GM1.4

Sedimentary dynamics and fluxes are influenced by both autogenic and allogenic forcings. A better understanding of the evolution of sedimentary systems through time and space requires us to decipher, and therefore to characterise, the impact of each of these on the Earth’s landscape. Given the current increase in the concentration of atmospheric carbon, studying the impact of rapid and global climate changes is of particular importance at the present time. Such events have been clearly defined in the geologic record. Among them, the Paleocene-Eocene Thermal Maximum (PETM) has been extensively studied worldwide and represents a possible analogue of the rapid current climate warming.

The present project focuses on the Southern Pyrenees (Spain) where excellent exposures of the Paleocene-Eocene interval span a large range of depositional environments from continental to deep-marine. These conditions allow us to collect data along the whole depositional system in order to document changes in sediment fluxes and paleohydraulic conditions. Because hydrological conditions have an impact on sediment transport through hydrodynamics, paleoflow reconstructions can shed light on changes in sediment dynamics. This information is reconstructed from the statistical distributions of channel morphologies, characteristic system dimensions including bankfull channel depth and width, and grain-sizes.

With this approach, our aim is to provide both qualitative and quantitative assessments of the magnitude and extent of the perturbation of sedimentary fluxes along an entire source-to-sink system during an episode of extreme climate change. This will lead to a better understanding of the impact of abrupt climate change on earth surface systems in mid-latitudinal areas, with possible implications for current climate adaptation policy.

This research is carried out in the scope of the lead author’s PhD project and is part of the S2S-FUTURE European Marie Skłodowska-Curie ITN (Grant Agreement No 860383).

How to cite: Prieur, M., Whittaker, A. C., Schlunegger, F., Sømme, T. O., Braun, J., and Castelltort, S.: Impact of extreme hydrological perturbation on sediment distribution from source to sink, PETM, Spain., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7032, https://doi.org/10.5194/egusphere-egu21-7032, 2021.

The Black Sea-Caspian Sea region is a vast and geomorphologically variable area where sea level changes, large rivers and their migration, and numerous interacting climate systems and aeolian regimes lead to a highly dynamic and complex situation of sediment supply and reworking. The area is blanketed by extensive loessic and sandy aeolian deposits, extending from northern Iran, through the Caucasus piedmont, Caspian lowland, and into the Crimea and East European Plain, as well as marine, fluvial and alluvial sediments. While loess deposits are especially extensive adjacent to major rivers such as the Volga, Don and Dnieper, the provenance, transport and nature of loess in this complex and highly dynamic environment remains poorly known.

Both, the Black Sea and the Caspian Sea experienced several transgressive and regressive phases during the Pleistocene, with temporary connections occurring over the Manych passage and resulting in the formation of marine terraces over a wide area, which are dry at present. The sea levels of the Caspian and Black seas and long-range north to south sediment transport are heavily influenced by the great rivers draining the previously glaciated East European Plain, the Volga, Don and Dnieper. In addition, the Black Sea and Caspian Sea are surrounded by mountain ranges, with the Carpathians in the west, the North Anatolian Mountains south of the Black Sea, the Crimea-Caucasus orogen and the Alborz mountains extending from northeast of the Black Sea to south of the Caspian Sea, all of which may act as sediment source regions. Furthermore, more distal orogens lying to the east, such as the Ural, Altai, Pamir and Kopet-Dag, and their palaeo-drainage systems, also represent potential sediment source areas for the Caspian Sea basin. The Karakum desert lying to the east of the south Caspian combines the potential of being a sediment sink for material from these mountains, as well as a secondary source for the Caspian Sea and the large loess area in northern Iran.
Here we apply U-Pb dating of detrital zircons to constrain the major sediment generating regions in this large area, transport pathways, and to further address the implications for sediment generation and cycling. In addition to loess, we aim to constrain the sediment transport pathways both for fluvial, marine and aeolian systems more generally, and to reconstruct the network of sediment routing in the Black Sea-Caspian Sea region. Our results reveal great spatial variability in zircon provenance and indicate the contribution of multiple source regions and transport pathways for most analysed samples and sites. Rivers have the strongest control on sediment erosion and distribution and are also in control of aeolian deposits, while not much sediment mixing seems to occur within the sea basins.

