Experiments on Density and Turbidity Currents: Ii. Uniform Flow of Density Currents

Middleton, Gerard V.

doi:10.1139/e66-044

Cited by 183 publications

(117 citation statements)

References 5 publications

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“…This forms the basis of the well known Chezy equation that has been applied to submarine density flows (Kuenen, 1952;Middleton, 1966;Komar, 1969Komar, , 1977Bowen et al, 1984;Prior et al, 1987;Ren et al, 1996;Xu, 2010;Khripounoff et al, 2012). This equation can be expressed (Bowen et al, 1984) as;…”

Section: Chezy Equationmentioning

confidence: 99%

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How are subaqueous sediment density flows triggered, what is their internal structure and how does it evolve? Direct observations from monitoring of active flows

Talling

Paull

Piper

2013

Earth-Science Reviews

201

184

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Subaqueous sediment density flows are one of the volumetrically most important processes for moving sediment across our planet, and form the largest sediment accumulations on Earth (submarine fans). They are also arguably the most sparely monitored major sediment transport processes on our planet. Significant advances have been made in documenting their timing and triggers, especially within submarine canyons and delta-fronts, and freshwater lakes and reservoirs, but the sediment concentration of flows that run out beyond the continental slope has never been measured directly. This limited amount of monitoring data contrasts sharply with other major types of sediment flow, such as river systems, and ensure that understanding submarine sediment density flows remains a major challenge for Earth science. The available monitoring data define a series of flow types whose character and deposits differ significantly. Large (N 100 km 3 ) failures on the continental slope can generate fast-moving (up to 19 m/s) flows that reach the deep ocean, and deposit thick layers of sand across submarine fans. Even small volume (0.008 km 3 ) canyon head failures can sometimes generate channelised flows that travel at N 5 m/s for several hundred kilometres. A single event off SE Taiwan shows that river floods can generate powerful flows that reach the deep ocean, in this case triggered by failure of recently deposited sediment in the canyon head. Direct monitoring evidence of powerful oceanic flows produced by plunging hyperpycnal flood water is lacking, although this process has produced shorter and weaker oceanic flows. Numerous flows can occur each year on river-fed delta fronts, where they can generate up-slope migrating crescentic bedforms. These flows tend to occur during the flood season, but are not necessarily associated with individual flood discharge peaks, suggesting that they are often triggered by delta-front slope failures. Powerful flows occur several times each year in canyons fed by sand from the shelf, associated with strong wave action. These flows can also generate up-slope migrating crescentic bedforms that most likely originate due to retrogressive breaching associated with a dense near-bed layer of sediment. Expanded dilute flows that are supercritical and fully turbulent are also triggered by wave action in canyons. Sediment density flows in lakes and reservoirs generated by plunging river flood water have been monitored in much greater detail. They are typically very dilute (b 0.01 vol.% sediment) and travel at b 50 cm/s, and are prone to generating interflows within the density stratified freshwater. A key objective for future work is to develop measurement techniques for seeing through overlying dilute clouds of sediment, to determine whether dense near-bed layers are present. There is also a need to combine monitoring of flows with detailed analyses of flow deposits, in order to understand how flows are recorded in the rock record. Finally, a source-to-sink approach is needed because the character of subm...

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Section: Chezy Equationmentioning

confidence: 99%

“…The Chezy equation (Eq. (1)) was developed originally for the body of a flow (see Middleton, 1966;Benjamin, 1968;Komar, 1977;Bowen et al, 1984). However, as with previous work, we use measurements of frontal flow speed.…”

Section: Chezy Equationmentioning

confidence: 99%

How are subaqueous sediment density flows triggered, what is their internal structure and how does it evolve? Direct observations from monitoring of active flows

Talling

Paull

Piper

2013

Earth-Science Reviews

201

184

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“…best known models for geological applications are based on a steady balance between gravity and friction forces acting on the head [45], or on a semi-infinite flow [35,36,46,47] (Eq. (1)).…”

