Transcript Document

Features of
erosion
LITHOSPHERE
GLACIATION
These slide-shows are all on the Geography Blog, if you wish to copy
any notes from them; we will not be stopping in class for you to do
this
FEATURES OF GLACIAL EROSION
These are the features you will need to be able
to describe, explain their formation, draw a
labelled sketch of and recognise on an OS map.
CORRIES
U-SHAPED
VALLEYS
RIBBON LAKE
ARETES
PYRAMIDAL PEAKS
HANGING VALLEYS
TRUNCATED SPURS
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LITHOSPHERE
Features of
erosion
GLACIATION
CORRIES
Snow collects in hollows, especially on the less sunny
north and east facing slopes, turns to glacial ice and
moves downwards under the force of gravity
Rocks are plucked out and the hollow is widened by
abrasion to become a corrie.
A corrie is a deep, rounded hollow with a steep back wall.
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LITHOSPHERE
Features of
erosion
GLACIATION
Read the in formation on the formation
of corries in your notes and textbook
page 91
There is a bullet-pointed list of actions
explaining in order how a corrie is
created.
Learn this at home!
Also learn how to draw and label
sketches.
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LITHOSPHERE
GLACIATION
Corries
• Snow accumulates in mountain hollows when more snow falls in winter than
melts in the summer.
• North/North-east facing slopes are more shaded so snow lies longer.
• Accumulated snow compresses into neve and eventually ice.
• Plucking, when ice freezes on to bedrock, fractures it and incorporates it into
the glacial ice.
• Abrasion, when the angular rock within the glacial ice grinds away the valley
sides and floor, over-deepening the hollow along with rotational movement of
glacier.
• Glacier moves downhill due to gravity.
• Rotational movement not so powerful at corrie edge, allowing rock lip to form
which traps water as ice melts, leaving a lochan.
• Up to 1 mark for a correctly named example.
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LITHOSPHERE
Features of
erosion
NOTE;- the labels should not
just name the features. They
should describe what is happening
in the sketch and name the
processes.
GLACIATION
MAXIMISE
YOUR
MARKS !
This makes these labels -and the
diagram- worth more marks than
one where bits only are named!
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LITHOSPHERE
Features of
erosion
GLACIATION
Answer these questions in the usual way;Q1. Where is the bergshrund and what causes it?
A. It is at the top of the back-wall, where the ice
is ripping away from the rock because of gravity
pulling the ice downhill.
Q2.What erosion process greatly affects the
backwall, and how does this affect the rock
texture here?
A.Plucking is the main process here and it leaves
the rock jagged and rough.
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LITHOSPHERE
Features of
erosion
GLACIATION
Q3.The debris created by plucking is active
elsewhere in the corrie- where and with what
results?
A.Abrasion uses the plucking products to smooth,
deepen and enlarge the floor/ basin of the corrie.
Q4. Describe how corries, aretes and pyramidal
peaks are all related features.
A. To create an arete, there has to be more than
one corrie eroding the land between them into an
arete. The eroded corrie back-walls eat into the
summit of the mountain creating a pyramidal peak,
where several aretes come together.
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LITHOSPHERE
Features of
erosion
Formation of a corrie
GLACIATION
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Recap – this is the sort of diagram that you should be able to
draw under exam conditions. Practice doing this.
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LITHOSPHERE
Features of
erosion
GLACIATION
Back
wall
scree
lip
Once the glacier retreats, the corrie may be filled
with water. A small, generally circular loch is
formed. This is known as a tarn or corrie lochan.
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LITHOSPHERE
Features of
erosion
GLACIATION
On an OS map,
corries are shown
as horseshoeshaped features.
scree
N
Note the contours are
very close together,
especially on the steep
backwall. Note also the
bare rock symbol.
Note the eastfacing aspect;
snow lasts longer
before melting.
tarn
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LITHOSPHERE
Features of
erosion
GLACIATION
Red Tarn
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LITHOSPHERE
Features of
erosion
GLACIATION
ARETE
An arete is a narrow, sharp-edged ridge
which forms the side walls of corries or
separates different glacial valleys.
