Wave heights in deep ocean water may be only a few feet and pass under ships with little disturbance, but in shallow coastal waters wave heights can reach 100 feet with devastating impact on local shipping and shoreline communities. Successive crests may arrive at intervals of every 10-45 minutes and wreak destruction for several hours.
The Pacific coast of the United States is at greatest risk from tsunamis, primarily from earthquakes in South America and the Alaska/Aleutian Island region. For example, the 1964 Alaska earthquake generated tsunamis up to 20 feet in height along the coasts of Washington, Oregon, and California and caused extensive damage in Alaska and Hawaii. The death toll from these tsunamis was 122 compared with only 9 nearer the epicenter of the earthquake itself. Tsunamis are clearly the leading earthquake-related threat to the inhabitants of Hawaii. More recently, tsunamis triggered by earthquakes accounted for the majority of the deaths and serious injuries in Nicaragua (1992), northern Japan (1993), and Indonesia (1992 and 1994) (54-56).