Gelisols: Permafrost Soils and Their Suborders

What makes a soil a Gelisol

NRCS gives the order a depth test. A soil is a Gelisol if it has permafrost within 39 inches (100 cm) of the surface, or if it has gelic materials within 39 inches (100 cm) and permafrost within 79 inches (200 cm).^[1]

Permafrost is ground that stays frozen, and the Soil Science Society of America places Gelisols in the Arctic and Antarctic and at extremely high elevations; they make up about 9% of the world’s glacier-free land. The name comes from the Latin gelare, to freeze.^[2]

They’re also one of the two newest orders: Soil Taxonomy added Gelisols, with Andisols, in its 1999 second edition, and our soil orders page walks through the editions.^[3]

Permafrost, the active layer and frost churning

The gelic materials in the definition are mineral or organic soil materials that show cryoturbation (frost churning) or ice segregation, in the active layer, the layer that thaws each season, or in the upper part of the permafrost. Frost heaves are one form of that freeze-thaw churning.^[1][2]

The frozen layer shapes how the land can be used: it affects how water moves down through the soil, and it can limit how deep plant roots go.^[2]

Histels, Orthels and Turbels

NRCS describes three suborders, told apart by organic carbon and churning:

• Histels are the Gelisols with large amounts of organic carbon. They’re used as wildlife habitat.
• Orthels show little or no evidence of cryoturbation and are used mostly as wildlife habitat.
• Turbels show cryoturbation as irregular, broken or distorted horizon boundaries, and are used mostly as wildlife habitat too.^[1]

Histels connect to the Histosols: peat, mucky peat and muck qualify as Soil Taxonomy’s diagnostic organic materials (sapric, fibric and hemic) only in Histosols and in this suborder.^[4] The survey data doesn’t record suborders, so none gets an acreage here.

Gelisols in Alaska

In the United States, NRCS says, Gelisols are known to occur only in Alaska.^[1]

USDA’s survey puts 99.998% of the order’s 125.2 million acres in Alaska. The remaining 2,216 acres sit in Washington and Wyoming, one mapped soil component in each.^[5]

Most widespread Gelisol series

The list holds the series with a published official description: Klasi, Tajittro and Klawasi, all mapped most in Alaska.^[5][6]

Download the Gelisols data (CSV)

What Gelisols are like

More than 99.9% of described Gelisol acres have an O horizon, and the most common sequences are O–A–C (79.6 million acres), O–C (20.3 million acres) and O–A–B–C (11.3 million acres). An A horizon turns up on 78.1% of the acres, a B horizon on only 9.6%.^[5]

In hydrologic terms, 58.0% of the acres are in soil group D, where water soaks in slowly, and another 36.7% in a dual group such as B/D, where the first letter applies only once the land is drained.^[5][8]

The first mineral layer, under organic material on 94.8% of the acres, is strongly acid more often than any other pH class (47.8%), and its median organic matter, 10%, is the highest of any order with a median.^[5][9]

Low soil temperatures make soil-forming processes proceed very slowly, the decomposition of organic material among them, and most Gelisols store large quantities of organic carbon.^[10]

Farming and land use

None of the order’s acres is rated prime farmland, against 12.5% of all US soil acres, and only 2.6% of rated acres are in the cultivable capability Classes I–IV; Class VI alone holds 66.3%.^[5][11][12]

NRCS’s use for all three suborders is the same: mostly wildlife habitat.^[1]

When permafrost thaws

The frozen condition of Gelisol landscapes makes them sensitive to human activities, the University of Idaho notes, and in its Turbels description NRCS points to areas where fire or land clearing has changed the soils’ thermal properties enough for the permafrost to thaw; Cryepts occur there instead.^[10][1]

The sources this page relies on don’t describe building practice on permafrost. For a specific site, the building site checker shows USDA’s own ratings for the soil mapped there.

Gelisols compared with other orders

Gelisols rank seventh of the twelve orders by US acres, almost all of it in one state, and none of their acres is prime farmland.^[5][11]

Histosols show a dash: their surface is organic material (peat or muck), so a topsoil (A) or surface pH median would describe mineral soil beneath it.

Frequently asked questions

What are Gelisols?

Soils with permafrost within 39 inches (100 cm) of the surface, or with gelic materials within 39 inches (100 cm) and permafrost within 79 inches (200 cm).^[1]

What is permafrost?

Ground that stays permanently frozen. In Gelisols it lies near the surface and shapes how water moves down and how deep roots can grow.^[2]

What is the active layer?

The seasonal thaw layer above the permafrost, where frost churning (cryoturbation) and ice segregation mark gelic materials.^[1]

Where are Gelisols found in the US?

In Alaska: NRCS knows them only there, and USDA’s survey puts all but 2,216 of their 125.2 million acres in the state.^[1][5]

Can you farm Gelisols?

None of their acres is rated prime farmland, and NRCS lists wildlife habitat as the main use of all three suborders.^[5][11][1]

What are the three kinds of Gelisols?

Histels, with large amounts of organic carbon; Orthels, with little or no frost churning; and Turbels, whose horizon boundaries are broken or distorted by it.^[1]

What does ‘Gelisol’ mean?

It comes from the Latin gelare, to freeze.^[2]