Encyclopedic Entry

Heed the warning signs.

Photograph by Andrea Diedrich, MyShot

Swim Safely
More than 100 drownings due to rip currents occur every year in the United States.

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.

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

beach

Noun

narrow strip of land that lies along a body of water.

Encyclopedic Entry: beach

contribute

Verb

to give or donate.

current

Noun

steady, predictable flow of fluid within a larger body of that fluid.

Encyclopedic Entry: current

dune

Noun

a mound or ridge of loose sand that has been deposited by wind.

Encyclopedic Entry: dune

feeder wave

Noun

wave that contributes to a rip current.

Great Lakes

Noun

largest freshwater bodies in the world, located in the United States and Canada. Lake Huron, Lake Ontario, Lake Michigan, Lake Erie, and Lake Superior make up the Great Lakes.

hurricane

Noun

tropical storm with wind speeds of at least 119 kilometers (74 miles) per hour. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region.

hurricane season

Noun

time of year when the risk of hurricanes is greatest. Atlantic hurricane season runs from June 1 to November 30.

inshore hole

Noun

sudden, deep depression in the seafloor that can form quickly.

lake

Noun

body of water surrounded by land.

low tide

Noun

water level that has dropped as a result of the moon's gravitational pull on the Earth.

marsh

Noun

wetland area usually covered by a shallow layer of seawater or freshwater.

Encyclopedic Entry: marsh

natural hazard

Noun

event in the physical environment that is destructive to human activity.

obstacle

Noun

something that slows or stops progress.

ocean

Noun

large body of salt water that covers most of the Earth.

Encyclopedic Entry: ocean

parallel

Adjective

equal distance apart, and never meeting.

pier

Noun

platform built from the shore and extending over water.

reef

Noun

a ridge of rocks, coral, or sand rising from the ocean floor all the way to or near the ocean's surface.

rip current

Noun

a strong flow of water running from the shore to the open ocean, sea, or lake.

Encyclopedic Entry: rip current

rip tide

Noun

strong current that runs along the surface of the ocean from shore to open sea. Also called rip current.

river

Noun

large stream of flowing fresh water.

Encyclopedic Entry: river

sand

Noun

small, loose grains of disintegrated rocks.

sandbar

Noun

underwater or low-lying mound of sand formed by tides, waves, or currents.

sea

Noun

large part of the ocean enclosed or partly enclosed by land.

Encyclopedic Entry: sea

sediment

Noun

solid material transported and deposited by water, ice, and wind.

Encyclopedic Entry: sediment

shore

Noun

coast.

silt

Noun

small sediment particles.

Encyclopedic Entry: silt

stream

Noun

body of flowing fluid.

surf

Noun

waves as they break on the shore or reef.

surf line

Noun

point in the ocean at which waves begin to break.

surf zone forecast

Noun

document produced by the National Weather Service that predicts the wave action of specific areas.

tide

Noun

rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.

Encyclopedic Entry: tide

topography

Noun

the shape of the surface features of an area.

undertow

Noun

underlying current of water that flows seaward from the shore.

wave

Noun

moving swell on the surface of water.

weather pattern

Noun

repeating or predictable changes in the Earth's atmosphere, such as winds, precipitation, and temperatures.

Credits

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Writers

Kim Rutledge
Melissa McDaniel
Diane Boudreau
Tara Ramroop
Santani Teng
Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt

Illustrators

Tim Gunther
Mary Crooks, National Geographic Society

Editors

Kara West
Jeannie Evers

Educator Reviewer

Nancy Wynne

Producer

Caryl-Sue, National Geographic Society

Sources

Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

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