Pattern Of Accretion Research Articles

Erosion and accretion patterns on intertidal mudflats of the Yangtze River Estuary in response to storm conditions

Understanding of erosion and accretion patterns over intertidal mudflats during storm periods is vital for the management and sustainable development of coastal areas. This study aimed to investigate the effect of the 2014 storm Fung-wong on the erosion and accretion patterns of the Nanhui intertidal mudflats in the Yangtze estuary, China, based on field measurements and Delft3D numerical modeling. Results show that prolonged easterly winds during the storm enhance the flood velocity, weaken the ebb velocity, and even change the current direction. The current velocity, wave heights, and bed-level changes increased by 1–1.43 times, 2.40–3.88 times, and 2.28–2.70 times than those of normal weather, respectively. The mudflats show a spatial pattern of overall erosion but increasing erosion magnitude from the high (landward) mudflat to the low (seaward) mudflat during the storm. The magnitude of bed-level change increases with increasing wind speed, but the spatial pattern of erosion and accretion remains the same. The main reason for this pattern is the longer submersion duration of the low mudflat compared with the high mudflat, so the hydrodynamic process is longer and stronger, leading to an enhancement in bed shear stress and sediment transport rate. Wind speed increases the hydrodynamic intensity but does not affect on the submersion duration over each part of the intertidal mudflat. This study is helpful to improve the understanding of physical processes during storms on intertidal mudflats and provides a reference for their protection, utilization, and management, as well as for research in related disciplines.

A quantitative analysis of multi-decadal shoreline changes along the East Coast of South Korea

South Korea's east coast is facing several issues related to coastal erosion because of sea-level rise, typhoon-induced storm surges, and various coastal development projects. In recent decades, high storm waves have frequently appeared on the east coast, causing casualty, beach erosion, and coastal infrastructure damage, drawing significant public attention. Thus, we analyzed the multi-decadal shoreline changes to understand the coastal dynamics and the forces responsible for the spatio-temporal changes along the 173 km coastline. The shorelines covering 38 years between 1984 and 2022 were derived from Landsat images and the change statistics, i.e., linear regression rate (LRR), endpoint rate (EPR), weighted linear regression (WLR), and net shoreline movement (NSM), were calculated at a 100 m alongshore intervals using Digital Shoreline Analysis System (DSAS), revealed several distinct behaviors of shoreline position. The long-period (1984–2022) assessment showed an average shoreline change rate (LRR) of 0.17 m/year with an estimated mean erosion and deposition rate of −0.57 and 2.07 m/year, respectively. The long-term surface gain and loss of the backshore region exhibited that the net surface gain of the east coast is 421.13 ha, and the net loss is 181.82 ha. The assessment of decadal shoreline changes showed a cyclic pattern of erosion (from 1984–1990 and 1999–2010) and accretion (from 1990–1999 and 2010–2022). Furthermore, a secondary level of investigation was conducted to address a wider variety of coastal behaviors by segmenting shoreline change rates based on coast types and average slopes along coastlines. It was observed that the frequent coastal deformation is associated with a flatter beach compared to a steep one. This study found that the artificial structures constructed along the east coast have not completely solved or stopped the erosion issues but shifted it from one location to another. The analysis of local and regional shoreline changes had shown that typhoon-induced storm surges, high storm waves, and anthropogenic activities like encroachment and the development of artificial coastal structures were the primary drivers of coastline changes along the east coast. Finally, we proposed a decision-making classification scheme that can be used to determine the mechanism of decision for protective and preventive measures against further coastal deterioration.

Phosphatides and Cholesterol in the Rat Body: Effects of Growth, Diet and Age

Data are presented on the content of phosphatides, free and total cholesterol, and neutral fat in 152 male rats from birth to 3 years of age. The ratio of phosphatides to total cholesterol remained remarkably constant at near 4 (mol ratio of 2) for the first year of life with a variety of diets. Two- and three-year-old rats showed a highly significant decrease in this ratio, corresponding to an increase in total cholesterol of about 10%, with no change in phosphatides. The percentage of free cholesterol decreased steadily throughout life from 90 to 72, diet and senescence having no effect thereon. The pattern of accretion of neutral fat with stock diet was in many respects very different from the common pattern observed for both phosphatides and cholesterol. The substitution of more concentrated, refined or purified diets of varying fat content (2% to approximately 40%) for the crude stock diet led to no change in phosphatides or cholesterol. These same rats showed large increases in neutral fat.