How to cite: Költringer, C., Stevens, T., Lindner, M., Baykal, Y., and Kurbanov, R.: Quaternary sediment sources, sinks and transport pathways in the Black Sea-Caspian Sea region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4124, https://doi.org/10.5194/egusphere-egu21-4124, 2021.

The Patagonian Andes were subject to a range of geophysical drivers of landscape incision during the Last Glacial Interglacial Transition and Early Holocene, including tectonic and isostatic uplift, and base level fall triggered by rapid lake drainage events. Deciphering the drivers of river system response during this period is complex, and magnitudes and timescales of landscape change are poorly constrained. Herein, a remotely sensed time series of modern lake elevation change and terrace development is investigated for the Laguna del Viedma valley (Argentina) as a modern analogue of Late Quaternary landscape evolution. The aim of the research was to constrain the timing of terrace formation following lake-level fall of the Laguna del Viedma over a ~35 year period from 1985-2019. The objectives were to: 1) use satellite imagery from the period 1985-2019 to document landform, glacier and lake changes in the study area; 2) use remotely sensed imagery to map the landforms of the Laguna del Viedma valley; and 3) analyse terrace elevations using GIS. In total 7 terrace surfaces were distinguished by remotely sensed geomorphological mapping. The highest, and vegetated, T1 terrace surface (+75 m) was likely formed at the end of the last Holocene neoglacial advance. Viedma glacier recession at this time caused the abandonment of an ice-lateral spillway and allowed a subglacial drainage pathway leading to less stable lake level elevations and terrace formation. Whether the abandonment of T1 was associated with the 4 ka or 0.15 ka neoglacial termination constrains ~45 m of incision, at a rate of 0.01-0.33 m/yr, down to the T3 floodplain level by 1985. There then followed ~20 m of incision to the T4 level, which must have occurred by 2006, constraining a minimum rate of incision of 0.95 m/yr. The time series demonstrates rapid terrace formation occurred by vertical incision and lateral erosion, with mass movements contributing to lateral terrace recession. The implications of the data-set are discussed within the context of the Late Quaternary palaeohydrology of Patagonia where lake level falls of 10s to 100s of metres occurred within most large river systems from 42-52 ⁰S demonstrating that base level falls from lake drainage, and catastrophic floods events, were likely a major driver of landscape change in the region.

How to cite: Thorndycraft, V.: Remotely-sensed time series of rapid terrace formation in the Laguna del Viedma valley (Patagonia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14866, https://doi.org/10.5194/egusphere-egu21-14866, 2021.

In the relatively short and steep catchments of New Zealand’s Alps and Front Range, river systems traverse several process domains, from steep boulder-bed cascades to shallower braided range-front streams. Headwater streams (slope gradient >0.1 m·m^-1) typically operate in a state of ‘supply limited’ conditions, where the river’s ability to carry sediment far exceeds the supply of material from upstream. With the catastrophic delivery of 13M m³ of landslide detritus following the 2016 7.8 Mw Kaikōura Earthquake, a tributary of the upper Hapuku River was filled to depths of up to 30 m, as debris spilled 1 km downstream from the delivery point. Nine airborne LiDAR surveys along the 12 km corridor have captured the transformation of the system from step-pool cascade to an unstable aggrading braidplain deposit to a vigorously incising channel, within four years of the event. With this rare window into disequilibrium conditions, we document the dramatic shifts in channel behaviour and dramatic reworking of the debris train following the landslide. There are two distinct phases: (1) a highly dynamic and unstable aggradation phase, with supply from upstream greatly exceeding river transport capacity and (2) exhaustion of supply from upstream and downcutting, maintaining high sediment transport rates through recruitment of material in the valley deposit. With a catchment area of only 3 km², the upper river has transferred more than 4.2×10⁶ m³ of coarse-grained material in 9 storm events of relatively modest intensity. This sequence of surveys provides an unprecedented picture of dramatic changes to a steepland river system in the aggradation/degradation cycle, which are very seldom captured owing to both the remoteness of such sites and the relative rarity of such events. A temporal picture of the valley sediment budget demonstrates the remarkable capacity of alpine systems to absorb disturbance through storage in the upper reaches, modulating the timing and the sedimentary character of materials being transferred to the reaches downstream. The case study highlights the utility of repeat LiDAR surveys for large-scale process studies and provides insights for assessing residence times of major landslide deliveries following large earthquake events.

