Fluvial Systems and Climate in the Southwestern U.S.

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Fluvial Systems and Climate in the Southwestern U.S.(EAR-0309518Jon D. PelletierUniversity of ArizonaABSTRACTFluvial systems respond to changes in climate through erosion and deposition, creating a geomorphic and stratigraphic record of those changes. Alluvial fans of the southwestern U.S. preserve an excellent record of these changes from time scales of hundreds to millions of years. A large database of river and fan terraces has been developed from decades of field and laboratory work. These terraces are a major component of the Southwestern landscape, controlling flood hazards, soil development, ecosystems, and even human history. Our ability to read this record is limited, however, by a poor understanding of fluvial-system response. For example, is climate change or tectonics the major trigger of episodes of alluvial-fan deposition in the Southwest? Can the internal dynamics of the fluvial system be responsible for many of the terraces we observe? Does deposition occur during humid periods, arid periods, or the transitions between them? What are the time lags between environmental changes and fluvial-system response? To answer these questions, the project will focus on two distinct times scales. PI will reconstruct Quaternary cycles of erosion and deposition from time scales of 10 kyr to 1 Myr. This long-term focus will enable him to determine the effects of the magnitude and timing of different triggering events for the same basin. In addition, PI will reconstruct the spatial and temporal variability of latest Pleistocene and Holocene erosion and deposition from time scales of 100 yr to 10 kyr in our study area in Cuyama Valley, CA. This work will enable specific fluvial-system dynamics and hillslope-response mechanisms to be evaluated.PI has developed a process-based numerical model of channel flow and sediment transport in complex topography to enable him to better understand how fluvial systems respond to climatic changes. This model uses existing digital data sets together with scenarios of climatic and tectonic changes to model the fluvial-system evolution for specific study areas. The proposed research will determine the signatures of terrace age and morphology for each entrenchment mechanism so that the dominant processes that shape alluvial fans of the Southwest can be determined. To do this, forward modeling of fluvial-system response to different climatic and tectonic histories will be performed and their results compared against the ages and geometries of alluvial-fan terraces in our study areas.A strong background in quantitative methods is critical to providing geoscience students with the skills they need to take part in cutting-edge science. As a second phase of this project we will develop and integrate an interactive version of the numerical model into our classroom laboratory in collaboration with geoscience-education experts.