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Cold environments and Glaciation (Why are cold environments fragile?…
Cold environments and Glaciation
Cold environments
4 types
polar
areas of ice around the poles
Very cold and little precipitation
Vegetation is largely absent
alpine
mountainous areas
most biodiverse
significantly warmer than other cold environments
more precipitation
periglacial
permafrost
no glacial ice
high latitudes
little precipitation
active layer
low growing plants
glacial
Ice sheets and glaciers
mostly found in polar regions
Reasons for cold and dry conditions
cold
Windchill
Katabatic winds from the mountains
Lack of insolation (incoming solar radiation) in polar regions
Fresh snow and ice has a high albedo
85%
dry
High pressure systems in polar levels mean low levels of precipitation
Cold air can hold little water vapour
Glaciers
2 types
Warm based (temperate or alpine)
long and thin
found at altitude
water present in the glacier allows movement
movement allows erosion
create v shaped valleys
Cold based (ice sheets)
cannot move because they are frozen to the bedrock
found in polar regions
Antarctica/Greenland
Formation of glacial ice
Snow falls
It is compacted by snow falling on top of it
Halfway stage of snow and glacial ice is called firn or Neve
Glacial ice is formed when there is no air left in it
It takes 25 years for glacial ice to form
Glacial system
Inputs (accumulation)
Precipitation
Avalanches
Blown snow
Outputs (ablation)
calving
melting
sublimation
evaporation
Glacial budget
total inputs - total outputs
PMP - Pressure Melting Point
Types of movement
Internal deformation
Ice crystals orientate themselves downslope due to gravity
Only type of movement to occur in cold based glaciers
Very slow
Basal flow - regelation slip
Ice melts around obstacles on the bedrock and refreezes when the pressure drops again
Basal flow - creep
Ice crystals deform to get around obstacles on the bedrock due to pressure
Extensional/rotational flow
Depends on the gradient of the slope
steep gradient = higher velocity = thinner ice = crevasses
gentle gradient = lower velocity = thicker ice = bulges
Rotational flow
Glacial landforms
Erosional
Roche moutonee
Arete
Corrie
Pyramidal peak
Striations
Chatter Marks
Crag and tail
Glacial trough
Truncated spurs
Hanging valleys
Depositional
Erratics
Moraines
Recessional
Lateral
Medial
Terminal
Push
Ground
Drumlins
Fluvioglacial
Outwash
material dropped by the meltwater
rounded
sorted
stratified
Varves - layers of outwash caused by the seasons. Summer outwash is larger and has a thicker layer because there is more meltwater and it has more energy. Winter outwash is smaller and it has a thinner layer because there is less meltwater.
Erosional
Overflow channels
Proglacial lakes
Meltwater channels
Nye channels
cut into the bedrock
Rothlisberger channels
cut into the ice
Depositional
Outwash plains and braided streams
Kettle holes
Eskers
Kames
Why is fluvioglacial erosion so powerful?
Hydrostatic pressure
Huge summer discharge
High energy pulses (flashy discharge)
Glacial deposits are easily eroded
Till
material dropped by the glacier
unsorted
unstratified
angular
Periglacial processes
Frost heave
This occurs when ice lenses form underneath rocks underground. The ice lenses from because large solids lose their heat quicker than the surrounding soil which has moisture in it. As the ice lenses form they expand, pushing the rocks upwards. Eventually they reach the surface
Freeze thaw weathering
Water gets into cracks in the rock and overnight as the temperature drops it freezes. As it freezes it expands and this widens the crack. The ice melts the next day and leaves the wider crack. This happens again and again until bits of rock break off.
Solifluction
When the active layer thaws in summer it starts to move downhill due to the excess lubrication and this forms solifluction lobes
Nivation
If there is a depression in the ground underneath some snow then freeze thaw weathering occurs. When the snow melts the meltwater carries away the weathered material and leaves a larger depression called a nivation hollow
Frost creep
This is the gradual downslope movement of individual soil particles. As freeze thaw cycles occur the soil is lifted and then dropped down again, moving it down the slope. This only occurs on gentle slopes because otherwise the whole active layer would fall away.
Periglacial landforms
Pingos
Large mounds with an ice core
2 types
open system (hydraulic)
Water that has drained into talik in the valley bottom freezes and domes upwards
closed system (hydrostatic)
When a lake drains permafrost begins to encroach on the talik that was once underneath the lake. It freezes and forms a mound
If cracks appear in the pingo the ice core melts and the pingo collapses creating an ognip
Solifluction lobes
Nivation hollow
Formed as the result of nivation
Ice wedge polygons
Stone polygons/stripes (patterned ground)
Formed as the result of frost heave
Why are cold environments fragile?
small changes in temperature can affect the highly adapted wildlife very negatively
Litter does not decompose in the cold conditions
Vegetation takes a long while to recover because it is difficult to grow in cold conditions
Used for leisure
Extraction of resources can be harmful
Climate change affects cold environments the most