Geography - Glaciers > Unit 3 > Flashcards

Unit 3 Flashcards

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1
Q

What is weathering and what are the two types?

A

weathering - the breakdown of rock where its located

  1. physical processes - freeze-thaw weathering
  2. chemical processes - carbonation
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2
Q

What is erosion?

A

the removal of rock by ice, water, wind or gravity

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3
Q

What are the 4 stages involved in freeze-thaw weathering?

A
  1. in glacial environments temperatures can fluctuate above and below 0 degrees
  2. water fills the crack, freezes and expands by 9%
  3. When the water freezes it exerts pressure on the crack
  4. repeated freeze-thaw weathering fractures the rock
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4
Q

What characteristics that are needed in the rock for freeze-thaw weathering to occur?

A

rock has to be porous/permeable to allow water into cracks

whether the rock is hard or soft can affect the rate at which it occurs

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5
Q

What type of climate is required for freeze-thaw weathering to occur?

A

temps have to fluctuate above/below 0 degrees, water also must be present so precipitation is required

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6
Q

What altitude /aspect is needed for freeze-thaw weathering to occur?

A

altitude = has to be high enough, to be cold enough for temps to drop below 0 degrees

aspect = north facing in Northern Hemisphere, as this again is most likely to provide temps below 0 degrees (shaded for longer periods of time)

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7
Q

What is dilation and what is the process known as?

A

when rocks fracture under the pressure/release of pressure from glaciers

occurs when glacier is melting, as the glacier will lose weight

process = pressure release

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8
Q

What are the 4 different stages of dilation?

A
  1. glacial ice (known as the overburden) pushes down on the rock beneath, causes the bedrock beneath to become compressed
  2. glacier retreats/melts (overburden is eroded), reducing the pressure, causes the rock to relax upwards which creates cracks that are parallel to the surface
  3. pressure continues to be reduced (overburden continues to be eroded away), causes the fractures to expand, releasing pressure
  4. As the cracks form, material is created for erosion
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9
Q

How does abrasion work? How do different sized rocks affect the bedrock?

A

As a glacier moves, embedded bedrock at the base is scraped against bedrock, wears it away. The subglacial debris itself can be worn away and converted to rock flour

large rock = scratches bedrock

smaller (fine silt and sand) rock = smooths, polishes bedrock, sandpapering effect

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10
Q

What are the six factors that affect the rate of abrasion?

A
  1. ice thickness
  2. subglacial meltwater
  3. speed of glacier movement
  4. supply of debris
  5. relative hardness of debris/rock
  6. shape of debris
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11
Q

How does ice thickness affect the rate of abrasion?

A

the thicker the ice, the more pressure applied (deeper scratches, eroded deeper)

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12
Q

How does subglacial meltwater affect the rate of abrasion?

A

the more meltwater = more lubrication and faster rate of movement

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13
Q

How does the speed of glacier movement affect the rate of abrasion?

A

faster the glacier moves = quicker abrasion, going to come in contact with debris

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14
Q

How does the supply of debris affect the rate of abrasion?

A

more debris = more abrasion

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15
Q

How does the relative hardness of debris affect the rate of abrasion?

A

angular = sharp, scratches bedrock
rounded = smooth, sandpaper affect
or sub angular/rounded

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16
Q

What is plucking also known as?

A

Quarrying

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17
Q

How and where does plucking occur?

A

occurs when meltwater seeps into cracks, freeze - thaw weathering occurs and debris is trapped in ice
the and on the down - valley side of rock obstacles (regelation slip)

affective at the base of glaciers due to the presence of meltwater from pressure melting

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18
Q

What are the six stages of plucking on a regelation slip?

