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GG101 Week 12 Lecture 1.docx

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James Hamilton

GG101 Week 12 Lecture 1 Glacial Processes  Glacial Ice o process: snow to firn to glacial ice o firn = snow that survives a melt season  denser than wild snow  Glaciers o large mass of perennial snow and ice, that typically shows movement in response to gravity  Morphology o ice sheets  large ice mass, of area greater than 50,000 km^2, these ice masses cover the underlying topography o ice caps  a large ice mass, sufficient to bury underlying topography but with an area less than 50,000 km^2  example: Barnes ice cap, Baffin island o ice field  a level area of ice of variable size  lacks the prominent dome shape seen in sheets and caps  example: Columbia Icefield Alberta/BC  Glacier Classification o Valley Glaciers  a long narrow glacier confined between valley walls  usually fed by cirque glaciers or functions as an outlet glacier for ice fields, caps or sheets o Cirque Glaciers  a small body of ice, firn and snow that occupies a depression, hollow or bowl on a mountain side o Others (e.g. Piedmont) o Thermal Regime (Temperature)  cold based (polar)  basal ice temperature is well below the pressure melting point (freezing point), ice is frozen to the bed  warm based (temperature)  basal ice temperature is at or near the pressure melting point (freezing point), ice is not frozen to its bed, water may be present  Mass Balance o the annual budget between inputs (precipitation) and outputs (melting, evaporation, sublimation, etc) for a glacier  if mass balance is positive, the glacier gains mass:  more inputs than outputs  glacier gets bigger  if mass balance is negative, the glacier loses mass:  more output than inputs  glacier gets smaller o a glacier may be divided into:  Accumulation Zone  where mass balance is positive  Ablation Zone  where mass balance is negative  ice moving from accumulation zone to ablation zone  Zones and Equilibrium (firn) line  flow of ice within a glacier  Motion of Glacial Ice o rates of movement are typically metres to tens of metres per year  rates vary with (3 variables) ice temperature, slope and ice thickness
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