Collaborative Research: The Role of Debris Flows in Shaping Mountainous Terrain

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This project will investigate the role of debris flows in shaping mountain ranges. This is a fundamental problem in geomorphology because debris flows are clearly very important transport processes in steep terrain, carrying vast quantities of sediment every year. Yet so little is known about their role in shaping terrain that they have been essentially ignored in landscape evolution models. This project will help fill this critical knowledge gap with a comprehensive program of data collection, topographic analysis, process monitoring, and model development and testing. Data will come from two complementary study areas that are among the best in the world for studying debris-flow dynamics. The first is the central Apennines of Italy, where remarkably detailed data on rates of Quaternary fault-block motion offer an unparalleled natural laboratory for studying landscape response to tectonic forcing. The second is the Oregon Coast Range, where a strong history of process research provides a rich database for testing and refining models of valley formation by debris-flow scour. In the Apennines, geomorphic mapping and automated process monitoring will paint a picture of the nature of flow dynamics, including frequency-magnitude characteristics and processes of bed wear. Digital topographic analysis of ~200 steep mountain channels undergoing different known rates of relative uplift will yield a large database on the response of debris-flow-dominated channels to tectonic forcing. These data will be used to develop, test, and refine a 1D physically based model of valley long-profile evolution driven by debris-flow erosion under varying rates of tectonic uplift. In the Oregon Coast Range, where much is already known about the nature and extent of debris flows, research will concentrate on developing a debris-flow module in an existing landscape evolution model, and testing the ability of this model to account for observed distributions of topography, soil thickness, and process dynamics. Broader impacts: A successful theory for steep mountain headwaters and their response to tectonic forcing has applications in land-use impact analysis and seismic-hazard assessment. This project will train two graduate students and give them national and international contacts. A cutting-edge landscape evolution model will be made more accessible by the development of open-source graphical interface and visualization tools. The project's outreach component will broaden the impact of the research by bringing project materials, including state-of-the-art visualizations of landscape evolution, into the undergraduate classroom as a set of guided-inquiry exercises. Development and application of a standards-aligned version for the secondary- school level will be piloted through workshops with high school science teachers in an economically and racially diverse urban school district.