Earth Surface Processes and Landforms最新文献

Schmidt hammer exposure-age dating (SHD) ostensibly allows for rapid and cost-effective deglaciation age estimates of presently undated glacial landforms, but this method requires a statistically strong relationship between Schmidt hammer data and landform age data (i.e. a calibration curve) to work. Schmidt hammer rebound values (R-values) were measured on 34 glacial erratics in the U.S. State of Wisconsin that were previously dated using cosmogenic ¹⁰Be exposure-age geochronometry (~82–12 ka). Mean R-values (R_mean) are reproducible between two Schmidt hammer operators; however, we observe no statistically meaningful relationship between R_mean and erratic exposure age despite following similar methods that others have used to produce strong SHD calibration curves elsewhere. Furthermore, we observe no clear relationships between R_mean values and geographic, topographic, lithological, environmental, and climatic factors at each erratic location. Our goal was to produce a SHD calibration curve for the North American Great Lakes region where geochronological data, which can be used to constrain the timing of Laurentide Ice Sheet retreat following the Last Glacial Maximum, are geographically sparse. Although we were unsuccessful in producing a SHD calibration curve, we do not believe our results are ‘negative’. We suggest that factors such as erratic transport distance, buildup of weathering residues on rock surfaces, erratic diminution during transport, the rate of fracture propagation through erratics, and others—all of which remain untested or unaccounted for in this study—may affect measured R-values.

Fine sediment environments in estuaries, shaped by the dynamic equilibrium between geomorphic and ecological processes, provide valuable ecosystem services. Previous studies have shown that anthropogenic structures like jetties and protective walls disrupt sediment transport and flow patterns, exacerbating ecosystem instability, particularly under high-intensity hydrometeorological events. However, the nonlinear evolution of fine sedimentary systems, such as intertidal marshes, makes it challenging to differentiate the implications of seasonally varying natural processes from long-standing anthropogenic modifications. This study aims to evaluate the influence of coast-parallel and perpendicular-to-coast structures on sediment dynamics and coastline evolution in a cold-temperate river-estuarine setting. High-resolution digital surface models (DSMs) were generated using unmanned aerial system (UAS) photogrammetric surveys conducted over 4 years for comparing two contrasting coastal sectors, composed of mixed marsh and beach systems located within the fluvio-tidal transition zone of the St. Lawrence Fluvial Estuary (SLFE). These DSMs were analysed alongside historical coastline positions, modelled wave data, atmospheric temperatures, water level records, and archival documentation of human interventions to assess seasonal and geomorphic changes over the past 70 years. The results highlight that shorter perpendicular structures potentially promote fine sediment deposition and colonisation from pioneer marsh vegetation, leading to marsh creation. In contrast, longer structures can trigger a positive feedback loop resulting in decreasing elevation of marsh surfaces. The magnitude of geomorphic changes in the SLFE is primarily linked to the strong seasonality behind fluvial and landfast ice processes, rather than storm events. While human structures can amplify or dampen natural dynamics, these results illustrate how integrated and adaptable designs can enhance marsh development, resilience and sustainability.

Over the past three decades, changes in flow-sediment regime and bed material altered the pattern of suspended load transport in the braided reach of the Lower Yellow River, especially after the operation of the Xiaolangdi Reservoir. However, the potential impacts of flow-sediment regime and bed material composition on sediment transport remain poorly understood. In order to analyze the non-uniform sediment transport patterns and its geomorphic implications, the longitudinal transport efficiencies (LTE) of different grain size groups were quantified using the measured hydrological and sediment data during the period 1986–2020 at key hydrometric stations. An integrated relationship incorporating the effects of both incoming flow-sediment regime and bed material composition was developed to predict LTE variations, with relative contributions of two factors being further quantified. Results show that dam operation fundamentally altered the sediment transport dynamics in the braided reach, shifting from deposition-dominated (LTE <1.0) to erosion-dominated (LTE >1.0) conditions, accompanied by significant channel adjustments and bed material coarsening. The developed integrated relationship effectively captured these transport dynamics with the Nash-Sutcliffe efficiency coefficients greater than 0.69, providing a robust framework for predicting LTE variations across all the study periods in the dam-regulated river. In particular, size-dependent responses were observed, where fine suspended sediment transport remained to be primarily controlled by the incoming flow-sediment regime due to the limited supply from fine fraction of bed material (constituting < 5% recently), whereas the transport of medium and coarse suspended sediment fractions exhibited additional dependence on the bed material supply (contributing 42.5% and 26.8% after upstream damming), reflecting divergent adjustment mechanisms within the non-uniform suspended sediment.

