Journal of Geophysical Research: Earth Surface最新文献

Dynamical changes at the termini of tidewater glaciers may trigger sustained acceleration, thinning, and retreat, increasing a glacier's contribution to sea level rise. However, processes at the ice-ocean interface occur across a range of spatial (cm to km) and temporal (minutes to years) scales, making these processes difficult to capture with many existing observational strategies. To fill this observational gap, we installed two autonomous terrestrial laser scanners overlooking the terminus at Helheim Glacier, East Greenland, the first in 2015 and the second in 2018. Each laser scanner system scans every six hours during non-winter months and once a day during winter; together, these systems generate an extraordinary amount of data, including georeferenced point clouds, digital elevation models, velocity, and strain rates of Helheim Glacier. Our results show that large surface depressions form at a near-consistent location on the lee side of a subglacial ridge and have increased in occurrence over time. We also present the first inferences of Helheim Glacier's grounding zone location and observed over 3 km of grounding zone retreat between 2018–2019. Furthermore, we identify and catalog calving events that we compare with our velocity products. We find that Helheim Glacier does not undergo sustained acceleration after individual calving episodes, and variations in calving style do not impact velocity responses. Our work reveals the insensitivity of Helheim Glacier to iceberg calving during our observational record and the importance of high temporal resolution data in inferring grounding zone dynamics.

Seasonal variations in salt marsh edge retreat are often attributed to fluctuations in nearshore wave forcing. This study, conducted along the central coast of Jiangsu, China, demonstrates that monsoon-driven seasonal sea-level variability, rather than offshore wave conditions, exerts the primary control on retreat rates. UAV and GNSS-RTK surveys from 2020 to 2022 reveal accelerated marsh edge retreat during summer–autumn, coinciding with elevated sea levels. Idealized wave modeling shows that higher sea levels reduce energy dissipation across nearby tidal flats, facilitating greater wave energy transmission to the marsh edge. Field observations further show seasonal changes in tidal flat elevation, with erosion in summer–autumn and deposition in winter–spring. These morphological changes appear to result from sea-level-driven variations in nearshore wave forcing, where enhanced summer wave action erodes the tidal flat, increasing water depth and further reducing dissipation, thereby reinforcing wave energy transmission to the marsh edge. These findings highlight the dominant role of seasonal sea-level variability in driving lateral marsh retreat, while suggesting that tidal flat morphological adjustments may amplify the seasonal erosion response by reinforcing nearshore hydrodynamic contrasts.

Bedload transport is a key fluvial process. Yet, it is challenging to measure in natural streams, and continuous time series are rare. Seismic methods show promise for continuous monitoring of bedload transport. However, comparisons with direct bedload measurements are required for calibration and validation, and few such data sets exist. We collected high temporal resolution seismic and bedload flux data from 19 flash flood events that occurred during 5 years at the Arroyo de los Pinos experimental watershed in central New Mexico. We use this data set to investigate the variation of seismic signals with bedload flux across events. To compare seismic and bedload data, we first isolated seismic power-spectral density (PSD) in the 30–80 Hz frequency range, largely to exclude local noise sources. Next, we computed the linear regression of recorded PSD with bedload flux measurements to determine the robustness of correlation. We found a good correlation between median PSD in the 30–80 Hz range and bedload flux (Spearman's ρ = 0.77). To further investigate variation in the bedload-PSD relationship, we sieved sediment captured in bedload samplers and determined variations in PSD according to grain size. We found a significant positive correlation between PSD and the median grain size of bedload in motion, but the peak frequencies did not correlate with grain size.

The Ganges-Brahmaputra-Meghna delta faces growing risks from subsidence, sediment depletion, and sea-level rise. Sustaining delta elevation requires continued sediment supply, yet the spatial and seasonal dynamics of sediment retention across the fluvial system remain poorly resolved. This study employed a process-based two-dimensional model (Delft3D FM) to simulate suspended and bedload sediment transport across the Ganges, Brahmaputra and Padma Rivers in Bangladesh under contrasting monsoon conditions. Model results showed that over 35%–40% of annual suspended load was retained within the fluvial system, particularly in the upstream braided (Brahmaputra) and meandering (Ganges) reaches and their adjacent floodplains. The Padma reach also contributed notable retention, particularly under reduced Brahmaputra flow dominance. Seasonal variability governs sediment transport, with 80%–95% of annual suspended sediment delivered during the monsoon. Backwater effects in the Padma reach modulate sediment transport by altering flow gradients near fluvial-tidal transition zone. However, sediment transport and retention within and upstream of this zone remain spatially variable, shaped by discharge intensity and channel morphology. Bedload transport remains active in the Brahmaputra reach but becomes increasingly variable downstream, especially in the Ganges-Padma corridor. These findings clarify spatial contrasts in fluvial sediment routing and deposition, providing a system-scale basis for mass balance assessments and sediment management. Identifying key zones of sediment retention and bypass is essential for maintaining sediment connectivity and supporting delta resilience under increasing environmental and anthropogenic stress.

