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Hillslopes and Soils
This project is aimed at advancing our understanding of soil transport by "diffusive" processes, notably due to biological activity (bioturbation) and raindrop impacts, and the coupled evolution of soils and hillslopes undergoing diffusive transport. It is also aimed at clarifying effects of chemical denudation related to first-order geochemical processes acting at the soil-bedrock interface and within the soil. Our work involves collaborations with William Dietrich (Berkeley), Peter Haff (Duke), Arjun Heimsath (Dartmouth), Mark Schmeeckle (Arizona State) and Kyungsoo Yoo (Delaware).
Splash of medium sand 7/500 second after impact of a 4 mm drop at terminal velocity.
Soil Transport
The most commonly assumed soil-transport relation for diffusion-like processes has the form q = -D grad z, where q is the the soil flux, D is a diffusion-like coefficient and z is land-surface elevation. Our work on biomechanically driven soil creep suggests that, in certain situations, the coefficient D contains the soil thickness h, in which case the transport relation has the form of a "depth-slope" product, q = -Kh grad z, where K is a transport coefficient. In related work our high-speed imaging of rainsplash transport indicates that the downslope asymmetry of particle trajectories related to slope is far stronger than previously suspected.
Furbish, D. J., Hamner, K. K., Schmeeckle, M. W., Borosund, M. N. and Mudd, S. M. 2006. Rainsplash of dry sand revealed by high-speed imaging and sticky-paper splash targets. Journal of Geophysical Research – Earth Surface. (in press)
Heimsath, A. M., Furbish, D. J. and Dietich, W. E. The illusion of diffusion: Field evidence for depth dependent sediment transport. Geology, 33, 949-952.
Simulation of hillslope relaxation following initially steady-state condition, with stochastic roughening; soil transport is proportional to product of soil thickness and land-surface slope.
Coupled Hillslope-Soil Evolution
Spatial variations in certain soil properties — thickness, particle sizes and mineral concentrations — represent a "dynamic stratigraphy" that contains information about the co-evolution of soils and hillslope geometry, including responses to changing boundary conditions. We are pursuing theoretical, numerical and field-based work to learn how to "read" this stratigraphy. An important part of this work, led by Simon Mudd in collaboration with Kyungsoo Yoo, is centered on meshing effects of chemical denudation with mechanical transport in models of hillslope evolution.
Mudd, S. M. and Furbish, D. J. Using chemical tracers in hillslope soils to estimate the importance of chemical denudation under conditions of downslope sediment transport. Journal of Geophysical Research – Earth Surface, 111, F02021, doi: 10.1029/2005JF000343.
Mudd, S. M. and Furbish, D. J. Lateral migration of hillcrests in response to channel incision in soil mantled landscapes. Journal of Geophysical Research – Earth Surface, 110(12), F04026, doi: 10.1029/2005JF000313.
Mudd, S. M. and Furbish, D. J. 2004. Influence of chemical denudation on hillslope morphology. Journal of Geophysical Research – Earth Surface, 109, F02001, DOI:10.1029/ 2003JF000487.
Furbish, D. J. 2003. Using the dynamically coupled behavior of land-surface geometry and soil thickness in developing and testing hillslope evolution models. in P. Wilcock and R. Iverson (Eds.), Prediction in Geomorphology, American Geophysical Union, Geophysical Monograph 135, Washington, D.C., 169-181.
Furbish, D. J. and Fagherazzi, S. 2001. Stability of creeping soil and implications for hillslope evolution. Water Resources Research, 37, 2607-2618.
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