Landslides that occur in coastal environments drive cascading consequences such as large wave forces, flooding, and infrastructure damage in coastal communities. It can be difficult to classify these slides as subaerial or submarine, and the mechanics of wave generation associated with partially submerged failures is less clear. Limited physical modelling has been conducted that encompasses both the triggering of granular landslides and subsequent waves associated with partially and fully submerged mass movements. The focus of previous studies has primarily been on the waves generated in the direction of failure (seaward) and not on the waves formed above and behind the failure (landward). To address this research gap, a series of large-scale granular collapse experiments were conducted by releasing columns of river stone (0.75 m and 0.50 m high) into a laboratory flume reservoir with water depths ranging up to 1.10 m to explore the wave generation and runup processes in both seaward and landward directions. The columns were released by a rapid pneumatically actuated vertically rising gate designed to enable the near instantaneous loss of support of the source volumes resulting in granular collapse. The wave amplitude is measured using wave capacitance gauges and the failure mechanics are captured with high-speed cameras. This work also provides the first experimental data set of the landward propagating wave and runup associated with submerged granular collapse experiments. Overall, the seaward wave amplitudes measured in these highly instrumented, large-scale physical models agree with empirical relationships developed in a previous study using smaller-scale models. From these observations, a new analytical solution relating the initial column submergence to the magnitude of the landward trough wave is presented. The physical model results presented in this study accurately quantify the wave amplitude and runup observations in both the seaward and landward directions and could serve as a first order approximation for risk assessment for tsunamis generated by submerged and partially submerged mass failures.
