Human settlements have historically concentrated near rivers due to their transportation benefits and fertile lands, despite the inherent flood risks. To mitigate these flood risks, societies have implemented various interventions, including flood control structures such as embankments. Although these structures can reduce the frequency of small or moderate floodplain inundation, which can support economic growth, they also create a false sense of security, leading to increased settlement in floodplains. This, in turn, can exacerbate the impact of high flood events that exceed the design capacity of flood protection structures. The increasing frequency of flood hazards, driven by changing climatic conditions and changes in land use, raises critical questions about whether these flood control structures alone can serve as long-term sustainable solutions for flood mitigation. In this context, this research investigates how flood control embankments and sediment transport affect river morphology, channel capacity, and flood inundation by simulating various extreme flood scenarios in Himalayan river reaches in Nepal. The results show that river embankments can reduce the extent of floods for low-flow or high-frequency floods, up to the designed discharge. However, in rivers with moderate to high sediment transport rates, the construction of embankments and channel confinement can significantly alter sediment mobility, potentially increasing downstream flood risks and compromising embankment stability during extreme events. This research highlights the importance of evaluating multiple aspects of river embankments, particularly their impact on river morphology, sediment mobility, and flood risk management in sediment-rich rivers undergoing rapid urbanisation and climate change. In these contexts, sediment transport effects should be considered in embankment design and floodplain planning.
Keywords: River embankments, Sediment transport, Flooding, River morphology, Himalayan Rivers
How to cite: Thapa, S., Sinclair, H. D., Creed, M. J., Borthwick, A. G. L., Watson, C. S., and Muthusamy, M.: Sediment Transport and Flood Risk: Impact of River Confinement with Embankments on River Morphology and Flood Dynamics in Sediment-rich Himalayan Rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19886, https://doi.org/10.5194/egusphere-egu25-19886, 2025.
Thousands of large (> 2 ha) rock slope failures affect the Neogene marine sedimentary cover rocks of Aotearoa New Zealand. These soft rock slope failures damage lifeline infrastructure, entire suburbs, agricultural land, and deliver disproportionate volumes of fine sediment to rivers. Most of the landslides are primed by, and adjacent to, major river corridors suggesting the interaction and coupling with rivers. The millennial-scale longevity of the landslides, their propensity to reactivate, and 10% being active today, provides an opportunity to explore the evolution of the landslides and their response to fluvial processes over a range of time scales from the late-glacial to present day. Here we present a range of case-studies along with results from local monitoring and regional statistical analyses that explore the relationship between fluvial erosion processes and that of landslide activation, reactivation, and active movement rates. We show that at regional scales, and millennial timescales, fluvial incision and stream power explain the density and position of landslides in the landscapes. At decadal scales, and for active landslides, undercutting by major storms can switch landslides between dormant and temporarily-active states. For active landslides, on daily to seasonal timescales, stream flow can control the rate of landslide movement and sediment delivery, the effect varies with the competency of the river. Our local and regional analyses suggest that the soft rock landslides are a highly disproportionate source of sediment delivery to rivers, contributing to some 10 – 30 % of the modelled catchment sediment loads (despite representing only ~0.2 % of the total area of these catchments). Soft rock landslides tend to deliver weak, fine-grained sediment which is readily eroded and suspended, while providing minimal contribution of coarse bedload. Consequently, their impact on river morphology is considerably different in geometry and more transient compared to that of rapid and hard rock landslides.
How to cite: McColl, S., Fuller, I., Massey, C., Neverman, A., Smith, H., and Willams, F.: Multiscalar interaction between river erosion and landslide activity, and the implication for landslide hazards and fluvial sediment dynamics in soft rock landscapes. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1277, https://doi.org/10.5194/egusphere-egu25-1277, 2025.
Quantifying erosion in a catchment across different spatial and time scales is key to understand landslide hazards and the role in long-term sediment generation. In this context, disentangling the contributions of localized landslides to catchment-wide erosion remains challenging due to their stochastic nature and the occurrence of sediment storage. To address this, we measured cosmogenic 10Be, 26Al and 14C concentrations in detrital quartz across a dense network of nested sub-catchments to quantify denudation rates, assess sediment production variability, and trace the source-to-sink cascade within a 12 km2 basin.
The study area, the Gürbe catchment, is located at the northern margin of the Swiss Alps and comprises two distinct geomorphological zones. The upper zone, (c. 1,800–1,200 m a.s.l.), is characterized by steeply dipping Mesozoic limestone cliffs transitioning into Mesozoic-Cenozoic Flysch hills overlain by till. Mapping indicates that sediment production here is dominated by overland flow and channel erosion, with minimal connectivity between hillslopes and channels. In contrast, the lower zone, starting at an elevation of 1,200 m a.s.l. and extending to the Gürbe fan at c. 800 m a.s.l., is underlain by Flysch bedrock, partially mantled by till and interspersed with Neogene Molasse formations. The boundary between the upper and lower zone is marked by a glacially conditioned knickzone, indicating the onset of intensive channel incision. Mapping shows that this lower zone is characterized by a complex topography with pronounced scarps and depressions indicative of deep-seated landslides, some of which are directly coupled to the Gürbe trunk channel, while others supply material via tributary excavation.
Cosmogenic nuclide concentrations reveal distinct patterns. In the upper zone, 10Be and 26Al concentrations are high, yielding denudation rates of c. 0.1 mm/yr. However, concentrations are lowest in the lower zone tributaries leading to a concentration decrease downstream along the Gürbe trunk channel.Accordingly, 10Be and 26Al-based denudation rates calculated for the tributaries in the lower zone are significantly higher, reaching values up to 0.3 mm/yr.In addition, 26Al/10Be ratios in the upper zone align with the surface production ratio 6.75, consistent with sediment production through overland flow erosion. Contrarily, in the tributary material, 26Al/10Be ratios are up to 8.8, suggesting that a significant proportion of this sediment originates from deep-seated landslides. The 14C derived denudation rates are two to three times higher than the 10Be derived denudation rates ranging from 0.2 mm/yr in the upper zone to 1 mm/yr in the most active tributary of the lower zone. We interpret the 14C data as a combined effect of sediment storage and subsequent stochastic, unpredictable and rapid release of substantial amounts of deep material into the system, leading to apparent 14C-based erosion rates that are much higher than the long-term averages measured with in-situ 10Be.
In summary, this study demonstrates that by combining field-based mapping with the analysis of multiple cosmogenic nuclides, it is possible to (i) identify the origin of the sediment, (ii) determine the corresponding mechanisms of sediment generation, and (iii) estimate the time scale for sediment transfer across a geomorphologically diverse catchment.
How to cite: Schmidt, C., Mair, D., Schlunegger, F., McArdell, B., Christl, M., Haghipour, N., and Akçar, N.: From Overland Flow to Landslides: Deciphering Sediment Flux and Erosion Histories with Cosmogenic 10Be, 26Al, and 14C, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19414, https://doi.org/10.5194/egusphere-egu25-19414, 2025.
