What determines the downstream evolution of turbidity currents?

• Published in: Earth and planetary science letters Vol. 532; p. 116023
• Main Authors: Heerema, Catharina J., Talling, Peter J., Cartigny, Matthieu J., Paull, Charles K., Bailey, Lewis, Simmons, Stephen M., Parsons, Daniel R., Clare, Michael A., Gwiazda, Roberto, Lundsten, Eve, Anderson, Krystle, Maier, Katherine L., Xu, Jingping P., Sumner, Esther J., Rosenberger, Kurt, Gales, Jenny, McGann, Mary, Carter, Lionel, Pope, Edward
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.02.2020
• Subjects: autosuspension; dissipation; flow behaviour; ignition; submarine canyon; turbidity current; submarine canyon; autosuspension; turbidity current; flow behaviour; ignition; dissipation
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2019.116023

Seabed sediment flows called turbidity currents form some of the largest sediment accumulations, deepest canyons and longest channel systems on Earth. Only rivers transport comparable sediment volumes over such large areas; but there are far fewer measurements from turbidity currents, ensuring they are much more poorly understood. Turbidity currents differ fundamentally from rivers, as turbidity currents are driven by the sediment that they suspend. Fast turbidity currents can pick up sediment, and self-accelerate (ignite); whilst slow flows deposit sediment and dissipate. Self-acceleration cannot continue indefinitely, and flows might reach a near-uniform state (autosuspension). Here we show how turbidity currents evolve using the first detailed measurements from multiple locations along their pathway, which come from Monterey Canyon offshore California. All flows initially ignite. Typically, initially-faster flows then achieve near-uniform velocities (autosuspension), whilst slower flows dissipate. Fractional increases in initial velocity favour much longer runout, and a new model explains this bifurcating behaviour. However, the only flow during less-stormy summer months is anomalous as it self-accelerated, which is perhaps due to erosion of surficial-mud layer mid-canyon. Turbidity current evolution is therefore highly sensitive to both initial velocities and seabed character. Summarising model for turbidity current behaviour in submarine canyons underlain by loose sand. Small increases in initial velocity cause major differences in subsequent flow velocities and runout distance, causing divergence in flow behaviour (purple, dark blue and light blue lines). However, flows can sometimes self-accelerate and ignite within the mid-canyon (green dotted line), due to changes in substrate strength and erodibility. There is a threshold initial transit velocity (red line) above which turbidity currents can autosuspend (purple line). •Turbidity currents form the largest sediment deposits and deepest canyons on Earth.•First detailed measurements from many sites along a turbidity current pathway.•Flow behaviour diverges; small increases in initial speed lead to longer runout.•After initial acceleration, fast flows reach a near-uniform state of autosuspension.•The only flow in summer is anomalous, perhaps due to erosion of surficial-mud layer.