frozen ground or permafrost

altitudinal zonation of permafrost

the vertical subdivision of an area of mountain permafrost into permafrost zones, based on the proportion of the ground that is perennially cryotic.

altitudinal limit of permafrost

the lowest altitude at which mountain permafrost occurs in a given highland area outside the general permafrost region.


a large depression of the ground surface produced by thawing of a large area of very thick and exceedingly ice-rich permafrost.

air thawing index

the cumulative number of degree-days above 0°C for the air temperature during a given period.

air freezing index

the cumulative number of degree-days below 0° C for the air temperature during a given time period.

aggradational ice

the additional ground ice formed as a direct result of permafrost aggradation.


the process by which two objects are bonded together by ice formed between them.

adfreeze strength

the tensile or shear strength which has to be overcome to separate two objects that are bonded together by ice.

active-layer thickness

the thickness of the layer of the ground that is subject to annual thawing and freeing in areas underlain by permafrost.

active-layer failure

a general term referring to several forms of slope failures or failure mechanisms commonly occurring in the active layer overlying permafrost.


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