Gradually, as the thickness of the fast ice increases, the breakage phenomena occurs more 

 rarely. Fast ice reaches its maximum development at the end of March and the beginning of April. 

 Even though at this time its thickness continues to increase, solar radiation weakens the ice simul- 

 taneously and because of this the resistance of the fast ice to all sorts of breaking effects decreases. 



Fast ice can be formed out of ice of common accretion and out of rafting ice. The first is 

 characteristic of small bays and gulfs protected from the wind and currents, the second at open 

 shore lines. 



From the data which has been given, it is clear, as had already been established as a result 

 of the work of the Toll expedition, that the following are the most conducive conditions for the 

 development of fast ice; 



1. An extensive shore line, especially if archipelagos of islands are located near the shores. 



2. The absence of strong, constant currents and tidal phenomena which would assist in 

 breaking up the fast ice . 



3. Shallows, where the cooling of water always occurs considerably faster than above great 

 depths and where ice formation, all other conditions being equal, begins earlier. The importance 

 of shallows also manifested in the fact that ice heaping of various sorts, having considerable verti- 

 cal measurements, ordinarily becomes grounded on shallower places like banks, rocks and shal- 

 lows. Later, these heapings, under the pressure of the ice from the sea, increase in size, become 

 more durable, and play the role of off-shore islands in the development of fast ice. 



All the enumerated conditions are centered in the region of the New Siberian Islands, where, 

 opposite the mouth of the Yana, the fast ice extends along the meridian for 270 miles, and along 

 the 74th parallel for 350 miles (figure 40). Lappo correctly differentiates this region in relation 

 to ice as a special fast-ice region, noting that the ice in it forms and melts under completely 

 different conditions from neighboring regions. According to aerial reconnaissance data, the fast- 

 ice area here is equal to approximately 380, 000 cubic km in March and April of 1943. Neverthe- 

 less, shallow water is the determining condition for fast-ice distribution along the Siberian shore 

 (with the exception of the Khatangskisaliva where the tidal phenomena are considerable and fast 

 ice, because of this, does not extend far from the shore, and along the Chuckchee shore where the 

 fast ice is broken by the Chuckchee current) . 



Separate ice heapings in the seas, washing the Siberian coastline, often have a displacement 

 (draft) up to 25 m. Because of this, it is considered that, on an average, the 25 m isobath is a 

 limit of fast ice distribution along the indicated shore. It is clear that at high altitudes fast ice 

 forms even occur over greater depths in narrow straits. 



Figure 104 shows the distribution of fast ice in the White Sea during 17-18 April, 1942, i.e., 

 approximately during the height of its development. If follows from the drawing that in the White 

 Sea, where stamukh does not play an important role, the fast ice line extends from the shore to 

 approximately the ten-meter isobath. Fast ice attains its greater development at the summits of 

 the Kandalakshski and Onezhskii Gulfs, in accordance with the general rule: along involuted 

 shores, fast ice is better developed than along convoluted. 



It can be approximately considered that along the White Sea, fast ice, by the time it is fully 

 developed, occupies less than ten per cent of the sea's surface. 



113 



