286 



EARTH FEATURES AND THEIR MEANING 



operation of the glacier broom that the inland ice is given its charac- 

 teristic shield-like shape (Fig. 312). The granular nature of the 

 snow carried by the wind is well brought out by the little snow 

 deltas about the margins of Greenland ice tongues (Fig. 313). 

 Obviously because of the presence of the vigorous anticyclone, no 

 snows such as nourish mountain glaciers can be precipitated upon 

 continental glaciers except within a narrow marginal zone, and, 

 as shown by Nansen rock dust from the coastland ribbon and 



from the nunataks 



' ' : ^;V: ;l ; ;x; : ;;.:S7 ; v '" of Greenland, is car- 



.. . .... ,'.-v '-'.-> .-;:/.' ried by a few miles 



^ inside the western 



margin, and not 

 %;_. at all within the 



eastern. 



Field and pack 



FIG. 314. Sea ice of the Arctic region in lat. 80 5' N. 

 and long. 2 52' E. (after Due d'Orleans). 



ice. Within polar 

 regions the surface 

 of the sea freezes 

 during the long 

 winter season, the 

 product being known as sea-ice or field-ice (Fig. 314). This ice 

 cover may reach a thickness by direct freezing of eight or more 

 feet, and by breaking up and being crowded above and below 

 neighboring fragments may increase to a considerably greater 

 thickness. Ice thus crowded together and more or less crushed is 

 described as pack ice or the pack. 



The pack does not remain stationary but is continually drifting 

 with the wind and tide, first in one direction and then in another, 

 but with a general drift in the direction of the prevailing winds. 

 Because of the vast dimensions of the pack, the winds over widely 

 separated parts may be contrary in direction, and hence when cur- 

 rents blow toward each other or when the ice is forced against a 

 land area, it is locally crushed under mighty pressures and forced 

 up into lines of hummocks the so-called pressure ridges. At 

 other times, when the winds of widely separated areas blow away 

 from each other, the pack is parted, with the formation of lanes or 

 leads of open water. 



If seen in bird's-eye view the lines of hummocks would accord- 



