Property:CSDMS meeting abstract
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The interplay between economic development and climate change exerts countervailing effects on human wellbeing, particularly concerning temperature-related mortality. While economic growth may enhance adaptive capacity and healthcare access, climate change intensifies extreme heat events, posing significant health risks. Carleton et al. (2022) and Barrage (2024) have quantified the effects of climate change and income growth on temperature-related mortality, providing insights into future health trajectories. To discern when climate change impacts on mortality become distinguishable from natural variability, this study introduces the concept of Time of Emergence (ToE). By identifying the ToE, this research – one of the first to apply ToE analysis to climate impacts rather than climate hazards – assesses the moment when climate-induced mortality becomes detectable beyond natural fluctuations, offering insights into the timing and magnitude of extreme-temperature impacts. The findings unveil that in warm regions, climate change may impede or nullify the reductions in temperature-related mortality typically driven by development, underscoring the urgency for targeted adaptation measures and policy interventions to mitigate health risks associated with climate change. +
The kinematics of sediment grains on a riverbed govern bedload transport, influencing water quality, aquatic ecosystems, river morphology, and landscape evolution. Previous studies suggest that hop distance distributions exhibit Gaussian-like behavior for large hops and exponential-like behavior for a mixture of short and long hops. Assuming flow hydraulics as the primary driver of these variations in hops, we numerically investigate the effects of flow conditions on the ensemble distributions of hop distances, particle velocities, travel times, and resting durations. This was done through high-fidelity simulations using coupled fluid dynamics/discrete element method (CFDEM), which integrates LIGGGHTS with OpenFOAM. For monodisperse grains (0.5 mm), hop distances follow a Weibull distribution, while velocity distributions are exponential, with scale factors increasing with flow strength. The relationship between streamwise hop distances and travel times follows Lx ∼ Tpα, with α ranging from 1.50 to 1.76. Travel times exhibit an exponential distribution, whereas resting times follow a Weibull distribution, both with scale factors increasing under higher flow conditions. For bidisperse grains (0.5 mm and 1 mm), the velocity distributions of each grain size independently follow an exponential distribution, while the combined velocity distribution conforms to a hypoexponential distribution - a weighted sum of exponential distribution of both sizes. This result suggests that, despite mechanical interactions between grains, the velocity distributions of each grain size remain statistically independent. These findings provide insight into the probabilistic nature of bedload transport and the role of flow dynamics in shaping sediment motion.
Keywords: Velocity distribution, hop distance, travel time, resting time +
The last 22 ka, since the Last Glacial Maximum (LGM), is known for significant millennial scale changes in global climate (Barker and Knorr, 2021). Sedimentary deposits in lacustrine and marine basins bear archives of corresponding changes in sediment accumulation. Yet given the scale that the global climate exerts on geomorphological processes on Earth’s surface, generalizations of the relationship between the climate and the erosion remain inconclusive. Whether the possible generalizations could even be applied to all regions has also remained unclear.
Erosion rates are a first-order response to climate of a region. The variability of erosion rates through time are needed for dating of buried surfaces, quantifying soil carbon budgets, and assessing landscape stability. Until now, a truly global analysis of comparing interregional erosion rates has not been available. Recent work in Madoff and Putkonen (2022) addresses this by generating global maps of regional erosion rates since the LGM. These results are supported by corresponding published sediment accumulation rates in sink areas corresponding to given watershed. Results show the spatial extent of higher erosion rates and larger ranges of variability through time in the Arctic and subarctic in contrast to the tropics and mid-latitudes. These results also indicate that the regional variability decreases the further from the past ice sheets a given location is. Finally, a clear take home message from these results is that the regional erosion rates vary both through time and space for the past 22 ka.
* Barker, S., Knorr, G., 2021. Millennial scale feedbacks determine the shape and rapidity of glacial termination. Nature Communications. 12.
