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A-level - Geography > Topic 2 - Glaciation EQ3 > Flashcards

Topic 2 - Glaciation EQ3 Flashcards

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1
Q

What are the four main types of glacial erosion?

A
  • abrasion
  • plucking/quarrying
  • glacial crushing
  • basal ice melting
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2
Q

Outline the erosional process abrasion?

A
  • sandpapering effect of ice as it grinds over and scours a landscape
  • happens because of freeze-thaw which creates sharp angular rock fragments - which are carried beneath the ice and scratch bedrock forming striations
  • fine material smoothes and polishes the rock
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3
Q

Outline the erosional process plucking/quarrying?

A

Basal meltwater penetrates joints and cracks and freezes around parts of the underlying bedrock at the base of a glacier - any loosened rock fragments are plucked away by the immense pulling force of the glacial ice

• plucking leaves very jagged landscapes

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4
Q

What can increase abrasion in glaciers?

A

Thick fast-moving ice, with large amounts of coarse, angular basal debris will result in more abrasion and formation of striations

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5
Q

Explain the glacial erosional process glacial crushing?

A
  • direct fracturing of weak bedrock by weight of ice above
  • bedrock needs to be weakened first by intense freeze-thaw weathering or repeated glacial advance and retreat, which causes dilation

Produces large, angular blocks of rock

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6
Q

Explain the glacial erosional process basal ice melting?

A

Basal ice melting beneath temperate glaciers produces large volumes of meltwater which cause fluvial erosion processes (abrasion,attrition,corrosion)

  • subglacial meltwater travels fast and under high pressure - which can cause rocks to be dislodged and removed
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7
Q

Explain what cirque/corries are - describe the features of them?

A

Small masses of ice that occupy enlarged, deep armchair-shaped hollows in mountains
- have a steep cliff-like back wall (with large pile of scree at base)
- raised rock lip at the front of the hollow - acts as a dam and traps water forming tarn (lake)
- often overspill from the hollows to feed valley glacier

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8
Q

Explain what valley glaciers are?

A

Larger massses of ice that move down - from either an ice field or cirque/corrie

  • usually follow former river courses
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9
Q

Outline and explain the processes which contribute to the formation of a Corrie?

A

1) Periglacial processes - specificaly nivation, increase the size of a hollow on the north face of a mountainside - small glacier forms

2) ice moves under own weight in circular way (rotational movement)

3) small Corrie fills with ice, flows out onto the main valley glacier

4) mountain top weathered by freeze-thaw breaking sediment off, which falls into the ice

5) erosion of the back wall by plucking which pulls of rock developing a vertical shaped jagged appearance

6) rocks in glacier scrape away the floor by abrasion - forming a deep bowl shape

7) less erosion at the front of Corrie (ice is thinner) lip/rock bar forms

8) ice melts forming deep lake in hollow - called tarn

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10
Q

Explain what arêtes are and how they form?

A

Plucking and abrasion on the back wall of two cirques/corries on a mountainside mean they erode backwards towards one another - forms a narrow, knife-edge ridge between the two corries (known as arête)

Common in the present landscapes like the Alps and past like the lack district

Freeze-thaw action important

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11
Q

Explain what pyramidal peaks are?

A

When three or more corries erode back-to-back, creating a sharp, pointed mountain summit (pyramidal peak) - plucking involved

  • freeze-thaw weathering sharpens point
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12
Q

Outline the formation of pyramidal peaks?

A

1) snow gathers in 3 or more hollows back to back - compresses into ice

2) glaciers abrade there or more deep hollows (using material they scrape away) - rocks are plucked from the back wall and embedded within glacier

3) freeze-thaw weathering sharpness the peak

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13
Q

Outline the formation of glacial troughs - what landform is formed?

A

A V-shaped river valley is widened and deepened - result of powerful plucking and abrasion (by basal slip) by a valley glacier, which goes through landscape rather than around it

  • forms a U-shaped valley with steep sides and a wide, flat floor
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14
Q

Outline the formation of truncated spurs - what landform is formed?

A

Valley glaciers are less flexible than rivers and remove the ends (truncates) of interlocking spurs by plucking and abrasion as they move down the river valley

  • form steep rocky valley side where spurs of a river valley used to interlock before glaciation
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15
Q

Outline the formation of hanging valleys - what landform is formed?

A

Powerful thicker glacial ice in the main glacial trough eroded vertically downwards more rapidly than thinner ice (lacks mass) - floors of the tributary valleys are left high above the main valley floor

  • forms a small tributary V or U shaped valley high above the main glacial trough floor (waterfalls often present due to rivers flowing over edge)
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16
Q

Outline the formation of ribbon lakes - what landform is formed?

