River profile evolution by plucking in lithologically heterogeneous landscapes: Uniform uplift vs. tilting

Abstract

Recent studies provide a theoretical framework for understanding the incision of bedrock rivers by plucking. These studies motivated the development of a numerical model that simulates plucking to explore the evolution of channel profiles in lithologically diverse terrain. In the main governing equation, the incision rate is calculated as a function of the difference between the boundary shear stress and a threshold shear stress needed to entrain blocks from the bed. Because an earlier study suggested that plucking is the primary incisional process in the northern Sierra Nevada (CA), the model was calibrated to approximate the conditions in the region. The profiles of the simulated rivers are stair‐stepped, with sharp breaks‐in‐slope at lithological boundaries. This characteristic is common to rivers draining the northern Sierra Nevada, suggesting that the size of blocks available for plucking, as mediated by the fracture density, may be the primary control on their gradients. Moreover, the numerical experiments highlight the role of threshold shear stresses in the post‐orogenic persistence of steep reaches and relict terrain. Finally, comparisons of profiles evolved under tilting or uniform uplift scenarios provide insights into how these different uplift modes affect profile evolution. For example, whereas uniform uplift generates a single migrating knickpoint at the range front, multiple migrating knickpoints can form simultaneously along a river in a tilting landscape. © 2020 John Wiley & Sons, Ltd.

Lateral bedrock erosion and valley formation in a heterogeneously layered landscape, Northeast Kansas

“…Our data suggest that fracture spacing in the overlying limestone units at each site predicts the potential transport and removal of collapsed blocks from the channel bank (e.g., Gabet, 2020). The limestone units at the North Fork site tend to have a larger fracture spacing and collapse as boulders up to $1 m in diameter, whereas the limestone blocks that detached from the channel bank at the Nature Trail site during this study were estimated $0.2 m maximum in diameter and readily transported away from the bank by the stream (Figure SB7).…”

Uncovering the Controls on Fluvial Bedrock Erodibility and Knickpoint Expression: A High‐Resolution Comparison of Bedrock Properties Between Knickpoints and Non‐Knickpoint Reaches

“…In an effort to improve representation of specific fluvial incision processes within numerical landscape evolution models, much recent work has focused on developing models which incorporate abrasion processes, including rock strength as the primary force resisting abrasion (Gasparini et al., 2007; Lamb et al., 2008; Sklar & Dietrich, 2004). Despite hypotheses that plucking is generally the dominant erosional mechanism and discontinuities are therefore the more significant bedrock property in setting erodibility, very few models have explicitly incorporated erosion via plucking (Chatanantavet & Parker, 2009; Gabet, 2020; Hurst et al., 2021). Our results corroborate the hypothesized significance of discontinuities, suggesting that landscape evolution modeling efforts may be best spent focusing on further explicit incorporation of plucking behavior, perhaps by parsing of K‐ type erodibility coefficients into separate rock strength and (more heavily weighted) discontinuity spacing components, incorporating a threshold term for block entrainment (e.g., Gabet, 2020), or through variable slope exponents to reflect dominant erosional process (Whipple et al., 2000).…”

How Lithology Impacts Global Topography, Vegetation, and Animal Biodiversity: A Global‐Scale Analysis of Mountainous Regions

“…Recent studies investigating global-scale interactions between climate, tectonics, and topography have proven useful in elucidating coherent trends for such problems (Chen et al, 2019;Harel et al, 2016). All else being equal, more competent rocks form steeper slopes compared to less competent rocks (Gabet, 2020b;Gilbert, 1877;Hack, 1960), but we still lack quantification of this effect on a global scale. Similarly, the effect of bedrock lithology on vegetation has been long been established (Unger, 1836) but has mostly been studied at local or regional scales (Hahm et al, 2014;Wentworth, 1981;Whittaker & Niering, 1968).…”