Lake Lucerne Research Articles

Soil-biodegradable plastic films do not decompose in a lake sediment over 9 months of incubation

Abstract. Agriculture relies heavily on the use of plastic mulch films, which increase crop yields and can lower water demands. In recent years, soil-biodegradable mulch films have been marketed to replace the non-biodegradable, conventional polyethylene-based mulch films. These biodegradable mulch films are designed to be ploughed into the soil after use to be biodegraded in situ by soil microorganisms. However, research has shown that part of the mulch film material may be transported from the fields to neighboring environments, including aquatic ecosystems. Research on potential biodegradation of soil-biodegradable plastics in freshwater habitats is lacking. Here, we investigated the mineralization of soil-biodegradable agricultural mulch films in freshwater lake sediments of Lake Lucerne, Switzerland. Two types of commercial soil-biodegradable mulch films were incubated within lake sediment cores, along with traditional polyethylene (PE) plastic, and the production of CO2 and CH4 was followed over time relative to non-plastic-containing control sediments. After the 40-week incubation period, the films were visually intact and showed no signs of mineralization. Gas analyses showed no additional production of either CO2 or CH4 in the degradable mulch film incubations, compared to the control or PE plastic incubations. We conclude that these two used soil-biodegradable mulch films have a low biodegradability in lake sediments, likely reflecting that the microbial community structure in the lake sediment lacks active microbial degraders. Our results highlight the importance of preventing transport of soil-biodegradable mulch films from agricultural soils to surrounding aquatic environments.

A GIS framework for prediction of basin‐wide post‐failure geometry of confined subaqueous landslides

AbstractStability analysis of submarine and sub‐lacustrine slopes requires special attention to the strain‐softening nature of clay‐rich sediments. Utilizing the often‐used infinite slope assumption using the peak strength is inadequate for the task at hand as the well‐known limit equilibrium method may provide non‐conservative estimate of marine slopes’ stability. In this paper, a GIS based framework is developed to account for a more suitable shear band propagation slope‐failure criterion for basin‐wide stability calculations. After determining the slab failure prone areas, the framework employs analytical criterion for retrogressive failure above the slab and depth‐integrated finite element method for calculating the size of confined slides at the toe. This allows predicting the landslide's post‐failure configuration and the overall landslide coverage zone. The framework is first benchmarked to prove its competence and then applied to the well documented Zinnen Slide and the southeastern banks of the Küssnacht Basin, Lake Lucerne, Switzerland. The results of the application show good agreement with the observed basin geomorphology.

On the seismic response and earthquake-triggered failures of subaqueous slopes in Swiss lakes

