ICG2022-5

Critical Zone Observatories (CZOs) explore the deep evolution of landscapes from the bottom of groundwater to the top of vegetation, representing a bridge between geology, geomorphology and ecology. Human impacts on the landscape, notably agriculture and urbanisation, are key drivers of terrestrial landscape change, with these challenges providing a focus of a new class of 3^rd generation Critical Zone Observatories (CZOs).  Four of these CZOs were established in China to understand how environmental processes, from the top of vegetation through 10’s to 100’s of metres of soil to bedrock, interact and are affected by land management.  The China CZOs cover vastly different geomorphological settings in karst, loess, and red soil environments that encompass over 1/3 of China’s land area and support 25% of the population. The 4^thCZO lies in the peri-urban coastal zone, reflecting urban migration that is growing in China, with over 1/6 of China’s population already migrated from rural areas and 52% of the population in cities.

This talk provides an overview of key geomorphologically relevant findings from these CZOs, obtained by a team of over 50 principal-/co-investigators and many other postdoctoral scientists and students. An over-arching theme is integrating humans into critical zone science to tackle threats to landscape tipping points being crossed, impacting on food and environmental security.  While 2^nd generation CZOs capture human impact, the role of human decision-making has been largely overlooked. A 3^rd generation approach to CZ science emerged from the China-UK CZO programme (2016-2020). Here, human geography informed knowledge exchange research complemented traditional multidisciplinary CZ science. This provided novel insights into human-environment interactions (and humans as geomorphic agents) that aided the interpretation of empirical data and helped identify the greatest financial pressures on farmers that also adversely impact their local landscape. It also illustrates how scientific sampling in heavily human-modified landscapes can be adjusted to better incorporate the impacts of humans as geomorphic agents. The approach also identified how local people chose to learn more environmentally and economically sustainable farming methods, thereby guiding fit-for-purpose knowledge exchange activities between CZ scientists and key stakeholders. We thus outline the benefits of incorporating learnings about human behaviours and their beneficial impacts into CZO projects. We demonstrate that human geography needs to form a key dimension of multi-disciplinary CZ science approaches to enable identification of the mechanisms underlying human contributions and pressures on CZ functions. Crucially, deep understanding of impacts of environmental and economic stressors on human livelihoods can provide the rationale for policy and local action to achieve resilient social-ecological systems. We thus show how 3^rd generation CZOs that combine physical and human geography, underpinned by local knowledge, can provide practical feedback to communities in stressed environments, enabling better achievement of sustainable development goals and planetary health.

How to cite: Naylor, L. A. and the UK China CZO Team: Humans as geomorphic agents: including humans in critical zone science to enhance Anthropocene landscape sustainability, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-551, https://doi.org/10.5194/icg2022-551, 2022.

THE ROLE OF MAN ON LAND COVER DYNMICS IN THE JAKIRI AREA,

NORTH WEST REGION OF CAMEROON

By

Clement Anguh Nkwemoh & Destain Wirsiy

The University of Yaounde 1

ABSTRACT

Several Landscape degradation forms have attracted our attention in the Jakiri area on the North Eastern edge of the High Lave Plateau of Cameroon. Landscape degradation has become a major issue in contemporary studies, owing to its impact on society. This study aims to identify mainly various human factors responsible for Land cover dynamics. In order to complete this research, we adopted Classical and Empirical Approaches. These relied on the collection of data from secondary and primary sources. Questionnaires were administered to 310 farmers and 84 pastoralists in 17 villages. Focus Group Discussions and Interviews were equally carried out. The topographic map of Nkambe NB32XVII scale: 1:200 000, was exploited. The MSS, TM and ETM + Enhanced Thematic Mapper Plus as well as ASTER images for 2007 were used. Data was treated with the use of SPSS, ArcGIS and ERDAS IMAGINE software. The study reveals that anthropogenic actions are predominant in degradation meanwhile physical factors are only contributory in the degradation processes that rendered the Jakiri Plateau susceptible to soil erosion and mass movements. The Normalized Different Vegetation Index (NDVI) revealed a decrease in NDVI values from +0.92 in 1988, +0.74 in 2001 and +0.5 in 2020, showing a vegetation decrease. Meanwhile, the Land Cover Classification revealed a change in forest/land cover, from 24.4% in 1988 to 9.83% in 2020 with a decrease in forest cover of 14.5%. On the contrary, built up area, grassland (savannah) and bare surfaces have witnessed an increase in land cover classes from 34.4%, 10%, 31.2% in 1988 to 37.7%, 14%, 38% in 2020. Our study equally identified population pressure, deforestation, rudimentary agricultural activities, overgrazing and the introduction of eucalyptus cultivation as a form of agroforestry that transformed the landscape of Jakiri. The solutions that have been proposed, focus on landscape restoration through improved farming systems such as agroforestry, and also the application of certain technical methods. The solutions are socially just, flexible, adaptable, economically viable and most importantly ecologically sound.

Keywords: Anthropic activities; vegetal degradation, GIS, Land cover change; agrarian and

technical measures

How to cite: Nkwemoh, C. and Wirsiy, D.: The role of man on Landcover dynamics of the Jakiri Area of the North West Region of Cameroon, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-122, https://doi.org/10.5194/icg2022-122, 2022.

Iron ore has been mined in the Erzberg area for at least 900 years, possibly as long as 1500 years. This mining history can be divided into three periods of impact on the landscape. Due to the inefficiency of the early smelting techniques and the low production levels, the first period remained free of serious impacts. A huge demand for energy for ore smelting characterized the second period, resulting in supra-regional deforestation for charcoal production. The third period of mechanized surface mining is marked by the creation of large man-made landforms. In the Erzberg area, both historical documentation and modern recording of the mining activities are exceptionally good and provide an opportunity for i) a qualitative identification and description of the associated landscape changes and ii) a first attempt to quantify them. Qualitative analysis of the documents provided a detailed description of how distinct anthropogenic impacts and landforms have emerged, and identified the procedures that caused medieval supra-regional deforestation. A slope exposure opened along a creek allows interpretation of the geomorphic effects of the historical forest depletion. Quantification of the extent of deforestation was carried out for a forest area close to the mining site. The results allow a reconstruction of the condition of the forest at this site over two centuries. For quantification of the earth material moved by man in mechanized surface mining denudation rates for the Erzberg site were computed and compared with the sediment budget of a nearby river catchment. This comparison suggests that on the local scale man is two to three orders of magnitude more effective in transforming the landscape than geomorphic processes.

How to cite: Embleton-Hamann, C. and Premm, S.: Landscape Change due to Thousand Years of Iron Ore Production in the Erzberg Area (Styria, Austria), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-129, https://doi.org/10.5194/icg2022-129, 2022.

Salt domes are bodies of halite-gypsum-anhydrite salt exposed at the Earth’s surface. They typically comprise positive topographic expressions, reaching heights of 10s to 100s m. In plan-view, they display elliptical through to elongated shapes that span metre to km-scale length-width-area-volume dimensions. Salt domes are typically found in drylands, where rainfall-humidity levels are sufficiently low, inhibiting dissolution. Salt is considered to move upwards to the surface by diapiric processes, linked to rock density differences and elevated compressive forces. Thick (>100 m) layers of lacustrine-marine evaporitic sediment are buried to km-scale depths over geological timescales. Salt density = ~2200 kg/m³), becomes buoyant and diapiric due to overburden pressure when buried by >1-3 km thickness of higher density (~2500 kg/m³) sediment cover. Salt movement is further enhanced by tectonics, especially in collisional plate settings. Here, compression provides additional diapiric driving forces, with any resulting folded-faulted strata providing a structural-stratigraphic framework for salt migration pathways. Accordingly, geologists use the term ‘salt diapir’ reflecting the movement-emplacement process, or ‘salt plug’ to reflect its stratigraphic configuration with respect to bounding strata and structures. ‘Salt dome’ is a geomorphological term linked to salt’s surficial geomorphic expression.

