THE GEOGRAPHIC SOCIETY'S ALASKAN EXPEDITION 



43 



HIDDEN GLACIER IN 1906 



This photograph was taken from the same point as the view of Hidden glacier in 1909, given 

 on page 42. The glacier has advanced nearly two miles in three vears 



America. In our expedition especial 

 study was made of the piedmont ice 

 bulbs into which so many of the glaciers 

 expand on emergence from their moun- 

 tain valleys ; and in this connection the 

 ablation moraines which accumulate on 

 the wasting surfaces of the stagnant 

 piedmont ice masses, and the deposits ac- 

 cumulating around their margins, were 

 given particular attention. A statement 

 of the results of these studies must for 

 the present be postponed. 



Another line of inquiry to which at- 

 tention was given was the cause of glacier 

 motion, upon which the advancing gla- 

 ciers throw light. The sudden forward 

 movement of a glacier, such as observed 

 in Yakutat Bay, is difficult to explain on 

 the basis of some of the current hypo- 

 theses for glacial motion. On the hypo- 

 thesis of plastic or viscous flowage. on 

 the other hand, the phenomena are all 

 -easily explained. A number of facts of 

 observation in the summer of 1906 and 



1909 tend toward the verification of this 

 hypothesis. The discussion of this sub- 

 ject must also be left for our final report. 



Other problems which will be dis- 

 cussed in the full report deal with ques- 

 tions relating to the former extension of 

 the glaciers. During the period of maxi- 

 mum glaciation, ice filled the entire 

 Yakutat Bay inlet and discharged ice- 

 bergs into the Pacific ; and at the same 

 time the Copper River Valley was filled, 

 and ice occupied the entire Prince Wil- 

 liam Sound, at least on the eastern side 

 to which our studies were confined. The 

 erosive work performed by these great 

 glaciers has, in part, shaped the various 

 inlets and valleys, while their deposits 

 have left records of considerable scien- 

 tific interest. 



In view of the fact that only two parts 

 of the coast have so far been studied, it 

 will not, of course, be possible to enter 

 into a comparative study of the phe- 

 nomena of former glaciation of all 



