Loss of capacity, not competence, as the fundamental process governing deposition from turbidity currents

Hiscott, Richard N.

doi:10.2110/jsr.64.209

Cited by 175 publications

(159 citation statements)

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“…2013). More generally, the relationship between flow speed and the mass of sediment suspended (capacity) and grain size suspended (competence) is of fundamental importance for flow behavior, as noted previously (Kuenen and Sengupta 1970;Hiscott 1994). For instance it governs whether incorporation of eroded material into a flow will lead to acceleration or deceleration (Fig.…”

Section: (B) Supercritical-flow Dynamics and Depositsmentioning

confidence: 82%

Key Future Directions For Research On Turbidity Currents and Their Deposits

Talling

Allin

Armitage

et al. 2015

Journal of Sedimentary Research

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163

117

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Turbidity currents, and other types of submarine sediment density flow, redistribute more sediment across the surface of the Earth than any other sediment flow process, yet their sediment concentration has never been measured directly in the deep ocean. The deposits of these flows are of societal importance as imperfect records of past earthquakes and tsunamogenic landslides and as the reservoir rocks for many deep-water petroleum accumulations. Key future research directions on these flows and their deposits were identified at an informal workshop in September 2013. This contribution summarizes conclusions from that workshop, and engages the wider community in this debate. International efforts are needed for an initiative to monitor and understand a series of test sites where flows occur frequently, which needs coordination to optimize sharing of equipment and interpretation of data. Direct monitoring observations should be combined with cores and seismic data to link flow and deposit character, whilst experimental and numerical models play a key role in understanding field observations. Such an initiative may be timely and feasible, due to recent technological advances in monitoring sensors, moorings, and autonomous data recovery. This is illustrated here by recently collected data from the Squamish River delta, Monterey Canyon, Congo Canyon, and offshore SE Taiwan. A series of other key topics are then highlighted. Theoretical considerations suggest that supercritical flows may often occur on gradients of greater than , 0.6u. Trains of up-slope-migrating bedforms have recently been mapped in a wide range of marine and freshwater settings. They may result from repeated hydraulic jumps in supercritical flows, and dense (greater than approximately 10% volume) near-bed layers may need to be invoked to explain transport of heavy (25 to 1,000 kg) blocks. Future work needs to understand how sediment is transported in these bedforms, the internal structure and preservation potential of their deposits, and their use in facies prediction. Turbulence damping may be widespread and commonplace in submarine sediment density flows, particularly as flows decelerate, because it can occur at low (, 0.1%) volume concentrations. This could have important implications for flow evolution and deposit geometries. Better quantitative constraints are needed on what controls flow capacity and competence, together with improved constraints on bed erosion and sediment resuspension. Recent advances in understanding dilute or mainly saline flows in submarine channels should be extended to explore how flow behavior changes as sediment concentrations increase. The petroleum industry requires predictive models of longer-term channel system behavior and resulting deposit architecture, and for these purposes it is important to distinguish between geomorphic and stratigraphic surfaces

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Section: (B) Supercritical-flow Dynamics and Depositsmentioning

confidence: 82%

Key Future Directions For Research On Turbidity Currents and Their Deposits

Talling

Allin

Armitage

et al. 2015

Journal of Sedimentary Research

Self Cite

163

117

View full text Add to dashboard Cite

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“…The proposal of Eq. (13) is therefore a strong argument for a capacity perspective on particle suspension, as opposed to a competence perspective (Dorrell et al, 2013;Hiscott, 1994). Of course the dichotomy cannot be complete, and the role of grain size in limiting the suspended particle concentration will be discussed in Sect.…”

Section: Discussionmentioning

confidence: 99%

Physical theory for near-bed turbulent particle suspension capacity

2017

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Abstract. The inability to capture the physics of solid-particle suspension in turbulent fluids in simple formulas is holding back the application of multiphase fluid dynamics techniques to many practical problems in nature and society involving particle suspension. We present a force balance approach to particle suspension in the region near no-slip frictional boundaries of turbulent flows. The force balance parameter contains gravity and buoyancy acting on the sediment and vertical turbulent fluid forces; it includes universal turbulent flow scales and material properties of the fluid and particles only. Comparison to measurements shows that = 1 gives the upper limit of observed suspended particle concentrations in a broad range of flume experiments and field settings. The condition of > 1 coincides with the complete suppression of coherent turbulent structures near the boundary in direct numerical simulations of sediment-laden turbulent flow. thus captures the maximum amount of sediment that can be contained in suspension at the base of turbulent flow, and it can be regarded as a suspension capacity parameter. It can be applied as a simple concentration boundary condition in modelling studies of the dispersion of particulates in environmental and man-made flows.

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“…2U LU/Lx), and depositional when the opposite is true (i.e., LU/ Lt , 2U LU/Lx) (e.g., Kneller 1995). This assumes that the flow is carrying its full capacity of sediment so that there is a dynamic balance between the fluxes of sediment entrainment and settling (e.g., Allen 1991;Hiscott 1994;Pratson et al 2001;Kneller and McCaffrey 2003). Deceleration of the flow therefore decreases the entrainment of sediment from the bed, which results in deposition.…”

Section: Conceptual Modelmentioning

confidence: 99%