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LITHOSPHERE
Features of
erosion
GLACIATION
On a map an arete
is hard to see. It is
a long ridge between
to corries or
valleys.
The red lines mark
the spines of the
three aretes.
= arete
These corries and arete are
in the Cairngorms.
bare rock
scree
horn
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LITHOSPHERE
Features of
erosion
GLACIATION
Striding Edge
Striding Edge
arete on
Helvellyn,
Lake District
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LITHOSPHERE
Features of
erosion
GLACIATION
MATTERHORN
Pyramidal peaks are also called horns.
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LITHOSPHERE
Features of
erosion
GLACIATION
A VALLEY GLACIER
The next few slides will help to explain the
formation of this feature.Before and after
landscape
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LITHOSPHERE
Features of
erosion
GLACIATION
13
Stages in the formation of a U-shaped valley
Take the handout and use page 284 of ‘Wider World’
to add the labels.
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Features of
erosion
GLACIATION
These are the actions that form this feature.
LITHOSPHERE
a) A glacier flows into an earlier 'V' shaped valley.
b) The glacier abrades and plucks the sides and floor of
the river valley.
c) The valley is greatly deepened, widened and
straightened.
d) When the ice melts the valley is 'U' shaped.
e) It now has very steep sides and a fairly flat floor.
f) Any rivers are called 'misfit streams’ because they
are far too small to have cut the valley.
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LITHOSPHERE
Features of
erosion
GLACIATION
Truncated spurs
Former hill spurs are ‘truncated’- their ends are cut
off by the ice action to form steep, sheer cliffs.
The yellow lines
show where the
spurs were
before they were
chopped off!
Note how they
defined a Vshaped valley.
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LITHOSPHERE
Features of
erosion
GLACIATION
A U-shaped valley in Canada.
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Features of
erosion
LITHOSPHERE
When a glaciated valley is
submerged or drowned by a
rise in sea level, a fiord is
formed.
GLACIATION
The sea lochs of western
Scotland are the best
examples of fiords in the
British Isles.
Fiord/fjord
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LITHOSPHERE
Features of
erosion
GLACIATION
A hanging valley
Vertical erosion in the main
glacier is far greater than in
the tributary glaciers. So
the valleys are not the same
depth.
After the glacier has
retreated, rivers flowing
down the tributary join the
main valley via a waterfall
Can you spot the river
delta,too?
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LITHOSPHERE
U-shaped
valleys have
few contours
on their
floors.
Note the
very steep
sides.
Features of
erosion
GLACIATION
Truncated
spur
There is
a hanging
valley
here.
waterfall
Misfit
stream
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LITHOSPHERE
When a glacier
moves along the
valley, some
parts are
deepened more
than others.
Features of
erosion
GLACIATION
When the glacier
retreats, the
deepest parts fill
with water and
become lakes.
Ribbon lakes
The English Lake
District owes its
character to these
narrow ribbon lakes
along its valley
floors.
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LITHOSPHERE
GLACIATION
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LITHOSPHERE
An alluvial fan
Erosion/
deposition
GLACIATION
Caused when a
stream falling from
a side valley
reaches flatter
ground on the valley
floor.
Material is dropped
at the ‘break of
slope’ to form this
fan shape.
alluvium = silt deposited by a river
(This is really a
depositional feature.)
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LITHOSPHERE
A crag and tail
Plug of
volcanic
rock
Erosion/
deposition
GLACIATION
Edinburgh Castle
tail
These are partly erosional, partly depositional features.
The rock face facing the ice is steepened by glacial
erosion. Softer rock on the other slope is protected
from erosion to form a tail of boulder clay.Edinburgh
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LITHOSPHERE
Features of
erosion
GLACIATION
Identify
the
features
marked on
the diagram
by matching
them to the
names of
features
listed
below.
Arête; Hanging Valley; Corrie;
'U' shaped Valley; Alluvial Fan; Pyramidal Peak;
Corrie Tarn; Misfit Stream;
Ribbon Lake; Truncated Spur; Screes.
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