large scale dam removal on the elwha river washington usa river channel and floodplain geomorphic change abstract a substantial increase in fluvial sediment supply relative to transport capacity causes complex large magnitude changes in river and floodplain morphology downstream although sedimentary and geomorphic responses to sediment pulses are a fundamental part of landscape evolution few opportunities exist to quantify those processes over field scales we investigated the downstream effects of sediment released during the largest dam removal in history on the elwha river washington usa by measuring changes in riverbed elevation and topography bed sediment grain size and channel planform as two dams were removed in stages over two years as 10 5 million t 7 1 million m3 of sediment was released from two former reservoirs downstream dispersion of a sediment wave caused widespread bed aggradation of 1 m greater where pools filled changed the river from pool riffle to braided morphology and decreased the slope of the lowermost river the newly deposited sediment which was finer than most of the pre dam removal bed formed new bars largely pebble granule and sand material prompting aggradational channel avulsion that increased the channel braiding index by almost 50 as a result of mainstem bed aggradation floodplain channels received flow and accumulated new sediment even during low to moderate flow conditions the river system showed a two to tenfold greater geomorphic response to dam removal in terms of bed elevation change magnitude than it had to a 40 year flood event four years before dam removal two years after dam removal began as the river had started to incise through deposits of the initial sediment wave 1 2 million t of new sediment 10 of the amount released from the two reservoirs was stored along 18 river km of the mainstem channel and 25 km of floodplain channels the elwha river thus was able to transport most of the released sediment to the river mouth the geomorphic alterations and changing bed sediment grain size along the elwha river have important ecological implications affecting aquatic habitat structure benthic fauna salmonid fish spawning and rearing potential and riparian vegetation the response of the river to dam removal represents a unique opportunity to observe and quantify fundamental geomorphic processes associated with a massive sediment influx and also provides important lessons for future river restoration endeavors

paraglacial rock slope stability glaciation and deglaciation along with their associated climatic and non climatic processes modify slope stresses and influence slope stability paraglacial slope failures are those that are a part of or influenced by the transition from glacial conditions to non glacial conditions gravitational failure of rock slopes is a primary and dominant process of slope evolution in mountainous terrain and is the subject of this paper which 1 reviews the approaches taken for researching paraglacial rock slope failure patterns and processes 2 summarises the spatial and temporal patterns of post glacial failures 3 assesses the factors influencing slope stability during glaciation and deglaciation 4 explores some of the applications of paraglacial research and 5 highlights some of the outstanding issues to be resolved and provides recommendations for terminology relating to paraglacial slope processes

extrusion tectonics of the okhotsk plate northeast asia based on focal mechanism geologic and lineament data faulting in the chersky range northeast asia changes from right lateral transpression between north america and eurasia to left lateral strike slip between north america and the okhotsk plate the location of the okhotsk eurasia boundary is poorly constrained available data suggest this boundary is right lateral the okhotsk plate is being compressed and extruded from between north america and eurasia resulting in high levels of microseismic activity along the southern flanks of the chersky range

morphology and sedimentology of a tributary confluence bar in a regulated river north tyne u k the form and structure of a tributary confluence bar in a regulated channel are analysed and related to channel adjustment to the imposed flow regime the bar is characterized by a tripartite structure with two facies and by marked lateral coarsening characteristics which relate to the changing hydraulic conditions within the narrowing channel form

nature of the continent ocean transition on the non volcanic rifted margin of the central great australian bight a region of 50 120km width defines the continent ocean transition cot in the central great australian bight it is characterized by a thin apron of post break up sediments overlying complexly deformed sediments and intruded crust bounded landward by a basement ridge complex and oceanward by rough oceanic basement recently acquired deep reflection and refraction seismic data have significantly enhanced understanding of the cot and basement ridge modelled gravity and magnetic data and features interpreted from seismic data are consistent with aspects of extensional and break up models proposed for the west iberia margin many of the features and relationships observed beneath the outer margin of the central great australian bight can be explained by extension within a lithosphere scale pure shear environment involving four layers brittle upper crust and upper mantle and ductile lower crust and lower lithospheric mantle the cot is interpreted to be underlain by extended continental lithosphere thus the continentocean boundary is unequivocally defined between oceanic crust and the cot and appears to be associated with sea floor spreading magnetic anomaly 33 indicating that break up and sea floor spreading did not commence until c 83 ma early carnpanian time later than the currently accepted 95ma age the major part of the basement ridge complex is probably a combination of serpentinized peridotites and mafic intrusions or extrusions derived by mantle upwelling and limited partial melting the magmatic products of this process probably cooled during chron 34 producing a distinctive magnetic anomaly but one that does not relate to break up and sea floor spreading

pulsation tectonics as the control of continental breakup abstract new data from the recent ipod drilling of dsdp site 534 in the blake bahama basin give a definitive age for the spreading center shift involved in the breakup of the north american atlantic margin a basal callovian age 155 m y is determined for the blake spur anomaly marking this spreading center shift that signals the birth of the modern north atlantic ocean this is some 20 m y younger than previously thought one implication of this result is that this spreading center shift starting north atlantic breakup is now of an age which could be assigned to the spreading center shift needed to end the rifting in the gulf of mexico it is suggested that this might be one and the same event another implication of this younger age for the blake spur event is that relatively high spreading rates are now required for the jurassic outer magnetic quiet zone along the north american margin this association of a relatively high spreading rate with a magnetic quiet zone is similar to that for the mid cretaceous and implies a link between the processes controlling plate spreading which are in the upper mantle and the processes controlling the magnetic field which are in the outer core the cycles of fast and slow spreading and quiet and reversing magnetic field have a period of 60 100 m y a theory of pulsation tectonics involving the cyclic eruption of plumes of hot mantle material from the lowermost d layer of the mantle could explain the correlation plumes carry heat away from the core mantle boundary and later reach the asthenosphere and lithosphere to induce faster spreading the pulse of fast spreading in the jurassic apparently caused the breakup of the north atlantic other pulses of fast spreading appear to correlate with major ocean openings on various parts of the globe implying that this might be a prevalent process i suggest rifting of passive margins may be controlled by the more fundamental global processes described by the theory of pulsation tectonics the term pulsation tectonics is appropriate for this new unifying theory explaining variations in the magnetic field plate motions and paleoenvironment the word pulsation was used by grabau 1934 for a long term rhythm nearly the length of a geological time period in which there were widespread transgressions and regressions of seas over whole continents thus pulsations are just the long term cycles of vail et al 1977 grabau s pulsation theory prophetically invoked large scale tectonic changes in the ocean basins as a cause for eustatic changes in contrast to local continental tectonics although he offered no explanation of the ocean changes the cyclic character of crustal movements called for in the theory of pulsation tectonics revives many ideas of these past advocates of non steady state tectonics and provides modern mechanisms that explain the observations on plate motions and the magnetic fields data which were totally unknown to these past authors

