Most people are familiar with the idea of the sea eroding or destroying land. For example, storm waves can remove rock from many coasts. Some loose rock is swept out to sea, but some is moved along the shore. Groynes, or sea walls, which jut out from the coast in many resorts, are built because of this movement. Without them, the waves would periodically remove the beaches.
In places where the coast changes direction, however, as at headlands, the waves often drop their loads and form new land. The long fingers of sand, gravel and pebbles dumped by the waves are called spits. Some spits join two headlands, creating lagoons. Others link the mainland to islands, forming natural bridges.