Waves

I can...

• identify and describe wave motion found in the marine environment and in everyday situations

Ocean Waves

Surfers ride ocean waves, using the motion of the water to carry them to the shore. What causes waves? You can find the answer in a bowl of soup! If you blow on the soup to cool it, your breath makes small ripples on the surface of the liquid. Ocean waves are just large ripples, set in motion by steady winds.

Ocean waves begin on the open ocean. Their height depends on how fast, how long, and how far the wind blows over the water. An increase in any one of these variables can cause an increase in wave height. Normal winds produce waves of 2–5 m in height. Hurricane winds can create waves 30 m high—two thirds of the height of Niagara Falls! Even on a calm day, there is a steady movement of smooth waves. These smooth waves are called swells. They are caused by winds and storms far out in the ocean.

Whether large or small, waves on the water have features in common with all the other types of waves studied by scientists – such as sound waves, light waves, or radio waves. First, waves have height, as shown in the figure above. A wave’s height is measured from its crest (the highest part of the wave) to its trough (the lowest part of the wave). Second, ocean waves also have a wavelength, which is the distance from one crest to the next. Third, waves have a speed of motion, which is measured by the time required for one wave to pass a given point.

Breaking Waves

Near the ocean surface, water particles move in a circular motion as wave passes. As each particle moves, it bumps into the next particle and passes its energy along.

When a wave reaches shore, it changes shape (see the figure below). As the trough of the wave touches the beach, it is slowed down by friction. The crest of the wave, however, continues moving at the same speed. The wavelength shortens, and the wave height increases. The crest of the wave eventually outruns the trough and topples forward. The wave collapses onshore in a tumble of water called a breaker.

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