| Term: | Active layer |
| Definition: |
The layer of ground that is subject to annual thawing and freezing in areas underlain by permafrost; also known as seasonal frost. NSIDCCryosphere
The layer of ground that is subject to annual thawing and freezing in areas underlain by permafrost. IPCC2013 The layer of ground that is subject to annual thawing and freezing in areas underlain by permafrost IPAPermafrost The Active Layer is a layer of ground that is subject to annual thawing and freezing in areas underlain by Permafrost. In the zone of Continuous Permafrost the Active Layer generally reaches the Permafrost Table; in the zone of Discontinuous Permafrost it often does not. The Active Layer includes the uppermost part of the Permafrost wherever either the salinity or clay content of the Permafrost allows it to thaw and refreeze annually, even though the material remains cryotic (T < 0C). The Active Layer depth may vary considerably from one year to another depending on a number of variables (cf. Active Layer Thickness). If the ground thermal regime is no longer in long-term climatic equilibrium, Active Layers tend to show trends of increasing thickness. TrombottoGeocryology That part of the soil included with the suprapermafrost layer (i.e., existing above permafrost) that usually freezes in winter and thaws in summer. Its bottom surface is the frost table, beneath which may lie permafrost or talik. The depth of the active layer varies anywhere from a few inches to several feet. (Also called frost zone, mollisol.) AMSglossary Upper zone of soil in higher latitude locations that experiences daily and seasonal freeze-thaw cycles. PhysicalGeography GCW |