There is a wide spectrum of tsunami caused by different geological phenomena ranging from earthquakes to submarine sediment flows, rockfalls, volcanic eruptions, landslides and smaller but more frequent meteorite impacts. Historical and geological records indicate that these phenomena can producing tsunami ranging from the barely perceptible to waves fifty to a hundred metres high and capable of destroying everything up to ten kilometres inland from the coastlines that they impact. Furthermore, tsunami are not "third world" disasters: major tsunami capable of causing thousands of deaths strike the Japanese coastline on average every few decades. Other tsunami, produced on the opposite side of the Pacific ocean, have propagated nearly half way around the world and caused near-simultaneous tsunami disasters in places as widely separated as Japan, Hawaii and California.

Nor is the Pacific rim the only region to have been affected by tsunami: a tsunami generated by an earthquake in 1755 destroyed large parts of Lisbon and Cadiz, and geological evidence suggests that collapsing volcanoes in the Canary Islands have generated tsunami which crossed the Atlantic and hurled 2000 ton boulders up 30 metre high cliffs in the Bahamas. In this century alone other tsunami have occurred in places ranging from Norwegian fjords to Greek islands. Tsunami have impacted what are now highly-developed coastlines in the past and will do so again in the future: the only difference is that their effects will extend much further inland than their physical extent, because these coastal areas now contain infrastructure elements such as port facilities and power plants whose destruction or damage can cause massive indirect economic losses.