Salt dome morphology features widely in geological-geomorphological literature, where dome shape is commonly linked to different stages of diapiric growth. Jahani et al (2007), analysed 43 domes from the Zagros Mountains (Iran), proposing six dome types:  A = buried diapirs, B = high relief active diapirs, C = high relief active diapirs with a salt fountain and glacier, D = like C but with more erosion and without fountain, E = dead and highly eroded diapirs with an empty crater, F = linear diapirs emerging along faults. Although such process-form based classification schemes are well-conceived and likely correct, they surprisingly lack quantitative analytical underpinning of their morphological dimensions. Thus, the purpose of this research is to investigate whether quantitative morphological relationships between salt dome shape and diapiric process-based classification exist.

We focused upon the classic Eastern Fars region studied by Jahani et al (2007) and their 6-fold classification scheme (above). We compiled a spatially expanded database of 67 domes (A = 3%; B = 28%; C = 18%; D = 34%; E = 12%; F = 4%) and their morphological attributes (area [111-0.6km²], relief [1.2-0.7km], length/width ratio [1-6], volume [20- -14km³], hypsometry [curve and integral], slope [mean 33-5°] using 12m TanDEM-X data and satellite imagery for measurement and visualisation purposes. The database was supplemented with geological information sourced from Iranian geological survey maps, including dome relationships to geological units (age/lithology) and tectonic structures (folds/faults).

Results reveal at best a weak qualitative and quantitative relationship between dome morphology and diapir growth and erosion evolution processes. We discuss this finding and suggest that dome location with respect to fold structural configuration as a confinement control provides an improved, and hitherto unexplored, salt dome classification opportunity.

Jahani, S., et al., 2007. The salt diapirs of the eastern Fars Province (Zagros, Iran): A brief outline of their past and present. In Thrust belts and foreland basins. Springer. pp. 289-308. 

How to cite: Stokes, M. and Bahrami, S.: Salt dome morphology: a quantitative analysis of diapiric process-based classification schemes, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-314, https://doi.org/10.5194/icg2022-314, 2022.

Extending some 60 m below ground, and with explored lengths of more than 1 500 m, the Gobholo cave system in Eswatini is one of the largest granite cave systems documented in the scientific literature. The cave system is found in the Gobholo valley, approximately 10 km east of Mbabane. The valley is drained by the Gobholo River, which has a subsurface flow through the cave system for more than 1,8 km. The Gobholo valley itself is located on the Mbabane granite pluton which is made up of the Mswati granite, of 2,7 Ga. in age. It is a porphyritic granite of coarse grain which forms part of the Kaapvaal Craton. The Kaapvaal Craton is an old yet stable landscape composed primarily of granitoids, gneiss, and other metamorphosed volcanic and sedimentary rocks varying in age between 2.5 – 3.6 Ga. The Mbabane Pluton is remarkably affected by tectonics as evidenced by a network of NNE-SSW and NW-SE fault lines and lineations, which account for the deep dissecting and near perpendicular valleys, with the Gobholo Valley being one of these.

A notable feature of this cave system, compared with other granite caves reported in the literature, is that it has elements of both solutional-depositional systems, as well as the ‘typical’ boulder systems in which the interstitial fines have been washed out between large, buried scree-slope boulders. The research focusses on the structure and composition of the granitic bedrock, and compares its mineralogy with the geochemistry of the water of the Gobholo River. Remote sensing and GIS are used to map the spatial arrangement of landforms, geological structure, and digital modelling of the terrain. These are further used to explain the geomorphic processes of the study area. The analysis and modelling of the Gobholo Valley is of key importance in this research, as it informs the discussions and conclusions on the genesis and dynamics of the Gobholo granite cave system.

How to cite: Masilela, M., Beckedahl, H., and Dlamini, W.: Understanding the Geomorphology of the Gobholo Granite Cave System in Eswatini, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-76, https://doi.org/10.5194/icg2022-76, 2022.

Peatlands are a globally important wetland habitat, estimated to contain over a third of terrestrial soil carbon, placing their preservation and restoration at the forefront in debates around climate change mitigation. Anthropogenic activities, however, are driving peatland degradation loss both directly and indirectly. One such activity, is the creation of linear disturbances such as roads and tracks. The expansion of these networks, frequently in pursuit of resources, or the desire to explore remote regions, is rapidly outpacing research, with long time lags often experienced before impacts are appreciable.

In 2013 an experiment was established at Moor House, an upland blanket peatland in northern England to examine the impacts of temporary plastic mesh tracks on peatland functioning. A 1.5 km long plastic mesh track was installed and split into five different treatments based on frequency of usage. The tracks were abandoned in 2015/16, and no further vehicular usage occurred. In 2020, 18 7m long sections of this track were removed, to intensively examine the ecohydrological effects of removal compared to leaving the track to overgrow. The impacts of different treatments were evaluated on the ecohydrology; removed vs abandoned track, previous usage frequency, delayed usage, and unsurfaced track. Detailed surficial structural (nanotope) assessments of the tracks were carried out, to compare ruts, centres and controls. Additionally, soil moisture measurements, overland flow sediment, peat cavity strength measurement, hydraulic conductivity, bare peat occurrence and vegetation diversity were recorded.

Across all treatments alteration of the surface nanotopography was observed, loss of vegetation diversity after track removal and a reduction in vegetation height across all treatments occurred compared to controls, both on the track and along track edges. Our nanotope surveys augmented vegetation recovery assessments, demonstrating how different conclusions can be drawn, depending on whether vegetation-only or more complete assessments of surface condition are undertaken. Peat cavity strength on the tracks, measured using a peat specific penetrometer, suggests the persistence of vehicular compaction in the post abandonment and track removal periods. We also present data from overland flow sediment traps, hydraulic conductivity, and soil moisture surveys. Our findings suggest that where mesh track is to be removed, then additional revegetation interventions are required. We demonstrate that because the impacts of tracks, including mesh tracks, even after only light, short duration use, are long-lived, careful consideration of the necessity of tracks is required prior to their construction on peatland.

How to cite: Williams-Mounsey, J., Grayson, R., Crowle, A., and Holden, J.: Temporary tracks, persistent impacts? An evaluation of short-term usage peatland tracks., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-361, https://doi.org/10.5194/icg2022-361, 2022.

An analysis and assessment of the effects of human activity on geomorphic processes related to denudation/sedimentation and landscape change, is presented. The analysis focuses on changes occurred during the last couple of centuries and is based on a variety of case studies from different regions as well as global assessments. Data compiled show that certain geomorphic processes are experiencing an important acceleration, in particular since the 1950’s. The acceleration seems to have a global character and suggests a “global geomorphic change” is taking place, largely due to anthropogenic landscape changes.

            Denudation directly caused through activities involving excavation, transport and accumulation of geological materials has increased by a factor of 30 between 1950 and 2015. Direct plus indirectly human-induced denudation (triggered by land surface alteration) is presently at least one order of magnitude greater than denudation due to purely natural processes. A general increase of sedimentation rates seems to have taken place since the end of the 19^th century, and more intensely after the mid-20^th century. This appears to respond mainly to land surface changes, in conjunction with climate change.

            Slope movements, which represent an important contribution to denudation, sediment generation and landscape evolution, show a clear intensification, in particular after mid-twentieth century. Frequency of disasters related to such movements (an indirect measure of process frequency) in specific regions, as well as continent and global levels, has grown considerably and the general increasing trend observed is not satisfactorily explained by climate change. It rather appears to reflect increasing landscape (land use and land cover) changes. A similar increase in the frequency of flood-related disasters has been recorded.

            The results obtained suggest that the extensive landscape changes described, related to the intensification of human activities affecting land surface, represent a geomorphic change of a global extent. This change shows an acceleration coinciding with the “great acceleration” proposed as one of the manifestations of the Anthropocene.

How to cite: Remondo, J., Cendrero, A., Forte, L. M., Beylich, A. A., and Cienciala, P.: An assessment of geomorphic change and its effects on denudation and landscape evolution, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-644, https://doi.org/10.5194/icg2022-644, 2022.

In the Mediterranean region, natural soil loss susceptibility is enhanced by human pressure, that has a long history and seems to be the main driver of changes in sediment supply during the Anthropocene. Badland areas in non-arid landscapes can be ideal sites to investigate the role of human activities in triggering erosion processes in the current context of global change, as their origin has been related to scenarios of widespread land degradation. So far, little attention has been given to the relationship between slope processes and river morphodynamics in badland landscapes. In this context, the exploration of sediment connectivity can be informative, considering the rapid morphoevolution and consequent off-site effects.

