Journal of Geophysical Research: Earth Surface最新文献

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.

Wave-influenced deltas are the most abundant delta type and are also potentially the most at-risk to human-caused changes, owing to the effects of wave-driven sediment transport processes and the relatively short timescales on which they operate. Despite this, the processes controlling wave-influenced growth are poorly understood, and the role of fine-grained cohesive sediment (mud) is typically neglected. Here we simulate idealized river deltas in Delft3D across a range of conditions to interrogate how relative wave-influence and fluvial sediment composition impact delta evolution on decadal-centurial timescales. Our simulations capture the barrier-spit formation and accretion process characteristic of prograding wave-influenced deltas, consistent with behaviors observed in natural systems. Barrier-spit accretion exhibits multi-decadal cyclicity driven by subaqueous accumulation of fluvial sediment near river mouths. Using a range of metrics, we quantify how waves and mud influence delta morphology and dynamics. Results show that waves stabilize and simplify channel networks, smooth shorelines, increase shoreline reworking rates, reduce mud retention in the delta plain, and rework mouth bar sediments to form barrier-spits. Higher fluvial mud concentrations produce simpler and more stable distributary networks, rougher shorelines, and limit back-barrier lagoon preservation. Our findings reveal distinct controls on shoreline change between river-dominated and wave-influenced deltas and demonstrate that mud plays a critical role in delta evolution, even under strong wave influence. These insights could enhance paleoenvironmental reconstructions and inform predictions of delta responses to climate and land-use changes.

The Froude number (Fr) is an important parameter that affects turbulence structures, bedload transport, and bedforms in mountain rivers. In a prior study by Liu et al. (2024, https://doi.org/10.1063/5.0222673), turbulence structures in open channel flow through a boulder array placed on seven layers of spheres (comprising the channel bed), with Fr ranging from 0.15 to 0.89, have been quantified. This paper investigates the drag (F_x) and lift (F_z) forces on the spheres of the top layer of the bed surrounding the boulders and their response to the boulder-induced turbulence and hyporheic flow. The time-averaged drag and lift forces (F_x and F_z) in the vicinity of boulders reach up to 6 and 4 times the reach-averaged shear force (F_sph), respectively, and their standard deviations are even higher, being 2.9 or 4.4 times the time-averaged forces, respectively. Consequently, maximum instantaneous forces on the surrounding bed spheres can approach values of an order of magnitude greater than F_sph. The pre-multiplied spectra of force fluctuations, which decompose the total fluctuations into components of different length scales, reveal three predominant contributions: (a) a 1.6D length-scale contribution at high Fr, (b) a 2.1D length-scale contribution at low and intermediate Fr, and (c) a 4.5D length-sale contribution at low and high Fr, where D is the boulder diameter. These correspond to elongated rollers, oscillating boulder wakes, and hyporheic flow, respectively. Cross-correlations between force and velocity fluctuations indicate that forces on the bed spheres in boulder wakes are governed by hyporheic flow at low and high Fr, and by vortex shedding at intermediate Fr. The contributions from hyporheic flow to total drag and lift force fluctuations are highest at high Fr, reaching up to approximately 30% and 50% locally, respectively. Finally, regions of sediment deposition are predicted based on three types of criteria: near-wall shear stress, time-averaged forces, and instantaneous forces, among which regions based on the instantaneous forces align remarkably well with the deposition patterns observed by Papanicolaou et al. (2018, https://doi.org/10.1029/2018jf004753) for different Fr.

Glaciers worldwide are retreating because of climate change. However, local human activities also influence their dynamics. Here, we model the impact of gold mining operations on Davydov Glacier in the Inner Tien Shan, Kyrgyzstan, from the Little Ice Age through 2100 under different Shared Socioeconomic Pathway climate scenarios using a 3D thermomechanical ice flow model. Satellite observations and model simulations reveal that mining activities over the past two decades shortened the Davydov Glacier by ∼2 km in the central section and reduced its volume by 160 million m³, compared to a scenario where the glacier would have solely evolved due to climate forcing. If mining ceases, the glacier could temporarily advance by up to 100 m. However, by 2060, the glacier will retreat beyond the mining site, with no differences between mining and no-mining scenarios. By 2100, volume losses range from 40% to 99%, depending on the climate scenario. A return to the Little Ice Age (LIA) climate could allow full recovery within 500 years. However, mining-induced landscape changes would cause the glacier to regrow under LIA conditions to more than twice its original extent, reaching up to 2.5 times its original volume and a thickness of up to 600 m. This study highlights how human activities near glaciers can significantly impact their geometry, stability, and long-term evolution, emphasizing the lasting consequences of landscape modifications on glacier response.

The Antarctic ice shelves significantly influence global sea level changes by buttressing the grounded ice sheet and regulating ice flux discharge. Rift propagation and coalescence can lead to large tabular iceberg collapse, thereby altering ice shelf stability and accelerating ice flux discharge into the ocean. To explore rift propagation patterns on the Ross Ice Shelf, we extracted rift geometry over the past two decades using satellite imagery and analyzed transient rift propagation dynamics and energy release using seismic observations. We also discussed the relationship between rift propagation and environmental forcings, and identified rift propagation mechanisms through strain rates. The results indicate significant differences in rift propagation patterns, with rifts being more sensitive to environmental forcings than crevasses. Rift propagation exhibits distinct seasonal and diurnal patterns, where seasonal variations are regulated by ice surface temperature, sea ice concentration, and significant wave height from combined wind waves and swell, while diurnal variations are closely related to ocean tidal fluctuations. Rift elongation is primarily driven by tensile stress but is effectively constrained by ice flow suture zones. In contrast, rift widening is enhanced through the combined effects of ice rise shear stress and oceanic erosion. By integrating satellite imagery and seismic observations, this study explores rift propagation patterns across both decadal-scale changes and transient dynamic processes, providing key insights into the impact of rift propagation on ice shelf stability. These findings contribute to improving predictions of Antarctic ice sheet mass balance and global sea level change.

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.