a self regulating model of bedrock river channel geometry 1 the evolution of many mountain landscapes is controlled by the incision of bedrock river channels while the rate of incision is set by channel shape through its mediation of flow the channel shape is itself set by the history of bedrock erosion this feedback between channel geometry and incision determines the speed of landscape response to tectonic or climatic forcing here a model for the dynamics of bedrock channel shape is derived from geometric arguments a normal flow approximation for channel flow and a threshold bed shear stress assumption for bedrock abrasion the model dynamics describe the competing effects of channel widening tilting bending and variable flow depth transient solutions suggest that channels may take 1 10 ky to adapt to changes in discharge implying that channel disequilibrium is commonplace if so landscape evolution models will need to include bedrock channel dynamics if they are to probe the effects of climate change

the motion of rigid ellipsoidal particles in slow flows abstract preferred orientations of fabric elements in tectonites are usually interpreted with reference to two continuum models namely those of march 1932 and jeffrey 1922 it is argued that the first of these is usually inappropriate if the fabric elements are rigid inhomogeneities embedded in a deformable matrix jeffrey s model is more applicable but until recently its use has been limited to problems involving axisymmetric particles and simple flow geometries in this paper jeffrey s equations have been solved numerically in order to investigate the behaviour of more general systems the motions of two particle shapes one a prolate spheroid the other a triaxial ellipsoid are considered in parallel for four specified flow geometries which involve pure or simple shear and combinations of both any departures from particle axisymmetry or from simple flow geometries have a significant effect on particle behaviour compared with that predicted by spheroid simple flow solutions

long term change in tidal dynamics and its cause in the pearl river delta china abstract this paper focuses on identifying changes in the tidal range and the duration of the flood tide in the pearl river delta region china mann kendall test and regression methods are employed to verify the existence of trends in the annual tidal range and duration series from the 1950s to 2005 at 17 stations in the 3 major tributaries of the delta the research results indicate that generally there is an increasing trend in the tidal range and flood tide duration at most of the stations in the channel network moreover the more upstream the location of the station the more obvious the change in trend is and these increasing trends are all significant at the stations in the upper part of the delta specifically the tidal range at shilong station in the east river has increased abruptly since the middle of the 1980s such that the mean level of post 1990 data is approximately three times that for pre 1985 most stations near the mouth of the estuary show significant downward trends in the tidal range and flood tide duration results of the intersection point of the mann kendall test curves for these pearl river delta stations appear mostly in 1980s 1990s indicating that a noticeable change point occurs during this period human activities in the pearl river delta reached their peak during the 1980s among these large scale and long term sand excavation modified the hydrodynamic regime dramatically in a way that increased the water depth and lowered the level of the riverbed leading to an increased tidal prism and upstream movement of the tidal limit land reclamation is also likely to have had a relatively large effect on the tidal range and flood tide duration at stations near to the estuary mouth changes in other factors such as freshwater flow and sea level rise seem to be of relatively minor importance it is noteworthy that in a dry season the tidal dynamics are greatly enhanced and has resulted in strong saltwater intrusion into the estuary in recent years

vibrational and elastic properties as a pointer to stishovite to cacl2 ferroelastic phase transition in ruo2 abstract the high pressure behavior of ruo2 has been investigated using the first principles calculations based on the density functional theory here we report the calculated properties on structure electronic elastic phonon and electron phonon coupling of rutile and cacl2 type ruo2 our calculated lattice constants and bulk modulus agree reasonably well with the available theoretical and experimental data results of our calculations of zone center phonon modes at ambient and high pressures are in good agreement with raman scattering measurements elastic shear modulus and phonon analysis confirm the ferroelastic phase transition from rutile to cacl2 phase in ruo2 it is clearly illustrated that the first transition is associated with macroscopic shear instability which arises from the strong coupling between elastic constants and softening of raman active b1g mode the observed pressure of phase transition in experimental measurements was reproduced more accurately than in previous calculations and the difference between observed and calculated transition pressure is only of the order of few percentage we have also analyzed the rotation angle for o r o corresponding to b1g mode and found that the rotation of bond about 80 is required for transition from rutile to cacl2 phase in ruo2 in addition the mode gruneisen parameter is discussed the electron phonon interaction in both rutile and cacl2 type ruo2 at high pressure is also discussed

small scale heterogeneity in the mid lower mantle beneath the circum pacific area abstract data from a western united states short period seismic network are investigated in order to detect anomalous later p wave arrivals within a time window from 50 s to 170 s after direct p waves for deep and intermediate depth earthquakes at circum pacific subduction zones we interpret the anomalous arrivals as s to p scattered waves from heterogeneities in the mid lower mantle the searched regions depths from 4800 km to 2200 km cover approximately 2 of the entire lower mantle the heterogeneous scattering objects are located by array processing of the seismic waves using semblance with careful investigations of arrival time slowness and azimuth of the later phases relative to direct p waves we usually observe two or three later phases which are separated in arrival time by 5 20 s and have similar arrival azimuth and slowness this observation suggests that a few scatterers often form a cluster with a typical spacing of 100 200 km vertically more than ten clusters or groups of s to p scattering objects are detected in the mid lower mantle beneath the circum pacific regions northern kuril izu bonin mariana northern fiji and west coast of south america the s to p scattering objects are found in a depth range from 1100 to 1800 km and the most prominent objects of each region tend to be located around the middle of the depth range the amplitudes of the scattered waves range from 1 to 10 of the direct p waves with exceptionally large values as large as 40 the associated magnitudes of the changes in elasticity is not tightly constrained but probably are nearly 1 and may occasionally exceed 4 of shear velocity considering their high efficiency at converting short period waves wavelengths of 5 10 km the changes in elastic properties at the heterogeneous objects appear to occur within several kilometers seismic tomography studies have not detected prominent seismic wave speed anomalies except for those beneath south america which appear to be located in the former farallon plate and those at north of fiji which appear to be located around the pacific superplume the mid lower mantle heterogeneity should represent sharp chemical variations in major element composition of the lower mantle rocks the most plausible tectonic explanation of the variations is remnant of subducted and folded former oceanic crust which preceded the current subduction of the pacific plate the extreme estimates of low shear velocity 4 may indicate the prominent drops in the shear modulus due to ferro elastic phase transition in stishovite sio 2 our observations imply that heterogeneity of kilometer scale persists for billions of years despite of stirring due to convection and therefore is ubiquitous in the lower mantle it is qualitatively consistent with some recent convection models

two dimensional strain determination by the inverse surfor wheel abstract a simple method of two dimensional strain determination from the preferred orientation of deformed lines is presented it is based on the change of probability of intersecting lines on a given traverse as a function of traverse orientation the method can be applied to real lines such as grain boundary outlines or to virtual lines such as the tie lines between centre points of neighbouring grains in this manner estimates for the strain of surfaces i e of the particles enclosed by the surfaces and of bulk strain can be obtained

controls and limits on bedrock channel geometry 1 data on channel geometry in naturally incising bedrock rivers reveal variable relationships between channel width slope and erosion rate to explain the range of relationships between these parameters we propose an optimized channel geometry model the model reproduces previous theoretical and numerical modeling scaling relationships however to explain the field data the model must incorporate the effects of immobile sediment cover that reduces vertical incision efficiency adding sediment to a system for a given rate of base level fall both widens and steepens the channel we also find that a constant width to depth ratio is only valid for streams where the shear stress required for sediment transport is insignificant compared to the shear required to erode at the imposed base level fall our model offers an explanation of seemingly contradictory field observations of controls on channel width and shows that channel width fundamentally controls the erosive potential of a river especially when it carries a significant bed load

