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Coastal Landscapes

Coastal sand dunes and aeolian processes

  • 2 things to know
  • Component 1 Section A

Overview

How wind moves sand on a beach, embryo dune and foredune or yellow dune.

What you need to know

Answer each one before you reveal it.

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Key term

What conditions are needed for coastal sand dunes to form?

Key term

Explain how wind moves sand on a beach.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What conditions are needed for coastal sand dunes to form?

    Model answer

    A dune system needs a large supply of dry sand, a wide beach exposed at low tide and strong onshore winds. An obstacle such as driftwood or a plant is also needed to trap the sand.

  2. 2

    Explain how wind moves sand on a beach.

    Model answer

    Wind lifts grains and bounces them along the surface in saltation, and each landing dislodges further grains by surface creep. Only the very finest particles are carried in true suspension.

  3. 3

    What wind speed is generally needed to begin moving dry sand?

    Model answer

    Dry sand begins to move at a wind speed of roughly 4 to 5 m s⁻¹. Wetter or coarser sand needs a stronger wind.

  4. 4

    Describe an embryo dune.

    Model answer

    An embryo dune is a low mound of sand no more than a metre high at the top of the beach. Sand couch and sea rocket trap the first grains around an obstacle.

  5. 5

    What is a foredune or yellow dune?

    Model answer

    A yellow dune is a larger ridge, often 5 m to 10 m high, with much bare sand still showing. Marram grass colonises it and traps sand rapidly.

  6. 6

    Why is marram grass so important in dune formation?

    Model answer

    Marram grass has long roots that bind the sand and rolled leaves that limit water loss. The plant grows upward through fresh sand, so the dune builds higher as sand accumulates.

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