Date of Award
Master of Science (MS)
Department of Geography-Geology: Hydrogeology
Landscapes record information about the tectonic, climatic, and lithologic environments in which they form (Yang et al., 2015). When one or more of these environmental conditions change spatially or temporally, the landscape responds through erosion and thus, develops representative geomorphic features (Ritter et al., 2011). Since the nineteenth century, it has been clear that bedrock strength and erodibility play an important role in landscape evolution and geomorphology (Lifton et al., 2009). However, the nuances of variable erodibility remain poorly understood. The implications of this limited understanding lies within landscape evolution models. While these models show strong qualitative relationships between longitudinal river profile morphometry and tectonic or climatic processes, major discrepancies remain over the relationship between bedrock strength and river incision. As these models strive to become more accurate, they are limited by our understanding of discrete characteristics of substrate erodibility. For this reason, the Southern Guadalupe Mountains are an excellent location to focus on these issues. Minor variations in carbonate lithology in this region will provide a focused insight on the relationships between discrete changes in bedrock strength, erodibility, and longitudinal stream profile morphometry. Additionally, this study is among the first to utilize longitudinal stream profiles in the Southern Guadalupe Mountains, Texas with the intent to explore the landscape for tectonic and lithologic influences on landscape evolution.
Here, the relationships between rock strength and vertical river incision are explored using classic type-N Schmidt hammer analysis and longitudinal stream profiles obtained from digital elevation models. Qualitative exploration of longitudinal stream profiles in the Southern Guadalupe Mountains has revealed high-elevation, low-relief equilibrium profiles in the upstream segments of rivers crossing steep normal faults. It is likely that upstream, downthrown, hanging walls have produced mid profile pseudo-base levels in upper reaches of rivers by producing dam-like structures. Downstream of these structures, profiles are convex and show evidence for possible increased localized uplift rates, or significantly decreased erosional efficiency. Statistical results show that mean rebound values from type-N Schmidt Hammer analysis can be used to predict stream gradient, knickpoint development, and residual errors inherent in Flint’s Law (river incision model) only under relatively simple tectonic and hydrologic regimes. These relationships do not hold true in circumstances where large confluences and/or faulting disrupts major stream channel networks, or in areas under topographic disequilibrium. Finally, geologic units with different, yet statistically similar rebound values were found to influence stream gradients differently. This suggests that lumping lithologies together based on similar rebound values is an overgeneralization and should be avoided.
Schoenmann, Samuel T., "Evaluating Relationships between Rock Strength and Longitudinal Stream Profile Morphometry in the Southern Guadalupe Mountains, Texas" (2017). Theses and Dissertations. 774.