recent morphological changes in the mekong and bassac river channels mekong delta the marked impact of river bed mining and implications for delta destabilisation abstract the mekong delta in vietnam is the world s third largest delta densely populated the delta has been significantly armoured with engineering works and dykes to protect populations and infrastructure from storms and shrimp farms from saltwater intrusion considerable development pressures in vietnam and in the upstream countries have resulted in the construction of several dams in china and in important channel bed aggregate extractions especially in cambodia the effects of these developments impact the delta dynamics in various ways in this study changes in the channel morphology of the mekong proper and the bassac the two main distributaries in the 250 km long deltaic reach from the cambodian border to the coast were analysed using channel depth data for 1998 and 2008 the channels display important and irregular bed changes over the 10 year comparison period including significant incision and expansion and deepening of numerous pools the mean depth of both channels increased by more than 1 3 m both channels also showed correlative significant bed material losses respectively 90 million m 3 in the mekong and 110 million m 3 in the bassac over the 10 year period these important losses over a relatively short period and weak correlations between bed incision and hydraulic parameters suggest that the marked morphological changes are not in equilibrium with flow and sediment entrainment conditions and are therefore not related to changes in river hydrology we claim that aggregate extraction currently practised on a very large scale in the mekong delta channels and upstream of the delta is the main cause of these recent morphological changes these changes are deemed to contribute actively to rampant bank erosion in the delta as well as to erosion of the mekong delta shoreline other contributory activities include the numerous dykes and embankments the role of existing dams in bed losses remains unclear in the absence of reliable data on the mekong sediment load future large scale hydropower dam development on the lower mekong main stem will have cumulative effects with aggregate extraction leading to increased morphological changes that will further impact the delta especially in terms of sediment supply and coastal erosion

distribution of bedrock and alluvial channels in forested mountain drainage basins mountain river networks often consist of both bedrock and alluvial channels1 5 the spatial distribution of which controls several fundamental geomorphological and ecological processes6 7 the nature of river channels can influence the rates of river incision and landscape evolution1 2 as well as the stream habitat characteristics affecting species abundance and aquatic ecosystem structure8 11 studies of the factors controlling the distribution of bedrock and alluvial channels have hitherto been limited to anthropogenic badlands12 here we investigate the distribution of channel types in forested mountain drainage basins and show that the occurrence of bedrock and alluvial channels can be described by a threshold model relating local sediment transport capacity to sediment supply in addition we find that valley spanning log jams create alluvial channels hospitable to aquatic life in what would otherwise be bedrock reaches the formation of such jams depends critically on the stabilizing presence of logs derived from the largest trees in the riverside forests suggesting that management strategies that allow harvesting of such trees can have a devastating influence on alluvial habitats in mountain drainage basins

a statistic for estimating strain with confidence intervals from deformed line distributions with an application to schists and gneisses of the western gneiss region west central norway abstract it is shown how to calculate the axial ratio of the strain ellipse r s from a deformed set of lines assuming that they were initially uniformly distributed and deformed passively using an exact but simple relationship between r s and the mean resultant length r of the distribution the method applies to distributions of lines modified under a general 2d deformation w k w k is the kinematical vorticity number by using the circular variance for circular data expressions for confidence intervals and confidence levels are calculated for strain modified distributions of lines these expressions indicate that confidence interval widths decrease with increasing r s and more importantly that the method is incapable of accurately estimating low strains the method was applied to 18 gneiss and schist samples from joa west central norway and found to produce realistic strain estimates which are internally consistent and concur with field relationships

beyond threshold hillslopes channel adjustment to base level fall in tectonically active mountain ranges numerous empirical and model based studies argue that in general hillslopes and river channels increase their gradients to accommodate high rates of base level fall to date however few data sets show the dynamic range of both these relationships needed to test theoretical models of hillslope evolution and river incision here we utilize concentrations of 10 be in quartz extracted from river sand on the eastern margin of the tibetan plateau to explore relationships among short term 10 2 10 5 a erosion rate hillslope gradient and channel steepness our data illustrate nonlinear behavior and a threshold in the relationship between erosion rate and mean hillslope gradient confi rming the generalization that hillslopes around the world are limited by slope stability and cease to provide a metric for erosion at high rates 0 2 mm a the relationship between channel steepness index and erosion rate is also nonlinear but channels continue to steepen beyond the point where threshold hillslopes emerge up to at least 0 6 mm a demonstrating that channel steepness is a more reliable topographic metric than mean hillslope gradient for erosion rate and that channels ultimately drive landscape adjustment to increasing rates of base level fall in tectonically active settings

post stishovite phase boundary in sio2 determined by in situ x ray observations a laser heating diamond anvil cell experiment with an angle dispersive x ray diffraction using synchrotron radiation source at the spring 8 has been developed to observe the phase transition in silica sio2 between the p42 mnm rutile type and pnnm cacl2 type up to pressures of 100 gpa and at temperatures up to 2200 k the transition was observed in the vicinity of 55 gpa at room temperature and showed a positive temperature dependence of the transition pressure the phase boundary was determined to follow the equation p gpa 51 2 0 012 0 005 t k our result gives a transition pressure of near 80 gpa and a depth of 1900 km at an expected lower mantle temperature of 2000 2500 k therefore this sio2 transition is not the cause of recent observations of seismic anomalies between 800 and 1600 km depth in the mid lower mantle

feedbacks between erosion and sediment transport in experimental bedrock channels natural bedrock rivers flow in self formed channels and form diverse erosional morphologies the parameters that collectively define channel morphology e g width slope bed roughness bedrock exposure sediment size distribution all influence river incision rates and dynamically adjust in poorly understood ways to imposed fluid and sediment fluxes to explore the mechanics of river incision we conducted laboratory experiments in which the complexities of natural bedrock channels were reduced to a homogenous brittle substrate sand and cement a single sediment size primarily transported as bedload a single erosion mechanism abrasion and sediment starved transport conditions we find that patterns of erosion both create and are sensitive functions of the evolving bed topography because of feedbacks between the turbulent flow field sediment transport and bottom roughness abrasion only occurs where sediment impacts the bed and so positive feedback occurs between the sediment preferentially drawn to topographic lows by gravity and the further erosion of these lows however the spatial focusing of erosion results in tortuous flow paths and erosional forms inner channels scoops potholes which dissipate flow energy this energy dissipation is a negative feedback that reduces sediment transport capacity inhibiting further incision and ultimately leading to channel morphologies adjusted to just transport the imposed sediment load copyright 2007 john wiley sons ltd

morphological change in the pearl river delta china morphological changes in the pearl river delta prd have been investigated using bathymetric charts underwater digital elevation models remote sensing data and geographic information systems water depths were extracted from digitized charts to explore the accretion erosion characteristics of three estuarine environments and to provide quantitative estimates of changes in sediment volumes multi temporal satellite images have been used in combination with topographical data to analyze the coastline changes prd has gained an abundant amount of sediment of almost 9 45 105 km3 above the 10 m isobath in the period roughly between 1970 and 2010 the average sedimentation rate was 3 15 104 km3 yr between 1976 and 2006 the coastline extended seaward by 579 2 m on average with a mean net extension rate of 19 3 m yr the results suggest that the prd experienced a major phase of accretion with net erosion only in some local zones coastline extension associated with major morphological changes has accelerated in recent decades changes in boundary conditions such as sea level rise seem to have relatively minor impacts on the dramatic changes in the morphology of the estuaries the seaward extension of the coastlines shows an increasing trend whereas the sediment supply from the delta displays a decreasing trend a detailed comparative analysis demonstrates that land reclamation in the prd is the most significant factor that progressively alters the delta morphology overwhelming the effects of subsidence and sediment supply

