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.

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 (I_s) is significantly more variable than water discharge intermittency factor (I_w) worldwide. Both I_s and I_w behave as a predictable function of climate zone, with rivers in arid and cold climates more intermittent (lower I_s and I_w) 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, I_s 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.