USING GROUND-BASED LIDAR TO ANALYZE FRACTURE CHARACTERISTICS AS POSSIBLE CONTROLS ON THE VARIABILITY OF VALLEY MORPHOLOGY IN THE BUFFALO RIVER WATERSHED, ARKANSAS
Type of DegreeMaster's Thesis
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The Buffalo National River (BNR) is a bedrock river that incises a sequence of Ordovician and Mississippian sedimentary rocks as it meanders west to east across the southern point of the Ozark Dome. A previous study utilizing a Geographic Information System (GIS) has found that there are four main lithologic reaches of the BNR. Two reaches are composed mainly of the Mississippian Boone Formation, which is made up of limestone with prominent chert beds, and two reaches are composed mainly of the Ordovician Everton Formation, which is made up of mostly quartz arenite. Boone Formation reaches have been found to have a larger valley width than Everton Formation reaches. Previous studies have shown that the variability in valley width can be attributed to the differential chemical weathering of these two formations, but to date the variability of fracture characteristics within each formation have not been studied. Spacing and orientation of fractures in rocks exert strong controls on river morphology at the reach and outcrop scale. Using a combination of terrestrial LiDAR scans and field techniques, the fracture characteristics of each of these formations have been analyzed. These data were then synthesized into a common geomechanical classification scheme. Data from the field indicate that the variability in valley width of the BNR can be attributed to the highly brecciated nature of the chert beds of the Boone Formation. An understanding of the distribution of fractures within formations is essential to determining a mechanistic understanding of the morphology of bedrock rivers as a whole. Across landscapes, fractures focus erosion resulting in incision that follows fracture patterns. If rock erodibility is assumed to scale with fracture density, then an analysis of fracture characteristics on the Boone and Everton formations determines a potential first-order control on the development of valley morphology within the BNR.