Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

PART 1B > Glaciers > Flashcards

Glaciers Flashcards

1
Q

3 ways of measuring glaciers

A

glaciological, geodetic, gravimetric

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Three approaches to calculating past
contributions of glaciers & ice caps to
sea level

A

Statistical area-weighted
extrapolations of locally- or
regionally-derived glaciological &
geodetic data over most glaciers on
earth

Geodetic approach only, using repeat
DEMs from ASTER satellite

Gravimetric approach using GRACE
data

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

DEM stands for

A

direct elevation model

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

4 essential ingredients of a model

A
  • A spatial domain to run your model. Do you want to model conditions at
    a single point? Or investigate two-dimensional spatial patterns?
  • A Mathematical description of the system – either empirical (i.e., derived
    from data), or based on physical principles (e.g., Newton’s Laws).
  • Suitable inputs. For glacier mass balance, we need meteorological data
    (e.g., precipitation & temperature) to calculate accumulation & ablation.

Real-world observations to calibrate &
validate the mode

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

3 main options for spatial domain of glacier model

A

0 dimensional applications that treat glaciers as a single bulk entity

1 dimensional applications that split glaciers into a series of bulk elevation bands

2 dimensional applications that are fully spatially distributed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

equation for SMB

A

Bn = c + a + R

where c is accumulation, a is ablation (defined negatively), R is refreezing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

three main types of glacier mass balance model

A
  • Degree Day (also known as temperature index) models
  • Energy Balance (also known as physically-based) models
  • Hybrid (also known as enhanced degree day / temperature index) models
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

+ves and -ives of degree day model

A

Advantages

  • Quick & easy
  • Only requires air temperature as input - easy to apply in data sparse,
    remote regions
  • Good for predicting melt in future if future air temperatures modelled
    well

Disadvantages
* Model is empirical - extrapolating over space & time is uncertain
* Not physically-based - offers limited insight into processes
* Limited information on spatial patterns across glacier, or temporal
information at sub-seasonal scales.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

+ves and -ves of energy balance model

A

Advantages

  • Physically-based – offers good insight into the processes occurring
  • Good for investigating spatial patterns, and short, sub-daily, time periods
  • Does not depend on empirical relations, so easy to apply to other
    glaciers & different time periods

Disadvantages

  • Computationally expensive
  • Requires many meteorological inputs so application often limited to
    locations with lots of observations
  • Arguably less useful for future predictions where some of the climate
    drivers, e.g. cloudiness, humidity, wind speeds are less well predicted
    than, e.g. air temperature
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Advantages & Disadvantages of Hybrid Models

A
  • Account for spatial patterns
  • Variant 1 requires no extra field measurements; Variant 2 requires Gs measurements
  • Depends on empirical relations, so not easy to apply to other glaciers & time periods
  • More computationally expensive than classic DD method but less than EB approach
  • Variant 1 could be useful for future predictions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

outline the maths behind c (accumulation)

A

Precipitation usually treated as
linear function of elevation
* Air temperature threshold (e.g. 1oC)
used to distinguish between snow or
rain
* Works well on a glacier-average
scale over whole summers
* Works less well at smaller spatial
and temporal scales
* Does not account for local
topographic features or snow
redistribution by wind.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

outline the traditional approach to monitoring meteorological inputs to glaciers

A

Automatic weather station (AWS) on
or near glacier.
* Meteorological variables then
extrapolated over the DEM.
* e.g. temperature assuming a
standard atmospheric lapse rate (6.5
˚C per km).
* e.g. precipitation assuming
regionally measured gradient.
* BUT… most glaciers are in remote
locations & so it is often difficult to get
local measurements.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q
A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

outline the new approach ~(last 20 years ) to monitoring meteorological inputs to glaciers

