From formula (7) it follows that an ice floe, the buoyancy coefficient of which is 0. 1, the 

 thickness 40 cm, and the area 2.4 x 4. 37 (10. 5 m2) (tlie dimensions of a 12 ton tractor), will sink 

 under a load of 0. 4 tons. Therefore, if an ice floe is to support the weight of a tractor exclusively 

 by its own buoyancy, its area should be no less than 300 square m. 



It follows from this example that if we want to use the buoyancy of ice for supporting a load, 

 we should distribute the load over large areas of ice. 



LITERATURE: 62, 76, 77, 101. 



Section 68. Density of Snow 



The most notewortliy property of a snow cover is its significant density. 



Another no less noteworthy property of snow is its ability to change its density due to the 

 action of pressure by the above- lying layers, wind, solar radiation, temperature, and the humidity 

 of the air and liquid precipitates, basically raising the density in the course of time, but, in 

 separate instances, even lowering it. 



Some aspects of natural snow are of practical interest. 



"Wild Snow" is very fluffy, has almost no cohesion, pours like flour. Such types of freshly- 

 fallen snow are often observed during a full calm and low air temperature. The density of such 

 snow is about 0. 01 to 0. 03. 



"Sandy Snow" falls at extremely low temperatures. Sleds and skis move over it with 

 difficulty which in part confirms the observations of Koch and Wegener in Greenland. 



"Frozen Windcrust and Windrind" are formed by wind pressure. This pressure is consid- 

 erable. For light winds (5 m/sec) it equals about 3 kg/m2, for a fresh breeze (9 m/sec) it is 

 about 6 kg/m2 and for storm winds (30 m/sec) it is about 74 kg/m2. Pure snow made dense by 

 wind has a dull crust and surface covered with ripples. Frozen wind crusts of great strength are 

 called "snow boards. " 



"Spring Snow" is snow which disintegrates into individual grains. It presents an excellent 

 surface for skiing since the grains are wetted by melt water and move with respect to each other 

 practically without friction. 



"Spring Rind" forms on spring snow when its surface temperature decreases. It usually 

 consists of a thin layer of ice found above snow and separated from it by a thin air layer. 



"Sun Rind" forms at low air temperatures as a result of the melting of upper snowflakes and 

 their freezing together. 



"Rain Rind" forms after light rain falls over very cold snow. 



The density of snow fallen on the surface of land or ice increases not only due to wind pres- 

 sure and other factors but also due to the weight of above-lying layers. The latter case is taken 

 into consideration. 



173 



