Section 4.7: Earth Surface Process Modelling

Research projects

Our section’s work is organised around various projects that involve for the most part a modelling component. They cover a broad range of topics that are focused on the quantitative understanding of Earth surface evolution, the parameterisation of processes and the nature and efficiency of the links with climate, tectonics and life. Here you will find a list of ongoing projects as well as projects that are “on offer” to give you an idea of the type of projects that we propose to prospective post-docs and PhD students. Of course, we also welcome any great idea that you may have. Contact us if you are interested.

Drainage Reorganization of SW Germany and its relation to differential uplift and cuesta landscape evolution

In areas of mid- to low relief, small perturbations can drive rapid and large scale drainage reorganization (Wickert et al., 2013). The European main water divide that runs through SW German and separates the Rhine from the Danube catchment, has moved significantly since the Miocene induced by large scale drainage reorganization (Ziegler and Dèzes, 2007). Drainage reorganization is driven by differential uplift in SW Germany, and the interactions of river networks with the layered sedimentary stratigraphy of varying erosional resistance. The mountainous regions of the Black forest and Swabian Alb are a result of differential uplift combined with drainage reorganization. However, despite good constraints on total uplift and major river captures, we still lack detailed knowledge of rates and patterns of Neogene uplift and the effects of drainage reorganization on the development of the prominent cuesta landscape of SW Germany. SW Germany exhibits a prominent cuesta landscape, with at least two major escarpments. In the west, this cuesta landscape is bounded by the Black forest mountains. Despite the knowledge of major river reorganization events, it remains unclear if the cuesta landscape is related to drainage reorganization or just a product of tilted stratigraphy. Moreover, the timing of uplift and tiling in the region and especially the Black forest is not constrained well.

I am searching for a motivated student interested in the development of fluvial topography and its relation to tectonics. You should perform an analysis of the modern Rhine, Danube and Neckar drainage system. You will map signs of river captures in the present landscape (wind gaps, barbed tributaries) and analyze modern river profiles, including mapping of knickpoints and differentiating between lithological and regional kickpoints. These results can be compared to mapping of old river terraces and incision rates, as well as constraints on regional uplift. With observations from this analysis we should be able to make arguments about how and when the cuesta landscape of SW Germany really formed and better determine the timing of uplift in the regions of the Black Forest and Swabian Alb. Tectonically interested students could even model the uplift of the Back forest due fault movement in the Oberrheingraben and the faulting response to erosion after reorganization. For the analysis we can also make use of a database of rock erodbilities, which is currently being developed at GFZ. Skills in Matlab and an interest in surface processes and tectonics are beneficial. The project outcome should be delivered in English, but for literature research good German skills are beneficial.

PI: Dr. Richard Ott.


The development and calibration of a quantitative (and predictive) model for the propagation of a weathering front under a wide range of tectonic and climatic conditions

We have recently developed a simple 2D model for the propagation of a weathering front under the assumption that the velocity of the front is in proportion to the velocity of the fluid circulating in the overlying regolith layer. The model couples a surface process model with a hydrological model to predict the velocity of the fluid and the front propagation. The predictions of the model agree (to very first order) with how regolith thickness varies between orogenic and anorogenic systems. It requires, however, further calibration and validation that can only be achieved in three dimensions. The project’s main ambition is the generalisation of the model to three dimensions and its calibration using a database of regolith thickness that is presently being assembled.

PI: Prof. Jean Braun.


The inversion of a large and multi-variate geological dataset to constrain the landscape and tectonic evolution of Taiwan using an existing landscape evolution model in a Bayesian framework

We have developed very efficient methods to solve the basic equations governing surface/bedrock erosion in tectonically active mountain belts and the transport of sediment to the adjacent areas (foreland, margins, etc). Because of their high efficiency, the model can be used inside an optimisation procedure to invert large datasets pertaining to the tectonic and topographic evolution of a mountain belt. This project main objective is to use this method to invert a large, multi-variate database consisting of thermochronological data, past and present sediment flux estimates as well as sediment provenance studies from Taiwan to derive the most plausible tectonic and surface topographic evolution scenario over the past n million years of geological history of the island.

