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By Amanda Briney
Waves are the forward movement of the ocean's water due to
the oscillation of
water particles by the frictional drag of wind over
the water's surface.
Size of a Wave
Waves have crests (the peak of the wave) and troughs (the lowest
point on the wave).
The wavelength, or horizontal size of the wave, is determined by
the horizontal distance between two crests or two troughs.
The vertical size of the wave is determined by the vertical
distance between the two. Waves travel in groups called wave trains.
Different Kinds of Waves
Waves can vary in size and strength based on wind speed and
friction on the water's surface or outside factors such as boats.
The small wave trains created by a boat’s movement on the water
are called wake.
By contrast, high winds and storms can generate large groups of
wave trains with enormous energy.
In addition, undersea earthquakes or other sharp motions in the
seafloor can sometimes generate enormous waves, called tsunamis (inappropriately
known as tidal waves) that can devastate entire coastlines.
Finally, regular patterns of smooth, rounded waves in the open
ocean are called swells.
Swells are defined as mature undulations of water in the open
ocean after wave energy has left the wave generating region.
Like other waves, swells can range in size from small ripples to
large, flat-crested waves.
Wave Energy and Movement
When studying waves, it is important to note that while it
appears the water is moving forward, only a small amount of water is actually
moving.
Instead, it is the wave’s energy that is moving and since water
is a flexible medium for energy transfer, it looks like the water itself is
moving.
In the open ocean, the friction moving the waves generates
energy within the water. This energy is then passed between water molecules in
ripples called waves of transition.
When the water molecules receive the energy, they move forward
slightly and form a circular pattern.
As the water’s energy moves forward toward the shore and the
depth decreases, the diameter of these circular patterns also decreases.
When the diameter decreases, the patterns become elliptical and
the entire wave’s speed slows.
Because waves move in groups, they continue arriving behind the
first and all of the waves are forced closer together since they are now moving
slower.
They then grow in height and steepness.
When the waves become too high relative to the water’s depth,
the wave’s stability is undermined and the entire wave topples onto the beach
forming a breaker.
Breakers come in different types -- all of which are determined
by the slope of the shoreline.
Plunging breakers are caused by a steep bottom; and spilling
breakers signify that the shoreline has a gentle, gradual slope.
The exchange of energy between water molecules also
makes the ocean crisscrossed with waves traveling in all directions.
At times, these waves meet and their interaction is called
interference, of which there are two types.
The first occurs when the crests and troughs between two waves
align and they combine. This causes a dramatic increase in wave height.
Waves can also cancel each other out though when a crest meets a
trough or vice-versa.
Eventually, these waves do reach the beach and the differing
size of breakers hitting the beach is caused by interference farther out in the
ocean.
Ocean Waves and the Coast
Since ocean waves are one of the most powerful natural phenomena
on Earth, they have a significant impact on the shape of the Earth’s
coastlines.
Generally, they straighten coastlines. Sometimes though,
headlands composed of rocks resistant to erosion jut into the ocean and force
waves to bend around them.
When this happens, the wave’s energy is spread out over multiple
areas and different sections of the coastline receive different amounts of
energy and are thus shaped differently by waves.
One of the most famous examples of ocean waves impacting the
coastline is that of the longshore or littoral current.
These are ocean currents created
by waves that are refracted as they reach the shoreline. They are generated in
the surf zone when the front end of the wave is pushed onshore and slows.
The back of the wave, which is still in deeper water moves
faster and flows parallel to the coast.
As more water arrives, a new portion of the current is pushed
onshore, creating a zigzag pattern in the direction of the waves coming in.
Longshore currents are important to the shape of the coastline
because they exist in the surf zone and work with waves hitting the shore.
As such, they receive large amounts of sand and other sediment
and transport it down the shore as they flow.
This material is called longshore drift and is essential to the
building up of many of the world’s beaches.
The movement of sand, gravel, and sediment with longshore drift
is known as deposition. This is just one type of deposition affecting the
world’s coasts though, and have features formed entirely through this process.
Depositional coastlines are found along areas with gentle relief
and a lot of available sediment.
Coastal landforms caused by deposition include barrier spits,
bay barriers, lagoons, tombolos and
even beaches themselves.
A barrier spit is a landform made up of material deposited in a
long ridge extending away from the coast.
These partially block the mouth of a bay, but if they continue
to grow and cut off the bay from the ocean, it becomes a bay barrier.
A lagoon is the water body that is cut off from the ocean by the
barrier.
A tombolo is the landform created when deposition connects the
shoreline with islands or other features.
In addition to deposition, erosion also
creates many of the coastal features found today. Some of these include cliffs,
wave-cut platforms, sea caves, and arches.
Erosion can also act in removing sand and sediment from beaches,
especially on those that have heavy wave action.
These features make it clear that ocean waves have a tremendous
impact on the shape of the Earth’s coastlines.
Their ability to erode rock and carry material away also
exhibits their power and begins to explain why they are an important component
of the study of physical
geography.
Amanda
Briney
Geography
Expert
Education
M.A.,
Geography, California State University - East Bay
B.A.,
English and Geography, California State University - Sacramento
Introduction
Professional
geographer, writer, and scholar
Certificate
of Advanced Study in Geographic Information Systems (GIS)
More
than 10 years of experience writing about a broad array of geographical topics
Experience
Amanda
Briney is a professional geographer and writer who contributed to ThoughtCo for
more than 10 years. She wrote countless articles on a wide range of topics such
as an introduction to the subject of geography, reviews of ecotourism,
discussions about environmental determinism, and the structure of Latin
American cities. The scope of her work also includes other formats such as
histories, guides, and fact sheets about many parts of the world. An ultimate
scholar, Amanda also contributes work to academic venues and the GIS Lounge, an
informational portal about geography.
Amanda
enjoys all aspects of geography and mapping but is especially interested in
examining natural landscapes through spatial analysis. As such, she holds a
certificate in Geographic Information Systems (GIS) from California State
University. She also attended Diablo Valley College where she studied air photo
interpretation and the formation of the Earth's landscapes.
Education
Amanda
Briney received a Master Arts (M.A.) in Geography from California State
University–East Bay. She also holds a Bachelor Arts (B.A.) in English and
Geography from California State University–Sacramento and earned a Certificate
of Advanced Study in Geographic Information Systems (GIS) from California State
University.
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