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a small mountain lake or pool.

telescoped ice

deformed sea ice in which one piece has overridden another; also called rafted ice.


a physical quantity characterizing the mean random motion of molecules in a physical body; in other words, it is a measure of the degree of hotness or coldness of a substance.

temperature profile

the graphic or analytical expression of the variation in ground temperature with depth.

temperature-gradient metamorphism

snow metamorphism that occurs when there are strong differences in temperature between the bottom and top of a snow layer.


the lowest end of a glacier, also called the glacier toe or glacier snout.
Glacier at the head of Canon Fiord, Ellesmere Island, Canada

terrestrial radiation

longwave radiation emitted by the earth, including its atmosphere.

thaw basin

a depression of the permafrost table created by naturally induced thawing.

thaw bulb

a zone of thawed ground below or surrounding a man-made structure placed on or in permafrost and maintained at temperatures above 0 degrees Celsius.

thaw consolidation

time-dependent compression resulting from thawing of frozen ground and subsequent draining of excess water.

thaw consolidation ratio

a dimensionless ratio describing the relationship between the rate of thaw and the rate of consolidation of a thawing soil, which is considered to be a measure of the relative rates of generation and expulsion of excess water during thaw.

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.