Enquiry question 2: what processes operate within glacier systems

  • Created by: ivac2000
  • Created on: 24-01-18 16:01

Mass balance

  • glaciers develop from compaction of snow and ice
  • zone of accumulation where snow is added - more snow added = compacted into layers and bottom layers become ice
  • the force of gravity moves ice downhill - near the snout glacier ice may melt - called the zone of ablation
  • for eqilibrium - ablation and accumulation zone must be similar
  • difference between accumulation and ablation is called surface mass balance
    • can be affected by climate change - alters rates of ablation and accumulation
    • positive and negative feedback
    • positive mass balance - more accumulated than ablated
    • negative feedback is the opposite
    • equilibrium line seperates the zone of accumulation and ablation
  • accumulation - direct snowfall, sublimation (solid turns to gas), avalanches and wind deposition
  • ablation - melting, carving (splitting of ice), evaporation and avalanches
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Glacial movement

  • polar and temperate glaciers have different rates of movement
  • movement depends on:
    • amount of precipitation
    • amount of ablation
    • steepness of ice
    • thickness of ice
    • permeability of the surface that the ice sits on
    • proximity to the equilibrium line
    • altitude
    • slope
    • size of glacier
    • variations in mass balance
    • positive or negative system
    • lithology (charecteristics of underlying rock)
  • movement is also dependent on
    • basal slip: glacier sliding over the bed due to melt water under ice - increases the movement
    • regelation creep: melting and refreezing of ice which causes slippage
    • internal deformation: when the weight of the ice causes the deformation of ice crystals - usually at glacier bed where pressure is at its highest
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Glacier landform system

  • glaciers alter landscapes by numerous processes
    • abrasion
      • rocks become embedded in the glacier and rub against the bedrock whilst glacier moves
      • causes the wearing away of the land scape
      • produces a smooth surface
      • leaves scratches on the surface called striations
    • quarrying
      • occurs within valley glaciers where pieces of bedrock are transported and eroded
    • plucking
      • same as quarrying
      • occurs when rocks become frozen to the glacier and are plucked from the ground as the glacier moves forward - leaves a jagged landscape behind
    • crushing
      • crushing and scraping of a glacier as it moves
      • causes erosion along the soil and rock that it sits on
      • weight of the glacier may cause physical stress to the ground and pluck up boulders that are deposited downstream
    • basal melting
      • the melting point of water decreases under pressure
      • water melts ara lower temperature under thicker glaciers
      • leads to basal sliding - glacier floats above a layer of meltwater which acts as a lubricant - allowing the glacier to move faster
    • subaerial freeze thaw
      • water gets into the cracks of rocks, freezes and then expands by 10%
      • repeated action puts pressure on a rock
      • eventually causing it to shatter
  • glacial landforms
    • cirques/corries
      • deep rounded hollows capture the snow
      • plucking/erosion steepen the back wall
    • aretes
      • seperates two glaciated valleys
      • forms from erosion of two back to back corries
    • pyramid peaks
      • forms erosion between three or more corries
      • producing a peak rather than a ridge
    • glacial troughs
      • abrasion grinds a v-shaped valley to produce a u-shaped valley
    • truncated spurs
      • formed when glacier curts and erodes through interlocking spurs (number of ridges)
    • hanging valleys
      • main valley erodes quicker than tributary vallets - leaving it a higher/hanging platform
    • ribbon lakes
      • glacier moves on top of hard rock
      • plucking causes abrasion which creates hollows that fill with ice/rainwater
  • ice sheet scouring
    • roches moutonees
      • small rocks are not always removed and become polished by abrasion
    • knock and lochan
      • scoured lowalnd which displays alternating roches mountonees and small lakes
    • crag and tail
      • a tapered ridge of glacial deposits extended to one side
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Glacial deposition

  • deposition involves the process in which sediment, soil and rocks are added to a landform
  • features of glacial deposition involve
    • medial - formed of two lateral moraines meeting in the middle of glacier and depositing material
    • lateral - material deposited at the sides of a glacier
    • recessional - forms at the end of a glacier when retreating glacier stays stationary for a sufficient time
    • terminal moraine - material deposited at the snout of a glacier on the valley floor
    • drumlins - elongated hills of glacial deposition - made of material accumulate under the glacier
    • till plains (lowland) - till (clay) deposited when ice sheets detatch from glacial body
    • ablation till (lowland) - accumulation of till by the melting of stagnant ice
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Glacial meltwater

  • water movement within a glacier system
    • can be in the form of supraglacial, englacial and sub-glacial flow
  • glacial and fluvioglacial (meltwater erosion/deposition) have different characteristics and form specifically
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