THE FLOW OF GLACIERS in 



by the snow which falls on the higher mountain ridges, 

 and is squeezed into the form of ice instead of snow 

 powder by its own weight as it slips down the inclines, 

 warmed by the unclouded sunshine. The big glaciers 

 move much more rapidly (or perhaps one should say 

 less slowly) in the middle than at the sides. The 

 measurements which have been made differ in different 

 glaciers and in different parts of the same glacier, and 

 show smaller movement in winter than in summer. 

 The advance of the sides is retarded, as in the case 

 of an ordinary river of flowing water, by friction against 

 the rocks, which enclose the glacier as its banks enclose 

 a river. A good average case shows a flow downwards 

 in summer of half a foot a day at the sides and a foot 

 and a half in the middle. The distance below the 

 snow-line to which the flowing glacier descends down 

 a mountain gorge before it melts away and becomes 

 a river of liquid water depends, as does the rate at 

 which it moves, in the first place, on the temperature of 

 the region and on the sharpness of the slope. A glacier 

 will flow downwards (as will a lump of pitch) along 

 a scarcely perceptible incline, but more slowly than 

 down a steeper incline, and it will, consequently, get 

 further down into the warm valley without altogether 

 melting away when the slope is steep. 



But apart from these considerations, the bigger and 

 thicker (or deeper) the glacier, that is to say, the more 

 snow which each year falls at its starting-place and goes 

 to making it, the further down will it flow before melting 

 away ; and it is the heavy snowfall of many years ago 

 or of a series of years long past which has to-day reached 

 in the form of ice the lower end of the glacier. So, 

 though the lower end of the glacier may melt more 

 quickly if the valley has become hotter, yet the heavy 

 snowfalls of fifty years ago may only now have reached 

 the valley, and may quite counterbalance the melting 

 action of the warmer summers. Or reverse conditions, 



