ICG2022-2

ICG2022
Methods and Techniques in Geomorphology 

Much of the excitement in being geomorphologists involves developing new methods and pushing forward existing techniques to understand better the dynamics and evolution of the Earth's surface systems that we study. The current thematic session is dedicated to novel and exciting approaches for studying landscapes and landforms. We particularly encourage submissions that (1) propose new or develop existing geomorphologic techniques; (2) examine how a combination of several techniques to target a single problem produces new insights regarding each of the techniques and/or provides a richer understanding of the geomorphic system; (3) explore how methods developed for other (sub)disciplines could be adopted and developed for geomorphologic applications; and (4) consider the gaps between the time and length scales inherent to the applied techniques and those that characterized the natural system.

Conveners: Liran Goren, Martin Stokes, Pedro Cunha, Aldina Piedade
Orals
| Tue, 13 Sep, 17:00–19:00|Room Sala Almedina-C2D
Poster
| Attendance Tue, 13 Sep, 16:30–16:45 | Display Mon, 12 Sep, 09:00–Tue, 13 Sep, 19:00|Poster area

Orals: Tue, 13 Sep | Room Sala Almedina-C2D

Chairpersons: Liran Goren, Martin Stokes, Pedro Cunha
17:00–17:15
|
ICG2022-440
Natalie Barbosa, Juilson Jubanski, Ulrich Münzer, and Florian Siegert

High mountains represent one of the most dynamic environments on earth. Landscape changes are expressed by subtle movements such as creeping permafrost and slow landsliding, or sudden events, such as landslides, rockfalls, and debris flows, which extend over wide areas, imposing hazards to human life and infrastructure. Monitoring topographic changes in high mountains are paramount to understanding mass-transport systems, detecting related environmental variability, and assessing natural hazards. 

Due to the differences in the speed of topographic changes, monitoring high mountains requires high-resolution datasets over long periods of time and wide extents. Digital photogrammetry enables the computation of digital surface models (DSM) at various resolutions according to the scales of aerial photographs and has proved useful to monitor landscape changes in different geomorphological environments. High-resolution satellites provide long-time observations with wide coverage, but their resolution (1 m to 3 m) is often coarse to monitor small changes. On the other hand, UAV surveys, with a resolution as high as 1 cm, are limited to narrow areas. National mapping agencies have been performing digital aerial surveys at high-resolution (ca. 20 cm) for more than a decade, nevertheless, differences in acquisition technologies, lack of planning oriented to monitor geomorphological changes, uneven timestamps, and particularities of the individual surveys, pose challenges to the usage of these high-resolution datasets. 

The AlpSenseRely project, Alpine remote sensing of climate-induced natural hazards, aims to explore the feasibility of using aerial imagery to reconstruct morphometric landscape changes and establish a monitoring concept for alpine natural hazards.

The Hochvogel summit is located at 2 592 m a.s.l. at Allgäu High Alps, Germany/Austria. The Hochvogel’s southwestern slope is characterized by constant rockfall activity. Additionally, a meter-size-long fracture at the summit poses a catastrophic rock failure scenario (Leinauer et al., 2020, 2021). In 2016 a total of 130 000 m3 was detached from the southwestern slope of the summit and impacted the basin sediment mobilization and accumulation patterns. Observations on the basin response are key to understanding the response of the basin to sporadic high sediment input, relating environmental conditions, and constraining models of catastrophic events.

This contribution presents the retrospective topographic changes recorded at the Hochvogel slopes since 2010 in a total of seven UltraCam acquisitions at 20 cm resolution. We propose the usage of a 3D coregistration to improve the quantification of small sub-meter topographic changes. Eroded and sedimented volumes are computed for the ca. 400 000 m2 southwestern basin using a fully free-source workflow based on python and semi-automatic filtering of errors. 

 

References:

Leinauer, J., Jacobs, B. and Krautblatter, M. (2020), “Anticipating an imminent large rock slope failure at the Hochvogel (Allgäu Alps)”, Geomechanics and Tunnelling, Vol. 13 No. 6, pp. 597–603.
Leinauer, J., Jacobs, B. and Krautblatter, M. (2021), “High alpine geotechnical real time monitoring and early warning at a large imminent rock slope failure (Hochvogel, GER/AUT)”, IOP Conference Series: Earth and Environmental Science, Vol. 833 No. 1, p. 012146.

