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A- Level Physical Geography > How are glacial landforms developed > Flashcards

How are glacial landforms developed Flashcards

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1
Q

Weathering

A
  • happens everywhere
  • significant in formation of glacial landforms
  • uses heat energy to produce chemical altered materials
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2
Q

Physical/mechanical weathering - Freeze-thaw

A
  • water enters cracks and joints and expands when it freezes
  • causes rock to split further and for pieces to break off
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3
Q

Physical/mechanical weathering - Frost shattering

A
  • water becomes trapped in rock pores and freezes and expands causing rock to disintegrate
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4
Q

Physical/mechanical weathering - Pressure release

A
  • known as dilation
  • weight of the overlying glacier is lost because of continued erosion
  • causes vertical pressure release
  • upper layers of rock expand producing disintegration of rock masses
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5
Q

Chemical weathering - Oxidation

A
  • some rock minerals react with oxygen (iron)
  • becomes soluble in acidic conditions destroying original structure
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6
Q

Chemical weathering - Carbonation

A
  • rainwater combines dissolved CO2 from the atmosphere and produces carbonic acid
  • reacts with calcium carbonate in rocks (limestone) to produce calcium-bicarbonate which is soluble
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7
Q

Chemical weathering - Solution

A
  • some salts are soluble in water
  • other minerals (iron) are soluble in very acidic water
    any process by which a mineral dissolves in water is a solution
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8
Q

Biological weathering

A

Tree Roots
- roots grow into cracks
- outward pressure exerted causes rocks to split and break
Organic Acids
- produced during plant and animal litter decomposition
- causes soil and water to become acidic causing them to react with minerals
- “Chelation”

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9
Q

Mass movement

A
  • when forces keeping material on a slope exceed forces pushing material off a slope
  • main mass movements are on steep slopes
  • adds material to glacier for abrasion
  • input to a system
  • causes erosion and landscape change
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10
Q

Mass movement - Rock fall

A
  • slopes of 40 degrees or more
  • rocks can be detached by physical weathering
  • transport removes material
  • material may accumulate as a straight lower angle scree slope
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11
Q

Mass movement - Slides

A
  • movement along a slip plane or a rotational slide
  • rotational slides are known as “slumps”
  • slides may occur due to steepening and undercutting of valley sides at the base of the slope
  • slumps are common in weaker rocks (clay is weak and heavy when wet)
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12
Q

Erosion - Abrasion

A
  • when the glacier moves along the floor and sides of the valley there is lots of friction
  • rocks and debris scrapes along the surfaces creating striations (sandpaper)
    -if debris is small and fine there I a polishing effect as it removes jagged rocks
  • the debris that wears down creates rock flour which can colour meltwater streams milky white
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13
Q

Erosion - Plucking

A
  • meltwater gets into cracks in the valley floor and side
  • meltwater freezes and becomes attached to the glacier
  • when the glacier moves the rock moves and is plucked out the valley
  • when pressure melting point is reached it aids basal plucking
  • plucked rocks provide material for abrasion
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14
Q

How does presence of basal debris affect glacial abrasion

A
  • pure ice cannot carry out abrasion
  • basal debris is essential for abrasion
  • when basal debris increases erosion increases
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15
Q

How does debris shape and size affect glacial abrasion

A
  • embedded particles extert downwards pressure proportional to their weight
  • larger debris is more effective and causes more abrasion
  • finer debris has a polishing effect on the - sharp debris erodes in a more concentrated area
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16
Q

How does hardness of particles and bedrock impact glacial abrasion

A
  • more erosion when basal debris is hard and bedrock is weak and soft
  • if bedrock is harder than basal debris, friction is too great, no erosion takes place
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17
Q

How does ice thickness impact glacial abrasion

A
  • the greater the thickness of the ice, the more basal pressure, the higher thee rate of abrasion
    -when ice is too thick, ice cannot move, causing no abrasion
  • ice is too thick to move at around 200-400m
18
Q

How does basal water pressure affect glacial abrasion

A
  • a meltwater layer is vital to sliding and therefore for erosion to take place
  • the glacier can be buoyed if the water is confined and under pressure reducing pressure and erosion
19
Q

How does sliding of basal ice impact glacial abrasion

A
  • abrasion requires basal siding
  • more sliding = more erosion
20
Q

How does movement of debris to the base impact glacial abrasion

A
  • abrasion does not only wear bedrock but also basal debris
  • if basal debris is not replenished erosion stops
21
Q

