Properties of Ocean Waves

Ocean waves are how energy is transmitted through water. The visible part of the wave, at the surface of the ocean, is the smallest part of the wave. The rest of it goes deep under the surface of the wave. The most energetic ocean waves reach all the way to the ocean floor.

How does an ocean wave work?

In deep water, individual parts of the ocean surface move up and down in sequence. This pushes the energy of the wave horizontally through the water.

The height above average sea level of the up-down motion is called the wave’s amplitude. It is based on the amount of energy which is being transmitted by the wave, as well as on the amount of volume and surface area available to transmit that energy. The crest of the wave is its highest point, and the trough of the wave is its lowest point. The distance between crests is the wavelength of the ocean wave.

Outside major storms, most waves do not carry enough energy to make them higher than a few feet. Even tsunamis are usually only a few inches high on the open ocean.

However, waves can be reinforced by or canceled out by other waves which interact with them. They also interact with local ocean currents. In general, crests add to crests, but troughs cancel out crests. The final height of an ocean wave on the open sea is the sum of all the wave heights at that spot. This is why people say that every seventh wave is much higher than the others.

When several ocean wave crests come together just right, it is called a rogue wave. These kinds of waves can be over 100 feet high, even though they are still in the open sea. However, rogue waves are highly localized. Less than a mile away, the water may show no sign that there is a rogue wave nearby. Studies from satellites have found as many as 10 rogue waves around the world in a year.

When the wave reaches shallow water, the ocean floor interferes with the up and down motion. This pushes the wave motion upwards, making the wave higher. The same thing happens when a wide wave front runs into a narrowing channel.

When the ocean wave grows too high for its own structure to support it, it breaks. This creates the foaming action as the wave starts to topple over.

When the geography is just right, very high wind-generated ocean waves which come in with a great deal of energy sometimes break so that they create a half pipe or nearly full pipe. These kinds of waves are popular among extreme surfers.

What causes an ocean wave?

= Wind =

Most ocean waves are caused by wind energy. As the wind blows across the surface of the ocean, friction between the moving air and the water transfers kinetic energy from the air to the water. The stronger the wind, the higher and deeper the resulting waves.

On a wide shoreline under moderate winds, the size of the waves is determined mostly by the speed of the wind, although other factors also play a role. For example, sustained winds will build up much higher waves than gusty winds, even when the wind speeds are the same.

= Tectonics =

Most tsunamis are started when a piece of land suddenly displaces a large volume of water. Undersea subduction earthquakes can move large amounts of land up, down, or sideways in seconds, displacing a corresponding volume of surrounding water.

A large solid mass of rock or ice which enters the ocean suddenly can also displace enough water to create a tsunami. These kinds of events can be rockslides, glacier calving, or even the impact of a meteor.

= Heat energy =

A few ocean waves result directly from the sudden uneven application of heat energy. The heat flashes its immediate surroundings into steam. The sudden expansion of the water around the steam bubble pushes out the wave. Because this also involves the sudden displacement of ocean water, these kinds of ocean waves are also called tsunamis.

However, ocean wave production through direct heat application is very rare. To start a wave, the heat energy has to be strong, sudden, and uneven. Undersea volcanoes and smokers, which generate most of the ocean’s undersea heat energy, are usually slow and steady. The sun’s energy heats the surface of the water too evenly to generate waves directly, although the same energy does cause the wind which creates ocean waves indirectly.

The heat from nuclear weapons tests can generate ocean waves. A falling meteor can also do it, if its incoming kinetic energy was high enough to be turned into enough heat energy to flash its immediate surroundings into steam upon contact. However, nearly all meteorites are much too small to generate enough heat for the steam bubble to matter.