How to cite: Barbosa, N., Jubanski, J., Münzer, U., and Siegert, F.: Reconstruction of morphometric changes over a decade in a high active alpine area using UltraCam aerial imagery., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-440, https://doi.org/10.5194/icg2022-440, 2022.

17:15–17:30
|
ICG2022-522
Sebastián Granados-Bolaños, Nicola Surian, Christian Birkel, Adolfo Quesada-Román, and Guillermo E. Alvarado

The use of unmanned aerial vehicles (UAVs or “drones”) in geosciences is growing rapidly and is significantly contributing to the geomorphological analysis of diverse landforms and their dynamics in a variety of environments around the world. Specifically, UAVs in geomorphology have proved to be a robust and versatile tool due to their ability to acquire large volumes of high-resolution data in a relatively short time and at low-cost compared to other surveying methods. This technology is evolving rapidly and is becoming each time more relevant for the analysis of surface processes. It allows the rapid mapping of highly dynamic geomorphological features with high-resolution which is particularly useful for the study of fluvial processes. Depending on the environmental conditions and flight parameters, common low-cost (<$3000) commercial UAV models such as the DJI Phantom 4 V.2 used in this research can map over 30 hectares of surface in less than 20 minutes, proving to be a valuable tool for monitoring fluvial processes, especially in tropical humid environments where cloudiness can be an important obstacle for other survey methods such as photogrammetric-piloted airborne missions or satellite imagery. We present the results of the usefulness of UAV technology in fluvial geomorphology with several case studies in diverse humid tropical environments of Costa Rica, Central America.  We illustrate how UAV surveying can acquire high-resolution digital terrain and surface models for hydraulic modeling, geomorphic analysis, and forensic reconstruction of flood events in two urban rivers. We also illustrate how low-altitude photogrammetric flights can detect channel changes with centimetric resolution under dense pristine forest coverage, a challenging environment for monitoring river dynamics. Additionally, we used UAV photogrammetric post-processing for automated analysis of particle size distribution detection in river channels. Finally, we exemplify how this technology can be used for riparian vegetation analysis under diverse conditions. The post-processing of the orthomosaics and surface models allowed to construct high-resolution indexes such as Visible Atmospherically Resistant Index (VARI), vegetation height, Leaf Area Index (LAI), and other datasets for ecological analysis of riverine environments.

How to cite: Granados-Bolaños, S., Surian, N., Birkel, C., Quesada-Román, A., and Alvarado, G. E.: UAV applications in humid tropical fluvial geomorphology , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-522, https://doi.org/10.5194/icg2022-522, 2022.

17:30–17:45
|
ICG2022-407
Aliki Konsolaki, Emmanuel Vassilakis, Maria Stavropoulou, Evangelia Kotsi, and George Kontostavlos

Technical advancements have widened the limits of remote sensing and Terrestrial Laser Scanning technology in studying underground cavities. Furthermore, the use of Unmanned Aerial Systems has proven to be a significant advantage in the study of caves, as under certain circumstances during the data processing, it is plausible to combine TLS and UAS data for generating a complete 3D model, representing surface and subsurface simultaneously. The use of state-of-the-art laser scanning equipment either terrestrial or handheld accompanied by total station measurements on a series of ground control points, has resulted in the scanning and detailed mapping the entire Melissani and Drogarati caves, in Cephalonia Island, in Greece, including hidden cavities. This study attempted not only to delineate a new methodology for compiling a highly detailed cave map, but also to identify structural discontinuities and faults for further investigation of the influence of rock failures in causing rock falls and further damage in the caves. Both show caves attract many visitors and since they are located at an area of very high seismicity, where large earthquakes occur very frequently, the risk is rather high.

The methodology is based on the synergy of equipment in different working levels, since the cave environment is by far one of the most difficult cases to survey, led to hazard identification in high detail and accuracy throughout the cavity. The fieldwork includes the generation of a unified point cloud for the underground cavity, generated by scanning at several bases inside the cave and by entering smaller cavities by holding the mobile scanner. The bundling of the partial point clouds is possible since the proposed methodology includes the establishment of a dense network of Ground Control Points, which are measured with Total Station equipment for gaining actual coordinates. After the merging of the partial scans were combined into a single point cloud, the methodology continues with further processing including filtering and noisy points removal. Moreover, the final product is combined with the point cloud that was generated after the photogrammetric processing and the methodology is completed with exporting the results in file formats that can be imported in several geotechnical or discontinuity recognition software for further interpretation. The results along with the produced 3D models could be utilized to determine areas susceptible to different failure types. The assessment of rock stability within a cave by combined innovative equipment, techniques, and research methods could be considered by the management authorities for the maintenance and/or re-design the tourist routes.

