What is tsunami ?

A tsunami is a series of waves that occur in an ocean or other large body of water and that are caused by some activity that displaces large amounts of water. Tsunami is the Japanese word for "harbor wave."

Tsunamis are caused by thrust-type submarine earthquakes, submarine volcanic eruptions, slumps, meteor impact, or coastal landslides.

Although it's relatively rare event, since 1992 tsunamis have claimed about 2000 lives worldwide.