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thaw hole

vertical hole in floating ice formed when a puddle melts through to the underlying water.

thaw penetration

the downward movement of the thawing front during thawing of frozen ground.

thaw settlement

compression of the ground due to thaw consolidation.

thaw sink

a closed thaw basin with subterranean drainage.

thaw slumping

a slope failure mechanism characterized by the melting of ground ice, and downslope sliding and flowing of the resulting debris.

thaw strain

the amount that frozen ground compresses upon thawing.

thaw unconformity

a boundary sometimes identified in perennially frozen ground, representing the base of a relict active layer, as well as the corresponding earlier permafrost table.

thaw weakening

the reduction in shear strength due to the decrease in effective stresses resulting from the generation and slow dissipation of excess pore pressures when frozen soils containing ice are thawing.

thaw-sensitive permafrost

perennially frozen ground which, upon thawing, will experience significant thaw settlement and suffer loss of strength to a value significantly lower than that for similar material in an unfrozen condition.

thaw-stable permafrost

perennially frozen ground which, upon thawing, will not experience either significant thaw settlement or loss of strength.

thawed ground

previously frozen ground in which all ice has melted.

thawing (of frozen ground)

melting of the ice in frozen ground, usually as a result of a rise in temperature.

thawing front

the advancing boundary between thawed ground and frozen ground.

thawing index

the cumulative number of degree-days above 0 degrees Celsius for a given time period.


an optical instrument used to visually track a radiosonde balloon and determine its bearing and elevation while in flight.

thermal conductivity

the quantity of heat that will flow through a unit area of a substance in unit time under a unit temperature gradient.

thermal diffusivity

the ratio of the thermal conductivity to the volumetric heat capacity.

thermal erosion

the erosion of ice-bearing permafrost by the combined thermal and mechanical action of moving water.

thermal expansion (or contraction) coefficient

the volume change per unit volume of a substance due to a one degree change in its temperature.

thermal pile

a foundation pile on which natural convection or forced circulation cooling systems or devices have been installed to remove heat from the ground.

thermal properties of frozen ground

the properties of the ground governing the flow of heat through it, and its freezing and thawing conditions.

thermal regime of the ground

a general term encompassing the temperature distribution and heat flows in the ground and their time-dependence.

thermal talik

a layer or body of unfrozen ground (in a permafrost area) in which the temperature is above 0 degrees Celsius due to the local thermal regime of the ground.

thermal-contraction crack

a tensile fracture resulting from thermal stresses in frozen ground.

thermal-contraction-crack ice

ice formed in thermal contraction cracks in the ground.

thermo-erosional cirque

the usually steep, horseshoe-shaped headwall of a retrogressive thaw slump.

thermo-erosional niche

a recess at the base of a river bank or coastal bluff, produced by thermal erosion of ice-bonded permafrost.

thermodynamic equilibrium thickness

the thickness at which ice no longer grows because it is so thick that heat from the ocean can no longer be conducted through the ice; it may take several years of growth and melt for ice to reach an equilibrium thickness.


study of the links between heat and energy. First law of thermodynamics states that heat is energy and the amount of energy within a system cannot change.


an instrument continuously recording temperature.


the process by which characteristic landforms result from the thawing of ice-rich permafrost or the melting of massive ice.

thermokarst lake

a lake occupying a closed depression formed by settlement of the ground following thawing of ice-rich permafrost or the melting of massive ice.
Increased thawing of frozen ground could create more thermokarst features, like this lake. —Credit: Andrew Slater

thermokarst mound

a hummock remaining after melting of the ice wedges surrounding an ice-wedge polygon.

thermokarst terrain

the often irregular topography resulting from the melting of excess ground ice and subsequent thaw settlement.


an instrument for measuring temperature; in meteorology, generally used to measure the temperature of the air or the soil.


a passive heat transfer device installed to remove heat from the ground.