How did the Hukou Waterfall of the Yellow River form?

Abstract

Waterfalls are steep steps in river sections that longitudinally break river channels, typically found in drainage systems with tectonically active conditions. However, large waterfalls can also form in tectonically inactive areas, creating a phenomenon that is not yet fully understood. The Hukou Waterfall, located in the Jinshaan Gorge of the Yellow River, an area generally considered tectonically stable, preserves datable landforms and provides an opportunity to study the formation and propagation processes of waterfalls. In this study, we reconstruct the paleochannel associated with the recession of the Hukou Waterfall by correlating fluvial terraces and paleo-outlets. Our results suggest that the waterfall once existed at a paleo base level approximately 65 m higher than its current position. The migration rates of the waterfall varied between 16.9 and 30.3 cm/a during its recession, with faster recession during inter-glacial periods. Based on these findings, we estimate that the Hukou Waterfall entered the Jinshaan Gorge between 233.5 and 260.0 ka, and propose that the Hukou Waterfall originated from a sudden drop in base level due to drainage integration between the Fenwei Basin and the Sanmen Gorge. Our analysis also shows that migration rates, as well as overburden on waterfall-related terraces, correlate with cyclic climate patterns, highlighting the role of climate variability in driving waterfall migration over time. These findings may help refine models of river incision, base-level change, and knickpoint migration, contributing to the broader understanding of waterfall migration patterns in response to both climate and tectonic changes and offering a template for studying landform evolution in other river systems worldwide.