Search Results (70)

Active continental margins, generally characterized by narrow shelves incised by canyons, are pervasively shaped by submarine landslides that can occur near coastal areas. In this context, creating landslide susceptibility maps is the first step in landslide geohazard assessment. This paper focuses on shallow-water submarine landslides along the Capo d’Orlando continental margin and presents a related susceptibility map using the Weight of Evidence method. This method quantifies the strength of the association between a landslide inventory and predisposing factors. A geomorphological analysis of the continental shelf and upper slope yielded a landslide inventory of 450 initiation points, which were combined with five specifically selected preconditioning factors. The results revealed that the most favourable conditions for shallow-water landslides include slopes between 5° and 15°, proximity to faults (<1 km), proximity to river mouths (<2 km), the presence of consolidated lithologies and sandy terraces, and slopes facing NE and E. The landslide susceptibility map indicates that susceptible areas are in canyon heads and flanks, as well as in undisturbed slope portions near canyon heads where retrogressive landslides are likely. The model results are robust (AUC = 0.88), demonstrating that this method can be effectively applied in areas with limited geological data for preliminary susceptibility assessments. Full article

The remote sensing inversion of the Suspended Sediment Concentration (SSC) at the Yellow River estuary is crucial for regional sediment management and the advancement of monitoring techniques for highly turbid waters. Traditional in situ methods and low-resolution imagery are no longer sufficient for high-accuracy studies. Using SSC data from the Longmen Hydrological Station (2019–2020) and Sentinel-2 imagery, multiple models were compared, and the random forest regression model was selected for its superior performance. A non-parametric regression model was developed based on optimal band combinations to estimate the SSC in high-sediment rivers. Results show that the model achieved a high coefficient of determination (R² = 0.94) and met accuracy requirements considering the maximum SSC, MAPE, and RMSE. The B4, B7, B8A, and B9 bands are highly sensitive to high-concentration sediment rivers. SSC exhibited significant seasonal and spatial variation, peaking above 30,000 mg/L in summer (July–September) and dropping below 1000 mg/L in winter, with a positive correlation with discharge. Spatially, the SSC was higher in the gorge section than in the main channel during the flood season and higher near the banks than in the river center during the dry season. Overall, the random forest model outperformed traditional methods in SSC prediction for sediment-laden rivers. Full article

Under global climate change, sustainable management of plant resources in alpine canyon regions faces severe challenges. M. esculenta, highly valued for its edible and medicinal properties, is widely harvested for consumption by residents in the upper Dadu River–Minjiang River region. This study employs ensemble models to simulate the potential distribution of M. esculenta in this region, predicting the impacts of future climate change on its distribution, centroid migration of suitable habitats, and niche dynamics. Additionally, a production dynamics model integrating ecological suitability and nutritional components was developed to delineate current and future potential cultivation zones for M. esculenta. The results indicate that current high-suitability areas and core cultivation zones of M. esculenta are predominantly distributed in a patchy and fragmented pattern. The high-suitability habitats in the upper Dadu River–Minjiang River region have three distribution centers: the largest spans southern Danba County, southern Jinchuan County, and northeastern Kangding City, while the other two are located in northeastern Li County, southwestern Aba County, and northwestern Ma’erkang City, with sporadic distributions in Heishui County, Maoxian County, and Wenchuan County. First-level cultivation areas are primarily concentrated in Kangding City, Danba County, Ma’erkang City, Li County, and surrounding regions. Under climate change, low-suitability areas and third-level cultivation zones for M. esculenta in the region have increased significantly, while high- and medium-suitability areas, along with first- and second-level cultivation zones, have decreased notably. Concurrently, suitable habitats and cultivation zones exhibit a migration trend toward higher northern latitudes. The most pronounced changes in suitable areas and cultivation zones, as well as the largest niche migration, occur under the high-emission climate scenario. This study facilitates the formulation of suitability-based management strategies for M. esculenta in the upper Dadu River–Minjiang River region and provides a scientific reference for the sustainable utilization of mountain plant resources under climate change. Full article

