Tsunamis are primarily associated with earthquakes in oceanic and coastal regions. As the tsunami crosses the deep ocean, its length from crest to crest may be a hundred miles or more, and its height from crest to trough will only be a few feet or less. They can not be felt aboard ships nor can they be seen from the air in the open ocean. When the tsunami enters the shoaling water of coastlines in its path, the velocity of its waves diminishes and the wave height increases. The term tsunami was adopted for general use in 1963 by an international scientific conference.
Tides are the result of gravitational influences of the moon, sun, and planets.
Although tsunamis are usually generated by earthquakes, tsunamis are less commonly caused by landslides, infrequently by volcanic eruptions, and very rarely by a large meteorite impact in the ocean. Earthquakes generate tsunamis when the sea floor abruptly deforms and displaces the overlying water from its equilibrium position. Waves are formed as the displaced water mass, which acts under the influence of gravity, attempts to regain its equilibrium. The main factor which determines the initial size of a tsunami is the amount of vertical sea floor deformation. This is controlled by the earthquake's magnitude, depth, fault characteristics and coincident slumping of sediments or secondary faulting.