If you’ve ever taken a bath or swum in a lake or pool, you’ve probably enjoyed creating your own waves. Unlike solid objects, water is fluid and easy to move around. The harder you push with your hands, the bigger the waves will be.

Now imagine what happens in the ocean when an earthquake occurs underground. If you’ve ever felt an earthquake or seen one on television, you know that they have the power to shake the ground and move large buildings.

When an earthquake occurs under the ocean floor, the earthquake’s massive energy is transferred to the water above it, creating a series of water waves called a tsunami. The word tsunami comes from the Japanese words tsu (harbor) and nami (wave).

In addition to earthquakes, tsunamis can be caused by other events that generate enough energy to displace a large volume of water, such as volcanic eruptions, landslides, meteors, and even underwater tests of nuclear devices. Given the frequent earthquake and volcanic activity in the Pacific Rim, tsunamis happen often in Japan.

Tragically, because of the huge amounts of water and energy involved, tsunamis can cause tremendous damage to coastal areas. On December 26, 2004, a massive earthquake in the Indian Ocean caused a series of devastating tsunamis along the coasts of the areas bordering the Indian Ocean. One of the deadliest natural disasters in history, waves up to 100 feet high crashed into coastal communities, killing over 230,000 people in 14 countries, including Indonesia, Sri Lanka, India, and Thailand.

You may recall the earthquake and tsunami that occurred in Japan on March 11, 2011. That tsunami resulted in mass destruction including a nuclear power plant that released radiation into the Pacific Ocean.   

Normal ocean waves created by the wind have an average wavelength (measured from crest to crest) of approximately 330 feet and an average height of about 6.6 feet. A tsunami, on the other hand, can have a wavelength of 120 miles or more. Traveling at up to 500 miles per hour in the deep ocean, a tsunami’s height might only be as little as 3 feet, making it almost impossible to detect, even for a ship in the area.

As a tsunami approaches a coastline, though, things begin to change dramatically. As it approaches shallow waters, an effect known as wave shoaling compresses and slows the wave to below 50 miles per hour. Wavelength also decreases dramatically, but amplitude — the height of the wave — increases greatly, leading to the unmistakable wall of water that causes such destruction along coastlines.

Approximately 80% of tsunamis happen in the Pacific Ocean, although they’re possible in any large body of water, including lakes. Tsunamis cannot be prevented and can rarely be predicted with precision. In the event of an earthquake, oceanographers, geologists, and seismologists often urge potentially-affected areas to issue tsunami warnings.

Regions that experience tsunamis regularly have developed tsunami warning systems to give as much advance warning as possible to people who live along the coastline. In Japan, for example, coastal communities are well-educated about earthquakes and tsunamis. Japanese shorelines feature tsunami warning signs and warning sirens atop nearby hills.

Although tsunamis cannot be prevented, some tsunami-prone countries use engineering lessons learned from earthquakes to reduce shoreline damage. Many Japanese coastal communities have built tsunami walls, floodgates, and channels to block or redirect water from incoming tsunamis.

One of the best ways to make a coast tsunami-proof, though, is quite natural: plant trees! Scientists noticed that some locations in the path of the 2004 Indian Ocean tsunami suffered little damage because trees, such as coconut palms and mangroves, absorbed the tsunami’s energy. In fact, one small Indian village saw little damage because the tsunami broke against a forest of over 80,000 trees that had been planted along the shoreline just two years earlier in an attempt to set a Guinness World Record.

32 Join the Discussion

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  1. This is really interesting, but tsunami’s are really really sad. Have you seen the one in Japan? :(
    But they are interesting at the same time! :)
    I can’t wait to see what the next is! I honestly have NO idea! :)

    • We’re sad about the tsunami in Japan, too, Abby. :-( Sometimes it helps to talk to a parent or teacher about how you’re feeling when something like this happens. It also helps to understand why the tsunami happened. We hope today’s Wonder will do that for the people who visit Wonderopolis!

      We’re sure glad you stopped by today! You’re an AWESOME Wonder Friend and we enjoy reading your comments!

    • We feel the same way, Christina! Remember you can always talk to a grown-up like a parent or teacher if you need to. Sometimes it helps to talk about it when sad things happen. Thanks for being a super great Wonder Friend!