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

a two dimensional morphological model based on next generation circulation solver ii application to caofeidian bohai bay china abstract this paper is a companion of a two part papers on the development of a two dimensional morphological model curwac2d sed based on next generation circulation solver in this paper the model developed in paper i is applied to the large scale construction of near harbor industrial zone with deep water harbor by reclamation in caofeidian bohai bay which is a typical sandbar lagoon bay type tidal inlet system characteristics of tides currents waves and sediments in caofeidian are firstly analyzed with field data from comprehensive field observations carried out in 2008 these data are then used for model calibration and validation showing a good agreement between simulated results and field measurements for tides currents and suspended sediments the verified model is applied to study the effects of the construction of caofeidian embankment and the on going engineering scheme on hydrodynamics and sediment transports as compared with no constructions under three representative tide conditions and their combinations with normal and strong waves as well as on morphology evolution the simulated results indicate that the present scheme leads to morphological changes in caofeidian with acceptable rates of erosion and sedimentation however some attentions should be paid to erosion at offshore wharf in front of caofedian foreland which may lead to potentially increasing landslide risks due to steep slope and sedimentation in laogonggou creek

modelling flanking structures using deformable high axial ratio ellipses insights into finite geometries flanking structures develop locally around material inhomogeneities the evolution of these structures is investigated here by modelling peturbations around a deformable ellipse using a 2d analytical solution non unique instantaneous and finite geometries are predicted and it is shown that in terms of slip and curvature complex histories are possible under simple shear whereas under pure shear instantaneous geometries map directly into finite state geometries single flanking structures are of limited use in kinematic analysis but can help constrain the kinematics when interpreted in conjunction with other structural features flanking structures exhibiting a range of ce cross cutting element orientations have more potential as kinematic indicators flanking structures serve as an excellent example of the role that material homogeneity can play in locally producing complex structures in a relatively simple bulk flow field

holocene delta evolution and sediment flux of the pearl river southern china delta progradation and sediment flux of the pearl river delta prd southern china during the holocene are presented based on analyses of borehole data on the delta plain results indicate that the delta prograded into the drowned valley because of early holocene inundation from 9 to 6 cal ka bp as sea level rise decelerated the sea level reached its present level at about 6 cal ka bp and as a consequence a large portion of the drowned valley was covered by the estuary with more than 160 rock islands and platforms the scattered landmasses promoted active deposition and acted as deposition nuclei during deltaic evolution consequently apart from exhibiting a general tendency towards progression prd development occurred less regularly over time and space because of deposition around island boundaries during the last 2 ka mainly because of significantly increased human activities which have trapped sediments in the encircled tidal flats along the front of delta plains the shoreline has advanced rapidly estimated sediment fluxes for the three periods 9 6 6 2 and 2 0 cal ka bp based on the sediment volume analysis were 17 25 22 30 and 44 58 million t a 1 respectively copyright c 2016 john wiley sons ltd

does decreasing paraglacial sediment supply slow knickpoint retreat in four rivers in western scotland for which there is a well constrained record of relative base level fall the rate of postglacial bedrock erosion is quantifi ed by measuring the concentration of in situ cosmogenic 10be on strath terraces downstream of headward retreating knickpoints along channel gradients in 10be exposure age show two distinct trends upstream younging and constant age which we interpret as diagnostic of knickpoint retreat and diffusive transport limited incision respectively we show that bedrock channel incision and regional formation of strath terraces began shortly after deglaciation ca 11 5 ka and that knickpoint retreat rates peaked in the early to mid holocene erosion rates have since decreased by two orders of magnitude converging in the late holocene to low rates independent of stream power per unit channel area we infer this regional slowing in postglacial knickpoint retreat to be the result of the depletion of paraglacial sediment supply over the holocene leading to a defi ciency in tools for bedrock erosion our results imply that episodes of major fl uvial erosion may be in tune with glacial cycles and that sediment depletion following glacial interglacial transitions may be an important cause of bedrock erosion rate variations in rivers draining glaciated landscapes

temporal and spatial variability of sediment flux into the sea from the three largest rivers in china abstract the yellow yangtze and pearl rivers supply over 90 of the sediment flux from china to the western pacific ocean trends and abrupt changes in the water discharge and sediment load of the three rivers were examined and compared based on data updated to the year 2011 at the seasonal and annual scales the total water discharge from the three rivers shows a statistically insignificant decreasing trend with a rate of 0 62 10 9 m 3 a and the total sediment load shows a statistically significant decreasing trend at a rate of 31 12 10 6 t a from the 1950s to 2011 the water discharge of the entire yellow river and the upstream portion of the yangtze river shows significant decreasing trends and that of the mid lower stream of yangtze river and the entire pearl river shows insignificant trends the sediment loads in the three river basins all show significant decreasing trends at the annual and seasonal scales and a dramatic decrease in the 2000s resulted in a more obvious decreasing trend over the studied period from the 1950s to the 2000s the contribution of sediment flux from the yellow river to the ocean decreased from 71 8 to 37 0 and the contributions of the yangtze and pearl rivers increased from 24 2 and 4 0 to 53 0 and 10 0 respectively inter annual variations in water discharge and sediment load were affected by climate oscillations such as the el nino southern oscillation and the long term decreasing trend in sediment load was primarily caused by human activities dam constructions and soil conservation projects were the major causes of sediment reduction from the 1970s to the 2000s the decrease in total sediment load from the three rivers caused by climate change and human activities was 2 24 10 8 t a 23 0 and 7 5 10 8 t a 77 0 respectively in the coming decades the sediment flux from the three rivers into the sea will decrease further with intensifying human activities resulting in many challenges for the management of river basins and river deltas

morphodynamic responses to the deep water harbor development in the caofeidian sea area china s bohai bay vast bay type tidal inlets can be found along the coastal zones of china they are generally suitable for deep water channels and large harbors because of the presence of large water depth and good mooring conditions the deep channel in front of the head of caofeidian island in bohai bay china is a typical bay type tidal inlet system the tidal current a type of reverse flow makes the key contribution to maintain the deep water depth the co action of waves and tidal currents is the main dynamic force for sediment motion waves have significant influence on the sediment concentration based on the characteristics of waves tidal currents sediment and seabed evolution in caofeidian sea area a 2d mathematical model for sediment transport under influence of waves and tidal currents is developed to study the development schemes of the caofeidian harbor the model has been verified for spring and neap tides in winter as well as in summer of 2006 the calculated tidal stages flow velocities flow directions and sediment concentrations at 15 stations are in good agreement with the observations furthermore the calculated data on pattern and magnitude of sedimentation and erosion in the related area agree well with the observations this model has been used to study the effects of the reclamation scheme for caofeidian harbor on the hydrodynamic environment sediment transport and morphological changes attentions are paid to the project inducing changes of flow velocities and morphology in the deep channel at the south side of caofeidian foreland in the laolonggou channel and in various harbor basins the conclusions can provide the important foundation for the protection and use of bay type tidal inlets and the development of harbor industry

bedding parallel shear thrusting and quartz vein formation in witwatersrand quartzites abstract evidence is presented which clearly demonstrates the presence of thrust faults in the gold bearing sedimentary rocks of the witwatersrand supergroup a package of these rocks subjected to shear strain allowed overlying beds on the northern margin of the witwatersrand basin to move outwards in a n nw direction movement took place on ductile shear zones which were parallel to the bedding and often reveal excellent examples of ramp and duplex structures it has also been established that syntectonic foliation planes were utilized as planes of shear in certain circumstances quantitative estimates of strain for the pile which are of necessity minimum values give 1 fluids from which vein quartz formed played a critical role in the shear plane movement and may have relieved a portion of the overburden load during deformation

channel width response to differential uplift 1 the role of channel width and slope adjustments to differential uplift in rivers within actively deforming terrains remains contentious here high resolution topographic surveying of formerly antecedent outwash channels demonstrates marked changes in channel width as a primary response to differential uplift for five late quaternary alluvial paleochannels crossing small folds along the active ostler fault zone of southern new zealand nearly continuous measurements of paleochannel width and concomitant incision reveal abrupt narrowing of widths toward minimum values at channel positions coincident with the initial uplift when the magnitude of differential uplift is sufficiently small narrowing alone permits these channels to remain antecedent in the context of a unit stream power model for fluvial erosion observed limits on the magnitude of channel narrowing suggest that above some threshold amount of differential uplift continued incision requires concomitant changes in channel gradient thus when crossing small growing folds alluvial rivers simply narrow their channels whereas larger folds that demand greater incision prompt an initial narrowing followed by channel steepening

