2022 CSDMS meeting-016

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Channel Incision in Layered Rocks: Insights from the SPACE Model

Grace Guryan, (she/her),University of Texas at Austin Austin Texas, United States. gguryan@utexas.edu

Joel Johnson, University of Texas at Austin Austin Texas, United States. joelj@jsg.utexas.edu

Nicole Gasparini, Tulane University New Orleans Louisiana, United States. ngasparini@tulane.edu

This work explores how feedbacks between erosion and sediment production in landscapes with layered stratigraphy influence channel evolution. In layered rocks, contrasts in erodibility cause erosion rates to vary through space and time, complicating landscape response to external forcing from climate and tectonics. Recent studies have used the detachment-limited stream power incision model to explore the complex variations in erosion rates that arise from channel incision through layered rocks. However, these studies do not capture the effect of sediment cover on channel evolution. This work uses the recently developed Stream Power with Alluvium Conservation and Entrainment (SPACE) model (Shobe et al. 2017) to explore how sediment cover influences landscape evolution and modulates the topographic expression of erodibility contrasts in mixed bedrock-alluvial rivers incising through horizontally layered rocks. The SPACE model allows for the simultaneous treatment of bedrock, fully alluvial, and mixed bedrock-alluvial channels and transitions smoothly between detachment- and transport-limited behaviors. Here, we use the SPACE model to explore how sediment load influences effective erodibility in layered strata, motivated by topographic and lithologic variability found in the Guadalupe Mountains of Texas and New Mexico. We use the Landlab Toolkit to simulate fluvial incision through alternating horizontal layers of hard and soft rock using the SPACE model. While the SPACE model does not treat individual grains, the relative influence of grain size is modeled by systematically varying particle settling velocity and the erodibility of the alluvial across model runs. We find that sediment cover strongly modulates landscape response to uplift, and model runs with “finer” sediment (lower particle settling velocity and more erodible alluvium) reach a steady average elevation more quickly than model runs with coarser sediment. As particle settling velocity is increased, normalized channel steepness increases in soft rock layers and decreases in hard rock layers. We also explore how sediment flux at the watershed outlet varies as soft and hard layers are exposed in different proportions. Finally, we compare how erosion rates vary through space and time as relative sediment size increases. This work illustrates the importance of feedbacks between erosion and sediment production for landscape evolution, particularly in layered rocks where erosion rates vary in space and time.