The difference between the amount of ice a glacier gains in winter and the amount lost in summer. A glacierA glacier is a large, persistent body of land-based ice that forms over many years where the accumulation of snow is greater than its loss (ablation). The ice in a... More which is gaining mass has a positive mass balanceThe difference between the amount of ice a glacier gains in winter and the amount lost in summer. A glacier which is gaining mass has a positive mass balance: more ice is... More: more ice is added in the winter than is lost in the summer. A negative mass balance indicates that the glacier is losing mass.

Two related terms are accumulationEncompasses all the ways in which a body of ice (a glacier or ice sheet) gains mass at its surface, such as snowfall and rime formation. However, it excludes ice... More* and ablationEncompasses all the ways in which ice mass is lost from the surface of a glacier or ice sheet, such as melting at the surface or the base (underside), and evaporation. However, ablation... More. In a glacier there are generally two distinct zones, the accumulation zone (where snow cover remains at the end of the summer) and (at lower altitude) the ablation zone, where all the winter snowfall melts over the summer.

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