Jakob Rom

Subsidence in already emplaced lava can be caused by contraction as they cool, degassing and collapse. In this study, we present preliminary estimates of short-term volume change associated with the January (14 Jan, 07:58 UTC – 16 Jan, 01:08 UTC) and February (8 Feb, 06:03 UTC – 9 Feb, afternoon) 2024 eruptions at the Sundhnúkagígar crater row, Iceland. Surface elevation changes were derived from a series of multi-temporal pre- and post-eruptive Digital Elevation Models (DEMs) based on stereo imagery collected by UAV and manned aircraft, using a photogrammetric workflow in the Agisoft Metashape software. Volume changes were quantified from DEMs of Difference (DoDs) by integrating surface elevation changes over the mapped lava field, accounting for random, spatially correlated, and systematic errors. Positive and negative lava volume estimates represent the areal integration of surface uplift and subsidence respectively, as a result of the eruption, rather than strictly representing net mass addition or removal at a given location. Positive changes may reflect lava emplacement or internal redistribution of previously erupted material, whereas negative changes indicate thermal contraction, lava drainage, degassing, or collapse of the cooling lava surface. All reported volumes refer to changes integrated over the mapped lava field only. During the January eruption, rapid emplacement between 14 and 15 January resulted in a dominance of positive volume change, with 0.463 ± 0.0005 Mm³ of positive and −0.233 ± 0.0004 Mm³ of negative volume change. Between 15 and 17 January (approximately 48 h after eruption onset), volume changes were dominated by surface lowering, with −0.094 ± 0.0009 Mm³ negative versus 0.047 ± 0.0006 Mm³ positive volume change, reflecting contraction and internal redistribution as the dominating processes. From 17 January to 13 February, volume changes were minor, with 0.049 ± 0.001 Mm³ positive and −0.040 ± 0.001 Mm³ negative. For the February eruption, the analysis was constrained by the geological setting and the short repose time between eruptions, as rapid resurfacing of the lava field by subsequent eruptive activity limited the temporal persistence of measurable surface changes. On 8 February, comparison of DEMs acquired at 13:15 and 17:05 UTC shows a dominance of negative volume change, with −1.65 ± 0.01 Mm³ of negative versus 1.35 ± 0.01 Mm³ of positive volume change. Between 8 February (17:05 UTC) and 13 February, negative changes −2.07 ± 0.06 Mm³ exceeded positive changes 1.15 ± 0.04 Mm³. Ongoing work aims to further refine these results by quantifying vertical surface subsidence rates to better characterize post-eruptive surface change behaviour.

Climate-driven glacier retreat is fundamentally restructuring sediment transfer systems in Alpine catchments, yet quantifying these changes over timescales relevant to global warming remains challenging. Established approaches to sediment connectivity assessment, such as DEM-based connectivity indices or sediment flux measurements, face limitations when applied across centennial timescales due to inconsistent data quality and sparse temporal or spatial coverage.We present a graph-theoretic framework for analyzing structural sediment connectivity evolution across three glaciated catchments in the Central European Alps (Grastal, Kaunertal, Martelltal) over approximately 150 years since the Little Ice Age maximum. Our approach derives sediment cascade graphs from multitemporal geomorphological maps, using landforms as fundamental spatial units. The key methodological challenge lies in enabling meaningful comparisons across study sites of different sizes and configurations, and across time periods characterized by heterogeneous source data.To achieve temporal depth, we integrate diverse data sources: historical topographic maps (1870s–1930s), georeferenced terrestrial photographs, aerial imagery processed with Structure-from-Motion photogrammetry (1940s–1990s), and recent ALS-derived products. Graph creation follows a semi-automatic workflow combining GIS-based flow routing with manual sediment source identification from DEMs of Difference and orthoimagery. We specifically address hydrological sediment connectivity, focusing on fluvial transport processes that dominate sediment export from glaciated systems.We develop and apply graph metrics designed to be robust against variations in network size and data quality, enabling direct comparison of structural properties across catchments and time periods. These metrics characterize pathway architecture, the topological positioning of barrier landforms (lakes, braidplains, alluvial fans), and potential functional sediment connectivity under event-scale forcing through a simplified routing model.Results indicate that the three catchments exhibit distinct evolutionary trajectories, with network structural changes and barrier formation capable of substantially modulating the response to deglaciation. The approach demonstrates that graph-based representations can be consistently derived from heterogeneous historical sources, offering a transferable methodology for investigating how sediment cascade structure mediates landscape response to climate forcing across decadal to centennial timescales.

