Effects of liquefied beds on the basal layers of turbidity currents

Abstract Controlled laboratory experiments of turbidity currents (TCs) flowing over three types of beds (compacted beds, loose-sand beds, and liquefied beds) reveal that liquefied mobile beds play an important role in driving the denser basal layer of turbidity currents by supporting sediments in suspension more effectively over space and time. Based on measured near-bed concentration and velocity, as well as deposit characterization, a relationship was established between the spatial evolution of the TCs and the presence of liquefied and/or fluidized beds. Velocity and sediment concentration profiles of TCs were measured throughout the 4-m-long flume during 4 min to 6 min runs. Deposit thickness and grain-size distributions were analyzed after each experiment. Results indicate similar values of hydraulic and sedimentological properties for both loose beds and compacted beds. Moreover, TCs flowing over liquefied beds were capable of maintaining higher near-bed concentrations along the entire flume. Additionally, values of median grain size were larger in the deposits generated by TCs that flowed over liquefied beds when compared to loose beds and compacted beds. This indicates the role of liquefied beds on sustaining near-bed sediments in suspension and on increasing the sediment-transport competence of TCs. The observations shed light on the occurrence of long-term turbidity currents driven by dense basal layers, directly observed in deep ocean environments.