GM2.6 | Dates, Rates and Bytes: Quantifying Geomorphological Processes and Landscape Dynamics using advances in geochronology
EDI

Numerical frameworks are essential for understanding and interpreting landscape evolution. Over recent decades, geochronological techniques such as cosmogenic nuclides, thermochronology, radiocarbon and luminescence dating have improved in accuracy, precision, and temporal range. Developments in geochronological methods, data treatment and landscape evolution models have provided new insights into the timing, duration and intensity of landscape evolution processes. The combination of temporal constraints with numerical modelling has enormous potential for improving our understanding of landscape evolution. The focus of this session is to bring together geochronology, data science and models of Quaternary landscape change.

This session includes studies of erosional rates and processes, sediment provenance, burial and transport times, bedrock exposure or cooling histories, landscape dynamics, and the examination of potential biases and discordances in geochronological data and model-data comparisons. We welcome contributions that apply novel geochronological methods and that intersect different geochronological techniques and numerical modelling with landscape evolution analysis, with particular focus on cosmogenic nuclides. This includes the determination of rates and timing of landscape change as well as stochastic events, or that highlight the latest developments and open questions in the application of geochronometers to landscape evolution problems.

Co-organized by CL5
Convener: Georgina King | Co-conveners: Zsófia Ruszkiczay-Rüdiger, Romano Clementucci, Sebastien Lenard, Gerald Raab, Ann Rowan, Apolline Mariotti
Orals
| Mon, 24 Apr, 16:15–18:00 (CEST)
 
Room G1
Posters on site
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
Hall X3
Posters virtual
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
vHall SSP/GM
Orals |
Mon, 16:15
Mon, 14:00
Mon, 14:00

Orals: Mon, 24 Apr | Room G1

16:15–16:20
16:20–16:30
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EGU23-9975
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GM2.6
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solicited
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Highlight
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On-site presentation
Darryl Granger

Cosmogenic nuclides have become a well-established tool in geomorphology for quantifying surface process rates and for dating landforms and sedimentary deposits such as terraces, alluvial fans, lakes, and cave infills.  In many cases, these sedimentary deposits can tell us not only about landscape evolution, but if they contain artifacts or fossils, they can also inform us about human evolution, migration, and the development of stone tool technology.   

Burial dating with 26Al and 10Be is becoming increasingly important in archaeology and paleoanthropology, particularly in areas that lack volcanic rocks suitable for dating. The development of isochron methods has improved both the precision and reliability of dating results, lending confidence to the age interpretations.  However, because cosmogenic nuclides reflect the exposure and burial history of rocks near the ground surface, it is important to recognize that properly interpreting the depositional age requires understanding the surface processes responsible for sediment erosion and deposition. 

Cosmogenic nuclides have now been applied to archaeology and human evolution at a variety of sites across Africa, Asia, and Europe.  In most cases, the new dates conform to pre-existing models and provide a fuller picture of human occupation of the landscape.  However, a few sites have challenged current paradigms.  I will present recent studies from caves and terraces in South Africa and China that have produced surprising results, pushing the boundaries of where early humans were found. 

How to cite: Granger, D.: Cosmogenic nuclide dating applied to human evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9975, https://doi.org/10.5194/egusphere-egu23-9975, 2023.

16:30–16:40
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EGU23-11609
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GM2.6
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On-site presentation
Natural versus anthropogenic erosion in Central Brazil, a confrontation of time and space scales
(withdrawn)
Lionel Louis Siame, Lucas Espíndola Rosa, Luis Felipe Cherem Soares, José Guilherme de Oliveira, Olivier Evrard, Houda Barhoumi, Laëtitia Leanni, Adrien Duvivier, Pierre-Henry Blard, Didier Bourlès, and Sophie Cornu
16:40–16:50
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EGU23-7262
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GM2.6
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On-site presentation
Tibor J. Dunai and Steven A. Binnie

The Early to Mid-Pleistocene Transition (MPT) between ~ 1.2 Ma to ~500 ka (also termed as ‘900 ka event’) marks a change in climatic periodicity, from 41 ka cycles to 100 ka cycles of increased intensity. In non-glaciated areas of Europe this climatic shift has been associated with pronounced acceleration of river incision, in part driven by increased sediment loads from periglacial hillslope processes. Until the Pleistocene, low-relief landscapes are thought to have dominated throughout Europe. Utilizing novel in-situ cosmogenic Krypton in zircon methodology (Dunai et al. 2022), we find direct evidence that this was indeed the case, and that these landscapes were profoundly transformed during the MPT.

Our study area (Vogtland, Saxony, Germany) was never glaciated but was within 50 km of the ice margins during the largest Quaternary glaciations. For our study, we utilize a unique source of megacryst zircons (Ebersbrunn diatreme), whose exhumation, dispersal and burial history is recorded by cosmogenic Krypton. The megacryst zircons are found in the fluvial sediments of the current catchments downstream of the source (Raumbach, Göltzsch, Weiße Elster), however, also in a distal catchment (Weida), now disconnected from the source due to late Pleistocene superimposed drainage (Weiße Elster valley).

The cosmogenic Krypton data from the megacryst zircons is commensurate with a long (1 to 3 Myr) exposure at or near the surface, or exhumation at a very low rate (<0.1 mMyr-1), followed by a period of burial of 600 to 900 kyr and a recent re-emergence in the active fluvial system. Samples collected further from the source (≥15 vs. 5 km) have longer burial histories. The extremely low erosion rates inferred prior to burial (<0.1 mMyr-1) are unprecedented for temperate regions in Europe, and late Quaternary erosion rates of landscapes with similarly moderate relief are two orders of magnitude faster. In situ cosmogenic 10Be and 26Al results on vein-quartz from the region address the latter findings.