the equilibrium alluvial river under variable flow and its channel forming discharge when the water discharge sediment supply and base level vary around stable values an alluvial river evolves toward a mean equilibrium or graded state with small fluctuations around this mean state i e a dynamic or statistical equilibrium state here we present analytical relations describing the mean equilibrium geometry of an alluvial river under variable flow by linking channel slope width and bed surface texture the solution holds in river normal flow zones or outside both the hydrograph boundary layer and the backwater zone and accounts for grain size selective transport and particle abrasion we consider the variable flow rate as a series of continuously changing yet steady water discharges here termed an alternating steady discharge the analysis also provides a solution to the channel forming water discharge which is here defined as the steady water discharge that given the mean sediment supply provides the same equilibrium channel slope as the natural long term hydrograph the channel forming water discharge for the gravel load is larger than the one associated with the sand load the analysis illustrates how the load is distributed over the range of water discharge in the river normal flow zone which we term the normal flow load distribution the fact that the distribution of the imposed sediment supply spatially adapts to this normal flow load distribution is the origin of the hydrograph boundary layer the results quantify the findings by wolman and miller 1960 regarding the relevance of both magnitude and frequency of the flow rate with respect to channel geometry

explosion contamination of the northeast siberian seismicity catalog implications for natural earthquake distributions and the location of the tanlu fault in russia russian regional seismicity catalogs including those in the annual earthquakes of the ussr are contaminated by industrial explosions in northeastern russia explosions occur in tin coal and gold mines as well as in the construction of roads railways and dams most seismically recorded mining and construction related explosions have magnitudes of about 2 0 and occur during local daytime in addition explosions in placer mining areas are concentrated from midwinter to early spring when frozen placers are broken up for the summer processing season we analyzed the temporal variation of over 87 000 events occurring in northeast russia using a newly compiled seismicity catalog to identify areas where there may be explosion contamination areas with temporal biases indicative of mining or other explosions include the yana river delta and chukotka placers the southern amur district coal mining the trace of the baikal amur railroad construction lazo quarry the south yakutian gold fields and the kolyma gold belt the locations and estimates of the level of explosion contamination of the catalog suggest that the natural seismicity may be lower and not as diffuse along the plate boundaries in northeastern russia than previously thought use of only nighttime events from the seismicity catalog which should have a minimum of explosions helps to clarify the extension of the tanlu fault into russia and may ultimately help elaborate tectonics in other areas of eastern russia

paleomagnetism of cretaceous units of the mametchinskiy peninsula kuyul region northeastern russia implications for development and evolution of the northwest pacific basin abstract the northernmost part of the kamchatka peninsula of northeastern russia located along the northwestern margin of the bering sea consists of zones of complexly deformed accreted terranes progressing from the northwestern bering sea inland are the olyutorskiy ukelayat and koryak superterranes which were accreted to the okhotsk chukotsk volcanic plutonic belt ochvb during the campanian maastrichtian koryak to middle eocene olyutorskiy respectively to constrain the accretion paleolatitude of the koryak superterrane we paleomagnetically sampled a sedimentary series on the mametchinskiy peninsula at the mametchinskiy peninsula in the northeastern penzhinskaya guba 61 45 n 163 75 e a gently deformed well bedded section of fine grained lower to lower upper cretaceous turbidites the mametchinskaya and tylakrylskaya formations are exposed these strata which represent the lower part of the sedimentary cover of the terranes in this region and the forearc of ochvb were sampled at 39 sites three to seven samples per site within the ainyn terrane more than 1000 m of section of cenomanian turonian age was sampled at a basal locality sample groups i and ii sites 1 18 19 29 and at an upper locality of valanginian barremian age sample group iii sites 30 39 along the western shore of the peninsula thermal demagnetization and principal component analysis of the demagnetization data show lower temperature a and higher temperature b magnetic components although group iii samples did not display a coherent a component the a component of group i and ii samples was observed as a single polarity lower unblocking temperature component generally removed by 100 400 c this component failed the fold test at the 95 confidence level with respect to direction the a component is similar to both the present day field and axial geocentric dipole directions expected at this site the b component was observed during thermal demagnetization steps up to 580 c and was always of downward directed inclination coherence of bedding corrections within each section do not allow statistically meaningful fold tests within groups i ii or iii assuming the b component represents a cretaceous magnetization two overall models are proposed in the first model preferred with the highest clustering of directions k value 36 7 n sites 36 indicates significant poleward motion of the ainyn terrane observed paleolatitude m1 61 0 6 5 expected north america plate reference site paleolatitude e 74 0 3 5 in the second model no significant poleward displacement is implied m2 72 0 9 6

grain size sediment transport regime and channel slope in alluvial rivers the general relationship between channel morphology and the grain size of sediment in the channel bed is an important but poorly known aspect of alluvial rivers an analysis of an equation for total sediment flux in the limits of suspension bedload and mixed modes of transport indicates distinct steady state regimes of channel morphology such regimes are readily seen in published data for modern alluvial rivers by way of a conventional shields plot or a plot of channel slope as a function of relative grain size d h and the ratio ws u where d and ws are respectively mean diameter and fall speed of bed sediments and h and u are respectively mean depth and friction velocity of the flow with slope and mode of transport in an alluvial river constrained by grain size and channel depth alone estimates of discharge and sediment flux follow directly introduction of the sediment flux relationship into conventional diffusion models for the evolution of an alluvial system provides nominal estimates of

analogies to oceanic behaviour in the continental breakup of the western woodlark basin the woodlark basin d entrecasteaux island region off northeast papua new guinea fig 1 offers a rare glimpse of the propagation of active rifting and continental breakup1 into orogenically thickened and subsequently extended lithosphere2 10 rifting continental breakup and the subsequent formation of oceanic lithosphere by sea floor spreading often involve rupture controlled by propagation of a rift tip11 20 we recognize several tectonic elements in the evolving western woodlark intracontinental system that are close geometric analogues of wholly oceanic propagators and a kinematic development that can be viewed as an extrapolation of oceanic tectonics the response to deformational stresses in the final stages of breakup in a thick relatively hot and hence weak continental lithosphere appears akin to that of oceanic lithosphere

flexural rigidity and shoot reconfiguration determine wake length behind saltmarsh vegetation patches vegetation patches play an important role in controlling sediment deposition in shallow aquatic environments such as coastal saltmarshes and fluvial systems however predicting deposition around vegetation patches is difficult due to the complexity of patch morphology and their dynamic interaction with the flow here we incorporate a biomechanical model parameterized using field data within a 3d computational fluid dynamics cfd model which allows prediction of individual shoot reconfiguration within patches due to flow forcing the model predicts velocity attenuation and bed shear stresses within the wake of the patch which agree spatially with accretion patterns measured in the field using terrestrial lidar the model is applied to sparse patches of suaeda maritima located in saltmarshes of coastal habitats to explore the role of i shoot distribution ii patch geometry iii shoot flexural rigidity and iv bulk flow velocity in determining the length of the predicted wake region we demonstrate that for suaeda maritima with intermediate rigidity the vertical shear layer over the vegetation controls the length of the predicted wake region consequently reconfiguration due to flexural rigidity strongly impacts on wake length confounding the relationship between patch height and wake length a simplified model for predicting wake length based on shoot reconfiguration is applied to the simulation data and shows good agreement the results demonstrate that the observed wake characteristics can be well explained by intraspecific variability in flexural rigidity thus demonstrating the importance of biomechanical traits in determining flow vegetation sediment interactions

