persistent scatterer interferometric synthetic aperture radar for crustal deformation analysis with application to volcan alcedo galapagos 1 while conventional interferometric synthetic aperture radar insar is a very effective technique for measuring crustal deformation almost any interferogram includes large areas where the signals decorrelate and no measurement is possible persistent scatterer ps insar overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms existing ps methods have been very successful in analysis of urban areas where stable angular structures produce efficient reflectors that dominate background scattering however man made structures are absent from most of the earth s surface furthermore existing methods identify ps pixels based on the similarity of their phase history to an assumed model for how deformation varies with time whereas characterizing the temporal pattern of deformation is commonly one of the aims of any deformation study we describe here a method for ps analysis stamps that uses spatial correlation of interferogram phase to find pixels with low phase variance in all terrains with or without buildings prior knowledge of temporal variations in the deformation rate is not required for their identification we apply stamps to volcan alcedo where conventional insar fails because of dense vegetation on the upper volcano flanks that causes most pixels to decorrelate with time we detect two sources of deformation the first we model as a contracting pipe like body which we interpret to be a crystallizing magma chamber the second is downward and lateral motion on the inner slopes of the caldera which we interpret as landsliding

effects of tectonic deformation and sea level on river path selection theory and application to the ganges brahmaputra meghna river delta the set of active rivers of the ganges brahmaputra meghna gbm delta in bangladesh overlies an active plate boundary that continually modifies the landscape of the delta by deformation the response of rivers to spatially variable subsidence from tectonic tilting or other causes has been thought to include preferred occupation of regions of higher subsidence in this paper we develop further the theoretical framework for analysis of the interplay of tectonics and river dynamics and apply this model to conditions in the gbm delta first we examine the overall competition between variable subsidence and channel dynamics and find that tilting in bangladesh should be strong enough to influence river path selection we then present new theory for the effect of subsidence that is spatially not temporally variable we find a constant residence timescale on different parts of the delta and differing frequencies of avulsion to these locations and describe the effects of incision or floodplain deposition on these quantities we present estimates of the channel residence timescale of the jamuna brahmaputra river reconstructed from the lithology provenance and dating of sediment cores we apply our framework to a map of regional subsidence to predict the effects on avulsion for the jamuna river comparison between our predicted 2150 years and our stratigraphically based estimates of avulsion timescale 1800 years shows encouraging consistency

land subsidence in the nile delta inferences from radar interferometry the nile delta formed by progression of a complex system of deltaic fans throughout the pleistocene with the modern delta being formed from sediments supplied by at least ten distinct distributaries throughout the holocene with an average elevation of approximately 1 m above sea level within 30 km of the coast and a predicted rise in sea level of 1 8 5 9 mm yr the subsidence of the northern delta has become a topic of major concern to the egyptian population and government the nile delta is home to more than 50 million people and the major agricultural production area for egypt we evaluated the modern rates of subsidence of sections of the northeastern nile delta a total length of 110 km up to 50 km from the coastline using persist ent scatterer radar interferometry techniques applied to 14 ers 1 and ers 2 scenes the area covered includes the present active depocenter of the damietta promontory and the nearby mendesian depocenter that was active up to recent times to 2500 years ago the highest subsidence rates 8 mm yr twice average holocene rates do not correlate with the distribution of the thickest holocene sediments but rather with the distribution of the youngest depositional centers major deposition occurred between 3500 yr bp and present at the terminus of the damietta branch the adjacent slightly older 8000 2500 yr bp mendesian branch depositional center is subsiding at slower rates of 2 6 mm yr results are interpreted to indicate that 1 modern subsidence in the delta is heavily influenced by compaction of the most recent sediments and 2 highly threatened areas are at the terminus of the damietta and possibly the rosetta branches where active deposition is occurring

holocene sedimentary sequence foraminifera and ostracoda in west coastal lowland of bohai sea china abstract the holocene sedimentary sequences in the west coastal lowland of the bohai sea consists in ascending order of pre transgression river and lake sediments transgressive tidal flat and estuarine sediments shelf sediments and prograding delta and river deposits the delta deposits are the thickest and are typically composed of two imbricating yellow river delta superlobes that acted at different periods there are three marker horizons in the sequence at 1 the bottom of marine sediments 2 the bottom of shelf deposits and 3 the boundary between two imbricating delta superlobes environmental changes were mainly controlled by a rising sea level prior to 6000 bp and by delta progradation after 6000 bp stratigraphic distribution of foraminifera and ostracoda vary according to variations in salinity and sedimentation rate there is no evidence that the yellow river delta developed during the holocene transgression but rather during a later prograding phase an understanding of the shelly ridges in the coastal lowland indicates that the ridges were formed at a similar level to the present and there is no evidence for holocene sea levels 1 2 m higher than the present sea level

