342 



Transactions. 



Art. XLIII. — Note on the Rate of Erosion of the Hooker and Mueller 



Glaciers. 



By P. Marshall, M.A., D.Sc, F.G.S., F.R.G.S., Professor of Geology, 



Otago University. 



{Read before the Otago Institute, tjth August, 1912.] 



Much discussion, and even controversy, has taken place amongst geological 

 observers in all countries in regard to the importance of glacial erosion. 

 By some, almost unlimited powers have been ascribed to it ; by others, 

 almost all effectiveness has been denied to it. Spirited as the discussions 

 have been, there have yet been but few attempts to estimate the rate at 

 which glacial erosion is acting at the present time. Whereas elaborate 

 measurements have been made in regard to the rate at which rivers and 

 all flowing water lowers the land-surface, glaciers and glacial streams have 

 been to a great extent immune from such inquisitive activity. 



In New Zealand in particular no attempts have been made to estimate 

 the amount of sediment contained in the water of rivers that flow from 

 glaciers. It was with the idea of initiating local inquiry that the following 

 records were made. It was originally intended to take samples of the water 

 of the Mueller River where it issued from beneath the ice of the glacier. 

 It was, however, found that the outlet of the river had so changed its 

 position that it was practically impossible to obtain samples of the water. 

 This forced me to take samples from beneath the Hooker Bridge, a quarter 

 of a mile below the Mueller outlet, and two miles below the source of the 

 Hooker River. Wliile this is somewhat unsatisfactory, it is thought that 

 the amount of sediment contained in the water is practically the same as 

 at the point where the rivers ac ually issue from beneath the ice. 



It is, of course, recognized that the amount of sediment suspended in 

 glacial water represents the amount of rock removed by one only of several 

 different activities that are effective in glacial regions. The suspended 

 matter is of an extremely fine and impalpable nature and of a pale-grey 

 colour, and it almost certainly represents the material derived from the 

 filing action of rock-fragments dragged over the rocky bed of the glacier 

 during the slow movement of the ice. The amount and nature of the 

 erosion due to the transport of moramic matter, to the plucking action of 

 the ice, and to solution are not here referred to. The quantities of sediment 

 were as follows : — ■ 



Nov. 17, 1911 



„ 18, „ 



„ 19, „ 



„ 20, „ 



5> 23, ,, 



25 



Feb. 3^ 1912 



7 



„ 17, „ 



„ 29, „ 



Mar. 15, „ 



„ 25, „ 



The average of these estimations is 1 part of sediment in 15,523 parts 

 of water. 



