Earth Surface Processes and Landforms最新文献

Deckenschotter are glaciofluvial gravels that cap isolated bedrock plateaus and are largely disconnected from today's local drainage. They were deposited when glaciers from the Alps were first extensive enough to reach the northern Swiss foreland, thus providing a unique record of the foreland landscape and its evolution during the earliest Quaternary glaciations. To decipher this record, we employ two robust methodologies: cosmogenic ²⁶Al/¹⁰Be burial dating and GIS-based topographic analysis. ²⁶Al/¹⁰Be burial ages from both new and published sites are calculated using a consistent procedure with the P-PINI code. Detailed swath projected and local 360° profiles were generated with GIS data in an R-toolset developed specifically for this study. Integrating results from both methodologies with outcrop sedimentological data, we interpret three main periods of Deckenschotter deposition: 1.3–1.2, 1.1–1.0 and ~0.8 Ma. The interpreted age ranges indicate glaciers must have reached the forelands in response to intensifying climatic cooling across the Mid-Pleistocene Transition (1.25–0.75 Ma). Deckenschotter outcrops provide a disjointed image of past topography from which we piece together glacial meltwater pathways in each time interval. Between the glacial phases, stepwise incision of 50–100 m occurred as depicted in the projection profiles, with some spatial variability in magnitude of incision. Incision was driven by decreasing sediment supply during glacial terminations, set against a backdrop of minor foreland uplift. While the path of the Aare River has changed little since the Early Pleistocene, the Rhine River has radically altered its path. Initially a tributary of the Danube River with northward flow, glacial modification to topography led to its re-routing to the west into the lower base-level Aare River-Upper Rhine Graben system. Based on our analysis, we estimate this event occurred after ~0.8 Ma.

Paleoenvironmental analysis in the Brazilian semiarid region is challenging. The low occurrence of flooded regions limits the preservation of pollen and accumulation of organic matter. In well-drained sites, the high pH and intense erosion destroy phytoliths. The low studies performed in limestone caves indicate that the semiarid climate conditions were established in the last 5 kyr before the present in Northeastern Brazil. In these conditions, alluvial deposits are potential sources of information about the recent past evolution of semiarid regions once the size, selection and composition of sediments reflect erosion and transport. This study aimed to analyse the recent past drainage evolution in the Borborema Plateau and Sertaneja Low Surface, two of the driest regions in Brazil. Four Fluvisols and one Cambisol were described in alluvial fans. Physical, chemical and sedimentological analyses were performed. Selected horizons were dated according to the OSL method. Variability of texture, mineral chemical composition and organic carbon content indicate discontinuities in all soil profiles. Layers of very poorly selected coarse material deposited in high-energy depositional systems are interbedded with clay-rich layers deposited by low-energy energy. The abundance of Fe, Si, Ti, Ca and K indicates variation in the source of the deposited materials. The age variation between the soil profiles indicates four evolutionary stages between 2,700 and ~100 yr. The higher age variance between layers in the Borborema Plateau indicates frequent and low-magnitude sedimentation events. These events are typical of semiarid climates because they reflect low sediment transport capacity by the ephemeral rivers. On the other hand, the lower age variation between the layers and buried A horizons suggest intense aggradation intercalated by stabilized periods, when vegetation was established and bioturbation formed A horizons.

Evolution of coastal landforms, including the formation and development of tidal channel networks in salt marshes, is shaped by the interaction of surface water hydrodynamics, sediment transport and vegetation dynamics. However, the impact of vegetation expansion on tidal channel geomorphology remains unclear. In this study, an ecogeomorphic model coupling abiotic and biotic processes was developed to investigate the effects of vegetation expansion (i.e., seeding and cloning) on tidal channel morphodynamics. The numerical model results demonstrate that vegetation expansion promotes the formation and development of tidal channels. With vegetation cover, the number, total length, area and volume of tidal channels markedly increase. Vegetation also reshapes the cross-sections of tidal channels, increasing channel depths and decreasing their width-to-depth ratios. The synergistic effect of seeding and cloning is more significant than either process alone, leading to enhanced flow convergence and bed shear stress. Consequently, the channel erosion is enhanced, laying the foundational framework for the formation and growth of tidal channel networks. A high expansion rate enhances the effect of vegetation on tidal channel morphodynamics, leading to more developed tidal channel networks. This study focuses on tidal channel networks in salt marsh ecosystems and advances understanding of the geomorphological evolution of tidal channel networks subject to vegetation expansion, and it offers further implications for the management of coastal wetland ecosystems.

