Journal of Geophysical Research: Earth Surface最新文献

Channels form meander bends, whether in rivers or on glaciers, volcanoes, coastlines, or the seafloor. Therefore, isolating meander bends is instrumental in characterizing channel shape and its relationship to the surrounding environment. The common approach of delimiting meander bends using inflection points yields isolated arcs that differ from traditional depictions. This study develops a geometric algorithm for mapping meander bends to bridge this gap. The approach accounts for two perceptual factors: observer viewpoint and the scale of significant deviations in the river path. The channel centerline is divided into three elements: arcs of positive/negative curvature, and effectively straight reaches with dimensionless amplitude (A_st*) below a threshold. Meander bends are formed by connecting reaches between arcs of similar curvature and trimming to where the openness, or viewshed, falls below the value for a straight line (180°). A case study for the Beatton River, Canada, shows the method captures the full extents of meander bends and reproduces a common classification (simple vs. compound) and scaling between wavelength and channel width ($��\lambda �\approx �$ 12w_c) from visual interpretation. The number and extents of meander bends change with A_st*; 0.1 < A_st* < 1 prevents over-segmentation without lumping adjacent meander bends. The approach further indicates two mapping solutions that correspond to viewpoints on opposite sides of the river. By harmonizing the geometric definition of a meander bend with its traditional depiction, this approach advances the quantitative analysis of channels across geologic environments. A companion study tests whether the mapped meander bends have characteristic shapes.

River meander bends are widely considered to have recurring shapes. Formal classifications of meander bends have provided an important framework for basic research and practical applications in river engineering and restoration. However, the central role of expert interpretation in both mapping and classifying meander bends leaves persistent uncertainty for whether their shapes do form patterns or instead represent a continuum of forms. This study analyzes meander bend shapes derived in a companion paper about the Beatton River, Canada, to test whether meander bends show repeating shapes without the prior assumption that such patterns exist. Meander bends are compared using Fréchet distance, a curve similarity measure, and evaluated for common shapes using agglomerative hierarchical clustering. The case study indicates that normalizing meander bend coordinates by wavelength and amplitude yields clusters of meander bends with internally consistent shapes. Characteristic meander bends for each cluster are derived by averaging the normalized coordinates and rescaling by the mean amplitude and wavelength for the source meander bends. Whereas automatically mapped meander bends vary in number and extent with a dimensionless amplitude threshold (A_st*), the characteristic meander bends are generally robust against variation in this parameter within its effective range (0.1 $��\le �$ A_st* $��\le �$ 1). By establishing a test for characteristic shapes among populations of multifarious meander bends, the analysis enables new tests for environmental controls on channel form, a standard for assessing the fidelity of numerical models for planform evolution, and a method to design nature-based templates for river restoration and engineering.

The fluvial–tidal transition zone (FTT) is a critical interface where complex interactions between river flow, tides, and sedimentation shape geomorphic systems and influence the dynamics of aquatic environments. However, few previous studies have integrated real-time hydrodynamic data with sedimentary deposits. In particular, the range of depositional conditions over which mud accumulates remains poorly constrained, and little is understood about how these deposits are preserved in the stratigraphic record. To address this knowledge gap, we examined co-located hydrodynamic instrument data and sedimentary deposits from the lower Waihou River, Aotearoa New Zealand. Results reveal that “dynamic mud” events, including fluid mud and rapidly deposited mud, dominate the spatial and temporal record, with few “static mud” events in which mud is deposited through gravitational settling. We suggest that dynamic mud conditions with the potential for deposition may occur throughout the tidal cycle, although cyclic tidal successions are never fully preserved. Many of the trends in sedimentation observed in studies of larger systems are not present in this small muddy river system, indicating the significance of climatic and river-flow characteristics on the sedimentary record. This work underscores the importance of studying systems of multiple sizes across diverse climatic regimes to establish holistic facies models to reconstruct geological history accurately.

