Glacier Blanc     Above an altitude of 2200m, nearly all precipitation is in solid form. The Glacier Blanc has its origin in north facing slopes at over 4000m. Here the net accumulation is approximately 2m per annum. Melt here is rare and the snow is dry. Here snow accumulates and recrystallises by internal deformation to form glacier ice. The ablation zone of the Glacier Blanc forms below a series of steep slopes over which the ice flows and fractures to form seracs. This occurs at about 2950m, the net accumulation of snow gives way to net ablation, i.e. melt is greater than the build up of snow. This transition is marked by what is known as the neve line, where there is no net accumulation or ablation. This line descends as low as 2750m on north facing slopes, but is 2950m on south facing areas. Lower section of the Glacier Blanc At about 2000m, the glacier has a net ablation of about 8 metres a year, though accumulation usually continues until May. This value increases with decreasing altitude. For every 100m, about 1m of additional melt occurs. Ablation is also affected by sediment on the ice. If there is no sediment, then the glacier will reflect the heat. If there is a thin layer of sediment, then heat will be absorbed and there will be more melt. If the layer of sediment is thick, then the glacier will be protected from melting by the stones. The regime of the Glacier Blanc has been reconstructed from climatic data for the period 1880-1946 and measured since 1947. The survey shows the net loss of ice since 1947 and a retreat of the glacier.