Penetration depth and radial intrusion dynamics of particle-laden plumes in a uniform stratified ambient

The release of particle-laden tailings plumes during deep-sea mining represents a major source of environmental disturbance, yet the mechanisms controlling their transport in stratified ocean ambient remain poorly studied. In this study, we conducted a series of laboratory experiments to investigate the dynamics of particle-laden plumes generated by injecting a suspension of deep-sea sediments into a linearly stratified saline environment. We examined plume descent, maximum descending depth, and subsequent intrusion behavior, with emphasis on the role of particle sedimentation. Results show that the initial stage of a particle-laden plume resembles that of a single-phase buoyant plume: both descend under the influence of negative buoyancy and overshoot the neutral buoyancy level to form a radial intrusion layer. The maximum vertical penetration during this stage can still be predicted using classical plume theory, with a characteristic scale of approximately 3.8 plume length scale, indicating the persistence of geometric similarity. However, as the plume evolves, suspended particles progressively settle out, reducing the effective buoyancy flux carried by the descending mixture. The loss of particulate buoyancy leads to upward of the intrusion layer. Experimental comparisons demonstrate that the final intrusion depth of particle-laden plumes can be smaller than that of single-phase plumes. Based on experiments, we further established an empirical relationship between the final intrusion depth and the fractional buoyancy contribution of the source fluid relative to total buoyancy. The formulation provides a quantitative link between plume intrusion dynamics and source composition, offering a useful parameterization for environmental assessments. Moreover, analysis of the radial intrusion revealed that the intrusion radius follows a power-law scaling with time. Overall, this work clarifies the transition of particle-laden plumes from buoyancy-driven collapse to inertia-dominated intrusion, highlights the role of sedimentation in controlling final plume structure, and provides experimental constraints for predictive modeling of tailings dispersal in the deep sea. The findings contribute to a better understanding of plume dynamics in a stratified ambient.