WORKING GROUP 6 
AVGEVICH 
381 
all of them associate in pairs. Within the limits of each pair the distances be 
tween the lines are the multiples of X which equals 120 m. We believe that such 
proportionality of distances between the lines of thread-like cracks is another 
indicator of the wave nature of fast-ice cracks. 
Planimetric developments of oblique aerial photographs coupled to the 
chart of the surveyed area constitute yet another proof of the effect of moving 
water masses on the break-up of fast-ice. The processing of only one of the many 
series of oblique aerial photographs enabled us to conclude that the thread-like 
cracks cover nearly 24 sq.km, of the ice surface, extending in one direction for a 
length of eight kilometres. After the planimetric development had been oriented 
on the report chart, all the cracks were found to be parallel to the general 
direction of the shoreline. This characteristic is quite sufficient to prove 
that ice cracks are not the result of unilateral roughness of the sea but are only 
caused by the interference of two types of waves. The interaction between 
these waves of different phases is responsible for the different distances be 
tween adjacent cracks recorded on aerial photographs. 
This interconnection between the ice and its environment explains the pre 
dominance, noted by Professor M. M. Somov, of ice-floes of four or five definite 
sizes among a mass of large pieces of broken ice. It can now be asserted that 
the thread-like cracks of fast-ice, undetectable by the naked eye, completely 
predetermine the course of the subsequent mechanical disintegration of sea-ice 
and the original form of its brash. This is clearly illustrated by the aerial photo 
graph in fig. 10 which shows freshly broken-up ice, the separate elements of 
which are almost alike in form and size. The pieces of ice have very straight 
edges and are remarkable in their exceptional geometrical form. Further 
more, the two opposite edges are directly or almost directly parallel to each 
other. These edges are 800 metres in length, which also indicates a certain 
regularity, causing precisely this type of disintegration of the ice. 
The scientific and practical importance of this interconnection is indispu 
table: we can now evolve methods for a far more accurate prognostication of 
periods when fast-ice begins to break up. It also becomes possible to plot the 
areas of this weakened ice on ice charts, which greatly simplifies the solution 
of the problem of a forced break-up of fast-ice with the least expenditure of 
man-power and at a minimum outlay. 
It should be noted, in conclusion, that further development of the methods 
of complex interpretation of aerial photographs of sea-ice should undoubtedly 
reveal other interconnections and regularities of which, so far, we know 
nothing. With this aim in view, we must continue to improve methods of 
aerial photo interpretation and increase its informative value. We must not 
confine ourselves to single occasional surveys. We need numerous regular 
surveys yielding photographs which can be used for comparison. In this sphere, 
great advantage can be derived from surveys carried out on various scales 
to obtain simultaneously macro-, meso- and micro-pictures of the state 
of ice. We must also systematically process the materials of single vertical