A rip current is a strong flow of water running from a beach back to the open ocean, sea, or lake. They can be more than 45 meters (150 feet) wide, but most are less than 9 meters (30 feet). They can move at 8 kilometers (5 miles) per hour. Rip currents are one of the most dangerous natural hazards in the world. The United States Lifesaving Association (USLA) estimates that 80 percent of its rescues are related to rip currents.
Rip currents are sometimes confused with undertows. Undertows are also currents, but they run along the ocean floor and can pull beachgoers beneath the waters surface. Rip currents run along the surface of the water, and do not pose the same hazard.
Rip currents are also known as rip tides. This is an inaccurate name. Strong tides, especially low tides, can contribute to the strength of a rip current, but rip currents really have nothing to do with tides. Rip currents can occur on almost any beach with breaking waves.
Rip Current Formation
Rip currents are formed by a beachs topography. Topography is the surface features of an area. Rip currents can occur in areas with hard-bottom (rocky) or soft-bottom (sand or silt) beach topography.
A beachs topography includes the area outside the water, such as dunes or marshes. Beach topography also includes the area within the water, like sandbars, piers, and reefs. Rip currents often form around these parts of a beachs topography.
Rip currents can form in a gap between sandbars, piers, or parts of a reef. Such underwater obstacles block waves from washing directly back to sea. The water from these waves, called feeder waves, runs along the shore until it finds an opening around theobstacle.
The stream of water, now a rip current, rushes to the opening, just like water down a drain. A rip current flows more quickly than the water on either side of it, and may stir up sediment from the beach. This sometimes makes rip currents easy to spot as dark or muddy lines running from the beach out toward the ocean. Rip currents are also usually more calm-looking than the surrounding water. Once past the obstacle (between the sandbars or piers), a rip current loses pressure and stops flowing.
Beaches without breaking waves, like those on most lakes or rivers, do not have rip currents. Every beach with breaking waves, including beaches on large lakes like Lake Superior in North America, can develop rip currents.
Beaches that suffer from strong weather patterns, like hurricanes, can develop the most dangerous rip currents. As hurricanes develop far out at sea, they create strong waves that crash into the shore with great force. These waves can build up sandbars and create inshore holes. Inshore holes are deep depressions in the ocean bottom. Strong waves, deep inshore holes, and sandbars can create powerful rip currents. In places like western Australia and the U.S. state of Florida, strong rip currents are one of the first signs of an approaching hurricane.
Rip Currents and People
The strength of rip currents can be seasonal. During hurricane season (from June to November) there is a greater chance for rip currents to develop. The U.S. National Weather Service issues a Surf Zone Forecast in many beach areas. These areas include Boston, Massachusetts (on the Atlantic Ocean), Duluth, Minnesota (on Lake Superior), Brownsville, Texas (on the Gulf of Mexico), and Honolulu, Hawaii (in the Pacific Ocean). The Surf Zone Forecast predicts the strength of waves and includes a Rip Current Outlook. The Rip Current Outlook advises swimmers of the risk (high, moderate, or low) of rip currents on an areas beaches.
Surfers often take advantage of rip currents for a ride out to sea. Rather than using energy to paddle, they will find a rip current and coast along on their surfboard. Rip currents lose their power at the surf line, the area where waves begin to break. Surfers can coast out to the surf line on a rip current and wait for the perfect wave.
A swimmer caught in a rip current can be in much more danger than a surfer. The United States Lifesaving Association (USLA) recommends that swimmers who find themselves in a rip current do not try to swim back to shore. Even strong swimmers are unlikely to be able to swim against the current. They are much more likely to find themselves exhausted, an even more dangerous position.
The USLA advises swimmers caught in a rip current to swim parallel to shore. Rip currents are usually narrow enough to be escapable this way. Floating along the current past the surf line (where the rip current disappears) is also an option, but that can be a long way from shore. Swimming back might require a lot of energy.
