or road of gravel or cinder is strewn on the ice in the early spring between the ship and the open 

 water. A rather considerable interval of time is required for the subsequent effect. During the 

 German Antarctic Expedition of the ship Gauss (1901 to 1903), a strip of rubbish 10 m wide was 

 scattered along the bow of the ship in order to facilitate the freeing of the vessel. During January 

 a furrow formed under the layer of rubbish and the ice cracked along this furrow on 8 February and 

 the ship was able to reach the open water. 



LITERATURE: 24, 62, 107, 111. 



Section 114. Breaking of Ice During Melting 



The basic process which promotes the final destruction of the ice cover is the breaking of the ice 

 fields and fast ice mto smaller and smaller parts. 



As we have seen in the preceding chapter, ice is broken apart by the wind, the currents and 

 the waves at any time of the year but in the spring, when the ice is weakened by thawing; the frac- 

 ture of ice requires less force and occurs with certain peculiarities. These peculiarities stem from 

 the fact that the small chunks and grated ice, which are always formed in greater or lesser quantity 

 during the breaking of the ice, melt very quickly and expanses of open water appear between the 

 floes, thus giving the individual floes a certain freedom of movement. 



Whatever the causes for the breaking up of the field into separate parts, it is natural that the 

 outer contours of these parts will be accidental (random) and will have comparatively sharp angles. 



Various forces will react in various ways on the broken-off parts. If the ice field, before the 

 fracture, was moving with a certain speed and in a certain direction under the influence of current 

 or winds, then the broken parts of this field, of various sizes and shapes, will move with various 

 speeds and in various directions. Under the influence of the wind, for example, certain floes may 

 begin to turn about in such a way that the wind pressure on the floe balances the resistance of the 

 water and the coriolis force. Due to inertia, large ice floes start their movements by wind influ- 

 ence somewhat later and due to resistance of the water move slower than the small floes. Under the 

 influence of ebb and flood tides, the individual parts of the broken-up ice field will sometimes press 

 together, sometimes move apart, and so forth. 



Thus immediately after the break-up of the ice field there are created the rotating and ad- 

 vancing movements of separate parts with various speeds and directions. These movements 

 acquire particular importance in the case of comparatively open ice where they inevitably result in 

 collisions. The first consequences of this are the rubbing off and breaking away of the more 

 projecting and sharper comers of the floes. Just as sharp rocks and stones are rounded into small 

 boulders and rounded pebbles by surf action rubbing them against each other, the movement of the 

 floes and the collisions and rubbing one against the other give the individual floes an oval or rounded 

 shape. 



Another result of the movement and subsequent colliding is the thickening of the edges of the 

 ice fields and the floes. In the collisions the sharp comers of the ice fields are partly broken-off 

 and ground into small chunks and grated ice, partly driven down under the edges, and partly thrown 

 up onto the edges of the colliding floes. In both cases the thickness of the edges of the floes is 

 gradually increased. Similar processes, as we have seen, bring about the formation of small walls 

 (raised rims) on the disks of pancake-type ice. 



308 



