Coastal Erosion: Processes, Landforms, and Examples

Coastal Erosion

Factors Influencing Wave Size and Energy

The size and energy of a wave are influenced by:

• How long the wind has been blowing
• The strength of the wind
• The fetch (the distance the wind blows over the surface of the water)

Rate of Coastline Erosion

The rate of coastline erosion is influenced by:

• Type of rock (e.g., chalk and limestone form steep cliffs)
• Strength of waves
• Speed of waves

Destructive Waves

Destructive waves are created in storm conditions. They are characterized by:

• Being created from big, strong waves when the wind is powerful and has been blowing for a long time
• Occurring when wave energy is high and the wave has traveled over a long fetch
• Eroding the coast
• Having a stronger backwash than swash
• Having a short wavelength and being high and steep
• High energy

Constructive Waves

Constructive waves are created in calm weather and are less powerful than destructive waves. They are characterized by:

• Breaking on the shore and depositing material, building up beaches
• Having a swash that is stronger than the backwash
• Having a long wavelength and being low in height

Processes of Coastal Erosion

Hydraulic Action

Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed, which weakens the cliff and causes erosion.

Abrasion/Corrasion

Bits of rock and sand in waves grind down cliff surfaces like sandpaper.

Attrition

Waves smash rocks and pebbles on the shore into each other, causing them to break and become smoother.

Solution/Corrosion

Acids contained in seawater dissolve some types of rock, such as chalk or limestone.

Cliff Erosion

Cliff erosion occurs in a series of steps:

1. Weather weakens the top of the cliff.
2. The sea attacks the base of the cliff, forming a wave-cut notch.
3. The notch increases in size, causing the cliff to collapse.
4. The backwash carries the rubble towards the sea, forming a wave-cut platform.
5. The process repeats, and the cliff continues to retreat.

Coastal Landforms

Caves, Arches, Stacks, and Stumps

Caves occur when waves force their way into cracks in the cliff face. The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action is the predominant process.

If the cave is formed in a headland, it may eventually break through to the other side, forming an arch.

The arch will gradually become bigger until it can no longer support the top. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.

The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure, and it will eventually collapse to form a stump.

An example of these landforms in Britain is Old Harry Rocks, a stack found off a headland in the Isle of Purbeck.