Glaciation EQ3 Flashcards
Arête
A narrow knife-edged ridge between two cirques.
Plucking and abrasion on the back wall on the two corries mean they erode towards one another, creating a narrow ridge. Freeze thaw is also important
Glacial erosion processes
abrasion
plucking
crushing
basal sliding
Abrasion- material rubs against The Valley sides and floor, wearing them away by a process similar to sandpaper
Plucking- when meltwater freezes the underlying bedrock to the base. Any loose rock fragments are plucked away as the glacier slips forward.
Crushing- the direct fracturing of weak bedrock by the wight above it
Basal melting- large volumes of meltwater can cause fluvial erosion such as abrasion, hydraulic action, attrition and corrosion.
Pyramidal peak
A pointed mountain with 3 or more corries.
Erosion backwards creating a sharp pointed mountain summit.
Glacial trough
A u shaped valley with steep sides and a wide flat floor.
Formed when a v shape valley is widened and deepened as a result of plucking and abrasion
Truncated spur
A steep rocky valley where spurs of a river valley used to interlock before glaciation
Hanging valley
A small tributary v-shaped or u-shaped valley high above one glacier floor, often with a waterfall.
Glacial ice erodes downwards faster than thinner ice in tributaries. The floor of tributaries are left high above the main valley floor.
Ribbon lake
Areas of increased plucking and abrasion by The Valley glacier deepen part of The Valley floor.
Crag and tail
Is formed when a very large resistant object or crag, obstructs the flow of a glacier. The ice forced around the obstruction eroding weaker rock. However material in the lee (shelter side) of the obstruction is protected by the crate and leans the formation of a gently sloping tail of deposited material.
Knock and lochan
A glacially scoured lowland area which has alternating Roche moutonnée and eroded hollows which often contain small lakes. They are often found on rocks where alternate resistant and weekly jointed rocks as this allows differential erosion.
Roche moutonée
The stoss is smoothed and polished by abrasion but plucked on the lee side. This is because increased pressure on the stoss side cause the ice to melt over the out crop of rock. When it reaches the lee the water refreezes as there is less pressure. Loose rock is frozen to the base and when the glacier slips loose rock is pulled away creating a jagged edge by plucking.
Medial moraine
Is formed when two glaciers meet and lateral moraines come together on the surface. When the glacier melts sediment is dropped as unsourced angular morainic material and a medial moraine is left on The Valley form.
Terminal moraine
A prominent ridge of glacial debris formed when a glacier reaches its maximum limit during sustained advance.
Lateral moraine
Debris deposited along the side of the glacier, comprising both rockfall debris from above and debris ground up by the ice marginal process
Recessional moraine
Ridge of debris representing a stationary or minor re-advance phase during otherwise general retreat.
Till plains
When a sheet retreats, large amounts of material are deposited over a sizeable area due to melting.
Lodgement till
Till is deposited by actively moving ice forming landforms such as drumlins.
ablation tills
material deposited on the ground when the ice melts
mixture of fine and coarse angular rock fragments, with much less sand, silt and clay than lodgement till
drumlins
formed of till
elongated features that can reach a kilometre or more in length, 50m in width, over 50m in height
one end is quite steep whilst the other end tapers away to ground level
the stoss end is the steeper of the two ends and used to face into the ice flow
ice contact features depositional
kames, kame terraces, eskers
mostly consist of sand and gravel but may include bits of clay and silt
ice contact features formed by fluvio glacial
kettle holes
outwash plains
kames
irregular shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier, and is then deposited on the land surface with further melting of the glacier
kame terraces
composed of sand and gravel, but form along the sides of glacier rather than at its snout, they are formed by the actions of meltwater streams that flow along the sides of the ice, trapped against it by the valley walls
eskers
formed on washed sands and gravels, most eskers are formed within the ice-walled tunnels by streams which flow under and within glaciers, when the ice melts away water deposits remain as winding ridges
kettle holes
formed by blocks of ice that are separated from the main glacier by either the glacial ice retreating or by blocks calving off the glacier snout and falling forwards
proglacial lakes
formed as meltwater from a glacier pool, depending on type of dam that holds the meltwater, proglacial lakes can either be stable long after the glacier melts
outwash plains
created by meltwater from glaciers, meltwater flowed out from the foot of the glacier carrying with it huge loads of sediment that were deposited as the velocity of the water slowed further from the glacial edge
meltwater channels
formed as a result of glacial erosion, two main types of meltwater channels formed from this process are subglacial and lateral
how is a corrie formed
1 - snow collects in a sheltered hollow on the side of mountain
2 - snow accumulates and compacts into ice, forming a glacier
3 - glacier erodes the back wall of the hollow by freeze thaw weathering and plucking, making it steeper
4 - glacier erodes the base of hollow by abrasion, making it deeper
5 - glacier moves downhill due to gravity and pressure
how ice sheet scouring causes the formation of landforms
landscapes of areal scouring are found to be associated with zones of basal melting and occur beneath much of the former ice sheet centre