anthropogenic and geologic influences on subsidence in the vicinity of new orleans louisiana new measurements of ongoing subsidence of land proximal to the city of new orleans louisiana and including areas around the communities of norco and lutcher upriver along the mississippi are reported the rates of vertical motion are derived from interferometric synthetic aperture radar insar applied to uninhabited aerial vehicle synthetic aperture radar uavsar data acquired on 16 june 2009 and 2 july 2012 the subsidence trends are similar to those reported for 2002 2004 in parts of new orleans where observations overlap in particular in michoud the 9th ward and chalmette but are measured at much higher spatial resolution 6 m the spatial associations of cumulative surface movements suggest that the most likely drivers of subsidence are groundwater withdrawal and surficial drainage dewatering activities high subsidence rates are observed localized around some major industrial facilities and can affect nearby flood control infrastructure substantial subsidence is observed to occur rapidly from shallow compaction in highly localized areas which is why it could be missed in subsidence surveys relying on point measurements at limited locations

recent advances in sar interferometry time series analysis for measuring crustal deformation abstract synthetic aperture radar sar interferometry is a technique that permits remote detection of deformation at the earth s surface and has been used extensively to measure displacements associated with earthquakes volcanic activity and many other crustal deformation phenomena analysis of a time series of sar images extends the area where interferometry can be successfully applied and also allows detection of smaller displacements through the reduction of error sources here we review recent advances in time series sar interferometry methods that further improve accuracy this is particularly important when constraining displacements due to processes with low strain rates such as interseismic deformation we include examples of improved algorithms applied to image deformation associated with the 2010 eruption of eyjafjallajokull volcano in iceland slow slip on the guerrero subduction zone in mexico and tectonic deformation in western anatolia turkey

subsidence and evolution of the thessaloniki plain greece based on historical leveling and gps data comparison of historical leveling and of recent gps data reveal that the wider thessaloniki plain north greece a 2500 years old delta has subsided in the last 50 years up to 3 5 m these results are consistent with independent estimates of subsidence in the suburbs of thessaloniki and testify to a plain wide effect rather localized increased subsidence resulting from hydrocompaction due to intense pumping is superimposed on the plain wide subsidence the latter seems to mimic the long term tendency of landscape change as the correlation between recent surface deformation and deformation derived from boreholes reveals furthermore differential subsidence seems to control the flow of rivers and the overall morphology of the delta the significance and necessity of geoid corrections in the comparison of historical and gps data is also indicated

early cenozoic two phase extension and late cenozoic thermal subsidence and inversion of the bohai basin northern china abstract the bohai basin is one of a family of early cenozoic extensional basins that lie along the eastern margin of asia from russia to vietnam initial extension was probably triggered by subduction roll back of the oceanic pacific plate from the asian continent there were two phases in the bohai basin s rift history the earlier paleocene early eocene phase resulted in the deposition of the kongdian formation and the fourth lowest member of the shahejie formation in a series of elongate half grabens these half grabens have master faults with a nne ssw orientation secondary normal faults are typically clockwise oblique to the master faults indicating a component of dextral transtension deposition was focused in the west and south of the present basin these rocks are mainly alluvial fan and fluvial red beds the architecture of the basin underwent an important change at ca 43 45 ma middle eocene beginning with the deposition of the third member of the shahejie formation in part these sediments were deposited in the same half grabens as the kongdian formation but the bozhong depression in the central part of the basin originated at this time and became the major depocentre the bozhong depression superficially resembles a pull apart basin it formed when continued transtension of the earlier tertiary fault systems to the east and west created an extensional overlap between them during this phase the basin as a whole had a geometry with elements typical of both pull apart and transtensional basins regional extension in many east asian basins ended at the end of the oligocene probably because of the onset of transpression within eastern asia caused by the collision of australia with the philippine sea plate dextral transpression caused minor inversion of some of the earlier normal faults in bohai but as a whole the basin began to subside in a post rift phase of thermal subsidence that has lasted until the present day

assessment of ground subsidence using gis and the weights of evidence model abstract the weights of evidence model one of the bayesian probability models was applied in evaluating a ground subsidence spatial hazard near abandoned underground coal mines aucms at magyori area samcheok city in korea using gis using ground subsidence location and a spatial database containing information such as mining tunnel borehole topography geology and land use the weights of evidence model was applied to calculate each relevant factor s rating for the magyori area in korea seven major factors controlling or related to ground subsidence were determined from the probability analysis of the existing ground subsidence area depth of drift and distance from drift from the mining tunnel map slope gradient obtained from the topographical map ground water level and permeability from borehole data geology and land use tests of conditional independence were performed for the selection of factors allowing 6 combinations of factors to be analyzed for the analysis of mapping ground subsidence spatial hazard the contrast values w and w of each factor s rating were overlaid spatially the results of the analysis were validated using receiver operating characteristic roc with the previous ground subsidence locations in the case of all factor used the area under the roc curve auc showed 0 9667 which corresponds to an accuracy of 96 67 in the case of the combinations the case of distance from drift depth of ground water and land use used showed the 90 71 auc 0 9071 accuracy which is the best result produced in this analysis the results can be used for hazard prevention and land use planning near aucm areas

