Three Great Tsunamis: Lisbon (1755), Sumatra-Andaman (2004) and Japan (2011)

Tsunamis are primarily caused by earthquakes. Under favourable geological conditions, when a large earthquake occurs below the sea bed and the resultant rupture causes a vertical displacement of the ocean bed, the entire column of water above it is displaced, causing a tsunami. In the ocean, tsunamis do not reach great heights but can travel at velocities of up to 1000 km/hour. As a tsunami reaches shallow sea depths, there is a decrease in its velocity and an increase in its height. Tsunam...