Plateau dunes are unique landforms which formed as erosion relicts in blow-out areas in Late Plei... more Plateau dunes are unique landforms which formed as erosion relicts in blow-out areas in Late Pleistocene sandy deposits. They are negative forms in contrast to normal dunes where sand is accumulated (positive form). Plateau dunes are located in the European Aeolian Sand Belt in the Netherlands, Germany and Denmark and they are flat-topped features with a bog in the central part often covered by a thin aeolian sand layer. A conceptual model of formation and further development of plateau dunes in time are presented in detail, using 14 C dates of buried peat layers and OSL dates of sandy sediments. Special focus is on the influence of climate factors, pedology, and human activity on the formation of plateau dunes.
Traditionally, topographic surveying in earth sciences requires high financial investments, elabo... more Traditionally, topographic surveying in earth sciences requires high financial investments, elaborate logistics, complicated training of staff and extensive data processing. Recently, off-the-shelf drones with optical sensors already reduced the costs for obtaining a high-resolution dataset of an Earth surface considerably. Nevertheless, costs and complexity associated with topographic surveying are still high. In 2020, Apple Inc. released the iPad Pro 2020 and the iPhone 12 Pro with novel build-in LiDAR sensors. Here we investigate the basic technical capabilities of the LiDAR sensors and we test the application at a coastal cliff in Denmark. The results are compared to state-of-the-art Structure from Motion Multi-View Stereo (SfM MVS) point clouds. The LiDAR sensors create accurate highresolution models of small objects with a side length > 10 cm with an absolute accuracy of ± 1 cm. 3D models with the dimensions of up to 130 × 15 × 10 m of a coastal cliff with an absolute accuracy of ± 10 cm are compiled. Overall, the versatility in handling outweighs the range limitations, making the Apple LiDAR devices cost-effective alternatives to established techniques in remote sensing with possible fields of application for a wide range of geo-scientific areas and teaching. In geosciences, terrestrial laser-scanning and airborne laser-scanning (TLS & ALS) techniques are applied for topographic land surveying on a wide range of scales 1-3. LiDAR is a common technique to measure distances by timing the return pulse, emitted from a laser transmitter to the laser receiver 4. The rapid evolution of digital processing techniques, as well as a new generation of technologies in remote sensing, is leading to a revolution in digital elevation modeling and geomorphological terrain analysis 5. Nevertheless, the acquisition of a digital terrain model, independent from the scale, requires high capital and logistical costs in the order of several thousand of euros, especially with airborne laser-scanning techniques 6. Therefore, data acquisition of airborne large-scale remote sensing datasets is often outsourced to third party organizations, concomitantly data acquisition is planned well in advance regardless of unforeseeable events. However, many processes studied in geosciences, like coastal cliff erosion, are irregular processes in time and space. Coarse temporal resolution observations may limit pivotal process understanding 7. Terrestrial laserscanning (TLS) allows the acquisition of digital terrain models up to a medium-scale of a few kilometers with a high temporal and spatial resolution 8,9. Usually, terrestrial laser scanners cost at least several thousands of euros, requiring trained operators and line of sight, only allowing a limited number of scanning positions, and are restricted in access to rough terrain. Hand-held mobile laser scanner (HMLS) can overcome some of those limitations, but are rarely used in geosciences 10. Furthermore, TLS and HMLS still require highly skilled field handling and post processing 11. Recent advances in photogrammetry and the availability of lightweight unmanned aerial vehicles (UAVs) offer a potential low-cost alternative to ALS and TLS in order to build 3D surface models with a high temporal and spatial resolution 6,12. However, current high-resolution 3D models based on UAV data and Structure-from-Motion Multi-View Stereo (SfM MVS) pipelines are still expensive as they rely on differential global navigation satellite systems (DGNSS), ground control points (GCPs), commercial software and data processing on an external computing device 13. Moreover, UAV missions rely on certain weather conditions, entail a sophisticated setup, high operational complexity and SfM MVS techniques present challenges by managing and processing large volumes of data 14,15. Furthermore, the use of UAVs are subject to a growing number of regulations and restrictions prohibiting flight. Multiple studies compared the two techniques concluding both should coexist, with their respective primary fields of application 16-18. The commonness of smartphones nowadays, together with advances in sensor technologies, opens new possibilities for scientific applications as well as low-cost, crowd-sourced observations in mapping surface changes
Field observations of the suspended sediment concentrations in the inner nearshore zone are made ... more Field observations of the suspended sediment concentrations in the inner nearshore zone are made with the use of a pump-sampling system to derive time-averaged profiles and with the use of optical devices to get instantaneous information. Distributions of the suspended sediment concentrations over the water depth under different hydraulical conditions result in characteristic profiles in different morphological units. The net near bed sediment fluxes are small, and composed of an oscillating component to the beach and a mean component directed offshore.
