Journal of Geophysical Research: Earth Surface最新文献

Coastal depositional environments, particularly salt marshes, are among the morphologies most vulnerable to relative sea-level rise (RSLR). Their ability to withstand changing conditions is closely related to their capacity to accrete sediment, gaining elevation at a rate comparable to RSLR. Sedimentation, decomposition of organic remains, and autocompaction are among the main processes that govern the long-term evolution of marsh elevation, with soil compressibility that controls the salt marsh thickening. In fact, autocompaction may significantly offset elevation gain from sediment deposition. Autocompaction is especially apparent in the shallowest decimeter depth where sediments have the highest porosity and are most compressible. However, the geomechanical characterization of these landforms is uncommon worldwide. Laboratory geotechnical testing faces challenges in terms of (a) reliability due to sampling disturbance of these soft soils, and (b) representativeness of in situ conditions because of the dense root network of halophytes in the upper 0.1–0.3 m depth. Here we quantify for the first time the compressibility of the shallowest decimeters of salt marsh soils by novel field-scale loading tests carried out in representative salt marshes of the Venice Lagoon, Italy. The data collected are analyzed using an advanced 3D coupled flow-consolidation simulator with nonlinear constitutive models. Our analysis reveals that salt marshes exhibit considerable variability in soil compressibility within the upper 1–2 m, with differences of up to 2 orders of magnitude. This variability is attributed to several factors, including lithology, depositional environment, and soil age. Moreover, they are characterized by a preconsolidation stress ranging from 2 to 8 kPa, linked to the specific depositional environment, which plays a major role in their mechanical response. The quantification of these parameters will allow a reliable prediction of the salt marshes fate in the Venice Lagoon following global environmental changes and local human interventions.

River deltas have complex vertical sediment dynamics within their distributary channel networks. These dynamics suggest that remotely sensed suspended sediment concentration (SSC), which captures surface conditions, is insufficient for investigating delta mixing. Here, we propose a method for mapping the Rouse number using AVIRIS-NG imagery from NASA's airborne spectrometer to investigate vertical mixing patterns. The method is based on the inversion of the equation relating depth-averaged and surface SSC from the Rouse theory. We test this method and its assumptions using a global river data set. We apply this approach to the Wax Lake Delta, Louisiana, USA during high discharge (riverine case) and low discharge (tidal case). Our results indicate that the estimated Rouse number effectively reveals patterns of vertical mixing in both cases. Furthermore, we reproduce 3D SSC fields at the distributary channel outlets using the Rouse number and surface SSC maps. Understanding these mixing patterns is crucial for river delta restoration efforts. Our findings suggest that these new remote sensing data offer significant insights into delta dynamics.

Three blue-ice areas in the upper reaches of Rennick Glacier, East Antarctica, are investigated using satellite remote sensing to assess the influence of meso- to large-scale glaciological structures on cryoconite hole distributions. In total, 15,299 cryoconite holes and 1 600 structures were geospatially analyzed, which indicate that cryoconite holes are commonly concentrated in areas with prominent meso-scale ice structures. The emergence of debris entrained in primary stratification promotes the development of cryoconite holes along the surface expression of debris-bearing layers. Differential ablation of penetrative structures and their constituent ice facies can form a ridge-and-furrow ice-surface topography that captures supraglacial hydrology and sediments. As a result, trains of cryoconite holes develop in furrows that trace the surface expression of planar layers. Large-scale topographic barriers that form at flow-unit boundaries constrain cryoconite holes within discrete flow units by inhibiting the transport of supraglacial sediments. The majority of cryoconite holes are located in low-slope (<5°) areas where sediments are less susceptible to stripping events. Cryoconite holes on steeper slopes are preferentially located near flow-unit boundaries where the topographic expression of meso-scale structures can offset the influence of larger-scale topography by preventing sediments from being washed down-slope. Although a range of variables can influence the distribution of cryoconite holes, meso- to large-scale structures play an important role in the development of ice-surface topography and the delivery of sediments from different sources, which can strongly influence the distribution and composition of cryoconite holes.

