Landscapes Live

Thursday, 30 November 2023 at 16:00 CEST

Kathryn Fitzsimmons (University of Tübingen)

To register: https://durhamuniversity.zoom.us/meeting/register/tJIvdOmhpj8jGtUBedPqWp0l0flQp3vPU98F 

What can dryland sediments tell us about landscapes through time?

Abstract: Almost half of the Earth’s land surface comprises deserts and desert margins. These so-called drylands include substantial swathes of unconsolidated sediment which preserve information about past conditions and interactions between the atmosphere and Earth surface. Under conditions of accelerated global change, desert margins in particular are hypothesized to become increasingly unstable. Since drylands also host some 40% of the world’s human population, this increasing instability will become a central concern for the future. In this lecture I would like to discuss the wealth of information contained within dryland sediments with respect to what they can tell us about landscape and hydroclimate change through time, with a focus on the Australian continent. We will take a look at the evidence for past environments across a range of scales, from interrogating intracrystalline charge within quartz grains for information about provenance and timing of deposition, to examining the morphology of lake margin shorelines and dunefields which provide the key to interactions between landforms, hydroclimate and synoptic-scale climate circulation.

Thursday, 7 December 2023 at 16:00 CEST

Joel Scheingross (University of Nevada), Marisa Repasch (University of Colorado), and Neils Hovius (GFZ)

To register:

Lithospheric flexure controls on geomorphology, hydrology, and river chemistry in the Andean foreland basin

Abstract: Tectonics exerts a strong control over the morphology of Earth’s surface that is apparent in active mountain belts. In lowland areas, subtle processes like lithospheric flexure and isostatic rebound can impact Earth surface dynamics, hydrologic connectivity, and topography, suggesting that geomorphic and hydrologic analyses can shed light on underlying lithospheric properties. Here we examine the effect of lithospheric flexure on the geomorphology, hydrology, and river water chemistry of the Rio Bermejo fluvial system in the east Andean foreland basin of northern Argentina. Results show that proximal to the mountain front, foredeep basin subsidence causes sedimentation along a braided channel belt that is superelevated relative to the surrounding flood basin. During floods, water flows from the superelevated channel into the groundwater reservoir, causing a net loss of discharge with distance downstream. Further downstream, forebulge uplift forces channel narrowing, high lateral migration rates, and incision up to 13 m into older river deposits. This incision locally allows groundwater flow into the river, causing a ~20% increase in river solute load. Groundwater emerges from the forebulge into the backbulge, predominantly as spring-fed channels. Here, channel migration rates decrease, suggesting a switch from net uplift to subsidence that reduces the depth to the groundwater table. This analysis shows that subtle lithospheric flexure can have significant effects on river channel morphology that determine hydrologic flow paths, and ultimately influence geochemical and ecological patterns. We suggest that these effects may elucidate lithospheric properties that are otherwise inferred from bulk geophysical observations. 

Thursday, 02 November 2023 at 16:00 CEST

Daniel Garcia-Castellanos (CSIC, Geosciences Barcelona)

Lakes and saddles pacing the life of landscapes. From the Messinian Mediterranean to the outburst flood scale.

Abstract: Lake basins are local topographic minima separated from the surrounding landscape by topographic sills or saddles. Lakes are geologically-ephemeral features that tend to fill with sediment and water and to reintegrate in the fluvial network unless some mechanism sustains the local topographic basin (e.g., tectonic deformation). I will review evidence and modeling results for different geological scenarios (Miocene Iberian basins; Messinian Salinity Crisis) that highlight the importance of lakes in regulating the large-scale evolution of drainage and landscape. In one side, lakes accelerate geomorphological changes by facilitating the capture/piracy of drainage basins but, on the other hand, they can delay them when cancelling lake outlets, trapping water and sediment (endorheic basins). The opening of such landlocked basins is often geologically fast, but I will show that, in some cases, these lake overtoppings or captures can occur in the form of cataclysmic outburst floods that leave a recognizable sedimentological and geomorphological record. Examples include the Agassiz, Bonneville, and Zanclean floods. Future LEMs need to incorporate the frequency and mechanics of such lake outburst events to improve our understanding of what governs the long-term rates of sediment transport.

