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

• Published in: Deep-sea research. Part I, Oceanographic research papers Vol. 89; pp. 11 - 34
• Main Authors: Xu, J.P., Sequeiros, Octavio E., Noble, Marlene A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.07.2014; Elsevier; Pergamon Press Inc
• Subjects: Canyons; Deep sea; Earth sciences; Earth, ocean, space; Exact sciences and technology; Grain size; Hydrology; Hydrology. Hydrogeology; Marine; Marine and continental quaternary; Monterey canyon; Morphology; Oceanography; Roughness; Sand; Sediment transport; Sediments; Slopes; Surficial geology; Turbidity; Turbidity currents; Velocity; United States; Pacific Ocean; Monterey Canyon; United States > US; USA; INE, Pacific, Monterey Canyon; Turbidity currents; Grain size; Monterey canyon; Sediment transport; morphology; thickness; flow mechanism; concentration; evolution; velocity; North America; sand; grain size; suspended materials; granulometry; sediment transport; marine environment; turbidity currents; sediments; streamflow; gravity flows
• ISSN: 0967-0637; 1879-0119
• DOI: 10.1016/j.dsr.2014.04.001

The capacity of turbidity currents to carry sand and coarser sediment from shallow to deep regions in the submarine environment has attracted the attention of researchers from different disciplines. Yet not only are field measurements of oceanic turbidity currents a rare achievement, but also the data that have been collected consist mostly of velocity records with very limited or no suspended sediment concentration or grain size distribution data. This work focuses on two turbidity currents measured in Monterey Canyon in 2002 with emphasis on suspended sediment from unique samples collected within the body of these currents. It is shown that concentration and grain size of the suspended material, primarily controlled by the source of the gravity flows and their interaction with bed material, play a significant role in shaping the characteristics of the turbidity currents as they travel down the canyon. Before the flows reach their normal or quasi-steady state, which is defined by bed slope, bed roughness, and suspended grain size, they might pass through a preliminary adjustment stage where they are subject to capacity-driven deposition, and release heavy material in excess. Flows composed of fine (silt/clay) sediments tend to be thicker than those with sands. The measured velocity and concentration data confirm that flow patterns differ between the front and body of turbidity currents and that, even after reaching normal state, the flow regime can be radically disrupted by abrupt changes in canyon morphology. •Two field turbidity currents are presented, “sandy” vs. “silty”.•Sandy flow is thinner and faster while silty flow slower and thicker.•Frontal speed of the sand flow is as high as 6m/s.•Highest sediment concentration is more than 2%.•Medium sands deposit in sediment traps 70m above bed.