downstream effects of flaming gorge reservoir on the green river colorado and utah the green river is one of the principal tributaries in the colorado river basin and drains 44 700 m 2 in wyoming colorado and utah since october 1962 flows of the green river have been regulated by flaming gorge reservoir which is located 412 river miles upstream from its confluence with the colorado river mean annual runoff has not been affected by the reservoir the duration of the relatively large discharges that transport most of the annual sediment load however has decreased significantly as a result the mean annual sediment discharge has decreased by 54 to 3 21 10 6 tons from 6 92 10 6 tons at the jensen gage located 105 river miles downstream from the reservoir and by 48 to 8 83 10 6 tons from 17 0 10 6 tons at the green river utah gage located 290 river miles downstream from the reservoir sediment supply to i he channel equals the annual transport within a relatively short distance 68 river miles downstream from the reservoir downstream from river mile 166 the supply of sediment from upstream plus tributary inflow exceeds the transport of sediment by 5 4 10 6 tons per year on an average the quasi equilibrium that appears to have existed prior to the reservoir no longer occurs along a majority of the green river in response to the reduced peak discharges the bankfull channel width of the green river has decreased by 10 adjustment of the channel to decreased peak flows and altered sediment loads is nowhere complete at present it appears that a century or more will be required for the green river to adjust to the effects of flaming gorge reservoir

relations between sill intrusions and bedding parallel extensional shear zones in the mid continent rift system of the lake superior region abstract the mid continent rift system is a continuous u shaped feature extending from kansas north through the lake superior region and then south through michigan the logan sills on the northwest side of the lake were intruded during the rifting stage 1109 ma deformation features in the country rock adjacent to the logan sills indicate two episodes of shear strain the first consists of minor thrusts and mesoscopic shear bands both suggesting top to the south southwest movement parallel to the bedding the second rotates the previously formed shear bands in the opposite sense top to the north northeast and is localized at the basal contact between the sills and the country rock we attempt to explain the relations observed with a tectonic model in which sill intrusions take advantage of bedding parallel shear zones that are the surface expression of a south dipping detachment plane the detachment plane steps up in the layered proterozoic sedimentary sequence and allows extension during rifting in this scenario the first episode of shear strain might be related to bedding parallel extension and the second to shear stress induced by the intrusion of magma along the detachment from the south the polarity of both events is supported by small scale kinematic indicators such as veins fiber growths and foliation

using simulated emergent vegetation to alter stream flow direction within a straight experimental channel river restoration programs often use vegetation to enhance the biological functionality recreational opportunities and aesthetic beauty of degraded stream corridors yet none has used vegetation for the purpose of inducing a straight channel to meander a flume based study was designed to alter the flow pattern within a straight degraded stream corridor by using simulated emergent vegetation of varying density placed at key locations within the channel placement of vegetation zones was determined using an empirical relation for equilibrium meander wavelength based on the imposed flow rate surface flow velocities were quantified using particle image velocimetry the study showed that i flow velocity can be markedly reduced within and near the vegetation zones ii flow can be diverted toward the opposite bank and iii vegetation density controlled the magnitude of these effects

vortex structure and sediment deposition in the wake behind a finite patch of model submerged vegetation abstracta submerged patch of finite width vegetation may produce vortex structures in its wake in both the vertical and horizontal planes this experimental study used velocity and deposition measu

channel changes due to river regulation the case of the piave river italy this paper deals with the channel changes of the piave river in the eastern alps italy which have occurred during this century in response to human interventions in the fluvial system the flow regime and the sediment supply of the river have been considerably altered by hydroelectric dams flow diversions and gravel mining in addition river dynamics have been affected by the construction of streambank protection structures to document these changes a historical analysis was performed using maps and aerial photographs morphological features that were examined included planform configuration channel width braiding index and bed elevation the results indicate that as a consequence of decreases in the flows and sediment supply remarkable channel changes have occurred in the river during this century especially during recent decades the channel has undergone a general narrowing with a decrease in average width to 35 per cent of its initial value while the braiding index has decreased from about 3 to 1 5 in several reaches the planform pattern has changed from braided to wandering the observed trends of channel change suggest that the river has not yet reached a new equilibrium condition and it may therefore be predicted that reductions in width and braiding intensity are likely to continue in the immediate future copyright 1999 john wiley sons ltd

prediction of the depth averaged two dimensional flow direction along a meander in compound channels abstract for overbank flows in meandering channels the flow direction along a meander varies and is affected by floodplain vegetation this study proposes a model for predicting the depth averaged two dimensional flow direction depth averaged flow angle along a meander in smooth and vegetated meandering compound channels laboratory experiments were performed in smooth and vegetated channels measurements show that the height of the secondary current cell in the main channel is increased by dense floodplain vegetation comparing with that in a non vegetated channel a method of determining the height of the cell is proposed at the middle section between the apex and exit sections where the secondary current cell is absent the depth averaged flow angle is independent of the height of the cell beyond the middle section a new secondary current cell is formed and the flow angle is highly dependent on the height of the cell the proposed model is thoroughly verified using the flume experimental and field observed data good agreement is obtained between predictions and measurements indicating that the proposed model is capable of accurately predicting the depth averaged flow angle along a meander in smooth and vegetated meandering compound channels

gravimetric determination of the continental oceanic boundary of the argentine continental margin from 36 s to 50 s fil arecco maria alejandra universidad de buenos aires facultad de ingenieria argentina

a depth averaged two dimensional model for flow sediment transport and bed topography in curved channels with riparian vegetation 1 a depth averaged two dimensional numerical model has been developed to simulate flow sediment transport and bed topography in river channels with emergent and submerged rigid vegetation and large woody debris the effect of helical flow in bends is considered by adopting an algebraic model for the dispersion terms in the depth averaged two dimensional momentum and suspended sediment transport equations and by adjusting the bed load transport angle the governing equations are discretized using the finite volume method on a nonstaggered curvilinear grid model validity has been assessed using experimental data observed in both fixed and movable bed laboratory flumes and a natural channel with submerged and emergent rigid vegetation in general mean flow velocities sediment transport rates and changes in bed topography predicted by the model agree well with the experimental observations for laboratory and field cases root mean square relative errors for velocities were less than about 13 and 44 respectively and about 50 of errors for changes in bed topography were less than 14 5 and 8 of the flow depth respectively

tectonics of the laptev sea and moma rift systems northeastern ussr abstract examination of the topography seismicity focal mechanisms and structure of the extension of the arctic mid ocean ridge into the laptev sea suggests that the present day features of the upper crust are consistent with an asymmetric simple shear extensional system on a large scale the topographically high upper plate side alternates from severnaya zemlya and taimyr peninsula across the rift zone to the new siberian islands and then back across to the kharaulakh range and the omoloi river basin the activity of this system is indicated by moderate size normal faulting earthquakes and the extensive development of extensional structural features a weakly developed axial graben with a few teleseismic earthquakes is developed in the eastern laptev sea further south a nw striking pliocene rift system commonly known as the moma rift extends through the northern cherskii range although there is a broad zone of elevated heat flow and isolated volcanoes this system is transpressional at the present time the zone of major seismicity passes south of the rift system near the indigirka river and indicates that the rift is not acting as the plate boundary the moma rift is also asymmetric but with the lower plate southwest side being topographically higher the moma system is inactive along most of its length and only reached an early stage of development before activity ceased

