Glacier Mass Balance and Regime: Data of Measurements and ...

November in the south), and summer (1 June – 30 September in the north, 1 December – 30 April 30 inthe south).The glaciological method (so-called “stakes and pits” method) is based on the method developedin hydrology, particularly in snow-hydrology, to measure snow-water balance in a basin. The methodwas applied, possibly the first time, to study the regime of Rhone Glacier at the end of 19th century(Mercanton, 1916). In the 20th century, the method was developed in more detail and applied to studythe regime of several glaciers around the Atlantic coast in Northern Europe (Thorarinsson, 1940;Ahlmann, 1948). Continuous and uninterrupted measurements started in 1945 on Storglaciären, inKebnekaise, Sweden Lapland (Schytt, 1962; Holmlund et al., 1996) and spread in consequent years byresearchers working in mountain areas in Europe, North America, the Arctic and Asia.Reports of direct measurement by the “stakes and pits” method have often implied that theydetermine the change in mass of ice in a column from the surface to the bottom of glacier; in reality,these measurements usually pertain only the uppermost recent annual layer. The basic equation of thisglaciological method for a point is,db/dt = ρdh/dt + œGρ/dt dz , (1)where ρ is the density of the ice layer of thickness h, changing over period of time t (Hubley, 1954).Thefirst term on the right side is the change in ice mass over a period of time with constant density and thesecond member is the change in density over period of time over a column of thickness z.For practical application equation (1) can be rewritten as:b i = ρ 0 ∆h+ (ρ 2 h 2 – ρ 1 h 1 ). (2)Here b iis the mass balance at a site, ρ 0 is the density of ice (usually considered to be 0.90 g cm -3 , butmay vary from 0.82 to 0.92 (Shumskiy, 1959), and ∆h is the change, relative to the top of a stake, of thesurface level of ice. The first term in the right side of equation (2) can usually be applied to determinethe ablation and balance of solid ice. The second right hand term of (2) is applied for porous material(snow and firn) with changing density over time (e.g., between two consecutive surveys). Thus, equation(2) can be used to calculate mass balance at any point (site) on a glacier where measurements are carriedout. The general recommendation is to carry out measurements at sites on a glacier twice a year todetermine annual (or net) mass balance (∅strem and Brugman, 1991). The first survey is usually takenat the beginning of a mass balance year (or the end of the previous year) in order to mark the summersurface.28