Sediment concentrations, flow conditions, and downstream evolution of two turbidity currents, Monterey Canyon, USA

Xu, Jingping; Sequeiros, Octavio E.; Noble, Marlene A.

doi:10.1016/j.dsr.2014.04.001

Cited by 72 publications

(78 citation statements)

References 90 publications

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“…2; Xu et al 2004Xu et al , 2013Xu et al , 2014Xu 2010Xu , 2011. This is part of collaborative work by Paull and others at the Monterey Bay Aquarium Research Institute (MBARI), who are developing new sensors embedded in moving near-bed layers that record their acceleration and sense of rotation, and techniques for recovering data from such sensors through gliders.…”

Section: Suggestions For Key Future Research Directionsmentioning

confidence: 99%

“…It is already the location of detailed and technologically sophisticated monitoring efforts (Paull et al 2010a), including the first velocity and density profiles through active flows ( Fig. 2; Xu et al 2004Xu et al , 2010Xu et al , 2013Xu et al , 2014Xu 2010). A major Monterey Bay Aquarium Research Institute (MBARI), US Geological Survey, and UK Natural Environment Research Council monitoring experiment is already funded from 2014-2017, which includes deployment of a seafloor observatory, event detectors along the flow path of the sandy floor of the canyon, and four sets of ADCP moorings at water depths of 300 m to 1850 m. An extensive set of cores (including vibracores taken with a remotely operated vehicle (ROV); Fig.…”

Section: Suggestions For Key Future Research Directionsmentioning

confidence: 99%

“…Sediment concentration is the critical parameter controlling such flows, yet it has never been measured directly for flows that reach and build submarine fans. Indeed, studies in only six locations (Xu et al , 2013(Xu et al , 2014Xu 2011;Hughes Clarke et al 2012, 2014Cooper et al 2012;Khripounoff et al 2003Khripounoff et al , 2012Vangriesheim et al 2009;Ayranci et al 2012; Lintern and Hill, personal communication; see Talling et al 2013) have estimated sediment concentrations for turbidity currents in shallow water, typically using backscatter values from acoustic Doppler current profilers (ADCPs). This indirect technique for measuring sediment concentration (backscatter is also affected strongly by additional parameters including grain size) has large uncertainties and cannot penetrate into high sediment concentrations at the base of the flow.…”

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confidence: 99%

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Key Future Directions For Research On Turbidity Currents and Their Deposits

Talling

Allin

Armitage

et al. 2015

Journal of Sedimentary Research

165

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: Suggestions For Key Future Research Directionsmentioning

confidence: 99%

Section: Suggestions For Key Future Research Directionsmentioning

confidence: 99%

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confidence: 99%

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Key Future Directions For Research On Turbidity Currents and Their Deposits

Talling

Allin

Armitage

et al. 2015

Journal of Sedimentary Research

165

117

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“…() and Xu et al . () using sediment traps. These authors found that sand was suspended in turbidity currents in the Monterey Canyon (USA) to a height of at least 70 m above the canyon floor.…”

Section: Discussionmentioning

confidence: 99%

Linking submarine channel–levee facies and architecture to flow structure of turbidity currents: insights from flume tank experiments

2017

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Submarine leveed channels are sculpted by turbidity currents that are commonly highly stratified. Both the concentration and the grain size decrease upward in the flow, and this is a fundamental factor that affects the location and grain size of deposits around a channel. This study presents laboratory experiments that link the morphological evolution of a progressively developing leveed channel to the suspended sediment structure of the turbidity currents. Previously, it was difficult to link turbidity current structure to channel–levee development because observations from natural systems were limited to the depositional products while experiments did not show realistic morphodynamics due to scaling issues related to the sediment transport. This study uses a novel experimental approach to overcome scaling issues, which results in channel inception and evolution on an initially featureless slope. Depth of the channel increased continuously as a result of levee aggradation combined with varying rates of channel floor aggradation and degradation. The resulting levees are fining upward and the grain‐size trend in the levee matches the upward decrease in grain size in the flow. It is shown that such deposit trends can result from internal channel dynamics and do not have to reflect upstream forcing. The suspended sediment structure can also be linked to the lateral transition from sediment bypass in the channel thalweg to sediment deposition on the levees. The transition occurs because the sediment concentration is below the flow capacity in the channel thalweg, while higher up on the channel walls the concentration exceeds capacity resulting in deposition of the inner levee. Thus, a framework is provided to predict the growth pattern and facies of a levee from the suspended sediment structure in a turbidity current.

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“…Recently, both laboratory experiments (Baas, 1994;Cartigny et al, 2013) and direct observations in submarine canyons (Talling, 2013;Xu et al, 2014) have shown that turbidity currents are commonly supercritical, whereas in open-channel flows, ripples and dunes form under subcritical conditions; thus the absence of angular bedforms results from the unique velocity and concentration profiles of density currents (Parker et al, 2013). However, experimental work has also confirmed the presence of downstream-migrating angular bedforms that are dimensionally similar to dunes in supercritical flow (Sequeiros et al, 2010); thus the Froude number may not be a good predictor of bed morphology in turbidity currents.…”

Section: Introductionmentioning

confidence: 99%

The influence of grain size on the velocity and sediment concentration profiles and depositional record of turbidity currents

Tilston

Arnott

Rennie

et al. 2015

Geology

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Cross-stratification formed by migrating dunes is ubiquitous in fluvial channel deposits, yet cross-stratification, specifically formed by dunes, is comparatively uncommon in deep-marine channel deposits subjected to similarly unidirectional flows, the reasons for which is the subject of much debate. In part, this is related to the difficulty associated with acquiring high-resolution data sets; natural turbidity currents are highly destructive, whereas physical models are hampered by the shortcomings of conventional laboratory instrumentation. Consequently the internal structure of turbidity currents is poorly understood, thus hindering the ability to identify the linkages between flow properties and depositional characteristics. In this study we use a medical-grade computed tomography scanner coupled with a three-dimensional ultrasonic Doppler velocity profiler to characterize the flow field and depositional morphology across a range of grain sizes (d 50 : 70-330 µm) and sediment concentrations (5%-17.5% by mass). Results show that the development of angular bedforms is suppressed in all flows with particle concentrations greater than 9.5% by mass, but notably also in all flows with particles <230 µm and sediment concentrations down to 5%, the lowest slurry densities used in these experiments, by mass. This suggests a first-order control on the response of the bed by the makeup of the overriding current. More fundamentally, we propose that grain size controls the character of near-bed density stratification, which is a requisite condition to generate the hydrodynamic instabilities that create the initial bed defects, which then lead to the development of angular bedforms like ripples and dunes.

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Sediment concentrations, flow conditions, and downstream evolution of two turbidity currents, Monterey Canyon, USA

Cited by 72 publications

References 90 publications

Key Future Directions For Research On Turbidity Currents and Their Deposits

Key Future Directions For Research On Turbidity Currents and Their Deposits

Linking submarine channel–levee facies and architecture to flow structure of turbidity currents: insights from flume tank experiments

The influence of grain size on the velocity and sediment concentration profiles and depositional record of turbidity currents

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