Glaciation – Features
Corrie
1. Snow collects in a north facing slope and turns into neve through the process of nivation as
the air is removed and the snow gets compressed.
2. Overtime this neve becomes compressed as layers build up and becomes firn, this may take
25-100 years
3. Freeze thaw happens above the glacier, this is where water expands and contracts due to
the freezing and melting of water within cracks, this weakens the rock and eventually it will
drop off onto the glacier below
4. Glacier moves down hill by the force of gravity
5. As they move downhill crevasses form, usually on the steepest parts of the glacier, the
bergshrund is found below the headwall and allows for material from freeze thaw to enter
the glacier
6. As it moves it plucks on the backwall – this steepens the back wall
7. Plucking is where the glacier freezes round a rock and is then ripped out as the glacier moves
down hill
8. Also abrasion occurs under the glacier
9. Abrasion is like sand paper – englacial moraine (which is there due to plucking and freeze
thaw) rubs the base of the glacier and deepens and smoothes the corrie floor
10. The backwall is also steepen through freeze thaw – this occurs above the glacier and
continues to steepen when the glacier has melted due to the difference in temperatures
above and below freezing
11. The glacier rotates as they move down hill over deepening the corrie floor as it follows the
floor of the corrie
12. It is additionally over deepened by abrasion as the glacier is at its deepest at this point; this
often leaves a corrie lip
13. Often a lochan/tarn is left behind
Arête
1. An arête is a narrow ridge between 2 corries; famous examples are Striding Edge in the Lake
District and Crib Goch in North Wales.
2. The glacier forms when snow collects in a north facing hollow and collects over years. The
snow becomes glacial ice by the process of nivation. Once this process is completed the ice
is called firn.
3. It is classed as a glacier when the ice starts to move by the force of gravity,
4. Steep sides are created from plucking by the glacier
5. Plucking is where the glacier freezes round a rock and is then ripped out as the glacier moves
down hill
6. The floor is deepened by abrasion - Abrasion is like sand paper – englacial rock and ice
through the weight of the glacier abrades the bottom of the corrie smoothing and
deepening the floor
7. This is usually deepened by the rotational movement of the glacier which over deepens the
corrie floor
8. Over time the 2 corries push back
9. This creates a knife edge ridge between the 2 corries and this is called a arête
10. Freeze thaw continues to steepen the walls after Glaciation, this is where water expands and
contracts due to the freezing and melting of water within cracks, this weakens the rock and
eventually it will drop off onto the glacier below or form talus slopes below the arête if the
glacier has melted.
Pyramidal Peak
1. Pyramidal peaks are steep mountains surrounds by at least 3 corries, a famous example of
this is the Matterhorn.
2. Between the corries leading to the summit are arêtes
3. The corries form by Snow collects in a north facing slope and turns onto neve through the
process of nivation as the air is removed and the snow gets compressed.
4. Overtime this neve becomes compressed as layers build up and becomes firn, this may take
25-100 years
5. Freeze thaw happens above the glacier, this is where water expands and contracts due to
the freezing and melting of water within cracks, this weakens the rock and eventually it will
drop off onto the glacier below
6. The freeze thaw helps to steepen the backwall of the corries creating a pyramidal peak with
steep sides
7. Glacier moves down hill by the force of gravity
8. As they move down hill crevasses form, usually on the steepest parts of the glacier, the
Bergshrund is found below the headwall and allows for material from freeze thaw to enter
the glacier
9. As it moves it plucks on the sides of the glacier – this steepens the back wall creating a steep
wall
10. Plucking is where the glacier freezes round a rock and is then ripped out as the glacier moves
down hill
11. Also abrasion occurs under the glacier
12. Abrasion is like sand paper – englacial moraine (which is there due to plucking and freeze
thaw) rubs the base of the glacier and deepens and smoothes the corrie floor
13. Abrasion helps to deepen the corrie floor again making the peak higher than the
surrounding area
14. The backwall is also steepen through freeze thaw – this occurs above the glacier and
continues to steepen when the glacier has melted
U-shaped Valley, mis-fit stream, Ribbon Lake
1. U-shaped valleys are where a glacier has changes the shape of a V-shaped Valley created by
river processes.
