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Glossary
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a flat-topped iceberg that shows horizontal banding; typically form by breaking from an ice shelf.
taigathe open northern part of the boreal forest; consists of open woodland of coniferous trees growing in a rich floor of lichen (mainly reindeer moss or caribou moss), and is generally cold and swampy; lies immediately south of the tundra; in spring, it is often flooded by water from northward flowing rivers, the lower reaches of which are still frozen.
talika layer or body of unfrozen ground occurring in a permafrost area due to a local anomaly in thermal, hydrological, hydrogeological, or hydrochemical conditions.
tarna small mountain lake or pool.
telescoped icedeformed sea ice in which one piece has overridden another; also called rafted ice.
temperaturea 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.
the graphic or analytical expression of the variation in ground temperature with depth.
temperature-gradient metamorphismsnow metamorphism that occurs when there are strong differences in temperature between the bottom and top of a snow layer.
terminusthe lowest end of a glacier, also called the glacier toe or glacier snout.
longwave radiation emitted by the earth, including its atmosphere.
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 consolidationtime-dependent compression resulting from thawing of frozen ground and subsequent draining of excess water.
thaw consolidation ratioa 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 holevertical hole in floating ice formed when a puddle melts through to the underlying water.
thaw penetrationthe downward movement of the thawing front during thawing of frozen ground.
thaw settlementcompression of the ground due to thaw consolidation.
thaw sinka closed thaw basin with subterranean drainage.
thaw slumpinga slope failure mechanism characterized by the melting of ground ice, and downslope sliding and flowing of the resulting debris.
thaw strainthe amount that frozen ground compresses upon thawing.
thaw unconformitya boundary sometimes identified in perennially frozen ground, representing the base of a relict active layer, as well as the corresponding earlier permafrost table.
thaw weakeningthe 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 permafrostperennially 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 permafrostperennially frozen ground which, upon thawing, will not experience either significant thaw settlement or loss of strength.
thawed groundpreviously 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 frontthe advancing boundary between thawed ground and frozen ground.
thawing indexthe cumulative number of degree-days above 0 degrees Celsius for a given time period.
theodolitean optical instrument used to visually track a radiosonde balloon and determine its bearing and elevation while in flight.
thermal conductivitythe quantity of heat that will flow through a unit area of a substance in unit time under a unit temperature gradient.
thermal diffusivitythe ratio of the thermal conductivity to the volumetric heat capacity.
thermal erosionthe erosion of ice-bearing permafrost by the combined thermal and mechanical action of moving water.
thermal expansion (or contraction) coefficientthe volume change per unit volume of a substance due to a one degree change in its temperature.
thermal pilea 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 groundthe properties of the ground governing the flow of heat through it, and its freezing and thawing conditions.
thermal regime of the grounda general term encompassing the temperature distribution and heat flows in the ground and their time-dependence.
thermal talika 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 cracka tensile fracture resulting from thermal stresses in frozen ground.
thermal-contraction-crack iceice formed in thermal contraction cracks in the ground.
thermo-erosional cirquethe usually steep, horseshoe-shaped headwall of a retrogressive thaw slump.
thermo-erosional nichea recess at the base of a river bank or coastal bluff, produced by thermal erosion of ice-bonded permafrost.
thermodynamic equilibrium thicknessthe 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.
thermodynamicsstudy 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.
thermographan 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 lakea lake occupying a closed depression formed by settlement of the ground following thawing of ice-rich permafrost or the melting of massive ice.
a hummock remaining after melting of the ice wedges surrounding an ice-wedge polygon.
thermokarst terrainthe often irregular topography resulting from the melting of excess ground ice and subsequent thaw settlement.
thermometeran 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.
thomson crystala large ice crystal found in deep, stagnant water-filled cavities of a glacier.
thufurperennial hummocks formed in either the active layer in permafrost areas, or in the seasonally frozen ground in non-permafrost areas, during freezing of the ground.
the fissure at the line of junction between an immovable icefoot or ice wall and fast ice, the latter being subject to the rise and fall of the tide.
tidewater glaciermountain glacier that terminates in the ocean.
(1) in mountainous regions, the line above which climatic conditions do not allow the upright growth of trees (2) the poleward limit of tree growth, also known as the tree line.
tonguea projection of the ice edge up to several km in length caused by wind and current; usually forms when a valley glacier moves very quickly into a lake or ocean.
total annual freezing indexthe cumulative number of degree-days, calculated by adding all the negative mean daily air temperatures (degrees Celsius) for a specific station during a calendar year.
total annual thawing indexthe cumulative number of degree-days, calculated by adding all the positive mean daily air temperatures (degrees Celsius) for a specific station during a calendar year.
total water content (of frozen ground)the total amount of water (unfrozen water plus ice) contained in soil or rock.
transient talika layer or body of unfrozen ground (in a permafrost area) that is gradually being eliminated by freezing.
tributary glaciera small glacier that flows into a larger glacier.
Tropic of Cancerthe northern parallel of maximum solar declination, approximately 23° 27′ N latitude; the farthest northern latitude at which the sun can appear directly overhead, which occurs on the day of the summer solstice.
Tropic of Capricornthe southern parallel of maximum solar declination, approximately 23° 27′ S latitude; the farthest southern latitude at which the sun can appear directly overhead, which occurs on the day of the summer solstice.
tropopausethe boundary layer between the troposphere and stratosphere, where an abrupt change in temperature lapse rate usually occurs; it is defined as the lowest level at which the lapse rate decreases to 2 degrees Celsius per kilometer or less, provided that the average lapse rate between this level and all higher levels within 2 kilometers does not exceed 2 degrees Celsius per kilometer; occasionally, a second tropopause may be found if the lapse rate above the first tropopause exceeds 3 degrees Celsius per kilometer.
lower part of the atmosphere, extending from the surface up to a height varying from about 7 to 9 kilometers (4.3 to 5.6 miles) at polar regions to approximately 17 kilometers (10.6 miles) in tropics; characterized by decreasing temperature with height, appreciable vertical wind motion, appreciable water vapor content, and weather.
in meteorology, an elongated area of relatively low atmospheric pressure; the opposite of a ridge.
treeless terrain, with a continuous cover of vegetation, found at both high latitudes and high altitudes.
turbic cryosola mineral soil showing marked evidence of cryoturbation, as indicated by broken horizons and displaced material.
turf hummocka hummock consisting of vegetation and organic matter with or without a core of mineral soil or stones.
turf-banked (solifluction) lobea solifluction lobe with its front covered by a vegetation mat.
turf-banked (solifluction) terracea solifluction terrace with its front covered by a vegetation mat.
two-layer permafrostground in which two layers of permafrost are separated by a layer of unfrozen ground.
two-phase thermosyphona passive heat transfer device, filled with a temperature-dependent liquid/vapour combination, installed to remove heat from the ground.
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