Earth Surface Processes and Landforms最新文献

Debris flows are powered by sediment supplied from steep hillslopes where soils are often patchy and interrupted by bare-bedrock cliffs. The role of patchy soils and cliffs in supplying sediment to channels remains unclear, particularly surrounding wildfire disturbances that heighten debris-flow hazards by increasing sediment supply to channels. Here, we examine how variation in soil cover on hillslopes affects sediment sizes in channels surrounding the 2020 El Dorado wildfire, which burned debris-flow prone slopes in the San Bernardino Mountains, California. We focus on six headwater catchments (<0.1 km²) where hillslope sources ranged from a continuous soil mantle to 95% bare-bedrock cliffs. At each site, we measured sediment grain size distributions at the same channel locations before and immediately following the wildfire. We compared results to a mixing model that accounts for three distinct hillslope sediment sources distinguished by local slope thresholds. We find that channel sediment in fully soil-mantled catchments reflects hillslope soils (D₅₀ = 0.1–0.2 cm) both before and after the wildfire. In steeper catchments with cliffs, channel sediment is consistently coarse prior to fire (D₅₀ = 6–32 cm) and reflects bedrock fracture spacing, despite cliffs representing anywhere from 5% to 95% of the sediment source area. Following the fire, channel sediment size reduces most (5- to 20-fold) in catchments where hillslope sources are predominantly soil covered but with patches of cliffs. The abrupt fining of channel sediment is thought to facilitate postfire debris-flow initiation, and our results imply that this effect is greatest where bare-bedrock cliffs are present but not dominant. A patchwork of bare-bedrock cliffs is common in steeplands where hillslopes respond to channel incision by landsliding. We show how local slope thresholds applied to such terrain aid in estimating sediment supply conditions before two destructive debris flows that eventually nucleated in these study catchments in 2022.

Recent studies have demonstrated the rock glacier destabilisation and permafrost thawing induced by warming climate represent a continuous threat to life, infrastructure and socio-economic development in the mountainous regions of the Hindu Kush Himalaya. This study presents the first systematic rock glacier inventory for the Shigar and Shayok basins, quantifying rock glacier geomorphology and kinematics based on morphological evidence using Google Earth images and interferometric synthetic aperture radar (InSAR). The certainty index of each inventoried rock glacier is recorded, along with its geomorphological properties and kinematic attributes. The rock glacier velocity is estimated through the InSAR time series analysis of Sentinel-1 images from 2020 to 2021, with temporal baselines at 12-day intervals. We developed a rock glacier inventory consisting of 84 rock glaciers covering an area of 29 km² for the Shigar Basin and 2206 rock glaciers encompassing 369 km² for the Shayok Basin. Among these rock glaciers, 69% and 52% are categorised as active rock glaciers, respectively. Rock glaciers in both catchments are confined to elevations between 3600 and 5875 m a.s.l., with a mean area of 0.22 km². The maximum recorded velocity for active rock glaciers in the Shigar Basin is 101 ± 9 cm year⁻¹, with a median of 27 ± 10 cm year⁻¹, and in the Shayok Basin 114 ± 10 cm year⁻¹ (median of 29 ± 9 cm year⁻¹). Temporal variations in the surface velocities of the rock glaciers reveal that they increase with rising temperatures in both catchments, highlighting the seasonality in the rock glacier surface velocity. In total, we recorded the kinematic attributes of 98% of the inventoried rock glaciers in the study area.

The dimensionless critical shear stress (τ*_c) needed for the onset of sediment motion is important for a range of studies from river restoration projects to landscape evolution calculations. Many studies simply assume a τ*_c value within the large range of scatter observed in gravel-bedded rivers because direct field estimates are difficult to obtain. Informed choices of reach-scale τ*_c values could instead be obtained from force balance calculations that include particle-scale bed structure and flow conditions. Particle-scale bed structure is also difficult to measure, precluding wide adoption of such force-balance τ*_c values. Recent studies have demonstrated that bed grain size distributions (GSD) can be determined from detailed point clouds (e.g. using G3Point open-source software). We build on these point cloud methods to introduce Pro+, software that estimates particle-scale protrusion distributions and τ*_c for each grain size and for the entire bed using a force-balance model. We validated G3Point and Pro+ using two laboratory flume experiments with different grain size distributions and bed topographies. Commonly used definitions of protrusion may not produce representative τ*_c distributions, and Pro+ includes new protrusion definitions to better include flow and bed structure influences on particle mobility. The combined G3Point/Pro+ provided accurate grain size, protrusion and τ*_c distributions with simple GSD calibration. The largest source of error in protrusion and τ*_c distributions were from incorrect grain boundaries and grain locations in G3Point, and calibration of grain software beyond comparing GSD is likely needed. Pro+ can be coupled with grain identifying software and relatively easily obtainable data to provide informed estimates of τ*_c. These could replace arbitrary choices of τ*_c and potentially improve channel stability and sediment transport estimates.

