What is a Tsunami?

Here is a summary of the key points you need to know about tsunamis for GEOG3, check out the video below which is some raw footage of the Japan tsunami to give you an idea of the time scale and destruction involved. It's hard to imagine how long the waves are actually moving inland for, scary!

• A tsunami is a series of waves, called a wave train, which can be up to 100km long and 1 hour apart.

• These waves can reach heights of 30meters, although most of them are no more than 3 meters

• About 80% of tsunamis happen within the “Ring of Fire”. They are usually caused by underwater earthquakes when the ocean floor rises at a plate boundary and displaces the water above it.

• They have also been know to be caused by underwater landslides, volcanic eruptions or meteorites impacts.

• They race across the sea at up to 500 miles an hour and can cross the entire Pacific Ocean in less than a day while their long wavelengths mean they lose very little energy along the way.

• In deep ocean, tsunami waves may appear only a foot  high but as they approach the shore shallow water slows them down and the tops of the waves move faster than the bottoms so they grow in energy and height.

• A tsunami’s trough, the low point beneath the crest, often reaches shore first, producing a vacuum effect that sucks coastal water seaward exposing harbours and sea floors.

• Flooding can extend 10 miles inland, lifting giant boulders, flipping vehicles and demolishing houses.