Abstract

Landscape curvature and regolith chemistry responds to both tectonic and climate factors. To explore this, we are studying how topographic position and climate affect depth and extent of weathering. We present results from field observations and theoretical models of weathering for ridgetop (one-dimensional) and hillslope (two-dimensional) examples. The model was developed describing steady-state regolith production caused by mineral dissolution (Lebedeva and Brantley, 2013). The hillslope model shows that when erosion rates are small and vertical porefluid infiltration is moderate, the convex hill weathers at both ridge and valley in the erosive transport-limited regime. For this regime, the reacting mineral is weathered away before it reaches the land surface: in other words, the model predicts completely developed element-depth profiles at both ridge and valley. In contrast, when the erosion rate increases or porefluid velocity decreases, denudation occurs in the weathering-limited regime. In this regime, the reacting mineral does not weather away before it reaches the land surface and simulations predict incompletely developed profiles at both ridge and valley.

Model predictions suggest that an increase in Precipitation – Evapotranspiration for either completely or incompletely developed profiles will cause both the thickness of regolith and thickness of the reaction front to increase. In contrast, an increase in temperature causes an increase in the dissolution rate constant which in turn causes a decrease in the thickness of the reaction front for both types of profiles.

To understand the importance of climate and topographic positions, these model-derived ideas will be compared to i) a climosequence of soils developed on loess along the Mississippi valley, ii) a climosequence of soils developed on shale, iii) soils developed on shale on the north and south sides of an east-west trending catchment (the Susquehanna Shale Hills CZO).

Citation

BRANTLEY, Susan L., DERE, Ashlee, LEBEDEVA, Marina, WHITE, Timothy (2013): Assessing the Extent of Reaction Versus Depth at Ridgetops and Hillslopes to Understand Controls on Denudation. GSA Annual Meeting.

This Paper/Book acknowledges NSF CZO grant support.