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How do tsunamis develop?

A tsunami is a huge wave in the ocean that develops as a result of an earthquake.  It can reach a height of 100 feet (30 meters).  A tsunami can travel even faster than a commercial jet.  This powerful wall of water reaches the coast and can cause a lot of damage. 

Usually, it is an underwater earthquake that causes a tsunami to develop.  This happens when the plates underneath the Earth's surface move so that one slips under another.  From deep in the ocean the energy of the earthquake causes the water level to rise above sea level.  Gravity causes the water to spread into a wave that travels at an incredible speed and with amazing power. A tsunami gets bigger as it gets closet to shore.  When it hits shallow water the huge wave travels more slowly.  The water from along the shore moves into the ocean, and then the massive wave crashes into the shore and keeps traveling inland.