You're out on the open sea, wind in your hair, salt on your lips. Maybe you're hauling up fishing nets, singing a shanty, or tying some knots. Then suddenly, out of nowhere, a 35 meter high sweet-holy-mother-of-mermaids wall of water!

This is a thing that really happens, folks, and it's not a tsunami. It's a rogue wave.

(SciShow theme)

By definition, a rogue wave is greater than twice the height of surrounding waves. Technically that could be a five meter wave rolling with some shorties, or it could be a 30 meter nautical nightmare.

Though long feared by mariners, most oceanographers thought tales of rogue waves flipping ships and snatching keepers from their lighthouses were just yarn spun by imaginative or possibly drunk sailors. Until New Year's Day 1995 when far out in the North Sea a freak wave slammed into the Draupner Oil Platform off Norway. A wave-measuring device measured it at 25.5 meters high, about the size of an eight-story building. This was the first scientifically documented occurrence of a rogue wave, and it blew some minds.

Rogue waves are different from tsunamis, which are caused by a mass displacement of water from something like a landslide, earthquake, or shift in the ocean floor. Tsunamis roll in steadily and aren't dangerous until they approach shore. If you're sailing in the open ocean, you might not even notice a tsunami sliding by. But you will definitely notice a rogue wave. It sneaks up like a big salty ninja, sinks your ship, and then vanishes again. And the thing is, even though thanks to satellite imagery and fancy oceanic instruments we now know that deep water rogue waves occur on a semi-regular basis, we still aren't sure exactly how they work.

We know that wind blowing across water creates steady waves, and the stronger the wind, the bigger the waves. Irregular waves can form when a strong ocean current collides with waves moving in the opposite direction of the current. These currents can condense, or focus those waves, shortening their frequency and compressing them together into giant killers.

Rogue waves are fairly common off the coast of South Africa where the Agulhas Current intersects with opposing trade winds and things get a little messy. But sometimes, these bizarre waves form far away from such currents and no one is sure why.

One theory suggests that, since swells travel at different speeds, faster waves may chase and eventually climb over the slow ones, piggy-backing into one really big wave. But others believe that in certain unstable conditions a wave can actually suck energy from its neighbors, reducing their size while growing into an enormous freak, kind of like the Highlander.

It's difficult to create such water waves in a lab, so researchers are experimenting using light and micro waves. Ultimately, this research could save a lot of lives, and also money. As many as a hundred large ships are mysteriously lost at sea each year, and yeah, maybe some  of those fall prey to ghost pirates or become kraken fodder, but many are likely lost to rogue waves. The better we understand these sneaky freaks the better we can forecast and withstand them.

Thanks for watching this episode of SciShow! If you have any questions, comments, or suggestions for us, you can find us on Facebook or Twitter or of course down in the comments below, and if you want to keep getting smarter with us here at SciShow, you can go to youtube.com/scishow and subscribe.