion, attrition, abrasion, and corrosion.

    • The four main processes involved in transporting material are solution, saltation, suspension, and traction.

    • The sub-aerial processes involved in shaping the coastline are weathering and mass movement.

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    Coastal Erosion and Deposition
    Frequently Asked Questions about Coastal Erosion and Deposition

    What causes coastal erosion and deposition?

    Both coastal erosion and deposition are caused by the action of waves. There are two main types of waves responsible for this, destructive waves and constructive waves

    What is coastal erosion and deposition?

    Coastal erosion is the wearing away of land by destructive waves, currents, and wind. As a result of coastal erosion, the shoreline will retreat causing land loss. Globally, this is a massive issue. Deposition happens when the sea loses energy and it drops the sand, rock particles, and pebbles it has been carrying. Constructive waves are responsible for this as the swash is stronger than the backwash.

    What are the four types of coastal erosion?

    The four processes of coastal erosion are corrosion, abrasion, attrition, and hydraulic power.

    What is the most significant danger of coastal areas?

    The most significant danger to coastal areas comes from natural events such as hurricanes, coastal storms (storm surge), tsunamis, and landslides (mass movement), as well as longer-term risks of coastal erosion and sea-level rise.

    What is the negative effect of coastal erosion?

     The negative effects of coastal erosion are the damage it can cause to transport and infrastructure through storm surges and mass movement. In addition, changes to the soil structure result from seawater contaminating the farming land through flooding, causing economic loss and the destruction of property.


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