The Glacier System

Abstract

A glacier, whether it be a valley glacier, an ice cap or an ice sheet, is an ice mass at the surface of the earth. It can be considered as an open system with input, storage, transfer and output of mass. It is a system in dynamic equilibrium where the mass balance depends on input and output. Input or accumulation includes all those ways in which mass is added to a glacier: solid precipitation, wind-drift snow and avalanching, growth of superimposed ice, freezing of water and condensation of vapour to the ice surface. Output or ablation includes all the ways in which mass is lost from a glacier: melting, evaporation, wind deflation and iceberg calving being the most important. The balance is the difference between accumulation and ablation over the entire glacier for one year. The area in which there is an excess of accumulation over ablation, or net accumulation, is called the accumulation zone, while the area in which there is an excess of ablation over accumulation, or net ablation, is called the ablation zone. The boundary between the two zones is given by the equilibrium line where, over a year, ablation equals accumulation.