Option Unit: Coasts
Exam Date: 22nd May
Common 4/6 mark questions
Diagrams – annotate (explain using a diagram)
Old Harry Rocks, Swanage.
Formation of a stump
These are formed in headland
rocks that have a fault. The action
of the sea will exploit the fault,
through erosional processes such
as hydraulic action. In time the
fault will widen to form a cave.
Abrasion occurs at this point as
eroded material is carried by the
waves and used to erode the cave.
When the cave is eroded through
an arch is formed. The sea will
continue to erode the bottom of the
arch. Weathering will also take
place on the bare rock faces. It will
collapse in time, as it is pulled down by the pressure of its own weight and gravity. This leaves
behind a column of rock not attached to the cliff, known as a stack. Continued erosion and
weathering will lead to the formation of a stump that is visible only at low tide.
Wave Notch (cut) platform
The erosion of a cliff is greatest at its base where
large waves break. Here hydraulic action (the force of
waves crashing into cliffs and the air trapped in the
cracks and breaking them apart) and abrasion (waves
hurling eroded material and pebbles against the cliff)
take place.
Undercutting occurs and eventually the overhanging
cliff collapses downwards - this process continues and
the cliff gradually retreats and becomes steeper.
As the cliff retreats, a gently-sloping rocky platform is
left at the base, this is known as a wave-cut platform
which is exposed at low tide.
Longshore Drift
Waves rarely approach a beach at right-angles. They usually approach at an angle that depends
upon the prevailing wind. The water that rushes up a beach after a wave breaks is called
the swash. The swash picks up sand and shingle and carries it up the beach. When the water returns
down the beach it is called backwash. Due to gravity, the backwash and any material it is carrying
tends to move straight down the beach. The result is that material is transported along the beach in
a zig-zag movement. This is called longshore drift.
Longshore drift is usually in one direction only - that of the prevailing (main) wind. For example, the
prevailing wind in Britain is from the south-west. This causes material to be moved from west to east
along the south coast of England.
Impact of coastal erosion on People
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Loss of land / home. People are made homeless, can’t sell property
Loss of businesses – can’t make a living
Transport links (roads) may be affected
Use of taxes going towards coastal defense instead of service (schools, hospitals etc)
The advantages and disadvantages of different coastal management strategies
Holderness Coast
The Holderness coast is in the north east of England in the county of Yorkshire. It is South of
Newcastle on the North Sea. This is one of the most vulnerable coastlines in the world and
it retreats at a rate of one to two metres every year.
1) Mappleton - Groynes (hard engineering)
Can be made of wood or rock and are long
vertical structures placed at right angles to the
beach to trap sediment. This builds up the beach,
absorbs some of the waves impact and therefore
protects the cliffs from erosion.
Advantages: Allows the build-up of a beach.
Beaches are a natural defence against erosion
and an attraction for tourists.
Disadvantages: They have resulted in areas
further down the coast (Sue Earles farm) being
starved of beach material resulting in more
erosion!
Can be costly to build and maintain.
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2) Sue Earles Farms - Managed Retreat (soft
engineering)
This allows the natural erosional processes of the
sea to occur, areas of low value land are allowed
to flood hopefully protecting more important areas
further down the coast.
Advantages: A natural option and allows money
to
be spent elsewhere.
Disadvantages: Can cause conflict as people want their land to be protected. People who
loose land may need to be compensated.
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3) Withernsea - Sea Wall & rock armour (hard Engineering)
Curved Sea wall - Placed at the base of a cliff to reflect the waves energy.
Disadvantages: They are very expensive at approximately £10,000 per km, very ugly (visual
pollution), building them causes a lot of disruption and the cost of maintenance is high.
Advantages: Extremely effective at protecting areas from erosion and flooding.
Rock armour - Large rocks placed at the bottom of the cliff to absorb the wave energy, they
are effective at dispersing the waves energy.
Disadvantages: Environmentally ugly and may put off tourists.
Advantages: Cheaper than sea walls and less disruption is caused during building.
You should also revise some of the other soft and hard coastal management strategies