Three-dimensional laboratory experiments of sediment transfer across a canyon-mouth transition: From landslides to turbidity currents

Understanding the initiation, transformation, and deposition of submarine sediment gravity flows is a major challenge because these processes control sediment transfer from continental margins to deep-water basins, influence reservoir architecture, and contribute to significant geohazards worldwide. This study addresses this challenge through a unique series of 3D laboratory experiments that capture the complete evolution of two distinct natural flow types across an abrupt transition from a confined canyon to an unconfined horizontal basin, while allowing three-dimensional flow expansion and spontaneous geotechnical failures to develop over evolving depositional surfaces. Data from eight flow runs (out of sixteen experiments) confirm the occurrence of five hyperpycnal turbidity currents and three geotechnical landslides. Rapid sediment deposition from fully turbulent turbidity currents generated significant sand–clay accumulations at the canyon mouth. These deposits were subsequently liquefied, remobilized, and collapsed downslope under relatively simple triggering conditions. The resulting landslides evolved downstream into debris flows and dilute turbidity currents. The experiments demonstrate a strong coupling between slope instability, flow transformation, confinement, and depositional architecture, which collectively control sediment distribution in submarine environments. Flow transformations occur primarily through internal processes—such as liquefaction, water entrainment, and rheological changes—rather than external forcing. This finding highlights the importance of upstream sediment accumulation and instability in controlling downstream depositional architecture and suggests that lobe development cannot be fully understood without accounting for this feedback. These experiments also demonstrate that laboratory observations provide a reliable framework for interpreting flow transformations and the resulting depositional record in natural canyon-to-basin settings.