microfabric reconstruction via quantitative digital petrographic image analysis for weakly foliated gneisses abstract detection and documentation of petro structural features such as alignment features of minerals grains and extraction of such spatial property data are two fundamental steps for structural geology such tasks were mostly carried out manually however manual analysis is laborious and potentially biased these drawbacks are less obvious when the foliation is well developed and the amount of platy mineral is higher for samples with weakly developed foliation and low platy mineral content automatic method is required for subjective interpretation a semi automatic computerized method of 3d foliation orientation reconstruction via two dimensional petrographic shape fabric analysis from serial oriented digital microphotograph has been developed and demonstrated in this study the foliation is reconstructed by fitting a best fitting plane to the maximum modal peaks of micro textural parameters spo for different mineral groups of platy and granular minerals from each thin section on a stereonet for four coarse grained biotite gneiss samples collected along the jialie fault se tibet china regardless of platy or granular mineral aggregates the reconstructed foliations showed similar orientation within 10 angular variation to the field measurement the 10 angular variation can be maintained if the foliations are reconstructed by consecutive thin section groupings 50 angular intervals and a horizontal thin section the angular spread increased to 30 for thin section groupings with 50 to 100 angular intervals with a horizontal thin section major advantages of the computerized photometric methods demonstrated by this study are the reduction of human prejudice and obtaining quantified and repeatable data sets

the role of sediment in controlling steady state bedrock channel slope implications of the saltation abrasion incision model abstract the saltation abrasion model is a mechanistic model for river incision into bedrock by saltating bedload which we have previously derived and used experimental data to constrain all parameter values here we develop a method for applying the saltation abrasion model at a landscape scale and use the model as a reference for evaluating the behavior of a wide range of alternative incision models in order to consider the implications of the saltation abrasion model as well as other models for predicting topographic steady state channel slope to determine the single valued discharge that best represents the effects of the full discharge distribution in transporting sediment and wearing bedrock we assume all runoff can be partitioned between a low flow and a high flow discharge in which all bedload sediment transport occurs during high flow we then use the gauged discharge record and measurements of channel characteristics at a reference field site and find that the optimum discharge has a moderate magnitude and frequency due to the constraints of the threshold of grain motion and bed alluviation by high relative sediment supply incision models can be classified according to which of the effects of sediment on bedrock incision are accounted for using the predictions of the saltation abrasion model as a reference we find that the threshold of motion is the most important effect that should be represented explicitly followed in order of decreasing importance by the cover effect the tools effect and the threshold of suspension effect models that lack the threshold of motion over predict incision rate for low shear stresses and under predict the steady state channel slope for low to moderate rock uplift rates and rock strengths models that lack the cover effect over predict incision rate for high sediment supply rates and fail to represent the degree of freedom in slope adjustment provided by partial bed coverage models that lack the tools effect over predict incision rate for low sediment supply rates and do not allow for the possibility that incision rate can decline for increases in shear stress above a peak value overall the saltation abrasion model predicts that steady state channel slope is most sensitive to changes in grain size such that the effect of variations in rock uplift rate and rock strength may affect slope indirectly through their possible but as yet poorly understood influence on the size distribution of sediments delivered to channel networks by hillslopes

channel response to low water levels in the pearl river delta a multi decadal analysis abstract the pearl river delta is a composite delta with one of the densest channel networks in the world to analyze the internal erosion deposition characteristics of the net channel area this paper studies the upstream evolution characteristics using digital elevation model data from local channel sections we attempt to establish the relationship between the changes in low water level and erosion rate by using the accumulated data for the main stream and hydrological stations over the past 50 years including the distributions of flow and sediment at the top of the net channel area and the erosion deposition data of a typical channel section in fact the net channel area has been in a forced erosion state artificial sand excavation for a long time forcing the flow and sediment distributions at makou and sanshui stations to adjust from 1993 to the present although the incoming sedimentation is far less than the net erosion and there are similarities and differences in the sources of the incoming flow and sediment from the main stream the internal characteristics of the upper and lower reaches of the delta have not changed substantially they have always been stable slow deposition channels the forced undercutting is concentrated within width depth ratios of approximately 50 250 which still meets the evolution characteristics of the natural channel artificial sand excavation during the 1980s tended to enhance the characteristics however the sudden increase in the undercutting rate has forced chaotic changes in the low water level since 1990 and the sediment transport rate decreased sharply the phenomena of salt tides retrogression and retrogressive erosion generally happen the water level evolution in the net channel area is chaotic and continuous undercutting is still occurring

asymmetric shape preferred orientations as shear sense indicators abstract mineral shape preferred orientations can be characterized by plotting aspect ratios against grain length orientation and such plots commonly display asymmetric patterns in xz sections perpendicular to foliation and parallel to the direction of maximum elongation in most cases the asymmetries cannot be discerned by superficial examination of thin sections the sense of asymmetry can be defined by a the shape of the highest aspect ratio per grain length orientation curve and b the relative orientations of the most elongate grain and the mean or median of the population as a whole observed senses of asymmetry display consistent relationships to known senses of shear and they therefore provide a useful alternative to or check on other methods of shear sense determination examples of quartz plagioclase microcline amphibole and biotite shape preferred orientations are described and they include recrystallized mosaics as well as populations of discrete mineral grains the examples include mineral preferred orientations that evolved by plastic deformation anisotropic crystal growth and mechanical rotation of inequidimensional grains

rapid response of the changjiang yangtze river and east china sea source to sink conveying system to human induced catchment perturbations abstract in order to investigate human impact in the changjiang east china sea source to sink conveying system we analyze the siltation and erosion state of the estuary shelf deposition systems and discuss the response intensity and timing of the depositional system of the changjiang subaqueous delta and the related changjiang distal mud results show that after the three gorges dam was put into operation in 2003 the abrupt reduction of the sediment discharge to the estuary disturbed the equilibrium between the estuary coast shelf deposition systems modifying the siltation erosion balance and seabed sediment types from the changjiang subaqueous delta to its distal mud areas the degree of response to catchment changes diminishes with a larger response lag from north to south of the distal muds influenced by dam emplacements the change of the changjiang east china sea source to sink conveying system can be divided into three stages i e pre 1950 1950 2002 and post 2003 before 1950 the source to sink system remained relatively stable between 1950 and 2002 man made fluvial impoundments created an important sink for terrigenous sediment of the upstream regions but without profound system changes in contrast after 2003 the morphodynamic patterns for the entire mid lower reaches of the changjiang river the subaqueous delta and the distal muds shifted rapidly from siltation to erosion within a short period of time furthermore the upper reaches of the river became disconnected from the source to sink conveying system and the mid lower reaches of the river together with its subaqueous delta and northern distal mud area were converted into net sediment sources as such the sink area has shrunk while the source area expanded for the changjiang east china sea source to sink conveying system

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

self organization of river networks to threshold states numerical models in which grid cells self organize so that the shear stress in each cell equals a predetermined threshold value are remarkably successful in producing the fundamental structure of river networks such models are a reasonable approximation of networks characterized by near constant dimensionless shear stress bed shear stress7sol bed grain size with each cell s threshold value being proportional to median bed grain size previous work has shown that this is the case for channels cut into alluvium and that the characteristic narrow range of is different for gravel and sand bed channels channels in the italian apennines that are slowly incising into weak bedrock but which are covered by a veneer of gravel for most of the time are shown to be characterized by the same as alluvial gravel bed channels thus threshold models capture the fundamental behavior of many river networks even in areas of long term bedrock incision

natural rotated inclusions in non ideal shear abstract kinematic analysis of rotated winged inclusions is often couched in terms of ideal simple shear with reference to a specific model based upon porphyroclasts of circular section however many natural winged inclusions are not porphyroclasts commonly their geometries as well as the orientation distribution of the inclusions themselves reflect the non ideal nature of the shearing deformation during which they formed stair stepped sigma shaped geometries may reflect the immaturity of a structure developed in non ideal shear or a mature structure developed in ideal simple shear stair stepped delta shaped geometries indicate that deformation approximated to ideal simple shear in plane delta shaped geometries and skewed inclusion orientation distributions are indicators of non ideal shear