SUMMARY Seismically triggered subaqueous mass movements in lakes may generate tsunamis that can cause significant damage on the shore. In this study, we assess the seismic response and stability of subaqueous slopes in Swiss lakes based on recorded seismological data, historical and geological information and geotechnical surveys. We performed seismic investigations at multiple locations in Lake Lucerne using Ocean Bottom Seismometers (OBS). For these locations, we derived ground-motion amplification functions from local and regional earthquakes and horizontal-to-vertical spectral ratios (H/V) from the earthquake and ambient vibration recordings. The results show (1) very high amplification levels, often exceeding values of 50–100 in the frequency range between 1 and 10 Hz, (2) the fundamental frequency of resonance in the range of 0.5–3.5 Hz and (3) laterally variable site response even for closely located stations. We sought also the signatures of non-linear site response in the H/V curves or ground-motion amplification functions but found only weak indicative effects and no clear evidence. This is most likely due to the low levels of ground motion recorded during the OBS campaigns. We conducted back analyses of historical earthquakes in Switzerland with available documental and/or geological evidence of induced (tsunamigenic) subaqueous slope failures in Swiss lakes. The data set of historical events was complemented with a selection of instrumentally recorded earthquakes in Switzerland. For the analyses, we selected multiple sites in Swiss lakes which failed in the past or are prone to failure in the future. We modelled the ground motion at these locations assuming Swiss standard reference rock conditions (vs30 = 1105 m s−1). The modelled ground motion intensity measures (IM) included peak ground acceleration (PGA), peak ground velocity (PGV) and pseudospectral acceleration (PSA) at 0.3, 1 and 2 s. We estimated the minimum ground motion and macroseismic intensity at reference rock conditions required to trigger the failures of subaqueous slopes. In addition, we defined a threshold for the seismic triggering of such failures in terms of moment magnitude (Mw) and epicentral distance (Re) as: $$\begin{eqnarray} M_{\rm w}=2.891+1.904\log_{10}(R_e+5.166)\: {\rm for}\: R_e\ge 3.7\: {\rm km}. \end{eqnarray}$$ Our results are consistent with previous studies based on worldwide observations. Furthermore, we related the modelled ground motions to the Swiss seismic hazard products and estimated the return period of critical ground shaking responsible for triggering subaqueous slope failures (with potential for tsunami generation) to be in the range of 36–224 yr. Finally, based on previously collected geotechnical data (in situ Cone Penetration Testing and laboratory sediment analysis), we determined the most likely values of the seismic coefficient k to be used with the ground motion IMs modelled at reference rock conditions in infinite slope stability analyses to estimate the factor of safety (FS). For PGA, we found a k = 1; for PGV, k = 2; for PSA0.3s, k = 0.6; for PSA1s, k = 2 and for PSA2s, k = 5.5. These estimates are conservative and affected by the trade-off between the thickness of unconsolidated sediments and the slope angle. Thus, we recommend applying them to slopes with a low-to-moderate gradient (<15°) and sediment thickness of more than 2 m.

Unravelling megaturbidite deposition: Evidence for turbidite stacking/amalgamation and seiche influence during the 1601 ce earthquake at Lake Lucerne, Switzerland

ABSTRACTMegaturbidites are commonly used to reconstruct the seismic history (palaeoseismology) of areas where large earthquakes occur. However, the depositional mechanisms and sedimentary characteristics of these deposits are not yet fully understood. This study unravels the sequence of sediment deposition that occurred in Lake Lucerne (Vitznau Basin) following the 1601 ce earthquake in central Switzerland. During this event, slope failures were triggered, generating mass flows and turbidity currents that led to the formation of mass‐transport deposits and a megaturbidite. These deposits are sampled in 28 sediment cores, which are examined with X‐ray computed tomography scans (medical and μCT), grain‐size analysis and natural remanent magnetisation. This suite of analyses allows a detailed reconstruction of turbidite stacking and amalgamation in the centre of the basin, followed by settling of finer sediments influenced by a lake seiche. Initial deposition of mass‐transport deposits is followed by sandy turbidites reaching the depocentre. Some of these turbidite sands can be linked to their source areas, and evidence is found of some turbidites being overridden by mass flows in the peripheral parts of the megaturbidite deposit. Hereafter, sedimentation becomes controlled by seiche‐induced currents, which rework fine sediments upon deposition, leading to subtle grain‐size variations at the base of the seiche‐influenced sub‐unit and a ponded geometry of the megaturbidite. As the seiche movement dampens, a relatively muddy, homogeneous sub‐unit is deposited that drapes the basin plain. Overall, this study provides the first highly detailed sedimentological analysis of megaturbidite deposition in a lake, demonstrating the distinct sedimentological imprint of lake seiching and turbidite amalgamation/stacking. This will improve the recognition and interpretation of earthquake‐induced megaturbidites in other lake records or isolated basins, and demonstrates the value of using (μ)CT scans in combination with traditional sedimentological parameters to reconstruct the depositional processes of megaturbidites.

A taxonomic revision of ten whitefish species from the lakes Lucerne, Sarnen, Sempach and Zug, Switzerland, with descriptions of seven new species (Teleostei, Coregonidae).