A

Areas of increased plucking and abrasion by the valley glacier deepen part of the valley floor (result of confluence of glaciers or weaker rocks) - sometimes lake forms behind terminal moraine after glaciation

  • results in a long, narrow lake along the floor of a glacial trough
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17
Q

Outline landforms associated with cirque and valley glaciers - give 7?

A
  • Corrie/cirque
  • aréte
  • pyramidal peak
  • glacial trough
  • truncated spur
  • hanging valley
  • ribbon lake
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18
Q

Give 3 landforms formed through ice sheet scouring?

A
  • roches moutonnées
  • knock and lochan
  • crag and tail
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19
Q

Outline what features can enhance formation of ribbon lakes within glacial troughs?

A
  • weaker bedrock allows increased vertical erosion
  • merging of a tributary glacier - leads to greater erosion of the valley floor due to increased ice mass
  • narrowing of the valley and resulting thicker ice leads to increased vertical erosion
20
Q

Outline the formation of the landform crag and tails?

A
  • Very large object resistant to scouring (‘crag’) obstructs the flow of a glacier - the ice is forced around the obstruction (at the stoss end) , eroding weaker rock
  • Material immediately in the lee of the obstruction is protected by the crag - leads to formation of a gently sloping tail of deposited material - sheltering effect diminishes with distance, explaining the slope

Eg Edenborough castle on a crag - the royal mile is on the tail

21
Q

Outline the formation of the landforms Knock and lochan?

A
  • Scouring at the base of a glacier excavates areas of weaker rock - forming hollows that fill with meltwater and precipitation after ice retreats
  • forms a lowland area with alternating small rock hills (knock) and hollows contains small lakes (lochan)
22
Q

Outline the formation of the landforms Roche moutonnée?

A
  • more resistant rock outcrop causes ice movement by creep and regelation around it - as ice slides over the rock, it scours and smoothes the stoss, refreezing on the ice causes plucking
  • forms a mass of bare rock on the valley floor with a smooth stoss (up-valley side) and a steep jagged lee (down-valley side)
23
Q

Outline how roaches moutonés demonstrate abrasion?

A
  • upstream side - experiences increased pressure due to the resistance of the outcrop to moving ice causes localised pressure melting
  • leads to basal slip and abrasion - as the glacier slides over the outcrop

Upstream side shows polishing and striations

24
Q

Outline how roaches moutonés demonstrate plucking?

A
  • downstream side experiences reduced pressure causes meltwater to freeze - forming a bond between rocky outcrop and overlying glacier
  • as glacier moves forwards, loose rock is plucked away, leaving a jagged surface
25
Q

Outline the formation of the landform lateral moraines?

A
  • debri from freeze-thaw weathering of valley sides falls onto a glacier, transported and deposited at the edge of the glacier when it melts
  • forms a ridge of till deposited along the valley sides
26
Q

What are moraines?

A

Collective term for rock material carried by a valley glacier and deposited to from a range of landforms

  • 4 types - Lateral, medial, terminal, recessional
27
Q

Explain the deposition of glaciers?

A
  • glaciers deposit load when velocity is reduced or because they have become overloaded with debri, or ablation increases
  • till - material deposited directly below ice
  • rock fragments deposited by ice are known as erratics
28
Q

Outline the formation of the landform medial moraines?

A
  • at the confluence of two tributary glaciers, lateral moraines join to form a medial moraine(deposited during ice melt and retreat)
  • forms a ridge of till deposited in the middle of the valley (parallel to valley sides)
29
Q

Outline the formation of the landform terminal moraines?

A
  • debris is deposited at maximum extent of glacier, especially if glacier is in equilibrium and the snout is stationary (debris continuously supplied to same place)
  • forms a high ridge of till extending across a valley at right angles to valley sides
30
Q

Outline the formation of the landform recessional moraines?

A
  • Debris is deposited during interruptions in the retreat of glacier ice - when the glacier remained stationary long enough for a ridge of material to build up
  • forms a lower ridge of till across valley - parallel to terminal moraine
31
Q

Give 5 landforms which demonstrate ice-contact features (4 moraine types + …..)?

A
  • lateral moraines
  • medial moraines
  • terminal moraines
  • recessional moraines
  • drumlins
32
Q

Outline the formation of the landform drumlins?

