iCE GLOSSARY 



ABLATION: (V.C.) — The disappearance of an ice or snow surface by 

 melting and/or evaporation. Some writers limit the meaning to include 

 all changes leading to the formation of vapor directly from ice, i. e., 

 sublimation; other writers apply the term in a wider sense to the com- 

 bined processes by which the surface wastes. 



ABRASION: 



(1) (II.B.) — The act or process of rubbing or wearing away, as the 

 abrasion of rock or earth by glaciers. 



(2) (II.B.) — The resulting injury or other effects of abrading; an 

 abraded place, as the abrasion left by glacial action. 



ACTIVE GLACffiR: (II.A.2.)— A glacier in motion. 



ACTIVE LAYER: (II.B.)— The zone, subject to annual freezing and 



thawing, between the surface of the ground and the permafrost. The 



depth of the active layer differs from one locality to another, ranging 



from a few inches to several feet. 

 AGE (of ice) : (I.A.3.) — The stage in the ice cycle from inception to 



dissolution. Not to be confused with Ice Age, a subdivision of geologic 



time. 



Under standard conditions fresh water freezes at 32°F., but sea water 

 freezes at various lower temperatures depending on its salinity. The 

 greater the salinity, the lower the freezing point. For sea water of average 

 salinity (about 35 parts per thousand) the freezing point is 29°F. Ice 

 forms first in shallow water near the coast or over shoals and banks, par- 

 ticularly in bays, inlets, and straits in which there is no current; also in 

 regions with reduced salinity, such as those near the mouths of rivers. It 

 spreads from these areas as centers. Such ice, broken up and carried sea- 

 ward by winds or currents, facilitates ice formation in "deeper water. Ice 

 not melted during the previous season also acts in the same way. Wave 

 action ordinarily hinders the formation of ice to some extent by mixing 

 the waters of the upper layers. The presence of old ice damps out waves or 

 swell and at the same time tends to assist the beginning of the freezing 

 process by cooling the water. 



The first sign of freezing is an oily or opaque appearance of the water 

 caused by the formation of ice spicules and ice crystals in the form of 

 thin plates about one-third of an inch across. These consist of fresh ice 

 free from salt and increase in number until the sea is covered by slush of 

 a thick, soupy consistency. Slush does not have any degree of hardness. 

 It causes the sea surface to have a grayish or leaden color and causes the 

 wind ripples to disappear. Slush generally does not exceed a thickness of 

 12 inches. 



Ice crust is the next stage of development. It is generallv transparent, 

 has some degree of hardness, and is frequently rubbery. Newly-formed ice 



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