structural characteristics of the northern okinawa trough and adjacent areas from regional seismic reflection data geologic and tectonic implications abstract analysis of regional multi channel seismic data from the northern okinawa trough and adjacent shelf provides some important constraints on the structural development of the area the sedimentary strata in the northern east china sea shelf basin separated from the okinawa trough by the taiwan sinzi belt are affected by the miocene compressional tectonism and truncated by the late miocene unconformity in contrast those in the western margin of the northern okinawa trough are cut by numerous normal faults and the late miocene horizon forms a conformable surface this suggests that the taiwan sinzi belt acted as a buttress for the northern okinawa trough against the compressional tectonism our data also reveal the ho basin in the western margin of the northern okinawa trough previously known only from proprietary industry data the longwan ridge lying between the ho basin and the northern okinawa trough may be the youngest of the relict arcs or buried ridges in the area the abrupt along strike change in the fault polarity near the northern margin of the depocenter of the ho basin suggests a nw trending left lateral transfer zone or fault the western boundary of the northern okinawa trough is characterized by the gently deepening seafloor whereas that of the southern okinawa trough is marked by steep border faults suggesting more rapid subsidence in the south this together with the well developed symmetric axial faults in the south and the greater width and the lack of well developed axial zone in the north may suggest focused rifting extension in the southern okinawa trough and diffuse rifting extension in the northern okinawa trough we postulate that the diffuse rifting extension in the northern okinawa trough is due to the tectonic perturbation caused by the convergence or subduction of the topographically high and buoyant amami plateau at the northern ryukyu arc

temporal and spatial scales of geomorphic adjustments to reduced competency following flow regulation in bedload dominated systems abstract because of the combined effects of reduced sediment transport capacity and competency following flow regulation morphological changes are expected to occur in channels downstream from dams and specifically at tributary junctions where local inputs of water and sediment occur using a combination of historical aerial photographs mainstem and tributary channel pebble counts and hec ras flow modeling for two watersheds in south central vt one unregulated and the other regulated since 1961 we document the time series of post regulation channel narrowing and associated bar growth due to the influx of tributary sediment channel adjustments at regulated tributary junctions have been significant in ca 50 years following impoundment with channels downstream of the confluences narrowing over 15 after an initial ca 20 year lag before the onset of accelerated narrowing moreover flow modeling suggests that downstream of regulated confluences the modern median grain size d50 along the channel bed is immobile no significant channel narrowing has occurred either above or below unregulated tributary junctions or on the mainstem upstream of regulated confluences however greater channel sediment fining is observed upstream of regulated confluences than above unregulated confluences thus the primary mode of mainstem channel adjustment differs up and downstream of regulated tributaries these confluence effects have occurred where the tributary drainage area is only 0 2 times that of the mainstem well below the threshold ratio of 0 6 required for significant geomorphic effects at unregulated confluences highlighting the geomorphic scale shift of dams lastly we evaluate the downstream length required for a river to recover from the impacts of impoundment and demonstrate that even distal locations are impacted by flow regulation unlike the impacts of flow regulation in the western us where channel incision and bar erosion predominate following impoundment we find that in situations where bed incision is minimal and where sediment loads are low but bed caliber high bar growth and channel narrowing are significant adjustments at tributary junctions following impoundment therefore at our sites the effects of dams on reduced competency may be more profound than on reduced sediment transport capacity highlighting the importance of geologic and geomorphic settings in understanding fluvial responses to impoundment

contour mapping of relic structures in the precambrian basement of the reelfoot rift north american midcontinent a new contour map of the basement of the reelfoot rift constructed from drill hole and seismic reflection data shows the general surface configuration as well as several major and minor structural features the major features are two asymmetric intrarift basins bounded by three structural highs and the rift margins the basins are oriented normal to the northeast trend of the rift two of the highs appear to be ridges of undetermined width that extend across the rift the third high is an isolated dome or platform located between the basins the minor features are three linear structures of low relief oriented subparallel to the trend of the rift two of these located within the rift basins may divide the rift basins into paired subbasins these mapped features may be the remnants of initial extensional rifting half graben faulting and basement subsidence the rift basins are interpreted as having formed as opposing half graben and the structural highs are interpreted as having formed as associated accommodation zones some of these features appear to be reactivated seismogenic structures within the modern midcontinent compressional stress regime a detailed knowledge of the geometries of the reelfoot rift s basement features therefore is essential when evaluating their seismic risk potential

structural dynamic model of the chersky seismotectonic zone continental part of the arctic asian seismic belt abstract to construct a model for modern geodynamics of the chersky seismotectonic zone continental part of the arctic asian seismic belt we analyzed the available data on its structural tectonic setting depth structure kinematics of active faults morphotectonic features of modern topography tectonic stress fields as derived from the earthquake focal mechanisms as well as the types of late cenozoic fold and rupture deformation it is established that the yana indigirka and indigirka kolyma segments in the central part of the chersky zone underwent transpression due to collision of the eurasian eu and north american na lithospheric plates this was only possible if in course of the plate convergence the kolyma omolon block in the frontal part of the na plate formed the active indentor under the block pressure geodynamic settings experience horizontal compression in which case some of the blocks are being extruded along the system of northwestern and southeastern strike slip faults this results in the formation of major seismogenic structures with a high seismic potential in the marginal and frontal parts of the chersky zone

earthquake depth distributions in central asia and their relations with lithosphere thickness shortening and extension this paper examines the relationship between seismogenic thickness lithosphere structure and rheology in central and northeastern asia we accurately determine earthquake depth distributions which reveal important rheological variations in the lower crust these variations exert a fundamental control on the active tectonics and the morphological evolution of the continents we consider 323 earthquakes across the tibetan plateau the tien shan and their forelands as well as the baikal rift ne siberia and the laptev sea and present the source parameters of 94 of these here for the first time these parameters have been determined through body wave inversion the identification of depth phases or the modelling of regional waveforms lower crustal earthquakes are found to be restricted to the forelands in areas undergoing shortening and to locations where rifting coincides with abrupt changes in lithosphere thickness such as the ne baikal rift and w laptev sea the lower crust in these areas is seismogenic at temperatures that may be as high as 600 c suggesting that it is anhydrous and is likely to have great long term strength lower crustal earthquakes are therefore a useful proxy indicating strong lithosphere in places that are too small in areal extent for this to be confirmed independently by estimating effective elastic thickness from gravity topography relations the variation in crustal rheology indicated by the distribution of lower crustal earthquakes has many implications ranging from the support of mountain belts and the formation of steep mountain fronts to the localization and orientation of rifting in combination these processes can also be responsible for the separation of the front of the thin skinned mountain belts from their hinterlands when continents separate

dip analysis as a tool for estimating regional kinematics in extensional terranes abstract in basin analyses that rely almost solely on seismic reflection data to configure the underlying structure it has become common practice to use extensional fault geometries to infer kinematic histories this procedure relies on the existence of fault geometries predicted by ideal orthogonal extension and assumes the structure is well constrained in areas where data are sparse or of equivocal quality this often leads to circular analysis that is ideal orthogonal extension is assumed to have been operative then under constrained fault geometries are mapped according to model predictions fault geometries so derived are subsequently used as evidence that orthogonal extension was operative and that the direction of extension is determinable we develop an alternative tool for inferring kinematics which is independent of fault geometries the method relies on the empirical evidence that the dip of the hangingwall s is systematic and predictable in extensional systems even when fault geometries are non ideal although not without significant limitations dip analysis can provide additional constraints for structural and kinematic interpretations especially where seismic reflection data are the main source of information and dip domains define discrete crustal blocks

