Earth Surface Processes and Landforms最新文献

An unprecedented precipitation event in the hyper-arid Atacama Desert of Northern Chile occurred in March 2015. Geomorphic alterations to the river channel and the coastal zone, coupled with the exceptional magnitude of the rainfall, caused catastrophic damage and loss of life. On the coast of the El Salado watershed, legacy mine tailings infilled the watershed-ocean connection, while the river channel was altered both by tailings and urbanization. The consequences of this event resulted from the coupling of anthropogenic geomorphic changes with an unusual climate event. Lack of field data, complex geomorphology and sediment loads influenced by human activity make analysing floods in these regions especially challenging. The objective of this work is to improve our understanding of the factors that control flood hazards by using numerical simulations to reconstruct the 2015 flood in El Salado. We carry out unsteady two-dimensional simulations fully coupled with the sediment concentration to identify the influence of tailing deposits, considering high-resolution data of the pre- and post-2015 flood topography. The results highlight the importance of specific event-based studies, using models that can help designing better strategies for climate change adaptation and risk mitigation, while providing information for risk reduction and channel restoration.

Despite artificial rainfall simulation proves invaluable for the study of soil erosion processes and model construction, it still fails to fully replicate the characteristics of natural rainfall. Currently, most artificial rainfall experiments have carried out a large number of continuous high-intensity rainfall due to the focus on the characteristics of short duration and high intensity of natural rainstorm but have ignored the erosion effects caused by intermittent rainstorm with low intensity and long duration. In this study, two sets of artificial rainfall simulation experiments of intermittent low-intensity rainstorm (RR1) and continuous high-intensity rainstorm (RR2) were conducted to evaluate the effects of rainfall characteristics on erosion morphology, runoff generation and soil loss. The evolution morphology monitored by a digital close-range photogrammetry technology demonstrated the difference between the two rainstorm regimes. The soil surface was damaged more seriously under rainfall of RR2, and the rill morphological indicators of RR1 were all less than that of RR2. As rainfall proceeded, morphological indicators except for rill width-depth ratio gradually increased. As a result, the runoff rate and sediment yield between two regimes were distinct. The segmented and total soil loss, average runoff rate and sediment concentration of RR1 were all less than that of RR2, with the total soil loss of the two rainstorm regimes being 275 and 683 kg, respectively. Water infiltration, rainfall intensity, duration and frequency may be the main factors leading to the difference in soil loss and erosion morphology between two rainstorm regimes. The inconsistency of these factors can easily cause the deviation of understanding of soil erosion mechanism. Therefore, the comparison of erosion effects under different rainstorm regimes has important implications for the improvement of natural rainstorm simulation and the comprehensive understanding of erosion mechanism.

Experimental floods have been increasingly used as a promising practice to rehabilitate river ecosystems downstream of dams; however, the morphological and habitat dynamics they determine under different sediment supply conditions still poses relevant research and management questions. This study investigates the morphological and fish mesohabitat dynamics following an experimental flood, in two river reaches subject to different sediment supply regimes. We chose the lower Spöl River (Switzerland) as a relevant case study, subject to an experimental flood program for several years. Downstream of the dam, a tributary supplies large amounts of sediment to the Spöl dividing the study area into two homogeneous reaches with different sediment availability but similar flow conditions during the experimental flood. We analyzed and quantified the changes in morphology and fish habitat suitability for the Brown Trout (Salmo trutta) at the mesoscale in these two reaches caused by the 2021 experimental flood, which lasted 11 h and had a peak magnitude corresponding to a 1-year return interval in the pre-dam flow regime. We found almost no correlation between changes in the channel morphology and in habitat suitability for this event. In the upstream reach, located immediately downstream of the dam, we observed a narrower channel with a regular longitudinal sequence featuring nearly immobile coarse rapids, interspersed with more dynamic, finer riffles. Here, reach-scale morphodynamics and the shifts of the mesohabitat mosaic and the suitable habitats were below 10%. Conversely, the downstream reach, characterised by a wider channel and much higher sediment supply of well-sorted, finer bed material, was dominated by alternate bar instability and migration at the reach scale, which caused a 45% shift in its pre-flood habitat mosaic. Nevertheless, in the same reach, the overall suitability of habitats remained relatively unchanged. We attributed these different dynamics to two main factors: (i) more prolonged bedload mobility conditions and (ii) the occurrence of bar migration in the downstream reach compared to the upstream one. This study (i) underscores the critical importance of considering sediment supply from downstream tributaries when designing and monitoring the effects of experimental floods, (ii) supports the use of morphodynamic models in the related planning and monitoring phases and (iii) shows the relevance of integrating morphodynamics and eco-hydraulic analysis to support the implementation of such flow restoration programs.