Limited by water and heat conditions, the southwest alpine valley area has a dry climate, complex terrain, low vegetation coverage, and a very fragile ecological environment. The runoff plots of different slope gradients (10°, 15°, and 20°), slope lengths (2, 5, and 10 m) and reverse slope terrace (RST) in the Lancang River arid valley were taken as the objects. Through in situ observation of the slope runoff and sediment yield of six natural erosive rainfalls, the contribution rate of different factors was quantified, and the effect mechanism was revealed. The main results were as follows: (1) Sediment yields of different rainfalls were closely correlated with rainfall type and duration. Under the conditions of heavy rain (rain II and III), there was a critical slope gradient, and the maximum sediment yield was achieved when the slope gradient was 15°. (2) The runoff and sediment reduction benefits of horizontal terraces were 24.88% and 46.25%, and these benefits were increased by 1.47 times and 1.30 times after setting the RST, and the sediment reduction benefits increased significantly with the increase in the number of RSTs (p < 0.05). (3) In this study, rainfall intensity contributed the most to the runoff yield rate (34.5%), followed by slope length (15.1%) and horizontal terrace (7.2%). Slope length, rain intensity, and horizontal terrace order contributed 25.9%, 18.0%, and 11.4% to the sediment yield rate, respectively. (4) There was a significant linear correlation between sediment yield and runoff yield on different slopes (p < 0.05). The critical runoff yield rate decreased with the increase in slope length, the RST significantly increased the critical runoff yield rate (2.91 times), and it increased with the increase in RST numbers. This study can provide a scientific basis and reference for the prevention and control of soil and water loss and ecological restoration on the slope of the arid valley in the southwest alpine and canyon area. Full article

To help fish to bypass dams and other human-made barriers, some fishways have ingeniously incorporated extended tunnel sections. This innovative design not only optimizes the overall structure of the fishway but also significantly reduces disturbances to the surrounding ecosystem. However, the potential challenges posed by long tunnel sections to fish upstream migration remain insufficiently studied and poorly understood. This study conducted in situ experiments utilizing a passive-integrated-transponder (PIT) system to quantitatively assess the effects of dark and natural light environments on the upstream migration behavior of plateau-endemic fishes (Schizothorax macropogon, Schizothorax waltoni, and Schizothorax oconnori) in a vertical-slot fishway. A 655 m section of the fishway was selected for the experiment, with shading cloth used to simulate the dark environment (DE) of tunnel sections, and its removal serving as the natural light environment (NE). The results showed that in the DE, the upstream behaviors of S. macropogon, S. waltoni, and S. oconnori were not hindered. The entry efficiency at the experimental segment (Ee) of all three species exceeded 65% in the DE, which was higher than that in the NE. The passage efficiency (Ep) of S. macropogon and S. waltoni showed no significant difference between the DE and NE, whereas S. oconnori exhibited a significant difference, with an overall Ep of 0% in the NE and 75.0% in the DE. Additionally, the DE caused a temporary disruption to the diel migration rhythms of the three species. The transit speeds (St) of S. macropogon and S. waltoni were both elevated in the DE, with S. waltoni showing a particularly significant increase; its average St in the DE (0.080 m/s) was much higher than in the NE (0.021 m/s). Ridge regression analysis further indicated that the DE was the primary factor influencing the St and had a positive effect on upstream behavior. Moreover, differences in the upstream migration performances of different species under varying light conditions highlighted species-specific sensitivity to light. This study offers key insights for fish passage design in canyon hydropower projects and highlights the potential of tunnel-type fishways in restoring river connectivity. Full article

The Yellow River (YR), China’s second-largest river, is rich in water resources, particularly in its upper reaches, which are characterized by mountainous canyons and considerable hydropower potential. Since the 1950s, 24 reservoirs have been constructed along a 918 km stretch of the upper Yellow River (UYR), creating the highest concentration of cascade reservoirs. This development has had significant ecological impacts on the surrounding environment. This study examines the relationship between reservoir attributes and climate factors to evaluate the environmental effects of reservoirs in the UYR. (1) Following reservoir construction, the average annual temperature and precipitation increased by 3–10%, though seasonal and spatial distributions varied. Temperature increases were most pronounced in winter, while precipitation decreased in some regions during spring and summer, although the overall trend remained positive. (2) The ecosystem experienced significant post-construction changes, including reductions in arable land, grassland, and unused land, while water bodies, construction land, and forests expanded. Consequently, the ecosystem within the reservoir area now accounts for 5.2–12.5% of the total area of the region. (3) Temperature and precipitation were closely linked to reservoir attributes, with storage volume (CAP) and long-term average flow (DIS) significantly affecting precipitation, while surface area (AREA) and normal storage level (FSL) had a greater influence on temperature. In conclusion, the dual impacts of reservoir construction on local climate and land use highlight the complex environmental mechanisms involved, providing valuable insights for future reservoir development and ecological protection in the Yellow River Basin and similar regions. Full article

