3. Glacial Budgets Flashcards
Define Glacial Budget/Mass Balance.
The glacial budget/mass balance 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. It is composed of inputs (e.g. precipitation in the form of snow and ice, and avalanches which add snow, ice and debris from the valley side), stores (e.g. ice, meltwater, debris), transfers/throughputs (e.g. extensional and compressional flow), and outputs e.g. water vapour (from evaporation of water on the ice surface and sublimation - the direct change of state from ice to water vapour), calving (the formation of icebergs - where blocks of ice fall from the glacier’s snout into the sea), and water in liquid form from ablation (melting). The debris deposited at the snout (moraine) can also be considered an output.
Explain the Glacial Budget/Mass Balance.
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.
You get more accumulation than ablation in the upper part of a glacier - so it’s called the zone of accumulation.
You get more ablation than accumulation in the lower part of a glacier - so it’s called the zone of abaltion.
Between the two zones is the line of equilibrium (where accumulation and ablation are equal) which seperates net loss from net gain and represents the snow line on the glacier.
If there’s more accumulation than ablation over a year, the glacier has a positive regime/positive mass balance. The glacier grows and advances forwards.
If there’s less accumulation that ablation over a year, the glacier has a negative regime/negative mass balance. The glacier shrinks and retreats backwards.
If there’s the same amount of accumulation and ablation over a year, the glacier stays the same size and the position of the snout doesn’t change - the glacier appears to be stationary, although ice is still advancing down the valley from the zone of acummulation into the zone of abalation.
In temperate (alpine)/warm-based glaciers, there is a negative balance in summer when ablation exceeds accumulation, and the reverse in winter.
