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the physical process by which a vapor becomes a liquid or solid; the opposite of evaporation; in meteorological usage, this term is applied only to transformation from vapor to liquid; any process in which a solid forms directly from its vapor is termed sublimation, as is the reverse process.


the transport of energy entirely resulting from the random motions of individual molecules, and not from any concerted group movement; occurs in response to temperature gradients; contrasts with convection, in which energy is transported by molecules moving together in coherent groups.

congelation ice

an advanced form of new ice that forms as a stable sheet with a smooth bottom surface.
A photograph in natural light of the vertically oriented pores in congelation ice. (Photo courtesy of Ted Maksym, United States Naval Academy.)

conglomeric cryogenic fabric

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which coarser soil particles form compound arrangements.

consolidated pack ice

pack ice in which the floes are frozen together; ice cover 10/10ths.

construction methods in permafrost

special design and construction procedures required when engineering works are undertaken in permafrost areas.

constructive metamorphism

snow metamorphism that adds molecules to sharpen the comers and edges of an ice crystal.

continuous permafrost

geographic area in which permafrost occurs everywhere beneath the exposed land surface with the exception of widely scattered sites, such as newly deposited unconsolidated sediments that have just been exposed to the freezing climate; mean annual soil surface temperatures are typically below -5 degrees Celsius (23 degrees Fahrenheit).

continuous permafrost zone

the major subdivision of a permafrost region in which permafrost occurs everywhere beneath the exposed land surface with the exception of widely scattered sites.


the transport of energy resulting from the concerted movement of molecules in coherent groups; contrasts with conduction in which energy is transported by the random motions of molecules; atmospheric convection is nearly always turbulent and results in the vertical transport and mixing of atmospheric properties.

convection cloud

cumuliform cloud which forms in the atmosphere as a result of convection; such clouds are also called clouds of vertical development, a cloud that has its base in the low height range but extends upward into the middle or high altitudes.

coriolis force

apparent force, due to the rotation of the earth, which acts normal to, and to the right of the velocity of a moving particle in the northern hemisphere, the movement of the particle being considered relative to that of the earth.


an overhanging accumulation of ice and wind-blown snow, characteristically found on the edge of a ridge or cliff face.


any fracture or rift in floating ice not sufficiently wide to be described as a lead.


a way that snow or ice can move by deforming its internal structure.

creep of frozen ground

the slow deformation (or time-dependent shear strain) that results from long-term application of a stress too small to produce failure in the frozen material.

creep strength

the failure strength of a material at a given strain rate or after a given period under deviatoric stress.


open fissure in the glacier surface.
Explorers examine a crevasse on Lyman Glacier in 1916. (Photo courtesy of the United States Forest Service. Archived at the World Data Center for Glaciology, Boulder, CO.)

crevasse hoar

a kind of hoarfrost; ice crystals that develop by sublimation in glacial crevasses and in other cavities with cooled space and calm, still conditions under which water vapor can accumulate; physical origin is similar to depth hoar.


a hard snow surface lying upon a softer layer; crust may be formed by sun, rain or wind, and is described as breakable crust or unbreakable crust, depending upon whether it wil break under the weight of a turning skier.

crust-like cryostructure

the cryostructure of a frozen deposit of angular blocks that are coated with ice, whereas large spaces between the blocks are not filled with ice.


A deposit of dust and soot, often bound by microbial mats, that is formed on melting glaciers and ice sheets. The deposits are often found in pothole-like pockets on the ice surface.



the boundary between cryotic and noncryotic ground as indicated by the position of the 0 degrees Celsius isotherm in the ground.


the combination of thermophysical, physico-chemical and physico-mechanical processes occurring in freezing, frozen and thawing earth materials.

cryogenic aquiclude

a layer of ground which, because of its frozen state, has a low enough permeability to act as a confining bed for an aquifer.

cryogenic fabric

the distinct soil micromorphology resulting from the effects of freezing and thawing processes.

cryogenic temperature

in international materials science, this term refers to temperatures generally below -50 degrees Celsius, but usually to temperatures within a few degrees of absolute zero (-273 degrees Celsius).


the study of the genesis, structure and lithology of frozen earth materials.


the study of soils at temperatures below 0 degrees Celsius, with particular reference to soils subject to intensive frost action, and to soils overlying permafrost.


a layer of unfrozen ground that is perennially cryotic (forming part of the permafrost), in which freezing is prevented by freezing-point depression due to the dissolved-solids content of the pore water.


the process through which cryoplanation terraces form.

cryoplanation terrace

a step-like or table-like bench cut in bedrock in cold climate regions.


soil formed in either mineral or organic materials having permafrost either within 1 meter (3.3 feet) below the surface or, if the soil is strongly cryoturbated, within 2 meters (6.6 feet) below the surface, and having a mean annual ground temperature below 0 degrees Celsius.


one of the earth's spheres of irregular form existing in the zone of interaction of the atmosphere, hydrosphere and lithosphere, distinguished by negative or zero temperature and the presence of water in the solid or super-cooled state; the term refers collectively to the portions of the earth where water is in solid form, including snow cover, floating ice, glaciers, ice caps, ice sheets, seasonally frozen ground and perennially frozen ground (permafrost).


the structural characteristics of frozen earth materials.


a suction developed in freezing or partially frozen fine-grained materials as a result of temperature-dependent differences in unfrozen water content.