The taxonomy of the endemic whitefish of the lakes of the Reuss River system (Lucerne, Sarnen, Zug) and Lake Sempach, Switzerland, is reviewed and revised. Lake Lucerne harbours five species. Coregonusintermundiasp. nov. and C.suspensussp. nov., are described. Coregonusnobilis Haack, 1882, C.suidteri Fatio, 1885, and C.zugensis Nüsslin, 1882, are redescribed. Genetic studies have shown that C.suidteri and C.zugensis are composed of several distinct species endemic to different lakes. The names C.suidteri and C.zugensis are restricted to the species of lakes Sempach and Zug, respectively. The whitefish populations previously referred to as C.suidteri and C.zugensis from Lake Lucerne are described as C.litoralissp. nov. and C.muellerisp. nov., respectively. Furthermore, the whitefish from Lake Zug that were previously referred to as C.suidteri are described as C.supersumsp. nov. A holotype is designated for C.supersum that was previously one of two syntypes of C.zugensis. The other syntype is retained for C.zugensis. Coregonusobliterussp. nov. is described from Lake Zug, and C.obliterus and C.zugensis from Lake Zug are extinct. Finally, we describe C.sarnensissp. nov. from lakes Sarnen and Alpnach. Coregonussuidteri from Lake Sempach shows strong signals of introgression from deliberately translocated non-native whitefish species, which questions if the extant population still carries a genetic legacy from the original species and thus may need to be considered extinct. Coregonussuspensus is genetically partially of allochthonous origin, closely related to the radiation of Lake Constance. It is therefore compared to all known and described species of Lake Constance: C.wartmanni Bloch, 1784, C.macrophthalmus Nüsslin, 1882, C.arenicolus Kottelat,1997, and C.gutturosus Gmelin, 1818.

Basin Sediments Geometry and Strength as Controls for Post‐Failure Emplacement Style of Alpine Sub‐Lacustrine Landslides

AbstractPredicting the evolution of underwater mass movements in their post‐failure stage is vital for risk assessment of offshore structures and ensuring safety of coastal communities threatened by tsunami waves. In the absence of sedimentological and geotechnical data, variability of the post‐failure behavior in a specific marine or lacustrine setting is often attributed to predisposition factors such as the slope height‐drop and depth to the basal shear surface. In this paper, the contribution of other geometrical parameters such as the slope inclination and the relative thickness of the frontal basin sediments is investigated using a coupled Eulerian‐Lagrangian finite element framework. An emphasis is given to the important role of the strength difference between the slope and frontal basin sediments. The suggested framework is first validated against the well‐documented Zinnen slide in Lake Lucerne (Switzerland), successfully reproducing the post‐failure geometry and capturing the main features observed in published seismic profiles. It is then applied in a parametric study to illustrate the decisive role of the frontal basin sediments in determining the post‐failure geometry of underwater mass wasting in similar settings.

Geotechnical characterization and stability analysis of subaqueous slopes in Lake Lucerne (Switzerland)

Tsunamis occur not only in marine settings but also in lacustrine environments. Most of the lacustrine tsunamis are caused by seismically- or aseismically-triggered mass movements. Therefore, an assessment of the stability of subaqueous slopes is crucial for tsunami hazard assessment in a lake. We selected Lake Lucerne (Switzerland) as a natural laboratory to perform an in-depth geotechnical characterization of its subaqueous slopes. This lake experienced documented tsunamis in 1601 and 1687. Some of its slopes still bear sediment volumes with a potential for tsunamigenic failure. To identify such slopes, we interpreted available reflection seismic data and analyzed the bathymetric map. Then, we performed 152 dynamic Cone Penetration Tests with pore pressure measurement (CPTu) and retrieved 49 sediment cores at different locations in the lake. These data were used to characterize the failure-prone sediments and to evaluate the present-day static stability of subaqueous slopes. Obtained results allowed the definition of three classes of slopes in terms of static stability: unstable slopes, stable slopes close to the unstable state, and stable areas. Non-deltaic slopes with thicker unconsolidated fine-grained sediment drape and moderate-to-high slope gradients (> 5–10°) have the lowest Factor of Safety. In agreement with previous studies, the failure plane for the non-deltaic slopes is embedded within the fine-grained glaciolacustrine sediments. Deltaic slopes with prevailing coarse-grained sediments mostly appear statically stable. Finally, we generalized the measured undrained shear strength profiles {s}_{u}(z) into the depth-dependent power-law models. These models define the {s}_{u} of Lake Lucerne’s sediments and can be applied to other lakes with similar sedimentation history.