This study investigates the potential of field-based induced polarization (IP) methods to provide in-situ estimates of soil cation exchange capacity (CEC). CEC influences the fate of nutrients and pollutants in the subsurface. However, estimates of CEC require sampling and laboratory analysis, which can be costly, especially at large scales. Induced polarization (IP) methods offer an alternative approach for CEC estimation. The sensitivity of IP measurements to the surface properties of geological materials ought to make them more appropriate than DC resistivity and electromagnetic induction methods, that are sensitive to bulk electrical properties. Such abilities of IP are well demonstrated in the laboratory; however, applications are lacking at field scales. In this work, the ability of field-based IP to characterize the CEC of floodplain soils is assessed by implementing a methodology that allows for direct comparison between IP and soil parameters. In one field, soil polarization and CEC exhibited the expected positive correlation; but multi-frequency measurements showed no clear advantage over single-frequency measurements. In another field, coarser soils (with low CEC) exhibited a high polarization. These coarser soils were characterized by anomalous magnetic susceptibility values, and hence the polarization was attributed to the presence of magnetic minerals. Although better than order-of-magnitude estimates of CEC were possible in soils without substantial magnetic minerals, better characterization of porosity, saturation, cementation and saturation exponents, and pore fluid conductivity would improve predictions. However, the measurement of these parameters would require similar efforts as direct CEC measurements. This study contributes to bridging the gap between laboratory-derived relationships and their applicability in field applications. Overall, this work provides valuable insight for future studies seeking to understand polarization mechanisms in soils at the field scale.

Accurate estimations of the sediment transport capacity (T_c) are essential for soil erosion modelling. However, the applicability of existing T_c equations to colluvial soils with high steep slopes and high gravel content is limited. In this study, the variation of T_c with shear stress (τ), unit stream power (P) and stream power (ω) is investigated for different slopes and flow discharge. We also evaluate the applicability of the Yalin, Govers and GUEST equations (based on τ, P and ω, respectively) for estimating T_c on steep–slope colluvial deposits. Experiments were conducted using colluvial soil in a non-erodible rill flume. The results reveal that T_c follows a power function with τ and ω and a linear function with P. The regression results of the three hydrodynamic parameters and T_c agree with the T_c equation forms of the corresponding equations. The Yalin equation, developed based on gently sloping erodible bed conditions, simulates overall low T_c values for steep sloping non-erodible bed conditions (P.O._0.5–2 = 42.8%). The accuracy is significantly improved by correcting the sediment transport coefficient K_t (P.O._0.5–2 = 100%). The accuracy of the Govers-simulated T_c values under steep slope conditions, based on gentle slope conditions, decreases with increasing slope gradient (P.O._0.5–2 = 37.14%), which is attributed to the large amount of coarse-grained sediment present in this study. Thus, we retained the original form of the equation and further improved its accuracy by adjusting the coefficients (P.O._0.5–2 = 94.29%). As T_c increases, the GUEST equation can accurately simulate T_c. The accuracy is improved by calibrating the F-value (P.O._0.5–2 = 100%). Using dimensional analysis, the equations built based on hydraulic conditions (excess current power, shear stress, flow velocity, etc.) and median particle size can accurately simulate T_c values (P.O._0.5–2 = 100%). These findings provide a basis for the development of erosion models for avalanche deposits on steep slopes.

