What is longshore drift caused by?

As a field expert in coastal geomorphology, I can explain the phenomenon of longshore drift. Longshore drift is the process by which sediments, such as sand or shingle, are moved along a coastline in the direction that the wind is blowing. This movement is primarily caused by the action of waves and currents, particularly when they approach the shore at an angle rather than directly. When waves approach the shore at an angle, they create a longitudinal current along the beach. The wave refraction causes the waves to bend around obstacles and head more directly toward the shore. As the waves break, they release their energy and push water and sediment back towards the ocean, creating a zigzag pattern of water movement known as a rip current. This back-and-forth movement of water results in the sediment being moved along the shore, a process we call longshore drift. The rate of longshore drift can be influenced by several factors, including the intensity of the waves, the angle at which they approach the shore, the shape and size of the sediment particles, and the topography of the coastline. In areas with strong wave action and a consistent wave direction, longshore drift can significantly alter the shape of the coastline over time.

The transport of sand and pebbles along the coast is called longshore drift. The prevailing wind (the direction the wind ususally blows from) causes waves to approach the coast at an angle. The swash carries the sand and pebbles up the beach at the same angle (usually 45o).