Different rates of flow in glaciers

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A-Levels Glaciation Mindmap am Different rates of flow in glaciers, erstellt von EmmaSmile am 06/05/2013.
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Different rates of flow in glaciers
  1. The sides and base of a glacier move at a slower rate than centre surface ice, causing production of crevasses
    1. Compressing flow
      1. Occurs when there is a reduction in the gradient of valley floor, ice decelerates and ice mass thickens - erosion at its maximum
      2. Extending flow
        1. Occurs where there is an increase in the gradient of the valley, ice accelerates and becomes thinner leading to reduced erosion
        2. Rotational flow
          1. Occurs within corries - ice moving downhill pivots around a point producing rotational movement
          2. Glacial surges
            1. Occur from time to time when excessive build up of meltwater under glacier leads to rapid forward movement of up to 300m in one day, can be hazardous to those living in glacial valley below snout
            2. Factors affecting rates of movement
              1. Thickness needs to exceed 60m before ice moves downslope
                1. Movement faster over impermeable suface as presence of basal meltwater facilitates movement
                  1. Greatest velocity at firn line due to proportional relationship between thickness and velocity
                    1. Centre of ice thickest - moves more rapidly than margins
                      1. Steep glaciers flow faster than gentle ones
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