Definition: a rock ridge that juts out to sea, allowing erosion of the sides and the head of the promontory

Standard models of coastal erosion refer to the opening of caves in headlands along lines of weakness, their extension to form tunnels and arches and the collapse of arches to form stacks to give a sequence of change. On many coasts it is rare to find good examples of this model but the relatively rapid rate of coastal erosion on Shetland provides numerous examples of headlands that are progressively tunnelled to seaward and which have arches and stacks standing offshore. Papa Stour, in particular, show a wonderful array of tunnelled headlands, partially unroofed caves, arches, geos and stacks.