Seismic data reveal that the shelf edge of the Pearl River Mouth Basin in the northern South China Sea is characterized by slope channels that have consistently migrated in a north-easterly direction over millions of years. Previous research suggests that the channel migration is driven by the interplay between along-slope bottom currents and downslope turbidity currents. Here, we propose an alternative interpretation, suggesting the migrating channels are actually a series of channel–levee systems and the migration is driven by their own evolution of erosion–deposition under the influence of the Coriolis force. A detailed interpretation of high-resolution seismic data reveals seven types of architectural elements, characteristic of channel–levee systems, which are erosional bases, outer levees, inner levees, channel-axis fills, marginal slumps, drapes, and lobes. An analysis of the sequence stratigraphy and stacking pattern of channels suggests that channel migration from the middle Miocene to the present is discontinuous with at least three regional discontinuities within the channel migration sequence marked by regional drapes. Down-dipping reflections along the margin of channels, previously interpreted as bottom-currents deposits, are here reinterpreted as mass-transport processes along steep channel walls. The migration is most prominent in the middle reach, where erosion and deposition coexist and dominate alternately in two different phases. During the long-term canyon-filling turbidity currents prevailing phase, deposition dominates, leading to the development of a prominent asymmetric right-hand (west) inner levee due to the Coriolis force. In contrast, during the canyon-flushing turbidity currents prevailing phase, erosion dominates and the preferred right-hand (west) inner levee enforces the flow to erode eastward, then drives the channel migrating eastward. The alternating effects of erosion and deposition ultimately result in unidirectional channel migration. Full article

In high-mountain canyon regions, many settlements are located on large, deep-seated ancient landslides. The deformation characteristics, triggering mechanisms, and long-term developmental trends of these landslides significantly impact the safety and stability of these communities. However, the deformation mechanism under the influence of human engineering activities remains unclear. SBAS-InSAR (Small Baseline Subset-Interferometric Synthetic Aperture Radar) technology, UAV LiDAR, and field surveys were utilized in this study to identify a large ancient landslide in the upper Jinsha River Basin: the Zhongxinrong landslide. It extends approximately 1220 m in length, with a vertical displacement of around 552 m. The average thickness of the landslide mass ranges from 15.0 to 35.0 m, and the total volume is estimated to be between 1.48 × 10⁷ m³ and 3.46 × 10⁷ m³. The deformation of the Zhongxinrong landslide is primarily driven by a combination of natural and anthropogenic factors, leading to the formation of two distinct accumulation bodies, each exhibiting unique deformation characteristics. Accumulation Body II-1 is predominantly influenced by rainfall and road operation, resulting in significant deformation in the upper part of the landslide. In contrast, II-2 is mainly affected by rainfall and river erosion at the front edge, causing creeping tensile deformation at the toe. Detailed analysis reveals a marked acceleration in deformation following rainfall events when the cumulative rainfall over a 15-day period exceeds 120 mm. The lag time between peak rainfall and landslide displacement ranges from 2 to 28 days. Furthermore, deformation in the high-elevation accumulation area consistently exhibits a slower lag response compared to the tensile deformation area at lower zones. These findings highlight the importance of both natural and anthropogenic factors in landslide risk assessment and provide valuable insights for landslide prevention strategies, particularly in regions with similar geological and socio-environmental conditions. Full article

Submarine slides, gas hydrates, shallow gas, and volcanoes considered to be potential geohazards have been well delineated using three-dimensional (3D) seismic data and well log data in the Pearl River Mouth Basin, South China Sea. Seismic characteristics, distribution maps, and controlling factors of these geohazards have been well analyzed showing the influence of regional tectonics and sedimentary processes. Recently, shallow gas and gas hydrates are confirmed by drilling expeditions, which are considered important unconventional resources. Moreover, the mapped features of various geohazards show the spatial overlays and that they are connected each other. To delineate well the relationships between gas hydrates, shallow gas, and the potential geological features such as submarine slides, gas chimneys, faults, and volcanoes, the seismic attributes and interpretations are displayed using 3D seismic data to show the interplay between them. Gas hydrates and shallow gas occur and are widely distributed above sills, volcanoes, gas chimneys, and faults within the submarine slides and migrating canyon because large amount of hydrocarbon gas can migrate from the deep layer to the shallow layer along different pathways. This study aims to show the correlation among various geological bodies and their effects on shallow gas and gas hydrate distributions. Full article

