CHAPTER VIII 

 MELTING OF SEA ICE 



Section 108. Phases of Weakening and Destruction of Sea Ice 



Two processes constitute the main factors in the destruction of an ice cover — evaporation and 

 melting. In the first, the ice is transformed into water vapor; in the second, into water. 



Evaporation is proportional to the above-water surface of the ice. It is obvious that other 

 conditions being equal, the more cut up the ice surface, the greater the evaporation. 



Melting occurs as a result of the ice absorbing solar radiation or atmospheric heat in propor- 

 tion to the above-water surface, and the absorbing of heat from the adjacent water in proportion to 

 the sub-surface area of the ice. 



Since the ratio of surface area of bodies to their volumes is greater when their dimensions 

 are smaller, it is natural that the influence of evaporation and melting is felt primarily by small ice 

 formations. In this connection, the breaking of ice fields into smaller parts by various factors ac- 

 quires special significance. Breaking occurs more readily when the ice is less thick and tough. 

 The firmness or solidity of the ice, as we have seen, depends in significant degree on the ice tem- 

 perature. Therefore, breaking up is usually preceded by weakening of the ice due to absorption of 

 the sun's radiation and heat from the atmosphere and the water. 



Melting of ice starts first near the shores, partly due to the influence of shore drainage and 

 soiling or dirtying of the littoral ice (which contributes to increased absorption of radiation), and 

 partly due to the great crushing of the littoral, floating ice floes. 



Weakening, breaking up, and melting of sea ice go forward in parallel fashion, and do not 

 cease until the ice is completely demolished. Nevertheless, the process of demolition may be con- 

 ditionally divided into stages of weakening and destruction. 



1. The first phases of weakening of ice are the internal deformations which are brought about 

 in the sea ice inamediately after its temperature, having reached a minimum, begins to rise due to 

 the influence of various factors. These internal deformations are accompanied by a descending 

 movement of the brine and an increase in the ice porosity. With the appearance of the sun over the 

 horizon in the spring, the shiny, silvery ice-rind (korka) begins to form on the surface of the 

 snow. Simultaneously, the accumulation of heat from solar radiation begins under the ice-rind. 

 With continuing increase in the height of the sun and start of daily variation in air temperature 

 there begins a reduction of the snow cover, settling of the hummocks, floating away of the sharply 

 jutting sections of the ice floes, and development of thermal cracks which weaken the ice. 



2. The next phase in the weakening process is the gradual melting of the winter ice cover and 

 formation on the ice surface of snow-water puddles. In case of chance freezing, these water pud- 

 dles are covered with a thin rind of ice which protects the water from cooling. Simultaneously the 



295 