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

syntectonic vein development in a thrust sheet from the external french alps abstract the geometry and age relations of syntectonic veins within calcareous rocks of one imbricate sheet within a thrust belt in the external french alps are described the earliest veins developed during the main ductile deformation by cleavage parallel extension the majority of the syntectonic veins developed towards the end of the deformation and after the formation of second folds they include a conjugate set of normal shears an abundant set of upright extension veins and en echelon sets the dominantly simple shear strain making up the main ductile phase of deformation occurred by a mechanism of grain to grain pressure solution the stretching lineation records the overall direction of thrust sheet movement a change in the microchemical mechanism of pressure solution is thought to have caused the change from first to second phase deformation as recorded by slaty cleavage and crenulation folds in the field from the shear and vein geometries directions of principal stress have been inferred the directions rotated throughout the deformation the maximum principal stress being inclined to bedding during simple shear strain becoming normal to bedding during the phase of abundant vein growth and becoming vertical at the very end of the deformation

mid mantle layering from sks receiver functions 1 many seismic data on mid mantle discontinuities are related only to subduction zones here we use a method that is applicable outside subduction zones the idea is to use sks to p converted phases that are generated in the receiver regions and can be detected in s receiver functions in two regions southern africa and western europe we have detected apparently the same 1200 km discontinuity but at a depth that varies from 1170 km africa to 1240 1270 km europe the s velocity contrast at this discontinuity is 0 1 km s i e half of the value in subduction zones the 1200 km discontinuity may correspond to the phase transition of sio2 from stishovite to cacl2 structure the small s velocity contrast is compatible with scenarios in which small remnants of old subducted oceanic lithosphere thermally equilibrated and partly reacted are finely dispersed in a bulk mantle matrix

characterization of slow slip rate faults in humid areas cimandiri fault zone indonesia in areas where regional tectonic strain is accommodated by broad zones of short and low slip rate faults geomorphic and paleoseismic characterization of faults is difficult because of poor surface expression and long earthquake recurrence intervals in humid areas faults can be buried by thick sediments or soils their geomorphic expression subdued and sometimes undetectable until the next earthquake in java active faults are diffused and their characterization is challenging among them is the ene striking cimandiri fault zone cumulative displacement produces prominent ene oriented ranges with the southeast side moving relatively upward and to the northeast the fault zone is expressed in the bedrock by numerous ne w and nw trending thrust and strike slip faults and folds however it is unclear which of these structures are active we performed a morphometric analysis of the fault zone using 30 m resolution shuttle radar topography mission digital elevation model srtm dem we constructed longitudinal profiles of 601 bedrock rivers along the up thrown ranges along the fault zone calculated the normalized channel steepness index ksn identified knickpoints and use their distribution to infer relative magnitudes of rock uplift and locate boundaries that may indicate active fault traces we compare the rock uplift distribution to surface displacement predicted by elastic dislocation model to determine the plausible fault kinematics the active cimandiri fault zone consists of six segments with predominant sense of reverse motion this geometric characterization implies a maximum earthquake magnitude along its 100 km length of m7 3 but its geometric complexity suggests greater segmentation and smaller events

south flank of the yangtze delta past present and future abstract chenier plain and mudflat development in the south flank of the yangtze delta are examined by multi disciplinary methods over different spatiotemporal scales and changing human earth interactions the study site contains a narrow belt of elongated ridge complexes that formed along the sediment deficient open coast from 6500 to 4000 yr bp since then and until the past two decades shoreline progradation has accelerated due to increasing sediment supply fueling rapid deltaic expansion superimposed on this trend are a series of discrete sand dominated ridges deposited during several stormy intervals tidal flat development is regulated by complex estuarine processes short term morphodynamic variations at the site are caused by the alternations of tides and waves while intermediate morphodynamic variations are controlled by the multi decadal shifting of river stem channel and stormy climates the ongoing rapid accretion on the tidal flats is predicted to continue into the near future because the estuarine buffer effect is expected to balance the adverse impacts of decreasing riverine sediment discharge and rising sea level technological developments during the last 2000 years are exemplified by seawall construction against sea flooding marking a transition from passive to active dike construction has been used more frequently and intensively to reclaim land since the 1970s in support of the booming socioeconomic development in the region lessons from complex morphodynamic change and human earth interactions in the southern yangtze delta admonish us to not reclaim coastal wetland by lower flat enclosures constructing new dikes near the low waterline while an optimal alternative would be to implement upper flat enclosures constructing new dikes around the high waterline on the continuously accretionary tidal flats with auxiliary biological restoration engineering to satisfy both socioeconomic development and sustainable wetland conservancy

interpreting quaternary uplift rates at the mendocino triple junction northern california from uplifted marine terraces analysis of the altitudinal spacing of 14 flights of marine terraces indicates a spatial pattern of varying uplift rates that agrees with that determined from previously dated terraces for the past 3 81 ka and temporal changes in uplift rates from 1 m ka to 3 5 m ka that may reflect response to changes in tectonic regime during passage of the mendocino triple junction mtj a possible mechanism for regional uplift is growth of a slab window south of the mtj the region of most rapid uplift is 25 43 km south of the mtj immediately south of the northern boundary of the slab window the coastline is tilted upward to the south in the region directly above the southern edge of the subducted gorda plate at point delgada 55 km south of the present mtj where the northern edge of the slab window passes approximately 300 ka uplift rates have been 1 2 m ka for at least 330 ka more than 1 4 m y after passage of the southern edge of the subducted slab at the mendocino coast uplift rates have been less than 0 4 m ka for at least 330 ka

delta development and channel incision during marine isotope stages 3 and 2 in the western south yellow sea abstract approximately 4100 km of high resolution seismic profiles recently obtained from the western south yellow sea were subdivided into seven seismic units by six major seismic surfaces three sediment cores between 60 and 71 m in length obtained from localities on the seismic profile lines were analyzed for sedimentary characteristics clay mineral components and benthic foraminiferal and ostracod assemblages and were also dated by ams 14 c and optically stimulated luminescence to document the environmental history of the region stratigraphic units in the cores were confidently correlated with seismic units in the profiles stratigraphic correlation among these three cores and the previous well studied core qc 2 was facilitated by the cold water deposits in marine isotope stage mis 5 the three cores document the sedimentary sequence during the period from mis 6 up to mis 1 strata formation and sedimentary environment changes since mis 5 are strongly controlled by sea level fluctuations most of the successions were formed in mis 5 mis 3 and mis 1 with major erosions in mis 4 and mis 2 particularly our data revealed the presence of a large delta active during mis 3 likely from the early stage of mis 3 to about 40 cal kyr bp that was subsequently affected by channel incision the delta succession and incised channel fills have a high concentration of smectite in their clay mineral components suggesting that the paleo yellow river was the main contributor to the delta development and channel incision the delta sequence has a coarsening upward trend and consists of two seismic facies the upper facies shows lateral alternations of chaotic and oblique or very low angle reflectors which correspond to sandy proximal delta front and delta plain facies and the lower facies is characterized by seaward dipping clinoforms which correspond to muddy distal delta front and prodelta facies the top surface of the delta inclines very gently seaward consistent with a deltaic development associated with the sea level fall in mis 3 the incised channel system consists of two main channels with multiple tributaries in a dendritic pattern the incised channel fills begin with fluvial and then estuarine sediments which are truncated by a transgressive ravinement surface and capped by transgressive deposits the main incision channels have a terraced cross sectional morphology which is interpreted to reflect multiple episodes of sea level fall during incision presumably from the late mis 3 to the last glacial maximum

