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outlet glacier

a valley glacier which drains an inland ice sheet or ice cap and flows through a gap in peripheral mountains.


a nearly colorless (but faintly blue) gaseous form of oxygen, with a characteristic odor like chlorine; has a formula of O3 and a molecular weight of 48; found in trace quantities in the earth's atmosphere at all times, primarily in the stratosphere between heights of about 10 to 50 kilometers (6 to 31 miles; the ozonosphere or ozone shield) where its production results from photochemical processes involving ultraviolet radiation; its maximum concentration occurs between 20 to 25 kilometers (12 to 16 miles); in the lower atmosphere, ozone is commonly formed as a product of electrical discharges through the air.

ozone shield

stratospheric ozone layer, giving protection to the earth's surface due to intense absorption of harmful solar ultraviolet radiation by the gas.


stratospheric ozone layer, giving protection to the earth's surface due to intense absorption of harmful solar ultraviolet radiation by the gas.

pack ice

ice that is not attached to the shoreline and drifts in response to winds, currents, and other forces; some prefer the generic term drift ice, and reserve pack ice to mean drift ice that is closely packed.


a peaty permafrost mound possessing a core of alternating layers of segregated ice and peat or mineral soil material.

palsa bog

a poorly-drained lowland underlain by organic-rich sediments, which contains perennially frozen peat bodies (peat plateaux) and, occasionally, palsas.

pancake ice

pieces of new ice approximately circular, up to 10 centimeters (4 inches) thick and 0.03 to 3 meters (0.1 to 9.8 feet) in diameter, with raised edges that form from rubbing against each other; formed from the freezing together of grease ice, slush or shuga, or the reaking up of ice rind or nilas.
(Photo courtesy of the National Oceanic and Atmospheric Administration/Department of Commerce.)


(1) a term used loosely by many meteorologists for almost any meteorological quantity or element (2) an arbitrary constant or variable appearing in a mathematical expression; changing it can give various outcomes for the phenomena represented.

partial pressure

in a mixture of gases, each gas has a partial pressure, which is the pressure the gas would have if it occupied that volume alone.

partially-bonded permafrost

ice-bearing permafrost in which some of the soil particles are not held together by ice.

passive construction methods in permafrost

special design and construction methods used for engineering works in permafrost areas where preservation of the frozen condition is feasible.

passive single-phase thermal pile

a foundation pile provided with a single-phase natural convection cooling system to remove heat from the ground.

passive two-phase thermal pile

a foundation pile provided with a two-phase natural convection cooling system to remove heat from the ground.

past weather

predominant characteristic of the weather which had existed at an observing station during a given period of time (during the preceding hour or six hours), specified in the international synop code.


a collection of pack ice, less than 10 kilometers (6.2 miles) across, whose limits can be seen from the masthead.

patterned ground

a general term for any ground surface exhibiting a discernibly ordered, more or less symmetrical, morphological pattern of ground and, where present, vegetation.
A photograph taken from the air reveals patterned ground surrounding thaw lakes in Alaska’s Arctic National Wildlife Refuge. —Credit: U.S. Fish and Wildlife Service


a deposit consisting of decayed or partially decayed humified plant remains.

peat hummock

a hummock consisting of peat.

peat plateau

a generally flat-topped expanse of peat, elevated above the general surface of a peatland, and containing segregated ice that may or may not extend downward into the underlying mineral soil.


peat-covered terrain.


the extreme relief of ablation hollows found most often at high altitudes in the tropics; the resulting spikes of snow resemble repentant souls.


a layer of frozen ground which forms as part of the seasonally frozen ground (in areas free of permafrost or with a lowered permafrost table); remains frozen throughout one or several summers, and then thaws.

perennial snow

snow that persists on the ground year after year.


the conditions, processes and landforms associated with cold, nonglacial environments.

periglacial phenomena

landforms and soil characteristics produced by periglacial processes.

periglacial processes

processes associated with frost action in cold, nonglacial environments.


an artificial mixture of frozen soil materials cemented by pore ice, which forms a concrete-like construction material used in cold regions.


layer of soil or rock, at some depth beneath the surface, in which the temperature has been continuously below 0°C for at least several years; it exists where summer heating fails to reach the base of the layer of frozen ground.

permafrost aggradation

a naturally or artificially caused increase in the thickness and/or areal extent of permafrost.

permafrost base

the lower boundary surface of permafrost, above which temperatures are perennially below 0 degrees Celsius (cryotic) and below which temperatures are perennially above 0 degrees Celsius (noncryotic).

permafrost boundary

(1) the geographical boundary between the continuous and discontinuous permafrost zones (2) the margin of a discrete body of permafrost.

permafrost degradation

a naturally or artificially caused decrease in the thickness and/or areal extent of permafrost.

permafrost extent

the total geographic area containing some amount of permafrost; typically reported in square kilometers.

permafrost limit

outermost (latitudinal) or lowest (altitudinal) limit of the occurrence of permafrost.

permafrost region

a region in which the temperature of some or all of the ground below the seasonally freezing and thawing layer remains continuously at or below 0 degrees Celsius for at least two consecutive years.