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Langston, Abigail L ¹ ; Tucker, Gregory E ²

¹ University of Colorado
² University of Colorado

The processes that form the weathered bedrock profile in mountain catchments are not well understood and directly influence the evolution of mountain topography. Our study focuses on the landscape evolution of the Boulder Creek watershed. The goal of this long term study is to create a model that realistically predicts erosion rates from both chemical and physical processes and predicts changes in topography in response to changing climate regimes on both glacial and interglacial timescales. The weathering of fresh bedrock into mobile regolith is strongly dependent on the amount and chemical composition of water that reaches the unweathered bedrock. We have concentrated our efforts to quantify the magnitude of water throughout soil profiles in the Betasso catchment, in the eastern area of the Boulder Creek watershed. Two sites within the Betasso catchment were chosen to install soil moisture probes and water potential probes. One site, with a profile of 3 pairs of sensors is near the top of the catchment on an open, relatively flat area. The second site with a profile of 3 pairs of sensors is in a steeply sloping gully in the Betasso catchment. The soil moisture probes and the water potential probes were installed at various depths to determine the amount of water that percolates through the soil profile and into the saprolite layer. Snow depth sensors directly above the profile site measure the amount of water that can saturate the soil profile during the winter and a tipping bucket rain gauge measures rainfall. The magnitude, residence time, and chemical saturation of the water that reaches the bedrock influences the bedrock weathering rate, which determines how quickly individual mineral grains are freed to move down slope.