Transcript LM Y8Rev 1 Jun18

Revision 1
1
This is what we need to talk about
What are the 3 processes that change the
shape of the land?
What do each of the 3 words mean?
[Think of the little man!]
What are 4 ways water eroded rock?
What are the 4 ways water moves the
rock?
What do these words all mean? Attrition,
Abrasion, Hydraulic action, Corrosion,
Traction, Saltation, Suspension, Solution
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There are 3 processes at work
I am using
my
hammer to
wear away
this rock
Erosion
I am
carrying
away the
pieces
Transport
I cannot
carry them
any further
so I drop
them
Deposition
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Water erosion by waves
.
What
can you
see
here?
4
This shows that the sand has been
transported and deposited
What can you see and
why is it like that?
5
Deposition is a bit easier!
Is what happens when the water runs out
of energy and drops whatever it is
carrying
Kiama Downs Beach,
just north of Sydney
Where is that?
See those rocks in
the foreground?
They are being
eroded away and will
end up on the beach.
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So there are 3 processes at work
I am using
my
hammer to
wear away
this rock
Erosion
I am
carrying
away the
pieces
Transport
I cannot
carry them
any further
so I drop
them
Deposition
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Erosion 1
Attrition is the collision of rock fragments in the
water against one another.
The waves carrying rocks that knock against each
other and pieces get broken off, making them
smoother and rounder
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Erosion 2
Abrasion occurs when rocks and stones carried by the
waves wear away the base of the cliffs
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Erosion 3
Hydraulic action.
When waves fall against the cliffs, air is forced into
the cracks and is squashed.
As the wave withdraws, the air expands causing little
explosions and so the cracks become enlarged
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Erosion 4
Corrosion is the process by which water reacts
chemically with soluble minerals in the rocks and
dissolves them.
If you would like to
watch the animation
from which the
diagrams for erosion
came from, there is
ias link on the wiki
page to the BBC
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Transportation 1
A waves carry or transport eroded materials
such as mud, sand, boulders and dissolved
materials. Sometimes this is towards the land
or sometimes is it away from the land but often
it is along the coast to somewhere else
These materials are known as its load.
The load is carried along by four processes.
traction
saltation
suspension
solution
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Transportation 2
Traction is where boulders or stones are rolled
along the ocean-bed by the force of the water
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Transportation 3
Saltation is when small pebbles bounce
along and leapfrog over each other.
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Transportation 4
Suspension very fine particles such as
clay, silt and fine sand are carried along
in the river.
They are held up by the water as they
float because they are very, very small!
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Transportation 5
Transportation in solution is when
dissolved materials resulting from
corrosion (when the eroded material is
dissolved out of the rocks) and are
invisible to the naked eye.
You cannot see
anything
because they are
too small!
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Deposition
A waves drop their load when the speed or volume of
the waves decrease.
The load, which it carries, is deposited.
The heavier material is deposited first and the finer
material carried further.
Deposition is likely to occur when:
waves enter an area of shallow water
waves enter a sheltered area
there is little wind
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Match the word to the definition
Attrition
Abrasion
Hydraulic
action
Corrosion
Traction
Saltation
Suspension
Solution
The water dissolving away the cliffs
The force of the water wearing
away the cliffs
Tiny particles of clay or sand being
carried away by floating in the
waves
Rocks hitting each other, breaking
pieces off, making them smaller and
smoother
Rocks wearing away the coast line
Langer boulders being dragged
along the floor of the ocean
Dissolved chemical being taken away
by the wave
Smaller pebbles leapfrogging over
each other as they move
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Can you sort the
words we have
learnt into erosion
and deposition?
Try here!!
http://classtools.net/my/dust
bin35961TESTER.htm
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Changes in the
shape of the coast
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Next set of questions
How is a wave cut platform made?
Can you label a cave, an arch, a stack and a
stump?
Could you put them in the right order and
explain how one comes from the other?
Do you know how long shore drift works?
Do you know the difference between a
tombolo and a sand spit?
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Erosion
How easily a coast is eroded depends on
how hard the rock is
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How cliffs are eroded
The tougher rocks of
the headlands are
gradually eroded away
by all the methods of
erosion and gradually
a small ‘Wave-cut
notch’ is made.
As it gets bigger, the
overhanging rock will
eventually tumble into
the sea.
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How cliffs are eroded
Over time the cliff retreats leaving a wave-cut
platform just below the surface, that show when the
tide is out
This is in Dorset near Purbeck at Kimmeridge Bay.
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There are some special coastal
features
These form where chalk or limestone form
the hard band of rock.
Here the erosion is help by solution or
corrosion. If the water is slightly acid,
then the calcium carbonate that makes up
these rocks will dissolve slowly.
The rocks were laid down millions of years
ago in a warm sea and are made mostly of
the shells of molluscs.
