CHAPTER X 

 WEATHERING— DENUDATION— EROSION 



WEATHERING 



1. Due to Evaporation. Ablation, in the sense of loss of volume through evaporation, 

 sublimation, &c., has already been discussed in Chapter II., but some notes may 

 here be given as to the weathering effects which may result from it. 



The effect of ablation on salt water ice was well seen in the case of the sea 

 spray which had been heaped over our cases by the great blizzard of February 19-21, 

 1908. About a month afterwards an attempt was made to recover a case of 

 bottled beer and four volumes of the Challenger Reports, and after digging down 

 3 or 4 feet the search was abandoned. In February 1909 the ice had so far 

 ablated that the site of this trench was only just discernible, and when a trench 

 was sunk for another 18 inches within 2 feet of the former one the Challenger 

 volumes were recovered. Thus between 3 and 4 feet of this ice had been removed 

 in the twelve months just past.* 



One more effect of the ablation is worthy of comment. The prismatic ice 

 of the southern half of Blue Lake (where it was especially prevalent) evaporated 

 very rapidly, and the evaporation proceeded much more rapidly down the opaque 

 partitions between the crystals than down the crystals themselves, so that they 

 remained standing apart as individual hexagons. 



2. Due to Change of Temperature. Cape Royds is so littered with morainic 

 debris that it is impossible to tell with any degree of accuracy how important a 

 factor in the breaking up of rock is differential contraction and expansion, the 

 result of sudden changes of temperature. That this agent of weathering is im- 

 portant, however, can be easily seen. After one of the sudden variations of 

 temperature, which were very common at the cape, it was quite a usual thing 

 to find the drifts at the foot of cliffs sparsely covered with flakes of freshly 

 exfoliated rock fragments. 



Screes were not nearly as common at Cape Royds as at Cape Barne, but 



• Mention should be made of the fact that this ice formed from the freezing of the sea spray was 



not dense ice, but more or less fibrous, with numerous air spaces. The removal of this 3 to 4 feet from 



its surface was due no doubt in part to sublimation and in part to thaw. It would of com'se, by reason 



of its salinity, thaw more rapidly than fresh water ice. 



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