* Madoff, R.D., Putkonen, J., 2022. Global variations in regional degradation rates since the Last Glacial Maximum mapped through time and space. Quaternary Research. 1–13. https://doi.org/10.1017/qua.2022.4 +
The long-term (3000 years) morphodynamics of backbarrier tidal basins is studied using a shallow-water hydrodynamic and wind-wave model (Deltf3D-FLOW-WAVE), modified to include fully-coupled marsh organogenic accretion, biostabilization, drag increase, and wave-induced marsh edge erosion. The latter process is implemented with a novel probabilistic algorithm. In simulations run with only sand, a flood tidal delta forms adjacent to the inlet, but marshes do not establish. In simulations run with only mud, instead, marshes establish at the basin margins and prograde seaward. If enough mud is supplied to the basin from the shelf, marsh progradation counteracts edge erosion. Marsh progradation does not completely fill the basin, but leaves open a few km-wide channels, large enough for waves to resuspend sediment. Starting from a basin (almost) filled with marshes, a drop in the external mud supply or an increase in the rate of relative sea level rise cause the basin to empty out by marsh edge erosion, while the marsh platform, aided by reworking of the sediment released by marsh retreat and mudflat deepening, keeps pace even with fast rates (10 mm/yr) of relative sea level rise. Even if the marsh does not drown, the marsh retreats faster if the rate of sea level rise increases, because more sediment is sequestered to fill the newly created accommodation space and is thus not available for marsh progradation. This study suggests that prediction of marsh erosion requires a basin-scale sediment budget, and that edge erosion, not platform drowning, is likely to dominate marsh loss. +
The low-lying tidal reaches of the Ganges-Brahmaputra delta relies on a system of polders (embanked landscapes) to prevent against tidal inundation and storm surge. These polders have increased the total habitable and arable land allowing the region to sustain a population of ~20 million people. An unintended consequence of poldering has been the reduction of water and sediment exchange between the polders and the tidal network, which has resulted in significant elevation offsets of 1-1.5 m relative to that of the natural landscape. Tidal River Management (TRM) and other engineering practices have been proposed in order to alleviate the offset. Previous work suggests if implemented properly with sufficient suspended sediment concentrations (SSC), TRM can be effective on timescales of 5-20 years. However, communities must also agree on how and when to implement TRM. Here, we expand previous numerical simulations of sediment accumulation through field-based constraints of grain size, compaction, and sea level rise. We then model human decision-making for implementation of TRM practices.
Our sediment model employs a basic mass balance of sediment accumulation as a function of tidal height, SSC, settling velocity, and dry bulk density. Tidal height is determined from pressure sensors and superimposed sea level rise rate, as defined by the representative concentration pathways of the IPCC. SSC varies within a tidal cycle (0-3 g/L) and seasonally (0.15-0.77 g/L). Multiple grain sizes (14-27 µm) are used as proxies for settling velocity by Stokes’ Law. Dry bulk density (900-1500 kg/m3) is determined from sediment samples at depths of 50-100 cm. The human dimension is introduced through an agent-based model for community decision-making regarding TRM. +
The lower Mississippi River drains a watershed of over 3.2 million square kilometers. The continental flux of water, sediment, and nutrients passes through the state of Louisiana in the last stretch of its journey to the Gulf of Mexico. A portion of the river detours, pronounced during high flow events, to the gulf through a series of natural and manmade diversions. Systemic understanding of the Mississippi River sediment and water resources partitioning among various outlets or diversions is crucial to the sustained function of the Northern Gulf of Mexico’s communities, habitats, and industries. This study discusses the development and application of a Delft3D FM 3-dimensional hydrodynamic, salinity, and temperature model of the Northern Gulf of Mexico. We used this model to analyze and quantify the tradeoffs among various management scenarios for freshwater allocation in the lower Mississippi River through existing and proposed infrastructure and natural openings. We also explored the possibility of varying the operational strategies of existing structures to investigate the changes in service and protection to communities in the receiving basins. To maximize the benefits of the Mississippi River’s water, sediment, and nutrients, this study emphasizes the continued analysis of management scenarios as an important step in the preservation and protection of the coast of the Gulf of Mexico while sustaining the support of relevant industries. We synthesized scoring metrics to facilitate communication of the efficacy of various management scenarios. The scoring metrics provide an evaluation framework covering physical, ecological and indirect socioeconomic criteria. This approach can be used for other complex natural systems to explore viable strategies and tradeoffs balancing ecosystem services with socioeconomic interests. +
