Cliff

A cliff is a steep or near-vertical slope that forms where the land surface drops sharply. Cliffs occur in many settings: along rocky coasts, beside rivers and lakes, in mountains, and in dry regions. Their shape depends on the rocks and on the processes that wear them away. At a coast, waves can erode the base of a rock face, while rain, frost, temperature changes, and gravity weaken the upper parts.

Over time, pieces of rock may break away, causing the cliff to retreat inland. A cliff does not have to be completely vertical, and its height can range from a few metres to several hundred metres. Some cliffs are made of hard rock that resists erosion, while others develop where layers of softer material are removed more quickly.

The boundary between a cliff and an ordinary steep slope is therefore not defined by one universal height or angle. Cliffs can also form when rivers cut down into resistant rock or when tectonic forces lift and fracture the ground. Their faces may contain ledges and cracks, while plants grow where soil and moisture collect.

The shape of a cliff records the combined effects of geology, weathering, erosion, and gravity. In some places, its retreat leaves a rock platform, a valley wall, or isolated blocks. Because these processes act at different rates, a cliff changes gradually even when the change is too slow to notice from one day to the next.