Explainer What is a tsunami and what kind of damage can it cause?

Tsunami alerts were issued across parts of the Pacific on July 30 after an 8.8-magnitude earthquake off Russia's far east.

- 

TOKYO -

Here are key facts about tsunamis and the damage they can cause.

SHOCK OF WATER

A tsunami is a shock of water that spreads through the sea, usually triggered by a strong earthquake beneath the ocean floor.

The sudden, violent movement of the earth's crust can thrust up or drive down a section of the seabed - with the rift displacing vast quantities of water that move as waves.

Tsunamis radiate in all directions from their source and can cover enormous distances, sometimes at the speed of a jet plane.

They are a rare phenomenon but can create dangerously powerful currents and cause deadly flooding in coastal areas.

OTHER CAUSES

Large quakes are the main driver of tsunamis, but the phenomenon can also be sparked by other cataclysmic geographic events, such as volcanic eruptions and landslides.