Based on our data and external constraints on climate and landscape evolution in Europe, the most likely scenario is that of a formerly stable, low-relief Plio-Pleistocene landscape whose transformation in response to periglacial processes commenced during marine isotope stage (MIS) 22 and was largely concluded by MIS 16. Incision of drainage that developed during and after the MPT formed the current moderate relief landscape.

Dunai et al. (2022) Geochronology, https://doi.org/10.5194/gchron-4-65-2022

How to cite: Dunai, T. J. and Binnie, S. A.: Transformation of a low-relief periglacial landscape during the Mid Pleistocene Transition revealed by cosmogenic Krypton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7262, https://doi.org/10.5194/egusphere-egu23-7262, 2023.

16:50–17:00
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EGU23-6902
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GM2.6
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ECS
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On-site presentation
Sabrina Niemeyer, Hella Wittmann, and Tibor J. Dunai

The Vogelsberg area in Hessen, Germany, comprises the largest contiguous volcanic complex in Central Europe, covering an area of about 2300 km². After volcanic activity ceased during the mid-Miocene, the complex was subject to extensive erosion and weathering. Fluvial erosion has shaped the area, which is now characterised by Pleistocene valleys and a radial river system exposing primitive alkali basalts and basanites. However, the inference of catchment-wide weathering and erosion rates from the most commonly used cosmogenic nuclide – mineral pair (e.g. 10Be from quartz) remains challenging in such an environment due to the mafic nature and nominally quartz-free composition of the local bedrock. Due to these method-related obstacles only few cosmogenic studies have focused on basaltic regions until now, even though basalt weathering is globally an important CO2 sink.

The development and establishment of the novel method using terrestrial cosmogenic krypton (Kr) in the weathering-resistant mineral zircon (Dunai et al. 2022) allows quantification of denudation on quartz-poor lithologies over hundreds of kyr timescales. We exploit the method’s advantage and sampled zircons from sediments of streams radially draining the Vogelsberg and measured Kr isotope abundances to assess the time-integrated erosion patterns shaping the volcanic complex. Integrating over millennial timescales, the 10Be(meteoric)/9Be system will be applied to the same catchments. The 10Be/9Be system can be measured on sediment of any type of lithology including mafic rock (Dannhaus et al. 2018), and thus presents an inter-method validation of the Kr method. We will present the krypton results and discuss basalt weathering in a currently temperate climate through the lens of the different methodological approaches applied.

 

Dunai et al. (2022) Geochronology, https://doi.org/10.5194/gchron-4-65-2022

Dannhaus et al. (2018) GCA, https://doi.org/10.1016/j.gca.2017.11.005

How to cite: Niemeyer, S., Wittmann, H., and Dunai, T. J.: Deriving basin-wide denudation rates of basaltic rocks using cosmogenic Kr isotopes, vulcanic complex Vogelsberg, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6902, https://doi.org/10.5194/egusphere-egu23-6902, 2023.

17:00–17:10
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EGU23-5206
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GM2.6
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ECS
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On-site presentation
Richard Ott, Nicolas Perez-Consuegra, Dirk Scherler, Andres Mora, Kimberley Huppert, Jean Braun, and Gregory Hoke

Erosion rates are commonly used to study tectonic uplift and sediment export from mountain ranges. However, the scarcity of erosion rate data often hinders detailed tectonic interpretations. Here, we present 25 new erosion rates from the Northern Andes of Colombia, determined from cosmogenic 10Be measurements, to study spatial and temporal patterns of uplift along the Central and Eastern Cordillera. These rates, along with published data and precipitation-corrected normalized channel steepness measurements, were used to create high-resolution erosion rate maps. The results show that the southern Central Cordillera has relatively uniform erosion rates, averaging around 0.3 mm/a, while the northern Central Cordillera exhibits rapidly eroding canyons dissecting slowly eroding low-relief surfaces. We interpret that long-term, steep slab subduction has led to an erosional steady-state in the southern Cordillera Central, while Late Miocene slab flattening caused an acceleration in uplift in the northern Cordillera Central which the landscape has not yet adjusted to. The Eastern Cordillera also displays pronounced erosional disequilibrium, with a slowly eroding central plateau rimmed by faster eroding western and eastern flanks. Our maps suggest recent topographic growth of the Eastern Cordillera, with deformation focused along the eastern flank, which is also supported by balanced cross-sections and thermochronologic data. Spatial gradients in predicted erosion rates along the eastern flank of the Eastern Cordillera suggest transient basin-ward migration of thrusts. By using our erosion maps to estimate sediment fluxes, we find that the Eastern Cordillera exports nearly four times more sediment than the Central Cordillera. Our analysis shows that accounting for spatial variations in erosion parameters and climate gradients reveals important variations in tectonic forcing that would otherwise be obscured in traditional river profile analyses. Moreover, given relationships between tectonic, and topographic evolution, we propose that the dynamic landscape evolution of the Northern Andes, as revealed by our erosion maps, is primarily linked to spatial and temporal variations in slab dip, with potentially additional influences from inherited Mesozoic rift structures.

How to cite: Ott, R., Perez-Consuegra, N., Scherler, D., Mora, A., Huppert, K., Braun, J., and Hoke, G.: Erosion rate maps of the Northern Andes highlight spatio-temporal patterns of uplift and quantify sediment export, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5206, https://doi.org/10.5194/egusphere-egu23-5206, 2023.