Sedimentary records of event deposits are crucial for regional natural disaster risk assessments and hazard history reconstructions. After Super Typhoon Haiyan passed through the South China Sea in 2013, five gravity cores were collected along the typhoon path in the southern South China Sea basin (>3800 mbsl). The results showed that Super Typhoon Haiyan deposits with clear graded bedding are preserved at the top of all cores. The thickness of the typhoon layers ranges from 20 to 240 cm and is related to changes in typhoon intensity. The lack of river-connected submarine canyon systems limited the transportation of terrestrial sediments from land to sea. Super Typhoon Haiyan-induced large surface waves played an important role in carrying suspended sediment from the Philippines. The Mn-rich layers at the bottom of the typhoon layers may be related to the soil and rock composition of the Palawan region, which experienced tsunami-like storm surges caused by Super Typhoon Haiyan. These Mn-rich layers may serve as a proxy for sediment export from large-scale extreme terrigenous events. This study provides the first sedimentary record of extreme typhoon events in the deep ocean, which may shed light on reconstructing regional hazard history. Full article

Current dynamic response analyses of arch dams under an oblique incidence of seismic waves have overlooked the effects of canyon contraction deformation. This study investigated the influence of the incident direction and incident angle of seismic waves on the comprehensive displacements, as well as the damage, of arch dams under canyon contraction conditions. When SV waves are incident obliquely along the river direction, the peak displacements of the dam crest and arch crown beam increase with increasing canyon contraction. The displacement of the dam reaches its maximum when the incident angle is 0°, indicating that the SV wave vertical incidence is the most unfavourable incidence mode affecting the displacement. Dam damage cracking is most severe in the case of a canyon contraction of 60 mm and an incidence angle of 0°. The dam damage cracking index in this case increases only by 7.6% compared to a canyon contraction of 0 mm and an angle of incidence of 0°. However, the change in canyon contraction when a seismic wave is incident obliquely can cause serious damage cracking to the dam. When the SV wave is incident obliquely along the cross-river direction, the dam damage cracking index in this case increases by 110% compared to the case where the canyon contraction is 0 mm, and the incidence angle is 0°. Therefore, it is necessary to comprehensively consider the influences of canyon contraction and the oblique incidence of seismic waves in the seismic design and safety review of arch dams. Full article

Slow-moving landslides are often precursors of catastrophic failure, posing a major threat to human life and property safety. Interferometric synthetic aperture radar (InSAR) has become a crucial tool for investigating slow-moving landslides hazard because of its high-precision detection capability for slow surface deformation. However, landslides usually occur in alpine canyon areas and vegetation coverage areas where InSAR measurements are still limited by temporal and spatial decorrelation and atmospheric influences. In addition, there are several difficulties in monitoring the multiscale characterization of landslides from the InSAR results. To address this issue, this paper proposes a novel method for slow-moving landslide hazard assessment in low-coherence regions. A window-based atmosphere correction method is designed to highlight the surface deformation signals of InSAR results in low-coherence regions and reduce false alarms in landslide hazard assessment. Then, the deformation annual velocity rate map, coherence map and DEM are used to construct the InSAR sample set. A landslide hazard assessment model named Landslide-SE-Unilab is subsequently proposed. The global–local relationship aggregation structure is designed to capture the spatial relationship between local pixel-level deformation features and global landslides, which can reduce the number of missed assessments and false assessments of small-scale landslides. Additionally, a squeeze-and-excitation network is embedded to adjust the weight relationship between the features of each channel in order to enhance the performance of network evaluation. The method was evaluated in Kangding city and the Jinsha River Valley in the Hengduan Mountains, where a total of 778 potential landslides with slow deformation were identified. The effectiveness and accuracy of this approach for low-coherence landslide hazard assessment are demonstrated through comparisons with optical images and previous research findings, as well as evaluations via time-series deformation results. Full article

