Abstract
Abstract. Landslides are the main source of sediment in most mountain ranges. Rivers then act as conveyor belts, evacuating landslide-derived sediment. Sediment dynamics are known to influence landscape evolution through interactions among landslide sediment delivery, fluvial transport and river incision into bedrock. Sediment delivery and its interaction with river incision therefore control the pace of landscape evolution and mediate relationships among tectonics, climate and erosion. Numerical landscape evolution models (LEMs) are well suited to study the interactions among these surface processes. They enable evaluation of a range of hypotheses at varying temporal and spatial scales. While many models have been used to study the dynamic interplay between tectonics, erosion and climate, the role of interactions between landslide-derived sediment and river incision has received much less attention. Here, we present HyLands, a hybrid landscape evolution model integrated within the TopoToolbox Landscape Evolution Model (TTLEM) framework. The hybrid nature of the model lies in its capacity to simulate both erosion and deposition at any place in the landscape due to fluvial bedrock incision, sediment transport, and rapid, stochastic mass wasting through landsliding. Fluvial sediment transport and bedrock incision are calculated using the recently developed Stream Power with Alluvium Conservation and Entrainment (SPACE) model. Therefore, rivers can dynamically transition from detachment-limited to transport-limited and from bedrock to bedrock–alluvial to fully alluviated states. Erosion and sediment production by landsliding are calculated using a Mohr–Coulomb stability analysis, while landslide-derived sediment is routed and deposited using a multiple-flow-direction, nonlinear deposition method. We describe and evaluate the HyLands 1.0 model using analytical solutions and observations. We first illustrate the functionality of HyLands to capture river dynamics ranging from detachment-limited to transport-limited conditions. Second, we apply the model to a portion of the Namche Barwa massif in eastern Tibet and compare simulated and observed landslide magnitude–frequency and area–volume scaling relationships. Finally, we illustrate the relevance of explicitly simulating landsliding and sediment dynamics over longer timescales for landscape evolution in general and river dynamics in particular. With HyLands we provide a new tool to understand both the long- and short-term coupling between stochastic hillslope processes, river incision and source-to-sink sediment dynamics.
Highlights
Landsliding is a highly effective erosional mechanism that dominates sediment mobilization rates in moderate-to-steep topographic settings (Hovius et al, 1997; Ouimet et al, 2007; Broeckx et al, 2020)
Landscapes are the outcome of external perturbations, such as climate or tectonic variability, and internal dynamics originating from the coupling between fluvial incision and hillslope response (Burbank and Anderson, 2011; Glade et al, 2019)
The role of sediment dynamics in altering fluvial erosion and sediment transport is clearly illustrated in the numerical experiment (Figs. 9 and 10) where 5–10 kyr are required for the landscape to evolve back to a steady state after a pulse of landsliding
Summary
Landsliding is a highly effective erosional mechanism that dominates sediment mobilization rates in moderate-to-steep topographic settings (Hovius et al, 1997; Ouimet et al, 2007; Broeckx et al, 2020). Long-term landscape evolution in non-glaciated settings is mainly controlled by the interplay between tectonic uplift and fluvial dynamics (Whipple and Tucker, 1999; Wobus et al, 2006). Hillslope failure through mass wasting chokes the rivers with sediment and prevents further bedrock incision until landslide-derived sediment has been evacuated from the system (Larsen and Montgomery, 2012; Ouimet et al, 2007; Korup et al, 2010; Shobe et al, 2016; Glade et al, 2019). Unraveling the dynamic interplay between landslides and fluvial processes is key to understanding long-term landscape evolution and the associated sediment dynamics in mountainous terrain (Egholm et al, 2013). Increased insight into the spatial distribution of landslides has resulted in improved landslide susceptibility assessments (Guzzetti et al, 2006), but processes regulating landslide rate assessments (Broeckx et al, 2020) and landslide-derived sediment dynamics remain less well understood (Hovius et al, 2011; Croissant et al, 2017, 2019; Zhang et al, 2019; Broeckx et al, 2020)
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