Tsunamis generated by long and thin granular landslides in a large flume

Abstract

In this experimental study, granular material is released down slope to investigate landslide‐generated waves. Starting with a known volume and initial position of the landslide source, detailed data are obtained on the velocity and thickness of the granular flow, the shape and location of the submarine landslide deposit, the amplitude and shape of the near‐field wave, the far‐field wave evolution, and the wave runup elevation on a smooth impermeable slope. The experiments are performed on a 6.7 m long 30° slope on which gravity accelerates the landslides into a 2.1 m wide and 33.0 m long wave flume that terminates with a 27° runup ramp. For a fixed landslide volume of 0.34 m3, tests are conducted in a range of still water depths from 0.05 to 0.50 m. Observations from high‐speed cameras and measurements from wave probes indicate that the granular landslide moves as a long and thin train of material, and that only a portion of the landslide (termed the “effective mass”) is engaged in activating the leading wave. The wave behavior is highly dependent on the water depth relative to the size of the landslide. In deeper water, the near‐field wave behaves as a stable solitary‐like wave, while in shallower water, the wave behaves as a breaking dissipative bore. Overall, the physical model observations are in good agreement with the results of existing empirical equations when the effective mass is used to predict the maximum near‐field wave amplitude, the far‐field amplitude, and the runup of tsunamis generated by granular landslides.

Runup of granular landslide‐generated tsunamis on planar coasts and conical islands

“…The wave characteristics are dependent on the landslide impact parameters [Fritz et al, 2003a[Fritz et al, , 2003b[Fritz et al, , 2004Zweifel et al, 2006;Heller and Hager, 2010;Mohammed and Fritz, 2012;McFall and Fritz, 2016;Bregoli et al, 2017;Miller et al, 2017]. The governing tsunami generation parameters investigated in this study are the water depth h, slide impact velocity v s , slide thickness s, slide width b, slide volume V s , slide length scale L s 5 V s /(sb), and shoreline radius r c .…”

Waves and Sediment Transport Due to Granular Landslides Impacting Reservoirs

“…Moreover, large and fast landslides often generate greater wave amplitudes, as indicated by laboratory experiments (e.g., Fritz et al, 2003aFritz et al, , 2003b and the numerical results in section 3.3. Notably, Miller et al (2017) and Meng (2018) suggested that the wave amplitudes of long and thin granular landslides are mainly affected by the effective mass, which is defined as the landslide mass entering the water body at the moment that the leading wave reaches its maximum wave height. Figures S21 and S22 show the dependence of e on the initial landslide volume and velocity, respectively, which are normalized by bh 2 w0 and ffiffiffiffiffiffiffiffiffi gh w0 p , respectively.…”

Non-Hydrostatic Modeling of Waves Generated by Landslides with Different Mobility

“…Experiments were performed in a landslide flume consisting of an 8.23 m long slope inclined at 30 • to the horizontal to gravitationally accelerate landslides into a 33.0 m long and 2.1 m wide horizontal wave flume described in detail by [12], shown in Figure 1. Tests with different mobility were selected as end-member examples in the present study.…”

“…where the sliding mass with bulk density ρ s impacts the water on slope α at velocity v s parallel to the slope. It has thickness s on impact with the water, and the resulting wave is generated over the effective time ∆t e that momentum is imparted from the slide to the water [12]. The fluid momentum flux (M f ) is given by:…”