Catch the Wave

The surprising science of ocean waves

- By Nick D'Alto

They ripple across the water and lap up against a seashore. They rise and fall in mid-ocean, and surfers can ride big ones all the way to shore. Ocean waves are always moving. Except not in the way most people think. Because amazingly, it's only the wave that's moving forward, and not the water itself. The water in a wave is really only moving up and down, turning in small circles round and round.

Let's see how this happens. As the top of the wave, called the crest, moves forward, water in front of the crest rises in a circular motion to meet it. Meanwhile, water behind the crest begins to fall. This water keeps falling, until it reaches the bottom of the circle. That marks the bottom of the wave, called the trough. As this process repeats over and over, the wave moves forward. But the water the wave is made of remains where it is!