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What Causes Tsunamis? A Guide to How Tsunamis Form



You probably already know that tsunamis are long, tall waves that can be disastrous to anything nearby.

But what causes tsunamis?

And how do tsunamis form?

Let’s dive into this guide of how tsunamis work.

Earthquakes cause 80% of tsunamis

tsunami subducting plate

Over 80% of tsunamis are caused by earthquakes. But landslides, volcanoes, weather and even asteroids can also generate tsunamis.

Typically, earthquakes occur along two convergent plate boundaries like in the diagram below. The diagram depicts a subducting plate with an overriding plate riding above it.

Friction generates slow distortion

tsunami distortion

The descending plate sinks into the overriding plate. But they stick to each other building an enormous amount of friction.

Over time, the descending plate creates a slow distortion into the overriding plate. These frictional forces can last for years building up energy.

Sudden displacement of the ocean

tsunami earthquake

When there is a rupture at the two stuck plates, it releases a tremendous amount of energy forming an earthquake.

This causes a sudden displacement in the ocean. But the size of the tsunami depends on the depth of the ocean at this location.

A rupture creates a tsunami

tsunami wave spreading

Waves radiate outwards. They can be enormous in size up to 500 mph. Unlike wind-driven waves, tsunamis can travel the entire water column from the ocean floor to surface.

Depending on the depth of the ocean floor, tsunamis can reach heights of over 500 meters. But when these waves hit the shore, they lessen as low as 10 feet high.

Not all tsunamis reach the shore as giant waves. But when they do, they can be disastrous.

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