Program (Fall 2022):
06 October 2022 - Gino de Gelder (University of Grenoble) "Inverting marine terrace morphology to constrain paleo sea-level"
Abstract: Quantifying paleo sea-level variations is of fundamental importance to understand the complex relations between paleo-climate, -ice-sheets and geodynamics, yet uncertainties prior to the Holocene currently span several tens of meters. The world’s coastlines present an enormous geomorphologic dataset of relative sea-level changes, and recent studies have shown how they can be used within forward landscape evolution models. We take a next step, and apply a Bayesian approach to invert the geometry of marine terrace sequences to paleo sea-level. Using a Markov chain Monte Carlo sampling method, we test our model on both synthetic profiles and observed marine terrace sequences from Santa Cruz (Ca, US) and the Corinth Rift (Greece). The synthetic profiles – with known input parameters – show that there are optimal values for uplift rate and erosion rate to obtain a well-constrained inversion. Both the inversion of synthetic profiles and real sequences show how sea-level peaks are easier to constrain than sea-level troughs, but that also solutions for peaks tend to be non-unique. Synthetic profiles and profiles from several sites in the Corinth Rift both show how inverting multiple profiles from a sequence can lead to a narrower range of possible paleo sea-level, especially for sea-level troughs. This last result emphasizes the potential of inverting coastal morphology, suggesting that joint inversion of globally distributed marine terrace profiles may eventually catalyse a better understanding of local/global paleo sea-level and glacio-isostatic adjustments.
20 October 2022 - Steffi Tofelde (University of Potsdam) "What sets the width of valley floors?"
→ To register:
Abstract: The geometries of river valleys range from deeply incised canyons with narrow or no floodplains to cross-sections of kilometer-wide, densely populated plains. The shape of river valleys is the product of the interplay between tectonic uplift and erosion by rivers. Rivers deepen valleys through vertical incision and widen valleys by lateral erosion of the enclosing valley walls. While the processes and rates of river incision have been studied extensively in recent decades, comparably little is known about lateral river erosion and controls on valley-floor width. Field measurements of valley floors are sparse, but generally indicate that valleys are narrower at sites of enhanced uplift and row wider with greater river discharge and in softer lithologies. However, the order-of-magnitude scatter in these data suggests other, as yet unquantified, factors that influence valley-floor width. Paired river terraces - staircases of ancient floodplains preserved at different heights on either side of the valley - preserve information about past valley widths. We extracted valley width and height from climatically formed, alluvial river-terrace sequences and showed that valley height explains 90-99% of the variance in valley width at a given site. To explain the observed valley-width-height relationship, we propose that the amount of lateral sediment supply from valley walls, in addition to river discharge and lithology, controls valley-floor width.
27 October 2022 - David Montgomery (University of Washington, Seattle) "The geomorphology of farming and health — how soil health connects to human health"
→ To register:
Abstract: We all know that diet matters and have heard the adage "you are what you eat." But dig a little deeper and it becomes clear that what our food eats—how we grow crops and raise animals—rounds out the full story. Farming practices intimately influence soil health which in turn affects the amount of health protective micronutrients and phytochemicals in our crops. And what we feed livestock affects the mix of fats in meat and dairy products. Modern farming practices reliant on frequent tillage, excessive applications of soluble nitrogen fertilizers, and reliance on pesticides have degraded agricultural soils and reduced the amount of beneficial compounds in foods. Yet farmers in both the industrialized and developing worlds are changing their practices to improve soil health through minimizing soil disturbance, planting cover crops, and diversifying the crops they grow. These practices combine ancient wisdom with modern science revealing that there are ways to farm that provide sufficient yields and foods suffused with the array of compounds that help underpin human health. It turns out that what’s good for the land is good for us too.
03 November 2022 - Nathan Brown (University of Texas, Arlington) "Resolving surficial processes using luminescence thermochronology "
→ To register:
Abstract: Luminescence dating is commonly used to constrain when sediment was last exposed to sunlight. For mineral grains within the dark interior of a rock outcrop, however, the luminescence signals relate to thermal exposure. For example, with grains kept at a constant temperature for time periods longer than several hundred thousand years, luminescence signals can be used to estimate that storage temperature over a wide range, from upper-crustal through atmospheric temperatures (paleothermometry). Conversely, grains which have changed temperature recently can embed information about their time-temperature history (thermochronology).
In this presentation, I will review the basic principles underlying luminescence thermochronology, some example applications, and future research directions, with emphasis on understanding surficial processes. Advantages of this technique include the ubiquity of target minerals (primarily K-feldspar), its sensitivity to low temperatures and recent time periods, as well as the diversity of luminescence signals which can be measured from a single sample to gain additional information of a sample’s geothermal history.
10 November 2022 - Laure Guerit (CNRS and University of Rennes) "Title to be announced"
→ To register:
17 November 2022 - Clément Désormeaux (Aix-Marseille University) "Investigation of stochastic-threshold incision models across a climatic and morphological gradient "
→ To register:
Abstract: Long-term landscape evolution is controlled by tectonic and climatic forcing acting through surface processes. Rivers are the main drivers of continental denudation because they set the base level of most hillslopes. The mechanisms of fluvial incision are thus a key focus in geomorphological research and require accurate representation and models. River incision is often modeled with a stream power model (SPM) based on the along-stream evolution of drainage area and channel elevation gradient but can also incorporate more complex processes such as threshold effects and statistical discharge distributions, which are fundamental features of river dynamics. Despite their importance in quantitative geomorphology, such model formulations have been confronted with field data only in a limited number of cases. Here we investigate the behavior of stochastic- threshold incision models across the southeastern margin of the French Massif Central, which is characterized by significant relief and the regular occurrence of high-discharge events.