the laptev sea rift abstract in north eastern siberia the active mid ocean gakkel ridge interacts with the continental shelf of the laptev sea extension has affected the shelf since at least the early tertiary and has resulted in the formation of a complex horst and graben system we present new seismic data from the laptev sea including deep seismic soundings the most prominent rift basin is the ust lena rift with a minimum e w width of 300 km at latitude 75 n and a cenozoic infill up to 13 km in thickness the asymmetric shape of the basin and conclusive evidence for a detachment imply a simple shear geometry the suggested rift model combines a ramp and flat geometry for the detachment with ductile stretching beneath the detachment a major west dipping hingeline listric fault separates the ust lena rift from the laptev horst the 100 150 km wide laptev horst is subdivided into three units by narrow rift grabens another prominent rift graben is the anisin basin which is located in the northern shelf area though the laptev sea rift formed in interaction with an active mid oceanic ridge there are indications that the laptev sea rift is of the passive rift type the rift was developed east of a sw ne trending transfer zone which links the gakkel ridge to the laptev sea rift

focal depths and mechanisms of large earthquakes on the arctic mid ocean ridge system as part of a global study of the source characteristics and tectonic implications of large earthquakes on mid ocean ridges we report on the focal depths and mechanisms of the six largest earthquakes that have occurred in the last 20 years on the arctic mid ocean ridge system for each earthquake we invert the long period p and sh waveforms to estimate the parameters of the best fitting point source including seismic moment centroid depth double couple source orientation and source time function three of the earthquakes occurred on the oceanic spreading center in the eurasian basin along ridge segments spreading at half rates of 4 6 mm yr these events have mechanisms very similar to those of ridge crest earthquakes on the mid atlantic ridge almost pure normal faulting on planes that dip at approximately 45 and strike parallel to the rift axis moments of 4 5 1024 dyn cm centroid depths of 1 2 km beneath the seafloor and water depths inferred from the predominant period of water column reverberations appropriate to epicentral locations within the median valley the remaining three earthquakes also characterized by normal faulting are associated with the continuation of the divergent plate boundary 2 3 mm yr half rate onto the continental shelf of the laptev sea where the crust becomes transitional in nature one of the largest known spreading center earthquakes august 25 1964 m0 1 1026 dyn cm occurred where the oceanic ridge intersects the outer edge of the continental slope waveform inversion for this event can resolve unilateral rupture from north to south landward along a fault at least 30 km in length the preferred centroid depth is 5 km beneath the seafloor in crustal material with an unusually low shear velocity but a centroid depth as great as 15 km cannot be ruled out two earthquakes beneath the continental shelf have significantly greater centroid depths 10 20 km than mid ocean ridge earthquakes indicating a thicker brittle regime and a cooler thermal structure than are typical of oceanic spreading centers the tectonic environment of these events is more representative of rifted continental lithosphere than of a mid ocean ridge

unusually deep earthquakes in east africa constraints on the thermo mechanical structure of a continental rift system shudofsky 1985 has established that earthquakes associated with the east african rift system have well constrained focal depths as great as 25 30 km using published heat flow measurements as a guide to the local geotherm we find through simple stress envelope calculations that the deepest earthquakes probably occur in the lower crust in a region where the lithosphere is strong these results are at odds with the commonly held idea that seismicity in zones of continental extension is limited to the shallow upper crust because of elevated temperatures accompanying lithospheric thinning any model of the rifting process in east africa must account for the fact that these regions exhibit considerable strength down to lower crustal levels

multiscale flow vegetation sediment feedbacks in low gradient landscapes abstract low gradient fluvial landscapes 1 50 cm km 1 occupy diverse settings inland tidal and deltaic wetlands large river floodplains lowland streams but share many commonalities because of low flow energies these landscapes have abundant vegetation that is submersed or frequently inundated their sediment loads are predominantly fine with large loads transported in suspension the complexities of fluvial vegetation interactions and fine sediment transport have made these landscapes relatively poorly studied in the field of geomorphology yet the importance of understanding their dynamics is paramount these landscapes will be among the first inundated by rising seas and or are presently the focus of the world s largest restoration projects in this synthesis interactions between flow vegetation and sediment documented in inland and tidal marshes chalk and coastal plain streams large river floodplains and deltas are reviewed and classified into feedback processes occurring over a range of five spatiotemporal scales despite different morphologic appearances the feedback processes governing the coevolution of landscapes and vegetation are broadly consistent across settings though modified in their effects by life history traits of vegetation characteristics of the sediment supply external boundary forcing and initial conditions longitudinally elongated patches are common in many settings arising from stress divergence feedbacks however their ultimate morphology is strongly dependent upon the activation of patch or multipatch scale feedbacks which depends on initial densities at the time of colonization generally flow vegetation sediment feedbacks play a dominant role in landscape morphology when the setting is depositional and little initial topographic differentiation is present in that case these feedbacks can explain the apparently paradoxical emergence of high sinuosities or parallel drainage in very low gradients importantly for management flow vegetation sediment interactions may activate a chain of positive feedbacks that engages progressively larger scales resulting in massive destruction of marsh vegetation or topographic homogenization interrupting these feedbacks requires intervention over all scales activated

sediment patterns near a model patch of reedy emergent vegetation this laboratory study describes the sediment patterns formed in a sand bed around circular patches of rigid vertical cylinders representing a patch of reedy emergent vegetation the patch diameter was much smaller than the channel width two patch densities solid volume fraction 3 and 10 and two patch diameters 22 and 10 cm were considered for flows above the threshold of sediment motion patterns of sediment erosion and deposition were observed around and within the patch scouring within the patch was positively correlated with turbulent kinetic energy in the patch for sparse patches sediment scoured from within the patch was mostly deposited within one patch diameter downstream of the patch for dense patches which experience greater flow diversion sediment scoured from the patch was carried farther downstream before deposition along the patch centerline differences between the sparse and dense patch patterns of deposition are explained in the context of flow diversion and wake structure which are related to a nondimensional flow blockage parameter while sediment was redistributed near the patch observations suggest that net deposition was not recorded at the reach scale

seasonal controls on meteoric 7be in coarse grained river channels cosmogenic 7be is a natural tracer of short term hydrological processes but its distribution in upland fluvial environments over different temporal and spatial scales has not been well described we measured 7be in 450 sediment samples collected from perennial channels draining the middle of the connecticut river basin an environment that is predominantly well sorted sand by sampling tributaries that have natural and managed fluctuations in discharge we find that the 7be activity in thalweg sediments is not necessarily limited by the supply of new or fine grained sediment but is controlled seasonally by atmospheric flux variations and the magnitude and frequency of bed mobilizing events in late winter 7be concentrations in transitional bedload are lowest typically 1 to 3 bq kg 1 as 7be is lost from watersheds via radioactive decay in the snowpack in mid summer however 7be concentrations are at least twice as high because of increased convective storm activity which delivers high 7be fluxes directly to the fluvial system a mixed layer of sediment at least 8 cm thick is maintained for months in channels during persistent low rainfall and flow conditions indicating that stationary sediments can be recharged with 7be however bed mobilizing rain on snowmelt events in late spring can reset 7be amounts and concentrations in the channel as previously buried old sediment with low 7be is mixed into the thalweg we conclude that given proper temporal and spatial sampling 7be is a valuable tracer of seasonal timescale mass transport and exchange in coarse grained fluvial systems copyright 2013 john wiley sons ltd