How to cite: Tunnicliffe, J., Howarth, J., and Massey, C.: The transformation of a steepland river valley following an earthquake-triggered landslide near Kaikōura, NZ, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10867, https://doi.org/10.5194/egusphere-egu21-10867, 2021.

The understanding of the interplay between natural and human induced factors in the occurrence of landslides remains poorly constrained in many regions, especially in tropical Africa where data-scarcity is high. In these regions where population growth is significant and causes changes in land use/cover, the need for a sustainable management of the land is on the rise. Here, we aim to unravel the occurrence of landslides in the 40 km-long Ruzizi gorge, a rapidly incising bedrock river in the Kivu Rift in Africa that has seen its landscape disturbed over the last decades by the development of the city of Bukavu (DR Congo). Careful field observations, historical aerial photographs, satellite imagery and archive analysis are combined to produce a multi-temporal inventory of 264 landslides. We show that the lithological context of the gorge and its extremely high incision rate (> 20 mm year^-1) during the Holocene explains the presence of a concentration of large landslides (up to 2 km²) of undetermined age (well before the first observations of 1959) whose occurrence is purely natural. They are mostly of the slide type and do not show morphologic patterns of recent activity. The landslides that occurred during the last 60 years are flow-like shallower slope failures of smaller size (up to 0.12 km²) and tend to disappear rather quickly (sometimes within a few years) from the landscape as a result of rapid vegetation growth, land reclamation and (human-induced) soil erosion. They are primarily related to threshold slopes and precipitation plays a frequent role in their onset. However, land use/cover changes also affect their occurrence. This study provides useful information for a more accurate evaluation of the landslide hazard in the area, particularly with respect to the growth of the city of Bukavu that has developed without the consideration of naturally instable slopes. It also stresses the need and added value of building accurate landslide inventories in data-scarce regions.

How to cite: Mugaruka Bibentyo, T., Dille, A., Depicker, A., Smets, B., Vanmaercke, M., Nzolang, C., Dewaele, S., and Dewitte, O.: Landslides, river incision and environmental change: the Ruzizi gorge in the Kivu Rift, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11067, https://doi.org/10.5194/egusphere-egu21-11067, 2021.

The mechanisms of high-speed and long-runout landslides are mainly reflected in the geomorphological morphology and internal sedimentology of the deposits. The geomorphic and sedimentary characteristics of ancient Dora Kamiyama rockslide in Tibet Plateau was discussed based on field investigation and multidisciplinary tests. The landslide area is divided into three zones: the source area (I), the translation area (II), and the accumulation area (III). Geomorphic features include toreva block, the levee, the transverse ridge, the longitudinal ridge, the hummock and the ridge confined by troughs and the carapace composed of giant blocks were analysed,which are considered as indicators of the dynamic process of the landslide during transport. 3 stages of the rockslide dynamic motion were proposed, including extensional, compressional and radial motions, respectively. Sedimentary features of facies in the rockslide was revealed, including carapace facies, blocky facies, fragmented facies, shear zones, and basal mixed zones, the mineral change process of the rockslide during the movement process and the temperature change of the sliding surface can be obtained based on analyzing the minerals change near the shear zone. The temperature field of the landslide and its movement process can be reconstructed through the temperature change of the shear zone. The results show that frictional heating was generated during complex dynamics interactions. The friction temperature generated by sliding near the fragmented facies was about 870–1470 °C. Based on sedimentary evidence, the dynamic evolution of the rockslide in response to temperature changes were reconstructed based on frictional thermal analysis.

