How Do Rip Currents Work?

Rip currents are dangerous flows of water that can drag you away from the shore and out into the deep. Learn how they form, what to watch for, and how to escape one by swimming sideways or riding it out in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/environmental/earth/oceanography/rip-current.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff,
Lauren bobobum here. If you've been around beach is enough,
you've probably run across the sign at some point with
a warning to avoid a particular area because of a
rip current. Rip currents are responsible for about one hundred

(00:21):
and fifty deaths every year in the United States. In Florida,
they kill more people on average than thunderstorms, hurricanes, and
tornadoes combined, and they're the number one concern for beach lifeguards.
About eighty percent of all beach rescues are related to
rip currents. These scary statistics exist partially because lots of

(00:43):
swimmers aren't familiar with how rip currents work and how
to survive if you happen to get caught in one.
So today let's talk about all that and how to
hopefully avoid them in the first place. A rip current
is a narrow but powerful current of water running erpendicular
to a beach out into the ocean or lake. These

(01:04):
currents may extend hundreds of feet or meters outward, but
they're typically less than thirty feet or nine meters wide,
and they can move it a pretty good clip, often
five miles or eight kilometers an hour or faster, which
doesn't sound that fast until you consider that it's like
being dragged at a brisk jog by something that doesn't
tire out. A rip currents form when water gets blocked

(01:28):
in near a beach and then suddenly finds a way
back out to the open water and rushes out. They're
dangerous because they're unpredictable. This is different from ripped tides,
which happen like liquid clockwork, when the tide pulls water
out through an inlet or similar into the sea. They're
still dangerous and can be more powerful than rip currents,

(01:49):
but at least they're predictable. Always heed any warning signage
you see at a waterfront. Rip currents are also different
from undertoe. Undertow describe the water that washes back from
the shore where the waves break up on the land.
It flows underneath the next wave and may continue out
along the seafloor into the open water. Undertow is a normal,

(02:12):
continual feature of any body of water big enough to
have waves. It's what you feel when the receding water
pulls at your feet for a moment before the next
wave hits, but it's only strong right at the shoreline
and usually not dangerous to anyone but small kids who
might get knocked over. They can wind up below the
water line and struggle to get back up. Always keep

(02:33):
an eye on kids in the water. Rip currents, by contrast,
move along the surface of the water. They're so hazardous
because they catch you off guard. One minute you're bobbing
along peacefully in the surf, and the next you're being
dragged out to sea at top speed. They occur in
all kinds of weather and on a wide range of beaches.

(02:55):
Unlike a violent, choppy water, rip currents can look calm,
so you might not noticeable until you're right in the
middle of it. Rip currents are anomalous occurrences, but they're
borne out of ordinary, everyday waves. On a basic level,
you can think of waves as traveling fluctuations in water level.
Some external force off in the wind pushes on the water,

(03:18):
creating a swell, which is passed along the surface. The
energy of the wave, which may be built up by
more pressure from the wind, is passed from water molecule
to water molecule. The water itself doesn't actually travel much.
It mostly just bobs up and down, only the energy
keeps going until the swells reach the shore. In areas

(03:41):
with a rocky shore, the wave breaks as it's deflected.
On a sandy beach with a gently sloping shore, the
swell pushes up hill. The climb up the beach drains
the energy from the breaking waves, and the water eventually
flows downhill back to the sea as undertow. Normally, undertow
move with minimal force. The slight slope of the beach

(04:03):
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 into deeper water.
A rip current occurs when the receding flow becomes concentrated
in a particular area. There are a number of things

(04:26):
that can cause this, but the most common is a
break in a sand bar. Sandbars are long, narrow hills
of accumulated sand along the outer part of a shore.
They are formed by the motion of the waves and tides.
Some sandbars stay short, but some can build up pretty
tall and may even peak above the water's surface. When

(04:47):
a large sand bar forms, it can produce a sort
of basin along the shoreline. Incoming waves can rise up
over or move up against the sand bar with enough
force to push water into the basin, but the receding water,
moving the long the seafloor, has a hard time making
it back over the sandbar to return to the open water.
This is something like a bathtub with the drain plugged up.

(05:09):
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 coaxed to flow back off
shore by the undertow and gravity, but is kept in
by the sand bar. In some cases, the pressure of
the water trying to recede may be strong enough to
break through part of the sand bar. Other times, water

(05:33):
will flow along parallel to the beach until it reaches
a low point of the sandbar. In either case, once
it finds an opening, the water that's piled up inside
the basin rushes out to sea, just as the water
in your bathtub rushes out when you unplug the drain.
The resulting rip current pushes water from the basin through
the narrow opening and spits it out on the other

(05:55):
side of the sandbar. Because waves keep pushing more water
into the basin between the sand bar 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

(06:16):
the sand bars opening to the water's edge, but the
current will also pull in surrounding water from each 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 water
makes its way through the opening in the sand bar,
the pressure equalizes and the current will dissipate. You can

(06:38):
sometimes see rip currents from the beach. They disrupt incoming
waves and can stir up sand or sediment from the seafloor,
So keep an eye out for a narrow break in
the waves or for a column of froth or differently
colored water pushing off shore. If you get caught in
a rip current, it's crucial that you keep your wits
about you. A rip currents may knock you off your

(07:00):
feet in shallow water, and if you thrash or get disoriented,
you might end up being pulled along under the surface,
but if you relax your body and float, the current
should keep you near the surface. Your first instinct might
be too swim against the current back to shallow water.
In most cases, even if you're a strong swimmer, this
will only wear you out. Rip currents can be way

(07:22):
too strong to fight head on. Instead, swim sideways parallel
to the beach and out of the current. Think of
it like your wiley coyote. You want to run sideways
out of the way of the boulder and not try
to outrun it. If you can break sideways out of
the current, you can swim back to shore more easily
with help from the waves. But if it's too hard

(07:44):
to swim parallel while you're being dragged outward by the current,
just wait until it 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. If
you don't think you can swim all the way back
to the beach, get past the rip current and just
tread water. Call for help, signal the people on the beach,
and if all us fails, concentrate on floating and let

(08:05):
the waves help carry you in. People drown when they
expend all their energy brashing or struggling to swim. To
survive a rip current or any crisis in the water,
you have to keep calm and conserve your energy. If
you're on the beach and see someone else caught in
a rip current, call for help from a lifeguard or
emergency services. Don't dive in and try to swim out

(08:27):
to the person unless you are both very sure of
yourself and the situation, and you have a raft, buggy board,
or life preserver with you to give to the person
who's struggling. The most effective way to fight rip currents
is to follow basic swimming safety. Never go in deep
water alone, and if you aren't a strong swimmer, stick
to the shallows. Ideally, you should only swim in areas

(08:49):
where there's a lifeguard or other strong swimmer on the
beach who can keep an eye on things. Today's episode
based on the article what is a ripcurrent? On HowStuffWorks
dot Com written by Tom Harris. Brain Stuff is production
of iHeartRadio in partnership with how stuffworks dot Com and
is produced by Tyler Klaange. For more podcasts from my

(09:11):
heart Radio, visit the iHeartRadio app, Apple podcasts, or wherever
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