ANTARCTIC ADVENTURE AND RESEARCH 



Bay Ice or Fast Ice 



The general principles governing the formation of 

 bay ice are much the same as in the case of pack ice. 

 But owing to the proximity of land, a number of 

 special forms are developed. These include pressure 

 ridges, shear cracks, and cloven-hoof ice. The ice foot 

 also may be briefly considered here. All these features 

 w^ere well shown in Granite Harbor, from which the 

 following examples are taken. 



A prominent feature in the sea-ice (near land) is 

 the presence of permanent breaks to which Scott and 

 Wilson gave the name "shear crack." These are due 

 primarily to the tension in the sea-ice existing between 

 two islands, or an island or cape or an ice tongue and 

 cape. The sea-ice is of course raised or lowered by 

 the tide, and is affected no doubt by currents and winds 

 to a lesser degree. Thus there were numerous fairly 

 permanent examples off Cape Evans. Their features 

 were all much the same. The two edges of the broken 

 sea-ice (somewhere near six feet thick) would grind 

 together and large fragments would fall between the 

 moving masses. In places the adjoining edges were 

 pressed together so strongly that the edges upturned, 

 forming a wall of ice six feet high. Even in the 

 middle of winter one could always see open water in 

 these shear cracks, which were accordingly favorite 

 places for seals. 



An interesting series of nearly a dozen shear cracks 

 due to the pressure of the Mackay Tongue was ob- 

 served in Granite Harbor. They are shown in Figure 



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