late cretaceous cenozoic deformation of northeast asia abstract the plate tectonic paradigm implies rigid plates and narrow plate boundaries in contrast diffuse plate boundaries are common both in the oceans and continents r g gordon annu rev earth planet sci 26 1998 615 642 and their history is difficult to constrain especially in remote tectonically complex areas such as northeast asia m e chapman s c solomon j geophys res 81 1976 921 930 here we show how extensive north atlantic marine magnetic r macnab et al eos 76 1995 449 458 and gravity data d t sandwell w h f smith j geophys res 102 1997 10039 10054 can be used to unravel with tight confidence limits successive periods of deformation over 80 million years along the diffuse continental eurasian north american plate boundary a period of compression in the late cretaceous 14 mm yr in the laptev sea to 20 mm yr in kamchatka led to thrusting in the verkhoyansk mountains and was followed by extension from 68 to 40 ma when 400 km of extension was accommodated by the formation of a series of grabens including the moma rift system since 40 ma time varying compression and transpression along the moma rift system created strike slip faults thrusts and folds at rates up to 6 3 mm yr in the laptev sea region 600 km of extension from latest late cretaceous to present created the laptev sea and lena rift systems the deformation predicted by our model fits most geological features formed in the laptev sea and central northeast asia during late cretaceous cenozoic times the most recent deformation late miocene pliocene is not very well constrained since our model lacks data younger than 11 ma the deformation that occurred in kamchatka reflects a complex tectonic setting and our model s predictions are only tentative

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

classification of geomorphological effects downstream of dams abstract the effects of dams on downstream geomorphology are reviewed and a typology is devised consisting of nine cases the classification can be seen as a further development of lane s balance between water discharge sediment load grain size and river slope depending on changes in released water flow and changes in released sediment load relative to the transport capacity of the flow it is possible to estimate resulting cross sectional geomorphology the longitudinal extent of changes and their variability with time and the tributary response to altered mainstream cross section changes are also discussed

prediction of velocity profiles and longitudinal dispersion in salt marsh vegetation to predict the behavior of solutes and suspended particles in wetlands it is necessary to estimate advection and longitudinal dispersion to better understand these processes measurements were taken of stem frontal area velocity vertical diffusion and longitudinal dispersion in a spartina alterniflora salt marsh in the plum island estuary in rowley massachusetts vegetation volumetric frontal area peaked at 0 067 6 0 007 cm 21 near 10 cm from the bed if the velocity profile in a dense emergent marsh canopy depends on the local balance between pressure forcing and vegetation drag the velocity will vary inversely with canopy drag i e velocity is minimum where the frontal area is maximum in fact the minimum velocity was observed at 10 cm from the bed the momentum balance therefore provides a way to predict the velocity profile structure from canopy morphology the vertical diffusion coefficient also depends on canopy characteristics such that the vertical diffusion coefficient normalized by the velocity and stem diameter had a constant value of 0 17 6 0 08 at this study site the canopy morphology also controls the longitudinal dispersion observed in this study to be 4 to 27 cm 2 s 21

application of the critical coulomb wedge theory to hyper extended magma poor rifted margins the critical coulomb wedge theory ccwt has been extensively used in compressional tectonics to resolve the shape of orogenic or accretionary prisms while it is less applied to extensional and gravitational wedges despite the fact that it can be described by the same equation in particular the hyper extended domain at magma poor rifted margins forming the oceanward termination of extended continental crust satisfies the three main requirements of the ccwt 1 it presents a wedge shape 2 the rocks forming the wedge are completely brittle frictional and 3 the base of the wedge corresponds to a low friction decollement however hyper extended margins present a fully frictional behaviour only for a very thin crust therefore this study is limited to the termination of hyper extended continental crust which deforms in the latest stage of continental rifting in this paper we define a method to measure the surface slope and the basal deep of this wedge that we apply to 17 hyper extended magma poor rifted margins in order to compare the results to the values predicted by the ccwt because conjugate pairs of hyper extended magma poor rifted margins are commonly asymmetric due to detachment faulting the wedges in the upper and lower plate margins corresponding respectively to the hanging wall and footwall of the detachment system are different while the stress field in the upper plate wedge corresponds to a tectonic extensional wedge the one in the lower plate matches that of a gravity extensional wedge using typical frictional properties of phyllosilicates e g clays and serpentine the shape of the hyper extended wedges can be resolved by the ccwt using consistent fluid overpressures our results show that all lower plate margins are gravitationally stable and therefore have a close to critical shape whereas the tectonic extensional wedges at upper plate margins are critical sub or sup critical due to the detachment initial angle and the duration of the tectonic activity in this paper we discuss the geometry and structural evolution of the most distal parts of hyper extended continental margins and the formation of extensional allochthons during hyper extension using the ccwt theory

vegetated mixing layer around a finite size patch of submerged plants 1 theory and field experiments 1 dynamics of a vegetated mixing layer around a patch of submerged plants was examined theoretically and experimentally in a lowland river theoretical analysis explored analogy with hydrodynamic mixing layers and introduced equations that describe expansion of the layers and alterations in mean flow field experiments provided empirical data for validation of the theory and examination of the effects of population density on the mixing layer dynamics detailed measurements assessed the structure of turbulent flow plant morphology biomechanical properties bending and streamlining due to interaction with the flow the theory was compared with the field experiments and an agreement was concluded it was found that near the upstream edge of the patch the vegetated mixing layer expands similar to the canonical mixing layers although its statistics scale on the velocity differential characteristic for the stabilized part downstream mean momentum flux reduces in magnitude and reverses in direction while turbulence became dominant this was observed to stabilize the velocity differential and increase the mean velocity of the layer that result in its limited growth described by a logarithmic function the population density of vegetation was found to control the flow in dense vegetation the analogy with mixing layers resembled best while in sparse vegetation the flow behaved similar to the boundary layers this theory can be used for quantitative assessment of seasonal effects in natural vegetated rivers because the population density of vegetation varies during the vegetation season the companion paper focuses on the structural properties of turbulence in the vegetated shear layers

bed morphological changes around a finite patch of vegetation for the appropriate management and restoration of rivers isolated vegetation is often a practical means for improving stream habitat and ecology the effect of a finite vegetation patch on flow and bed morphology in an open channel was investigated using laboratory experiments the patch containing emergent and submerged vegetation was modeled using circular cylinders and located mid channel along a side wall several configurations of the patch and submergence ratio i e water depth to the height of vegetation and two flow conditions i e below and above the sediment motion threshold were considered for flows below the sediment motion threshold erosion occurred primarily on the opposite side of the patch and near the leading edge of the patch the degree of scouring depth observed in both these regions was affected by the submergence ratio and it increased with the non dimensional flow blockage i e the product of the patch density and width in contrast for flows above the sediment motion threshold sediment accumulated within and around the patch due to a reduction in bed shear stress which was strongly influenced by the flow blockage and the obstruction ratio i e the ratio of patch width to channel width the eroded area observed within the patch was consistent with the interior adjustment region where the deceleration and diversion of flow occurred through the patch as the flow blockage increased or as the obstruction ratio decreased the deposition rate within and behind the patch decreased furthermore the deposition rate increased with an increase in the ratio of flow rate through the patch to total flow rate regardless of the submergence ratio copyright 2014 john wiley sons ltd

