Dunwich – Geology
Dunwich is now nothing more than a very small village on the coast of
Suffolk. Yet it was once a great port and one of East Anglia’s most important
trading centres. Its demise has not been a result of war or famine but
rather the very make up of the area – its geology. The shoreline
has moved inland by over 500m in the last five hundred years and the
process continues, but why?
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A fisherman's hut clings to the edge of the cliff at Dunwich (2005) |
The coastal cliffs at Dunwich are made up of soft Tertiary and Pleistocene
clays and sands easily eroded by the sea.
Stretching for about a mile down the coast, Dunwich cliffs are fronted
by a shingle beach (frequently recharged) which provides some protection
from
sea erosion, but the sea is remarkably close to the cliff and the slightest
storm waves on a high tide inevitably result in more undermining of
the fragile and loosely held together materials of the cliff.
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Dunwich beach with huts.
(old post card)
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Two types of erosion affect the cliffs of Dunwich; soil creep and gulley
erosion.
Soil creep - an almost imperceptible movement of individual particles
down a slope over a long period of time.
The yellow sand particles in the cliff swell when it rains, lifting
them at right angles to the slope direction. When dried out, they
shrink again,
but the influence of gravity pulls the particles vertically down.
Whilst soil creep cannot be observed, its effects can often be observed; a few years ago bones were seen sticking out of the edge of the cliff, presumably from a grave in one of the church graveyards. The sandy soil
forms terracettes (or lobes) at the base of the slope, where it has begun
to pile up.
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Dunwich Cliffs
Terracettes are formed at the base of the cliff by the effects of soil creep.
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Gulley erosion – deep V shaped drops in the cliff face with a fan-shaped
scree slope below.
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Dunwich cliff
Planting local grasses does go some way towards holding the cliff edge.
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The red sands on the southern part of the cliffs are more fertile and despite planting grasses the cliff face remains very unstable and there is a lot of gulley erosion in the winter months, made worse by drainage over the top of the cliff.
Please be aware that walking close to the edge of the cliff is very dangerous as even a footfall can result in a cliff fall. |
