THE MECHANICS OF GLACIERS. I.^ 



I. Law of flow. — If we consider the ice flowing through two 

 cross-sections of a glacier, it is evident that for a glacier in equi- 

 librium, that is, one neither increasing nor diminishing in size, 

 the quantity flowing through the lower section must equal that 

 flowing through the upper one diminished by the quantity 

 melted between them, if we are in the region of melting (the 

 dissipator) ; or. increased by the quantity of ice accumulated 

 between the sections, if we are in the region of accumulation 

 (the reservoir). Keeping the upper section at the neve-line and 

 moving the other one down the glacier, the melting area between 

 the sections increases and therefore the flow through the lower 

 section becomes less. Now placingthe lower section at the neve- 

 line and moving the upper we see that the amount of accumulation 

 between the sections increases, and consequently the flow through 

 the upper section diminishes, as we move it higher up the reser- 

 voir. If we keep our two sections at a fixed distance apart, and 

 move them to different parts of the glacier, the difference of the 

 flow through the sections must increase as we go down the dis- 

 sipator, because the rate of melting increases, and must increase 

 as we go up the reservoir because the accumulation increases. 

 We can say then that the greatest flow occurs through a section at the 

 nevc-li?ie and diminishes as we go up or dow7i the glacier from there ; 

 and, moreover, that tlie rate of diminution of the flow becom.es greater 

 the further zve go from the fieve-li?ie. This is the law of flow, and is 

 perfectly general ; it depends only on the law of the indestructi- 

 bility of matter, and the observed facts that the ice of glaciers 

 moves, and that there is accumulation above, and dissipation 

 below, the neve-line. 



The steeper the dissipator's slope the more rapidly will the 



' Read before the Geological Society of America, at the "Philadelphia Meeting, 

 December, 1895. 



912 



