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"Why does the water level drop before the tsunami hits? Because it is like a tide, the tide goes out before it comes in. Traditionally we used to call these features ‘tide waves’ because they behave like a tide. The water particles haven’t traveled from the epicenter of the earthquake, they have oscillated back and forth and the tidal flow does just the same. As the tsunami approaches water is drawn back from the beach to effectively help feed the wave. In a tide the wave is so long that this happens slowly, over a few hours. In a short small ‘wind wave’ we see it happening every few seconds as we dodge waves on the beach. A tsunami is short enough to have a rapid effect, in minutes, but long enough to carry enormous energy."
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