Wildfires are among the natural or anthropogenic disturbances affecting mountain catchments. Wildfire’s role as a geomorphic agent has been recognized in many landscapes worldwide, especially where sediment transport increased in response to post-fire intense rainfall. Vegetation removal, changes to soil hydraulic properties, and degradation of outcropping rocks have been identified as direct effects of fires on hillslopes. These effects can lead to rain-induced enhanced runoff and soil erosion processes, with consequent formation of overland flows entraining sediments and ash progressively downstream. According to a cascading mechanism, overland flows can then generate high-magnitude debris flows. This kind of hydro-geomorphic response has been commonly observed in burned catchments, sometimes together with shallow landslides. Notably, when catchments include urban settlements, post-fire debris flows pose significant hazards to life and property.
Every year, the Mediterranean basin is affected by thousands of wildfires that spread through different topographic settings, from lowland to steep mountains. Accordingly, post-fire debris flows are more likely to occur in catchments with high relief and hillslope-to-channel connectivity, where severe wildfires burn dry vegetation over steep hillslopes covered by erodible soils. These conditions are quite common in southern Italy, where intense rainstorms associated with convective cells occur in the late summer-autumn period, such as after wildfires of the summer season. In the Campania region, more than a hundred post-fire debris flows have been documented in the last two decades. This contribution focuses on one of the last events that occurred on August 27, 2024. The scientific relevance of this event is due to new insights on both mechanisms controlling the hydro-geomorphic response, and a better comprehension of the impacts on urban settlements. Specifically, a preliminary analysis of the following points is presented: 1) predisposing and triggering conditions of debris flows; 2) sediment source areas; 3) the role played by human modifications of the natural drainage network; 4) impacts on people and urban structures. In addition, a series of weak points that are hampering the implementation of effective strategies for risk reduction are discussed. This and other minor events recorded during the Autumn of 2024 in the region suggest that accurate prediction tools need to be developed, together with in-depth analyses of natural factors that control the post-fire sediment cascade. This is crucial to protect people living in post-fire settings that, according to the climate change scenarios, may be exposed to more severe geo-hydrological risk conditions in the next years.
How to cite: Gariano, S. L. and Esposito, G.: Fire-to-debris flow sequences in small catchments: sediment dynamics and impacts on urban settlements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13272, https://doi.org/10.5194/egusphere-egu25-13272, 2025.
Constraining the timing of landslides is crucial for deciphering their triggering mechanisms. Recent years have seen a high number of landslides in tropical regions emphasizing the need to explore the links between climate and slope instability over longer timescales. While considerable data exists for alpine, arctic, and arid regions, limited preservation of geomorphological features accounts for the lack of data in tropical environments (e.g., Pánek, 2019). The Rwenzori Mountains in Uganda offer a natural laboratory for such a study. The upper part of the range features multiple rockfall deposits that disrupt the glacially sculpted landscape, while the lower elevations are characterized by recent debris flows and active landslides. However, no chronological data currently exist for the major rockfall deposits in the Rwenzori Mountains. To address this gap, we used in-situ produced 10Be dating to establish the chronology for seven individual rockfall deposits. The concentrations of 10Be are relatively consistent, ranging from 1.61 ± 0.11 × 10⁴ to 2.96 ± 0.08 × 10⁵ atoms per gram of quartz. The resulting 10Be ages range from 0.8 ± 0.1 ka to 9.2 ± 0.6 ka, clustering during three distinct periods: 9–8 ka, 6–4.5 ka, and 2–1 ka. The 9–8 ka and 6–4.5 ka clusters correspond to periods of enhanced precipitation during the African Humid Period (~10–5 ka; Mason et al., 2024). They specifically align with the onset of warmer temperatures and a temperature optimum based on local lake records (Garelick et al., 2022). The more recent cluster (2–1 ka) aligns with a brief temperature increase (Garelick et al., 2022). These findings suggest that increased temperatures and precipitation create favourable conditions for triggering rockfall in the Rwenzori Mountains, highlighting the interplay between climate and slope instability in tropical glacial landscapes.
How to cite: Margirier, A., Stübner, K., Oehler, S., Lachner, J., Rugel, G., Niyonzima, P., Nalwanga, R., and Schmidt, C.: Climate-driven rockfall activity over the last 10 ka in the Rwenzori Mountains (Uganda): Insights from 10Be dating, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1699, https://doi.org/10.5194/egusphere-egu25-1699, 2025.
Changes in the properties of severe climatic events like rainstorms and droughts are expected to impact erosion rates significantly under modern global warming. Also over the recent geologic past and especially in drylands catchments, hydrological and vegetation transitions following changes in spatiotemporal properties of climatic phenomena have been suggested as triggers for periods of enhanced erosion that affected societies' sustainability and left pronounced topographic imprints. However, these potential drivers remain incompletely understood and quantified. This is, in part, because the discrete events that trigger erosion are hard to observe and the fine-scale processes needed to model erosion are computationally intensive to run over landscape evolution timescales.
To address this, we developed a new catchment-scale landscape evolution model based on the Landlab toolkit that explicitly represents episodic failures, sub-minute hydrology, overland-driven sediment transport, and erosion-vegetation links. We validated the model against event-based runoff and sediment records from the Lucky Hills site in the Walnut Gulch Experimental Watershed, Arizona, USA. After validation, we conducted a set of stochastic numerical experiments of landscape evolution in response to changes in sub-daily rainfall distribution, without considering changes in vegetation properties. We ran an additional set of simulations that integrated the landscape evolution model with historical and future climate records for the High Plains of Colorado, driven by a convection-permitting weather model (CPM). This experimental set allows us to explore changes in vegetation cover and its influence on sediment yield and topographic evolution under modern global warming.
We found that changes in the tail of the sub-daily rainfall distribution—changes similar to recent observations under modern global warming—could raise the total sediment yield by ~40% and alter the catchment morphology. Modeled sediment yield increased in response to the rising frequency of rare, high-magnitude storms, even when there was no significant change in the mean storm properties or annual rainfall. Further, we found that catchment erosion could increase even under a reduction in the mean conditions if the sub-daily rainfall distribution shifted toward a heavier tail. Numerical experiments driven by the CPM data confirm that under projected future conditions in the High Plains, erosion is expected to increase, even though the mean conditions become drier. Our simulations also reveal that the presence of vegetation impacts the morphology of the catchment, reducing channel density and preserving gullies' headcuts. Overall, this study contributes insight into the role of rainstorm properties and vegetation cover on landscape evolution, illuminates potential climatic triggers for past aggradation and degradation stages in low-order catchments, and provides valuable information for erosion risks under anthropogenic climatic and environmental changes.
How to cite: Shmilovitz, Y., Rossi, M. W., Gensini, V., Ashley, W., Haberlie, A., and Tucker, G. E.: Translating high-resolution climate change projections into erosion-vegetation feedbacks, sediment dynamics, and multi-century topographic evolution of dryland catchments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14201, https://doi.org/10.5194/egusphere-egu25-14201, 2025.
Turbidity currents are the final link of the sedimentary source-to-sink chain as they transport continental sediments to deep sea depocenters through underwater land sliding events. Their triggers are numerous: floods, storms, earthquakes, or simple destabilization of continental slope sediments due to overload. Turbidite sediments generally originate from widespread drainages, making them ideal targets for geological reconstructions integrated over large areas and are thus key sedimentary archives to track past, large-scale continental processes.
To interpret the information contained within turbidites, it is however crucial to correctly date them. In most studies, turbidites are considered as instantaneous deposits and dated using foraminifera of the over and underlying hemipelagic layers, and the absolute age of the sediments they transport is rarely constrained.
