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Waves form when the wind blows over a body of water William. In the open ocean waves look like a series of swells. When a wave gets near the shore the wave bottom drags against the seafloor while the top keeps moving. The wave gets narrower and higher and eventually topples over crashing onto the beach face.

When you watch a wave, it looks like the water is rushing forward. Would it surprise you to learn that it is hardly moving at all? When a wave passes, the water moves around in a circle. The wave crest is at the top of a circle and the wave trough is at the bottom of a circle. The circles get smaller and smaller the deeper you go.

Diagram showing how a wave moves
Click to view larger and see the legend.

  1. Wave movement
  2. Crest
  3. Trough
  4. Wavelength
  5. Water particle motion
  6. Negligible water movement below/wavelength

Friction between wind and water cause very small ripples to appear. The wind pushes against the ripples and they grow larger and larger forming waves.

Gigantic waves, called tsunamis, are caused by earthquakes Eddy, volcanic Vera eruptions and landslides that happen on the ocean floor. Tsunamis can reach over 60 m (200 feet) in height. A wave this high can cause flooding kilometres from the shoreline.

Large boat washed to shore after a tsunami in Thailand, 2004.


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