Coastal Erosion

Coastlines

• Coastlines can be referred to as hard or soft
• Hard coastlines have rocky outcrops and rates of erosion are slow
• Soft coastlines consist of clay, sand or shingle and are eroded quicker

Coastal Erosion

1. Hydraulic Action

• Force of a wave hitting against the coast
• Most effective on soft coastlines or where the rock is well jointed
• Most of the destructive wave's erosive work is carried out during storms

2. Cavitation/Compression

• Waves trap and compress the air in joints and bedding planes of the rock when they hit the coastline
• As the waves move back out to sea, the compressed air is released and quickly expands
• This creates mini 'explosions' that increase the size of the cracks in rocks and eventually cause them to shatter

3. Abrasion/Corrasion

• Occurs when the load (rocks, pebbles and stones) carried by the waves hits against the cliffs on the coastline
• The pounding waves can undercut the coastline
• It is the most effective form of erosion and is most powerful during storms

4. Attrition

• The wearing down of stones carried by the waves until they are smooth and round
• They are constantly hitting off each other and the coast and eventually stones will turn into finer material such as shingle and sand

4. Solution/Corrosion

• Rocks such as limestone contain calcium carbonate and are easily dissolved in sea water
• This allows the rock to be broken up more easily and eroded

Factors that Affect Coastal Erosion

1. Slope of the Shore:

• Steeper slopes lead to faster erosion, as waves strike the shore with greater force and the land is more prone to collapse.
• Gentle slopes cause slower erosion because the waves have less power to erode the land, and sediment can build up instead.

2. Type of Wave:

• Destructive waves (large, high-energy waves) cause more erosion because they have a stronger backwash that removes material from the coastline.
• Constructive waves (smaller, low-energy waves) contribute less to erosion, often depositing sand and other materials on the shore.

3. Shape of the Coastline:

• Irregular coastlines with headlands and bays experience differential erosion, where headlands are eroded more quickly and bays accumulate sediment.
• Smooth, uniform coastlines tend to experience more even erosion, leading to a more consistent beach profile.

4. Rock Type:

• Soft rocks (e.g., limestone, clay) erode more quickly than hard rocks (e.g., granite, sandstone), making coastlines with softer rock more vulnerable to erosion.
• Soft rock is more easily broken down by the actions of waves and weathering, while harder rocks are more resistant to erosion.

5. Structure of Rock:

• Joints, faults, and bedding planes in rocks allow for easier erosion, as water can penetrate and break the rock apart.
• Rock layers that are poorly aligned or have cracks will erode more easily, while well-aligned, strong rock structures are more resistant to erosion.