evaluating deep subsidence in a rapidly accreting mangrove forest using gps monitoring of surface elevation benchmarks and sedimentary records abstract ultimately the fate of mangrove forests depends on substrate elevation gains keeping pace with relative sea level rise rslr some of the world s largest mangrove forests occur on tectonically active margins river deltas and sedimentary basins where sea level trends are largely controlled by vertical land motion i e subsidence so that rslr can be markedly higher than sea level rise induced by climate warming the rod surface elevation table marker horizon rset mh method has been applied globally to evaluate coastal wetland resilience to slr by quantifying net rates of elevation change relative to a benchmark a limitation of the rset method is that the stability of the benchmark i e vertical trend is unknown and rslr in wetlands is typically inferred from regional tide gauge records in the present study we evaluate rslr in a rapidly subsiding avicenna marina mangrove forest with a large terrigenous sediment supply firth of thames new zealand using independent and complimentary methods 1 campaign gps surveys of the stability of three rset benchmarks driven 18 m into unconsolidated sediment a tide gauge some 10 km distant and a reference station located on basement rock 2007 2016 that are tied to a network of satellite based geodetic sites and 2 137cs validated 210pb sediment accumulation rates sar measured in cores as a proxy for rslr the similarity of deep subsidence rates at the rset benchmarks located several hundred metres apart 7 7 0 5 to 9 4 0 5 mm yr 1 provides confidence in these results these subsidence rates are two to five fold higher than recorded at the nearby tide gauge 3 6 0 7 mm yr 1 and reference station 1 6 0 5 mm yr 1 weighted average 210pb sar of 9 9 mm and 9 3 mm yr 1 yield similar estimates of deep subsidence i e 8 4 and 6 9 mm yr 1 slr adjusted for vertical land motion indicating that this geological process is the major driver of the long term sea level trend in the mangrove forest our findings suggest that regional tide gauge records may not provide reliable estimates of rslr for all coastal wetlands due to local subsidence associated with natural processes and human activities subsidence rates and rslr within coastal wetlands can be evaluated using campaign gps surveys of rset benchmarks and independently from longer term sedimentary records finally evaluations of the resilience of coastal wetlands to rising sea levels over the coming decades must be based on measurements of rslr from these systems themselves

instantaneous mapping of high latitude convection with coherent hf radars coherent hf radars at goose bay labrador and schefferville quebec are used to study plasma convection in the high latitude ionosphere maps of the two dimensional flow pattern are obtained by merging simultaneous sets of radial velocity data each with a time resolution of a few minutes from a time sequence of such maps we have separated the changes in flow due to magnetic local time mlt variations over the region of observation from those due to ut time variations we study in detail the convection in the early morning sector observed on october 15 1989 when the interplanetary magnetic field imf reversed from southward to northward this imf reversal was not associated with a clear response in the nightside convection but rather with several sudden changes some of which anticipated the bz reversal we suggest that these changes are associated with delayed and superposed ionospheric responses to previous imf perturbations or to local effects after the imf reversal from south to north our observations of westward and southwestward velocities in the 71 77 invariant latitude range are consistent with the earlier simulations for bz 0 and by 0 during the period of steady northward imf after the reversal the convection pattern was observed to reconfigure slowly a region of large westward velocities progressively moved poleward while convection in the low latitude part of the field of view faded away the time constant of this slow reconfiguration was about 1 hour and varied with mlt such that it was larger closer to midnight these data combined with particle data from successive passes of the dmsp satellites provide information on the contraction of the polar cap after the imf bz reversal and on the mlt dependency of the velocity at which this contraction occurs they show that the polar cap contracts more rapidly in the daytime than in the nightime and more rapidly in the postmidnight sector than in the premidnight sector

effects of peat compaction on delta evolution a review on processes responses measuring and modeling abstract peat is most compressible of all natural soils compaction of peat layers potentially leads to substantial amounts of land subsidence peat is common in many distal parts of holocene deltas which are often densely populated it is known that land subsidence due to peat compaction may have serious societal implications in such areas as it may cause damage to construction works and lead to land inundation effects of peat compaction on the natural evolution of deltas are however poorly understood whereas this might be an important control on delta evolution at both local and regional scales the main objective of this paper is to review current knowledge concerning the peat compaction process and its effect on delta evolution in holocene settings and to identify gaps in this knowledge an overview is given regarding 1 the compaction process 2 presumed and potential effects of peat compaction on delta evolution 3 field methods to quantify peat compaction and 4 numerical models to calculate the amount and rate of peat compaction peat compaction and formation influence channel belt elevation channel belt geometry and channel belt configuration last mentioned aspect mostly concerns the influence of peat compaction on avulsion which is one of the most important processes controlling delta evolution interactions between peat compaction peat formation and avulsion have seldom been studied and remain unclear partly because factors such as peat type organic matter content sediment sequence composition and groundwater table fluctuation are so far not taken into account peat compaction and formation potentially influence avulsion as 1 a decrease in accommodation space created by peat compaction underneath a channel causes superelevation and or an increase in lateral migration 2 the high cohesiveness of peat banks inhibits lateral migration which increases bed aggradation decreases sediment transport capacity and hence increases crevassing frequencies which possibly evolve into an avulsion although the low regional gradient in peatlands will hinder this and 3 peat compaction and oxidation in flood basins following groundwater table lowering leads to relief amplification of channel belts at delta scale variations in compaction rates might stimulate the occurrence of nodal avulsions to quantify effects of peat compaction on delta evolution and to determine the relative importance of different factors involved field research should be combined with numerical models describing peat compaction and formation the model should be validated and calibrated with field data

