BU~': ·· ' ~.X-t~ .:1 kt..-. .--~~ Earth Flows: rc iJ&O. "' ~,. Morphology, Mobilization, and Movement G E 0 L 0 G I C A L S U R V E Y P R 0 F E S S I 0 N A L P A P E R 1 2 6 4 ~~ .BURtAU OF MIN.fiS LIBRARY; SPOKANE. WASH. MAR 151984 PltA!)f '<ETURN lO LIBRARY Earth Flows: Morphology, Mobilization, and Movement By DAVID K. KEEFER and ARVID M. JOHNSON GEOLOGICAL SURVEY PROFESSIONAL PAPER 1264 A study of the factors controlling earth-flow occurrence and the velocity of an active earth flow UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1983 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging in Publication Data Keefer, David Knight Earth flows: Morphology, mobilization, and movement. (Geological Survey professional paper 1264) Bibliography: p. 53-56 Supt. of Docs. no.: I 19.16:1264 1. Earthflows. 2. Earthflows-California. I. Johnson, Arvid M. II. Title. III. Series: United States. Geological Survey. Pro­ fessional Paper 1264. QE599.A2K43 1983 551.3 83--600499 For ~ale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Page Abstract -------------------------------------------------------------------------- 1 The Davilla Hill earth-flow complex-Continued I ntrod ucti on --------------------------------------------------------------------- 1 Studies of active earth flows and ground-water conditions, Previous studies -------------------------------------------------------- 2 1974-78--Continued Classification and terminology -------------------------------------- 4 Subsurface displacements -------------------------------------- 29 Acknowledgments ------------------------------------------------------- 4 Water levels -------------------------------------------------------- 32 Earth-flow morphology, materials, and settings -------------------- 5 Water contents ---------------------------------------------------- 32 Topography, climate, and geology in areas of earth-flow oc- Unit weights, void ratios, and saturation ----------------- 33 currence ----------------------------------------------------------------- 5 Laboratory swell tests ------------------------------------------- 33 San Francisco Bay region -------------------------------------- 5 Piezometric and tensiometric measurements, August Other regions ------------------------------------------------------- 8 1975-February 1978 ------------------------------------------- 36 Morphology -------------------------------------------------------------- 8 Analysis of mobilization ----------------------------------------------- 38 Idealized earth-flow morphology ----------------------------- 10 Measurement of shear-strength parameters, using di- Subsurface features: Basal shear surfaces, lateral shear rect-shear tests ------------------------------------------------- 39 surfaces, and associated zones of deformation -------- 13 Slope-stability analysis of earth flows ---------------------- 40 Earth-flow complexes ------------------------------------------------- 16 Discussion ---------------------------------------------------------------- 41 Materials ------------------------------------------------------------------ 17 A model for earth flow ------------------------------------------------------ 41 The Davilla Hill earth-flow complex ------------------------------------ 22 Earth-flow mobilization ----------------------------------------------- 43 Description ---------------------------------------------------------------- 22 Model of a moving earth flow --------------------------------------- 43 Location and setting --------------------------------------------- 22 Velocity measurements ----------------------------------------- 43 Morphology and history of movement --------------------- 24 Shear surfaces and adjacent zones of disturbance ------ 46 Material -------------------------------------------------------------- 27 Distribution of displacements --------------------------------- 47 Subsurface geometry ------------------------------------------- 27 Surges ---------------------------------------------------------------- 4 7 Studies of active earth flows and ground-water conditions, Velocity, boundary slip, and boundary roughness ------ 48 197 4-78 ------------------------------------------------------------------- 28 Internal deformation --------------------------------------------- 51 Surface displacements ------------------------------------------- 28 Composite model -------------------------------------------------- 51 Correlations of precipitation with mobilization and rate Conclusions ---------------------------------------------------------------------- 52 of movement ----------------------------------------------------- 29 References cited --------------------------------------------------------------- 53 ILLUSTRATIONS [Plates are in pocket] PLATE 1. Map showing earth-flow complexes in Eden Canyon and vicinity, Alameda County, California 2. Map and cross section showing the Hidden Valley earth-flow complex, Alameda County, California 3. Maps and cross section showing the Davilla Hill earth-flow complex, Alameda County, California Page FIGURE 1. Location map of part of San Francisco Bay region ------------------------------------------------------------------------------------------------------ 3 2. Photographs of typical earth-flow deposits ---------------------------------------------------------------------------------------------------------------- 5 3. Bar graphs showing inclinations of slopes on which earth flows occur ---------------------------------------------------------------------------- 6 4. Block diagrams showing idealized earth flow ------------------------------------------------------------------------------------------------------------- 8 5-7. Photographs showing: 5. Main scarps and crown cracks of earth-flow complexes --------------------------------------------------------------------------------------- 10 6. Deposits in zones of depletion of earth flows ----------------------------------------------------------------------------------------------------- 11 7. Toe of earth-flow deposit in Bear Valley area --------------------------------------------------------------------------------------------------- 11 8. Diagram showing cross-section through pressure ridge flanking earth flow at Kirkwood Creek, Mont. -------------------------------- 11 9. Photograph showing lateral ridge in earth flow at Melendy Ranch complex -------------------------------------------------------------------- 12 10. Block diagrams showing formation of lateral ridges ---------------------------------------------------------------------------------------------------- 12 11. Photograph of lateral ridge in earth-flow deposit in Cordelia, Calif., area ----------------------------------------------------------------------- 13 12. Photograph of slickensided lateral shear surface on inner flank of lateral ridge at Melendy Ranch complex -------------------------- 13 11J IV CONTENTS Page FIGURE 13. Diagram showing multiple basal shear surfaces underlying earth-flow toe at Beltinge, England ----------------------------------------- 13 14-16. Photographs showing: 14. Types of cracks disrupting earth flows ------------------------------------------------------------------------------------------------------------- 14 15. Slickensided shear surfaces ---------------------------------------------------------------------------------------------------------------------------- 14 16. Lateral shear surfaces in zones of depletion of earth flows at Davilla Hill complex -------------------------------------------------- 15 17. Block diagram and map of trench cut through earth-flow deposit in Cordelia, Calif., area ------------------------------------------------- 15 18. Photograph of convoluted contact between materials in trench cut through earth-flow deposit in Cordelia, Calif., area ---------- 15 19. Diagram showing earth-flow deposits exposed in wall of gully near Davilla Hill complex --------------------------------------------------- 16 20. Photograph of earth-flow complexes occupying long narrow channels ----------------------------------------------------------------------------- 16 21. Aerial view of two earth-flow complexes in Cordelia, Calif., area ---------------------------------------------------------------------------------- 16 22. Photograph of hummocky earth-flow complex near Pleasanton, Calif. ---------------------------------------------------------------------------- 17 23. Chart showing plasticity indexes and liquid limits of earth-flow materials ----------------------------------------------------------------------- 22 24. Geologic map of Eden Canyon area, showing location of Davilla Hill earth-flow complex --------------------------------------------------- 23 25. Chart showing daily precipitation in Eden Canyon, July 1974-February 1978 ------------------------------------------------------------------ 25 26. Photographs showing Davilla Hill earth-flow complex ------------------------------------------------------------------------------------------------- 26 27-28. Graphs showing: 27. Cumulative displacements of survey stakes on earth flows ---------------------------------------------------------------------------------- 30 28. Displacement of survey stakes on earth flows of Davilla Hill complex ------------------------------------------------------------------- 31 29. Photograph and graph showing measurement of subsurface displacements