How to cite: Konsolaki, A., Vassilakis, E., Stavropoulou, M., Kotsi, E., and Kontostavlos, G.: Laser Scanning methods and techniques for high-detail 3D modelling of caves, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-407, https://doi.org/10.5194/icg2022-407, 2022.

17:45–18:00
|
ICG2022-561
Dorota Chmielowska and Barbara Woronko

Recognition of quartz-sand grain shape, particularly its roundness and sphericity,  is essential in reconstruction of sedimentary settings, transport conditions, duration of transport and post-sedimentary weathering. It is assumed that in currents environments (e.g. aeolian, fluvial) the increasing transport duration is reflected in progressively higher degree of roundness and sphericity of quartz grains. Furthermore, during transport, grains are gradually reduced to similar size and similar roundness; this leads to the accumulation of sediments with similar grain size distributions in differing environments. However, the question still remains: to what extent is the shape of a grain is the result of processes in given environment (e.g. aeolian or fluvial) and how much of its shape is inherited from other environments. The description of shape is subjective and reduction to a mathematical formula is time-consuming and in many cases impossible to apply (e.g. in field studies). One of the solutions is the automatic analysis of particle shape using the Morphologi G3SE. This study aimed to verify  the efficacy of automatic image analysis (AIPS) in discerning quartz sand grain shape and associated sedimentary settings. Quartz grains (0.8-1.0 mm)  from three sedimentary environments: angular, fresh grains (GNU) and aeolian (GRM) and fluvial grains (GEL) and with similar degree of roundness (well and very well rounded) were analyzed in terms of four shape-description parameters: Circularity High Sensitive (Circularity HS); Convexity; Solidity; Aspect Ratio. Next, principal component analysis (PCA) and discriminant analysis were applied to the obtained AIPS data. The parameter that best distinguishes the shape of GNU, GRM, and GEL grains is Circularity HS, associated with the degree of roundness, whereas Aspect Ratio was useful for analysing the degree of grain sphericity. The GRM and GEL grains with a high degree of roundness and either low or high sphericity should be characteristic for a long-term reworking by aeolian and fluvial processes. The presence of grains with low sphericity and high roundness in the environments where saltation transport prevails indicates that their shape has been inherited. Such grains require special attention to the Aspect Ratio values. Detailed analysis of grain features - such as sphericity and roundness enables accurate interpretation of transport environments in terms of transport duration and sediment maturity.

How to cite: Chmielowska, D. and Woronko, B.: Shape of quartz grains as an indicator of duration of transport in sedimentary environments and inheritance of shape – efficacy of automatic image analysis, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-561, https://doi.org/10.5194/icg2022-561, 2022.

18:00–18:15
|
ICG2022-550
Timothée Jautzy, Gilles Rixhon, Régis Braucher, Laurent Schmitt, Romain Delunel, Pierre Valla, and Aster Team*

Assessing the rates at which mountain ranges erode is fundamental to disentangle interactions between the various factors controlling their denudation. Measurements of in situ-produced cosmogenic nuclides in modern riverborne sediments allow inferring catchment-wide denudation rate averaged over several thousand years. This well-established method allows determining the main factor(s) controlling the denudation in those mountain ranges displaying strong gradient(s) in e.g., lithology, morphometry or climate. However, the validity of this method depends on several assumptions. One of these is the cosmogenic steady-state for which it is assumed that the nuclide production equals the nuclide removal by erosion. Paired-nuclide analysis consisting in measuring the concentrations of two different nuclides from the same sampling material allows testing the validity of this assumption. Although this was commonly undertaken in the early days of the method, the overwhelming majority of cosmogenic-derived denudation rates now settle on a single nuclide, which is 10Be.

