A rip current forms when part of a longshore current is drawn away from the coast – perpendicular to the beach.
Courtesy of NOAA
Currents at the Coast
Ocean waves often move towards a beach at an angle. This moves water along the coast in a longshore current. Longshore currents grow stronger when the waves come towards the beach at a large angle. The currents also are stronger if the waves are very large, and if the beach has a steep slope.
Longshore currents move sand along the beach, eroding it from some areas and depositing it in other areas. This process is called longshore drift and it is able to, over time, move entire islands in the direction of the current. Places with longshore drift need new maps made as the shape of the coastline changes over time.
Longshore currents can carry more than just sand. They can carry people too. Thus, these currents can be very dangerous for people swimming in the ocean. Rip currents that carry swimmers into deep water form when part of a longshore current moves away from the beach. This happens usually where there is a change in the shape of the seafloor.
The water in a rip current moves fast - at one to two feet per second and some are as fast as eight feet per second. If a person swimming is caught in a rip current, they will be swept far from shore. But because rip currents only happen in small areas, usually not more than 25 meters (80 feet) wide, swimming parallel to the shore should get the person out of the current.
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