In this work, we bring new light on the age of the material remobilized by turbidity currents by using 14C on both foraminifera and vegetal debris contained in turbidites from three different cores of the Ogowé turbiditic system, western Africa. Two of these turbidites from two different cores are also investigated at higher resolution with 20 foraminifera samples and 38 vegetal debris samples (~1 sample every 5 cm vs. 1 sample/turbidite for the rest of the cores). The radiocarbon ages measured in the turbidites, when compared to the depositional ages of under- and overlying hemipelagic layers provide quantitative information on the total transportation time from the source to the depositional environments, including both the duration of transport on land, and the potential storage of the sediments onshore and offshore (on the continental margin). To compare these results to a smaller, highly-connected turbiditic system, we apply the same method to turbidite sands from the Var turbiditic system, southeast France. To compare these results we apply the same method to turbidite sands of the Var system in SW France. The Var drainage is smaller than that of the Ogowé, is affected by significant relief (maximum altitude of 2916 m) and steep slopes, and possesses no continental margin, creating a very efficient connection from continent to the deep sea.
Our results shed new light on the transport and residence time of turbidites which varies from 1 ka to 15 ka, on the residence time of sediments on the continental slopes or margins ranging from null to about 7 ka, and on the depositional sequences and mechanisms of turbidites. We are able to show that the transport time of sediments in such distal environments can vary on the order of 10 ka and is therefore important to constrain.
How to cite: Charreau, J., Large, E., Hage, S., Dennielou, B., Toucanne, S., and Blard, P.-H.: Quantification of source-to-sink transport time of turbidite sands from continental erosional to marine depositional environments , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18215, https://doi.org/10.5194/egusphere-egu25-18215, 2025.
Duricrusts are hard mineral layers that develop in regions with contrasting climatic conditions, ranging from tropical to arid environments. These formations are distributed worldwide and can be found, e.g. in Europe, Africa, and South America. Typically found capping hills, inverting landscapes, and shielding underlying softer material, duricrusts play a crucial role in preserving landscapes and altering sedimentary archives. They act as both sources and sinks within geomorphic and sedimentary systems, depending on the spatial and temporal scale of analysis. This research focuses on the influence of duricrusts on landscapes and how they impact the sedimentary record.
Duricrust formation is explained by two main hypotheses: the hydrological hypothesis and the laterisation hypothesis. The hydrological hypothesis suggests that duricrust-forming elements are transported from distant sources and accumulate through processes associated with water table fluctuations. In contrast, the laterisation hypothesis attributes their formation to in-situ processes, where the underlying material undergoes leaching of soluble elements and compaction and cementation of less soluble ones.
Recently, we introduced two new numerical models (EGU abstracts: Fenske et al., 2022, 2023, 2024). These models incorporate a dimensionless hardening factor, κ, to account for reduced surface erodibility, i.e. a distinctive feature of duricrusts. Using independently constrained parameters derived from field data, hydrology, climate, and geochronology, our models successfully reproduce observed conditions for duricrust formation. Additionally, we improved the computation of regolith and duricrust ages to better align modelled results with empirical data.
Simulations demonstrate that, according to the hydrological model, duricrust thickness depends on the water table fluctuation range, λ. Duricrust formation is highlighted when two dimensionless numbers, W and Rt, exceed 0.1 and 1, respectively, indicating that duricrusts form preferentially under stable tectonic conditions. Conversely, according to the laterisation model, duricrust thickness is driven by vertical material supply, such as uplift or base-level drop, and duricrust formation occurs when Ω > Ωmin. This suggests that duricrusts evolve continuously in tectonically active cratonic environments. Tracing these dimensionless parameters and the computed ages through time provides tectonic and climatic constraints on duricrust formation across the geological timescale.
To illustrate these findings, we present a case study of Kaw Mountain in the Guiana Shield. The geological record preserved in duricrust ages enables the simulation of different stages of uplift since the Cretaceous, including a quiescent, dry 20-million-year period during the Oligo-Miocene, followed by a wetter and more active period after the Mid-Miocene Climatic Optimum. Additionally, the presence of duricrusts increases slope steepness, which accelerates erosion. This explains the typical topography observed at Kaw Mountain, with limited extensive duricrust covers in a mountainous region while accounting for the persistence of flat surfaces over time. In areas suitable for duricrust formation, achieving topographic steady-state is unlikely.
These results confirm the ability of our models to simulate duricrust formation under real-world conditions. The established tectonic and environmental parameters for duricrust formation serve as valuable tracers to reconstruct past conditions. Furthermore, these models have significant potential for future applications in understanding how duricrusts influence topographies and the geochronological record.
How to cite: Fenske, C., Braun, J., Guillocheau, F., and Robin, C.: Duricrust Influence on the Geological Record: Insights from Numerical Modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21581, https://doi.org/10.5194/egusphere-egu25-21581, 2025.
The EOT (Eocene-Oligocene Transition) stands out among the greatest reorganizations of the global climate during the Cenozoic era, marking a shift from the Late Eocene “greenhouse” state to “icehouse” conditions on the Oligocene (34-33.5 Ma). While its temporal framework is well established and its global characteristics are increasingly understood, further research is required to assess the regional imprints of this major climatic shift. In this regard, records from epicontinental basins are particularly valuable, as they provide excellent archives to complement global perspectives of environmental change.
This study aims to shed light on how the signals produced by the EOT were transmitted and archived, focusing on changes in the weathering products, sediment production, and water discharge in fluvial systems. To achieve this, we investigated the Paleogene record of the Almazán Basin in central Spain. The EOT is identified within an outstanding exposed fluvial system (Gómara Fm.), supported by a well-defined chronostratigraphic framework.
We applied a multiproxy approach that includes sedimentology, rock magnetism, geochemistry and paleohydraulic estimates to selected stratigraphic intervals encompassing the EOT. New demagnetized samples enhanced the resolution of the EOT. Magnetic properties were measured on discrete samples, across the EOT in order to understand changes in weathering conditions. In addition, we measured paleochannel parameters to provide paleohydraulic estimates enabling assessments of shifts in slope and water discharge.
All analyses and measurements were integrated within a comprehensive stratigraphic framework. We will discuss the meaning of the observed shifts and the changes in magnitude. The findings are discussed in the context of environmental changes associated with the EOT, highlighting their implications for understanding regional responses to this critical climatic transition.
How to cite: Li, J., Valero, L., McLeod, J. S., Beamud, E., Guàrdia, J., and Garcés, M.: The impact of the Eocene-Oligocene transition on a midlatitude fluvial system (Almazán Basin, Spain), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11048, https://doi.org/10.5194/egusphere-egu25-11048, 2025.
The regionally significant lower-middle Triassic Sherwood Sandstone Group (SSG) of the British Isles records the early stages of the breakup of Pangea and is an important aquifer and subsurface reservoir. It was deposited by a major north-flowing river system, which was sourced in northern France and flowed towards the East Irish Sea Basin, and reaches a maximum thickness of 1.6 km. However, the vertical and lateral amalgamation of fluvial sandstones and conglomerates of the SSG, coupled with its interpreted arid continental environment of deposition, have traditionally rendered the impacts of climate and tectonics on sedimentation uncertain. Developing a better understanding of these interactions for this palaeodrainage system is key to appraising source-to-sink sediment routing trends. This would allow improved predictions to be made of the volumetrics and heterogeneity of sandstone reservoir fairways for carbon capture and storage (CCS).
