The word tsunami comes from the Japanese term tsu-nami, meaning "harbor wave". A tsunami is a series of strong waves that is caused by movement in the seafloor. Tsunamis are mostly caused by earthquakes, but they can also result from landslides that fall into the sea, volcanic acitivity or meteorite strikes. 

A tsunami sets the water mass of the sea in movement. A wave caused by a tsunami can be hundreds of kilometers long and even 10–30 meters tall. A tsunami wave can move at a speed between 500 and 900 km/h. The speed of the wave depends on the depth of the sea in which the tsunami originates.

As the tsunami moves towards the shore, its speed decreases but its waves grow taller. Tsunami waves cannot be evaded by running.

The destructive capability of a tsunami is caused by its strong current, which can even move cars. Gently sloped beaches are extremely suspectible to tsunami damage, as the water can move further inland.

Nowadays, many countries use tsunami warning systems that give a signal whenever a large earthquake occurs in the seafloor. After this, sea levels are studied near the origin of the earthquake, and the tsunami warning is either given or cancelled depending on this information.