the Hintereis Glacier. 175 



flow-stresses are small, they assist to produce crevasses 

 running up the glacier and having the same angle of slope 

 with the sides of.' the glacier as those produced by the 

 shoulders and bays of the valley sides. 



The tendency to produce longitudinal crevasses will be 

 constant where the glacier is flowing down a valley the 

 sides of which are getting less steep ; for the sides will be 

 sinking and cross tensile stresses will be set up. The central 

 nearly longitudinal crevasses of the Hintereis Glacier appear 

 to be due to this cause. 



We thus appear to have stresses set up in a glacier 

 flowing down valleys whose sides have been cut into by 

 stream erosion, which will give rise to crevasses inclined 

 upwards from the sides. Also, where a valley is gettiag 

 wider and the sides less steep, longitudinal crevasses will be 

 produced near the middle of the glacier. The strains pro- 

 duced by differential flow, called attention to by Hopkins, 

 are much too small, of themselves, to produce crevasses, 

 although they may assist the other forces to give the 

 crevasses the upward trend. 



Viscosity of Glacier Ice. — Our previously given equations, 

 (21), (22), and (23), would have been better written as 

 follows : — 



"=i> P (w) slloul<lbe i= to (*+?)' 



/ O? \ 2 



for b belongs to the factor for infinite width and (-5 — -„l 



\cr + b £ ) 



is the factor F p for Parr's section, the factor F e for the 

 elliptic section being 2 , 2 . 

 Equation (22) becomes 



F« „ _ 0-526 



p 

 and (23) becomes 



F,x F « =0-583 x 0^=0-523, 



79-46 X19900 2 

 V 2x0-0000654 X 

 = 125 x 10 12 poises. 



The alteration, it will be seen, does not alter the value 

 obtained for the viscosity of glacier ice. 



In equation (11) should be -. 

 V V 