Ice-mass change induces regionally varying patterns of sea-level change due to gravitational, rotational, and deformational (GRD) effects, which in turn influence marine-based ice stability in Antarctica. For improved projection of the Antarctic Ice Sheet (AIS), there is a need for including GRD effects in modeling and improving understanding of basin-by-basin sensitivity of ice evolution to GRD effects under a range of climate scenarios. We couple a high-resolution, higher-order ice-sheet model with a 1D global sea-level model that fully captures GRD effects, and simulate ice evolution in Antarctica under the Ice Sheet Model Intercomparison Project for CMIP6 experiments. We perform two sets of coupled simulations incorporating 1D Maxwell solid Earth structure suitable for West and East Antarctica and show that the Amundsen Sea Embayment (ASE) in West Antarctica has the highest sensitivity to GRD effects—in high-emission scenarios, grounding-line retreat accelerates by hundreds of kilometers by 2300 without GRD effects, but GRD effects delay this retreat on a timescale of decades. However, we find that delay times do not show a clear relationship to the strength of climate forcing alone. Furthermore, GRD effects can influence ice-sheet dynamics more than the choice of climate model for a given emissions scenario. In contrast, East Antarctica exhibits minimal sensitivity to GRD effects throughout the study period. These findings underscore the critical role of GRD effects in shaping future West AIS evolution, highlighting the importance of constraining the regional 3D Earth structure and bed topography in West Antarctica, particularly the ASE.

Accurately predicting Greenland's ice mass loss is crucial for understanding future sea level rise. Approximately 50% of the mass loss results from iceberg calving at the ice-ocean interface. Ice mélange, a jammed, buoyant granular material that extends for 10 km or more in Greenland's largest fjords, can inhibit iceberg calving and discharge by transmitting shear stresses from fjord walls to glacier termini. Direct measurements of these resistive force dynamics are not possible in the field, thus, we created a scaled-down laboratory experiment to study jammed-packed ice mélange mechanics. We recorded videos of the mélange surface motion and subsurface profile during slow, quasistatic flow through a rectangular fjord, and recorded the total force on a model glacier terminus. When the wall friction is low, the ice mélange moves as a solid plug with little or no particle rearrangements. When the wall friction is larger than the internal friction, shear zones develop near the walls, and the buttressing force magnitude and fluctuations increase significantly. Associated discrete particle simulations illustrate the internal flow in both regimes. We also compare our experimental results to a continuum, depth-averaged model of ice mélange and find that the thickness of the mélange at the terminus provides a good indicator of the net buttressing force. However, the continuum model cannot capture the stochastic nature of the rearrangements and concomitant fluctuations in the buttressing force. These fluctuations may be important for short-time and seasonal controls on iceberg calving rates in fjords with thick and persistent ice mélange.

Beach-and-foredune-ridge plains archive paleoenvironmental changes within their morphology and stratigraphy. Despite advances in integrating modern process data with coastal sedimentary archives, we lack a quantitative understanding of how coastal progradation processes such as time-varying wave, current, and sediment transport processes impact stratigraphic and morphologic records. To address this gap, we pair geophysical, sedimentological, and morphological data with hydrodynamic and sediment-transport modeling to understand the processes impacting paleoenvironmental archives (e.g., beach slopes, grain size, and morphology) in four beach-ridge plains along Virginia's coast (USA). We quantify these processes at three periods (800 CE, 1880 CE, and modern) using Delft3D model grids derived from stratigraphic, historical, and modern bathymetric data. We hold model boundary conditions consistent across scenarios to focus on local (kilometer-scale) physical processes driving ridge morphology and architecture. Key differences among the ridge plains are primarily related to orientation with respect to regional wave conditions; specifically, beachfaces are steeper and coarser on ridge plains formed by shore-parallel spit-elongation compared with those formed through cross-shore progradation. Model results show modest differences in sediment-transport patterns and fluxes over the last 1200 years; present-day and historical spits and inlets trap medium and coarse sand, resulting in finer sediments reaching downdrift barriers and attendant shallower beachfaces. Spatial variations in beach-ridge stratigraphy and morphology remain consistent through time, indicating that at this site, beach-ridge archives reflect primarily local forcings. This work offers an example of how to cautiously interpret beach-ridge stratigraphic and morphological records.

