The Theory of Glacier motion. Z^^ 



glaciers. Again, so far as we know, the crystals forming a 

 glacier are in contact with each other when its temperature 

 is below zero. Capillary fissures only develop between the 

 . crystals when the ice begins to melt. These fissures do not 

 apparently exist at all, nor is ice permeable to liquids when 

 below the freezing point, and at a temperature therefore 

 where the growth of the crystals can alone take place, and 

 if we limit the actual growth of the glacier crystals to the 

 winter when the temperature may perhaps be sufficiently 

 low, we cannot appeal to that growth to explain the motion 

 of glaciers, which is greatest in summer. 



If we are to attribute the continuous motion of the 

 glacier to this growth of its crystalline components, we must 

 also remember how very slight the motion would be. 

 The water which permeates the capillaries merely fills 

 spaces already in existence, and cannot, therefore, by itself 

 cause any thrust, while in freezing its bulk is only increased 

 by one-ninth of itself; nor can we well see how, when 

 the fissures and capillaries are filled by the infiltration of 

 water in the spring, they can re-open again. No force is 

 available for the purpose. It is not enough to appeal to the 

 water and to the effect of freezing in dilating it — we must 

 also find some force by which the separate crystals of ice 

 shall each year be pulled asunder so as to again cause voids 

 {id., 364). Heim, in criticising the theory to which in a 

 measure he was favourably inclined, urged first on broad 

 grounds that if, as Forel argued, the growth of the glacier 

 was due to the freezing in winter of the water which per- 

 meates it in summer, it is hard to see why in Greenland, 

 where the summers are so short and the winters so long, the 

 ice should nevertheless move much faster than that of the 

 Alpine glaciers {Heim, 299). 



Again, according to Forel, the external cold must first 

 freeze the water in the superficial capillaries, and gradually 

 freeze up those in the lower depths of the glacier. If this 



