THE INFLUENCE OF THE EARTH'S ROTATION UPON 

 THE LATERAL EROSION OF STREAMS^ 



HENRY M. EAKIN 



Introduction 



It is a well-known fact that rotation of the earth upon its axis sets 

 up a tendency in bodies in motion upon its surface to deviate from a 

 straight course, in the northern hemisphere to the right, and in the 

 southern, to the left. Different writers^ have considered the possible 

 results of this tendency in modifying stream erosion, but in general 

 little importance has been attached to it, striking results of its opera- 

 tion not being commonly observed. 



The most satisfactory analysis of the problem is Gilbert's, in which 

 he notes certain processes involved in stream erosion not usually 

 considered and endeavors to make a quantitative measurement of 

 the effect of the deflective force acting relative to them. He points 

 out that centrifugal force is developed on the curves of meandering 

 streams. Velocity being a factor of this force, so-called "threads" 

 of higher velocity will tend more strongly toward the outer bank on 

 curves. The rotational deflective force depending also upon velocity 

 will affect the "threads" of higher velocity more strongly. The effect 

 of this stronger tendency of the swifter threads one way or the other 

 he expresses as a "selective influence," whereby they migrate 

 nearer one bank or the other, displacing threads of lower velocity 

 and accelerating lateral erosion. In the northern hemisphere the 

 rotational deflective force acts in conjunction with centrifugal force 

 on right curves, and on left curves in opposition to it. Consequently 

 the locus of maximum velocity would be shifted toward the outer 

 bank more strongly on right curves than on left curves, the cross- 



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



2 Dunker, Zeitsch. jilr die gesammten Natiirwissenschajten (1875), 463; Klock- 

 mann, Jakrb. Preuss. Geol. Landesamt (1882); Geikie, Textbook 0} GeoL, I, 23; Cham- 

 berlinand Salisbury, Geology, I, 184; Jefferson, Bull. Geol. Soc. Am., XVII, 333-50; 

 Gilbert, Am. Jour. Sci., 3d ser., XXVII, 427. 



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