LITHOSPHERE
GLACIATION
Glaciation
Learning Intentions
Be able to understand the processes
which occurred during the last ice age.
Be able to describe and explain the
formation of features formed during
glacial periods.
1
Processes Of Weathering
LITHOSPHERE
Freeze-Thaw
Water enters
crack
GLACIATION
Ice freezes and exerts
pressure from inside rock
Rock breaks up
over time
2
LITHOSPHERE
GLACIATION
Processes Of Erosion Plucking
Water can enter cracks in the rock and
freeze, as it does so it freezes the glacier
and rock together.
As the glacier moves it literally pulls the
rock out and is likely to occur more when
temperatures fluctuate around 0ºC.
3
Processes
Of Erosion Plucking
GLACIATION
LITHOSPHERE
The water from this process often comes from
the friction between ice moving over rock.
Another source of the water is a result of
melting of the ice; during the day it melts, but
refreezes at night.
Plucked Rock
4
LITHOSPHERE
GLACIATION
Processes Of Erosion Abrasion
This is when rock under the ice or stuck in
the bottom of it, scrape away at the
surface of the bed rock surface.
The rock comes from the debris produced
by Freeze Thaw and Plucking.
The bedrock is scratched, polished,
smoothed and eventually worn away by the
scouring action.
5
LITHOSPHERE
GLACIATION
Processes Of Erosion Abrasion
Striations or scratches can
be left on the rock
6
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
7
wall.
Corries Task 3 Q2
GLACIATION
LITHOSPHERE
Match the letters to the descriptions.
Flat Base
b
Horse shoe
shape
Steep sides
Cliffs/
Outcrops/Scree
d
a
c
LITHOSPHERE
GLACIATION
S
N
Layers
Ice
Hollow
Corrie Development 1
LITHOSPHERE
GLACIATION
Corrie Formation
Stage 1
Snow collects in hollows high up in the
mountains, usually in north facing slopes.
Pressure causes the lower layers of ice
to turn to ice.
Gravity and reduced friction cause the ice
to move downhill.
The hollow in which the snow and ice
collected is eroded by the ice to form a
much deeper, steeper hollow called a
Corrie.
10
Corrie DevelopmentGLACIATION
2
LITHOSPHERE
FT
PL
RS
L
AB
GLACIATION
LITHOSPHERE
Corrie Formation
Stage 2
As meltwater under the ice seeps into cracks the rock in the
hollow is weathered by freeze thaw action.
Then when the meltwater freezes onto the rock plucking takes
place.
The backwall and sidewalls of the hollow are eroded quickly by
these two processes.
Abrasion due to rocks taken in by frost shattering and plucking
deepens the hollow.
The glacier slips in a rotating movement, which means that it is
eroding the most at the back wall and base. So with less erosion
at the base so a lip starts to form, which has deposits of rocks
left on it by the glacier
12
Corrie DevelopmentGLACIATION
3
LITHOSPHERE
Lip
Scree
Lochan
LITHOSPHERE
GLACIATION
Corrie Formation
Stage 3
When the ice melts a corrie can clearly be
seen.
It is an armchair shaped hollow in the
mountainside with steep sidewalls and steep
backwall and a flat base.
Sometimes after glaciation, corries fill with
meltwater to form corrie lochs or tarns.
14
LITHOSPHERE
Features of
erosion
GLACIATION
Formation of a corrie
15
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.
16
LITHOSPHERE
Features of
erosion
GLACIATION
Red Tarn
17
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.
18
LITHOSPHERE
GLACIATION
Arete Formation
Aretes are formed when two corries are
found back to back or side by side in the
mountain area.
Plucking and freeze thaw action erode the
backwalls of both corries towards each
other.
The land between them gets narrower and
narrower until all that remains is a steep
knife-edged ridge of rock.
19
LITHOSPHERE
Features of
erosion
GLACIATION
Striding Edge
Striding Edge
arete on
Helvellyn,
Lake District
20
LITHOSPHERE
Features of
erosion
GLACIATION
MATTERHORN
Pyramidal peaks are also called horns.
21
Pyramidal PeaksGLACIATION
LITHOSPHERE
b
Pyramidal Peak
Diagram Of Pyramidal Peak
Erosion
c
a
c
LITHOSPHERE
GLACIATION
Pyramidal Peak Formation
Found where 3 or more corries are located in the
same mountainside.
