Environmental Engineering Reference
In-Depth Information
equivalent of the Palaeozoic Capitan Reef (Texas/New Mexico) and Wenlock Edge reef
along the Anglo-Welsh border. The latter was formed when 'Britain' was located at 30° S
during the Silurian period 420 Ma ago.
Barrier coasts have developed in mid-Wales, East Anglia and south-east Yorkshire,
with substantial longshore drift associated with low tidal range coasts (Figure 17.11).
Chesil Beach (Dorset) and Dungeness are formed in part by the onshore migration of
offshore shingle bars. The southern North Sea and Baltic coasts of mainland Europe have
long offshore barriers impounding large lagoons. The most impressive barrier coastline is
found on the North American passive margin. It extends with few interruptions for over
7000 km from the Yucatan peninsula, around the northern Gulf of Mexico and along the
Atlantic coast from Florida to Massachusetts.
ROCKY COASTS
The review of coastal landsystems is completed by the least diversified but most
extensive, accounting for 75 per cent of all coastlines. Rocky coasts, unprotected by
barriers, face direct attack by the sea as it mounts the final assault on continental land
surfaces by sub-aerial processes. Wave erosion causes the coastline to retreat at rates
determined by effective wave energy and geological resistance. Wave conditions, tidal
influence and tectonic settings were described earlier. The erosion front is normally
marked by a cliff and a trail of residual land-system components marking its retreat
(Figure 17.12).
Assuming constant sea level, marine erosion is concentrated towards the cliff base and
may be represented initially by a
wave
-
cut notch
. This will eventually destabilize
overhanging rock to the point of failure and the
