GCSE COASTS
1a CONSTRUCTIVE
DESTRUCTIVE
WAVES
1b COASTAL EROSION
EG COASTLINE
Erosion Processes p63 BP
1.Corrasion / Abrasion
2.Scouring
3.Hydraulic Action
4.Solution
5.Attrition
Coastal erosion processes create a number of
significant landforms. There are a number of
factors which affect the rate of this erosion:
i) Rock Type – A more resistant rock, such as
granite, will be eroded slowly, whilst a less
resistant rock, such as clay or mud, can be
eroded very quickly.
ii) Jointing / Faulting – The more faults and
joints a rock has the more susceptible it is to
erosion, both from coastal and sub-aerial
processes.
Coastal Rock Arrangement – A
coastline with rocks that run
parallel to the coast is called a
concordant or “Pacific”
coastline. One that has rocks
running at right angles to the
coast is called a discordant or
“Atlantic” coastline.
DISCORDANT COASTLINE
Rocks are at right angles to the sea
HEADLAND
HARD ROCK
SOFT ROCK
BAY
HEADLAND
HARD
SOFT
Discordant Coastline
Headlands and Bays
- Formed on an Atlantic (discordant)
coastline due to the softer rock
being eroded quicker than the harder
rock.
- Beaches form in the bays where
the soft rock has been eroded away.
- Headlands of more resistant, hard
rock are left behind.
Concordant Coastline
ROCKS ARE PARALLEL TO THE SEA
ARD ROCK
BAY
BAY
OFT ROCK
OFT ROCK
ARD ROCK
ARD ROCK
EG Lulworth Cove, Dorset
Wave Cut
Platform
Formation
Fig 18.4 p301
Add in the
Retreating cliff
lines
The sea uses its four erosion methods during high
and low tide to create a notch. This means the cliff
above is unsupported and collapses – retreating
inland. This process is called ‘UNDERCUTTING’. The
cliff is vertical and steep.
Cliffs & Wave Cut Platforms
- Cliffs are formed when destructive
waves attack the bottom of the rock
face between high and low water mark.
- The area under attack is eroded using
the major processes of coastal erosion.
- Points of weakness, such as faults and
joints are attacked most, and eventually
a wave-cut notch is gouged out.
The rock above overhangs the notch, and as it is cut
deeper into the rock, gravity causes the overhanging
rock to collapse.
- The loose rocks are removed by the sea and
transported along the coast by long shore drift.
- The whole process of undercutting the cliff begins
again.
- As the cliff is eroded backwards it leaves behind a
wave-cut platform, at the level of the low water
mark.
- This platform is rarely eroded, as the waves energy is
concentrated on eroding the area between the high and
low water mark, and not the rock that is underneath
them.
Model Answer Erosion Headland Formation
A cave is formed in the rock as various
processes of coastal erosion operate on it.
Hydraulic action (which involved mini
explosions of air under water) eats out the
notch to form a cave. A cave is eroded further
by the processes of attrition, corrosion
(solution) abrasion and scouring. This
eventually forms an arch. Over time the arch
weakens and collapses leaving an stack. The
stack erodes over time to form a stump.
Caves, Arches, Stacks and Stumps
- Mainly seen on headlands.
- Waves start by attacking the main points of weakness
in the rock: the joints and faults.
- A point of weakness is increased in size until it
becomes a cave.
- The waves continue to attack the cave, which finally
results in an arch being formed through the headland.
- The arch is attacked both by coastal erosion and subaerial erosion and finally the roof of the arch falls into
the sea.
- This leaves behind a stack, which is then slowly
eroded down to become a stump.
