G&H1: Mechanics

Question 1

5 accumulation inputs

Answer 1

Snowfall, wind-blown drift, avalanches, condensation, surface water freezing

Question 2

What is rime?

Answer 2

condensed moisture that transforms from gas to solid and bypasses the liquid phase

Question 3

accumulation requirements

Answer 3

Sub-zero temperatures
atmospheric moisture
mountains and mountainous regions (prefferably)
(local variations)

Question 4

What is the actual process of accumulation known as?

Answer 4

Firn compaction.

Question 5

What is firn?

Answer 5

any H20 substance between the snow and ice phase

Question 6

What is the density of snow, firn and ice?

Answer 6

snow = 5-300kgm-3
firn = 400-830kgm-3
ice = 917kgm-3

Question 7

What is the density of ice similar to?

Answer 7

water (997kgm-3)

Question 8

ablation outputs

Answer 8

calving
melting
evaporation/sublimation

Question 9

What is sublimation?

Answer 9

transition from solid ice to gas that again bypasses the liquid phase

Question 10

Steady state concept

Answer 10

glaciers are in an equilibrium between seasonal variations fluctuations. If they are perturbed outside of this equilibrium then the equilibrium will adjust

Question 11

What would happen to the steady state if temperatures suddenly rose?

Answer 11

The glacier would retreat over a long timer period with seasonal variations during this long term retreat. Eventually the glacier would stop retreating and this new position would mark the boundary of the new glacier at which the seasonal variation would then fluctuate around

Question 12

What is the driving stress?

Answer 12

The total pressure or tension exerted upon a glacier.

Question 13

What is the role of the driving stress?

Answer 13

The stress will force the glacier to move/ will drive it forward or backward

Question 14

What is the calculation for driving stress?

Answer 14

= Pi (ice density CONSTANT) x g (Gravitational CONSTANT) X H (glacier height) x SinA (A is the slope of the glacier)

Question 15

What happens to the driving stress if the glacier slope angle is 0?

Answer 15

There is no driving stress because the glacier is flat

Question 16

What is the key control on the driving stress of the glacier?

Answer 16

slope

Question 17

What are the 3 glacier motion mechanisms?

Answer 17

1) internal ice deformation (Uf)
2) sliding at the bed (Us)
3) shear in underlying deformable sediments (Ud)

Question 18

What is the internal ice deformation?

Answer 18

the glacier body is forced to flow as a result of driving stress causing ice deformation. the rate of deformation is dependent upon the driving stress.

Question 19

what law governs the internal ice deformation and how?

Answer 19

Glen’s Flow Law. This law dictates the viscosity of the ice which therefore determines how much the ice deforms

Question 20

What is sliding at the bed?

Answer 20

The glacier is able to slide over the bed

Question 21

What determines the rate of basal sliding?

Answer 21

whether the glacier is frozen to the bed, the bed roughness (friction), amount of entrained debris (sandpaper effect), availability of water at the bed (lubrication)

Question 22

What is shear in underlying deformable sediments?

Answer 22

Think of the bed underneath the glacier as a series of logs that roll as the glacier moves thereby also facilitating that movement of the glacier

Question 23

What affects the amount of deformable sediments?

Answer 23

water content and pressure of sediments. High pressure means that the sediments are weak and therefore very deformable

Question 24

Why is deformable sediment movement not known much about and how do we know what we currently know?

Answer 24

Because the bed is hard to access and so we use models to simulate the bed to provide information