(2) 



hi fl2 '" fin' 



In such a way with the received average proportion of the height of the above- and under-water 

 parts, which is equal to 5, under the hummock, which is raised over the surface level of the ice 

 field 1 m, the ice under the lower surface of the ice field must be theoretically submerged 5 m. 

 The greatest height of an ice column observed at the time of the drift of the station "North Pole" 

 was about 10 m. Consequently, the underwater part of this column during conditions of an isostatic 

 balance must project from under the lower surface of the ice fields 50 m. 



As we have seen, the hummocks do not usually appear isostatic . Their underwater part is 

 washed out; the above-water parts of the hummocks press on the ice fields, creating their greater 

 draught and results in formula (1). 



Thus, the time of hydrological cuts, carried out by Khmyznikov, in the fall of 1928, in the 

 Yanskom Bay and in the straits of the New Siberian Islands (Laptev, Eternikan, and Sannikov), the 

 thickness of the above- and under-water parts of the well-developed fast ice were determined, con- 

 sidering them from the level of the water, which had filled the cut. It was shown at this time that 

 the proportion of the emersion of the underwater part to the height of the above water part was 

 equal on the average to 12, with a maximum of 17 and a minimum of 7. In such a way, the fast ice 

 was shown to be significantly more submerged in the water than results from the formula. A 

 similar phenomenon was also observed on the river where the water from the cut sometimes poured 

 out along the surface of the ice. In rivers flowing to the north, such a phenomenon is usual in the 

 spring and is explained by the hydraulic pressure — the river, covered by a solid ice cover, flows 

 as in a tube. In the fast ice, this phenomenon is related to the large area of ice, and indicates an 

 overburdening of ice by an additional weight of snow. We have already seen in columns 5 and 6, 

 table 70, that in Dixon Bay, the surface of ice in February 1944 was on the average . 8 cm lower 

 than the surface of the water. 



This carving of the well- developed fast ice contributes to its breaking up in the spring and to 

 the immersion of ice fields which will be discussed later. 



In individual cases, hummocking proceeds so that more ice is packed under the ice than ought 

 to be for isostatic balance. Besides that, we have seen that individual blocks of underwater parts 

 of ice hummocks are sometimes interspersed under ice fields. Both in this and in other cases, the 

 ice protrudes upwards. 



On 24 November 1938, it was observed on the Sedou that the level of the water was lower than 

 the surface of the ice by 1 to 1. 5 m; after the ice in some places burst and broke, 10 to 15 m; 

 trenches were formed with vertical walls of considerable height. 



These facts prove that at points where recorded observations were carried out there was no 

 isostatic balance: in the ice of the new Siberian Island straits, the isostatic surface passed lower 

 than the level of the sea; on the ice field of the Sedov where the described fissures were formed, 

 the isostatic line passed higher than the level of the sea. 



It has already been noted that the vertical movements of individual parts of the ice field are 

 increased by the isostatic balance, particularly in summer when the forces of cohesion counter- 

 acting the hydrostatic forces are weakened. The following observation of the Sedov appears as a 

 characteristic example of isostatic movement in the ices in the central part of the Arctic Basin. 



278 



