A glacier is a perennial system on a human scale, a stock of solid water (snow, firn, ice). It is continually renewed by the combined accumulation (snowfall, snow brought by the wind or avalanches) upstream and ablation (melting) downstream. It flows continuously under the effect of its weight, the upper parts, where the accumulation prevails, towards the lower parts, where the ablation dominates. The altitude at which accumulation equals ablation, where the mass balance between gain and loss is zero, corresponds to the equilibrium line. In the Mont Blanc massif, this line was at an elevation of 2800 m.a.s.l. in between 1995 and 2011. Since that it raised to 3200 m.a.s.l.

For a small and steep glacier like the Charpoua glacier, this change in temperature has strong consequences. The Charpoua glacier is a temperate glacier. It means that its base is at 0°C and more, so not frozen to the bedrock. When the temperature are rise, ice at the base melts, the resulting water acts like a lubricant, the basal friction drops and the glacier starts to collapse. According to Ludovic Ravanel (CNRS researcher in Edytem Institute) the recent summer temperature anomalies are not the main drivers. It is more likely caused by the local geography in complex balance between its steep topography, its subglacial hydrology and the strong input of avalanche coming from its right side (South face of the Drus).

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