The Chalk Coast of Sussex

Abstract

The Chalk coast of Sussex is a celebrated landscape comprising vertical or near-vertical cliffs, fronted by fringing flint-gravel beaches and extensive shore platforms. The unprotected cliffs are retreating rapidly at a long-term average of ~0.35 m year−1, primarily through intermittent local mass failures of varying dimensions. The Chalk is composed of several formations with different physical and mechanical properties that impact on both the character of the failures and the resulting cliff profiles. The rate of cliff retreat varies along the cliffs and appears to have changed over decadal and much longer timescales. The cliff-foot beaches are composed of a combination of grey flints derived directly from erosion of the Chalk and browner flints, excavated from the Chalk long ago and subsequently incorporated into later deposits from which they have been re-excavated. Erosion of the cliffs and platforms is insufficient to maintain the beaches and they are dwindling in volume. The shore platforms slope seaward at angles between 1° and 4° and display a seaward zonation in micro-topography. They are being lowered at an average rate of ~0.4 mm year−1 by a combination of chemical and mechanical, marine and sub-aerial processes, and through bioerosion. In addition, they undergo layer stripping through step erosion and block detachment. The coastline is protected from future development by incorporation in the South Downs National Park, but faces threats from updrift development affecting littoral drift, and potential increased storminess and rising sea levels due to climate change and continuing isostatic adjustment.