A

Climate reanalysis (e.g. ERA-40, ERA
Interim, ERA 20C, JRA55, NOAA 20CR).
* Produced by ‘reanalysing’ observations
using a weather/climate model.
* Global fields of meteorological variables
(e.g., temperature, precipitation) on a
moderate resolution grid (typically 1
degree lat./long.). So we can model any
glacier!
* BUT… reanalyses are produced using
models so are subject to uncertainty (e.g.
biases)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

outline some parameters that must be estimated that are used in a model

A
  • DDFs for snow and ice (for a DD model) * snow and ice albedo (for an EB model) * temperature lapse rate
  • precipitation gradient
  • threshold temperature for rain / snow
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is calibration

A

we adjust uncertain model parameters so model output agrees
well with real-world observations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is validation

A

we test our calibrated model to see how well it performs against real-world observations.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what do we do if we do not have have measurements of parameters

A

we have to
calibrate (or ‘tune’ or ‘optimize’) them.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what does DD model stand for

A

degree day

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is DDF stand for

A

degree day factor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

outline the work of Orleans and Fortune 1992

A
  • Applied energy balance model to 12 glaciers around the world
  • Examined sensitivity to a 1 ̊C increase in air temperature.

Key conclusion:

Maritime glaciers are more sensitive to air temperature changes than continental glaciers..

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

why are Maritime glaciers are more sensitive to air temperature changes than continental glaciers..

A

relationship between temperature & melt is exponential. So perturbing temperature has greater impact in warmer maritime regions.

  • More precipitation will fall as rain in warmer maritime regions compared to sub- zero continental regions
  • A positive feedback loop: melting lowers albedo, which increases melting
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is perturbing temperature

A

term used to describe a departure from the regular flow of atmospheric currents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

outline hock et al 2007

A

compared 5 models of varying complexity ( 3 DD and 2 EB).

Applies to Storglaciaren, calibrated using ERA 40 reanalysis

used regional climate model output to predict MB up to 2100

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q
A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

how are models used to calculate global glacier MB

A

we first calibrate for a few glaciers where measurements have been made.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

outline why glacier hydrology is important

A
  • Glaciers are a natural reservoir, storing water in high precipitation, cold years; releasing it in low precipitation, warm years.
  • Glacier hydrology modulates effects of surface melting on stream runoff.
  • Controls quantity and quality (sediment, chemistry) of water in glacier-fed streams.
  • May increase risk of flooding – ‘jökulhlaups’, Glacier Outburst Floods (GLOFs).
  • Implications for water resource management.
  • Controls spatial & temporal distribution of water pressure beneath glaciers, & therefore glacier movement (sliding/sediment deformation).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

3 types of hydrology

A

supraglacials, englacial and subglacial hydrology

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

what is a moulin

A

an erosional feature which occurs on the surface of a glacier. formed by erosion by meltwater, creating circular inlet down that meltwater can enter the body of the glacier

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what is a crevasse and how does it form

A

deep crack that forms due to movement and resulting stress of the moving ice

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

what does TDR stand for

A

time domain reflectrometry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

how does TDR work

A

probes are installed in snow in the accumulation area

they measure two way travel time through the snow of EM waves - this time is affected by the water content of snow

when EM pulse encounters a change in material properties (such as boundary between ice and water) part of the signal reflects back to surface.

time delay is measured to determine distance to and nature of material change

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

where does the majority of englacial water flow

A

in small pipes or larger conduits fed by crevasses / moulins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

what is glacio speleology

A

study of caves/cave like structures within glaciers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

