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The coasts of Greenland mostly consist of hard rock with relatively small rates of erosion. However, isostatic uplift following the retreat of Holocene ice sheets is creating soft sediment bluffs consisting of deltas or beach ridges. Hitherto, very little has been known about the rates and processes of soft sediment bluff erosion along the coast of Greenland. Here, we investigate a bluff section at the south coast of Disko Island in western Greenland. The height of the bluff ranges from one to 30 m along a three km long section of the coast. The bluff consists of a heterogeneous matrix of hard rock outcrops with pockets of coarse clastic sediments in between, overlain by parallel beach ridges with discontinuous permafrost. Sea ice along the coast limits wave activity between December and May.A series of oblique aerial images from July 2019 and July 2021 was obtained to create Structure from Motion Multi-View Stereo (SfM MVS) point clouds. Changes were detected by multi-scale model-to-model cloud comparison (M3C2). Climate data from the nearby town of Qeqertarsuaq were used to identify precipitation events to estimate erosion events at the bluff. This data were utilized in conjunction with satellite derived bathymetry and wave data to estimate wave run-up and erosion at the coastline for a series of hydrodynamic conditions.We find the absence of soil on top of the uplifted beach ridges strongly influences runoff patterns. Without the water retention capability of the soil, water directly infiltrates into the soft sediments, or runs off the surface of the hard rock areas. This leads to an accumulation of water in the soft sediment pockets and gullies, making them especially vulnerable to erosion. The sedimentary bluff is eroding by two coupled processes: (i) Precipitation-driven surface runoff downslope the bluff face and (ii) wave-driven erosion at the bluff base of sediment that is delivered by the surface runoff. Typical erosion rates are up to half a meter per year. Longer ice-free periods with extended wave action should further increase coastal bluff erosion rates in Greenland in the future.

Landslides are a frequent natural hazard occurring globally in regions with steep topography. Additionally, landslides are playing an important role in landscape evolution by transporting sediment downslope. Landslide inventory mapping is a common technique to assess the spatial distribution and extend of landslides in an area of interest. High-resolution digital elevation models (DEMs) have proven to be useful databases to map landslides in large areas across different land covers and topography. So far, Denmark had no national landslide inventory. Here we create the first comprehensive national landslide inventory for Denmark derived from a 40 cm resolution DEM from 2015 supported by several 12.5 cm resolution orthophotos. The landslide inventory is created based on a manual expert-based mapping approach, and we implemented a quality control mechanism to assess the completeness of the inventory. Overall, we mapped 3202 landslide polygons in Denmark with a level of completeness of 87 %. The landslide inventory can act as a starting point for a more comprehensive hazard and risk reduction framework for Denmark. Furthermore, machine-learning algorithms can use the dataset as a training dataset to improve future automated mapping approaches. The complete landslide inventory is made freely available for download at https://doi.org/10.6084/m9.figshare.16965439.v1 (Svennevig and Luetzenburg, 2021) or as web map (https://data.geus.dk/landskred/) for further investigations.

Stones on the seabed in coastal marine environments form an important hard substrate for macroalgae, and hence for coastal marine reefs. Such reef areas constitute important ecosystem services, e.g. storage of organic carbon in macroalgae or “blue carbon” as well as important habitats to fish for living, hiding and feeding. Information and knowledge about stone locations and geometry in coastal marine environments are often obtained as part of seabed habitat mapping. Usually, seabed habitat mapping is based on geophysical surveys using multibeam echo sounding along with side-scan sonar imaging in combination with biological ground-truthing. However, coastal areas are challenging to map with full spatial coverage due to the shallow water conditions. Furthermore, the research vessels often have too large drafts to sail in very shallow water close to the coastline. An alternative is to use airborne LiDAR technology. Topo-bathymetric LiDAR (green wavelength of 532 nm) has made it possible to derive high-resolution data of the bathymetry in coastal zones (e.g. Andersen et al., 2017). This technology can cover the transition zone between land and water, and the time consumption for data acquisition is small compared to vessel borne methods. However, the processing of the data still requires manual decision steps, which makes it rather time consuming, and to some extent subjective.The aim of this study was to investigate the possibility of developing an automated method to classify stones from topo-bathymetric LiDAR data in coastal marine environments with shallow water ( Acknowledgement:This work is part of the project "ECOMAP - Baltic Sea environmental assessments by opto-acoustic remote sensing, mapping, and monitoring", supported by BONUS (Art 185), funded jointly by the EU and the Innovation Fund Denmark. ReferencesAndersen MS, Gergely A, Al-Hamdani Z, Steinbacher F, Larsen LR, Ernstsen VB (2017). Processing and performance of topobathymetric lidar data for geomorphometric and morphological classification in a high-energy tidal environment. Hydrology and Earth System Sciences, 21: 43-63, DOI: 10.5194/hess-21-43-2017.

