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One of my favorite parts about going to the beach is watching the ocean.  When Squeaks and I visit, we like to sit for a while just watching the waves splash against the rocks and sand, and sometimes, when it's hard for Squeaks to fall asleep, he'll listen to sounds of the ocean waves to help him relax and get sleepy.  Most waves are like that, small and calm, but once in a while, there's a really extreme kind of wave.  It's called a tsunami or sometimes a tidal wave or seismic wave, and it's huge.  

The wave can be taller than a house.  Tsunamis usually only happen in the part of the world near the Pacific Ocean and there are only one or two a year, but they make a big splash.  Regular ocean waves aren't usually very big and they follow a pattern.  The water moves back a little bit and then it rises up into a kind of half circle shape and splashes onto the shore.  During a tsunami, the water does something similar but it moves much more.  The water pulls far away from the beach, going back and back until, whoosh, the water comes zooming back in all at once as a giant wave.

Yeah, it's really strange to imagine.  Tsunamis don't happen a lot because a lot of different things need to come together to cause one.  It all starts way out in the ocean with a big movement on the ocean floor.  Good question, Squeaks wants to know what could make the ocean floor move around like that.  Well, earthquakes do that sometimes, and it can also happen when underwater volcanoes erupt.  Yes, there are volcanoes underwater and when something like an earthquake or a volcano makes the ocean floor shift quickly, it pushes water out of the way super fast.  That's called displacement.  The water gets moved to a different place.  It's what creates the waves.  It's just like when you drop an ice cube into a glass of water or even when you get into the bathtub.  You displace the water and the moving water creates waves.  But when the ocean floor moves around, that creates much bigger waves than just dropping an ice cube into a cup of water, and the waves get bigger and bigger as they get closer to shore.

A tsunami wave can grow almost 30 meters tall.  Way taller than most buildings!  When a wave that big hits the shore, it can be very powerful and smaller waves can follow behind the first one, bringing in a lot of extra water.  The water can flood whole towns, covering houses, schools, and everything else for a while.  Eventually, the water pulls back into the ocean and sometimes, it'll take things with it, like trees or cars.  That's some strong water.

Tsunamis can be dangerous, Squeaks, but we have lots of ways to know when a tsunami might happen and to stay safe when they do.  Some scientists have earthquake sensors that can tell them when there might be enough displacement to cause a tsunami.  When they know a tsunami could happen, they send messages to the people that live by the beach so everyone in town can go somewhere safe, and if there are people on the beach, they'll see the ocean start to pull very far away, getting ready for that big wave, so that's a clue to get to safety.

Where do people go?  Well, to stay safe during a tsunami, the best thing to do is to move somewhere high above the ocean so that the tsunami and the flooding afterwards won't be able to reach you, but thankfully, tsunamis don't happen a lot and there are lots of scientists keeping an eye out just in case.  That way, we get to safely enjoy the ocean.

Have you ever been to the ocean?  What else would you like to learn about it?  Have a grown up help you leave a comment below or send us an email to kids@scishow.com.  Thanks, and we'll see you next time here at the Fort.

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