Extremely characteristic are the wave-formed alluviums which are formed on the flat ice 

 fields as a result of the affecting wind. These alluviums are made transversely and longitudinally. 

 Transverse deposits are formed in the case of great masses of snow and remind one of the Helm- 

 holtz waves. Longitudinal deposits are formed with powerful winds and small quantities of snow 

 appear as their characteristic form. 



Padalka Informed me that at the time of the flights over the region of Franz Joseph Land 

 north at the end of March and at the beginning of April, all the snow deposited by wind was stretched 

 out from southeast to northwest. This could be caused by the evidently predominant southeast 

 winds and besides that by the absence of rotations of the individual ice fields. In the region between 

 Franz Joseph Land, the wind-deposited snow was stretched out only in two directions, from the 

 south to the north, from east to west. In the region to the north of Novaya Zemlya, no such cor- 

 rectness relative to the location of the wind-deposited snow was noted. 



Snow cover on ice shows a great influence on the growth of ice. It has already been observed 

 that according to the observations at the Northern Duina River in the winter of 1941-42 the ice with 

 the surface clear of ice was at the end of winter 1-1/2 times thicker than the ice which was formed 

 under the natural snow cover (thickness of 30 to 40 cm). 



But, large masses of snow usually crush ice down to where water protrudes from beneath the 

 base layer of ice. Mixing with this water, snow is transformed into ice, and in such a way, the 

 general thickness of the ice increases (see also Section 85). 



During the summertime, masses of snow which have collected on ice fields melt, and are the 

 basic source of formation of snow puddles (snezhnitsa) and melt water lakes on them. 



LITERATURE: 25, 77, 88, 107. 



Section 103. Isostatic Phenomena 



Ice formation in the sea, which has already been discussed, proceeds calmly and propor- 

 tionally only under exceptional circumstances. Falling deposits are not proportionally distributed 

 along the surface of the ice. In connection with this, the accretion of the ice from below does not 

 proceed proportionally. Hummocking contributes the greatest transgressions to smoothness in the 

 process of ice formation. 



Let us assume that at a certain moment a previously flat ice field was broken as a result of 

 hummocking blocks of ice packed over and under the ice. If the floatage of the blocks packed under 

 the ice exactly counterbalances the weight of the blocks of ice which have been piled on the ice, no 

 changes in the ice adjacent to the hummock are produced. If the weight of the above-ice part of the 

 hummock shows more floatage than its under-ice part, the adjacent ice will sag downwards; if it is 

 less, it will protrude upwards . 



An interesting phenomenon exists in connection with this, which is called "isostasy" by the 

 geologists, the question of which has been theoretically treated by Pratt and Airy for the crust of 

 the earth. 



Let the transverse section of the ice field be represented in figure 99 and let the upper and 

 lower surfaces be dissected and let the densities along the vertical be unequal. The line mn repre- 

 sents the water line (level of the sea) . Let us construct such a line on our section which would 

 correspond to the water line of any vertical column cut out from the given ice field. If it would be 



276 



