Controls on Lateral Spreading Rates of Sustained Turbidity Currents

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Turbidity currents are turbulent underflows capable of carving extensive submarine channel networks and depositing major accumulations of sediment in submarine fans. Turbidity currents are driven by gravity, and their excess density is provided by sediment held in suspension by fluid turbulence. They can be triggered through a variety of mechanisms, including re-suspension of sediment by earthquakes or over-steepened slopes, and by sediment-laden rivers in flood. Understanding how turbidites (deposits formed by turbidity currents) record turbidity current dynamics is critical when using turbidite successions in the rock record to infer paleogeography, paleoclimatic events, or paleoseismicity. Furthermore, their capacity to damage offshore infrastructure and equipment makes their prediction societally important. Finally, submarine fans serve as some of the world's most prolific hydrocarbon reservoirs and economic extraction of these hydrocarbons relies on accurate modelling of the extent and architecture of these deposits. *** Previous studies have focused on streamwise variability within turbidity currents. A natural continuation of this work is to consider planform evolution of submarine fan systems. Frontal and lateral spreading rates of turbidity currents provide a first-order control on the geometry of submarine fans, yet the variety of factors controlling turbidity current expansion remain poorly constrained. A series of experimental turbidity currents will be generated in an unconfined basin that is 5 m wide x 5 m long x 1 m deep to study the various inputs that affect turbidity current expansion, including interstitial fluid density, sediment concentration, and basin gradient. A second phase will consist of successions of turbidity currents to investigate how spreading rates are reflected in large-scale submarine fan architecture. Video cameras, time-lapse photography, velocity profiles, and a high-resolution laser scanner will be used to characterize turbidity currents. Further studies will examine the effects of interstitial fluid density on run-out distances of turbidity currents and the effects of basin geometry on the development of Taylor-Görtler vortices. Subsurface datasets and field compilations will be used to compare experimental results with natural turbidite systems. *** This work will support 2 PhD students, 3 MSc students, and 3 undergraduates. Results will build a more accurate understanding of the relationships between submarine fan geometry and gravity flow characteristics, which can ultimately be tied back to climatic or tectonic controls. Understanding the spreading behaviours of river-derived turbidity currents is critical to understanding the delivery, distribution, and burial of sediment, nutrients, and contaminants within basins. Furthermore, improving models of submarine fan morphology will lead to more accurate predictions of hydrocarbon reservoirs, resulting in more informed and economical recovery of hydrocarbons.