tlie Hintereis Glacier. 171 



reduction in the freezing-point of o, 000249 C. per kg. 

 Taking the theoretical figure we should have in a glacier 

 a gradient of about o, l C. per 14,800 cm. Using a coefficient 

 of conduction for ice of 0*0057 the flow of heat per annum 

 per sq. metre 



_ 0-0057 x lOOOOx 31536000 x 0-1 



~ 11800 

 = 12,000 gram calories. 



This is only about one forty-fifth part of the heat produced 

 by friction, so it would seem that unless the ice coming from 

 the higher slopes is much below the freezing-point, glacier 

 ice, especially near the bottom, must contain some water. 



Crevasses. — In addition to being a substance possessing a 

 very high viscosity, ice is also brittle and elastic. The 

 brittleness of ice is well shown by the numerous crevasses 

 which score glacier surfaces. 



The most simple form of crevasse is that which occurs at 

 an ice fall ; the crevasses then run across the glacier. But 

 there are crevasses which run roughly at angles of 45° or 60° 

 with the sides, and extend from the edge in an upward direc- 

 tion, while others run longitudinally or nearly so. The 

 explanation generally adopted for the inclined crevasses is 

 that put forward by Hopkins. 



Hopkins pointed out that as a glacier moves more slowly 

 near the sides than it does in the middle, surface distortion 

 takes place as a result of shear, and that in such a case 

 compression and tensile strains are set up which reach a 

 maximum at 45° with the side. These tensile strains were 

 assumed by him to be sufficiently great to cause rupture. 

 Hitherto our knowledge of the distribution of the crevasses 

 caused by glacier flow has not been sufficiently detailed to 

 allow of a thorough examination of the sufficiency of this 

 theory to explain the facts. 



Blumcke and Hess, however, have supplied the details 

 necessary for such an examination in the case of the Hintereis 

 Glacier. Fig. 11 is a map of the glacier tongue showing the 

 crevasses and the contour-lines. Owing to the surface shear 

 being partly the result of slip, the actual velocity curve 

 across the glacier is as shown by curve a, fig. 9. Here the 

 maximum rate of shear is near the side, and the shear force 



is rj — '. 

 n 



_ 19 k v1 a 12 '00001236 noM 

 = lloxw l ~ — — — — =0-94 kg. per cm. 2 

 Io70 ° ■ 



