MOSAIC (Modelling of Snowmelt And Its Consequences)
The conceptual framework is dealing with different aspects of snowmelt and its consequences.
Particular regions at high latitudes are to a great extend characterised by the existence of
seasonal snow covers. Their spatial structure and course of development, metamorphism and depletion
are consequences of climatic and terrain conditions, as well as their dependence on structure and
state of the sublayer. Snow covers strongly modify not only the regional climate, but also geomorphic
processes, soil development, vegetation and fauna, and finally life conditions and economic
possibilities by influencing energy balance and water budget. At the end of the snowmelt period,
energy balance and water budget have strongly changed in comparison to the previous snow-covered
The snowmelt period not only is a transitional season, but also possesses its own dynamics, which
is of great importance, e.g. for nutrient and sediment budgets. The occurrence of so called slush
streams, periodically or episodically observed in arctic and subpolar areas, can reach catastrophic
dimensions under extreme meteorological conditions. During these events, an activation of geomorphic
and hydrologic processes takes place, which would never be possible under so-called 'normal'
conditions. Short-term sediment transports, caused by extremely high discharge values, can dominantly
contribute to the total sediment yield of a drainage basin.
The research work within MOSAIC included:
Slushflow is the expression for the downhill movement of water-saturated snow. The movement is
restricted to channels and occurs on gentle slopes of less than 20°. They can therefore be easily
distinguished from avalanches, which are normally triggered on slopes with an inclination of more
than 20°. The extent of slush flows has a wide range. High-energy variants show extreme velocities
of over 20 m/s and runoff values of up to several thousand m3/s. Slushflows have been
reported from Arctic and subpolar regions, but there are also indications of their occurrence in
the Swiss Alps.
A new physical concept for the mechanism of slushflow release is being developed based on the
assumption that mainly the development of a hydrostatic pressure gradient due to the generation
of an inclined water level in the snow cover is responsible for the initiation of slushflows. The
snowpack condition is decisive for the release of slush flows, since the hydrostatic pressure
gradient is compensated by the shear stability of the snow matrix as long as the pressure gradient
does not exceed a certain threshold value. Another part of the project is the investigation and
evaluation of the model prerequisites for the development of a physically based and fully distributed
snow melting model.
The slush flows were investigated in two expeditions to Spitsbergen and in two field campaigns to Kärkevagge, Northern Sweden