Within the temperate ice of ice stream shear margins, high strain and accompanying recrystallization likely result in longitudinal foliation characterized by thin, steeply dipping ice layers with distinct variations in grain size and bubble content. The sensitivity of ice permeability to these factors, particularly grain size, implies that foliation causes shear-margin ice to be hydraulically anisotropic. In this study, the permeability of foliated ice is measured in disks cut from cores from Athabasca Glacier, allowing permeability anisotropy to be assessed. We collected cores oriented normal and parallel to foliation from beneath the weathered crust of the glacier. Permeability values range from approximately $��6�\times �1�0^{�-�13�}��\text{to}��1�0^{�-�16�}�$ m² and correlate with the textures and orientations of foliation layers. Results indicate that the anisotropic permeability of foliated ice can be approximated using a model that incorporates an empirical grain-size/permeability relationship and a model of vein clogging by air bubbles. For water flow parallel to foliation, the arithmetic mean of the area-weighted permeability closely approximates the bulk permeability; for flow perpendicular to foliation, measurements agree with the harmonic mean permeability, weighted to the thickness of each layer. These findings imply hydraulic anisotropy spanning several orders of magnitude in temperate glacier ice, with water flux governed by the most and least permeable layers in the flow-parallel and flow-perpendicular cases, respectively.

Landslides are among the most recognizable evidence of hillslope erosion in tectonically active mountains. Yet, how much of the distribution of landslides of different ages relates to, or is inherited from, the pattern of topographic metrics of landscape evolution remains partially unresolved, and especially so in tropical areas. We derive such metrics for 650 catchments of $��{10}^1�$-$��{10}^2�$ $��{\text{km}}^2�$ in size, including their mean hypsometric integral, local relief, geological lineament density, and steepness variations and knickpoint density of river channels as proxies of tectonic activity. We test how these proxies match with, if not explain, the distribution of some 14,000 prehistoric and modern landslides in the northern Colombian Andes. A $��K�$-means cluster analysis of catchment hypsometry reveals four distinct groups of catchments. We interpret these groups to reflect different states of transience with clear contrasts in mean local relief, average hillslope inclination, channel steepness, and landslide density. We propose that tectonic uplift, base-level changes, and passing waves of incision control these different states of transience. Yet, we find that landslides occur widely without much spatial association to, or amassing near, major channel knickpoints. This observation reflects what we would expect from a threshold landscape in which landslides abound irrespective of contrasts in local river incision rates. Still, we notice a pronounced amassing of landslides near transient divides, where prehistoric landslides are preferentially preserved. In summary, we infer that, in our study area at least, differences in catchment hypsometry might be more useful to track potential tectonic controls on landslide patterns than comparing these to knickpoint distributions or channel metrics.

Rapid long-runout loess landslides pose serious threats to human activities. However, associated kinematic processes, such as mass transport and energy conversion, are not fully understood, limiting disaster prediction and prevention. Herein, numerical models were established to quantitatively investigate the kinematic process of rapid long-runout loess landslides via the finite–discrete element method (FDEM). These models were calibrated according to the Dabuzi rapid long-runout loess landslide deposit and laboratory tests. We conducted systematic numerical simulations to explore the mass transport and energy conversion of a rapid long-runout landslide, focusing on the influences of the sliding volume and the traveling path topography undulation depicted by the fractal dimension. The rapid evolution of the mass structure from continuous to discontinuous, the transition from a solid state to fluid-like state, and the mutual influence of mass transport and energy conversion were quantitatively characterized during the landslide kinematic process. With increasing topographic surface's fractal dimension, the maximum displacement, maximum velocity, and volume expansion ratio of the landslide exhibited linear decreasing trends, and the accumulation morphology changed. Variations in these parameters with the sliding volume were opposite to those of the fractal dimension case, except for the deposit volume expansion ratio. Particularly, the surface mass always displayed extreme long-runout motion displacements. The mass transport characteristics, like the transition from acceleration to deceleration, were driven by the mutual conversion of potential energy to kinetic energy and the dissipation of friction and fracturing. The deceleration process was initially dominated by fracture energy dissipation and then by friction energy dissipation.

