Tsunami's are usually created by underwater earthquakes or volcanos.  Here you'll find brief animations that show how earthquakes and tsunamis are created and in some cases document actual tsunamis (example the 2004 and 1960 tsunamis) using computer animations.

What's an Earthquake?  (includes sound)

What's a TSUNAMI?  (with sound)

More detailed TSUNAMI info (includes satellite photos of the December 26, 2004 15+m high tsunami that killed 250,000)    (no sound)

NOAA Animation of the 2004 Indonesia Tsunami (silent)

This animation (2.3 MB), produced by Professor Nobuo Shuto of the Disaster Control Research Center, Tohoku University, Japan, shows the propagation of the earthquake-generated 1960 Chilean tsunami across the Pacific. Note the vastness of the area across which the tsunami travels - Japan, which is over 17,000 km away from the tsunami's source off the coast of Chile, lost 200 lives to this tsunami. Also note how the wave crests bend as the tsunami travels - this is called refraction. Wave refraction is caused by segments of the wave moving at different speeds as the water depth along the crest varies. Please note that the vertical scale has been exaggerated in this animation - tsunamis are only about a meter high at the most in the open ocean. (The QuickTime movie presented here was digitized from a video tape produced from the original computer-generated animation.)