Journal of Geophysical Research: Earth Surface最新文献

We analyze the dynamics of evolving lava-fed deltas through the use of shallow-layer mathematical models and analog laboratory experiments. Numerical and asymptotic solutions are calculated for the cases of planar and three-dimensional flows fed by a point source upstream of the shoreline. We consider several modes of delta formation: a reduction in the driving buoyancy force; an enhanced viscosity of the submerged material; and the production of a granular subaqueous platform, over which a subaerial current can propagate. These modes of delta formation result in different behaviors. Under a steady supply of fluid upstream, the buoyancy-driven case develops a solution with a steady subaerial delta and a subaqueous current which propagates at a constant speed, while the granular platform model extends the delta indefinitely. We determine a late-time power-law relation for the shoreline extent with time in this case. When the viscosity contrast is large, the model with an enhanced subaqueous viscosity is shown to mimic the initial dynamics of the granular platform model, but ultimately reaches a steady shoreline extent at sufficiently late times, as for the buoyancy-driven model. The distinct behaviors of these models are further illustrated through laboratory experiments, utilizing the gelling reaction of sodium alginate solution in the presence of calcium ions as a novel analog for the abrupt rheological changes that occur when lava makes contact with water. These experiments provide quantitative verification of the buoyancy-driven model in the absence of the reaction, and demonstrate the effects of a subaqueous platform qualitatively in its presence.

The spatial arrangement of grains in gravel-bed rivers significantly influences sediment transport, flow resistance, and ecological conditions. Inferring historical flow information from spatial grain arrangements has garnered considerable interest among researchers. This study presents a robust and feasible method for such inference, focusing on quantitative approaches to estimate grain arrangement through inclination analysis. Two parameters based on inclination analysis are proposed for estimating grain arrangement. Quantitative relationships between these parameters and grain arrangements are established using artificially generated grain surfaces with predefined grain features. Additionally, the degree of imbrication, represented by the standard deviation of inclination curves, is examined using these generated surfaces. At the macroscopic level, the irregular inclination curve of a riverbed arises from the spatial variability of local hydrodynamic processes, leading to different local grain arrangements. Leveraging this feature at the microscopic level, the spatial distribution of grain orientation, or the grain azimuth field, is obtained using the proposed quantitative relationship. To explore the relationship between this grain azimuth field and flow velocity directions, a three-dimensional turbulent model based on Detached Eddy Simulation is deployed to simulate the detailed flow field near a gravel bed surface. Comparisons between the grain azimuth field and the flow velocity field highlight similarities, affirming that historical flow direction can be inferred from grain arrangement information. This study contributes to advancing the understanding of the intricate connections between grain arrangements and historical flow dynamics in gravel-bed rivers.

Mangrove forest development critically depends on the establishment and survival of seedlings. Mechanistic insights into how water levels, waves and bed level dynamics influence the establishment process of individual mangrove seedlings are increasing. However, little is known about how spatial and temporal changes in water levels, waves and bed level dynamics across elevation gradients in mangrove forests facilitate/limit seedling dynamics. For this study, a new seedling establishment and growth model was integrated into a process-based hydrodynamic and morphodynamic numerical model. This biophysical model was applied to a fringing mangrove forest located in the southern Firth of Thames, Aotearoa, New Zealand. This study quantifies the increasing establishment density and survival probability of mangrove seedlings from the lower-elevated unvegetated intertidal flat toward the higher-elevated mature mangrove forest. Three cross-shore zones with distinctive seedling dynamics were identified: (a) a zone with daily tidal inundation where seedling dynamics are episodic and limited by the dispersal of individual propagules that rapidly anchor to the substrate by root growth, (b) a zone with daily to bi-weekly tidal inundation where seedling dynamics respond to variations in spring-neap tidal cycles and, (c) a zone with less than bi-weekly inundation where seedling dynamics are governed by high propagule supply and seedling survival probability. The seedling establishment density and survival probability are dominated by annual extremes in tidal hydroperiod and bed shear stresses, respectively. The obtained parameterizations can be used to incorporate seedling dynamics in decadal-timescale mangrove forest development models that are instrumental for mangrove management and restoration.

