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Quantifying the Effects of Climate Change and Land-Use on Erosion Rates Using Cosmogenic Radionuclides and LiDAR-Based Process Mapping: Andrew Cyr   Andrew Cyr
Project Title: Quantifying the Effects of Climate Change and Land-Use on Erosion Rates Using Cosmogenic Radionuclides and LiDAR-Based Process Mapping
Mendenhall Fellow: Andrew Cyr, (650) 329-4820, acyr@usgs.gov
Duty Station: Menlo Park, CA
Start Date: December 18, 2008
Education: Ph.D. (Earth and Atmospheric Sciences), Purdue University, 2008
Research Advisor: Jonathan Stock, (650) 329-4968, jstock@usgs.gov; Kevin Schmidt, (650) 329-5302, kschmidt@usgs.gov; David Miller, (650) 329-4923, dmiller@usgs.gov; Robert Finkel, le Centre Européen de Recherce et d'Enseignement des Géosciences de l’Environnment, L'Université Paul Cézanne, Aix-en Provence, France, 04 4297 1764, finkel@cerege.fr
Project Description: The Desert Southwest is an important region of the United States, accommodating growing populations in large urban areas (Los Angeles, San Diego, Las Vegas).  However, the ways that the landscape in this region, specifically erosion processes and rates, responds to climate changes are poorly understood.  Some conceptual models suggest that erosion increases during wetter climate intervals, because water aids in the weathering of rock into sediment and streams are better able to transport that sediment (for example, Christenson and Purcell, 1985).  Other models suggest that hillslopes supply more sediment during drier climatic intervals, when the loss of vegetation due to increasing aridity makes the available sediment more prone to erosion (for example, Wells and others, 1987; Bull, 1991; Harvey and Wells, 1994; Harvey and others, 1999).  Understanding the potential responses of desert systems to changes in aridity has become especially important in the face of recent climate change.

In order to address this problem we are using the sedimentary record preserved in alluvial fan deposits in the eastern Mojave Desert, southern California (fig. 1), to examine connection between hillslope erosion rates and past climate change.  Alluvial fans are good targets because they can contain a long record of sediments derived from an easily determined area.  We are attempting to examine the links between erosion and climate change by:

      1. Determining the ages of alluvial fan deposits for comparison to the existing climate record of the Mojave Desert region (e.g. Comrie and Glenn, 1998; Barron et al., 2003, 2004).  This will allow is to infer whether sediments deposited in alluvial fans were deposited during wet or dry climate intervals.
      2. Using cosmogenic beryllium-10, a rare element whose concentration in rock and sediment is inversely proportional to the erosion rate, to determine both paleo-erosion rates at the time that alluvial fan sediments were deposited and modern erosion rates.
LEFT, Shaded relief map of the Providence Mountains area showing the locations of samples collected to date for this study. RIGHT, Photographs of Providence Mountains front (top) and sample collection (bottom).
Figure 1. LEFT, Shaded relief map of the Providence Mountains area showing the locations of samples collected to date for this study. RIGHT, Photographs of Providence Mountains front (top) and sample collection (bottom).

Anticipated Results: The combination of both modern and ancient erosion rates of watersheds in the Mojave Desert with a precise geochronology of alluvial fan deposits will help to define a functional relationship between climate fluctuations and changes in hillslope erosion and sediment supply rates.  The results of this study will also help to constrain models of desert landscape response to possible future changes climate, as well as potentially contribute to geologic hazard assessment in these types of systems.

References:
Barron, J.A., Bukry, D., and Bischoff, J.L., 2003, A 200-yr-long record of climate from the Gulf of California, in West, G.J., and Blomquist, N.L., eds., Proceedings of the Nineteenth Pacific Climate Workshop, Asilomar, Pacific Grove, CA, March 3-6, 2002, Technical Report 71: Interagency Ecological Program for the San Francisco Estuary, Sacramento, CA, p. 11–21.

Barron, J.A., Bukry, D.M., and Bischoff, J.L., 2004, High resolution paleooceanography of the Guaymas Basin, Gulf of California, during the past 15,000 years: Marine Micropaleontology v. 50, p. 185–207.

Bull, W.B., 1991, Geomorphic Responses to Climate Change: New York, Oxford Press, 326 p.

Christenson, G.E., and Purcell, C., 1985, Correlation and age of Quaternary fan sequences, Basin and Range province, southwestern United States, in Weide, D.L., ed., Soils and Quaternary geology of the southwestern United States,: Geological Society of America Special Paper 203, p. 115–122.

Comrie, A.C., and Glenn, E.C., 1998, Principal components-based regionalization of precipitation regimes across the southwest United States and northern Mexico, with an application to monsoon precipitation variability: Climate Research vol. 10, p. 201–215.

Harvey, A.M., and Wells, S.G., 1994, Late Pleistocene and Holocene changes in hillslope sediment supply to alluvial fan systems, ZZYzx, California, in Millington, A.C., and Pye, K., eds., Environmental change in Drylands: Chichester, Wiley, p. 67–84.

Harvey, A.M., Wigand, P.E., and Wells, S.G., 1999, Response of alluvial fan systems to late Pleistocene to Holocene climatic transition: Contrasts between the margins of pluvial Lakes Lahontan and Mojave, Nevada and California, USA: Catena, vol. 36, p. 255–281.

Wells, S.G., McFadden, L.D., and Dohrenwend, J.C., 1987, Influence of late Quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont, eastern Mojave Desert, California: Quaternary Research vol. 27, p. 130–146.


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