PI: Prof. Jean Braun.


The study of how macroevolutionary processes link to landscape evolution and climate variations using a newly developed population dynamic/evolutionary model

We have developed a simple evolutionary model that is coupled to our landscape evolution model. The model includes factors controlling environmental fitness, spatial competition, mutation and dispersal and predicts population evolution as well as the emergence of genetically specific sub-populations. The model can also be used to compute synthetic phylogenetic trees that can be compared to trees now commonly derived from genetic data. The main objective of this project is to use the model to further investigate the effect of landscape evolution on population dynamics and genetics in either a theoretical manner or to explain how landscape evolution may control species diversity ardor endemism in a given location.

PI: Prof. Jean Braun.


The appropriate modelling of carbonate and lacustrine landscapes where drained area - flux scalings break down

Landscape evolution models generally rely on a version of the stream power law whereby water discharge Qw and sediment flux Qs implicitly scale with drainage area A. This scheme works reasonably well in most of Earth’s landscapes however it fails to capture two common elements: 1) lakes, and 2) highly permeable lithologies. Lakes are common in postglacial and active tectonic landscapes where they act as sediment traps and disrupt the sediment routing system. At the outlet of a lake, the scaling between Qs and A is lost as Qs is essentially reset to zero and the erosivity of the stream is accordingly decreased. In highly permeable lithologies such as limestone, surface runoff does not scale with drained area as a significant fraction, if not all, of the water is rooted subterraneously through karst systems. In these cases, the stream power scaling of water and sediment fluxes with drained area is lost and landscape evolution models based on it will fail to simulate the resulting patterns of erosion. The objective of this project is to modify current routing schemes to account for such situations.

Project under the supervision of Luca Malatesta.


Landslide/Debris Flow Frequency Analysis and Hazard Assessment Using Geospatial, Climate Big Data and Machine Learning

Debris flows and Landslides present geomorphological hazards in Alpine regions, threatening life, infrastructure, and property. The magnitude of debris flows become larger due to larger amounts of sediment delivered to the channels and as a result of the predicted increase in heavy precipitation events due to climate change. Landslides are a process with causal links to climate change, primarily through precipitation, but in some cases also through temperature-induced changes of snowfall. We propose to develop a machine learning approach for figuring out the controlling factors and thresholds for debris flows and landslides. We will use this modeling framework to test the hypothesis that natural patterns exist such that geospatial and climate characteristics can be correlated with debris flow/landslide frequency utilizing a machine learning approach. We will use this approach to study and predict debris flow frequency in the western US and the Alps under climate change conditions. By applying our techniques to the database, the study also has the broader impact of leading to improved hazard assessment of debris flows in critical regions of the Western US and the Alps.

PI: Dr. Hui Tang.

[1] Peruccacci, S., Brunetti, M. T., Gariano, S. L., Melillo, M., Rossi, M., & Guzzetti, F. (2017). Rainfall thresholds for possible landslide occurrence in Italy. Geomorphology, 290, 39-57.

[2] Nikolopoulos, E. I., Destro, E., Bhuiyan, M. A. E., Borga, M., & Anagnostou, E. N. (2018). Evaluation of predictive models for post-fire debris flow occurrence in the western United States. Natural Hazards and Earth System Sciences, 18(9), 2331-2343.


