A glacier's mass balance (the net gain or loss of ice/snow mass over a given period) is closely tied to the position of its equilibrium line altitude (ELA), the elevation dividing the accumulation zone (net snow/ice gain) above from the ablation zone (net snow/ice loss) below; when the ELA moves upward (rises to a higher elevation), the proportion of the glacier's area in the ablation zone increases relative to the accumulation zone, resulting in a negative overall mass balance (net mass loss).