As a tsunami leaves the deep water of the open ocean and travels into the shallower water near the coast, it transforms. If you read the “How do tsunamis differ from other water waves?” section, you discovered that a tsunami travels at a speed that is related to the water depth – hence, as the water depth decreases, the tsunami slows. The tsunami’s energy flux, which is dependent on both its wave speed and wave height, remains nearly constant. Consequently, as the tsunami’s speed diminishes as it travels into shallower water, its height grows. Because of this shoaling effect, a tsunami, imperceptible at sea, may grow to be several meters or more in height near the coast. When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide, a series of breaking waves, or even a bore.
Tsunami Warning Centers
Pacific Tsunami Warning Center -Areas of responsibility - warnings for Pacific basin teletsunamis to almost every country around the Pacific rim and to most of the Pacific island states. Interim warning center for Indian Ocean, Caribbean Sea & South China Sea
West Coast/Alaska Tsunami Warning Center - Areas of Responsibility - U.S. West, Alaskan, Atlantic, Puerto Rico, Virgin Islands, and Gulf of Mexico coasts as well as the east and west coasts of Canada