Earth flows; morphology, mobilization, and movement

------------------------------------------------------------------------1 I ntrod ucti on --------------------------------------------------------------------1 Previous studies -------------------------------------------------------2 Classification and terminology -------------------------------------4 Acknowledgments ------------------------------------------------------4 Earth-flow morphology, materials, and settings -------------------5 Topography, climate, and geology in areas of earth-flow occurrence ----------------------------------------------------------------5 San Francisco Bay region -------------------------------------5 Other regions ------------------------------------------------------8 Morphology -------------------------------------------------------------8 Idealized earth-flow morphology ----------------------------10 Subsurface features: Basal shear surfaces, lateral shear surfaces, and associated zones of deformation -------13 Earth-flow complexes ------------------------------------------------16 Materials -----------------------------------------------------------------17 The Davilla Hill earth-flow complex -----------------------------------22 Description ---------------------------------------------------------------22 Location and setting --------------------------------------------22 Morphology and history of movement --------------------24 Material -------------------------------------------------------------27 Subsurface geometry ------------------------------------------27 Studies of active earth flows and ground-water conditions, 197 4-78 ------------------------------------------------------------------28 Surface displacements ------------------------------------------28 Correlations of precipitation with mobilization and rate of movement ----------------------------------------------------29 Page The Davilla Hill earth-flow complex-Continued Studies of active earth flows and ground-water conditions, 1974-78--Continued Subsurface displacements -------------------------------------29 Water levels -------------------------------------------------------32 Water contents ---------------------------------------------------32 Unit weights, void ratios, and saturation ----------------33 Laboratory swell tests ------------------------------------------33 Piezometric and tensiometric measurements, August 1975-February 1978 ------------------------------------------36 Analysis of mobilization ----------------------------------------------38 Measurement of shear-strength parameters, using direct-shear tests ------------------------------------------------39 Slope-stability analysis of earth flows ---------------------40 Discussion ---------------------------------------------------------------41 A model for earth flow -----------------------------------------------------41 Earth-flow mobilization ----------------------------------------------43 Model of a moving earth flow --------------------------------------43 Velocity measurements ----------------------------------------43 Shear surfaces and adjacent zones of disturbance -----46 Distribution of displacements --------------------------------4 7 Surges ---------------------------------------------------------------4 7 Velocity, boundary slip, and boundary roughness -----48 Internal deformation --------------------------------------------51 Composite model -------------------------------------------------51 Conclusions ---------------------------------------------------------------------52 References cited --------------------------------------------------------------53