gelisols

Gelisols are an order in USA soil taxonomy. They are soils of very cold climates which are defined as containing permafrost within two metres 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 characteristic of Gelisols. In the United Nations Food and Agriculture Organization soil classification system, Gelisols are known as Cryosols. Structurally, Gelisols have no B horizon and have an A horizon resting on the permafrost. Because organic matter accumulates in the upper layer, most Gelisols are black or dark brown in colour, followed by a shallow mineral layer. Despite the influence of glaciation in most areas where Gelisols occur, chemically they are not highly fertile because nutrients, especially calcium and potassium, are very easily leached above the permafrost. The permafrost greatly restricts the engineering use of Gelisols, as large structures (eg. buildings) subside as the frozen earth thaws when they are put in place. Gelisols are found chiefly in Siberia, Alaska and Canada. Smaller areas are found in the Andes (mainly near the intersection between Chile, Bolivia and Argentina), Tibet, northern Scandinavia and the ice-free parts of Greenland and Antarctica. Fossil Gelisols are known from as far back as Precambrian ice ages 900 million years ago. In USA soil taxonomy, Gelisols are subdivided into: - Histels - Gelisols that have large quantities of organic matter.
- Turbels - Gelisols that have evidence of extensive mixing by frost action (cryoturbation) in the form of irregular, broken, or distorted horizon boundaries, involutions, an accumulation of organic matter on top of the permafrost, ice or sand wedges, or oriented rock fragments.
- Orthels - common Gelisols that don't meet criteria of the other suborders.

Gelisols

See also