I'm pretty sure that's the relation between accumulation and ablation: if the glacier's mass balance is positive, then it's gaining more ice than it looses; assume good climates for glacial growth. If it's negative, then it's loosing ice; probably warm, dry conditions.
Mass balance is used as an indicator of glacial health and of a glacier's growth and decay.
That's for the mass balance gradient, right? Also, what about the influence of bed (wet or dry, bare rock, and sediment) part and the relation of flow to elevation and gradient?