Ru Wang, Mia Hughes, David Hodgson, Jeff Peakall, Helena Brown, Edward Keavney, Gareth Keevil

Turbidity currents are a primary mechanism for transporting sediments, pollutants, and organic carbon into the deep ocean. They are strongly influenced by seafloor topography because of their relative bulk density and associated gravitational influence being 3-4 orders of magnitude smaller than in terrestrial systems. Marked run-up of turbidity currents on slopes poses a hazard to seafloor infrastructure, and leads to distinctive depositional patterns, yet the prediction of run-up heights remains poorly understood because the present calculations are derived from 2D experimental configurations and/or numerical modelling and merely limited to scenarios in which the flow strikes the topographic barriers orthogonally.
Here we present the results of 3D experiments in unconfined settings that are used to develop a new analytical model that improves the prediction of maximum run-up heights of turbidity currents that encounter topographic slopes of varying gradients and flow incidence angles. We show that existing predictive models based on 2D confined flows focusing on frontal topographic configurations underestimate the run-up heights of turbidity currents by approximately 15-40%. Experimental results highlight the importance of considering the energy contribution from internal pressure in the fluid, and lateral flow expansion and divergence in unconfined flows. Our findings reveal that intermediate slope gradients (ca. 30°) and (near-)perpendicular flow incidence angles generate the highest run-up heights, up to 3.3 times the flow thickness. Novel analytical models are presented subsequently for predicting maximum run-up height as a function of both the gradient and incidence angle, comparing the models to the newly observed data. Such models provide relatively more realistic estimates of run-up heights for flows on three-dimensional slopes typical of natural systems.
These findings are critical for improving sediment transport models, predicting the distribution of sediments, pollutants, and organic carbon in deep-sea environments, assessing seafloor geohazards, and reconstructing ancient deep-water basin palaeogeographies.