RESTRICTED 



Along open coasts the fast ice is liable at all times to break up and 

 drift away. This break-up may not occur, however, in regions where 

 the configuration of the land is such as to shelter the ice from the 

 prevailing winds, and especially where offshore winds blowing in 

 from opposite sides of an embayment are opposed to each other and 

 so hold the ice firmly in place. Stranded bergs sometimes act as 

 anchors to fast ice, preventing it from breaking out and drifting 

 to the open sea. 



Pack ice is composed of sea ice frozen in the open sea, of detached 

 fragments of fast ice formed along the coastline, and to a lesser extent 

 of disintegrated particles of land ice. These elements are not uni- 

 formly influenced by winds and currents; as a result there is a dif- 

 ferential movement with a decisive effect upon the composition and 

 stability of the pack. This conglomeration drifts under the influence 

 of wind, tide, current, and the component due to the earth's rotation. 



Pack ice is classified according to compactness of arrangement into 

 consolidated pack^ close pack^ open pack^ and drift ice. The ice 

 masses themselves, according to size, may be ice fields., floes., hlocks., or 

 pancakes; according to surface, may be level., or hummocked; ac- 

 cording to thickness, may be light (up to 2 feet in thickness) or heavy 

 (more than 10 feet in thickness). 



Figure 7. — Pancake ice. This is new ice formed after 2 or 3 days of freezing temperature. 



