Debris-flow mobilization from landslides

Field observations, laboratory experiments, and theoretical analyses indicate thatlandslides mobilize to form debris flows by three processes: (a) widespreadCoulomb failure within a sloping soil, rock, or sediment mass, (b) partial orcomplete liquefaction of the mass by high pore-fluid pressures, and (c) conver-sion of landslide translational energy to internal vibrational energy (i.e. granulartemperature). These processes can operate independently, but in many circum-stances they appear to operate simultaneously and synergistically. Early work ondebris-flow mobilization described a similar interplay of processes but relied onmechanical models in which debris behavior was assumed to be fixed and gov-erned by a Bingham or Bagnold rheology. In contrast, this review emphasizesmodels in which debris behavior evolves in response to changing pore pressuresand granular temperatures. One-dimensional infinite-slope models provide in-sight by quantifying how pore pressures and granular temperatures can influencethe transition from Coulomb failure to liquefaction. Analyses of multidimen-sional experiments reveal complications ignored in one-dimensional models anddemonstrate that debris-flow mobilization may occur by at least two distinctmodes in the field.