Accumulation and ablation areas
The net mass balance at each point tells us which parts of the glacier are gaining mass (known as the accumulation area) and which parts are losing it (the ablation area). These two areas are divided by the equilibrium line.
Sketch showing the accumulation area, ablation area and equilibrium line altitude of a glacier (A) in cross section and (B) in plan view. bn = net mass balance, t1 and t2 indicate the glacier surface in year 1 and year 2. (Williams and Ferrigno 2012)
Credit: U.S. Geological Survey Department of the Interior/USGS