Tectonic and climatic control on spatial-temporal evolution of debris-flow fans

Episodic shifts in the position of a debris-flow channel are critical for debris-flow fan evolution and understanding flow hazards because avulsions distribute debris-flow deposits through space and time. However, both the mechanisms of flow avulsion and their effects on the long-term evolution of debris-flow fans are poorly understood. This project will develop a new landscape evolution model to study how debris flow fans evolve through time in response to different types of forcing (tectonics, sediment supply, climate, etc.). The project will analyze new high-resolution topographic data based on remote sensing and satellite image and carry numerical simulations revealing the control factors landscapes in the western United States, Alps, and Argentina Andes. The research will produce a new approach to assessing landslide/debris flow risk based on landscape shape analysis, as well as a way to evaluate the role of climate warming on the evolution of alpine areas.

PI: Dr. Hui Tang.

[1] Staley, D. M., Wasklewicz, T. A., & Blaszczynski, J. S. (2006). Surficial patterns of debris flow deposition on alluvial fans in Death Valley, CA using airborne laser swath mapping data. Geomorphology, 74(1-4), 152-163.

[2] McGuire, L. A., & Pelletier, J. D. (2013). Relationships between debris fan morphology and flow rheology for wet and dry flows on Earth and Mars: A numerical modeling investigation. Geomorphology, 197, 145-155.


The appropriate modelling of carbonate and lacustrine landscapes where the scaling between drained area and fluxes breaks down

Landscape evolution models generally rely on a version of the stream power law whereby water discharge, Qw, and sediment flux, Qs, implicitly scale with drainage area A. This scheme works reasonably well in most of Earth’s landscapes however it fails to capture two common elements: 1) lakes, and 2) highly permeable lithologies. Lakes are common in postglacial and active tectonic landscapes where they act as sediment traps and disrupt the sediment routing system. At the outlet of a lake, the scaling between Qs and A is lost as Qs is essentially reset to zero and the erosivity of the stream is accordingly decreased. In highly permeable lithologies such as limestone, surface runoff does not scale with drained area as a significant fraction, if not all, of the water is rooted subterraneously through karst systems. In these cases, the stream power scaling of water and sediment fluxes with drained area is lost and landscape evolution models based on it will fail to simulate the resulting patterns of erosion. The objective of this project is to modify current routing schemes to account for such situations.

Project under the supervision of Luca Malatesta.


The implementation of high resolution stratigraphic outputs in landscape evolution models

Commonly, the main output of landscape evolution models (LEMs) is a topography whose morphometrics are then compared against that of natural landscapes. Though, the morphology of a natural landscape only reflects a moment in time — now — and is not the most robust proxy to evaluate a model. LEMs should incorporate outputs reflecting standard geological records such as stratigraphy and thermochronology instead of mainly relying on morphometrics. Stratigraphic outputs can be used to track surface evolution through time against real datasets in a way that morphometrics cannot. The project will seek to implement full resolution stratigraphic models in subdomains of the LEMs after completion of the coupled run (e.g. with a geodynamic model) using constraints (flux, tracers) of the full LEM as boundary conditions for the stratigraphic output.

Project under the supervision of Luca Malatesta.

 

 

Numerical Modeling of Debris-Flow Initiation Mechanism and Magnitude in the Alpine Environment

Debris flow is very common in the Alpine environment, which caused destruction of property and loss of lives in these regions. Our understanding of initiation mechanisms and evolution of debris flows is limited due to a lack of direct observations and measurements. We need to combine existing debris flow/landslide database and numerical deterministic simulations to study the initiation mechanism and magnitude. Illgraben in southwest Switzerland, with at least ten years of record at debris basins, is selected for this study because they provide a wealth of geological and geophysical data. There are several possible triggering mechanisms of debris flows in the Illgraben channel system (e.g., failures of landslide dams, hillslope landslides, snowmelt runoff from avalanche deposits or runoff events generated by heavy summer storms). We have developed a 2D model for the initiation and propagation of runoff-generated debris flow in a burned area. The model couples shallow water equations with soil erosion model. In this project, we focus on identifying different initiation mechanisms and developing a numerical model based on this debris flow database. Based on the proposed numerical model, physically based thresholds will be derived to estimate the hydrodynamic conditions coinciding with the timing of debris flow activity in the Alpine environment.