Section: Existing Modeling Methodsmentioning

confidence: 99%

Phenomenological Modeling of Catastrophic Dilute Gravity Flows

Hugot

Zaleski

Joseph

2000

Oil & Gas Science and Technology - Rev. IFP

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Résumé -Modélisation phénoménologique des écoulements gravitaires catastrophiques dilués -Les sédiments déposés en eaux profondes sont à l'origine de nombreux réservoirs pétroliers. C'est pourquoi les processus régissant leur mise en place suscitent actuellement un intérêt grandissant, en particulier dans le domaine de la modélisation numérique. En tenant compte de la problématique et des contraintes imposées par les données géologiques, la méthode que nous avons adoptée pour obtenir un modèle mathématique pour les écoulements gravitaires finis, turbulents et dilués, est la suivante : le mouvement bidimensionnel créé par la libération instantanée d'un volume fini de fluide lourd (suspension de particules) dans un fluide plus léger (eau) est étudié théoriquement, sur pente variable, comme modèle pour les écoulements gravitaires. Ces écoulements développent une structure longitudinale caractéristique, comparable à une demi-lentille déformable, pour laquelle la hauteur est petite par rapport à la longueur. Cette géométrie est imposée à l'écoulement gravitaire. En utilisant l'approximation de Boussinesq, la dynamique de l'écoulement est supposée régie par un équilibre entre les forces motrices de gravité, d'inertie et de friction turbulente. L'étude du champ de vitesse interne longitudinal de l'écoulement permet de formuler une loi de variation pour la vitesse d'étalement. Une équation, incluant les effets d'incorporation d'eau à l'interface suspension-fluide ambiant, quantifie la variation du volume total de l'écoulement. Enfin, une équation de transport pour la fraction volumique des particules est proposée en supposant que : -la turbulence crée une distribution uniforme de la densité dans l'écoulement ; -les particules sont advectées à la vitesse moyenne de l'écoulement ; -les particules chutent ou sont érodées dans la sous-couche visqueuse de l'écoulement. Le système couplé d'équations différentielles non-linéaires obtenu est résolu numériquement. Le modèle est ensuite validé sur les modèles réduits expérimentaux réalisés par Laval (1988). La comparaison entre les prédictions théoriques et expérimentales montre un bon accord. Une étude analytique du système, par des méthodes d'analyse locale sur les temps longs, montre l'évolution des solutions lors de la prise en compte de nouveaux phénomènes et la consistance des solutions numériques obtenues. Le modèle présenté mène à des temps de calcul très faibles sur micro-ordinateur. Simple et complet, il constitue un premier pas vers une compréhension quantitative de l'impact de paramètres extérieurs -

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“…A large number of experimental studies on turbidity layers are available (e.g. Middleton, 1966;Sumner et al, 2009), however natural turbidity layers and other sedimentladen transient currents are hard to observe and study, due to their irregular occurrence and often destructive nature (Hay, 1987). Hence our knowledge of the turbidity layers is based largely on indirect observations of the modern seafloor from multibeam bathymetry surveys (Kuijpers et al, 2002), highresolution seismic surveys especially those designed for observations of geohazards (Bulat and Long, 2001;Meiburg and Kneller, 2010) and the study of contourites (Masson et al, 2010;Koenitz et al, 2008); together with direct observation of suspended sediment of the neptheloid layer from optical backscatter or transmissometer and sampling either in Niskin bottles or sediment traps (Bonnin et al, 2002;van Raaphorst et al, 2001;Hosegood and van Haren, 2004).…”

Section: Introductionmentioning

confidence: 99%

Mapping turbidity layers using seismic oceanography methods

2012

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Abstract. Using a combination of seismic oceanographic and physical oceanographic data acquired across the FaroeShetland Channel we present evidence of a turbidity layer that transports suspended sediment along the western boundary of the Channel. We focus on reflections observed on seismic data close to the sea-bed on the Faroese side of the Channel below 900 m. Forward modelling based on independent physical oceanographic data show that thermohaline structure does not explain these near sea-bed reflections but they are consistent with optical backscatter data, dry matter concentrations from water samples and from seabed sediment traps. Hence we conclude that an impedance contrast in water column caused by turbidity layers is strong enough to be seen in seismic sections and this provides a new way to visualise this type of current and its lateral structure. By inverting the seismic data we estimate a sediment concentration in the turbidity layers, present at the time of the survey, of 45 ± 25 mg l −1 . We believe this is the first direct observation of a turbidity current using Seismic Oceanography.

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Experiments on Density and Turbidity Currents: Ii. Uniform Flow of Density Currents

Cited by 183 publications

References 5 publications

How are subaqueous sediment density flows triggered, what is their internal structure and how does it evolve? Direct observations from monitoring of active flows

How are subaqueous sediment density flows triggered, what is their internal structure and how does it evolve? Direct observations from monitoring of active flows

Phenomenological Modeling of Catastrophic Dilute Gravity Flows

Mapping turbidity layers using seismic oceanography methods

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