Geophysical mass flows often consist of various types of materials with different surface roughnesses. Predicting the dynamics of flows such as rock-ice avalanches, where particles have highly distinct surface friction, remains challenging due to the limited knowledge on how friction differences impact the rheology and microstructure. To study the flow of surface friction-different granular mixtures, we conducted discrete element method simulations of dense granular flows with varying concentrations of a highly frictional and a less frictional particle type. Each mixture is characterized by three interparticle friction coefficients defined for contacts between similar and dissimilar particle species. We show that the mixture rheology can be modeled by combining the rheologies of single-phase flows having interparticle frictions equal to those that exist in the mixture, weighted according to particle contact probabilities. Furthermore, by applying the contact probabilities on a recently developed friction-dependent constitutive model, it is possible to predict the rheology and micro-structural parameters of a wide range of mixture scenarios and flow geometries requiring only the interparticle friction coefficients as inputs. Results here improve the determination of the flow resistance due to friction differences in geophysical flows, allowing for more reliable predictions of their dynamics, which in turn are necessary for hazard risk reduction and mitigation.

Surface deformation plays an important role in permafrost studies as it is closely associated with the hydrological-thermal dynamics of the active layer and permafrost, affecting the stability of infrastructure. In this study, we have identified a significant underestimation of surface deformation over permafrost using Sentinel-1 InSAR, which is attributed to unwrapping errors in interferograms. Specifically, the inclusion of interferograms with longer temporal baselines in the SBAS network will cause unwrapping errors to occur more frequently and severely, leading to a more pronounced underestimation, exceeding 3 times in severe cases. To address this issue, we propose a novel correction strategy to mitigate unwrapping errors by correcting long-span interferograms with reliable short-span interferograms in the temporal domain. Here, 12-day interferograms are utilized as the reliable interferograms for the correction. The results show that the seasonal deformation amplitude over an ice-rich permafrost location on the Tibetan Plateau increases to approximately 110 mm after applying the correction, compared to the previous underestimation of only about 28 mm. The proposed correction method facilitates accurate retrieval and verification permafrost products from InSAR time series, such as the ground ice/water storage and thickness of the active layer. This in turn deepens our understanding of surface deformation in permafrost regions under a warming climate. Moreover, the proposed correction method demonstrates its promise as an effective strategy for mitigating underestimation issues in various InSAR studies that suffer from unwrapping errors.

Geomorphic features near strike-slip faults, including offset channels, have long been used in paleoseismology. Recent numerical models suggest that slip rate information can also be expressed far upstream of faults as catchments respond to stream lengthening and shortening due to stream captures along the fault. Slow-moving faults show dynamic catchment-wide responses with migrating ridges and changing basins, whereas fast faults have more stable basins and distinct topography near and far from faults. Such patterns hold promise for revealing slip rate and geomorphic process information but have yet to be tested in end-member slip rate and climate environments. In this study, we examine the Salar Grande Fault (SGF) in the hyper-arid core of the Atacama Desert. We use InSAR to provide a first quantitative estimate of slip rate for the SGF of 0.2–0.6 mm/yr. We then analyze topographic profiles parallel to the fault, located near and far from it (Profile Relief Ratio (PRR)) and cross-divide metrics on fault-perpendicular ridgelines as proxies for ridge mobility and relative slip rate. Our results show that the hillslopes and channels respond to slow strike-slip faulting, even in a hyper-arid environment. However, the low erosion conditions do diminish the magnitude of the landscape response, yielding a PRR value indicative of a relatively faster-moving fault. These findings improve our understanding of the geomorphic response to strike-slip faulting and emphasize the importance of considering climatic and erosive conditions when assessing relative slip rates.