Monday, March 14, 2011


By now everyone has to know that the English translation for tsunami is "harbor wave", but a tsunami isn't just one wave. The most dramatic video we're seeing out of Japan this week is of the crest of the first wave roaring over land, but a tsunami is a series of waves; it's a series of pulses of water. A dripping faucet creates the same conditions in your bathtub: the drop displaces the water it falls into, and the energy of that displacement lifts water in concentric circles moving out from where the drop falls. You see it when you toss a rock into a pond: a single rock triggers multiple ripples.

And the water coming ashore is not the water that was displaced at the site of the earthquake. 2-D depictions of how the mechanism works make it look like the sudden uplift of the ocean floor raised a bolus of water at that spot which then raced to shore. But what happens is that the shift transfers energy into the water above it, then the energy travels through the water; the water itself stays where it is. If you've ever swum out past the breakers and floated on the ocean swells behind them, you understand how the energy of the waves lifts and flows through you, but you and the water stay, pretty much, in the same place.

Austin Public Library's collection of books about tsunamis has swelled, as you can imagine, since the 2004 Boxing Day Tsunami in Sumatra.

And give this blog post about earthquakes another read.

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