Jingtao Lai

and 2 more

In mountain rivers, sediment from landslides or debris flows can alluviate portions or even full reaches of bedrock channel beds, influencing bedrock river incision rates. Various landscape evolution models have been developed to account for the coevolution of alluvial cover and sediment-flux-dependent bedrock incision. Despite the commonality of their aims, one major difference between these models is the way they account for and conserve sediment. We combine two of the most widely used sediment conservation schemes, an Exner-type scheme and an erosion-deposition scheme, with the saltation-abrasion model for bedrock incision to simulate the coevolution of sediment transport and bedrock incision in a mixed bedrock-alluvial river. We compare models incorporating each of these schemes and perform numerical simulations to explore the transient evolution of bedrock incision rates in response to changes in sediment input. Our results show that the time required for bedrock incision rates to reach a time-invariant value in response to changes in sediment supply is over an order of magnitude faster using the Exner-type scheme than the erosion-deposition scheme. These different response times lead to significantly different time-averaged bedrock incision rates, particularly when the sediment supply is periodic. We explore the implications of different model predictions for modeling mixed bedrock-alluvial rivers where sediment is inevitably delivered to rivers episodically during specific tectonic and climatic events.

Xueyun Lu

and 4 more

The interactions between climate, tectonics and surface processes have become a research hotspot in Earth science in recent years. Although various insights have been achieved, the relative importance of climatic and tectonic forcing in influencing the evolution of mountain belts still remains controversial. In order to investigate the tectonic and topographic evolution, as well as the formation mechanism of the eastern Himalayan syntaxis, we developed a comprehensive 2D climatic-geomorphological-thermomechanical numerical model and conducted over 200 experiments to test the influences of convergence rate, average precipitation and initial geothermal gradient on orogenic wedge. The results indicate that, for a specific orogenic wedge, its tectonic and topographic evolution primarily relies on the relative strength of tectonic and climatic forces, rather than their respective magnitudes. A syntaxis is the result of the combined effects of tectonic forces, climatic forces and geothermal field. In mountain belts, once the convergence rate and average precipitation fall within a Type D zone determined by the crustal thermal structure, a sustained, stationary, localized and relatively rapid erosion process will be established on the windward flank of the orogenic wedge. This will further induce sustained and rapid uplift of rocks, exhumation and deformation, ultimately forming a syntaxis. In this context, syntaxis is the inevitable system's outcome under various physical laws, including conservation of mass, momentum and energy, rheology, orographic precipitation, surface processes, etc. Orogens are best viewed as complex open systems controlled by multiple factors, none of which can be considered as the sole cause of the system's outcome.