TWO GLACIAL STAGES IN ALASKA^ 



STEPHEN R. CAPPS 

 U.S. Geological Survey, Washington, D.C. 



The existing glaciers of Alaska are of such wide distribution 

 and are such striking scenic features that they have attracted 

 the attention of many glacialists. The coastal glaciers, many of 

 which are of large size and relatively accessible, have been most 

 frequently visited and described, and the literature on Alaskan 

 glaciers now includes a large number of titles. The fact has been 

 generally recognized by those who have studied the glaciation of this 

 territory that the area at present covered by glaciers is much smaller 

 than the area which was formerly covered by glacial ice, and glaciers 

 no longer exist at many localities where the surface still shows 

 conspicuous evidence of their former presence. This evidence 

 consists of such physiographic features as typical glacial mountain 

 valleys, U-shaped in cross-section; glacial lakes; moraines and 

 hanging tributary valleys, and of such other evidence as is afforded 

 by smoothed, polished, and striated rock surfaces; glaciated pebbles 

 and bowlders; erratic bowlders, and deposits of glacial till. 



It is beyond the scope of this paper to outline the areas in 

 Alaska which are known to have been formerly covered by glacial 

 ice. Brooks^ published in 1906 a map showing the limits of glacia- 

 tion, as known at that time. Tarr and Martin^ have recently pub- 

 lished a revision of Brooks's map, based on somewhat more recent 

 information. On both of these maps a number of areas have been 

 shown as glaciated about which no detailed information is available, 

 and the outlines as given can be corrected only after much more 

 field work has been done. 



' Published by permission of the Director of the U.S. Geological Survey. 



^ A. H. Brooks, " Geography and Geology of Alaska," U.S. Geol. Survey Paper 45, 

 1906, PI. XII. 



3 R. S. Tarr, and L. Martin, Alaskan Glacier Studies, National Geographic Society, 

 914, Map I. 



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