What Is a Rip Current? 5 Images to Help You Recognize and Escape One

The Editor says: Every summer, crowds flock to the beach — and accidents spike along with the crowds. Rip currents are one of the most common causes of those accidents. Even seasoned beachgoers like us at BlueTrend can't always spot one at a glance. Follow along as we use five images to explain exactly what a rip current is and what to do if you get caught in one. <Full article reprinted from Hong Caiyang's Facebook post>

How Waves Form

Wind, gravity, the Coriolis force from Earth's rotation, ocean currents, seafloor friction, and a host of other forces push seawater toward the shore. The combined effect causes water to move toward the coastline in a circular motion. In deeper water, wave amplitude is small; but where the seafloor rises or suddenly becomes shallow, a large volume of water surges upward. The wave crests in the upper layer travel faster than the wave troughs in the lower layer, causing the waves to break — producing the white foam you see on the surface (as shown in Figure 1).

An Uneven Coastline

Coastlines are rarely straight. Where the shoreline bulges outward, the seafloor is usually relatively shallow (because that area is more resistant to erosion), and breaking waves tend to form there. Conversely, areas along the shore where waves rarely break correspond to deeper water.

When large volumes of water surge onto the beach, that water must eventually flow back out to sea. Because the "convex" sections of the shoreline are constantly fed by breaking waves, the water naturally retreats through the deeper "concave" sections — and that retreating flow is what we call a rip current (as shown in Figure 2).

What Is a Rip Current?

A rip current is an extremely powerful flow of water. When tidal conditions align, or where the depth difference between shallow and deep areas is especially pronounced, even strong swimmers will find it nearly impossible to fight against one. In Figure 3 below, notice that these dangerous rip currents form precisely in spots that look, at first glance, calm and safe — places where there are no breaking waves.

What to Do If You Get Caught in a Rip Current?

If you are swept into a rip current, do not panic — and do not try to fight it. Rip currents weaken as they move farther from shore. Refer to Figure 4 below, which is a simplified diagram of a rip current and the accompanying longshore current. Once a rip current travels a certain distance from shore, it is compressed and converged by the longshore current on either side, forming a flow structure that resembles a "neck" and a "head." The area outlined with black dashed lines represents the "neck." Swimming sideways out of the neck — going with the flow to either side — is how you escape a rip current.

If the water is clear and you are on a sandy beach, take a look at the seafloor — you will see ripple marks in the sand (see Figure 5 below). Because of inertia and the circular motion of waves, these ripple marks run parallel to the shoreline. Remember what we said earlier: the "convex" sections of the coastline tend to generate breaking waves that push water toward shore, while the "concave" sections tend to generate rip currents that pull swimmers out to sea.

So when you can see the bottom, calmly look for the line connecting the crests of those ripple marks. Try to swim toward the nearest crest line by exiting the rip current at its weakest point — the "neck" or "head." Once you reach that line, the incoming breaking waves will carry you back to shore on their own, without any exhausting struggle on your part.

You might wonder: how do you know whether you're at the neck or the head of the rip current? Simple — the neck is roughly at the same depth as the longshore current, which corresponds to the depth where you can see waves on the surface just beginning to form white foam.

Once you have escaped the rip current, swim out at a 45- to 90-degree angle relative to the current direction — either diagonally or perpendicular to it — and let the breaking waves carry you safely back to shore.

Summary

Before entering the water, observe the shape of the coastline. The more frequently it alternates between convex and concave sections, the greater the chance that rip currents are forming off the concave areas.
Before getting in the water, take a moment to read the current direction and the wave patterns. Deep water doesn't produce white breaking waves — especially avoid swimming near any straight, wave-free channel like the one shown in Figure 3.
If you are unfortunately caught in a rip current, relax your body. Don't struggle and don't fight it. Wait until the current carries you to the depth where waves are just beginning to break, then try swimming parallel to the shoreline to one side.
The head of a rip current is typically only 10 to several hundred meters wide — and often just a few dozen meters. Floating calmly outward and then escaping to the side is actually not that difficult. There's no need to panic.
If you can see ripple marks on the seafloor, quickly locate a line of crest points and swim toward it. Follow that direction and the natural current will help guide you back to shore.

Finally, three quick reminders:

Whenever possible, swim only at beaches staffed by lifeguards. No matter how confident you are in your swimming ability, if something goes wrong and no one around you notices, the outcome can be tragic.
Many swimming and water-safety courses are offered during the summer. You don't need to learn how to rescue others — but Taiwan is surrounded by rivers and ocean, so you should at least learn enough to keep yourself safe and avoid panicking in the water.
If any danger arises in or near the water, your first priority is to call out loudly and draw the attention of those around you. Only then focus on applying whatever self-rescue techniques apply to your situation.

海編"布魯陳"

我是布魯陳，平常喜歡帶著大相機下海找生物，如果你有海洋議題歡迎找我聊聊，約我吃飯更歡迎！