A Robust Workflow for Acquiring and Preprocessing Ambient Vibration Data from Small Aperture Ocean Bottom Seismometer Arrays to Extract Scholte and Love Waves Phase-Velocity Dispersion Curves

The phase-velocity dispersion curve (DC) is an important characteristic of the propagation of surface waves in sedimentary environments. Although the procedure for DC estimation in onshore environments using ambient vibration recordings is well established, the DC estimation in offshore environments using Ocean Bottom Seismometers (OBS) array recordings of ambient vibrations presents three additional challenges: (1) the localization of sensors, (2) the orientation of the OBS horizontal components, and (3) the clock error. Here, we address these challenges in an inherent preprocessing workflow to ultimately extract the Love and Scholte wave DC from small aperture OBS array measurements performed between 2018 and 2020 in Lake Lucerne (Switzerland). The arrays have a maximum aperture of 679 m and a maximum deployment water depth of 81 m. The challenges related to the OBS location on the lake floor are addressed by combining the multibeam bathymetry map and the backscatter image for the investigated site with the differential GPS coordinates of the OBS at recovery. The OBS measurements are complemented by airgun surveys. Airgun data are first used to estimate the misorientation of the horizontal components of the OBS and second to estimate the clock error. To assess the robustness of the preprocessing workflow, we use two array processing methods, namely the three-component high-resolution frequency-wavenumber and the interferometric multichannel analysis of surface waves, to estimate the dispersion characteristics of the propagating Scholte and Love waves for one of the OBS array sites. The results show the effectiveness of the preprocessing workflow. We observe the phase-velocity dispersion curve branches in the frequency range between 1.2 and 3.2 Hz for both array processing techniques.

Shallow‐Water Tsunami Deposits: Evidence From Sediment Cores and Numerical Wave Propagation of the 1601 CE Lake Lucerne Event

AbstractThe 1601 CE earthquake (Mw ca. 5.9) in “Unterwalden,” Central Switzerland, triggered multiple subaqueous mass movements and a subaerial rockfall that generated tsunami waves with run‐up heights of up to 4 m and several hundred meters of inundation along the coastal lowlands of Lake Lucerne. In the shallow Lucerne Bay, historical chronicles reported an oscillation of the water with an initial amplitude of ∼1–2 m and a period of 10 min, which continued for several days after the event with decreasing amplitude. Here, we investigate the lake‐tsunami process chain from subaqueous mass movement‐generated tsunami to wave propagation and ultimately to sediment resuspension, transport, and deposition in the shallow‐water environment. The effects of the historical tsunami on Lucerne Bay are reconstructed using sediment‐core analysis and numerical simulation of wave propagation. A 60‐cm‐thick event deposit was recovered along a sediment‐core transect in the shallow waters and radiocarbon dated to 1306–1442 cal CE. The event deposit has a sharp basal contact with carbonate shell fragments followed upwards a normally graded succession of siliciclastic sand to silt with a high proportion of horizontally bedded wooden particles. The numerically simulated tsunami waves are characterized by a water‐surface displacement of up to 1.5 m and generate bed shear‐stresses that are likely capable of remobilizing large amounts of sediments in the Lucerne Bay area. Our study successfully links the sedimentology of event deposits with physical principles of sediment mobilization derived from numerical wave‐forward modeling, providing a tool to improve the identification and interpretation of potential tsunami deposits.