OLD HARRY
Model Answers Rock Types Sheet
1a) The slate rock must be harder (more resistant) than the sandstone as it
sticks out on the coastline as headlands (2)
1b) The limestone must be harder than the sands and clays because although
the limestone is closer to the sea, and therefore more easily eroded, the sands
and clays have been eroded BEHIND the limestone to form coves – eg Lulworth
cove (2)
2a) Headlands are sections of rock jutting out into the sea – whereas bays are
indentations into the coastline where the sea has eaten it away (2)
2b) Arches look like headlands except they have a hole at the base and stumps are
large towers or columns of rock sticking out of the sea
3a) Erosion occurs in both headlands and bays. As the headlands are made up of hard
rock they are eroded more slowly. Processes such as hydraulic action and abrasion
will be important in their formation. Bays will be eroded more quickly as they are
made of softer rock. Material eroded at the headland cliffs will also be transported to
the bays
3 b) First of all hydraulic action attacks small notches in the cliff face. Over time –
this is enlarged
..to form an arch. The arch is then eroded until the top collapses away forming a
stack. Erosion from the sea then leads to the stack collapsing forming a stump. (6)
4. In Devon = DISCORDANT COASTLINE = the rocks lie at right angles to the
sea. This forms headlands (on the resistant rock - SLATE) and bays (on the weaker
rock - SANDSTONE). In Dorset = CONCORDANT COASTLINE = rocks lie
parallel to the sea. This forms isolated parallel rock features in the limestone and
coves behind in the weaker sands and clays. (9)
5. Devon = headlands will get more PRONOUNCED as the bays will
be eroded at a quicker rate
Dorset = the weak rock behind the limestone (sands and clays) will be
eaten out even more to form very large coves. Some of the coves may
join up with each other too. The limestone (which is more resistant)
will slowly get eaten away and will end up as isolated rock outcrops
in the sea – standing alone (5)
1c COASTAL
TRANSPORTATION
EG COASTLINE
Groynes are used to stop LSD
Q3 Advantages
•It stops the beach from being eroded away – eg
tourist towns such as Bournemouth have
constructed groyne systems
• By trapping beach material (through groyne
construction) this protects the cliff from being
eroded
Disadvantages of groynes
•Look horrible and costs at lot of money
•Divide the beach up into unnatural sections
•Towns further down the coast may suffer because
there is no sediment coming along as it has been
trapped further up by groynes
1d COASTAL
DEPOSITION
SEA
Spurn Head Spit
LSD
SALT
MARSH
Spits
- A long, narrow ridge of sand attached at one end to the coast.
- Built up by long shore drift transporting material along the
coast.
- At a bend or break (for an estuary) in the coastline the
material being carried is dropped. However it is deposited
away from the coastline.
- As the spit builds out to sea the end is affected more by the
wind and by wave currents, causing the end to curve towards
the shore, to create a hook end.
- Material often accumulates in the area of standing water that
occurs behind a spit, and this can lead to the formation of salt
marshes.
- Spits can be areas where large sand dunes build up, nearer
the back of it.
Beaches
-Created by constructive waves depositing material
(sand, shingle and pebbles) that has been transported
from further along the coast.
-LSD also transports and deposits material from and
to them
- They lie between high and low watermark and are
gently sloping, towards the sea.
-A constantly changing feature, beaches may be built
up at certain times of the year, and eroded away at
others, depending on the type of waves hitting them
at the time. Often this change can be seasonal.
-The best natural coastal defence feature
TOMBOLO
Tombolos
-A bar of deposited material
linking the mainland to an
island.
-Draw Fig 1.68 p47
Bars
- A ridge of sand that blocks off
a bay or river mouth. It will
create a lagoon behind if it is
across a non-river bay.
1e OS MAP WORK
2 COASTAL
MANAGEMENT
Unfortunately, the sea defences
stop the erosion, but this allows
mass movement time to takeover.
Rainwater seeps into the porous
TILL and causes ROTATIONAL
SLUMPING.
BEACH
NOURISHMENT
Humans are affected by the
retreat of the cliff (loss of land,
housing, etc.) They erect sea
defences
which
stop
the
erosion (groynes, revetments,
gabion cages and anti-tank
blocks.
Holderness Coast
Weak
Boulder
Clay
A(i) Lulworth Cove is a circular shaped hollow in the
coast. It is steeper towards the back and the gradient drops
off towards sea level. It is made of 3 types of rock:
limestone at the front, followed by sand and clay then
chalk. The mouth of the cove is 50m wide and the
maximum width of the cove is 350m. (3)
A (ii) This stretch of coastline is a concordant coastline –
where the rocks are lying parallel to the sea. The limestone
is eventually eroded and breached and the sea attacks the
weaker sands and clays until it hits the resistant layer of
chalk at the back of the cove. (3)
b) HOLDERNESS COAST
Physical environment – the coasts here are made of weak rocks –
called boulder clay which have been carried by the icesheets at the
end of the last glacial period (= Devensian 10,000 yrs ago). The cliffs
around Mappleton have been affected – eg Mr Cross and Sue Earle’s
farm, Easington Gas Terminal in danger of falling into the sea.
Human Environment – Groynes have been added to Mappleton which
have prevented LSD from taking sediment further down the coastline.
This has meant that the coast has been built up at one point but
attacked at other places. Dairies have been affected and gas terminals
as well as people’s property. (7)
c) For:
•It protects the coastline and preserves peoples: property (Mr Cross),
businesses (Sue Earle) , industry (gas terminal)
•Groyne encourage a beach to grow which can help tourism and bring
money to the area
Against:
•Looks very ugly
•Very expensive to build
•No guarantee it will last forever
•Some people suffer if groynes are built and sediment is trapped – eg
Mr Cross (who was cross!) (6)
d) SPIT = eg Spurn Head – is a hooked shaped landform which
typically runs along a coastline with a hooked shaped end often where
a river estuary meets the coast. It is formed by the process of
Longshore Drift bringing material along the coastline in a zig-zag
fashion. A saltmarsh often forms behind the spit as the sediment can
build up here in shallower waters. (6)