2. Corries feed the lower valleys with glaciers; corries collect snow and then by the process of
nivation turn the snow into glacier ice.
3. These move downhill by the force of gravity
4. The valley before glaciation had interlocking spurs created where the river wound its way
around the valley
5. The glacier as it is big and heavy straightens the valley by abrading the bottom and plucking
the sides
6. Abrasion is where englacial moraine sandpapers the valley floor smoothing the floor and
deepening it
7. Plucking is when the ice freezes around the rock and then as the glacier moves “rips” the
rock out of the cliff
8. Abrasion deepens the valley while the plucking steepens the sides of the valley and widens
the valley floor
9. Freeze thaw continues above the glacier creating lateral moraine, this is where water
expands and contracts due to the freezing and melting of water within cracks, this weakens
the rock and eventually it will drop off onto the glacier below
10. Talus slopes are left on either side of the valley from the lateral moraine when the glacier
has melted, this create a parabolic shape valley rather than a classic U-shaped valley.
11. After the glacial period the valley floor can have a long lake within the floor, this is called a
ribbon lake. This is where the floor has been over deepened by abrasion. It may have a
moraine dam which stops the water from escaping
12. If the valley becomes flooded it is called a ffyord
13. A mis-fit stream is a small stream left in the large U-shaped valley; the stream could not have
created the valley as it does not have enough erosion capacity.
14. The interlocking spurs have been removed by abrasion and plucking creating truncated
spurs.
15. Freeze thaw continues to add material to the talus slopes when the glaciers have melted,
Hanging Valley
1. A hanging valley is formed where 2 glacier meet as they travel downhill by the force of
gravity
2. Corries feed the lower valleys with glaciers; corries collect snow and then by the process of
nivation turn the snow into glacier ice.
3. The glacier as it is big and heavy straightens, deepens and widens both valleys by abrading
the bottom and plucking the sides
4. The bigger glacier has greater capacity for more downward erosion due to its increased
weight, so deepens the larger valley more than the smaller valley
5. both glaciers straighten the valleys and truncate any interlocking spurs
6. It does this in 2 main ways;
7. Abrasion is where englacial moraine sandpapers the valley floor smoothing the floor and
deepening it, as one glacier is heavier the abrasion will deepen the base more
8. Plucking is when the ice freezes around the rock and then as the glacier moves “rips” the
rock out of the cliff leaving a jagged and steep wall
9. Abrasion deepens the valley, while plucking steepens the sides of the valley and widens the
valley floor
10. Freeze thaw continues above the glacier creating lateral moraine, this is where water
expands and contracts due to the freezing and melting of water within cracks, this weakens
the rock and eventually it will drop off onto the glacier below
11. this material is then used as a tool for erosion by the glacier in the process of abrasion
12. After glaciation when the glaciers have melted the smaller valley is less deep than the larger
valley so is left “hanging” above the bigger glacier
13. There is a steep drop between the two glaciers which have been created by the differing
erosion rates, steepened by plucking on the sides and deeper due to increased abrasion
14. this often has a waterfall flowing over it with a alluvial fan below the waterfall
15. Freeze thaw continues to steepen the valley sides after the glacier has melted
Roche Moutonnee
1. A glacier moves downhill by gravity
2. As it moves the glacier may pass over an exposed rock surface.
3. The pressure increases in the glacier due to the exposed rock, and the ice being forced over
the exposed rock
4. As the pressure increases the ice melts on the stoss side (upstream)
5. The glacier slides smoothly (due to the melting ice) over the exposed rock it may abrade and
polished the exposed rock surface
6. Abrasion is where englacial moraine “sand papers” the exposed rock polishing, smoothening
and deepening the valley floor
7. It may leave striations (scars along the rock showing the direction of the glaciers movement)
on the exposed rock due to englacial moraine scratching the surface
8. The pressure is released so on the downstream side (lee side) so the ice refreezes (this is
called regelation) around the rock and causes plucking to occur
9. Plucking is where the glacier freezes around the rock and then as the glacier moves the rock
is ripped out leaving jagged exposed rock
10. This leaves a steep and jagged lee side
11. Roche Mountonnees therefore have a smooth upper slope (stoss) and rougher blocky down
slope (lee) due to regelation and plucking
FluvioGlacial Features (Made with water from the glacier)
Esker
1.