Anthropocene hillslope morphodynamics and sediment connectivity within a representative badland area located in southern Tuscany (Italy) was explored, in order to better delineate the recent erosion dynamics. The relative importance of the role of man activities in the medium-term landscape evolution and how far it can be connected to the triggering and/or mitigation of hillslope processes is discussed.

In order to achieve these general purposes, the research approach included i) a multitemporal survey of the erosion dynamics at catchment scale, ii) the analysis of the land use changes during the last century and iii) the geomorphometric indexing of the structural connectivity of a representative catchment located in the Upper Orcia River valley, starting from a 1 m resolution DEM (Digital Elevation Model) derived from LiDAR (Laser Detection and Ranging).

Starting from the mid-20^th century, the area has been subjected to artificial reforestation with conifers (performed mainly on upland areas), impressive land reclamation (many badland areas have been levelled due to the enlargement of croplands), pasture decrease as a consequence of rural land abandonment, with the subsequent increase in the vegetation cover. Everything merges with a recent reduction of hillslope denudation rates, that can be related to the observed channel adjustments during the last decades.

Outcomes of this research can be useful for a deeper comprehension of the effects of man-induced changes on the slope-channel systems and, in a wider context, can be helpful for supporting the decision making in a perspective of sustainable development.

How to cite: Vergari, F., Troiani, F., Cavalli, M., Faulkner, H., and Del Monte, M.: Anthropocene erosion dynamics and sediment connectivity in a central Italy landscape with badlands, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-281, https://doi.org/10.5194/icg2022-281, 2022.

Debris flows (DFs) are widespread geomorphic processes in the high areas of Carpathians, being highly efficient sediment transfer processes from slopes to channel network.  They often damage the transportation infrastructures, inhabited areas and threaten the recreational and other human activities. To minimize the negative impact of DF activity, it is crucial to understand the role of various conditions and factors which lead in the past to debris flow triggering. In this context, information on long-term DF activity needs to be known, to understand the DFs behavior and to predict the future trends of this potential natural hazard in the context of documented climate change. However, in Carpathians, as in most of the mountain areas worldwide, the lack of historical records about past hydrogeomorphic process activity in term of temporal frequency and spatial extent hampers the possibility to have a good knowledge of the past DF activity. Indirect reconstructing methods, e.g., dendrogeomorphic methods can be used to reconstruct past DF activity in forested mountain areas. When DFs along their paths cross the forests, they disturb the trees leaving in their growth rings distinct signs of the past DF events. Dendrogeomorphic approaches are based on the analysis of growth anomalies caused by the mechanical disturbance of DFs on trees and recorded in treir rings, allowing to reconstruct with annual and even seasonal resolution past geomorphic activity. Dendrogeomorphology became in the last decades an established technique applied to reconstruct past geomorphic process activity, helping to understand dynamics of various geomorphic processes.  Dendrogeomorphic methods have been extensively applied to reconstruct DF activity in various mountain regions, while in Romanian Carpathians DF activity has been rarely reconstructed through these methods, and if available the reconstructed activity has focused only on individual case studies at a local scale. The aim of this study is to investigate past DF activity at a regional scale through dendrogeomorphic methods. In this sense, study sites which includes multiple tracks of both natural and anthropogenically-influenced DFs crossing the forested slopes were chosen in Calimani Mountains (Eastern Carpathians). In each investigated site, growth anomalies identified in the rings of disturbed trees sampled allowed to reconstruct DF event chronologies. Analysis of rainfall data recorded at the weather station located close to the study sites revealed that local DF processes may be the result of extreme rainfall events occurring mainly during summer seasons. An increase in DF event frequency in the anthropogenically-influenced areas compared with the DF event frequency in natural areas was observed, suggesting that sediment availability possibly represent another factor for varying DF activity. The dendrogeomorphic reconstructions realized here represents a first attempt to assess the regional patterns of DF activity in Romanian Carpathians, with promising perspectives to extend similar dendrogeomorphic investigations in other regions of the Carpathian Range.

How to cite: Pop, O.: Regional debris-flow chronology reconstructed through dendrogeomorphic methods in Calimani Mountains (Eastern Carpathians, Romania), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-226, https://doi.org/10.5194/icg2022-226, 2022.

The upper Driva drainage basin in central Norway (Oppdal-Hjerkinn) is situated in a cold climate and mountainous environment and ranges with a total drainage basin area of 1630 km² from 220 to 2286 m a.s.l. The mean annual air temperature at Oppdal (545 m a.s.l.) is 4.3°C, and mean annual precipitation at Oppdal amounts to 532 mm. The lithology in the drainage basin is complex and varied, and is dominated by metamorphic rocks (mostly gneisses and schists). Vegetation cover varies between tundra vegetation in the high and rather flat areas of the uppermost drainage basin area, situated at elevations around 900-1200 m a.s.l., tree vegetation (mostly birch and pine) in the lower parts of the incised tributary valleys of the Driva main river and grasslands in the agriculturally used areas close to the lower sections of the main river Driva. Relevant geomorphological processes include chemical and mechanical weathering, rockfalls, snow avalanches, debris flows, slides, wash processes, fluvial erosion, fluvial streambank erosion and down-cutting,  and fluvial solute, suspended sediment and bedload transport.

This ongoing GFL research on sediment sources, controls and spatiotemporal variability of fluvial bedload transport includes detailed field-based studies with extensive granulometric and shape analyses of bedload material, and high-resolution bedload transport measurements applying different tracer techniques, Helley-Smith samplings, and underwater video filming together with impact sensor measurements. Specific focus is on selected stream channel stretches in the six tributary systems Svone, Kaldvella, Stølåa, Tronda, Vinstra and Ålma, and on three selected stream channel stretches of the Driva main river in the upper Driva drainage basin system. Stationary hydrological stations are monitoring runoff continuously as discharge occurs in all tributary systems year-round. The runoff regime is nival with mean annual runoff amounting to 576 mm for the entire upper Driva drainage basin.

The temporal variability of fluvial bedload transport is largely controlled by thermally and/or pluvially determined runoff events. The selected tributary systems display varying grain-size compositions and shape characteristics of bedload material together with different bedload transport rates and yields. These detected spatial variations are explained by different lithologies, different levels of sediment connectivity and spatially varying sediment availabilities in the different tributary systems. The activation of sediment sources is generally strongly determined by thermally and/or pluvially induced events. The clearly highest share of annual bedload transport occurs during the snowmelt period in spring. Altogether, fluvial bedload transport is of high relevance for the total fluvial transport in the upper Driva drainage basin. However, within the different selected tributary systems the relative importance of fluvial bedload transport, as compared to suspended sediment transport and solute transport, ranges from very low in Ålmadalen to very high in Vinstradalen.

How to cite: Laute, K. and Beylich, A. A.: Field-based analysis of sediment sources, spatiotemporal variability and rates of fluvial bedload transport in the cold climate and mountainous upper Driva drainage basin in central Norway, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-81, https://doi.org/10.5194/icg2022-81, 2022.

A four-day glacier-melt flood (13-16 August, 2013) caused an abrupt geomorphic change in the proglacial gravel-bed Scott River, that drains the small (10 km2) Scott Glacier catchment (SE Svalbard). This type of floods occur on Svalbard increasingly during periods of abnormally warm or rainy weather in summer or early autumn, and the probability of occurrence grows in direct proportion to the increase in temperature and/or precipitation intensity. In the summer 2013 measurement season, the highest daily precipitation (17 mm) occurred on August 13. During the following four days, it constituted in total 47mm i.e. 50% of the precipitation total for the measurement period of 2013. The largest flood in 20 years, was caused by high precipitation with a synchronous rise in temperature from about 1.0 to 8.6 °C. These values exceeded multi-year averages (32 mm and 5.0 °C, respectively), at average discharge 0.9 m3·s–1 (melt season mean 1986–2011). These conditions caused a rapid and abrupt response of the river with dominant (90%) glacier-fed. The increase of discharge to 4.6 m3·s–1, initiated by the glacial flood, mobilized significant amounts of sediment in the river bed and channel. Geomorphic changes within the alluvial fan as area of 58,820 m2, located at the mouth of the Scott River, were recorded by multi-sites terrestrial laser scanning using a Leica Scan Station C10, and then estimated using Geomorphic Change Detection (GCD) Software. Flood-induced total area of lowering (erosion) covered 38% of the alluvial fan (6,030 m2), resulting in the removal of 1,182 ± 121 m3 of sediment volume. During the final phase of the flood, two times more sediments (1,919 ± 344 m3) was re-deposited within the alluvial fan surface, causing significant aggradation on 62% of its area (17,190m2). These geomorphic changes resulted in an average lowering (erosion) of the alluvial fan surface of 0.2 m and an average rising (deposition) of 0.1 m.

