The coast is where the land meets the sea or ocean. Some coasts are shaped by the action of waves crashing against them. The rocks are gradually worn away, sometimes creating cliffs, the steep edge between the land and the sea. Bays are carved out where the coastal rocks are softer. In other places, the sea shapes the coast by piling up sand and shingle to make new land.

Wave erosion

Hard rocks erode slowly. They stand out as headlands. Waves wear away softer rocks more easily. The waves undercut cliffs by gnawing away at the bottom, causing them to collapse. Eventually, a small cove widens into a bay.

​​​​​​​A cliff gradually “retreats” after more and more rock is worn away by the waves. A flat area forms at the base of the cliffs, called a wave-cut platform. It may become covered by sand or shingle, forming a beach.​​​​​​​

Sometimes waves may carve a hole, called an arch, right through a headland. If the roof of the arch later collapses, part of it is left standing alone in the sea. This is called a stack.

Beaches

Rocks worn away from a coastline are ground down by the pounding waves into fragments: shingle or sand. Sea currents carry sand and shingle from one part of the seashore to another. When the current slows, the sand or shingle is laid down. A spit may form across a bay or estuary. If it reaches right across to the other side, it forms a bar.