WORKING GROUP 6 
AVGEVICH 
377 
The interpretation of ice photographs of the Ob inlet provided a charac 
teristic proof of the effect of the ice on the shore and the shoaliness of the 
coastal zone. It has been found that the ice sheet of this water area, stretching 
for 750 km and about 60 km wide, from the day of its formation and during the 
entire period it remains frozen up, collects an overburden of accumulated or 
ganic - mineral matter carried along by the wind. The peculiar distribution of 
this overburden is determined, on the one hand, by the outline of the shore and 
its capacity to supply overburden and, on the other, by the migration of young 
ice at the beginning of winter. The young ice, on which the overburden already 
collects near the shore, shifts, in the course of time, as a result of the local drift, 
to the middle of the bay and remains there till spring. As the ice sheet begins 
to melt, there occurs an intensified melting of ice in the sections carrying the 
overburden. But as soon as the concentrating organic - mineral layer exceeds 
the maximum thickness at which the overburden accelerates melting, the pro 
cess of ice disintegration slows down noticeably. For some time, the ice covered 
with overburden retains a higher mechanical strength than pure ice. 
This amply overburdened ice was called black-ice. Fig. 4 shows the stages 
of its formation. This ice is formed first of all by the melting of hummocks 
which effectively accumulate mineral and organic substances blown off the 
bay shores by the wind. After this, extensive areas of black-ice (fig. 5) develop 
on the surface of the ice sheet. The more closely the process of ice sheet forma 
tion is connected with the congelation of the socalled pancakeice, the greater 
the extent of black-ice. 
In view of its characteristic features, pancake ice is also regarded as having 
the greatest capacity for accumulating overburden. The melting of pancake 
ice which has taken a considerable amount of the overburden, is accompanied 
by the restoration of the pattern typical of the aggregation of this ice observed 
in autumn. As they merge together, the separate lenses of the overburden build 
up a closed surface of black-ice. Direct control measurements have shown that 
in this case, the thickness of the overburden layer varies from 15 to 25 mm. 
In our study of the sources of overburden and its thickness, we resorted to 
aerial photographs of the bay shores, obtained simultaneously with the aerial 
survey of the ice. Interpretation of these photographs has revealed the pre 
sence of a large number of sand lenses along the shore and has enabled the 
establishment of their total extent. This work resulted in a sketchmap shown 
in Fig. 6. It should be noted, that the sand contained in the lenses was extre 
mely fine and the size of its grain, as laboratory investigations have shown, did 
not exceed 0.1-0.2 mm, which is sufficient proof of its high mobility. 
The numerous aerial surveys of the Ob inlet in the course of the clearing of 
its ice have shown that black-ice was the last to disappear. We have found, at the 
same time, that it is not carried by the current into the Kara Sea but, owing 
to the constancy of easterly wind during this season, it is driven to the western 
shore of the bay and drifts south to meet the stream of river water. Sometimes, 
black-ice migrates in this direction with such intensity that it frequently shifts 
far to the south. In this case, the blocks of black-ice, 0.5-0.8 cubic metres in