The lower shoreface, a transitional subaqueous region extending from the seaward limit of the surf zone to beyond the closure depth, often serves as a sediment sink or source in sandy beach environments over annual to millennial time scales. Despite its important role in shoreline dynamics, however, the morphodynamics of the lower shoreface remain poorly understood. Previous work highlights discrepancies between equation-based theoretical equilibrium contours and bathymetric data, indicating that models may not accurately reproduce real shoreface cross-shore profiles. Here, we combine energetics-based suspended sediment transport formulae (Ortiz & Ashton 2016, JGR-ES) with wave climate and sedimentological data from Rockaway Peninsula, NY, to understand controls on shoreface morphology and differences between modeled and empirical equilibrium profiles. Analyzing a full wave climate time series from Wave Information Studies (WIS) spanning 40 years at one hour intervals reveals how different components of the wave climate affect suspended transport rates, particularly at varying depths. This results in a different steady-state, or equilibrium profile compared to one computed using single wave parameter inputs. The computed profile shape further changes when computations include reduction in sediment settling velocity due to offshore sediment fining, based on field observations. These profile are then compared to USGS bathymetric shoreface profile shapes at Rockaway and other locations. Our preliminary results appear to rectify the gap between modeled and empirical equilibrium profiles, moving towards a more thorough understanding the evolution of the lower shoreface. +
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The majority of process studies on alluvial fans have focused on gravely fans. Many fan systems, however, are sourced from basins composed of fine-grained sediments. Deposition on such fans involves deposition from hyperconcentrated- or mud-flows. Many of such fans occur where there is sufficient vegetation to affect and, often, obscure depositional processes.
The modeling effort to be presented is motivated by the occurrence of fine-grained alluvial fans on Mars that feature a network of distributaries floored with coarser sediment and what we interpret to be fine-grained overbank deposits that comprise the bulk of the sediment. We have identified active fine grained fans in the arid Atacama desert deriving sediment from the higher Andes and lowland deposition dominated by muddy sheetflow sediment.
We are constructing a simulation model for deposition on such fans based on the fan-delta model of Sun et al. (2002). The model routes water and sediment through multiple distributaries that can branch, recombine, and avulse. Modeling flow and bedload sediment through the distributaries is relatively straightforward, but overbank deposition and avulsion processes are more problematic to characterize realistically (e.g. avoiding development of "holes" in fans or preventing evolution to a fixed distributary pattern). Our observation of overbank processes on the Atacama fans demonstrates the importance of sedimentation by long shallow sheetflow floods in addition to local levee aggradation. These processes are being implemented into our fan model. +
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The modern Ohio River network is a Rubrik’s Cube for anyone interested in dynamic river reorganization. Throughout the Quaternary, the cyclic growth of North American ice sheets forced the Ohio drainage network to oscillate between a north-flowing (towards the Gulf of St. Laurence or Hudson Bay) and west / south-flowing (towards the Gulf of Mexico, i.e., the modern river) configuration. These cycles produced a network of overprinted paleo valleys that reflect multiple episodes of river reorganization (the so-called “Teays” paleo river network). The overprinted nature of these valleys makes it very difficult to assess the timing of specific stream capture events. In order to unravel this complex history of river reorganization, geomorphologists can begin by constraining the timing of individual stream capture events that do not overprint older episodes of drainage reversal.
One such event is likely present in Hocking Hills State Park in central Ohio, known for its hundreds of 30-50 m-tall waterfalls. These knickpoints were likely created when the upper reaches of the Salt Creek watershed were blocked by one of the ice sheets, forming a glacial lake that spilled over a drainage divide and rerouted the channel network from a west-flowing to a south-flowing configuration. The stream capture event would have also produced a local base level drop that created the knickpoints. This hypothesis implies that the knickpoints were all created at the same time; if true, we can constrain the timing of the capture event using catchment averaged erosion rates and knickpoint celerity models.
However, the hypothesis also implies that the waterfalls should be located at the same approximate χ value. This is not the case; rather, there is prominent, N-S trend in χ values. Without an explanation for this trend, any age constraints on the capture timing will be suspect.
