Topic 2 - Glaciation EQ3

Question 1

What are the four main types of glacial erosion?

Answer 1

• abrasion
• plucking/quarrying
• glacial crushing
• basal ice melting

Question 2

Outline the erosional process abrasion?

Answer 2

• 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

Question 3

Outline the erosional process plucking/quarrying?

Answer 3

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

Question 4

What can increase abrasion in glaciers?

Answer 4

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

Question 5

Explain the glacial erosional process glacial crushing?

Answer 5

• 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

Question 6

Explain the glacial erosional process basal ice melting?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

Explain what valley glaciers are?

Answer 8

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

• usually follow former river courses

Question 9

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

Answer 9

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

Question 10

Explain what arêtes are and how they form?

Answer 10

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

Question 11

Explain what pyramidal peaks are?

Answer 11

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

• freeze-thaw weathering sharpens point

Question 12

Outline the formation of pyramidal peaks?

Answer 12

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 backwall and embedded within glacier

3) freeze-thaw weathering sharpness the peak

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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)

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

Give 3 landforms formed through ice sheet scouring?

Answer 18

• roches moutonnées
• knock and lochan
• crag and tail

Question 19

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

Answer 19

• 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

Question 20

Outline the formation of the landform crag and tails?

Answer 20

• 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 endibrough castle on a crag - the royal mile is on the tail

Question 21

Outline the formation of the landforms Knock and lochan?

Answer 21

• 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)

Question 22

Outline the formation of the landforms Roche moutonnée?

Answer 22

• 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)

Question 23

Outline how roaches moutonés demonstrate abrasion?

Answer 23

• 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

Question 24

Outline how roaches moutonés demonstrate plucking?

Answer 24

• 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

Question 25

Outline the formation of the landform lateral moraines?

Answer 25

• 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

Question 26

What are moraines?

Answer 26

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

• 4 types - Lateral, medial, terminal, recessional

Question 27

Explain the deposition of glaciers?

Answer 27

• 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

Question 28

Outline the formation of the landform medial moraines?

Answer 28

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

Question 29

Outline the formation of the landform terminal moraines?

Answer 29

• 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

Question 30

Outline the formation of the landform recessional moraines?

Answer 30

• 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

Question 31

Give 4 landforms which demonstrate ice-contact features?

Answer 31

• lateral moraines
• medial moraines
• terminal moraines
• recessional moraines
• drumlins

Question 32

Outline the formation of the landform drumlins?

Answer 32

• 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’