What causes rip currents?
Swimmers beware, the red flag is up and the currents are ripping. Surfers, enjoy the easy paddle out.
What causes this current that pulls things in its path out to sea? In general, the answer is waves, but we can be more specific.
A common type of rip current forms when waves break and push water onshore. It can't pile up there forever, since the weight of the water tries to push it back out to sea. The ocean, being efficient (or lazy if you prefer), finds the easiest way out, often through a break in the sandbar or reef. The water rushes out of this gap, pulling surfers and swimmers out rather quickly
But rips don't always need a conveniently placed gap in the seafloor. In fact, even if the bottom was perfectly uniform along the shore, rip currents can still form as long as you have waves.
When multiple swells are in the water, which is often the case, the waves interact and can peak up into those lovely A-frames. Since waves only really move water towards the shore when they're breaking, water can start to pile up just inshore of the wave's peak.
After a set of these waves, a lot of water has accumulated in a relatively small section of the beach, and the ocean does its best to level everything out. So, water goes sideways, and then out. These types of rips are called transient rips, since they change location over time. When those A-frame waves break a little further down the line, the same process happens over there, potentially causing a rip where you've been posted up.
If you pay attention to the shore during some sets, you can see how the waves are pushing you away from the point that just broke or continuously down the line.
Both of these rip types are dangerous for swimmers, leading to over 100 deaths per year. The ocean is powerful, and that's always something to think about. In my own experience freediving and doing surf photography, I've had a couple of bad rip experiences, where I could see that I was moving backwards while trying my best to get to shore between reefs. It's a humbling reminder of the ocean’s power when you have to resort to going over the falls a few times to get in.
Understanding rip currents isn't just about safety - it's a total game changer for paddling out. Rips are especially powerful near structures like piers and jetties, where water can't move alongshore and is pushed out to sea. Next time you're at the beach, try to spot these offshore flows and figure out what's causing them. Look for areas where the waves aren't breaking as much, or where you see debris or foam moving steadily seaward.
If you're paddling out and suddenly find yourself making suspiciously good progress, congratulations - you've found one. Used wisely, rips are a great option to get outside with dry hair.
Further Reading: