136 POLAR PROBLEMS 



nesses of 30 to 40 feet to be of usual occurrence among fragments of 

 these heaped-up ice fields in the region north of the New Siberian 

 Islands. 



The Pack of the Kara Sea As a Local Formation 



In considering the ice cover of the Kara and Siberian Seas one 

 cannot help noticing a very sharp distinction between the character 

 of the ice in these two water basins. Observations show that the 

 greater part of the ice of the Kara Sea is formed in that sea itself and 

 that the ice of the Arctic Pack can be met with only in its northern 

 end, whither it is carried as separate fragments, strikingly different 

 in thickness and shape from the local ice. North of the Kara Sea the 

 edge of the Arctic Pack lies considerably to the north, and only seldom 

 during winter does it approach the latitude of Cape Chelyuskin, 

 for this edge in winter is usually pushed back by the predominant 

 southern winds to its northernmost limits. The absence of consider- 

 able masses of heavy heaped-up ice leads to less active ice formation 

 during the winter, and in the Kara Sea the process of hummocking 

 generally produces much less effect than in the Siberian Sea, for 

 example. The Kara Sea has greater depths than the Siberian Sea, 

 which do not allow the formation of numerous grounded hummocks, 

 and correspondingly it has a less wide zone of immobile fast-ice near the 

 shore. The conditions of ice formation in the Kara Sea are favorable 

 to the development of extensive smooth areas of ice, some of which, 

 by being cemented together by frost, are transformed into many- 

 years-old formations. Many old fields that I had occasion to measure 

 and that were 5 to 8 feet thick at the end of the period of melting, were 

 quite level and showed no trace of heaped-up ice. The one-year-old 

 ice of the Kara Sea has a thickness from 3 feet to i foot at the end of 

 summer, depending on the conditions of melting, and it gradually 

 reaches the limit of thickness of summer ice formed by natural freez- 

 ing, a limit determined by Weyprecht as S}4 feet at the end of the 

 period of melting. Part of the ice is certainly transformed into heaped- 

 up masses, usually consisting of ice, i to i^ feet thick, from the 

 autumn break-up; their thickness seldom exceeds 12 to 14 feet, al- 

 though separate hummocks may be as much as 10 to 12 feet high 

 above sea level and 50 to 60 feet thick. Fragments of hummocks 

 grounded at depths of 4 to 5 fathoms are rather usual, and many are 

 found on the 3-fathom line. The ice of the Kara Sea generally has no 

 such distinctive eroded forms as the heavy ice of the Siberian Sea, 

 as it does not rise much above the water ; the ice fields and their parts 

 contain smoother areas; in the coastal fast-ice, areas of broken-up 

 hummocks predominate; grounded and floating hummocks are usually 

 gathered at points of the shore that project into the sea, such as capes, 

 inshore islands, etc. ; the hummocks of the open sea due to the breaking 