Supraglacial lakes have been observed to drain within hours of each other, leading to the hypothesis that stress transmission following one drainage may be sufficient to induce hydro-fracture-driven drainages of other nearby lakes. However, available observations characterizing drainage-induced stress perturbations have been insufficient to evaluate this hypothesis. Here, we use ice-sheet surface-displacement observations from a dense global positioning system array deployed in the Greenland Ice Sheet ablation zone to investigate elastic stress transmission between three neighboring supraglacial lake basins. We find that drainage of a central lake can place neighboring basins in either tensional or compressional stress relative to their hydro-fracture scarp orientations, either promoting or inhibiting hydro-fracture initiation beneath those lakes. For two lakes located within our array that drain close in time, we identify tensional surface stresses caused by ice-sheet uplift due to basal-cavity opening as the physical explanation for these lakes' temporally clustered hydro-fracture-driven drainages and frequent triggering behavior. However, lake-drainage-induced stresses in the up-flowline direction remain low beyond the margins of the drained lakes. This short stress-coupling length scale is consistent with idealized lake-drainage scenarios for a range of lake volumes and ice-sheet thicknesses. Thus, on elastic timescales, our observations and idealized-model results support a stress-transmission hypothesis for inducing hydro-fracture-driven drainage of lakes located within the region of basal cavity opening produced by the initial drainage, but refute this hypothesis for distal lakes.

Editors of the Journal of Geophysical Research—Earth Surface express their appreciation to those who served as peer reviewers for the journal in 2023.

This study investigates the upper Magdalena river basin (Colombia), which is characterized by tectonic activity, tropical climate, heterogeneous lithological assemblages, and anthropic influence. It aims to comprehend factors controlling sediment generation, flux, and composition by incorporating petrographic data from 27 recent fluvial samples along with geochemistry, geomorphological parameters, historical precipitation, land cover, landsliding and suspended sediment load data. The analysis shows mismatches between sand composition and drainage lithology distribution. A new set of endmember mixing models is presented, quantifying the impacts of erodibility, sand generation potential (related to lithology), and sediment connectivity between hillslopes and river outlets (related to geomorphology). Results show enhanced sediment generation from sedimentary rocks (up to 40%) due to high erodibility, and decreased sediment flux from low- to medium-grade metamorphic rocks (up to 60%) due to controlling morphometric parameters. Overrepresentation of plutonic and high-grade metamorphic rocks and underrepresentation of volcanic rocks (up to 100%) are controlled by mineralogical and textural parameters. Enhanced landsliding activity in areas with volcanic activity occasionally overshadows basin-wide compositional trends driven by morphological and lithological characteristics, as it controls rare overrepresentation of volcanic and low-grade metamorphic detritus in the sand fraction. Sediment retention by hydroelectric dams significantly decreases suspended sediment flux by 30%, while deforestation plays a minor role in sediment flux. This study underscores the importance of coupling sediment generation, geomorphology and the distribution of stochastic events related to seismic activity in any sediment production-focused study and for developing numerical models in Quantitative Provenance Analysis (QPA).

The composition of 27 fluvial silt and clay sediments was used in this study to identify and quantify the processes in the upper valley of the Magdalena river in South Colombia. The combination of seismic activity, intense precipitation, and landsliding resulted in limited chemical weathering and a very efficient transfer of weathered products to the transfer zone of both tributary rivers and the main trunk. Inputs from plutonic, high-grade metamorphic, volcanic, and low- to medium-grade metamorphic lithologies vary in coarse silt-sized versus fine silt- and clay-sized sediments, reflecting inherited textural parameters and mineralogy. Plutonic and high-grade metamorphic rocks mostly produce sand-sized sediments, up to two times more than coase silt and up to 10 times more than fine silt to clay. The prevalence of siltstone in the area enhances the contribution of sedimentary rocks to fine silt and clay (up to 50% higher than to sand). Volcanic rocks mainly produce coarse silt (up to 2.5 times more than sand). Low-grade metamorphic detritus is enriched in silt and clay (up to 5–7 times). These findings highlight the critical role of lithology in regulating sediment generation. The study's approach can establish or modify factors modeling lithological control on suspended sediment flux, such as in the BQART equation.

