Glacial Processes Flashcards
Polar and temperate glaciers
-all ice moved under the influence of gravity downslope from high mountains to low outwash plains
-weight, mass and slope angle increase the shear stress point
-the momentum of the movement builds towards the zone of ablation, which maintains dynamic equilibrium
-temp and pmp differentiates them both
Pressure melting point
-the temperature at which ice melts at a given pressure
-melting point of water depends on the air pressure above the ice
-as air pressure increases, the temperature at which ice melts lowers
Warm based glaciers
-occurs in temperate regions like southern Iceland and Norway
-melting in summer months
-meltwater lubricates the sides and base of the glacier, which assists basal sliding and increases rates of erosion, transportation and deposition
-temp at the base is just at or just above the pmp
Cold based glaciers
-occurs in polar regions such as central Greenland and Antarctica
-temp is below the mp, with low rates of precipitation, resulting in low levels of accumulation
-no basal sliding
-movement is by internal deformation
Basal sliding
-friction, pressure and heat from ice movement leads to melting
-the meltwater then acts as a lubricant assisting glacial flow
Enhanced basal creep
-basical ice bends around bedrock outcrops, PMP is not reached and ice crystals deform around the crop
Regelation creep
-basal ice undergoes increased resistance and pressure on the upslope of bedrock outcrop
-pressure melting occurs and this eases the flow over the outcrop
-pressure is reduced on the downslope of the crop and the meltwater refreezes
Internal deformation
-occurs in both cold and warm based glaciers
-where individual ice crystals oriented themselves in the direction of glacial movement and slide past one another
Rotational flow
-occurs in depressions/ hollows where glacial ice forms
-the ice rotates/ pivots as it starts to move downslope
Compressional flow
-Ice mass thickens as slope gradient reduces and movement slows
-erosion potential increases, which could lead to a steeper gradient and extensional flow
Extensional flow
-ice mass thins and movement increases when slope gradient steepens
-erosional potential decreases
Factors affecting ice movement
-lithology permeable bedrock allows meltwater to percolate through, slowing glacier movement
-altitude rates of snowfall and accumulation increases with altitude therefore alpine glacier have higher rate of moment
-slope angle greater slope leads to greater movement
-mass balance higher rates of accumulation increases thickness and gradient of the ice which increases velocity
-ice temp cold base glaciers move slower than warm as the ice does not deform readily and freezes to the bedrock