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.

As part of the DFG research group “Sensitivity of high alpine geosystems to climate change since 1850” (SEHAG), high-resolution multibeam sonar data was collected from the proglacial Grastallake in the Ötztal valley during a boat survey in the summer of 2025. The Grastallake has an area of approximately 63,000 m², a maximum depth of approximately 16 m, and lies at an altitude of 2,584 m. The lake is situated in a former cirque, and its shores and the surrounding are partly composed of loose material and partly of solid rock. In the western part, there is a large whaleback with already known Egesen-moraines on top. On the southern and eastern shores, larger active debris flow cones are coupled to the lake, with meltwater runoff from the higher Grastalferner glacier flowing into the lake as a perennial stream via the eastern debris flow cone. Due to the permanent inflow from the glacier and the topographic conditions of the catchment area, the eastern debris flow cone is very active and has intensively been reshaped by several extreme debris flow events during the last years.The bathymetric data was collected using a Norbit multibeam sonar (WBMS), which was supplemented by an SBG INS system (dual GNSS patch antenna system, SBG Eclipse D) by Kalmar Systems. Since the underwater topography of the lake was unknown and its high turbidity due to the glacier inflow, the first step was to conduct a rough survey of the lake. This step made it possible to create a coarse depth map on site in order to identify spots with shallow water, determine the system settings, and draw up a navigation plan along strips. After field work the recorded data was processed using Quinertia for trajectory calculation and Opals for strip adjustment. This resulted in a final 3D point cloud with an average point density of 400 points per square meter, which was converted to raster data in order to perform spatial analyses.Using the data, geomorphological forms were mapped in a first step. In addition to a previously unknown late glacial moraine section, the underwater deposits of recent debris flows became visible. In addition to mapping, geomorphological structures were used for spatial analysis, such as comparing the depositions of debris flows above and below the water. Since the data is very well suited for mapping underwater structures, this case study demonstrates the enormous potential of bathymetric data acquired by multibeam sonar measurements, that has rarely been used for geomorphological studies to date. Multitemporal analysis in the sense of a 4D analysis could only be carried out to a limited extent in this case study. However, with the data now available, multitemporal analysis, i.e., quantification of sediment input into lakes, will also be possible in the future. This would then enable assessments to be made of the hazard potential of newly formed lakes in the proglacial area and of their lifespan.

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.

Debris flows are a major natural hazard in mountainous regions worldwide and significantly impact the sediment budgets in alpine areas. However, the development of debris flow frequency under climate change conditions has not yet been conclusively clarified, as long-term, comprehensive event records (i.e. not biased towards large events) are scarce. As alpine debris flows are predominantly triggered by high-intensity and short-duration rainfall events, precipitation records can be useful for inferring potential triggers, particularly under transport-limited conditions. As high-resolution precipitation measurements are rarely available over long periods of time, we employed dynamical downscaling of a Regional Climate Model (RCM) based on the Advanced Weather Research and Forecasting model (WRF). This approach resulted in a high-resolution climate model dataset covering most of the Central Alps, with a spatial resolution of 2x2 km and a temporal resolution of 15 minutes. This model enabled us to analyse high-intensity, short-duration rainfall events since the end of the Little Ice Age in 1850.We compared the RCM with a debris flow record in the Horlachtal catchment in Tyrol, Austria. By analysing remote sensing datasets such as historical and recent aerial imagery, airborne lidar data and lichenometric dates, we identified 991 individual debris flows in the area between 1947 and 2022. Combining the observation dataset with the RCM rainfall data enabled us to take an integrated approach to assessing changes in debris flow frequency in the Horlachtal and their climatic drivers since 1850. The results provide insights into possible future trends in debris flow frequency in a changing climate, showing a weak positive long-term trend for the Horlachtal. The RCM's coverage allows for similar studies in other Alpine regions, offering more detailed insights into the spatial variability of changes in debris flow activity within the Central Alps.

