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What causes waves?
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What Causes Waves?


Everyone has seen waves on a lake or oceans. But what are they? Waves are actually energy. Energy, not water, moves across the ocean's surface. Water particiles only travel in a small circle as a wave passes.

Tsunamis, often erroneously called tidal waves, result when underwater earthquakes and volcanic eruptions disrupt the water's surface. Most other waves are caused by wind driving against water. When a breeze of two knots or less blows over calm water, small ripples form and grow as the wind speed increases until whitecaps, comprised of millions of tiny air bubbles, appear in the breaking waves. Waves may travel thousands of miles before rolling ashore and dissolving as surf.

A wave's size and shape reveals its origins. A steep, choppy wave out at sea is fairly young and was probably formed by a local storm. Slow, steady waves near shore which rear high crests, and plunge into foam come from far away, possibly another hemisphere.

No two waves are identical, but they all share common traits. Every wave, from a tiny ripple to a huge tsunami, has a measurable wave height, the vertical distance from its crest (high point) to its trough (low point). Wind speed, duration, and fetch (the distance it blows over open water) determine how high a wave grows. The maximum height in feet is usually one half or less the wind speed in miles per hour. Wave height decreases gradually as the wind dies and the wave approaches shore. When it touches bottom, it slows, the back overtakes the front, forcing it into a peak, curves forward, and dissolves into a tumbling rush of foam and water called a breaker.

Spilling breakers, a favorite with surfers, are turbulent water with foam cascading down the front. They form on gently sloping or flat shores and roll great distances before breaking.

Plunging breakers form when the bottom rises abruptly toward the shore. As the crest folds over, it creates a large air pocket, followed by a smooth splash-up. Experienced surfers can sometimes crouch under the falling crest and lock themselves inside the air tube. However, plungers can hurl 135 pound boulders more than 100 feet in the air and can damage buildings 100 - 300 feet above the sea surface.

Waves are fun on a hot summer's day, but they are also a constant reminder of the sea's awe-inspiring power.

How are waves energy?
The best way to understand waves as energy is to think of a long rope laid on the ground. If you pick up one end and give it a good snap --there's a ripple effect all the way to the other end -- just like the waves on the ocean! That means that energy is applied at one end and it moves to the other end. The energy is released at the other end of the rope, just as the energy of waves is releases on shores.

What provides the energy?
In the case of ocean waves, wind provides the energy. Wind causes waves that travel in the ocean. The energy is released on shorelines.

What determines the size of the wave?
The size of a wave depends on:


  1. the distance the wind blows (over open water) which is known as the "fetch",
  2. the length of time the wind blows, and
  3. the speed of the wind.
The greater these three, the larger the wave.

Where are the largest waves found?
The largest waves are found in the open ocean. Waves continue to get larger as they move and absorb energy from the wind. When the wave height becomes one seventh the size of the wave length, the wave will fall over, making white caps. As they get closer and closer to shore, most big waves have broken down in size and speed.

Wave Parts
The crest is the highest part of the wave and the trough is the lowest. The distance between the crest and the trough is the wave height. The distance from crest to crest is the wave length. The period of a wave is the time it takes for each crest to pass a certain point.

bulletSTILL-WATER LINE - The level of the ocean if it were flat without any waves.
bulletCREST - The highest part of the wave above the still-water line.
bulletTROUGH - The lowest part of the wave below the still-water line.
bulletWAVE HEIGHT - The vertical distance between the crest and the trough.
bulletWAVE LENGHTH - The horizontal distance between each crest or each trough.
bulletWAVE PERIOD - The time it takes for two successive waves to pass a particular point. For example, it you are standing on a pier and start a stopwatch as the crest of a wave passes and then stop the stopwatch as the crest of the next wave passes, you have measured the wave period.
bulletWAVE FREQUENCY - The number of waves that pass a particular point in a given time period.
bulletAPMLITUDE - The amplitude is equal to one-half the wave height or the distance from either the crest or the trough to the