A complete, fluvial stratigraphic record for the last glacial period of the Western Andes in Peru is not available due to preservation issues and spatial variability in sedimentation. Deposits are typically restricted to incomplete records of fluvial terraces or localised occurrences of alluvial fans and landslides. These landforms are thought to have formed under a regime of climate cyclicity controlling increases in precipitation. Because of the fragmented preservation of these deposits, as well as dating uncertainties, it remains unclear if orbital climate cycles, such as the precession cycle, or suborbital cycles, such as the wet Heinrich events, are driving Andean sedimentation. In this paper, we try to answer this question through a sedimentological–stratigraphical analysis of a much more complete sedimentary sequence than usually found in the region. We present the results of a grain size analysis of 5000 clasts and 13 new luminescence ages of a 52-m-long, stratigraphic section of the Lima fluvial fan in Peru. Bayesian age–depth modelling resulted in a robust chronostratigraphic framework and derived sedimentation rates. The stratigraphic record registered sedimentation from 121.7 ± 4 to $�{6.3}_{�-�1.6�}^{�+�1.5�}$ ka. Three major sedimentation periods occurred between 121.7 to $�{110}_{�-�5�}^{�+�4�}$, 87 ± 1 to $�{67}_{�-�3�}^{�+�2�}$, and $�{31}_{�-�3�}^{�+�4�}$ to $�{6.3}_{�-�1.6�}^{�+�1.5�}$ ka. These periods registered various unconformities and coarsening–fining upward sequences which chronologically correlate to suborbital pluvial periods, recog

This work studies the multiple sources of impacts and disturbances in the Laja River (Central Chile) and evaluates the changes in water and sediment flows and planimetric geomorphic changes.

The disturbances sources correspond to hydroelectric plants, water withdrawals for irrigation and the sustained decrease trend in rainfall in the basin. The changes in the plan-view shape of the river reach were quantified using remote sensing techniques, through a supervised classification of Landsat 5 TM and 8 OLI satellite images, identified Water (W), Islands and Riverine Vegetation (IRV) and Bars and Banks Without Vegetation (BBWV), obtained a Kappa index>0,83 for a period of 15 years (2006–2021).

Compared with historical records, the period of analysis shows a decrease in annual rainfall by 17.5%. In addition, water withdrawals for irrigation have contributed to a 64% decrease in monthly stream discharge during the dry season. As a consequence of the decrease in annual rainfall and water withdrawals for irrigation, the sediment transport capacity has also decreased by 10.5%.

The changes in morphological driving variables (stream flows and sediment transport regimes) have manifested themselves in morphological changes, where it was possible to establish that a change in the channel form occurred in the last 15 years, going from a river with a single channel to a braided one. An important vegetation establishment has accompanied this morphological change on both riverbanks and the central bars. The colonizing vegetation corresponds to fast-growing non-native species (Salix spp., Populus spp. and Alnus spp). A stabilization of the channel form is expected, consolidating itself as a braided section with alternating vegetated bars.

The high primary porosity and permeability of eogenetic karst aquifers permit water recharged through secondary dissolution features to be temporarily stored in aquifer matrix porosity. The recharged water contains elevated dissolved organic carbon (DOC) concentrations that, when oxidized, enhance limestone dissolution and impact carbon cycling. We evaluate the relationship between DOC oxidation and limestone dissolution using observations at a stream sink-rise system and reversing spring in the Floridan aquifer, north-central Florida, USA, where subsurface residence times of recharged water are days and months, respectively. We estimate water chemical compositions during surface water-groundwater interactions at these two systems with mixing models of surface water and groundwater compositions and compare them with measured DOC, dissolved inorganic carbon (DIC), Ca²⁺ and dissolved organic nitrogen (DON) concentrations. Differences between measured and modelled concentrations represent net changes that can be attributed to calcite dissolution and redox reactions, including DOC oxidation. DOC losses and Ca²⁺ gains exhibit significant (p < 0.01) inverse linear correlations at both the reversing spring (slope = −0.9, r² = 0.99) and the sink-rise system (slope = −0.4, r² = 0.72). DOC oxidation in both systems was associated with decreases in the molar C:N ratio (DOC:DON). Significant (p < 0.01) positive linear correlations between increases in Ca²⁺ and DIC concentrations after correcting for DIC derived from calcite dissolution occurred at both the reversing spring (slope = 1.3, r² = 0.99) and the sink-rise system (slope = 1.61, r² = 0.75). Greater deviations from the expected slope of −1 or +1 at the sink-rise system than at the reversing spring indicate DOC oxidation contributes less dissolution at the sink-rise system than at the reversing spring, likely from shorter storage in the subsurface. A portion of the deviation from expected slope values can be explained by the dissolution of Mg-rich carbonate or dolomite rather than pure calcite dissolution. Despite this, slope values reflect kinetic effects controlling incomplete consumption of carbonic acid during dissolution reactions.