Climate and land use exert profound influences on runoff-sediment dynamics, but the interaction influence of factors such as rainfall and vegetation restoration on the multi-scale spatiotemporal distribution of connectivity levels has not been yet fully understood, especially in arid and semi-arid regions. In this study, the connectivity index, Pearson's correlation analysis and Geographical Detector Model (GDM) are combined to assess the connectivity level at different spatial and temporal scales, and to elucidate the explanation level of connectivity by each factor and its interaction. The results reveal a consistent decline in multi-year average connectivity, with high connectivity values predominantly concentrated near riverbanks and lower values typically found in the forested regions to the east and west of the basin. Moreover, the GDM reveals that in 2035, the interactive explanatory power of rainfall erosivity (R) and the aggregated weighting factor (AWC) is superior (0.343) than the interaction between rainfall erosivity (R) and AWC in 2020 (0.339). The spatial distribution pattern of the connectivity is significantly correlated with static topographic elements (especially slope factors) and is co-regulated by climate change and dynamic succession of vegetation cover. Monthly scale analysis further validates this finding: when the normalised R-value ($��R_n�$) > 0.18, high rainfall erosivity factor in July and August significantly increase the connectivity of the basin by breaking through the vegetation constraints. Spatial and temporal integration of climate, land use, and connectivity can contribute valuable insights into the dynamic interplay between surface processes and soil-water resource management.

In mountain regions, present and future climate warming affects the spatio-temporal distribution, magnitude and frequency of geomorphic processes and vegetation response. Mountain biogeomorphology investigates the feedback between vegetation and geomorphic components and dynamics in alpine landscapes. Though sediment properties are known to provide important controls on vegetation colonization, species composition and provision of mountain microhabitats, they often receive considerably less attention than landform types and geomorphic processes. In this study, we aim to (i) elucidate biogeomorphic relationships between sediments and vegetation across landforms, (ii) identify key sediment and linked soil properties in mountain biogeomorphic systems and (iii) develop a workflow for routinely including sedimentological observations into mountain biogeomorphic research. We do so by investigating sediment granulometry and chemistry at four localities in the Swiss Alps, each dominated by different geomorphic processes (debris flow, soil erosion, solifluction, rock glacier creep), and integrating these data with vegetation information. Using multivariate statistics, we show that sediment properties, geomorphic processes and species composition are closely related across landforms, with different vegetation classes on stable terrain, coarse carbonate-rich sediments, active solifluction and active soil erosion. Our data suggest that these relationships can be explained by previously described geomorphic activity-related thresholds for biogeomorphic feedbacks, as well as possible thresholds related to sediment texture, with coarse grain sizes limiting plant colonization and biogeomorphic feedbacks. Sediment properties matter most for vegetation where geomorphic disturbances are low or absent. Based on our results, we propose that the median grain size of both coarse (>2 mm) and fine (≤2 mm) sediments, bulk P, K, Fe, Ca and N concentrations and total organic carbon (TOC) are key sediment and linked soil variables for mountain biogeomorphic research. We propose a workflow to effectively incorporate sediment data into mountain biogeomorphology and suggest directions for further research into sediment-vegetation interactions.

Downed wood in river corridors displays diverse states of decay and piece shapes. Decaying wood provides habitat and nutrients for diverse organisms as well as subsidies to floodplain soils. We characterized the decay and piece shape categories of downed large wood in channels and floodplains of seven river corridors in Colorado, Montana, North Carolina, and Utah, USA, to evaluate how proportions of wood in these categories varied with respect to location (channel, floodplain), disturbance history with respect to recent overbank flows capable of transporting large wood, wood recruitment (fluvial transport, tree fall), and biome. We hypothesized that decay state and piece shape would differ more between floodplain and channel locations in river corridors with no recent inundation-related large wood transport on the floodplain than in river corridors with recent floodplain inundation. Results support our hypothesis with respect to decay but not piece shape. Decay state differs more between floodplain and channel locations in river corridors with no recent disturbance. These results have implications for efforts to retain and reintroduce decayed wood in floodplains.

Single- and multi-thread gravel-bed ephemeral channels in semi-arid and arid regions have a characteristic repeating, channel-wide pattern of low angle, fine-grained ‘flats’ alternating with steeper, coarse-grained ‘bars’. The genesis of these macroforms, while a topic of ongoing discussion, has not been fully elucidated. We have documented the formation of these macroforms after both artificially homogenising the bed material of a reach of the Nahal Yatir in the northern Negev, Israel, and ensuring its surface was planar. Here, we integrate the empirical data gained from these field experiments with a novel mathematical model. The model we propose, within a one-dimensional framework, is based on the analysis of flow over an initially planar, erodible bed consisting of a bimodal grain size mixture of sediment. We apply linear stability analysis to derive a solution that provides insight into the formational dynamics of these macroforms. Our results indicate that bar-flat patterns may arise from a free-instability mechanism driven by sediment size heterogeneity, provided that the standard deviation of the sediment grain size distribution (GSD) is sufficiently large. Application of the model to a selection of ephemeral channels of the northern Negev suggests that repeating bar-flat patterns are likely to develop during the recession of flash flood hydrographs, specifically when flow conditions approach the critical threshold for bedload transport. Besides providing a possible explanation for the formation of these macroforms, this study also contributes to a broader understanding of geomorphic processes in dryland river systems.

