3.1.3

Lithology & Vegetation

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Lithology and Coastal Recession

Lithology plays an important role in the rate of coastal recession.

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Bedrock lithology

  • When Geographers talk about the physical properties of different rocks, this is known as bedrock lithology.
  • The existence of sedimentary, igneous and metamorphic rocks affects the rate of recession along a coastline.
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Igneous rocks

  • Igneous rocks, such as Basalt and Granite, form from the crystallisation of magma. They are more resistant to erosion and weathering.
  • This is because igneous rocks contain crystals which increase the strength of the rocks and reduce the number of lines of weaknesses that would be exploited by physical processes.
  • Igneous rocks can either be intrusive (formed from magma inside the Earth) or extrusive (formed when magma escapes through vents on the Earth’s surface).
  • The average rate of erosion of igneous rocks is 0.1-0.5 cm per year.
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Sedimentary rocks

  • Sedimentary rocks, such as Limestone and Sandstone, form from the build-up, compacting and hardening of sediments into layers over time by lithification.
  • Sedimentary rocks that have been formed in a shorter geological time scale tend to be more susceptible to erosion and weathering and erode at a faster rate compared with those formed over a longer geological time.
    • E.g. limestone and chalk.
  • The average rate of erosion of sedimentary rocks is 2-6 cm per year.
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Metamorphic rock

  • Metamorphic rocks, such as slate and marble, are formed from the change in the structure of sedimentary and igneous rocks, caused by variations in heat and pressure.
  • The process of change is referred to as the rocks having been metamorphosed.
  • Marble is an example of a metamorphic rock that has been formed from the changing structure of limestone caused by the re-crystallisation of calcite.
  • Metamorphic rocks are resistant to erosion.

Vegetation

Vegetation is important in supporting the development of sandy coastlines and so plays an important role in the rate of coastal recession.

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Sand dunes

  • Sand dunes need a continuous supply of sand, powerful winds to transport sand and obstacles to trap the sand, like plants.
  • A typical sand dune transect goes from the mobile dunes nearest the sea (embryo, fore and yellow) to the fixed dunes nearest the backshore (grey dunes and dune slack).
  • Sand dunes contain two types of plants:
    • Xerophytes, which can withstand periods of dry weather.
    • Halophytes, plants that can withstand high concentrations of salt from seawater.
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Vegetation succession on dunes

  • Typical plants that colonise embryo and foredunes are sea rocket and sea crouch. These plants have deep roots and can tolerate high concentrations of salt.
  • Yellow dunes tend to be colonised by marram grass. These plants also have long deep roots and are salt tolerant.
  • Heathers are commonly found in grey dunes because of the higher rates of humus.

Jump to other topics

1Tectonic Processes & Hazards

2Option 2A: Glaciated Landscapes & Change

3Option 2B: Coastal Landscapes & Change

4Globalisation

5Option 4A: Regenerating Places

6Option 4B: Diverse Places

7The Water Cycle & Water Insecurity (A2 only)

8The Carbon Cycle & Energy Security (A2 only)

9Superpowers (A2 only)

10Option 8A: Health & Human Rights (A2 only)

11Option 8B: Migration & Identity (A2 only)

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