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Dynamic Earth: Physical Geography > Glaciation > Flashcards

Glaciation Flashcards

1
Q

how much more frequent is nuisance flooding today than 50 ya?

A

300-500%

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2
Q

how many people live in areas below the projected tideline by 2050

A

150 million people

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3
Q

how much has the sea level risen since 1850

A

21-24cm

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4
Q

since when has the ocean been warming rapidly causing thermal expansion?

A

1980s/90s

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5
Q

where is much of the ice loss occurring?

A

fringes of the antarctic ice sheet-> up to 10m a year

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6
Q

what are ice shelves

A

ice connected to the ground sheet but extending over the ocean (floating)
- thinner and more likely to melt

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7
Q

effect of ice shelves on the flow of the overall glacier

A

slow the flow and therefore ice loss

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8
Q

compare the east and west antarctic ice sheets

A

east antarctic ice sheet contains more ice but may be more stable than the west antarctic ice sheet which is mostly on land below sea level

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9
Q

last time temperatures were similar to today, what level were the seas?

A

6-9m higher

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10
Q

when was the last time CO2 was as high as present?

A

the Pliocene-> sea levels at least 6m higher

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11
Q

what occurred to sea levels about 20,000 yrs ago?

A

global warming event after ice age, meltwater pulse 1A caused 15m change in levels over a few 100 yrs

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12
Q

what sea do the antarctic ice sheets flow into?

A

Ross Sea

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13
Q

in what way can warming actually lead to ice sheet build up>

A

more snow

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14
Q

5 ways that glaciers impact humans

A
  1. meltwater= source of freshwater
  2. changes to ecosystems due to glacial changes
  3. driver of local tourism
  4. power from meltwater
  5. glacier floods= hazards
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15
Q

what is a glacier

A

a piece of ice that persists year on year and is massive enough to deform under its own weight

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16
Q

what is an ice sheet

A

over 50,000 km2, any changes in underlying topography dont impact ice flow

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17
Q

what is an ice cap

A

less than 50,000 km2, still not impacted by underlying topography

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18
Q

what is an ice stream

A

channel of relatively fast flowing ice-> flow from middle to edges

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19
Q

what are calved pieces of ice also known as

A

ice bergs

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20
Q

what is the constraining factor on alpine glaciers

A

topography

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21
Q

3 essential factors to form a glacier

A

land surface, persistent cold temperatures, precipitation

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22
Q

what is glacial mass balance

A

how the mass of the glacier changes over time

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23
Q

what occurs in the accumulation zone

A

snow falls and persists at the top of the glacier

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24
Q

equilibrium line

A

usually corresponds with the freezing level

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25
Q

in which zone does the glacier melt

A

ablation zone

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26
Q

what occurs when the equilibrium line goes up

A

the glacier decreases

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27
Q

what happens when the equilibrium line goes down

A

the glacier increases

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28
Q

supraglacial water

A

on top of the glacier

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29
Q

englacial water

A

through the glacier

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30
Q

moulins

A

near vertical shafts that allow supraglacial water to enter the glacier

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31
Q

subglacial water

A

water below the glacier

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32
Q

N-channels versus R-channels

A

N-channels-> cut down into the channel

R-channels-> cut up into the (warmer) ice

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33
Q

how can we measure or detect subglacial drainage systems

A

radar

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34
Q

what is the effect of water at the base of the glacier

A

increases flow

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35
Q

why do cracks form on the surface of glaciers

A

less pressure on top than below

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36
Q

regelation

A

freezing point decreases due to pressure when approaching an obstacle. water flows around obstacle and refreezes on downslope side

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37
Q

what is the process by which glaciers move under their own weight

A

ice deformation

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38
Q

surging glaciers

A

meltwater builds up in subglacial reservoirs before overflowing, causing a rapid increase in sliding

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39
Q

what occurs to clasts when entrained and carried by glacier over time

A

they go from angular to smoothed

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40
Q

why is less work done on the landscape in v cold polar regions

A

ice only moves by internal deformation

41
Q

what do glacial troughs and hanging valleys mark

A

where glacier tributaries once joined the main glacier

42
Q

stoss and lee features

A

subglacial features caused by regelation
debris cracked off during refreezing
forms gentle slope up and steep cracked slope down

43
Q

rouche moutonées

A

small stoss and lees

44
Q

eskers

A

r-channels fill with sediment over time and are left behind when glacier melts

45
Q

how can eskers climb hills?

A

high pressure forces water upwards

46
Q

where are drumlins common

A

areas which had warm fast flowing ice

47
Q

flutes

A

like stoss and lee forms but the cavity side gets filled with sediment

48
Q

what is left behind by pro-glacial lakes

A

glacial flour, builds up in layers

49
Q

what is surface-exposure dating?

