102 POLAR PROBLEMS 



important role in the development of the width of the fast-ice belt, 

 acting, in a way, like skerries on which immovable new ice wedges 

 and creates a bulwark against the breaking up of the fast-ice, a 

 process which is normally caused by the shock of the pack ice. 



Kolchak, assuming the average height above water of floating 

 hummocks to be 12 feet and their draft consequently 60-70 feet, 

 sets 12 fathoms, or 24 meters, as the average limit of depth for the 

 free motion of hummocks. In depths shallower than this the floating 

 hummocks become grounded, forming the so-called stamukhi. "Thus 

 the whole area of fast-ice is as though confined between the shore and 

 the rampart of ice heaps that lie approximately along the line of 12 

 fathoms depth (from the side of the open sea), many of which touch 

 bottom at this depth and most of which in any case are grounded 

 near that depth line" (Kolchak). 



The Arctic coast of Eurasia and especially the shore of the East 

 Siberian Sea are distinguished by an extent of shallow water nowhere 

 else found in the Arctic Sea, and this is the reason why the fast-ice 

 attains such great widths in that region, amounting at its widest 

 place off the mouth of the Yana River to 270 miles — a unique phe- 

 nomenon even for the Arctic Sea. 



The outer limit of the fast-ice, which is in touch with the region 

 of pack ice, is subjected to the constant shocks or outward thrusts 

 of the pack-ice masses and is characterized either by ridges of massive 

 hummocks or by polynyas (areas of open water; see pp. 117 and 118). 



In this condition, increasing, however, its thickness up to May, 

 the fast-ice exists until summer, when its destruction begins — like 

 its formation- — first near the shore and then spreading thence into 

 the sea. 



The first stage of the decay of the fast-ice is caused by the thaw- 

 ing of the land snow and the flow of melt-water upon the ice, forming 

 the so-called "offshore water." Then follows the melting of snow 

 on the ice, the water from which, filling the open cracks in the ice, 

 freezes quickly in them when it meets the sea water with its tem- 

 peratures of -1° to -1.8° C. and closes these cracks, thus preventing 

 the water from flowing out under the ice. On the other hand cracks 

 that do not extend all the way through the ice are widened by the 

 expansion of this melt-water freezing in them. This occurs at the 

 end of May or beginning of June. Then, with the rising of the air 

 temperature, the fresh ice in the cracks disintegrates; the cracks 

 break open, and the water, in a layer which is as much as 2 to 3 feet 

 thick, flows under the ice, having furrowed its surface with a net of 

 channels, depressions, hollows, etc., and having widened the cracks. 



In a few days all of the water, excepting that which has filled up 

 the hollows, flows under the ice. Then, with the further rise of the 

 air temperature and the help of rains, the ice continues its self- 



