THE EFFECT OF SUPERGLACIAL DEBRIS ON THE 

 ADVANCE AND RETREAT OF SOME CANADIAN 

 GLACIERS. 



Observations on rates of motion, amounts of advance or retreat 

 of glaciers, and kindred statistics are now being collected from all 

 quarters of the globe in the hope of deducing some general laws of 

 ice-motion in the present, and of throwing some hght on glacial 

 conditions in the past.^ 



Obviously the advance of glaciers is influenced by two factors: 

 (i) rate of motion, and (2) rate of waste. Any cause increasing the 

 rate of motion will tend to push the front of the ice forward, and this 

 advance will be held in check only by the amount of waste. Waste 

 will be increased either by a rise in temperature, producing increased 

 melting and evaporation, or by increased exposure to dry air pro- 

 ducing evaporation. A glacier may advance, therefore, either from 

 increased motion or from decreased waste. 



Observations on the advance or retreat of existing glaciers have 

 been correlated almost exclusively with the factors influencing rate 

 of motion. The rate of waste is usually neglected, or is regarded 

 as of secondary importance. Of secondary importance it may be 

 in the case of any one glacier, since the daily and annual ranges in 

 temperature about the freezing-point are approximately the same 

 in successive years. Hence it may be safely assumed that the amount 

 of water lost by any one glacier will differ from year to year mainly 

 in proportion to changes in the mass of the ice, which in turn is 

 affected by rate of motion. But when different glaciers are com- 

 pared, it becomes evident that rate of waste is an important factor 

 in determining the position of the ice-front. 



Glaciers differ from each other in rate of waste, as they do in 

 rate of motion, and a sluggish glacier, slow-moving and slow- wasting, 

 may advance farther than one whose rate of motion is faster, but 

 whose rate of waste is also faster. 



I Harry Fielding Reid, Journal of Geology, 1895 to date. 



722 



