An equilibrium profile is reached when platform retreat and cliff retreat occur at the same pace. However, shore platforms protruding into the sea also focus wave energy by wave refraction, which can partly offset the wave attenuation function. Cliff and shore platform both retreat by erosional processes the rate of cliff retreat strongly depends on the width of the shore platform. Wave attenuation on the shore platform reduces cliff recession rates. These shore platforms result from cliff retreat the outer edge marks the cliff position in the past – often millennia ago, in the case of erosion-resistant rock.
In many cases cliffs are fronted by shore platforms, which can be tens to many hundreds (or even thousands) of meters wide. A common coastal cliff morphology is the slope-over-wall profile: a rounded weathered top and a vertical wall below. Such more rounded (often vegetated) cliffs, are called “bluffs”. Some rocky coasts consist of steep plunging cliffs this is observed when subaerial erosion is minor compared to marine erosion or in cases of volcanic activity or tectonic subsidence.Ĭliffs which are degraded by subaerial weathering processes are more gently sloping. This diversity depends, among other things, on mineralogy, lithology, tectonic history, climate, waves and tides. It is estimated that about half of the world's coastline is backed by a cliff. Form and height depends on the type of rock - 'hard' rock (metamorphic, igneous and sedimentary rocks) and 'soft' rock (earth cliffs). Sea cliffs owe their existence in some way to erosion by the sea. A more precise characterization of sea cliffs is a break in slope between 15 degrees and the vertical, variable in height, found at the contact between the land and sea. Pat DoodyĪ cliff is defined in the Oxford English Dictionary as "a steep rock face, especially at the edge of the sea".
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