Plucking and freeze-thaw action of the backwalls
of each corries occurs to such an extent that the
rounded summit is eroded into a sharp peak or
point.
The rock erodes back so that the mountain becomes
steeper and the three corrie walls come close enough
to converge
This leaves a pointed and jagged (freeze thaw) peak
eg. The Eiger (The Alps)
23
U Shaped ValleyGLACIATION
LITHOSPHERE
b
d
Deep
valley
a
Steep sides
c
Straight
valley
Loch in
wide valley
LITHOSPHERE
GLACIATION
U-shaped Valley – Misfit
Steam
25
LITHOSPHERE
GLACIATION
U-shaped Valley – Ribbon
Lake
26
LITHOSPHERE
Features of
erosion
GLACIATION
A VALLEY GLACIER
The next few slides will help to explain the
formation of this feature.
27
GLACIATION
LITHOSPHERE
U Shaped Valleys
Ice starts to flow
out of corries or
off ice caps
It flows down V
shaped river valleys
GLACIATION
LITHOSPHERE
Ice moves down river valley
Usual erosion occurs
Abrasion deepens
Plucking erodes sides back
Glacier also bulldozes
rock out of the way
U shaped valley
develops
LITHOSPHERE
GLACIATION
U-shaped valley formation
When a glacier erodes its valley, a classic U shape
is formed, the side walls tend to be steep and
possibly curving inwards at the base, and the
valley floor almost flat.
U shaped valleys start life as V shaped river
valleys that existed before glaciation. Ice moves
down the V shaped valley and glaciers erode it and
change its shape as the ice moves.
Plucking and freeze-thaw action truncate spurs of
rock and steepen the valley sides and abrasion
deepens and flattens the valley floor. Over time
the valley also becomes straighter.
30
LITHOSPHERE
GLACIATION
Misfit Stream
After glaciation when the ice melts, the
river which originally flowed on the floor of
the V-shaped valley may once again begin
to flow through the U-shaped valley.
It is now called a Misfit Stream. It is so
called because it looks out of place in the
now large valley and also because it did not
contribute to its formation.
31
LITHOSPHERE
GLACIATION
Ribbon Lake
At some points in the U-shaped valley, glaciers
erode more deeply than elsewhere.
This might have been because the rock was softer
and more easily eroded or because 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 Lake.
The lake takes on the same shape as the valley in
which it was formed – so tends to be long and
quite narrow.
32
Truncated Spurs GLACIATION
LITHOSPHERE
Truncated Spur
Steep Cliffs Overlooking U
shaped valleys
Often Scree collects
underneath
Truncated Spurs GLACIATION
LITHOSPHERE
Bulldozed by glaciers
Abrasion & plucking help with erosion
Post glaciation freeze-thaw has
created more scree below
Truncated Spurs GLACIATION
LITHOSPHERE
Cliff
Face
l
Scree
k
m
Steep
Sides
U Shaped
Valley
LITHOSPHERE
GLACIATION
These are deep U shaped valleys formed by the erosion of valley glaciers
As glaciers emerge from the lip of their corries they merge and form a more
powerful glacier which erodes more readily
They follow the course of former V shaped river valleys
As they progress down the valley through their own weight (gravity) they
erode like a corrie glacier
The top of the valley sides are eroded by freeze thaw weathering, mid
height of the valley by plucking and the base by abrasion
This means that the former V shaped valley will widen, steepen and
deepens
When a U shaped valley cuts across a water shed it is called a glacial breech
The interlocking spurs of the river valley literally have their noses cut off by
the ice, leaving a ridge descending into the valley which suddenly steepens,
sometimes into an outcrop or a cliff face
The steepest part of the valley is often at the trough head (start) where the
descending corrie glaciers move quickly under gravity. Other more eroded
points tend to be a result of the glacier moving over weaker rock which
abrades readily, deepening the base
This over deepening can fill in with water leaving a ribbon loch
eg, Loch Avon (Cairngorms)
LITHOSPHERE
Features of
erosion
GLACIATION
Stages in the formation of a U-shaped valley
37
LITHOSPHERE
Features of
erosion
GLACIATION
A U-shaped valley in Canada.
38
Features of
erosion
LITHOSPHERE
When a glaciated valley by
the coast 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
39
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?
40
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
41
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.
42
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.
(This is really a
depositional feature.)
alluvium = silt deposited by a river
43
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.
44