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Geography > Glacitation - Unit 4 > Flashcards

Glacitation - Unit 4 Flashcards

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1
Q

What is weathering?

A

The breakdown of rock where it’s located. This involves:

  • Physical processes, e.g. freeze thaw
  • Chemical processes, e.g. carbonation
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2
Q

What is erosion?

A

The removal of rock by ice, water or wind

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3
Q

Explain the 4 steps in freeze-thaw weathering

A
  • In glacial environments, temperatures may fluctuate either side of 0°C
  • When water freezes it expands by 9% in volume
  • When water freezes it exerts pressure on the crack
  • Repeated freeze thaw cycle fractures the rock
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4
Q

What’s dilatation?

A
  • Pressure release
  • Rocks can fracture when the overlying pressure is released
  • Can occur when a glacier is melting, losing weight and hence exerting less downward pressure
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5
Q

What are the 3 erosional processes?

A
  • Abrasion
  • Plucking
  • Sub-glacial meltwater erosion
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6
Q

Describe abrasion

A
  • As a glacier moves the weathered rock debris embedded in its base (subglacial debris) it scrapes against the bedrock and wears it away
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7
Q

What factors will result in the most abrasion?

A
  • Thick ice (stronger/more pressure, create more meltwater)
  • Lots of subglacial meltwater (increases debris as there’s more thawing)
  • Debris angular/ a lot of it (more powerful/ easier to break down and more likely to scratch the rock)
  • Faster movement of glacier (covers a larger distance in a smaller time)
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8
Q

Describe plucking (quarrying)

A
  • Large downwards pressure from weight of glacier
  • Causes melting
  • Water refreshes to obstacles
  • Plucked from bedrock when glacier moves
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9
Q

What type of rocks are susceptible to plucking?

A

Highly jointed or fractured rocks

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10
Q

Describe sub-glacial meltwater erosion

A
  • Meltwater channelled beneath glacier
  • High velocity meltwater erodes material at glacier’s bed
  • Forms large subglacial meltwater channels
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11
Q

Explain process of cirque formation

A

Stage 1:
- FTW occurs in small hollows on north-facing slopes = rock disintegrates
- Summer meltwater removes rock debris, which enlarges hollow
- Process = nivation
- Snow lasting more than 1 year becomes compacted & eventually turns into ice, known as neve
Stage 2:
- Further accumulation of ice adds weight = rotational movement of ice
- Movement aided by meltwater from pressure melting
- Rock fragments from back wall of hollow removed through plucking = steep, jagged & angular
- Rock fragments transported by ice causes abrasion
- Meltwater enters system through a crevasse (bergschrund)
- Pressure release causes dilatation cracks
- May start to move over lip & out of rock basin it has created
- Exhibit abrasion of upglacier & plucking on downglacier side

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12
Q

What is a cirque?

Example?

A
  • A large amphitheater shaped hollow

- Cwm Idwal

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13
Q

What is an arête?

Example?

A
  • A sharp ‘knife-edge’ ridge which has been produced by 2 cirques eroding back towards each other
  • Striding edge, Lake District
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14
Q

What are pyramidal peaks?

Example?

A
  • Where 3 or more cirques around a mountain have been formed
  • As they continue to develop back to back the remaining central area of the mountain becomes sharper and steepened
  • Glyder Fawr above Cwm Idwal
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15
Q

How are arêtes and pyramidal peaks formed?

A
  • Snow gathers and forms ice on a rounded summit

- Frost-shattering makes peaks jagged

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16
Q

How do glacial troughs form?

Example?

A
  • Glacier moves through non-resistant rock and erodes the valley into a U-shape
  • Yosemite Valley
17
Q

How do truncated Spurs form?

Example?

A
  • As a glacier moves down a river valley it erodes each spur
  • Over time the Interlocking Spurs erode back to become a truncated spur, which often have a steep cliff face
  • Half Dome - Yosemite
18
Q

How do hanging valleys form?

Example?

A
  • Formed by tributary glaciers which enter a glacial trough
  • Smaller valleys meet the main glaciated valley
  • They lie suspended above in the valley side
  • They may often possess waterfalls
  • Yosemite
19
Q

What is a ribbon lake?

A

A long and narrow, finger-shaped lake, usually found in a glacial trough

20
Q

What is a roche moutonnee?

A

A piece of resistant rock on the floor of a glacial trough that has undergone abrasion of the upvalley side and plucking on the downside valley
- Typically 1-5m high and 5-20m long

21
Q

How are Roche moutonnees formed?

Example?

A
  • Pressure of obstacle produces meltwater as PMP is reached
  • Glacier moves over obstacle (basal sliding) as it lubricated the base and reduces friction
  • Abrasion on upvalley side leaves striations
  • Pressure meltwater seeps into cracks in bedrock
  • Pressure is released and meltwater refreezes, widening joints
  • As glacier moves, pieces of rock are ‘plucked’, leaving it steep and jagged
  • Pen Y Benglog
22
Q

What is a crag and tail?

A

A meso-scale landform consisting of a rock hill and tapering ridge

23
Q

How is a crag and tail formed?

Example?

A
  • The more resistant rock is not eroded as easily as the surrounding softer rock
  • This leaves a steep upglacier side and leads to the formation of the crag
  • Soft rock is eroded as glacier moves over it
  • The soft rock on down glacier side is protected by crag so less susceptible to erosion
  • With distance from the crag, the softer rock is less protected and erosion can occur freely, this leads to the formation of a tapered down-glacier side
  • Edinburgh Castle
24
Q

What are striations?

A

Scratches on the hard bedrock produced by the process of glacial abrasion

25
Q

How are striations formed?

Example?

A
  • Debris frozen in the basal ice is dragged across the bedrock
  • Isle of Skye
26
Q

What are chatter marks?

A

Small intermittent fractures in the bedrock

27
Q

How are chatter marks formed?

Example?

A
  • When the basal debris within the ice is not in continuous contact with the bedrock
  • Yosemite National Park
28
Q

How is polished rock formed?

Example?

A
  • The ice can polish the bedrock if sand and silt is found in the basal ice layer as opposed to angular rock fragments
  • Central Park, New York
29
Q

How are ribbon lakes formed?

Example?

A
  • Glacier moves over an area containing alternate bands of resistant and non-resistant bedrock
  • Glacier erodes the non-resistant rock more quickly by abrasion, creating a hollow = rock basin
  • On either side of the rock basin, the more resistant rock is eroded less (rock bars)
  • Rock bars act as dams between which rainwater may accumulate after the retreat of the ice age, filling up the rock basin and creating a river lake
  • Llyn Ogwen

Geography (15 decks)

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