This study investigates suspended sediment transport in two glaciated catchment areas of the Eastern Central Alps within the DFG Research Group SEHAG (Sensitivity of High Alpine Geosystems to climate change since 1850). The main objective of this work is to characterize the conditions that trigger suspended sediment transport and the resulting sediment dynamics, emphasizing the sediment supply activated under specific hydrometeorological conditions.The methodology combines continuous meteorological data with monthly suspended sediment measurements conducted during the ablation period of 2024 using manual samplers at strategically positioned sampling stations across the Upper Kaunertal and Martelltal catchments. Two primary research questions are addressed: (1) How do suspended sediment concentrations and loads vary spatially and temporally when comparing glacier terminus locations with downstream stations? (2) What characteristic patterns emerge in the suspended sediment samples under different hydrometeorological conditions?During days dominated by glacial melt, the suspended sediment samples show a typical diurnal peak around 15:00-16:00, with concentrations up to 2.5 g/l in Kaunertal and 11.8 g/l in Martelltal, following the glacial hydrograph. However, notable increases of up to 1169 % occur during precipitation events, suggesting the activation of different sediment sources. These findings provide insights into how different hydrometeorological conditions activate distinct sediment sources and contribute to the understanding of sediment dynamics in glaciated catchments. The results lay the foundation for future suspended sediment monitoring.

Studies on the simulation of erosion in high alpine geosystems are still rare. Using the physically based soil erosion model Erosion3D (E3D), we show the simulation of fluvial erosion on a steep and unvegetated slope in a Little Ice Age (LIA) glacier foreland over several years. The study area is located in the proglacial area of the Zufallferner glacier in the Martell Valley (South Tyrol, Italy). The slope erosion is mainly due to fluvial erosion and process dynamics. A digital elevation model (DEM), various soil physical properties and precipitation data were used as input parameters for the E3D model. The DEMs were generated either from airborne LiDAR surveys (2013 and 2019) or from UAV-based structure-from-motion (SfM) photogrammetry (2023). Additional soil parameters required for E3D, such as bulk density, soil moisture, cover information, grain size distribution, erosion resistance, hydraulic roughness and the skin factor were determined. For this purpose, three rain simulations were carried out during a field campaign in August 2023 and corresponding soil samples were collected and analysed in the laboratory. The precipitation data as input for E3D comes from a data set that was created with a regional climate model (RCM). The Advanced Research WRF (ARW) module of the Weather Research and Forecasting (WRF) model (version 4.3) was used for the dynamic downscaling of the ERA5 climate data. This approach provided precipitation data for the Martell Valley with a temporal resolution of 15 minutes and a spatial resolution of 2x2 kilometres.The E3D simulations were calibrated by comparing the modelled erosion volume of a specific slope section with the erosion volume derived from the DEMs of Difference (DoD) for 2023 and 2021. Spatial and temporal validation was then performed by comparing the E3D simulated erosion volumes with the volumes calculated from the corresponding DoDs (2013 to 2019 and 2019 to 2021). The E3D simulation results show that the net erosion volume of the entire slope section for each epoch agrees well with the calculated erosion volumes from the DoDs and is within their respective error ranges. These results confirm the suitability of the E3D model for simulating geomorphological activity on this slope within an LIA glacier foreland. Finally, we aim to improve the temporal resolution of geomorphological activity on the selected slope section using E3D simulations. By allowing an annual quantification of erosion between 2013 and 2023, the model enables a deeper understanding of the relationship between erosion dynamics and precipitation events.

