A bottom-up control on fresh-bedrock topography under landscapes

TLDR

Hilly landscapes are typically covered by soil and underlain by a weathered bedrock zone that can extend tens of meters before reaching fresh bedrock, influencing water runoff, water chemistry, erosion processes, and atmospheric processes through plant uptake, yet the spatial pattern of the underlying fresh‑bedrock surface remains essentially unknown. We present a testable model that predicts hillslope form and the depth to fresh bedrock. The model predicts that depth increases upslope and depends strongly on bedrock porosity, permeability, and the rate of channel incision at the base of the hillslope.

Abstract

Significance Hilly landscapes are typically mantled with soil and underlain by a weathered bedrock zone that may extend tens of meters beneath the surface before reaching fresh bedrock. The weathered bedrock zone influences water runoff to channels, the chemistry of that water, the rates and processes of erosion, and atmospheric processes due to plant uptake of moisture and return to the atmosphere. However, the spatial pattern of the underlying fresh-bedrock surface is essentially unknown. We present a testable model that predicts hillslope form and the depth to fresh bedrock. The depth increases upslope and depends strongly on the porosity and permeability of the bedrock and the rate of channel incision at the base of the hillslope.