GCSE Geography | Weathering and Mass Movement (Coastal Landscapes 2)

Weathering processes have a significant impact on the coastline - weathering is the breaking down of rock in situ. It is caused by the weather, e.g. changes in temperature and levels of precipitation, or animals and plants.

Weathering

There are several types of weathering....

Biological weathering

This is caused by animals burrowing into the cliff face and weakening the rocks, or plant roots getting into cracks and making them bigger.

Chemical weathering

This is caused by rainfall which creates a chemical reaction when it hits rocks.

• Carbonation - rainfall contains carbonic acid which can react with calcium carbonate in limestone, this forms calcium bicarbonate, which is soluble so gets dissolved and carried away in solution
• Hydrolysis - acid from rainfall breaks down rock, making it rot
• Oxidation - oxygen and water react, breaking down rocks

Mechanical (physical) weathering

This is caused by extremes of temperature or changes in moisture - these changes cause rocks to become disintegrated.

• Freeze-thaw (frost shattering) weathering - this happens when water enters cracks in the rock. At night when the temperature plummets the water can freeze, which makes the water expand, putting pressure on the rock, making the crack bigger. When the ice thaws the pressure on the rock is relieved. The repetition of freezing and thawing will cause the rock to break away - this often collects as scree at the cliff base
• Onion skin (exfoliation) weathering - this happens because of temperature changes. When rocks are heated during the day they will expand, and then cool and contract at night. The repetition of expansion and contraction applies stress to the outer layers of rock, which causes them to peel away or flake off over time
• Salt weathering - this happens when salt from sea spray enters cracks in the rock. This salt can evaporate and crystallise which puts pressure on the rock, making it weaker

Mass movement

Mass movement is rock, soil or mud moving down a slop due to gravity - heavy rainfall is usually the cause, however weathering processes are responsible for the severity of movement.

Sliding

Landslides refer to the downhill movement of large volumes of rock, soil and mud. They can happen on steep hillsides and cliff faces. A landslide can occur after heavy rainfall has weakened the slope - the rainwater infiltrates the soil and then percolates down into the rock layer, making the rock saturated and heavy. This heavy saturated rock can then slide down along a weak bedding plane, taking vegetation down with it, aided by the lubricated wet rocks underneath.

• Rock slides - large amounts of rock slides down a cliff as a block - the leading edge of the rock slide will end up as a pile of rocks at the cliff base
• Mudflows - these are wet and rapid slides, usually on steep slopes that lack vegetation (so the soil is not held in place) - the saturated soil will spread out over a large area at the base of the cliff

Rock falls

Rock falls occur when fragments of rock break away from the cliff face, often due to freeze-thaw weathering. These are common on steep cliffs and the rock fall material collects are the bottom to form a fan-shaped scree slope.

Slumping

Slumping occurs when material moves down a concave cliff face - making the material rotate backwards into the cliff face as it slips down, which is why it often called rotational slip.