New technology allows the reconstruction of postmining landforms using geomorphic design principles. It is important that such designs be evaluated and if needed, redesigned or reshaped so that soil loss is minimised and to ensure the landscape is geomorphically and ecologically integrated with the surrounding landscape. One tool to assess geomorphic landforms is to use a computer-based landscape evolution model (LEM). LEMs allow different designs to be input and will highlight where erosion will occur and type of erosion (i.e. sheetwash, riling, gullying) as well as erosion rate. At the Santa Engracia abandoned mine (East-Central Spain), postmining landscapes were designed using geomorphic principles (GeoFluv method and Natural Regrade software) and later constructed. The SIBERIA LEM was used to assess the erosional behaviour of these landscapes. Using suitable topsoil, vegetation and an organic blanket reduces erosion, and if vegetation can be established, the modelling demonstrates minimal gully erosion. The erosion forecast (5.3 to 6.3 t ha⁻¹ year⁻¹) is significantly lower than the initial surface (~350 t ha⁻¹ year⁻¹) using conventional (terraced) mine restoration. The predicted erosion rates and gullying are less than for the unmined (natural) Alto Tajo environment. Importantly, with the ability to spatially forecast gully location, erosion reduction measures can be undertaken. The method described here provides a robust assessment procedure and highlights the potential strengths and weakness of a design therefore supporting lower cost construction and repair with a higher chance of restoration success. The combination of geomorphic landform design and assessment using a LEM for this project (LIFE RIBERMINE) presents a new standard for mine rehabilitation in Europe.

Electric resistivity surveys in karst environments are commonly employed to establish parameters that can help in the evaluation of collapse risk related to sinkhole or cave formation. However, these surveys are often executed from the surface with consequent limits in resolution and identification potential as a function of coverage thicknesses. Application of these methodologies directly inside known caves, for a better understanding of their formation mechanisms, is uncommon due to accessibility problems, the nontrivial referencing issues that arise when operating in an underground environment and the challenging 2D/3D interpretation issues emerging from the presence of the cavity itself. This paper reports on the application of electric resistivity tomography along with specific geological and topographic mapping, inside the Borna Maggiore di Pugnetto karst collapse cave. Comprehensive knowledge of this cave, developed in mica-rich and carbonate-rich calcschists, is problematic with traditional investigations, due to the cave breakdown that masks its structure. In this study, the 3D geometry of the cave is reconstructed using a topographical survey. This reconstruction is then utilised to perform a 3D inversion of the electrical resistivity tomography (ERT) dataset. The results of both 2D and 3D inversions are compared and discussed, focusing on the survey's ability to identify resistivity anomalies within the 3D volume surrounding the cave. Additionally, an open-source script is provided to facilitate the replication of this 3D modelling and inversion in similar underground contexts. Results of the paper show the effectiveness of the proposed surveys in the delineation of genesis and actual structure of the cave. The paper also proposes a methodological approach that can be adopted in similar contexts to enhance the understanding of speleogenesis.