How to cite: Kociuba, W.: Geomorphic Change Caused by Flood at Scott River Alluvial Fan, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-413, https://doi.org/10.5194/icg2022-413, 2022.

Permafrost degradation by ongoing climate warming has expanded the erodible thermokarst landscapes, enhanced the thermal erosion, and altered the sediment transport processes in cryosphere basins. Thermal-activated sediment sources and enhanced sediment export due to developed hillslope-channel connectivity can increase the annual sediment flux and accelerate the sediment response to hydroclimatic disturbances, thus complicating suspended sediment concentration (SSC) and discharge (Q) relationships and forming various hysteretic patterns. Yet, the commonly used sediment rating curve (SSC=a×Q^b with a and b as static fitting parameters) is unable to capture the SSC-Q hysteretic patterns and most single-event-scale hysteresis models mainly emphasize the pluvially enhanced sediment transport (e.g. rainstorms), but overlook the thermally-erosional processes.

To rebuild dynamic SSC-Q relationships and hysteresis in sediment transport in cryosphere basins, we propose a Sediment-Availability-Transport (SAT) model by extending traditional rating curves to incorporate the time-varying sediment availability regulated by thermal-fluvial processes and long-term storage exhaustion. In the SAT-model, increased thermal erosion is represented by basin temperature; enhanced fluvial erosion is represented by runoff increase; sediment transport capacity is represented by total runoff. Specifically, thawing permafrost as temperature rising can enhance sediment generation by forming active layer detachment, retrogressive thaw slump, and thermal erosion gully from hillslopes, and fluvio-thermal erosion along the riverbank, associated with a time-lag in the sediment response due to the time for temperature accumulation to melt cryosphere and long-travel distance from thermal-activated sediment sources to the basin outlet. A surge in basin water supply during intense rainfall and excessive melting with a certain time-lag can increase sediment availability and fluvial erosion by flushing the erodible slope and scouring the river channel. Moreover, sediment storage is assumed to be continuously depleted throughout a hydrological year and leads to sediment exhaustion.

With the support of multi-decadal daily SSC and Q in-situ observations (1985-2017), the SAT-model can be parameterized and validated in the permafrost-dominated Tuotuohe basin on Tibetan Plateau. In Tuotuohe, thermal erosion processes are found to be best captured by an eight-day average temperature, associated with an exponential amplification of SSC. Fluvial erosion is best captured by a two-day runoff increase and shows a linear amplification of SSC. Moreover, the warming-wetting climate over the past decades has expanded the thermokarst landscapes and boosted the slope-channel connectivity by thermal gullies, which leads to the significant inter/intra-annual variation in SSC-Q relationships and reduces the performance of the sediment rating curve. Yet, the SAT-model can robustly reproduce the long-term evolution, seasonality, and various event-scale hysteresis of SSC, including clockwise, counter-clockwise, figure-eight, counter-figure-eight, and more complex hysteresis loops. Overall, the SAT-model can explain over 75% of long-term SSC variance, outperforming the sediment rating curve approach by 20%, with stable performance under an abrupt hydroclimate change.

Part of the results is also published in Water Resources Research: Zhang et al., 2021. Constraining dynamic sediment-discharge relationships in cold environments: The sediment-availability-transport (SAT) model.;. Li et al., 2021. Air temperature regulates erodible landscape, water, and sediment fluxes in the permafrost-dominated catchment on the Tibetan Plateau.

How to cite: Zhang, T., Li, D., and Lu, X.: Basin-scale sediment transport and sediment concentration-discharge relationship modeling in a permafrost-dominated basin, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-24, https://doi.org/10.5194/icg2022-24, 2022.

Bivariate relationships have been extensively researched in fluvial geomorphology. The relationship between process-process, form-form, or process-form gives great insight into the dynamics of channel morphological variables. One of the most extensively adopted concepts in bivariate relationships in fluvial geomorphology has been the use of hydraulic geometry.  The hydraulic geometry despite its many advantages and applications has been identified to focus more on general trends rather than innumerable individual variations. In recent times, a growing concept on bivariate observations within fluvial systems is the geomorphic covariance structures (GCS). GCS has been defined as linked bivariate observations of any two river morphological variables along a continuum. These variables could also accommodate the abiotic and biotic variables. In its strictest sense, GCS does not necessarily connote a statistical covariance though sometimes it could, it focuses more on a complete bivariate spatial series. In this study, we investigated coherent patterns for GCS for selected morphological variables along the alluvial-bedrock continuum for 83 reaches within the Upper Ogun River Basin. In interpreting the bivariate spatial series along the alluvial-bedrock continuum, we made use of “in-phase” and “out-of-phase”. In-phase signifies a positive relationship and out-of-phase signifies an inverse relationship. The morphological variables were measured using standard procedures and derived variables were determined using hydraulic equations. As the river flows from an alluvial section into a bedrock section; slope and total stream power were out of phase, hydraulic radius and velocity are in phase across the continuum, bankfull with and slope were out of phase, while slope and total stream power were more in phase within the bedrock section than in the alluvial section and finally, width and total stream power were out of phase. The alluvial section within the Upper Ogun River Basin is either unconfined or partly confined while bedrock channels are confined and underlain by migmatites. Flow within the bedrock channels is restricted while flow within the alluvial channels is more dispersed and free-flowing. The inherent dynamics operating within these two distinct channel types are capable of providing a detailed extent as to the observed bivariate relationships between these selected morphological variables using geomorphic covariance structures.

How to cite: Olusola, A., Ogunjo, S., Fashae, O., Onafeso, O., and Adelabu, S.: Geomorphic covariance structures of selected channel morphological variables across the alluvial-bedrock continuum in the Upper Ogun River Basin, Southwestern Nigeria, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-43, https://doi.org/10.5194/icg2022-43, 2022.

Sieve-lobe deposits are morphological features typical for gravel-rich and matrix-poor alluvial fans. Each sieve-lobe deposit is composed of open-framework, clast-supported, moderately-sorted gravels. Lobes form during sieve-deposition process where gravel is transported as bedload during short and intense rainfall events and abruptly deposited after the water quickly infiltrates into permeable underlying ground. Despite being a common morphological feature qualitatively described in several alluvial fan studies it lacks a detailed sedimentological description based on quantified data. The formative conditions and depositional activity of sieve lobes as well as subsurface architecture of a sieve-lobe built alluvial fan is largely unknown. In this study we present (i) a detailed sedimentary facies analysis based on sedimentary structure and texture of recent sieve lobes, (ii) a three-year aerial survey of sieve-lobe depositional activity, (iii) a direct linkage of depositional activity to specific rainfall triggers, and (iv) a depiction of subsurface architecture of intertwined sieve lobes.

The study was done in the Planica Valley (NW Slovenia), a typical post-glacial alpine valley, where several gravel-rich Holocene alluvial fans are located.  The study was performed on one of the more active alluvial fan, which is predominantly built of sieve-lobe deposits. The sedimentological analysis is based on granulometry, grain morphology, and grain fabric of 11 sieve lobes that differ in size and age. Sieve lobe generation was detected by aerial surveying using Small Unmanned Aircraft (SAM) and photogrammetric modelling of the surface of the deposits. Detected surface changes were temporally correlated with precipitation records from the nearby meteorological station. Ground-penetrating radar (GPR) technique was used to depict architecture and geometry of sieve-lobe built alluvial fan.

Sedimentary analysis reveals that majority of sieve lobes belong to textural group of gravel and some to sandy gravel, containing almost negligible percentage of mud fraction, which rarely exceeds 2.0%. Almost uniformly and regardless of age and size, all sampled sieve lobes exhibit downward coarsening, with distal parts of lobe being significantly coarser than proximal. Clasts are angular to subangular, predominantly moderately to highly spherical and not orientated.

