  In nature, submarine slope failures usually carry thousands of cubic-meters
of sediments across extremely long distances and cause tsunamis and damages to
offshore structures. This paper uses the granular column collapse experiment to
investigate the effect of slope angle on the runout behavior of submarine
granular landslides for different initial volumes. A two-dimensional coupled
lattice Boltzman and discrete element method (LBM-DEM) approach is adopted for
numerically modeling the granular column collapse. Columns with four different
slope angles and six different volumes are modelled under both dry and
submerged conditions. The effects of hydrodynamic interactions, including the
generation of excess pore pressures, hydroplaning, and drag forces and
formation of turbulent vortices, are used to explain the difference in the
runout behavior of the submerged columns compared to the dry columns. The
results show that at any given slope angle, there is a threshold volume above
which the submerged columns have a larger final runout compared to their dry
counterpart, and this threshold volume decreases with slope angle.
