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icing glade

an area kept clear of trees and shrubs by the annual occurrence of icings.

icing mound

a seasonal frost mound consisting exclusively of thinly layered ice, formed by freezing of successive flows of water issuing from the ground or from below river ice.

inactive ice wedge

an ice wedge that is no longer growing.

inactive rock glacier

a mass of rock fragments and finer material, on a slope, that contains either an ice core or interstitial ice, and shows evidence of past, but not present, movement.

infrared radiation

electromagnetic radiation of wavelengths between approximately 0.75 and 1000 millimeters; see also atmospheric radiation, terrestrial radiation, longwave radiation.

inland ice sheet

an ice sheet of considerable thickness and an area of more than about 50,000 square kilometers (12.4 million acres), resting on rock; inland ice sheets near sea level may merge into ice shelves.


(1) exposure of an object to the sun (2) intensity of incoming solar radiation incident on a unit horizontal surface at a specific level.

instrument shelter

structure to protect certain instruments from insolation and weather while at the same time ensuring sufficient ventilation.

interfacial water

water that forms transition layers at mineral/water and mineral/water/ice interfaces in frozen ground.

intermediate discontinuous permafrost

(1) (North American usage) permafrost underlying 35 - 65% of the area of exposed land surface (2) (Russian usage) permafrost underlying 40 - 60% of the area of exposed land surface.

internal ice stress

a measure of the compactness, or strength of the ice; plays an important role in the deformation of the ice and formation of features such as ridges and leads.

interstitial ice

ice formed in narrow spaces between small rocks and sediment in soil.

intrapermafrost water

water occurring in unfrozen zones (taliks and cryopegs) within permafrost.

intrusive ice

ice formed from water injected into soils or rocks.


in meteorology, a departure from the usual (normal) decrease or increase with altitude of the value of an atmospheric property; also, the layer through which this departure occurs (the inversion layer); this term almost always refers to a temperature inversion.

isoband cryogenic fabric

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which soil particles form subhorizontal layers of similar thickness.


a line of equal or constant pressure; it most often refers to a line drawn through all points of equal atmospheric pressure.


a line drawn through geographical points recording equal amounts of precipitation during a specific period.

isolated cryopeg

a body of unfrozen ground, that is perennially cryotic (T < 0 degrees Celsius) and entirely surrounded by perennially frozen ground.

isolated patches of permafrost

permafrost underlying less than 10% of the exposed land surface.

isolated talik

a layer or body of unfrozen ground entirely surrounded by perennially frozen ground.

isostatic rebound

Isostatic rebound (also called continental rebound, post-glacial rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age



a line of equal or constant temperature.

jet stream

relatively strong winds concentrated within a narrow stream in the atmosphere; generally refers to a quasi-horizontal jet stream of maximum winds embedded in the midlatitude westerlies, and concentrated in the high troposphere.


(1) a large outburst flood that usually occurs when a glacially dammed lake drains catastrophically (2) any catastrophic release of water from a glacier.

katabatic wind

any wind blowing down an incline; if the wind is warm, it is called a foehn or chinook; if cold, it may be a fall wind (bora), or a gravity wind (mountain wind); the opposite of anabatic wind.


the part of a ridge below the ocean surface; wind, ocean currents, and other forces can push sea ice into piles that rise and form small mountains below the level sea ice surface.

kinetic-growth metamorphism

snow metamorphism that builds angular facets on crystals and makes cup and scroll shaped crystals.


a general term for all types of coarse clastic formations on slopes of 2-3 to 40 degrees, moving downslope mainly due to creep.

lake ice

floating ice formed in lakes.

lake talik

a layer or body of unfrozen ground occupying a depression in the permafrost table beneath a lake.


thin plate, sheet or layer; laminae (plural).

land sky

the relatively dark appearance of the underside of a cloud layer when it is over land that is not snow covered; this term is used largely in polar regions with reference to the sky map; land sky is brighter than water sky, but is much darker than ice blink or snow blink.

lapse rate

the rate of change of any meteorological element with height.

large-scale atmospheric processes

atmospheric processes with a representative scale (large-scale) of 10,000 kilometers (6,200 miles); in meteorology, it is a scale in which the curve of the earth is not negligible; the large-scale atmospheric flows are essentially nearly hydrostatic, nearly geostrophic and wave-like in appearance; they exist mainly in response to the latitudinal differences in radiative heating, to the particular value of the coriolis force and to the spatial distribution of the oceans and continents.

latent heat of fusion

the amount of heat required to cause a change of phase from solid to liquid, or the heat released when the phase change is from liquid to solid; in the case of melting snow, the phase change from ice to water requires a significant amount of heat—160 times that required to raise the temperature of the same amount of ice by just 1 degree Celsius; until the required amount of heat is supplied to completely melt all of the ice being considered, no further increase in temperature will occur.