Tidal waves actually have nothing to do with tides, and nothing to do with ordinary ocean waves. Find out what causes them on this Moment of Science.
Ordinary ocean waves are caused by the action of wind, like ripples on a wind-blown pond. Even the impressive surf of the Pacific got its start as wind blowing across the open water. The height of such waves depends on how fast the wind is blowing, and how much open water the wind travels across.