Seiches and the slide/seiche dynamics; subcritical and supercritical subaquous mass flows and their deposits. Examples from Swiss Lakes

Four historically documented large and potentially dangerous lacustrine waves in Swiss lakes show that these waves have been seiches (standing waves) triggered by sublacustrine slides; a statement which is in accordance with the experience of seismologists who see earthquakes triggering seiches in lakes. Nevertheless, large historical waves in Switzerland have recently been modeled as progressive shallow water waves (tsunamis), probably because the slide/seiche dynamics are not known, and experiments with subaquatic slides fail to generate seiches in test–flumes. It appears that these tests exhibit a small shear–energy/slide–energy ratio ε, if compared with the situation in lakes. These facts incite a shear–stress lemma that states that ε is the constituent factor for the slide/seiche coupling. The structure of the subaqueous mass flow deposit (MFD) in lakes Lucerne and Geneva suggests the occurrence of subcritical and of supercritical slide flows. The former would generate a contortite, a MFD with contorted bedding, the latter a debrite (mudclast conglomerate). Potential slide energy considerations are used for an estimation of the amplitudes of large seiches produced by subaquatic slides, a proceeding that yields partly similar and partly very different results, as compared with numerical tsunami simulations.

Flugbilder. Franz Ludwig Pfyffers „Relief der Urschweiz“ und andere Geländemodelle als Medien der wissenschaftlichen Aneignung der Alpen im späten 18. Jahrhundert

Among the processes of “conquering, developing and appropriating mountains” is occupied by the emergence of mountain topography. In the eighteenth century raised relief, as a terrain model, played one of the most important roles in this process.
 This was a period when more reliable topographic data began to be collected on the basis of measurements carried out across the Alps. Possibilities of their cartographic representation were limited at the time. A graphic method for presenting orthogonal projection by means of contour curves was not invented until the nineteenth century. Before that three-dimensional terrain models were the only way to correctly represent various levels of landscape. Terrain models were accepted at the time as the best method for presenting mountain landscapes.
 The first attempt to carry out a comprehensive measurement of the Alps over a vast area of a continuous mountain range and represent it on a low relief was made in 1786 and concerned an area in central Switzerland around Lake Lucerne. At that time Franz Ludwig Pfyffer von Wyher, an officer in French service, became famous for advanced surveying techniques and terrain models, both civilian and military. His famous relief depicts around one-tenth of today’s Switzerland, with two-thirds of the area encompassing the Alps and foot of the Alps. From that moment on other authors began to create their models of Alpine landscape. These reliefs were appreciated by contemporary naturalists, especially those studying the Alps, because they enabled them to view the complex topography of the range, which had been impossible before. They drew attention to a number of natural and geological phenomena, and made it possible to come up with new findings relating to the following questions: At what altitude should the snow line be placed? Where is the boundary of vegetation? Where do coniferous forests begin? Where is the line of glaciers? What is the structure of the mountains? Obviously, they were not sufficient to provide all answers to the above questions, but thanks to a “bird’s eye” perspective they made it possible to place special studies of the various disciplines within a broader context, both with regard to the relevant subject matter and between disciplines.

Z lotu ptaka. „Relief Praszwajcarii” Franza Ludwiga Pfyffera oraz inne modele terenu jako media naukowego zawłaszczania Alp w późnym XVIII wieku

