Abrasion can happen when any material moves against another one. It happens when stones rub against the bed of a river, when sand is blown against a rock in a sandstorm, and when rock carried by ice in the bottom of a glacier rubs against the rock over which it is flowing.

Abrasion produces fine material that is easily carried by water, ice or wind. It is of silt size, a size between sand and clay.


In mountains

In certain circumstances, abrasion can be very severe. This is the case, for example, when rock fragments get caught in the bottom of a glacier. As the glacier moves down its valley, the weight of the ice grinds any rock fragments against the valley floor. This wears away the floor of the valley, often also chipping out more fragments at the same time. These chippings make new rock fragments to continue with abrasion.


In rivers

Rivers carry fine rock particles (called sediment) that wear away, or abrade, the banks and bed of the river channel. At the same time, stones bump together, gradually grinding one another down and making the stones smaller and more rounded. This is called attrition.


In coasts

During a storm, breaking waves can throw sand and sometimes pebbles against cliffs. At the same time the sand and pebbles bump together as they are rolled about by the waves on the beach, making them finer and more rounded. This is called attrition. This is how pebbles become worn down to sand.