Wave Generation by Fluidized Granular Flows: Experimental Insights Into the Maximum Near‐Field Wave Amplitude

Abstract

Tsunamis can be generated by an impulsive displacement of water resulting from the entrance of pyroclastic density currents (PDCs). The maximum wave amplitude is of primary interest regarding tsunami modeling and applications to hazard assessment. This study explores tsunami generation by fluidized granular flows and analyzes published relationships predicting maximum wave amplitudes from PDC characteristics. A fluidized column of glass beads is released from a reservoir, flows down an inclined plane and enters a water‐filled flume, generating waves. Fluidized flows of greater mass enter the flume with greater velocities; however, all the analyzed flows impact the water with a supercritical impact Froude number. Flows of greater mass generate a single, high‐amplitude wave, followed by a longer‐period trough. The solitary‐like leading wave propagates along the flume with a nearly constant amplitude. In contrast, the leading wave is followed by a low‐amplitude trough and a second low‐amplitude crest when generated by lower mass flows. Dispersive effects are stronger for waves produced by flows of lower masses, causing the decrease of the amplitudes with distance from the shore. Increased breaking and dissipation cause decreased amplitudes of the waves generated in shallow water depths. The predictive equations, determined based on the impact Froude number and the water depth in the constant‐depth section of the flume, provide relatively good predictions of the maximum wave amplitudes. A new approach is proposed, which calculates the impact Froude number considering the water depth value where the wave generation occurs, providing an improved understanding of the wave generation process.

Large‐Scale Physical Modeling of Wave Generation and Runup on Slopes From the Collapse of Partially and Fully Submerged Granular Columns

“…The amplitude and consequences of waves generated from subaerial landslides can be extreme: the seismically triggered 1958 Lituya Bay landslide in Alaska generated a tsunami wave with a runup of 524 m, the highest recorded in history (Fritz et al., 2009; Miller, 1960); whereas the 1963 failure at Vajont, Italy generated a wave that overtopped a dam, flooded the valley, and destroyed villages, resulting in the loss of over 2000 lives (Barla & Paronuzzi, 2013; Genevois & Ghirotti, 2005). Waves associated with subaerial landslides have been thoroughly investigated in the laboratory using solid block experiments (e.g., Heller & Spinneken, 2013; Kamphuis & Bowering, 1970; Panizzo et al., 2005), experiments with dry granular landslides (e.g., Huber, 1980; Fritz et al., 2004; Mohammed & Fritz, 2012, Miller et al., 2017), and experiments using flows with greater velocities and distal reach ranging from snow avalanches (e.g., Zitti et al., 2016), saturated flows (e.g., Bullard et al., 2023; de Lange et al., 2020), pyroclastic density currents (e.g., Lipiejko et al., 2023) and finally, to water as a fully fluidized material (e.g., Bullard, Mulligan, Carreira, & Take, 2019; Bullard, Mulligan, & Take, 2019). Through this wide range of experimental data sets, relationships have been derived to predict the maximum wave amplitude formed at impact based on the characteristic properties of the landslide (e.g., Fritz et al., 2004; Heller & Hager, 2010; Mulligan & Take, 2017) and validation exercises have been conducted with numerical simulations aimed to capture landslide momentum transfer, wave propagation, and wave runup (e.g., Mulligan et al., 2020).…”