quantitative evidence that compaction of holocene sediments drives the present land subsidence of the po delta italy 1 deltas are highly dynamic coastal systems that over the last few decades have generally experienced a substantial area loss caused by trapping of river sediments in upland drainage basins as well as land subsidence due to natural and anthropogenic causes a major example is the po delta in the mediterranean in northeastern italy this area has experienced as much as 3 m of land subsidence from the 1930s to the 1970s primarily because of the extraction of gas bearing waters however present subsidence rates are largely unknown and the ground settlement is supposedly controlled by natural long term deep processes we have combined radar interferometric point target analysis ipta with previous geomorphological investigations on aerial satellite images and seismic surveys and geochronological data from core samples and geomechanical in situ tests to assess the current sinking of the delta and to understand the processes controlling the vertical movement the high density of the measurable point targets more than 15 000 allows characterization of the spatial variation in the vertical land motions vlm ranging from 1 to 15 mm yr we find that subsidence rates are significantly correlated with the age of highly compressible holocene deposits that compose the shallowest 30 40 m of the sedimentary sequence a typical log type consolidation equation applicable at the scale of the entire delta has been obtained we conclude that the consolidation of late holocene sediments is the major cause of the present land subsidence in the po river delta this finding has significant impact on the understanding of many other modern deltas that were formed in the lower holocene epoch

substorm triggering by new plasma intrusion themis all sky imager observations 1 a critical long standing problem in substorm research is identification of the sequence of events leading to substorm auroral onset based on event and statistical analysis of themis all sky imager data we show that there is a distinct and repeatable sequence of events leading to onset the sequence having similarities to and important differences from previous ideas the sequence is initiated by a poleward boundary intensification pbi and followed by a north south n s arc moving equatorward toward the onset latitude because of the linkage of fast magnetotail flows to pbis and to n s auroras the results indicate that onset is preceded by enhanced earthward plasma flows associated with enhanced reconnection near the pre existing open closed field line boundary the flows carry new plasma from the open field line region to the plasma sheet the auroral observations indicate that earthward transport of the new plasma leads to a near earth instability and auroral breakup 5 5 min after pbi formation our observations also indicate the importance of region 2 magnetosphere ionosphere electrodynamic coupling which may play an important role in the motion of pre onset auroral forms and determining the local times of onsets furthermore we find motion of the pre onset auroral forms around the harang reversal and along the growth phase arc reflecting a well developed region 2 current system within the duskside convection cell and also a high probability of diffuse appearing aurora occurrence near the onset latitude indicating high plasma pressure along these inner plasma sheet field lines which would drive large region 2 currents

observations of the relationship between ionospheric central polar cap and dayside throat convection velocities and solar wind imf driving convection observations from the southern hemisphere super dual auroral radar network are presented and examined for their relationship to solar wind and interplanetary magnetic field imf conditions restricted to periods of steady imf analysis is concentrated on two specific regions the central polar cap and the dayside throat region an example time series is discussed in detail with specific examples of apparent direct control of the convection velocity by the solar wind driver closer examination however shows that there is variability in the flows that cannot be explained by the driving scatterplots and histograms of observations from all periods in the year 2013 that met the selection criteria are given and their dependence on solar wind driving is examined it is found that on average the flow velocity depends on the square root of the rate of flux entry to the polar cap it is also found that there is a large level of variability that is not strongly related to the solar wind driving

possible connection of polar cap flows to pre and post substorm onset pbis and streamers 1 recent analysis of a short period of observations has led to the hypothesis that enhanced meso scale flows from well within the region of open polar cap field lines may cross the nightside polar cap boundary into the closed field line region and contribute to the triggering of equatorward earthward meso scale flows across the ionospheric equatorial portion of plasma sheet fields lines and lead to pbis and streamers this includes the streamers that have been postulated to bring new plasma equatorward earthward and lead to substorm onset meso scale structure of flow within the polar cap often studied near the dayside polar cap boundary has not previously been generally recognized as significant within the nightside polar cap here we have taken advantage of new capabilities to measure polar cap convection by the resolute bay incoherent scatter radar and the rankin inlet polardarn radar coordinated with themis all sky imager observations to study flow measurements from well within the polar cap to near the polar cap boundary we present evidence that flow structures moving from the polar cap toward the nightside polar cap boundary may be important for triggering the flows that lead to substorm onset streamers the new observations also have given evidence that the flow structures come from deep within the polar cap and have given unexpected evidence that a continuation of flow structures moving from the polar cap toward the nightside polar cap boundary after substorm onset may be important in controlling the poleward expansion and duration of post onset auroral activity

