Transcript longshore drift

YOU SHOULD MAKE SURE YOU KNOW
THE CONTENT OF ALL THESE SLIDES
AND COMPLETE ALL ACTIVITIES
You need to know the words below, check you have them
in your books.
SWASH – movement of water up the beach as a wave
breaks.
BACKWASH – movement of water down the beach as
water from wave returns to the sea.
FETCH – the length of the stretch of water that the waves
have travelled across to reach the coast.
PREVAILING WIND – the direction the wind usually blows
from.
You
need to be able
to describe
the differences
between
constructive
CONSTRUCTIVE
DESTRUCTIVE
WAVES
WAVES
ERODE
BUILD THE
BEACH BECAUSE
SWASH
BACKWASH
IS
STRONGER
IS STRONGER
THAN
THAN
BACKWASH
SWASH
And
destructive
waves.
• HYDRAULIC POWER – The force of water and air
pushed into cracks and shattering the cliff.
• CORRASION – The force of pebbles and rocks thrown
against the cliff, breaking pieces off.
• ATTRITION – Pebbles rubbing together in the water and
making smooth rocks.
• CORROSION – A chemical reaction that is particularly
good at wearing away limestone.
YOU MUST MAKE CERTAIN THAT YOU
UNDERSTAND WHAT THE PROCESSES
DO. THEY ARE THE KEY TO SCORING
HIGH MARKS ON MANY SIX MARK
QUESTIONS. IF YOU DON’T
UNDERSTAND THEM, YOU CANNOT
SCORE MORE THAN TWO OUT OF SIX!
METHODS OF TRANSPORT
How material is carried in the water
SOME ROCKS WILL DISSOLVE IN THE SEA.
TINY MATERIAL IS CARRIED ALONG IN THE WATER
PEBBLES BOUNCE ALONG THE BOTTOM.
LARGE ROCKS ARE DRAGGED ALONG THE BOTTOM.
Look at the diagram carefully. You can see that the prevailing wind is
blowing at an angle to the coast. This affects the direction of the swash.
The backwash is affected by gravity and moves back towards the sea at
right-angles to the coast.
This is a really important idea for the coats unit. You need to practise
remembering the diagram so that you could draw it in an exam. Remember
that a diagram with no labels is no good.
Without looking at the previous slide. Draw a
diagram to explain longshore dirft. Underneath it,
explain how longshore drift happens. Use all the
words below.
ANGLE
PREVAILING WIND
BREAK
GRAVITY
BACKWASH
RIGHT-ANGLES
TRANSPORTATION
WAVES
SWASH
THE WORDS ON THE PREVIOUS
SLIDE ARE GREAT WORDS TO
WRITEANGLE
IN THE MARGIN IN THE
PREVAILING WIND
EXAM WAVES
BEFORE STARTING AN
BREAK
ANSWER.
CAN YOU REMEMBER
GRAVITY
THEM SWASH
ALL? CLICK TO CHECK.
BACKWASH
THERE RIGHT-ANGLES
WERE 9 TO REMEMBER!
TRANSPORTATION
WHAT DO THE FOLLOWING WORDS MEAN?
CLICK TO CHECK YOUR ANSWERS.
CORROSION
SALTATION
A chemical reaction that wears away rocks
such as limestone.
Material bounces along to seafloor.
CORRASION
TRACTION
Cliffs are eroded by the force of rocks
thrown in the water breaking pieces off.
Large rocks are dragged along the
seafloor.
ATTRITION
SUSPENSION
The smoothing of rocks and pebbles as they bash
against each other in the sea.
Small material is carried along in the water.
HYDRAULIC POWER
SOLUTION
Rocks are forced apart and shattered as air and
water are pushed into cracks.
Some rocks slowly dissolve in the water
and are carried in solution.
As the notch gets deeper the overhang
unsupported
Corrasion attacksbecomes
the cliff between
theseand falls under the
force
of gravity.
This leaves a “shelf”
two marks the most.
Hydraulic
power
between
high
andforce
low tide called a wave cut
forces air and water
into small
gaps
platform.
pieces of rock to break
off. The notch
gets deeper into the headland, leaving an
overhang.
Original cliff position
HIGH TIDE MARK
LOW TIDE MARK
Draw a diagram to show how wave cut
notches and platforms are formed.
Write a description of what happens making
sure you explain how the processes work.
Include the words below…..
High Tide
Low Tide
Corrasion
Hydraulic Power
Overhang
Notch
Deeper
Retreat
Weathering makes the top of the
arch thinner. Eventually it will
collapse.
Weaknesses in the rock are attacked by
corrosion (dissolving the rock around the
weakness) and hydraulic power which
The weakness
grows into a cave over time
shatters pieces of rock around the crack
as
asthe
hydraulic power and corrasion
the force of water and air pushes into
continue to act on the cliff. Eventually the
cliff.
cave will cut through the headland leaving
an arch.
