Date of Graduation

12-2023

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Marshall, Jill A.

Committee Member

Covington, Matthew D.

Second Committee Member

Aly, Mohamed H.

Keywords

Boulders; Erosion; Hillslopes

Abstract

Geologists often use landscape form to infer landscape processes through time. While climate and tectonics shape geomorphic form, the potential range of spatial or temporal scales that can shape any specific landscape can render landscape process-form based hypotheses too general for consideration. Contributions by mathematical modeling have helped bridge the gap between inferring processes from form, notably in how sediment transport dynamics shape hillslopes. However, few models encapsulate the movement of large rock blocks ( >2 meters across) and their potential impact as hillslope sediment transport disruptors. The Upper Buffalo River watershed (BRW) in the Ozarks of northern Arkansas has hillslopes peppered with massive blocks. The processes responsible for block detachment and transport are unclear, resulting in the ability to infer landscape process through landscape form uncertain. Here, I investigate possible controls on block volume, block transport, and the potential for aspect-driven differences in weathering and transport mechanisms. I hypothesize differences in block size and transport mechanisms will lead to different hillslope concavities between north and south-facing hillslopes. Additionally, the often-documented aspect-driven differences in moisture retention and diurnal temperature swings in temperate landscapes on north and south-facing slopes may lead to quantifiable differences in block size and slope distributions. To test these hypotheses, I combine field measurements, GIS analysis, and compare my results to recent process-form block transport models. Data from three north-facing and three south-facing hillslopes suggests that aspect-driven differences in moisture retention and diurnal temperature swings on north and south-facing slopes are not a significant factor in the BRW and thus are not a dominate control on block detachment, volume, transport, and distribution, and do not control hillslope steepness and hillslope concavity. However, my data does suggest that aspect-driven differences in weathering or transport rates may be a controlling factor in the variability of surface weathering and large block upslope sediment dam volume. Ultimately, the lack of predictable relationships between block distributions and hillslope form a) makes distinguishing whether local or non-local transport dominants on north or south-facing slopes in the BRW difficult, b) calls for local soil data on moisture retention and diurnal temperatures, and c) suggests additional process models are needed to reliably relate hillslope form to processes in slow eroding and lithologically complex settings such as the Ozarks. Future investigation into hillslope block distribution, transport, and form should include how layered sedimentary sequences may account for the lack of consistent hillslope concavities and block distributions, as geomorphic aspect-related asymmetry and generalized block transport models have yet to include geologic heterogeneities. A more detailed understanding of the Bloyd Formation’s heterogeneous rock properties and mechanics would also provide insight on how aspect may influence fracture propagation and thus block volume, water retention and transport mechanisms.

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