The scheme of the structure and texture of a hummock is shown in figure 96, according to 

 Burke. In every hummock, he distinguishes a core, ropak, and podsovy. 



In the very formation, the ice in the middle part of the hummock is subjected, according to 

 Burke, to the greatest jamming from the sides, and also from the top (the weight of the blocks) and 

 from below (Archimedes' forces). As a result, the middle part, after freezing under pressure, is 

 transformed into an ice block with a relatively rounded form which sometimes reaches large dimen- 

 sions. Such rounded ice blocks were noted among other types in the period of thawing, when the 

 weaker parts of the ice hummock had already disintegrated. According to the White Sea terminol- 

 ogy, the over water parts of the hummocks are called ropaki but the underwater parts of the hum- 

 mock are called podsovy. 



According to the observations of the Zarya, which were already mentioned, the angle flow for 

 the hummocks from a complete break-up is about 20° to 30°. The average angle of slope of the 

 hummock measured on 24 March 1939 at the time of the drift of the Sedou, was about 20° . 



We may assume how Makarov did this; at the beginning, the over- and under-water ice parts 

 of the hummock represent isosceles prisms with a characteristic angle of flow for a given hummock 

 which is equal both for the under-water and above-water parts of the hummock. The weight of the 

 prism of the over-ice part of such a hummock is equal to 



P = ^ khabbi = kh^bS^ctg a, (i) 



where P = the weight of the prism, 



h = the height of the hummock, 



a = the width of the hummock, 



b = the length of the prism, 



k = the volume of the prism, filled with ice, or the coefficient of filling 

 of the hummock, 



a = the angle of slope, 



6^ = the ice density. 



This weight for the balance must be equal to the floatage of the corresponding prism of the 

 under-ice part of the ice hummock, with the same angle of slope; in other words, the identity must 

 exist 



P = kbK h^ ctg a = fcft {K — Si) z2 ctg a. 



This identity was obtained on the assvunption that in the under-ice part of the hummock, the 

 same part of its volume was filled by the ice as the over-ice part. Reducing the equation we derive 



=»K 



■^. (2) 



270 



