THE GLACIER'S SURFACE FEATURES 



393 



FIG. 419. Lines of flow upon the surface of the 

 Hintereisf erner glacier in the Alps (after Hess) . 



The moraines. The horns and comb ridges which rise above 

 the glacier surface are continually subject to frost weathering, 

 and from time to time drop their separated fragments upon the 

 glacier. Falling as these do from considerable heights, they reach 

 the ice under a high velocity, and rebounding, sometimes travel 

 well out upon its surface before coming to a temporary rest. Upon 

 a fresh snow surface of the neVe* their tracks may sometimes be 

 followed with the eye for considerable distances, and their fall 

 is a constant menace to Alpine climbers. Below the ne"ve" the 

 larger number of such frag- 

 ments remain near the 

 cliff, and the lines of flow 

 of the ice within the gla- 

 cier surface are such that 

 blocks which reach points 

 farther out upon the gla- 

 cier are later gathered in 

 beneath the cliff at the side (Fig. 419). The ridge of angular rock 

 debris which thus forms at the side of the glacier is called a 

 lateral moraine (see Fig. 411, p. 385, and Fig. 420). 



At the junction of two glacier 

 streams, the lateral moraines are joined, 

 and there move out upon the ice sur- 

 face of the resultant glacier as a medial 

 moraine. Thus from the number of 

 medial moraines upon a glacier sur- 

 face it is possible to say that the im- 

 portant tributary glaciers number one 

 more (Fig. 420). 



The plucking and abrading processes 

 in operation beneath the glacier, quarry 

 the rock upon its bed, and after shap- 

 ing and smoothing the separated rock 

 fragments, these are incorporated with- 

 in the lower layers of the ice as engla- 

 cial rock debris. In spaces favorable 

 for its accumulation, a portion of this material, together with much 

 finer de*bris and rock flour, is left behind as a ground moraine 

 upon the bed of the glacier (see Fig. 421). 



PIG. 420. Lateral and medial 

 moraines of the M er de glace 

 and its tributary ice streams. 



