other by cracks which are called, with relation to the shore, interior and exterior tidal cracks 

 (figure 116). 



The steeper the angle of slope and the less the amplitude of the tide, the closer together will 

 be the exterior and interior cracks. The more gradual the slope of the shore and the greater the 

 amplitude of tide and thickness of ice, the further apart will be the tidal cracks and the more 

 clearly defined. 



Ice formation in the sea never occurs with identical intensity. This is explained in part by 

 the changes in meteorological conditions but mainly by ocean conditions. Therefore, freezing goes 

 forward by leaps or stages and each stage is characterized by a crack. According to observations 

 of the Zarya:, on a sloping shore stretching out over a great distance, the number of tidal cracks 

 was sometimes as high as seven. Only two of these, those nearest the sea, were active (i.e. , 

 variations of level were noticeable in them) . The other five had been active in the past but with the 

 thickening of the ice they remained in the coastal strip of sea frozen through to the bottom . Usually 

 the plane of the tidal cracks is vertical. Sometimes it inclines towards the shore and in very rare 

 instances towards the sea. 



The distance of the tidal cracks from the shore depends on the slope of the beach and the 

 amplitude of the tide. In Kozhevnikov Bay (Khatangski Gulf) the tidal cracks are formed up to 1 to 

 1.5 m from the shore. 



In shallow water the tidal cracks follow very closely the outlines of the coastline. This fact 

 is sometimes used in winter surveys of routes at shallow coasts where it is impossible to identify 

 the coastline otherwise. 



In the case of spring tides and strong driving winds, the ice on the surface may be higher than 

 the ice frozen to the bottom. Then the sea water rises above the latter and forms the so-called 

 winter water-lanes along the coast (Zabreg). This water, mixing with the snow which covers the 

 coastal ice and then freezing, forms (on the surface of the sea ice) snow ice which is distinguished 

 by its dull white color. When the surface ice is driven off the shore it may actually be lower than 

 the ice frozen to the bottom. 



Analogous tidal cracks are formed around islands and ice formations which are lying on 

 shoals. Usually in such cases there are several radial cracks present within the circular tidal 

 crack. Similar circular and radial cracks are observed near individual shoals where the depth is 

 less than the amplitude of the tide plus the greatest thickness of the ice cover. Over such shoals 

 at the start of ice formation the ice cover at ebb tide has a slanting dome- shaped swelling. With 

 subsequent growth and strengthening of the ice cover the circular crack, which encompasses the 

 ends of the radial cracks, usually has its larger opening facing down, while the radial cracks, on 

 the other hand, have the larger opening facing up. 



With increase in amount of ice cover, the slope of the slabs which form a swelling over the 

 sub-surface rock continually increases and in certain cases reaches 45°. The inclined slabs 

 freeze together with the sea water which falls into the cracks between them . Thus a very stable 

 formation is created rising to one or two m over the surface of the smooth ice with diameter up to 

 7 m and similar to a crater in form (figure 117). Such crater-shaped heapings of ice ("ice tents") 

 are especially characteristic of rocky shores where the littoral zone contains many sub-surface 

 stones. Analogous phenomena were observed by the Toll expedition along the low and declivitous 

 shores of Zemlya Bunge over the shafts of sludge ice which had become soaked from long immer- 

 sion in the water and were therefore heavy and prone to sink. 



332 



