The processes of wave refraction leads to the creation of bays. On coastlines with alternating soft and hard rock, differential erosion occurs. This means that erosion occurs at different rates. The soft rock is eroded more quickly than the hard rock. An example of hard rock is sandstone and an example of soft rock is limestone. The process of the formation of bays and headlands can be seen along the coastline of the Cork and Kerry.
The sea picks out weaknesses in the rocks and it is eroded. Where hard rock is present erosion is resisted and headlands develop. Consequently, headlands and bays are usually found together. Abrasion and hydraulic action erode a bay. Abrasion is caused by stones, rock and other eroded debris being hurled against the coastline by powerful waves. Hydraulic action is the sheer force of the water as it rushes against the coastline.
A beach will be deposited in the bay by the process of refraction. As waves approach the bay, wave energy is concentrated on the headlands. Most of the wave energy is used up before the waves enter the bay. Since the waves have less energy, they deposit material rather than remove it and so a bay-head beach forms.