Wave processes are well known for developing spit systems in large or elongated lakes by inducing... more Wave processes are well known for developing spit systems in large or elongated lakes by inducing longshore sediment transport for spit migration, while bathymetric interaction is less studied. In this study, we investigate the combined effects of wave processes, antecedent topography and lake level changes on the development of Holocene spit systems in the Danish lake Mossø. Wave climate prediction and a digital elevation model were used to provide a conceptual model for the development of the spits system, while optically stimulated luminescence (OSL) dating of spit sand and antecedent topography analyzed via boreholes and seismic survey data were used to evaluate effects on spit migration other than wave setting. We found that spit migration stagnated during the Holocene when reaching areas of deeper waters, but continued following shallowing after deep basin infilling with lacustrine sediments. During periods of bathymetrically induced stagnation of prominent spits, less stable or more slowly migrating spits became prominent in the development of the spit system. No clear effects on spit migration caused by lake level fluctuations could be demonstrated. However, such fluctuations may have been important for the stabilization of spits and subsequent development of a major barrier shoreline.
Landslides are a frequent natural hazard occurring globally in regions with steep topography. Add... more Landslides are a frequent natural hazard occurring globally in regions with steep topography. Additionally, landslides play an important role in landscape evolution by transporting sediment downslope. Landslide inventory mapping is a common technique to assess the spatial distribution and extent 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 complete landslide inventory is freely available for download at
An automated layer counting technique is developed to estimate the chronology of a marine sedimen... more An automated layer counting technique is developed to estimate the chronology of a marine sediment core and this technique is validated with Pb210 chronology. The marine sediment core was sampled in front of the delta of Mittivakkat Glacier meltwater river in the Sermilik Fjord, SE Greenland, and is a proxy of the sediment delivery from a glacial drainage basin to a fjord. The estimated time series was based on automatic lamination detection (varves) on a line scan of the core using gray scale intensities, and covered the last two centuries. The estimated time series of sediment accumulation rates was coupled to modelled runoff from the Mittivakkat Glacier and compared with local climatic parameters (air temperature and precipitation) and with the Atlantic Multidecadal Oscillation (AMO) index. Maxima in the sediment accumulation rate at the bottom of the side-fjord, about 1 km from the delta, mostly depended on glacier ablation and consequently on changes in river runoff, which were initiated by the air temperature. This was especially the case during transition from colder periods towards warmer, where short-lived maxima in sediment accumulation rates were followed by lower rates, even though the temperature remained high. This suggested a quite rapid glacial response to changes in climatic forcing, and/or a hysteresis effect, where sediment stored in the glacier/valley system was evacuated soon after a temperature dependent increase in discharge. The air temperature was in turn controlled by the AMO index.
Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetra... more Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetrating radar (GPR) data collected across a raised beach ridge system on the island of Samsø, Denmark. The internal architecture of the beach ridge and swale deposits is divided into characteristic radar facies. We identify downlap points interpreted to mark the transition from the beachface to the upper shoreface and, thus, sea-level at the time of deposition. This new data set shows that beach steps can be preserved and resolved in GPR reflection data. This is important, as downlap points identified at the base of the beach steps should be corrected for beach step height in order to be used as a marker of sea-level. Identification of beach steps in combination with observed changes in dips of the interpreted beachface reflections can give information about changes in the morphodynamic conditions of beach ridge progradation through time. The vertical levels of identified downlap points are combined with an age model based on optically stimulated luminescence-dated samples to reconstruct RSL for the past c. 5000 years. Overall, the reconstruction shows that the period between c. 4800 and 3800 yr BP was characterized by relatively high RSL values around 2.3 m above DVR90 (Danish Vertical Reference 1990). A marked decrease in RSL of c. 1.3 m occurred between c. 3800 and 3600 yr BP at a rate of c. 5 mm/yr. After c. 3500 yr BP, the RSL curve shows a gradual decrease at a rate of c. 0.6 mm/yr.
Systematic observations of wind speed and direction have been collected at Skagen Fyr (Skagen Lig... more Systematic observations of wind speed and direction have been collected at Skagen Fyr (Skagen Lighthouse), northern Denmark from December 1860 to August 2012. Wind speed and wind direction are analyzed based on two data sets given in Beaufort and m/s respectively and based on these data storminess variation is analyzed. Changes in wind climate during this time interval cover the final phase of the relatively cold Little Ice Age and the following warming since the late 19th century. Since the end of the Little Ice Age the wind pattern has clearly changed in terms of both strength and direction. Between 1860 and 1875 storminess (wind events exceeding Beaufort 8) is extremely high, but since then storminess decreases. Around 1870 the annual drift potential (DP) is also extremely high and reaches up to 9600 vector units (VU); since 1980 DP levels are below 3000 VU and decreasing. Resultant drift direction (RDD) is towards the east or east-northeast until about 1960 when it steadily becomes more and more northerly. Most storms occur during autumn and early winter. Summers are less stormy but characterized by unidirectional winds. Since the end of the Little Ice Age most inland parabolic dunes on Skagen Odde have undergone a general stabilization. This shift in dune dynamics is primarily related to continued dune management, but the change in wind climate including an overall decrease in storminess (including a marked decrease in summer storminess) and an increase in southerly and south-westerly winds probably contribute to dune stabilization.
Plateau dunes are unique landforms which formed as erosion relicts in blow-out areas in Late Plei... more Plateau dunes are unique landforms which formed as erosion relicts in blow-out areas in Late Pleistocene sandy deposits. They are negative forms in contrast to normal dunes where sand is accumulated (positive form). Plateau dunes are located in the European Aeolian Sand Belt in the Netherlands, Germany and Denmark and they are flat-topped features with a bog in the central part often covered by a thin aeolian sand layer. A conceptual model of formation and further development of plateau dunes in time are presented in detail, using 14 C dates of buried peat layers and OSL dates of sandy sediments. Special focus is on the influence of climate factors, pedology, and human activity on the formation of plateau dunes.
Traditionally, topographic surveying in earth sciences requires high financial investments, elabo... more Traditionally, topographic surveying in earth sciences requires high financial investments, elaborate logistics, complicated training of staff and extensive data processing. Recently, off-the-shelf drones with optical sensors already reduced the costs for obtaining a high-resolution dataset of an Earth surface considerably. Nevertheless, costs and complexity associated with topographic surveying are still high. In 2020, Apple Inc. released the iPad Pro 2020 and the iPhone 12 Pro with novel build-in LiDAR sensors. Here we investigate the basic technical capabilities of the LiDAR sensors and we test the application at a coastal cliff in Denmark. The results are compared to state-of-the-art Structure from Motion Multi-View Stereo (SfM MVS) point clouds. The LiDAR sensors create accurate highresolution models of small objects with a side length > 10 cm with an absolute accuracy of ± 1 cm. 3D models with the dimensions of up to 130 × 15 × 10 m of a coastal cliff with an absolute accuracy of ± 10 cm are compiled. Overall, the versatility in handling outweighs the range limitations, making the Apple LiDAR devices