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

Climate change is making coastal regions increasingly vulnerable to hazards, including rapid subaerial and submarine landslides, which can result in catastrophic tsunamis. Due to the complex geomechanics of failure, limited physical modeling studies have been conducted that encompass the entire problem including the triggering of granular landslides, the waves generated by partially and fully submerged mass failures, and the runup of these waves on local and distal slopes. In the present study, for the first time, waves in both the seaward direction (in the direction of failure for both submarine and partially submerged slides) and the landward direction (opposing the direction of failure only for submarine slides) are investigated during morphological evolution of the granular material. A series of large‐scale experiments are conducted under varying levels of submergence in water by releasing columns of gravel‐sized material into a range of different reservoir depths. This is accomplished using a pneumatically actuated vertical lift gate designed specifically for these experiments. The wave amplitudes measured in the seaward direction agree with empirical relationships developed in a previous study using smaller‐scale models, and a new analytical solution relating the column submergence to the trough‐led wave amplitudes in landward direction is presented. These novel predictions of wave amplitude and runup in both the seaward and landward directions indicate strong dependence of the wave behavior on the submergence depth and granular properties, improving our understanding of tsunamis generated by mass failures in coastal regions. Plain Language Summary Landslides can occur from above water or underwater, and both types can generate hazardous waves. Climate change is destabilizing slopes and causing more landslides into water, and there is a need to study how these waves form and how they impact coastal areas in detail. In the present study, a series of large‐scale laboratory flume experiments are conducted to examine this problem by measuring waves with digital cameras and probes. The experiments each begin with a vertical column of gravel‐sized particles that are released by rapidly opening a gate specifically designed for this research. The collapse of the granular material generates waves in the forward direction (seaward) and in the backward direction (landward) and both waves also cause runup on slopes at each end of the flume. Different column heig