ARCTIC SEA ICE 103 



destruction by melting, a process that is now assisted very much by 

 the river-borne and wind-borne debris from the land. 



All this together imparts an exceedingly rough character to the 

 surface of ice. The most rapid destruction of the fast-ice takes place 

 near the mouths of rivers, where polynyas of considerable size are 

 formed by the impact of relatively warm river water and its subse- 

 quent overflowing onto the ice. 



All these factors contributing to the destruction of the fast-ice 

 create a possibility, especially near and along shore at the end of 

 June or in July, of a local insignificant motion of the fast-ice taking 

 place, its edges breaking up, its chafing against the shore, and so 

 on. All this increases the dimensions of the polynyas and, generally, 

 the ratio of the area of open water to the area of ice and prepares 

 greater space for the movement of the whole fast-ice. 



At the same time, out at sea, farther from the shores, these factors 

 play a considerably less important r61e in the destruction of the fast- 

 ice, but there also the melting of the considerable snow hills (Rus- 

 sian, sugrohi) around the ice protuberances, hummocks, and stamukhi 

 do their work, i. e. hummocks, stamukhi, and other protuberances 

 thaw off, piled-up pieces become packed, forming more compact 

 masses, and so on, while on the outskirts of the fast-ice the shock 

 of the pack ice assists the process of destruction. Owing to the 

 fact that the fast-ice itself up to the moment of its destruction does 

 not represent a continuous ice cover but is honeycombed with cracks 

 of different kinds (tidal cracks; cracks caused by air temperature 

 changes and by temperature differences in the various layers of 

 the ice; cracks caused by ice pressure) and owing to the formation 

 of open water near and along the shore on the one hand and to the 

 pressure of the pack ice on the other, the parts of the fast-ice first 

 begin to be disconnected among themselves under the influence of 

 winds and currents. Then the increasing number of cracks, channels, 

 and polynyas bring about the motion of the larger areas; with the 

 first strong wind these break into smaller pieces ; and finally all the rest 

 of the fast-ice passes over into the pack ice. During the summer 

 part of this former fast-ice disappears entirely owing to the repeated 

 breaking and cracking into pieces due to the collision of separate 

 parts and owing to melting; for the same reasons part of it forms 

 piled-up formations in the zone of the former fast-ice that drift to the 

 north into the region of the winter pack ice, which, in turn, feeds the 

 Arctic Pack. 



With the beginning of the new frosts those parts of the fast-ice 

 that have been caught by the newly formed ice in the zone of the 

 fast-ice give rise again to those insertions of old ice into the new 

 which assist in the formation of the new fast-ice, and the cycle is 

 repeated. 