17:10–17:20
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EGU23-8714
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GM2.6
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ECS
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On-site presentation
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Maxime Bernard, Peter van der Beek, Cody Colleps, and Julien amalberti

Constraining the impact of Quaternary glaciations on landscape dynamics is required to better understand the interaction between tectonics, climate, and erosion. Over the years, low-temperature thermochronology such as apatite (U-Th)/He (AHe) has been used to quantify glacial erosion in different climatic and tectonic settings. However, in some contexts, AHe records lack temporal resolution because of limited exhumation due to glacial incision and/or low geothermal gradients. In addition, significant spatial variability in erosion can affect the quality of thermal-kinematic inversions when combining spatially distributed AHe data. This effect may be significant in glacial settings where a switch from a fluvial to a glacial landscape induced a significant change in the spatial distribution of erosion.

However, the 4He/3He thermochronology can extract lower-temperature and higher-resolution thermal histories from an AHe dataset. The method uses the spatial distribution of natural 4He in an apatite crystal, which reflects the rate of cooling through the AHe partial retention zone. It has been successfully applied to track glacial incision and relief-development histories that would have been untraceable with conventional AHe thermochronology. Consequently, thermochronology data can now provide more detailed and localized thermal history. While 4He/3He thermochronology has been successfully used in settings where background exhumation rates are moderate, the sensitivity of the technique remains untested in settings with notably low exhumation-rates, such as at passive margins.

Here, we couple a glacial landscape-evolution model (iSOSIA) with a new version of a thermo-kinematic model (PecubeGUI), incorporating radiation-damage effects on helium diffusion, to explore the ability of apatite (U-Th)/He and 4He/3He thermochronometers to record glacial incision. To do so, we model a range of synthetic glacial scenarios in different tectonic, climatic, and thermal settings.  Our landscape-evolution models include glacial, fluvial and hillslope erosion, as well as sediment transport. We assess model predictions of thermochronologic parameters, including age-elevation relationships and 4He/3He spectra, and their evolution when switching from a steady-state fluvial to a glacial topography. This modelling exercise aims to provide a guide for sampling strategies and interpretations for both conventional apatite (U-Th)/He and 4He/3He thermochronology when working in glacial settings, considering their particular tectonic and climatic context.

How to cite: Bernard, M., van der Beek, P., Colleps, C., and amalberti, J.: Spatial and temporal distribution of glacial erosion as recorded by apatite (U-Th)/He and 4He/3He thermochronology., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8714, https://doi.org/10.5194/egusphere-egu23-8714, 2023.

17:20–17:30
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EGU23-11600
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GM2.6
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ECS
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On-site presentation
Melanie Bartz, Georgina E. King, Frédéric Herman, Leif S. Anderson, Shigeru Sueoka, Sumiko Tsukamoto, and Takahiro Tagami

The interactions between Earth surface processes, climate and tectonics determine the landscape in mountain regions. The Japanese Alps uplifted throughout the Quaternary and now reach elevations of up to 3,000 m. However, quantifying relief changes in response to tectonic activity, magmatism and Late Quaternary glaciation is challenging due to the young age of the Japanese Alps and the difficulty of measuring surface processes at the timescale of glacial-interglacial cycles. Here, we use ultra-low temperature thermochronometers based on the luminescence of feldspar minerals and the electron spin resonance (ESR) of quartz minerals, in combination with inverse modelling to derive rock cooling rates and exhumation rates histories at 104-106 years timescales. We focus on the Tateyama region in the Hida range of the Japanese Alps, which was glaciated during the late Quaternary period. In total, 19 new samples were analyzed by luminescence and ESR thermochronometry. While most luminescence signals have already reached their upper dating limit, ESR signals (Al and Ti centres) yielded ESR ages of between 0.5-0.9 Ma. In general, thermal stability is lower for the Al centre compared to that of the Ti centre, but both centres constrain similar exhumation rates. Inversions reveal rock cooling rates on the order of 30-80 °C/Ma, which can be inverted to erosion rates of <1 mm/a within the past 1 Ma. In the next step, we will relate these rates to the climate and tectonic history of the Tateyama region.

How to cite: Bartz, M., King, G. E., Herman, F., Anderson, L. S., Sueoka, S., Tsukamoto, S., and Tagami, T.: High-relief exhumation history in the Japanese Alps within the past 1 Ma inferred from trapped charge thermochronometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11600, https://doi.org/10.5194/egusphere-egu23-11600, 2023.

17:30–17:40
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EGU23-6922
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GM2.6
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ECS
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On-site presentation
Anya Towers, Simon Mudd, Mikael Attal, Steven Binnie, Fiona Clubb, and Tibor Dunai

Inferring erosion rates from 10Be or 26Al concentrations in stream sediments has become standard practice in geomorphology. In formerly glaciated landscapes, however, this technique is problematic because repeated phases of shielding and exposure during the past glacial and interglacial periods can lead to 10Be or 26Al concentrations that are difficult to interpret. Cosmogenic in-situ 14C has a short half-life (~5,730 years) that means 14C atoms in stream sediments cannot be inherited from before the glacial period and inferred erosion rates will reflect post-glacial, Holocene erosion. Using cosmogenic in-situ 14C, we report the first millennial-scale erosion rates in the post-glacial landscapes of Glen Feshie, within the Cairngorm mountains of Scotland.

The River Feshie contains active gravel reaches that cut through glacial outwash terraces. We counterintuitively find the lowest inferred erosion rates (0.06 mm/yr) in the steepest side tributary and the highest inferred erosion rates at the low-relief outlet of Glen Feshie near the confluence with the River Spey (0.21 mm/yr). Based on field observations, we interpret that hillslopes have been largely inactive and contributed limited sediment fluxes. To provide further insight into the highest erosion rate documented furthest downstream, we consider the hypothesis that sediment from the hillslopes with higher concentrations of 14C has been diluted with lower concentration material from the terraces. Further, we hypothesise that if terraces that border the channel increase in height downstream, their incision could have remobilised an increasing amount of sediment with lower 14C concentrations downstream, leading to increased dilution and the observed concentrations. Results show terrace height above the channels does not increase downstream and averages approximately 2 meters. We therefore suggest terrace height does not account for higher erosion rates, and present a cosmogenic-nuclide mixing model to explore the degree to which the input of sediment that has been shielded from cosmic rays in terraces can explain the observed concentrations in stream sediments.   