Vegetation restoration significantly decreases soil erosion. Although runoff shear stress is not divided into grain and form shear stresses, the dynamic mechanisms of soil erosion remain unclear. To explore the dynamic mechanisms of soil erosion, two herbaceous plants, namely, Bothriochloa ischcemum (Linn.). Keng (BI) and Artemisia vestita Wall. ex Bess (AG), were planted at six planting densities of 5, 10, 15, 20, 25 and 30 plants m⁻² to obtain different vegetation characteristics. A simulated rainfall experiment (rainfall intensity of 1 mm min⁻¹) was conducted on runoff plots (length and width of 2.0 and 0.5 m, respectively), and the flow velocity, runoff rate and soil loss rate were measured. The results showed that the grain and form shear stresses ranged from 0.04 to 0.16 and 1.40 to 3.88 Pa under six planting densities, respectively. Grain shear stress decreased with planting density in both BI and AG grasslands. The form shear stress exhibited a greater magnitude in BI grasslands at a lower planting density, whereas in AG grasslands, the highest form shear stress was observed at a planting density of 20 plants m⁻². Vegetation can significantly reduce soil loss. Compared with that in bare soil, soil loss amount in the BI and AG grasslands were 68.08 to 95.08% lower. The reduction in soil loss amount was enhanced by the increased planting density. The BI grasslands were more effective in reducing soil loss than the AG grasslands. The amount of soil loss was mainly influenced by the interaction between vegetation and runoff characteristics, which explained the majority of variation (49.48%). The total soil loss increased with increasing grain shear stress and decreased with increasing vegetation coverage, root collar area and soil organic matter as a power function. With increasing total runoff, total soil loss increased linearly. Finally, the amount of soil loss was simulated using the grain shear stress, root collar area, soil organic matter and total runoff. The performance of the model used in this study was satisfactory.

Desertification is defined as land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors. High-spatial-resolution desertification monitoring with long time series and accurate area quantification in the Alxa Desert has yet to be fully elucidated. Here, we exploited Landsat satellite images to develop a method for the monitoring of high-resolution, large-scale desertification dynamics using a Desertification Difference Index (DDI) model based on albedo and Topsoil Grain Size Index (TGSI). On this basis, we examined the spatial–temporal changes in the extent of desertified land and ascertained the impact of various factors (temperature, precipitation, total livestock) on the desertification process. We made a detailed classification of desertification (five types) and found that non-desertification accounted for the smallest proportion of the entire study region (annual mean 2.00 × 10⁴ km², 7.8%), while severe desertification contributed the largest proportion (annual mean 7.88 × 10⁴ km², 30.9%). Over the past 20 years, there has been a substantial reduction in extremely severe (−251 km²/yr) and moderate (−230 km²/yr) desertification areas, demonstrating the effectiveness of desert management. Regionally, considerable attention should be paid to the eastern Tengger Desert in terms of desert control; temporally, special attention should be paid to summer. High temperatures can exacerbate extremely severe, and severe desertification, contrary to the effect of increasing precipitation. Dynamic changes in desertification will become more complex under predicted climate change patterns, indicating that desertification prevention should be prioritized over control.

Wildfire influences geomorphic process rates, increasing the potential for runoff-generated debris flows in steep watersheds. Runoff-generated postfire debris flows (PFDFs) often initiate when overland flow rapidly mobilizes sediment from steep hillslopes and channels. Fire effects on soil hydraulic properties, including their magnitude and temporal persistence, can therefore play an influential role in determining the degree to which fire increases debris-flow potential and the time period for heightened debris-flow hazards following fire. There is a paucity of measurements that quantify the timing of changes in soil hydraulic properties throughout the first 1–2 years after fire. Here, we monitored rainfall and debris-flow activity in two watersheds burned by the 2022 Contreras Fire in Arizona, USA, over the first 1.5 years following fire. We quantified changes in soil hydraulic properties during 11 site visits using in-situ measurements with a tension infiltrometer to provide insight into the temporal persistence of heightened debris-flow hazards. Specifically, we estimated field-saturated hydraulic conductivity (K_fs), wetting front potential (h_f) and sorptivity (S). We further tracked changes in soil water repellency, ground cover and soil physical and chemical properties, including bulk density, carbon and organic matter content to help explain temporal trends in soil hydraulic properties. Seasonal variations in K_fs, h_f and S were substantial, leading to non-monotonic relationships between these properties and time since fire. Rainfall-runoff modelling demonstrates that the magnitude of these seasonal changes are sufficient to influence runoff ratios and suggest postfire debris-flow susceptibility could change over timescales as short as several months. A comparison of K_fs, h_f and S at similar times during the first and second postfire years indicates that K_fs h_f and S decreased immediately following the fire. We observed two debris flows, which occurred during the first three months after the fire. The relatively short time associated with notable fire effects on soil hydraulic properties, combined with substantial increases in ground cover during the first postfire year, help explain observations that PFDFs primarily initiate in the first rainy season following fire in the Southwest USA.

