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Module 8 Shorelines
Terms in this set (33)
(tearing down) Wind, waves, tidal currents, and tsunamis all cause coastal erosion, but waves are by far the most powerful force. Most coastal erosion is caused by destructive wave action. Erosion works with longshore drift to simultaneously sculpt away and build up coastal landscapes
is like the action of sandpaper. It occurs when rock fragments are hurled at sea cliffs by breaking waves, gradually wearing down the sides of the cliffs. The little pieces of rock and sand that strike the cliff grind against it, just like sandpaper grinds away at a piece of wood.
occurs when the pressure of breaking waves compresses air inside tiny rock cracks; the compressed air exerts a force on the rock and gradually breaks open the cracks and weakens the rock. It is like filling up your bike tires with too much air. The more air you insert, the more your bike tires expand outward. As they expand outward, they thin and weaken. The rocks along the coast thin and weaken as they are filled with compressed air that exerts a force on them. when pressure compresses air inside tiny rock cracks
is the loss of shoreline material as a result of the constant pounding of breaking waves.
The salt in seawater also corrodes the rocks it hits. Corrosion occurs when the salty seawater dissolves some of the rocks along the shoreline. Slightly acidic seawater has the same effect.
occurs when sand grains grind against each other, gradually reducing in size and becoming easier to wash away.
occurs at the base of a cliff, where waves swirl around and loosen material. The action is similar to swirling around a mug of hot cocoa in order to get all the cocoa powder dissolved in your milk. The swirling action accelerates the movement of materials and hastens coastal erosion.
is as much a process of coastal landform development as is erosion.
A landform produced when sea caves are excavated so deeply by crashing
waves that two caves eroding on opposite sides become joined. The
overlying rocky roof is left as an arch. (erosion)
A small hollow chamber formed by erosional action of ocean waves against
a rocky coastline. (erosion)
A steep face of rock produced by wave erosion (erosion)
A steep, isolated island of rock, separated from the shoreline by the action
of waves, as when the overhanging section of a sea arch is eroded away. (erosion)
Narrow piece of land protruding into the water formed by sand deposits.
An indentation in the shoreline where water accumulates
A body of water cut off from a larger body of water.
A narrow passage between two bodies of land.
Forms where sediments build up parallel to land.
A deposit of sand between an island and the mainland. It forms when wave
refraction, or the bending of a wave around an island, causes the build up of
sand along both sides of an island
the size and and energy of a wave is determined by
-how long the wind has been blowing
-strength of the wind
-distance the wave has traveled (fetch)
destructive wave (short wavelength, high energy waves)
larger in height, more energy. These types of waves are created during storm
conditions by powerful winds that have been blowing for a long time, have a large fetch, and lots
of energy. Their strong backwash erodes the shoreline and destroys beaches because more
materials are swept back to sea than are deposited in the swash.
little beach building
scours the beach, pulling sand and shingle down beach
constructive wave (long wavelength, low energy waves)
smaller in height, less energy. Constructive waves
are created in calm conditions, with low-energy winds, and have a weak backwash. Constructive
waves break on the shoreline, deposit materials in the swash, and build up beaches. Because of
their weak backwash, more materials are deposited than are swept away.
pushes material up the beach
Sediment is carried up the
shoreline by the swash and back out to sea by the backwash. But when the backwash goes back
out to sea, it travels at a right angle to the shore. This movement is called longshore drift. It slowly
transports material laterally along the coast. You may have noticed longshore drift if you have
ever gone swimming in the ocean and discovered that you were 100 yards to the left or right of
where you began.
Explain the difference between swash and backwash. Which one is most responsible for erosion?
Which one predominately causes deposition?
Swash is the water that washes over the shoreline when a wave breaks on the coast. Backwash is the
water that falls back out to sea. Swash carries sediment with it and builds the beach up. Backwash
carries sediment away from the shoreline and back out to sea.
are wooden, concrete, or rock barriers built perpendicular to the sea. Sand builds up on one side and helps slow down erosion. But sand does erode from the other side of a groyne, so many groynes must be built in succession to each other. Groynes require very little maintenance, but many coastal communities find them unattractive, so they are decreasing in popularity.
can be built along beaches to diminish the energy of waves. They can be likened to armor that protects the shore from wave pounding and the energy of destructive waves.
is a collection of large rocks placed along a shoreline to protect it from the energy of breaking waves. It has the advantage of being effective against wave pounding. But it does not stop longshore drift, and it rarely holds up during a severe storm. It also reduces the recreational value of a beach and is unpopular with tourists and other beachgoers
are mesh cages filled with boulders and rocks that are placed in front of areas vulnerable to erosion. The disadvantage of these is that they wear out quickly and are not very attractive to recreational beachgoers.
are enormous stone structures sunk offshore to alter wave direction and diminish wave energy. Waves break further offshore, thus reducing their erosive power.
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