A
  1. glacier encounter obstacle as it moves downslope, increases pressure as glacier pushes against obstacle so PMP is reached, base starts to melt
  2. meltwater lubricates base, allows it to move over obstacle
  3. meltwater flows into cracks in the bedrock below
  4. once the base has moved over glacier, the pressure drops, means the base will refreeze as its no longer at PMP
  5. as it refreezes glacier exerts pressure on rock, eventually breaking pieces away
  6. As the glacier refreezes to the bedrock beneath it, it ‘plucks’ away the broken rock as it continues to move downslope
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19
Q

How does sub-glacial meltwater erosion occur?

A

meltwater can get channeled beneath glacier, before emerging at the snout as a pro-glacial stream

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20
Q

How does increasing the velocity of meltwater affect the rate or subglacial erosion?

A

increase velocity = creates bigger meltwater channels

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21
Q

What are the 4 erosional processes?

A
  1. hydraulic action
  2. abrasion
  3. attrition/CORRASION
  4. solution/CORROSION
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22
Q

How does hydraulic action work?

A

water forces air to be trapped, pressured into cracks, this constant pressure eventually causes rocks to crack and break apart

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23
Q

How does abrasion work?

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A

erosion where the sediment is grinded and pounded against a surface e.g. bedrock

24
Q

How does corrasion (attrition) work?

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A

the rocks + pebbles being carried by water collide against each other, weakening/breaking them down into smaller, rounded pebbles