Among the processes of “conquering, developing and appropriating mountains” is occupied by the emergence of mountain topography. In the eighteenth century raised relief, as a terrain model, played one of the most important roles in this process.
 This was a period when more reliable topographic data began to be collected on the basis of measurements carried out across the Alps. Possibilities of their cartographic representation were limited at the time. A graphic method for presenting orthogonal projection by means of contour curves was not invented until the nineteenth century. Before that three-dimensional terrain models were the only way to correctly represent various levels of landscape. Terrain models were accepted at the time as the best method for presenting mountain landscapes.
 The first attempt to carry out a comprehensive measurement of the Alps over a vast area of a continuous mountain range and represent it on a low relief was made in 1786 and concerned an area in central Switzerland around Lake Lucerne. At that time Franz Ludwig Pfyffer von Wyher, an officer in French service, became famous for advanced surveying techniques and terrain models, both civilian and military. His famous relief depicts around one-tenth of today’s Switzerland, with two-thirds of the area encompassing the Alps and foot of the Alps. From that moment on other authors began to create their models of Alpine landscape. These reliefs were appreciated by contemporary naturalists, especially those studying the Alps, because they enabled them to view the complex topography of the range, which had been impossible before. They drew attention to a number of natural and geological phenomena, and made it possible to come up with new findings relating to the following questions: At what altitude should the snow line be placed? Where is the boundary of vegetation? Where do coniferous forests begin? Where is the line of glaciers? What is the structure of the mountains? Obviously, they were not sufficient to provide all answers to the above questions, but thanks to a “bird’s eye” perspective they made it possible to place special studies of the various disciplines within a broader context, both with regard to the relevant subject matter and between disciplines.

Investigating the subsurface in a shallow water environment using array and single-station ambient vibration techniques

SUMMARYSingle-station and array ambient vibration techniques are widely used in onshore environments, in particular to retrieve the subsurface structure and shear-wave velocity profiles. We apply these techniques offshore in Lake Lucerne (Switzerland) using single-station and array Ocean Bottom Seismometer (OBS) data. This lake has experienced tsunamigenic subaquatic slope failures in the past and still has sediment-charged slopes that might fail in the presence of a seismic or aseismic trigger. The application of traditional onshore methods offshore brings additional challenges related to the processing of recorded data. To overcome these challenges, we perform multibeam bathymetry surveys to precisely locate the OBS on the lake floor and airgun shootings to determine the orientation of the horizontal components of the seismometer and to correct the time drift of the recorder. Then we obtain surface-wave phase velocity dispersion curves of Scholte and Love waves, and Scholte wave ellipticity curves at six subaquatic slopes. After the estimation of the dispersion curves, we deal with their modal identification using mode attribution analysis. The shear-wave velocity and thickness of the sedimentary layers at the investigated slopes are inferred using a transdimensional Bayesian inversion algorithm. The resolved velocity profiles show very low shear-wave velocities in shallow lake sediments and allow us to improve the understanding of the local stratigraphy. This research contributes to the assessment of stability and tsunamigenic potential of subaquatic slopes in Lake Lucerne.

Depth integrated modelling of submarine landslide evolution

Submarine landslides are a major geohazard among worldwide continental slopes, posing significant threats to offshore infrastructure, marine animal habitats and coastal urban centres. This study establishes an original numerical package for time-efficient modelling of the entire submarine landslide evolution covering the pre-failure shear band propagation, slab failure and post-failure dynamics. The numerical scheme is based on the conservation of mass and the conservation of momentum and combines the shear band propagation theory and the depth-integrated method, with the consideration of the drag force from the ambient water. Shear band propagation in the weak layer and slab failure in the sliding layer are controlled by the strain softening and rate dependency of the corresponding undrained strength parameters. The post-failure behaviour in the sliding layer, such as retrogression upslope and frontally confined and frontally emergent mechanisms downslope, is also simulated. The numerical results from the proposed method are comparable to the analytical solutions and the large deformation finite element analysis. Application of this method to a back analysis of the St. Niklausen slide in Lake Lucerne reproduced the observed shape of the mass transport deposits, the position of the main scar and the travel distance. Because of its easy implementation and efficiency, the proposed numerical method for modelling of submarine landslides seems promising for practical applications.

Conspecific migration and environmental setting determine parasite infracommunities of non-migratory individual fish.