To this end, we apply quantitative paleohydrological methods to reconstruct key characteristics of the fluvial system throughout its depositional fairway using both architectural and bedform-based analyses. We collected outcrop measurements from 37 key field sites across England from south to north, of dune-scale bedforms (n=1278), architectural elements (n=270), palaeocurrent (n=820), and grain size (n=157). From these data, bankfull flow depths, palaeoslopes, unit discharge and river planform are quantified from empirical-numerical approaches.
We firstly illustrate the temporal evolution of the fluvial system through the chronostratigraphically dated Devon coast section in the south-west of England. Our results quantitatively develop on previously inferred climatic trends in the British Isles. We recover median bankfull flow depths of 1.5 to 2m, and palaeoslopes of 0.0006 to 0.001. The lowest SSG unit illustrates the presence of large, pebble-grade rivers with high bankfull discharge: a consequence of the fluvial system’s response to the Permo-Triassic Extinction at 252 Ma. The upper SSG reflects a return to more uniform hydrological and sedimentological conditions and a decrease in palaeoslope, due to progressive topographic decay and a climatic recovery by the mid-Triassic.
To the north, the spatial variation of sedimentological and palaeohydraulic character indicates that the fluvial system that deposited the SSG was more complex than previously interpreted. Results indicate the trunk river was fed by multiple tributaries that drained local sediment sources in addition to the typically identified source from northern France. These findings may have substantial implications for palaeoclimate, regional drainage patterns and CCS, with reservoir properties in the SSG likely variable as a result.
How to cite: Yan, X., Hampson, G. J., and Whittaker, A. C.: A new perspective of the Sherwood Sandstone: spatio-temporal dynamics of a fluvial system revealed by quantitative paleohydrology, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12318, https://doi.org/10.5194/egusphere-egu25-12318, 2025.
Posters on site: Mon, 28 Apr, 14:00–15:45 | Hall X2
The extreme outburst floods that have occurred within orogenic terrain on the Tibetan Plateau during the Late Quaternary are closely linked to tectonic and climatic factors. Such floods likely induced very rapid, short-term geomorphic impacts on the evolution of mountain drainage systems and patterns of sedimentary movement. We report here the discovery of multistage glacially-dammed lake outburst floods that occurred along the middle-lower reaches of the Yarlung Tsangpo River in the Himalayan orogenic belt since the Middle Pleistocene by combining comprehensive geomorphic, stratigraphic and geochronologic investigations. The differential uplift of the active north-trending rift zones and the Namche Barwa Syntaxis has resulted in localized topographic lift and the formation of river knickpoints, contributing to the development and stabilization of glacial dams. River damming and outburst events have also been influenced by glacial-interglacial climate fluctuations since the Middle Pleistocene. Based on the analysis of the knickpoint migration process, the repeated glacial dams had been effective in impeding headward river erosion during glacial periods. The focused erosion and extensive mobilization of sediment by low-frequency, high-energy floods have resulted in a repeated pattern of material transport and deposition from the Tibetan Plateau interior to its exterior. Furthermore, the dammed lake and outburst floods may have significantly impacted any downstream prehistoric human settlements.
How to cite: Wang, H., Wang, P., Hu, G., and Liu, T.: Impact of Late Quaternary dammed lake-outburst floods along the Yarlung Tsangpo River on the sedimentary and landscape evolution, Southern Tibet, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2976, https://doi.org/10.5194/egusphere-egu25-2976, 2025.
Coastal areas represent complex, nonlinear depositional systems that form important stratigraphic records. These records are frequently used to reconstruct past natural hazards, including earthquakes, tsunamis, and storms, as well as to investigate processes associated with sea-level changes and the impacts of climate change. Of course, the underlying assumption is that understanding past events and processes can improve our ability to anticipate future environmental changes, hazards, and their consequences. While the geologic record provides tangible evidence of past phenomena, the inherent complexity and nonlinearity of coastal systems introduce significant uncertainties. These uncertainties affect what is preserved, how it is recorded, and ultimately how the record is interpreted. Often, we address these challenges through qualitative assumptions, which may inadvertently introduce biases into our interpretations.
In this study, we develop and apply a Monte Carlo-based stratigraphy generation model to explore and quantify uncertainties associated with coastal depositional environments and their responses to natural hazards. This approach provides a systematic framework to better understand how a stratigraphic record is formed due to changing environments, and how earthquakes, tsunamis, and storms influence the stratigraphic record. To analyze the impacts of these uncertainties, we employ Shannon’s entropy as our main quantitative tool.
Our findings shed light on the environmental conditions under which key events are most likely to be missed or misinterpreted within the geologic record. Additionally, we demonstrate how identical hazard sequences can produce differing stratigraphic signatures depending on varying and dynamic environmental contexts. These results underscore the remarkable complexity of the stratigraphic record and its susceptibility to potential interpretation biases. By quantifying uncertainty and variability, our work offers critical insights into the processes governing the preservation and interpretation of coastal stratigraphy, with implications for advancing hazard assessment and stratigraphic analysis.
How to cite: Weiss, R. and Dura, T.: Where have all the hazards gone? Studying complexity, uncertainty, and nonlinearity in coastal stratigraphy through Monte-Carlo simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5248, https://doi.org/10.5194/egusphere-egu25-5248, 2025.
Over past decades, sustained meltwater discharge has formed rapidly growing proglacial deltas in the fjords and bays along the glaciated coast of Alaska. These deltas are efficient traps of glaciofluvial sediment, buffering sediment flux from land to the ocean and altering coastal ecosystems. In addition to seasonal meltwater discharge, rates of proglacial sediment transport in Alaska can be elevated by episodic Glacier Lake Outburst Floods (GLOFs). Here we explore the contribution of GLOFs to sediment accumulation on two deltas that simultaneously formed at the head of Lituya Bay, Glacier Bay National Park, Alaska. Both deltas share a similar tectonic, climatic, and glaciologic setting. However, one of them, Lituya delta, is frequently flooded during outbursts of an ice-dammed lake, while the other, Crillon delta, had no reported lake outburst floods. Our goal is to quantify the competing roles in sedimentation during average seasonal and extreme GLOF discharges. To this end, we tracked the growth of the two deltas from a time series of satellite images, measured clast sizes on the deltas, and conducted a multi-beam depth survey of Lituya Bay. We find that the lake outburst floods cover most of Lituya delta almost every year, transporting boulders up to 7 m in diameter and carving deeply incised channels into the delta. By contrast, the average clast size on Crillon delta is approximately one order of magnitude smaller and the distributary channels are less deep than on Lituya delta. In the past six decades, both deltas have rapidly prograded into the bay. However, Lituya delta grew 45% more in area than Crillon delta under comparable catchment properties, suggesting that the geomorphic work during outburst floods greatly surpasses that of the 'normal' glaciofluvial discharge from Crillon Glacier. Overall, we find that at least 0.57 km3 of sediment accumulated in Lituya Bay between 1959 and 2023, one of the highest sedimentation rates in the coastal mountain ranges of Alaska. Out of this volume, 0.23 km3 of sediment accumulated within the exposed area of Lituya delta alone, nearly twice the volume compared to Crillon delta with 0.13 km3. In our contribution, we will assess the spatial and temporal variability of delta growth and discuss the relative contributions of glacier advance and retreat, sediment sources, and outburst floods. Thereby, our work enhances the understanding of how GLOFs and shifting climatic and glaciological conditions impact coastal sedimentation.