PI: Dr. Hui Tang .

[1] Bennett, G. L., Molnar, P., McArdell, B. W., Schlunegger, F., & Burlando, P. (2012). Patterns and controls of sediment production, transfer and yield in the Illgraben. Geomorphology, 188, 68-82.                

[2] Bennett, G. L., Molnar, P., Eisenbeiss, H., & McArdell, B. W. (2012). Erosional power in the Swiss Alps: characterization of slope failure in the Illgraben. Earth Surface Processes and Landforms, 37(15), 1627-1640.

[3] Bennett, G. L., Molnar, P., McArdell, B. W., & Burlando, P. (2014). A probabilistic sediment cascade model of sediment transfer in the Illgraben. Water Resources Research, 50(2), 1225-1244.


Modelling and inverting deep marine stratigraphy

Though the deep marine environment (below the continental shelf break) contains some of the most extensive and complete deposits on Earth, there are few process-based approaches for modelling the development of deep marine stratigraphy. Charlie Shobe's project at the GFZ, funded by an EU Marie Curie fellowship, focuses on building an efficient model for deep marine sediment transport and deposition. Coupling the new deep marine model with existing shallow marine and terrestrial model components will enable inversion of deep marine stratigraphy to extract past perturbations to passive continental margin landscapes.

Project investigators: Charlie Shobe, Jean Braun

 

 


Linking landscape evolution and life

Geomorphological processes can have a large impact on terrestrial ecosystem evolution and can therefore play an important role in macroevolutionary processes through time. We investigate how landscape evolution and climate interact to alter the connectivity and spatial distribution of habitats, influencing gene flow and range limits of communities within these habitats. Using numerical modeling paired with data of major geologic events, species distribution, and phylogenies, I aim to test if and how speciation events in the phylogenetic record can be explained by topography, drainage reorganization and climate change.

Project Investigators: Katherine Kravitz, Jean Braun


Orographically-enhanced precipitation for landscape evolution modeling

The goal of this project is to evaluate the effectiveness of coupling an existing model of orographic precipitation to a landscape evolution model. Precipitation in mountainous terrain can vary dramatically over short distances, and frequently varies an order of magnitude from the windward to leeward sides of a mountain range. Moreover, we see a distinct contrast in terrain slope on opposing sides of mountain ranges today, suggesting a correlation between orography and precipitation. Most landscape evolution studies do not account for the spatial variability in precipitation. This project evaluates whether the Linear Theory (LT) of Orographic Precipitation (Smith and Barstad, 2004) effectively simulates the asymmetric pattern of precipitation as compared to modern rainfall estimates from the Tropical Rainfall Measurement Mission (TRMM). Preliminary results suggest that the LT model can do a remarkably good job of reproducing rainfall statistics *if* the number of yearly events can be adequately estimated.

Project Investigators: Dominik Schneider and Jean Braun 


Development of open-source software for interactive and exploratory modelling

Implementation of fast and extensible landscape evolution models

In geomorphology as well as in many other areas of scientific research, the growing use of computer programs, notably for running simulations, is affected by issues of reproducibility and reusability. In these areas, a lot of numerical experimentation often leads to full-featured model implementations with complex codes and interfaces that become hard to maintain. Following good software engineering practices, we try to overcome these issues by providing a common,generic framework for building computational models and running simulations. This framework encourages model creation or extension using a fine-grained modular approach, which is suited for development of scalable implementations and which leaves much room for experimentation. Highly connected to the Python scientific ecosystem,this software is also designed to increase interactivity. We use the framework to implement a set of efficient algorithms (FastScape) into versatile models of landscape evolution that will potentially include many different erosion processes (e.g., bedrock river incision, hillslope erosion, marine transport and sedimentation, glacial erosion, etc.) and their control by climate or tectonic factors.  

Project investigators: Benoît Bovy  and Jean Braun .

