Glaciation Revision Session
National 4/5 Geography
What you need to know…
1. Formation of Glacial Landforms:
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Corrie
Arêtes & Pyramidal Peaks
U-Shaped Valley
Hanging Valley
2. Identification of Landforms
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O.S. Maps
Photographs
3. Land Use
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Explain Land Use Suitability
Land Use Conflicts
Solutions to Conflict
What evidence is there that this is a glaciated landscape?
Corries
Arêtes & Pyramidal Peaks
U-Shaped Valleys
Glacier Formation
Glaciers form when snow is
compressed by the weight of
more snow falling on top of it.
The snow is first compressed
into firn crystals.
It is then further compressed
into glacial ice.
Processes of Glacial Erosion
Freeze Thaw (Frost Shattering)
Water in cracks in the rock freezes and expands.
After many cycles of freezing and thawing lumps of rock are
broken off.
Plucking
Glacier ice freezes into cracks in rocks and when the glacier
moves it pulls out chunks to leave a jagged surface.
Abrasion
Rocks stuck in the ice grind away the bedrock under the
glacier.
Corrie Formation
Before Glaciation:
During Glaciation:
After Glaciation:
Snow collects in a natural
hollow on the North side of
a mountain.
The weight of the snow
eventually compresses
the snow underneath,
turning it into ice.
The hollow is deepened and
steepened by the glacier.
Plucking steepens the backwall
and abrasion (sandpaper effect)
hollows out the bottom.
Freeze thaw above the glacier
also steepens the backwall.
Once the Glacier melts a corrie
is left behind.
This is an armchair shape with
3 steep sides and 1 open one.
A tarn or lochan may be
found in the bottom.
Arêtes & Pyramidal Peaks
Arêtes are formed when 2 corries
are found back to back.
Plucking and freeze thaw action
erodes the backwall of both
corries towards each other.
A steep knife-edged ridge of rock
is created.
Where 3 or more corries are
located in the same mountainside
a pyramidal peak will form.
U-Shaped Valley
When a glacier erodes its valley,
a classic U shape is formed, with
steep side walls and a wide flat
valley floor.
U shaped valleys start life as V
shaped river valleys that existed
before glaciation.
Plucking and freeze-thaw action
truncate spurs of rock and
steepen the valley sides.
Abrasion deepens and flattens
the valley floor. Over time the
valley also becomes straighter.
Ribbon Lochs
At some points in the U-shaped valley, glaciers erode
more deeply than elsewhere because:
1.
the rock was softer and more easily eroded
or
2.
the ice was thicker at this point and therefore
more powerful.
Where ice did this, it would create an overdeepened
hollow which after glaciation filled with meltwater to
become a Ribbon Loch.
The lake takes on the same shape as the valley in
which it was formed – so tends to be long and quite
narrow.
Exam Style Question
With the aid of a diagram, explain the formation of a corrie. (6 marks)
Tips:
• Divide your answer into 3 sections:
– Before Glaciation
– During Glaciation
– After Glaciation
•
Include an explanation of the processes taking place (plucking and abrasion)
Sample Answer: Corrie Formation
Before Glaciation:
Corries form in bowl like hollows on the NE sides of mountains (1). A small hollow on the
side of a mountain will start to fill with snow all year round as temperatures get
persistently colder (1). Over the years this snow will be compressed by the weight of
further snow fall to form firn (1) and eventually glacial ice (1).
During Glaciation:
The glacier erodes by three different processes. Freeze thaw weathering (1) occurs
mainly at the top of the back wall (1). Water enters cracks in the rock, freezes and
expands, putting pressure on the sides. Repeated freeze thaw will eventually cause the
rock to split and break up, so that it falls down the back of the glacier (1). About mid
height of the back wall plucking (1) takes place, this is when water trickles into cracks and
again freezes. This time the ice forms a bond between the rock and the glacier itself. As
the glacier moves along it literally plucks the rocks attached to it out of the cliff (1).
Some of the rock remains stuck to the glacier. At the base of the corrie the erosion is
dominated by abrasion (1), where rocks embedded in the glacier are dragged along the
rock surface, eroding it make it smooth and bowl shaped (1).
After Glaciation:
When the glacier melts it leaves behind a steep backwall and a deep bowl (1), which often
fills in with water forming a lochan or a tarn (1).
Sample Answer: Corrie Formation
Before Glaciation:
Corries form in bowl like hollows on the NE sides of mountains (1). A small hollow on the
side of a mountain will start to fill with snow all year round as temperatures get
persistently colder (1). Over the years this snow will be compressed by the weight of
further snow fall to form firn (1) and eventually glacial ice (1).
During Glaciation:
The glacier erodes by three different processes. Freeze thaw weathering (1) occurs
mainly at the top of the back wall (1). Water enters cracks in the rock, freezes and
expands, putting pressure on the sides. Repeated freeze thaw will eventually cause the
rock to split and break up, so that it falls down the back of the glacier (1). About mid
height of the back wall plucking (1) takes place, this is when water trickles into cracks and
again freezes. This time the ice forms a bond between the rock and the glacier itself. As
the glacier moves along it literally plucks the rocks attached to it out of the cliff (1).
Some of the rock remains stuck to the glacier. At the base of the corrie the erosion is
dominated by abrasion (1), where rocks embedded in the glacier are dragged along the
rock surface, eroding it make it smooth and bowl shaped (1).
After Glaciation:
When the glacier melts it leaves behind a steep backwall and a deep bowl (1), which often
fills in with water forming a lochan or a tarn (1).
What evidence is there that this is a glaciated landscape?
Corrie
Pyramidal Peak
Hanging Valley
U-Shaped Valley
Arête
Ribbon Lake
Land Use in Glaciated Areas
Land Use Suitability in Glaciated Areas
Hill Sheep Farming
– Cold & wet climate – poor for growing crops.
– Steep slopes unsuited for growing crops.
– Thin soils are not fertile enough to grow crops.
Tourism
– Amazing scenery for tourist.
– Many great routes for hill-walkers.
Positives of Tourism
Negatives of Tourism
Creates 3000 jobs related to tourism in
the Cairngorms.
Skiing damages vegetation and erodes
the soil.
Tourism makes £500 million a year for
the Highlands of Scotland.
Footpaths are eroded by feet trampling
the soil. Can cost £100 per metre to
mend a path.
Tourism makes up 80% of the local
economy.
Salaries for workers are low and
employment is seasonal.
Locals can take advantage of tourist
facilities.
Tourists make the roads very congested.
This increases commute times for locals.
Land Use Conflicts
Why do you think these two land uses might be
in conflict with each other?
V
What solutions can you suggest to deal with this
conflict?
Land Use Solutions
Problem:
Footpath Erosion
Solutions:
1. Routes signposted.
2. Stones laid on footpaths.
3. Footpaths fenced off
from fields.
4. New routes planned
away from affected
areas.
Problem:
Litter & Vandalism
Solutions:
1. Designated picnic areas
with litter bins.
2. Park Wardens supervise
and educate.