Journal of Geophysical Research: Earth Surface最新文献

We investigated quasi-2D sand ripple geometry (i.e., ripple height, ripple wavelength, and ripple asymmetry) on a mound subject to the influence of waves, currents, and combined wave-current flows. The results of this study quantify how ripple geometry is influenced by bed slope and combined wave-current flows. The geometry of the ripples is shown to depend on the combined wave-current flow ratio and the local bed slope. Under wave-only conditions, the wave-driven ripple length and height decreased as a function of depth and local slope. Under combined wave-current conditions, the ripples increased in height and wavelength on the stoss slope of the mound, and decreased on the lee slope of the mound. Existing ripple geometry predictors, developed for combined flows on flat sand beds, were unable to predict ripple geometry on the sloped bed accurately. We propose correction factors for ripple geometry predictors to account for slope effects and combined wave-current flow conditions. Applying the correction factors significantly improves the predictor performance for predicting ripple height, wavelength, and asymmetry on sloping beds.

Rock-ice avalanches are a destructive natural disaster in mountainous regions. Along their propagation, they erode bed materials such as snow and rock. However, the mechanisms behind these processes remain unclear. Here, we have experimentally investigated the flow characteristics, erosion, deposition and impact of gravel-ice mixtures with different ice contents and bed materials. First, the flow characteristics of rock-ice avalanches have been analyzed and associated with erosion. It is found that the flow velocity and depth increase with ice content. The erosion rate is positively correlated with the flow velocity, the flow depth, and the ratio of particle collision stress to total stress, indicating that the driving mechanism of the erosion is the particle collision stress, instead of quasi-static shear. The bed material determines dominant erosion patterns and influences subsequent deposition. Then, the deposition characteristics were quantified. The deposited masses with erodible snow and ice are similar, as the higher flow mobility on snow gives more released mass reaching the deposition zone, and the smaller snow density leads to a lower eroded mass in the deposition zone. Deposition length and width keep increasing with ice content or slope angle, while deposition height first increases and then decreases. Finally, the avalanche impact force is investigated. The ice content has positive and negative effects on the impact force at different stages due to the combined effect of enhanced velocity and decreased density. The outcomes of this study offer new insights into the dynamics of rock-ice avalanches, and provide important implications for their risk assessment.

Biotite weathering in granite is known to induce micro-crack propagation. Conversely, fracture propagation exposes fresh surfaces to percolating fluids and enhances fluid flow, which accelerates chemical weathering. These feedback mechanisms between weathering, microcracks and larger fractures remain under-explored. To bridge this gap, a weathering-induced damage model is coupled with a cohesive fracture model to study the joint effects of topographic, tectonic, and weathering stresses in granite. Weathering is simulated over 250 years in sinusoidal topographies. Numerical results suggest that without pre-fracturing, horizontal tectonic stresses are needed to trigger weathering. Under tensile horizontal tectonic stress, simulations indicate that weathering advances vertically beneath the valleys, consistent with field observations. The model predicts that where compressive tectonic stresses are transmitted beneath and parallel to valley bottoms and side slopes, surface-parallel fracturing is promoted, and weathering regions spread laterally beneath both the valleys and ridges, in conformity with fractures observed parallel to and subparallel to the surface. Simulations also indicate that the stress concentrations beneath a valley promotes mode-I fracture propagation where the horizontal tectonic stress is tensile, but does not significantly impact mixed-mode fracture propagation subparallel to the surface where the horizontal tectonic stress is compressive.

Mountain building reorganizes drainage networks, influencing riverine biodiversity. Northern Italy offers a natural experiment in the impact of tectonic and geomorphic processes on aquatic species distribution. We combined geomorphic analysis with environmental DNA from rivers to assess the influence of tectonically driven drainage reorganization on genetic diversity, targeting an endemic fish species, Telestes muticellus (Risso et al., 1826, https://www.biodiversitylibrary.org/bibliography/58984). In the Northern Apennines, horizontal shortening and topographic advection in an orogenic wedge have been hypothesized as leading to river capture and drainage divide migration. In addition, slab rollback has produced a spatial transition from contraction to extension that is more pronounced from north to south, with normal faulting producing range-parallel drainage only in the southern regions. In contrast, the adjacent Ligurian Alps are a remnant of the Alpine orogen with little modern deformation. We found distinct zones of geomorphic characteristics from north to south, including divide asymmetry and frequency of range-parallel drainage. Analysis of DNA sequences shows cross-divide assemblage characteristics that correlate with the geomorphic zonation. In terms of directional measures of assemblage change, the Northern Apennines show higher values of overlap, gain, loss, turnover, and nestedness than those in the Ligurian Alps. Main drainage divide asymmetry correlates positively with genetic distance and gain, loss, and turnover of DNA sequences from Adriatic to Ligurian sites and negatively with overlap and nestedness. Since the species is confined to freshwater environments, tectonically driven drainage reorganization can explain its spatial genetic differentiation.

