Influence of chemical denudation on hillslope morphology

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Abstract
Models of hillslope evolution involving diffusion‐like sediment transport are conventionally presented as an equation in which the changes in land‐surface elevation or soil thickness are balanced by the divergence of soil transport and tectonic uplift, soil production, or both. These models typically do not include the loss or gain of mass in hillslope soils due to processes of chemical weathering and deposition. We formulate a more general depth‐integrated equation for the conservation of soil mass on a hillslope that includes a term representing chemical deposition or denudation. This general depth‐integrated equation is then simplified to determine the one‐dimensional form of a steady state hillslope which experiences both mechanical and chemical denudation. The differences in morphology between hillslopes only experiencing diffusion‐like mechanical sediment transport and hillslopes experiencing both diffusion‐like mechanical sediment transport and chemical denudation are explored. Under the conditions of a downslope increase in local soil lowering rate due to chemical weathering the hillslope profile will depart from the parabolic shape predicted by models that incorporate only linear diffusion‐like mechanical sediment transport. In addition, hillslopes that experience both chemical and mechanical denudation may have a convex‐concave profile at steady state. A necessary condition for such steady state profiles is that the chemical denudation rate must exceed the mechanical denudation rate. We further suggest that combinations of other physical parameter values (such as total denudation rate, average soil depth, sediment diffusivity, and the increase in soil depth away from the divide) that lead to steady state convex‐concave hillslope profiles may exist in a wide variety of natural settings.

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