HR: 1330h
AN: H42C-1089    [PDF]
TI: Arid Climate Landscape Evolution and the Pediment Problem
AU: * Strudley, M W
EM: mws10@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Box 90230 Duke University, Durham, NC 27708 United States
AU: Murray, A B
EM: abmurray@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Box 90230 Duke University, Durham, NC 27708 United States
AU: Haff, P K
EM: haff@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Box 90230 Duke University, Durham, NC 27708 United States
AB: Although widely disseminated throughout many different climatic environments, pediments, or gently sloping, laterally extensive surfaces characterized by a thin veneer of alluvium covering bedrock, are particularly well developed in granitic desert locales such as the Mojave and Colorado Deserts in southern California and the Sonoran Desert in western Arizona. These features form a transitional zone within the piedmont of many exposed batholithic mountainous bodies, separating a zone of bare bedrock erosion in the steep mountain mass from a depositional zone in the alluvial basin. Well developed pediments in granitic environments commonly contain bedrock outcroppings (tors or inselbergs) that may remain uncovered indefinitely and sharp slope discontinuities at the piedmont junction separating the pediment surface from the mountain mass. Pediments have been the focus of debate in geomorphic circles for over half a century. While some geomorphologists have proposed that pediments and their associated tor fields represent unearthed relict landforms, others propose unique modes of sediment transport that form and maintain the beveled form of pediment surfaces. We hypothesize that a simple relationship between bedrock weathering and alluvial thickness could explain this range of enigmatic features and phenomena, a relationship that Anderson (2002) incorporates in his proposed explanation for high alpine surfaces and tors. Field observations suggest that the transformation of bedrock to regolith is most rapid with a finite covering of regolith. This weathering rule, combined with a simple set of sediment transport rules provides a mechanism through which pediment surfaces are produced. We examine the development of pediment surfaces and associated features using a 3D numerical, distributed-parameter landscape evolution model incorporating the most pertinent landscape development processes acting in arid regions. Temporally and spatially variable rainfall (storm size, duration, and coverage), soil types, and rock types can be accommodated. A linear diffusive transport mechanism redistributes sediment downslope, parameterizing the aggregated effects of tree throw ({\it Yucca brevifolia}), rodent burrowing, rain splash, and soil creep. Sediment flux due to stream flow is nonlinear in water flux, and is modulated by storm averaged infiltration capacity, which is dependent on soil type, depth, and antecedent soil moisture conditions.
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1815 Erosion and sedimentation
DE: 1886 Weathering (1625)
DE: 9350 North America
DE: 9604 Cenozoic
SC: Hydrology [H]
MN: 2003 Fall Meeting