Pressure of the ice on its bed causes melting
2.
Surface meltwater also runs to base of ice through crevasses due to seasonal melt or changing long
term climate trends
3.
This water then flows in a tunnel beneath the ice.
4.
As the water carries fine sediment along, the tunnel can fill and leave behind a long sinuous ridge of
graded material once the ice has fully melted
5.
The material is transported the same way a river transports material through saltaion, suspension
and traction
6.
When the glacier melts the material is deposited in long "snake" like patterns along the valley floor
7.
The material is sorted into different sizes as the water carries bigger paprticles only during greater
flow rates of the englacial stream
Kame Terrace
1.
Kame terraces are formed when the glacier and snows melt around the glacial areas
2.
They are found on areas where the ice sheet is retreating where water collects around the snout of
the glacier
3.
Or along the sides of the valleys as the ice in contact with the valley side melts quicker due to the
darker colour of the valley side
4.
Glacial streams often run down these areas as well
5.
This causes large pools of water to form; they are often dammed at the end
6.
As the glacier is impermeable water collects on the surface
7.
The water usually has sediment within it due to the nature of erosional processes occurring in the
glacier (abrasion, plucking)
8.
As the water collects and settles in these ponds or lakes the sediment is deposited due to the water
being stationary
9.
The material is then deposited on the floor in layers
10. Once the glacier melts this material is deposited along the valley floor in mounds usually around the
side of the valley or where the ice lakes formed
11. The deposited material is different to moraines as the material is sorted due to the movement of
water
Kettle Holes
These are hollowing left in the landscape when the ice has melted
As glaciers retreat they can often leave sub surface blocks of ice (dead ice as it is not longer connect to the
glacier)
Over time these melt and the ground above collapse to form hollows
They can then be in filled with water creating kettle holes – Loch Morlich is believed to be a kettle hole
Glacial Till
Traditionally called boulder clay this is material deposited by the glacier.
Its main characteristic is its unsorted nature
The glacier has deposited any material it has been carrying and deposited on the landscape
The stones are not jagged but not smooth like rivers and coastal loads.
It can have any size stones within the Till and is help together by rock “flour” the fine particles of the rock
ground together by glacial erosion
It shows the extent of Glaciation due to it being deposited where ever a glacier has disappeared
There is more in the lower stages of the glacier
In parts of Germany it can be over 70m deep!
Drumlin
As an ice sheet decays and dies back towards the mountains it will drop unsorted piles of moraine as heaps of
boulder clay. If the climate changes again and gets colder, the ice will re-advance over these piles, smoothing
them into long half-egg shaped mounds.
The front is the highest part while the tail slopes in the direction of the glaciers movement
They often form in clumps and are known as basket of eggs topography
Lateral/Medial Moraine
These are moraine mounds found in the same direction of travel of the glacier
Lateral moraines are material that has been deposited onto the glacier from the sides of the glacier
often by freeze thaw, when the glacier melts it retreats leaving this material on the side of the valley,
often this can form the parabolic shape of the U-shaped valleys
Medial moraines are formed where 2 glacier join mean 2 lateral moraines join and become one
moraine in the middle of the glacier
Terminal moraine
Eroded material is picked up by the glacier and carried upon, within and beneath it as it moves downhill
As the ice passes down into more temperate climates it begins to melt (ablation) and eventually it melts away
completely.
It drops its entire load as a line along its decaying front
As the glacier melts more ice behind it takes its place and then melts and deposits what its carrying as well
The whole system acts as a conveyor belt moving material from up the glacier down to the lower reaches of
the valley
This starts to build up a large mound in front of the final line of the glacier
The terminal moraine shows the furthest reaches of the glacier, the other side of the glacier – no glacation has
occurred and is usually an outwash plain
Other push or smaller recessional moraines may be present behind the glacier as the glacier increases and
decreases in size
Outwash Plains
These are where water from the glacier has washed through the despotised material.
It also carries its load from the glacial erosion with it
As the streams have varying flow rates due to temperature changing relating to the glacial melt it
can carry different size sediment at different times of the day or different seasons within the year
This varying amount of water means the sediment is sorted into sizes depending upon the flow of
water from the glacial discharge
Due to this deposition and transportation occurring the outwash plain is characterised by braided
streams