Glaciology I

Question 1

Why is Glaciology important?

Answer 1

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

Question 2

Glaciology in the news

Pine and Thwaites Glacier

Answer 2

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.

Question 3

Glaciers and climate change

There is a lot of overlap but…

Answer 3

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

Question 4

Glacier motion

Three elements make up the surface velocity of a glacier:

Answer 4

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

Question 5

What is Creep?

Answer 5

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

Question 6

Glen’s Law

Answer 6

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

Question 7

Shear Stress

Answer 7

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

Question 8

Implications of Glen’s Law

e = Aτn

Answer 8

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

Question 9

Shallow approximation model

Answer 9

Uc = 2A/ n + 1(pgsinα)nHn + 1

Where h = glacier depth

Question 10

Basal sliding

This occurs when…

Answer 10

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

Question 11

Boulton and Jones (1979) showed that…

Answer 11

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

Question 12

Σ = (Pi - Pw)tanφ + C

Answer 12

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

Question 13

Effective pressure

Answer 13

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

Question 14

What are sticky spots?

Answer 14

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

Question 15

Stick slip motion

Answer 15

Stick (ice and till moving together, slowly)

Slip (just the ice moving, rapidly)

Question 16

Subglacial movement

Answer 16

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

Question 17

Pressure melting point

Answer 17

The temperature that ice freezes depends on pressure:

Question 18

Cold-based Glaciers

Answer 18

Entire glacier bed is below the pressure melting point

Only move by internal deformation (creep)

Question 19

Warm based glaciers

Answer 19

Glacier base above pressure melting point

Move by creep, sliding and possible deformation

Question 20

Ice cores

Answer 20

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

Question 21

When was the last glacial maximum?

Answer 21

Last glacial maximum around 20,000 years ago

Question 22

Heat sources

Answer 22

the faster the glacier moves, it warms up

Question 23

Polythermal

Answer 23

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