GCSE Geography | Landforms of Erosion: Cliffs and Wave-cut Platforms (Coastal Landscapes 6)

Processes of erosion have led to the formation of distinctive coastal features - we call these erosional landforms.

Cliffs are formed by coastal erosion. Processes of weathering weakens the rock, processes of erosion undercut the base of the cliff, and over time processes of mass movement transport material down to the beach.

Cliffs

Some UK coastlines are known for their spectacular cliffs, such as the Seven Sisters (pictured below) along the coast of Sussex - these white chalk cliffs rise up to 200 metres above sea level and are almost vertical. They have horizontal bedding planes with layers of hard rock jutting out. There are wave-cut notches along the base, with fallen rocks at the cliff base, and stretches of wave-cut platform which is exposed at low tide.

Geology affects the rate at which cliffs retreat. Hard resistant rocks will recede slowly - for example, the coastline at the Seven Sisters is eroding by about 60cm a year, and the granite cliffs at Lands End in Cornwall only erode by about 9cm per year. Whereas the soft boulder clay cliffs at the village of Happisburgh on the North Norfolk coast are eroding at 3 metres per year, and the Holderness Coast in Yorkshire is eroding at about 2 metres a year, making it one of the most quickly eroding coastline in Europe.

The geology also affects the result of erosion - erosion causes soft rocks to slump, whereas erosion of hard rocks leads to the formation of steep cliffs and wave-cut platforms.

How do cliffs and wave-cut platforms form?

The process starts off with a piece of land sloping down to the sea - processes of weathering, such as freeze-thaw, will weaken the rock. At the section of the cliff base between the high and low watermark erosion will occur. The erosional processes here are hydraulic action, where the sheer force of the water enters rocks and weakens them from within, and abrasion, where the sea is hurling shingle at the cliff, so it scratches and scrapes away pieces of rock. This erosion continues and over time rock will break away from the cliff base and collect on the beach, before the material is removed by destructive waves, leaving a wave-cut notch. This wave-cut notch will become larger, leaving the cliff above it unsupported. Eventually the wave-cut notch becomes so large that the overhanging cliff collapses due to gravity - the cliff above will have already been weakened by processes of weathering.

Hydraulic action, abrasion and freeze-thaw weathering will repeat the process of wave-cut notch formation and cliff collapse, causing the cliff to retreat. At the cliff retreats it will usually increase in height - this is because the land down to the sea is sloping, so the lower land has already been lost.

As the cliff retreats it leaves a wave-cut platform, which will often be covered at high tide. This is the old base of the cliff. Parts of the wave-cut platform will be very smooth due to abrasion from the incoming waves, whereas other parts will be much more rugged and maybe covered in algae or crusted with barnacles.

What are wave-cut platforms like?

• Area exposed rock at the base of a cliff
• Very gently sloping - less than 5 degree angle
• Usually only visible at low tide
• Rock pools form in between the areas of rock - lots of crabs here
• Parts can look quite rocky, whilst other bits are very smooth due to attrition
• There are deep cracks in some places
• Often covered in seaweed that has been thrown in by destructive waves
• Lots of barnacles cling to the rock - their grip is so hard that they become part of the rock