Thursday, 1 June 2023 at 16:00 CEST

Duna Roda-Boluda (Vrije Universiteit Amsterdam)

To register: https://durhamuniversity.zoom.us/meeting/register/tJcuduChrTsqGNTNCPgC0LCKlqiRoWayo0c9

Where, how, and how fast do the Southern Alps of New Zealand erode?

Abstract: The Southern Alps of New Zealand are one of the fastest uplifting orogens on Earth, and one of the orogens from which we base a lot of what we know on the interaction of tectonics, climate and erosion. However, on 102-103 yr timescales, the rates and patterns of erosion are not well-constrained. To address this, first I will present a new data set of 10Be derived, catchment-averaged denudation rates from the western Southern Alps of New Zealand, and compare them to rock-uplift rate estimates. Next, I will show how our data supports enhanced erosion in the 1500-2000 m elevation window, where periglacial and paraglacial processes have previously been proposed to be most active. Then, with a new data set of 10Be concentrations from 17 recent landslide deposits, and published and reinterpreted landslide erosion rates, I will discuss the implications of our data on the erosional locus and dominant erosional processes on the range. Finally, I will present some on-going work testing whether paired in-situ 14C-10Be measurements can be used to trace bedrock depth-provenance, and hence, landslide-sourced sediment.

Thursday, 8 June 2023 at 16:00 CEST

Gregory Ruetenik (Czech Academy of Sciences)

Popular power laws: New revelations from classic methods for understanding landscapes

Abstract: Here I will present 2 studies at different scales, making use of common tools in geomorphology in new ways.  First, I will discuss the influence of landslide-derived sediment on rivers throughout Taiwan in response to typhoon Morakot in 2009, one of the most intense typhoons on record. Using rating curves for the entire island over the past decade, the exhumation of landslide-derived sediment and its persistence within the river network can be estimated. Second, I will present a global analysis of 10Be-derived erosion rates as they are modelled directly using a landscape evolution model, making use of stream-power based erosion plus diffusion.  This direct modelling approach can help resolve parameters at a global scale while taking into account inherent uncertainty of such global studies.

Thursday, 15 June 2023 at 16:00 CEST

Daniel Peifer (University of Tuebingen)

Mobile wind-gaps as a dominant mechanism for drainage reversal

Abstract: River systems are dynamic features that adjust their planform geometry in response to variations in tectonics, climate and exposed lithologies. These drainage reorganisation events can have significant impacts on landscape evolution, sediment budgets, provenance, and associated biodiversity. Despite their importance, many aspects of drainage reorganisation remain poorly understood, including the processes that cause drainage reversal, by which flow is reversed in the trunk stream but not on (barbed) tributaries. Inspired by field observations, I here propose that drainage reversals tend to occur naturally in the aftermath of a lateral river capture event. Our hypothesis is that the abrupt local abandonment of the antecedent river pathway creates a 'wind-gap', i.e. a former river valley section turned into an in-valley drainage divide. This wind- gap  then  moves  further  downstream  in  the  direction  of  the  antecedent  river, causing its progressive reversal. To test this hypothesis, I conduct 2-D landscape evolution model simulations in which I force lateral capture of steady- state rivers by adjacent river systems experiencing more aggressive headward erosion. My simulations reproduce the expected formation of wind-gaps near the capture point. Landscape response to instantaneous river capture drives rapid erosion rates in the 'captured' system and reduced erosion rates in the 'beheaded' system that are considerably lower than the background uplift rate. Consequently, the wind-gap migrates towards the beheaded valley. I observe mobile wind-gaps leading-the-edge of river flow reversal in the formerly upper reaches of the beheaded river. The moving wind-gap progressively captures side tributaries to the beheaded river (i.e. creating further barbed tributaries), and captured catchment size affects wind-gap velocity. Our proposed mechanism is consistent with the post-capture morphology of many well- documented examples of drainage reversals and wind-gap locations. This study highlights the meaning of wind-gaps in the evolution of river systems and provides new insights into the mechanisms of drainage organisation, all central for interpreting a range of earth and biological data. 

