Transcript landforms of coastal erosion (cliffs 30 marks)

Physical Geography
•
•
•
•
Must be familiar with
The sea
Rivers
Glaciation
• But only need to study one in detail
Wave creation – The wind blowing across the surface of the sea creates
waves. The ability of waves to shape the coast is influenced by the
strength of the wind and the length of time it blows.
The size of the wave depends on the FETCH, Which is the distance a
wave has travelled before it reaches the land.
Large fetches = BIG WAVES, because the wind has had longer to blow
over the surface of the sea, creating bigger swells, e.g. The West Coast of
Ireland
Why are waves generally larger in the south west?
Wave energy depends on the fetch, the strength of the
wind and the length of time over which the wind has blown.
fetch = the distance over
which the wind has blown
Look at an atlas or a wall map to find out the largest fetch
around the British Isles.
Swash and backwash
Backwash
Swash
Waves – Swash & Backwash
• Swash – As the wave reaches the shore
it breaks. The white foamy water that
flows up the beach is called the Swash.
• Backwash – When the water runs out of
speed it stops and it flows back down
the beach into the sea. This is called the
backwash.
Constructive waves
• They have a strong Swash which transports
and deposits material on the beach.
• They have a weak Backwash which does not
carry much material back to the sea.
• As a result they construct/add material to the
beach.
Constructive Waves
Destructive waves
• They have a weak Swash.
• They have a very strong Backwash
which wears away and carries away
material form the beach.
• Therefore, there is a lot of erosion and
they destroy/destruct the coastline.
Destructive Waves
Sea erosion
Is the breaking down of coastlines by the
force of waves
Sea Erosion
•
Sea erosion is caused by Destructive
waves. They erode the coast in 4
ways.
1.
2.
3.
4.
Hydraulic Action
Air Compression
Abrasion
Attrition
How waves erode
• Hydraulic action is the power of the
water itself
• Compressed air is where air gets
trapped in cracks by waves. The
increase in pressure shatters the rock
• Abrasion is when erosion occurs
because rocks are slammed against the
coast
• Attrition is when the stones carried by
the waves are themselves worn down
Landforms of Sea Erosion
•
Like rivers, the sea creates many features
or landforms as a result of erosion. These
include,
1.
2.
3.
4.
Cliffs
Bays and Headlands
Sea caves, sea arch, sea stack, sea stump
Blowhole
For a landform, you must
1.
Name it
2.
Example
3.
Describe it
4.
How was it formed
5.
Diagram showing formation
Bays and Headlands
Bays and Headlands
• A bay is wide deep opening into the coastline.
• A headland is a piece of land jutting out into the
sea.
• Bays and headlands form when there are
different types of rocks occur along the
coastline.
• The softer rocks are eroded quickly creating a
bay.
• The harder rocks are eroded slowly and so they
stick out into the sea
• E.g. Dublin Bay & Howth Head
A cliff (2)
Ex. Cliffs of Moher or Downpatrick head co. Mayo (2)
Description
• A cliff is a high rock face that slopes
steeply up from the sea shore (2)
• Depending on rock composition the cliff
can retreat at a rate of up to 1m per
year. (2)
Formation
• Often coastlines are made up of hard
and soft rocks beside each other. The
soft rock is eroded more easily than
the hard and so bays and headlands
are formed (differential erosion)
(2M)
• Wave refraction (when the waves
bend due to the depth of sea level,
book pg 166) means wave energy is
greatest at headlands and cliffs begin
to form. (2M)
Formation
1. Destructive waves erode a notch at
the base of a headland (2M)
2. The notch deepens by the processes
of Hydraulic action, compressed air &
abrasion (explain) (6M)
3.
The notch becomes so deep that the rock above collapses
forming a cliff (2M)
4.
The fallen debris lies at the bottom of the cliff, protecting it
from further erosion. Gradually the hydraulic force of the sea
removes this debris depositing it on the sea bed some
distance out to sea. This accumulation of debris is called a
wave built terrace. (2M)
5.
Overtime, the repeated collapse of the rock at the cliff face
causes it to retreat inland. Eventually the force of the sea is
unable to erode a notch this far inland and mass movement,
such as slumping, takes over as the primary cause of cliff
formation.
6.
As the cliff retreats a wave cut platform (SLOPY ROCKY
LANDFORM LEFT BEHIND AS CLIFF RETREATSEXPOSED AT LOW TIDE) is formed at the cliff base. (2M)
• The structure of the rock plays an important part in
determining the type of cliff that is formed. (vertical or
sloping)
• Cliffs made from unjointed rock such as granite or
schist are harder to erode and form more gently
sloping cliffs, e.g. Slieve in Donegal. (2M)
• Soft coastlines made of glacial till are the least
resistant to erosive power of the sea. Every tide can
wash soil from the base of these cliffs and heavy
rainfall may cause slumping, e.g., Killiney in County
Dublin. (2M)
Homework
2008, 2007, 2006, 2005
Examine with the aid of a labelled diagram or
diagrams, the processes that have led to the
formation of any one irish landform of your
choice.
Caves, Arches, Stacks &
Blowholes
Sea caves
Form when waves erode a crack or
weakness in a headland
Sea arch
• Forms when
two caves
meet or when
one cave
burrows right
through a
headland.
Sea stack
• Formed when a
sea arch
collapses