A new geological map of the Lau Basin (southwestern Pacific Ocean) reveals crustal growth processes in arc-backarc systems

A 1:1,000,000-scale lithostratigraphic assemblage map of the Lau Basin (southwestern Pacific Ocean) has been created using remote predictive mapping (RPM) techniques developed by geological surveys on land. Formation-level geological units were identified in training sets at scales of 1:100,000–1:200,000 in different parts of the basin and then extrapolated to the areas where geological data are sparse. The final compilation is presented together with a quantitative analysis of assemblage-level crustal growth based on area-age relationships of the assigned units. The data sets used to develop mapping criteria and an internally consistent legend for the compilation included high-resolution ship-based multibeam, satellite- and ship-based gravity, magnetics, seafloor imaging, and sampling data. The correlation of units was informed by published geochronological information and kinematic models of basin opening. The map covers >1,000,000 km2 of the Lau-Tonga arc-backarc system, subdivided into nine assemblage types: forearc crust (9% by area), crust of the active volcanic arc (7%), backarc rifts and spreading centers (20%), transitional arc-backarc crust (13%), relict arc crust (38%), relict backarc crust (8%), and undivided arc-backarc assemblages (<5%), plus oceanic assemblages, intraplate volcanoes, and carbonate platforms. Major differences in the proportions of assemblage types compared to other intraoceanic subduction systems (e.g., Mariana backarc, North Fiji Basin) underscore the complex geological makeup of the Lau Basin. Backarc crust formed and is forming simultaneously at 12 different locations in the basin in response to widely distributed extension, and this is considered to be a dominant pattern of crustal accretion in large arc-backarc systems. Accelerated basin opening and a microplate breakout north of the Peggy Ridge has been accommodated by seven different spreading centers. The result is an intricate mosaic of small intact assemblages in the north of the basin, compared to fewer and larger assemblages in the south. Although the oldest rocks are Eocene (~40 m.y. old basement of the Lau and Tonga Ridges), half of the backarc crust in the map area formed within the last 3 m.y. and therefore represents some of the fastest growing crust on Earth, associated with prolific magmatic and hydro-thermal activity. These observations provide important clues to the geological evolution and makeup of ancient backarc basins and to processes of crustal growth that ultimately lead to the emergence of continents.

Pattern of dune accretion and its climatic implication in the southern Thar Desert margin, western India

Pattern of dune accretion and its climatic implication in the southern Thar Desert margin, western India

Numerical Investigation of Sea-Bottom Morphological Changes by the Interaction of Tidal Flow and Idealized Coastal Geometries

Carbajal, N.; Montano-Ley, Y.; Paez-Osuna, F.; Soto-Jimenez, M., and Tuxpan, J., 2020. Numerical investigation of sea-bottom morphological changes by the interaction of tidal flow and idealized coastal geometries. Journal of Coastal Research, 36(5), 981–991. Coconut Creek (Florida), ISSN 0749-0208.Different idealized geometries, resembling shallow tidal-dominated seas with different geographical features like bays, islands, and headlands, were investigated by applying a two-dimensional hydrodynamic-numerical and morphological model. The geometries were exposed to fast oscillatory tidal velocities and unbounded sediment availability. The interaction between the oscillatory tidal flow and the seabed, in all the experiments, generated vorticity and small bed perturbations that evolved to incipient shoals or bed forms. The reversing tidal regime created asymmetric sediment transport, which in turn triggered sediment accretion at specific areas. The flow, residual circulation, and vorticity produced by mixed tides, and, in the presence of coastal morphological features like headlands, bays, and islands, also triggered the generation as well as the enhancement of asymmetric shoals. Experiments applying only one tidal component revealed a more symmetric pattern of vorticity and sediment accretion. Satellite images of areas of the Gulf of California including an island, bay, and headland were compared with the predicted tidal morphodynamics. They reflected quite well, in all cases, accretion areas located in sites similar to those predicted in the present numerical investigation.