How to cite: Towers, A., Mudd, S., Attal, M., Binnie, S., Clubb, F., and Dunai, T.: Post-glacial catchment denudation rates from 14C concentrations in Glen Feshie, Scotland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6922, https://doi.org/10.5194/egusphere-egu23-6922, 2023.

17:40–17:50
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EGU23-6006
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GM2.6
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On-site presentation
Bradley W. Goodfellow, Arjen P. Stroeven, Alexander Lewerentz, Kristina Hippe, Jakob Heyman, Nathaniel A. Lifton, Marc W. Caffee, and Jens-Ove Näslund

The aim of this study is to test the Holocene relative sea-level (RSL) curve (or shoreline displacement curve) for east central Sweden using 14C produced in situ in quartz-bearing bedrock (in-situ 14C). The original RSL curve is instead based on radiocarbon dating of organic material from isolation basins. Having an accurate RSL curve is crucial from at least two aspects. In Sweden’s safety assessments for a planned spent nuclear fuel repository and for the existing repository for low- and intermediate level waste, the RSL curve is used to constrain the emergence above sea level in landscape development models. Also, the RSL is used to constrain model estimates of rates and depths of glacial and subaerial erosion from cosmogenic 10Be and 26Al produced in situ in quartz in bedrock surfaces.

Avoiding vein quartz and hydrothermally altered bedrock, five samples of granitoid bedrock were taken along an elevation transect extending southwards from Forsmark, the location of the planned spent nuclear fuel repository. Because all samples derive from bedrock outcrops positioned below the highest postglacial shoreline, they target the timing of progressive landscape emergence above sea level. To further assess the accuracy of in-situ 14C dating, we took an additional five samples from bedrock outcrops 100 km west of Forsmark, above the highest postglacial shoreline. The in-situ 14C concentrations in these samples should reflect local deglaciation ages.

The ten new in-situ 14C measurements provide robust age constraints that compare favorably with the original RSL curve derived from radiocarbon dating of organic material in isolation basins and with the regional deglaciation chronology. Inferences of limited rates and depths of bedrock erosion over the past 1 Myr, inferred from 10Be and 26Al inheritance and which are critically dependent on the RSL curve, therefore glean strong support from these new in-situ 14C measurements.

How to cite: Goodfellow, B. W., Stroeven, A. P., Lewerentz, A., Hippe, K., Heyman, J., Lifton, N. A., Caffee, M. W., and Näslund, J.-O.: Last ice sheet recession and landscape emergence above sea level in east central Sweden, evaluated using 14C produced in situ in quartz, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6006, https://doi.org/10.5194/egusphere-egu23-6006, 2023.

17:50–18:00
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EGU23-1380
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GM2.6
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On-site presentation
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Andrea Hampel, Andreas Wölfler, Armin Dielforder, Ralf Hetzel, and Christoph Glotzbach

Compared to the Western European Alps, the ice extent during the Last Glacial Maximum (LGM) and the subsequent deglaciation history of the Eastern Alps east of the Tauern Window remains less well constrained. Also, considerable discrepancies exist between the mapped LGM ice margin (Ehlers and Gibbard, 2011; van Husen, 2004, 2011) and the ice extent predicted by ice-sheet models (Seguinot et al., 2018). Here we present the first 10Be surface exposures ages from two regions east of the Tauern window (Gurktal and Lavantal Alps), which provide constraints on the LGM ice extent and the deglaciation history (Wölfler et al., 2022). Our results show that the deglaciation of the Gurktal Alps occurred between 16-14 ka, which agrees with the predictions from ice-sheet models and implies that the LGM ice cover was greater than mapped. This finding also supported by our analysis of high-resolution DEMs that revealed glacially streamlined ridges and macroscale glacial striations consistent with modelled ice flow directions (Seguinot et al., 2018). In contrast, the 10Be ages from the Lavantal Alps located farther east are either LGM in age or pre-date the LGM, indicating that these regions were ice-free or only partially covered by LGM ice. Based on these results, our future investigations will aim at obtaining more age data from the Eastern Alps to refine the location of the LGM ice margin and the deglaciation history, which is also crucial for climate-evolution and postglacial-rebound models.

 

References

Ehlers J, Gibbard PL, Hughes PD (2011) Quaternary glaciations - Extent and chronology. A closer look. Developments in Quaternary Science 15.

Seguinot J., Ivy-Ochs S, Jouvet G, Huss M, Funk M, Preusser F. (2018) Modelling last glacial cycle ice dynamics in the Alps. The Cryosphere 12: 3265–3285.

van Husen D. (2004) Quaternary glaciations in Austria. In: Quaternary Glaciations: Extent and Chronology Part I: Europe, Ehlers J, Gibbard PL (eds). Elsevier: London: 1–13.

van Husen D (2011) Quaternary Glaciations in Austria. In Quaternary Glaciations – Extent and Chronology: A Closer Look, Ehlers J, Gibbard PL, Hughes PD (eds). 15: 15–28.

Wölfler A, Hampel A, Dielforder A, Hetzel R, Glotzbach C (2022) LGM ice extent and deglaciation history in the Gurktal and Lavantal Alps (eastern European Alps): first constraints from 10Be surface exposure dating of glacially polished quartz veins, Journal of Quaternary Science  37: 677-687. https:// doi.org/10.1002/jqs.3399

How to cite: Hampel, A., Wölfler, A., Dielforder, A., Hetzel, R., and Glotzbach, C.: LGM ice extent and deglaciation history in the Gurktal and Lavantal Alps (Eastern European Alps): first constraints from 10Be surface exposure dating of glacially polished quartz veins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1380, https://doi.org/10.5194/egusphere-egu23-1380, 2023.