How to cite: Lützow, N., Hughes, K. E., Zimmermann, M., Korup, O., Bookhagen, B., Bdolach, G., Truffer, M., Clague, J. J., Geertsema, M., Higman, B., Kwoll, E., and Veh, G.: Rapid proglacial delta growth from meltwater pulses in Lituya Bay, Alaska, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5970, https://doi.org/10.5194/egusphere-egu25-5970, 2025.
Earthquakes can trigger the failure of tens of thousands of landslides throughout tectonically active landscapes. Predicting the location and magnitude of landslides triggered by seismic shaking remains challenging and adds to the risk of those living in these steep landscapes. In addition to the serious human impact, the geomorphic consequences of the simultaneous triggering of thousands of landslides are likely significant. Moreover, the long-term impact of earthquake triggered landslides on landscape evolution remains relatively unexplored, including the potential for geomorphic patterns or processes to be used to identify regions of landsliding. Here we present first findings on the use of a numerical landscape evolution model to explore how earthquake triggered landslides modulate sediment transport processes and feedbacks, the morphometric implications of these feedbacks, and the strength of these impacts when compared to other geomorphic processes. We implement the landscape evolution model using the Landlab modeling ecosystem and simulate fluvial and hillslope processes as well as explicit landsliding. While analyzing landslide behavior through various timescales (From hundreds of years to tens of thousands of years), we focus on the spatial occurrence and clustering of landslides, test the impact of environmental factors such as precipitation variability and investigate the impact of spatially and temporally varying earthquake triggers. We propose the use of topographic signatures including hilltop concavity, drainage density, and slope-area relationships as ways to validate our models.
How to cite: Morgan, P., Campforts, B., Tucker, G., Morey, S., and Duvall, A.: How do earthquake triggered landslides contribute to landscape evolution?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7505, https://doi.org/10.5194/egusphere-egu25-7505, 2025.
Both glaciers and debris flows can shape the landscape in high mountain areas close to drainage divides. As the glacier erodes the landscape, it leads to drainage divide migration and an asymmetric landscape. During divide migration, catastrophic mass movement events, such as rock avalanches and debris flows, may intensify. The intensive erosion ability induced by debris flow could trigger effects on the landscape as well. However, we still cannot quantify the effects of debris flow on divide migration in glacier-dominated regions. Here, we propose a new numerical framework combining erosion from glaciers, fluvial processes, and debris flows in a long-term landscape evolution framework. Our preliminary results show that debris flow processes can slow down divide migration speed within the glacier-dominated regions. An intensive erosion ability of debris flow can make the divide move to the glacier side. Under the effects of debris flow, the effects trigger a longer glacier response time. Debris flow and glacier work together to decrease the divide’s elevation. Our new model can help us to understand the effects of debris flows and glaciers on long-term landscape evolution under climate changes.
How to cite: Liu, D., Tang, H., Lai, J., and Turowski, J.: Coupling glacier and debris flow processes to long-term landscape evolution model for drainage divide migration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9910, https://doi.org/10.5194/egusphere-egu25-9910, 2025.
Mass transport deposits (MTDs) play a crucial role in source-to-sink systems. They document the rapid, en-masse transport and burial of large volumes of sediments and organic matter from shallow-marine to deep-marine environments. Understanding the distribution, composition, and formation of MTDs is essential, as it forms the basis for elucidating their role in sedimentary basin evolution and biogeochemical cycles.
The wedge-top siliciclastic successions of the Miocene Cilento Group, Southern Apennines (Italy), record multiple episodic, large-scale mass transport events within a fragmented foreland basin system. This study focuses on two megaturbidites, integrating high-resolution stratigraphic logging and petrographic analysis to characterize their sedimentary architecture and assess the transport and depositional processes that shaped them.
These megabeds have consistent lateral extents spanning tens of kilometers, with an average total thickness of 55 meters. A westward thinning trend likely reflects the influence of basin physiography and flow direction. Distinctive coarser-grained turbiditic beds in the uppermost sections exhibit lateral, localized, and channelized features, suggesting coeval gravity flows superimposed on the main depositional event. Petrographic analysis shows that the megaturbidites are predominantly composed of quartz-rich siliciclastic sediments in a calcite-rich matrix, with grain sizes ranging from fine sand to silt. The megaturbidites also contain benthic and planktonic foraminifera reworked from various water depths, along with terrigenous organic matter. These findings indicate complex sediment sources and transport pathways extending from the continental shelf (i.e., a foramol-type platform) to the basin plain.
This study provides information about the source of organic matters, preservation mechanisms, and basin morphology. These insights will contribute to a better understanding of the tectonic-climatic dynamics of the central Mediterranean during the middle to late Miocene and the implications of spatial and temporal variability in sediment transfer in source-to-sink systems.
How to cite: Kim, D., Fildani, A., Forzese, M., Giustolisi, C., Iannace, A., Maniscalco, R., Parente, M., Punturo, R., Relvini, A., Valente, A., and Ogata, K.: Catastrophic remobilization of shelf sediments into deep-marine settings: high-resolution stratigraphic studies of Miocene megabeds in the Cilento Group, Southern Apennines, Italy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18673, https://doi.org/10.5194/egusphere-egu25-18673, 2025.
Between 1990 and 2020, retreating glaciers have created accommodation space for ~20,000 new glacier lakes globally (+38%), increasing the total glacier lake area by ~2,000 km² (+9%). Among these, large glacier lakes (>1 km2) have drawn substantial attention due to their roles in hydropower production, freshwater supply, tourism, and landscape protection. Researchers have also stressed their high hazard potential, given that their dams might collapse and release catastrophic outburst floods. Any sustainable use and effective hazard mitigation of large glacier lakes thus require a deeper understanding of their geomorphic setting and long-term dynamics.
Using a global catalogue of large lakes mapped within 10 km of contemporary glaciers (Zhang et al., 2024), we find that large lakes comprised only 3.8% (n = 2,781) of global lake abundance in 2020 but accounted for 77% of the total lake area. While the total area of large lakes has grown by 35% overall since 1990, only 14% of individual lakes have significantly expanded. By contrast, the majority remained either stable (73%) or even shrank (13%), suggesting that large glacier lakes can be persistent features in high mountain landscapes. Greenland, Arctic Canada, Patagonia, Alaska, and Western Canada host three-quarters of these lakes, often in low-relief, widely deglaciated catchments disconnected from their parent glaciers. More than half of all large lakes are surrounded by tundra, forests, or grasslands, likely reducing geomorphic activity on adjacent slopes. Where Little Ice Age (LIA) glacier outlines are available, we observe that large lakes have formed both before (e.g., Scandinavia, European Alps) or after (e.g., Southern Andes, Himalayas) this period. Importantly, only a handful of large proglacial lakes had historic outbursts, underscoring their stability on centennial timescales.
Average erosion rates in their feeding catchments suggest that many large lakes may persist for another 103–105 years before being entirely filled with sediments, all other constraints held constant. While some large lakes may still occasionally produce catastrophic outbursts, our analysis points to the smaller, disproportionally more abundant lakes in similar geomorphic settings, which have a comparable, if not higher hazard potential. These findings call for focused research on the dynamics of these smaller glacier lakes to better inform hazard assessments and mitigation strategies.
