(4) glacial landform development

• what is abrasion


  • angular material carried by the glacier rubs away at the valley floor and sides
  • coarser material may leave striations or chatter marks
  • finer material smoothes and polishes rock surfaces
  • debris involved is worn into rock flour which colours streams and lakes in glacial areas
• what is plucking


  • mechanism by which glaciers detach and remove large chunks of rock from their beds,
  • fracturing --> entrainment
  • as it moves it plucks away masses of rock
  • mainly occurs at the base of a glacier
  • well-jointed rocks, with cracks due to dilation when rock is removed above causing pressure release
• what are the two types of erosion


  abrasion and plucking
• what factors affect the amount and rate of erosion

  • geology
  • temperature
  • season
  • size of rock
  • speed of glacier
  • gradient
• explain freeze-thaw weathering


  • in areas where day and night temperatures are suitable
  • ice occupies nearly 10% more space than water
  • water enters cracks and freezes overnight, causing pressure
  • cracks widen and rock breaks off
  • on steep slops, the broken material collecting at the base is called scree
  • this often falls onto the glacier and into crevasses, forming moraine
  • rocks are broken off the back and side walls of a valley
• what is carbonation


  • dissolving of calcium carbonate
  • carbon dioxide dissolved in water forms a weak carbonic acid
  • this reacts with calcium carbonate in the rock to form calcium bicarbonate, which then dissolves
  • the lower the temperature, the more effective carbonation is due to increased carbon dioxide
• what is oxidation


  when a substance reacts and combines with oxygen
• what is solution


  any process by which a mineral dissolves in water
• what is hydrolysis


  chemical reaction between rock minerals and water
• what is hydration


  water molecules added to rock minerals create new minerals of larger volumes
• what is nivation


  • complex series of processes, combined action of freeze-thaw, carbonation, solution, solifluction, mass movement and meltwater erosion and transport
  • operates under a patch of snow leading to disintegration of rock surface forming enlarging hollows
  • may evolve into a corrie
  • can form nivation hollows
• what is rock fall


  on slops of 40 degrees or more, especially if the surface is bare, rocks may become detached from the slope by physical weathering processes. these fall to the foot of the slope under gravity. transport processes may then remove this material, or it may accumulate as a relatively straight, lower-angled scree slope
• what are linear slides


  movement along a straight line slip plane, such as a fault or bedding plane between layers of rock
• what are rotational slumps 


  movement along a curved slip plane, common in weak rocks like clay which become heavier when wet
• what are the three ways that debris is transported

  • supraglacial
  • englacial
  • subglacial
• what is supraglacial movement


  on top of the glacier's surface
• what is englacial movement 


  within the body of the glacier
• what is subglacial movement


  at the base of the glacier
• explain glacial deposition


  • glaciers deposit their load when their capacity to transport material is reduced. this usually occurs as a direct result of ablation during seasonal periods of retreat or during de-glaciation.
  • material can also be deposited during advance or when the glacier becomes overloaded with debris.
  • all material deposited during glaciation is known as drift.
  • this can be subdivided into till, which is material deposited directly by the ice and outwash or glacio-fluvial activity, which is deposited by meltwater