cost-effective alternatives to established techniques in remote sensing with possible fields of application for a wide range of geo-scientific areas and teaching. In geosciences, terrestrial laser-scanning and airborne laser-scanning (TLS & ALS) techniques are applied for topographic land surveying on a wide range of scales 1-3. LiDAR is a common technique to measure distances by timing the return pulse, emitted from a laser transmitter to the laser receiver 4. The rapid evolution of digital processing techniques, as well as a new generation of technologies in remote sensing, is leading to a revolution in digital elevation modeling and geomorphological terrain analysis 5. Nevertheless, the acquisition of a digital terrain model, independent from the scale, requires high capital and logistical costs in the order of several thousand of euros, especially with airborne laser-scanning techniques 6. Therefore, data acquisition of airborne large-scale remote sensing datasets is often outsourced to third party organizations, concomitantly data acquisition is planned well in advance regardless of unforeseeable events. However, many processes studied in geosciences, like coastal cliff erosion, are irregular processes in time and space. Coarse temporal resolution observations may limit pivotal process understanding 7. Terrestrial laserscanning (TLS) allows the acquisition of digital terrain models up to a medium-scale of a few kilometers with a high temporal and spatial resolution 8,9. Usually, terrestrial laser scanners cost at least several thousands of euros, requiring trained operators and line of sight, only allowing a limited number of scanning positions, and are restricted in access to rough terrain. Hand-held mobile laser scanner (HMLS) can overcome some of those limitations, but are rarely used in geosciences 10. Furthermore, TLS and HMLS still require highly skilled field handling and post processing 11. Recent advances in photogrammetry and the availability of lightweight unmanned aerial vehicles (UAVs) offer a potential low-cost alternative to ALS and TLS in order to build 3D surface models with a high temporal and spatial resolution 6,12. However, current high-resolution 3D models based on UAV data and Structure-from-Motion Multi-View Stereo (SfM MVS) pipelines are still expensive as they rely on differential global navigation satellite systems (DGNSS), ground control points (GCPs), commercial software and data processing on an external computing device 13. Moreover, UAV missions rely on certain weather conditions, entail a sophisticated setup, high operational complexity and SfM MVS techniques present challenges by managing and processing large volumes of data 14,15. Furthermore, the use of UAVs are subject to a growing number of regulations and restrictions prohibiting flight. Multiple studies compared the two techniques concluding both should coexist, with their respective primary fields of application 16-18. The commonness of smartphones nowadays, together with advances in sensor technologies, opens new possibilities for scientific applications as well as low-cost, crowd-sourced observations in mapping surface changes
Field observations of the suspended sediment concentrations in the inner nearshore zone are made ... more Field observations of the suspended sediment concentrations in the inner nearshore zone are made with the use of a pump-sampling system to derive time-averaged profiles and with the use of optical devices to get instantaneous information. Distributions of the suspended sediment concentrations over the water depth under different hydraulical conditions result in characteristic profiles in different morphological units. The net near bed sediment fluxes are small, and composed of an oscillating component to the beach and a mean component directed offshore.
Wave processes are well known for developing spit systems in large or elongated lakes by inducing... more Wave processes are well known for developing spit systems in large or elongated lakes by inducing longshore sediment transport for spit migration, while bathymetric interaction is less studied. In this study, we investigate the combined effects of wave processes, antecedent topography and lake level changes on the development of Holocene spit systems in the Danish lake Mossø. Wave climate prediction and a digital elevation model were used to provide a conceptual model for the development of the spits system, while optically stimulated luminescence (OSL) dating of spit sand and antecedent topography analyzed via boreholes and seismic survey data were used to evaluate effects on spit migration other than wave setting. We found that spit migration stagnated during the Holocene when reaching areas of deeper waters, but continued following shallowing after deep basin infilling with lacustrine sediments. During periods of bathymetrically induced stagnation of prominent spits, less stable or more slowly migrating spits became prominent in the development of the spit system. No clear effects on spit migration caused by lake level fluctuations could be demonstrated. However, such fluctuations may have been important for the stabilization of spits and subsequent development of a major barrier shoreline.
