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'Soft' rock sea cliffs
Softer rocks are general formed from unconsolidated material which is relatively
easily eroded. Two forms can be identified:
- Structures where undercutting creates pressure resulting in rotational slips.
These may be large or small and can occur in limestones and shales which are
more prone to erosion than 'hard' rocks;
- Glacial deposits and some younger sedimentary rocks such as chalk and more
recent Tertiary clays can be eroded relatively easily. Rapidly eroding rocks
such as mudstone and 'soft' sandy glacial material.
The rates
of erosion determine the nature of the vegetation and associated
animals that develop. On the softest sediments erosion may be very rapid such
that virtually no vegetation develops and the surfaces are in a constant state
of movement (State
1, mobile cliffs). Where the rate of movement slows and more stable
structures can develop on the cliff slopes then a semi-stable state (State
2) can be defined. These semi-stable cliffs are frequently protected
by artificial structures, leading to an increase in stability (State
3). Where rotational slips occur that remain stable for some time,
scrub and even woodland can develop, leading to a stable cliff (State
4).
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