USING GROUND-BASED LIDAR TO ANALYZE FRACTURE CHARACTERISTICS AS POSSIBLE CONTROLS ON THE VARIABILITY OF VALLEY MORPHOLOGY IN THE BUFFALO RIVER WATERSHED, ARKANSAS

The Buffalo National River (BNR) is a bedrock river that incises a sequence of Mississippian and Ordovician sedimentary rocks as it meanders west to east across the southern point of the Ozark Dome. Previous research identified lithology at river level as a primary control on valley width, regardless of position along the longitudinal profile. Upstream to downstream the river flows through the Mississippian Boone Formation, which is made up of limestone with prominent chert beds, and then the Ordovician Everton Formation, which is made up of mostly quartz arenite. A fault brings the Boone Formation back to the surface and this pattern is repeated. The Boone Formation reaches have a greater 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 fractures within each formation have not been studied. The 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. Preliminary data from the field indicate that the variability in valley width of the BNR can be attributed to the high frequency of fracturing within 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 development of bedrock river valleys 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 will help determine a potential first-order control on the development of valley morphology within the BNR.