Formation and Evolution of Headlands on Soft Cliff Coasts: Lessons from the Isle of Wight

The standard model of headland formation assumes a coastline with discordant geology where the less resistant rock is eroded at a higher rate than the more resistant geology. Once formed variations in rock strength and wave refraction balance out until the recession rate for the headlands and bays are equal and the indentation is maintained as recession continues. This paper presents new hypotheses on the formation and evolution of headlands on soft rock cliff coasts. These headlands appear to form behind localised intertidal shore platforms such as those seen on the southwest coast of the Isle of Wight. The longshore variations in platform elevation are controlled by geological structure and the geotechnical properties of the component lithologies. The presence of relatively resistant beds outcropping in the intertidal zone cause localised increases in the intertidal level. It is hypothesised that these intertidal platforms act to a) regulate the wave energy reaching the cliff base and b) block longshore transport of beach sediment building up a protective beach updrift and starving the down drift coast. The resulting longshore variations in recession rates will lead to the formation of a subtle headland. Once formed, the fate of these headlands is controlled by the balance between wave refraction concentrating wave energy towards the platform/headland feature and wave attenuation over the platform surface. If an understanding of how these localised intertidal shore platforms can effectively manipulate recession rates it may be possible to develop a low impact, non-intrusive coastal defence option.