404 I. P. Kocx. 
the ice further: out, where the water is deeper, floats in the sea. 
Thus the tide makes the floating sheet of ice rise and fall, whereas 
the ice foot!) along the coast is stationary. In this manner tidal 
cracks arise. 
The freezing of the water in the tidal cracks, together with the 
inevitable horizontal shiftings in the floating sheet of ice, in its turn 
occasions tidal pressure ridges. 
The formation of the ice foot takes place throughout the winter, 
as long as the ice increases in thickness. The factors which, generally 
speaking, determine the dimensions of the ice foot are the more or 
less evenly sloping character of the bottom, the altitude of the flood 
wave and the thickness of the ice, to which, however, must be 
added the effects of the tidal pressure ridges, as well as a few other 
factors, which in themselves have no connection with the formation 
of the ice foot (pressure ridges between drift ice and ice foot, accumu- 
lation of snow on the ice foot, sprinkling of sea spray when the 
wind blows on the shore) but which, when acting together with the 
ice foot, may materially increase its dimensions. 
The difference between flood and tide only in exceptional cases 
exceeds 2 m?), and the limit of the thickness of one season ice may 
be put at a similar figure”). By a purely theoretical estimate we 
consequently arrive at the conclusion that in Northeast Greenland 
the ice foot should be formed on the very part of the shore situated 
between the high water mark and the low water mark, whereas the 
tidal cracks would be found at depths, which at low water are 
situated between 0 and about 2 metres. In forming this conclusion 
we have, however, among other things, paid no attention to the tidal 
pressure ridges. 
Generally speaking the tidal cracks must open at the fall of the 
water and close up again at its rise. However, the freezing of the 
water in the cracks, the tumbling down of fragments of ice, the 
accumulation of snow and minor lateral shiftings prevent the cracks 
from ever closing up altogetber. During the closing up there appear 
in this manner horizontal pressures round the tidal crack, by which 
1) The designation “ice foot” is also used with quite a different meaning from the 
one given above, that is for the foot which often projects .below the water from 
the edge of a floe or from an iceberg. 
In Danmarks Havn the tide wave never reached 2m, but on several occasions 
it came very near to it. In Germania Harbour, where the conditions correspond 
more closely with those of the outer coast, the flood wave only on one single 
occasion rose beyond 1.5 m. 
On the Danmark-Ekspedition the thickness of the fjord ice has only in ex- 
ceptional cases been measured at more than 2m (Hydrographical observations 
from the Danmark-Ekspedition by ALF TROLLE. Medd. om Grønl. XLI, pp. 395— 399). 
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