ABLATION iiti 



Ablation at Cape Royds was measured by us hi two ways. (1) By fixing bamboo 

 poles into the lake ice, and marking on the pole the exact level of the ice-surface at 

 the time the pole was fixed. Measurements, taken at intervals, showed that the 

 surface was becoming progressively lowered. (2) Blocks of ice, approximately 

 cubical, were cut from the ice of the lakes, and these were suspended in a position 

 out of doors where sun and air had free access to them, and were weighed from time 

 to time. 



We fixed a bamboo pole in the ice of Coast Lake, near the centre of the lake, 

 on April 3, 1908. At the time this bamboo was fixed in position in the ice it was 

 noticed that in many parts of the lake the delicate tips of the freshwater algae, so 

 numerous in these lakes, projected about 2 inches above the surface of the ice. It 

 is almost certain that the tips were about level with the surface of the water when 

 the lake was first frozen over towards the end of summer. That is, from about the 

 beginning of February to the beginning of April, about 2 inches of ice had been 

 ablated. On June 13, 1908, it was found, when the measurements were made from 

 the mark on the bamboo pole at Coast Lake to the surface of the lake-ice, that 1'35 

 inches of ice had been ablated. It was a matter of great surprise to us that such a 

 large amount of ablation had taken place during such a cold period, when the thermo- 

 meter was mostly below 0° Fahr. At Pony Lake, close to our winter quarters at 

 Cape Royds, the ablation was even greater. Dr. Mawson fixed a bamboo pole in the 

 ice on this lake on April 18, and, on measuring it on June 12, found the amount of 

 ablation to be 15 inches. That is, in the case of Coast Lake, 1"35 inches of ablation 

 had taken place in seventy days, and, in the case of Pony Lake, 1'50 inches of 

 ablation in fifty-five days. The bamboo pole at Coast Lake was measured again on 

 June 20, 1908, when it showed only a little over 1"3 of an inch total ablation. A 

 straight-edge, in the form of a light board with parallel sides, was used on this 

 occasion, in order to ensure greater accuracy, as there seemed a slight tendency for 

 the ice immediately around the base of the bamboo to be slightly lowered below the 

 level of the surrounding ice. This reading is thei'efore perhaps more reliable than 

 the one taken on June 13. It is hardly likely that the surface of the lake ice would 

 have gained in height In the interval. On July 13 we fixed up another ablation- 

 pole, this time in the ice of Blue Lake. On July 16 we fixed a second ablation- 

 stick in Blue Lake. On July 22 we fixed another ablation-stake at Blue Lake, 

 and also one at Clear Lake and one at Green Lake. 



On August 5 we measured the ablation-pole at Coast Lake, and the amount of 

 ablation since April 3 was TQ inches. On October 2 we re-measured the bamboo 

 pole at Coast Lake, and made out the total ablation to be about 1 '63 inches, that is 

 from April 3 until October 2. This seems inconsistent with the measurement, taken 

 on August 5, of a total ablation already at that date of 1'9 inches, but it must be 

 remembered that, in the intervals between the measurements, a good deal of snow 

 had fallen and covered this lake, temporarily at any rate ; and, in the second place, 



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