How to cite: Yang, Z., Liu, S., Wang, L., Liu, G., and Fu, X.: Geomorphic and sedimentary characteristics of ancient Dora Kamiyama rockslide in Tibet Plateau - implications of dynamic process and frictional heating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-531, https://doi.org/10.5194/egusphere-egu21-531, 2021.

The present contribution is centred on (1) a need of paradigm and methodological shift for transported sediment volumes, due to the advent of point-cloud technologies and (2) an attempt of solution for debris-flow and heterogeneous material.

Point-cloud technologies such as terrestrial and aerial LiDAR and photogrammetrically-based data have broken the inverse correlation between resolution and space-scale. Indeed, defining landforms at a centimeter vertical and horizontal scale, along several tens of kilometers was until very recently a pandora box, which both acquisition technologies and the democratization of computing capacity have allowed scientists to open. Unexpectedly, new challenges and the need to shift some of the traditional paradigms have emerged. In the present contribution, the author asks the question of whether the faithful tandem "topographic change and erosion/deposition" needs a revisit or not. The hypothesis of this question is imported from soil engineering, where questions of compaction and decompaction are essentials (and well understood). In other words, when sediments and soils are being eroded and redeposited, does the relation between erosion and deposition holds when using high-resolution topography? To this first question, the author then proposes one solution (already explored with TLS) using SfM-MVS photogrammetry to measure in-situ the density of heterogenous

Using simple laboratory experiments on different sediments to simulate (a) the effects of compression/decompression, and (b) the effects of self-comminution during transport, the author demonstrates that material fragmentation, and abrasion modifies the shape of the particles and their size resulting in variable bulk-volumes (as defined by the topography) for similar level of deposition energy, and that this volume change even further when the relay of processes are differentiated, resulting in further variation in the topographically measured volumes. In other words, the result show that high-resolution topography and topographical change does not signify high-resolution volumetric change, both in term of bulk and solid-phase volumes. It therefore appears that Geomorphology and Earth-Surface Processes Research need to integrate the use of soil density estimates from field-survey and also in the relay of processes model (i.e. should we expect compaction or decompaction from one type of deposit to another, and is the sediment transport modality expected to modify the shape and size of sediments significantly?).

Finally, the author presents one of the tool he has been working on for environment where compaction and decompaction is important: the transition between rockfalls/debris-flows/pyroclastic-flows and debris-flows, fluviatile flow in heterogeneous media. The author shows how SfM-MVS photogrammetry can be used to replace the sand-cone density estimation method with a higher-fidelity and an estimate of calculated error. Using “reverse-engineering”, this density calculation method combined with high-resolution topography could be used to then estimate and defines the transport modalities of sediments from one location to another.

How to cite: Gomez, C.: The Need to Develop Compression and Decompression Data for Geomorphologists to Improve Sediment Volume Estimates from High-Resolution Topographic Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3593, https://doi.org/10.5194/egusphere-egu21-3593, 2021.

The key to an efficient basin management, taking into account both the liquid (river water runoff and its quality) and the solid (sediment sources and delivery) components lies in the way we approach the complex problem of sediment-generating areas in a river basin. This complexity is manifested both through the primary geomorphological processes that contribute to the mobilization of significant amounts of alluvia from the slopes and along the river valleys, and the various environmental and anthropogenic factors that act as restrictors or catalysts of sediment transfer.

In the present study, we aim to analyze the various categories of anthropogenic factors, operating at different spatial scales (local or at subcatchment/river sector level), which contribute, together with the intrinsic geomorphological potential, to the sediment supply or, conversely, to the inhibition of erosion, transport and accumulation processes.

Tracking sediment mobilization, transfer, intermediate storage and final delivery in a lithologically and geomorphologically complex environment, such as the Jiu River Basin (10,070 km²), located in SW Romania, is a difficult task which can become even more challenging when we factor in the contribution of some additional elements of an anthropic nature. In our study area, represented by a Carpathian and Danubian river basin, some of the most significant issues impacting the research include, on the one hand, the existence of reservoirs and dams, the strengthening of anti-flood embankments or the presence of water diversions, to cite only hydrotechnical interventions, or the impact of coal mining on landforms, slope processes and sediment sources, on the other hand.  All these factors can act locally or regionally and they can surpass the influence exerted by the natural factors, thus being responsible for the reduction, storage, or, on the contrary, for the acceleration of specific hydro-sedimentary fluxes on certain paths.

