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Glaciers and Glaciation > Week 1: Importance of glaciers > Flashcards

Week 1: Importance of glaciers Flashcards

1
Q

Glacier =

A

Snow and ice mass which, if accumulates to sufficient thickness, deforms under own weight and flows (Sugden 1994)

Cover 10% Earth’s surface
75% freshwater

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2
Q

IMPORTANCE OF GLACIERS

A

Glacio-EUSTASY (global)

Glacio-ISOSTASY (local)

Local/global climate systems

Ice cores/palaeoclimate records

Hazards

Glacial ‘respiration’ and nutrient fluxes

Source of water

Tourism

Sediment resources (sands/gravels)

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3
Q

Glacio-isostasy

A

England/Scotland rises 102mm/yr

Will take 10-20,000 years to re-equilibriate

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4
Q

Local/global climate systems

A

Greenland meltwater –> Labrador Sea

1) reduce surface convection in N Atlantic due to freshwater flux
2) slows gyre
3) affects NW Europe’s summer climate

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5
Q

Hazards

A

Outburst floods (GLOF)

Surges

Ice avalanches

–> position important e.g. earthquakes, geothermal heat flux

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6
Q

Glacial respiration and nutrient fluxes

A

Hodsen et al 2007: CO2 flux of cryconite across an entire arctic suprglacial ecosystem

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7
Q

Size facts

A

AIS 30.1 million km3

GIS 2.28 million km3

EQUIVALENT TO 70M OF SEA LEVEL

Other smaller make up 180,000 km3

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8
Q

Controls on glacier distribution (and explained)

A

LATITUDE
- low solar energy = less energy to melt ice

ALTITUDE

  • thinner air holds less heat energy
  • -> glaciers near equator!

CONTINENTALITY

  • no moisture source = drier air
  • rain shadow effect
  • ALSO sea ice reduces moisture from oceans e.g. Europe
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9
Q

Types of classification

A

SIZE/RELATIONSHIP TO TOPOGRAPHY

BASAL THERMAL REGIME

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10
Q

Classification; size/relationship to topography

A

Largest = ice sheets = unconstrained by topography

Transition from constrained –> unconstrained as grows

Example of constrained: valley/cirque/niche glacier

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11
Q

Classification; basal thermal regime

A

Cold-based, warm, polythermal

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12
Q

Marine glaciers: ice rise =

A

Ice moves towards sea, bumps into island and rises over

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13
Q

Marine glaciers: sea-ice ice shelf =

A

Long term, thickens until shelf forms e.g. N Pole

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14
Q

Direction of ice flow

A

Acc zone –> ELA –> ablation zone

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15
Q

ELA = (and usual value)

A

Altitude when acc = abl

Usually 0.6 i.e. contour below 60% of total glacier area

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16
Q

Acc > abb

A

+ve mass balance
Low temps +/ greater snowfall
Decrease ELA

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17
Q

Acc < abl

A

-ve mass balance
High temps +/ less snowfall
Increase ELA

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18
Q

Identifying mass balance

A

Annual misbalance

Aerial photos/satellite images

Accumulation Area Ratio (AAR)

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19
Q

Methods of acc (major to minor)

A 
Snow
Wind blown drift
Avalanches
Condensation (rime = rapid frost formation)
Freezing rain/external water
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20
Q

Methods of abl (major to minor)

A 
Calving (wet/dry, DOMINANT)
Melting (top down thinning)
Wind blown drift (scoured from top)
Avalanches
Evaporation
Sublimation (e.g. Antarctica)
DEFLATION
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21
Q

How does ice form?

A

Reduce voids and increase density
e.g. New snow = 50-70kg/m2
Glacier ice = 830-917kg/m2

22
Q

Firn =

A

Snow which has survived a melt season

Forms ice when air can’t transit in/out of system

23
Q

Types of snow zone

A

Warm/wet

Cold/dry

24
Q

Warm/wet snow zone, how ice forms

A 
Melting
Refreezing
Rounding
Joining 
... of grains
25
Q

Cold/dry snow zone, how ice forms

A

Sintering = bonds form under heat and pressure

26
Q

Why is englacial ice not a simple layer cake stratigraphy?

