Beaches and Dunes

Beaches are the classic depositional landform of a coastline, but they are far less permanent than they look. They form wherever the sea is actively dumping material rather than eroding it, and their character can change dramatically with the seasons.

Most of the sediment that builds a beach does not come from the sea at all. It is carried down to the coast by streams and rivers, or it is produced by the waves themselves as they erode the shore. This is why beaches appear even along rugged, rocky coasts — as scattered patches where deposition happens to win out over erosion.

A beach is a temporary feature. The broad, sandy stretch you see in one season may be stripped back to a narrow band of coarse pebbles in another, as wave energy shifts. Most beaches are made of sand-sized material, but not all. Where the sediment is coarser, you get what are called shingle beaches, made up of very small pebbles and even cobbles.

Just behind the beach, the story continues. The wind lifts and winnows sand from the beach surface and deposits it inland as sand dunes. Along low, sedimentary coasts, these dunes commonly build up into long ridges that run parallel to the coastline — a signature feature of such shores.