Thursday, 09 November 2023 at 16:00 CEST

Andrew Wickert (University of Minnesota)

Intermediate Timescales in Fluvial Geomorphology

Abstract: 

To understand rivers, we can resolve turbulence and sediment transport over single floods or abstract these detailed physics into heuristic rules that function over millions of years. But between the time of an eddy's swirl and a mountain's rise lie years to millennia of landscape change. Critically, these intermediate time scales encompass the decades to centuries needed to make effective predictions and plans for ongoing climate- and land-use impacts on rivers. They also bracket late-Quaternary-to-modern river evolution, whose record enables robust tests of our models and understanding of river dynamics. Here we will explore how environmental change sends waves of aggradation and incision through river networks, how river-channel width adjusts to changing streamflow, and how the glacially altered and agriculturally impacted landscapes of central North America may be our key to the fluvial geomorphic cypher.

Thursday, 05 October 2023 at 16:00 CEST

Bethan Davies (Newcastle University)

Accelerating glacier volume loss on Juneau Icefield driven by non-linear processes

Abstract: Large icefields and ice caps in high latitude regions are currently contributing significantly to global sea level rise, with Alaska leading contributions from glaciers. This contribution is likely to accelerate since icefield topography drives a non-linear response to climate change. Here we show that icefield area and volume loss from Juneau Icefield has accelerated exponentially over the last few decades, with catastrophic losses reaching -5.91 ± 0.80 km3 a-1 from 2010-2020.  Thinning is now pervasive across the icefield plateau, resulting in glacier fragmentation, especially rapidly after 2005. This glaciological threshold response to a warming climate is underlain by the plateau hypsometry. The non-linear behavior is concerning for the future viability of this icefield and for plateau icefields and ice caps globally, with implications for future projections of sea-level contributions.

Thursday, 16 November 2023 at 16:00 CEST

Ryan Venturelli (Colorado School of Mines)

Retreat, Recovery, and Subglacial Radiocarbon: Untangling past [in]stability of the West Antarctic Ice Sheet

Abstract:  Reconstructions of past ice sheet behavior enable us to refine physical models that predict how much, how fast, and from where Antarctic ice mass loss will contribute to future sea level rise. Geological constraints on paleo ice thickness obtained from above the modern ice surface (e.g., exposure age data from deglaciated nunataks) and on paleo ice extent obtained outboard from modern margins (e.g., sediment core and geomorphic data from the ice-free continental shelf) have served as the primary tools to decipher the topology of the Antarctic Ice Sheet from the Last Glacial Maximum to present. Recent efforts to recover sediment and bedrock from beneath grounded ice in Antarctica offer insight into the southernmost extent of grounding line retreat, yielding a more complete view of ice dynamics through the last deglaciation. In this talk, I will present results from recent subglacial access efforts that have provided the first direct constraints on a less extensive West Antarctic Ice Sheet in the Holocene compared to today. These new constraints on the timing and extent of grounding line retreat prior to the modern observational record allow for a mechanistic understanding of the drivers of marine ice-sheet evolution, subglacial ecosystem processes, and subglacial Antarctica’s role in global biogeochemical cycling. I will conclude by presenting new geochemical and sampling tools under development to enable future work constraining ice-sheet history. By generating this process-to-paleo perspective on the co-evolution of cryospheric, geologic, biologic, and oceanographic systems and combining it with detailed ice-sheet modeling experiments, we can create the context required to reduce uncertainty in sea-level projections on societally relevant timescales.

Thursday, 23 November 2023 at 16:00 CEST

Josh Ahmed (University of Hull)

The Dynamic Life and Times of Oxbow Lakes

Abstract: Oxbow lakes are some of the most recognisable features on Earth, preserving historic river channel for nutrient, contaminant, and sediment sequestration and forming important diversity hotspots within the riparian corridor. Despite the significant value they provide through ecosystem services, little is known about how the lakes physically and chemically obtain these specialist conditions and how they evolve through time, particularly since previous work has focused on surface water conditions at low temporal resolutions. In this presentation, I will discuss recent advances in our understanding of the evolution of oxbow lakes based on some of the world’s most dynamic rivers in the Bolivian Amazon Basin. Remotely-sensed observations of oxbow lakes reveal that their temporal evolution is dynamic and highly variable in space and time, meaning single point observations may only provide limited insight to their long-term evolution. Moreover, this dynamism is strongly linked to lake physiochemistry, which is inextricably linked to the provision of ecosystem services. Inevitable changes in hydrology – driven by climate and land-use changes – could disrupt these dynamics, threatening the riverside communities and wildlife that rely on the lakes for survival.