Landslides are a frequent natural hazard occurring globally in regions with steep topography. Add... more Landslides are a frequent natural hazard occurring globally in regions with steep topography. Additionally, landslides play an important role in landscape evolution by transporting sediment downslope. Landslide inventory mapping is a common technique to assess the spatial distribution and extent 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 complete landslide inventory is freely available for download at
An automated layer counting technique is developed to estimate the chronology of a marine sedimen... more An automated layer counting technique is developed to estimate the chronology of a marine sediment core and this technique is validated with Pb210 chronology. The marine sediment core was sampled in front of the delta of Mittivakkat Glacier meltwater river in the Sermilik Fjord, SE Greenland, and is a proxy of the sediment delivery from a glacial drainage basin to a fjord. The estimated time series was based on automatic lamination detection (varves) on a line scan of the core using gray scale intensities, and covered the last two centuries. The estimated time series of sediment accumulation rates was coupled to modelled runoff from the Mittivakkat Glacier and compared with local climatic parameters (air temperature and precipitation) and with the Atlantic Multidecadal Oscillation (AMO) index. Maxima in the sediment accumulation rate at the bottom of the side-fjord, about 1 km from the delta, mostly depended on glacier ablation and consequently on changes in river runoff, which were initiated by the air temperature. This was especially the case during transition from colder periods towards warmer, where short-lived maxima in sediment accumulation rates were followed by lower rates, even though the temperature remained high. This suggested a quite rapid glacial response to changes in climatic forcing, and/or a hysteresis effect, where sediment stored in the glacier/valley system was evacuated soon after a temperature dependent increase in discharge. The air temperature was in turn controlled by the AMO index.
Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetra... more Changes in relative sea-level (RSL) during the Holocene are reconstructed based on ground-penetrating radar (GPR) data collected across a raised beach ridge system on the island of Samsø, Denmark. The internal architecture of the beach ridge and swale deposits is divided into characteristic radar facies. We identify downlap points interpreted to mark the transition from the beachface to the upper shoreface and, thus, sea-level at the time of deposition. This new data set shows that beach steps can be preserved and resolved in GPR reflection data. This is important, as downlap points identified at the base of the beach steps should be corrected for beach step height in order to be used as a marker of sea-level. Identification of beach steps in combination with observed changes in dips of the interpreted beachface reflections can give information about changes in the morphodynamic conditions of beach ridge progradation through time. The vertical levels of identified downlap points are combined with an age model based on optically stimulated luminescence-dated samples to reconstruct RSL for the past c. 5000 years. Overall, the reconstruction shows that the period between c. 4800 and 3800 yr BP was characterized by relatively high RSL values around 2.3 m above DVR90 (Danish Vertical Reference 1990). A marked decrease in RSL of c. 1.3 m occurred between c. 3800 and 3600 yr BP at a rate of c. 5 mm/yr. After c. 3500 yr BP, the RSL curve shows a gradual decrease at a rate of c. 0.6 mm/yr.
Systematic observations of wind speed and direction have been collected at Skagen Fyr (Skagen Lig... more Systematic observations of wind speed and direction have been collected at Skagen Fyr (Skagen Lighthouse), northern Denmark from December 1860 to August 2012. Wind speed and wind direction are analyzed based on two data sets given in Beaufort and m/s respectively and based on these data storminess variation is analyzed. Changes in wind climate during this time interval cover the final phase of the relatively cold Little Ice Age and the following warming since the late 19th century. Since the end of the Little Ice Age the wind pattern has clearly changed in terms of both strength and direction. Between 1860 and 1875 storminess (wind events exceeding Beaufort 8) is extremely high, but since then storminess decreases. Around 1870 the annual drift potential (DP) is also extremely high and reaches up to 9600 vector units (VU); since 1980 DP levels are below 3000 VU and decreasing. Resultant drift direction (RDD) is towards the east or east-northeast until about 1960 when it steadily becomes more and more northerly. Most storms occur during autumn and early winter. Summers are less stormy but characterized by unidirectional winds. Since the end of the Little Ice Age most inland parabolic dunes on Skagen Odde have undergone a general stabilization. This shift in dune dynamics is primarily related to continued dune management, but the change in wind climate including an overall decrease in storminess (including a marked decrease in summer storminess) and an increase in southerly and south-westerly winds probably contribute to dune stabilization.
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