Journal of Geophysical Research: Earth Surface最新文献

Combined flows in which the unidirectional flow is a turbidity current that is superimposed by gravity waves, have complex flow dynamics. We present data from laboratory-generated combined flows, that demonstrate the effects a wave field has on turbidity current sediment transport and the dynamics of mixing. The combined flows had a net increase in down slope sediment transport and the measured wave velocities within the body of the combined flows were both greater in magnitude and statistically distinct from those measured in the wave field alone. To explain these findings, we applied a turbulence model and an eddy viscosity model to our measured velocity data of the current. We found that the sediment transport effects are explained by two distinct modes of waves influence over the dynamics of current mixing. In one mode, combined flows are isolated from the ambient fluid in a “jet-sharpening” process. In the other mode, the combined flows' Reynolds stress is enhanced, and both cases result in increased sediment transport. Our results have important implications for understanding modern transport in wave-influenced hyperpycnal flows in the modern and geologic record.

Understanding ice dynamics across varying temporal scales is essential for accurately assessing the contribution of the Antarctic Ice Sheet to global sea level rise. Investigations of seasonal timescale ice dynamics illuminate how glaciers respond to environmental forcings and improve the accuracy of discharge-based mass balance estimates. Here, we generated a high-precision, monthly ice velocity field for Byrd Glacier by combining ITS_LIVE image-pair products with ALOS-2 offset tracking measurements. We then applied seasonal signal detection methods to systematically analyze the ice velocity variations. Our results reveal a distinctive dipole-like seasonal flow pattern of Byrd Glacier: from austral spring through summer, ice velocities decrease by an average of ∼40 m/yr in the grounding zone, while flow speeds on the downstream ice shelf increase by ∼20 m/yr. Empirical orthogonal function (EOF) analysis indicates that these seasonal variations are primarily governed by physical processes operating at the grounding zone. We propose that the dipole signal is best explained by interactions between seasonal incursions of high-salinity shelf water (HSSW) and the subglacial hydrological system. Although sea surface height anomalies have been suggested as a potential driver, their modeled amplitudes and in-phase patterns indicate that they are unlikely to be the dominant contributors. In contrast, the HSSW–subglacial hydrology framework provides a consistent explanation for both the velocity magnitude and the out-of-phase behavior. Although further observations and modeling are needed, findings highlight the complexity of Antarctic glacier seasonality and the need for improved observations and coupled modeling to clarify mechanisms and implications for ice sheet mass balance.

During the late Cenozoic, the outward growth of the Tibetan Plateau significantly influenced the tectonic, climatic, and geomorphic evolution of surrounding regions. The Qinling Mountains, at the eastern front of the Tibetan Plateau, have been involved in plateau expansion since the late Cenozoic, and the Hanzhong Basin, its unique late Cenozoic intermontane basin, preserves rich information on plateau growth. In this study, geomorphic indices, apatite fission track dating, and river-profile inversion were conducted on catchments around the Hanzhong Basin. Results reveal that drainages north of the Hanzhong Basin generally exhibit high steepness indices, especially those in the west, but southern drainages show greater variation. River-profile inversion documents two phases of accelerated relative rock-uplift at 15-10 Ma and 5-2 Ma on northern drainages. We interpret that high steepness indices and uplift rates in the west reflect tectonic forcing, expressed as pronounced relative rock-uplift and enhanced subsidence of the western basin, whereas the heterogeneous steepness in the south reflects the differential uplift. Integrating tectonic and sedimentary evidence, we propose a new surface deformation model in which the outward expansion of the Tibetan Plateau since ∼15 Ma has forced the rigid Bikou Terrane to wedge eastward, thus reactivating the Mianlue Fault and inducing extensional faulting within the Qinling Mountains and subsidence of the Hanzhong Basin. Synchronously, a series of transpressive faults formed in the Micang Shan and governed the landscape.