 

Quaternary erosion of the Hercynian low-mountain ranges strewn across the European alpine foreland (where much of the recent work was undertaken) has received little attention so far. Among them, the Vosges Mountains (VM) are particularly suitable for assessing denudation via cosmogenic nuclides since they display a strong N-S gradient for potential factors controlling denudation. First, the geological basement allows a bipartite subdivision: the heterogeneous crystalline core in the southern part contrasts with the much more homogeneous sandstone cover in the northern part. Second, a clear topographic and morphometric gradient is reflected by steep and gently-sloping hillslopes in the southern and northern part, respectively. Third, a sharp N-S precipitation gradient (>1000mm/yr) is recorded, well matching the imprint left by former glaciations: whereas the southern part hosted abundant valley glaciers, the northern part was free of ice.

 

This study thus aims to test the validity of the cosmogenic-based approach by sampling 22 catchments draining the whole VM for a paired-nuclide analysis (26Al-10Be). Lithological, morphometric and climatic characteristics were also quantified for each catchment. Our results show that almost half (10/22) of the samples violate the steady-state assumption. Interestingly, a vast majority of these unsteady catchments are located in the south of the massif which was massively and repeatedly glaciated during cold stages. The impact of former glaciations on the cosmogenic steady-state was confronted with the surface of glacial and fluvio-glacial deposits in each catchment. The negative relation suggests a complex exposure history in the formerly glaciated catchments (i.e., bedrock inheritance and/or sediment reworking). Whilst this unsteadiness most probably prevents the observation of a N-S gradient in denudation rates, it importantly emphasises the importance and need for using a second nuclide to infer reliable denudation rates at the massif-scale when glacial erosion is involved.

*Georges Aumaître, Didier L. Bourlès, Karim Keddadouche

How to cite: Jautzy, T., Rixhon, G., Braucher, R., Schmitt, L., Delunel, R., Valla, P., and Team*, A.: The need for a second nuclide: former glaciations impact the validity of 10Be-derived denudation rates in the Vosges Mountains (NE France), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-550, https://doi.org/10.5194/icg2022-550, 2022.

18:15–18:30
|
ICG2022-247
Identifying temporal and spatial denudation variations using in-situ terrestrial cosmogenic nuclides along vertical profiles on enrooted bedrock.
(withdrawn)
Gerald Raab
18:30–18:45
|
ICG2022-485
Tracking sediment provenance using quartz luminescence sensitivity in thenorthwestern Amazon basin (Colombia): insights for paleodrainage reconstruction
Carolina Cruz, Fabiano Pupim, André Sawakuchi, Mauricio Parra, Ian del Rio Garcia, Caio Breda, Giovanny Rodriguez, and Sebastián Marulanda
18:45–19:00
|
ICG2022-740
How to constrain the uplift history and landscape evolution processes of the youthful stage mountain by the landscape evolution model?
(withdrawn)
Haopeng Geng, Shun Cai, and Baotian Pan
Display time: Mon, 12 Sep 09:00–Tue, 13 Sep 19:00

Poster: Tue, 13 Sep, 16:30–16:45 | Poster area

Chairpersons: Pedro Cunha, Liran Goren, Martin Stokes
P3
|
ICG2022-170
Michele Camillo Gabriele Licata, Mauro Bonasera, Victor Buleo Tebar, Giandomenico Fubelli, and Battista Taboni

In recent years, digital mapping systems have gained interest among geomorphologists thanks to the fast evolution of technology. However, a mapmaker still uses traditional cartographic supports as printed topographic maps, which need to be   subsequently digitalized. Every step adds an additional level of cartographic error, often difficult to quantify. A solution can be to map the landforms directly in digital format during the fieldwork through an ad hoc system.

With the purpose of making a “native” numerical cartography, GOGIRA (Ground Operative-system for GIS Input Row-data Acquisition) has been realized. GOGIRA consists of a set of hardware and software tools to digitalize real-world geomorphological elements and obtain georeferenced shapefiles. It is currently composed by two devices for data acquisition: an Android App for data collection and a Python-based software for coordinate computation. The technologies have been chosen to be enough accurate but cheaper than already available topographic tools. Each device uses an “Arduino Nano” board and low expensive sensors like MPU6000 (3 axis accelerometer + 3 axis gyroscope) or BNO055 (3 axis accelerometer + 3 axis gyroscope + 3 axis magnetometer).