3 ways englacial passages form and cite

A
  1. incision of surface streams or base of crevasse followed by roof closure
  2. hydrologically driven ice fracturing
  3. exploitation of pre existing permeable structures within the ice

gulley et al 2009

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

outline shreves theory and the equation

A

theoretical direction of water flow calculated by considering hydraulic potential throughout ice

this is the sum of
gravitational potential (height above sea level) + pressure potential (overburden pressure).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

what is a conduit

A

a passageway within which water flows

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

if snowpack is isothermal, what does this mean

A

it is uniform, at 0 degrees C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

how does snow melt

A

conduction, infiltration of water, refreezing and release of latent heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

what does K equal in shreeves theory

A

a fraction where 1 is when max pressure potential and 0 atmospheric pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

when does subglacial drainage occur

A

wherever ice at a glacier bed reaches the pressure melting point

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

what is the pressure melting point

A

is when ice melts at a given pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

list some ways we learn of subglacial drainage characteristics

A

radio-echo sounding

use of artificial tracers

monitoring

manipulation of conditions via boreholes

monitoring runoff properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

4 main sources of subglacial water

A

surface, englacial and basal melt,

subglacial meltwater

45
Q

what determines the relative importance of the sources of subglacial meltwater

A

climatic regime at ice surface,

temperature of glacier ice

ice flow dynamics

nature of glacier bed

46
Q

why might basal Melt be the dominant source in antarctica

A

the surface temps never reach above the freezing point, but the ice temps reach pressure melting point near the glacier bed.

47
Q

two main types of subglacial drainage system

A

distributed or slow

channelised or fast

48
Q

outline the different steady state discharge and effective pressure relationships

A

smaller fluxes can be stable in cavities, as it rises the effective pressure drops.

inverse relationship between discharge and effective pressure

more water going through increases water pressure - this causes cavities to become unstable, behave like channels, meaning water pressure drops, and effective pressure rises

49
Q

what is the effective pressure

A

ice overburden pressure - water pressure

50
Q

what is the relationship between steady state discharge and effective pressure

A

direct- as discharge increases the water pressure decreases as channels widen, leading to greater effective pressure

51
Q

outline what happens to cavity system when water discharge is increased

A
  • Water pressure will rise, due to piling water from above
  • this will increase sliding which increases cavity XSA
  • increase in WP means effective pressure falls, lowering the creep closure rate
  • however on net cavity has enlarged less than discharge did
  • as discharge is velocity times XSA and discharge went up more, velocity must have too
  • this raises water pressure
52
Q

list the % of air in each layer of sintering

A

snow - 90%

coarse grained snow - 50%

firn - 20-30%

glacial ice - 20% as bubbles

53
Q

define sintering

A

the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.

54
Q

2 types of ice

A

massive ice and glacial ice

55
Q

3 types of ductile deformation

A

elastic, viscous, plastic

56
Q

what is deformation

A

how a material responds to an applied stress

57
Q

what is elastic deformation

A

a stretch goes back to where it came from

58
Q

what is viscous deformation

A

permanent deformation, not going to snap back, will continue oozing out

speed is proportional to the stress being given

59
Q

plastic deformation

A

elastic at first until a critical stress is met, then permanent movement

60
Q

what type of deformation is ice

A

between viscous and plastic- viscoplastic

61
Q

how is deformation measured

A

in terms of strains

62
Q

how is the measure of stress

A

measured in pressure.

Newtons/Metres2 = pascals

63
Q

how is strained measured

A

how much change since original position

(end position - start) / start

it is a proportion, a unitless ratio

64
Q

why is strain meaningless in viscous flows

A

strain keeps increasing as stress is applied

65
Q

what unit is strain rate

A

per years

66
Q

two types of deformation

A

pure shear and simple shear

67
Q

outline pure shear

A

an object that squishes in one direction, onto the sides

extension and compression

68
Q

outline simple shear

A

parallel surfaces moving past each other

material deforms in a way that layers slide over each other. this results in a change in angles between lines that were originally perpendicular

69
Q

what is the stress/strain relationship known as

A

glens flow law

70
Q

outline the stress/strain relationship

A

logarithmic scales, it is not linear

exponential scale

strain rate = ice hardness*stress^usually 3

71
Q

why is the exponent usually 3 glens flow law

A

when we plot it is the most fitting value for the viscoplastic movement , but some think it should 4.

works most of the time with n=3

72
Q

how does ice hardness change with temperature and give example

A

increases significantly with fall in temp

ice hardness increase by factor of 1000 from 0 to -55 degrees

73
Q

other factors affecting ice hardness

A

water content

impurities

74
Q

ice at 0 degrees is how much viscous than water?

