SEA ICE SHELF: (LA.) — Sea ice floating in the area of its formation 

 and separated from fast ice, of which it may have been a part, by a 

 tide crack or a family of such cracks. 



SEA SMOKE: (V.B.)— Frost smoke. 



SERAC: (II.B.) — A sharp ridge or pinnacle of ice among the crevasses 

 of a glacier. 



SHEAR CRACK: (I.C.l.a. or II.B.) — A crack in sea ice or glacier ice 

 caused by two different forces acting tangentially and simultaneously 

 on adjacent areas. The sheared parts undergo a displacement parallel 

 to the plane of the crack. 



SHEET ICE: (I., III., or V.)— Ice formed in a relatively thin, smooth 

 layer over a water surface. This term should not be confused with ice 

 sheet, a continuous layer of ice covering a large land area. 



SHELF ICE: (II.A.4.a.) — A thick ice formation with level surface ex- 

 tending seaward from the land but attached thereto. Shelf ice may be 

 formed in three ways: (1) By an extension of land ice onto water, (2) 

 by the accumulation of snow upon sea ice which has persisted for sev- 

 eral seasons, and (3) by a combination of (1) and (2), resulting in 

 areas of land ice extending onto the water interspersed with areas of 

 persistent sea ice covered with accumulations of snow. 



The chief characteristics of shelf ice are: (1) A shape conforming 

 to the boundaries of the coast, (2) a seaward edge usually floating freely 

 in deep water, (3) vertical cliffs up to 150 feet high on the seaward edge, 

 and (4) prominent horizontal banding and clean-cut joint faces from 

 which tabular icebergs are calved periodically. See land ice. (Figs. 

 78, 84.) 



SHOCK CRACK: (I.C.l.a.)— Concussion crack. 



SHORE CLEARING: ( I. C. lb.)— Shore lead. 



SHORE ICE: (I.B.l.b.) — Ice that has been cast onto the shore or beached 

 as a result of the action of wind, waves, current, tide, or the force of an 

 adjacent ice area. Such action may cause the shore ice to be rafted or 

 heaped or may form ice boulders. See fast ice. (Figs. 55, 56.) 



SHORE ICE BELT: (I.B.l.a.)— Ice foot. 



SHORE LEAD: (I.C.l.b.) — A lead between floating ice and the shore or 

 between floating ice and fast ice (Frontispiece) . 



SIKUSSAK: (I.A.3.e.) — Very old sea ice trapped in fiords. Sikussak 

 resembles glacier ice since snowfall and snowdrifts contribute to its 

 formation. 



SINKING: (V.B.) — An optical phenomenon, the opposite of looming, 

 in which an object on or slightly above the geometrical horizon apparent- 

 ly sinks below it. Cf. looming. 



SIZE (of floating ice) : (I.A.2.) — The linear extent of individual frag- 

 ments of ice. In general, ice fragments are angular or circular. The 



9559340—52—6. 



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