fresh thaw water may accumulate in summer. The fresh water 

 that seeps through the ice refreezes on the bottom of the ice thus 

 causing an upward migration of debris frozen in the ice. It is not 

 uncommon to see ice covered with rocks, shells, seaweed, and 

 diatoms that have been brought to the surface. 



Arctic ice usually grows up to 5 or 6 feet in a year. Growth 

 continues through the summer by the addition of the new ice on 

 the bottom of the layer. A second year may add 1 or 2 more feet 

 to the thickness. Eight feet is about the maximum thickness of 

 level ice, since at that point the ice acts as sufficient insulator to 

 stop any refreezing at the bottom. Under the influences of tide, 

 wind, current, and sea swell, the floes are pushed together or 

 against the shores. This causes buckling, ridging, and rafting 

 of the ice. Ice thus piled up may be 30 to 40 feet thick; and the 

 ridges may be 100 feet high. When such pressure is released, 

 leads and open water appear. 



Ice first forms along the shore, in the bays, and at the mouths of 

 rivers. In the fall and early winter, the polar pack which is con- 

 tinually in motion, coming in and moving off the shore, grinds this 

 new ice and piles it up against the beach. When the pack moves 

 off, a layer of new ice forms in the lead. This process continues 

 until about the beginning of December, when the coastal ice 

 becomes frozen fast to the bottom. This fast ice is a solid, station- 

 ary mass extending 4 to 8 miles from the shore. The fast ice is 

 useful as a winter highway for sledges. The ice reaches a maxi- 

 mum thickness in April or May and then begins to crack and rot. 

 Pools form on the surface and travel is difficult. 



Between the fast ice and the pack there is a lead which inter- 

 mittently opens and closes as the pack moves. Pressure ridges are 

 formed and the grinding of the ice continues along this flaw zone 

 during the winter. 



Throughout the entire year approximately three-fourths of the 

 Arctic Sea is covered by heavy pack-ice which is essentially im- 

 penetrable. During the winter, the bordering seas and bays are 

 ice-locked and are unnavigable. The maximum extension of the 

 heavy pack and land-fast ice is in early spring. In April and May 

 pack-ice covers the areas along the east coast of Greenland, the 

 Canadian archipelago, the Labrador coast, the western and north- 

 ern Alaskan coasts, and the Siberian northern coast as far west as 

 Kolguev Island. The Kara Sea, Gulf of Ob, and the Yenisei estu- 



37 



