Rip currents are responsible for about 150 deaths every
year in the United States. In Florida, they kill more people
annually than thunderstorms, hurricanes
combined. They are the number-one concern for beach
lifeguards: About 80 percent of all beach rescues are related
to rip currents.
Despite these startling statistics, many swimmers don't
know anything about rip currents, and they have no idea how to
survive when caught in one. In this edition of HowStuffWorks,
we'll find out what causes rip currents, how you can recognize
them and what you should do if one takes you out to sea.
Misnomers A rip current is a narrow,
powerful current of water running perpendicular to the
beach, out into the ocean. These currents may extend 200 to
2,500 feet (61 to 762 m) lengthwise, but they are typically
less than 30 feet (9 m) wide. Rip currents can move at a
pretty good speed, often 5 miles per hour (8 kph) or faster.
These currents are often called "riptides," but this is a
misnomer. Tides are the rising and falling of water
levels in the ocean. They are primarily caused by the moon's
gravitational pull, and they change gradually and
predictably every day. Rip currents are caused by the shape of
the shoreline itself, and they may be sudden and unexpected.
Rip currents may also be referred to as "undertow," which
is just as inaccurate. Undertow describes a current of water
that pulls you down to the ocean bottom. Rip currents move
along the surface of the water, pulling you straight
out into the ocean, but not underneath the water's surface. A
rip current may knock you off your feet in shallow water,
however, and if you thrash around and get disoriented, you may
end up being pulled along the ocean bottom. But if you
relax your body, the current should keep you near the
Rip currents are terrifying because they catch you off
guard: One minute you're bobbing along peacefully in the surf,
the next you're being dragged out to sea at top speed. They
occur in all sorts of weather and on a wide range of beaches.
Unlike violent, crashing waves, you probably won't notice a
rip current until you're right in the middle of it.
In the next section, we'll find out what causes this
frightening phenomenon and see why it claims so many lives
Let 'er Rip Rip currents are anomalous
occurrences, but they are born out of ordinary, everyday
ocean waves. On the most basic level, you can think of
waves as travelling fluctuations in water level. Some
external force (usually the wind) pushes on the ocean,
creating a swell of water, which is passed along the ocean's
surface. The energy of the wave, which may be built up by
additional wind pressure, is passed from water molecule to
water molecule. The water itself doesn't actually travel; only
the energy keeps going.
Eventually, some waves meet up with land. In areas with a
rocky shore, the water surge "crashes" as it is deflected. On
a sandy beach with a gently sloping shore, the swell simply
pushes uphill. The climb up the beach drains all the energy of
the surge, and the water eventually flows downhill, back to
the ocean -- in other words, the water finds its own level
Ordinarily, this receding flow of water moves with
minimal force. The slight slope of the beach effectively
spreads out the force over a great distance, so it's not
particularly strong at any one point. And since it's weaker
than the opposing force of incoming waves, the receding flow
usually won't carry you out to sea.
A rip current occurs when the receding flow becomes
concentrated in a particular area at a particular time.
There a number of things that can cause this, but the most
common is a break in a sandbar. Sandbars are long,
narrow hills of accumulated sand along the outer part of the
shore. They are formed by the motion of waves and tides.
When a large sandbar forms, it can produce a sort of
basin along the ocean shore. Waves move up against the
sandbar with enough force to push water into the basin, but
the receding water has a hard time making it back over the
sandbar to return to sea. This is something like a bathtub
with the drain plugged up: Just as the water in a bathtub is
being pulled downward by gravity but is blocked by the drain
plug, the receding wave is being pulled outward by the ocean
(and by gravity), but is kept in by the sandbar.
A simplified version of a shore with a sandbar.
Sandbars sometimes peak out above the water, but more often
they will be submerged just below the
In some cases, the backward pressure of the receding water
may be strong enough to break through part of the sandbar.
Other times, the water flows along parallel to the beach until
it reaches a low point on the sandbar. In either case, the
water that has piled up in the basin rushes out to sea
once it finds an opening, just as the water in your bathtub
rushes out when you unplug the drain.
The resulting rip current sucks in water from the
basin and spits it out on the other side of the
sandbar. In the next section, we'll examine this water flow in
greater detail and find out what you should do if a rip
current pulls you out into the ocean.
Go with the Flow In the last section, we saw
that rip currents occur when water rushes through a low point
in a sandbar. Since waves keep pushing more water into the
basin between the sandbar and the beach, the rip current may
continue for several minutes, or even several hours. Some rip
currents are brief occurrences, but others are long-term
fixtures of an area.
Typically, the strongest part of a rip current is the
direct line between the water's edge and the sandbar
opening, but the current will also pull in water from either
side of the basin. In this way, a rip current might pull you
sideways, parallel to the beach, before it pulls you
outward, away from the beach.
Once the receding wave makes its way through the sandbar
opening and meets up with water at its own level, its
pressure immediately drops. Overall, the water flow
pattern has a mushroom shape.
Depending on its severity, you may be able to see a rip
current from the beach. Strong rip currents disrupt incoming
waves and stir up sand from the ocean floor. When you're at
the beach, keep an eye out for narrow, muddy streaks in
the ocean where there aren't any waves breaking.
If you get caught up in a rip current, it's crucial that
you keep your wits about you. Your first instinct may be
to swim against the current, back to shallow waters. In most
cases, even if you're a strong swimmer, this will only wear
you out. The current is too strong to fight head-on.
Instead, swim sideways, parallel to the beach (see
illustration below). This will get you out of the narrow
outward current, so you can swim back in with the waves
helping you along. If it's too hard to swim sideways while
you're being dragged through the water, just wait until the
current carries you past the sandbar. The water will be
much calmer there, and you can get clear of the rip current
before heading back in.
People drown when they thrash about in the water or expend
all of their energy swimming. To survive a rip current,
or any crisis in the water, you have to keep calm, and you
have to conserve your energy. If you don't think you can swim
all the way back to the beach, get past the rip current and
tread water. Call for help, signal to people on the beach and,
if all else fails, wait for the waves to carry you in.
If you're on the beach and see somebody else caught in a
rip current, call for help from a lifeguard or the police.
Don't immediately dive in and swim out to the person. It's too
risky to swim out there yourself unless you have a raft,
boogie board or life preserver with you.
The most effective way to fight rip currents is to follow
basic swimming safety rules: Never go in the ocean
alone, and if you aren't a strong swimmer, stick to
shallow waters (although even shallow waters can be
dangerous). Ideally, you should only swim in areas where there
is a lifeguard or strong swimmer on the beach who can keep an
eye on you.
To learn more about rip currents and ocean safety, check
out the sites listed in the Links section. If you plan to swim
in the ocean anytime soon, it's a good idea to learn
everything you can about rip currents. After all, they are the
beach's number-one killer.