Glacier- Formation Flashcards
What is glacier formaiton dependent on?
Balance of input/output
What is temperature change dependen on?
Specific heat capacity
Specific heat capacity for ice is?
1.751J at -50C or 2J at -10C
Specific heat capacity for H2O?
4.127J at 0C.
Which state changes release energy?
Evporation and freezing
Watts
Equal to one joule per second, measured against surface area per square metre
What is energy flow of a glacier compose dof?
Incident Solar Radiation
Reflected Infrared Radiation
Letent Heat transfer by condensation
Latent Heat consumed or released during melting and freezing
Why does TOA atmospheric radiation decrease with altitude?
Diffusion and filtration.
Optical Depth
This is an extinction coefficienct of an atmospheric layer inegrating distance, humidity, cloudiness and concnetration of other particles.
What does incidient SW radiaiton depend on with declination?
Latitude, slope gradient and time of day.
What is an example of influence of clouds on energy balance?
Where clear air, SW up to 1200Wm-2, whilst cloudiness reduced to few percent
What is the equation of radiant flux?
Emissivity multiplied by SB constant multiplied by temperature^4
What does sensible heat depend on?
Gradient between atmosphere and glacier, transfer of molecular momentum
What does the atmosphere-glacier gradient depend on?
Turbulence and convectionf of boundary level air
What is glacial energy most variable with?
Higher temperatures, strong winds and rougher surfaces.
Why are glaciers blue?
Perferential ABSORPTION of blue light
Why is ice temperature variable?
Because its meltin point varies with temperature, decreasing with increasing pressure.
What is the melting point of the base of a glacier?
at -1.27C if 2000m thick about 17.6MPa
What is ice temperature regulated by?
Atmospheric surface energy exchange, geothermal heat flux at bed, frictional heat at bed by sliding.
Why might glacial temperature rise occur in winter?
Refreeze of meltwater with released energy.
How may snow reduce conductivity?
Air bubbles with less conductive ability.
How is geothermal heat flux generated?
Radioactive decay, increasing basal ice temperature
How is frictional heat on ice generated?
Sliding at the base
What does dT/dt equal?
Shear stress x shear strain rate divided by ice density x specific heat capacity of the ice
Basal Sliding
This is the act of a glacier sliding over the bed due to meltwater under the ice acting as a lubricant
What are the three types of glacial structure?
Temperate
Cold
Polythermal
Temperate Glaciers
Where melting point is everywhere except a surface layer a few metres thick, due to seasonal temperatures.
Where do temperatre glaciers exist?
Where winter snowfall and summer melt is highest, as snow insulates ice from low winter temperatures.
Cold Glaciers
These are everywhere below melting point, thus frozen to their beds.
Polythermal Glaciers
These are composed of both cold and warm ice
Orographic Lift
This occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain
What is the most prominent source of accumulation?
Snow precipitaiton, but also supercooled water carreid from winds.
How does ice formation occur?
Compaction of multitude of layers, filling air-pores and increasing bulk density.
H2O differential densities per cubic metre?
40-200kg for snow, 830-910 fir ice and 1000kg for liquid water at 0c
What is requried for firn-ice transformation?
Density increase, filling of air pores, compacting bubbles, pressure.
How does compression form ice?
Restructuring of crystals
How do melt and refreeze increase copaction rate?
Water percolation into pores of the snow force air outwards, and frezing.
Dynamic Recrystallization
This involves nucleation of new dislocation-free grains followed preventing propogation of cracks.
What causes reduction in glaciers?
Melting, evaporation, sublimation, wind scouring, iceberg calving