Temporal surface changes are clearly visible on SAM-derived digital orthophoto and digital elevation models. Correlating surface changes to meteorological records shows that sieve lobes form with a subannual frequency, usually after rainfall events exceeding 50 mm of rainfall in 24-hours. During such events more than 1000 m³ of sediment was deposited.

GPR data from a radargram parallel to the direction of sediment transport displays stratified and progradational reflectors with sigmoid shapes that are continuous for 10s of metres and have 10° dip. Radargrams orientated perpendicular to the direction of sediment transport exhibit stratified hummocky and discontinuous reflections of up to 10 metres long. The reflection patterns are interpreted as series of stacked sieve-lobe deposits confirming formation of the studied alluvial fan predominantly by sieve-deposition process.

This study provides the first detailed quantified facies analysis of sieve deposits observed in nature. Monitoring of their deposition shows that they represent major building blocks of gravel-rich alluvial fans, and their deposition is directly linked to intense precipitation triggering events.

How to cite: Novak, A., Vrabec, M., Popit, T., Vižintin, G., and Šmuc, A.: Facies analysis, depositional activity and subsurface architecture of sieve lobe built alluvial fan (Planica Valley, NW Slovenia), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-88, https://doi.org/10.5194/icg2022-88, 2022.

The sediment dynamics of river systems are of significant importance from an ecological, social and engineering viewpoint and are defined by complex relationships of numerous variables. It is widely accepted amongst authors that as flow increases as does the amount and size of sediment entrained. Threshold theories surrounding this have been proposed by many authors including Hjulstrom, Van Rijn, Du Boys and Shields. The aim of this research is to investigate thresholds of motion for sediments within bi-modal riverbeds, including examining incipient motion for various particle sizes. Previous research methods which have investigated this have focused on either field methods using small sample populations from sediment traps and sediment tracers or laboratory studies (flume models). In this paper an alternative method is presented utilising repeat UAV imagery of two gravel-bed river reaches in England to identify individual sediment clasts and monitor movement. By determining whether a sediment has moved or stayed and comparing this to a maximum flow rate during the interval between surveys, derived from hydraulic modelling, a maximum local shear stress value can be established for when each grain is mobilised. Initial findings have shown that as flow increases so does the amount of sediment moved. However, the size of mobilised sediment does not necessarily increase. Sediments over a certain size (0.3 m B-Axis length) display little movement despite rising shear stress values. Shielding and exposure are also investigated to examine why these larger sediments remain stable despite increasing local shear stress values. This has shown that in non-uniform gravel-bed rivers bed armouring and sediment sorting can heavily impact transportation. Armouring of coarser sediments consolidates a bed leaving finer sediments exposed to the flow and constantly moving through the system. Furthermore, this bi-modal sediment impacts roughness within the channel. A smooth channel with cohesive material decreases roughness, whereas in a non-uniform channel with larger grains roughness increases; this is turn makes movement of grains more difficult. The conclusions established within this research are of significant importance to understanding the complex relationships and various parameters for sediment dynamics within these systems.

How to cite: Remers, A., Heritage, G., and Entwistle, N.: An investigation into the threshold of sediment motion, in two non-uniform English gravel-bed rivers, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-123, https://doi.org/10.5194/icg2022-123, 2022.

The societal importance of understanding physical landscape response to rapidly progressing anthropogenic climate change is very high. Detecting geomorphic and sedimentary signals of modern climate change is essential for management decisions affecting human health and safety, infrastructure, economics, energy–food–water security, and ecosystems. This presentation examines challenges in measuring and attributing the influence of contemporary climate change on geomorphic and sedimentary systems, and opportunities for improving these efforts.

Foremost among the challenges to detecting modern climate-change impacts are short and incomplete records. Because anthropogenic climate change accelerated substantially after around 1970, its detection often requires robust, high-resolution data from before and after that time. For some purposes a small number of data points can be informative (documenting glacier extent using photographs taken decades apart), whereas investigations of other processes require daily or at least sub-annual data (fluvial sediment fluxes; documenting landslide patterns). Direct measurements rarely continue long enough, with consistent sampling frequency and methods, to resolve signals at the level of detail needed to detect or attribute change to climatic effects. Isolating signals in ‘noisy’ natural systems is notoriously difficult; individual extreme events (floods, storms, fires) can remain apparent for decades, obscuring more subtle change. Climatic influence also must be disentangled from land-use and tectonic effects. Data availability is commonly biased toward places with human land use, either because land uses motivated the site selection or because people witnessed and reported disasters. Variable connectivity and storage in sediment-routing systems (e.g., floodplains or dams in river basins) also affects climate signal detection downstream.

However, the scientific community has opportunities to make useful progress. Data are needed from many more locations, at greater spatial and temporal resolution, to resolve the nature and extent of ongoing climate-change effects. This can be done by establishing and continuing time-series measurements with consistent methods and frequency. We can utilize paleo-records wherever possible, such as studying high-sedimentation-rate lake deposits instead of relying on laborious in-stream sediment-flux measurements. Optimal research sites are those with little human land-use influence and a high signal-to-noise ratio—high sensitivity to climatic change (high-sediment-yield, low-storage catchments; steep slopes with little stabilizing vegetation) and places where warming has been fastest, e.g., high-latitude and high mountain settings. For certain landscape processes, it is useful to establish a global list of sites likely to respond earlier and more strongly than other locations, as has been done recently in the landslide community. We can better define the role of superimposed, cascading landscape disturbances and their relative timing and seasonality (e.g., fires, storms, and growth and senescence of vegetation). We encourage sharing data and methodological improvements across disciplinary and national boundaries and building a community network/platform to synthesize such improvements. There are instances where sufficient data exist to detect recent climatic influence but where no signal is apparent yet. Thus, reporting of both negative and positive results, that highlight climate-change effects or lack thereof, is essential to demonstrating rates, regional patterns, and nuances of process.

How to cite: East, A., Sankey, J., Li, D., Zhang, T., and Warrick, J.: Measuring and attributing geomorphic and sedimentary responses to modern climate change: challenges and opportunities, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-167, https://doi.org/10.5194/icg2022-167, 2022.

Bedrock channel erodibility is a nonunique model-dependent parameter that scales hydraulic forcing to fluvial bedrock erosion. In landscape evolution modeling, erodibility coefficients are often assumed constant and uniform, and are often empirically calibrated to the form of natural landscapes. This approach lumps a wide range of variables into erodibility, including not only rock properties but also erosion processes (and their possible variations with discharge), climatic controls on hydrographs and rock weathering, and effects of coarse sediment supply.  Our goals are to better understand (a) how field measurements of rock properties could be combined to better quantify bedrock erodibility, (b) how bedrock erodibility may vary with discharge as different fluvial erosion processes become more or less dominant, and (c) how flood discharge variability and coarse sediment load influence “effective” erodibility in simple stream power incision model formulations.

Building on previous work, we first present new equations to calculate erodibility. Our rather complex erodibility model incorporates core-scale (i.e. unfractured) rock strength, discontinuity spacing (fractures, bedding planes), and climate-dependent bedrock susceptibility to weathering (which influences strength and fracturing), and accounts for abrasion and block plucking erosion processes. The model attempts to include feedbacks between these factors in a physical way, using variables that could be constrained from field data. Second, we explore the parameter space of these erodibility equations by modeling bedrock channel profile evolution for a range of conditions and varying rock properties, using preliminary constraints from field data collected in the semi-arid and lithologically variable Guadalupe Mountains, New Mexico and Texas, USA. Finally, we generalize our results by estimating uncertainties that may arise from assuming constant and uniform erodibility coefficients in simple stream power erosion models, compared to erodibilities that potentially vary spatially and temporally.

How to cite: Johnson, J., Guryan, G., Anderson, S., Gasparini, N., Tranel, L., and Heimsath, A.: Modeling bedrock channel erodibility as a function of measurable rock properties and climate, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-459, https://doi.org/10.5194/icg2022-459, 2022.

The Kneiss Islands and the outlet of the Wadi Leben watershed (Tunisia), is an internationally recognized site, classified ZICO (1990) and Ramsar (2007) for the high fish productivity of its shallow waters, which makes these areas a favorable breeding ground for migratory birds. The difficulties to access to the sea make these areas slightly degraded. However, the sustainability of this site is now being jeopardized with anthropogenic pressure becoming progressively stronger on this littoral zone and the upstream watershed.

