What was the cause of a tsunami?

Answer 1

A strong incoming tide at the mouth of some rivers produces a bore (a wave) that moves up the river against the current.

Answer 2

A tsunami is typically caused by an underwater earthquake, volcanic eruption, or submarine landslide that displaces a large volume of water and creates a series of powerful waves. The sudden movement of the Earth's crust disrupts the water above, setting off a chain reaction that forms a tsunami.

Answer 3

an undrewater earthquake