CoastView - shoreplatform
General description of the shoreplatform
A gently sloping shore platform usually extends seawards from the base of the cliffs for up to 200 m, to below the low water mark. The upper part is frequently covered by sand or shingle but the rest is a bare chalk platform. The platform is most steeply sloping in the vicinity of Eastbourne and Beachy Head, where it reaches a gradient of 4° (1:14).35 In some places the platform is smoothly sloping but elsewhere it descends in a series of steps up to 1 m in height, sometimes capped by a band of flint. The platform surface is often dissected by systems of runnels that deepen seawards. Water movement is concentrated along these runnels during the rise and fall of the tides.
Retreat of the cliffs is accompanied by lowering of the platform surface, and backwearing of the steps and seaward margins of the platform. In 1981 - 2, Ellis measured the lowering of the platforms between Brighton and Newhaven at 44 sites, and found that rates varied from 1 mm to 10 mm per year, with an average of 3 mm per year. Most of the lowering occurred in the winter months.
Lowering and backwearing have many causes. Large pieces of chalk are sometimes broken off either by frost action or the pounding of waves, and exceptionally severe frosts can break up the whole surface of the platform.37 Limpets and other molluscs dissolve the surface of the chalk with their secretions while some bore deep tunnels into the surface. Solution of the chalk, and wetting and drying in the presence of salt, helps weaken the surface which, in some places, becomes soft and slimy. In stormy weather the sea often turns milky with suspended particles of chalk removed from the platform.
Recent investigations of the shore platform of East Sussex have been carried out in the ESPED-project (see a summary report on european shoreplatforms) and two student dissertations have investigated erosion around groynes and in runnels.
Photographic evidence (time-series) for shoreplatform erosion and seasonal vegetation change can be found in the section on contemporary coastal processes.