Permafrost is being degraded worldwide due to the change in external forcing caused by climate change. This has also been shown to affect the morphodynamics of active rock glaciers. We studied these changes, depending on the analysis, on nine or eight active rock glaciers, respectively, with different characteristics in multiple epochs between 1953 and 2017 in Kaunertal, Austria. A combination of historical aerial photographs and airborne laser scanning data and their derivatives were used to analyse surface movement and surface elevation change. In general, the studied landforms showed a significant acceleration of varying magnitude in the epoch 1997–2006 and a volume loss to variable degrees throughout the investigation period. Rock glaciers related to glacier forefields showed significantly higher rates of subsidence than talus-connected ones. Besides, we detected two rock glaciers with deviating behaviour and one that showed an inactivation of its terminal part. By analysing meteorological data (temperature, precipitation and snow cover onset and duration), we were able to identify possible links to these external forcing parameters. The catchment-wide survey further revealed that, despite the general trend, timing, magnitude and temporal peaks of morphodynamic changes indicate a slightly different sensitivity, response or response time of individual rock glaciers to fluctuations and changes in external forcing parameters.

Alpine rivers have experienced considerable changes in channel morphology over the last century. Natural factors and human disturbance are the main drivers of changes in channel morphology that modify natural sediment and flow regimes at local, catchment, and regional scales. In glaciated catchments, river sediment loads are likely to increase due to increasing snowmelt and glacier melt runoff, facilitated by climate change. Additionally, channel erosion and depositional dynamics and patterns are influenced by sediment delivery from hillslopes and sediment in the forefields of retreating glaciers. In order to reliably assess the magnitudes of the channel-changing processes and their frequencies due to recent climate change, the investigation period needs to be extended to the last century, ideally back to the end of the Little Ice Age. Moreover, a high temporal resolution is required to account for the history of changes in channel morphology and for better detection and interpretation of related processes. The increasing availability of digitised historical aerial images and advancements in digital photogrammetry provide the basis for reconstructing and assessing the long-term evolution of the surface, in terms of both planimetric mapping and the generation of historical digital elevation models (DEMs). The main issue of current studies is the lack of information over a longer period. Therefore, this study contributes to research on fluvial sediment changes by estimating the sediment balance of a main Alpine river (Fagge) in a glaciated catchment (Kaunertal, Austria) over 19 survey periods from 1953 to 2019. Exploiting the potential of historical multi-temporal DEMs combined with recent topographic data, we quantify 66 years of geomorphic change within the active floodplain, including erosion, deposition, and the amounts of mobilised sediment. Our study focuses on a proglacial river that is undergoing a transition phase, resulting from an extensive glacier retreat of approximately 1.8 km. This has led to the formation of new channel networks and an overall negative cumulative sediment balance for the entire study area. We found that high-magnitude meteorological and hydrological events associated with local glacier retreats have a significant impact on the sediment balance. The gauge record indicates an increase in such events, as well as in runoff and probably in sediment transport capacity. Despite this, the sediment supply has declined in the last decade, which can be attributed to a lower contribution of the lateral moraines coupled to the channel network and less sediment sourced from the melting Gepatsch Glacier as evidenced by roches moutonnées exposed in the current/most recent forefield. Nonetheless, we observed significant erosion in the tributary, leading to the transport of sediment downstream. Overall, this study enhances our understanding of the complexity of sediment dynamics in proglacial rivers across various spatial and temporal scales and their relationship to climate change factors.

Uncrewed aerial systems (UAS) combined with Structure‐from‐Motion photogrammetry has already proven to be very powerful for a wide range of geoscience applications and different types of UAS are used for scientific and commercial purposes. However, the impact of the UAS used on the accuracy of the point clouds derived is not fully understood, especially for the quantitative analysis of geomorphic changes in complex terrain. Therefore, in this study, we aim to quantify the magnitude of systematic and random error in digital elevation models derived from four commonly used UAS (XR6/Sony α6000, Inspire 2/X4s, Phantom 4 Pro+, Mavic Pro) following different flight patterns. The vertical error of each elevation model is evaluated through comparison with 156 GNSS‐reference points and the normal distribution and spatial correlation of errors are analysed. Differences in mean errors (‐0.4 to ‐1.8 cm) for the XR6, Inspire 2 and Phantom 4 Pro are significant but not relevant for most geomorphological applications. The Mavic Pro shows lower accuracies with mean errors up to 4.3 cm, thus showing a higher influence of random errors. QQ‐plots revealed a deviation of errors from a normal distribution in almost all data. All UAS data except Mavic Pro exhibit a pure nugget‐semivariogram, suggesting spatially uncorrelated errors. Compared to the other UAS, the Mavic Pro data show trends, i.e. differences increase with distance across the survey (doming) and the range of semivariances is ten times greater. The lower accuracy of Mavic Pro can be attributed to the lower GSD at the same flight altitude and most likely, the rolling shutter sensor has an effect on the accuracy of the camera calibration. Overall, our study shows that accuracies depend highly on the chosen data sampling strategy and that the survey design used here is not suitable for calibrating all types of UAS camera equally.