How to cite: Veh, G. and Carrivick, J.: Stable giants? Persistence and hazard potential of world's largest glacier lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19424, https://doi.org/10.5194/egusphere-egu25-19424, 2025.
An often quoted type example of the adaption of a geomorphic system due to external forcing, can be found in south-eastern Tibet. In this area, it is hypothesised that uplift of Tibet resulted in a major drainage reorganisation; prior to plateau uplift, it is proposed that a continental-scale drainage network including the upper Yangtze, Mekong and Salween, used to flow into the palaeo-Red River (Clark et al, 2004). Since documentation of the timing of uplift of Tibet is important to understanding broad research questions related to crustal deformation processes and the impact of the Himalaya-Tibet orogen on climate, the evolution of this geomorphic system is well studied. Yet the timing of proposed drainage reorganisation is still debated, with a range of suggested timings between Eocene and Pleistocene, if indeed major reorganisation occurred at all.
The most commonly used approach to determining the timing of this proposed drainage reorganization involves source to sink provenance studies, with interrogation of sedimentary archives. Using this approach, the majority of studies have used detrital zircon U-Pb dating as a provenance tool. Proposed recognition of “characteristic” zircons of upper Yangtze provenance in the palaeo-Red River archive, and their subsequent disappearance up section, has been used to argue that the upper Yangtze used to flow into the Red River, with subsequent river capture of the upper Yangtze away from the Red River into its present course due to Tibetan plateau uplift.
In order for this approach to document river capture, the detrital zircon U-Pb signature of the upper Yangtze must be identifiable in the palaeo-Red River repository. Previous compilations used to characterise the zircon U-Pb signatures of the various contributing terranes to the upper Yangtze and Red River drainage basins were largely comprised of data from igneous rocks. However, this neglects the contribution of zircons from older sedimentary rocks of these terranes. We compiled all published detrital zircon U-Pb data (n=29,545) from Late Triassic and younger sedimentary rocks from these terranes (Li et al, 2024). Our compilation shows that the zircon U-Pb spectra from these various terranes are similar, and there is no unique characteristic of the upper Yangtze. Therefore the similarity in zircon U-Pb signature between the upper Yangtze region, and Cenozoic rocks from palaeo-Red River basins may result from similarity in the various local hinterland source regions, rather than requiring that the upper Yangtze used to flow into the Red River.
This case study highlights the importance of consideration of the adequacy of source region characterisation and the impact of recycling, when using sedimentary archives to document geomorphic evolution.
How to cite: Li, S., Najman, Y., Vermeesch, P., Barfod, D., Millar, I., and Carter, A.: A critical appraisal of the interrogation of sedimentary archives to investigate the proposed forcing of drainage network reorganisation by plateau uplift in Southeast Tibet., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1400, https://doi.org/10.5194/egusphere-egu25-1400, 2025.
The sedimentary record of fluvial systems is crucial for understanding the impact of climate change on landscapes over time. While fluvial dynamics in temperate and arid/semi-arid regions have been well-studied, research on Quaternary fluvial processes in tropical mountainous areas is still limited. This study proposes an evolutionary model for the piedmont regions of the Eastern Andean Cordillera, on Caquetá (1°N) and Guaviare (4°N) rivers basin in Colombia, which are characterized by increased tectonic activity in the northern part of the region during the late Cenozoic. We employ a combination of geomorphological mapping and luminescence dating (OSL and IRSL) to investigate sediments forming alluvial fans and river terraces. Our results reveal three levels of river terraces and three alluvial fan units in the Caquetá River basin, as well as eight river terrace levels and six alluvial fan units in the Guaviare River basin. The sedimentary deposits of the alluvial fans and river terraces in both areas are primarily coarse-grained, dominated by conglomerates and sandy-conglomeratic units (Gm, Gt, Sgm). The floodplains of the Caquetá River are composed mainly of fine-grained sediments (silt and clay). In contrast, the Guaviare River floodplains are predominantly coarse-grained and conglomeratic. This difference is attributed to increased tectonic activity in the northern region, which has intensified erosion and sediment transport. The OSL dating in the Caquetá River basin has allowed the identification of three evolutionary phases: (i) 120 to 65 ka, marked by active alluvial fans with braided distributary channels; (ii) 65 to 15 ka, characterized by valley incision and drainage reorganization, leading to the formation of tributary networks like modern systems; and (iii) the last 15 ka, dominated by low terraces and meandering floodplains. In the Guaviare River basin, OSL and IRSL data suggest that the distributary system remained active from at least 300 ka to 50 ka, with floodplains forming during the early Holocene (10 ka). Tectonic activity, including faulting, has also been recorded on river terraces (4°N) dating to at least 110 ka. Paleoenvironmental and palynological data indicate that the shift from distributary to tributary systems is linked to changes in precipitation patterns in the Northern Tropical Andes, driven by the shifting position of the Intertropical Convergence Zone (ITCZ) due to insolation cycles. Decreased rainfall, associated with northern ITCZ positions, supported alluvial deposition in both distributary and tributary systems. A phase of valley incision during MIS 3, followed by a reduced precession and obliquity signal amplitude, promoted the transition to a more stable landscape with a dominant tributary fluvial pattern. The integration of cosmogenic nuclides (10Be and 26Al; in preparation), alongside OSL and IRSL dating, will further enhance our understanding of paleo-erosion and erosion rates, improving the robustness of the proposed paleoenvironmental model for the Colombian Eastern Andean Cordillera. (FAPESP grant #2021/14947-6)
How to cite: Breda, C., Bookhagen, B., Parra, M., Sawakuchi, A., Cruz, C., Souza, P., Monsalve, G., Cardona, A., and Pupim, F.: Fluvial Evolution of the Eastern Andean Piedmont: Late Quaternary Sedimentary Records from the Caquetá and Guaviare Rivers, Colombia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6916, https://doi.org/10.5194/egusphere-egu25-6916, 2025.
It is hypothesized that lithospheric reorganisation, including slab breakoff and tearing, leads to shifts in crustal buoyancy, which then influences rock uplift, erosion and weathering on the surface. This process can be ideally studied in compressional orogenic settings with complex fluvial drainage systems, such as the European Alps. Changes in uplift and erosion can be studied using sedimentary provenance techniques, such as major element geochemistry and petrographic point counting. First we use modern-day fluvial sands to understand how major element geochemistry and petrography reflect the modern erosional pattern of the Alps. In a second step, the signatures of modern river sands are compared to those of sandstones deposited in the Alpine foreland basin, which was a major sedimentary sink throughout the Oligocene and Miocene.
Here, we present two datasets consisting of major element geochemistry (ca. n=180) and petrography (ca. n=200) data of modern Alpine rivers. We use smaller rivers draining specific source rock types within the orogen to define geochemical and petrographic end-member lithological fingerprints. These fingerprints are subsequently used to deconvolve via unmixing modeling 9 larger fluvial drainage basins in the Alps: the Adige, Dora Baltea, Drau, Enns, Inn, Mur, Rhine, Rhone andSalzach rivers. We compare themodeled relative contributions of specific source rocks/areas with the modern-day erosion patterns in those drainage basins based on geological maps and published erosion rates. The comparison with detrital spectra in foreland basin deposits provides insights into the change of watershed locations and river networks from the Miocene to today.