glacial erosion evolution of river long profiles and the organization of process domains in mountain drainage basins of coastal british columbia 1 in glaciated british columbia canada quaternary climate changes are responsible for profound spatial reorganization of earth surface processes these changes have left a landscape characterized by topographic anisotropy associated with a hierarchy of glacial troughs the evolution of glaciated landscapes is examined by analyzing the structure of geomorphic process domains and channel long profiles to identify process domains we use channel surveys and gis analysis to construct slope area transects of the channel network this analysis reveals generalized process form disequilibrium with a mismatch between topographic signatures and currently active geomorphic process domains at the landscape scale of source colluvial channels contributing area 1 km2 the glacial paraglacial signature commonly overrides that produced by contemporary debris flows along the axis of former ice flows relict glacial cirques introduce a hanging fluvial domain at contributing areas as small as 8 10 2 km2 and produce complex channel long profiles similar to those observed for rivers responding to tectonic forcing slope area relations typical of unglaciated equilibrium environments do not apply here the concept of process domains appears to hold however some major glacially forced modifications in the alluvial colluvial transition are observed and the definition of a depositional colluvial subdomain is proposed comparison between field and gis measured slopes reveals that gis associated error is not uniform between process domains and that gis based plots do not successfully discriminate field based process domains the combination of glacial and post glacial fingerprints and the effects of ongoing earth surface processes generate a complex landscape whose glacial signatures may persist until the onset of the next ice age

sand mining impacts on long term dune erosion in southern monterey bay abstract southern monterey bay was the most intensively mined shoreline with sand removed directly from the surf zone in the u s during the period from 1906 until 1990 when the mines were closed following hypotheses that the mining caused coastal erosion it is estimated that the yearly averaged amount of mined sand between 1940 and 1984 was 128 000 m 3 yr which is approximately 50 of the yearly average dune volume loss during this period to assess the impact of sand mining erosion rates along an 18 km range of shoreline during the times of intensive sand mining 1940 1990 are compared with the rates after sand mining ceased 1990 2004 most of the shoreline is composed of unconsolidated sand with extensive sand dunes rising up to a height of 46 m vulnerable to the erosive forces of storm waves erosion is defined here as a recession of the top edge of the dune recession was determined using stereo photogrammetry and lidar and gps surveys long term erosion rates vary from about 0 5 m yr at monterey to 1 5 m yr in the middle of the range and then decrease northward erosion events are episodic and occur when storm waves and high tides coincide allowing swash to undercut the dune and resulting in permanent recession erosion appears to be correlated with the occurrence of el ninos the calculated volume loss of the dune in southern monterey bay during the 1997 98 el nino winter was 1 820 000 m 3 which is almost seven times the historical annual mean dune erosion of 270 000 m 3 yr the alongshore variation in recession rates appears to be a function of the alongshore gradient in mean wave energy and depletions by sand mining after cessation of sand mining in 1990 the erosion rates decreased at locations in the southern end of the bay but have not significantly changed at other locations

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

cover effect in bedrock abrasion a new derivation and its implications for the modeling of bedrock channel morphology the sediment load of a bedrock river plays an important role in the fluvial incision process by providing tools for abrasion the tools effect and by covering and thereby protecting the bed the cover effect we derive a new formulation for the cover effect in which the fraction of exposed bed area falls exponentially with increasing sediment flux or decreasing transport capacity and explore its consequences for the model of bedrock abrasion by saltating bed load erosion rates predicted by the model are higher than those predicted by earlier models in a closed system the maximum erosion rate is predicted to occur when sediment supply is equal to transport capacity for a flat bed by optimizing the channel geometry to minimize the potential energy of the stream and using representative values for both discharge and grain size we derive equations for the geometry of a bedrock river and explore how predictions for width slope and bed cover vary as functions of drainage area rock uplift rate and rock strength the equations predict a dependence of channel width on drainage area similar to the relations using a simple shear stress incision law the slope area relationship is predicted to be concave up in a log log regime with a curvature dependent on uplift rate however this curvature does not deviate sufficiently from a straight line to allow discrimination between models using empirical data dependence of channel width and slope on rock uplift rate can be separated into two domains for low uplift rates channel geometry is largely insensitive to uplift rate due to a threshold effect at high uplift rates there is a power law dependence bed cover is predicted to increase progressively downstream and to increase with increasing uplift rate in our model the width to depth ratio is a function of both tectonic and climatic forcing this indicates that the scaling between channel width and bed slope is neither a unique indicator of tectonic forcing at steady state nor a signature of transience or steady state we conclude that sediment effects need to be taken into account when modeling bedrock channel morphology

the progradation and retrogradation of two newborn huanghe yellow river delta lobes and its influencing factors abstract in this paper 342 landsat satellite images were used to study the evolution of the qingshuigou and qing8 lobes during 1976 2016 sea level correction and statistical analysis were used to eliminate the effect of sea level fluctuations on the shoreline positions the results revealed that the evolution of the two newborn huanghe delta lobes was mainly influenced by the river sediment discharges river channel changes course shifts floods droughts and marine hydrodynamic forces during 1976 2016 the total land gain of the two lobes was 377 km2 according to mean tide line and the average epeirogenetic efficiency of river sediment discharge was 0 020 m2 ton which was greatly less than that when the channels were natural the artificial stabilization of the deltaic channels had negative impact on the land gain assuming no artificial adjustment to the deltaic channels the total land gain would increase 435 km2 the land gain of the two lobes was a function of the cumulative sediment discharges shoreline lengths and course shift bonuses under the circumstance of historical river channel changes the critical sediment discharge maintaining the area balance of the two lobes was a function of historical shoreline lengths which increased linearly from 61 m ton in 1976 to an average of 163 m ton during 1996 2016 in the future there are two ways to increase the land gain under the less huanghe sediment discharge reducing artificial disturbance of deltaic channels and letting the river enter the sea through the southwest coast of qingshuigou lobe

incremental deformation and fabric development in a kcl mica mixture abstract the history of deformation and of mica reorientation is described in a kcl mica mixture in the middle of a kink like experimental shear zone the history was reconstructed by deforming several specimens to successively greater total strains and assuming the more deformed specimens passed through the states of strain and fabric exhibited by the less deformed specimens a pseudo differentiated layering is described which arises from the original network distribution of the mica grains without benefit of any differentiation process a comparison is made between the observed mica fabrics at various strains and those predicted by the march model taking the measured initial preferred orientation of the micas into account the actual reorientation processes in the material are found to be more efficient than the march transformation at shortening strains less than about 70 but less efficient at higher strains these departures from marchian behavior are explaned qualitatively comparison is also made between observed and predicted intensities of mica preferred orientation assuming a hypothetical random orientation of micas in the starting material for the march calculation

belemnites strain analysis and regional tectonics a critical appraisal abstract deformed belemnites offer great potential for estimating strain in deformed rocks there are two fundamental approaches 1 fragmentation and 2 reorientation of the belemnite guard the fragmentation approach is based on measurements of the original fragment and final fragment plus intervening gap belemnite lengths three variants exist standard ramsay strain reversal ferguson and modified standard hossain methods of which the second is the most accurate but also the slowest the third method is both simple and relatively accurate strain ellipse estimates are conventionally determined from the best fit envelope to plots of belemnite elongation 1 e against orientation badoux beach method but this demands a large number of belemnites per locality we describe an improved strain ellipse construction which requires only few belemnites the reorientation approach is based on strain induced shape modification of belemnite orientation distributions two variants exist the standard sanderson and modified standard lloyd methods but they are essentially similar we describe an adaption of the lloyd method which involves constructing distribution moment ratio plots contoured in terms of strain ratio and initial standard deviation the relative merits of the two approaches are considered using data from the rivet thrust sheet exposed in the la grave region of the external french alps we find that whereas the fragmentation approach yields relatively simple strain estimates true extensions and a strain ellipse the reorientation approach only provides an estimate of the in plane strain ratio if the exact shape of the belemnite orientation distribution before deformation is known the implications of these results are discussed in terms of local belemnite deformation histories and the evolution of the la grave thrust belt and the alpine orogeny