We used Landlab-based landscape evolution models (LEMs) to explore several possible explanations for the trend in χ values. We found that following a single capture event, the trend can be explained by the specific combination of (a) the pre-capture channel topology; (b) the precise capture location; and (c) the spatial extent of different rock layers. We believe that this in an “Occam’s razer” scenario, because it allows the χ trend to be explained by a single, stream capture forcing. However, without the insights provided by our LEMs, we would have considered multiple forcings or stream capture events to be more likely. These simulations are a novel and interesting case study in how LEMs can be applied to understand unique complexities of specific field sites and also have important implications for using knickpoint celerity models to assess landscape evolution.
The morphodynamics of coast and estuarine environments are known to be sensitive to environmental change and sea-level rise. However, whilst these systems have received considerable individual research attention, how they interact and co-evolve is largely unknown. Through a novel coupling of numerical models, this research is designed to explore the complex behaviour of these systems in terms of fluid flows and sediment fluxes. This includes elucidating the relative influence of various controls on system behaviour and exploring the effects that variable sea levels and changing wave climates may have on their evolution over the mid to longer term.
This research is being carried out through the modification and coupling of the one-line Coastline Evolution Model (CEM) with the hydrodynamic LEM CAESAR-Lisflood (C-L). Progress to date includes a new version of the CEM that has been prepared for integration into C-L. This model incorporates a range of more complex sedimentary processes in quasi-2d and boasts a graphical user interface and visualisation.
The model is being applied and tested using the long-term evolution of the Holderness Coast, Humber Estuary and Spurn Point on the east coast of England (UK). Holderness is one of the fastest eroding coastlines in Europe and research suggests that the large volumes of material removed from its cliffs are responsible for the formation of the Spurn Point feature and for the Holocene infilling of the Humber Estuary. Over the next century it is predicted that climate change could lead to increased erosion along the coast and supply of material to the Humber Estuary and Spurn Point. How this manifests will be hugely influential to the future morphology of these systems and the flood and erosion risk posed to coastal communities. +
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The morphodynamics of large anabranching sand-bed rivers is investigated using a numerical model of hydrodynamics, sediment transport, bank erosion and floodplain development, operating over periods of several hundred years. Model sensitivity to key parameters is examined, and simulated channel and natural river morphology are compared in terms of the statistical characteristics of channel width, depth and bar shape distributions, and mechanisms of unit bar, compound bar and island evolution. Model results provide insight into controls on the frequency of mobile sand bars and the stability of larger vegated islands. +
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The morphology of the Earth’s surface is continuously evolving under multiple factors (tectonics, climatic, etc). As the interface between the lithosphere and the atmosphere, the critical zone provides the prime record of these changes and can be directly monitored. Understanding the physical processes that control temporal changes is important to quantify and predict them.
In this context, we aim to constrain the effect of physical rock weathering on erosion rates and their variation over seasonal cycles. We focus our studies on marly badland catchments in the southeast of France. The Draix-Bléone Critical Zone Observatory allowed data collection and experiments over the last 35 years and represents an ideal environment for this project (Mathys et al, 2005). The marly badland of Draix are subject strong weathering and erosion processes, caused by a variety of physical processes, resulting in the formation of a spatially and temporally variable regolith layer. Significant production of regolith is observed during the winter and rapid washing of slopes during the spring and early summer (Bechet et al., 2016). Based on regolith characteristics from the field we will build a 1D model of the dynamic of the regolith. Characterizing the seasonal variability and climatic dependence of regolith production is a prerequisite to predict yearly variations in sediment flux and its evolution under changing climate conditions.
We sampled the upper part of the regolith in the Draix catchment, in four targeted places, to obtain grain size distributions and water contents. Characteristics of the detrital cover that affect the rate of weathering. High-resolution photogrammetry records will enable comparing surface changes (roughness, thickness, grain size) over the seasons. Furthermore, we cleaned a 1m² surface on a ridge of regolith to monitor weathering processes and estimate regolith production during each season. We aim to repeat this exercise at the end of each season; the resulting difference in thickness removed should represent the new regolith formed
Two years of field campaigns are scheduled. We will use our field observations on the temporal variation of regolith characteristics to inform a 1D model of regolith dynamics. In parallel, the second goal of the project will be to spatialize and implement the latter description into a landscape evolution model based on Landlab (Hobleyet al., 2017) to simulate the effects of regolith dynamics on catchment-scale erosion. The development of this new module will be helpful to follow critical-zone evolution in different soil cover contexts.
