Glacial Erosion
1. Rocks frozen
into glacier ice.
Ice
2. Glacier moves
3. Rocks scrape along the
valley floor and erode it.
Valley
Floor
This type of erosion is called abrasion.
Glacial Erosion
1. Ice freezes around
bits of rock
3. Bits of rock are taken from
the rock face with the ice
Ice
2. The Glacier moves
Rock
This type of erosion is called plucking
Formation of a Corrie
How to answer the question:
‘Explain how a corrie was formed.’
• Mention what the shape
was like before
• Mention what the shape
is like afterwards
• Mention how the shape
was changed
Before Glaciation
• Snow falls in a hollow
high in the mountains
• The snow
compresses into ice
During Glaciation
• The ice moves downhill
as a glacier
•At ‘A’ freeze thaw
weathering makes the
backwall steeper and jagged
•At ‘B’ plucking makes the
backwall steeper and
jagged
A
B
C
•At ‘C’ abrasion deepens and
smoothes the hollow
For full credit marks mention how
abrasion, plucking & freeze thaw work
After Glaciation
• The corrie
has steep
sides and
steep
back wall
The
lip is
emphasised
by moraine
deposited by
the glacier
Often
• The
hollow is
deeper
water
fills the
corrie known
as a tarn
1. Two Glaciers erode
back to back into a
mountain by plucking
as they move
downhill.
2. This forms 2 corries.
3. Plucking makes the
ridge narrower and
this is called an Arete.
4. Freeze-thaw
weathering makes the
Arete sharper
1. Where glaciers start in a
hollow they move
downhill and erode by
plucking and abrasion to
form corries.
2. Three or more corries
form back to back or side
by side
3. Where the corrie
sidewalls meet they form
ridges which become
narrower by plucking.
4. These are called Aretes.
Three Arêtes meet to
form a pyramidal peak
5. The peak becomes
sharper by freeze-thaw
weathering
Formation of U-shaped valley
Before glaciation a v-shaped valley
During the ice age a glacier moves down
the valley.
Rocks trapped in the bottom of the ice act
like sandpaper wearing away the valley by
abrasion.
The glacier deepens, straightens and
widens the valley by abrasion.
After the ice melts a U-Shaped valley
remains
After Glaciation there is sometimes a misfit stream or ribbon lake in the bottom of
the valley
1. Erosion in the main glacier is far
greater making a deeper valley.
Map View
2. Erosion in the tributary glaciers is
less making a shallower valley.
3. The shallower valleys are left
‘hanging’ above the deeper main
valley.
4. Waterfalls often fall over the edge
at the end of the hanging valley
into the main valley.
5. At the base of a waterfall alluvial
fans are sometimes found as a
result of deposition
Tributary Main
valley
valley
Cross Section
Tributary
valley
Main
valley
Ribbon Lakes
1. Glaciers move down a former v-shaped valley
and erode the valley by abrasion and plucking
turning the valley into a u-shape.
2. Some ribbon lakes form when the glacier meets
softer rock.
3. The glacier erodes more deeply at these points.
4. After the glacier has melted the deeper parts fill
with water to form ribbon lakes
Ribbon Lake
Hard
Rock
Soft Rock
Hard
Rock
Side view of valley
before Glaciation
Hard
Rock
Soft Rock
Hard
Rock
Side view of valley
after Glaciation
How Till is formed
1. The temperature rises due to climate change at the end of
the ice age or the temperature rises as the glacier reaches
lower land.
2. The glacier begins to melt. The snout moves back up the
valley.
3. The melting ice cannot hold the rocks, gravel and sand that
have been trapped in it.
4. All this material is deposited as the glacier continues to melt.
5. The moraine is all mixed up with different sizes of material.
6. Where the glacier has been it leaves behind moraine on the
floor of the valley called ground moraine, till or boulder
clay.
Terminal Moraine
Drumlins
Melting Glacier
Till
Outwash
Plain
How Drumlins are formed
1. The temperature rises due to climate change at the end of the
ice age.
2. The glacier begins to melt. The snout moves back up the
valley.
3. The melting ice cannot hold the rocks, gravel and sand that
have been trapped in it.
4. All this material is deposited as the glacier continues to melt.
5. The moraine is all mixed up with different sizes of material.
6. A large rock is deposited and traps more moraine around it
forming a drumlin
7. The glacier continues to move when it is melting and makes
the drumlin smooth
Terminal Moraine
Drumlins
Melting Glacier
Till
Outwash
Plain
How Terminal Moraine is formed
1. The glacier pushes the moraine in front of it like a bulldozer
2. The temperature rises due to climate change at the end of
the ice age.
3. The glacier begins to melt. The snout moves back up the
valley.
4. The melting ice cannot hold the rocks, gravel and sand that
have been trapped in it.
5. All this material is deposited as the glacier continues to melt.
6. The moraine is all mixed up with different sizes of material
7. The furthest point the glacier reached is marked by a ridge
of material running across the valley called terminal moraine
Terminal Moraine
Drumlins
Melting Glacier
Till
Outwash
Plain
How the outwash plain is formed
2.
3.
4.
5.
The temperature rises due to climate change at the end of
the ice age.
The glacier begins to melt. The snout moves back up the
valley and melt-water streams carry material down the
valley.
The outwash plain is in front of where the glacier has been
and is deposited by melt-water.
The outwash plain is made from sorted sands and gravels.
Gravels are deposited in the spring when there is more
melting. Sands are deposited in the autumn when there is
less melting
Drumlins
Melting Glacier
Till
Terminal Moraine
1.
Outwash
Plain
1.
2.
3.
4.
5.
6.
7.
8.
The temperature rises due to
climate change at the end of
the ice age.
The glacier begins to melt.
Tunnels form in the melting ice
Meltwater streams flow in the
tunnels
Deposits are laid down along
the course of where the stream
has been.
The snout moves back up the
valley
Long, winding ridges of sorted
material known as eskers are
left where these streams have
been
Gravels are deposited in the
spring when there is more
melting. Sands are deposited
in the autumn when there is
less melting
How an esker is
formed