My Science School

On a quiet day, you can hear the waves roll in and splash near the shore. On a stormy day, they thunder.

Waves are made by wind blowing along the top of the water. The water seems to be moving forwards - but it only moves up and down. A cork floating on the water would bob up and down as a wave moved under it. This is because the water in a wave does not move forwards. Only the shape of the wave moves forwards.

When a wave reaches land, it “breaks”. The bottom of the wave drags on the ground where the water is shallow. The top keeps going. It spills onto the beach, and then slides back again. This is the only place where the water in a wave moves forwards and back. Everywhere else it just moves up and down.

The biggest waves of all are made by earthquakes under the ocean floor. These waves are called tsunamis. Hundreds of kilometres from shore, a tsunami may only reach 30 or 60 centimetres. People on a ship at sea may not even feel it. But as a tsunami approaches land, it can form a wall of water more than 30 metres high.