Research on the glacier
Some people use the glacier for hiking, others think of the glacier as an important water reservoir for power production in the country, while others use the glacier for research, including climate research.
A lot of work is being done to monitor the development of Jostedalsbreen. Today, changes in the glacier front are measured on 13 of Jostedalsbreen's glacier arms, and the mass balance on Nigardsbreen and Austdalsbreen is measured. This is part of NVE's glacier monitoring. To gain knowledge about the glacier further back in time, old images, historical documents, dating of moraine ridges and analysis of sediment can be used.
Mass balance
Schematic cross section of a glacier.
The mass balance on a glacier is the net change in the mass of the glacier over one year. The glacier's mass balance can be compared to an account where the addition of snow and ice is the income while the loss of mass is the expense. If the glacier gains more mass than it loses, there is a positive mass balance. If the glacier loses more mass than is added, there is a negative mass balance.
The "income" of the glacier, i.e. the mass the glacier receives in the form of snow and ice, comes from direct snowfall, avalanches and wind-blown snow from surrounding mountains. This is called accumulation. The "expense" of the glacier, or loss of mass, is mainly processes such as melting, evaporation and sublimation, in addition to any ice avalanches and calving. Loss of mass on a glacier is called ablation.
What determines income and expenses?
The different seasons contribute differently to the mass balance. In autumn and spring, snow often falls on the upper parts of the glacier, while it melts on the lower parts. The glacier will mainly receive snow on the entire surface in winter, and there is little or no melting.
In summer, only the very uppermost parts may receive some snow, but the majority of the glacier loses snow and ice at this time of year.
Mass balance measurements
It is common to measure the mass balance in the autumn, after the summer melt has finished. This allows us to see whether or not the glacier received more snow and ice than what melted during the summer.
The area of the glacier where all the snow and some of the ice melts each summer, the lower part or blue ice, is called the glacier's melting area, or ablation area. The area of the glacier where not all the snow melts away in the summer is called the glacier's nutrient area, or accumulation area.
For a glacier in equilibrium, there is a ratio between the area of the accumulation area and the ablation area. On most glaciers in Norway, the accumulation area is 65±5%.
Brake measurements on Jostedalsbreen. Photo: NVE
Tuftebreen. The equilibrium line is in the divide between blue ice and snow. Photo: Pål Gran Kielland.
Equilibrium line
During the melting season, the boundary between this year's snow and blue ice will creep upwards on the glacier, and this boundary is called the snow line. The equilibrium line is the height of the glacier where the snow line lies at the end of the melting season (September/October). Here, the accumulation is equal to the ablation (the boundary between this year's snow and blue ice). The height of the equilibrium line indicates the condition of the glacier. Heavy winter precipitation and/or a cool summer means that the equilibrium line will be low on the glacier and opposite. For example, several years with a positive mass balance/low equilibrium line will cause the glacier front to advance after a few years.
Gravitational forces cause ice flow that will transport the excess mass from the accumulation area to the ablation area.
