Characteristics

• polar glaciers 


  0 degrees

  edge of ice sheets

  slow movement

  frozen to the bedrock
• warm base glaciers 


  smaller in size

  advance and retreat cycles

  meltwater acts as a lubricant to create less friction

  moves via basal sliding and internal deformation
• nivation


  makes hollows deeper by freeze-thaw weathering

  1. at 0 degrees freeze and thaw cycles occur
  2. water expands by 9 % each time
  3. frost shattering breaks off rock fragments
  4. when snow melts, meltwater transports the debris away
  5. the hollow becomes deeper and wider creating a nivation hollow
• frost action 


  fluctuating temperatures allow for cycles of freezing and thawing

  water enters the crevasses of rocks

  when temperatures drop below 0 degrees

  the water freezes and expands

  this places pressure on the rock

  over time this cycle repeats causing the rock to fragment
• plucking


  ice in contact with rock surfaces can thaw and refreeze in cycles over time around rocks jutting out of the valley sides

  when the glacier moves forward it plucks away the rock fragments
• abrasion


  debris carried along by the glacier can scrape material on the valley sides and floor giving it a polished look
• supraglacial 


  on top of the glacier
• englacial


  within the body of the glacier
• subglacial 


  at the base of the glacier
• till deposition


  unsorted mixture of material deposited by a glacier

  points in the direction the glacier is flowing

  it can be deposited as moraine
• ablation till


  dropped by a glacier as it melts
• basal sliding

  • pressure melting point
  • there is more melting around protruding rocks as there is more pressure
  • refreezes down stream as less obstruction reduces the pressure
• rotational flow

  • when a glacier moves in an arc shape in a hollow
  • the curved movement back and forth creates a rocking motion that erodes the back wall
• internal deformation


  ice bends to flow down hill like liquid

  which is caused by ice crystals shifting past each other
• extensional flow

  • gravitational force pulls the ice downhill as the head of the glacial valley is steep
  • this fast movement creates tension which causes the ice to fracture into layers
  • these layers then slip downwards
• compressional flow

  • at the snout of a glacier ice movement slows as the gradient of the valley evens out
  • this causes the ice to compress
  • the higher pressure created causes the ice to fracture into layers and slip forward
• meltwater

  • pressure melting point
  • surface meltwater filters through the glacier and travels through tunnels underneath the glacier
• meltwater erosion

  • hydraulic action -> pressure of the ice means water flows very quickly
  • it also means it can carry loads of sediment which are used as further tools of erosion
  • it has a high erosive power
• meltwater channel example


  glen valtos in the isle of lewis
• percentage of land covered by permafrost

  20 to 25 %
• discontinuous permafrost


  where the mean annual temperature is below 0 degrees for an average of two years

  only patches of ground are frozen
• continuous permafrost 


  all the ground is frozen as annual temperatures are below -5 degrees
• solifluction


  the permafrost is impermeable to water

  the active layer however thaws and refreezes in cycles

  as the layer becomes waterlogged, it increases in weight and starts to flow downhill on a gradient
• solifluction lobes


  when one section of soil moves faster downhill than the other sections around it
• frost creep


  water expands and refreezes causing soil particles to be forced upwards

  when the soil thaws once again, the soil particles move vertically downhill and end up further down the slope