Review of the missing link between field and modeled submarine debris flows: Scale effects of physical modeling

Submarine debris flows occur under the cloak of the sea and are giants among other types of landslides on planet Earth. They pose a significant threat to sustainable offshore development and marine ecosystems. Existing research on these flows mainly rely on back-analyzing field events and conducting miniaturized experiments. However, it is unclear whether the dynamics of miniaturized flows are similar to field ones. In this review, dimensional analysis is used to evaluate laboratory and field data collated from the literature to compare the dynamics of submarine debris flows at different scales. Miniaturized flows are demonstrated to have disproportionately low yield stress and viscosity compared to field flows. The low yield stress is caused by the need to reduce the clay content of a model debris mixture so that it can flow under substantially reduced gravitational driving stresses in laboratory conditions. Consequently, some proposed scaling relationships in the literature derived from laboratory experiments need to be used with caution. Specifically, both the Reynolds and Bingham numbers cannot independently provide a scale-invariant criterion for distinguishing between laminar and turbulent flows. Instead, the Hampton number, with a threshold >0.001, is proposed for the design of the yield stress and clay contents of laboratory flows. Moreover, reduced model viscous stress drastically reduces erosion potential, which limits the existing understanding of the excess fluid pressures generated at the flow-bed interface, and thus flow mobility. The mobility of field flows is generally attributed to hydroplaning. However, this conjecture mainly stems from experiments with impervious boundaries. Such an idealization exaggerates the effects of excess fluid pressures that develop during hydroplaning. An enhanced understanding of the differences in dynamics between field and modeled flows can improve the design of future experiments to model submarine debris flows.