G&H2: thermodynamics

Question 1

What happens to ice density with temperature?

Answer 1

Density increases when temperature falls until 4 degrees celsius. From here the density decreases with more temperature decreases

Question 2

What affects ice temperature?

Answer 2

1) surface energy
2) geothermal heat flux
3) frictional heat

Question 3

What is the main source of surface heat?

Answer 3

solar constant

Question 4

What is the solar constant at equator?

Answer 4

1370 w m-2

Question 5

What influences solar constant?

Answer 5

milankovitch cycles, latitudinal variations, sunspots, albedo

Question 6

What is the albedo of fresh snow and ice?

Answer 6

fresh snow = 90%

ice = 30%

Question 7

What is the geothermal heat flux source?

Answer 7

radioactive decay of iron and nickel

Question 8

What is the mean geothermal heat flux at Greenland and Antarctica?

Answer 8

Greenland = 60wm-2
Antarctica = 50wm-2

Question 9

What affects the geothermal heat flux intensity?

Answer 9

1) crust thickness
2) tectonic history and proximity to boundary
3) local subglacial topography (higher at the valley sides)

Question 10

What is the main source of frictional heat?

Answer 10

Internal deformation and basal sliding

Question 11

How is the frictional heat generated by internal deformation and basal sliding?

Answer 11

conservation of gravitational potential energty

Question 12

What controls the ice temperature and flow at the surface, base and middle of a given body?

Answer 12

surface = solar constant
base =  geothermal
middle = function of ice flow and advection of cold ice

Question 13

What is glens flow law?

Answer 13

the determination of how much ice will deform as a result of applied stress

Question 14

What is rheology?

Answer 14

the relationship between stress and strain that determines how how much ice will deform as a result

Question 15

What is the elastic region on a graph between stress and strain of a glacier?

Answer 15

the stress applied will cause deformation but this wont be permanent

Question 16

What is the plastic region on a graph between stress and strain of a glacier?

Answer 16

Permanent deformation caused by excessive stress

Question 17

What is the fracture region on a graph between stress and strain of a glacier?

Answer 17

The ice will fracture because of too much stress exerted

Question 18

what has an important influence upon the rheology of a glacier and how?

Answer 18

temperature because it can soften the ice so that it is more flexible towards increased applied stress

Question 19

What is the positive feedback between ice movement and stress?

Answer 19

The friction reaches such a point that it causes the ice to heat up and so the ice can tolerate more stress exerted upon it and so more deformation happens and more friction then heating

Question 20

Describe the rheology of cold, warm and polythermal glacier?

Answer 20

cold = frozen to base to only internal deformation can happen
warm = pressure melting point at base means there is a supply of lubrication to the base of the glacier which encourages basal sliding
polythermal = in between both the cold and warm means a mixed rheology that is unique to each glacier

Question 21

What sort of glaciers are cold based - describe their shape and location

Answer 21

thin and located in high latitudes because here the climate is cold enough that it freezes the glacier to the bed and so the accumulation of material just spreads out

Question 22

What sort of glaciers are warm-based - describe their location?

Answer 22

mid-latiudes

Question 23

What glacier thermal regime causes subglacial bedforms

Answer 23

warm-based because it can move at the base and therefore cause damage whereas the cold based glacier just preserves the landscape

Question 24

What is the relationship between ice depth, and ice movement?

Answer 24

the rate of flow change with glacier height is greatest at the base of the glacier i.e. at the base, small increases in height feature a greater change in flow speed so at the top the speed is greatest usually then as you go down the depths at first the flow change is minimal but as you get deeper the flow rate change starts decreasing faster. See diagram on lecture notes