Parasite infracommunities tend to be stochastic in nature, although environmental characteristics such as the type of water source in streams and host traits can have an effect on the biotic assemblages and by extension the parasite fauna. We examined the effect of water source and the rate of adult fish migration on the metazoan parasite infracommunities of conspecific juvenile brown trout, Salmo trutta L. among streams flowing into Lake Lucerne (Switzerland). Juvenile (1 to 2-year old) fish harboured higher parasite species richness in groundwater-fed than in surface water-fed streams, whereas the rate of fish migration did not affect infracommunity richness. Heteroxenous species were more common in groundwater-fed streams with high and medium rates of trout migration, whereas infracommunities in surface water-fed streams and streams with low rates of fish migration were dominated by one monoxenous parasite or lacked infections. Similarity in the parasite infracommunity composition of juvenile trout across streams was explained by the interaction between type of water source and adult migration rates. Our conclusions support that similarity in the parasite composition of resident freshwater conspecifics can be predicted by the local environmental settings and host migratory behaviour, whereas parasite richness is mainly influenced by the environmental characteristics.

Using PIT-tags and portable antennas for quantification of fish movement and survival in streams under different environmental conditions.

While PIT-tag tracking using mobile antennas is being increasingly used to study fish movement and survival in streams, little is known about the limitations of the method, especially over longer periods of time and under different environmental settings. We used 6 years of data combining tagging, mobile antenna tracking and recaptures of Salmo trutta in multiple small streams in the Lake Lucerne drainage area in Switzerland to evaluate the relative importance of different environmental and intrinsic factors affecting the efficiency of the method. Our study system and experimental design allowed us to accurately verify the continuous presence and survival of recaptured fish in the stream after tracking, which meant that we could estimate detection probability with high confidence. The mean detection probability of tagged trout was 43%, but we found that fish length had a strong negative effect on detection probability, especially in males. Multivariate axes of stream environmental features did not predict efficiency but stream width alone was significantly positively correlated with efficiency. Additionally, stream temperature when tracking had a positive effect on fish detectability. Tag loss at recapture was globally rare (<8%) but common in large postspawn females (>30%). Based on the escape response of fish after detection, we could estimate the proportion of ghost tags, which reached a plateau of around 80% 2 years after tagging. We finally showed that our models of tag loss, fish detection and escape response are needed to interpret detection events. Our results highlight that individual variation in detection probability and tag loss is high and has to be considered for analysis.

Propagation of frontally confined subaqueous landslides: Insights from combining geophysical, sedimentological, and geotechnical analysis

Subaquatic mass movements are common in marine and lacustrine environments, but due to their barely predictable nature, direct observations of these processes are limited so that knowledge is only indirectly obtained by investigating the resulting mass-transport deposits (MTDs). Most research focuses on the most common frontally emergent slides, fast-moving events able to generate turbidity currents and tsunamis. Geohazards of frontally confined slides and mechanisms behind their typical fold-and-thrust deformation structures are however still poorly understood.We investigate frontally confined MTDs in Lake Lucerne (Switzerland) by integrating bathymetric and high-resolution seismic data with geotechnical information derived from in situ Cone Penetrometer Tests and short core analysis. Investigated MTDs consist of three units: i) a mass-slide deposit, located at the base of the slope consisting of a coherent slope sequence, ii) a fold-and-thrust system developed in basin sediments, and iii) an overrunning mass flow deposit, consisting of remolded slope sediments. The deformed and thrusted basin sediments show higher undrained shear strength compared to the undisturbed basin sequence. We propose that this strengthening is caused by lateral compression leading to fluid expulsion in the high-plasticity basin sediments by the bulldozing sliding mass. Relative kinematic indicators document that the fold-and-thrust deformation structures occur rapidly. Thus, they should be considered in tsunami hazard analysis. Furthermore, our data highlight that the slope angle of the gliding surface and basin topography are key controlling factors for slope stability and propagation of basin-plain deformations, respectively. Our integrated study supports and refines propagation models proposed in marine environments, revealing the potential of investigating smaller-scale easier-to-access MTDs in lakes.

