What causes a longshore current?

• A. Waves striking the coast at an angle
• B. Wind blowing parallel to the shore
• C. River discharge into the ocean
• D. Submarine canyons

Answer: (A)

A longshore current is primarily caused by waves striking the coast at an angle. When waves approach the shore, they often do so at an angle rather than directly head-on. This results in a movement of water parallel to the coastline as the waves break and then recede. This angled impact creates both a swash—a water flow moving up the beach—and a backwash—a water flow returning to the sea. The net result is a current that flows along the shore, known as a longshore current. This phenomenon is significant because it can influence sediment transport along the coastline and significantly affect coastal erosion and deposition processes.

The other options do not accurately describe the main cause of longshore currents. Wind blowing parallel to the shore can create surface currents, but it does not create longshore currents in the way that waves do. River discharge can alter coastal ecosystems and sediment distribution in estuarine environments, but it does not create distinct longshore currents. Submarine canyons are underwater geological features and do not directly contribute to the formation of longshore currents either. Thus, the angle at which waves strike the coast is the foundational reason for the development of longshore currents.