References:
Bechet, J., J. Duc, A. Loye, M. Jaboyedoff, N. Mathys, J.-P. Malet, S. Klotz, C. Le Bouteiller, B. Rudaz, and J. Travelletti (2016), Detection of seasonal cycles of erosion processes in a black marl gully from a time series of high-resolution digital elevation models (DEMs), Earth Surf. Dynam., 4, 781–798, doi: 10.5194/esurf-4-781-2016.
Hobley, D. E. J., J. M. Adams, S. S. Nudurupati, E. W. H. Hutton, N. M. Gasparini, E. Istanbulluoglu, and G. E. Tucker (2017), Creative computing with Landlab: an open-source toolkit for building, coupling, and exploring two-dimensional numerical models of Earth-surface dynamics, Earth Surf. Dynam., 5, 21–46, doi: 10.5194/esurf-5-21-2017.
Mathys, N., S. Klotz, M. Esteves, L. Descroix, and J. M. Lapetite (2005), Runoff and erosion in the Black Marls of the French Alps: Observations and measurements at the plot scale, Catena, 63, 261–281, doi: 10.1016/j.catena.2005.06.010.
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The motion of sediment in water is caused by fluid pressure gradient forces, primarily drag, on sediment grains. Turbulence-resolving experiments show significant temporal and spatial variability of fluid and sediment motion and particle forces at all stages of sediment transport. The signature of turbulence structures and their modification by sediment is apparent from incipient motion to vigorous suspension.<br>
This presentation introduces a numerical model that combines large eddy simulation (LES) of turbulence and the distinct element method (DEM) of granular motion. The LES and DEM models are fully coupled in momentum. Information from the LES is used to specify forces on the DEM particles, and those particle forces are given in an equal and opposite direction in the filtered and discretized Navier-Stokes equations at each grid cell in the finite volume LES.
Parameterization of turbulent sediment transport processes is the basis of any well founded model of morphodynamics in fluvial and marine environments. Current parameterizations rely on a mixture of theory and empirical evidence. LES-DEM simulations can be performed in conditions that are difficult to reproduce in the laboratory and that stretch the limits of theory. It is hard to build an apparatus that can produce sediment transport under field-scale cnoidal waves, on sloping beds, with currents of arbitrary direction, and a range grain size distributions. Further, even in simple unidirectional flows only rough empirical relations exist for the critically important suspended sediment rate of entrainment.<br>
Validation of the LES-DEM approach is essential before development of transport relations for large-scale morphodynamic models. A series of LES-DEM simulations of unidirectional flow over flat beds of medium sand, ranging from no transport, to bedload, to vigorous suspension are presented. Simulations of flat sand beds under oscillatory waves and unidirectional flow downstream of a backward-facing step are compared to laboratory measurements. Simulations over ripples and through vegetation are also presented.<br>
Examples of some of the simulations can be previewed at the links below.<br>
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START_WIDGET"'-e3e977584442e979END_WIDGET<br>
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The movement of sea ice is influenced by a number of factors, from winds to ocean currents. As climate change continues to occur rapidly, understanding sea ice drift in the Arctic is a key parameter to understanding the effects of rising temperatures in the region. Recent literature has shown that the Arctic and the Antarctic are most affected by global warming, which raises questions regarding climate justice, as most of the carbon emissions causing anthropogenic climate change are produced in other regions. To analyze this impact, we employ artificial intelligence to predict sea ice drift velocity based on external features. Machine learning is the process of computers gaining insights by seeing and correlating large quantities of data. Using external parameters, including wind speed, and drift velocity ground truth as the inputs of the model, we train multiple different architectures and compare the results. Particularly, we experiment with a convolutional neural network (CNN), a random forest (RF), and a support vector machine (SVM). We also experiment with various model specifications. This research leads to a greater understanding of the Arctic’s response to climate change. +
The natural elevation of the vast, flat landscape of the lower Ganges-Brahmaputra-Meghna (GBM) remains remarkably stable despite persistent relative sea level rise (rSLR). This stability stems from the tight coupling of the land and tides through a robust negative feedback induced by periodic flooding with sediment-rich water. As water levels increase, the inundation depth and duration also increase resulting in more sediment deposition. This has a stabilizing effect and largely negates the initial increase in water level such that the elevation surface appears unchanged. We refer to this stable elevation as the equilibrium elevation.
Here, we investigate the strength of the inundation feedback and the resulting equilibrium elevation. We identify three main controls on this feedback - (1) annual rate of rSLR, (2) mean tidal range (TR), and (3) mean suspended sediment concentration (SSC). We explore the realistic parameter space of each using a simple, zero-dimensional mass balance model. Specifically, we ask (1) what equilibrium elevations are feasible, (2) how these equilibrium elevations compare to tides (e.g., relative to mean sea level (MSL) or mean high water (MHW)), and (3) how equilibrium elevation impacts the duration (hydroperiod) and intensity (depth) of a typical inundation cycle. Results show an incredibly robust feedback for most conditions with the notable exception of low SSCs (< 0.1 g/L). This low, yet realistic value of SSC represents a tipping point at which the equilibrium elevation drops precipitously. At higher rates of rSLR (> 8mm/yr) and lower TR (< 2 m) the equilibrium elevation results in complete drowning of the platform. +
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The overall size of the Chesapeake Bay “dead zone” is quantified by the Bay’s hypoxic volume (HV), i.e., the volume of water with dissolved oxygen (DO) less than 2 mg/L. In order to improve estimates of HV, DO was subsampled from the output of three dimensional model hindcasts at times/locations matching the set of 2004-2005 stations monitored by the Chesapeake Bay Program. The resulting station profiles were then input into an interpolation program to produce Bay-wide estimates of HV in a manner consistent with non-synoptic, cruise-based estimates. Interpolations of the same stations sampled synoptically as well as multiple other combinations of station profiles were examined in order to quantify uncertainties associated with interpolating HV from observed profiles. The potential uncertainty in summer HV estimates resulting from profiles being collected over two weeks rather than synoptically, averaged ~5 km^3. This is larger than that due to sampling at discrete stations and interpolating/extrapolating to the entire Bay (2.4 km^3 ). As a result, sampling fewer, selected stations over a shorter time period is likely to reduce uncertainties associated with interpolating HV from observed profiles. A function was also derived, that, when applied to a subset of 13 stations, significantly improved estimates of HV. Finally, multiple metrics for quantifying Bay wide hypoxia were examined, and cumulative hypoxic volume was determined to be particularly useful, as a result of its insensitivity to temporal errors and climate change. A final product of this analysis is a nearly three-decade time series of improved estimates of HV for Chesapeake Bay. (Submitted March 2013 to Journal of Geophysical Research. For a pdf pre-print contact Carl Friedrichs at cfried@vims.edu .) +
The present study uses the Sedflux stratigraphic model to simulate the Late Pleistocene evolution of the Eastern Beaufort Continental Shelf, Canadian Arctic. During this period, the proximity and the dynamics of the Laurentide Ice Sheet created a complex glacial environment. Modeling such environments thus presents challenges. Modules and input parameters have to be able to simulate major fluctuations in sea-level and sediment supply, an ever evolving source of sediments, a large outwash plain, sudden outburst floods, permafrost aggradation, glacial isostasy, etc. In addition, detailed understanding of glacially-influenced environments in general and the glacial history of the local region specifically make it difficult to estimate parameters such as sediment supply. This poster thus presents the challenges and the potential solutions in using SEFLUX to simulate the stratigraphy of a glaciated shelf such as the Beaufort Shelf. +
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The propagation of environmental signals through the sediment routing system and their subsequent preservation or removal from the rock record is a central theme in current stratigraphic research. The identification of cyclicity and order in stratigraphic sequences with regard to vertical facies successions, thicknesses, and grain size trends is often used as indicator of preservation of non-random, extra-basinal signals (i.e. climate, tectonics, and base level). However, it is less clear to what extent the processes that alter these signals post-deposition (re-working, scour, and erosion) enhance or diminish cyclicity and order within preserved sediments. Furthermore, stratigraphic trends are often identified in subjective, qualitative terms and may be based more on a priori perception of order derived from depositional systems models than statistically robust trends inherent in the sediment archive. Here, we use a statistical metric to objectively evaluate order vs. disorder in the stratigraphic record in an attempt to identify the likelihood of a disordered (random) response to orderly (non-random) depositional processes. We utilize a quantitative geochemical and sedimentological dataset from the