land subsidence at aquaculture facilities in the yellow river delta china 1 differential interferometric synthetic aperture radar is applied to the coast of the yellow river delta yrd in china like many deltas the coastline of the yrd is dominated by aquaculture advanced land observation satellite phased array l band synthetic aperture radar sar and envisat advanced sar data acquired between 2007 and 2011 show that subsidence rates are as high as 250 mm y at aquaculture facilities likely due to groundwater pumping these rates exceed local and global average sea level rise by nearly 2 orders of magnitude and suggest that subsidence and associated relative sea level rise may present a significant hazard for asian megadeltas

river mouth bar formation riverbed aggradation and channel migration in the modern huanghe yellow river delta china this paper addresses the recent 1970s 1990s processes of river mouth bar formation riverbed aggradation and distributary migration in the huanghe river mouth area in the light of station based monitoring field measurements and remote sensing interpretation the results show that the morphological changes of the river mouth bar have been closely associated with the largely reduced fluvial discharge and sediment load landforrn development such as bar progradation occurred in two phases i e before and after 1989 which correspond to faster and lower bar growth rates respectively fast riverbed aggradation in the mouth channel was strongly related to river mouth bar progradation during 1976 1996 about 2 8 of the total sediment loads were deposited in the river channel on the upper to middle delta therefore the river water level rose by a few meters from 1984 to 1996 the frequent distributary channel migration which switched the radial channel pattern into the se directed pattern in the mid 1980s was linked with mouth bar formation marine conditions also constrain seaward bar progradation furthermore the history of river mouth bar formation reflects human impacts such as dredging and dyking in order to stabilize the coastal area c 2005 elsevier b v all rights reserved

how much subsidence is enough to change the morphology of river deltas understanding the effect of subsidence on fluviodeltaic morphology is important not only to maintain sustainable coastal cities and habitats but also to interpret the information contained in the stratigraphic record while tectonic steering in alluvial environments has been investigated similar studies in fluviodeltaic environments are limited to physical experiments and field observations we perform numerical experiments with a parcel based cellular model to analyze the deltaic surface and subsurface responses to regional subsidence we quantify model results using robust metrics and show that while sediment partitioning and shoreline pattern vary gradually with increasing subsidence rate channel mobility and stratigraphic connectivity of channel deposits show a threshold transition conditions for this transition are captured with a dimensionless filling index defined as the ratio between the rates of accommodation creation and sediment supply a channel locking mechanism activates when exceeds 0 6 and is responsible for the threshold transition

magmatic and tectonic extension at mid ocean ridges 1 controls on fault characteristics we use 2 d numerical models to explore the thermal and mechanical effects of magma intrusion on fault initiation and growth at slow and intermediate spreading ridges magma intrusion is simulated by widening a vertical column of model elements located within the lithosphere at a rate equal to a fraction m of the total spreading rate i e m 1 for fully magmatic spreading heat is added in proportion to the rate of intrusion to simulate the thermal effects of magma crystallization and the injection of hot magma into the crust we examine a range of intrusion rates and axial thermal structures by varying m spreading rate and the efficiency of crustal cooling by conduction and hydrothermal circulation fault development proceeds in a sequential manner with deformation focused on a single active normal fault whose location alternates between the two sides of the ridge axis fault spacing and heave are primarily sensitive to m and secondarily sensitive to axial lithosphere thickness and the rate that the lithosphere thickens with distance from the axis contrary to what is often cited in the literature but consistent with prior results of mechanical modeling we find that thicker axial lithosphere tends to reduce fault spacing and heave in addition fault spacing and heave are predicted to increase with decreasing rates of off axis lithospheric thickening the combination of low m particularly when m approaches 0 5 as well as a reduced rate of off axis lithospheric thickening produces long lived large offset faults similar to oceanic core complexes such long lived faults produce a highly asymmetric axial thermal structure with thinner lithosphere on the side with the active fault this across axis variation in thermal structure may tend to stabilize the active fault for longer periods of time and could concentrate hydrothermal circulation in the footwall of oceanic core complexes

current subsidence rates due to compaction of holocene sediments in southern louisiana 1 relative contributions of geologic and anthropogenic processes to subsidence of southern louisiana are vigorously debated of these shallow sediment compaction is often considered dominant although this has never been directly observed or effectively demonstrated quantitative understanding of subsidence is important for predicting relative sea level rise storm surge flooding due to hurricanes and for successful wetland restoration despite many shallow borings few appropriate stratigraphic and geotechnical data are available for site specific calculations we overcome this by determining present compaction rates from monte carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the holocene of southern louisiana this approach generates distributions of present compaction rates that are not expected to exceed 5 mm yr but may locally locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes

changes in sediment yield of the yellow river basin of china during the holocene this research reconstructs the changes in sediment yield of the yellow river based mainly on a large number of 14 c dates collected from the literature the total volume of sediment yield of the basin during the holocene is estimated to be 8 0 x 10 12 tons the annual sediment yield had an increasing trend over the holocene from 0 68 0 72 0 79 to 1 0 1 x 10 9 tons over each 2500 year period from the early holocene to the present the changes in sediment yield are ascribed to both natural and anthropogenic reasons in which the latter became important in the late holocene the mean rate of increase in natural sediment yield throughout the holocene is estimated to be about 0 027 x 10 6 ton year and the natural annual sediment yield is projected to be 0 95 x 10 9 tons at the present the increasing trend of natural sediment yield is reasoned to be the consequence of evolution of landforms enhanced by tectonic movement and climatic change in the loess plateau the principal sediment source of the river towards a condition favorable to soil erosion comparing the estimated annual natural sediment yield with the current annual sediment load of 1 6 x 10 9 tons of the river it is clear that human activities have augmented natural soil erosion by about 41 in the yellow river basin furthermore an estimate of the overall pattern of anthropogenic sediment yield shows an accelerated increasing trend which is approximately correspondent with that of population in the loess plateau area c 2002 elsevier science b v all rights reserved

