A tsunami (pronounced soo-NAH-mee) is a set of ocean waves that are most commonly generated by earthquakes in coastal regions. When an earthquake occurs, the vertical shifting of ocean and continental plates essentially stir up energy within the ocean and this results in the large or long-lasting waves we call tsunamis.

 

Tsunamis appear as rapidly advancing or receding tides or bores, which are giant walls of water. Unlike regular waves, tsunami waves do not break as they arrive on shore, and instead behave more like flood waves, rushing inland for a period of time before receding.

 

Predicting when a tsunami will happen is difficult, but once an earthquake occurs, scientists can map when and where a tsunami will arrive using deep-ocean data. This is useful in warning people who live inland on a tsunami’s path.

 

Source: NOAA.gov's Tsunami page