Controlling factors for post-failure evolution of subaqueous landslides

Subaqueous slope failures can evolve in various patterns. Whereas some slides run out and further evolve into highly mobile turbidity currents, others maintain a continuum-like structure and remain frontally confined. The different failure modes impose different hazard scenarios, making an understanding of their origin crucial for reliable hazard assessments. Yet many of the factors controlling their post-failure behaviour remain not well understood. In this paper, a procedure is presented for the analysis of the post-failure evolution of subaqueous landslides, using a coupled Eulerian–Lagrangian finite-element analysis approach. The procedure is applied to analyse the St Niklausen slide in Lake Lucerne (Switzerland), providing a good prediction of observed landslide features, without back-calibration of input parameters. The approach is further applied to investigate the influence of controlling parameters, highlighting effects of different strength parameters, the surrounding water and the slope stratigraphy and geometry on the landslide dynamics. The procedure presented can be generally applied to predict the post-failure evolution of subaqueous landslides and facilitates the extraction of the moving soil–water boundary, which can serve as source input for tsunami propagation modelling.

Novel Spectra-Derived Features for Empirical Retrieval of Water Quality Parameters: Demonstrations for OLI, MSI, and OLCI Sensors

The empirical (regression-based) methods for estimation of water quality parameters are mostly built upon the features derived from the original feature space of optical imagery (e.g., band ratios). This article aims at examining novel features to retrieve in-water constituents including chlorophyll-a (Chl-a), total suspended solids (TSS), and colored dissolved organic matter (CDOM). In this article, direction cosines and transformation of either color space or the coordinate system are applied to the original feature space in order to derive new features. A full-search approach is exploited to identify the optimal band combination for a given type of feature. The proposed analysis seeks for a band combination among all the possible ones that yield the strongest correlation through regressing a given feature against the concentration of the constituent of interest. The effectiveness of the proposed features is examined against standard ones using radiative transfer simulations, in situ measurements, and satellite imagery in a wide range of in-water optical conditions. The simulated and in situ data enabled in-depth analyses on the efficacy of recent satellite sensors with the primary focus of the aquatic science community [Operational Land Imager (OLI), MutiSpectral Instrument (MSI), and Ocean and Land Color Instrument (OLCI)] for retrieval of in-water constituents. TSS and Chl-a concentration of two alpine lakes (Lake Constance and Lake Lucerne) are also mapped using a real OLI image. The results suggest the effectiveness of the proposed features that can be leveraged to estimate the constituents in inland/coastal waters. OLI-based retrievals of in-water constituents proved difficulties in optically complex waters, whereas enhanced spectral resolution of MSI and OLCI permitted accurate estimates.

Reconstruction and actual trends of landslide activities in Bruust–Haltiwald, Horw, canton of Lucerne, Switzerland

Abstract. A spatiotemporal reconstruction of slope movements on the edge of Lake Lucerne near the municipality of Horw, canton of Lucerne, is presented. The reconstruction was realized by analyzing growth reactions of beech (Fagus sylvatica L.) and fir (Abies alba Mill.) trees growing on this slope. Before dendrochronological sampling, a detailed geomorphological mapping of the landslide was conducted with the aim to determine the spatial extent of the sliding area. For tree-ring analyses, 124 increment cores from 62 trees were analyzed following standard techniques of dendrogeomorphology. In addition, long micro-sections were prepared from the entire cores to extend the common eccentricity analyses by microscopic determination of the onset of reaction wood in fir and beech. Results clearly show that the area is moving at least since 1948. A significant concentration of events was observed between the years 1990 and 2000 as well as after 2006. The definition of a threshold to define events using an eccentricity index alone is problematic and needs to be adapted to specific site conditions. For this reason, we recommend always combining the application of an eccentricity index with a detailed visual (anatomical) inspection to check for the occurrence of reaction wood.