Orogen‐scale drainage network evolution and response to erodibility changes: insights from numerical experiments

Abstract

The continuous feedbacks among tectonics, surface processes, and climate are reflected in the distribution of catchments on active mountain ranges. Previous studies have shown a regularity of valley spacing across mountain ranges worldwide, but the origin of this geomorphological feature is currently not well known. In this work, we use a landscape evolution model to investigate the process of fluvial network organization and the evolution of regular ridge-and-valley patterns on simulated mountain ranges. In particular, we investigate the behavior of such patterns when subjected to a perturbation in landscape processes from a previous steady state, resulting from a sudden variation in the pattern of bedrock erodibility, from homogeneous to a gradient. We analyze the time evolution of the mean ratio λ' between the linear spacing of adjacent valleys and the half width of the mountain range. We show how a valley spacing ratio of~0.5 is first achieved at steady state under uniform bedrock erodibility. After applying the gradient of bedrock erodibility across the landscape, we observe that λ' first increases and then decreases to a new steady-state value that is smaller than the original value. A detailed analysis of the simulations, through observations of surface 'snapshots' at repeated time intervals, allows to gain some insight into the mechanisms governing this fluvial network reorganization process, driven by the migration of the main divide toward the side characterized by lower bedrock erodibility. On both sides of the range the new steady-state valley spacing is obtained through mechanisms of catchment reorganization and competition between adjacent fluvial networks. In particular, catchment reorganization is characterized by the growth of smaller catchments between shrinking larger catchments on the side with lower erodibility, and the growth of larger catchments on the side with higher erodibility.

Complexity and non‐linearity in earth surface processes – concepts, methods and applications

“…() and Giachetta et al . (): the Real‐Space Cellular Automaton Laboratory (ReSCAL). The model, at its core, mimics multiple physical processes by focusing on interactions between neighbouring cells ('doublets').…”

“…At a similar spatial scale, Giachetta et al . () focus on the complex rearrangement dynamics of valleys in mountain ranges. They study how the regular spacing of valleys that has been recognized across mountain ranges worldwide (Hovius, ), is formed after steady state topography is perturbed.…”

Plio-Quaternary uplift of the Iberian Chain (central–eastern Spain) from landscape evolution experiments and river profile modeling

“…Modeling of longitudinal river profiles has been used to reconstruct the histories and patterns of regional and local tectonic uplift. In this study we designed a two-step modeling experiment: in the first step we reconstruct the paleotopography of the Iberian Chain during the Pliocene and the Quaternary (Section 3) using a landscape evolution model SIGNUM (Refice et al, 2012;Giachetta et al, 2014) and in the second step, we model the stream profile evolution of rivers draining the Iberian Chain (Section 4). The numerical model, SIGNUM, represents the land surface by a set of points with three-dimensional coordinates, connected by edges to form a triangulated irregular network (TIN).…”

“…In the first step we use a landscape evolution model called SIGNUM (Refice et al, 2012), which has been successfully used to investigate the feedbacks between uplift and erosion in active tectonic settings and the reorganization of drainage network at the orogen scale (e.g. Capolongo et al, 2011;Giachetta et al, 2014). SIGNUM is suitable to simulate the transient response of a synthetic topography representing the Iberian Chain to a tectonic perturbation over 10 6 year time scale.…”

Tectonics, sedimentation and surface processes: from the erosional engine to basin deposition

“…The perturbation is analogous to that studied by Bonnet () through a change in precipitation. Although both studies show that drainage basins reorganize so as to maintain a spacing ratio close to 2 as in studies by Hovius (); Talling et al () and Castelltort and Simpson (), in the study of Giachetta et al () this reorganization occurs through the lateral enlargement and capture of drainage area from a few large catchments by numerous smaller ones, a mechanism different from the splitting of drainage basins evidenced in the laboratory experiments of Bonnet (). These results are not exclusive of each other as they perhaps rather stem from different sediment transport conditions in the channels (detachment versus supply‐limited) as suggested by Giachetta and colleagues.…”