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Glaciation Landforms |
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Landforms
created by glacial erosion
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The landforms
created by glacial erosion are:
Corries
Arêtes Pyramidal Peaks Glacial Troughs (U-Shaped Valleys) Truncated Spurs Hanging Valleys |
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How is a
corrie formed?
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Snow collects in a natural hollow on the
side of a mountain. Over time, further snow collects in the
hollow. This extra weight compresses the snow underneath,
turning it into ice.
The ice is pulled downhill by
gravity, it doesn’t move straight down, it moves in
a curved way
The hollow is deepened
and widened by the corrie glacier through
the processes of abrasion and
plucking.
This over
deepening leads to an ‘armchair’
shape characteristic of a corrie and
causes a ‘rock lip’ to be
formed.
Plucking
and freeze-thaw mean that
the back wall of the corrie
is very steep.
When the ice melts,
a small lake may be
left behind the lip,
this is called a
corrie-lake or a
tarn.
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Fieldsketch of
Cwm Idwal looking south-west
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Formation of
an arête
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Arêtes are
‘knife-edged’ ridges formed between two corries which have
formed next to each other.
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Formation of a
pyramidal peak
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Pyramidal peaks
are formed when
three or more corries form around a mountain. They cut backwards
to leave a “horn” or “pyramidal peak” in the middle.
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| Differences between river and glacier valleys. | ||
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Unlike a river, a
glacier fills the entire valley and so has much more power
to erode.
It does not have
to wind around interlocking spurs and can widen, deepen and
straighten its valley.
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Glacial Trough
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•Glacial
troughs can also be called U-shaped valleys because they’re
shaped like a U.
•Misfit
stream: this is a small stream in the bottom of a
glacial trough, it looks too small to have made the
valley.
•Steep
valley sides, some material has slumped down
to make the sides a bit gentler over the
years
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Characteristics of a glacial trough
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Between truncated spurs are hanging valleys which have
not been eroded as deeply as the main valley.
Interlocking
spurs are truncated as the glacier cuts straight
through the landscape.
The river
that flows through the valley after the ice age is
described as a misfit stream.
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Landforms
created by glacial deposition
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 Moraines
Drumlins
Erratics
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What is a
moraine?
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Moraine is a type of landform that
is created when a glacier deposits the material (till) that
it has been transporting. It is made up of unsorted angular
rocks. It shows the furthest point a glacier reached.
Sometimes water gets trapped behind the terminal moraine, in
the glacial trough. This makes a ribbon lake. There are
several types of moraine:
 Lateral
Medial
Ground
Recessional
Terminal
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How are
drumlins formed?
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When a glacier is
moving slowly, it doesn’t have much energy. This means it
can’t erode and transport material – it can only shape the
clay underneath.
This
makes smooth hills. Some people say they look like
eggs.
It is common to find several drumlins
grouped together. A collection of
drumlins is called a swarm.
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What are erratics?
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An erratic is a
boulder that is different to the bedrock upon which it is
sitting. They have been transported and deposited by a
glacier. Therefore erratics are useful indicators of
patterns of former ice flow.
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What happens when ice melts ?
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Eskers
•Any
material that was carried in a stream under the glacier gets
left as a long wiggly ridge.
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Kames
•Any
debris that was in a crevasse gets dropped to the valley
floor in a heap.
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Formation of ribbon lakes
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Ribbon lakes are
long, narrow lakes found on the valley floors of glacial
troughs. They can be formed due to a combination of erosion
and depositional processes.
When a
glacier moves along its valley, areas of softer rock
may be eroded more easily, or the glacier may be
joined by a tributary glacier to increase its power
to erode. When the glacier retreats, the deepened
sections fill with meltwater and become lakes.
Deposition of moraine across the valley can also act
as a dam,
trapping the meltwater and thereby creating a ribbon
lake.
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