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:
The greater these three, the larger the wave.
- the distance the wind blows (over open water) which is known as the
- the length of time the wind blows, and
- the speed of the wind.
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
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.
|STILL-WATER LINE - The level of the ocean if it were flat without any
|CREST - The highest part of the wave above the still-water line.
|TROUGH - The lowest part of the wave below the still-water line.
|WAVE HEIGHT - The vertical distance between the crest and the trough.
|WAVE LENGHTH - The horizontal distance between each crest or each trough.
|WAVE 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.
|WAVE FREQUENCY - The number of waves that pass a particular point in a
given time period.
|APMLITUDE - The amplitude is equal to one-half the wave height or the
distance from either the crest or the trough to the|