Thursday, 22 June 2023 at 16:00 CEST

Vivi K. Pedersen (Aarhus University)

The influence of surface processes on the solid Earth, ice sheets, and sea level

Abstract: In this talk I will focus on the influence of surface processes on solid-Earth deformation, ice-sheet behavior, and sea-level changes over Quaternary timescales where erosion and deposition by glaciers and ice sheets have modified Earth’s surface significantly through numerous glacial cycles. These changes in the topography and the volumes of sediments deposited offshore, have caused signifcant isostatic adjustments and local sea-level changes, owning to erosional unloading and depositional loading of the lithosphere. In addition, changes in topography and bathymetry have the potential to influence the flow and the extent of ice sheets, and thus the sea-level equivalent ice volume that can be stored in a given landscape. Unfortunately, few studies have investigated the importance of these geomorphic processes for glacial settings on glacial-interglacial timescales, despite large erosion rates and the inherent importance of sea-level changes for ice-sheet dynamics and stability. 

Here I focus on the North Atlantic margins and explore the importance of these geomorphic processes in the context of the Greenland ice sheet and the former Scandinavian ice sheet. These two margins of the North Atlantic complement each other well as they both hold unique observations. Particularly, I will present some quantitative estimates of erosion-driven uplift in North and North-East Greenland, and assess what this might tell us about early glaciations in these regions. In addition, I will look to Scandinavia to explore the importance of glacial erosion and deposition for solid-Earth deformation and sea level over just a few glacial cycles. Finally, I will show some preliminary results using a dynamic ice-sheet model to explore the influence of landscape evolution for the behavior of the former Scandinavian ice sheet.

Thursday, 25 May 2023 at 16:00 CEST

Jorge Lorenzo-trueba (Montclair State University)

Modelling barrier islands and fluvio-deltaic environments across time scales: Insights from a moving-boundary approach

Abstract: In this presentation, I will introduce a moving-boundary framework for evolving coastal landscapes focusing on low-lying environments such as barrier islands and fluvial deltas. Borrowing and adapting ideas from heat transfer numerical techniques, I will first introduce an enthalpy framework for modeling the evolution of fluvial deltas under glacial cycles that accounts for the changes in relief and concavity of the fluvial surface. Model and laboratory results suggest that such changes in the fluvio-deltaic profile geometry can lead to a delayed response to sea-level variations, often resulting in net upstream erosion during sea-level rise and potentially complicating the reconstruction of paleo sea-level from fluvio-deltaic deposits. Second, I will discuss how episodic barrier retreat, accompanied by partial overstepping and barrier sediment deposition, can occur even for constant sea-level rise and shelf slope. These results contrast the more common interpretation that such barrier deposits reflect episodes of rapid sea-level rise or changes in topography. Third, I will show how a similar moving boundary approach can also be used to quantify the relative effect of anthropogenic changes and natural processes on the evolution of barrier-marsh-lagoon systems over decadal to centennial time scales. These examples indicate that moving boundary treatments can be powerful tools for studying landscape evolution over a range of temporal and spatial scales.

Thursday, 23 March 2023 at 16:00 CET

Wolfgang Schwanghart (University of Potsdam)

Trouble with transience - the (shared) stream power model in rejuvenating landscapes

The stream power model is commonly used in landscape evolution models and fundamental for us to infer tectonics from topography. In this talk, I'll demonstrate that the two main applications of the stream power incision model - modelling longitudinal river profiles and response times to perturbations - are difficult to reconcile. Parameters derived from longitudinal river profiles do not explain the pace of upstream propagation of knickpoints, and vice versa. The recently introduced shared stream power model consolidates these issues, but has a major consequence: We vastly underestimate the role of sediment transport in shaping river longitudinal profiles.

