Gelisols are an order in
USDA soil taxonomy. They are
soils of very cold climates which are defined as containing
permafrost
Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface ...
within two meters 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
World Reference Base for Soil Resources (WRB), Gelisols are known as Cryosols. In soil taxonomy, Gelisols key out before the
Histosol
In both the World Reference Base for Soil Resources (WRB) and the USDA soil taxonomy, a Histosol is a soil consisting primarily of organic materials. They are defined as having or more of organic soil material in the upper . Organic soil materia ...
s. In the WRB, the Histosols key out before the Cryosols. Organic permafrost soils are therefore Gelisols (Histels) in the soil taxonomy and Histosols (Cryic Histosols) in the WRB.
Structurally, Gelisols may have a
B horizon and more commonly have an
A horizon
A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. ...
and/or O horizon resting on the permafrost. Because
soil organic matter Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal detritus at various stages of decomposition, cells and tissues of soil microbes, and substances that soil microbes synthesize. SOM provides numerous b ...
accumulates in the upper layer, most Gelisols are black or dark brown in
soil color Soil color does not affect the behavior and use of soil; however, it can indicate the composition of the soil and give clues to the conditions that the soil is subjected to.Brady, Nyle C. & Ray R. Weil ''Elements of the Nature and Properties of ...
, 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 (e.g. 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
, image_flag = Bandera de Bolivia (Estado).svg
, flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center
, flag_alt2 = 7 × 7 square p ...
and
Argentina),
Tibet, northern
Scandinavia and the ice-free parts of
Greenland and
Antarctica.
Fossil Gelisols are known from as far back as
Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
ice ages 900 million years ago.
Suborders
In
USDA soil taxonomy, Gelisols are subdivided into:
* Histels: organic soils similar to
histosol
In both the World Reference Base for Soil Resources (WRB) and the USDA soil taxonomy, a Histosol is a soil consisting primarily of organic materials. They are defined as having or more of organic soil material in the upper . Organic soil materia ...
s except that they have permafrost within two meters below ground surface. They have 80% or more organic materials from the soil surface to a depth of 50 cm or to a glacic layer or densic, lithic, or
paralithic A paralithic horizon is a weathered layer of bedrock
In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet.
Definition
Bedrock ...
contact, whichever is shallowest. These soils occur predominantly in
subarctic
The subarctic zone is a region in the Northern Hemisphere immediately south of the true Arctic, north of humid continental regions and covering much of Alaska, Canada, Iceland, the north of Scandinavia, Siberia, and the Cairngorms. Generally, ...
and low arctic regions of continuous or widespread permafrost. Less than one-third of the active layer (the soil between the ground surface and a permafrost table) or an ice layer which is at least 30-cm thick has been cryoturbated.
* Turbels: soils that show marked influence of cryoturbation (more than one-third of the depth of the active layer) such as irregular, broken, or distorted horizon boundaries and involutions and areas with patterned ground. They commonly contain tongues of mineral and organic horizons, organic and mineral intrusions and oriented rock fragments. Organic matter is accumulated on top of the permafrost and ice or sand wedges are a common features. Turbels occur primarily in the zone of
continuous permafrost.
* Orthels: soils that show little or no cryoturbation (less than one-third of the depth of the active layer). Patterned ground (except for polygons) generally is lacking. Orthels occur primarily within the zone of
discontinuous permafrost, and in alpine areas.
See also
*
Active layer
*
Pedogenesis
*
Pedology (soil study)
*
Soil classification
References
* Soil Survey Staff: Keys to Soil Taxonomy. 12th edition. Natural Resources Conservation Service. U.S. Department of Agriculture. Washington D.C., USA, 2014.
*
*
*
*
Further reading
* W. Zech, P. Schad, G. Hintermaier-Erhard: Soils of the World. Springer, Berlin 2022, Chapter 2.3.1.
External links
profile photos (with classification)WRB homepage
profile photos (with classification)IUSS World of Soils
{{Soil type
Pedology
Types of soil
Geography of the Arctic
Permafrost