Posters on site: Mon, 24 Apr, 14:00–15:45 | Hall X3

X3.27
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EGU23-2068
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GM2.6
Jörg Robl, Kurt Stüwe, Fabian Dremel, Moritz Liebl, Christoph von Hagke, and Derek Fabel

The Bohemian Massif is the relic of a major Paleozoic mountain range that is known to have exhumed and its surface levelled in the Permian. The southern part of the Bohemian Massif with high grade metamorphic rocks and magmatic intrusions dips towards the south under the weakly consolidated Neogene sediments of the Molasse Basin. However, Neogene landscape evolution is largely unconstrained, but the occurrence of marine sediments several hundred meters above sea level is a clear indication of significant surface uplift during the last few million years. The landscape is characterized by rolling hills and extended planation surfaces above an elevation of about 500 m. However, at lower elevations deeply incised gorges confined by steep hillslopes are abundant and contrast impressively with the low relief landscapes above. A continental drainage divide follows the central ridge of the Bohemian Massif with the Vlatava (Moldau) and the Danube (Donau) draining the regions north and south of the drainage divide. In this study we aim quantifying spatial and temporal variations of landscape change in the Bohemian Massif during the last few million years. To characterize the two contrasting landscape states, we computed landscape metrics based on digital elevation models (e.g. normalized steepness index, geophysical relief). To determine the rate landscape change we determined catchment-wide erosion rates from the concentration of cosmogenic 10Be in river sands.

Results show that the landscape is characterized by out-of-equilibrium river profiles with knickpoints abundantly occurring at elevations between 450 m and 550 m separating steep channel segments at lower elevations from less steep channels at higher elevations. Hypsometric maxima at or close above knickpoint elevations along with high and low values in geophysical relief downstream and upstream of major knickpoints support the idea of landscape bimodality. Furthermore, we found a strong drainage divide asymmetry, which evidences for the reorganization of the drainage network of the region. Across-divide gradients in channel steepness predict the northward migration of the Danube-Vltava drainage divide including growth and shrinkage of tributary catchments. Erosion rates of the 20 investigated catchments are very low (20 – 50 m per million year) compared to the Alps or other active mountain ranges. The lowest erosion rates occur in catchments with a large fraction of planation surfaces at mid-altitudes. Highest erosion rates occur in elongated catchments of Danube tributaries. Based on our results we suggest that the occurrence of contrasting bedrock properties between Molasse sediments and the crystalline basement represents a superior control on the topographic evolution of the entire region. The transition from soft sediments of the Molasse basin to much less erodible basement rocks during progressive river incision in a setting of low but long last uplift distinctly changes the channel steepness and relief, the course of the receiving streams, and their susceptibility to sudden changes in flow direction (river capture) of the million years’ time scale.

How to cite: Robl, J., Stüwe, K., Dremel, F., Liebl, M., von Hagke, C., and Fabel, D.: Old orogen - young topography: Landscape Rejuvenation in the Bohemian Massif, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2068, https://doi.org/10.5194/egusphere-egu23-2068, 2023.

X3.28
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EGU23-17271
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GM2.6
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ECS
Gerald Raab, John Gosse, and Alan Hidy

Understanding topographic relief evolution and its changes over hundreds of thousands to million-year timescales remains challenging. Recent approaches usually combine numerical modelling of terrestrial cosmogenic nuclide (TCN) exposure ages on strath terraces, exhumation histories based on thermochronology, drainage basin evolution, and basin stratigraphy. However, even when combined, these methods are unable to measure the rate changes with precisions needed to differentiate climate from tectonic drivers over multiple glacial cycles and longer timescales.

Muon-paleotopometry is a new approach that may address the methodological gap in determining relief generation. Muon-paleotopometry utilizes the dependence of cosmic ray muon flux on crustal shielding depth. The spatial pattern of concentrations of multiple muon-induced TCN measured along a near-horizontal transect under valleys and peaks relates directly to the history of changes (positive or negative) in crustal thickness. It enables paleotopometry above the sample datum over an isotope-specific monitoring duration. By sampling at depths of hectametres, long-lived TCNs are not sensitive to minor short-term (<105-yr) changes owing to cut and fill terraces or transgressions for instance, but short-lived isotopes may provide constraints on this. The method uses concentration differences among samples, so is not significantly impacted by limitations in knowledge of muon flux and interactions at those depths. Early proof-of-concept investigations at Dalhousie (M. Soukup, Hon. Thesis, 2017) provided encouraging results to allow for the current large-scale relief investigation of the European Alps.

How to cite: Raab, G., Gosse, J., and Hidy, A.: Muon Paleotopometry – Measuring crustal thickness variations with muons?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17271, https://doi.org/10.5194/egusphere-egu23-17271, 2023.

X3.29
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EGU23-2346
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GM2.6
Kurt Stüwe, Gerit Gradwohl, Joerg Robl, Lukas Plan, Derek Fabel, and Fin Stuart

We present cosmogenic nucleide data that help to understand the ill-constrained  uplift history of the Eastern Aps. Well accepted, but indirect evidence  for this uplift history includes: (a) the onset of flexural subsidence of the foreland basins, or (b) the formation of the Periadriatic line (recording the onset of continent-continent collision in the Alps). Both are often used to suggest about 30 Ma as the starting date for the surface uplift of the range. Since this time the fine interplay of many kilometres of upwards rock uplift and downwards erosion resulted in net surface uplift of some 2-3 kilometres but reference frames that allow to discern between rock uplift and surface uplift are often hard to identify. One way of measuring surface uplift rates is through the study of areas where erosion did not occur. That is, dating and identifying relicts of ancient base levels for example in caves, sediments or paleosurfaces.

