Subaerial Processes

Geography: Edexcel A Level, topic 3.2.4

Processes of Weathering

Weathering describes the breaking down of rocks where they are. Mechanical, chemical and biological weathering are the three main processes.

Mechanical weathering

Mechanical weathering is when rocks are broken down without their chemical composition being changed.
Salt weathering is the main type of mechanical weathering affecting coasts:
Seawater gets into cracks in rocks.
Salt crystals form when the seawater evaporates. These crystals then expand and put pressure on the rock.
Over time, the repeated evaporation of saltwater widens the cracks in the rock so much that the rock breaks apart.

Chemical weathering

Chemical weathering is when rocks are broken down because of their chemical composition being changed.
Carbonation weathering is a type of chemical weathering that takes place when it is warm and wet:
Carbon dioxide dissolves in rain, making it a weak carbonic acid.
The acidic rainwater dissolves types of rock that contain calcium carbonate.

Biological weathering

Biological weathering is when rocks are broken down by living things.
E.g. plant roots can weather rocks by getting into cracks and pushing them apart as they grow.
E.g. Algae can cause the breakdown of rocks from the release of chemicals.
The activity of animals near the coast is also an example of biological weathering.
E.g. some animals scrap and secrete acid on the rock, like the Piddock shells.

Mass Movement

Mass movement describes when rocks and loose material shift down slopes. This happens when gravity overcomes the force supporting the material. Mass movements can cause rapid coastal retreat and are common when the material is saturated.

Slides

Slides are when material moves down a slope in a straight line.

Slumps

Slumps are when material moves down a slope with a rotation.
Slumps happen slower than rockfalls and often happen when unstable permeable rock overlays more stable impermeable rock.
A combination of heavy rainfall and erosion processes cause the rotational movement of the cliff.

Rockfalls

Rockfalls are when material breaks apart because of erosion and weathering and then rolls down a slope.
The fallen fragments at the base of the cliff create talus scree slopes.

Test yourself on Subaerial Processes

Which of the following is NOT a type of weathering process?
What is the main type of mechanical weathering affecting coasts?
Salt Weathering
Which of the following is NOT a type of mass movement?
What type of mass movement is being shown in this diagram?

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