Thursday, 4 May 2023 at 16:00 CEST

Jeffrey Kwang (University of Minnesota Twin Cities)

The Future of Soils in the Midwestern United States

Abstract: Soil erosion associated with agriculture reduces crop productivity, and the redistribution of soil organic carbon (SOC) by erosion has potential to influence the global carbon cycle. Agricultural practices, such as tillage, strongly influence the erosion and redistribution of soil and SOC. However, tillage is rarely considered in predictions of soil erosion in the U.S.; hence, regionwide estimates of both the current magnitude and future trends of soil redistribution by tillage are unknown. In this presentation, we show the development of a landscape evolution model that simulates tillage erosion to predict soil loss and SOC patterns within agricultural fields. This model requires the specification of only two physical parameters: a plow mixing depth, Lp, and a hillslope diffusion coefficient, D. Using LiDAR derived digital elevation models and nationwide estimates of SOC (Soil Survey Geographic Database), we forecast soil and SOC redistribution in the Midwestern U.S. over centennial timescales. Our model predicts that (1) present-day rates of soil and SOC erosion are initially high but will rapidly decelerate due to the diffusive topographic evolution and (2) surficial SOC decreases across the landscape due to the progressive depletion of SOC in eroding soil profiles and SOC profile inversion in aggrading soil profiles. The reduction in rates of SOC erosion with time suggests that agriculture’s influence on the global carbon cycle will diminish in the future. With our model, we also simulate scenarios that include the widespread adoption of low-intensity tillage (i.e., no-till farming) and find that its adoption will significantly decrease soil/SOC redistribution and surficial SOC reduction. Our findings indicate the further adoption of low-intensity tillage has the potential to greatly reduce soil degradation and benefit soil sustainability.

Thursday, 30 March 2023 at 16:00 CEST

Erin Seagren (Simon Fraser University)

Fluvial erosion, drainage reorganization, and the evolution of the Puna Plateau

Understanding the full response of drainage systems to changes in tectonics and climate is key for using rivers to ‘read’ the history of landscapes. Though classically studied in profile, the planform patterns of rivers also record boundary condition changes and reorganization of these patterns may influence landscape form. However, it is less clear how controls of planform drainage patterns translate to landscape evolution and the space and timescales that planform patterns integrate. Given large climate and base level gradients across their margins, orogenic plateaus are especially susceptible to topographic changes following drainage reorganization and are an ideal natural laboratory to investigate how planform river patterns record tectonics and climate.

Using terrestrial cosmogenic nuclides (TCN), geomorphic, structural, and existing thermochronologic evidence, I examine the patterns and controls of fluvial erosion rates – the ultimate driver of drainage reorganization – and planform drainage patterns at the Puna Plateau margin in NW Argentina. While TCN-based fluvial erosion rates are linked to the spatial variability of vegetation within a catchment, broader scale drainage patterns and reorganization appear unrelated to climate. Instead, I find drainage patterns across the plateau margin and foreland are linked to tectonically-set base level differences and the structural setting of the region. This broad tectonic control results in the general stability of the plateau margin and long-lived structure-parallel drainages in the foreland. Planform drainage patterns can be used to discriminate tectonic and climatic controls of landscape evolution, though the appropriate time and spatial scales need careful consideration.

Thursday 9th February 2023 at 16:00 CET 

Taylor Schildgen (GFZ, Potsdam)

Alluvial channels: Complex conveyors of sedimentary signals from erosional sources to depositional sinks

Periodic climate change commonly leaves traces in our landscapes, such as in alluvial fan lobes, river-terrace sequences, and in geochemical and sedimentary cycles within stratigraphic sequences. Using such records to reconstruct past climate forcing commonly assumes a direct and simple link between climate forcing and the creation of these archives. However, sediment moving through alluvial channels can be temporarily stored or released as channels aggrade with sediment or cut back into their banks and bed. Because channels aggrade or incise as a function of the ratio of sediment discharge to water discharge, the same climate forcing that we aim to reconstruct from landscape archives can induce adjustments to alluvial-channel profiles that directly impact downstream propagating sedimentary signals. I will present a summary of field data collected from the Central Andes over the past decade that shows how different field sites record different periodicities in climate forcing, despite experiencing a very similar paleoclimate history. Next, I will discuss how a recently developed alluvial-channel model can explain these predictions in a general sense. Ongoing work is focused on using this model framework to predict (1) how the amplitude and lag times of sedimentary signals recorded in fan lobes, terraces, or stratigraphic sequences are affected over a wide range of parameter space, (2) how channel-network geometry may further complicate these predictions, and (3) where we might look to better test model predictions.