modes of extensional faulting controlled by surface processes we investigate the feedbacks between surface processes and tectonics in an extensional setting by coupling a 2 d geodynamical model with a landscape evolution law focusing on the evolution of a single normal fault we show that surface processes significantly enhance the amount of horizontal extension a fault can accommodate before being abandoned in favor of a new fault in simulations with very slow erosion rates a 15 km thick brittle layer extends via a succession of crosscutting short lived faults heave 10 km using simple scaling arguments we quantify the effect of surface mass removal on the force balance acting on a growing normal fault this leads us to propose that the major range bounding normal faults observed in many continental rifts owe their large offsets to erosional and depositional processes

interplay between faults and lava flows in construction of the upper oceanic crust the east pacific rise crest 9 25 9 58 n the distribution of faults and fault characteristics along the east pacific rise epr crest between 9 25 n and 9 58 n were studied using high resolution side scan sonar data and near bottom bathymetric profiles the resulting analysis shows important variations in the density of deformational features and tectonic strain estimates at young seafloor relative to older sediment covered seafloor of the same spreading age we estimate that the expression of tectonic deformation and associated strain on old seafloor is 5 times greater than that on young seafloor owing to the frequent fault burial by recent lava flows thus the unseen volcanically overprinted tectonic deformation may contribute from 30 to 100 of the 300 m of subsidence required to fully build up the extrusive pile layer 2a many longer lava flows greater than 1 km dam against inward facing fault scarps this limits their length at distances of 1 2 km which are coincident with where the extrusive layer acquires its full thickness more than 2 of plate separation at the epr is accommodated by brittle deformation which consists mainly of inward facing faults 70 faulting at the epr crest occurs within the narrow 4 km wide upper crust that behaves as a brittle lid overlying the axial magma chamber deformation at greater distances off axis up to 40 km is accommodated by flexure of the lithosphere due to thermal subsidence resulting in 50 inward facing faults accommodating 50 of the strain on the basis of observed burial of faults by lava flows and damming of flows by fault scarps we find that the development of layer 2a is strongly controlled by low relief growth faults that form at the ridge crest and its upper flanks in turn those faults have a profound impact on how lava flows are distributed along and across the ridge crest

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

overbank and channelfill deposits of the modern yellow river delta abstract the huanghe is noted for its high transport rate of silt and clay which may reach depth averaged values of 200 kg m 3 during peak discharge the sediment load transported through the river on entering the delta plain amounts to 1012 kg per year in contrast to most other large deltas only one distributary channel is active at any one time the high sediment load causes the rivermouth to prograde at a yearly rate of 1 4 km into the shallow less than 20 m deep bohai gulf the vertical aggradation of the channel belt and mouth bar complex is also rapid decimetres per year on average so that after a normal average of twelve years increasing channel instability and avulsion create the start of a new delta lobe a series of satellite images covering the last fifteen years has provided insight in the evolution of the river pattern as well as the progradation of the delta front a newly developed distributary passes from a multichannel to a single straight channel system and ends with the formation of meanders the protruding mature delta lobe shows a radiating pattern of crevasse channels overbank crevasse deposits are made of vertically stacked dm scale waning flow sequences structurally characterized by from bottom to top small scour and fills even parallel lamination and climbing ripple crosslamination accumulation rates on crevasse splays can be predicted on the basis of estimated river sediment discharge it can be concluded that each sequence has been deposited within a few hours and that tidal waterlevel fluctuations may have played a role in the generation of a single sequence

impact of anthropogenic subsidence on relative sea level rise in the fraser river delta subsidence is a common cause of amplified relative sea level rise flooding and erosion in coastal environments in particular subsidence due to sediment consolidation can play a significant role in relative sea level rise in large deltas we use a combination of insar interferometric synthetic aperture radar leveling and global positioning system data to map absolute vertical land motion in the fraser river delta western canada we show that primary consolidation of shallow holocene sediments is the main cause for the slow subsidence 1 to 2 mm a affecting the delta lowlands in addition parts of the delta undergo increased anthropogenic subsidence rapid subsidence rates 3 to 8 mm a are associated with recent artificial loads and exhibit a first order exponential decrease with a time constant of 20 years consistent with the theory of consolidation assuming two sea level rise scenarios of 30 or 100 cm by the end of the twenty first century natural subsidence will augment relative sea level rise in the fraser holocene lowlands by 50 or 15 anthropogenic subsidence will augment relative sea level rise by 130 or 40 potentially raising it to as much as 1 2 m in deltaic lacustrine and alluvial environments anthropogenic sediment consolidation can result in significant amplification and strong spatial variations of relative sea level rise that need to be considered in local planning

