railroad. I noted no change in the fissures as a 52 ton locomotive passed over the road. Such 

 longitudinal thermal fissures are caused on ice roads which are constructed on fast ice. 



Occasionally, "gorges" are formed at the intersection of two fissures. At first glance, these 

 represent the greatest possible danger, but in the described case I did not notice any movement of 

 the ice.* 



When appraising the dangerousness of fissures, it is necessary to remember that in the 

 course of time any breaks and fissures are gradually closed. As already noted, thin ice grows 

 more quickly than thicker ice. Thus, a peculiar cushion of ice grows under each fissure, which 

 compensates for its harmful influence. 



LITERATURE: 17, 62, 76, 77. 



Section 93. Wind Pressure on Ice Fields 



Wind, with its pressure, exerts a double effect on ice fields: it moves ice fields (wind drift 

 of ice, see Chapter 11), causing fluctuating movements of the ice fields, which are accompanied 

 by wind waves behind it on the ice cover and break-up of the ice fields. 



Let us assume that air molecules move in the wind with one and the same velocity and in one 

 and the same direction (horizontal). Let us further assume that a hummock is situated on the ice 

 field with the slope toward the wind (figure 85). 



'y////////////, 



Figure 85 . Pressure of the wind on ice hummocks . 



*The road foreman described to me how he attempted to fill the fissures and gorges with 

 water. He noted that the ice formed from the poured water did not hold fast to the main mass of ice. 



245 



