Headlands and bays are commonly found in coasts that have alternating bands of resistant rocks and less resistant rocks.

A bay in Northern Ireland

Formation of headlands and bays

The shoreline may be straightened through a process called wave refraction.

When waves approach a coast with headlands and bays, they slow down after hitting the headlands first. Thus, the wave front becomes curved (wave refraction).

With a curved-in wave front at the headlands, erosion takes place as the energy of the waves is concentrated. On the other hand, there is a curved-out wave front at the bays, so deposition takes place as the energy of the wave is spread out.

Thus, after a long period of time, the shoreline would become straighter.