  2. I read a book called Escaping The Giant Wave. It is such a good book about to kids who have to escape a tsunami. I think the tsunami in Japan was so sad.

    • Thanks for sharing about the tsunami book you read, Lily M/C!

      Yes, the tsunami was very sad. We can help by thinking good thoughts for the people of Japan, though, and talking about our feelings with a grown-up or our friends. It helps to talk about stuff when we’re sad. Thanks so much for visiting Wonderopolis today! :-)

  3. Hi! This is Lynn from Mrs. Caplin’s class. This wonder was very absorbing. I can’t believe that a tsunami moving at 500 miles per hour can be 3 feet or less in height! I remember last year, I read a book about a tsunami and it was very interesting. While reading this wonder, I also thought back to what the people in the book felt like during the tsunami, which helped me understand the wonder better!!

    I also didn’t know that tsunami means ”Harbor Wave” so that was new, as well. Now, I am wondering what scientific instrument do scientists use to measure how fast tsunamis are going without getting in the way of one? I knew that a tsunami was a deadly natural disaster, but this wonder helped show me that it is not only deadly, but it can hit many countries at once which is very interesting!!

    • WOW! You sure learned a lot from this Wonder of the Day®, Lynn! Thank you for sharing this comment with everyone in Wonderopolis! :-)

    • The destruction some tsunamis cause is really sad, we agree, kkf! Thank you for visiting this Wonder and for leaving us this comment to share your feelings!

    • It makes us super happy to know that you liked exploring this Wonder, Rithik! Thanks for letting us know and THANKS for being a GREAT Wonder Friend! :-)

    • Thank you for sharing your personal connection to this Wonder about tsunamis, Moa! That must have been a super scary experience for you and your family. We are thankful that you weren’t seriously hurt..we care about all of our Wonder Friends!

  4. Thanks for the great site for students. I love it! I am hoping to allow my students to all post comments using this e-mail account that I created for anyone in my class to use. Will that work, since many of the students do not have their own e-mail address?

    • Hi Miss Berg, thanks for introducing us to all your WONDERful students! They are more than welcome to comment using your email account. Thanks so much for asking and thinking ahead! We look forward to WONDERing with all of you! :)

  5. It’s amazing to see the video!!! Thanks. I knew this website from a teacher. She always posts things on this websites. I’m a big fan of this website. :)

    • Hey Zack! It was great to learn about how planting trees ahead of time can help prevent or minimize the damage from tsunamis, wasn’t it? Have you ever planted a tree with your class or family? It can have a lot more benefits plus be a lot of fun! What do you think? :)

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Have you ever wondered…

  • What is a tsunami?
  • How do tsunamis form?
  • Can tsunamis be prevented?

Wonder Gallery

wave-e1379768421356Vimeo Video

Try It Out

Like many types of natural disasters, tsunamis are fascinating because of their destructive power. Explore tsunamis in greater depth by checking out one or more of the following activities with a friend or family member:

  • When natural disasters strike, children of all ages are likely to have many questions they want answered. It’s natural for children to be curious. The National Center for Family Literacy offers some helpful tips for parents and teachers for how to discuss disasters with children. Read through these tips to learn how to discuss natural disasters in a way that will provide reassurance while teaching valuable lessons about the science of the world around us.
  • Another way to engage children in a helpful discussion about a disaster is to work with them side-by-side on a craft. With just a few simple supplies, you can create your own ocean in a bottle. Can you use this craft to summarize what you learned about tsunamis from today’s Wonder of the Day? What might a tsunami inside your bottle look like?
  • A more challenging way to discuss the science behind natural disasters is to explore the scientific principles at work through a science experiment. To better understand how ocean waves are created and behave, head to the kitchen, grab a few pans and try the Let’s Make Waves science experiment. Using this experiment, you can learn more about waves and how they’re created during a tsunami!


Still Wondering

Visit National Geographic Xpeditions’ Wave Heights lesson to learn about the varying heights of ocean waves and what causes the variation. Explore the parts of a wave and see how geography affects wave heights.


Test Your Knowledge

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