Karst hillslopes are generally characterized by different land uses. Land use and slope position impact soil erosion seriously, which in turn impacts the process of soil development and the patterns of soil properties. However, the impact of land use on soil physicochemical properties and the spatial variations and correlations between them are not fully understood on karst hillslopes. Therefore, nine sites had similar soil types, slope gradients, elevations, slope aspects and previous tillage practices were selected to conduct further research. This study was conducted to quantify the spatial distribution, variability and correlation of soil physical and chemical properties and stoichiometries as impacted by different land uses on a karst hillslope in Southwest China. Soil physical properties were significantly affected by slope position and soil depth. The soil bulk density and clay content increased with soil depth, while the opposite was true for the sand content. For the three land uses, the soil bulk density varied the most at the lower slope position, while clay and sand particles varied the most at the middle slope position. The mean spatial coefficient of variation (CV) of soil physical properties was ranked as sand (11.08%) > clay (7.77%) > bulk density (6.85%) > silt (3.81%). The mean spatial CV of soil chemical properties was ranked as available K (44.49%) > total P (16.77%) > total C (16.31%) > total N (13.09%) > available P (8.45%) > total K (7.51%). Overall, soil physicochemical properties exhibited significant spatial differences with slope location and land use on karst hillslopes. Soil chemical properties had greater spatial variation than physical properties, moreover, there were significant correlations between them. The results not only contribute to a deeper understanding of the impact of land use on the erosion process and mechanism on karst hillslopes but also provide a scientific understanding of the sustainable restoration of karst ecosystems.

Geophysical and morphosedimentary investigations were conducted at Strathcona Lake, a High Arctic proglacial lake and its catchment connected to the Taggart Lake Glacier, northwest corner of the Prince of Wales Icefield in Ellesmere Island (eastern Canadian Arctic Archipelago). The mapping of glaciomarine landforms and units provides, together with updated radiocarbon information, a framework for catchment evolution and sediment delivery to the lake during deglaciation and glacio-isostatically induced relative sea level fall. A staircase of deltas with descending altitudes provide evidence for a spatially diachronous timing of ice retreat from the catchments around Strathcona Lake. Swath bathymetric mapping coupled with acoustic sediment stratigraphy show draped infills with a transition from marine to rhythmically bedded lacustrine sediments produced by hyperpycnal flows. Multiproxy investigations on a set of sediment cores highlight proglacial varves interrupted by rhythmites resulting from the erosion of fluvially incised glaciomarine sediments stored in the catchment. Pluricentimetric proglacial varves formed during the last century in response to periods of intense glacial melt, notably since the 21st century. The sedimentary record suggests the varved sediments from Strathcona Lake can be used to reconstruct the melting history of the Prince of Wales Icefield. This work provides a geomorphological, sedimentological, and geochemical framework that should guide future varve-based reconstructions of glacial and climatic variability in Ellesmere Island.

Topography plays a critical role in soil migration and redistribution, but few studies have been conducted to quantify its effects on sediment deposition. In this study, we established a physical simulation and analysis framework to investigate the erosional and depositional impacts of two-dimensional slope terrain, specifically applied to Xiannangou small watershed in the loess hilly region. The results showed that the slope gradient, slope length, and slope shape have significantly influence the distribution of soil erosion and deposition. The magnitude of the erosion/deposition rate (Y_r) determines the relative intensity of slope erosion and deposition, where Y_r < 0 indicates erosion and Y_r > 0 signifies deposition. The erosion rate on straight slope exhibited a positive correlation with slope length, while the erosion/deposition rate on concave and convex slopes exhibited fluctuations with slope length. Soil erosion predominantly occurred along the main flow line and the middle slope, aligning with the observed distribution of gully and slope erosion in the field. The sediment deposition was primarily concentrated on the lower slope or the lowest outlet of the basin, notably in gullies and gentle slopes where the terrain slows, especially during transition from steep to gradual slopes. These results can effectively predict the relative erosion/sedimentation rate of two-dimensional slopes, significantly contributing to a comprehensive understanding of how topography influences soil erosion and deposition. This study thoroughly considers the role of sediment deposition in the soil erosion process, providing a more accurate reflection of soil erosion/deposition in small watersheds. It addresses the existing deficiency in sediment consideration within soil erosion evaluation and supports the enhancement of soil erosion model.

Accurate extraction of ground fissures caused by intense coal mining has the potential to significantly improve the efficiency of environmental monitoring in mining areas. However, the extraction results using previous methods have often exhibited issues of discontinuity and substantial deviation from ground truth data, resulting in low extraction accuracy. In this study, a novel approach, ENVINet5-OBIC, for extracting ground fissures in mining areas is proposed, which integrates object-based image classification (OBIC) with the pixel-based deep learning model ENVINet5. ENVINet5-OBIC uses OBIC to segment high-resolution unmanned aerial vehicle (UAV) images across different scales, effectively considering shape, texture and correlative information between adjacent pixels. Furthermore, by utilizing homogeneous objects as building blocks, it establishes a deep learning model for the automated extraction of ground fissures. Experimental results show that ENVINet5-OBIC performs better when compared with OBIC, U-Net, PSPNet and ENVINet5 methods in terms of continuity, accuracy and error reduction. In addition, the ground fissure area extracted by ENVINet5-OBIC closely aligns with ground truth data. This study provides a more effective method for automatic extraction of ground fissures, which improves the efficiency of environmental monitoring in mining areas.