Glacier mass balance

Glacier mass balance is the difference between the mass a glacier gains and loses over a defined period. It tracks whether the glacier is growing or shrinking.

Accumulation zone: The part of a glacier where annual gains of snow and ice exceed losses. Snowfall and wind-deposited snow add mass in this region.
Glacier: A persistent body of ice formed from accumulated snow that deforms and flows under its own weight. Mass balance describes the gains and losses of this moving ice body.
Glacier monitoring: Systematic observation of glacier geometry, motion, and mass change over time. Repeated balance measurements provide a direct record of glacier change.
Glacier retreat: The landward movement of a glacier’s terminus over time. Persistent negative mass balance commonly drives retreat, though terminus response can lag.
Ablation zone: The part of a glacier where annual losses of snow and ice exceed gains. Melting, sublimation, and calving remove mass here.
Water equivalent: The depth of water produced if a given mass of snow or ice melts over a specified area. It expresses snow and ice changes on a common mass-per-area scale.
World Glacier Monitoring Service: An international organization that coordinates and distributes data on glacier change. It compiles standardized mass-balance observations from glaciers worldwide.
Glacier surge: A temporary, large increase in glacier flow speed that redistributes ice toward its terminus. A surge can advance a terminus without indicating positive whole-glacier mass balance.
Equilibrium line altitude: The altitude on a glacier where annual accumulation equals annual ablation. It separates the glacier’s net-gain area from its net-loss area.
Glacier terminus: The lower end of a glacier, where its ice meets the surrounding landscape or water. Terminus changes can accompany mass loss but do not alone measure it.

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