12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 28 



15 feet high.) New sheets form and the process is repeated until the 

 ocean is covered with ridges of rough ice (pi. 5, fig. 2) to a con- 

 siderable distance at sea. This distance varies with seasons but may 

 be 6 or 8 miles. However, the outer few miles of ice over water more 

 than 100 feet deep are never stable. Storms open leads and these 

 close again. Leads remain open for varying lengths of time, but a 

 layer of ice several inches thick usually forms within a few days, and 

 if there are no onshore winds of sufficient force to pile it up, it con- 

 tinues freezing to a greater thickness. Eventually the pressure of the 

 outer ice breaks it up and piles it up several layers thick (pi. 5, figs. 

 I, 2). Leads may be from a few feet to several miles wide, and from 

 a few hundred feet to several miles long. The ice ridges may be 100 

 feet or more across, 20 feet or more in height, and a few hundred 

 feet to several miles in length. Thus the shore ice presents a series 

 of ridges of varying length, breadth, and height, and between these 

 may be areas of varying size that are relatively smooth and level, 

 where the vagaries of storms and currents have permitted the ice to 

 form without being disturbed. 



Nearly every fall the floating, drifting ice offshore, which is old 

 ice sometimes almost equaling icebergs in size, comes shoreward and 

 grounds. Since ice is about seven-eighths under water, this ice 

 grounds offshore where the water is 60 to more than 100 feet deep 

 and forms what is spoken of as "the big pressure ridge." Owing to 

 the force of ice behind it, it may pile up as high as 30 feet or more. 



The following are the days in the years 1941 to 1947, inclusive, on 

 which the ice permanently formed an unopen ridge offshore : 



1941 November i 1945 October 20 



1942 November 10 1946 November 9 



1943 October 15 1947 October 13 



1944 October 18 



In 1948 the ice broke up on July 23, and on only one day through- 

 out the remainder of the summer was the pack ice not visible from 

 shore and then it could be seen from any elevation of 20 feet, or a 

 height above ground of 8 or 9 feet. A useful equation for the curva- 

 ture of the earth, and, therefore, the distance objects can be seen at 

 sea, is V/i+^V/i. The shore at Point Barrow base is 11 feet above 

 sea level, so the horizon, to a man whose eyes are 5 feet above ground, 

 is Vi6+-^Vi6 or 5:^ miles. If the ice itself is 10 feet high, then it 

 can be seen from shore when it is about 9 or 10 miles out. 



Three times during the summer of 1948 the edge of the pack ice 

 approached shore, and many small ice floes were grounded. One 