Debris-flow fans form by repeated deposition of debris-flow sediments. Catchment lithology affects debris-flow grain-size distribution, and thereby rheology, erosive potential and depositional morphology. We can therefore expect that lithology also influences debris-flow fan characteristics. Here, we determine how catchment lithology affects the surface morphology and sedimentology of debris-flow fans and by extension their spatiotemporal evolution. We study nine fans along the eastern margin of northern Owens Valley, California, USA, originating from catchments with contrasting lithologies, and similar climate, tectonics and geological history.

Results show that debris flows originating from catchments comprising magmatic rocks are rich in cobble- to boulder-sized grains. The coarse sediment along the flow fronts and margins minimizes lateral spreading of debris-flow lobes, forming distinct levees and thick depositional mounds. In contrast, debris flows originating from catchments dominated by sedimentary rocks are rich in relatively fine gravel. Their fine-grained levees and lobes lack strongly frictional margins, spread more easily and form distinctly thinner and wider deposits. Debris flows originating from catchments with metamorphic lithologies show intermediate grain size and depositional morphology.

These contrasts in debris-flow characteristics guide the morphology and spatiotemporal development of debris-flow fans. Fine-grained debris flows spread laterally and tend to fill topographical lows, whereas lateral spreading of coarser-grained flows is hampered, instigating a low tendency to fill topographic lows. The more efficient topographic compensation on fans formed by fine-grained debris flows causes smaller elevation differences across a less rugged surface and is likely to lead to higher avulsion frequencies. The limited mobility and spreading of coarse-grained debris flows promote frequent deposition on top of and directly adjacent to channel margins, forming well-defined channels bordered by thick composite levees and raised fan sectors. These results illustrate how catchment lithology can affect the morphology, sedimentology and evolution of debris-flow fans, providing guidelines for reading their depositional archives and avulsion hazard assessment.

While rock–organism thermal interactions on rocky shores have known biogeomorphological relevance, the influences of rock thermal properties on the conditions experienced by rock-dwelling organisms (epiliths) remain understudied. This is a significant gap given the potential ecological and biogeomorphological consequences of changing average and extreme temperatures for coastal ecosystems. Using field block exposure trials in Southern England (including the 2023 September heatwave) alongside laboratory simulations, the thermal responses of four contrasting substrates (limestone, sandstone, basalt and concrete) were compared under the same heating conditions. Indicative organism temperatures were simultaneously obtained using biomimetic sensors (robolimpets [RLs] and robomussels [RMs]) attached to the substrate surfaces. Highly divergent thermal behaviours were observed, with peak substrate surface temperatures (T_max) differing by up to 13.2°C (basalt vs. limestone) under heatwave conditions in the field. Relative substrate temperatures were consistent between the field and laboratory (T_max limestone < sandstone < concrete < basalt), corresponding to key material properties such as density and colour; and hotter surfaces were always associated with higher biomimetic temperatures. The degree of association between surface and biomimetic temperatures differed between the two sensor types, attributed to more efficient conductive heat transfer (from substrate to organism) in the case of RLs. Thermal divergence between the two types of sensors was also mediated by rock type, with substrate porosity and evaporative cooling effects having a modulating effect. Biomimetic T_max also diverged under increasingly extreme scenarios depending on the substrates the sensors were attached to. These observations demonstrate how geomorphological approaches can contribute to thermal biology research (hinting at a new ‘thermal biogeomorphology’), with implications for patterns of physiological stress, the crossing of critical thermal limits, and resulting changes in the distribution and abundance of geomorphologically relevant species. Key challenges going forward, such as addressing sensor limitations and scale issues, are also identified.

The end of the last glaciation triggered major environmental changes with implications for geomorphological systems, ecosystems and societies. From the Last Glacial Maximum (LGM) to the start of the Holocene, landscapes have undergone profound changes, with increased temperature and modification of precipitation regimes affecting the way sediments are produced and transported at the Earth's surface. Records of past denudation rates are essential for understanding how landscapes responded to this transition and are required to assess the sensitivity of this response to local environmental, climatic and geomorphic contexts. Several methods, based on terrestrial cosmogenic nuclides (TCN) inventories, are available to constrain palaeo-denudation rates over millennial timescales, but few datasets exist that display strong signals regarding the dependency of this response to the setting, and the diversity of the approaches limits the possibilities for a global analysis. In this study, we propose a new method to constrain changes in erosion rates over the Pleistocene–Holocene transition, using the well-known concept that erosion rates derived from TCN concentrations are integrated over a timescale inversely proportional to the erosion rate. By combining TCN data with topographic information, we constrain the amplitude of erosion changes at 10 ka across neighbouring basins that are eroding at different rates. We highlight a complex pattern, with an overall several-fold increase in denudation rate when entering the Holocene. Intertropical high-relief areas appear to be more prone to displaying an increase in denudation rates, which might reflect a stronger sensitivity of these landscapes to periglacial processes, monsoon regime and/or threshold hillslope dynamics.