SEA-ICE 85 



of their being crushed to pieces. When the edges of ice floes 

 are forced together in strong breezes, hummocky ice is formed. 

 The pressure of pack-ice is not, however, altogether due to 

 wind, but to the further cooling of the ice itself. According 

 to Otto Pettersson, sea-ice, unlike all other bodies, on being 

 subjected to further cooling expands. At first the expansion 

 is rapid, from - 10 C. slower, until at -20 C. sea-ice main- 

 tains an approximately constant volume. So the pack-ice 

 continues to exert pressure in sharp frosts even when the 

 weather is quite settled. The firmness of sea-ice shows the 

 greatest variation. Pancake-ice is newly-frozen ice of sufficient 

 thickness to prevent navigation, even though it will not support 

 a man's weight. 



Pack-ice disappears very rapidly in the Arctic regions in 

 summer. The chief factors in its disappearance are evaporation 

 from the surface, the movement of the water, the long Arctic 

 days of summer, and the reflection of the heat of the sun from 

 the rocky coasts. Instead of the ice-foot, as the ice frozen to 

 the shore is called, there is in summer a lane of water round 

 most of the Arctic islands and continental land, in which 

 whaling and exploring vessels are able to make considerable 

 progress. 



Fog and rain also exercise considerable influence. In 

 Antarctic regions the factors which make for disappearance of 

 the pack-ice are not so favourable. 



The Geographical Distribution of Sea-Ice. 



In the first place pack-ice may be considered, leaving ice- 

 bergs to be dealt with later. The greatest extent of pack-ice 

 is met with in the Arctic Ocean. The maximum extent is 

 generally in May, the minimum in August, though there is 

 considerable variation from year to year. In May most of the 

 land bordering the Arctic Ocean is fringed with pack-ice, the 

 most notable exceptions being the whole coast of Norway right 

 round the North Cape to Cape Sviatoj, which is never covered ; 

 the south coast of Iceland, and the west coast of Greenland. 