Ganges-Brahmaputra-Meghna delta (GMBD) to identify distinct fluvial sediment packages (defined as meter to 10s of meters thick sand packages similar in scale and character to modern bar forms) and statistical trends in their vertical successions across the delta. We begin by considering that the boundaries of these fining-upwards packages are defined by >50% increases in grain size from one sample to the next in a vertical succession (although other thresholds are evaluated as well). A runs metric “r” is then calculated by identifying streaks of increasing or decreasing sediment package thicknesses and volume weighted mean grain size. This metric is then compared to the output of a Monte Carlo simulation of 5000 synthetic boreholes created by random shuffles of the observed borehole data to determine the likelihood of a similar succession of sediment body thicknesses and grain size trends being generated by chance. Preliminary results indicate that the vast majority of observed thickness successions in the GBMD are statistically “disordered”, with regional variability correlated to discrete geomorphic provinces within the delta. Of note, sediment thickness trends from the main braidbelt exhibit the lowest probability of being generated by random chance, followed by the lower delta plain, and lastly by Sylhet basin, a semi-enclosed sub-basin in northeast Bangladesh that has experienced episodic occupation by the mainstem Brahmaputra River throughout the Holocene. Similar results (with some notable exceptions) are found within grain size runs analyses, with Sylhet basin exhibiting the least amount of order with regard to vertical changes in grain size. Previous studies have identified Sylhet basin as a site of rapid mass extraction, suggesting a possible inverse relationship between stratigraphic order and rates of sediment extraction in fluvial systems. These results lay the groundwork for future studies in the utility of simple statistical measures in identifying random vs. ordered successions of sediment packages as indicators of process-response relationships preserved in the stratigraphic record.
The recent incursion of Data Analytics and Big Data has inspired many fields to venture in. Although a late comer, as compared to financial and bioinformatic areas, geosciences have fast picked up momentum in past two years. We will summarize here quantitative efforts, which require computational means beyond a laptop, in machine learning, deep learning and visualization. The examples will be drawn from (1) delineation of three-dimensional sub-surface three -dimensional fault structure illuminated by tens of thousands of hypocenter from earthquake aftershocks in central Italy using unsupervised machine learning (2) Recurrent Neural Networks (RNN) for delineating earthquake Patterns Based on Complete Seismic Catalog created by large-scale finite element Modelling (3) A highly efficient computational interactive Virtual Reality (VR) Visualization Framework and workflow for Geophysical exploration (4) forecasting the intensity trend of the Earth's natural electromagnetic pulse field signal prior to large earthquakes using chaos theory and radial basis functions (RBF) as deep neural network. +
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The response of the wave-dominated coasts to sea-level rise is dominated not by inundation, but rather by the dynamic response of sediment transport processes to perturbations of the sea level. In a regime of sea level change, the predominant response of the wave-dominated shoreface depends upon the time-dependent response of the shoreface itself to changes in sea level as well as the potential changes to the shoreline. Sediment transport processes on the shoreface remain poorly understood, complicating predictions of equilibrium shoreface shapes and even net sediment transport directions. However, presuming an equilibrium geometry, energetics-based, time-averaged relationships for cross-shore sediment transport provide a framework to understand the characteristic rates and types of shoreface response to perturbations to either the sea level or the shoreline boundary. In the case of a sea-level rise, we find that the dominant perturbation for a barrier system is not the sea-level rise itself, but rather the movement of the shoreline by overwash. The characteristic response time of the shoreface itself increases significantly at depth, suggesting that the lower shoreface response to a sea level change can be significantly delayed. To study the interactions between the characteristic timescales of shoreface evolution and barrier overwash, we apply a numerical model of barrier profile evolution that couples shoreface evolution with barrier overwash. This integrated model provides a tool to understand the response of barrier systems to changes in sea level over the late Holocene to the modern. The model also investigates the potential behavior of barrier systems as they (and their human occupants) respond to predicted increased rates of sea-level rise over the coming centuries. +