Evolution of a Viscous Protoplanetary Disk with Convectively Unstable Regions

The role of convection in the gas-dust accretion disk around a young star is studied. The evolution of a Keplerian disk is modeled using the Pringle equation, which describes the time variations of the surface density under the action of turbulent viscosity. The distributions of the density and temperature in the polar directions are computed simultaneously in the approximation that the disk is hydrostatically stable. The computations of the vertical structure of the disk take into account heating by stellar radiation, interstellar radiation, and viscous heating. The main factor governing evolution of the disk in this model is the dependence of the viscosity coefficient on the radius of the disk. The computations of this coefficient take into account the background viscosity providing the continuous accretion of the gas and the convective viscosity, which depends on the parameters of the convection at a given radius. The results of computations of the global evolution and morphology of the disk obtained in this approach are presented. It is shown that, in the adopted model, the accretion has burst-like character: after the inner part of the disk ( R < 3 AU) is filled with matter, this material is relatively fast discharged onto the star, after which the process is repeated. Our results may be useful for explaining the activity of young FU Ori and EX Lup objects. It is concluded that convection may be one of the mechanisms responsible for the non-steady pattern of accretion in protostellar disks.

Response of long- to short-term changes of the Puri coastline of Odisha (India) to natural and anthropogenic factors: a remote sensing and statistical assessment

The coastal regions of India are densely populated and most biological productive ecosystems which are threatened by erosion, natural disaster, and anthropogenic interferences. These threats have made priority in appraisal of shoreline dynamicity as part of sustainable management of coastal zones. The present study assessed the long- to short-term dynamicity of shoreline positions along the coast of Puri district, Odisha, India, during the past 25 years (1990–2015) using open-source multi-temporal satellite images (Landsat TM, ETM + , and OLI) and statistical-based methods (endpoint rate, linear regression rate and weighted linear regression). The long-term assessment during 1990–2015 shows that shoreline accredited at the rate of 0.3 m a−1 with estimated mean accretion and erosional rate of 1.18 m a−1 and 0.64 m a−1, respectively. A significant trend of coastal erosion is primarily observed on the northern side of Puri district coast. A cyclic pattern of accretion (during 1990–1995 and 2000–2004) and erosion (during 1995–2000 and 2009–2015) was observed during the assessment of short-term shoreline change. It exhibited significant correlation with the landfall of severe cyclones and identified cyclic phases after severe cyclonic storms, i.e., phase of erosion, phase of accretion and phase of stabilization. Overall, the natural processes specifically the landfall of tropical cyclones and anthropogenic activities such as the construction of coastal structures, encroachment and recent construction in the coastal regulatory zone, and construction of dams in upper catchment areas are the major factors accountable for shoreline changes. The output of the research undertaken is not only crucial for monitoring the dynamism of coastal ecosystem boundaries but to enable long- to short-term coastal zone management planning in response to recently reported high erosion along the Puri coast. Moreover, the usage of open-source satellite imageries and statistical-based method provides an opportunity in developing cost-effective spatial data infrastructure for shoreline monitoring and vulnerability mapping along the coastal region.

Hydrological controls on the evolution of the Yellow River Delta: An evaluation of the relationship since the Xiaolangdi Reservoir became fully operational

AbstractThe Xiaolangdi Reservoir, which was constructed in the trunk of the Yellow River, has controlled the flow process into the mouth of the Yellow River to a significant degree since it began fully operating in late 2002. To evaluate the relationship between the new hydrological process and the evolution of the Yellow River estuary, this study presents a detailed investigation of the morphodynamic adjustment in the river mouth using remote sensing satellite images. It was shown that the mouth channel rapidly extended in length from 2002 to 2004, although it was shrinking during 1999–2001, and then it expanded very slowly with considerable shifts at the place where the river flow mixes with seawater. In late 2007, an avulsion occurred on the northern bank of the mouth channel, far upstream from where the river water mixes with seawater. During 2008–2012, the new mouth channel extended its length into the sea at a slow pace, whereas since late 2013, it has divided into two branches that alternately discharge the main flow into the sea. Although both the water and the sediment input in the new hydrological process are much smaller in quantity than before, the geomorphic adjustments still manifest an excessive input of both. Moreover, after the avulsion, the seasonal pattern of land accretion in the river mouth has been characterized, with erosion occurring mostly in the wet seasons and accretion mostly occurring in the dry seasons.

