flowing from these basins gradually flow into the lower altitudes, undergo constantly greater de- 

 struction and melting, and finally give rise to mountain rivers. 



In ratio to the increase in the geographic latitude, the snow line comes down lower and lower; 

 the extremity of the glaciers reach the level of the sea where they are of special interest to marine 

 studies. Actually, the glaciers determine here the shoreline, change the contours of the adjacent 

 sea bottom, and are a constant source of large masses of glacial ice in the sea. 



As has already been pointed out, several conditions are favorable to the formation of glaciers, 

 namely: high latitudes, high altitudes above sea level, and copious precipitation which is deter- 

 mined by the distribution of the land and the sea, marine currents and winds, and also the contours 

 of the locale . 



In some areas of the arctic and antarctic, all these factors are included. As a result, tre- 

 mendous "icecaps" are created, which almost completely cover separate islands and continents. 

 The main difference betweenthe arctic and the antarctic is the fact that in the center of the latter, 

 a tremendous and high continent (average height about 1, 500 m) is located; in the middle of the 

 arctic there is located the deep Basin (more than 4, 000 m deep). This determines the fact that the 

 main mass of the ice cover in the arctic is sea ice and in the antarctic is glacial ice. 



The main glaciation in the arctic is in Greenland, where 90 per cent of glacier ice in the 

 Northern Hemisphere is concentrated; it occupies an area of 1. 9 million square km, with an overall 

 area of this island equaling 2. 1 million square km. At the same time, the sea ice of the Northern 

 Hemisphere at the instant of its greatest development occupies an area of about 1200 million 

 square km. 



In the Northern Hemisphere, aside from Greenland, land ice reaching sea level is also 

 located on the outer shores of Baffin Bay. Smaller, isolated glaciation is found in the American 

 sector of the arctic — on Prince Patrick and Melville Islands. In the Eurasian sector of the arctic, 

 glaciation is located on the islands of the Spitsbergen archipelago, on White and Victorian Islands 

 (between Spitsbergen and Franz Joseph Land), on the islands of Franz Joseph Land (approximately 

 97 per cent of the area of the entire archipelago is covered by land ice), on Novaya Zemlya, on 

 Ulsakov and Schmidt Islands (between Franz Joseph Land and Sevemaya Zemlya), and on Severnaya 

 Zemlya. The only known place of glaciation east of Cape Cheliuskln is on the Belong Island, and 

 there the glacier reaches the sea only on Henrietta Island (figure 43), 



An investigation of the glaciation tn the Northern Hemisphere attracts attention first to the 

 fact that the more northerly parts of the land, namely Greenland and EUesmere Land, are free of 

 glaciers. Labrador, having a very low summer temperature (about 7°) and also being located in 

 the path of summer cyclones, is almost completely free of glaciers. The entire northern shore of 

 Spitsbergen is almost completely free of glaciers. It follows from these examples that high geo- 

 graphic latitudes and low summer temperatures are still not enough for the formation of glaciers. 

 Altitude above sea level is also not enough, nor are large horizontal distances. Thus, for instance, 

 the very small Victoria Island (about 6 km long) , located between Spitsbergen and Franz Joseph 

 Land, is almost completely covered by glacier ice, whereas higher and larger islands, located fur- 

 ther to the north along the northern shores of Spitsbergen, do not have an ice cover. Without a 

 doubt, the most important, other factors being equal, is the amount of precipitation. Thus, for in- 

 stance, it is known that in Iceland, along the dryer northern side, the snow line is located at 1, 000 

 to 1,300 m above sea level, while on the southern, moister side, it decreases to 600 to 800 m, 

 i.e. , it is located 300 to 500 m lower. 



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