大象传媒

Features formed by longshore drift are explained and illustrated. The formation of coastal sand dunes is also discussed. Longshore drift carries material along a beach in a zigzag fashion in the direction of the prevailing wind. The swash carries material both up and along the beach while the backwash only carries material down the beach. Longshore drift is the cause of a spit forming at the mouth of a river. Where a spit grows across a bay, a bar is formed. Where water flows in behind this, a lagoon is formed. A bar extending out to an island creates a feature called a tombolo. Onshore winds can also create depositional features. Where sand is blown inland, obstructions cause the sand to build up forming dunes.