Where is the seaward edge? A review and definition of shore platform morphology

Shore platforms are erosional coastal landforms that have attracted scientific attention since the mid 19th century. The defining element of a platform is width that is used in many calculations such as determining a platform's evolutionary state or inferring how wave energy is distributed along the shore. Although a critical variable, there are no uniform criteria for defining the seaward edge. Quantification of platform width has been driven by site-specific variables, with the seaward edge defined on the basis of tides, morphology, biology, processes and sediment coverage. The lack of a uniform definition has meant that comparative studies are difficult and results are possibly spurious, as widths derived from very different criteria can vary by an order of magnitude just on the basis of which criteria is used to determine its edge. In this review a combination of morphologic and process elements is used to define the seaward edge of a shore platform. The development of strict criteria is especially needed in an environment of rising sea levels if measurements of landscape change are to be made. In addition, the advent of seamless datasets that cross the land–sea boundary means that the delineation of platform morphology is no longer limited by physical access. This review concludes that the seaward edge of a shore platform will occur at or landward of wave base and should be defined as: the point where active erosion of the bedrock ceases, characterised by erosional features such as notches and block-plucking scars or the deposition of sediment of such a thickness that the underlying bedrock is not exposed during storm events.