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Mass balance measurements have been performed at 42 glaciers since the first measurements started at Storbreen in Jotunheimen in 1949. Since 1963 six glaciers in South-Norway has been measured continiously. In northern-Norway the longest mass balance record is at Engabreen where measurements started in 1970.
Studies of mass balance are performed by measuring the amount of snow accumulated during winter, and later measuring the amount of snow and ice removed by melting in the summer. The difference between these two parameters gives the net or annual balance. If the amount of snow accumulated during the winter is larger than the amount of melted snow and ice during the summer, the annual balance is positive and the glacier volume has increased. On the other hand, if the melting of snow and ice during the summer is larger than the supply of snow in the winter, the annual balance is negative and the volume decreases.
Methods The mass balance is calculated using the so-called glaciological method within a stratigraphic system (Østrem and Brugman, 1991). The balance is calculated between two successive "summer surfaces" (i.e. surface minima). Winter balance is normally measured in April or May by probing to the previous year’s summer surface along profiles which are unchanged from one year to the next. Stake readings are used to check the probings in certain areas, where possible. Since the stakes can disappear during particularly snow-rich winters, and since it is often difficult to distinguish the summer surface by probing alone, snow coring is also used to support the probing. Snow density is measured in pits at one or two locations at different elevations on each glacier. Summer and annual (net) balances are obtained from stake measurements, usually made in September or October. Below the glacier’s equilibrium line the net balance is always negative, meaning that more snow and ice melts during a given summer than accumulates during the winter. Above the equilibrium line, in the accumulation area, the net balance is always positive, and some winter snow remaions throughout the summer.
Mass balance program Mass balance measurements are currently performed on 14 glaciers in Norway (2010). In southern Norway six of the glaciers have been measured since 1963 or earlier, and they constitute an west-east profile reaching from the very maritime Ålfotbreen glacier, close to the western coast, to the very continental Gråsubreen, in the eastern part of Jotunheimen. Storbreen in Jotunheimen has the longest series of all glaciers in Norway starting in 1949. Engabreen has the longest series in northern Norway starting in 1970. The results are published in the the report series "Glaciological investigationsin Norway in ..." from NVE, and the data are submitted to the World Glacier Monitoring Service (www.wgms.ch).