Why do glaciers ‘grow’ and ‘shrink’?
• A glacier is a form of storage. For storage to be in an equilibrium state the input (precipitation/snowfall) at the accumulation zone and output (melting) at the ablation zone should be equal. In other words the mass balance is zero. This balance can be changed as a result of changes in the input (more or less snowfall) and/or changes in the amount of melting (due to warming). Changes in snowfall can result because of changes in the overall annual precipitation, and/or changes in the timing of the precipitation (eg, more falling in the summer as rain). Changes in melting can occur as a result of increased average annual air temperatures, and/or changes in the solar radiation. Melting will be affected if the glacier is covered by moraine, dust, or soot particles (eg, a thin layer of soot on the glacier surface that increases heating, or a thick layer of debris on the surface that acts as an insulator).