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Tsunami cause distribution (Copyright Geoscience Australia) - More>>

What causes a tsunami?

Tsunami are waves caused by sudden movement of the ocean due to earthquakes, landslides on the sea floor, land slumping into the ocean, large volcanic eruptions or meteorite impact in the ocean.

Earthquakes

Most tsunami are caused by large earthquakes on the seafloor when slabs of rock move past each other suddenly, causing the overlying water to move. The resulting waves move away from the source of the earthquake event.

Landslides

Underwater landslides can cause tsunami as can terrestrial land which slumps into the ocean. The Scripps Institution of Oceanography demonstrates how a landslide induces a tsunami using animation.

Volcanic Eruptions

Less common are tsunami initiated by volcanic eruptions. These occur in several ways:

• Destructive collapse of coastal, island and underwater volcanoes which result in massive landslides;
• pyroclastic flows, which are dense mixtures of hot blocks, pumice, ash and gas, plunging down volcanic slopes into the ocean and pushing water outwards; and
• a caldera volcano collapsing after an eruption causing overlying water to drop suddenly.