How does removal of fine debris impact glacial abrasion

A
  • to maintain high rates of abrasion rock flower needs to be removed so large particles can abrade the bedrock
  • rock flour is removed by meltwater
22
Q

Nivation

A

a combination of
- freeze thaw
- solifluction
- transportation by running water
- chemical weathering

23
Q

Solifluction

A

slow flow of fine water and saturated material from high to low ground

24
Q

Nivation hollow

A

a depression formed by freeze-thaw and meltwater transport of weathered rock particles beneath a permanent area of snow

25
Q

Transportation

A

Rockfall
- rocks fall onto ice (gravity)
Avalanches
- snow and rocks fall onto ice (gravity)
Debris flow
- melted snow and ice carrying mud, soil, and rocks
Aeolian deposits
- fine material deposited by wind
Volcanic eruptions
- ash and dust
Plucking
- large rocks plucked from the glacier valleys by moving ice
Abrasion
- sandpaper effect, wearing away rocks from valley sides

26
Q

Material postion

A

Supra-glacial
-surface of the ice
-weathering/rockfall

En-glacial
-within the ice
-sunk from surface
-covered with new snow/localised pressure melting caused it to sink

Sub-glacial
- base of the glacier
-from plucking or abrasion
-abrading bedrock

27
Q

Deposition

A
  • when glaciers deposit their load
  • often due to ablation (seasonal retreat/deglaciation)
  • either till/outwash
28
Q

Till characteristics

A
  • material deposited directly by ice
  • angular shape
  • unsorted
  • unstratified
    -glacial till drops in mounds rather than layers
29
Q

Lodgement till

A
  • deposition
  • deposited by advancing ice due to downwards pressure
  • subglacial debris is lodged into valley floor
  • left behind when glacier movs
30
Q

Ablation till

A
  • deposition
  • deposited by stagnant/retreating glaciers
31
Q

Outwash

A
  • deposition
  • deposited by meltwater
  • can create erosional and depositional landforms
  • meltwater released from glaciers in seasonal retreat/deglaciation
  • sorted horizontally (largest material further up valley)
  • stratified vertically (distinctive seasonal + annual layers)
  • smooth and rounded due to attrition
32
Q

Corries

A
  • armchair shaped hollows
  • found in upland hills/mountainsides
  • steep back wall
  • over-deepened basin
  • lip at the front
33
Q

Aretes and pyramidal peaks

A

Aretes
- narrow steep sided ridge
- found between two corries
- “knife edged”
- form from glacial erosion
- corries that are back to back
Pyramidal peaks
- three or more back to back corries

34
Q

Troughs

A
  • glaciers flow down pre-existing river valleys
  • as the move they erode the sides and floors
  • causes deepening and causes it to become wider and straighter
35
Q

Roche moutonnées + striations

A
  • projections of resistant rock found on the floor of glacial troughs
  • as ice passes over them there is localised pressure melting on the up-valley side
  • often stations embedded into it
  • on the down valley side pressure is reduced and meltwater refreezes leading to plucking and steepening
36
Q

Ellipsoidal basins

A
  • major erosional landforms created by ice sheets
37
Q

Terminal moraine + example

A
  • ridge of till extending across a glacial trough
  • maximum extent of the glacier
  • crescent shaped
  • Franz Joseph glacier in New Zealand has terminal moraine 430m high
38
Q

Lateral moraine + example

A
  • ridge of till running along the edge of a glacial valley
  • accumulates on top of glacier having been accumulated from valley sides
  • Athabasca glacier in Canada left moraine 1.5km long and 124m high
39
Q

Recessional moraine

A
  • series of ridges running transversely across glacial troughs
  • parallel to each other and terminal moraine
  • rarely exceed 100m high
40
Q

Erratics

A
  • individual dice of rock
  • different geology of deposited area
  • most likely eroded by plucking and weathering and rockfall
  • Sultan shale
  • deposited in carboniferous limestone
  • in Norber erratics in Yorkshire dales
41
Q

Drumlins

A
  • mound of glacial debris
  • streamlined into an elongated hill
  • can be 1km long and 100m high
  • aligned in direction of ice flow
  • may be formed by lodgement of subglacial debris
42
Q

Till sheets

A
  • formed when a large mass of unstratified drift is deposited at the end of period of ice sheet advance
  • smooths underlying surface

A- Level Physical Geography (3 decks)

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