This study investigated the shoreline evolution of the Tuscany coast (Italy) from 1878–1883 to 2019. The 205 km sandy coastline, divided into 821 sectors, each one 250 m long, was analyzed to understand how human activities have altered this once-pristine coast. Sub-period analyses highlighted the impacts, both positive and negative, of various shore-protection projects. Initially, regional beaches were undeveloped and accreting, except for a few river deltas where alternating phases of erosion and accretion were observed. Coastal erosion began at deltas’ areas due to the reduction in sediment inputs and, at other areas, enhanced by the development of human settlements and tourism activities. This triggered the construction of protection structures that shifted erosion processes downdrift, a process that induced the downdrift extension of the structures (according to the “domino” effect), determining the transformation of a completely natural and resilient environment into a largely rigid one. Beach nourishment projects, mostly using inland quarries, added about 1 million cubic meters of sediment from the 1980s to 2019. Currently, 57.8% of beaches are larger than in the 1880s, 9.4% did not change and 32.8% are narrower. Overall, the Tuscan coast gained 6.5 km² of beach surface with an average shoreline advancement of 32 m. Recent trends (2005–2019) show that 37.7% of the coast is eroding, 21.1% is stable, and 41.2% is accreting, with a total surface area increase of about 200,000 m². The beach surface area is still increasing despite the existing reduced sediment input due to the limited sediment loss resulting from the presence of morphological cells enclosed by very prominent headlands and the absence of submarine canyons that would otherwise direct sediments to the continental shelf. Full article

The shelf-edge trajectory is comprehensively controlled by tectonics, sediment supply, sea level, and climate fluctuations; its migration and evolution have a strong influence on what happens in the deep-water depositional system during the Quaternary. The shelf-edge trajectory pattern, sediment-budget partitioning into deep-water areas, and reservoir evaluations are focused topics in international geosciences. In this paper, the Qiongdongnan Basin (QDNB) in the northern South China Sea is taken as an example to study how shelf-edge trajectory migration patterns can influence the types of deep-water gravity flow which are triggered there. Through quantitatively delineating the Quaternary shelf-edge trajectory in the QDNB, four types of shelf-edge trajectory are identified, including low angle slow rising type, medium angle rising type, high angle sharp rising type, and retrogradation-slump type. A new sequence stratigraphic framework based on the migration pattern of shelf-edge trajectory is established. There are four (third-order) sequences in the Quaternary, and several systems tracts named lowstand systems tract (LST), transgressive systems tract (TST), and highstand system tract (HST) are identified. This study indicates that the type of deep-water gravity flow can be dominated by the shelf-edge trajectory migration patterns. When the shelf-edge trajectory angle (α) ranged between 0° and 4°, the continental canyons were mostly small-scaled and shallowly incised, with multiple large-scale sandy submarine fan deposits with few MTDs found in the deep-water area. When the angle (α) ranged from 4° < α < 35°, the size and incision depth of the continental slope canyons increased, relating to frequently interbedded sandy submarine fan deposits and MTDs. When angle (α) ranged from 35° < α < 90°, only a few deeply-incised canyons were present in the continental slope; in this condition, large-scaled and long-distance MTDs frequently developed, with fewer submarine fans deposits. When angle (α) ranged from 90° < α < 150°, the valley in the slope area was virtually undeveloped, sediments in the deep-sea plain area consisted mainly of large mass transport deposits, and submarine fan development was minimal. Since the Quaternary, the temperature has been decreasing, the sea level has shown a downward trend, and the East Asian winter monsoon has significantly enhanced, resulting in an overall increase in sediment supply in the study area. However, due to the numerous rivers and rich provenance systems in the west of Hainan Island, a growing continental shelf-edge slope has developed. In the eastern part of Hainan Island, due to fewer rivers, weak provenance sources, strong tectonic activity, and the subsidence center, a type of destructive shelf-edge slope has developed. The above results have certain theoretical significance for the study of shelf-edge systems and the prediction of deep-water gravity flow deposition type. Full article

Investigating fish diversity in canyon rivers through conventional fish surveys is challenging due to precipitous conditions, including steep slopes, rapid water flow, and complex habitats. Additionally, intensive construction of dams has further complicated the understanding of contemporary fish diversity in these rivers. In this study, we used the environmental DNA (eDNA) technique to assess fish diversity and examine the effects of dams on fish diversity in the Mabiehe River, a canyon river in the upper reaches of the Pearl River drainage. Water samples from 15 sampling sites were collected, yielding 9,356,148 valid sequences. Utilizing the NCBI public database, a total of 60 freshwater fish species were identified, with Carassius auratus, Cyprinus carpio, and Pelteobagrus fulvidraco being the most dominant species in the Mabiehe River. We also detected one nationally protected fish species, three provincially protected fish species, and six exotic species in this river. Furthermore, eDNA analyses demonstrated that the lotic river sections harbor more species and greater diversity than dammed sections, suggesting that dams might exert significant impacts on local fish diversity. Overall, this study supports the effectiveness of the eDNA technique as a complementary tool to traditional field surveys for monitoring fish biodiversity in canyon rivers. Full article