Waves in the ocean are energy moving through the water. They are often caused by wind, which pushes on the surface of the water and piles it up until gravity pulls it back down. This causes the water in a wave to move up and down in a circular pattern. The water stays mostly in one location, but the wave energy keeps moving on and makes the water it travels through go up and down.

When a wave gets near the shore, the ground underneath can interfere with the bottom of the circular pattern that the water makes, so it is pushed up until it becomes unstable and crashes forward. The size of a wave is determined by how hard the wind blows, how long the wind blows, and how much distance it blows over the water.