Glaciologists subdivide glaciers into glacier accumulation zones, based on the melting and refreezing occurring.[1][2] These zones include the dry snow zone, in which the ice entirely retains subfreezing temperatures and no melting occurs. Dry snow zones only occur within the interior regions of the Greenland and Antarcticaice sheets.[3][4] Below the dry snow zone is the percolation zone, where some meltwater penetrates down into the glacier where it refreezes. In the wet snow zone, all the seasonal snow melts. The meltwater either percolates into the depths of the glacier or flows down-glacier where it might refreeze as superimposed ice. A glacier's equilibrium line is located at the lower limit of the wet snow zone.