GOGIRA has been tested in Aosta and Tanaro Valley, in North-Western Alps of Piedmont Region (Italy). The first case study was chosen in the context of the active monitoring of a complex landslide system close to an important highway that connects Italy, France and Swiss. It was possible to remotely (distance from 0.5 to 2.7 km from targets) map an area of limited access due to steep slopes, high scarps and rockfall hazard. Small single elements were mapped, as rockfall scarps not detectable from topographic support. The time for the survey has revealed to be short (a couple of hours included the search of a good observation point). The second case study was picked during the preliminary fieldwork for the realization of rolling tanks to mitigate the hydrologic hazard in the anthropized Tanaro Plain. The area has been investigated both with traditional methods and GOGIRA system, if morphometry allowed. Scarps, karst springs and debris/rock flow tracks were mapped.

The results obtained from both the tests highlight complications in mapping polygonal elements regarding visibility and overlaying but show a particularly high reliability in collecting data on linear and punctual geomorphic elements.

How to cite: Licata, M. C. G., Bonasera, M., Buleo Tebar, V., Fubelli, G., and Taboni, B.: Digital geomorphological mapping with GOGIRA (Ground Operative-system for GIS Input Raw-data Acquisition) – An innovative system to numerical cartography., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-170, https://doi.org/10.5194/icg2022-170, 2022.

P4
|
ICG2022-228
Steven Binnie, Carlos Neto de Carvalho, Pedro Cunha, Diamantino Pereira, Paulo Pereira, and Tibor Dunai

The formation and development of major rivers limits the overall pace of the surrounding landscape evolution and drives sediment delivery from source to sink. The timings and rates of river incision may be a response to external influences, such as tectonic or climate driven base-level changes, or alternatively they may be linked to the breaching of internal thresholds, for example, drainage capture events. The Tejo and Douro rivers (also known as Tagus and Duero rivers) each drain a significant portion of the Iberian Peninsula and much of their courses through Portugal are typified by v-shaped valleys that are deeply incised into the surrounding topography. Earlier work has dated fluvial terrace deposits, mostly by luminescence techniques, but also by electron spin resonance and cosmogenic nuclide exposure dating. This has provided constraints on the late Pleistocene histories of the Tejo and Douro rivers, however, the timing of their transition from endorheic to exorheic is not precisely known and whether or not their histories are linked to a common mechanism is unclear.

This study aims to provide age constraints on the early history of the Tejo and Douro rivers, and to examine whether and to what degree the erosion rates of low relief, granite etchplain landscapes within the river’s catchment areas are responding to the trunk channel incision. We focus on reaches of the Tejo and Douro rivers located in the eastern sector of mainland Portugal. Samples were collected for cosmogenic nuclide (10Be and 26Al) surface exposure and burial dating to date upper fluvial terrace levels. In addition, a combination of cosmogenic nuclide exposure ages and depth profiles in bedrock outcrops, alongside basin-wide erosion rate determinations will be used constrain the pace of evolution of nearby granitic landscapes. Preparation of the samples for measurement is ongoing and we will present our initial findings.

How to cite: Binnie, S., Neto de Carvalho, C., Cunha, P., Pereira, D., Pereira, P., and Dunai, T.: The timing of formation of the Douro and Tejo rivers and implications for the evolution of the landscapes of central mainland Portugal, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-228, https://doi.org/10.5194/icg2022-228, 2022.

P5
|
ICG2022-353
Luca Lämmle, Archimedes Perez Filho, Alessio Valente, and Carlo Donadio

Fractal geometry methods offer a quantitative description of complex landscapes and can effectively elucidate the behavior of fluvial and coastal geomorphological systems. The bidimensional (2D) fractal geometry of a shoreline, obtainable with Koch’s curve method, may be expressed by a fractional number between 1.1 and 1.4. In this case, the former shoreline is less rugged than the latter, which tends to a Peano’s curve with a fractal dimension D = 2, that is a plan. These sizes, under initial analysis, may not supply direct information on the main processes responsible for modeling the coast. Actually, either erosion, sediment deposition, and tectonics could generate shapes with about the same fractal dimension, independently of their intensity, age, and time during which they acted, as a result of morphological convergence. From the results of research carried out along Mediterranean-type and Brazilian coastlands, it is possible to derive, from the fractal dimension, the primary and secondary processes behind modeling. Here distinguishing tectonic events from littoral dynamics, both responsible for coastal morphology and identifying which is predominant. Calculation and comparison of the 2D-fractal analysis over time along the selected littorals are useful for assessing sea storm impacts and tsunami flash remodeling, e.g., as a relationship between dimension and energy, and the post-event shoreline resilience time comparing the fractal dimensions before and after the main events related to the morphosedimentary features. The same principles can be applied to other geomorphological systems, such as dunes, river drainage networks, islands, and lagoons, representing an important tool for understanding and classifying these environments.

