CoachThe glacier mass balance is the change of the mass of a glacier over a year, usually given in metres of water equivalent averaged over its area. The surface mass balance is its part due to the processes at the surface, snowfall minus melting, runoff and sublimation; the rest is lost by calving and by melting at the base or under floating ice. The accumulation zone is the part of the surface where the surface mass balance over a year is positive, the ablation zone the part where it is negative, and the equilibrium-line altitude (ELA) the elevation of the line between them, where it is zero.