In this contribution we present 10Be, 21Ne, 26Al cosmogenic nucleide data of fluvial sediments sampled in some 50 caves across the Eastern Alps from elevations between 300 and 2500 m surface elevation. We collected samples that were interpreted to have been deposited during cave formation at the vadose-phreatic transition. As such, they form markers for base level and  the age of their burial into the cave may be interpreted as the time the cave was at base level some few hundreds of meters above sea level. Interpretation of our data indicates that the uplift rate of the Eastern Alps may be in the order of 200 m – 500 m per Million years for much of the Pliocene. As such, much of the observed surface uplift of the Eastern Alps may have occurred since the late Miocene and surface uplift is thus much faster than previously thought.

 

How to cite: Stüwe, K., Gradwohl, G., Robl, J., Plan, L., Fabel, D., and Stuart, F.: Surface uplift of the Eastern Alps. Much faster than we thought?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2346, https://doi.org/10.5194/egusphere-egu23-2346, 2023.

X3.30
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EGU23-11839
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GM2.6
Georgina King, Xiaoxia Wen, Melanie Bartz, Leif Anderson, Lily Bossin, Sumiko Tsukamoto, Yan Li, Frédéric Herman, Manabu Ogata, and Shigeru Sueoka

The impact of Quaternary climate change on landscape evolution, and more specifically the timing of incision of the overdeepened Alpine valleys, remains difficult to quantify with existing thermochronometric methods. Thermochronometers are used to determine rates of rock cooling, however most techniques are insensitive to temperature changes <60 °C that occur within the last kms of Earth’s crust. Recording cooling rates within this temperature range is essential if the impact of glacial-interglacial cycles on rock exhumation is to be resolved.

Electron spin resonance (ESR) thermochronometry applied to quartz minerals has the potential to span this thermal (and temporal) gap. We are developing this method by building upon previous studies (e.g. Scherrer, 1993) with the ultimate aim of constraining the timing of incision of the Rhône valley. Preliminary data from the Japanese Alps (King et al., 2020) indicate that ESR thermochronometry could resolve rates of <1 mm/yr over Quaternary timescales.

To determine a rock cooling history using ESR thermochronometry, signal accumulation and signal thermal loss must be robustly determined within the laboratory. We have collected a series of geological samples including rocks from boreholes that have known isothermal histories to investigate the potential of this technique. Our objective is to use the latter rocks to confirm the validity of our laboratory measurements and data-fitting/numerical models. Specifically, we have investigated known-thermal history samples from the MIZ1 borehole (Japan) and the KTB borehole (Germany) as well as samples from Sion in the Western European Alps.

Preliminary data reveal that the ESR dose response and thermal decay of different quartz samples is highly variable. Whereas the Al-centre of some samples exhibits linear dose response to laboratory irradiation up to 15 kGy, the Al-centre of other samples exhibits exponential, or double-exponential growth and saturates at doses of 3-4 kGy. The Ti-centre of most samples is well described by a single saturating exponential function, however samples from the MIZ1 borehole exhibit pronounced sub-linearity in the low-dose response region. Furthermore, whereas for some samples the Al-centre is less thermally stable than the Ti-centre, for other samples the inverse is observed. These observations suggest that a uniform measurement protocol and data-fitting approach may not be appropriate for quartz ESR data.

Inversion of two KTB samples yielded temperatures within uncertainty of borehole temperature, however results for the MIZ1 borehole are more variable and can only recover temperature at best within ~10%. Investigations into the cause of the poor results for the MIZ1 borehole are ongoing (i.e. measurement protocol, data-fitting/numerical model) and will be discussed. Preliminary data from Sion are promising and reveal consistent cooling rates.

 

Scherer, T., Agel, A., and Hafner S. S.: Determination of uplift rates using ESR investigations of quartz, KTB Rep. 93-2. Kontinentales Tiefbohrprogram der Bundesrepublic Deutschland Niedersächs. Landesamt Bodenforsch., Hannover, 121–124, 1993.

King, G.E., Tsukamoto, S., Herman, F., Biswas, R.H., Sueoka, S., Tagami, T. Electron spin resonance (ESR) thermochronometry of the Hida range of the Japanese Alps: validation and future potential. Geochronology 2, no. 1 (2020): 1-15.

 

 

 

How to cite: King, G., Wen, X., Bartz, M., Anderson, L., Bossin, L., Tsukamoto, S., Li, Y., Herman, F., Ogata, M., and Sueoka, S.: Will ESR thermochronometry reveal the timing of Rhône valley incision?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11839, https://doi.org/10.5194/egusphere-egu23-11839, 2023.

X3.31
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EGU23-10655
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GM2.6
Sachi Wakasa, Tatsuya Ishiyama, Daisuke Hirouchi, Nobuhisa Matta, Natsuko Fujita, and Tomoo Echigo

Surface exposure ages of marine and fluvial terraces based on in situ 10Be dating were determined to estimate formation ages and long-term rates of coastal uplift along the northern Pacific coast of Northeastern Japan. Surface rock samples were collected along the northern and southern coasts of Sanriku based on a reinterpretation of dispersed marine and fluvial terraces using DEM and aerial photographs. We collected three samples at the Samuraihama site from outcrops of pairs of marine and fluvial terraces distributed over the east-facing flank of the Kitakami Mountains. At the Yoshihama site, in contrast, where bedrock surfaces could be better exposed, we took vertical samples from weathered granite rocks on small trench walls dug on the middle marine terrace at Yoshihama Bay. Surface exposure ages from 10Be concentrations in quartz calculated from the measured 10Be/9Be ratios commonly suggest slow in both sites, whereas steep (~ 10°) dip domains on the marine terraces along the northern Sanriku coast may imply localized permanent strain accumulation.