Nd and Pb isotope mapping of crustal domains within the Makkovik Province, Labrador

AbstractThe Makkovik Province of eastern Labrador represents part of an accretionary orogen active during an early stage in the development of the Palaeoproterozoic southern Laurentian continental margin. New Nd isotope data for the eastern Makkovik Province suggest that accreted juvenile Makkovik crust was generated in the Cape Harrison domain during a single crust-forming event at c. 2.0 Ga. Pb isotope data support this model, and show a strong similarity to radiogenic crustal signatures in the juvenile Palaeoproterozoic crust of the Ketilidian mobile belt of southern Greenland. As previously proposed, an arc accretion event at c. 1.9 Ga triggered subduction-zone reversal and the development of an ensialic arc on the composite margin. After the subduction flip, a temporary release of compressive stress at c. 1.87 Ga led to the development of a retro-arc foreland basin on the downloaded Archean continental edge, forming the Aillik Group. Unlike previous models, a second arc is not envisaged. Instead, a compressive regime at c. 1.82 Ga is attributed to continued ensialic arc plutonism on the existing margin. The tectonic model for the Makkovikian orogeny proposed here is similar to that for the Ketilidian orogeny. Major- and trace-element analyses suggest that much of the magmatism in the Makkovik orogen results from post-accretionary ensialic arc activity, and that few vestiges remain of the original accreted volcanic arc. This pattern of arc accretion and intense post-accretion reworking is common to many accretionary orogens, such as the South American Andes and North American Cordillera.

Time Series Observation on Phytoplankton Dynamics in the Coastal Waters of the World Heritage Site of Indian Sundarban Mangrove Forest, NE Coast of Bay of Bengal

Sea levels on the Indian sub-continent are increasing at the rate of about 2.5 mm/year; the rate of increment is greater in the eastern coast, with an estimated sea level rise of about 3.14 mm/year. This suggests that mean annual sea levels in the Indian sub-continent will be some 15 cm higher in 2060 than what it was during 2000. The Indian Sundarbans in northeast coast of the country, at the apex of the Bay of Bengal is an extremely dynamic deltaic lobe sustaining a wide spectrum of mangrove flora and fauna. It is estimated that sea level in this deltaic lobe has increased by about 15 cm since the 1950s and this has been correlated with changes in the pattern and rates of erosion and accretion in the islands of the Indian Sundarbans. Such geo-physical phenomena may not only pose serious impact on the adjacent aquatic system by way of increasing turbidity, nutrient budget, salinity, pH etc., but the phenomenon has every possibility to shift the biodiversity spectrum of the adjacent land masses (supporting mangrove and mangrove associate species) and aquatic system due to salinization of land, alteration of soil pH, increased erosional activities leading to reduction of water transparency, increased salinity of the water bodies and invasion of the areas with more number of stenohaline species (preferably phytoplankton). The present paper is an attempt to scan the time series observation on phytoplankton dynamics in the coastal waters of Indian Sundarban mangrove forest, NE coast of Bay of Bengal. Twenty four stations have been selected in the present programme at different salinity gradients to evaluate the temporal variations of selective hydrological parameters like surface water temperature, salinity, pH, dissolved oxygen, transparency and nutrient load. Simultaneous data on phytoplankton diversity was also assessed to critically analyze the impact of temporal oscillation of hydrological parameters on the tiny, free floating, drifting, primary producer community. Duncan test applied on the data set of 25 years (1990 to 2015) revealed significant temporal variations of surface water temperature, salinity, pH, transparency, nitrate concentration, phosphate concentration and phytoplankton composition. Since 1990, nine stenohaline phytoplankton species have been recorded in the upstream regions of the deltaic lobe indicating a gradual shifting of aquatic phase towards high salinity. Few environmental variables like dissolved oxygen and silicate did not show variations at significant level. Although the time span is too short to predict potential impact of aquatic climate change on phytoplankton community of the mangrove dominated Indian Sundarbans, but significant temporal variation in the phytoplankton community since 1990 speaks in favour of using these tiny, free floating, drifting, primary producer community as potential bioindicators of aquatic climate change in short term scale.