seismological evidence for three dimensional melt migration beneath the east pacific rise the extent to which crustal processes along mid ocean ridges are controlled by either the pattern of mantle upwelling or the mode of magma injection into the crust is not known models of mantle upwelling vary from two dimensional passive flow1 to three dimensional diapiric flow2 3 4 similarly beneath a ridge segment bounded by tectonic offsets crustal magma chambers may be replenished continuously along the ridge5 6 7 or at a central injection zone2 3 4 from which magma migrates towards the segment s ends here we present tomographic images that reveal the seismic structure and anisotropy of the uppermost mantle beneath the east pacific rise the anisotropy is consistent with two dimensional mantle flow diverging from the rise whereas the anomalous isotropic structure requires a three dimensional but continuous distribution of melt near the crust mantle interface our results indicate that crustal magma chambers are replenished at closely spaced intervals along axis and that crustal systems inherit characteristics of scale from melt transport processes originating in the mantle

changing pattern of accretion erosion of the modern yellow river huanghe subaerial delta china based on remote sensing images abstract the yellow river shifted from the diaokou course to the qingshuigou course in 1976 and shifted again at the north bank of the qingshuigou course in 1996 as a result the entire modern yellow river delta has experienced complicated patterns of erosion and accretion multitemporal remote sensing data of landsat mss and tm from 1976 to 2000 totaling twenty scenes were used to examine the changing pattern of accretion and erosion of the modern yellow river subaerial delta with gis tools during the period 1976 to 2000 the maximum erosion occurred at the head of the last two abandoned promontories diaokou and shenxiangou promontories where the coastline retreated landward over 7 and 4 5 km respectively with mean net erosion rates of 0 29 and 0 19 km a respectively in contrast the maximum accretion occurred at the head of the qingshuigou promontory where the coastline advanced seaward over 20 km with a mean net accretion rate of 0 83 km a the coastline at the head of the q 8 promontory also advanced seaward 7 km with a mean net accretion rate of 0 29 km a during the period 1996 to 2000 total area of the diaokou and shenxiangou promontories was reduced by 141 3 km 2 with a mean net erosion rate of 6 03 km 2 a total area of the qingshuigou and q 8 promontories increased by 384 16 and 11 88 km 2 respectively with mean net accretion rates of 16 4 and 3 03 km 2 a respectively relative to the diaokou shenxiangou and qingshuigou promontories the west area of the diaokou promontory and south area of the qingshuigou promontory were relatively stable although minor erosion occurred the general pattern of accretion and erosion of the modern yellow river subaerial delta was divided into three stages rapid accretion stage 1976 1984 accretion erosion adjustment stage 1985 1995 and slow erosion stage 1996 present the factors affecting the pattern of erosion and accretion over the yellow river delta such as structural geology the yellow river sediment discharge coastal processes meteorological conditions human activity sea level rise and land subsidence were summarized the cumulative area of increase over the entire subaerial delta is closely correlated with the cumulative yellow river sediment discharge wave induced longshore current is the major driving force to transport sediment from eroded areas along the last two abandoned promontories diaokou and shenxiangou promontories mostly westerly and partially easterly together with these coastal processes is the geographical shift of the yellow river course associated with its discharge regime after 1976 leading to the accretion along the present qingshuigou promontory and then the q 8 promontory

estimation of sediment compaction and its relationship with river channel distributions in the yellow river delta china abstract the geomechanical properties of the stratigraphic sequences strongly influence the land surface subsidence as the latter can be caused by the sediment compaction depositional units of transitional environments such as coastal plain and deltas are characterized by a high lithological variability due to the history and complexity of the sedimentary processes therefore detailed modeling of the stratigraphic architecture is necessary to better understand the land surface subsidence process and accurately estimate its rates the frequent avulsion and rearrangement of the channel network in the modern yellow river delta since 1855 has led to the rapid accumulation and deposition of large amounts of sediment in the delta plain the compaction of the substratum sediment due to the new sediment load and the consolidation of younger deposits caused land surface subsidence we used 108 sediment core data covering the delta and obtained detailed stratigraphic structural information a detailed distribution of clay and soft clayey soils which are the primary contributors to land subsidence was identified furthermore the compaction rates and the consolidation at time of the subaerial area and neritic area for the entire modern yellow river delta were estimated we also analyzed the characteristics of present land subsidence by combining a ground movement dataset obtained by high resolution topographic surveys with synthetic aperture radar sar interferometry insar of satellite images the results show that during the early stages of the development of the active deltaic lobe the compaction of neritic sediments was the primary contributor to initial subsidence furthermore combined with the relevant sedimentary age and environment determined by previous studies we found that the spatial variation in compaction induced subsidence in the subaerial deltaic area over time is closely related to the historical distributions of the river channels in the modern yellow river delta our findings providing a better characterization of the spatial and time heterogeneity of the land surface subsidence of both subaerial and submarine areas significantly improved the previous knowledge on land subsidence of the yellow river delta our results also demonstrate that the subaerial delta becomes increasingly stable over time with the gradual decrease in the average subsidence rate of each deltaic lobe