How to cite: Wakasa, S., Ishiyama, T., Hirouchi, D., Matta, N., Fujita, N., and Echigo, T.: 10Be dating of middle-late Pleistocene uplifted marine terraces in northern Pacific coast of Northeastern Japan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10655, https://doi.org/10.5194/egusphere-egu23-10655, 2023.

X3.32
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EGU23-7899
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GM2.6
Zsófia Ruszkiczay-Rüdiger, Stephanie Neuhuber, Esther Hintersberger, Jesper Nørgaard, and Régis Braucher

Two published cosmogenic radionuclide (CRN) 26Al/10Be burial age calculation methods developed to correct for post-depositional production of nuclides in settings with low sediment overburden are compared. The advantages and limitations of simple (ISO; [1], [2]) and inverse modelling (INV, [3]) isochrons are investigated.

The studied dataset originates from the gravel of a Danube terrace in the Central Vienna Basin (Austria) [4]., where two horizons (5.5 m and at 11.8 m subsurface depth) were sampled. Each sample set contained 6 quartz or quartzite cobbles.

The advantage of ISO is that it is uninfluenced by changes in sample depth over time. However, the initial 26Al/10Be ratio is fixed and no pre- and post-burial denudation rates can be calculated. In addition to age, INV models source and sink denudation rates, but assumes constant depth over burial time.

For correct application of ISO and INV outliers, must be excluded. The robustness of both methods is tested by systematically including or excluding data points (bootstrapping) to estimate the dependence of numerical ages on sample selection either in the field, or during outlier identification.

For outlier identification the traditional method of data exclusion of points above or below the isochron line is used. In addition, a new way is introduced here: the post-burial production is calculated using the modelled burial age and denudation rate and compared to the measured inventories of 10Be and 26Al. If the fraction of post-burial production is equal or higher compared to the measured inventory and its ratio is considerably different for the two isotopes from the same sample, the datapoint is invalid.

In addition, the influence of each sample on the modelled burial age, tested by bootsrapping, is used to exclude samples with a large effect on the age.

The resulting ages at both levels using ISO and INV agree within errors with ISO being systematically slightly younger. The importance of outlier removal is stressed by the fact that inclusion of all samples results in a considerably older age of the stratigraphically higher level compared to the underlying one.   When outliers are excluded, burial ages of the two sampled horizons overlap within uncertainty, suggesting one single deposition event for the whole sediment package.

Interestingly, when the entire dataset is merged, both methods provide similar ages regardless of the outliers being excluded or kept in. This demonstrates that a larger sample number increases the robustness of a dataset considerably and decreases the sensitivity of either method to potential outliers.

In summary, both ISO and INV are robust ways of CRN burial age determination, provided that model presumptions are not violated and outliers are excluded or the sample number large enough to overprint the influence of outliers.

Funding: NKFIH FK124807; OMAA 90ou17; OMAA 98ou17.

 

References

[1] Balco, G., Rovey, C.W., 2008. American Journal of Science 308(10), 1083-1114.

[2] Erlanger, E.D., et al., 2012. Geology 40(11), 1019-1022.

[3] Pappu, S. et al., 2011. Science, 331(6024), 1596-1599.

[4] Ruszkiczay-Rüdiger, Zs. et al., 2021. Journal of Radioanalytical and Nuclear Chemistry, 329(3), 1523-1536.

How to cite: Ruszkiczay-Rüdiger, Z., Neuhuber, S., Hintersberger, E., Nørgaard, J., and Braucher, R.: Calculation of cosmogenic radionuclide burial ages: a comparison of two models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7899, https://doi.org/10.5194/egusphere-egu23-7899, 2023.

X3.33
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EGU23-11243
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GM2.6
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ECS
Romano Clementucci, Paolo Ballato, Lionel Siame, Faccenna Claudio, Racano Simone, Torreti Giacomo, Lanari Riccardo, Leanni Laetitia, and Valery Guillou

Transient topography represents an opportunity for extracting information on the combined effect of tectonics, mantle-driven processes, lithology and climate across different temporal and spatial scales. The geomorphic signature of transient conditions can be used to unravel the landscape evolution and to assess perturbations in uplift rates, especially in areas devoid of stratigraphic constraints. The Atlas-Meseta system experienced a large scale topographic rejuvenation during the Cenozoic through a combination of different processes. Despite the uplift, the Western Moroccan Meseta (WMM) represents a quiescent tectonic domain with deeply incised valleys and high-standing erosional surfaces (relict landscape). This topography is characterized by elevated non-lithological knickpoints, that delimit an uplifted relict landscape, implying a transient response to a change in uplift rates. Here, we determine denudation rates of selected watersheds and bedrock outcrops from cosmogenic nuclides and perform stream profile, regional and basin-scale geomorphic analysis. Denudation rates of the relict and the rejuvenated landscape range from 15 to 20 m/Myr and from 30 to 40 m/Myr, respectively. These results allow estimating the erodibility parameter for performing river-profile inversions and hence extracting rock uplift rates through time. Inverted rock uplift rates are 10-25 m/Myr from 45 to 22 Ma and 30-55 m/Myr from 22 to 10 Ma. Despite the different time scales, the inverted rates are consistent with 10Be averaged denudation rates (15-20 and 30-40 m/Myr) and river incision values from Pleistocene lava flows (<10 and ~50 m/Myr) for the rejuvenated and relict regions of the WMM. These results agree with geological data and indicate that the observed 400 m of surface uplift in the WMM started to develop at ~22-20 Ma. Given the wavelength of the topographic swell forming the topography of the WMM, uplift is here interpreted to reflect localized crustal thickening through magma addition or lithospheric thinning through mantle delamination. This event, however, represents only a first episode of uplift. The occurrence of ~7-Myr-old marine sediments at ~1200 m of elevation indicates that the adjacent Folded Middle Atlas experienced a more recent surface uplift at ~170 m/Myr. Considering the cumulative amount of surface uplift that varies eastward from 400 to 800 and 1200 m from the Meseta to the Tabular and the Folded Middle Atlas, as well as the spatio-temporal pattern of alkaline volcanism (middle Miocene and Pliocene to Present), we suggest that the most recent episode (second phase) of surface uplift was induced by a larger-scale process that most likely included upwelling of asthenospheric mantle and to a lesser extent crustal shortening and thickening in the Folded Middle Atlas.

