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Net loss of snow or ice by melting, sublimation, evaporation, or wind action during a specific period of time. The opposite of accumulation.

Net gain of snow or ice during a specific period of time. The opposite of ablation.

Active layer--
(annually thawed layer) Layer of ground that thaws in the summer and freezes again in the winter (equivalent to seasonally frozen ground).

Boat-like sled used for pulling squad equipment over snow.

Period of spring thaw during which the ground surface is excessively wet and soft, and ice is disappearing from streams and lakes. Duration of the breakup period varies usually from 1 to 6 weeks depending on regional and local climatic conditions. The breakup season causes difficult movement problems.

A cold injury which causes lesions--usually on the hands--caused by prolonged or repeated exposure to mild humid cold.

Warm dry wind which raises the temperature and melts snow from the ground.

Cold injury--
An inclusive term applied to injuries resulting from cold. The most common are frostbite, trenchfoot, immersion foot, and chilblains.

An overhanging formation of snow, usually formed on a mountain ridge, at the crest of a gully and/or a steep slope.

A fissure or crevice in a rock or ice formation.

A deep crack or fissure in the ice of a glacier.

Cyclonic storms--
A storm system of winds, often violent, with abundant precipitation and a usual diameter of 80 to 14,000 km (50 to 900 miles). It is characterized by winds rotating about a calm center of low atmospheric pressures, often at speeds as high as 80 to 120 kts. These storms are called hurricanes in the West Indies. The winds rotate clockwise in the Southern Hemisphere and counter-clockwise in the Northern Hemisphere.

Disposal bags--
Heavy waterproof bags into which personnel defecate-used because it is sometimes impractical to prepare pit latrines in swampy or frozen ground.

Dry snow zone--
Zone on icecap where maximum temperatures are not high enough to cause melting.

To place or hold a ski at a different angle than that of the supporting snow.

Fall line--
The imaginary line running directly down a slope in relation to the skier. The line of gravity pull or of straight descent down which a ball of snow would roll.

Fast ice--
All types of ice, broken or unbroken, attached to the shore, beached, stranded, or attached to the bottom in shoal water.

Periods during which the ground surface freezes and ice cover forms on streams and lakes. This period varies from 1 to 3 months depending on regional and local climatic conditions. Maintaining mobility during this period becomes easier as the period progresses.

A cold injury caused by freezing of the body tissues.

Frost boil--
Accumulation of excess water and mud in subsurface materials during spring thawing. It usually weakens the surface and may break through, causing a quagmire.

(See frost table).

Frost mound--
A localized uplift of land surface caused by frost heaving or by ground water pressure. Also called earth mound, earth hummock, pals, pingo, or pingok.

Frost table--
More or less irregular surface that represents the depth of penetration of the winter frost in the seasonal frozen ground. It may or may not coincide with the permafrost table.

Fuel tablets--
Concentrated chemical fuel dispensed in tablet form for heating rations, or starting wood fires.

General lowering of body temperature due to loss of heat at a rate faster than the body can produce it.

A mixture of sand, gravel, and water poured into forms and frozen. The process is much the same as making concrete except that ice (instead of cement) forms the bonding material.

Ice fog--
A fog of suspended ice crystals usually formed with the introduction of water vapor into clear, calm air of low temperature (-37 F. or lower). Ice fog is rare at temperatures above -37 F. and almost always present at temperatures below -50 F. Ice fog may form over a body of troops, herd of animals, bivouac areas, motor parks, convoys, and gun positions during firing.

Immersion foot--
An injury resembling trenchfoot caused by prolonged immersion of the extremities in water (generally from 74 to 88 F.).

Layer principle--
Attaining additional insulation by trapping dead air in the space(s) between successive layers of clothing. Two or more thicknesses of clothing, with intervening airspace, provide greater insulation than the same thickness of clothing of the same material in a single layer.

Poorly-drained organic terrain which is characteristic of the subarctic, covered with a thick, resilient carpet of water-sodden mosses and tussocks, and underlain by a high water table, peat of variable thickness, and often permafrost.

Pack ice--
Any large accumulation of floating ice driven closely together.

A pushing movement of arms and body with the ski poles against the snow to increase momentum in the glide. Single poling is referred to when each pole is used alternately to obtain this propulsion. Double poling is the use of both poles at the same time.

Zastruga (Russian)--One of a series of long parallel snow ridges occurring on the open plains and formed by the action of winds.

Snow anvil--
See Sastruga.

Snow bridge--
The snowmass that sometimes covers the surface opening of a crevasse.

Tractor sled train (for oversnow movement)--
A train usually composed of cargo sleds and towed by track laying vehicles.

The upper limit of tree growth in mountainous regions of the northern limit of tree growth in the Arctic.

Trench foot--
A thermal injury resulting from exposure to cold, short of freezing, in a damp or wet environment.

A flat or gently rolling area with a muck to rock surface over permafrost and consisting of a low mat of grasses, shrubs, and other plants. This area is found above or north of the treeline.

A condition of visibility which exists when an overcast sky prevents shadows and snow-covered terrain reflects light at about the same intensity as the sky causing the horizon to be indistinguishable and the recognition of irregularities in terrain very difficult. Only very dark objects can be seen. Fog will sometimes create a similar condition.

A sudden violent and cold downslope wind, which is common along mountainous coastal areas in the northern latitudes. A williwaw may last several days.

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