Adjustment of dryland stream channels over four decades of urbanization

Abstract Human settlements are increasingly expanding into drylands and mountain areas that are less accommodating to urban communities, creating hazards related to the conveyance of water and sediment. Comparatively few studies of urbanization effects on streams have focused on drylands, especially steep terrains. Development of the town of Fountain Hills in the foothills of the McDowell Mountains (Arizona, USA) since the 1970s provides an example of dryland streams adjusting to urbanization over several decades. Urbanization has introduced numerous roads with dip crossings that fragment channels, causing management challenges. Field surveys in 1987, 2006, and 2016 showed that wash channels in urban areas are up to ten times larger than comparable natural channels. Roads have exerted a spatial pattern of geomorphic influence, where channels downstream of dip crossings are narrower and deeper than those upstream, reflecting erosion with input of urban drainage. Repeat measurements showed that the pattern of downstream incision and upstream accretion has become less evident in the recent decade. The muted response by 2016 results from evolving management that has improved the conveyance of water and sediment, including stormwater controls and erosion protection. Additionally, comparison of channel changes at dip crossings with those at culverted crossings revealed greater impact at dip crossings. Less morphological change at culverts suggests more effective throughput of water and sediment. Results demonstrate successful adaptive management including decisions to employ culverts in recent developments. The evolving landscape of Fountain Hills provides a possible template for understanding and predicting changes in other dryland areas undergoing urbanization.

NUMERICAL MODELLING OF MORPHODYNAMICS AROUND A TIDAL INLET

A two-dimensional morphological model is used to study sediment transport and morphdynamics around a tidal inlet. The model includes the processes of erosion on side slope for the avalanching effects. The model has been tested against a laboratory study of an idealised tidal inlet configuration over 68 tidal cycles. The results show a reasonable agreement between the model and experiment measurements with a typical pattern of accretion at up-drift of the inlet and erosion at the down-drift. This study also reveals the importance of surface waves and cross-shore sediment transport to the evolution and migration of the tidal inlet.

Experimental Deposition of Carbonate Mud From Moving Suspensions: Importance of Flocculation and Implications For Modern and Ancient Carbonate Mud Deposition

Abstract Flume experiments with fine-grained carbonate particles (< 62.5 µm) show that they form floccules that travel in bedload, form current ripples, and deposit laminated sediments. In order to compare our flume experiments to work on sand transport, we ran flume experiments with medium sand and observed that the velocities at which sand grains started to move and form ripples were in the same range as those where floccules move and form ripples. These ripples are in essence identical to those formed by clay-mineral floccules or sand grains under similar conditions. In light of previous experiments with clay minerals, these results indicate that, of the key controls on mud deposition, flocculation and suspended-sediment concentration are more important than particle mineralogy or water chemistry, and are about as important as bottom shear stress for deposition. Suspensions of carbonate mud show the same pattern of flocculation, ripple formation, and bed accretion as observed previously in experiments with clay-mineral suspensions. The resulting carbonate mud deposits show internal low-angle (2–5 degrees) laminae, and in plan view a pattern of ripple foresets that is identical to rib-and-furrow structure in sandstones. Just as previously assumed for terrigenous muds, there has been a long-standing notion that accumulation of abundant carbonate mud reflects quiescent conditions of offshore and deeper-water environments. These experiments demonstrate unequivocally that carbonate muds can also accumulate in energetic settings. In the sedimentary record of carbonate rocks, interbedded grainstones and lime mudstones may thus not necessarily reflect shifts in depositional energy (or water depth), but alternatively may imply a shift in supplied sediment type. The observations we report suggest that published interpretations of ancient lime muds and derived paleoceanographic conditions may need to be reevaluated.

