Rock weathering effects on bedrock channel erosion determined via abrasion mill experiments

Blom, Tevis

Graduate Thesis Or Dissertation

Rock weathering effects on bedrock channel erosion determined via abrasion mill experiments Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/4t64gn55w

Abstract

The interplay of rock hardness, tectonic uplift, sediment supply, flood discharge, and flood periodicity lead to the overall landscape topography through local bedrock incision and sediment coverage effects. Rock weathering causes decreased rock strength through chemical and physical processes. This decreased rock strength should affect channel erosion rates, and therefore be accounted for in landscape evolution models Sklar (2001) investigates these processes via a saltation-hop erosion mill. However, experiments were made upon freshly cut rock surfaces. This study seeks to improve upon the Sklar data set by accounting for the effects of bedrock weathering. To this end, saltation-hop erosion mill experiments have been conducted on naturally weathered thalweg and flood level rock surfaces. Sample sites include bedrock channels in sandstone, basalt, granite, and metamorphic lithologies. Erosion rates from the naturally weathered flood level and thalweg surface are then compared with the erosion rate from a fresh saw cut surface. We find that the flood level or 'upper' samples produce erosion rates a factor of 1.5-6.6 higher than for thalweg samples where material has been removed. Likewise, we find that the upper samples produce erosion rates a factor of 7.5-10.3 higher than for freshly cut samples. Erosion rates were higher at the onset of mill processing, and decreased over time. This was particularly evident in the upper samples. Erosion mill surface evolution of the sample is recorded via a photographic data processing scheme which allows for an X-Y coordinate data representation of the sample surface. Data gathered will be used in subsequent channel evolution studies.

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