Erosional processes and the formation of wave-cut notches and platforms

Coastal erosion shapes the landscape by wearing away rock and creating distinct landforms. This process is primarily driven by the power of waves, which attack cliffs and gradually transform their structure over time.

How wave-cut notches and platforms are created

• Wave action at cliff base - Waves relentlessly strike the foot of a cliff, causing erosion.
• Formation of wave-cut notch - Over time, this erosion carves out a small indentation or notch at the base of the cliff.
• Enlargement and collapse - As erosion continues, the notch deepens, making the rock above it unstable until it eventually collapses into the sea.
• Removal of debris - The collapsed material is swept away by waves, leaving space for a new notch to begin forming at the cliff base.
• Cliff retreat - Repeated cycles of notch formation and collapse cause the cliff to retreat inland over many years.
• Creation of wave-cut platform - As the cliff moves back, a flat or gently sloping rocky surface, known as a wave-cut platform, is left behind at sea level.
• Influence of rock type - Cliffs made of hard rock often remain steep and vertical due to slower erosion, while softer rock cliffs erode more quickly, resulting in a more sloping profile.

Formation of headlands and bays along discordant coastlines

Certain coastlines feature alternating bands of different rock types, leading to varied rates of erosion. This creates contrasting landforms where some areas jut out into the sea while others curve inward.

Process of headland and bay formation

• Rock resistance variation - Coastal rocks differ in their ability to withstand erosion; soft rocks or those with many joints are less resistant, while hard, solid rocks resist erosion better.
• Differential erosion - Along a discordant coastline, where bands of resistant and less resistant rock run perpendicular to the shore, erosion happens unevenly.
• Bay formation - Less resistant rock, such as clay, erodes rapidly, forming a curved indentation or bay with a gentle, sloping shoreline.
• Headland formation - More resistant rock, like chalk, erodes much more slowly, leaving a protruding section of land with steep sides, known as a headland.

Development of caves, arches, and stacks from headlands

Headlands, often composed of tough, resistant rock, are not immune to erosion. Over time, wave action exploits weaknesses in the rock, leading to the creation of dramatic coastal features.

Stages of cave, arch, and stack formation

• Exploitation of weaknesses - Headlands typically have cracks or joints in the rock, which waves target through processes like hydraulic action and abrasion.
• Cave development - Persistent wave action enlarges these cracks, hollowing out a cave within the headland.
• Arch creation - As erosion continues, the cave deepens and eventually breaks through to the other side of the headland, forming a natural arch resembling a bridge over the sea.
• Arch collapse - Ongoing erosion weakens the rock supporting the arch, causing it to collapse over time.
• Stack emergence - The collapse of the arch leaves behind an isolated pillar of rock, known as a stack, standing separate from the headland in the sea.

In some coastal areas, these stages are evident, with limestone headlands showcasing caves, intact arches like a natural doorway, and lone stacks as remnants of collapsed arches.