The snow falls and then compacts by the successive accumulation of layers. It becomes névé when it moves from a density of 100g/l to 500g/l. Depending on the altitude and its exposure to the sun, the névé stops melting in summer. The accumulation of these successive névés causes the formation of ice due to compression. Its density is then 900 g / l. Under the effect of the slope and its own weight, the glacial tongue begins to slide. The crevice between the névé and the glacier is called the “bergschrund”.