Effect of Slide Deformation and Geometry on Waves Generated by Submarine Landslides: A Numerical Investigation
Authors: Das Kaushik , Green Steve , Basu Debashis , Janetzke Ron , Stamatakos John 
Published: July 2009

The impact of slide deformation and geometry on surface waves generated by submarine landslides is studied using a computational model based on Navier-Stokes equations. The volume of fluid (VOF) method is used to track the free surface and shoreline movements. The Renormalization Group (RNG) turbulence model and the Detached Eddy Simulation (DES) multiscale model are used to simulate turbulence dissipation. Three-dimensional simulations are first compared with available experimental data involving the generation of waves by a rigid block sliding down an inclined plane. The role of slide deformation on the characteristics of the generated waves is evaluated. The results from the simulations are compared with the experimental data for the rigid slide. Simulated results highlight the importance and complexity of slide deformation on the generated wave characteristics and runup/rundown at various locations. Computed results also show the complex three-dimensional flow patterns in terms of the velocity field, shoreline evolution, and free-surface profiles. Predicted numerical results for time histories of free-surface fluctuations and the runup/rundown at various locations are found to be in good agreement with the available experimental data for the rigid slide. The location of the slide (whether it is fully submerged or aerial) also seems to influence the runup and wave height.

Introduction

Tsunamis are surface waves caused by the impulsive perturbation of the sea. Apart from co-seismic sea bottom displacement due to earthquakes, subaerial and submarine landslides can also produce localized tsunamis with large and complex wave runup. The wave characteristics and hazards related to tsunamis generated by submarine landslides have been an area of active research (Masson et al. 2006, Fine et al. 2005, Longva et al. 2003). Submarine landslides, which often accompany large earthquakes, can disturb the overlying water column as sediment and rock slump down slope. Any type of geophysical mass flow including debris flows, debris avalanches, landslides, and rockfalls can create submarine landslide-generated tsunamis. Earthquakes can also play an indirect role as the landslide-triggering mechanism. In addition to bringing devastating consequences and destruction to human lives, landslide-generated tsunamis constitute a threat in terms of direct wave impact or currents to offshore installations including oil platforms, risers, pipelines, and ships and to coastal installations. Coastal or shallow water structures are more prone to destruction due to higher wave current velocities in these places. Although the generation and propagation of earthquake-generated tsunamis have been studied for several decades and are now relatively well understood, such is not the case for landslide-generated tsunamis. While the mechanisms that generate these types of tsunami flows are generally understood, the ability to predict the flows they produce at coastlines still represents a formidable challenge due to the complexities of coastline formations and the presence of numerous coastal structures that interact and alter the flow. The generation and effects of landslide-generated tsunamis are complex and variable.