Block quarry at the cliff
Abraded platform, inactive in the foreground, with storm beach and stripping of weathered sandstone
Block lift from the crest of small cuesta
Blackened and pitted surface on a relatively stable part of the platform
Shore platform processes
Significance: shore platform in many parts of the world are slow to
change. The high wave energy environment of the exposed outer coast of Orkney
provides high rates of erosion and allows the main processes which shape these platforms
to be identified.
At the base of the cliff is a storm beach, comprising cobbles and boulders of
mainly rounded sandstone clasts but with occasionally large angular blocks.
This passes seaward into rock surfaces which are neither frequently nor intensively abraded today. Although some rock surfaces may be smoothed they are blackened with Verrucaria maura and pitted by weathering. Small cuestas show no clear smoothing and a blackened and inactive dip slope and loss of blocks from the scarp face. Scars with little or no lichen cover shows sites of recent block removal. Block transport is from W-E, as show by the carry of blocks of distinctive size or lithology.
Towards the low water mark seaweed cover becomes extensive but evidence of recent block loss from scarp faces is provided by fallen and transported blocks in strike gulleys.
Processes of erosion
On the generally flat-lying Devonian sandstones and flagstones of Orkney and Caithness there is a strong association between platform width and the height of backing slopes. Platforms are wide and extensive wherever gentle slopes back the shore. This suggests that rock mass strength is the dominant control over platform extent. A corollary inference is that wave energy in even sheltered locations is or was sufficient to mobilise blocks from fissile lithologies, such as flagstone.