COMBINING FRACTURE MECHANICS AND RIVER EROSION: MAKING SENSE OF LITHOLOGICAL DISPARITIES IN DAMAGE PATTERNS AND UNPREDICTABLE EROSION RATESCOMBINING FRACTURE MECHANICS AND RIVER EROSION: MAKING SENSE OF LITHOLOGICAL DISPARITIES IN DAMAGE PATTERNS AND UNPREDICTABLE EROSION RATES

Incision of bedrock rivers sets the lower boundary condition on adjacent hillslopes such that the efficiency of river erosion ultimately drives the pace of landscape evolution. Erosion processes in bedrock river channels involves the coalescence of cracks yet the integration of cracking mechanics and fluvial erosion mechanics remains under-developed. In my research on the lithologic influences on bedrock channel erodibility, we found a distinct difference in the cross-channel damage pattern of lithologies separated by crystalline grain size. Coarse-grained rocks had increased damage on more frequently eroded surfaces while fine-grained rocks had decreased damage on more frequently eroded surfaces. These results are possibly explained by high subcritical cracking indices or crack memory effects and demonstrate the geomorphic response (damage, erosion, and channel morphology) of different lithologies to different periods and amplitudes of the thermal and mechanical stress cycles in nature. In flume experiments on the attrition of bedrock by gravel impacts, we found that erosion rates are highly inconsistent through time and are poorly described by the average kinetic energy of gravel impacts. These findings demonstrating that the coalescence of microcracks during attrition is a non-linear process that requires a better statistical understanding. Using these studies as a foundation, I discuss ideas for further research involving field work, experiments, and modeling efforts with the goal of collaborating with geomorphologists and rock physicists alike to better integrate rock mechanics in bedrock river erosion and other geomorphic problems.