Gelisols 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 environments containing permafrost, the active layer is the top layer of soil that thaws during the summer and freezes again during the autumn.