Sediment connectivity is an important property of geomorphic systems reflecting the potential to route material through themselves and hence modulating the propagation of geomorphic changes. While the relevance of the concept is clear, connectivity cannot be measured directly and the discussion on the best methods to quantify connectivity is still ongoing. Probably the most frequently used approach is based on the index of connectivity (IC) as it was developed by Borselli et al. (2008) and later adapted by Cavalli et al. (2013) for alpine catchments. This index aims at quantifying the structural connectivity that is governed by the spatial configuration and properties of system components. Nevertheless, the predictive capabilities of this index for functional connectivity, i.e. the actual transfer of sediment between the system components, have not been conclusively validated with field data. Most importantly, previous studies have, to our knowledge, not taken into account the spatial variability of the hydrometeorological forcing that leads to different functional connectivity in locations with similar structural connectivity.In this study, we use a unique dataset to test the predictive capability of the IC for hillslope-channel coupling of debris flows in the Horlachtal, Austria (described by Rom et al., 2023). The dataset consists of aerial imagery and two airborne LiDAR digital elevation models from which n=156 debris flows were mapped and quantified that were triggered by intense rainstorms on July 20th and 23rd, 2022. For this event, adjusted radar data (INCA data from the Austrian meteorological survey, ZAMG, and measurements from weather stations within the study area) give a high-resolution account of the spatial distribution of rainfall intensities and sums. Using these data, each debris flow was characterised with respect to (i) the meteorological forcing that affected its contributing area, (ii) morphometric properties of the latter, (iii) its sediment volume, and (iv) its runout length indicating functional connectivity, i.e. the degree of coupling to the main channel. Then we assessed the influence of structural connectivity (indicated by the IC) and hydrometeorological forcing on the observed functional connectivity. To our knowledge, this is the first study investigating the predictive capacity of the IC taking into account the spatial variability of the forcing. Among others, our results show that the IC is significantly higher for those debris flows that reached the main channel, compared to those that did not.

We show a long-term erosion monitoring of several geomorphologically active gully systems on Little Ice Age lateral moraines in the European Central–Eastern Alps, covering a total time period from 1953 to 2019 and including several survey periods in order to identify corresponding morphodynamic trends. For the implementation, DEM (digital elevation model) of Differences (DoDs) were calculated, based on multitemporal high-resolution digital elevation models from historical aerial images (generated by structure from motion photogrammetry with multi-view stereo) and light detection and ranging from airborne platforms. Two approaches were implemented to achieve the corresponding objectives. First, by calculating linear regression models using the accumulated sediment yield and the corresponding catchment area (on a log–log scale), the range of the variability in the spatial distribution of erosion values within the sites. Second, we use volume calculations to determine the total and the mean sediment yield (as well as erosion rates) of the entire sites. Subsequently, both the sites and the different time periods of both approaches are compared. Based on the slopes of the calculated regression lines, it can be shown that the highest variability in the sediment yield at the sites occurs in the first time period (mainly 1950s to 1970s). This can be attributed to the fact that within some sites the sediment yield per square metre increases clearly more strongly (regression lines with slopes up to 1.5). In contrast, in the later time periods (1970s to mid-2000s and mid-2000s to 2017/2019), there is generally a decrease in 10 out of 12 cases (regression lines with slopes around 1). However, even at sites with an increase in the variability in the sediment yield over time, the earlier high variabilities are no longer reached. This means that the spatial pattern of erosion in the gully heads changes over time as it becomes more uniform. Furthermore, using sediment volume calculations and corresponding erosion rates, we show a generally decreasing trend in geomorphic activity (amount of sediment yield) between the different time periods in 10 out of 12 sites, while 2 sites show an opposite trend, where morphodynamics increase and remain at the same level. Finally, we summarise the results of long-term changes in the morphodynamics of geomorphologically active areas on lateral moraines by presenting the “sediment activity concept”, which, in contrast to theoretical models, is based on actually calculated erosion. The level of geomorphic activity depends strongly on the characteristics of the sites, such as size, slope length, and slope gradient, some of which are associated with deeply incised gullies. It is noticeable that especially areas with influence of dead ice over decades in the lower slope area show high geomorphic activity. Furthermore, we show that system internal factors, as well as the general paraglacial adjustment process, have a greater influence on long-term morphodynamics than changing external weather and climate conditions, which, however, had a slight impact mainly in the last, i.e. most recent, time period (mid-2000s to 2017/2019) and may have led to an increase in erosion at the sites.