Browsing by Subject "Turbidity"
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Item Failure mechanics, transport behavior, and morphology of submarine landslides(2010-12) Sawyer, Derek Edward; Flemings, Peter Barry, 1960-; Mohrig, David; Lavier, Luc; Hornbach, Matthew; Shipp, R. Craig; Nikolinakou, MariaSubmarine landslides retrogressively fail from intact material at the headwall and then become fluidized by strain weakening; the final deposits of these flows have low porosity, which controls their character in seismic reflection data. Submarine landslides occur on the open slope and also localized areas including margins of turbidite channel-levee systems. I develop and quantify this model with 3-D seismic reflection data, core and log data from Integrated Ocean Drilling Program Expedition 308 (Ursa Basin, Gulf of Mexico), flume experiments, and numerical modeling. At Ursa, multiple submarine slides over the last 60 ky are preserved as mass transport deposits (MTDs). Retrogression proceeded from an initial slope failure that created an excavated headwall, which reduced the horizontal stress behind the headwall and resulted in normal faults. Fault blocks progressively weakened until the gravitational driving stress imposed by the bed slope exceeded soil strength, which allowed the soil to flow for more than 10 km away from the source area. The resulting MTDs have lower porosity (higher bulk density) relative to non-failed sediments, which ultimately produces high amplitude reflections at the base and top of MTDs. In the laboratory, I made weak (low yield strength) and strong flows (high yield strength) from mixtures of clay, silt, and water. Weak flows generate turbidity currents while moving rapidly away from the source area. They create thin and long deposits with sinuous flow features, and leave behind a relatively smooth and featureless source area. In contrast, strong flows move slowly, do not generate a turbidity current, and create blocky, highly fractured source areas and short, thick depositional lobes. In Pleistocene turbidite channels of the Mississippi Fan, deep-seated rotational failures occurred in the flanking levees. The rotational failures displaced material into the channel from below where it became eroded by turbidity flows. This system achieved a delicate steady state where levee deposition and displacement along the fault into the channel was balanced by erosion rate of turbidity flows. This work enhances our understanding of geohazards and margin evolution by illuminating coupled processes of sedimentation, fluid flow, and deformation on passive continental margins.Item Interactions between turbidity currents, turbidites and topography generated by a mobile substrate(2016-12) Minton, Brandon Wade; Mohrig, David; Kim, Wonsuck; Buttles, JamesModels for development and filling of submarine minibasins remain incomplete for the following reasons: (1) they seldom account for growth of seafloor topography via subsurface salt motion that coincides with turbidite sedimentation; (2) they seldom account for interactions between turbidity currents and seafloor topography that influence subsequent sedimentation patterns; and (3) they seldom consider the degree to which the evolution of seafloor topography associated with any single minibasin is affected by its neighboring minibasins. These points have now been addressed through a novel set of laboratory experiments. In the suites of experiments, turbidity currents consisting of 1.5% sediment by volume were released onto a 1.2 m x 1.2 m x 0.05 m platform filled by a composite layer of PDMS polymer and pliable putty (Silly Putty™). Interactions between pre-existing bed topography and turbidity currents result in differential loading of the substrate and influence depositional patterns. These interactions are achieved through a combination of blocking and focusing of currents by topography and by remobilization and removal of deposits from steeply sloping surfaces. Spatially varying deposit thicknesses generate locations that exceed the threshold load and begin to deform the mobile substrate. Turbidites of insufficient thickness are simply “along for the ride” and do not contribute to substrate deformation. Additionally, the tendency of the far-field surface to uplift or subside is preconditioned by the topography of the initial surface. These findings represent contributions towards the goal of better defining the important transition from turbidite sedimentation on an unconfined slope to deposition in minibasins.