Substituting this in formula (1) we get 



Regarding on the average, that 6 = 1.02 and 6^= .90, and assuming that the above- and 

 under-ice parts of the ice hummock represent heaps of blocks of ice with voids between them, 

 because of which the density of the ice hummock is half the density of the level ice, in other words, 

 assuming that the coefficient of filling is fc = 0. 5, we get from formula (3) 



'+TT'' 1.02-0.90^ '+2''- 



It is clear that if the ridges of the ice hummocks will touch one another, as is shown in 

 figure 102, the average thickness will be equal to 



<:7// VSoy V->^?^/ VJPHT \i^ol \o^:^r4 



Figure 102. An isostatically balanced hummock field. 



If the hummocking of the ice field is evaluated, as this is assumed by Gordienko, according 

 to the 10 Mark system, then formula (4) takes on the appearance of 



/ = / + ^2/z, (5) 



where iV = the number of marks of hummocks. 



In formula (5) we can regard i as the thickness of the level ice, as the thickness of the ice 

 accumulations reckoned with sufficient accuracy according to the degree days of frost, charac- 

 teristic for a given region. Almost with the same accuracy we can appraise the magnitude of the 

 summer melting for the given region. 



Whatever has to do with the marks of the heaping and the average height of the hummocks, 

 can be determined best of all by ice-air reconnaissance and also by sleigh excursions. 



Gordeev notes the following curious fact: in autumn 1937 at the time of the drift of the 

 fleet Sadko the area of the ice of fall formation in a radius of 1 km around the ships was photo- 

 graphed in plan. For six months of the drift, this area contracted more than two times due to the 

 hummocking, which occurred chiefly during the drift of the ice to the east. The average height of 

 the hummocks was about 3 m, and the greatest about 6.5 m over the level of the sea. 



284 



