In situ evidence of self-accelerating turbidity currents.

Abstract

Self-accelerating turbidity currents (SATCs) are hypothesized to be the primary mechanism for transporting vast amounts of sediment to the deep ocean. However, theoretical predictions of SATCs have preceded field observations by decades, leaving a critical gap in our understanding of this long-distance delivery process. Here, we present results from a four-year field survey of turbidity currents and bathymetric evolution in the Xiaolangdi Reservoir on the Yellow River (China), the world's most sediment-laden river. We provide definitive in situ evidence of SATCs, characterized by synchronous down-channel increases in sediment mass and current momentum, alongside massive channel incision at the event scale. Notably, these SATCs occur in a low-gradient lacustrine setting, challenging the prevailing hypothesis that such phenomena are restricted to steep submarine channels or high velocity conditions. We identify a dimensionless threshold, incorporating current velocity, channel slope, and sediment settling velocity, that governs SATC formation across sublacustrine and marine environments. This threshold provides a robust framework for predicting SATC occurrence and informs engineering strategies to sustain reservoir capacity and restore sediment connectivity in dammed river systems.