How to cite: Clementucci, R., Ballato, P., Siame, L., Claudio, F., Simone, R., Giacomo, T., Riccardo, L., Laetitia, L., and Guillou, V.: Cenozoic uplift history and topographic rejuvenation of the northern Atlas-Meseta system (Morocco), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11243, https://doi.org/10.5194/egusphere-egu23-11243, 2023.

X3.34
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EGU23-8283
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GM2.6
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ECS
Audrey Margirier, Georgina King, Christoph Schmidt, Julien Brondex, and Ann Rowan

In recent decades, most mountain glaciers have been losing mass in response to climate change, and the area of the ablation zone covered by rock debris is expanding. Debris-covered glaciers are expected to have a longer life expectancy than climatically equivalent clean-ice glaciers because supraglacial debris insulates the underlying ice surface and reduces ablation. In order to accurately predict how debris-covered glaciers will evolve under a changing climate it is essential to quantify the processes controlling their behaviour. We used luminescence rock surface burial dating to constrain the englacial transport time of debris within an alpine debris-covered glacier. We collected 24 samples embedded in the ice in the ablation zone of the Miage Glacier, in the Mont-Blanc Massif (Italy). The natural luminescence signal of rock slices was measured from the surface to a depth of ~10 mm using a protocol comprising IRSL50, IRSL225 and OSL125 measurements. Nine of our samples showed a plateau within the first 2 to 3 discs suggesting that the luminescence signal has the potential to be used to date the burial duration of debris. Among them, 5 and 7 samples passed the dose recovery test for the IR50 signal within 10% and 20% of unity respectively. Only 3 samples passed the dose recovery test for the IR225 signal within 10% of unity. After 24h bleaching in the solar simulator, typical residual doses are as high as 20-40% of the natural equivalent dose measured. We obtained preliminary non fading corrected ages for 5 samples in the range from ~0.8 to ~11 ka. Glacier model estimated englacial rock debris transport times are an order of magnitude lower than the oldest ages obtained suggesting either that some clasts were stored on hillslopes or within moraines prior to englacial transport or that calibration issues may have contributed to age overestimation. Further luminescence signal processing quality checks are required to assess the quality of our ages. If ultimately successful, our results, and the application of luminescence rock surface burial dating to englacially transported debris, will enhance understanding of the dynamics of debris-covered glaciers and inform the use of glacier models for debris covered glaciers, which will improve projections of the contribution of mountain glaciers to the sustainability of water resources in vulnerable catchments such as those in High Mountain Asia and South America.

How to cite: Margirier, A., King, G., Schmidt, C., Brondex, J., and Rowan, A.: Englacial transport time of rock debris: new constraints from luminescence rock surface burial dating, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8283, https://doi.org/10.5194/egusphere-egu23-8283, 2023.

Posters virtual: Mon, 24 Apr, 14:00–15:45 | vHall SSP/GM

vSG.3
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EGU23-4811
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GM2.6
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ECS
|
Arkaprabha Sarkar, Vimal Singh, Pankaj Kumar, Pavitra V. Kumar, and Rajveer Sharma

Soil loss is one of the major environmental threats the world is facing due to horizontal expansion of cities and increasing land abuse. It has been previously shown by workers that the abuse or improper use of land and soil had adversely affected early civilisations. Keeping into consideration the imminent threat, a number of methods have been proposed to estimate soil loss e.g. numerical models, monitoring-based field methods. However, these are either time-consuming or inherently carry a degree of uncertainty.

One method involves using environmental fallout nuclides as tracers of soil erosion and mapping areas of soil loss and accumulation. The commonly used nuclides in this technique are 137Cs and 7Be. 137Cs is a nuclear fission product and cannot be used to track soil dynamics older than 1940s, while 7Be has a very short half-life and is used to study soil dynamics in a seasonal scale.

In this study, we have proposed a method of using meteoric 10Be to trace long-term soil redistribution in a landscape. This cosmogenic nuclide is produced in the atmosphere and reaches the land surface by dry and wet fallout. Once it reaches the surface, it is adsorbed by the soil particles and it mobilizes along with the soil. Thus, higher concentrations indicate net soil accumulation, whereas, lower concentrations are due to net soil loss. The rate of delivery of 10Be flux estimated from global circulation models (GCMs) has been used to calculate rates of erosion.

We tested our method in Pranmati catchment, a small river catchment (~93 km2) in Uttarakhand, India and validated by comparing our findings with previously proposed geomorphic transport laws. Our results show that soil erodes from the high lying divergent (convex) topography and accumulates in the low lying convergent (concave) topography. The rates of erosion are also influenced by land cover – erosion in forests is much slower compared to grassland.

How to cite: Sarkar, A., Singh, V., Kumar, P., Kumar, P. V., and Sharma, R.: Inferring Long Term Averaged Soil Redistribution Pattern using Meteoric 10Be, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4811, https://doi.org/10.5194/egusphere-egu23-4811, 2023.