Coves form on concordant coastlines, where bands of rock of varying strength run parallel to the coast. Typically these will form where a narrow band relatively strong rock, like limestone or an igneous rock forms the coastline, with a band of a weaker rock, such as clays and sands, behind it. Often another band of strong rock, such as limestone or chalk will form the back of the cove. The action of waves in weak areas, such as joints and cracks, in the band of rocks which form the cliffs eventually break through the strong rock, exposing the weak rock behind. The weak rock is quickly eroded by wave action, sub-aerial processes and weathering (which causes slumping). Wave refraction occurs where waves travel through the narrow entrance and then disperse in the cove. Erosion is therefore equal at all points of the cove shoreline, and the perfect curve or circular shape is formed.