I am about going to the beach, and a lot of people are warning me to watch out for rip currents, but I don’t know why they occur or why they are so dangerous.
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All that water coming in from waves flows back to the ocean, but it doesn’t flow back out the way it comes in. Water will take the easiest path downward back to the ocean and when enough water is doing that it forms what amounts to a river. That river has all the water from those waves concentrated in one place, and it’s flowing the opposite direction of the waves out into the sea. This is a rip current – and it’s dangerous because of how strong it can get and how it can pull weak swimmers out into deep water fast. But if you are a good swimmer and get caught up in one, don’t panic, and swim parallel to the shoreline to get out of the ‘river’ and back into the water flowing towards the shore. And don’t ever use big floatation devices in the ocean, because those are much more likely to get caught in a current and impair your ability to swim.
EDIT: I incorrectly said “ripe tide” [which is a different but similar phenomenon](https://www.wboc.com/news/local/worcester/rip-currents-and-rip-tides-whats-the-difference/article_1c956c1d-1da1-50a4-9818-c48fef63fc03.html#:~:text=Rip%20currents%20are%20narrow%20currents,pulls%20out%20of%20an%20inlet).
A lot of rip currents happen when the shore forms a U or V shape. Even a small variation can make a difference. When the wave comes in it comes at a straight line. Now, as the line – hits the curved parts of the U the water continues going forward and a little bit in, the water is deflected in a little then continues forward. Once the water hits the furthest inland portion, it has accumulated a lot more water in that area and all has to go back out. Since there isn’t anything blocking the way, a large current of water flows back out straight from this point (the bottom of the U in my example).
To be clear, it doesn’t have to be a U shape, just a section where the shore is curved and will redirect the flow to the center of the curve.
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Basically, there’s a sandbar out from the beach itself, which creates a sort of lagoon. Waves crash over the sandbar, and overfill the lagoon. The extra water blows a hole in the sandbar and rushes back out to sea.
The currents are dangerous because they’re hard to spot, and very strong. People who get caught in them realise they’re being washed out to sea and panic, trying to swim back to shore. It’s effectively impossible to beat the current so they get exhausted and drown.
The key to surviving a rip, if you’re caught in one, is to either allow yourself to be carried all the way out (a few hundred metres at most) and then swim back (avoiding the rip) or to swim parallel to the shore, as rip currents are very narrow (maybe ten or twenty metres) and once you’re free of it you can swim back to shore.
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