The grounding zones (GZ) of marine-terminating glaciers, where ice transitions from grounded to floating, experience strong mechanical changes in response to ocean tides. The spatial and temporal dynamics of these changes remain poorly documented, as they require multi-scale observations capable of resolving internal ice deformation. Here, we use seismic observations, collected across different years and various scales, coupled with GNSS observations, to evaluate the brittle deformation at the GZ and shear margins of the Astrolabe Glacier (East Antarctica, Terre Adélie). Automatic detection of icequakes reveals that seismic occurrence patterns vary with tides and sensor locations. At a multi-kilometer scale, we observe and locate numbers of large-duration magnitude events (average Md around 0.0) associated with shear margins. At a smaller scale (a few hundreds of meters), using a dense array of seismic nodes deployed across the GZ and GNSS observations of vertical ice motion, we capture numerous small-magnitude events (Md as low as −4.0) with spatial and time occurrences set by tide-modulated GZ dynamics. At rising tides, seismicity is dominant on the floating part of the glacier, while at falling tides, it is dominant over its grounded part. Based on these observations, we propose a conceptual framework for the dynamics of icequake activity at the glacier GZ, accounting for its three-dimensional tidal-induced bending, generating strain rates large enough to induce brittle deformation. Our findings highlight the value of multiscale seismic observations of outlet glaciers for capturing GZ space and time high-resolution seismic and displacement responses to tidal forcing.

Berms composed of surface gravel and underlying sand and gravel mix (gravel berms) naturally form on beaches and can help mitigate coastal erosion and flooding. Previous studies suggest that subsurface sediments influence gravel berm behavior, although detailed investigations remain limited. Here, we present a novel integrated field approach to quantitatively monitor gravel berm subsurface sediments. From March to October 2023, surface and subsurface sediments were characterized using combined methods including mechanical excavation, image-based grain size analysis, GNSS, and ground penetrating radar (GPR) surveys, and compared with gravel berm topography at two beaches (South Carlsbad and Torrey Pines) in southern California with contrasting sediment characteristics. South Carlsbad consistently exhibited backshore gravel exposure and limited seasonal sand volume changes, whereas Torrey Pines exhibited varying backshore gravel exposure and more pronounced seasonal sand volume fluctuations. At both beaches, the gravel berms consistently had a surface pure-gravel (PG) layer overlying a mixed sand-gravel layer, with the PG layer thickness decreasing seaward. At Torrey Pines, the upper gravel berm profile changed seasonally from spring to late summer as sand gradually accumulated within the berm (resulting in a PG layer thickness decrease) and varied subsurface sediment composition. In contrast, in South Carlsbad, both upper gravel berms and subsurface sediment structures exhibited seasonal consistency, with little change in PG layer thickness. The combined approach enables detailed and repeatable assessment of gravel berm subsurface sediments, offering further insights into the links between internal sediment structure and surface morphology. The present results inform a new conceptual model of seasonal gravel berm evolution.

Landsliding in river valleys poses unique risks for cascading hazards and can damage infrastructure and cause fatalities. In postglacial valleys, many landslides are posited to occur in relation to lateral river erosion, but the dynamics of fluvial-hillslope interactions are not well understood. Here, we investigate a section of the Nooksack River in western Washington State where the channel is flanked by landslide-prone glacial terraces similar to those that failed in the 2014 State Route 530 “Oso” landslide. We map 216 landslides through time across 17 aerial imagery data sets (1933–2022) and analyze them in relation to river meandering and curvature. We observe dynamic feedbacks between lateral river meandering and valley-adjacent landsliding. Terrace lateral retreat rates of up to 25 m/year owing to combined fluvial erosion and slope failure occur on pinned, outer meander bends immediately downstream from peaks in river curvature (>0.0075 1/m); these locations are predisposed to both shallow and deep-seated landslides. Deep-seated landslides extending 17%–32% of the active valley width into the floodplain can displace the river away from the floodplain margin and change the channel planform. River-displacing landslides relocate meanders up- or downstream, thereby conditioning the location of subsequent landslides. This conceptual model of coupled landslide-driven meander displacement and valley-adjacent landsliding is exemplified across western Washington river systems. The distance between up- and downstream valley-adjacent landsliding scales with valley width, meander wavelength, and terrace height. Our results can advance our understanding of the river-hillslope interface in landscape evolution and can be used to inform hazard management in river corridors.

