accretion ice, breaks up at the moment of complete destruction into separate long needles, which 

 represent the remnants of the crystals.* 



It is natural that the projecting parts of sea ice — the hummocks and snow hills — are the first 

 to be subjected to thawing. The intensity of heating by direct solar radiation is directly propor- 

 tionate to the sine of the angle of incidence of the sun's rays, which is why the vertical walls of ice, 

 in polar regions are heated considerably more intensively than the horizontal surfaces. For the 

 same reason, upon the first appearance of the sun over the horizon, even with very low air temper- 

 atures, ice stalactites and icicles appear on the heapings which face toward the south and hang out 

 over the level ice. 



Under polar conditions, as we have seen, the diffused solar radiation has particular impor- 

 tance. The surface area of heaped ice accumulations, subject to the Influence of solar radiation, is 

 considerably larger than the area which these heapings occupy on the level ice. Thus the diffused 

 radiation also destroys the heaped-up masses in considerably greater degree than the level ice. 



Destruction of the heaped accumulations is greatly Increased by winds. With warm winds 

 condensation occurs accompanied by a discharge of heat; with cold winds there is evaporation of the 

 ice. In addition, the wind continually packs the snow by its pressure. 



All these factors are most destructive to the steeply projecting slopes and gradually the angu- 

 lar and sharply-cut form of the hummocked or heaped-up fields disappears and is replaced by the 

 smooth outlines of hills and ridges. 



Thus, with the passage of time, the upper surface of even those fields, which were extremely 

 hummocked in the beginning, commence to resemble more and more the form of sand dunes or 

 "sheep foreheads" - geological forms created as the result of movement of glaciers. Such forms, 

 of course, have their sloping side to the south and steep side to the north. 



According to Sedov observations, we may conclude that if the level ice thawed to the extent 

 of 50 to 70 cm from the top during the summer of 1939, the hummocks decreased in height by 2 to 

 3 m. 



LITERATURE: 62, 77, 88, 104, 107. 



Section 110. Snow Puddles and Lakes on Top of Ice 



Simultaneously with the settling of the hummocks and snow on the ice surface, the first dark 

 patches appear in the low places of the ice fields. These dark patches, consisting of snow saturated 

 with water, are the initial forms of the snow puddles and over-ice ponds and lakes which are formed 

 by thaw water flowing off into these low places from the surface of the nearby hummocks. ** 



*The falling apart into individual crystals in the thawing process is particularly characteristic 

 of nilas ice (frozen sludge), which has not been subjected to hummocking. Ice which has undergone 

 hummocking formation during its period of existence usually maintains the form of hard ice globules 

 right to its final disappearance. 



**In the majority of cases the ice fields consist of ice floes frozen together. These ice floes, 

 due to their continual bumpings and rotations, usually have a rounded form and are bordered with 

 small hummocks. For this reason, the low spots on the ice fields are the central parts of the ice 

 floes which have fused to form a field. 



300 