Our objective is to show the original hydro-sedimentary functioning of this Mediterranean watershed, shared between physical characteristics and intrusive agricultural practices in full reconversion (from local/traditional to international/globalized): (i) The upstream zone of the watershed is subject to sediment retention related to the implementation of a hydro-agricultural and anti-erosion system (water and soil conservation works); (ii) The intermediate zone, by its morpho-structural and sedimentogenetic characteristics, has favored the accumulation of sediments in the valley bottoms, which makes it not only a transfer zone but also a sediment-recharge zone that can substitute for the upstream; (iii) The downstream zone, which could be expected to be sensitive to these upstream conditions, which may have altered its morphosedimentary equilibrium and caused a retreat of the coastline and the estuary, and accelerate soil salinization in the coastal plain, records a completely different hydro-morphological behavior, where the role of high-magnitude, low-frequency events (i.e., exceptional floods) is highlighted to understand its recent geomorphological dynamics.

In a methodological point of view, this research is based on a systemic analysis used to better understand the hydro-sedimentary connectivity. Topographic field measurements were carried out on a small representative watershed (7 km²) in order to estimate sediment storage induced by agricultural practices. Results were then extrapolated at the watershed scale (1215 km²) according to a modeling approach. Channel adjustments including the linear and lateral erosion and sedimentation processes were then estimated according to twenty ¹³⁷Cs and ²¹⁰Pb dating carried out in the transfer zone as well as in the wetlands (Sebkhas and shotts) located at the outlet of the watershed.

As a conclusion, we indicate that Wadi Leben can be proposed as a model of hydro-morpho-sedimentary functioning showing the efficiency of sedimentary recharge as a key point of equilibrium of the watershed as soon as the river is capable of lateral displacements, thus joining the question of the re-dynamization of rivers in the perspective of the river-bed restoration. A balance sheet leading to the assessment of the sustainability of economic practices (agriculture, industry, tourism, fishing) in the context where change factors (water resources, hydrological regime, sedimentary stock) may affect the hydrosystem in its watershed in the more or less long term is also proposed.

How to cite: Viel, V., Bouaziz, R., Arnaud-Fassetta, G., and Dahech, S.: Systemic analysis of sediment connectivity in the Wadi Leben watershed, Tunisia (Mediterranean): Between morpho-structural potentialities, originality of the hydrographic network and societal reorganizations, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-204, https://doi.org/10.5194/icg2022-204, 2022.

It has been debated whether gradual, persistent river flows or infrequent outburst floods play more important roles shaping the rugged mountain landscape, partially tied to insufficient evidence based on reliable retrievals of erosion and sediment fluxes from historical outburst floods. The Himalayan Tsangpo Gorge, exhibiting rapid exhumation and outburst floods, provides a perfect avenue to shed light on this debate. Here we report the quantitative erosion and transport capacity of a recent catastrophic outburst flood in Himalayan which occurred in June 2000 by landslide-dam failure with a peak discharge of 10⁵ m³/s. The flood lasted for only ~10 hours, but equivalent to the cumulative effect of 10³ years of continuously gradual fluvial transport and erosion. The valley widened three times, triggering a large number of landslides, and extensive boulder bars were formed in the channel. These boulder bars protected the channel bed from incision but promoted extensive lateral erosion through increased roughness, resulting in widespread bank erosion and concurrent landslides, which will continue to do so until the next catastrophic flood remobilizes them. We provide direct evidence that highlights the dominance of recurrent outburst floods on drastic exhumation, deep gorge formation and long-term landscape evolution over rapidly uplifting mountains.

How to cite: Wang, X., Dong, X., Yang, L., Zhao, Z., Ronal Van Balen, R., Miao, X., Liu, T., Jef Vandenberghe, J., and Lu, H.: Outburst floods control the fluvial landscape evolution in Himalayan Tsangpo Gorge, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-223, https://doi.org/10.5194/icg2022-223, 2022.

Modern glaciers and processes operating within their foreland are often used as analogues to infer past glacial conditions and interpret dating results. As such, an important research question is how glacial landforms changed over time after being created by ice or released from under the ice, and how confident can we use them as modern analogues of past environments? Proglacial areas exposed because of glacier recession are among the most dynamic landscapes in polar and mountainous regions and are intensively modified by various geomorphological processes associated with ice margin retreat, meltwater activity, and paraglacial adjustment of topography. As these areas contain important traces of the former glacial regime and dynamics, quantification of the recent transformation of these areas is crucial in terms of glacial landsystem studies.

In this study, we quantified recent landscape dynamics in proglacial areas of Fjallsjökull and Hrútárjökull (SE Iceland) based on time series of unmanned aerial vehicle surveys (UAV) from 2014, 2016, 2017, 2018, 2019 and 2021. UAV data were processed using the structure from motion (SfM) approach to generate detailed (0.1 m ground sampling distance) orthomosaics and digital elevation models. Based on the results of geomorphic change detection, five types of landscape dynamics were identified: (1) Degradation of ice-cored moraines and expansion of the lake; (2) Ice margin retreat and melting; (3) Ice margin oscillation and dislocation of the esker; (4) Degradation of buried snout and development of pitted outwash; (5) Degradation of buried ice in the overdeepening. In general, the volume balance for Fjallsjökull/Hrútárjökull foreland over the 2014-2021 period was negative. Large-scale changes were related to the retreat of the glaciers’ margin, ice melting and drainage reconfiguration. A similar magnitude of volume loss was observed in places where the ice-cored moraines degraded, and the lake expanded. Degradation of buried ice and associated collapsing of outwash plain was responsible for minor volume loss. In some relatively small areas, gain in elevation was observed – it was primarily associated with ice margin pushing or transporting sediments during winter re-advances and, to a much lesser degree, by mobilizations of sediments due to debris flows. Relatively large areas of glacial foreland remained stable over the observation period. However, as an example of collapsing outwash indicates, topography adjustment due to the final melting of dead ice might occur several tens of years after the ice margin apparently retreated, and the ground was stabilized and vegetated.

This research was funded by National Science Centre, Poland, project number 2019/35/B/ST10/03928.

How to cite: Ewertowski, M., Evans, D., Tomczyk, A., and Śledź, S.: Mapping and quantification of proglacial landscape changes based on time-series of UAV surveys: A case study of a temperate glacial landsystem of Fjallsjökull/Hrútárjökull, SE Iceland, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-565, https://doi.org/10.5194/icg2022-565, 2022.

Coastal marshes from the northern Atlantic Iberian margin are unique sedimentary environments filtering and storing chemical pollutants, nutrients and terrestrial carbon,proxies that may allow deciphering their environmental transformation. The Nalón estuary marshes (Asturias, N Spain) have been severely impacted by human activities such as construction of dikes, land reclamation and coal and mercury mining effluents. We analyzed foraminiferal assemblages from 18 surface samples collected from salt marsh and tidal flat settings along the axis of the estuary and a 50-cm-long core recovered from the lower estuary San Juan de la Arena salt marsh in order to understand recent coastal sedimentation and erosion processes. Salt marsh surface samples are characterized by Trochammina inflata, Entzia macrescens, Miliamminafusca andHaplophragmoideswilbertitaxa in the living and dead assemblages. Tidal flat samples from the middle estuary are dominated bythe living speciesHaynesina germanica, Ammonia tepida, Cribroeplhidium excavatumand M. fusca. In turn, deadassemblages reveal an elevated proportion (max. 95%) of salt marsh taxa, much higher than those determined in other tidal flats from this coastal region, that could derive from the ongoing erosion of adjacent salt marsh areas.The stratigraphy of the sedimentary core is distinguished by two intervals with characteristic microfossil assemblages,whose depositional environment has been inferred from those analogues represented by the surface samples. The lowermost unit (50-28 cm), with a mixture of H. germanica, M.fusca, A. tepida and C. excavatum,has been interpreted as an intertidal flat environment, deposited before the development of the San Juan de la Arena salt marsh, namely previous to the 1950s, as observed in aerial photographs. The second unit (28-0 cm) is characterized mainly byE. macrescensand T. inflata, followed by M. fusca and H. wilberti, representing a salt marsh environment. The salt marshwas developed after the 1950s probably in response to an important accumulation of sediment in the lower estuary. However, as observed in aerial photographs, this salt marsh is no longer active owing to very active erosional processes, possibly associated to the construction of a dock in front of this area in ~2004-2006. On the whole, the foraminiferal analysis of the Nalón estuary sedimentary record hasrevealedsignificant changes in the sedimentation and erosion processesalong the middle and lower estuary during the 20^th and 21^st centuries.