25
How does corrosion (solution) work?
the chemical erosion of rocks in riverbank by the slightly acidic water - occurs in streams running through rocks such as chalk and limestone
26
Why are subglacial streams more powerful than ordinary streams?
they have increased hydrostatic pressure. this is because they are confined beneath the glacier so they're under an immense amount of pressure
27
Why do subglacial streams have different discharge patterns to normal streams?
- they're dependent on temp fluctuations rather than precipitation patterns - they flow fastest in the summer months, as temps are high so melting is more extreme - flow slowest in winter, melting is vastly reduced
28
What are the three types of erosional landforms? (in terms of size)
Macro = large Meso = medium Micro = small
29
What is a cirque/cwm/corrie?
it is a large amphitheater shaped hollow found at the source of a valley glacier
30
What are the two stages involved in cirque formation?
1. development of nivation hollow 2. enlargement of nivation hollow
31
How does a nivation hollow form?
1. A north facing slope receives little insolation 2. temp remains relatively cold, even during summer months (snow builds all year round), formation of firn occurs 3. freeze-thaw weathering occurs, due to temp fluctuation, providing loose material 4. the surface of glacier thaws in the summer, producing meltwater 5. rock debris is removed by meltwater streams of solifluction (its the movement of water downslope) in summer 6. process of removing rock debris and freeze thaw weathering, begins to enlarge hollow 7. the ground beneath the glacier remains permanently frozen
32
How does a cirque form? (Stage 2)
1. further accumulation of ice adds to the weight, resulting in rotational movement of ice. 2. movement aided by meltwater, due to PMP being reached 3. movement of glacial ice initiates the second stage 4. as it rotates it removes fragments from the back wall through process of plucking, this is why backwall is steep, jagged and angular 5. the fragments are transported by the rotating ice, which leads to abrasion at the base of the hollow (deepening it further) 6. rotation aided by surface meltwater, enters through a crevasse near the backwall (known as the bergshrund), this reaches from the surface to the base of the glacier -> it forms when the ice is pulled away from the back wall of hollow due to stress as it rotates 7. as erosion enlarges the hollow, moves rotationally releasing pressure causes dilatation cracks to form in underlying rock, parrallel to cirque. this weakens underlying rock, aiding further erosion
33
What is the last step in cirque formation?
As the growing glacier continues to rotationally slip , it may start to move over the cirque lip and out of the rock basin created the lip may experience abrasion and smoothing on the up glacier side as pressure increases and plucking on the downside
34
How do aretes form and what are some of their features?
features = a sharp 'knife edge ridge' -> which has been produced by two cirques eroding backwards towards each other
35
What is an example of an Arete?
Bristly ridge in Snowdonia
36
How do pyramidal peaks form and what are some of their features?
where three of more corries have formed around a mountain, become sharper and steeper
37
What is an example of a pyramidal peak?
Glyder Fawr above Cwm Idwal
38
How do glacial troughs form and what are some of their features?
where glaciers flow into pre-existing river valleys
39
What is an example of a glacial trough/valley?
Yosemite Valley, California
40
How do truncates spurs form and what are some of their features?
In a normal river valley, interlocking spurs are produced as the river erodes downwards into its bed and meanders side to side as the glacier moves down a river valley it erodes each spur, overtime the interlocking spurs become eroded back to become truncated spur often have a steep cliff face
41
How do hanging valleys form and what are some of their features?
Just like rivers have tributaries, so do glaciers (they have smaller glaciers joining them) Frequently the smaller glacier will have its flow impaired by the larger one. -> this coupled with its smaller size, means it has less erosive potential, won't carry out as much vertical erosion -> this results in a much smaller hanging valley compared to the much deeper main valley
42
What are the features of a ribbon lake and where are they found?
a ribbon lake is a long and narrow, finger shaped lake, usually found in a glacial trough
43
How do ribbon lakes form?
- Its formation begins when a glacier moves over an area containing alternate bands of hard and soft rock - the glacier will erode the softer rock quicker (via abrasion), creating a hollow called the rock basin - on either side of the rock basin, the more resistant rock is eroded less (these are known as rock bars), which act as a dome - the rock bars allow rainwater to accumulate in the rock basin (when the glacier has retreated/melted) - creating a ribbon lake
44
What is an example of a ribbon lake?
Windermere in the Lake district
45
What type of glacial landforms are the following? -> cirque -> Aretes and Pyramidal peaks ->glacial troughs ->truncated spurs -> hanging valleys ->ribbon lakes
Macro Landforms
46
What are the features of a roche moutonee, and what is their rough size?
a piece of resistant rock on the floor of a glacial trough that has smooth up-valley side and a steep/jagged down-valley side they're typically 1-5meters in height and 5-20meters in length
47
How do roche moutonees form?
1. Abrasion takes place on the up (stoss) side glacier, where high pressure pushes sub-glacial debris into obstacle and smooths it over 2. Pressure melting point occurs at high pressure as the base of the glacier which creates meltwater 3. Plucking takes place on the down (lee) side glacier, meltwater from PMP seeps into cracks and refreezes due to pressure (ice expands by 9%, debris freeze at the base of it. This creates a jagged lee-side
48
What is an example of a roche moutnonee?
Nant-Ffrancon Valley in Snowdonia, North Wales
49
What are the features of a crag and tail?
-> formed when a glacier moves over a band of resistant rock surrounded by two bands of less resistant rock -> crags can reach meters above sea level -> tails can stretch from over a km
50
What is an example of a crag and tail?
Edinburgh castle, Scotland
51
How does a crag and tail form?
1. Glacial ice eroded the weak sedimentary rock of the volcanic crag, this left behind a steepstoss 2. The more resistant volcanic rock isn't eroded, therefore the weak rock on the lee-side is protected therefore less erosion occurs, creating a gentle slope
52
What is the crag part of the crag and tail made out of?
volcanic activity 325 million years ago created outcrops of volcanic rock, which are more resistant than surrounding sedimentary rock
53
What type of glacial landforms are the following: -> roche moutonee -> crag and tail
Meso landforms
54
What are the features of striations and how do they form?
-> they are scratches on the hard bedrock produced by the process of glacial abrasion -> debris frozen in the basal ice is dragged across the bedrock to produce them, and therefore give a clear indication of the direction the ice was moving
55
What are the features of chatter marks and how do they form?
-> these are small intermittent chips/fractures/ gouges in the bedrock formed when the basal debris within the ice is not in continuous contact with the bedrock
56
What are the features of polished rock and how do they form?
ice can polish if sand and silt is found in basal ice layer, opposed to angular rock fragments
Geography - Glaciers
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