Thursday, 16 February 2023 at 16:00 CET 

Harrison Gray (United States Geological Survey)

What fault scarps can tell us about the nature of sediment transport

Fault scarps are 1-3-meter-tall features produced from vertical tectonic motions over very short, seconds-long, timescales followed by longer timescale, up to thousands of years) sediment transport which smooths the scarp over time. These rapidly created features offer a rare opportunity to test our models of land surface evolution because they represent a sudden perturbation in which different process models produce distinct outcomes. Here, I overview our recent work on exploring models incorporating nonlocal sediment transport and a new sediment tracing method built from the physics behind luminescence dating. Results from cellular automata modeling suggest that incorporating nonlocal sediment transport can better capture the scarp topographic profile over time and show a direct connection between sedimentological facies and geomorphic process rates. Comparing the model results against the sediment tracing data reveals complex sediment transport processes beyond the model predictions, including periods of simultaneous debris and wash facies forming processes, erosion, and reworking. Ongoing and future efforts explore convolution forms of nonlocal sediment transport compared with a global compilation of scarp profiles with implications for diffusion-based models of colluvial sediment transport. 

Thursday, 23 February 2023 at 16:00 CET 

Ellen Wohl (Colorado State University, Florida)

Rivers of Carbon: Using River Corridor Science to Understand Carbon Dynamics

A river corridor includes the active channel(s), floodplain, and underlying hyporheic zone. Conceptualizing rivers as corridors, rather than just channels, emphasizes interactions throughout valley bottoms, as well as integrated geomorphic, hydrologic, biotic, and biogeochemical processes. This talk focuses on the dynamics of organic carbon in river corridors, with an emphasis on how specific combinations of process and form maximize organic carbon storage within spatially discrete reaches of river corridor known as beads. The talk ends by exploring the management implications of carbon dynamics in river corridors and specifically the importance of targeting river corridors as potential carbon sequestration sites.

Thursday, 2 March 2023 at 16:00 CET 

Maya Stokes (Florida State University)

Geologic mechanisms of freshwater fish speciation in the southeast United States

The high biodiversity of mountain ranges across Earth suggests a link between geologic processes and biological evolution. Topographic uplift has been linked to the diversification of both terrestrial and freshwater species in many tectonically active landscapes. However, tectonically inactive mountain ranges also host exceptional levels of freshwater biodiversity. In this talk, I discuss how the erosional exhumation of ancient geologic structures has influenced landscape dynamics and driven the diversification of freshwater fish in the Appalachian Mountains. As rivers erode through layers of different kinds of rock, the spatial distribution of rocks at the surface of the landscape changes. Thus, for fish with habitat specificity linked to rock type, erosion can progressively expose either favorable or unfavorable rock types, creating either barriers or corridors. I utilize geologic and phylogenetic datasets to test these scenarios in darter species endemic to the southeast United States. The results demonstrate how erosion can drive the diversification of freshwater organisms in ancient mountain ranges long after tectonic activity ceases.

Investigation of stochastic-threshold incision models across a climatic and morphological gradient

Thursday, 9 March 2023 at 16:00 CET

Rebecca Hodge (Durham, University)

New approaches to understanding sediment transport and flow in rivers

Predicting rates of sediment transport and flow in rivers are long established problems in geomorphology. However, the complexities of the interactions between channel morphology, flow and sediment transport mean that our predictions still contain a considerable degree of uncertainty. In this talk I will outline how we have used novel approaches to measure and model fluvial systems in order to get new insights into flow and sediment transport processes. These approaches include using 3D printing to take rivers into the laboratory, using CT scanning to quantify the 3D structure of gravel beds, and using audio recordings to measure flow depths. I will also consider how these approaches could be developed in the future.