the rate and pattern of bed incision and bank adjustment on the colorado river in glen canyon downstream from glen canyon dam 1956 2000 closure of glen canyon dam in 1963 transformed the colorado river by reducing the magnitude and duration of spring floods increasing the magnitude of base flows and trapping fine sediment delivered from the upper watershed these changes caused the channel downstream in glen canyon to incise armor and narrow this study synthesizes over 45 yr of channel change measurements and demonstrates that the rate and style of channel adjustment are directly related to both natural processes associated with sediment deficit and human decisions about dam operations although bed lowering in lower glen canyon began when the first cofferdam was installed in 1959 most incision occurred in 1965 in conjunction with 14 pulsed high flows that scoured an average of 2 6 m of sediment from the center of the channel the average grain size of bed material has increased from 0 25 mm in 1956 to over 20 mm in 1999 the magnitude of incision at riffles decreases with distance downstream from the dam while the magnitude of sediment evacuation from pools is spatially variable and extends farther downstream analysis of bed material mobility indicates that the increase in bed material grain size and reduction in reach average gradient are consistent with the transformation of an adjustable bed alluvial river to a channel with a stable bed that is rarely mobilized decreased magnitude of peak discharges in the post dam regime coupled with channel incision and the associated downward shifts of stage discharge relations have caused sandbar and terrace erosion and the transformation of previously active sand bars and gravel bars to abandoned deposits that are no longer inundated erosion has been concentrated in a few pre dam terraces that eroded rapidly for brief periods and have since stabilized the abundance of abandoned deposits decreases downstream in conjunction with decreasing magnitude of shift in the stage discharge relations in the downstream part of the study area where riffles controlling channel elevation have not incised channel narrowing has resulted from decreased magnitude of peak discharges and minor post dam deposition these physical changes to the aquatic and riparian systems have supported the establishment and success of an artifact ecosystem dominated by non native species models for the channel response downstream from large dams typically consider factors such as the degree of sediment deficit the pre dam surface and subsurface grain size and the magnitude of post dam average flows these results suggest that it is also necessary to consider 1 the possibility of variable responses among different channel elements and 2 the potential importance of exceptional flows resulting from management decisions

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

dynamics of continental rift propagation the end member modes abstract an important aspect of continental rifting is the progressive variation of deformation style along the rift axis during rift propagation in regions of rift propagation specifically transition zones from continental rifting to seafloor spreading it has been observed that contrasting styles of deformation along the axis of rift propagation are bounded by shear zones the focus of this numerical modeling study is to look at dynamic processes near the tip of a weak zone in continental lithosphere more specifically this study explores how modeled rift behavior depends on the value of rheological parameters of the crust a three dimensional finite element model is used to simulate lithosphere deformation in an extensional regime the chosen approach emphasizes understanding the tectonic forces involved in rift propagation dependent on plate strength two end member modes are distinguished the stalled rift phase is characterized by absence of rift propagation for a certain amount of time extension beyond the edge of the rift tip is no longer localized but occurs over a very wide zone which requires a buildup of shear stresses near the rift tip and significant intra plate deformation this stage represents a situation in which a rift meets a locked zone localized deformation changes to distributed deformation in the locked zone and the two different deformation styles are balanced by a shear zone oriented perpendicular to the trend in the alternative rift propagation mode rift propagation is a continuous process when the initial crust is weak the extension style does not change significantly along the rift axis and lengthening of the rift zone is not accompanied by a buildup of shear stresses model predictions address aspects of previously unexplained rift evolution in the laptev sea and its contrast with the tectonic evolution of for example the gulf of aden and woodlark basin

upwarp of anomalous asthenosphere beneath the rio grande rift continental rifts are possible analogues of mid ocean ridges although major plate tectonic features are less clearly observed1 current thermal models of mid ocean ridges2 4 consist of solid lithospheric plates overlying the hotter less viscous asthenosphere with plate thickness increasing away from the ridge axis the lithospheric lower boundary lies at or near the melting point isotherm so that at greater depths higher temperatures account for lower viscosity lower seismic velocities and possibly partial melting upwarp of this boundary at the ridge axis concentrates heat there thus lowering densities by expansion and raising the sea floor to the level of thermal isostatic equilibrium at slow spreading ridges a major central graben forms owing to the mechanics of magma injection into the crust5 topography heat flow gravity and seismic studies support these models on the continents a low velocity channel has been observed although it is poorly developed beneath ancient cratons6 9 plate tectonic models have been applied to continental basins and margins10 12 but further similarities to the oceanic models remain elusive topographic uplift is often ascribed to airy type isostatic compensation caused by crustal thickening rather than thermal compensation in the asthenosphere here we discuss the rio grande rift in southwestern united states teleseismic p wave residuals show that regional uplift is explained by asthenosphere uplift rather than crustal thickening

predicting the type location and magnitude of geomorphic responses to dam removal role of hydrologic and geomorphic constraints abstract using a dam removal on the ashuelot river in southern new hampshire we test how a sudden spatially non uniform increase in river slope alters sediment transport dynamics and riparian sediment connectivity site conditions were characterized by detailed pre and post removal field surveys and high resolution aerial lidar data and locations of erosion and deposition were predicted through one dimensional hydrodynamic modeling the homestead dam was a 200 year old 4 m high 50 m wide crib dam that created a 9 5 km long relatively narrow reservoir following removal an exhumed resistant bed feature of glaciofluvial boulders located 400 m upstream and 2 5 m lower than the crest of the dam imposed a new boundary condition in the drained reservoir acting as a grade control that maintained a backwater effect upstream during the 15 months following removal non uniform erosion in the former reservoir totaled 60 000 m3 equivalent to 9 3 cm when averaged across the reservoir net deposition of 10 700 m3 was measured downstream of the dam indicating most sediment from the reservoir was carried more than 8 km downstream beyond the study area the most pronounced bed erosion occurred where modeled sediment transport increased in the downstream direction and deposition occurred both within and downstream of the former reservoir where modeled sediment transport decreased in the downstream direction we thus demonstrate that spatial gradients in sediment transport can be used to predict locations of erosion and deposition on the stream bed we further observed that bed incision was not a necessary condition for bank erosion in the former reservoir in this characteristically narrow and shallow reservoir lacking abundant dam induced sedimentation the variable resistance of the bed and banks acted as geomorphic constraints overall the response deviated from the common conceptual model of knickpoint erosion and channel widening due to dam removal with thousands of dams likely to be considered for removal or repair in the coming decades this study helps to advance predictions of the geomorphic response to dam removal and contributes to a broader understanding of the variability in both style and timing of fluvial responses to disturbances

channel narrowing by vertical accretion along the green river near green river utah the green river is the longest tributary of the colorado river near the town of green river utah the green river narrowed in two discrete phases during the twentieth century the first phase of narrowing decreased average width by about 5 and occurred between about 1930 and 1940 when the magnitude of 2 yr flood mean annual discharge and effective discharge decreased by about 30 28 and 37 respectively during this first phase of narrowing saltcedar tamarisk spp an invading non native tree began to establish itself in the study area but botanists of that time did not describe the tree as abundant channel width was stable in the 1940s and 1950s even though saltcedar were becoming already abundant on the river9s banks further narrowing of an additional 14 occurred after 1959 this latest period of narrowing began following three successive years when the magnitude of floods was less than the present 1 5 yr recurrence flood and when saltcedar were already abundant along the river the deposits that comprise the banks of the narrowing green river are composed of the suspended load of the river and these alluvial deposits are characterized by horizontal layers which indicate that they formed by vertical accretion a mechanism is proposed to explain the coarsening upward sequence of beds found in these vertically accreted deposits these changes in the channel of the green river are based on analysis of more than 2600 discharge measurements made by the u s geological survey resurvey of an abandoned measurement site matches of historical ground level photography and analysis of historical aerial photography within a geographic information system we have developed analytical techniques that permit analysis of width data from u s geological survey discharge measurements where gaging cross sections have adjustable beds and banks these techniques allow the spatially rich but temporally poor data from aerial photographs to be supplemented with gaging station data which add great detail about the timing and actual processes of channel narrowing that cannot be determined from aerial photographs alone such an analytical strategy provides a more complete record of historical channel adjustment than can be obtained by other means

