CHAPTER VII 

 DEFORMATION OF ICE 



Section 91. The Deformation of on Ice Cover 



As was already shown, the formation of sea ice occurs in a calm sea only in exceptional 

 cases and in comparatively small area; i.e. , at the shore of small bays and in unfrozen patches of 

 water (polynyas) which are situated between large ice fields. In the majority of cases, the young- 

 ice formations are subjected to various deformation processes from the very first moment of 

 origin. 



Changes in form and size of ice caused by temperature variations are designated "thermal 

 deformations, " while those caused by vertical and horizontal movements are classed as "dynamic 

 deformations. " 



We have subdivided both these deformations and others into two further classifications: rela- 

 tive to the structure and the properties of the sea ice (internal) and relative to the form and size 

 (external) . 



The internal thermal deformations can be conditioned by the separation of fresh ice from the 

 brine cells and capillaries with a reduction la the temperature of the sea ice. 



Since the volume of ice is approximately 9 per cent more than that of water from which it was 

 formed, it is clear that additional tensions occur which fracture the ice with every temperature 

 reduction in every salt cell. The developed pressure in this case reaches upwards of 1,200 

 kg/cm . 



After the beginning of a thaw, this process is even intensified. Actually, the melted water, 

 which penetrates from the surface ice along the capillary fissures to the lower (already cold) parts 

 of the ice, freezes, expands, and thus causes the formation of new thermal fissures. A net of very 

 fine fissures results from these processes, and ultimately weakens the sea ice. 



The external thermal deformations of ice are caused in the following manner. According to 

 the observations of Malmgren, the temperature of the surface-layer of ice fields in the Arctic 

 Basin, following approximately behind the air temperature, changes from -2° to -42° in the course 

 of a winter. In connection with this, great tensions occur which cause inner structural changes in 

 the ice, as well as jamming (and sometimes the break-up into blocks) and fissures. 



Internal dynamic deformations are caused by ice jams, and are usually accompanied by ex- 

 ternal deformations. Air bubbles and the brine of the salt cells and capillaries are squeezed out by 

 this process. The sea ice gradually becomes more monolithic and fresh. Moreover, at low tem- 

 peratures, strong jamming welds the structure into one complete unit in addition to increasing the 

 crystal size, as may be observed in the lower layers of the ice. 



241 