A

atoms from deep space hit the surface of rocks and make a reaction that expels some subatomic particles- measure how many were removed…
(shows when the rock was deposited by the glacier)

50
Q

in a warmer climate, is there a higher or lower proportion of 18O than a cooler climate?

A

higher

51
Q

what other gas matches quite closely with ice core proxy data

A

methane

52
Q

where does most mass come to ice sheets from

A

smaller, faster flowing ice streams or outlet glaciers

53
Q

nivometric component

A

percentage of precip falling as snow in an area

54
Q

give 5 controlling factors on distribution of ice and snow

A

latitude, altitude, relief, aspect, continentality

55
Q

snowline

A

where fresh snow still lies- retreats up glacier by late summer

56
Q

firn

A

wetted/compacted snow over a year old

57
Q

2 zones of the accumulation zone

A

dry-snow zone: no melt

wet-snow zone: entire snowpack is saturated by end of summer

58
Q

superimposed ice

A

water that refreezes at the base of the glacier

59
Q

how does snow transform to ice when water is present

A

melting, percolation and refreezing-> fast changes

60
Q

how does snow turn to ice when no water

A

slow process, packing and settling, changes to ice crystal size and shape from sublimation and deformation

61
Q

warm ice

A

at pressure melting point and contains water

62
Q

cold ice

A

at temps below pressure melting point, doesnt contain liquid water

63
Q

what does the thermal regime of the glacier control

A

the water system and range of processes that can occur at the bed of the glacier

64
Q

3 types of thermal regime

A

temperate glacier, cold glacier, polythermal glacier

65
Q

4 main morphologies of subglacial water systems

A
  1. thin sheet flow
  2. network of channels
  3. linked cavities
  4. braided system of canals
66
Q

what can cause R channels to close up

A

ice creep

67
Q

at what time of year are water pressures highest in r channels

A

spring, melting

68
Q

where do linked cavities form

A

downstream of bedrock bumps

69
Q

is water in a large canal at higher or lower pressure than a smaller canal

A

higher

70
Q

where are canals likely to occur

A

where low-slope glaciers overlie soft sediment

71
Q

how many glaciers mapped under the Antarctic ice sheet

A

over 400

72
Q

3 mechanisms of glacier flow

A

internal deformation, sliding, bed deformation

73
Q

what two factors cause drag at the bed

A

bed roughness (form drag) and rock to rock friction (frictional drag)

74
Q

enhanced creep

A

increased compressive stress upstream side of obstacle, most effective for larger obstacles

75
Q

Glens flow law

A

creep rate proportional to the 3rd power of the stress

76
Q

how fast are fast flowing glaciers

A

100-1000m a yr

77
Q

glacial crushing

A

direct fracturing of the bedrock due to weight of ice

78
Q

5 ways glacial crushing might occur

A

stress concentration due to stones in basal ice, pre existing weaknesses in bedrock, repeated cycles of loading and unloading, freeze-thaw, pressure release due to large amounts of rock removal

79
Q

product of glacial crushign

A

large, angular rocks

80
Q

outcome of chemical erosion due to meltwater

A

decomposition of minerals to ionic constituents

81
Q

3 factors that control erosion rates

A

changes in basal temp, glacier velocity, bedrock properties

82
Q

how much on average do valley glaciers erode each year

A

1mm

83
Q

how are the sediments resulting from glacial deposition classified

A

by the process of their deposition

84
Q

till

A

sediment deposited from a glacier

85
Q

lodgement till

A

frictional resistance between clast in transport at the base exceeds the drag imposed by the ice- grain by grain plastering

86
Q

deformation till

A

pre-existing subglacial materials folded, sheared and partially homogenised by movement above of debris rich ice

87
Q

meltout till

A

ice surrounding sediment melts

88
Q

flow till

A

continuous supply of water in summer, poor draining, common sediment flows, particle sorting

89
Q

crag and tail features

A

features of erosion: resistant rock left standing proud of surface, smaller cavities form behind more resistant rock

90
Q

chatter marks

A

formed when ice moves over the bed with stick-slip motions

91
Q

push moraines

A

glacier pushes sediment up to form a ridge

92
Q

dump moraines

A

ridges formed transverse to the flow from material delivered to the margin of the glacier by ice flow

93
Q

lateral moraines

A

parallel to sides of glaciers from dumped and frost-shattered matter

94
Q

hummocky moraines

A

irregular mounds of material from meltout of supraglacial or englacial matter

95
Q

de Greer moraines

A

linear ridges of sediment, transverse to the flow where a retreating ice mass borders on a glacial lake

96
Q

crevasse-fill ridges

A

glacier with deep crevasses sinks into soft water saturated sediments

97
Q

kettle holes

A

depressions from melting stagnant ice

98
Q

kames

A

mound of sediment forme when a hole in a melting stagnant ice mass becomes filled with sediment

Dynamic Earth: Physical Geography (11 decks)

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