With the course of time, the ice of the hummocks can be transformed into a more or less 

 level ice field by the action of the different order of balancing factors. Such, for example, appeared, 

 according to observations of Soviet airplanes in the circumpolar region. But generally, especially 

 in the periphery of the Arctic Basin and in the bordering seas, hummocks, a characteristic trait of 

 the ice landscape. 



I make the following assumptions for judging the average thickness of sea ices: 



1. Ice fields are isostatically balanced at every point. 



2. Hummocks are extended by bridges, whose transverse cut represents an isosceles 

 triangle . 



3. Blocks of ice comprising the above-ice and under-ice parts of the ice hummock are located 

 in such a way that they comprise that same part of their volume which is occupied by these parts. 



In other words, if the volumes of the above ice and under ice parts of the ice hummock are corre- 

 spondingly equal to Uj. and y then the volumes, being occupied by ice in these parts, are corre- 

 spondingly equal to kuh and fcy where h is the coefficient of filling of the ice hummock. A cut of 

 an even ice field with an ice hummock included in it is represented in figure 101. 



Figure 101. Above and under ice parts of 

 ice hummocks in isostatically 

 balanced ice. 



It is clear that its average thickness in the limits of the hummock, that is, the thickness of 

 the ice field, the above- and under- water parts of the ice hummock will be equally distributed in a 

 layer uniform in density along the upper and lower surface of the field, will be equal to 



icp = i + ^ih + z), (1) 



where i = the thickness of the level ice, 



h = the height of the above ice part of the hummock, 

 s = the height of the under ice part of the hummock, 

 k = the volume of the ice in a unit volume of the hummock. 



But, if on each of its verticals, the hummock is isostatically balanced, the relationship exists 

 between the heights of its above water and under water parts; 



Z_ ^ Sj (2) 



h S,^ — Si ■ 



283 