A

10^15 times (massive number)

75
Q

how does strain rate change through time and name phases

A

primary - initially drops under applied stress, due to stiffening, as ice grains redistribute

secondary - then softens due to recrystallisation and rotation of crystals

tertiary - reaches a steady state

76
Q

briefly distinguish stress and strain

A

stress is a measure of how hard a material is being compressed, stretched or twisted as the rest of applied forced

strain measures the amount of deformation that occurs as the result of stress

77
Q

outline example of stress and strain in relation to toothpaste

A

toothpaste comes out due to deformation (strain) resulting from an higher pressure on the surface than the nozzle (stress)

78
Q

define force

A

the physical influences which change the state of motion of a mass

mass times acceleration

79
Q

define stress

A

force per unit area

80
Q

unit for stress

A

pascal (newton/metres squared)

81
Q

two components of stress on a surface

A

stress acting at right angles to the surface (normal stress)

acting parallel to the surface (shear stress)

82
Q

what are the two equal and opposing tractions on normal stress

A

either pressing together across the surface compressive stress

or pulling away from it tensile stress

83
Q

how do the tractions work in shear stress

A

parallel but act in opposite directions

84
Q

at the base of a glacier what is the normal stress

A

mostly due to weight of overlying ice

85
Q

define traction

A

force per unit area on a surface of a specified orientation - a measure of force intensity

86
Q

define surface stress

A

a pair of equal and opposite tractions acting across a surface of specified orientation

87
Q

define shear stress

A

a pair of tractions acting parallel to a surface

88
Q

define normal stress

A

a pair of tractions acting at right angles to a surface

89
Q

two basic types of strain

A

elastic (recoverable)
permanent (irrecoverable)

90
Q

two forms of permanent deformation

A

brittle failure - where the material breaks along a fracture

ductile deformation - where material undergoes flow or creep

91
Q

what is it known as when a material undergoes a change in volume due to deformation

A

dilation

92
Q

why is transformation of now to ice dilation

A

the accumulation area of a glacier reduces in volume while increasing in density

93
Q

why is a glacier mostly constant volume strain

A

it is essentially incompressible. after snow is condensed to ice

94
Q

how is strain measured

A

comparing the shape and size before and after deformation.

95
Q

two fundamental types of strain

A

pure shear
simple shear

96
Q

outline pure shear

A

flattening or stretching of a material under compressive and tensile deviatoric stresses

97
Q

two ways of measuring strain

A

strain rate - amount per unit of time

cumulative strain - net amount that takes place in a given time interval

98
Q

what is rheology

A

the way in which strain rate varies with applied stress for a given material

99
Q

what is yield strength

A

the value of the applied stress at the onset of permanent deformation, measured in Pascals

100
Q

what does it mean if yield strength = 0

A

permanent deformation will happen at any stress, no matter howsmall

101
Q

what is the yield strength of ice

A

0

102
Q

the yield strength of subglacial sediments can be understood as the sum of which two properties…:

A

cohesion, friction

103
Q

what does glens flow law calculate

A

how much deformation do you get if you increase the force on ice

104
Q

glens flow law equation

A

E (strain) = A * T^3 (ice hardness*stress cubed)

105
Q

main control on ice hardness

A

temp

106
Q

why if we increase stress a little does strain increase a lot

A

strain is hardness * stress cubed

107
Q

how is shear stress calcualted

A

ice density x gravity x thickness of ice x sin of ice gradient

weight x sin of ice surface gradient

108
Q

why is the ice surface gradient important in shear stress

A

if it was flat, there would just be normal stress crushing the ice down

as it increases shear stress increases

how much of the weight of the ice that is generated through shear stress rather than normal stress depends on that gradient

109
Q
A

PART 1B (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions