How tsunamis happen
Tsunamis occur when a powerful quake shifts the seafloor, displacing water. Friday's disaster unleashed large fires in Japan.
March 11th, 2011
02:25 PM ET

How tsunamis happen

The power of water can be so destructive it can kill thousands of people in seconds with little warning.

The U.S. is lucky that it knew about a threat of a tsunami and had hours to prepare and evacuate following Friday's massive earthquake in Japan.

Japan was inundated with as much as 30 feet of water shortly after the 8.9-magnitude quake. Residents had about a 15-minute warning to get to higher ground. The death toll is already in the hundreds and still rising. Tsunami warnings were issued for the entire Pacific basin.

When a powerful earthquake moves the seafloor and displaces water, it spawns a tsunami, a series of waves that can travel through the water for thousands of miles at speeds up to 600 mph.

That's as fast as a jetliner.

We know how and why these things happen, but what scientists don't know is how big the waves will be when they arrive, how far apart they will be and which of the series of waves will be the largest. Often, the first tsunami wave isn't the biggest.

Tsunamis can't be seen from the air or felt on a ship. They are different from wind-whipped and tidal waves. Tsunami waves are shallow water waves, so there isn't a great difference between the average height of the deep open water and the height of a tsunami.

That changes when the tsunami reaches shallow water and land. The wave grows taller depending on the coastline. The waves can get especially high in harbors and bays as water gets funneled and lifted up from the seafloor.

It can be compared to the storm surge in a hurricane, but on a much larger, faster and forceful scale.

Friday's quake was the fifth most-powerful earthquake since 1900, according to the U.S. Geological Survey.  It is natural to compare this disaster to similar events in history. Who can forget the horrific Sumatran earthquake and tsunami in 2004 that killed nearly 300,000 people? The Chilean earthquake and tsunami last year is also fresh in most people's minds.

But it's been decades since the U.S. has seen casualties as a result of a tsunami.  In 1964,  11 people died in Crescent City, California, after a tsunami off Alaska. In 1960, 61 people in Hawaii died after a 35-foot tsunami followed an earthquake in Chile. In 1946, 159 people were killed in Hilo, Hawaii, after an Alaskan quake.

It's clear the U.S. will face this threat again, and there's no question deaths will occur when a big enough tsunami develops. It's scary to think about such things.

Since we can't predict when an earthquake will happen, we don't know if it will be days, weeks, months or years before another tsunami hits.

All we can do is plan "what if" scenarios and try to educate people that evacuating inland to higher ground is critical, and sometimes you only have time to evacuate "up" or to a higher floor in the building.

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Filed under: 2011 tsunami • Earthquake • Japan • Natural Disasters • Tsunami • World
soundoff (29 Responses)
  1. michael meetze

    is the world gme end

    March 11, 2011 at 8:06 pm | Report abuse |
  2. Brain Turdgion

    Brilliant! thank you Marie..and here I thought earthquakes caused them,your work here speaks for its self.

    March 11, 2011 at 9:02 pm | Report abuse |
  3. mb1972

    I think the tsunami happened because of a combination of George Bush perforating the planet with oil wells and global warming. Also, I bet their is a race aspect since Asians were dispropionately affected.

    March 11, 2011 at 10:40 pm | Report abuse |
    • Wonder Woman

      Are you serious or facetious? I'm afraid to ask which. I'll hope for the latter because the former is just so incredibly dimwitted and ignorant to think otherwise. Ever heard of science? Geology? Tectonic Plate Theory? Ring any bells? I just not.

      March 11, 2011 at 10:52 pm | Report abuse |
    • Ron Richards

      Wonder Woman really thinks you have a problem. Say it ain't so, Joe!

      March 11, 2011 at 11:19 pm | Report abuse |
    • Cassandra

      Lmao where the heck is the like button??? Rofl. That was funny. I believe he was being facetious guys.

      March 12, 2011 at 12:55 am | Report abuse |
    • Craig

      LOL on the Katrina reference.

      March 12, 2011 at 4:02 am | Report abuse |
    • Tom

      Don't barf, mb1972, these people are not representative of the human race. Aw, nuts. I hoped that if I said it, I'd believe it, but I don't. Watch out - Ima gonna tossa my cookies.

      March 12, 2011 at 8:42 am | Report abuse |
  4. GeorgeJones


    March 11, 2011 at 11:05 pm | Report abuse |
  5. lostinspace

    Wonder Woman, is your sarcasm detector not functioning? Mine is pegged and my BS Meter is really acting up also.

    March 11, 2011 at 11:21 pm | Report abuse |
  6. Annexian

    Heh, and a Tsunami alert system was (is!) one of the things on the "Toothpaste Budget" chopping block...

    March 12, 2011 at 12:10 am | Report abuse |
  7. Srich1213

    This blog thread is a failure. Refresh and let us try again, CNN

    March 12, 2011 at 12:13 am | Report abuse |
  8. PS

    CNN could post a story on how cute kittens are, and somehow the comments at the bottom would eventually decompose into a name calling match between the 'right' and the 'left'.
    Life must be tough these days in the US. How does anything ever get done? Can anyone in the US exist outside the context of religion/politics?
    Looks like you guys are turning into a never ending subjective argument. Makes me sad..... You guys used to be the cool kids on the block. Now you're the crazy cat lady.

    March 12, 2011 at 6:03 am | Report abuse |
    • Tom

      Sorry we disappoint you. I guess you'll just have to be satisfied with our technology, our generosity towards people beset by natural disasters, our higher-education system, our healthcare system (unless O'care becomes permanent law), our (often-disgusting but always popular) entertainment industry, our tolerance for diversity (compared to the Far East, the Middle East, Northern Africa, Sub-Saharan Africa, Western Europe, Eastern Europe, and Latin America), our willingness to pay huge amounts to support the UN, an organization that hates us, etc., etc., etc.

      March 12, 2011 at 8:51 am | Report abuse |
    • Jim

      PS, I'd definitely hit the "Like" button if there was one. Great observation from an outsider. Most Americans have no idea how we appear to the rest of the world, nor do they care. I read and watch BBC and other media sources to get another objective opinion. Thanks.

      March 12, 2011 at 9:52 am | Report abuse |
  9. PS

    In response to Tom above: thanks for helping me prove my point.
    Hey, my comment wasn't meant as a personal attack. You were able to run off a few things worthy of accolades that you should be proud of; you and your people are capable of great things, that's no doubt. It's just unfortunate that your Government has created an environment where, to use your term " tolerance for diversity" is unlikely. It would just me nice to see you guys get along, and actually have a reasonable conversation with each other (left/right).
    Then maybe you can get back to doing some of those great things you were talking about.

    March 12, 2011 at 9:07 am | Report abuse |
  10. vik

    strange, no mention of chuck norris cannonballing as a cause

    March 12, 2011 at 10:58 am | Report abuse |
  11. Arblu

    Why you people fight here everyone leave the own opinion and go away geez.... The end of the world it's pretty close and who brings that the bad people ... Let's pray and do better for God sake!

    March 12, 2011 at 11:10 am | Report abuse |
  12. ed Bailey

    Praying makes it ok to die cause you have already faced it!Craig you got my attention as j. Foxworthy would say. People like you restore my very dim view of civilation. Hope you on my jury when it time! Good speed to ya!

    March 12, 2011 at 3:30 pm | Report abuse |
  13. ed Bailey

    Bread, crap no cake?

    March 12, 2011 at 3:35 pm | Report abuse |
  14. bobcat

    No cake ed

    March 12, 2011 at 3:40 pm | Report abuse |