Collaborators: open to external contributions (open-source software)

xarray-simlab: https://github.com/benbovy/xarray-simlab

xarray-topo: gitext.gfz-potsdam.de/sec55-public/xarray-topo

 

 


Understanding the interactions between climate and fluvial erosion

There is a need to improve our understanding and modeling of how surface relief and topography affect rainfall patterns and the distribution of rainfall events both spatially and temporally, and in turn how this affects discharge distributions and patterns of erosion. In particular, it is important to develop a better understanding of the link between rainfall variability and mean, and discharge variability and mean in mountainous river catchments in order to build predictable models of long-term evolution of mountain belts, but also to predict the magnitudes and frequencies of natural hazards (e.g. landslides, floods). Currently, our understanding is limited by the assumption of uniformity of rainfall mean and variability in any catchment, which cannot be taken lightly in mountainous river catchments where the control of rainfall by orography cannot be neglected, as the mean rainfall intensity and variability varies greatly with altitude. Therefore, the main focus of this project is to answer these questions i.e. to overcome these severe limitations, and to improve the current model of the relation of rainfall to discharge characteristics by taking into account the orographic effect on precipitation, and also the effect of finite storm size in large catchments. The acquired knowledge would be used to predict how these forcings affect erosional processes characterized by a threshold (e.g. river incision, landsliding).

Project Investigators: Igor Lisac , Jean Braun , Niels Hovius .


Modelling the spatial pattern of denudation under a Quaternary ice sheet

Glacial erosion of the underlying bedrock depends on the conditions at the bed: a cold-based glacier is frozen to the bedrock, while a glacier with its bottom at the pressure melting point can slide over the bedrock and cause erosion. Cosmogenic nuclide studies in landscapes such as Scandinavia that were glaciated during the Quaternary glacial cycles suggest a complex pattern of glacial erosion:while some areas have been substantially eroded around the last glacial maximum or even later, others seem untouched by a number of recent glacial cycles. Using the shallow ice approximation that holds well for large ice sheets, we are modelling the temperature regime, sliding conditions, and the resulting glacial erosion pattern under the Scandinavian ice sheet over the Quaternaryglacial cycles. By attempting to reproduce the broad patterns of denudation observed in the cosmogenic nuclide studies with a simple glacial erosion model, we hope to understand the impact of a dynamic ice sheet on the underlying landscape over a time scale of multiple glacial cycles.

Project main investigators: Erik Tamre and Jean Braun. 


Velocity of escarpments and drainage divides

Rates of drainage divide migration

Bedrock river incision drives the topographic evolution of mountain ranges, orchestrating the adjustment of rivers and valleys towards a configuration with erosion rates everywhere equal to rock uplift rates. Analyses relating topography to climate and tectonics often assume landscapes approach this steady-state condition and thereby associate knickpoints, low relief plateau surfaces, and other transient topographic features with changes in external forcing. Because bedrock river incision rates depend on river discharge, migration of drainage divides and consequent changes in drainage area can also modify erosion rates and generate transient topography. The extent to which divide migration influences landscape evolution is uncertain because the rates and timescales over which drainage divides migrate are not well known. Small-scale laboratory experiments of uplifting landscapes exhibit persistent divide migration, whereas numerical landscape evolution models tend to develop static drainage networks under constant forcing. Sediment provenance studies and irregular channel network geometries indicate that drainage divides do migrate in nature, but only recently have efforts been made to systematically identify when and where divide migration occurs. We are developing analytic expressions for the velocity of drainage divides, based on equations commonly used to describe fluvial and hillslope erosion, and applying them to digital elevation datasets and topography generated by landscape evolution models. To validate our methods, we are comparing predicted divide velocities to modeled velocities, cross-divide differential erosion rates, and other recently proposed topographic indicators of divide mobility.  

Project investigators: Kim Huppert  and Jean Braun 


How important is short-term climate variability for the efficiency of erosion?

