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Gelisols are an order in USDA soil taxonomy. They are soils of very cold climates which are defined as containing permafrost within two meters (6 ft 7 in) of the soil surface. The word "Gelisol" comes from the Latin gelare meaning "to freeze", a reference to the process of cryoturbation that occurs from the alternating thawing and freezing ...
Entisols: Least soil profile development; ochric epipedon is common; no B horizons; most common order by surface area (16.3% of global and 12.2% of U.S. ice-free land). Gelisols : Soils with permafrost within 100 cm or cryoturbation (frost churning) within 100 cm plus permafrost within 200 cm; commonly at high latitudes and elevations; 8.6% of ...
[2] [3] Gleysoils may be sticky and hard to work, especially where the gleying is caused by surface water held up on a slowly permeable layer. However, some ground-water gley soils have permeable lower horizons , including, for example, some sands in hollows within sand dune systems (known as slacks), and in some alluvial situations.
Cryoturbation occurs to varying degrees in most gelisols. The cause of cryoturbation lies in the way in which the repeated freezing of the soil during autumn causes the formation of ice wedges at the most easily erodible parts of the parent rock .
Like Gelisols, Histosols have greatly restricted use for civil engineering purposes because heavy structures tend to subside in the wet soil. In USDA soil taxonomy, Histosols are subdivided into: Folists – Histosols that are not saturated with water for long periods of time during the year.
If the tephras are more basic or the climate is dry, amorphous colloidal materials, including allophane and imogolite develop, and the Andosols are given the Silandic qualifier. [5] In both cases, they contain many ferrihydrite and have a bulk density ≤ 0.9 kg/dm 3 . [ 6 ]
Unweatherable parent materials – sand, iron oxide, aluminium oxide, kaolinite clay. Erosion – common on shoulder slopes; other kinds also important.; Deposition – continuous, repeated deposition of new parent materials by flood as diluvium, aeolian processes which means by wind, slope processes as colluvium, mudflows, other means.
They also leave behind organic residues which contribute to humus formation. [3] Plant roots with their symbiotic mycorrhizal fungi are also able to extract nutrients from rocks. [4] New soils increase in depth by a combination of weathering and further deposition. The soil production rate due to weathering is approximately 1/10 mm per year. [5]