Coastal landforms are shaped by the powerful forces of erosion, where the sea wears away the land over time through various processes. These processes act differently depending on the rock type, coastal structure, and wave energy, leading to the formation of distinctive features like cliffs, wave cut platforms, headlands, bays, caves, arches, and stacks.
Coastal erosion involves several key processes:
- Hydraulic Action: The force of water and air being compressed into cracks in the rock. As waves crash against the coast, air trapped in fissures is compressed, and as the wave retreats, the pressure is released. This repeated compression and release weakens the rock, causing pieces to break off.
- Abrasion: This is the process described in the reference. Abrasion is a process that creates coastal erosion landforms through the movement of rock in waves crashing against rock faces. This means rocks, pebbles, and sand carried by the waves are thrown against the cliff face, grinding and wearing it away like sandpaper. It creates cliff faces and wave cut platforms.
- Attrition: Rocks and pebbles carried by the waves collide with each other, breaking into smaller, rounder pieces. This process doesn't directly erode the coastline but provides the material for abrasion.
- Solution (or Corrosion): The dissolving of soluble rocks (like limestone or chalk) by seawater.
These processes combine to sculpt the varied features of erosional coastlines. As the reference notes, Cliffs, wave cut platforms, headlands, bays caves, arches, and stacks are all different coastal erosional landforms.
Formation of Specific Coastal Erosional Landforms
Here's how some of these common landforms are created by erosion:
Cliffs
Cliffs are steep rock faces found at the coast. They are formed when destructive waves erode the base of the land. Processes like hydraulic action and abrasion (as mentioned in the reference, abrasion contributes to creating cliff faces) wear away a notch at the base of the cliff. As this notch is undercut, the overlying rock becomes unstable and eventually collapses. The collapsed material is then eroded and transported away by the waves, allowing the process to repeat, causing the cliff to retreat inland.
Wave Cut Platforms
Wave cut platforms are gently sloping areas of rock found at the base of a cliff, exposed at low tide. They are formed as the cliff retreats. Erosion at the base (again, the reference states abrasion helps create wave cut platforms) creates a notch and causes the cliff to collapse. The debris is removed, and repeated undercutting and collapse cause the cliff line to move inland. The eroded surface left behind at the base is the wave cut platform.
Headlands and Bays
These features form on coastlines where there are alternating bands of hard (resistant) and soft (less resistant) rock running perpendicular to the coast. Waves erode the softer rock faster than the harder rock. The areas of softer rock are worn away to form bays (inlets of the sea), while the more resistant rock stands out as headlands (promontories of land jutting into the sea). Bays are often sheltered, allowing deposition to occur and beaches to form, while headlands remain exposed to the full force of wave attack.
Caves
Caves are often the first stage in the erosion of a headland. They form when waves (using hydraulic action and abrasion) attack lines of weakness, such as joints or faults, in the rock at sea level on a headland. Erosion is concentrated in these weak areas, gradually carving out a hollow.
Arches
If a cave continues to be eroded through a headland, potentially from both sides meeting in the middle, it can form an arch. This is a natural tunnel through the rock that connects the two sides of the headland. Erosion continues on the base of the arch, widening it and making it less stable.
Stacks
A stack is an isolated pillar of rock standing in the sea, typically just offshore from a headland. It forms when the roof of an arch collapses due to continued erosion and weakening at its base and sides. The section of the arch attached to the mainland retreats, leaving the outer part as a freestanding stack.
Here is a summary table illustrating the relationship between processes and forms:
| Landform | Key Erosional Processes Involved | Description |
|---|---|---|
| Cliffs | Hydraulic Action, Abrasion | Steep rock face formed by wave undercutting and collapse. |
| Wave Cut Platforms | Hydraulic Action, Abrasion (formed as cliffs retreat) | Flat, rocky area at cliff base, exposed at low tide. |
| Headlands | Differential Erosion (less eroded resistant rock) | Promontory of resistant rock jutting into the sea. |
| Bays | Differential Erosion (more eroded less resistant rock) | Inlet of sea formed in areas of less resistant rock. |
| Caves | Hydraulic Action, Abrasion (exploiting weaknesses) | Hollow eroded into the base of a cliff or headland. |
| Arches | Hydraulic Action, Abrasion (erosion through a headland) | Rock tunnel formed when a cave erodes through a headland. |
| Stacks | Hydraulic Action, Abrasion (arch collapse) | Isolated rock pillar left after an arch collapses. |
These landforms demonstrate the dynamic nature of coastlines, constantly being shaped and reshaped by the relentless energy of the sea.