A
  • controversy over origin of drumlins - generally accepted that they are formed by deposition when glacier becomes overloaded with debris when exiting an upland area - deposits are streamlined and shaped by the moving ice (indicators of direction and extent of ice movement)
  • forms smooth elongated mounds of till, with a long axis parallel to the direction of ice movement and with a steep stoss, and gentle lee - found in large numbers in an area called ‘drumlin swarms’
33
Q

Give 3 lowland depositional features?

A
  • till plains
  • lodgement till
  • ablation till
34
Q

Outline the formation of till plains - what are they characterised by?

A

Formed when a sheet of ice retreats - melting results in deposition of large amounts of material over a sizeable area

  • results in a large relatively flat plain of till in lowland area - also called ground moraine
35
Q

Outline the formation of lodgement till - what are they characterised by?

A

Till deposited by active moving ice - forms landforms such as drumlins - is lodged or pressed into the valley floor beneath the glacier

  • forms deposits of angular rock fragments (clasts) in a fine matrix (unstratified, not layered, rock flour) same as ablation till
36
Q

Outline the formation of ablation till - what are they characterised by?

A

Till deposited by melting ice from stationary or retreating glaciers - forming landscapes such as terminal and recessional moraines

  • forms deposits of angular rock fragments (clasts) in a fine matrix - same as lodgement till
37
Q

Why is it hard to reconstruct past glaciation using relict glacial landscapes?

A
  • can be modified and confused by multiple glaciation and post glacial weathering and erosion
  • human activities like agriculture/urbanisation
38
Q

Why is it hard to reconstruct past glaciation using relict glacial landscapes?

A
  • can be modified and confused by multiple glaciation and post glacial weathering and erosion
  • human activities like agriculture/urbanisation
39
Q

With focus on Fluvio-glacial landforms give 3 ice contact features?

A
  • kames
  • eskers
  • kame terraces
40
Q

Outline how Fluvio-glacial ice contact feature Kames are formed - what are they characterised by?

A

Formed as meltwater streams emerge onto the outwash plain (or proglacial lake) at the glaciers snout - decrease in velocity causes deposition of sediment

  • forms an undulating mound of fluvio-glacial sand and gravel deposited along the valley sides
41
Q

Outline how Fluvio-glacial ice contact feature eskers are formed - what are they characterised by?

A

subglacial streams carry large amounts of rock debri due to high hydrostatic pressure inside tunnels - the streams often meander beneath the glacier, when the glacier retreats the debri load is deposited at a consistent rate - forming a ridge

Long, narrow, winding/meandering ridge of fulvio-glacial sand and gravel

42
Q

Outline how Fluvio-glacial ice contact feature Kame terrace are formed - what are they characterised by?

A

During summer the valley sides radiate heat, melting the edge of glaciers forming meltwater streams which deposit sediment - when the glacier retreats the sediment will fall to the valley floor

Forms a flat liner deposit of fluvio-glacial sand and gravel

43
Q

With focus on Fluvio-glacial landforms give 4 pro-glacial features?

A
  • sandurs
  • pro-glacial lakes
  • meltwater channels
  • kettle-holes
44
Q

Outline how Fluvio-glacial landforms focusing on the proglacial feature sandurs are formed - what are they characterised by?

A

As meltwater streams emerge from the glacier and enter lowland areas - they lose energy and deposit their debris load - coarse gravels deposited first (nearest to glacier) than the sand and finally clay (furthest from glacier)

  • forms a flat expanse of fluvio-glacial debri in front of the glaciers snout
45
Q

Outline how Fluvio-glacial landforms like proglacial lakes are formed - what are they characterised by?

A

Formed by the damming action of a terminal or recessional moraine during retreat of a melting glacier (or because hills block escape of meltwater)

  • can also be formed by meltwater trapped against an ice sheet as a result of isostatic depression of the crust around the ice

Forms a lake at the glaciers snout

46
Q

Outline how Fluvio-glacial landforms focusing on proglacial features like kettle hole are formed - what are they characterised by?

A

As glacier retreats, detached blocks of ice remain on outwash plain - meltwater streams flow over ice, covering them in deposits of fluvio-glacial deposits

  • ice melts and debris subsides to form a circular. depression, which fills with meltwater forming a kettle-hole lake
47
Q

Outline how Fluvio-glacial landforms focusing on proglacial features like meltwater channels are formed - what are they characterised by?

A

Meltwater can erode deep channels as a result of high hydrostatic pressure within the glacier and their high sediment load - can flow uphill due to pressure beneath glacier (larger than post-glacial streams) experience seasonal variations in discharge

  • forms a narrow channel cut into bedrock - underneath or along the front of an ice margin

A-level - Geography (21 decks)

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