In mountainous regions, risk mitigation requires an understanding of sediment-transport processes. We present new experiments conducted on a steep slope (33%) to study the transition from bedload to debris flow. The flume design was adapted to mimic alpine streams: instead of studying the mobility of a channel bed composed of uniform-sediments, we generate pulses of sediment by injecting water over a self-formed deposit of poorly sorted mixtures located at the flume entrance. The setup comprises ultrasonic sensors measuring the height of the water-sediment mixture and a force sensor measuring normal and tangential forces exerted on the bed. The experiments show that the highest discharges generate bedload. At lower discharges, mass failure of the deposit generates two regimes: a “static-dynamic” regime, where a granular pulse propagates without a clear water phase, and a “full-dynamic” regime, where concentrated pulses are driven by water flows. In both regimes, pulses are vertically and longitudinally sorted: the front contains coarse particles, the tail contains finer particles, and the body a mix, with coarser particles concentrated near the surface. Force analysis shows that, in the static-dynamic regime, mobility is governed by resistance at the front and thrust from body weight. In the full-dynamic regime, weight alone cannot explain the observed stresses, suggesting roles for additional factors, such as non-hydrostatic water pressure, acceleration, and vertical transfers. In both regimes, front resistance controls pulse mobility. Basal friction coefficient ($��{\mu }_b�$) analysis further shows that the transition to bedload occurs at the threshold discharge required to mobilize coarse particles alone in the channel.

This study presents the first high-resolution spatial and temporal analysis of wind flow, sediment transport and topographic evolution under simultaneous storm conditions across two morphologically contrasting beach-dune systems, characterized by a gently sloping dune face (11°) and a steep, scarped dune face (36°). Results demonstrate that the dune slope strongly controls near-surface wind acceleration, the development of secondary airflow structures (amplitude, spatial positions), and the continuity of sediment transport pathways. Over the gentle slope, airflow accelerates progressively up the stoss face, promoting sustained, landward-directed sediment fluxes across the entire beach–dune system and enabling efficient sediment recycling. In this configuration, beach-derived contributions account for only 12%–15% of the total sediment flux. In contrast, the steep scarp induces flow deceleration and separation at the dune toe, limiting sediment transfer from the beach and favoring seaward-directed transport associated with secondary vortices at the crest. These contrasting airflow organizations result in fundamentally different storm responses. The gently sloping dune undergoes landward translation with minimal net volume change, whereas the scarped dune experiences dominant marine erosion, leading to a 4 m retreat of the dune front and a sediment loss of ∼30 m³ m⁻¹. A new conceptual model of storm-driven airflow over contrasting dune morphologies is proposed, illustrating how inherited dune slope governs airflow structure and circulation patterns. Overall, these results identify inherited dune morphology as a primary control on airflow organization, sediment pathways, and dune resilience during extreme events.

The integration of the Green and Colorado Rivers shifted the continental drainage divide of North America, marking a key event in the hydrological and biogeographical evolution of the continent. Sedimentological and stratigraphic evidence shows that for integration to occur, the Green River likely cut through the Uinta Mountains between 8 and 1.5 Ma, long after the range formed more than 50 Ma. Though the Uinta Mountains have not been subject to active compressional tectonics since 50 Ma, the geomorphology of the range hints at some post-orogenic process influencing the topography of the range. The river networks draining the range preserve relict topography, which may form due to base-level fall or an increase in the rock uplift rate. By using a 2-D topographic inversion, we quantify the elevation change the relict topography has experienced relative to past base level. Based on the inferred pattern of elevation change to base level, we suggest the relict topography was most likely created by a rock uplift rate increase. Seismic tomographic images evidence a lithospheric drip beneath the range as the most likely driver of enhanced rock uplift. An estimate of the drip's velocity, and its imaged depth suggest that the drip detached between 2.3–4.7 Ma, matching the response time of the relict river network (2.1–4.6 Ma). Importantly, this fits existing age constraints for Green River incision through the Uinta Mountains, providing a mechanism for crustal deformation that could explain this event. Our findings demonstrate the profound impacts of geodynamic processes on topography, surface hydrology, and biogeography.

We present idealized 3-D discrete element simulations exploring how varying boundary roughness and grain-size distribution affect bulk granular-rheology and basal-force distributions. Boundary roughness has a direct control on the internal static friction coefficient. Further, when flows enter a highly energetic collisional regime, relatively smooth substrates promote the development of a dense plug-like flow, that is, supported by a basal granular temperature an order of magnitude greater than what is measured within the bulk. We show that in the low velocity limit, basal-force distributions are not only sensitive to averaged roughness but also sensitive to how the substrate is constructed. Additionally, varying the grain-size distribution by increasing the proportion of fine-particles increases internal energy fluctuations. We use this observation to define a dimensionless parameter comparing the changes in basal-force fluctuating energy and internal energy fluctuations as measured by the granular temperature. This scaling shows that a redistribution of fluctuating energy ultimately decreases the total power of basal-force spectra. We conclude this study by performing 1-D steady-state surface-wave propagation calculations, using basal-force data from our simulations as a source. Using the method of spectral moments shows that the dispersion of power in observed signals can be used to track changes in flow regime. The Green's functions used in the present study yield data that underscores the importance of receiver placement and suggests there is an optimal distance at which these changes can be observed. We suggest that a similar exercise can be used with empirical Green's functions to inform deployment strategies.

