Along the ice sheet margin lies the ablation zone (red), where summer meltwater runoff exceeds winter snowfall resulting in a net mass loss at the surface.



There, the snow cover deposited in winter melts away to expose darker bare ice at the surface in summer.



At the end of summer, the snowline marks the ablation zone area. Above the snowline lies the accumulation zone (blue), that is covered by a permanent snow layer.



The widest ablation zone is found in the southwest and contributes one third to the ice sheet runoff total, while northern Greenland is responsible for about one tenth.