The destructive potential of a rock avalanche can come from any single boulder. Rock avalanches across irregular terrain were simulated using the discrete element method (DEM) with high-performance computing to model particle quantities from one to millions. Simulations were validated against published miniature flume experiments and varied in terms of particle shape, rolling friction between particles, rolling friction on the flume, and restitution coefficient to quantify how various mechanisms of energy dissipation affect the avalanche runout sequence. Non-spherical particle shapes idealized as superquadrics demonstrated superior capability in representing the motion of angular particles and capturing physically observed runout sequences and inundation thicknesses when compared with equivalent simulations performed with spherical particles. Rheological rolling friction at the interparticle contacts had a significant effect on the runout sequence but proved to be an inferior substitute for geometric non-sphericity. Higher quantities of particles in rock avalanches produced lower average kinetic energies per particle due to the greater amount of energy dissipated through more frequent contact damping; however, the maximum single-particle kinetic energy still increased with particle quantity. The simulation results provide insight into how kinetic energies are distributed temporally and spatially across irregular terrain during rock avalanches, facilitating visualization of the locations of the highest impact energy for individual particles and for the entire avalanche. The locations of highest kinetic energy associated with individual particles do not always overlap with those associated with the whole avalanche, which signifies the importance of considering the destructive potential of individual boulders at multiple locations along runout paths.

Thwaites Eastern Ice Shelf (TEIS) is a partially confined floating extension of Thwaites Glacier, anchored by an offshore pinning point at its northern terminus. Over the past two decades, the shelf has experienced progressive fracturing around a prominent shear zone upstream of its pinning point, gradually compromising its structural integrity. Here we present an analysis of shear-zone fracture evolution from 2002 to 2022 and its control on the flow dynamics of the ice shelf using satellite remote sensing and in situ GPS observations. We compiled multi-year statistics of fracture length and orientation from Landsat and Sentinel-1 imagery and compared their changes with evolving flow dynamics and surface strain rates. Ongoing disintegration driven by the shelf's shearing against the pinning point occurred in two stages: propagation of large shearing fractures approximately parallel to flow earlier in the record, followed by the rapid formation of smaller tensile fractures approximately perpendicular to flow later in the record. We also observed velocity perturbations originating from the shear zone and propagating across the main ice shelf, observationally demonstrating the direct impact that shear-zone disintegration has on the dynamics of TEIS.

Due to their exposure to waves, volcanic island coasts typically retreat with cliff collapses and other erosional processes. Understanding how retreat rates vary over time and in response to environmental and other factors could be useful for geohazard assessment, coastal management and landform reconstruction. Historical eruptions can create new coasts with volcanic materials that are friable. The retreat of such coastlines can be fast and more easily observed than for many older rocky coasts. Here we assemble coastline retreat distances and rates of 12 coasts formed by historical eruptions from literature sources and remote-sensing data. In the cases with observations at many time steps, post-eruptive coastline retreat was initially rapid and declined with time. We adapt an empirical equation found earlier to represent the coastline retreat of a Surtseyan cone, finding that it represents the systematic variation in retreat distances with time well where coastal evolution is known in more than 5 time steps. The slowing is interpreted to arise from (a) increasing wave attenuation with abrasion platform widening, (b) exposure of progressively more resistant materials at cliffs, and (c) from increasingly taller cliffs, which lead to increasingly large volumes of debris from cliff collapses, temporarily protecting cliff bases. Coastline retreat rates also follow inverse power-law relationships with varied time intervals of measurement; hence, they are affected by erosion episodicity. Comparisons with wave height and precipitation surprisingly reveal no strong co-variation with the retreat rates. We hypothesize that varied lithology, fracture density and other factors dominate retreat rates of young volcanic coastlines.