HR: 0830h
AN: T21C-0472    [PDF]
TI: A Model for Downstream Topography Across a Normal-Fault Footwall
AU: * Brett, J
EM: jenefer.brett@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences, Parks Road, Oxford, OX4 1JU United Kingdom
AU: Parsons, B
EM: barry.parsons@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences, Parks Road, Oxford, OX4 1JU United Kingdom
AB: Detachment-limited fluvial erosion in bedrock channels is often modelled as a power law function of drainage area, $A$, and stream gradient, $S$; derived either from a relation between erosion and basal shear stress in the channel, or between erosion and stream power per unit area of channel bed. This function when coupled with a tectonic condition, such as a uniform uplift rate, yields a well known expression for equilibrium downstream channel topography. In this study we present a new derivation for bedrock channel topography across a linearly decaying uplift condition. This is a simple tectonic condition that is a useful first approximation for the decay of uplift rate with distance across a normal fault footwall. Though a reasonably simple solution (of the form of a Beta function) can be derived under the condition of linear decay in uplift rate downstream, the familiar linear relationship between $\log_{10}S$ and $\log_{10}A$, manifest in the analytical solution derived assuming a uniform uplift rate, no longer holds. Hence, the relatively standard form of channel profile analysis, involving linear fitting of downstream topography in $[\log_{10}S]$--$[\log_{10}A]$ space, is not appropriate. Therefore, we apply a technique of direct fitting of this new analytical solution to downstream channel topography for rivers draining across the back of the Paleochori fault, Northern Greece. Of particular interest in this model is that inclusion of an additional variable to the tectonic term, i.e. the gradient of uplift decay downstream, allows the separation of $m$, the channel drainage exponent, and $n$, the slope exponent. These terms are inseparable with simpler tectonic models, yielding only a ratio, $m/n$, which corresponds to the curvature of the channel profile under uniform uplift conditions. Therefore, this model provides a new method for extracting quantitative estimates of parameters that control fluvial erosion.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 3210 Modeling
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting