- Thermokarst
Thermokarst refers to a land surface that forms as
ice -richpermafrost melts. It occurs extensively inArctic areas, and on a smaller scale in mountainous areas such as theHimalayas and theSwiss Alps .The name is given to very irregular surfaces of marshy hollows and small
hummock s. These pitted surfaces resemble those formed by solution in somekarst areas oflimestone , which is how they came to have karst attached to their name without the presence of any limestone. Small domes that form on the surface due to frost heaving with the onset ofwinter are only temporary features. They then collapse with the arrival of next summer's thaw and leave a small surface depression. Some ice lenses grow and form larger surface hummocks, which last many years and sometimes become covered withgrasses andsedges , until they begin to thaw. These domed surfaces eventually collapse either annually or after longer periods and form depressions which contribute to uneven surfaces. These are included within the general label of thermokarst.The related term thermokarst lake, also called a thaw lake or cave-in lake, refers to a body of freshwater, usually shallow, that is formed in a depression by
meltwater from thawing permafrost. [Bucksch, Herbert. "Dictionary Geotechnical Engineering." New York, Springer, 1997.] Depressions are often produced by the collapse of ground levels associated with permafrost melt. Continued melting of the permafrost substrate can lead to the drainage and eventual disappearance of thermokarst lakes, leaving them, in such cases, a geomorphologically temporary phenomenon. [Phillips, Marcia, Lukas U. Arenson, and Sarah M. Springman, eds. "Permafrost." London, Taylor & Francis, 2003.] In recent years, thermokarst lakes have become increasingly common inSiberia and othertundra environments Fact|date=September 2008. This permafrost melting releasescarbon dioxide andmethane gases [http://www.ucar.edu/news/releases/2008/permafrost.jsp] .References
External links
* [http://www.newscientist.com/article.ns?id=mg18725124.500 New Scientist article]
* [http://www.ucar.edu/news/releases/2008/permafrost.jsp UCAR press release]
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