Glaciology I Flashcards

1
Q

Why is Glaciology important?

A

Understand past and present cryosphere behaviour to predict future.
Globally population is concentrated close to sea level.
Hazards- flooding and drought
Resources- water
Major landform and sediment producer

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2
Q

Glaciology in the news

Pine and Thwaites Glacier

A

Two glaciers that are moving quickly in Antarctica.
They are also retreating very quickly.
If they suddenly retreat, more ice would come in behind then (water too) and create an even bigger retreat in Antarctica.
It would dramatically effect sea level.

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3
Q

Glaciers and climate change

There is a lot of overlap but…

A

Climatic effects on glaciers include radiation and precipitation.
Glacial effects on climate include albedo and changes to jet stream.

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4
Q

Glacier motion

Three elements make up the surface velocity of a glacier:

A

Creep (Uc)
Sliding (Us)
Till deformation (Ud)
U = Uc + Us + Ud

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5
Q

What is Creep?

A

Ice is a semi viscous material and moves under its own weight

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6
Q

Glen’s Law

A
e = Aτn
Where:
e = strain rate 
A =  temperature 
τ = shear stress
n = 3
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7
Q

Shear Stress

A
Τ = pgh sinα
Where:
p = density of ice
g = gravity
h = thickness of ice
α = slope angle
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8
Q

Implications of Glen’s Law

e = Aτn

A

If τ is doubled (e.g. double the thickness)- deformation rate (movement) increase 8 times.
Warmer glaciers flow faster

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9
Q

Shallow approximation model

A

Uc = 2A/ n + 1(pgsinα)nHn + 1

Where h = glacier depth

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10
Q

Basal sliding

This occurs when…

A

There is a thin layer of melt water at the base of the glacier (Weertman, 1964)

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11
Q

Boulton and Jones (1979) showed that…

A

90% of glacier motion could take place in the underlying sediment, if a glacier rested on an unconsolidated bed.

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12
Q

Σ = (Pi - Pw)tanφ + C

A
Pi = pressure of ice
Pw = pore water pressure
(Pi - Pw) = effective pressure
tanφ = property of the sediment 
C = a constant
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13
Q

Effective pressure

A

Pi - Pw
High effective pressure = rigid bed
Low effective pressure = deforming bed

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14
Q

What are sticky spots?

A

Slower/ stationary parts of deforming bed (Alley, 1993)
Bedrock
Stiffer till
Frozen patches

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15
Q

Stick slip motion

A

Stick (ice and till moving together, slowly)

Slip (just the ice moving, rapidly)

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16
Q

Subglacial movement

A

Sliding
Subglacial shear
Subglacial shear at depth
Sometimes the sediment underneath is contributing to the overall movement

17
Q

Pressure melting point

A

The temperature that ice freezes depends on pressure:

18
Q

Cold-based Glaciers

A

Entire glacier bed is below the pressure melting point

Only move by internal deformation (creep)

19
Q

Warm based glaciers

A

Glacier base above pressure melting point

Move by creep, sliding and possible deformation

20
Q

Ice cores

A

At the ice divide to the bed (hopefully)

Isotopes: Oxygen/hydrogen Reconstruct temperature Electrical conductivity: ionic chemistry
Gases: Samples of past atmosphere
Dust: Atmospheric circulation Crystallography: shows stresses
Dating:
Layers, then model
Known events e.g. volcanic, radioactive fallout

21
Q

When was the last glacial maximum?

A

Last glacial maximum around 20,000 years ago

22
Q

Heat sources

A

the faster the glacier moves, it warms up

23
Q

Polythermal

A

Many glaciers are mostly temperate with a frozen margin – subpolar
They are kind of in between warm ice and cold ice
Glaciers can change from being a cold base to a warm base
The ice sheets are frozen in some places and melted in others