Shallow water coastal environments can be highly dynamic and comprise a range of dynamic geodiversity variables as well as a range of benthic habitats. It is challenging to map such dynamic shallow water coastal environments and their geodiversity variables and benthic habitats in high-resolution, high precision and full coverage, which is necessary in order to evaluate impact on the seabed and the benthic habitats from e.g. climate change (e.g. changing wind climate) or human disturbance (e.g. construction of wind parks, pipelines, etc.).We have conducted successive high-resolution, high-precision airborne topobathymetric lidar surveys in combination with seabed groundtruthing (e.g. seabed sampling and diver observations) along existing monitoring lines in Rødsand lagoon, Denmark, in the western Baltic Sea. The coastal lagoon is a Natura 2000 site, located near the planned fixed connection between Germany and Denmark.Here, we present high-resolution, high-precision mapping of geodiversity variables with a focus on seabed morphology and seabed sediments that constitute the abiotic structures of the benthic habitats. We demonstrate the role of the interaction between the dynamic coastal processes and the drowned underlying glacial landscape in relation to the spatial distribution of the seabed morphology and sediments as well as the benthic habitats. Finally, we discuss how to optimise the monitoring of dynamic geodiversity variables and abiotic benthic habitat structures in such dynamic shallow water coastal environments. AcknowledgementsThis work was carried out as part of “WP4 – In situ remote sensing of geodiversity for habitat mapping” within the project “ECOMAP – Baltic Sea environmental assessments by opto-acoustic remote sensing, mapping, and monitoring” funded by the BONUS EEIG and the Innovation Fund Denmark.

Coastal cliff erosion is often an underestimated process to understand shoreline evolution in Denmark. Cliff failure occurs episodically and not always coincides with the highest waves, making prediction difficult. Therefore, comprehensive knowledge about the spatial distribution of cliff erosion in Denmark and the historical rates of change are required to predict future shoreline change and sediment distribution. The erosion of coastal cliffs delivers a substantial amount of sediment in to the coastal zone and future changes in storm intensities and frequencies might influence the rates of cliff erosion.Historical aerial images, dating back to the mid of the 20th century are combined with a current high resolution digital elevation model (DEM), to map coastal cliff erosion across Denmark’s coastline and to calculate rates of change over the last decades at selected sites. Countrywide oblique aerial images further assist in mapping coastal cliff erosion processes. Landslides are characterized by polygons in the DEM. Morphometric indices are calculated out of the length, width and height of each site to distinguish between different processes. Furthermore, the rate of change is derived from the spatial displacement of the crown.In this presentation, we present a map of around 1500 (and counting) coastal cliff erosion sites mapped all across Denmark. Steep cliffs mainly occur at the Danish inner coast and along the fjords, determining the presence of coastal cliff erosion. The multi-temporal analysis of shoreline changes revealed erosion rates up to 30 m in the last 20 years leading to considerable loss of land and sediment redistribution. The spatial distribution of the mapped coastal cliff erosion processes (e.g. topples, slides etc.) shows a connection to the maximum extend of the ice sheet covering most parts of Denmark during the Last Glacial Period (Weichsel). This indicates an ongoing emergence for the postglacial landscape and highlights the importance of coastal cliff erosion in landscape evolution.