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FRAGILE ALPINE ENVIRONMENTS  
Snow and perennial ice

Alpine snow

 

During the cold winter months precipitation in higher elevations and higher latitudes usually falls in the form of snow. The water-saturated air cools down to below 0°C, and consequently the excessive humidity sublimates to ice crystals. Dust particles such as clay minerals in the air act as nucleating agents to freeze cloud droplets.

We distinguish two processes of nucleation (crystallisation): Heterogeneous and homogeneous nucleation. These two processes are shown in the animation below.

alpine_landscape

1 - Alpine landscape in snow (140K)

Act

Let it snow! Look at the differences between the processes of heterogeneous and homogeneous nucleation. Try to explain the processes to another student.

During precipitation, ice crystals associate to form snow flakes with different forms and sizes. The ice crystals forming snow flakes are only distinguishable under a microscope. Their shapes depend on temperature.



Accumulating on the ground, the seasonal snow cover has a variety of physical and chemical characteristics important for the biotic environment:

Snow
  • lowers the exchange of radiation, temperature and air between the soil surface and the atmosphere
  • is a source of water and nutrients
  • is a burden for underlying plants (Fig. 2)
  • is a habitat for microorganisms (Fig. 3 and 4)
  • hinders the mobility and access to food for winter-active birds and mammals (Fig. 5)

bending_spuce

2 - A young spruce tree bending under the load of a settling and creeping snow cover (32K)

spores

3 - Red resting spores of the snow alga Chlamydomonas nivalis in a snow probe (to the left a pollen grain of Pinus) (80K)

algae_on_snow

4 - This faint red areas are derived from snow algae. (76K)
Photo: T. Stucki

ibex

5 - An Ibex fighting its way through the snow (80K)
Photo: SLF
See more about Ibex on www.steinbock.ch (German)

Snow movements such as snow gliding and avalanches redistribute snow and break higher woody plants thus influencing the structure of vegetation (Fig. 6).
 

broken_trees

6 - Bent and broken trees in the runout zone of an avalanche (164K)
 

The difference between the influence of snow cover on the environment in polar regions and its influence in high mountains of temperate and tropical regions is mainly due to differences in temperature. Here, we focus on the snow cover of temperate mountains, especially the Alps.
 

 

 

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29 August 2011
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