Coastal Systems - Features of Coastal Erosion

A geographical coastal feature is a physical manifestation of processes operating upon a shoreline component: currents operating on sand, tides upon shores, waves colliding with cliffs…etc.

From a systems point of view, most features are in transition – they keep being subject to change as long as the processes that created them continues to operate.

If the processes change (as a result of isostatic uplift, for example), the feature may become a relict feature illustrating previous, but no longer current, conditions.

Other features may be transitory in a sequence from one to another (an arch results from one or more enlarged caves, but is often on the way to becoming a stack).

Key features of coastal erosion:

Headlands and bays: where harder, more resistant rock lies adjacent to softer, more easily eroded bands of rock. Where these are orientated at right angles to the coast, it is known as a discordant coast (opposite is concordant coast where a uniform rock forms the coastline).

Caves: enlarged from natural weaknesses, joints and bedding planes by marine erosion processes.

Arches: where a cave has eroded through a headland or curtain of more resistant rock. May be from the coalescence of two or more caves.

Stack: results from a collapsed arch roof. Frequently above marine erosional processes, an arch roof is degraded by subaerial weathering processes.

Stump: a reduced stack eroded at its base by marine processes and at its summit by subaerial weathering.

Wave-cut (marine) platform: wide, rock base of eroded cliffs that extends as cliffs retreat. Forms at inter-tidal zone between high and low tide in the area of maximum wave impact.

Wave-cut notch: point of maximum impact of destructive waves at the base of a cliff. Results in undercutting of the cliff face and subsequent rock fall.

The degree of natural erosion is affected by the components, processes and energy:

• Lithology: the nature of the rock at the coast
• Rock structure: the orientation, and degree of internal rock coherence (stability)
• Climatic environment: range of temperatures, intensity of rainfall, air pressure gradients.
• Energy inputs: high energy environments of strong winds, waves and currents versus low energy environments.