Landslide tsunamis: exploring momentum transfer to waves generated by a range of materials with different mobility impacting water

At impact with water, the velocity and thickness of a landslide are the key factors that govern momentum transfer and wave generation. These properties are not only a function of the size of the slide, but also a function of the landslide material, grain size, pore fluid, and other rheological parameters. The objective of this study is to determine the amplitude of waves generated from realistic landslides composed of both granular material and pore fluid in comparison with the waves generated by end-member landslides composed of only dry granular material or only fluid. To achieve this, laboratory experiments are conducted in a large-scale landslide flume and observations are collected using high-speed digital cameras and wave probes. Different source materials consisting of dry granular material, saturated granular material, and water are released down the landslide slope into the reservoir to generate impulse waves. The waves are analyzed to determine the amplitude and shape, and the effective time and length scales over which each landslide generates a wave. The observations are used to develop a mobility factor for all three landslide types based on the linear relationship between the length of forcing and the time of wave release. The measurements are compared to a predictive momentum-based relationship, and a modified equation is developed to account for the bulk mobility of the landslide. The improved equation can be applied to predict the maximum wave amplitude generated by a wide range of conditions for realistic landslides.