Cold Enviroments

Cold Enviroments

Glaciers movement
1. Basal Slippage
  1. this is a sliding effect of the glacier over the bedrock by either regelation slip or creep
    1. regelation slip operates most effectively with smaller obstacles, while creep is the process that overcomes larger obstacles
      1. on the upglacier side of an obstacle, the increasing pressure in the lower ice causes pressure metiling locally.
        this meltwater permits slippage of the ice cover the obstacle but then refreezes in the lower pressure conditions of the downside of the obstacle.
2. internal flow/ internal deformation
  1. this is the movement within the glacier ice resulting from the stresses applied by the force of gravity.
    1. Where ice crystals orientate themselves in the direction of the glaciers overall movement, they may slide past eachother.
      1. Such movements often result in the formation of crevasses within and at the surface of the ice
Landforms produced by glacial erosion
1. Aretes
  1. these are formed when 2 or more ciques erode back towards each other from opposing sides, they produce a knife edge ridge between them called an arete
    1. e.g. Striding Edge above Red Tarn, Lake District
2. Pyramid Peaks
  1. where 3 or more cirques erode back towards each other, a pyramind peak may form.
    1. e.g. the Matterhorn
Landforms
1. Roche moutonnes
  1. masses of more resistant rock that have smooth, rounded upvalley slopes formed by abrasion. the downvalley sides are steep and jagged.
    1. which reflects the plucking action that formed them
    2. Abrasion on the upvalley side may have left striations as pieces of rock debris within the ice were dragged accross the surface under great pressure
2. Rock Drumlins
  1. these are more streamlined bedrock and lack the jagged downhill slope.
3. Crag & Tail
  1. this consists of a larger mass of resistant rock or crag and a gently sloping tail of less resistant rock/ or sediment on one side.
4. Striations
  1. when glaciers move accross exposures of rock, angular debris embedded within the ice may leave paralell scratches and grooves called strations
Glacial Deposition
1. Till
  1. all material deposited directly by the ice, largely unsorted in nature
2. Fluvioglacial material
  1. sediments deposited by meltwater streams. these usually have been sorted with coarser material nearer the the original glacier snout.
    1. finer particles carried further way by the meltwaters.
Moraines
1. Lateral Moraine
  1. formed from debris fallen from the sides of the valley and transported along the edges of the glacier.
    1. After glaciation it appears as elongated embankments of debris at the sides of the valley.
2. Medial Moraine
  1. where 2 glaciers meet, the lateral moraine may combine to form a medial moraine towards the middle of the main glacier.
    1. this may eventually form some deposition features once the glacier has retracted.
      1. however the location of the medial moraine towards the middle of the valley may be destroyed by subsequent fluvioglacial action
3. Terminal Moraine
  1. this is often a high mound or series of mounds of debris that extend across a valley, it marks the furthest extent of the glacier
Influences on the rate of movement
1. snow and ice masses do not generally move downslope until the thickness exceeds 60m
2. steep glaciers flow faster than gently graded ones and thus are usually thinner
3. the amount of precipitation and ablation are significant factors
4. the greatest velocity is usually at the firn line, as velocity is directly related to thickness
5. the centre of the glacier, where the ice is thickest, moves more rapidly than the margins, where friction plays a considerable role in reducing speed

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