Coastal Landscape & Physical Processes (Edexcel GCSE Geography A)

Weathering & Mass Movement at the Coast

• Weathering is best defined as:

The break-down of rock in-situ

• Weathering does not involve the movement of the material; this is what makes it different from erosion

• Sub-aerial weathering describes coastal processes that are not linked to the action of the sea

  • Sub-aerial weathering includes freeze-thaw weathering (mechanical) and chemical weathering

• Weathering weakens cliffs, making them more vulnerable to erosion

Mechanical weathering

• Mechanical weathering physically breaks up rock

• Freeze-thaw is an example of mechanical weathering

The process of freeze-thaw weathering

Chemical weathering

• When a chemical process breaks down rocks, this is known as chemical weathering

• This process happens because:

  • Rainwater is slightly acidic through absorbing carbon dioxide from the atmosphere

  • This reacts with minerals in the rock, creating new material

• Rock-type affects the rate of weathering; e.g. limestone chemically weathers faster than granite

• The warmer and wetter the climate, the faster the chemical reaction

Biological weathering

• When living organisms break down rocks this is known as biological weathering

• This process occurs when:

  • Trees and other plants grow within the cracks in a rock formation

    • As the roots grow bigger, they push open cracks in the rocks making them wider and deeper

    • Over time, the roots of the growing tree eventually break the rock apart

The process of biological weathering

• Burrowing animals, such as rabbits, disturb the ground above the burrow, which puts pressure on any cracks, eventually leading to pieces falling off the rock

Mass movement

• Mass movement is the downhill movement of material under the influence of gravity

• Heavy rain can make cliffs unstable and increase the risk of mass movement

• Mass movement includes landslides, slumping and rockfalls

• Movement depends on:

  • The angle of slope (the steeper the slope, the faster the movement)

  • Nature of regolith

  • Amount and type of vegetation

  • Water

  • Type and structure of rock

  • Human activity

  • Climate

Landslide

• This is a movement of material 'en masse' which remains together until it hits the bottom of a slope

• This often occurs along a flat surface

Fall

• A rockfall happens when the slope is steep and the movement is rapid

• Falls happen as a result of:

  • Extreme weathering: Freeze-thaw action can loosen rocks that become unstable and collapse

  • Rainfall: Too much rain will soften the surface, leading to the collapse of the slope

  • Earthquakes can dislodge unstable rocks 

  • Hot weather can dry out soil, causing it to shrink and allowing rocks to fall

  • Wave action at the base of the cliff causes undercutting and leaves the rocks above unsupported

Slump

• Slumps are usually found on weaker rock types (i.e. clay)

  • The slopes become saturated and heavy after heavy or prolonged rainfall

• This type of mass movement is common at the coast and is also known as rotational slip

• Slumping involves a large area of land moving down the slope in one piece

  • Because of the way it slumps, it leaves behind a curved, indented surface

Erosion, Transportation & Deposition at the Coast

Erosion

• Destructive waves are responsible for the majority of erosion that happens along a coast

• They carve the coastline in three main ways:

  • Hydraulic Power/Action 

  • Attrition

  • Abrasion 

• There is also a fourth way that waves erode along the coast and that is by solution/corrosion 

Transportation

• Material in the sea has many sources:

  • Eroded from cliffs

  • Transported by longshore drift along the coastline

  • Brought inland from offshore by constructive waves

  • Carried to the coastline by a river

• Once in the water, the material is moved in different ways:

  • Traction 

  • Saltation

  • Suspension

  • Solution 

Longshore drift 

• Longshore drift is the main process of deposition and transportation along the coast 

• The process of longshore drift is shown in the diagram below

The process of longshore drift

Deposition

• Deposition will happen when transported material is dropped from the seawater

• This occurs when the velocity (speed) of the water flow slows down

• When the water speed slows down, there is not enough force to hold or suspend the material in the water anymore

• The material is dropped onto the ground

• Beaches are formed of sediment deposited in bays

• Saltmarshes and mudflats are formed in sheltered estuaries, usually behind spits