The height of the largest ice hummocks , which were measured by Gakkel and Khmyznikov in 

 the Chuckchee Sea (in the region of the catastrophe to the ship Chel iuskin) (68°18' north, 170°50' 

 west) was equal to 7.2 m, measured from the level of the water. 



The dimensions of the largest ice hummock which was measured by Badigin on 24 March 1939 

 at the time of the drift of the Sedo u at 86°27. 6' north, and 109° west were in meters: height 6.1, 

 width 32, length 60. The remaining measured hummocks were significantly lower; their average 

 height was about .5 m. 



In the boundary parts of the Central Arctic Basin, the height of the hummocks may be more. 

 Thus, Markham encountered ice columns up to 13 m high at the north end of Grinnelevaya Vemlya. 



The chief formation of ice hummocks from marginal crushing or from complete breakup de- 

 pend on the physical and especially on the mechanical properties of ice. 



Figure 91. An ice hummock from marginal crushing. 



In ice heaps on jams from marginal crushing, separate pieces of ice represent sometimes 

 surprisingly accurate forms of cubes or parallelepipetes . I saw such ice hummocks, for example, 

 in the northwest part of the Barents Sea. Usually, separate pieces of ice in ice hummocks formed 

 from the complete breakup are not so accurate and regular in form. Ice heaps resulting from 

 marginal crushing are, in general, characteristic for less durable annual ice, while ice heaps re- 

 sulting from the complete breakup are characteristic for standing and powerful ice fields, whose 

 edges usually they border. Since the durability of ice increases generally with lowering tempera- 

 tures, the ice hummocks from marginal crushing are formed more often in summer and fall, 

 whereas the ice hummocks from complete breakup are formed in winter. 



As we have seen, the greatest ice jamming is caused by the wind. 



Let us assume that in a certain region of the Arctic Basin, calm weather continued during the 

 course of several days. For this time, the wind drift of the ice field which is caused by the pre- 

 ceding wind, discontinues; separate leads and separations are prolonged by the young ice. 



261 