In order to connect these two categories of potential factors regulating sediment generation and transfer, the methodological approach consists in evaluating the internal – geomorphic upstream-downstream connectivity in relation/contrast with the disruptive anthropogenic factors. The proposed workflow can be divided in two steps: 1) the identification of the upstream sediment generating areas which are most connected to the downstream delivery/ storage/ accumulation areas (river network and river mouth) by applying the connectivity index (IC) proposed by Cavalli et al. (2013); and 2) the evaluation of potential hotspot areas exhibiting the highest degree of connectivity, as seen through the lens of the additional coupling or decoupling effects induced by the anthropic activities specific to the Jiu river basin: hydraulic structures and coal mining.

Outcome discussions will focus on mapping problematic sediment production, storage and transfer sectors, as evidenced by the impact of hydrotechnical works and artificial landforms from coal mining on the connectivity potential of the Jiu river basin.

How to cite: Morosanu, G. A. and Jurchescu, M. C.: Reconsidering the sediment connectivity and sediment transfer under the influence of hydraulic structures and coal mining in the Jiu river basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15317, https://doi.org/10.5194/egusphere-egu21-15317, 2021.

Bedload sediment transport was monitored from 2016 to 2020 in the Leitzaran River, in a reach affected by the removal of 7-meters high dam (Oioki dam). The removal was accomplished in two phases, the 3 first meters were removed in September 2018 and the second phase (September 2019) involved the removal of the remaining 4 meters. The study area was divided into three subreaches: control (unaffected by the dam), upstream and downstream of the dam. A sample of 300 RFID-tagged stones were seeded every year (100 at each reach).. Prior to this, the grain-size distribution of the surface sediment was characterized using the Wolman method. Then, the grain-size chosen for the tracer stones was distributed according to three Wentworth intervals: that corresponding to the surface d₅₀, d₅₀+1 (immediate upper interval), and d₅₀-1 (immediate lower interval). It was not possible to follow completely, and the lower interval had to be dismissed as the sediment was very small or narrow to insert the tracer.

We conducted an extensive surveying field campaign every summer.

The number of retrieved tracers was relatively high, around 40-70% (considering all field campaigns), although with differences amongst the different sub-reaches. The obtained results were organized by displacements and volumes of sediment moved. The maximum (3,500 meters) and higher mean displacement (~1,550 meters) were registered in the hydrologic year 2019/20. These values are from the upstream reach of the dam and match simultaneously with (i) the whole removal of the dam, and (ii) the period showing a lower discharge (note the critical discharge for the movement of our particles is ~25-30 m³·s^-1 (d₅₀ = 64.0≥Ø<90.5 mm); mean discharge and peak flow from 2013 to 2020 were ~5.3 m³·s^-1 and ~125.0 m³·s^-1, respectively and at the end of the watershed).

We also estimated the bulk bedload volumes during the time spanned by this research and we report how the hydrologic year 2019/20 was the more active in terms of displaced volumes, moving up to 27,500 tons in the upstream reach. In fact, this year also presents the maximum for the downstream reach.

At this moment, besides the raw data of displacements and volumes, our observations highlight how the fact that a copious load of sediment was made available with the dam removal seemed to be more determinant than the magnitude of the flow to get larger tracer displacements.

How to cite: García, J. H., Ibisate, A., Sánchez-Pinto, I., Vázquez-Tarrío, D., Ollero, A., Herrero, X., Ortiz Martínez de Lahidalga, J., and Beltrán de Lubiano, J.: Sediment displacement evolution after dam removal in a mountain river (Oioki dam, Leitzaran River), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8444, https://doi.org/10.5194/egusphere-egu21-8444, 2021.