Will it be a Rounded Hillslope, Complex Cliff, or a Set of Steps? - Using Landscape Evolution Modeling to Understand the Effect of Stratigraphic Arrangement on Hillslope Evolution.

Landscapes composed of heterolithic stratigraphy are globally widespread. The roll lithologic differences on landscape morphology are well understood, especially for fluvial systems. Modeling simulations of fluvial systems in complex stratigraphies have shown that unit arrangement and properties can have large impacts on landscape development via fluvial incision. Yet, the relative importance of these factors in governing landscape response and development for hillslopes has not yet been as thoroughly investigated. Controls on hillslope evolution in these landscapes could include the variation in lithological properties, stratigraphic organization, or layer thickness. The relative importance of these factors must be understood since many landscapes are composed of relatively flat lying rock units of variable erodibility. We focus our investigation to examine multiple layers of varying characteristics to understand their role in the rate of landscape response and hillslope evolution.

We build upon the modeling work of Glade et al. (2018) by extending their 1-D model, created to simulate a single resistant layer of a hogback, to include multiple sets of hard cliff-forming layers. Our study focuses on how variations in thickness, ease of weathering of cliff forming layers, and arrangement of resistant layer influence how a hillslope in heterolithic stratigraphies reach a new steady state after a boundary condition change. A suite of model runs was compared via geomorphic metrics such as elevation and slope distributions, as well monitoring elevation changes between timesteps. The original model's ability to generate large blocks that move downslope was preserved and utilized to specifically test how the presence of such blocks can have on rate at which the landscape evolves.

Results suggest the underlying stratigraphic architecture has an influence on how long it takes for hillslopes to reach a new steady state. We find that certain stratigraphic arrangements allow for overall faster landscape scape response than others. We propose that certain architectures allow for faster removal of hillslope material via block-by-block failure rather than through hillslope diffusion. Further work will be done to compare these results to known rates of landscape evolution for analogous landscapes across the globe.