Deep seismic reflection profile in Central Europe reveals complex pattern of Paleozoic and Alpine accretion at the East European Craton margin

AbstractThe first deep reflection seismic profile was acquired across the Teisseyre‐Tornquist Zone (TTZ), a major European suture zone, southeast of the Avalonia‐Baltica collision zone, portraying different tectonic deformation styles (thick‐ versus thin‐skinned) and Phanerozoic crustal accretion episodes over a relatively short distance (240 km). The overall crustal structure preserves image of the Neoproterozoic passive margin setting but with a significant overprint of the repetitive tectonic convergence (Cadomian to Alpine) acting at the Baltica margin. In contrast to the Avalonia‐Baltica collision zone, here the polygenetic crustal accretion occurring at the cratonic margin was ultimately shaped by significant strike‐slip faulting. TTZ is imaged as a narrow (10–15 km) transform zone separating the thinned East European cratonic crust from the Małopolska Block.

Detecting coastline change from satellite images based on beach slope estimation in a tidal flat

Beach heights and tidal variation have large impacts on the accuracy of estimates of coastline position and its historical changes of a wider and flatter beach based on remote sensing data. This study presents an approach to analysis of waterline movement based on the beach slope, estimated from two effective images with Landsat images data. Two images acquired at different stages of the tide were processed to delineate accurately the position of the waterline. Then waterlines were assigned heights using elevations predicted by a two-dimensional non-linear tidal assimilation model. Beach slope can be calculated piecewise using the heighted shorelines based on the equiangular triangle theory. The positions of the national tidal height datum coastline can be obtained by the beach slope calculation method to accurately monitor the changing of coastline. A change in the coastline of the southwest tidal flat of the Yellow River delta, from Tianshuigou to the Xiaoqing River mouth, was detected by combining field measurements of profiles and bathymetric data. The root mean squared error (RMSE) of the calculated slope of the intertidal zone was one order of magnitude less than the measured slope. The minimum error of self-consistency check is 0.2%. The RMSE between the coastlines estimated by the proposed method and those surveyed data varies from 53.98m to 217.72m. It is shown that this method is more suitable for the two years and over the time scales of shoreline change monitoring. To assess erosion/accretion patterns in the tidal flat, and the controlling factors, the volume of the beach was investigated as a possible indicator. The accepted coastline position and changes in the beach volume were used to monitor the changing pattern of accretion and erosion along the coast southwest of the recent Yellow River mouth.

A geophysical study of oceanic core complexes and surrounding terrain, Mid‐Atlantic Ridge 13°N–14°N

We describe a geophysical study of oceanic core complexes (OCC) and surrounding seafloor on the Mid‐Atlantic Ridge at 13°N–14°N and off‐axis to ∼1.9 Myr. Data include a detailed, deep‐towed side scan sonar, magnetic field and bathymetry survey, supplemented by concurrent sea‐surface bathymetry, magnetic field and gravity measurements. Using side scan and bathymetry, we infer areas and relative ages of seafloor volcanism, revealing a complex pattern of melt accretion across the median valley including close to its walls. We estimate tectonic and magmatic extension throughout the area, and find that average tectonic extension since chron 2 on plates containing OCCs is up to three times that on their conjugates. Deep‐towed magnetic data reveal asymmetric spreading (faster on OCC‐containing plates) and crustal magnetization that is highly heterogeneous on a scale of ∼5 km, suggesting that exhumed domes of OCCs have highly variable lithologies, perhaps comprising both serpentinized peridotite and gabbro. Improved fits to magnetic data are provided by models incorporating ∼45°of OCC footwall rotation. An axial zone of normal magnetization, of presumed Brunhes epoch, has highly variable width and amplitude, with parts of the ridge axis displaying very low or apparently reversed magnetization. Gravity requires that OCCs have dense cores capped by lower density zones several kilometers thick. Gravity data indicate longer term patterns of crustal thickness and melt distribution that are broadly consistent with numerical models of OCC formation and show that waxing magmatism may terminate OCCs.

