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Complementary Results on Experiment-Derived Classification of Submarine Sediment Gravity Flows

Abstract

A sequence of ten fully-equipped experiments of continuous flows of sediment gravity flows (SGF) was conducted in a long-glass flume (15 × 0.4 × 0.6 m) in order to identify variations in their depositional and hydrodynamic behavior in function of increments in sediment concentration and/or clay content. Mineral Coal (D50 = 55μm, d = 1,19) Kaolin (D50 = 6 μm, d = 2,6) mixtures were prepared to constitute distinct SGF with volumetric concentrations ranging from 2 and 40% and clay contents of 5, 12.5 and 50%. The mixture volumes were 200 and 400 liters, and the discharge varied from 50 to 60 l/min. Images of all simulated SGF were obtained using two video cameras and two medical ultrasound scanner. Velocity and concentration data were also collected using, respectively, 24 UVP probes and 6 UHCM probes. Results showed that significant changes occurred in the dynamics of flow as well as in the deposits generated as concentration/clay content increases. Low concentration flows (Cv< 7.5%) were thicker; lower velocity, and turbulence keep sediments in suspension. In line, more concentrated flows (CV> 10%), a bipartite flow stratification was observed. In the top layer, the predominant sediment-support mechanism was turbulence. However, in the basal layer, mass transport became predominant (Cv> 20%). When the clay content was greater than 12.5%, the formation of a mixed layer was fully inhibited. The Sediment-support mechanism also drives the depositional process: the sediment transported by turbulent flows was deposited grain by grain as flow decelerates, whereas the mass transported sediment was deposited just after an abrupt stop (injection stop), characterizing to a frictional (no clay) and/or cohesive freezing (with clay). The slicing analysis of the non-cohesive flow deposits showed that the amount of material deposited (thickness) and the grain size decreasing along the channel. In addition, increase in concentration provided greater flows competence, which can be identified by the larger sediment size in the most distal part of the channel. The increase in clay content, in turn, reduced the flow capacity of transport causing the formation of thicker deposits. Rheological aspects of these distinct flows can also explained the differences between SGF simulated. Finally, those new results can complement/better conception previous experiment-derived classification models for submarine sediment gravity flows.