How to cite: Lämmle, L., Perez Filho, A., Valente, A., and Donadio, C.: Fractal analysis and their applications in Geomorphology, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-353, https://doi.org/10.5194/icg2022-353, 2022.

P6
|
ICG2022-446
Karel Šilhán

Knowledge of the spatial distribution of landslides is essential for forestry, landscape planning or hazard assessment. In fact, dendrogeomorphic approaches are a useful tool to construct past landslide behaviour due to the known location of the sampled trees. The position of trees on the landslide surface can influence the detection of spatial patterns of landslide reactivation and significantly affect the amount and intensity of recorded landslide signals within a series of tree rings. This is due to the presence of different morphological zones with different movement mechanisms that generate landslide bodies. In this study, data from 1030 tree-ring series originating from 515 trees occupying ten different complex landslide sites in the Outer Western Carpathians were used to test the spatial distribution of landslide signals during reactivation events and to investigate the specific influence of six different landslide morphological zones on tree growth, with the aim of revealing the most valuable sites for future sampling at the landslide surface. Spatial patterns of landslide reactivation were tested using the Moran index. Signals from tree rings generally do not tend to cluster spatially. Thus, the analysis of spatial patterns can be used as a very stringent condition for verifying landslide events in the case of a limited number of tree-ring signals. Moreover, this analysis is only suitable for block-type landslides (not for flow-type landslides). Furthermore, this research presents a general model of the influence of movement mechanism on tree growth in the different morphological zones forming complex landslide areas. Finally, recommendations for future sampling strategies regarding tree location within specific morphological zones are made based on the results obtained. In general, trees on subhorizontal landslide blocks or in the plastic shallow movement zone should be preferred as opposed to trees on steep landslide sections or in the source zone, which should be avoided.

How to cite: Šilhán, K.: Spatial aspects of tree ring-based reconstruction of past landslides behaviour: where to sample?, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-446, https://doi.org/10.5194/icg2022-446, 2022.

P7
|
ICG2022-492
Fabrizio Garritano and Antonio Guerra

The objective of this paper is to use an unmanned aerial vehicle (UAV), to perform planialtimetric mapping of an erosive feature (gully) located in Rio Claro Municipality, Rio de Janeiro State. The study area is located within Piraí drainage basin, a tributary of Paraíba do Sul River, which presents a history of use and occupation strongly linked to the economic cycles of Brazil, where the native Atlantic Forest biome was cleared, in order to use the soil in a profitable way, making the exploration of sugar cane, coffee growing and opening of areas for pasture. The use of UAVs in geomorphological research effectively enabled a complete assessment of the erosion feature, where it was possible to make cross sections and longitudinal profiles, calculation of length, width and total area. In addition to being an equipment that facilitates the understanding and monitoring of areas of interest, the use of UAVs allows the capture of images of high resolution and precision, which are subsequently processed, giving rise to new ways of assessing the feature. In this way, it was observed in the two profiles, that there is a deep concentration in the soil, originated by the concentration of surface runoff in the area, where the soil is provided with vegetation cover, that is, it is possible to establish a relationship in the morphology of the interior of the cover feature red, where the blue and red profiles indicate that it remains with a preferential path of water, deeper, on the left bank, while the right bank changed the shape of the position of the sediments, since the most exposed area of this bank was due to sediments coming from the higher areas of the slope. To complement this research, soil samples were collected, to determine its physical and chemical properties (the bulk density results indicate that the soil has a high content of silt and fine sand and low aggregate stability, explaining the high susceptibility to erosion. Such properties, together with land use and inadequate management, generate highly impacted areas. Based on the results presented, it was possible to observe that the complementary use between the UAV and the analysis of soil properties allow a better understanding of the erosive processes, by providing a detailed visualization of the feature and better characterization of the soil. While the soil physical and chemical analyzes allow an understanding of the determining factors of its susceptibility to erosion, by the action of rain, such as its granulometric composition, porosity and aggregability. The use of the UAV brings a new way of understanding how the processes act and model the slopes. In the specific case of these gullies, the UAV made it possible to understand the differentiation of the evolution of the erosive process inside them, for the future elaboration of a diagnosis of the area, with a view to its possible recovery.

