Chapter 13 



RELATION OF LANDSLIDES TO SEDIMENTARY 

 FEATURES * 



D. J. Varnes 



Geologist, U. S. Geological Survey 



Denver Federal Center 



Denver, Colorado 



Landslides have been the subject of considerable study for many- 

 years, and in many different countries, not only because they are 

 of practical economic importance, but also because they are wide- 

 spread, effective, and interesting agents in the shaping of land forms. 

 There is now available a vast volume of observations by construc- 

 tion engineers, geologists, and interested laymen covering the many 

 diverse phases of landslides and other kinds of earth movement. Most 

 striking is the growing literature on the application of soil mechanics 

 to the stability analysis of certain types of landslides. The subject 

 of landslides now has many aspects that cannot be covered in a short 

 chapter. The discussion to follow, therefore, will be principally a 

 description of those features of sedimentary deposits which are recog- 

 nized as contributing to true landslides, or which must be considered 

 in their prevention, analysis, or cure. Some of the features described 

 are not limited to sedimentary deposits ; likewise many of the dynamic 

 processes operate as well in metamorphic or igneous terrains. 



To acquaint the reader with the terminology to be used, and with 

 the typical form of the several kinds of landslides, C. F. S. Sharpe's 

 classification and one of his illustrations, taken from Landslides and 

 Related Phenomena (1938), are reproduced in Figs. 1 and 2. Readers 

 familiar with this excellent work will recognize that much of what 

 follows is an enlargement on his "active" and "passive" causes as 

 applied to sedimentary deposits. 



For the present purpose, the role of the major factors of (1) physical 

 and chemical composition, (2) structure of the deposit, and (3) state 

 of stress in the material in the production of some of the types of 

 slides illustrated in Fig. 2 will be shown. 



* Published by permission of the Director, U. S. Geological Survey. 



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