Tidal waves are not ordinary waves. They are caused by some disturbances on the ocean floor. They don’t have anything to do with wind and tides. They are known as Tsunami, which is a Japanese word.
Usually, earthquakes on the ocean floor cause these waves. An earthquake on the ocean bottom produces a shock wave that travels through the water, with the same speed as that of sound. During the earthquake, the oceans floor shifts and slides. It is this motion and the shock of the disturbance that produces tidal waves.
In the beginning, they swell or rise just like an ordinary wave. Then the sea level falls for a few minutes, as if it were a low tide. And then, suddenly the great tidal wave comes in and begins at once to move across the sea at a great speed. They are known to have speeds ranging to 700 miles per hour. They can rise up to even more than a hundred feet in the air and can be very disastrous. They wipe out hundreds of villages and bring a great loss of life and property on the coastal regions through which they pass.
Below Tsunami info from Wikipedia (Read More):-
A tsunami (津波?) (pronounced /(t)suːˈnɑːmi/) is a series of water waves (called a tsunami wave train[1]) that is caused when a large volume of a body of water, such as an ocean, is rapidly displaced. The Japanese term is literally translated into "harbor wave."
Earthquakes, volcanic eruptions and other underwater explosions (detonations of nuclear devices at sea), landslides and other mass movements, bolide impacts, and other disturbances above or below water all have the potential to generate a tsunami. Due to the immense volumes of water and energy involved, the effects of tsunamis can be devastating.
http://en.wikipedia.org/wiki/Tsunami
