Examine how glaciers operate as a system. (25)
Glaciers can be classified according to the temperature of their base. In warm based glaciers e.g. the Alps, the base is warmer than the melting point of ice. It’s warmer because of the heat from friction caused by the glacier moving, or because of the geothermal heat from the earth. The ice at the bottom of the glacier melts, and the meltwater acts like a lubricant, making it easier for the glacier to move downhill. Ice at the surface also melts if the temperature reaches 0 degrees Celsius, and meltwater moves down through the glacier, lubricating it even more. Therefore, warm based glaciers move rather quickly, lots of movement means lots of erosion so warm based glaciers are highly erosive too. On the contrary, in cold based glaciers e.g. in Antarctica where glaciers cover 13,586,380km, the base is cold and the temperature is usually well below the ice’s melting point, so there’s very little melting and this lack of meltwater means cold based glaciers move very slowly. The ice is frozen to the valley floor which also slows movement. Even in summer the temperature is below freezing, the mean annual temperature of the interior is −57°C, so there’s not a lot of melting at the surface either. Consequently, cold based glaciers don’t erode a lot.
A glacier is a system which has inputs, outputs and stores. The main input of a glacier is obviously snow, either from precipitation or avalanches. First, the snow settles. It has a loose, fluffy consistency at this point. Over time, as more snow falls, the increased weight on top turns the fresh snow into a denser, more granulated kind of snow called firn or neve. Air is squeezed out, and particles of ice are compressed together by the continuing accumulation of snow and ice. Water also melts (meltwater) and refreezes in the air spaces, making the ice more dense, forming a glacier. The rate of formation varies with area and temperature. In Iceland, a warm based glacier, for example where there’s plenty of snow and warmer summers to produce the necessary meltwater, glaciers can form in about 10 years but in Antarctica, a cold based glacier, where there’s little snowfall and it’s too cold to produce meltwater, glaciers can take centuries to form. Other inputs include the condensation of water vapour from air, which then freezes. Also, the sublimation (the changing of a gas to a solid) of water vapour from the air directly to ice crystals. Bits of rock also form part of the glacier, so when the glacier erodes away the landscape rock particles are collected, also rock often falls onto the glacier from above and augments the size of the glacier; if only slightly.