Glaciers Flashcards
What are glaciers
A glacier is a large mass of ice that moves slowly over land. They are often called rivers of ice.
Inputs - snow and rain
Outputs - meltwater and moraine
How do glaciers grow
Glaciers grow when their inputs exceed their outputs.
When they grow (accumulate), the snout of the glacier advances.
When they shrink (ablate), the snout retreats.
What is meltwater
Water under the glacier -
Lubricates the glacier -helps it to move by a process called basal sliding
Meltwater - between ice and ground
If temperatures are cold enough, meltwater can freeze for that period of time, the glacier stops moving
What is moraine
a mass of rocks and sediment carried down and deposited by a glacier
State the glacial processes
freeze-thaw weathering
- erosion – abrasion and plucking
- movement and transportation – rotational slip and bulldozing
- deposition
Explain freeze-thaw weathering as a glacial process
As water enters the cracks in the mountain face it freezes in the cracks and expands by up to 9% which widens the crack , creating a weakness.
This process repeats until parts of the mountain face break off leaving a jagged landscape.
Often takes place at the top of the mountain where conditions are coldest which shapes the landscapes you see in glacial environments
As Glaciers advance, they ____________
As Glaciers advance they erode the landscape in two ways: abrasion and plucking
Explain the process of abrasion as a glacial (erosional) process
Bits of rock which are stuck in the ice grind against the rock below the glacier, wearing it away
Explain the process of plucking as a glacial (erosional) process
Meltwater at the base, back or sides of a glacier freezes onto rock (on the glacier bed). As the glacier moves forward it pulls out pieces of rock
How glaciers transport sediment
Rotational slip
Bulldozing
Describe the process of bulldozing as a movement and transportation process
As a glacier moves downhill it pushes loose sediment ahead of it by sheer force. This pushes the material downhill
Descibe the process of rotational slip as a movement and transportation process
When the glacier moves out of a hollow in a circular motion
Occurs in north facing hollows in uphill areas
Explain the process of deposition
Most of the deposition takes place at the snout of the glacier
If a glacier is overloaded with material, or when the ice melts, the material is deposited on the valley floor, forming landforms such as moraines and drumlins
What is till
Unsorted glacial sediment that forms moraine
What is outwash
This is when fine material such as sand and gravel (deposits of moraine) get washed away from the front of the glacier by small meltwater streams
The streams sort the material by size and deposit it in layers called outwash, in the front of the glacier
It is sorted as the water loses energy
Examplpes of formation of landforms resulting from erosion
corries, arêtes,
pyramidal peaks, truncated spurs, glacial
troughs, ribbon lakes and hanging valleys.
Describe the formation of corries
Initial formation. A corrie is formed when snow begins to build up in a small hollow, often facing North or North-East in the UK so less affected by direct sunshine.
The snow turns to ice and a small corrie glacier fills the hollow.
Development over time. The corrie glacier begins to move downhill by
rotational sliding, while freeze-thaw weathering, along with plucking, loosens and removes material from the back of the hollow, producing a
steep back-wall.
Moraine gets dragged along the base of the glacier,
deepening the hollow by abrasion and forming a rock basin.
Erosion at the front edge of the corrie is not so powerful, so a rock-lip develops, often made higher by deposition of some of the moraine.
When the ice begins to melt, the rock lip acts as a natural
dam to the meltwater, and a deep, rounded corrie-loch (or tarn)
sometimes forms.
Describe the formation of glacial trough
- Ice occupies a former river valley, often V shaped.
The glacier is fed by
several tributary glaciers that start in corries. These join together and
cause the ice to erode powerfully. - Processes include abrasion-where moraine within the ice to the sides has
a sandpapering effect on both sides and base, and plucking – where the ice following melting under pressure, freezes to the rock and tears part of it
away when it moves. - The valley is widened and deepened and the cross profile becomes a
steep sided trough with broad base and steep valley sides (U shaped
valley). The ice removes the interlocking spurs of the former river valley. - After the ice melts, the valley floor is filled with glacial debris and river
deposits. In places there may be ribbon lakes where water fills hollows.
Explain the formation of a hanging valley
Ice occupies a former river valley, often V shaped. The glacier is fed by
several tributary glaciers that start in corries. These join together and
cause the ice to erode powerfully by plucking and abrasion. The main
valley is widened by lateral erosion and deepened by vertical erosion
forming a glacial trough/u-shaped valley.
- Small glaciers can erode only shallow valleys while large glaciers can
erode much deeper valleys. A hanging valley is a shallow valley carved by
a small tributary glacier and so when the ice melts the height of the valley
floor is left “hanging” high above the valley floor eroded by the larger trunk
glacier. - If a river occupies a hanging valley it plunges as a waterfall to the floor of
the main valley and sometimes builds up an alluvial fan of coarse
materials
Formation of an arête
An arête is a knife-edge ridge often found at the back of a corrie or separating two glaciated valleys.
They are often extremely narrow and
form when erosion and weathering in two back-to-back corries cause the
land in between to become narrower.
Continued freeze thaw causes
aretes to become more jagged, with very steep sides.
Formation of pyramidal peaks
If three or more corries have formed on a mountain, erosion (plucking) may lead to
the formation of a single sharp-pointed pyramidal peak or horn.
This is due to plucking which steepens the back walls