Melt extraction pathways at segmented oceanic ridges: Application to the East Pacific Rise at the Siqueiros transform

[1] Throughout the global mid-ocean ridge system, transform faults offset spreading centers. Conductive cooling may be more efficient beneath transform faults, producing a thickened lithosphere that directs melt away from the transform. However, recent observations of thickened crust along transform faults at fast ridges suggest melt redistribution toward transforms, intra-crustal melt production, or efficient extraction of melt. We apply a 3-D model of melt migration and extraction along an oceanic transform domain bounded by ridge segments. Melt is assumed to travel vertically before collecting and migrating beneath a low-permeability boundary inclined towards the ridge axis. A melt extraction zone, which may be geologically interpreted as the presence of faults and/or dikes leading to rapid lateral and vertical melt migration toward plate boundaries, affects the pattern of crustal accretion at segmented ridges. First, we examine a generic ridge-transform-ridge geometry and then a model that represents the Siqueiros transform on the East Pacific Rise. On the basis of crustal thickness variations within the intra-transform spreading centers along the fast-slipping Siqueiros fault, we constrain the presence of a melt extraction zone within 10 km of the transform zone.

Coastline change of the Yellow River estuary and its response to the sediment and runoff (1976–2005)

The dramatic decreases in runoff and sediment have great impacts on erosion–deposition variation in the Yellow River estuary. This study extracted mean high tide lines of the Yellow River estuary from MSS, TM and ETM+ data from 1976 to 2005, and explored relationships between the accretion–erosion of land and the runoff and sediment load of the Yellow River. The results showed that the general pattern of accretion–erosion of the entire estuary was divided into four stages: rapid accretion stage (1976–1986), accretion–erosion adjustment stage (1986–1996), slow erosion stage (1996–2003), and slow accretion stage (2003–present). For maintaining the annual balance of the entire estuary (1976–2005) and Q8 estuary (most recent course of the Qingshuigou estuary from 1996 to 2005), critical annual runoff and sediment load are 140.36 × 10 8 m 3 year − 1 and 3.31 × 10 8 t year − 1 , and 85.0 × 10 8 m 3 year − 1 and 1.63 × 10 8 t year − 1 , respectively. In the future decades, the Q8 estuary is likely to maintain its shape and area balance or have a little accretion, but the entire estuary could be in an eroding state.

A Multiscalar Approach to Modeling the End of the Neolithic on the Great Hungarian Plain Using Calibrated Radiocarbon Dates

This article presents the results of a multiscalar analysis of 168 radiocarbon dates from Neolithic and Copper Age sites on the Great Hungarian Plain. We examined chronological patterns at different geographic scales to explore socioeconomic changes that occurred during the transition from the Neolithic to the Copper Age. The beginning and end of the Late Neolithic (5000–4500 cal BC) and Early Copper Age (4500–4000 cal BC) were modeled with14C dates calibrated with the CALIB 5.01 program and IntCal04 calibration curve. Our attempts to identify chronological subphases within these 500-yr-long periods were confounded by multiple intercepts in the calibration curve. The analysis indicated that terminal Late Neolithic (4700–4300 cal BC) and “transitional” Proto-Tiszapolgár occupations (4600–4250 cal BC) at tell sites were contemporary with initial Early Copper Age habitations (4450–4250 cal BC). Calibrated dates from small Early Copper Age settlements at Vészto-Bikeri and Körösladány-Bikeri document changes in community and household organization that took place over several decades during the transition to the Copper Age. Bayesian analysis indicated that the small fortified sites were occupied contiguously in phases of 30–50 yr. The younger Körösladány-Bikeri site was established before the older Vészto-Bikeri site was abandoned. When large nucleated Late Neolithic communities dispersed and established small Early Copper Age settlements, the pattern of vertical accretion that had created the Late Neolithic tells gave way to a pattern of horizontal settlement accretion at the smaller settlements.