Marshall. — Itatt of Erosion of Hooker and Mueller Glaciers. 343 



Records of a similar nature made in other countries are not very 

 numerous. The following are quoted from Hess, " Die Gletscher " : The 

 average for the Rhone Glacier is 1 part in 1,611 of water ; the Arvo, 1 in 

 4,166 ; the Aare, 1 in 7,042 ; the Muir Glacier, 1 part in 77 of water. From 

 such records the inference has been drawn that the rate of glaciation 

 depends largely upon the degree of glaciation, which is, of course, intense 

 in Alaska, where the Muir Glacier flows. 



Further records show that the annual variation is considerable. Thus, 

 iu 1890 the Bossons Glacier delivered water that contained 1 part of sedi- 

 ment in 437 parts of water, but in 1891 it contained only 1 part in 2,078 

 of water ; the Tour Glacier in 1890 contained 1 part in 4,115, and in 1891 

 1 part of sediment in 32,193 parts of water. 



It is probably in these records that an explanation is to be found of the 

 low average of sediment in the water of the Hooker River. In November, 

 when most of my samples were taken, the weather was extremely cold, 

 and light snow fell on several occasions at the Hermitage, though the total 

 precipitation was quite small, and the river during the whole of my visit 

 was very low— not higher than winter level, in the opinion of the guides. 

 Chief Guide A. Graham, who kindly took the later samples for me, states, 

 ■' The river, on the whole, has not varied much during the summer, so the 

 samples tha+ I am sendiug you, with those taken by yourself, should give 

 a fair average for this summer. With a summer like that of last year I am 

 sure that the sediment would have been in much greater quantity. I took 

 a sample of the water during one small fresh in February." 



It is, of course, well known that the summer of 1911-12 was the coldest 

 that has been experienced in New Zealand for a considerable time. 

 Calculations based on the amount of sediment stated above show that if 

 the erosion were supposed to be of equal amount over the whole of the 

 neve and glacier area the rock-bed would be undergoing removal at the 

 rate of -^^ iu. annually, or 1 ft. in 756 years. This is an extremely slow 

 rate when compared with the action of the Muir Glacier, which lowers its 

 bed by f in. annually. Despite the small amount of sediment in the water, 

 the high precipitation in the region causes the rate of erosion to be more 

 than twice as rapid as that of the Aare Glacier, which lowers its bed 1 in. 

 in 170 years, or 1 ft. in about 2,000 years. It is, however, probably true 

 that the effect of erosion is far more pronounced in the bed of the glacier, 

 where the ice is thickest, than elsewhere ; and if it is supposed that the 

 action is so distributed that half the total of sediment is derived from 

 5 square miles of glacier-floor, then that floor would be eroded a depth of 

 4,000 ft. — the depth of many of our glacial valleys — in about 1,000,000 

 years. The action appears to be somewhat more rapid than stream-action 

 in the same region. 



Objection may be offered to these statements on the ground that some 

 of the sediment is carried to the ice by streams that flow down the steep 

 glacial walls in that part of the glacial valley that lies below the ordinary 

 snow-line, and contribute water-derived sediment to the ice. This sugges- 

 tion is discounted by the very nature of the sediment in rivers that have a 

 glacial origin : it is unoxidized, and so fine that no settlement takes place 

 in twenty-four hours. The hillsides mentioned are covered with snow for 

 many months of the year, and their water is filtered by passing through 

 the lateral moraine before they join the glacier. Even when flooded after 

 heavy summer rain the water of these streams is almost clear of sediment. 



It is hoped that, with the assistance of Chief Guide Graham, further 

 lecorda will be made in future years. 



