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Tsunami

Author(s): Deanne Erdmann, MS, and Nancy Moreno, PhD

Tsunami Size and Speed

Normal, wind-generated deep ocean waves and tsunami waves differ in the length and in the amount of time that passes between successive peaks (tsunami waves can be as far as one hour apart). Regardless of type, a wave will lose energy at a rate inversely proportional to the wave's length. Because tsunami waves can exceed 100 miles in length, they can travel for long distances with very little energy loss. Thus, they still retain most of their energy when they reach land. Tsunami speed is related to the depth of water. In deep ocean waters, tsunami wave velocities can reach 600 mph. The speed decreases as the waves approach the shore; however, the waves compress and increase dramatically in amplitude as they enter more shallow water. Waves that would be barely noticeable in the open ocean may reach heights of 100 feet near landfall.