Collaborative Research: Bedrock and Sediment Controls on River Incision, Henry Mountains and Navajo Mountain, Utah

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

There has been considerable progress in the past decade on understanding the interactions among climate, erosion, and tectonics. This has been accomplished primarily with generic rule sets for river incision that lump together a diverse set of erosional mechanisms. Much has been gained from these generic analyses: we now know well what we need to know better and why. There is a clear need, however, to develop and test process-specific models of river incision into bedrock. In particular, the quantitative relationships among rock mass quality, sediment load, and erosional efficiency stand out as important unknowns; the lithologic and sediment controls on river morphology and incision rate must be better understood before landscapes can be confidently interpreted in terms of the climatic and tectonic factors that drive landscape evolution. Recent theoretical and experimental advances demonstrate that only detailed physically-based incision models provide a suitable framework for significant further progress, assuming a suitable field site can be found and a comprehensive data set systematically collected. We propose a coupled field, laboratory and theoretical investigation, focused on channels draining the Henry Mountains and nearby Navajo Mountain, Utah. These field areas present an excellent natural experiment for studing bedrock and sediment controls on river incision and morphology. Preliminary DEM and Remote sensing analyses and initial field observations reveal significant, systematic differences in channel morphology (slope, width, percent rock exposure, erosional bed forms, roughness) as a function of substrate lithology and diorite sediment supply. The two principal goals of the proposed research are (1) test, refine, and extend the saltation-abrasion river incision model [Sklar, 2003; Sklar and Dietrich, 1998; Sklar and Dietrich, 2001], and (2) to develop and test an in-situ method for objective measurerment of substrate erodibility (or rock mass quality) at geomorphically relevant scales. Specifically, we will test five focused hypotheses, exploiting the opportunity presented by field conditions in the Henry Mountains and nearby Navajo Mountain field sites. The saltation-abrasion model is the most fully developed river incision model to date and makes specific, testable quantitative predictions about the interrelations among channel morphology, sediment load, substrate erodibility, percent rock exposure, and incision rate. Model predictions supported by experimental data [Sklar, 2003; Sklar and Dietrich, 2001] have far-reaching implications orogen evolution and the interaction of tectonics and climate, but have not been tested in the field. Outreach and Broader Impacts: There is broad and growing recognition that dynamic interactions between tectonics and geomorphology play a fundamental role in orogenesis. Lithologic and sediment controls play a critical, but little studied role in landscape and orogen evolution. Fundamental advances in our understanding of the linkages between bedrock lithology, sediment characteristics and channel morphology are also of potentially enormous value in solving applied problems of anticipating, minimizing and mitigating for landuse impacts and restoring damaged riverine habitat. Much of the proposed study will define the core of a doctoral thesis research program of J. Johnson, an MIT Ph.D. student preparing for an academic career. Moreover, our study will engage one or more undergraduates each year at MIT in a special research project, and involve undergraduates at SFSU, a primarily undergraduate institution. In addition, this collaborative research project has the benefit of engaging L. Sklar - a recently hired assistant professor at SFSU - in NSFsponsored research, providing him the opportunity to participate in the supervision and training of an MIT graduate student. Also, in addition to dissemination of our results in the scientific literature, we are compiling a digital database in GIS format with public domain digital elevation data, geologic maps, satellite images, and geomorphic field data as layers that we will make publicly available on the Web. Finally, both the subject matter and field areas of this project are well suited to educational outreach. We propose to (1) develop poster displays and brochures for the general public at visitors centers at national parks, monuments and recreation areas in Utah, and (2) design a website to communicate our results in the context of canyon incision and the landscapes of the Colorado Plateau, especially the formation of Grand Canyon and Canyonlands. Informal discussions with park rangers at Canyonlands NP have been met with enthusiasm.