Date Thesis Awarded

7-2013

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Geology

Advisor

Gregory S. Hancock

Committee Member

Mark K. Hinders

Committee Member

James M. Kaste

Abstract

The rate at which landscapes evolve is limited by erosion in bedrock-floored channels in many settings, yet our understanding of erosion rates in bedrock channels remains incomplete. Numerical modeling suggests that variable erodibility in bedrock channels at the cross sectional scale, generally ignored in most bedrock channel evolution models, influences equilibrium channel geometry and slope. We explore rock erodibility and channel geometry and slope along the longitudinal profile of a bedrock river. Assuming that rock strength is an adequate proxy for rock erodibility (Sklar and Dietrich, 2001), we measured in situ rock compressive strength using a Type N Schmidt hammer at 17 cross sections along a ~2 km segment of Renick Run, a channel floored by limestone in western Virginia. We observe a statistically significant decrease in average rock compressive strength between the thalweg and channel margins in 14 of 17 cross sections, with maximum decrease in average rock compressive strength ranging from 21- 58% in individual cross sections. Average rock compressive strength also varies across bedrock meanders, where rock compressive strength is greater on the inside of meanders than on the outside of meanders. We speculate that variability in rock erodibility is produced by subaerial weathering that acts preferentially on channel margins and the outside of bedrock meanders. We do not observe a correlation between variable rock erodibility and channel geometry and slope, but we present evidence suggesting a correlation between variable rock erodibility and stream sinuosity. Comparisons of rock compressive strength in channel cross sections to rock of the same lithology exposed on hillslopes show that rock in the channel has both greater and lower compressive strength than hillslope rock.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

Comments

Thesis is part of Honors ETD pilot project, 2008-2013. Migrated from Dspace in 2016.

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