SELF-CONFINEMENT OF TURBIDITY CURRENTS THROUGH INCIPIENT LEVEE FORMATION: NOVEL EXPERIMENTAL APPROACH ALLOWS DIRECT EXPERIMENTAL MEASUREMENTS OF TURBIDITY CURRENT MORPHODYNAMICS

The complex and subtle processes acting as link between seafloor morphology and overall turbidity current dynamics are difficult to capture in experimental models, but essential in understanding and predicting the architecture of such submarine systems. Part of the difficulty consists of scaling-down sandy suspension-driven density flows over transitional to rough beds, while maintaining sediment by-passing conditions.

Previous experimental studies can be divided in two approaches: 1) saline density flows over erodible substrates, and 2) particulate density flows through pre-fixed channels that abruptly expand on unconfined expansion tables. This first approach has the disadvantage of replacing the suspension fall-out that controls the evolution of the bed morphology with bed load transport variations. Turbidite facies, however, show that bed load transport processes are uncommon in submarine channel deposits. In the second approach suspension transport is maintained but subtle morphologies are mostly lost due to very large deposition rates upon expansion.

Here we present the results of a new approach where sandy, suspension-driven turbidity currents were run over an unconfined and erodible bed under bypassing conditions. These results were achieved by increasing the discharge (~8 l/s), sediment concentration (~14 %v) and slope (8 deg), thereby allowing Froude scaling of the flow while maintaining turbulent conditions, and at the same time suspension scaling while maintaining transitionally rough boundary conditions.

The novel approach led to the formation of auto-generated channel-levee morphologies on an unconfined, erodible, sandy slope. The interaction between flow processes and morphology was measured with Ultrasonic Doppler Velocity Profiler probes. These measurements show how the formation of the incipient levees started to confine the flow; lateral velocities decreased as the levee growth continued.