Coastal Zone

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The Coastal Zone
How Waves Form
Waves are formed by the wind blowing over the sea.
Friction with the surface of the water causes ripples to form and these develop into
waves.
They can also be formed when volcanic eruptions shake the seabed. These
waves are called tsunamis .
Beach : a deposit of sand or shingle at the coast , open found at the head of the
bay.
Fetch : the stretch of open water over which the wind blows . The longer the fetch,
the more powerful a wave can become.
Crest : the top of a wave.
Swash : the forward movement of a wave up a beach.
Backwash : the backward movement of water down a beach when a wave has
broken.
Why Waves Break at the Coast
There is little horizontal transfer in open water which means there is a circular
orbit. When waves approach the shore there is a forward movement of water as
waves break and wash up on the beach.

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As the water become shallower , the friction with the seabed distorts the circular
motion and becomes more elliptical . This causes the crest of the wave to rise up
and then eventually topple onto the beach.
Constructive Waves
Constructive waves are waves that surge up on the beach with a powerful swash
which carries material up the coast.
They carry large amounts of sediment and build a beach, making it more
extensive .…read more

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Destructive Waves
Destructive waves have a weak swash and strong backwash, which means
material is removed from the coast.
They are formed by local storms close to the coast.
They are closely spaced and often interfere with each other, producing a chaotic
swirling mass of water.
They rear up to form towering waves before crashing down onto the beach.
They have a high frequency (1014 waves per minute).
They have a longer fetch than constructive waves.…read more

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It is
effective if the rock is porous or permeable .
Exfoliation (onion skin weathering): The heat makes the rock expand during the
day. As it cools at night, it contracts. Repeated cycles of this leads to the outer
layer peeling away from the rest of the rock. Water weakens rock making it more
vulnerable to flaking.
Rock is a poor conductor of heat which means that only the outer part of a rock
warms and cools
in response to
changes in
temperature.…read more

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Chemical weathering: A chemical change occurs during weathering. Rainwater,
being slightly acidic can slowly dissolve certain rocks and minerals. The parts
which are unaffected by chemical weathering form a fine clay deposit .
Solution : The process of rocks (e.g. rock salt) dissolving in rainwater.
Carbonation : The rainwater picks up the carbon dioxide from the air, causing the
rainwater to become becomes a weak carbonic acid .…read more

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Processes of Coastal Erosion
Coastal erosion: The wearing away of land by the sea.
Hydraulic power : The force of the water hitting the cliff and squeezing air into
cracks in the rock, causing rocks to break apart (captivation).
Abrasion : The effect of pebbles grinding over a rocky platform , causing it to
become smooth .
Corrasion : The force of bits of rock carried in the water blasting into the cliff.…read more

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Longshore drift: Transportation of sediment along the coastline caused by waves
approaching at an angle, making the sediment move along the beach in a
zigzag pattern .
1) The waves follow the direction of the prevailing (most common) wind.
2) They hit the coast an oblique angle (any angle that isn't a right angle).
3) The swash carries the material up the beach in the same direction as the
waves.…read more

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Headlands are most vulnerable to power of the waves, which explains the
presence of cliff and wavecut platforms.
Bay : a broad coastal inlet often with a beach.
Bays are sheltered from the full fury of the sea, which means that the waves are
less powerful and deposition dominates. This explains why a sandy beach is the
most common feature found in bays.
Cliffs do not erode at an even
pace.…read more

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Destructive waves remove the beach once again and expose the wavecut
platform.
Caves, Arches, Stacks and Stumps
Cave : a hollowedout feature at the base of an eroding cliff.
Arch : a headland that has been partly broken through by the sea to form a
thinroofed arch.
Stack : An isolated pinnacle of rock sticking out on the sea.
Stump : A stack which has been undercut and has collapsed and is only visible at
low tide.…read more

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Common characteristics on beaches are berms and ridges (small ridges which
represent different tides).
Spits
Spit: A long narrow finger of sand or shingle jutting out into the sea from the
coast.
As sediment is moved along the shore by longshore drift , it is deposited when
there is a change in coastline (e.g. river mouth or change of direction). Gradually,
as more and more sediment is deposited , the feature extends into the sea.…read more

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