SEA ICE 185 



sea water coming up through the tide crack.* This theory is rendered the more 

 probable by our further observation, that at the time of the return of the Southern 

 Supporting Party to Hut Point in November 1908 it was observed that the sea ice 

 on which we, together with the Southern Party, had been camped a few days before, 

 had been thrown into a series of broad undulations, with a difference of level of 

 2 feet between the centre of the trough and that of the centre of the nearest 

 crest. In this case the fold was parallel to the ice-foot at the point, but there were 

 slight evidence of tidal overflow along the ice-foot below Observation Hill. At the 

 same time this overflow was much masked by the fact that the sea ice was for the 

 most part there hidden from view by deep snow-drifts piled against the cliff". It 

 may be added that the old sea ice, possibly three or four years old, forming a zone 

 separating the " pinnacled ice " from the one-year ice, was covered with snow in 

 summer time to a depth of from 1 foot to 18 inches, and its surface was from 3 

 to 4 feet above sea-level. Less than 2 feet of this, however, appears to be actually 

 ice, and it seems probable that the whole thickness of this old sea ice is not more 

 than from 15 to 16 feet. It would be interesting to ascertain for how long this ice 

 would persist now that it has reached its present thickness, for every year its 

 resistance to disrupting agencies becomes greater, and the exceptionally heavy 

 weather of 1908 had very little effect on it. Its surface was comparable with the 

 type which we found worst for sledging on the Great Ice Barrier itself. The older 

 drifts were not quite sufficiently hard to bear the weight of a man, and at every 

 step one dropped 8 or 9 inches on to a firmer surface. As explained elsewhere, the 

 space between the two crusts was filled with coarse-grained snow powder, due to 

 a selective action of the thaw, the grains which were left having increased in size 

 at the expense of those which had been completely vaporised. The outer crust is 

 evidently due to the formation of fresh drifts on an old and wind-swept surface, 

 with its snow sastrugi a foot or 18 inches high, and also to the subsequent semi- 

 hardening of these drifts by the snow of the previous summer. 



After the surface of the sea had become firmly consolidated with ice in early 

 winter, but before the ice had acquired a thickness of more than a few feet, fracture 

 took place along certain definite lines (often approximately parallel to the shore-line) 

 through pressure of wind and tide, and subsequently along these fractured ridges 

 lines of pressure ice were raised. These ridges attained a height of from 10 to 

 20 feet. They could be seen forming chiefly during northerly winds, which forced 

 the sea ice past Cape Royds, and piled up the ice blocks particularly high between 

 Blacksand Beach and Flagstaff" Point. The formation of these pressure ridges was 

 a fine spectacle. While the northerly wind was blowing, as one watched from the 

 shore one saw roll after roll of sea ice forming one behind the other, as the whole 

 mass was steadily pressed against the coast-line by an unseen but irresistible force. 



* Later experiences with the Scott Expedition incline me to think that this phenomenon is better 

 explained by a flooding of the sea ice with the thaw-water from the Blue Glacier (R. E. Priestley). 



