THE WORK OF GLACIERS 



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land and noted its position from year to year. In fifteen years it had 

 moved 1428 meters, or about 100 meters a year. Forty-four years 

 later the remains of the hut were found 2408 meters lower down the 

 valley. Since these first measurements careful surveys have been 

 made from time to time, and it has been found that the motion of 

 Alpine glaciers seldom exceeds one third to two thirds meter (one to 

 two feet) a day. In 1861 the heads of three guides with some hands 

 and fragments of clothing appeared at the foot of the Bossons Glacier 

 on whose neve they had been buried beneath an avalanche forty-one 

 years before. So perfect was the preservation that they were easily 

 recognized by a guide who had known them in life. The rate of 

 movement had been eight inches a day. 



In large glaciers, however, the rate is much more rapid. It is 

 estimated that the Child Glacier in Alaska moves about 30 feet a day 

 during the summer, and a large glacier which drains the snow fields 

 of north Greenland is said to have moved more than 60 feet in a single 

 day. These latter figures are exceptional and apply only to very large 

 and thick glaciers. Large glaciers, however, do not always move 

 faster than small ones, since other conditions may counterbalance, 

 the greater thickness. 



Differential Movement of Glaciers. — By placing stakes in a 

 straight line across the surface of a glacier and a vertical row on a 



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Fig. 136. — Diagrams showing the movement of glaciers. A, a line of stakes 

 placed in a straight row across a glacier becomes more and more curved each day. 

 B, a line of stakes placed in a vertical row on the exposed side of a glacier becomes 

 more and more inclined. C shows the formation of marginal fissures produced by 

 the pulling of the more rapid central portions upon the slower marginal portions. 



side exposure, it was found that the middle of a glacier moves faster than 

 the sides (Fig. 136 A) and the top faster than the bottom (136 A, B). 

 In one glacier, while the top moved 6 inches, the middle moved only 4.5 

 inches, and the bottom 2.5 inches. The reason for the slower motion 

 of the sides and bottom is evidently to be found in the friction with 