Dry-snow slab avalanches are the most fatal type of avalanches, beginning with the failure of a weak snow layer below cohesive slabs. This failure can propagate within the weak layer, causing the overlying slab to fracture and slide. Avalanche forecasters are interested in evaluating crack propagation propensity and potential avalanche sizes. This study tests the hypothesis that two factors may stop dynamic crack propagation: snowpack heterogeneity and terrain variations. We develop a depth-averaged Material Point Method, which combines MPM with shallow water assumptions for efficient elastic-brittle modeling of avalanche release. We analyze two scenarios: pure-elastic and brittle slabs. In the pure-elastic case, we observe a significant decrease in slab tensile stress with increasing crack speed and provide an analytical formulation for this phenomenon. We evaluate the impacts of weak layer heterogeneity and fracture energy on crack stopping. In the brittle scenario, we explore the interaction between weak layer heterogeneity and slab fracture, quantifying their combined effects on crack arrest. Our results reveal a scaling law that relates crack arrest distance to dimensionless numbers indicative of weak layer and slab strength. The model is applied in case studies to predict release sizes based on field data, and also on synthetic 3D topographies, enhancing the understanding of factors influencing avalanche size and aiding future mitigation strategies.

Paraglacial landscapes are rapidly transforming as thinning and retreating glaciers expose adjacent slopes to new conditions. In Southcentral Alaska, a large slope instability at Portage Glacier has been deforming progressively up-glacier over the past six decades. The instability comprises two deep-seated rock slope segments, Portage A and Portage B, located above the thinning and retreating Portage Glacier and its proglacial lake. Portage B lies at the glacier terminus, while the down-glacier margin of Portage A is about 300 m further up-glacier. To understand the mechanisms driving slope deformation, we integrated field observations, historical imagery, structural and kinematic analysis, differential DEMs, InSAR, and coherence radar to capture both short- and long-term deformation patterns. We identified three distinct domains of movement: two in Portage A and one in Portage B. Our findings reveal that Portage A experiences rapid and variable displacement rates, whereas Portage B shows slower motion. Structural analysis indicates translational sliding and toppling as primary failure mechanisms controlled by pre-existing geological discontinuities. Glacier thinning is identified as a key factor, initiating movement and enabling the progressive spatial up-glacier propagation of deformation from Portage B to Portage A. But this process is not solely driven by thinning; rather, it reflects how ice loss progressively alters mechanical boundary conditions, granting kinematic freedom for the rock mass to deform along pre-existing structural discontinuities. Consequently, our results underscore the importance of considering both glacier thickness thresholds and structural geology to better understand and assess the onset and evolution of slope deformation in paraglacial environments.

This work introduces a physically based modeling framework to capture the spatio-temporal dynamics of dune vegetation under stochastic environmental disturbances. The model evaluates vegetation cover in response to random wind speed and runup within a cross-shore dimensionless framework. The wind speed is modeled as a compound Poisson process with Gamma-distributed properties, facilitating the computation of up-crossing times for various thresholds. The dune topography is represented by a swash zone with a Gaussian shape and a monotonic landward increase, parameterized by slope, wavelength, and height. Key disturbance conditions affecting vegetation, that is, runup-induced flooding in the swash zone and wind-induced scour on the backshore and crest, are addressed through threshold-based analysis. The model uses a state-dependent dichotomic process for vegetation dynamics, where growth and decay are influenced by external forcing and vegetation state. Analytical solutions of the master equation for the vegetation distributions reveal the impact of stochastic factors on vegetation growth and stability. Sensitivity analysis identifies dune steepness, forcing magnitude and variability, and relative roughness as critical parameters. These factors significantly affect vegetation distribution, with increased steepness leading to higher vegetation density at the backshore and reduced density at the shorefront. Validation is carried out against satellite imagery and high-resolution real elevation data from the U.S. coastline and confirms the robustness and accuracy of the proposed approach. The results enhance understanding of dune vegetation dynamics and offer a framework for coastal restoration strategies.

Barrier island resilience to climate impacts depends on sediment redistribution between the subaqueous shoreface and subaerial barrier during sea-level rise and storms. However, autogenic interactions between the upper and lower shoreface and their influence on the subaerial barrier are poorly characterized. Here, we explore the influences of various shoreface components on barrier morphology using a model of barrier and shoreface evolution under sea-level rise, the Articulated Barrier Shoreface (ABSF) Model. This reduced-complexity model divides the shoreface into upper and lower shoreface panels that respond independently to sea-level rise and deviations from the equilibrium slope. We couple the ABSF with the Lorenzo-Trueba & Ashton, 2014, https://doi.org/10.1002/2013jf002941 model (LTA), a barrier island evolution model driven by overwash and sea-level rise. Through this coupled framework, we examine the influences of upper and lower shoreface slopes, their respective depths, and sensitivity to wave climate on long-term barrier evolution. Results show that the relative depths of the upper and lower shoreface toes influence barrier response to rising seas, alongside overwash flux and closure depth. Notably, the lower shoreface response to sea-level change lags that of the upper shoreface over decades, diminishing the resilience of the barrier over centennial timescales by slowing the overall barrier response. In fact, the ABSF model predicts barriers will drown faster and more than predicted with a linear shoreface. Results highlight the shoreface as an important sediment reservoir for barrier islands and that differences in upper and lower shoreface responses can reduce barrier resilience to sea-level rise due to limited lower shoreface sediment accessibility.

