frozen ground or permafrost

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density of frozen ground

the mass of a unit volume of frozen soil or rock.

depth of seasonal frost penetration

the maximum thickness of the seasonally frozen layer.

depth of thaw

the minimum distance between the ground surface and frozen ground at any time during the thawing season in an area subject to seasonal freezing and thawing.

depth of zero annual amplitude

the distance from the ground surface downward to the level beneath which there is practically no annual fluctuation in ground temperature.

desiccation crack

crack or fissure developed in fine-grained soil material as a result of shrinkage during drying.

desiccation polygon

closed, multi-sided, patterned ground feature formed by desiccation cracks in fine-grained soil material, usually less than 2 meters (6.6 feet) in diameter.

design depth of frost penetration

(1) (North American usage) the mean of the three largest depths of seasonal frost penetration measured during the past thirty years, or the largest depth of seasonal frost penetration beneath a snow-free soil surface measured during the past ten years (2) (Russian usage) the mean of the depths of seasonal frost penetration measured during at least the last ten years with the ground surface free of snow and the groundwater level below the depth of seasonal frost penetration.

design freezing index

the cumulative number of degree-days below 0 degrees Celsius, calculated by taking the average of the seasonal freezing indices for the three coldest winters in the most recent 30 years of record.

design thawing index

the cumulative number of degree-days above 0 degrees Celsius, calculated by taking the average of the seasonal thawing indices for the three warmest summers in the most recent 30 years of record.

detachment failure

a slope failure in which the thawed or thawing portion of the active layer detaches from the underlying frozen material.

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