- condensation of water vapour from the air
- sublimation of water vapour from the air directly to ice crystals
- bits of rock collected when the glacier carves away at the landscape, and rocks that have fallen onto the glacier from above.
sublimation involves a direct change of state from a gas to a solid without passing through the liquid stage.
- the main store is ice
- melt wateris a small part of the glacier. it can be found on the ice, in the ice or below the ice
- glaciers also carry debris (rocks, gravel and sand)
melt water is considered a store when its in the glacier. when its flowing down the vally away from the glacier its no longer a store
outputs are losses from a glacier.
- ice can melt and flow out of the glacier as melt water
- surface snow can melt and evaporate
- ice and snow can melt and evaporate
- ice and snow can sublimate to water vapour
- snow can be blown away by strong winds
- with glaciers that end at the sea, blocks of ice fall from the front (the snout) of of the ice mass into water to create icebergs. this is called calving as if the glacier were a big old ice cow giving birth to a little ice calf. it can also happen where there's a lake at the front of the glacier.
- accumulation is the input of snow and ice into the glacial system. most accumulation is snow
- ablation is the output of water from a glacier
- the glacial budget is the balance between accumulation and ablation over a year - it shows whether the volume of water in the glacial system has increased or decreased. this determines whether the front of the glacier advances forwards or retreats back.
- you get more accumulation than ablation in the upper part of a glacier - so its called the zone of accumulation
- you get more ablation than accumulation in the lower part of a glacier - so its called the zone of ablation
- the place where accumulation and ablation are equal is called the glaciers equilibrium point
- if theres more accumulation than ablation over a year, the glacier has a posative regime. the glacier grows and advances.
- if there's less accumulation than ablation over a year, this is a negative regime and the glacier shrinks and retreats
the glacial budget changes throughout the year
- you get more ablation during warmer times of the year
- during the colder months there is more accumulation than ablation
- over the year this might balance out the glacier advances in winter but retreats in summer, so overall the volume of water in the glacier stays the same.
glacial budget diagram
cold and warm glaciers
glaciers can be classified according to the temperature of their base.
- in warm glaciers, the base is warmer than the melting point of ice. its warmer because of heat from friction caused by the glacier moving, or because of geothermal heat from the earth. this Ice at the bottom of the glacier melts, and the melt water acts as a lubricant making it easier for the glacier to move downhill. ice at the surface also melts if the temperature reaches zero degrees celsius and melt water moves down through the glacier lubricating it even more. lots of movement means erosion.
- in cold based glaciers the base is cold (the temperature is below the ice melting point) so there's very little melting. the ice is frozen to the base of the valley, so there's very little movement. there's hardly any melting at the surface either even in summer. this means that cold based glaciers don't cause very much erosion