VI. GEOLOGY 



The nature and depth of the bottom varied considerably, and It 

 was assumed that this change was caused by the steady movement of 

 the shelf ice pushing the relatively thinner fast ice along before 

 it. Several years ago the rate of this movement was determined to 

 be 8 inches per day at the site of the old air strip on the fast 

 ice off NAF McMurdo. A similar rate would cause the icehole station 

 to move about 20 feet per month. To determine the actual rate and 

 direction of movement, the location of the hut was fixed by taking 

 angles with a transit from the hut to Observation Hill, Crater Hill, 

 and Castle Rock on Ross Island. These locations have prominent 

 signals on their summits and their positions are well known. From 

 fixes of the hut's position made on 13 February 1960 and a year 

 later on 21 February 1961, it was determined that the hut had moved 

 249 feet to the south and 245 feet to the west during the 373 days. 

 At a rate of 8 inches a day as computed for the airstrip, 373 days 

 would total 248 feet, so that the two rates agree very well. 



Since the general direction of movement at the airstrip had 

 been northerly, it was assumed that the icehole hut also was moving 

 in that direction. However, the actual direction of movement at 

 the hut was a little south of southwest. This possibly may be ex- 

 plained by the position of the hut, which is far enough to the east 

 to be more affected by the southwesterly movement of ice along the 

 southern shores of Hut Point Peninsula than by the northerly move- 

 ment of the ice mass to the west. The southwesterly movement now 

 explains why the depths became increasingly greater toward the end 

 of observations. A northerly movement would have produced shallow- 

 ing depths according to the general depth trend pattern as shown by 

 the north and south sounding line. It also has been shown that 

 depths beneath the shelf ice south of the icehole hut, generally 

 increase southward (Robinson, 1962). 



In establishing the icehole station soundings were made during 

 February and early March 1960. Table 11 summarizes results obtained 

 by examining the very small bottom samples taken with the sounding 

 tube in the new ice area. A list of the types of rocks and remains 

 found is shown. Station numbers run from the icehole north to the 

 new ice edge and then start at the eastern edge of the new ice area 

 and run in a general westerly direction (Fig. 1). Samples A, B, and 

 C are small cores taken at the icehole on 6 and 30 May 1960 and on 

 24 October 1960. 



Table 12 summarizes findings from analyses of bottom samples 

 taken at the icehole station. After 29 December 1960, an area of 

 very hard bottom was reached in the course of the southwesterly 



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