Tsunamis are distinct from ordinary wind-driven ocean waves and are giant waves caused by earthquakes, volcanic eruptions under the sea or even by landslides in the coastal zones or by meteorites that fall dow in the oceans. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. However as the waves travel inland, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves (adapted from NOAA).
Tsunamis by NOAA