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

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.