How to cite: Neofitu, R., Stutenbecker, L., Glotzbach, C., and Falkowski, S.: Orogen-wide erosional patterns in the Alps: Insights from unmixing modeling of modern-day and Miocene orogenic fluvial sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12268, https://doi.org/10.5194/egusphere-egu25-12268, 2025.
Hillslope and channel processes in upland catchments combine to erode landscapes and release sediments. This underpins the genetic link between sediment generation and landscape drivers, such as tectonics and lithology, mediated by hillslope and channel processes; however, this link has yet to be thoroughly analysed from a process-based framework. Here, we focus on two well-constrained catchments in terms of tectonics and lithology in the Gulf of Corinth, Greece, to track how tectonic and lithological impacts on sediment grain size are translated through channel and hillslope processes. Topographic analysis reveals that both tectonic forcing and lithological variations can be translated into topography through bi-directional hillslope-channel couplings. In catchment 1, normal faulting initiated >600 ka is manifested by steepened hillslopes and concentrated mass wasting downstream of knickpoints. In catchment 2, which is perturbed only by active faulting <100 ka, the stronger and mass-wasting-prone bedrock steepens hillslopes and triggers pervasive mass wasting. Combined with the observation that mass wasting produces coarser grains, our data therefore show that both tectonic and lithological forcing are expressed in sediment grain size at the hillslope scale. However, if the bedrock is friable, tectonically induced coarsening of hillslope sediments can be erased by intense abrasion after they reach river channels. This is well-illustrated in catchment 1, where sandstone-siltstone-dominated tributaries do not export coarse sediments, despite intensive mass wasting driven by knickpoints. In contrast, lithologically controlled coarsening of hillslope sediments is preserved in catchment 2, as the sediments in this catchment are resistant to abrasion. In both catchments, selective transport filters out hillslope sediments coarser than the threshold for entrainment, but its impact attenuates rather than obliterates the forcing imprinted in coarse sediments. This non-obliteration effect arises because coarse sediment input itself can increase the entrainment threshold by influencing channel steepness. In short, our study demonstrates the central role of hillslope and channel processes in transmitting tectonics and lithology into sediment grain size.
How to cite: Zhou, Z., Whittaker, A., Bell, R., Hampson, G., Chandresh, R., Watkins, S., and Zondervan, J.: Tracking tectonic versus lithological impacts on sediment generation in catchments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10963, https://doi.org/10.5194/egusphere-egu25-10963, 2025.
A number of outstanding ring-shaped geological landforms have been known from the central Mologa-Sheksna Lowland (NW Russia), closely contouring the presumed local margins of the Ostashkov (Late Weichselian) glaciations advance, settled within the lacustrine-alluvial bogged plains. Visual examination of these landforms does not provide clear evidence on their genesis in frames of the accepted regional palaeogeographic context.
The “Bor-Timonino” (3.5 km across) and “Yana” (250 m across) sites are most well-preserved ring-shaped landforms in the contemporary relief, exhibit circling slightly elevated sand rims and flat-disk central parts filled with water and peat, respectively.These two landforms were investigated in 2018-2021 using ground penetrating radar (GPR), electric resistivity tomography (ERT), transient electromagnetic method (TEM), magnetic survey (MS) and auger drilling. The results show no clear correspondence of electric and magnetic properties of the constituent Quaternary deposits to the visible surface symmetry of the landforms. Only within the upper 5-10 m of the “Bor-Timonino” site, sandy rim base was traced uniformly around the landform, thus repeating its symmetry. In the deeper part of the section (down to 100 m) no structural patterns corresponding to the present-day relief were observed; it represents the sequence of practically undisturbed layers. A thin (10-30 cm) layer of buried peatsoil has been discovered at depth range of about 1.5 – 4.5 meters below ground surface at several sites within and beyond the ring-shaped landforms, overlain by the sandy deposits of the rims. This peatsoil has Late Glacial age (13.4 – 12.4 cal. ka BP), which indicates that the “Bor-Timonino” landform is presumably older.
Supported by the regional geological setting, several apparent ways of the ring-shaped landforms’ origins are suggested, i.e., cryogenic, fluvial, glacial or their combinations. It is possible, though not supported by direct evidence, that late Paleozoic paleokarst occurrences could have caused sinkhole formation at an early stage, which subsequently had been undergoing transformation leading to the ultimate appearance of “rim-disk” landforms. Impact, tectonic or volcanic processes are perceived to be unlikely to form such objects.
Nevertheless notable geophysical investigation has been carried out, there is no certainty about genesis of the ring-shaped landforms of the Mologa-Sheksna Lowland. Additional drilling of sand rims and terraces with subsequent lithological, geochronological, geochemical and mineralogical analyses are necessary to progress in this research. Except for their significance for fundamental geology or paleogeography, the ring-shaped landforms also wield great potential as prime sites of regional geoheritage, which is enforced by their position on the territory of Darwin Nature Biosphere Reserve.
How to cite: Sadokov, D., Bobrov, N., and Karpinskiy, V.: Geophysics, geology and geomorphology: controversial data on the provenance of ring-shaped landforms on the East European plain, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12603, https://doi.org/10.5194/egusphere-egu25-12603, 2025.
Coastal plains act as significant carbon sinks where they accumulate organic material in extensive peatlands. Coal-bearing stratigraphy thus provides a crucial paleoclimatic archive for carbon cycle dynamics over geological time. To better understand the rate of carbon uptake from the atmosphere into the terrestrial biosphere we turn to the geological record. Our aim is to investigate whether upstream climate forcing, or downstream climate-induced sea-level fluctuation acted as fundamental control on deposition in ancient paralic peatlands. Such potential allogenic controls need to be disentangled from autogenic forcing which is often prevalent in paralic successions. To filter out allogenic controls on coal-bearing stratigraphy we study the spatial extent, chronology (by means of magnetostratigraphy), isochronicity, and facies architecture of coal-bearing successions in the geological record.
Our work focusses on the Paleocene Fort Union Formation exposed in Eastern Montana and Western North Dakota (Williston Basin, USA). This formation is remarkable because facies associations remain strikingly uniform over 100’s of km’s distance, across proximal to distal transects. We focus on the lowermost Ludlow Member, exposed in the Little Missouri River Valley (ND) and across the northeastern flank of the Cedar Creek Anticline (MT). We use a combined approach of magnetostratigraphic correlation and sedimentological facies comparison to constrain the extent and temporal evolution of changing landscapes reflected in the studied stratigraphy. We show that distinct facies changes occurring in the Ludlow Member over stratigraphic thicknesses of only a few meters to a few tens of meters are laterally continuous and traceable over 100’s of km’s. Such findings have implications for understanding the sensitivity of peat-forming landscapes to short-lived climatic or eustatic changes and can ultimately inform us about the rates and volumes of carbon that gets sequestered in the terrestrial biosphere during distinct phases of changing climate or sea-level.
How to cite: van Dijk, G., Abels, H., Cuperus, M., Hilgen, F., Krijgsman, W., Maars, J., de Vries, S., and Kuiper, K.: The response of paralic peatlands to short-lived climatic or eustatic events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16764, https://doi.org/10.5194/egusphere-egu25-16764, 2025.
