Permafrost

Permafrost () is soil or underwater sediment which continuously remains below for two years or more; the oldest permafrost has been continuously frozen for around 700,000 years. Whilst the shallowest permafrost has a vertical extent of below a meter (3 ft), the deepest is greater than . Similarly, the area of individual permafrost zones may be limited to narrow mountain summits or extend across vast Arctic regions. The ground beneath glaciers and ice sheets is not usually defined as permafrost, so on land, permafrost is generally located beneath a so-called active layer of soil which free

thumb|Permafrost thaw ponds in Hudson Bay, Canada, in 2008 Thermokarst is a type of terrain characterised by very irregular surfaces of marshy hollows and small hummocks formed when ice-rich permafrost thaws. The land surface type occurs in Arctic areas, and on a smaller scale in mountainous areas such as the Himalayas and the Swiss Alps.

thermokarst depression in Russia

shallow depression formed by subsidence of the Arctic permafrost

ecological experiment

stand of trees displaced from their normal vertical alignment

landform of angular rock debris frozen in interstitial ice, former "true" glaciers overlain by a layer of talus, or something in between

thumb|Cut-away section of soil, showing movement of soil layers due to cryoturbation. In gelisols (permafrost soils), cryoturbation (frost churning) refers to the mixing of materials from various horizons of the soil down to the bedrock due to freezing and thawing.

release of methane in permafrost regions of the Arctic

thumb|Example of a periglacial landscape with both pingos and polygon wedge ice near [[Tuktoyaktuk, Northwest Territories, Canada]]

formation of moisture, diffused within soil or rock, which accumulates in a localized zone

thumb|The three types of talik: closed, open and through. A talik is a zone of year-round unfrozen ground located in the middle of a permafrost area. In regions of continuous permafrost, taliks often occur underneath shallow thermokarst lakes and rivers, where the deep water does not freeze in winter and thus the soil underneath does not freeze either. Sometimes closed, open, and through taliks are distinguished. These terms refer to whether the talik is surrounded by permafrost, open at the top (e.g. a thermokarst lake), or open both at the top and above an unfrozen layer beneath the permafro

crack in the ground formed by a narrow vertical block of ice

Yedoma () is an organic-rich (about 2% carbon by mass) Pleistocene-age permafrost with ice content of 50–90% by volume. Yedoma are abundant in the cold regions of eastern Siberia, such as northern Yakutia, as well as in Alaska and the Yukon. ==Characteristics== thumb|Alas landscape in Megino-Kangalassky District, Yakutia The landscape of yedoma areas is of glacier plains and hills with shallow depressions known as alas. Yedoma usually form in lowlands or stretches of land with rolling hills where ice wedge polygonal networks are present, in stable relief features with accumulation zones of poo

thumb|upright=1.6|Gelisols of the world thumb|upright=1.6|Tundra#arctic|Arctic Tundras are the typical environment for the formation of gelisols thumb|upright=1.6|Other gelisols are observed in Tundra#alpine|Alpine Tundras

layer of topsoil above permafrost

thumb|300px|The shoreline formations of Stolbovoy Island. Note the polygons on the lower left and the conical mounds along the seashore. Baydzharakh (; Yakut: Бадьараах, Baçaraakh) is a term based in the Yakut language, referring to a roughly cone-shaped natural rock formation. They are usually composed of siltstone, silty peat or loam.

sub-cycle of the larger global carbon cycle

Research Institute in Russia