EGU-GM Online Seminars in Geomorphology
19 May 2022 - Oliver Korup (University of Potsdam) "Mountainfall – Learning more about large landslides"
Abstract: Landslide research has become a rapidly growing field of modern geomorphology, and highlighted many feedbacks that extend beyond processes on hillslopes. Most models concerning the relevance of landslides in landscapes draw on increasingly detailed and systematic catalogues of frequent slope failures in active mountain belts. In contrast, the bulk of research concerned with landslide prediction relies on small training data sets and study areas to identify hillslope portions that are most prone to failure.
Either way, infrequent and large landslides that move millions of cubic metres have mostly eluded such systematic analyses except for volcanic and submarine settings. Yet the study of large terrestrial landslides offers fresh insights and challenges for models of slope stability, landscape evolution, hazard appraisals, and ecological disturbance. Most legacy of individual large landslides tends to reside much longer in landscapes than that of smaller landslides, and can involve lowered mountain peaks and drainage divides; redistributed crustal loads; unroofed magma chambers; blocked or diverted rivers; infilled valleys and inner gorges; glacier surges; outburst, tsunami, and turbidite deposits; and changes to habitats and biodiversity.
While these impacts may be preserved variably over several tens to millions of years, attempts at hind- or forecasting large landslides have been few, if not outnumbered by speculations about their recurrence. Seismology has opened new doors for detecting and monitoring large slope failures systematically, and augments the wealth of local case studies that have produced a heterogeneous array of data. In this presentation I review an updated global inventory of Earth’s largest terrestrial landslides, and show how incorporating topographic and age constraints can meaningfully improve probabilistic models of their size distribution and geometric scaling. These models pave the way for estimating the return periods of giant slope failures, associated erosion rates, hazard and risk levels, and appraising any potential response to climate change.
02 June 2022 - Eric Deal (ETH Zurich) "Title TBA"
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09 June 2022 - Helen Dow (maiden name: Beeson) (ETH Zurich) "Identifying causal links between tectonic processes and biodiversity in an orogenic wedge setting with a coupled landscape-biodiversity evolution model"
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Abstract: Landscapes and their associated ecosystems coevolve over geologic time. Correlative approaches have elucidated the importance of topographic diversity and tectonic history but have not identified specific causal links between tectono-geomorphic processes and biodiversity metrics. To address this issue, we coupled the numerical landscape evolution model DAC (Divide and Capture) with a mechanistic model for biodiversity that simulates evolution, dispersal, allopatric speciation, and extinction to develop hypothetical biological signatures of different functional groups to a variety of landscape histories. In our coupled model, DAC-Bio, suitable habitat for aquatic species is defined as the channel network with limitations on discharge and dispersal confined to the network. Suitable habitat for terrestrial species is defined using a combination of elevation, slope, aspect, and discharge which are measured at sub-grid scale from the simulated landscape and meant to represent more complex physical parameters such as temperature, precipitation, soil properties, and hydrologic environment. In addition to habitability requirements, species are assigned evolution characteristics (rate of adaptation and draw toward the surrounding population mean), dispersal characteristics (rate and ability to cross geographic barriers), and speciation rate (isolation time needed to form new species). We test how horizontal advection characteristic of mountain ranges formed as orogenic wedges influences the spatial and temporal patterns of species richness and species’ range sizes for both aquatic and terrestrial organisms. We find that horizontal advection promotes ongoing reorganization of the drainage network with stream capture occurring from small basins to large basins on the pro-wedge side of the orogenic wedge and from pro-wedge to retro-wedge basins. Advection promotes movement of terrestrial species up the pro-wedge side of the mountain range toward the main divide, and river captures promote geographic transfer of both terrestrial and aquatic species from the pro-wedge side of the mountain range to the retro-wedge side. These processes leave distinct biological signatures in diversification rates and species richness.
16 June 2022 - Anne Guyez (University of Toulouse) "How it glows tells how it flows: insights on sediment transfer in braided river from feldspar single-grain luminescence pIRIR analysis in (Rakaia and Waimakariri braided rivers, Aotearoa, New Zealand) and numerical simulations"
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Postponed - Stéphane Bonnet (University of Toulouse) "Imprint of landscape dynamics on the luminescence of fluvial sediments (Rangitikei River, New Zealand)"
Abstract: The luminescence of quartz and feldspars is commonly used for burial dating Quaternary sediments (e.g. OSL and IRSL methods) however several studies have shown in recent years that luminescence can also be used for tracing Earth’s surface processes. In this seminar I will illustrate how surface processes impact the distribution of luminescence signals of fluvial sediments. I will take as an example the case of the Rangitikei River where we have acquired over the last few years a large database of luminescence measurements carried out at the single-grain scale in fluvial terraces and modern sediments. I will show in particular that the distribution of the signals reflects the combined effect of two main processes whose relative influence changes over time and space in relation to landscape dynamics: on one hand the input of bedrock grains to the river and on the other hand the longitudinal bleaching (zeroing) of the signal during transport. I will also discuss the consequences in terms of uncertainty on the luminescence dating of terraces.
Postponed - - Kate Leary (New Mexico Tech)
Abstract: Intraplate settings far from tectonic plate boundaries are rife with geomorphic features indicative of topographic transience. Paleovalleys, wind gaps, complex turns and shapes of river networks, river captures, asymmetric drainage divides, knickpoints, the list goes on. Yet, the triggers are hard to pinpoint. The usual mechanisms invoked as triggers of these features are intraplate tectonism (i.e. neotectonics), dynamic topography, or climatic oscillations.
These landscapes typically contain neighboring hydrographic basins that flow to the same baselevel and over similar or even the same rocks but have different mean elevations and asymmetric drainage divides. Explaining such areas as a function of changes in external boundary conditions (i.e. reactivated structures or climate) over such small spatial scales would require a perfect spatiotemporal combination of events, which is conceptually/theoretically unsatisfying.
In this presentation, I will demonstrate how the exhumation of just one lithology of different resistance to erosion may provide a one-size-fits-all mechanism to explain many of the seemingly unrelated transient geomorphic features observed in intraplate settings, even in areas far from lithologic contacts. This mechanism requires no change in external forcing, is likely to repeat itself over geologic time, and likely cause systematic and dynamic changes in river network shapes, topography, and erosion rates. The importance of this mechanism goes beyond the understanding of landscape evolution. Changing network shapes back and forth is a recipe for shuffling the inhabiting biota over geologic time and, therefore, a potential pump of biodiversity.