A

Disruptions to layers relating to annual acc of snow

e.g. partial avalanches ‘jumble’ = new structures due to compression/extension

27
Q

Controls on ice formation

A

Temperature

Accumulation

28
Q

Temperature: control on ice formation

A

Warmer = faster

Important control on transformation

29
Q

Accumulation: control on ice formation

A

More snow = faster formation

30
Q

Examples of differing ice formation

A

ALASKA
Warm/wet with lots of snow into system
High densities at shallow depths = faster formation
Ice at 13m

GREEENLAND
Colder/drier
Takes longer for ice to form
Ice at 66m

31
Q

Controls on calving (and explained)

A

1) Water depth
Hf = (pw/pi)Dw
“Critical floatation depth” - will float if less than = calving feedbacks

2) Water T
Bottom up thinning

3) Tidal variation
Flexing

4) Glacier crevassing
5) Water discharge from glacier

32
Q

Freshwater density

A

1000 kg/m3

33
Q

Seawater density

A

1030 kg/m3

34
Q

Ice density

A

900 kg/m3

35
Q

Grounding line =

A

Point at which glacier begins to float

36
Q

Calving front =

A

Where calving occurs
If calving front = grounding line –> “tidewater glacier”
N.B. Doesn’t occur in cold polar environment e.g. Antarctica; 100s km from grounding line

37
Q

Energy balance at glacier surface:

A

Qm = Qs + Ql + Qh + Qe

Qm = energy available to melt ice

Qs = solar shortwave radiation

Ql = longwave (emitted) radiation

Qh = sensible heat transfer

Qe = latent heat transfer

38
Q

What affects energy balance at glacier surface?

A

ALBEDO i.e.

Supraglacial debris cover

(- albedo affected by surface texture/material made up of/debris cover)

39
Q

Typical albedos of clean ice vs debris covered ice

A

34-51%

10-15%

40
Q

THIN debris =

A

Increased absorption/re-radiation = more ablation

e.g. Cryconite holes = thin patches, accelerate abl not thick enough for blanket effect

41
Q

THICK debris =

A

Less conduction = increased protection = less ablation

N.B. ?False impression of +ve mass balance
Can bury glaciers for decades!

42
Q

Measuring glacial mass balance

A

DIRECT METHODS

GEODETIC (REMOTE SENSING)

HYDROLOGICAL

CLIMATIC CALCULATIONS

GRAVITY CHANGES

KINEMATIC MASS BUDGET

43
Q

Measuring glacial mass balance; direct methods

A

Accumulation - snow pits = depth/density

Ablation - stakes = ice surface changes

44
Q

Measuring glacial mass balance; geodetic

A

Aerial photos = area/altitude changes different years = vol changes
- DIFFICULT

Repeat satellite radar altimetry (radio waves) and LIDAR (Light Detection and Ranging - laser pulses)
= thickness changes within mm
- v useful for remote areas/large continental sheets

45
Q

Measuring glacial mass balance; hydrological

A

Net balance = option - runoff - evaporation

:) water resources/prediction/management

  • favours small glaciers b/c data collection required
  • can’t distinguish changes in snow/ice vol vs water storage
46
Q

Measuring glacial mass balance; climatic calculations

A

Meteorological data –> calculate surface energy balance and ablation
Statistical methods based on T

POSITIVE DEGREE DAYS (Braithwaite 1995) = sum of mean daily T for which T>0’C

  • assumes uniform conditions across large area
  • ignores calving
47
Q

Measuring glacial mass balance; gravity changes

A

Gravity Recovery And Climate Experiment satellites

Ice has a gravity influence

e.g. Alaska has summer/winter fluctuations but long term trajectory = -ve mass balance

48
Q

Measuring glacial mass balance; kinematic mass budget

A

FOR MARINE TERMINATING GLACIERS

1) Surface mass balance (climate model)
2) Mass lost from marginal flow (remote sensing)

49
Q

Steep mb gradient =

A

High rates acc/abl

Moist mid latitudes e.g. Norway

50
Q

Shallow mb gradient =

A

Low rates acc/abl

Arid/polar latitudes e.g. Arctic, Canada

51
Q

Why isn’t mb gradient linear

A

Should be due to lapse rate (0.4-0.9’C/100m)

  • acc increases with altitude UNTIL too cold for pption
  • debris cover
  • shading by topography
  • avalanching

Glaciers and Glaciation (29 decks)

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