The Rhoen Mountains, a relict periglacial landscape in central Germany, feature a wide range of openwork block accumulations. Although located in a temperate climate, those have characteristics comparable with cold regions of higher altitude or latitude such as arctic-alpine species, longer lasting snow patches or the discussed existence of summer or even year-round ice lenses in one of the largest of these landforms in the Central German Uplands. This study aims for a characterization of the microclimatic conditions of two neighbouring block accumulations. Therefore, temperatures were registered by data loggers along profiles, and snow dynamics were monitored using time-lapse cameras and terrestrial laser scans. These observations are finally compared with geophysical measurements to address the question of potential isolated low-altitude permafrost occurrences. Mean ground surface temperatures show an inverse thermal gradient along the Schafstein block accumulation. Furrows were identified as the cold spots in winter, whereas snow melt holes are signs of a chimney effect. In summer, cold air flows out at ventilation holes along the front causing temperatures of up to 25°C below air temperatures, although no clear signs of permafrost were detected. Temperature correlations reveal periods indicative of a recurring internal summer air circulation. Coarse blocky substrate also favours ground cooling of the smaller Mathesberg block accumulation compared with its surroundings. Winter temperatures are influenced by a persistent snowbank forming due to drifting and blowing snow at the leeward edge of a plateau as little amounts of snow are sufficient to be redistributed by westerlies. The prolonged melt of the snowbank might have had or still has a local hydrological and geomorphological impact. Uncertainties remain regarding the behaviour of the microclimate of block accumulations in a warming climate. Being ‘cold spots’ of high ecological value further investigations are suggested.

Slow-moving landslides play important roles in the landscape evolution and hazards planning. Studies along some strike-slip faults have shown that the geological structures and bed-rock lithology significantly contribute the distribution of slow-moving landslides. However, controls on the distribution of slow-moving landslides are poorly constrained in active orogenic regions, hindering our understanding of its role in the rapid orogenic process. The Hazara Kashmir Syntaxis in Pakistan is such a prominent geological structure of lesser Himalaya, where the inventory of slow-moving landslides is scarce. Here, we attempt the interferometric synthetic aperture radar phase-gradient stacking coupled with a deep-learning system to provide the first slow-moving landslides inventory (1066 presently active landslides, 2016–2023) in the Hazara-Kashmir region. Along with optical imagery and field investigations, we analyse the impacts of fault structures, bed-rock lithology, topography along with spatial distribution of earthquake and precipitation on the distribution of these slow-moving landslides. We find that 33% of the detected slow-moving landslides are distributed within 1000 m to active faults, and show a decreasing trend moving away from fault zones. This pattern strongly suggests that the active thrusting faults in this region significantly controls the distribution of slow-moving landslides, while topography and precipitation show less impacts. Our study reveals the spatial distribution of slow-moving landslides in a tectonic complex region with rapid orogenic process, and thus shows potential implications in geomorphology modelling and hazards evaluation for many less-monitored, contemporary uplifting high-mountain regions.

Due to their genesis, volcanic rocks present some singularities that make their geotechnical characteristics significantly different from other, more common types of rock masses, such as sedimentary and metamorphic rocks. The formation mechanisms of volcanic rocks are varied, rapid and generally high energy. These processes give this type of rock geotechnical behaviour and geomechanical properties that are completely different from those of nonvolcanic materials, due to their high heterogeneity and anisotropy. In volcanic rock slopes, applying widely used geomechanical classifications to assess the quality of any rock mass present several challenges due to their distinctive and singular characteristics, which detract from their validity. For this reason, the Center for Studies and Experimentation of Public Works (CEDEX) of the Ministry of Public Works, under the agreement signed with the Ministry of Public Works and Transport of the Government of the Canary Islands, carried out during 2017 and 2018 an exhaustive analysis and reviews of existing geomechanical classifications and their applications to volcanic terrains. They developed a new geomechanical classification called VSR (volcanic slope rating), based on data obtained from 85 slopes across the Canary Islands, which allowed for the estimation of the stability of volcanic rock slopes by evaluating seven geotechnical parameters. This article presents the work conducted to review and calibrate this tool, based on the study of 94 slopes of different lithotypes throughout the Canary Islands (lavas, pyroclasts, heterogeneous), culminating in the proposal of a new classification for pyroclastic massifs (with new parameters and different weightings) and the adjustment of the current classification for the other slopes (regarding the Surface Regularity parameter). Therefore, the VSR geomechanical classification was applied to assess the stability of these 94 slopes, revealing a strong fit for Types A and C (R² > 0.97), while the tool overestimated stability in Type B slopes, prompting a new classification proposal for this category.