Natural deposits of clastic sediments, often attributed to powerful palaeofloods, are characterized by thick parallel laminations of sand to fine-gravel-sized particles. These deposits traditionally have been explained by suspended sediment deposition onto rapidly aggrading beds with minimal bedload transport. However, the physical mechanisms controlling the transition from turbulent suspension to laminated deposition and the role of particle interactions in this process remain poorly constrained. In this study, we test this hypothesis within an analytical model that combines an understanding of turbulent, high-concentration flows with sediment deposition. We propose that the turbulence of clear water is modulated by sediment particles, altering the hydrodynamics of the sediment-laden flow and promoting laminated deposition. The results show that extremely high near-bed shear stresses during palaeofloods can suspend both coarse gravel (>100 mm) and sand-sized particles at high concentrations. Larger particles undergo significant comminution due to particle-on-particle interactions, reducing their size, while finer particles are enveloped in smaller turbulent eddies, leading to a saturated suspended sediment profile near the bed. This saturation, dominated by finer particles (around 1 mm and smaller), suppresses turbulence and facilitates the deposition of fine granules and sand as laminated bed deposits. The findings align with natural clastic deposit characteristics and demonstrate that suspended sediment dynamics, rather than bedload transport, exert the primary control on flow behavior and deposition during palaeofloods. A conceptual model is proposed to explain the development of fine-gravel and sand laminations in high-velocity flows, providing new insights into the formation of ancient flood deposits.

Geological materials have inherent uncertainties from variability in particle properties, such as inter-particle friction. Traditional deterministic models overlook this variability, leading to inaccurate predictions of geophysical flow behavior. We developed a novel 3D discrete element method framework incorporating stochastic field theory, capturing granular materials' random flow behavior. Combined with ring shear tests and PFC, we also propose a virtual ring shear test. The effect of coefficient of variation (COV) and correlation distance $��l_z�$ of inter-particle friction coefficient μ on particle mechanical properties is discussed. Monte Carlo simulations show ignoring μ uncertainty does not affect its strain softening and strengthening characteristics, but may overestimate shear strength. Under quasi-static shear, shear stress-shear displacement curves of heterogeneous samples with nearly identical particle arrangement but varied properties formed curve clusters of a certain width. The cluster width positively correlates with both $��l_z�$ and COV. Additionally, μ heterogeneity does not affect microscopic force chain's overall evolution trend, but significantly impacts its characteristic peak value. Specifically, as the average sliding friction coefficient decreases, the mean contact force reduces while the mean coordination number increases. Furthermore, we propose shear strength reduction coefficients for different confidence levels. These findings provide valuable insights into granular soil mechanical behavior during landslide evolution and hazard assessment.

Flow regime transitions from rock-ice avalanches to debris flows remain insufficiently quantified, particularly in terms of the relative influence of internal meltwater production versus external water entrainment. On 17 October 2018, a large rock-ice avalanche-debris flow occurred in the Sedongpu gully, Southeastern Tibet, traveling over 10 km and impounding the Yarlung Tsangpo River to form a landslide-dammed lake. Here we reconstruct the evolution of this catastrophic event using field investigations and a state-of-the-art multiphase thermomechanical model, and assess how ice/snow melt and substrate entrainment influence the flow regime transition. Our results suggest that the highly saturated entrained moraine fosters the swift transition from rock-ice avalanche to water-rich debris flow, increasing its mobility and destructive potential. Water influx from the saturated substrate, which resulted from glacial meltwater and precipitation, was a more dominant driver of the flow regime transition than internal ice melt, with notable ice fragments remaining within the final deposits. Climate-driven variations in substrate moisture and composition govern the flow regime as a rock-ice granular avalanche or debris flow, highlighting the influence of seasonal and climatic changes on shaping flow behavior and ultimate runout. Recognizing this external control is crucial for anticipating rock-ice flow behaviors in future warming scenarios.