Journal of Geophysical Research: Earth Surface最新文献

This study isolated hydro-morphodynamic mechanisms leading to mangrove propagule anchoring and seedling dislodgement under erosive flows. Red mangrove (Rhizophora mangle) propagules self-anchored in estuarine sediments over 112 days under simulated tidal pulses. Seedlings were tested under erosive flows at 1 week, 2 weeks, and 1 month after anchoring. One-month-old seedlings exhibited notable resistance, withstanding peak velocities of 17–22 cm/s and severe erosion (mean erosion depth 8.3 ± 0.9 cm, volume 1.9 × 104 ± 2.5 × 103 cm³). Seedlings oriented against the flow were more vulnerable to uprooting. Two-week-old seedlings oriented with the flow had a greater mean erosion depth (4.4 ± 1.2 cm, p < 0.05) than seedlings oriented upstream (1.5 ± 0.6 cm). Consistent with dislodgement mechanisms proposed in prior studies, the results conformed to three distinct uprooting pathways: instantaneous uprooting by hydrodynamic forces without bed erosion (Type I), removal facilitated by local scour around the roots of seedlings (Type IIa), and removal after large-scale bed degradation (Type IIb). Erosion depth and volume at the time of dislodgement varied systematically with the geomorphic mechanism of removal. Seedling resistance was closely linked to rooting structure; seedlings uprooted by Type IIb exhibited the longest single root length (mean: 8.6 ± 0.6 cm), highest total root length (mean: 134.4 ± 19 cm), and greatest root volume (mean: 61.1 ± 9.2 cm³).

Surge-type debris flows propagate as a sequence of surges, forming gradually thickening in situ deposition layers between surges that dynamically alter channel-bed conditions. Seismic recordings from Jiangjia Ravine reveal a progressive attenuation of ground motion amplitude with surge sequence, despite comparable flow magnitudes—indicating a decoupling between flow scale and seismic response. We attribute this to the accumulation and liquefaction of inter-surge deposition layers, rather than pre-existing deposits. To quantify this mechanism, we adopt an effective transmission parameter (ξ) within a fluvial seismology-based framework, and propose a sigmoid function linking ξ to normalized deposition layer thickness (H*). This formulation significantly improves the prediction of seismic power spectral density (PSD) across surges and provides a transferable approach to characterize subsurface flow–bed interactions. Our findings underscore the critical role of bed structure evolution during flow in modulating debris-flow-induced seismic signals, with implications for real-time monitoring and early warning in sediment-rich catchments.

This study employs the FUNWAVE-TVD phase-resolving model to simulate the formation and evolution of Low-energy Transverse Finger Bars (LTFBs) under idealized conditions representative of El Trabucador beach in Spain. The objective is to investigate the underlying mechanisms driving sandbar development and the factors influencing their geometric characteristics. The results confirm that wave-induced cross-shore transport over gentler-than-equilibrium profiles plays a fundamental role in LTFB formation. Experiments conducted on non-erodible beds reveal that double circulation cells can emerge independently of sediment transport. In contrast, on erodible beds, these double circulation cells transition into single circulation cells due to wave refraction caused by the developing bar structures. This transition underscores the dynamic coupling between hydrodynamics and morphology. Sensitivity analyses of the bed friction coefficient show the complex interplay between hydrodynamics and morphodynamics: higher bed friction produces more regular, thinner bars closely aligned with flow patterns, whereas lower bed friction leads to irregular, shorter bars less connected to flow patterns. Despite computational constraints limiting the full replication of natural systems, this study successfully captures key features of LTFBs and supports the formation mechanism proposed in recent literature. The alongshore wavelengths of the simulated sandbars align well with the smallest transverse bars observed at El Trabucador and reported in previous numerical studies.

The East Antarctic Ice Sheet (EAIS) formed circa 34 million years ago and now contains an ice volume equivalent to ∼52 m of global sea-level rise. Although the EAIS is approximately in balance today, there is substantial uncertainty regarding the sensitivity of sectors underlain by low-lying bed topography to future climate and ocean warming. This is especially pertinent for Coats Land (eastern Weddell Sea), where geological records of past ice-sheet changes are sparse. Here, we use airborne radio-echo sounding and magnetic data, satellite imagery, and isostatic modeling to map the subglacial geomorphology of Coats Land for the first time and constrain the regional geological and ice-sheet history. Our mapping reveals topographic features such as tilted highlands and deep, asymmetric depressions, which likely formed via regional extension associated with Gondwana breakup, concomitant with early Jurassic magmatism. We also document low-relief, seaward-dipping surfaces that we infer to be remnants of coastal plains formed by fluvial erosion after continental breakup. Subglacial troughs that were incised into (i.e., post-date) these pre-glacial erosion surfaces were selectively eroded by ice flowing south-to-north. The ice within these troughs is stagnant today, indicating that they did not form beneath the modern (east-to-west-flowing) EAIS. Based on local geomorphological and geochronological evidence, we infer that these troughs were most likely incised during an interval of the Oligocene–Miocene (ca. 34–14 Ma) when the regional ice configuration and bed topography were significantly different from today. Subsequent EAIS reconfiguration switched off these early outlets and facilitated widespread landscape preservation beneath regionally non-erosive ice.

