G&H2: thermodynamics Flashcards
What happens to ice density with temperature?
Density increases when temperature falls until 4 degrees celsius. From here the density decreases with more temperature decreases
What affects ice temperature?
1) surface energy
2) geothermal heat flux
3) frictional heat
What is the main source of surface heat?
solar constant
What is the solar constant at equator?
1370 w m-2
What influences solar constant?
milankovitch cycles, latitudinal variations, sunspots, albedo
What is the albedo of fresh snow and ice?
fresh snow = 90%
ice = 30%
What is the geothermal heat flux source?
radioactive decay of iron and nickel
What is the mean geothermal heat flux at Greenland and Antarctica?
Greenland = 60wm-2 Antarctica = 50wm-2
What affects the geothermal heat flux intensity?
1) crust thickness
2) tectonic history and proximity to boundary
3) local subglacial topography (higher at the valley sides)
What is the main source of frictional heat?
Internal deformation and basal sliding
How is the frictional heat generated by internal deformation and basal sliding?
conservation of gravitational potential energty
What controls the ice temperature and flow at the surface, base and middle of a given body?
surface = solar constant base = geothermal middle = function of ice flow and advection of cold ice
What is glens flow law?
the determination of how much ice will deform as a result of applied stress
What is rheology?
the relationship between stress and strain that determines how how much ice will deform as a result
What is the elastic region on a graph between stress and strain of a glacier?
the stress applied will cause deformation but this wont be permanent
What is the plastic region on a graph between stress and strain of a glacier?
Permanent deformation caused by excessive stress
What is the fracture region on a graph between stress and strain of a glacier?
The ice will fracture because of too much stress exerted
what has an important influence upon the rheology of a glacier and how?
temperature because it can soften the ice so that it is more flexible towards increased applied stress
What is the positive feedback between ice movement and stress?
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
Describe the rheology of cold, warm and polythermal glacier?
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
What sort of glaciers are cold based - describe their shape and location
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
What sort of glaciers are warm-based - describe their location?
mid-latiudes
What glacier thermal regime causes subglacial bedforms
warm-based because it can move at the base and therefore cause damage whereas the cold based glacier just preserves the landscape
What is the relationship between ice depth, and ice movement?
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
