This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Erosion of bedrock in river channels is a fundamental process governing the evolution of landscapes that has not yet been evaluated fully. The rate of this erosion and its location within a river channel depend on a river's energy available to do work on the river bed, the distribution of sediment cover, and the type of bedrock underlying the channel. Several recent modeling studies have examined the coupled evolution of channel cross-sections and longitudinal profiles, but field-based studies investigating bedrock channel erosion are rare. Moreover, few studies have explicitly considered the effects of weathering on bedrock channel geometry and long-term channel evolution. This project will test four hypotheses focused on evaluating how weathering affects bedrock channel erosion 1) bedrock is more highly weathered along channel margins than near the channel center; 2) the degree of weathering is not enhanced beneath sediment cover; 3) the abrasion rate of bedrock increases as the degree of weathering increases; and 4) where weathering is substantial, channel cross-sections are wide and shallow, and as weathering efficiency decreases, channel cross-sections become narrower and deeper. These hypotheses will be tested by measuring the cross-channel distribution of rock weathering at stream sites with both easily weathered rocks (e.g., weak sandstones, limestone) and weathering-resistant rocks (e.g., quartzite, granite) in three hydro-climatic settings. The degree of weathering will be quantified using two geochemical weathering indices, in situ using Schmidt hammers and fracture density and length, and in the laboratory using Brazilian tension splitting tests. Rock erodability will be gauged via abrasion mill experiments in the laboratory. The results from these investigations will allow weathering to be incorporated into existing numerical models of bedrock erosion.
Rock erosion by river channels forms some of the most spectacular topography on Earth (e.g., Grand Canyon), and is the most effective erosion process active in non-glaciated landscapes. Understanding the processes responsible for rock erosion by rivers and the rates at which these processes work is therefore fundamental to interpreting the history of Earth's surface. Using field investigations, laboratory measurements, and numerical modeling, several hypotheses will be tested that have important implications for documenting the nature and rate of bedrock erosion in river channels under various conditons This project will provide substantial educational and personnel development benefits, including support of undergaraduates, a graduate student, and a post-doctoral research fellow.