How to cite: Garritano, F. and Guerra, A.: Gully erosion monitoring in Rio Claro Municipality, Rio de Janeiro State, using - unmaned aerial vehicle (UAV), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-492, https://doi.org/10.5194/icg2022-492, 2022.

P8
|
ICG2022-553
Stefano Crema, Sebastiano Trevisani, Giorgia Macchi, Alessandro Sarretta, Lorenzo Marchi, and Marco Cavalli

The concept of roughness is fundamental for the investigation of a wide variety of earth surface processes as every process acting over a surface either encounters or generates rough surfaces (Smith, 2014). Acknowledging the crucial role that roughness has across Earth sciences and recognizing the past and ongoing efforts carried out in roughness formulation, quantification and scaling properties, the present work wants to tackle a very specific roughness usage in geomorphometric investigations. In recent years the geomorphological community has indeed (re-)discovered the hydrological and sediment (dis-) connectivity paradigm as a valuable approach to better characterize sediment dynamics and effective sediment contributing area. This rediscovery is also being favored by quantitative methods and available software tools to carry out connectivity assessment considering diverse approaches such as DTM-based indices or graph description of sediment routes. For our purpose, we take here as an example an index of connectivity (Cavalli et al. 2013) as it represents a parsimonious approach (only requiring a DTM) and due to its numerous applications in contrasting physiographic contexts. In the above-mentioned index, surface roughness enters as a weighting factor to represent impedance to the fluxes and is computed as a detrended surface variability by deriving the standard deviation of residual topography over a desired window size. The convenience of having easy-to-use software tools for computing such an index might represent a tempting easy path to carry out connectivity assessment with the risk of avoiding a robust reasoning on the most appropriate moving window and cell size for our specific application. We show how the tested roughness index changes its hydraulic significance in relation to the scale of analysis, in terms of DTM resolution and window size. In a complex topographical setting, at fine resolution the index can be reasonably interpreted as a proxy of flow impedance; however, at larger scales, it provides information on long-range morphologies, therefore becoming a proxy of topographic gradient more than flow impedance. This behavior, apart from being expected, should trigger an alert especially when carrying out geomorphometric analyses such as the one herein reported. In fact, as we increase the cell size, we drift towards a metric that represents a proxy of slope and this in turn is actually favoring the flow, thus conceptually misusing the original formulation and introducing the opposite information in respect to the one intended.

Through such an example we would like to raise awareness over a known scale-related issues when using roughness metrics and to elicit some discussion on the topic for more robust approaches in geomorphometry. The mere availability of a DTM in fact should never be regarded as a green light for proceeding with processing techniques without a profound thinking on the most appropriate analyses.

 

References:

  • Cavalli, M., Trevisani, S., Comiti, F., Marchi, L., 2013. Geomorphometric assessment of spatial sediment connectivity in small Alpine catchments. Geomorphology, doi: 10.1016/j.geomorph.2012.05.007
  • Smith, Mark W. (2014). Roughness in the Earth Sciences, Earth Science Reviews, doi: 10.1016/j.earscirev.2014.05.016

How to cite: Crema, S., Trevisani, S., Macchi, G., Sarretta, A., Marchi, L., and Cavalli, M.: Topographic surface roughness: use, misuse and abuse in geomorphometry, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-553, https://doi.org/10.5194/icg2022-553, 2022.

P9
|
ICG2022-569
Gilles Rixhon, Céline Bégorre, Cassandra Euzen, Coraline Fuchs, Timothée Jautzy, Jessica Laible, and Laurent Schmitt

Along with the development of “classical” optically stimulated luminescence (OSL) dating, portable luminescence readers have been increasingly employed in a wide breadth of geomorphological settings over the last decade. Portable measurements of bulk samples along depth profiles yield infra-red and optically stimulated luminescence net intensities (IRSL/OSL). The signal build-up depends on (i) the burial duration of the sediment, (ii) the dose rate, (iii) the inherited dose at time of burial, (iv) the mineral composition and (v) the luminescence sensitivity of the minerals. In fluvial landscapes, however, the handful of existing case studies mostly focused on the sole identification of alluvium’s unconformities via luminescence profiling. We argue here that this approach shall go beyond the mere one- (or sometimes two-) dimensional sedimentary screening and steer towards the production of three-dimensional chronostratigraphical information.

