zero at the bottom and at the lower surface of the ice, the graph of speeds under the ice should 

 represent a parabola with its horizontal axis running through the middle of the depth of the current. 



For comparative purposes there are shown in Figure 127 the graphs of current speeds of the 

 Volga at Kamyshin, constructed by Polyakov as a result of averages of H62 summer and 913 

 winter observations. 



0.2H 



0.4 H . 



0.6 H 



0.8 H 



0.2 0.4 0.6 0.8 1,0 



Figure 127 . Graphs of average current speeds of the Volga River at 

 Kamyshin. A — open river. 5 — river under ice. 



As may be seen from this figure, the graph of speeds at the lower ice surface shows greater 

 speeds than at the bottom, which, according to Polyakov, is due to the greater roughness of the 

 bottom at Kamyshin by comparison with the roughness of the lower ice surface. It is evident that 

 similar phenomena are also seen in sea currents which flow under fast ice. 



Sea currents ui their turn have a constant dynamic effect on fast ice, and if the current is 

 warm, a thermal effect as well. The dynamic effect consists in a washing away and smoothing of 

 the lower surface of the fast ice. It has already been shown that in calm regions, in the period of 

 ice formation, the lower surface of the ice is brush-shaped and the water directly adjacent to this 

 surface is filled with a quantity of ice particles of diverse shapes and sizes. With the presence of 

 currents, all these particles are carried into the interstices of the lower surface of the ice, which 

 they then fill up. In addition, as they flow around the sub-surface projections of hummocks the 

 sea currents gradually wash them away. It is clear that the effect of the sea currents in this re- 

 spect cannot, however, be compared with the washing away effect of tidal currents. 



Due to the thermal action of currents, ice formation is retarded in the freezing period, while 

 in the melting period the destruction of the fast ice cover is hastened. Table 87 set forth the water 

 temperatures in Yugorski Shar before its breakup in 1935. From the table it may be seen that the 

 water temperature under the ice began to rise from the 12 June and on 28 June the ice, which was 

 almost one meter thick, broke open. The high temperatures of the water under the ice was not 

 caused by local conditions. This warm water was carried there from the Pechorski Sea. 



LITERATURE: 77, 116. 



353 



