Shore Platform , S and Mass Movement : a Note L

Shore platforms and mass movement phenomena are important elements in the coastal scenery of the British Isles. Both features are particularly well developed along the English Channel coast. Where mass movement is of major importance it tends to inhibit the exposure of shore platforms. Under certain conditions it may temporarily protect the platform from further erosion. The factors which encourage the formation of shore platform and mass movement differ. Mass movement appears to be a secondary process, and does not seem to participate directly in either the primary formation of the shore platform or in its subsequent evolution; In a recent article (Earth Sci. 1nl, Vol. 2, No. 1) McLean and Davidson suggest that along the Gisborne coastline of New Zealand there is a genetic connection between the distribution of mass movement phenomena and shore platforms. Work by the present author on the shore platforms of the coasts of Britain does not confirm this observation. In fact the reverse situation is more common, shore platforms frequently being absent from, or at least only poorly developed along coastal areas dominated by large-scale, discrete types of mass movement such as falls, flows and slides. Along the English Channel coast areas with such well developed larg~-scale , mass movement features are quite sharply demarcated. A particularly large complex slide occurs between Dover and Folkestone at Folkestone Warren. Good examples are also to be found around the Isle of Wight, especially at Bouldnor on the northern coast of the island and at Undercliff on the southern coast. It is, however, along the Dorset and East Devon coast that major mass movement features are best displayed. Along the South Dorset coast they occur near St. Albans Head and Chapman's Pool, at Houns-tout. Gad Cliff and along the cliffs in Ringstead Bay. Further examples occur around the northern part of the Isle of Portland, and they reach their finest development along the predominently Lias Limestone cliffs of the West Dorset and East Devon coast (Fig. 1). Almost all cliffs, however, are subject to change by mass movement processes of very local extent. The Chalk cliffs of the Isle of Thanet, the South Foreland, the Seven Sisters, and their westward extension to Brighton provide almost annual examples of rock falls and yet the cliffline is not dominated by them, remaining for the most part a sheer, near-vertical face, with the scars and talus cones essentially of secondary significance. On these cliffs and others, small scale mass movement phenomena, involving fragments that weigh ounces and pounds rather than tons, and have a volume measured in cubic inches rather than in hundreds of cubic yards, also occur. Following a frost the fall of such miniscule fragments is particularly pronounced, the process being particularly effective during the cold winter of 1962/63. (Whether they are quantitatively more important in effecting cliff retreat awaits