What Is the Mass Balance of a Glacier, How Is It Measured and What Is Its Relationship to Climate.

Ice sheets, ice caps and valley glaciers compose the main elements of glacial environments. Many different processes deriving from their movement, as well as marine aeolian and fluvial influences, affect these environments putting them amongst the most complex present on Earth today.  
Vital to the health of a glacier is its mass balance. Mass balance comprises of accumulation; all processes that add mass to a glacier, minus ablation; all processes that subtract mass from a glacier in a given year.
Determining the health of a glacial system is dependent on mass balance. A glacier with a positive mass balance is out of equilibrium with processes of accumulation being larger than that of ablation, causing the glacier to advance. If it has a negative mass balance it is also out of equilibrium but will cause the glacier to retreat.
The upper region of a glacier is known as the accumulation zone and experiences mass gain predominantly during autumn and winter months when snowfall, avalanching and the freezing of rain are most likely to occur and result in a net gain of ice. In this zone there is survival of firn, snow that is wetted and compacted becoming re-crystalised into a more dense substance and finally becoming ice. Towards the snout of a glacier is the ablation zone and although it may experience snowfall during the winter months, it does not avoid net mass loss during the year.   Processes of surface melt and the subsequent run-off, internal melt, geothermal heat transfer, evaporation and wind erosion, all result in loss of ice from the glacier and usually occur during the summer months. During the autumn and spring months accumulation and ablation are generally balanced and ice mass remains fairly constant. The division between the accumulation and ablation zones is known as the equilibrium line.
In order to retain equilibrium and compensate for accumulation and ablation, glaciers must move. These changes are propagated down the glacier by kinematic...