Timescales of landscape response to divide migration and drainage capture: Implications for the role of divide mobility in landscape evolution

Abstract

Efforts to extract information about climate and tectonics from topography commonly assume that river networks are static. Drainage divides can migrate through time, however, and recent work has shown that divide mobility can potentially induce changes in river profiles comparable to changes caused by variation in rock uplift, climate, or rock properties. We use 1‐D river profile and 2‐D landscape evolution simulations to evaluate how mobile divides influence the interpretation of river profiles in tectonically active settings. We define a nondimensional divide migration number, NDm, as the ratio of the timescale of channel profile response to a change in drainage area (TdA) to the timescale of divide migration (TDm). In simulations of headward divide migration, NDm is much less than unity with no measurable perturbation of channel profiles. Only in simulations configured to induce rapid lateral divide migration are there occasional large stream capture events and zones where localized drainage area loss is fast enough to support NDm values near unity. The rapid response of channel profiles to changes in drainage area ensures that under most conditions profiles maintain quasi‐equilibrium forms and thus generally reflect spatiotemporal variation in rock uplift, climate, or rock properties even during active divide migration. This implies that channel profile form may not reliably record divide mobility, so we evaluate alternate metrics of divide mobility. In our simulations and an example in Taiwan, we find that simple measures of cross‐divide contrasts in topography are more robust metrics of divide mobility than measures of drainage network topology.

Extreme Memory of Initial Conditions in Numerical Landscape Evolution Models

“…It might be that with more sediment, our experimental landscapes would have achieved TSS; however, previous, long-term experiments still failed to reach TSS (Hasbargen & Paola, 2000). In addition, it would be useful to study how these processes interact with the feedback that control drainage network reorganization in current LEMs (see Whipple et al, 2017). To properly evaluate and benchmark the predictive capabilities of LEMs, it is important to understand how autogenic processes affect the steady state behavior of LEMs.…”

How concave are river channels?

“…In the absence of lithologic variability, climate gradients and tectonic transience, gradients in χ in the channel network between adjacent drainage basins are predicted to indicate locations where drainage divides are migrating (toward the catchment with higher χ) and drainage network reorganisation is ongoing . On the other hand, numerical simulations suggest that spatial variability in uplift is more important than temporal gradients in uplift rates (Whipple et al, 2016). Rivers draining across normal fault systems are often routed through the relay zones between fault tips, where uplift rates are lowest, capturing and rerouting much of the drainage area above the footwall (e.g.…”

Criteria and tools for determining drainage divide stability

“…When the 139 assumption of spatially uniform rate of uplift (or base level fall) and erosional efficiency (set 140 primarily by climate and rock properties) is violated, c-anomalies can develop and persist at 141 stable divides (e.g., Whipple et al, 2017c). In addition c-values are sensitive to the choice of x b 142…”