Characteristics of steady state fluvial topography above fault‐bend folds

Abstract

[1] In steady state convergent orogens, erosion balances lateral as well as vertical bedrock motions. For simple geometrical reasons, the difference between the total steady state erosion flux and its vertical component is up to 30% for typical fluvial slopes and bedrock streamline inclinations, suggesting that lateral advection is also likely to be expressed topographically. In order to understand these geomorphologic consequences, we focus on steady state topography developed on active fault-bend folds. First, we derive an analytical solution for the slopes of detachment-limited streams that incorporates lateral advection. Next, we conduct experiments using a numerical two-dimensional landscape evolution model (Channel-Hillslope Integrated Landscape Development model (CHILD)) incorporating linear diffusion on hillslopes and detachment-limited stream channel incision above a fault-bend fold. The concavity and steepness indices of steady state long profiles are functions of bedrock velocity magnitude and direction, streamflow direction, and fluvial erosivity. Asymmetry of mountain range profiles varies as a function of fluvial erosivity or bedrock velocity only if we account for the lateral velocity component. This asymmetry is equally sensitive to this lateral component, fluvial incision, and hillslope diffusion. However, the effect of diffusion on drainage divide position is significant only at high diffusivities, short length scales, low bedrock advection rates, or relatively low fluvial erosivity. Thus in most mountain ranges and fault blocks, drainage divide migration is expected to be dictated by stream channel erosion. Model results are shown to be consistent with topography in the Siwalik Hills, Nepal, which overlie fault-bend folds produced above the frontal fault systems in the Himalayan foreland.

Spatial relationship between topography and rock uplift patterns in asymmetric mountain ranges based on a stream erosion model

“…(1) as in many previous studies (e.g., Willgoose et al, 1991;Kirkby, 1994;Tucker and Slingerland, 1994;Kirby and Whipple, 2001;Miller et al, 2007) as…”

“…The main features of the topography, however, are considered to be primarily controlled by an advective stream process (Howard, 1994;Kooi and Beaumont, 1996). In fact, the numerical simulation of Miller et al (2007), in which the scale of their target (Siwalik Hills, Nepal) is about 20 km in the horizontal direction, demonstrated that diffusion does not visibly affect the asymmetry of the range under normal conditions. This study identifies the logarithmic relation between the topographic and rock uplift axes for a simple set of conditions (Figs.…”

“…Asymmetry of mountain ranges may be caused by horizontal rock movements (Adams, 1980;Willett et al, 2001;Herman and Braun, 2006;Miller et al, 2007), differential base levels of erosion (Ellis and Densmore, 2006), asymmetric distribution of rain and snow precipitation (Beaumont et al, 1992;Willett, 1999;Mitchell and Montgomery, 2006;Anders et al, 2008), or differences in lithology (Adams, 1980). Asymmetric rock uplift, however, should also result in asymmetric mountain ranges (Koons, 1989;Kooi and Beaumont, 1996;Kühni and Pfiffner, 2001).…”

Natural experiments in landscape evolution

“…One example of this is a long-lived fault-bend fold moving over a curving ramp, where the rate of rock uplift in the hangingwall (relative to the footwall) depends on the rate of thrust propagation and on the local dip of the fault plane (e.g. Hurtrez et al, 1999;Miller et al, 2007). Steady, non-uniform landscapes may also be found in transient settings where erosion rates are evolving in both space and time, but temporal variations are relatively subtle over the time scale required to lower the land surface by a depth comparable to the thickness of the soil (e.g.…”

2.13 Quantitative Modeling of Landscape Evolution

“…In south-eastern Australia, Van Der Beek and used a similar model to assess controls on landscape evolution and denudation history. Miller and Slingerland (2006) and Miller et al (2007) used landscape evolution modeling to suggest an explanation for the fact that drainage basins along opposite flanks of mountain ranges are aligned and commonly similar in planform. Miller and Slingerland (2006) and Miller et al (2007) used landscape evolution modeling to suggest an explanation for the fact that drainage basins along opposite flanks of mountain ranges are aligned and commonly similar in planform.…”