Doctoral Dissertation Research: Precipitation Pulses and Geomorphic Response During Periods of Late Quaternary Climate Change, Western United States

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Geomorphologists have long believed that periods of rapid climate change have significant impacts on colluvial and fluvial systems. New evidence suggests that precipitation pulses -- episodes of higher precipitation rates or more intense storms -- are associated with rapid climatic changes. In many settings, precipitation pulses would produce pulses of hillslope erosion, high sediment yield, and increased flood magnitude. Studies conducted in the desert Southwest and Midwestern U.S. suggest that large precipitation events, producing large floods, were especially frequent during rapid climate changes of the late Holocene. In the Great Basin, episodes of increased precipitation associated with rapid late Pleistocene climatic change are inferred from records of pluvial lake levels. Preliminary data suggest that late Pleistocene and Holocene episodes of rapid hillslope erosion in the Midwest and Great Plains may have been synchronous with each other and with precipitation pulses identified in the Great Basin. This doctoral dissertation research project will investigate the spatial extent of precipitation pulses and hillslope response across the Midwest, Great Plains, Great Basin, and Southwest over the past 20,000 years. The focus will be on colluvial aprons, which are slope wash deposits found along fluvial and lacustrine terraces. These aprons are found in each of the study regions. They typically record multiple episodes of slope erosion, they are sensitive to changes in precipitation regime, and they are amenable to optical (OSL) dating. At field sites in each region, episodes of erosion recorded by slopewash deposits in colluvial aprons will be dated using both optical and radiocarbon methods. These records will then be compared between regions.The results of this project may help explain episodic changes in hillslope erosion rates, sediment yield, and flood magnitudes, recognized in previous work on Quaternary geomorphic systems. For predicting response to future climate changes, it is particularly important to understand the spatial scale and mechanisms of past precipitation pulses. This project will contribute toward that goal by helping to constrain the actual geographic extent of pulses of increased precipitation and sediment yield presently identified in scattered localities. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.