Draw a diagram to show caves, arches and
stacks are formed.
Write a description of what happens making
sure you explain how the processes work.
Include the words below…..
Weakness
Corrosion
Corrasion
Hydraulic Power
Cave
Deeper
Weathering
Arch
Collapse
Stack
A spit is a deposition feature. For a
spit to form three factors are needed.
You will need to remember these and
label them on any diagram about spits.
3. An area where longshore drift
occurs.
1. Shallow Water
2. A sudden change in the
direction of the coastline
3. As the water gets deeper and the river
current stronger deposition stops. Wind
blowing from a different direction may curve
the end of the spit.
2. At the sudden change in
coastline the longshore drift
continues in the same
direction through the shallow
water.
1. Waves break on the beach at an
angle. Material is washed up the
beach in swash whilst gravity
carries the material back down the
beach in backwash. The is called
longshore drift.
LONGSHORE DRIFT
DEEP WATER
PREVAILING WIND
RIVER CURRENT
SECONDARY WIND
HOOKED END
SHALLOW WATER
CHANGE IN DIRECTION OF THE COASTLINE
CAVE
HYDRAULIC POWER
CORRASION
HEADLAND
HARD ROCK
LONGSHORE DRIFT
DIRECTION OF COAST
HIGH & LOW TIDE
SHALLOW WATER
CORROSION
DEEP WATER
CORRASION
RIVER CURRENT
HYDRAILIC POWER
HOOKED END
NOTCH
PREVAILING WIND
OVERHANG
COLLAPSE
PREVAILING WIND
STRONG BACKWASH
WEATHERING
ANGLE
WEAK SWASH
ARCH
SWASH
BEACH DESTROYER
HYDRAULIC POWER
BACKWASH
TALL
WEAK
GRAVITY
SHORT WAVE LENGTH
CORROSION
TRANSPORTATION
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Direction of longshore drift
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Description of
what it looks
like
How it works?
Disadvantages
Where it can be
seen?
Landscaped cliff to a more
Mappleton is ongentle
the Holderness
Coast
in
slope. Water
would
East Yorkshire. roll up the cliff base rather
than eat into it.
The cliff are made of glacial till (boulder
clay) and are very soft.
Grass at base of cliff helps
bind the soil
The Holderness coast has one of the
fastest erosion rates in the world – an
average of 2m per year. Sand trapped by rock
armour.
The threat to the main road (B1242)
through the village prompted the council to
protect the coast.
Great Cowden is down coast of
Mappleton. The beach has almost
disappeared here bacause of the sand
trapped at Mappleton.
Erosion increased from 2 metres per year
up to 20 metres lost in one year as waves
bashed the cliff 24/7. Sue Earl had to pay
for the demolition of her farm here.
Healthy beach at Mappleton as sand is
trapped by the rock armour which keeps
the waves from the cliff base.
Which coastline is Mappleton on?
What is the cliff made of at Mappleton?
Why did the council decide to protect
Mappleton?
How does planting grass at the base of the
cliff help?
What has been used to trap sand from
longshore drift?
Holderness
M.G.Q.
Boulder Clay
(Glacial Till)
M.G.Q.
M.G.Q.
To protect
the B1242
RootsM.G.Q.
grip the soil
Rock
Armour
M.G.Q.
What was the average erosion rate along
the Mappleton coast?
2 metres
per year
M.G.Q.
Name the place where erosion increased
after Mappleton was protected?
Great
Cowden
M.G.Q.
How much did the erosion rate increase
here?
20 metresM.G.Q.
lost in one year
How often did the waves reach the cliff
here?
24/7
M.G.Q.
Name the farmer who had her farm
demolished?
Sue
Earl
M.G.Q.
Holbeck Hall in Scarborough fell into
the sea in 1997 when the cliff
slumped at the base causing mass
movement.
Mudflow- occurs when the cliff become
so saturated with rainwater that the
cliff collapses and is mobile enough to
flow quite quickly on to the beach.
Blackpool became popular during the industrial
revolution with holiday makers from the north of
England. Today it faces problems of coping with
visitors and keeping its business against an
increasingly competitive global market.
Solutions:
Problems include:
•Investment in street cleaning equipment and
•Unemployment in winter months when attractions
maintaining a clean beach – earning an EU Blue
are closed.
Flag.
•Overcrowding and congestion at peak times.
•Extending the season into winter months by
•Competition
from resorts
abroad
more the
becoming a conference
centre
andwith
marketing
reliable weather.
illuminations.
•Keeping the
beach
clean.
•Providing
new
facilities,
some of which are indoor
– e.g. Pepsi Max.