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THE NATIONAL GEOGRAPHIC MAGAZINE 



FRONT OF COLUMBIA GLACIER IN I9IO, COMPARED IN HEIGHT TO BUNKER HILL 



MONUMENT 



The ice pinnacle, rising over 200 feet above the base, fell a few minutes after this picture was 



taken. Photo by Lawrence Martin 



had retreated small amounts since visited 

 by earlier parties, and a number seemed 

 to have maintained their positions. 



REASONS FOR OSCILLATIONS OF GLACIERS 



It is not perfectly clear why these gla- 

 ciers in Prince William Sound and on 

 Copper River are oscillating — some ad- 

 vancing and some retreating. Of course 

 the fundamental cause is involved with 

 snow supply and with rate of melting as 

 determined by temperature. Climatic 

 records are so incomplete that we cannot 

 settle this question. On the other hand, 

 it is possible that the snow supply of any 

 glacier or group of ice tongues might 

 have been increased by avalanching dur- 

 ing earthquakes, as is the case in Yaku- 

 tat Bay, rather than by increase of pre- 



cipitation. These Prince William Sound 

 and Copper River glaciers are outside 

 the zone affected by great avalanching 

 during the Yakutat Bay earthquakes of 

 September, 1899, though the advance of 

 La Perouse Glacier may possibly be due 

 to that seismic disturbance. There are 

 many other earthquakes, however, whose 

 origins were in or near the region of 

 these advancing glaciers, and one such in 

 October, 1900, was of considerable in- 

 tensity. 



The Yakutat Bay glaciers which have 

 so far advanced as a result of the earth- 

 quakes, including Nunatak Glacier, in 

 1910, are of variable sizes and have re- 

 sponded in order of size, the smaller 

 ones first. These advancing glaciers in 

 Prince William Sound are also of vari- 



