A glacier can be divided into two zones; the upper accumulation zone, where the snow mass accumulates and the lower ablation zone, where more glacier mass is lost, or ablated, than gained through snowfall. Ablation can occur due to melting, wind erosion and calving (National Snow and Ice Data Center, 2018). The point between the two zones where accumulation equals ablation is termed the equilibrium line. The equilibrium line is visible on temperate glaciers, a glacier at melting point that contains liquid ice. The line marking the boundary between new snow and old snow (firn) exposed by melting. However, the line tends to be diffuse on polythermal glaciers, which have a complicated thermal structure (Hambrey & Alean, 2016).
From collection: The Andean Glacier and Water Atlas