Low-lying beaches, important ecological and socio-economic assets, are vulnerable to storm erosion and flooding impacts, which are expected to increase due to climate change. This conceptual study uses the 2DH XBeach model to simulate the influence of the initial topobathymetric shape on the washover deposit formation during a beach overwash caused by an extreme storm, including a quantification of the wave chronology uncertainty. The employed initial alongshore-uniform (AU) topobathymetries have different cross-shore profiles, representing the real variability of Mediterranean beaches. The analysis also incorporates the presence of common alongshore-rhythmic morphological patterns, such as megacusps, rhythmic dunes, and crescentic bars, with varying wavelengths. The results in the AU scenarios show that washover deposits are also periodic alongshore, forming through a 2D self-organization process that establishes the natural wavelength of the modeled dry beach. The presence of megacusps in the initial topobathymetry can enhance washover deposit volumes up to a factor 4, especially for large initial wavelengths. Rhythmic dunes also influence the spatial distribution of the deposits, while crescentic bars generally have little direct effect on the deposit formation. These findings highlight the importance of using real and up-to-date topobathymetric data, including the presence of common alongshore-rhythmic morphological patterns, in modeling storm impacts on beaches. Furthermore, modeling studies under future climate change scenarios, must consider the uncertainty associated with the unknown shape of the topobathymetry and wave group chronology. The results could also have implications for developing effective coastal management strategies.

Glacial erosion and sediment evacuation are key in shaping polar and mountain landscapes and influencing downstream ecological and social systems. The glacier dynamics and hydrology responsible for these processes are closely linked to hydrological and climatic (hydro-climatic) conditions. Recent studies indicate that sediment export and glacier erosion respond strongly to hydro-climatic variations across millennia to individual events lasting hours to weeks. (a) Sedimentary records and numerical ice flow models indicate increased erosion during glacier retreat following climate warming. (b) Rising equilibrium line altitudes due to climate change enhance meltwater access to subglacial sediment, increasing sediment export markedly. (c) Changing meltwater dynamics over hydrological events, particularly daily variations in melt or precipitation events, strongly impact sediment transport capacity. We propose that hydro-climatic changes from millennia to hours, along with the climatic conditions themselves, provide a useful framework for examining glacier erosion. The sensitivity of glacier erosion and sediment export to hydro-climatic conditions likely introduces timescale biases when averaging glacier erosion over long or short periods. Major uncertainties in interactions amongst processes and their relevant timescales underscore the need to better understand climate change impacts on glacierized landscapes. Emerging observational methodologies combined with numerical models may provide new insights into the complex and interacting dynamics controlling glaciers' impact on sediment export.

Glacial erosion and sediment evacuation are key in shaping polar and mountain landscapes and influencing downstream ecological and social systems. The glacier dynamics and hydrology responsible for these processes are closely linked to hydrological and climatic (hydro-climatic) conditions. Recent studies indicate that sediment export and glacier erosion respond strongly to hydro-climatic variations across millennia to individual events lasting hours to weeks. (a) Sedimentary records and numerical ice flow models indicate increased erosion during glacier retreat following climate warming. (b) Rising equilibrium line altitudes due to climate change enhance meltwater access to subglacial sediment, increasing sediment export markedly. (c) Changing meltwater dynamics over hydrological events, particularly daily variations in melt or precipitation events, strongly impact sediment transport capacity. We propose that hydro-climatic changes from millennia to hours, along with the climatic conditions themselves, provide a useful framework for examining glacier erosion. The sensitivity of glacier erosion and sediment export to hydro-climatic conditions likely introduces timescale biases when averaging glacier erosion over long or short periods. Major uncertainties in interactions amongst processes and their relevant timescales underscore the need to better understand climate change impacts on glacierized landscapes. Emerging observational methodologies combined with numerical models may provide new insights into the complex and interacting dynamics controlling glaciers' impact on sediment export.

This study presents the first detailed characterization of bedforms within the Magdalena River Estuary (MRE), a large tropical estuary with marked seasonal variability. Three sets of high-resolution bathymetric surveys conducted under contrasting climatological conditions were used to quantify bedform morphology and analyze their temporal and spatial variability. Bedform dynamics were linked to hydrodynamic and sedimentologic processes previously documented for the MRE. The bedforms of the MRE were compared with those of several estuaries and rivers using a newly introduced statistical approach based on the Mahalanobis distance applied to bedform geometric parameters. This statistical method measures the difference between a set of features and a reference group, allowing for the comparison of bedform characteristics across systems. The results show that during the low-discharge season, salt-wedge intrusion into the MRE inhibits the development of bedforms, resulting in a lower-stage plane bed, whereas larger dunes become predominant along the river channel when the salt wedge is flushed out of the estuary during high discharges. However, the symmetric shape of these dunes reflects the tidal influence on the river channel dynamics even during high discharges. The Mahalanobis distance demonstrated a quantitative framework for discriminating between fluvial (unidirectional) and estuarine (bidirectional) flow regimes based on bedform geometry. This research also proposes a nomenclature for standardizing geometric features in bedform studies.