7.18 Long-Runout Landslides

Abstract

This chapter provides an overview of large (>10⁶ m³) volcanic and nonvolcanic long-runout landslides characterized by high velocities, large release and deposit volumes, and excess runout. Large long-runout landslides are very rare events and pose substantial challenges to quantitative hazard assessments. Despite several mechanistic theories, there is no commonly agreed-upon explanation of excess runout, which would also entail superposition of processes such as dynamic fragmentation, material bulking, and partial lubrication. Water as a lubricant plays only a minor or limited role given the ample evidence of dry excess runout. Numerical models based on shallow water equations provide some of the best means to realistically simulate rapid flow- and avalanche-like motion over three-dimensional terrain. However, such models critically depend on reliable initial conditions, such as failure volume and scar, material properties, and runout topography.