Tsunamis

Tsunamis are commonly refered to as tidal waves, harbor waves, and seismic sea waves. They are usually caused by earthquakes beneath the ocean surface but, can also occur due to submarine landslides or volcanic eruptions. These physical distrubances propagate long low waves which relates to small amplitudes and broad wavelengths. Waves heights ranging from 1-30 meters are fairly common but extreme cases such as Ryukyu islands (south of Japan)have experienced waves of up to 85 meters. At this proportion, these waves could have a devasting impact on a large area of land.

Tsumanis are unlike ordinary water waves on the ocean surface. "A large wind-generated wave may have a wavelength of 400m and be moving in deep water at a speed of 90km/hr. The wave height when it breaks on shore may be only .6 to 3m. Although in the middle of hurricanes the waves can be more than 15m high. A tsunami, however, may have a wavelength of 160km, and may be moving at 725km. In deep water the wave height may be only .6 to 2m, but near shore the tsunami may peak up to heights of 15 to 30m. This great increase in wave height near shore is caused by bottom topography; only a few localities have the combination of gently sloping offshore shelf and funnel-shaped bay that forces tsunamis to awesome heights"(McGeary, Plummer Physical Geology (1992).

In depth background discussion on Tsunamis in the Pacific
Hear da waves