Discharge variability and bedrock river incision on the Hawaiian Island of Kaua'i

The Hawaiian island of Kaua’i provides an ideal natural laboratory to evaluate the effects of discharge variability and thresholds on bedrock river incision because it has one of Earth’s steepest spatial gradients in mean annual rainfall and it also experiences dramatic spatial variations in rainfall and discharge variability, spanning a wide range of the conditions reported on Earth. Kaua’i otherwise has minimal variations in lithology, vertical motion, and other factors that can influence erosion. Moreover, river incision rates averaged over million year timescales can be estimated along the lengths of Kauaian channels from the depths of river canyons and lava flow ages. We are characterizing rainfall and discharge variability on Kaua’i using records from an extensive network of rain and stream gauges spanning the past century, and we are using these characterizations to model long-term bedrock river incision on Kauai with a threshold-dependent bedrock river incision law. 

Project investigators: Kim Huppert  (GFZ Potsdam), Jean Braun  (GFZ Potsdam), Eric Deal (MIT), Taylor Perron (MIT), Ken Ferrier (Georgia Tech)


Long-term topographic history of Madagascar

Since its separation from Africa at ~150 Ma and from India at ~90 Ma, Madagascar has its own geological, geomorphic and biogeographic histories, providing an exceptional opportunity for investigating the relationship between the region’s landscape evolution and its biogeography. This project will recover the long-term topographic history of Madagascar for the past 150 million years, based on inversion of the sedimentary records, thermochronological data and the present-day topography. The modelled landscape will reproduce evolution of the island’s stream networks and drainage basin geometry, which will be used to test existing hypotheses of the Malagasy biogeographic evolution.

Project main investigators: Ruohong Jiao and Jean Braun .

 

 


Substrate controls on topography and erosion in bedrock landscapes

In bedrock landscapes, the interactions between substrate, process and form can give rise to a wide range of complex morphological behaviors. These interactions are often highly non-linear, making it a challenge to unpack the substrate dependence of topography and erosion in such landscapes.This problem can be tackled in numerous ways. One approach involves quantifying the lengthscale(s) at which substrate properties and topography are correlated. This information can then be used to learn more about the nature of the physical processes acting on bedrock landscapes, and to improve the ways in which we parameterize them. We have developed a new application of wavelet analysis that allows such correlations to be determined for 2D curvilinear landscape features. We are currently using this method to explore the substrate dependence of physical processes acting on rock coasts at a broad range of scales, from meters to kilometers, with particular focus on the role of discontinuities. However, this method is generalizable to any planar curve constructed from pairs of coordinates.

Project Investigator: Sam Wilson-Fletcher 

Collaborators: Niels Hovius , Jean Braun , Benoit Bovy  (GFZ), Eric Deal (MIT)


Marine transport and sedimentation in landscape evolution models

Limited attention has been given to linking continental erosion to marine transport and sedimentation in large-scale landscape evolution models. Although either of the two environments has been thoroughly investigated, the details of how climate and tectonic events are recorded in the sedimentary and stratigraphic records have not been studied in a consistent quantitative manner. Xiaoping Yuan´s project at GFZ, funded by the TOTAL COLORS project, is to develop a new numerical model for marine sediment transport and deposition that is directly coupled to FastScape, a landscape evolution model that solves the continental stream power law and hillslope diffusion equation using fully implicit and O(n) algorithms. The model of marine transport and sedimentation is simulated by a nonlinear 2D diffusion model where a source term represents mass flux arising from continental river erosion.

