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Transactions of the Symposium on Photo Interpretation

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