Snow patch
Encyclopedia
Snow patch is a geomorphological pattern of snow
and firn
accumulation which lies on the surface longer time than other seasonal snow cover. There are two types to distinguish; seasonal snow patches and perennial snow patches. Seasonal patches usually melt during the late summer but later than rest of the snow. Perennial snow patches are stable for more than two years and also have bigger influence to surroundings. (Demek, 1987).
Snow patches often start in sheltered places where both thermal and orographical conditions are favourable for the conservation of snow such as small existing depressions, gullies or other concave patterns. Main process that creates these accumulations is called nivation
. It is a complex of processes that includes freeze–thaw action (weathering
by the alternate freezing and melting of ice), mass movement (the downhill movement of substances under gravity), and erosion by meltwater
which is main agent of the surroundings influence. (Berrisford, 1991).
There is high soil moisture around the snow patch that supports growing of specific vegetation. Snow patch vegetation is very distinctive. It is usually dominated by species that tolerate a shortened growing season and is predominantly herbaceous. With increasing duration of snow persistence, non – vascular plants predominated over vascular plants for example Salicetum herbaceae, Salix herbacea etc. (Wahren, Williams, Papst, 2001)
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
and firn
Firn
Firn is partially-compacted névé, a type of snow that has been left over from past seasons and has been recrystallized into a substance denser than névé. It is ice that is at an intermediate stage between snow and glacial ice...
accumulation which lies on the surface longer time than other seasonal snow cover. There are two types to distinguish; seasonal snow patches and perennial snow patches. Seasonal patches usually melt during the late summer but later than rest of the snow. Perennial snow patches are stable for more than two years and also have bigger influence to surroundings. (Demek, 1987).
Snow patches often start in sheltered places where both thermal and orographical conditions are favourable for the conservation of snow such as small existing depressions, gullies or other concave patterns. Main process that creates these accumulations is called nivation
Nivation
Nivation is a collective name for the different processes that occur under a snow patch. The primary processes are mass wasting and the freeze and thaw cycle, in which fallen snow gets compacted into firn or névé...
. It is a complex of processes that includes freeze–thaw action (weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
by the alternate freezing and melting of ice), mass movement (the downhill movement of substances under gravity), and erosion by meltwater
Meltwater
Meltwater is the water released by the melting of snow or ice, including glacial ice and ice shelfs over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing...
which is main agent of the surroundings influence. (Berrisford, 1991).
There is high soil moisture around the snow patch that supports growing of specific vegetation. Snow patch vegetation is very distinctive. It is usually dominated by species that tolerate a shortened growing season and is predominantly herbaceous. With increasing duration of snow persistence, non – vascular plants predominated over vascular plants for example Salicetum herbaceae, Salix herbacea etc. (Wahren, Williams, Papst, 2001)
Sources
- BERRISFORD, M.S. (1991): Evidence for enhanced mechanical weathering associated with seasonally late-lying and perennial snow patches, Jotunheimen, Norway, Permafrost and periglacial processes, vol. 2
- DEMEK, J. (1987): Obecná geomorfologie, Academia, Praha
- WAHREN, C.-H.; WILLIAMS, R.J.; PAPST, W.A. (2001): Alpine and subalpine snow patch vegetation on the Bogong High Plains, SE Australia, Journal of vegetation science, vol.12