Experimental migration of knickpoints: influence of style of base-level fall  and bed lithology

Grimaud, Jean‐Louis; Paola, Chris; Voller, V. R.

doi:10.5194/esurf-4-11-2016

Cited by 73 publications

(52 citation statements)

References 40 publications

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“…Numerical models show that lateral erosion mechanisms are important for strath-terrace formation (e.g., Finnegan & Dietrich, 2011;Hancock & Anderson, 2002). In laboratory experiments, Hasbargen and Paola (2000), Grimaud et al (2016), and Scheingross et al (2019) observed self-formed knickpoints in the incision of bedrock analogues under steady forcing. In the field, Seidl et al (1994) propose that knickpoint propagation acts as the primary process for bedrock lowering in Hawaiian channels.…”

Section: Discussionmentioning

confidence: 99%

Extreme Memory of Initial Conditions in Numerical Landscape Evolution Models

Kwang

Parker

2019

Geophysical Research Letters

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Landscape evolution models (LEMs) are dependent on their initial conditions (ICs). Commonly, LEMs use a horizontal surface with randomized perturbations as their IC and tend toward a steady state under constant forcing. The initial and steady state topographies are inherently linked, but they bear no obvious resemblance to each other. Here we reveal a connection by adding a shallow sinusoidal channel to the IC. This channel transforms into a deep canyon at steady state. Hence, the general behavior of LEMs is to indefinitely preserve topographic features from their ICs. Then we test whether experimental landscapes exhibit a similar behavior. In our experiments, we use the same sinusoidal signal, but find that it is ultimately erased. We believe that the culprit reorganizing processes are lateral channel migration and spatiotemporal variability in incision. Our results imply that LEMs are missing fundamental mechanisms and that long‐term preservation of ICs in erosional environments is unlikely.

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Section: Discussionmentioning

confidence: 99%

Extreme Memory of Initial Conditions in Numerical Landscape Evolution Models

Kwang

Parker

2019

Geophysical Research Letters

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“…Knickpoints, however, can likewise be a result of changes in lithology (Grimaud et al, 2014;Roy et al, 2015) and are certainly not a unique indicator of erosion dynamics (e.g. Tucker and Whipple, 2002;Valla et al, 2010;Grimaud et al, 2016). In this contribution we therefore attempted to understand how the sediment flux signal out of the eroding catchment may generate a distinguishable difference between the endmember models in terms of a response to a change in run-off.…”

Section: Discussionmentioning

confidence: 99%

Numerical modelling of landscape and sediment flux response to precipitation rate change

et al. 2018

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Abstract. Laboratory-scale experiments of erosion have demonstrated that landscapes have a natural (or intrinsic) response time to a change in precipitation rate. In the last few decades there has been growth in the development of numerical models that attempt to capture landscape evolution over long timescales. However, there is still an uncertainty regarding the validity of the basic assumptions of mass transport that are made in deriving these models. In this contribution we therefore return to a principal assumption of sediment transport within the mass balance for surface processes; we explore the sensitivity of the classic end-member landscape evolution models and the sediment fluxes they produce to a change in precipitation rates. One end-member model takes the mathematical form of a kinetic wave equation and is known as the stream power model, in which sediment is assumed to be transported immediately out of the model domain. The second end-member model is the transport model and it takes the form of a diffusion equation, assuming that the sediment flux is a function of the water flux and slope. We find that both of these end-member models have a response time that has a proportionality to the precipitation rate that follows a negative power law. However, for the stream power model the exponent on the water flux term must be less than one, and for the transport model the exponent must be greater than one, in order to match the observed concavity of natural systems. This difference in exponent means that the transport model generally responds more rapidly to an increase in precipitation rates, on the order of 10 5 years for post-perturbation sediment fluxes to return to within 50 % of their initial values, for theoretical landscapes with a scale of 100 × 100 km. Additionally from the same starting conditions, the amplitude of the sediment flux perturbation in the transport model is greater, with much larger sensitivity to catchment size. An important finding is that both models respond more quickly to a wetting event than a drying event, and we argue that this asymmetry in response time has significant implications for depositional stratigraphies. Finally, we evaluate the extent to which these constraints on response times and sediment fluxes from simple models help us understand the geological record of landscape response to rapid environmental changes in the past, such as the Paleocene-Eocene thermal maximum (PETM). In the Spanish Pyrenees, for instance, a relatively rapid (10 to 50 kyr) duration of the deposition of gravel is observed for a climatic shift that is thought to be towards increased precipitation rates. We suggest that the rapid response observed is more easily explained through a diffusive transport model because (1) the model has a faster response time, which is consistent with the documented stratigraphic data, (2) there is a high-amplitude spike in sediment flux, and (3) the assumption of instantaneous transport is difficult to justify for the transport of large grain sizes as an alluvi...

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“…Knickpoints however can likewise be a result of 10 changes in lithology (Grimaud et al, 2014;Roy et al, 2015) and are certainly not a unique indicator of erosion dynamics (e.g. Tucker and Whipple, 2002;Valla et al, 2010;Grimaud et al, 2016). In this contribution we therefore attempted to understand of the sediment flux signal out of the eroding catchment may generate a distinguishable difference between the end-member models in term of a response to a change in run-off.…”

Section: Discussionmentioning

confidence: 99%

Numerical modelling landscape and sediment flux response to precipitation rate change

Armitage¹,

Whittaker²,

Zakari³

et al. 2017

Preprint

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Abstract. Laboratory-scale experiments of erosion have demonstrated that landscapes have a natural (or intrinsic) response time to a change in precipitation rate. In the last few decades there has been a growth in the development of numerical models that attempt to capture landscape evolution over long time-scales. Recently, a sub-set of these numerical models have been used to invert river profiles for past tectonic conditions even during variable climatic conditions. However, there is still an 5 uncertainty over validity of the basic assumption of mass transport that are made in deriving these models. In this contribution we therefore return to a principle assumption of sediment transport within the mass balance for surface processes, and explore the sensitivity of the classic end-member landscape evolution models to change in precipitation rates. One end-member model takes the mathematical form of a kinetic wave equation and is known as the stream power model, where sediment is assumed to be transported immediately out of the model domain. The second end-member model takes the form of a diffusion equation, 10 and assumes that the sediment flux is a function of the water flux and slope. We find that both of these end-member models have a response time that has a proportionality to the precipitation rate that follows a negative power law. For the stream power model the exponent on the water flux term must be less than one, and for the sediment transport model the exponent must be greater than one in order to match the observed concavity of natural systems. This difference in exponent means that sediment transport model responds more rapidly to an increase in precipitation rates, on the order of 10 5 years for a landscape with 15 a scale of 10 5 m. In nature, landscape response times to a rapid environmental change have been estimated for events such as the Paleocene-Eocene thermal maximum (PETM). In the Spanish Pyrenees, a relatively rapid, 20 to 100 kyr, duration of deposition of gravel during the PETM is observed for a climatic shift that is thought to be towards increased precipitation rates. We suggest the rapid response observed is more easily explained through a diffusive sediment transport model, as (1) this model has a faster response time, consistent with the documented stratigraphic data, and (2) the assumption of instantaneous 20 transport is difficult to justify for the transport of large grain sizes as an alluvial bed-load.

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Experimental migration of knickpoints: influence of style of base-level fall and bed lithology

Cited by 73 publications

References 40 publications

Extreme Memory of Initial Conditions in Numerical Landscape Evolution Models

Extreme Memory of Initial Conditions in Numerical Landscape Evolution Models

Numerical modelling of landscape and sediment flux response to precipitation rate change

Numerical modelling landscape and sediment flux response to precipitation rate change

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