This study presents the outcomes of a luminescence-profiling approach performed in a wide array of fluvial depositional systems located in the Upper Rhine Graben and the adjacent Vosges Mountains (NE France). They include:

  • modern and historical overbank fines from the main stem (Rhine) and its tributaries (Bruche and Sauer Rivers);
  • palaeomeanders and swale-and-ridge topography (Bruche);
  • Holocene terrace deposits (Bruche);
  • fluvio-glacial deposits (probably) from the Last Glacial Maximum (Cleurie Valley).

We thus explore the ability of the reader to measure signals of varying intensities in different morpho-sedimentary units of clearly distinct ages. The results globally show:

  • a consistent pattern of downward increasing OSL/IRSL signal intensities, although some sharp contrasts (i.e., shifts of one order of magnitude in signal intensities) in some sequences could be identified (e.g., Rhine);
  • a larger scatter of OSL/IRSL signal intensities in the sandy fraction than in the silty fraction, probably reflecting the influence of grain size on the signal accumulation (requiring further investigation);
  • the potential of the portable reader as a rapid and efficient tool for tracing historical overbank fine deposition in floodplains.

How to cite: Rixhon, G., Bégorre, C., Euzen, C., Fuchs, C., Jautzy, T., Laible, J., and Schmitt, L.: Exploring the multi-faceted potential of luminescence profiling via the portable reader in various fluvial depositional systems (NE France), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-569, https://doi.org/10.5194/icg2022-569, 2022.

P10
|
ICG2022-9
Comparison of gully initiation thresholds estimation techniques: a case study from India
(withdrawn)
Anindya Majhi, Jan Nyssen, and Ann Verdoodt
P11
|
ICG2022-406
Manfred Frechen

Optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) methods using quartz and potassium-rich feldspar, respectively, have been successfully applied to deposits from a variety of different sedimentary environments to determine the time elapsed since the last exposure to sunlight. Coastal sediments including aeolian and shallow marine deposits have been proved to be excellent material for dating, because they fullfill the basic luminescence dating assumptions such as sufficient bleaching/zeroing prior to deposition. Furthermore, in combination with radiocarbon dating robust and reliable chronological frameworks have been provided.

In this paper, we present two luminescence dating case studies. The first one is about a sediment core including Holocene sediments from the German North Sea Coast, previously studied by Zhang et al. (2014) and extended by a sediment core from an inland barrier spit at Eiderstedt peninsula. The lithostratigraphic, sedimentological and chronological investigations yielded the following interpretation: The uppermost 1-2 meter of the sediments are of terrestrial origin and deposited after the construction of dykes along the coast during the 11th century. These results are in agreement with sedimentological and chronological results from two further localities in the vicinity of the key location. More than 20 m of shallow marine sediments are exposed including a marker horizon rich in shells and shell fragments giving evidence for the rapid Holocene sea-level rise and the arrival of the “sea” at around 8,300 Years BP at the locality under study. Wadden sediments, mud and sand flats sediments and beach wall or barriere spit sediments are typical for the Holocene sequence. A hiatus is found for the time period between 13,000 and 8,300 years BP. Last glacial deposits up to a depth of at least 70 m consist mainly of (reworked) aeolian and fluvial sediments.

The sediment successions along the coast of Sardinia provide important information about the Late Pleistocene – Holocene sea-level changes and sea-level elevations. However, the chronological results of different dating methods, such as OSL, IRSL, electron-spin resonance, radiocarbon, uranium/thorium and amino acid racemisation are not sound and have been a matter of debate for many years. We will discuss the reliability of the different dating methods and present new radiocarbon and luminescence dates as the second case study.

 

Zhang, J., Grube, A., Tsukamoto, S., Frechen, M. (2014): OSL and 14C chronologies of a Holocene sedimentary record (Garding-2 core) from the German North Sea coast.- Boreas, 43: 856-868.

How to cite: Frechen, M.: Advances in Nummerical dating for Reconstructing Coastal Environments from the German North Sea Coast and the Mediterranean Coast of Sardinia , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-406, https://doi.org/10.5194/icg2022-406, 2022.