Acknowledgements: Research supported by the Spanish MINECO RTI2018-095678-B-C21(MCIU/AEI/FEDER, UE) project.

How to cite: Gardoqui, J., Cearreta, A., García-Artola, A., Irabien, M. J., Gómez-Arozamena, J., and Villasante-Marcos, V.: Recent sedimentation-erosion processes along the Nalón estuary (Asturias, N Spain), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-689, https://doi.org/10.5194/icg2022-689, 2022.

Both internal and external Earth’s dynamics are constantly changing the landscapes and one of the most influent external components are the fluvial processes, altering the relief through erosion and fluvial deposition, as well as through its respective drainage network’s reorganization. The drainage basins dynamics seeks to achieve a balance between tectonic uplift and river erosion. The use of parameter Chi (χ) allows a comparison of basins in different scales, erosion and uplift rates, making it possible to determinate its steady or transient state and comprehends the dynamics de divisor migration of basins. Although the great advances have been reached in last decades, there are still many questions without answer. For the accomplishment of this study, two areas in the Serra do Mar of São Paulo and Paraná were chosen due to the presence of important river captures, which generated significant reorganizations in the drainage network. Furthermore, cosmogenic isotopes (¹⁰Be) data from existent literature in Serra do Mar of Paraná allows the estimation of the denudation rate of these basins in the long term. In this study, these rates are analyzed combined with values of Chi, verifying the influence of the captured rivers, which contribute to the understanding of landscape evolution. This study uses the Digital Elevation Model (DEM) SRTM 30m. The DEM data were treated in ArcGIS and analyzed in MATLAB, where oceanic and continental basins were selected, considering sea level as the base level. The analysis was made through functions of Topographic Analysis Kit (TAK), integrated to TopoToolBox, to generate longitudinal and elevation-Chi profiles and Chi maps plotted with knickpoints data and, for the Paraná basins, the product obtained were simultaneously analyzed with ¹⁰Be data. From the analysis of these data, was possible to notice the ocean basins are capturing the continental basins and, therefore, that these basins are in a transient state, which means that their divisor is migrating towards higher Chi values, thus, towards the interior of the continent. In Paraná basins, the retreating areas of the Serra do Mar escarpment directly related to places of high erosion rates on the oceanic slope. These results, although preliminary, attest the potential of analysis methods used, proving the influence of river captures in the disruption of the steady state between adjacent drainage basins located on the oceanic and continental slopes, as well as their influence on the differentiated retreat in the Serra do Mar escarpment.

How to cite: Coelho Giorio do Vale, C., Ferreira Fernandes, N., Villela Mafra Alvesda Silva, R., and Maria da Silva, L.: Effects of drainage captures in the retreat of Serra do Mar: an analyze using the combination of numerical models and cosmogenic isotopes, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-596, https://doi.org/10.5194/icg2022-596, 2022.

Drainage reversals occur when a channel reverses its flow direction by 180^o while exploiting its antecedent valley. This reorganization mode can critically impact landscapes' hydrologic and geomorphic functionality, but the processes inducing reversals and the related landscape dynamics have not been studied in detail. Reversals are commonly attributed to tectonic tilting. However, in many cases, independent evidence for tilting is missing. Furthermore, when reversals occur toward great escarpments, as was documented in many terrains around the globe, isostatic tilting is expected to occur away and not toward the escarpments.

The current study explores a natural laboratory for drainage reversals in the southeastern Negev Desert, Israel. We identified in this field area tens of highland channels that reversed their flow direction eastward and toward the Arava Valley Escarpment.

Reversals are established by observations of (1) barbed tributaries that join the main trunk with junction angles > 90^o and preserve the antecedent pre-reversal drainage topology; (2) a valley confined drainage divide (windgap) that separates the reversed channel from the antecedent, beheaded channel; and (3) series of terraces that grade west, toward the windgap and opposite to the active flow direction.

Based on field observations and morphometric analysis, we propose a new, tilting-independent, mechanism for inducing flow reversals. According to this mechanism, reversal is linked to localized windgap migration within the antecedent channel and away from the escarpment. Migration is driven by slope imbalance across the windgap with steeper slopes at the escarpment side, and by erodibility differences between the hard rocky interfluves and the more erodible valley fill.

Using a new algorithm for quantifying valley width, we find that the scaling between drainage area (A) and width (W) differs between reversed, beheaded, and non-reorganized valleys. In addition to providing markers for reorganization, the unique A-W scaling leads to feedback that promotes further windgap migration and generates longer reversals.

The oppositely grading terraces that accompany some reversed channels present an outstanding opportunity for quantifying the dynamic and rate of windgap migration. We hypothesize that the abandonment age of each terrace reflects the timing at which the paleo-windgap migrated past the location of the terrace, promoting the incision of the reversed channel that generated the terrace. Accordingly, the abandonment ages of the terraces can inform us about the timing and dynamics of windgap migration.

Absolute ages of terrace abandonment were constrained by luminescence dating, with complementary relative ages inferred from chronosequence of reg soils, which develop on abandoned terraces in hyper-arid environments. In agreement with the reversal model, we found that the degree of soil development and the abandonment ages of terraces increase with distance from the windgap eastwards. The average windgap migration rate has been ~1 mm/yr since 200 Kyr, an order of magnitude greater than the vertical incision rate of the reversed channel. The age-distance relations of the terraces indicate episodic windgap migration with a recent stalling. A similar age for other dated windages in the region hints at a regional, possibly climatic control on windgap migration.  

How to cite: Goren, L., Harel, E., Shelef, E., Crouvi, O., and Ginat, H.: Landscape evolution related to drainage reversals toward escarpments: Insights from the southeastern Negev Desert, Israel, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-266, https://doi.org/10.5194/icg2022-266, 2022.

Aeolian-Fluvial (A-F) processes along dunefield margins document environmental changes in arid zones around the world. In the present study, at the northwestern Negev dunefield (Israel) margins, high-resolution chrono-stratigraphic analysis of marginal Vegetated Linear Dunes (VLDs) and fine-grained alluvial plains was conducted. Nineteen stratigraphic sections were analyzed in detail. Dating included pre-measurements using Portable Optically Stimulated Luminescence (POSL), which were used to decipher representative samples for OSL dating. Selected hearth and vegetation samples were radiocarbon dated as well.

A-F processes along dunefield margins may generate reliable and detailed palaeoarchives, by combining POSL and OSL analyses. VLDs, prone to defined periods of activation and stabilization, control a gradual and lagged shift from aeolian to fluvial domination in the dune-dammed dunefield margins, succeeding dunefield stabilization.

In an aeolian-dominated environment, either fully or partly dammed fluvial systems aggregate upstream-sourced sediments along the dunefield margins, forming an alluvial plain. Dune-dam waterbody deposits include three distinct types: (a) event-based couplets, (b) massive structureless loam and (c) fine-laminas. These deposits that may remain preserved for substantial times bury usually truncated dune remains. Aeolian deflation of fine-grained sediments from dune-dam waterbody deposits, percolated into adjacent marginal VLD, initiating pedogenic processes. Altogether, dune-dam impoundments were found to be spatially dynamic processes, in which the dune-dammed fluvial system gradually propagates downstream from the dunefiled margin into the dunefield. Each impoundment was generated by slightly or distinctly different A-F mechanisms depending on the location of the damming-dunes in relation to the dunefield margins.  

In the northwestern Negev, three major sand incursions into <180 km² fluvial systems during the LGM, Heinrich-1 and Younger-Dryas, resulted in localized and usually seasonal waterbodies, utilized by EpiPalaeolithic hunter-gatherers . This study also revelaed that during the early Holocene a climatic shift, which left a signature in the Mediterranean Basin in the form of Sapropel-1, was recorded along the dunefield margins, forming the last, upper and significant portion of the alluvial plains. This aggregative environment was also utilized by Neolithic and Chalcolithic man in some basins, locally reactivating VLDs. After dune-dam breaching, a fluvial-dominated environment developed, characterized by floodplain deposition, and scour and fill patterns.

