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finger rafting

a process by which currents or winds push around thin ice so they slide over each other.
Nilas showing finger rafting. (Photo courtesy of Antarctic Sea-Ice Processes and Climate (ASPeCt).)
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firn

rounded, well-bonded snow that is older than one year; firn has a density greater than 550 kilograms per cubic-meter (35 pounds per cubic-foot); called névé during the first year.
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firn limit

the minimum elevation of firn lying on a glacier surface; each year's firn line marks a glacier's annual equilibrium line; also called firn line.
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firn line

the minimum elevation of firn lying on a glacier surface; each year's firn line marks a glacier's annual equilibrium line; also called firn limit.
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firn water table

the height of meltwater within saturated firn that is trapped over ice in a glacier.
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firnspiegel

a thin sheet of ice formed on the glacier surface by rapid refreezing of solar-heated snow or firn, usually at high elevations during spring.
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first-year ice

floating ice of no more than one year's growth developing from young ice; thickness from 0.3 to 2 meters (1 to 6.6 feet); characteristically level where undisturbed by pressure, but where ridges occur, they are rough and sharply angular.
(Photo courtesy of Ted Maksym, United States Naval Academy.)
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fjord

glacial troughs that fill with sea water.
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flaw lead

a navigable passage between pack ice and fast ice.
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floating ice

any form of ice found floating in water.

floe

separate patch of floating ice or flat sheet of unbroken pack ice, greater than 20 meters (22 yards) across.

flooded sea ice

ice that is pushed into the underlying ocean water by the weight of thick snow cover on its surface; the salty ocean water floods the snow cover and creates a salty, slushy layer; flooded sea ice is more common in the antarctic because of more snowfall and thinner sea ice than in the arctic.
(Photo courtesy of Ted Maksym, Unites States Naval Academy.)
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flow finger

a small percolation channel that is a beginning path for surface meltwater through snow or firn.
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fluted berg

an iceberg that is grooved into a curtain-like pattern; thought to be carved by small meltwater streams.

foehn

a warm wind blowing down an incline; a kind of katabatic wind.

fog

a hydrometeor consisting of a visible aggregate of minute water droplets (or ice crystals), suspended in the atmosphere near the earth's surface; according to international definition, fog reduces visibility below one kilometer, fog differs from cloud only in that the base of fog is at the earth's surface while clouds are above the surface; when composed of ice crystals, it is termed ice fog.

foliation

layering in glacier ice that has distinctive crystal sizes and/or bubbles; foliation is usually caused by stress and deformation that a glacier experiences as it flows over complex terrain, but can also originate as a sedimentary feature.
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forbes bands

alternate bands of light and dark on a glacier; usually found below steep narrow icefalls and thought to be the result of different flow and ablation rates between summer and winter.
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forel stripes

shallow, parallel grooves on the face of a large melting ice crystal.
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foundation pile

structure used when the soil near the ground surface is not strong and the weight of the building must be carried by deeper soil layers.

fragmic cryogenic fabric

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which soil particles form discrete units that are densely packed.

fragmoidal cryogenic fabric

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which soil particles form discrete units that are coalescing.

Fram Strait

a sea channel connecting the Arctic Ocean and the Nordic Seas, running between Greenland and Spitsbergen. Fram Strait is the passageway where most drifting sea ice exits the Arctic.

frazil

small needle-like ice crystals, typically 3 to 4 millimeters in diameter, suspended in water, that represent the first stages of sea ice growth; they merge under calm conditions to form thin sheets of ice on the surface, frazil crystals consist of nearly pure fresh water.
Frazil crystals. (Photo courtesy of Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory.)
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frazil ice

fine spicules or plates of ice in suspension in water.
Frazil crystals. (Photo courtesy of Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory.)
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free water

free water is that portion of the pore water that is free to move between interconnected pores under the influence of gravity.
Free water at the base of Dirt Glacier, British Columbia, in 1904. (Photo courtesy of C.W. Wright. Archived at the World Data Center for Glaciology, Boulder, CO.)

freeze-thaw cycle

freezing of a material followed by thawing.

freezeback

refreezing of thawed materials.

freezing (of ground)

the changing of phase from water to ice in soil or rock.

freezing degree-days

a measure of how cold it has been and how long it has been cold; the cumulative fdd is usually calculated as a sum of average daily degrees below freezing for a specified time period (10 days, month, season, etc.).

freezing drizzle

drizzle, the drops of which freeze on impact with the ground or with objects on the earth's surface or with aircraft in flight.

freezing front

the advancing boundary between frozen (or partially frozen) ground and unfrozen ground.

freezing index

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

freezing point

(1) the temperature at which a pure liquid solidifies under atmospheric pressure (2) the temperature at which a ground material starts to freeze.

freezing pressure

the positive pressure developed at ice-water interfaces in soil as it freezes.

freezing rain

rain, the drops of which freeze on impact with the ground or with objects on the earth's surface or with aircraft in flight.

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