Water

The delicate equilibrium of glaciers

Therefore in order to evaluate the “state” of a glacier, in particular if the glacier shows an advance or a retreat, it is not sufficient to evaluate the variations in the position of the front, but the delicate equilibrium of the snow supply, i.e. the formation of new ice, and the loss of ice in the ablation area must be considered. In other words, it is necessary to evaluate the variations in the volume of the glacier, studying the “balance” of these two factors, calculating what researchers call “mass balance”. Practically this means measuring supply and loss, as in a company balance-sheet, and to find, from the difference, if the volume of the glacier is increasing or decreasing . If the balance is positive and supply is greater than loss, the glacier will tend to expand, shifting the position of the front more downstream, while, if the balance is negative, the ice will decrease, its thickness will diminish and the front will retreat progressively upstrem. A stable front in time on the contrary indicates a stationary situation of equilibrium between supply and losses (however this does not mean that the glacier is still at all). The glacier’s response, however, is not immediate. Generally the glacier responds with a certain inertia, that also depends on its size, and it takes a few years of positive balances in order to see a glacier advance, and vice versa. Many glaciers in the Alps have been studied for decades, some for over a century, and researchers therefore have numerous series of measurements of the variations of the front and mass balance records, over long periods of time : this has enabled, through a comparison of the glaciers’ advance and retreat, together with the climatic and meteorology data, to understand how glaciers have reacted to the more recent climatic variations, thus enabling the formulation of hypotheses on the future of our glaciers.