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cliff
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crack
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cave
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arch
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stack
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stump
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Some examples
Old Harry’s Rock
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Long shore drift
The waves are blown in at an angle and ‘swash’
the pebbles up the beach
The water ‘backwashes’ down the quickest way
taking the pebbles with it –
So the sand and pebbles are moved from left to
right
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Long shore drift
The wooden partitions are called groynes.
What are they doing?
Why have they been put there?
But if the groynes were not there ……
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And this happens if the long shore drift
is allowed to carry on
Deposits and seed are
caught behind the shingle
bar and a salt marsh begins
to grow
The coast
changes
direction
But the long
shore drift
carries on
What is
this
feature
called? It
begins with
S
But the load gets dropped as
the longshore drift looses
power
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What can happen with longshore drift?
The sand and shingle
are dragged down
the coast from the
NW.
The blue line shows a
shingle bank
It continued across
the gap between the
main land and the
island to form a
tombolo.
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But in some places
our coast is
disappearing!
What can we do?
http://www.andrewdun
nphoto.com/
Erodedcliffp
acifica.jpg
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Do you know the difference between hard
and soft engineering?
Do you know the advantages and
disadvantages of each?
Could you decide from a picture whether
it was hard or soft engineering?
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Coastal Management
Rapid coastal erosion often poses a threat
to the settlement, industry and recreation
that has grown up along the coast and we
often look to protect the coast from
erosion through appropriate management
of the coastal system.
There are a number of possible
approached to coastal management:
1. Building Structures to defend the Coast
2. Pre-planning
3. Do-Nothing
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Building structures
Can be divided into 2 types
Hard Engineering
These solutions generally involve concrete,
metal, stone and other hard wearing materials
that are intended to stop erosion and take little
account of the environment.
Soft Engineering
These methods try not to disrupt the
environment and tend to be used where the
environment is more important than say a town
or road
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Hard Engineering solutions
vertical sea walls (formed of
concrete, rock, sheet piling or
timber)
revetments (sloping ramps of
concrete or rock)
flood embankments (formed of
metal, concrete, rock, timber,
rubble or turf)
rock armouring rip-rap is a general
term covering less tightly specified
dumped or placed rock structures)
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Hard Engineering solutions
gabions (wire baskets filled with
stone, stacked vertically or
stepped; often sloped to form
gabion mattresses)
groynes (fences or walls generally
perpendicular to the coastline,
designed to intercept sand and
gravel movement along the beach;
constructed from timber, sheet
piling, concrete or boulders;
modern designs are often Y-, T- or
L-shaped).
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Would you have these?
Advantages
They all manage to
absorb the energy
from the waves and so
reduce erosion
They are long lasting
Disadvantages
They are not
environment friendly
They are not pretty
They are expensive
What if
anything
could
make a
home
here?
http://en.wikipedia.org/wiki/File:11-807_riprap_photo.jpg
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Soft Engineering solutions
1. beach renourishment addition of sand or gravel to
a beach to restore former
levels
2.fencing - to reduce wave
scour and promote sand
deposition and to trap and
accumulate wind blown sand
3. dune grass planting stabilisation of bare sand
dune surfaces with
appropriate grasses which
will also trap wind blown
sand
4. establishing stabilising
plants on loose surfaces
1
http://en.wikipedia.org/wiki/File:
Beach_restoration_device.jpg
3/4
http://en.wikipedia.org/wiki/File:Helmg
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ras_kijkduin_februari_2005.JPG
Soft Engineering solutions
5. managed retreat
- rebuilding coast
inland and allowing
natural flooding of
defined areas to
form salt marshes
which then acts as a
form of natural
coastal defence for
areas inland.
http://en.wikipedia.org/wiki/File:Tolles
bury_bare_ground.jpg
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How does soft engineering stack up?
Advantages
They are more
environmentally
friendly
They tend to be
cheaper
They look nicer
Disadvantages
If they are trying to,
they slow up rather
than stop erosion
It might be your
house that gets
sacrificed?
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What is the feature you can see on this
map?
http://en.wikipedia.org/wiki/File:East_Riding_of_Yorks_outline_map_
with_UK.png
It is called Spurn Head
© Copyright Stanley Howe and licensed for
reuse under this Creative Commons Licence.
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This Spurn Head
What 2 features
can you see in the
picture which might
be helping the Head
from moving on?
What kind of
engineering is each
of them?
What do you think is
happening in the
lower pictures?
© Copyright Stephen McKay and licensed for reuse
under this Creative Commons Licence.
Crumbling sea wall
© Copyright Charles Rispin and
licensed for reuse under this Creative Commons Licence.
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This is salt marsh
Can you
remember
where that
forms on a
spit?
How does it
get there?
© Copyright Paul Glazzard and licensed for reuse under this Creative Commons
Licence.
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