Laboratory experiments modeling the transport and deposition of sediments by glacial plumes rising under an ice shelf

Motivated by the observation of sediments being carried by meltwater plumes originating at the base of a marine terminating glacier, laboratory experiments are performed to examine the transport and deposition of particles settling out from a buoyant line-plume rising along a sloping upper boundary. If the plume source has relatively high momentum and is located near the bottom of the domain, then a strong recirculating region develops near the source. Emanating from this region is a particle bearing buoyant plume that moves at near constant speed along the slope. Particles are observed to settle within the plume itself and then descend from the plume toward the tank bottom being drawn back in the direction of the source through a return flow driven by the plume's entrainment of the underlying ambient fluid. A light attenuation technique is employed to measure nonintrusively the depth of the sediment bed after the source is turned off and all the particles settled out. Sediments are found to accumulate near the source over the extent of the recirculating region and then decrease approximately linearly with distance from the source. Conceptual theoretical models suggest that the linearly sloping bed results from a combination of vertical mixing in the plume near the recirculation region and the return flow acting to detrain from the plume particles more effectively near the plume source where the shear between the plume and the return flow is largest. In many aspects the experiments are not representative of a steady glacial meltwater plume due to restrictions of the experimental setup, notably the relatively low Reynolds number of the flow. Nonetheless the experiments are suggestive of the complicated dynamics and sediment deposition patterns that may occur near the base of a marine terminating glacier, with a crude estimate of mean clay deposition at a rate of 6 cm per year over a distance of 2 km from the source.