HR: 17:00h
AN: H52E-05    [PDF]
TI: Spatial Patterns of Erosion in the Bolivian Andes Inferred From In Situ $^{10}$Be
AU: * Safran, E B
EM: safran@lclark.edu
AF: Environmental Studies Program, Lewis & Clark College, 0615 SW Palatine Hill Road, Portland, OR 97219 United States
AU: Aalto, R
EM: aalto@geomorphology.com
AF: Quaternary Research Center and Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195 United States
AU: Dunne, T
EM: tdunne@bren.ucsb.edu
AF: Donald Bren School of Environmental Science and Management, University of California Santa Barbara, 2400 Bren Hall, Santa Barbara, CA 93106 United States
AU: Bierman, P
EM: Paul.Bierman@uvm.edu
AF: Department of Geology, University of Vermont, Perkins Hall, Burlington, VT 05405 United States
AU: Finkel, R
EM: finkel@sirius.llnl.gov
AF: Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550 United States
AB: The Eastern Cordillera of the Bolivian Andes comprises some of the world's most rugged topography and serves as the major sediment source for the Amazon Basin. The upper Beni River basin drains a large portion of the range north of the Bolivian orocline, including most of the highest peaks. Erosion rates have been measured or modeled in these mountains using a variety of approaches, but measurements reported to date are too sparse to document in much detail spatial patterns of erosion rate throughout the basin. Here, we present concentrations of $^{10}$Be in quartz from alluvium at 48 sites sampling the montane tributaries of the upper Beni River. The $^{10}$Be concentration in our samples, derived from drainage areas between 1 and 70,000 km$^{2}$, ranges from 20,000 to 150,000 atoms/gram. Variations in $^{10}$Be concentration and thus model erosion rates are most pronounced among basins with drainage areas $<$ 10$^{3}$ km$^{2}$. To interpret erosion rates from $^{10}$Be concentrations, we account for the non-uniform distribution of quartz in polylithologic basins as well as for the effects of the rugged basin hypsometry on $^{10}$Be production rates. The resulting erosion rates are on the order of 0.1 to 1 mm/yr, similar to those derived from apatite fission track analyses. The cosmogenic radionuclides average erosion rates over thousands of years, long enough to smooth decadal-scale variations in sediment output but short enough to reflect valley-scale variations in erosion rate due to location in the network, dominant geomorphic process, and lithology.
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting