Case Study - Japanese Tsunami Causes of Tsunami (March 11th 2011)

Question 1

What happened to the ocean when the earthquake occurred?

Answer 1

The water on the ocean floor was displaced by the movement of the plate upwards.
The seabed lifts as a result of the earthquake and the water on top of it has to find somewhere else to go, so it forms giant waves.

Question 2

What does the giant wave form?

Answer 2

The displaced water forms the start of the tsunami.

Over the ocean, the waves are small, rising only a few cm high and aren’t noticed by passing boats.

Question 3

What is the most obvious sign that a tsunami is coming?

Answer 3

Coastal water retreating just before the waves reach shore. Prediction.

Question 4

What happens when the waves reach shallower water?

Answer 4

Height increases by several metres.
Shallow water slows the wave.
Waves get closer - more frequent.