Numerical Modeling of Tsunami Generation by Submarine and Subaerial Landslides

Abstract

Recent catastrophic tsunamis at Flores Island, Indonesia (1992), Skagway, Alaska (1994), Papua New Guinea (1998), andIzmit, Turkey (1999) have significantly increased scientific interest in landslides, and slide-generated tsunamis. Theoretical investigations and laboratory modeling further indicate that purely submarine landslides are ineffective at tsunami generation compared with subaerial slides. In the present study, we undertook several numerical experiments to examine the influence of the subaerial component of slides on surface wave generation, and to compare the tsunami generation efficiency of viscous, and rigid-body slide models. We found that a rigid-body slide produces much higher tsunami waves than a viscous (liquid) slide. The maximum wave height, and energy of generated surface waves were found to depend on various slide parameters, and factors, including slide volume, density, position, and slope angle. For a rigid-body slide, the higher the initial slide above sea level, the higher the generated waves. For a viscous slide, there is an optimal slide position (elevation) which produces the largest waves. An increase in slide volume, density, and slope angle always increases the energy of the generated waves. The added volume associated with a subaerial slide entering the water is one of the reasons that subaerial slides are much more effective tsunami generators than submarine slides. The critical parameter determining the generation of surface waves is the Froude number, Fr (the ratio between slide, and wave speeds). The most efficient generation occurs near resonance when Fr = 1.0. For purely submarine slides with p 2 ≤0.2 g-cm-3, the Froude number is always less than unity, and resonance coupling of slides, and surface waves is physically impossible. For subaerial slides there is always a resonant point (in time and space) where Fr = 1.0 for which there is a significant transfer of energy from a slide into surface waves. This resonant effect is the second reason that subaerial slides are much more important for tsunami generation than submarine slides.