March 21, 2011

Librarian Alissa Gonzalez wrote to me with a good question that I think many people are wondering about.

Dear Seymour: I read that many people, when receiving advanced warning of a tsunami, take their boats and sail out to sea to be safer (because the tsunami is only a huge, destructive wave at shore). I have been trying to explain this to someone with little success. Can you help me understand this better?

  Tsunami waves carry a huge amount of energy that is generated by the force of the earthquake.  When they are far out at sea, the waves are far apart, so that powerful energy is spread out over a broad space. The waves are not huge in height and may not even be very noticeable at a distance from a shore.

However, as tsunami waves get closer to shore, they pack closer together. That energy has to go somewhere, so it goes up, which means the height of the wave increases. The greater the height of the wave, the greater its destructive power, as it can wash over sea walls, over docks and boats, and even (as we saw in Japan) into communities where people live.

That’s why some sailors getting sufficient advance warning will take their ships out to sea to avoid having them crushed by the tsunami waves breaking on shore. 

Many readers have questions about earthquakes and tsunamis, and I have been writing often about them on the Seymour Science blog. You can read all about this subject by clicking on the label Earthquakes.



Posted by: Seymour Simon

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