Particle-laden gravity currents (PLGCs) are driven by the mass difference between a heavy fluid-particle mixture and a lighter ambient liquid. They often occur in natural and industrial situations, among which a typical situation is the release of a finite volume. Here, we focus on such ‘dam-break’ situations, which are studied using lock-release devices at the laboratory scale, and more specifically on Boussinesq turbidity currents generated from full-depth releases of vertical reservoirs. The objective of the present chapter is to describe the macroscopic scale of the early moments of the flow, namely the _slumping regime_, with respect to the relevant dimensionless parameters. For this, we combine a total of 288 runs from three different lock-release devices and from two-fluids numerical simulations, which allow us to cover a large range of particle types (size and density), volume fractions, bottom slopes and geometries. By tracking the front propagation through time, we extract the dimensionless slumping velocity ℱr and dimensionless characteristic slumping duration τ, on which we base our description. Our results show that the slumping velocity increases with the bottom slope, but decreases with the particle volume fraction when the latter exceeds a critical value. However, it remains independent of particle settling processes, which on the other hand affects the slumping duration. Hence, above a critical threshold, τ decreases as the ratio between the settling velocity and characteristic current velocity increases. For all these regimes, we derive scalings and energetic balances that reproduce the observed trends. The latter comparison confirms the role of initial energy transfer from the initial state towards the slumping phase on the resulting dynamics. This initial process and its characterization remain crucial to prescribe relevant initial conditions for large-scale predictive modeling.

The generation of topographic internal waves (IWs) by the sum of an oscillatory and a steady flow is investigated experimentally and with a linear model. The two forcing flows represent the combination of a tidal constituent and a weaker quasi-steady flow interacting with an abyssal hill. The combined forcings cause a coupling between internal tides and lee waves that impacts their dynamics of internal waves as well as the energy carried away. An asymmetry is observed in the structure of upstream and downstream internal wave beams due to a Doppler shift effect. This asymmetry is enhanced for the narrowest ridge on which a super-buoyancy (ω>N) downstream beam and an evanescent upstream beam are measured. Energy fluxes are measured and compared with the linear model, that has been extended to account for the coupling mechanism. The structure and amplitude of energy fluxes match well in most regimes, showing the relevance of the linear prediction for IW wave energy budgets, while the energy flux toward IW beams is limited by the generation of periodic vortices in a particular experiment. The upstream-bias energy flux - and consequently net horizontal momentum - described in Shakespeare [2020] is measured in the experiments. The coupling mechanism plays an important role in the pathway to IW induced mixing, that has previously been quantified independently for lee waves and internal tides. Hence, future parameterizations of IW processes ought to include the coupling mechanism to quantify its impact on the global distribution of mixing.