The formation of cliffs and wave cut platforms through erosion

Coastal erosion by waves shapes the landscape over thousands of years, creating dramatic features such as cliffs and wave cut platforms. This process involves several stages driven by the relentless action of the sea against the shoreline.

Stages of cliff and wave cut platform formation

• Initial notch creation - Waves erode the base of the shoreline through processes like hydraulic action, corrosion, corrasion, and pounding. This forms a small notch at the high water mark.
• Cave development - Over time, the notch deepens and widens due to continued wave action, eventually forming a cave.
• Cliff collapse - The rock above the cave or notch loses support as erosion progresses, becoming unstable and collapsing. This creates a steep cliff face.
• Retreat and wave cut platform - As the process repeats over many years, the coastline retreats inland, leaving behind a flat or gently sloping area of rock at the base known as a wave cut platform (WCP). An example is found at Robin Hood's Bay in Yorkshire, where cliffs stand behind an extensive WCP.

Factors affecting cliff characteristics

The size and steepness of cliffs are influenced by the type and hardness of the local rock.

The development of headlands and bays due to differential erosion

Not all coastal areas erode at the same rate. Variations in rock resistance lead to the formation of distinct landforms such as headlands and bays, creating a jagged coastline.

Process of headland and bay formation

• Differential erosion - When a coastline consists of alternating bands of hard and soft rock, the softer rock erodes faster under wave action compared to the harder rock.
• Headland creation - The more resistant hard rock remains, jutting out into the sea as a headland, often featuring steep cliffs.
• Bay formation - The softer rock is worn away more quickly, forming indented areas called bays, where beaches often develop from deposited sediment.

The specific shape and size of headlands and bays depend on the local geology.

The creation of caves, arches, and stacks in coastal environments

Headlands, being exposed to powerful wave energy, are particularly prone to further erosion, leading to the formation of unique features like caves, arches, stacks, and blow holes over time.

Stages of cave, arch, and stack formation

• Cave initiation - Wave energy targets weaknesses or cracks in the rock of a headland, eroding them to form one or more caves. A notable example is Fingal's Cave, Staffa.
• Arch development - Continued erosion enlarges a cave, sometimes breaking through the headland to form a natural arch. Additionally, wave compression of air in caves can weaken the roof along joints, causing collapses that create blow holes on the surface. A well-known arch is found at Durdle Door, Dorset.
• Stack emergence - The roof of an arch often becomes unstable over time and collapses, leaving an isolated pillar of rock called a stack, or a series of stacks. An example is The Needles off the Isle of Wight.

Coastal areas with limestone or chalk geology are especially vulnerable to this type of erosion.

The influence of local geology on coastal landform shapes

The characteristics of coastal landforms are heavily determined by the underlying geology of the area. Rock type and structure play a critical role in how erosion shapes the coastline.

The interplay of these geological factors means that the actual shape and size of the features formed will depend on the local geology.