Patterned grounds

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

rock formation on the Antrim coast of Northern Ireland

thumb|Ibyuk pingo near Tuktoyaktuk, northern Canada thumb|View from top of a pingo towards another, within a partly drained lake, the Arctic Ocean in the background (near Tuktoyaktuk). July 20, 1975.

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.

thumb|Mudcrack|Desiccation cracks in [[sludge]] thumb|Centripetal desiccation cracks in the Lower Jurassic [[Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm, southwestern Utah. A dinosaur footprint is at the center.]]

thermokarst depression in Russia

Sedimentary structures resulting from the interaction between sediment and bottom current

300px|thumb|upright=1.4|A group of well developed palsas as seen from above Palsas are peat mounds with a permanently frozen peat and mineral soil core. They are a typical phenomenon in the polar and subpolar zone of discontinuous permafrost. One of their characteristics is having steep slopes that rise above the mire surface. This leads to the accumulation of large amounts of snow around them. The summits of the palsas are free of snow even in winter, because the wind carries the snow and deposits on the slopes and elsewhere on the flat mire surface. Palsas can be up to in diameter and can re

results from ice forming beneath the surface of soil during freezing conditions

upright=1.6|thumb|Vertisols of the world thumb|A more detailed map of the global distribution of Vertisols

geologic discontinuity feature, often a diaclase, or a fault

Geometric land forms resulting from the freeze-thaw cycle

upright=1.25|thumb|Fresh mudcracks on the shore of The Wash, England Mudcracks (also known as mud cracks, desiccation cracks or cracked mud) are sedimentary structures formed as muddy sediment dries and contracts. Crack formation also occurs in clay-bearing soils as a result of a reduction in water content.

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

geologic structures formed during sediment deposition

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