Simulating Submarine Channels in Flume Experiments: Aspects of the Channel Incision Dynamic

We report the results of thirty laboratory experiments reproducing submarine straight canyons as well as meandering ones. Our experimental setup consists in 2 m X 0.5 m flume filled with fresh water. The flume bottom simulates a sub-marine ramp draped by a sediment blanket. A sustained density flow is simulated by a continuous brine stream injected at the top of the ramp. We control the three main parameters of the experiment: the slope of the plane, the input flow rate, and the brine density. It allowed us to test the reproducibility of the phenomenon and to roughly delineate a phase diagram specifying the channel incision conditions. An optical acquisition technique enables us to measure instantaneously the topography of the sediment surface at successive times, during the canyon formation and frontal lobe deposition. In this way we can define and then measure physical quantities representative of different channel types in order to visualize their evolution. Here we present a few aspects of the channel incision dynamic. After a development phase in which the bottom density current spreads over the bed, the channel inception phase suddenly begins, followed by a positive feedback mechanism facilitating further erosion. Then a phase of regressive erosion appears, and in some cases a steady state can be finally obtained. By computing the difference between successive maps, we can elaborate time-varying maps of sedimentation and erosion rates in the system. Stacking of these maps produce a 3D cube of sedimentation rates showing autocyclic phases of incision, by-pass and sedimentation. Cross-sections through this 3D cube show morphologies very similar to those observed on seismic acquisitions performed in the Recent Orenoque channel system.