Lake sediment cores reflect changing climate conditions as well as the complexities of spatial sediment sourcing, transport and deposition. In alpine valleys, glacier advance and retreat is often the primary driver of sediment flux. The source region of transportable sediment within the basin (valley floor, hillslopes, glacier headwall, channels) also evolves with the glacier footprint and therefore with climate. Runoff and sediment transport is likely to be enhanced due to ice loss during glacial retreat. Sediment transport and deposition in proglacial lakes near human infrastructure may complicate interpretation of lacustrine records. A sequence of lakes within two major valleys in the Many Glacier region of Glacier National Park, Montana, USA have multiple sediment sources which include glacial erosion, hillslope processes, and fluvial environments between lakes. In addition, the arrival of Euro-Americans in the region and the creation of a National Park with its concomitant infrastructure and visitation has likely affected sedimentation. We focus on a transect of cores from Fishercap Lake in the Swiftcurrent Valley to better understand variability in deposition rates and sources in the lake during the late Holocene and into the present, and compare this to sedimentation in adjacent (upstream and downstream) lakes to better understand the role of basin hypsometry and human impacts on subalpine valleys.
Fishercap Lake is less than 0.25 square km, shallow (~0.8 m), with a dense gravel layer less than a meter below the sediment-water interface that is uniform across the lake. Ground penetrating radar shows the gravel layer is a complex braided channel, reflecting a period of lake desiccation. Radiocarbon ages at the gravel unit are between ~1300-1660 AD; the most upvalley reach of the lake is 1-m deep with a basal age of 4400 radiocarbon years. High resolution C/N analyses of this core show changing organic sources over the late Holocene in response to climate variability during this time. Lead-210 ages in Fishercap Lake and two adjacent lakes show sedimentation rates are significantly higher in the last two centuries in all three lakes compared to late Holocene rates. Differences in the depositional records likely reflect lake morphology, basin hydrology, glacier proximity and geomorphic sources of sediment, despite identical climate forcing during this time. These observations have implications for our interpretations of lake core records of climate change in alpine valleys.
How to cite: MacGregor, K. R. and Myrbo, A.: Patterns of deposition in subalpine lakes during the late Holocene and Anthropocene, Glacier National Park, Montana, USA, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3787, https://doi.org/10.5194/egusphere-egu25-3787, 2025.
Sedimentary systems are affected by environmental conditions. Given current global warming, accurate predictions of the sensitivity of Earth surface processes to climate are urgently needed. To do so, the geological record provides various climate events from which we must read the narratives of how surface processes have adjusted.
Here, we take the example of the Paleocene-Eocene Thermal Maximum (PETM, ~ 56 Ma), the Cenozoic's most rapid and intense global warming. This event was caused by a massive release of carbon into the atmosphere, which led to global temperature rises of 5-8°C and hydroclimate disruptions. In turn, increased erosion rates and sediment transport are hypothesized from worldwide observations of siliciclastic progradation in the oceans and coarser sediments recorded in the alluvial plains. We need to quantify the increases in sediment flux and track the propagation of this Qs response signal from mountainous catchments to the oceans.
The PETM is well-recorded in the South Pyrenean Foreland Basin, from alluvial to oceanic depositional environments. These settings allow an integrative study of the response of sedimentary systems to the PETM from source to sink. First, a doubling of the sediment fluxes from the hinterland catchment is calculated from sedimentary volumes deposited and preserved in the Tremp basin, located at the foothill of the Pyrenees. Erosion models indicate that this doubling in sediment flux likely resulted from a doubling of the intensity of extreme rainfall events, with a minor impact from mean annual precipitation rates and temperatures.
The propagation of the hinterland Qs response signal to the alluvial plain is studied from fluvial channels in three localities in the Tremp Basin. The adjustment of the morphology of fluvial channels to the PETM varies from the Claret axial system to the Esplugafreda and Serraduy transverse systems. However, the total channel belt of all three systems widened by a factor of 8 during the PETM global warming. Moreover, paleohydraulic reconstructions indicate a 1.8-fold increase in flood-related bedload sediment flux. Therefore, the Qs signal of coarse sediments is slightly buffered downstream. On the contrary, enhanced channel mobility led to a 3-fold increase in the delivery of fine-grained sediments to the ocean during the warming event (Prieur et al., 2024). Therefore, the propagation of the PETM-related Qs signal along the South Pyrenean sedimentary system was enhanced due to increased dynamics of fluvial systems.
This integrative study shows the global response of a sedimentary system to a climatic perturbation from source to sink. Extreme rainfall events mainly drive the sensitivity of hinterland erosion, and this signal propagates to the alluvial plain and the ocean, implying modifications of the sedimentary systems' morphology and dynamics. Analog quantitative studies focusing on various climate changes worldwide are needed to frame the sensitivity of sedimentary systems to global warming.
This research was funded by the S2S-FUTURE European Marie Skłodowska-Curie ITN (grant agreement No 860383).
Prieur et al. (2024) Fingerprinting enhanced floodplain reworking during the Paleocene-Eocene Thermal Maximum in the Southern Pyrenees (Spain): Implications for channel dynamics and carbon burial. Geology, 52(9), 651-655. doi: 10.1130/G52180.1
How to cite: Prieur, M., Jaimes-Gutierrez, R., Robin, C., Whittaker, A. C., Braun, J., Fillon, C., Schlunegger, F., Sømme, T. O., and Castelltort, S.: Landscape sensitivity to global warming and signal propagation from source to sink: An integrative study of the PETM in the Southern Pyrenees (Spain), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17769, https://doi.org/10.5194/egusphere-egu25-17769, 2025.
We present the largest river intermittency dataset to-date, and the first to document both water and sediment transport intermittency globally. River intermittency describes the ratio between long-term average and instantaneous maximum transport rates of water or sediment (Paola et al., 1992). It is an important way of quantifying the distribution of river activity through time, and is especially useful when interpreting the frequency of threshold-surpassing events in the geologic past. Patterns of sediment flux are key to understanding transient landscape response to external drivers such as climate change in the past or future. But sediment intermittency is much more challenging to estimate than water intermittency, and interpretations of stratigraphy are limited without absolute constraints on modern-day intermittency.
Using a range of inputs from published datasets and empirical-theoretical transport models, we calculated and compiled water and sediment transport intermittency factors for over 300 river reaches worldwide. This new dataset spans 6 continents and all climate zones except polar, and describes discharge rates, catchment and bed characteristics, and planform morphology, among other geomorphic variables. We find that sediment transport intermittency factor (Is) is significantly more variable than water discharge intermittency factor (Iw) worldwide. Both Is and Iw behave as a predictable function of climate zone, with rivers in arid and cold climates more intermittent (lower Is and Iw) than those in tropical and temperate climates. However, river planform dominates the control on sediment intermittency. Braided rivers are on average 100x more intermittent than meandering rivers: with increasing channel count, Is values become consistently lower. This raises important questions about the connections between fluvial morphology, climate and the rates and patterns of transport, and demonstrates the extent to which river planform is intrinsically linked to geomorphic response to environmental change.
How to cite: McLeod, J., Ganti, V., Whittaker, A., Bell, B., Hampson, G., Slater, L., and Liu, Y.: Intermittent World: A Global Analysis of River Water and Sediment Intermittency , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10386, https://doi.org/10.5194/egusphere-egu25-10386, 2025.