In this study, the geomorphological evolution of an inner flank of the Cratère Dolomieu at Piton de La Fournaise/La Réunion was investigated with the help of terrestrial laser scanning (TLS) data, terrestrial photogrammetric images, and historical webcam photographs. While TLS data and the terrestrial images were recorded during three field surveys, the study was also able to use historical webcam images that were installed for the monitoring of the volcanic activity inside the crater. Although the webcams were originally intended to be used only for visual monitoring of the area, at certain times they captured image pairs that could be analyzed using structure from motion (SfM) and subsequently processed to create digital terrain models (DTMs). With the help of all the data, the geomorphological evolution of selected areas of the crater was investigated in high temporal and spatial resolution. Surface changes were detected and quantified on scree slopes in the upper area of the crater as well as on scree slopes at the transition from the slope to the crater floor. In addition to their quantification, these changes could be assigned to individual geomorphological processes over time. The webcam photographs were a very important additional source of information here, as they allowed the observation period to be extended further into the past. Besides this, the webcam images made it possible to determine the exact dates at which geomorphological processes were active.

Sediment-discharge events recorded at the outlet of high-mountain catchments provide an integrated signal of upstream geomorphic activity. At the same time, a key limitation of DEMs of Difference (DoDs) is that sediment source areas and geomorphic responses cannot be directly linked to individual events, especially when DoDs span extended time periods. To address this, we apply the method proposed by Skålevåg et al. (2024) to detect, cluster and characterise sediment-discharge events, which can subsequently be related to observed sediment mobilization signals in the DoD.15-min time series of water discharge and suspended sediment concentration from Gepatschalm, Kaunertal (Austria), covering the period 2008-2025, were used to detect the sediment-discharge events and derive 16 metrics, which were used to cluster the events with a Gaussian mixture model. Gridded meteorological data were used to characterise the clusters with respect to antecedent and intra-event forcing conditions. The resulting event catalogue was evaluated using DEMs of difference (DoDs) covering the entire catchment and investigation period.Over the 16-year period we identified a total of 850 sediment-discharge events. Clustering results reveal three patterns: (i) melt-dominated events (average contribution ~30% to annual suspended sediment yield), (ii) early- and late-season freeze–thaw-modulated events (~15%), and (iii) compound rainfall–melt events (~33%). A marked increase in event frequency was observed in 2022, which also recorded the highest annual suspended sediment yield in the dataset. The majority of 2022 events were assigned to clusters 2 and 3. Combining multiple DoDs from summer 2022 with gridded precipitation data allowed the identification of a distinct sediment-discharge event on 28 June 2022, which triggered fluvial erosion in a specific sub-catchment of Kaunertal. For this event and other events, the main sediment source areas can clearly be delineated with the DoD analysis. Skålevåg, A.; Korup, O.; Bronstert, A. (2024): Inferring sediment-discharge event types in an alpine catchment from sub-daily time series. In: Hydrology and Earth System Sciences Discussions.

Badlands are among the most rapidly developing landscapes and exhibit a significant degree of geomorphological activity. In semi-arid/ sub-humid landscapes, specific precipitation dynamics result in particularly rapid geomorphological development. This applies in particular to land cover and geomorphology. This study employs quantitative, multi-temporal analysis to examine the spatio-temporal changes in a sub-humid calanchi badland in the upper Val d'Orcia (Italy) over a period of ten years (2014-2024). Particular emphasis lies on the dynamics of geomorphological processes and topographical changes, while considering the variables of vegetation and precipitation. The analysis encompasses both extreme events and prolonged rainfall lasting several days, which are the primary factors for surface changes in subhumid badlands. The utilisation of UAS SfM-MVS in conjunction with precise dGNSS measurements facilitates high-resolution change detection and landform analysis across five distinct observation periods, each spanning two years (= five DoD). The interactions between vegetation and geomorphological processes are investigated using a semi-automatic mapping approach based on the Triangular Greenness Index (TGI) and the interpretation of topographical changes (DoD). The vegetation analysis are based on high-resolution orthomosaics with a resolution of 0.05 m, while the geomorphic change detection analysis is carried out on 2.5D rasterised digital surface models with a resolution of 0.25 m. The major results are as follows: The mean slope gradient of the entire study site remained largely stable despite certain areas showing enhanced geomorphic activity. The DoD analysis revealed four 'geomorphic hot spots', areas of enhanced geomorphic activity and sediment contribution from the tributaries to the main valley (the major deposition area). The annual erosion rates vary between -0.4 cm (2018-2022) and -4 cm (2022-2024). The observed topographic changes can be attributed primarily to high-magnitude events (complex landslides and debris-like flows) that occur irregularly. The multi-temporal mapping of landforms has revealed a significant reduction in water erosion, with a 50% decrease observed from 35% in 2014 to 17% in 2024. Furthermore, the combination of 2D-mappings and 2.5D DoD-analysis enabled the documentation of a geomorphological process previously unknown in badland areas, namely gravitational bulging. This describes the deformation of sediments in lower-lying clay layers as a response to water infiltration, high swelling capacities of clays and the pressure exerted by the sediment packages lying above them. A significant increase in vegetation cover has been observed, particularly in areas designated as potentially moist and gentle terrain, often the deposition areas from the previous period. In general, vegetation underwent a gradual transition, evolving from a fragmented to a continuous structure, primarily due to the widespread colonisation of the main valley and the landslide pathways. Although the area affected by erosion processes decreased over the course of the study period, erosion rates remained relatively constant. This indicates a shift from high-frequency to high-magnitude processes in the most recent observation period. Overall, the phase under consideration in this study (2014-2024) can be characterised as a phase of badland stabilisation.