Project investigators : Xiaoping Yuan  (GFZ, Potsdam), Jean Braun  (GFZ, Potsdam), Laure Guerit (GET, Toulouse, France), Brendan Simon (Geosciences Rennes, France)


Inverting south African topography, thermochronological and sedimentary data to infer the uplift history of the craton over the past 100 Myr

The origin of the anomalous topography of the southern part of the African continent remains highly debated. Some postulate that it is long-wavelength dynamic topography, the expression of upward flow in the underlying mantle; others associate it with the onset of doming and extension in the East African Rift. We are using the FastScape landscape evolution model to invert sedimentary data from the offshore basins surrounding the south African craton, along with low-temperature thermochronological data compiled by Jessica Stanley, to derive estimates of the magnitude, distribution and timing of the uplift of the craton. The idea is to use an optimization method (the Neighbourhood Algorithm) to perform a large number of forward landscape evolution model experiments varying the model parameters to find the optimum values that represent the data. In doing so, we hope to provide quantitative and uncertainty-bound estimates of the uplift history of the continent.

Main findings so far:

- Models which match the erosion history data well suggest uplift of the eastern margin in the Cretaceous (~100 Ma) followed by uplift of the western margin ~20 Myr later. These results suggest that the scenario proposed by Braun et al. (2014) of uplift caused by the continent moving over the African superswell is viable.

-The amplitude of this uplift is on the order of 1000 m, and best fitting results suggest that there was significant topography (~800-1000 m average elevation) on the continent before it was uplifted in the Cretaceous.

- The comparison between the eroded volumes of sediment in the marine basins and the amount of erosion that needed to reset the thermochronology data suggests a significant amount of chemical denudation during the Cretaceous erosion event.

-The data cannot resolve whether there was smaller amplitude phase of uplift in the Cenozoic.

We are currently investigating the compatibility of other proposed uplift geometries to see whether they are also able to match the observed data.

Project main investigators: Jessica Stanley, Jean Braun .

Collaborators: François Guillocheau, Cécile Robin, Guillaume Baby, Université de Rennes 1, France; Becky Flowers, University of Colorado; Rod Brown, University of Glasgow.


Developing a new, fast algorithm for marine transport and sedimentation to invert the stratigraphic record

The transport of sediment in the marine environment has commonly been modelled using simple transport law that leads to a representation of the process by a diffusion equation. Many processes remain, however, poorly understood (e.g. transport and deposition in deep sea fans) and are unlikely to be properly represented by a simple diffusion equation. Furthermore, most existing models are relatively inefficient, which makes them unsuitable for use in inverting the stratigraphic record. We are currenly developing a new numerical method to develope O(n) efficiency and an implicit integration in time such that computational time is drastically reduced and is more appropriate for optimization. This work is being carried out within the framework of the COLORS project funded by Total.

Project main investigators: Xiaoping Yuan , Jean Braun .

Collaborators: Delphine Rouby, Univerité Paul Sabatier, Toulouse; Ritske Huismans, University of Bergen.


The weathering of continental interiors and the formation of pediments

In 2016, in collaboration with researchers from the Université Rennes 1, we published a new, simple parameterization of the rate of vertical propagation of a weathering front. We assumed that the rate of weathering is controlled by the ability of water flowing through the regolith to remove the product of the dissolution from the weathering front and, therefore, by the velocity of water along the interface. This leads to a relatively simple behaviour where the mean rate of propagation of the front beneath a topographic feature (hill) and its geometry, i.e. whether it is thicker near the top of the base of the hill, are controlled by two dimensionless numbers that only depend on a few model parameters such as the dimension of the hill, the mean erosion rate at the surface, the mean precipitation rate, the hydraulic conductivity of the regolith and a factor relating the rate of front propagation to fluid velocity. We are now in the process of implementing this simple parameterization in the FastScape landscape evolution model and using it to study the formation of pediments. Pediments are the flat, low slope, erosional surfaces that characterise many continental interiors. Through our modeling, we hope to demonstrate that pediments are exhumed weathering fronts, the shape of which is mainly controlled by the process responsible for the formation and propagation of the weathering front and not by the process responsible for its exhumation.

Project main investigators: Jean Braun  and Jessica Stanley.

Collaborators: François Guillocheau and Cecile Robin, Université de Rennes 1.