How to cite: Robins, L., Roskin, J., Edeltin, L., Bookman, R., Yu, L., and Greenbaum, N.: Late Quaternary aeolian-fluvial palaeoarchives along dunefield margins, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-103, https://doi.org/10.5194/icg2022-103, 2022.

The research conducted in recent years has revealed that processes operating at depth play an important role in the morphogenesis of stepped tablelands in Central Europe (SW Poland, N Czechia), underlain by alternating layers of sandstone and fine-grained rocks of the Upper Cretaceous age. It has been demonstrated that underground erosion significantly contributes to the in situ disintegration of the marginal parts of sandstone plateaus and mesas, thereby producing distinctive ruiniform assemblages. They comprise chaotic boulder clusters replacing the cliff-lines, joint-aligned corridors, clefts opened due to the loss of mass from beneath, as well as plazas and courtyards with negligible surface runoff. While the widespread occurrence of sandy cones at the outlets of vertical fissures and allochthonous sandy aprons on the subjacent slopes testifies well to the efficiency of underground erosion, the mechanisms of detachment of sand grains remain unknown. This research aims to elucidate which processes are making the sandstone mechanically incoherent and susceptible for mechanical erosion at depth.

In older views weathering processes acting upon sandstone cliff-lines have either remained unspecified or a priori assumed to be mechanical breakdown. Yet, the presence of joint-aligned and highly disintegrated zones, often mimicking the grikes of the ‘classic’ karst terrains, as well as the widespread evidence of sandy detritus removal via subsurface drainage, allowed us to hypothesise that dissolution may be an important but neglected factor responsible for the loss of coherence of the sandstone rock mass.

Sandstone samples were collected from both disintegrated and non-disintegrated sandstone cliff-lines, as well as fresh debris originating from a recent rockfall event in one of the rock cities in Czechia. Loose grains of sand, already removed from the caprock and deposited at the foot of rock walls, were investigated too. Scanning electron microscopy equipped with energy dispersive spectrometer (SEM-EDX) was used to study micromorphological changes, diagnostic of intensive chemical weathering. This was supplemented by studies using the polarizing light microscopy, i.e. study of thin sections as well as x-ray diffraction (XRD) accompanied by thermal analysis (DSC-TG) to evaluate mineralogical composition of sandstone and to assess the secondary rock porosity.

The preliminary results revealed high degree of etching, mainly of syntaxial quartz overgrowths, with a number of v-shaped or irregularly shaped pits as well as large embayments. Interestingly, SEM-EDX analysis showed the presence of kaolinite, which might conform to the advanced chemical weathering of sandstone as well. It is supposed that solutional processes not only have prepared the rock for further erosional processes and the resultant development of ruiniform relief, but they also contribute to a variety of catastrophic mass movements due to the significant decrease of intact rock strength.

The results presented are the first outcomes of the new Q-MESA project (no. 2020/39/D/ST10/00861) funded by the National Science Centre, Poland.

How to cite: Duszyński, F., Bartz, W., Woronko, B., Jancewicz, K., Migoń, P., and Sauro, F.: Another one bites the quartz? How silica dissolution contributes to the development of ruiniform relief in the Central European sandstone tablelands?, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-199, https://doi.org/10.5194/icg2022-199, 2022.

Groundwater has been implicated as an important geomorphic agent in valley development. In unconsolidated sand and gravel, field observations and numerical simulations have shown that groundwater can lead to the formation of theatre-headed valleys. However, the temporal scale at which these valleys form and the influence of geologic heterogeneities on valley evolution remain poorly constrained. In bedrock, the development of valleys by groundwater remains controversial, and other processes (e.g. plunge-pool erosion, megaflooding) have been proposed to explain such landforms.

Here I will present two case studies, from the Canterbury coastline of New Zealand (unconsolidated sediments) and the Maltese Islands (limestone), to address these knowledge gaps.

In the first case study (New Zealand), I integrate field observations, luminescence dating, multi-temporal UAV and satellite data, time-domain electromagnetic data and slope stability modelling to show that theatre-headed valley erosion by groundwater in sand and gravel is an episodic process that occurs once every 227 d on average, when rainfall intensities exceed 40 mm/d. Valleys can be elongated at rates of 30 m/d via the formation of alcoves and tunnels by groundwater seepage, followed by retrogressive slope failure due to undermining and a decrease in shear strength. Valley location is determined by the occurrence of hydraulically conductive zones, such as relict braided river channels, and sand lenses.

In the second case study (Maltese Islands), I combine field and remote sensing observations from Gnejna Valley with numerical modelling to demonstrate that groundwater seepage is the key driver of theatre-headed valley formation in jointed limestones over clays. Erosion takes place via widening of joints and fractures by fluid pressure and dissolution, and creeping of the underlying clay layer, both of which lead to slope failure at the valley head and its upslope retreat. The talus is removed by creep and sliding on the valley bed. The location and width of the valley are determined by the location of a master fault and the extent of the damage zone. An exponential decrease of seepage away from the master fault gives rise to a theatre-shaped head.

How to cite: Micallef, A.: The role of groundwater in forming theatre-headed valleys in unconsolidated sediments and bedrock, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-287, https://doi.org/10.5194/icg2022-287, 2022.

The geomorphological process creating the birth and development of large-scale erosional surfaces remains somewhat unclear. In this regard, new insights on the process leading to the creation of such large-scale surfaces were revealed during intensive study on the morphotectonic evolution of the Sinai-Israel micro-plate.

A major erosion surface developed during the Oligocene – Early Miocene, (34-20 Ma) in the northern Red Sea and southern Levant as a result of the combined effects: the formation of an ~3000 km × 1500 km crustal dome above the Afar plume, affecting the northeastern sector of the Afro-Arabian continent, and widespread fluvial erosion that gradually truncated the northern edge of this dome. The truncation of the northward tilted Sinai-Israel plate exposed the Precambrian basement rocks at its southern tip, while a series of sandstone and carbonate units were exposed at its central and northern sector. The Syrian Arc anticlines, developed in the Late Cretaceous, were deeply truncated, exposing their Triassic – Jurassic section. During this event, a geological section, estimated to be 2000-500 m, was removed from the entire region. The Oligocene Regional Truncation Surface (RTS) developed by a continues fluvial and chemical erosion acting on a gentle uplifted region, on which the rate of tectonic uplift was smaller than the ability of the erosive agents to erode and transport the eroded products out of the region, deposited them in the eastern Mediterranean basin. These clastic sediments are holding large-scale gas reservoirs. The reconstruction of this erosive surface is important for detection of the tectonic activity that predates the plate separation of the Sinai-Israel plate and the development of the Dead Sea Transform, initiated in 18-16 Ma along a preexisting suture line. The development of the truncation surface was followed by the deposition of Early Miocene fluvial sediments, deposited within broad channels and valleys, gently incising the original Oligocene erosion surface.

General uplift, tectonic depressions and dome structures developed during the Middle Miocene to Early Pleistocene (16–1.5 Ma), locally deforming the general flat relief left by the previous erosional stage. This rapid tectonic activity promoted the breakup and evolution of the Sinai-Israel microplate generated the development of a deeply incised drainage system, bordered by large-scale cliff. This new erosive pattern is best demonstrated by the deeply incised valleys developed within the core of the Syrian Arc anticlines. The interaction between the anticlinal structure and the Oligocene truncation surface is dictating the configuration of the oval valleys, while their development as deeply incised valleys evolved during younger tectonic events in the Miocene. Another modification to the former flat landscape was caused during the 1.5-1 Ma tectonic event that uplifted and tilted the Negev region toward the Dead Sea Rift. At this stage, a new drainage system was developed, deeply incising the former flat surface. However, despite these modifications, the original Oligocene erosive surface is still dominating the present skyline in the entire Middle East. During most of the time, the landscape evolutionary processes were active under arid climates, contributing to good preservation of diverse geomorphological features.

How to cite: Yoav, A.: The genesis and development of large-scale erosion surfaces – insights from the Sinai-Israel micro plate, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-133, https://doi.org/10.5194/icg2022-133, 2022.