A tsunami is a series of waves that is created when a large volume of a body of water, such as an ocean, is rapidly displaced. The Japanese term is literally translated into "(great) harbour wave."
Earthquakes, volcanic eruptions and other underwater explosions (detonations of nuclear devices at sea), landslides, bolide impacts, and other mass movements above or below water all have the potential to generate a tsunami. Due to the immense volumes of water and energy involved, the effects of tsunamis can be devastating.
The Greek historian Thucydides was the first to relate tsunami to submarine quakes, but understanding of the nature of tsunami remained slim until the 20th century and is the subject of ongoing research.
Many early geological, geographical, and oceanographic texts refer to tsunamis as "seismic sea waves."
At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacing the ground. When a large earthquake epicenter is located offshore, the seabed sometimes suffers sufficient displacement to cause a tsunami. The shaking in earthquakes can also trigger landslides and occasionally volcanic activity.
In its most generic sense, the word earthquake is used to describe any seismic event—whether a natural phenomenon or an event caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by volcanic activity, landslides, mine blasts, and nuclear experiments. An earthquake's point of initial rupture is called its focus or hypocenter. The term epicenter refers to the point at ground level directly above the hypocenter.