shape fabric development in rigid clast populations under pure shear the influence of no slip versus slip boundary conditions abstract shape fabrics of elliptical objects in rocks are usually assumed to develop by passive behavior of inclusions with respect to the surrounding material leading to shape based strain analysis methods belonging to the rf family a probability density function is derived for the orientational characteristics of populations of rigid ellipses deforming in a pure shear 2d deformation with both no slip and slip boundary conditions using maximum likelihood a numerical method is developed for estimating finite strain in natural populations deforming for both mechanisms application to a natural example indicates the importance of the slip mechanism in explaining clast shape fabrics in deformed sediments

p m and g tectonites a classification based on origin of mineral preferred orientations abstract the mechanisms responsible for mineral preferred orientations can be used as the basis for a classification of tectonites p tectonites develop mineral preferred orientations by plastic deformation m tectonites by mechanical reorientation of inequidimensional grains and g tectonites by various growth processes intermediate tectonite types can be defined with the aid of a triangular diagram examples discussed include marble and quartzite p types slates m or mg types certain hornblende or feldspar rich schists g types granite derived gneisses and mylonites pm types and common schists mg or pmg types the classification is designed to promote a holistic approach to fabric studies in addition the pmg triangle provides a framework for tracking the sequential fabric development of tectonites

deformation mechanisms in some cover thrust sheets from the external french alps abstract rocks from two parts of the ultradauphinois zone of the external french alps have been examined and the mechanisms by which they were deformed have been assessed from petrographic data jurassic and triassic limestones deformed by pressure solution dissolving non ferroan calcite and precipitating ferroan calcite calcite pressure shadows are usually less elliptical in shape than pyrite pressure shadows and grain boundary sliding is therefore thought to have played a significant role eocene rocks deformed by a variety of mechanisms limestones show mylonitic textures whereas limestone conglomerates with a quartz sandstone matrix deformed by pressure solution of calcite and grain boundary sliding of quartz a model for enhanced diffusion of silica along mica seams is proposed to account for planar quartz mica boundaries greywackes deformed by incongruent pressure solution involving the metamorphic reaction of feldspar to mica and quartz coupled with the replacement of feldspar by calcite

a statistical approach to determination of a mineral lineation abstract a statistical model of the bipolar von mises type was applied to the analysis of mineral lineation defined by the preferred dimensional orientation of inequant grains on a foliation surface orientation data of 203 258 grains from each of four rock specimens fit the model well suggesting a useful analytical technique with three advantages 1 confidence in whether a metamorphic tectonite has a mineral lineation can be determined using a 2 test 2 the orientation of the mineral lineation can be represented by the mean direction with a specified confidence interval and 3 the degree of preferred dimensional orientation of grains can be quantified by the concentration parameter

the initiation and development of metamorphic foliation in the otago schist part 2 evidence from quartz grain shape data shape size and orientation measurements of quartz grains sampled along two transects that cross zones of increasing metamorphic grade in the otago schist new zealand reveal the role of quartz in the progressive development of metamorphic foliation sedimentary compaction and diagenesis contributed little to the formation of a shape preferred orientation spo within the analysed samples metamorphic foliation was initiated at sub greenschist facies conditions as part of a composite s1 bedding structure parallel to the axial planes of tight to isoclinal f1 folds an important component of this foliation is a pronounced quartz spo that formed dominantly by the effect of dissolution precipitation creep on detrital grains in association with f1 strain with increasing grade the following trends are evident from the spo data i a progressive increase in the aspect ratio of grains in sections parallel to lineation and the development of blade shaped grains ii the early development of a strong shape preferred orientation so that blade lengths define the linear aspect of the foliation lineation and the intermediate axes of the blades define a partial girdle about the lineation iii a slight thinning and reduction in volume of grains in the one transect and iv an actual increase in thickness and volume in the survivor grains of the second transect the highest grade samples within the chlorite zone of the greenschist facies record segregation into quartz and mica rich layers this segregation resulted largely from f2 crenulation and marks a key change in the distribution deformation and spo of the quartz grains the contribution of quartz spo to defining the foliation lessens as the previously discrete and aligned detrital quartz grains are replaced by aggregates and layers of dynamically recrystallized quartz grains of reduced aspect ratio and reduced alignment pressure solution now affects the margins of quartz rich layers rather than individual grains in higher grade samples therefore the rock structure is characterized increasingly by segregation layering parallel to a foliation defined predominantly by mica spo

an evolutionary model for the holocene formation of the pearl river delta china this paper reconstructs the evolutionary history of the pearl river delta over the last 9000 years and investigates land sea interaction in a large deltaic complex which formed under the influence

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

analysis of three dimensional strain modified uniform distributions andalusite fabrics from a granite aureole a method of analysing finite strain from an initial random distribution of lines or planes is presented the shape of the strain ellipsoid is mapped to the eigenvalue ratios of an orientation matrix the method is used to interpret the andalusite fabrics from the aureole of the ardara granite county donegal ireland the high flattening strains determined in the aureole are accompanied by oblate strains in the granite margins and support the concept of deformation produced by expansion of the pluton

how rivers react to large earthquakes evidence from central taiwan earthquakes and bedrock river incision are fundamental processes in the evolution of tectonically active landscapes yet little work has focused on understanding how a bedrock river responds to a single large earthquake data from the 1999 m w 7 6 chi chi earthquake in central taiwan show dramatic differences in river response that depend on the proximity to the rupture zone near the fault scarp vertical ground deformation intensifi es river incision on a time scale of years to decades while distal to the fault landslides induced by the earthquake mantle bedrock on the river bed with sediment impeding incision for decades to centuries as the material is evacuated this surprising spatial and temporal variability in bedrock incision caused by earthquakes has implications for the paleoseismic interpretation of bedrock terraces and for the evolution of tectonically active landscapes

tibetan plateau river incision inhibited by glacial stabilization of the tsangpo gorge much attention has focused on how and when the tibetan plateau formed but far less research has been done on the controls on river incision into the plateau itself oliver korup and david montgomery address this issue which also relates to the question of why the tibetan plateau is still there at all despite hosting one of the deepest gorges on earth the plateau edge is extremely well defined and according to widely accepted stream power theory should be heavily dissected by one of asia s most powerful rivers the yarlung tsangp or yarlung zangbo korup and montgomery propose that the southeastern edge of the plateau was preserved in part by the presence of glaciers that were large enough during the holocene to stall aggressive river downcutting along the plateau margin a considerable amount of research has focused on how and when the tibetan plateau formed in the wake of tectonic convergence between india and asia1 although far less enquiry has addressed the controls on river incision into the plateau itself2 widely accepted theory3 predicts that steep fluvial knick points river reaches with very steep gradients in the eastern himalayan syntaxis at the southeastern plateau margin should erode rapidly4 driving a wave of incision back into the plateau preservation of the plateau edge thus presents something of a conundrum that may be resolved by invoking either differential rock uplift matching erosional decay5 6 7 or other mechanisms for retarding bedrock river incision8 9 in this region where high stream power excludes the potential for aridity as a simple limit to dissection of the plateau10 here we report morphologic evidence showing that quaternary depression of the regional equilibrium line altitude where long term glacier mass gain equals mass loss was sufficient to repeatedly form moraine dams on major rivers such damming substantially impeded river incision into the southeastern edge of the tibetan plateau through the coupled effects of upstream impoundment and interglacial aggradation such glacial stabilization of the resulting highly focused river incision centred on the tsangpo gorge could further contribute to initiating and accentuating a locus of rapid exhumation known as tectonic anaeurysm6

origin of a preferential avulsion node on lowland river deltas river deltas are built by cycles of lobe growth and abrupt channel shifts or avulsions that occur within the backwater zone of coastal rivers previous numerical models differ on the origin of backwater scaled avulsion nodes and their consistency with experimental data to unify previous work we developed a numerical model of delta growth that includes backwater hydrodynamics river mouth progradation relative sea level rise variable flow regimes and cycles of lobe growth abandonment and reoccupation for parameter space applicable to lowland deltas we found that flow variability is the primary mechanism to cause persistent avulsion nodes by focusing aggradation within the backwater zone backwater scaled avulsion nodes also occur under less likely scenarios of initially uniform bed slopes or during rapid relative sea level rise and marine transgression our findings suggest that flow variability is a fundamental control on long term delta morphodynamics

