Recent topographic evolution and erosion of the deglaciated Washington Cascades inferred from a stochastic landscape evolution model

Abstract

In this study, we model postglacial surface processes and examine the evolution of the topography and denudation rates within the deglaciated Washington Cascades to understand the controls on and time scales of landscape response to changes in the surface process regime after deglaciation. The postglacial adjustment of this landscape is modeled using a geomorphic-transport-law-based numerical model that includes processes of river incision, hillslope diffusion, and stochastic landslides. The surface lowering due to landslides is parameterized using a physically based slope stability model coupled to a stochastic model of the generation of landslides. The model parameters of river incision and stochastic landslides are calibrated based on the rates and distribution of thousand-year-time scale denudation rates measured from cosmogenic 10 Be isotopes. The probability distributions of those model parameters calculated based on a Bayesian inversion scheme show comparable ranges from previous studies in similar rock types and climatic conditions. The magnitude of landslide denudation rates is determined by failure density (similar to landslide frequency), whereas precipitation and slopes affect the spatial variation in landslide denudation rates. Simulation results show that postglacial denudation rates decay over time and take longer than 100 kyr to reach time-invariant rates. Over time, the landslides in the model consume the steep slopes characteristic of deglaciated landscapes. This response time scale is on the order of or longer than glacial/interglacial cycles, suggesting that frequent climatic perturbations during the Quaternary may produce a significant and prolonged impact on denudation and topography.

Landscape Response to Lateral Advection in Convergent Orogens Over Geologic Time Scales

“…The fluvial channel response to tectonic perturbations is subsequently radiated to neighboring hillslopes by resetting their fluvial base level (e.g., Fernandes & Dietrich, ). The time scale of hillslope response varies with the hillslope topography and soil transport process and can range from abrupt response in the case of steep topography where soil transport is dominated by landslides (e.g., Moon et al, , and references therein) to a gradual response in the case of gentle hillslopes where soil transport is dominated by processes of soil diffusion (e.g., Culling, ; Hurst et al ).…”

Developing, choosing and using landscape evolution models to inform field‐based landscape reconstruction studies

“…For instance, observed phases of catchment sediment yield can be either connected to external controls or to internal sediment storage and release phases (van Gorp et al, ). Landscape response at these timescales will more often lag changes in external drivers, which models can demonstrate (Moon et al, ).…”

Modeling the Formation of Topographic Asymmetry by Aspect‐Dependent Erosional Processes and Lateral Channel Migration

“…Like most previously published LEMs, our model did not explicitly include channels (Howard, 1994; Moon et al, 2015; Tucker & Bras, 2000; Yetemen et al, 2015). This is in part due to the difficulty of coupling channel bank evolution with hillslope processes, the lack of adequate process laws for the evolution of channel cross sections, and the difficulty of representing relatively narrow channels in grids that span entire landscapes.…”