The rise in global temperatures is amplified in high-latitude regions, where snow and ice play a vital role in the hydrological cycle. Understanding the impacts of climate change on ecosystems and communities in Northern regions requires accurate hydrological data. Within Northern Canada, in situ data sparsity (in both spatial and temporal resolution) poses a challenge to robust characterization of hydrological trends. The increasing availability of satellite-derived data can provide an independent measure of terrestrial water storage. This study compares terrestrial water storage anomalies (TWSA) from Gravity Recovery and Climate Experiment (GRACE) and GRACE-FO to in situ and satellite-derived precipitation and evaporation products within the Mackenzie River Basin (MRB), Canada, a high-latitude basin characterized by low population density and significant contribution of freshwater to the Arctic Ocean. Declining trends in TWSA from GRACE/GRACE-FO in the MRB are not fully explained by corresponding trends in hydrological parameters. Water budget analysis reveals inconsistencies between GRACE/GRACE-FO derived TWSA and TWSA derived using precipitation, evaporation, and runoff data, which may be attributed to physical processes represented in the GRACE/GRACE-FO observations. Three models of glacial isostatic adjustment (GIA), namely the ICE6G_D (VM5a), Caron-18, and LM-17.3 models, were compared to examine the sensitivity of the GRACE/GRACE-FO-derived TWSA to the GIA model (correction) employed, revealing approximately ±1 cm of equivalent water height per year variability in the TWSA linear trend. The results suggest that robust characterization of regional mass processes (e.g., subsidence, residual GIA) within the MRB is necessary to isolate hydrological mass changes.

To investigate the long-term evolution of granitic regolith under cold temperate climate, we examined a 300 cm-thick regolith profile in the Oroqen Autonomous Banner, northeast China. We analyzed the mineralogy and U-series isotopic compositions of bulk regolith samples. Measurements of (²³⁴U/²³⁸U), (²³⁰Th/²³⁸U), and (²³⁰Th/²³⁴U) isotopic activity ratios indicate U-series disequilibrium, with complex variations in depth, ranging from 0.949 to 0.989, 0.906 to 1.036, and 0.926 to 1.059, respectively. The conventional “gain and loss” model could not be applied across the entire profile in a single simulation. By subdividing the profile into three subzones based on elemental and mineralogical depth variations, the “gain and loss” model was applicable to two subzones, excluding the middle portion. U-series disequilibrium-derived regolith production rates were 1.42 ± 0.03 m/Ma and 5.97 ± 3.98 m/Ma for these subzones. When compared to denudation rates (∼34 m/Ma) determined from in situ cosmogenic nuclides (¹⁰Be and ²⁶Al), the regolith production rates were substantially lower, suggesting that the profile is in a non-steady state. Our findings highlight the necessity of subdividing regolith profiles when applying the “gain and loss” model, and demonstrate the value of integrating U-series disequilibrium with in situ cosmogenic nuclides for assessing regolith evolution over long timescales. The evolution of regolith thickness, as a controlling factor of production rate, also has a significant impact on whether there is a coupling between the regolith production rate and the denudation rate.

At 23:59 (UTC + 8) on 18 December 2023, an earthquake of Ms 6.2 struck Jishishan County in Gansu Province, China, and triggered a large-scale, flow-like loess landslide in Zhongchuan Town, resulting in some 20 deaths. Originated from relatively gentle terrain, the loess flow displayed high mobility with a run-out distance of 3,200 m, suggesting that pore-water may play a critical role in the mobility of Zhongchuan flowslide. Following onsite investigations and soil sampling, we replicated the initiation process of the flowslide through dynamic back pressure direct shear tests under a constant shear stress condition. Two types of tests were conducted on saturated loess samples: elevated back pressure tests to simulate instability induced by high pore-water pressure, and dynamic loading tests to examine the evolution of pore-water pressure under seismic loading conditions. The experimental results, supported by microscopic analysis, indicate that elevated pore-water pressure is the key factor driving the progressive transformation of shear displacement from accelerated motion to instantaneous runaway. Meanwhile, dynamic loading substantially amplifies the generation of excess pore-water pressure. Moreover, the initial pore-water pressure was found to be a critical factor in both the initiation and high mobility of the Zhongchuan flowslide. These experiments quantitatively capture the in situ evolution of pore-water pressure throughout the liquefaction process, providing a physically based framework for understanding the mechanisms of loess landslides.