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Most tsunamis are caused by underwater earthquakes at subduction zones, where one of the plates that make up Earth’s crust is slipping beneath another. When sections of plates that have been locked together suddenly give under the strain, the seafloor can snap upwards or downwards.
When the seafloor moves, the water moves, too. Waves travel across the ocean and grow taller as they approach land where, sometimes, the water recedes from the shore as it is drawn back under the approaching wave.
The Effects of a Tsunami
The December 26, 2004 tsunami was spawned by one of the most powerful earthquakes ever measured.  The magnitude 9.3 temblor caused the entire planet to vibrate as much as half an inch. Had the necessary network of sensors been in place in the Indian Ocean, it would have detected a wave moving at the speed of a jet plane—more than 500 miles per hour.
Though its strength dissipated, the wave radiated far beyond the Indian Ocean.
Continue to Surviving Tsunamis. >>
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