coastline change of the yellow river estuary and its response to the sediment and runoff 1976 2005 abstract 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 36 108 m3 year 1 and 3 31 108 t year 1 and 85 0 108 m3 year 1 and 1 63 108 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

sensitivity of seafloor bathymetry to climate driven fluctuations in mid ocean ridge magma supply recent studies have proposed that the bathymetric fabric of the seafloor formed at mid ocean ridges records rapid 23 000 to 100 000 years fluctuations in ridge magma supply caused by sealevel changes that modulate melt production in the underlying mantle using quantitative models of faulting and magma emplacement we demonstrate that in fact seafloor shaping processes act as a low pass filter on variations in magma supply strongly damping fluctuations shorter than about 100 000 years we show that the systematic decrease in dominant seafloor wavelengths with increasing spreading rate is best explained by a model of fault growth and abandonment under a steady magma input this provides a robust framework for deciphering the footprint of mantle melting in the fabric of abyssal hills the most common topographic feature on earth

large scale imaging of high latitude convection with super dual auroral radar network hf radar observations the hf radars of the super dual auroral radar network superdarn provide measurements of the e b drift of ionospheric plasma over extended regions of the high latitude ionosphere with the recent augmentation of the northern hemisphere component to six radars a sizable fraction of the entire convection zone approximately one third can be imaged nearly instantaneously 2 min to date the two dimensional convection velocity has been mapped by combining line of sight velocity measurements obtained from pairs of radars within common volume areas we describe a new method of deriving large scale convection maps based on all the available velocity data the measurements are used to determine a solution for the distribution of electrostatic potential expressed as a series expansion in spherical harmonics the addition of data from a statistical model constrains the solution in regions of no data coverage for low order expansions the results provide a gross characterization of the global convection we discuss the processing of the radar velocity data the factors that condition the fitting and the reliability of the results we present examples of imaging that demonstrate the response of the global convection to variations in the interplanetary magnetic field imf in the case of a sudden polarity change from northward to southward imf the convection is seen to reconfigure globally on very short 6 min timescales

historical changes in the yellow river delta china abstract the lower yellow river delta has experienced numerous avulsions during the last 2000 years and the floodplain can be divided into four provinces alluvial fan western plain middle plain and eastern plain coastal deltas the yellow river delta complex is composed of several delta superlobes resulting from shifts in the lower river channel and each delta superlobe consists of several smaller lobes formed by shifts in the distributary channels these two kinds of channel shifts have resulted in a complicated imbrication pattern in the delta complex two imbricated delta superlobes are divided by a reworked bed and buried shelf deposits shelly ridges form the surface boundaries between the various delta superlobes the delta superlobes passed through an active stage a reworking stage and were then finally overlain by later superlobes

improvement of superdarn velocity measurements by estimating the index of refraction in the scattering region using interferometry 1 in past calculations of convective velocities from super dual auroral radar network superdarn hf radar observations the refractive index in the scattering region has not been taken into account and therefore the inferred ionospheric velocities may be underestimated in light of the significant contribution by superdarn to ionospheric and magnetospheric research it is important to refine the velocity determination the refractive index in the ionosphere at superdarn observation f region altitudes has typical values between 0 8 and close to unity in the scattering region where conditions are more extreme the index of refraction may be much lower a simple application of snell s law in spherical coordinates bouguer s law suggests that a proxy for the index of refraction at the scattering location can be determined by measuring the elevation angle of the returned ionospheric radar signal using this approximation for refractive index the doppler velocity calculation can be refined for each superdarn ionospheric echo using the elevation angles obtained from the superdarn interferometer data a velocity comparison of dmsp and superdarn observations has revealed that the superdarn speeds were systematically lower than the dmsp speeds a linear regression analysis of the velocity comparisons found a best fit slope of 0 74 when the elevation angle data were used to estimate refractive index the best fit slope rose 12 to 0 83 as most superdarn radars employ an interferometer antenna array for elevation angle measurements the improvement in velocity estimates can be done routinely using the method outlined in this paper

direct determination of large scale magnetospheric field aligned currents with superdarn the superdarn super dual a uroral radar network radars measure large scale 2d images of the plasma convection velocity v in the high latitude f region from the 2d convection maps plasma flow vorticity can be directly calculated we show that the vorticity is a direct measure of jm p the magnetospheric component jm of the field aligned current fac per unit height integrated pedersen conductivity v the maps of jm p show clearly the region 0 1 and 2 currents uncontaminated by the ionospheric fac component ji caused by ionospheric pedersen and hall conductivity gradients which are important in the nightside substorm sector the generation of the large scale magnetospheric fac images of jm gp from the superdarn convection vorticity is explained and examples of dayside fac patterns for northward and southward imf conditions are presented for the superdarn radar pair in canada at saskatoon and kapus kasing by summer 1995 fac images will be available from three northern hemisphere superdarn radar pairs with a field of view extending over some 12 hours mlt from western canada to scandinavia and from one antarctic radar pair