Characterizing the spatial distribution and dynamic nature of bed facies in gravel-bed braided rivers is challenging but necessary to understand fluvial and ecological processes. Topographic point cloud and image datasets are increasingly used in fluvial geomorphology to compare riverscapes over time and classify substrate facies. However, repeatable and efficient methods that operate at large spatial scales and also resolve bimodal or fine sediments remain underdeveloped. This study collected high-resolution lidar and optical imagery over a 56-km reach of the Rangitata River, New Zealand, generating a variety of multiscale lidar-derived, optical and local morphological predictors. Ensemble machine learning methods were used to classify facies at a 1 m resolution, and a sensitivity analysis incorporating downscaled and reduced-fidelity datasets was conducted to understand the importance of data acquisition strategies. We report the predictor importance by class, finding that the key predictors for fine sediment were colour and colour complexity, while lidar predictors including reflectance were key in differentiating shallow water. The classification method was found to be robust with decreasing lidar point density but the performance was degraded if either RGB or lidar datasets were removed entirely.

The sole use of spatially local predictors allowed an analysis of trends in fine sediment facies in a large braided river subject to hydrologic pressures. The quantity and proportion of exposed fine sediment increased downstream, indicating a decrease in transport capacity associated with river widening. This new lidar – machine learning – substrate processing pathway offers a synoptic view of river form and composition that can be used to parameterize numerical models and provide distributed insights into sediment transport and sorting processes. The approach is easy to customize and can readily adapted to predict different surface classes, providing a robust basis for change detection in natural scenes.

Coasts are some of the most dynamic environments on Earth. Coastal systems comprise physical environments together with a biological component, and, for much of the world, a human element, which in many cases imposes anthropogenic stresses. The biological component is especially prominent in the tropics, and the biogeomorphology of these coasts is dominated by the role played by key organisms: corals, which form impressive coral reefs, and mangroves, which fringe low-energy shorelines. Whereas the present is the key to the past, the past also sets the stage on which future changes play out. Coral reefs have played a prominent role in deciphering the trajectory of past sea-level change, and modern reefs are often founded on older Pleistocene reefs. Inheritance is apparent both at the scale of interglacial highstands and in terms of the Holocene landforms that characterise reef-top habitats. The stratigraphy of mangrove environments reveals their more passive response to sea-level rise, constrained by accommodation space provided by the prior topography. The suite of landforms that have developed during the past few millennia have resulted in a variable coastal landscape. Tidal incursion into low-lying terrain enables mangrove establishment, re-occupying former channel courses. The trajectory of past landform change has been contingent on biogeomorphological history, and the future response of these tropical systems will also reflect in part the legacy of their geomorphological evolution. The role of inheritance is investigated with respect to reef and wetland environments, illustrating how past coastal landforms predispose future response.

ROCCO ring-net flexible barriers play a crucial role in mitigating granular flows induced by landslides in steep mountainous regions. In geotechnical engineering practice, the design of these barriers critically depends on two key factors: the maximum jump height of the granular flow and its peak impact force. While ring-net flexible barriers are known for their deformability and permeability, these characteristics remain poorly understood from a quantitative perspective. To further reveal the impact-jump mechanisms of granular flows against ROCCO ring-net flexible barriers, an array of small-scale laboratory flume experiments were conducted. To modify the permeability of the barrier, three groups of particles with different median diameters were configured to control the relative diameter ratios between the ring-net mesh size and the grains from 2.0 to 3.6. The flow depth and velocity of the incoming granular flow were adjusted by altering the channel inclination to ensure the Froude number between 3 and 10 for dynamic similarity. Specifically accounting for barrier deformation and material outflow, the semi-empirical analytical models, grounded in the principles of momentum and mass conservation, were established. Futhermore, the proposed models were validated by comparing the normalized jump height, and the impact force coefficient at the moment of peak impact force between the prediction value and the experiment data. The experimental results show that both the incoming flow characteristics and the relative diameter ratio λ jointly determine the impact-jump mechanisms: pile-up or run-up. A larger λ tends to transition the impact-jump mechanism from pile-up to run-up under the flow conditions with a high Froude number Fr, while the corresponding maximum granular jump height and peak impact force decrease as expected. Comparison between the proposed models and experimental results indicates that barrier deflection determines the upper limit of the jump height, while the lower limit is further controlled by the outflow mass flux. The improved hydro-dynamic impact force model can adequately address most run-up scenarios, whereas, for pile-up cases, the contribution of the hydro-static force should also be considered.