Debris flows are frequent natural hazards whose destructiveness is controlled by the dynamics of their flow fronts, surges behind the front and large boulders. Understanding the mechanisms underlying the spatiotemporal variations in flow depth and velocity is limited by a lack of catchment-scale measurements. In this study, we present and analyze flow-depth and velocity measurements from a new monitoring setup which consists of high-frequency 3D LiDAR scanners installed at three different locations along the active debris-flow fan of the Illgraben. For the event analyzed herein, we observe that (a) the LiDAR-based velocities are in excellent agreement with measurements from a Pulse-Doppler (PD) radar and with manually tracked feature velocities; (b) the flow front decelerates as it travels along the fan and a watery pre-surge develops, likely due to a combination of segregation and vertical shear, which transport woody debris and small boulders to the front, as well as a horizontal velocity profile, required for transportation of large boulders through a mechanism we term “centerline advection”; (c) roll waves begin to develop on the lower part of the fan by coalescence of free surface instabilities and they exceed the front velocity by up to 2$��\times �$ to 3$��\times �$; (d) surges later in the event do not show an accumulation of boulders at the crest, but can accelerate individual boulders to velocities up to 2$��\times �$ the front. This study demonstrates that radar and LiDAR-based measurements improve our understanding of debris-flow processes, including front propagation and development of waves.

P-wave velocity profiles from seismic refraction reveal deep critical zone (CZ) architecture along profiles hundreds of meters long. However, extrapolating local velocity measurements to infer CZ architecture at regional scales (1–20 km²) remains challenging. Here, we present a strategy that transforms seismic observations from individual profiles into maps of CZ architecture spanning tens of square kilometers. Data from 15 seismic refraction profiles (approximately 6.6 km total length) collected in weathered crystalline rocks of the South Carolina Piedmont, USA, revealed approximately 400,000 m² of deep CZ architecture. Using casing depths from four boreholes, we show that the boundary dividing saprolite and fractured rock corresponds to a velocity of 1,870 m/s. Using velocity measurements from an outcrop within the survey area, we identify the bedrock velocity as 4,550 m/s. These velocities define a three-layer CZ structure comprising soil and saprolite, fractured bedrock, and unweathered bedrock. We developed an empirical relationship between CZ structure and minimum and maximum principal curvatures, enabling prediction of CZ architecture over approximately 17 km². The correlation between seismically inferred CZ structure and principal curvatures at our study site suggests that curvature metrics can be used to predict CZ structure at larger scales in crystalline terrains under subtropical climates. However, the empirical relationship struggled to predict CZ structure where landscape curvatures were near zero, suggesting that other variables likely contribute to local heterogeneity. Given that curvature is an important variable for erosion and groundwater flow, our results suggest it could be a promising metric for predicting CZ structure.

Seagrass meadows fulfill many essential ecological functions, of which an important one is to stabilize sediment. Therefore, they are perceived as a nature-based addition or alternative to conventional rigid coastal protection. The impact of seagrass meadows depends on their morphology, such as canopy height, shoot density, and spatial extent. However, deciduous, intertidal seagrass species are often simplified in modeling studies by adopting their annual mean height and density. This can lead to an erroneous estimate of their impact on hydro-morphodynamics and misconceptions about their contribution to coastal protection. Here, we assess the importance of seasonal changes in seagrass properties for morphological development, using a tidal basin in the Wadden Sea as an example. We applied numerical modeling to simulate the annual growth cycle of seagrass meadows and their interaction with hydro-morphodynamics. Based on validated seasonal changes in seagrass properties from field surveys and comparisons between scenarios of seagrass growth, our results show that adopting static seagrass parameters in modeling can lead to over- or underestimation of morphological changes induced by seagrass meadows. In some cases, it may even predict results contrary to simulations that consider seasonal changes in seagrass properties, particularly regarding the net sediment volume change in the intertidal zone. This highlights the essential necessity of considering the natural growth and decline cycles of seagrass meadows when assessing their role in coastal protection, especially in temperate zones where seasonal changes in seagrass properties are distinct.