Many landslide models assume a fully deformable body without any resistance against deformation. However, in reality, landslide bodies can display negligible to large deformation during motion. Examples for limited deformation include the prehistoric giant landslides of Flims and Köfels, or the Vajont landslide of 1963, where the structure of rock largely remained intact and the slides did not evolve into rock avalanches. Here, we propose a novel mechanical model for the controlled deformation of landslides. The model is based on the principle of material strength or resistance and includes a user-specified function that reflects the mechanisms (internal friction, cohesion, viscosity, and yield strength) that act against the deformation induced by the free-surface or the hydraulic pressure gradient of the landslide. This controls the landslide deformation and, in turn, also the motion and run-out, and offers a unique possibility to describe the landslide motion ranging from a fully non-deformable body sliding along the mountain slope to a completely fluidized motion without any resistance against the force associated with the free-surface pressure gradient. The latter is the situation often considered for the motion of granular flows such as avalanches of snow or rock, or debris flows. The former can play a substantial role in the dynamics, however, has not yet been considered in mass flow simulations, severely limiting the applicability of those models. We demonstrate the performance of the new model and its applicability, also with the advanced open-source computational mass flow simulation tool r.avaflow.

Titanite is a versatile recorder of crystallization age, temperature, and host lithology, via the U–Pb system, the Zr-in-Ttn thermometer, and elemental composition, respectively. The paragenesis of titanite renders it especially useful for tracing detritus derived from lithologies that are infertile for the commonly used detrital zircon U-Pb chronometer, such as sub-anatectic metamorphism of calc-silicates. Despite these advantages, detrital titanite analysis is underemployed, in part because the U–Pb system in titanite is often complicated by the incorporation of both inherited radiogenic Pb from precursor minerals during metamorphic reactions, and also bulk crustal common-Pb. Recent systematic analyses of large titanite compositional data sets from diverse source rocks have revealed that the elemental composition of titanite is provenance-specific. Here, we apply a workflow that incorporates a machine-learning classifier to a large and representative compositional database for titanite, encompassing >11,000 analyses, with c. 6,700 points passed to our model. Only medians of the subcompositions for 205 rocks are used for our model. We reliably discriminate (>90%) between metamorphic and igneous titanite. Application of this classifier to a detrital case study from the Nanga Parbat-Haramosh syntaxial massif of the western Himalaya reveals that titanite of different compositions formed during different orogenic events. Furthermore, titanite with significant common Pb solely derives from medium/low grade metasedimentary rocks. The method described here offers a pathway to increase the specificity of the provenance information derived from titanite; however, the published corpus of titanite data will have to be much larger before multi-class source-rock discrimination can be achieved reliably.

The role of coherent airflow structures capable of setting gravel-sized particles in motion is studied theoretically and experimentally. Specifically, a micromechanical model based on energy conservation is proposed to describe the incipient motion of large-particles ranging from rocking (incomplete entrainment) to incipient rolling (full entrainment). Wind tunnel experiments were conducted on an aerodynamically rough bed surface under near-threshold airflow conditions. Synchronous signals of airflow velocities upwind of the test particles and particle displacement are measured using a hot film anemometer and a laser distance sensor, respectively, from which coherent airflow structures (extracted via quadrant analysis) and particle movements are interlinked. It is suggested that the incipient motion of gravel-sized particles (rocking and rolling) may result from sufficiently energetic sweep events corresponding to aerodynamic drag forces in excess of the local micro-topography resistance. However, full entrainment in rolling mode should satisfy the presented work-based criterion. Furthermore, using an appropriate probabilistic frame, the proposed criterion may be suitable for describing processes of energy transfer from the wind to the granular soil surface, ranging from the creep transport of gravels to the “mechanical sieving” of mega-ripples, as well as the transport of light anthropogenic debris (such as plastics).