Glacier Mass Balance

Calculation of the Glacier Mass Balance is a more complex operation – in fact a series of measurements and surveys must be carried out. First of all, the quantification of the additional constituents, measuring the amount of precipitations on the ice, also bearing in mind the so-called “hidden precipitations”, such as hoarfrost, or ice formed by sublimation, and contribution by avalanches. In order to do this, the height of snow precipitation, during winter and spring, in fixed, special points of the glacier, is measured. Usually this is carried out by fixing  special long, thin rods, only a couple of centimetres in diameter, called “stakes” into the glacier in summer and inferring the thickness of the sheet of snow from the height of the protruding stoke.  Since for the balance, snowfall must be transformed into equivalent millimetres of water, also the density of the snow must be known. For this purpose, special trenches  are dug into the layer of snow, and its density is measured at various depths. These operations must be carried out in different points of the glacier, at different depths, so as to have a representative picture of the entire glacier.
Secondly, it is necessary  to determine the quantification of losses, determining the amount of ice removed by ablation. Most of the ablation, in the case of Alpine glaciers, is due to ice melting. In order to measure this parameter, series of stakes (which are usually the same used to measure the thickness of the snow layer), numbered and labelled, are positioned on the surface of the glacier with the help of special drills, up to a given depth. Periodically, during the summer period even daily, the height of the stake getting free as ice melts is measured. It is therefore possible to measure the thickness of ice that is lost in a determined period of time, and from this, with repeated measurements, to estimate the overall quantity of ice that is lost during the course of summer. On the  Forni glacier, in the Ortles-Cevedale Massif, for example, during the summer period, approximately 3-3.5 m of ice are removed by ablation, and between mid July and mid August melting reaches peaks of 4-5 cm a day (source of data : Smiraglia). The same stakes can also be used, measuring their movements vis-à-vis fixed points outside the glacier, to quantify the speed of the glacier movement downstream.
Since a large quantity of ice also melts at the glacier  base, where it collects forming sub-glacial lakes and streams, in the glacier mass balance it is important to include the measurement of the outflow of the streams springing out of the glacier front. The amount of water produced by surface ablation  should be subtracted,  in order to obtain overall  basal melting.
The determination of Glacier Mass Balance is a complex operation, and in Italy recordings are carried out systematically every year only of a very limited number of glaciers, among which Careser  (since 1966), Sforzellina (since 1986) in the  Cevedale range,  Chardonay  (since 1992) in the Gran Paradiso range. A general indication can also be obtained from observations, using aerial photographs, of the ratio between accumulation areas, covered with snow, and ablation areas at the end of the summer, or of the snow-limit: if this is at a low altitude,  the balance will be probably positive even it is not possible to obtain specific quantitative indications. Observation of the characteristics of the glacier front can also be indicative : at a similar altitude, a high and swollen front generally indicates a positive balance, while a “depressed” thinner front indicates the opposite.

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