Tsunamis are seismic sea waves of long period caused by disturbances on the sea floor.

They can be produced by submarine earthquakes, by debris avalanches and by underwater volcanic eruptions.

A number of waves may be produced and they may travel long distances to far-off shores. The height of a tsunami varies and may be affected by the sea floor bathymetry, resonance effects and other factors. Volcanic tsunami may also be produced by landslides or debris avalanches flowing into the sea around an island volcano.

 Large earthquakes before or during a volcanic eruption from a vent in a lake, may generate seiches (waves) on the lake. The mass entry of volcanic debris into a lake from an eruption itself may also create seiches. Low-lying land on the edge of a lake would be flooded by a seiche. Seiches may also travel down any rivers that flow from the lake.

What's it like to experience a tsunami and survive? New Zealanders tell their escape stories in this video