Dynamics of submarine avalanches : insights from small-scaled experiments

Abstract:

At the Earth-Sea transition, the sediment transfers from settled rivers to margins can be ensured directly from highly-concentrated plug-flows, such as hyperpycnal currents, commonly observed in medium-sized rivers after extreme events of flash floods or dam-failures; or indirectly from delayed collapses of deltaïc sediments after fluidization from freshwater outflows down the continental slope. Such hazardous phenomena can have dramatic consequences on both onshore and offshore environments, such as the destruction of communication cables or pipelines, and the formation of tsunamis. However, the description of such catastrophic episodes still lack of predictive models gained from idealized experiments and simulations. This study deals with the experimental modeling of short-lived sedimenting suspensions, made with water-fluidized beds of solid particles that travel along an horizontal flume, in order to better understand the transport and emplacement mechanisms of turbiditic systems. In the experiments presented here, suspensions of variable solid volume fractions above loose packing (Φ_s/Φ_pack), ranged from 0.1 to 1, are released within a fully immersed channel and recorded in aid of high speed video cameras. The images sequences analysis allow us to track the particles trajectories after the flow front propagation and their progressive sedimentation until the motion ceases. The mean flow velocities and runouts both increase with decreasing Φ_s/Φ_pack. We present here a physical model able to describe the key parameters that control the dynamics of such avalanches as well as their deposit geometry.