Cryogennous processes
Description
Cryogennous processes are caused by the action of frost. This action is a result of alternate freezing and thawing of water in pores and cracks of soil, rock and other material, usually at the ground surface.
Frost weathering (frost shattering, congelifraction, gelifraction or gelivation) is the mechanical breakdown of rocks by various processes. Most important fact of the frost weathering is that the freezing of water cause the 9% mass expansion. The ice nuclei during the freezing process attract unfrozen water from the adjoining pores and capillaries. The tension in the rock is then result of this water migration and growing of ice lenses. As the ice grows, the microcracks (i.e. existing planes of weakness – cracks and joints) grow and form the wedges. The other components of cryogenic weathering are various processes of chemical weathering (e.g. hydration, salt weathering) and organic weathering and pressure release (in recently deglaciated areas).
Cryogennous processes characteristically produce angular fragments of various sizes (from silt particles to boulders). In periglacial areas, cryogenic weathering determines the formation of some extensive features like blockfields, screes, talus slopes. The frost action is also crucial for mass movement processes like rock avalanches and rock falls.
The rate of cryogennous processes occurs depends on climatic factors and rock characteristics. Among climatic factors, the most important are the number of free-thaw cycles and the availability of moisture.
References:
[1] Goudie, A.S., 2004. Encyclopedia of Geomorphology, Routledge, London, 1156 s.
[2] Strahler A., Strahler, A., 2003. Introducing physical geography, Wiley, New York, 684 s.