strain analysis in a cover thrust zone external french alps abstract the la grave thrust zone is situated in the external french alps north of the pelvoux basement massif jurassic cover rocks are deformed and imbricated in a region some 15 km square strains have been measured using the statistical reorientation of belemnites the extension of belemnites and the shapes of pyrite pressure shadows orientation data are treated statistically following sanderson 1977 groups of 100 measurements do not provide very accurate results and generally underestimate the strain when compared with more accurate determinations from extension measurements in addition to providing reliable finite strain markers pyrite pressure shadows allow interpretation of the incremental strain history in the area studied strains accumulated irrotationally in the plane of the bedding the deformed autochthon to the basement massif and the lower thrust sheets were deformed by layer parallel shear and extensional flow which produced ls fabrics with a down dip lineation the higher thrust sheets were deformed by layer parallel shear and compressive flow which produced ls to l fabrics with a strike parallel lineation

overview of the monsoon influenced ayeyarwady river delta and delta shoreline mobility in response to changing fluvial sediment supply abstract a morpho sedimentary analysis of the ayeyarwady delta shoreline was conducted based on a field mission in myanmar in november 2016 and interpretation of satellite images spanning the period 1974 2019 these analyses were complemented by data on land to water conversion and vice versa within a 2 km wide coastal fringe and on meris derived seasonal and decadal scale evolution of suspended particulate matter spm off the delta the objectives were to 1 characterize the 450 km long delta shoreline and coastal sediment transport pathways 2 define the shoreline status stability erosion accretion and 3 identify potential causes of shoreline change and the future outcome of this status in terms of delta vulnerability the delta shoreline was characterized on the basis of qualitative alongshore tidal wave energy and sediment grain size patterns muddy sandy or a mixture of both and morphology sandy beaches and mudflats the deltaic coast exhibits a mixed wave and tide dominated morphology and comprises a western sector characterized by four of the five main distributary mouths separating inter distributary plains bounded by low overwash influenced beaches devoid of aeolian dunes the eastern sector in the gulf of martaban is embayed much less prograded and bounded by dominantly muddy shores this simple shoreline dichotomy reflects the overarching alongshore sediment redistribution and storage patterns that have accompanied the growth of the delta resulting in the two facies sand dominantly retained in the western sector where the multiple distributary mouths have constrained potential alongshore sand transport by low to moderate energy monsoon generated southwesterly waves and mud transported by the regional monsoon influenced coastal shelf circulation towards the eastern sector the recent multi decadal shoreline mobility in the ayeyarwady delta points to the influence of fluvial sediment supply on these two facies between 1974 and 2019 49 of the delta s shoreline underwent erosion mainly affecting the sandy beaches in the western sector whereas shoreline accretion is still prevalent along the large inter distributary plain east of yangon where coastal mud preferentially accumulates in the gulf of martaban we attribute erosion to reduced river sand supply generated by dams and by massive in channel sand mining upstream of the delta exacerbated by important channel dredging large scale deforestation resulting from land use changes agriculture and mining in the ayeyarwady catchment are probably contributing to enhanced fine grained sediment supply to the delta plain and the coast as reflected by the relative stability of coastal spm over a decade 2002 2012 and continued deposition in the accreting eastern sheltered part of the delta the coastal sediment balance will be further impacted in the future if planned dams are constructed without proper sediment management notably a significant reduction or prohibition of in channel sand mining the sandy beaches that armour the wave exposed western sector of the delta will continue to erode resulting in increased potential exposure of the delta to cyclones and sea level rise

strain analysis method using the maximum frequency of unimodal deformed orientation distributions applications to gneissic rocks abstract the effect of varying strain ratio r a on initially uniform and non uniform orientation distributions of passive marker lines is calculated the frequency graphs for uniform distributions have a unimodal form gaussian like distribution centered in the finite extension direction x of the strain ellipse the maximum frequency is related to the strain using non uniform distributions the frequency graph has a different unimodal pattern the difference between the measured strain ratio r with the maximum frequency and the true strain ratio r a to the initial distribution is quantified for different types of distribution the method is applied to samples of gneiss from southern spain using the orientation of tourmaline and feldspar lying in the schistosity plane with respect to the stretching lineation the strain of the marker distribution has been quantified and after distinguishing the initial type of distribution the true strain ratio of the whole rock in the schistosity plane can be estimated

preferred orientation developed by rigid markers in two dimensional simple shear strain a theoretical and experimental study abstract in a homogeneous two dimensional deformation linear markers embedded in a viscous matrix develop a preferred orientation along the principal axis of the strain ellipse theoretical analysis of marker rotation under two dimensional simple shear is used to derive an orientation distribution function this function shows that the relative density maximum increases with progressive strain its value being equal to the major minor strain ellipse axis ratio moreover the density is equal to the unity along the lines of no finite longitudinal strain experimentally observed preferred orientation is in good agreement with the expected theoretical distribution

the initiation and development of metamorphic foliation in the otago schist part 1 competitive oriented growth of white mica the 3d shape size and orientation data for white mica grains sampled along two transects of increasing metamorphic grade in the otago schist new zealand reveal that metamorphic foliation as defined by mica shape preferred orientation spo developed rapidly at sub greenschist facies conditions early in the deformation history the onset of penetrative strain metamorphism is marked by the rapid elimination of poorly oriented large clastic mica in favour of numerous new smaller grains of contrasting composition higher aspect ratios and a strong preferred orientation the metamorphic mica is blade shaped with long axes defining the linear aspect of the foliation and intermediate axes a partial girdle about the lineation once initiated foliation progressively intensified by an increase in the aspect ratio size and alignment of grains although highest grade samples within the chlorite zone record a decrease in aspect ratio and reduction in spo strength despite continued increase in grain size these trends are interpreted in terms of progressive competitive anisotropic growth of blade shaped grains so that the fastest growth directions and blade lengths tend to parallel the extension direction during deformation the competitive nature of mica growth is indicated by the progressive increase in size and resultant decrease in number of metamorphic mica with increasing grade from c 1000 relatively small mica grains per square millimetre of thin section at lower grades to c 100 relatively large grains per square millimetre in higher grade samples reversal of spo intensity and grain aspect ratio trends in higher grade samples may reflect a reduction in the strain rate or reduction in the deviatoric component of the stress field

local human activities overwhelm decreased sediment supply from the changjiang river continued rapid accumulation in the hangzhou bay qiantang estuary system we investigate the morphological responses of the hangzhou bay china located immediately south of the changjiang estuary to the drastic reduction of the sediment load from the changjiang river and the large scale coastal embankment schemes over past decades the spatial patterns of deposition and erosion sediment volume changes and the hydrodynamic and sediment dynamic feedback were analyzed on the basis of historical bathymetric and hydrographic data the results show that the sedimentation rates in the bay have generally increased rather than decreased over the past decades despite bed erosion having occurred in the northern bay mouth this observation reveals that the influence of the reduction in the changjiang river sediment supply on the morphological evolution of hangzhou bay has to date been insignificant mainly due to the buffering effect of existing sediment in the outer changjiang estuary the morphological change is mainly related to the implementation process of the coastal embankment sediment accumulation induced by progressive seaward coastal embankment has resulted in seaward aggradation from the qiantang estuary towards hangzhou bay analysis of the annually averaged high and low tidal levels and durations of rising and falling tides reveals that flood dominance in the inner bay has been increased due to the coastal embankment and sediment accumulation the ratio between annually averaged rising tide and falling tide durations have decreased from 0 85 to 0 63 the tidal prism at the interface between the inner and outer bay has decreased by about 25 since the 1980s while the net landward sediment flux has been intensified to a certain extent which is responsible for the intensifying sedimentation in the inner bay the local human activities have overwhelm the decreased sediment from the changjiang river although the coastal embankment will cease in the near future the morphological response to human activities is expected to continue on for a longer time