FEATURES OF GLACIAL EROSION

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Features of erosion
These slide-shows are all on the Prepwork folder
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
PYRAMIDAL PEAKS
ARETES
U-SHAPED VALLEYS
HANGING VALLEYS
TRUNCATED SPURS
RIBBON LAKE
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Features of erosion
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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Features of erosion
Read the section about corries in the booklet,
pages 28 and 29. 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 like a),b) and c).
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Features of erosion
NOTE- the labels on the first two sketches are
not just naming the features, like in sketch c).
They describe what is happening in the sketch,
naming the processes. This makes these labels
-and the diagram- worth more marks than one where
bits only are named!
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Features of erosion
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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Features of erosion
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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Features of erosion
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Formation of a corrie
Take a handout of the diagram and stick it into
your jotter.
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Features of erosion
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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Features of erosion
On an OS map, corries are shown as
horseshoe-shaped features.
scree
Note the east-facing aspect snow lasts longer
before melting.
N
Note the contours are very close together,
especially on the steep backwall. Note also the
bare rock symbol.
tarn
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Features of erosion
Red Tarn
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Features of erosion
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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Features of erosion
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.
These corries and arete are in the Cairngorms.
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Features of erosion
arete
Striding Edge
Striding Edge arete on Helvellyn, Lake District
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Features of erosion
MATTERHORN
Pyramidal peaks are also called horns.
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Features of erosion
A VALLEY GLACIER
The next few slides will help to explain the
formation of this feature.
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Features of erosion
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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
These are the actions that form this feature.
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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Features of erosion
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
V-shaped valley.
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Features of erosion
A U-shaped valley in Canada.
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Features of erosion
When a glaciated valley is submerged or drowned
by a rise in sea level, a fiord is formed.
The sea lochs of western Scotland are the best
examples of fiords in the British Isles.
Fiord/fjord
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Features of erosion
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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Features of erosion
Truncated spur
U-shaped valleys have few contours on their
floors.
There is a hanging valley here.
Note the very steep sides.
waterfall
Misfit stream
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Features of erosion
When the glacier retreats, the deepest parts fill
with water and become lakes.
When a glacier moves along the valley, some parts
are deepened more than others.
The English Lake District owes its character
to these narrow ribbon lakes along its
valley floors.
Ribbon lakes
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Erosion/ deposition
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.
An alluvial fan
(This is really a depositional feature.)
alluvium silt deposited by a river
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Erosion/ deposition
A crag and tail
Edinburgh Castle
crag
tail
Plug of volcanic rock
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.
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Features of erosion
Now play the glacial erosion dominoes game!
There is a mapping question sheet to try at this
point.
You will need a copy of the questions and the map
extract supplied.
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A ruler may also be quite useful.
The extract is of the area you will need to know
for the Rural Land Use section of the course.
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Features of erosion
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.