Download Erosion and Changing Coastlines Coasts are shaped by the sea

Erosion and Changing Coastlines
Coasts are shaped by the sea and the action of waves. The processes that take place
are erosion, transportation and deposition.
The action of waves
The power of waves is one of the most significant forces of coastal change. Waves
are created by wind blowing over the surface of the sea. As the wind blows over the
sea, friction is created - producing a swell in the water. The energy of the wind
causes water particles to rotate inside the swell and this moves the wave forward.
The size and energy of a wave is influenced by:
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how long the wind has been blowing
the strength of the wind
how far the wave has travelled (the fetch)
Waves can be destructive or constructive.
When a wave breaks, water is washed up the beach - this is called the swash. Then
the water runs back down the beach - this is called the backwash. With a
constructive wave, the swash is stronger than the backwash. With a destructive
wave, the backwash is stronger than the swash.
swash
backwash
Destructive Waves
effects of a high wave
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Destructive waves are created in storm conditions.
They are created from big, strong waves when the wind is powerful and has been
blowing for a long time.
They occur when wave energy is high and the wave has travelled over a long fetch.
They tend to erode the coast.
They have a stronger backwash than swash.
They have a short wave length and are high and steep.
Constructive Waves
effects of a low wave
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They are created in calm weather and are less powerful than destructive waves.
They break on the shore and deposit material, building up beaches.
They have a swash that is stronger than the backwash.
They have a long wavelength, and are low in height.
Coastal Erosion
The sea shapes the coastal landscape. Coastal erosion is the wearing away and
breaking up of rock along the coast. Waves have the power to erode, or break up,
and wear away rocks over time. Storm, or high-energy, waves breaking at the bottom
of a cliff move blocks of stone - rocks. Waves fling pebbles at the bottom of a cliff
and wear the cliff away. This process is called abrasion.
Destructive waves erode (wear away) the coastline in a number of ways:
Hydraulic action: Air may become trapped in joints and cracks on a cliff face. When
a wave breaks, the trapped air is compressed (crushed) which weakens the cliff and
causes erosion.
Abrasion: Waves ‘throw’ pebbles, bits of rock and sand at the bottom of cliff
surfaces which wears/grinds the cliff away like sandpaper.
Attrition : Waves smash rocks and pebbles on the shore into each other, and they
break and become smoother.
Solution. Acids contained in sea water will dissolve some types of rock such as chalk
or limestone.
Cliffs and shorelines can get undercut or worn away at the bottom. Then the cliff
above may collapse in a rockfall, or landslide. Video examples can be seen on our
website.
Along a coastline there are features created by erosion, these include cliffs,
headlands and bays, caves, arches, stacks and stumps.
Cliffs, wave-cut platforms and notches
One of the most common features of a coastline is a
cliff. Cliffs are shaped through a combination of erosion
and weathering - the breakdown of rocks caused by
weather conditions.
Soft rock like sand and clay, erodes easily to create
gently sloping cliffs but harder rock, like chalk, is more
resistant and erodes slowly to create steep cliffs.
Seven Sisters chalk cliffs
on East Sussex coast
The erosion of cliffs
The process of cliff erosion
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Weather weakens the top of the cliff.
The sea attacks the base of the cliff forming a wave-cut notch.
The notch increases in size causing the cliff to collapse.
The backwash carries the rubble towards the sea forming a wave-cut
platform.
The process repeats and the cliff continues to retreat (erode away).
Headlands and Bays
Headlands are formed when the sea attacks a
section of coast with alternating bands of hard and
soft rock.
The bands of soft rock, such as sand and clay, erode
more quickly than those of more resistant (harder)
Lulworth Cove in Dorset
rock, such as chalk. This leaves a section of land
jutting out into the sea called a headland. The areas
where the soft rock has eroded away, next to the headland, are called bays.
Lulworth Cove is a horseshoe shaped bay which formed because the inland rocks are
less resistant than the headland. It is obvious to see from this bay, how different
rock type are affected by the waves at different rates. These changes can happen
quickly over a period of years or over thousands of years depending on the type of
rock.
Geology is the study of the types of rocks that make up the Earth's crust. Coastlines
where the geology alternates between strata (bands) of hard rock and soft rock are
called discordant coastlines. A concordant coastline has the same type of rock along
its length. Concordant coastlines tend to have fewer bays and headlands.
Caves, Arches, Stacks and Stumps
Weathering and erosion can create caves, arches, stacks and stumps along a
headland.
See our video section.
http://www.highviewschool.org.uk/coastal-erosion-wave-actions/
Caves
Caves occur when waves force their way into
softer rock with cracks in the cliff face.
The waves contain sand and other materials
which grind away at the rock until the
cracks become a cave. This type of wave
action is called hydraulic action.
Cave at Hole Point, Dawlish, Devon
Arch
Durdle Door Arch in Dorset
If the cave is formed in a headland, it may eventually break through to the other
side forming an arch.
Stacks and Stumps
The arch will gradually become
bigger until it can no longer support
the top of the arch. When the arch
collapses, it leaves the headland on
one side and a stack (a tall column
of rock) on the other.
The stack will be attacked at the
base in the same way that a wavecut notch is formed. This weakens
the structure and it will eventually
collapse to form a stump.
Old Harry Rocks, Studland, Poole, Dorset
Information sourced from: http://www.bbc.co.uk/schools/gcsebitesize/geography/coasts/
http://www.3dgeography.co.uk/coast-diagram