National Snow and Ice Data Center

dry permafrost

permafrost containing neither free water nor ice.

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dump moraine

a mound or layer of moraine formed along the edge of a glacier by rock that falls off the ice; sometimes called a ground moraine.

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dynamic modulus of elasticity

the ratio of stress to strain for a material under dynamic loading conditions.

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dynamic Poisson's ratio

the absolute value of the ratio between the linear strain changes, perpendicular to and in the direction of a given uniaxial stress change, respectively, under dynamic loading conditions.

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earth hummock

a hummock having a core of silty and clayey mineral soil which may show evidence of cryoturbation.

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earth radiation

the total infrared radiation emitted from the earth's surface; to be carefully distinguished from effective terrestrial radiation, atmospheric radiation, and insolation.

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edge wasting

process by which warm water erodes iceberg above the waterline

effective terrestrial radiation

the difference between the outgoing infrared (longwave) terrestrial radiation of the earth's surface and the downward infrared counter-radiation from the atmosphere.

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electrical conductivity

the inverse of electrical resistivity.

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electrical properties of frozen ground

the dielectric constant (or relative permitivity), electrical conductivity and electrical resistivity are the major electrical properties governing the flow of electric current through frozen ground.

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electricity resistivity

the property of a material that determines the electrical current flowing through a centimetre cube of the material when an electrical potential is applied to opposite faces of the cube.

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electromagnetic wave

an oscillation of the electric or magnetic field associated with the propagation of energy; characterized by their wavelengths and amplitude; propagate at the speed of light.

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emissivity

the amount of electromagnetic energy (primarily at wavelengths longer than 1.0 micrometer) that an object emits; for example, the earth emits longwave radiation primarily in the infrared part of the electromagnetic spectrum, but also in longer microwave wavelengths; the emissivity of an object varies as the fourth power of its absolute temperature.

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end moraine

an arch-shaped ridge of moraine found near the end of a glacier.

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epigenetic ice

ground ice developed in epigenetic permafrost, or in previously formed syngenetic permafrost.

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epigenetic ice wedge

an ice wedge developed in epigenetic permafrost, or in previously formed syngenetic permafrost.

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epigenetic permafrost

permafrost that formed through lowering of the permafrost base in previously deposited sediment or other earth material.

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equator

the line of latitude 0°, which is equidistant from the poles, and which separates the Northern Hemisphere from the Southern Hemisphere.

equi-temperature metamorphism

snow metamorphism that occurs under relatively consistent temperature conditions.

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snow

equilibrium line

boundary between the accumulation area and ablation area where the mass balance is zero.

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snow

equilibrium metamorphism

snow metamorphism that occurs when there are large differences in convex and concave portions of a crystal.

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snow

equilibrium permafrost

permafrost that is in thermal equilibrium with the existing mean annual surface or sea-bottom temperature and with the geothermal heat flux.

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equilibrium zone

zone of a glacier in which the amount of precipitation that falls is equal to the amount that melts the following summer.

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equinox

either of the two points of intersection of the sun's apparent annual path and the plane of the earth's equator; in the northern hemisphere the spring (vernal) equinox falls on or about 21 March, and the autumnal equinox on or about 22 September.

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error

the difference between a measured value of a quantity and its true value; different types of errors are inherent to observations.

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esker

a sinuous ridge of sedimentary material (typically gravel or sand) deposited by streams that cut channels under or through the glacier ice.

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evaporation

the physical process by which a liquid or solid substance is transformed to the gaseous state; the opposite of condensation; in meteorology, evaporation usually is restricted in use to the change of water from liquid to gas, while sublimation is used to the change from solid to gas as well as from gas to solid.

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evaporation fog

fog formed as a result of evaporation of water that is warmer than the air.

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excess ice

the volume of ice in the ground which exceeds the total pore volume that the ground would have under natural unfrozen conditions.

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extending flow

when glacier motion is accelerating down-slope.

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extensive discontinuous permafrost

(1) (North American usage) permafrost underlying 65 - 90% of the area of exposed land surface (2) (Russian usage) permafrost underlying 70 - 80% of the area of exposed land surface.

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fabric

soil micromorphology.

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fall wind

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

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false ogives

bands of light and dark on a glacier that were formed by rock avalanching.

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