Lessons from Ontake-san: A comparative analysis of debris avalanche dynamics

摘要: Abstract Dynamic aspects of the long runout Ontake-san debris avalanche are evaluated by a comparison several models. An unsteady numerical model assumes two-dimensional flow an incompressible biviscous or Newtonian fluid, represented as continuum with free surface. Internal deformation flowing mass is considered, well boundary resistances. Thus thinning and deposit shape kinematics may be modeled. Parameters adjusted to match observed runout, additional constraints on velocity emplacement time. With abundant for Ontake-san, from careful field investigations Japanese research teams, our analysis indicates that substantial decrease in resistance occurred function displacement. Constant-property models tend overestimate peak velocities underestimate times. A staged increase mobility both constant volume variable leads results consistent data. Runout channel overflow area was also Qualitatively similar have been obtained other researchers using simple sliding block empirical parameters, slide rational parameter selection, modified flood simulation, multi-element frictional model. The relative merits these compared. mechanisms associated this displacement poorly understood, but question now identified target future at sites, some plausible considered. main reason probably involves entrainment river water saturated sediment, leading enhanced efficiency fluid pressure undrained shear; addition, progressive shearing reduced mean particle size angularity, cohesion friction (and apparent viscosity) near wetted perimeter. Hydroplaning — films slurries locally.