Part of the show Geology of Natural Disasters, Volcanoes and Earthquakes
Richard in Colchester asked:
Why are there two or three waves in a tsunami instead of one?
It's essentially the same principle as if you get a cube of sugar and drop it in your cup of tea. It sets up a disturbance in the water surface and it doesn't reach equilibrium again immediately, so you get a lot of oscillations instead of just one. This gives you more than just one wave. They all add together.