GLACIAL EROSION IN ALASKA 



*°5 



This deceptive appearance was so striking that, on asking fellow voy- 

 agers for an explanation of the hanging valleys, I have again and 

 again received the answer that the mouth of the valley has been 

 dammed and a lake formed behind it. So apparent is this explanation 

 that the captain of the steamer stated positively that there are always 

 lakes behind these lips. 



Thus the hanging valley is so abnormal a feature that even to 

 ordinary observers it seems to demand some special explanation. That 

 there are lakes in some of the hanging valleys is probable; but it is not 

 a necessary condition. The lip is not a dam; it is unconsumed rock in 

 a valley bottom that has been left high above the main valley by ex- 

 ceptional conditions which have deepened the main trough. It was of 

 course impossible to stop and go into the many hanging valleys which 

 we passed in the Inside Passage, but farther up the coast I was able to 

 enter such valleys and prove, what I was well aware of before, that the 

 lip is not a dam and that lakes form no necessary part of the hanging- 

 valley condition (see Figs. 7 and 8). 



Two other features of the valleys in the Inside Passage are note- 

 worthy. One is the fact that in both the main and tributary valleys 

 the rock walls have been smoothed and rounded by glacial action, prov- 

 ing the former extension of glaciers through this series of ' Keaches.' 

 The other is the remarkably uniform cross-section of both the main 

 and tributary valleys, as is so well illustrated in many of the accompany- 



Fig. 6. A Hanging Valley on the South Side of Xunatak Fiord. This valley lies 

 on the same side, but about a mile west of the succeeding pictures (Figs. 7, 8 and 9). The float- 

 ing ice is from Nunatak glacier about four miles distant. Photograph by Lawrence Martin. 