symmetry vs asymmetry of a hyper thinned rift example of the mauleon basin western pyrenees france abstract the aim of this study is to unravel the tectono sedimentary evolution of a hyper thinned rift based on the example of the mauleon basin a basin filled by thick synrift deposits the integrated study combines field data detailed geological mapping and seismic interpretation the field study focuses on the iberian margin of the mauleon basin seismic interpretation and well calibration along a n s transect of the mauleon basin enable imaging the transition with the northern conjugate margin the synrift records are very different on either side of the basin the southern margin is composed of a proximal turbiditic s l siliciclastic system whereas the northern margin is characterized by a carbonate system extending from the platform to the basin we recognize the mauleon rift as an apparent symmetric hyper thinned rift related to a southward dipping albian detachment and a northward dipping cenomanian one two stages of continental crustal thinning are inferred to explain the development of the mauleon basin first a barremian to earliest albian ductile pure shear thinning phase responsible for the lower crustal thinning and the formation of a symmetric sag basin second an albian cenomanian simple shear thinning phase responsible for the onset of the southward dipping saint palais detachment faulting and for evolution to an asymmetric basin the iberian margin appears as an upper plate and the european one as a lower plate during albian time at early cenomanian time the basin was affected by structural changes of the margins resulting from shift in detachment direction interpreted as flip flop detachment tectonics

sediment transport in a highly regulated fluvial system during two consecutive floods lower ebro river ne iberian peninsula the transfer of sediment through a highly regulated large fluvial system lower ebro river was analysed during two consecutive floods by means of sediment sampling suspended sediment and bedload transport were measured upstream and downstream of large reservoirs the dams substantially altered flood timing particularly the peaks which were advanced downstream from the dams for flood control purposes the suspended sediment yield upstream from the dams was 1 700 000 tonnes which represented nearly 99 per cent of the total solid yield the mean concentrations were close to 0 5 g l 1 the sediment yield downstream from the dams was an order of magnitude lower 173 000 tonnes showing a mean concentration of 0 05 g l 1 the dams captured up to 95 per cent of the fine sediment carried in suspension in the river channel preventing it from reaching the lowermost reaches of the river and the delta plain total bedload transport upstream from the dams was estimated to be about 25 000 tonnes only 1 5 per cent of the total load the median bedload rate was 100 gms 1 below the dams the river carried 178 000 tonnes around 51 per cent of the total load at a mean rate of 250 g ms 1 the results of sediment transport upstream and downstream from the large dams illustrate the magnitude of the sediment deficit in the lower ebro river the river mobilized a total of 350 000 tonnes in the downstream reaches which were not replaced by sediment from upstream therefore sediment was necessarily entrained from the riverbed and channel banks causing a mean incision of 33 mm over the 27 km long study reach altogether a significant step towards the long term degradation of the lower ebro river copyright 2005 john wiley sons ltd

s wave velocity structure of the upper mantle beneath the arctic region from rayleigh wave dispersion data abstract a new model of the upper mantle structure of the arctic region based on a representative dataset of rayleigh wave group velocity dispersion curves from 10 to 250 s period is presented a surface wave tomography procedure is used to image the group velocity distributions local dispersion curves are constructed and inverted to vertical s wave velocity sections up to the depth of 500 km results are presented in two forms as horizontal slices of s wave velocity variations relative to the average velocities at several mantle depths and as 2d velocity sections along three profiles crossing different tectonic units the model shows lateral and vertical velocity variations over the whole depth range within the study area the most prominent velocity heterogeneities are localized in the uppermost mantle up to the 200 km depth in this depth range the velocity anomalies are strongly correlated with the main tectonic structures the calculated s wave velocity distribution demonstrates that the upper mantle of the continental shields is characterized by high s wave velocities and contains regional velocity anomalies associated with small scale blocks low mantle velocities are attributed to the areas with high level of tectonic and seismic activity significant difference in deep velocity structure of the marginal seas and deep water oceanic basins of various ages is revealed the obtained model suggests some insights into the geodynamical evolution of the lithosphere of the arctic region

crustal thickness of northeast russia abstract the first order crustal structure of the magadan region and northeast sakha republic yakutia northeast russia is obtained by simultaneously inverting for origin times and travel time curves a total of 1210 observations are used as an average a 37 km thick 5 992 0 007 km s crust overlying an 7 961 0 015 km s mantle provides an excellent fit to phase data listed in the materialy po seismichnosti sibiri bulletin travel time curves for individual stations are very close to this average though there are variations in both crustal thickness and velocities upper mantle velocities and crustal thickness appear to increase along the southern edge of the okhotsk chukotka volcanic belt and decrease in the upper kolyma river basin and along the trace of the proposed moma rift crustal thickness is greatest at khandyga on the siberian platform and lowest at yubileniya which may lie within the currently active laptev sea rift system

sediment transport constraints on river response to regulation abstract we demonstrate that alluvial channel response to regulation depends on the characteristic mode of sediment transport in a channel and thus for a channel in supply transport equilibrium on the caliber of sediment mantling the channel bed as well as changes in characteristic water discharge and sediment load we find that regulated coarse gravel and cobble bed alluvial rivers dominated by bedload transport are predicted and observed to preserve the value of a dimensionless ratio of characteristic water discharge channel slope width and size of sedimentary particles mantling the bed associated with the critical conditions required for the onset of significant sediment transport the covariant geomorphic adjustment of such rivers to regulation is independent of the degree of sediment impoundment although the nature and rate of changes in any specific characteristic appear to be sensitive to changes in sediment supply in contrast covariant geomorphic changes in sand and fine gravel bed alluvial rivers dominated by weak suspension transport are predicted and observed to be dependent on the degree of sediment impoundment and commensurate with the change in the sediment concentration of characteristic formative flows in both cases specific geomorphic characteristics of alluvial rivers exhibit varied responses to regulation in different rivers but across all rivers a systematic covariation in channel slope width and grain size is observed that for a given mode of sediment transport preserves a characteristic value of the shields number

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

hydrodynamics of model posidonia oceanica patches in shallow water the hydrodynamics of simulated patches of the mediterranean seagrass posidonia oceanica were studied in laboratory flume experiments in which the height of the pronated canopy was always greater than half the total water depth the effects of variations in speed from 0 08 m s 21 to 0 24 m s 21 and patch configuration on the hydrodynamics were investigated significant speeds penetrated the patches to approximately half their height reducing speed did not change the flow patterns observed except to weaken and blur them flow encountering a single patch formed a turbulent wake at the height of the top of the canopy within this wake the vertical shear stress decreased monotonically downstream but the reynolds stress increased initially and then decayed when a second patch was positioned within the region where reynolds stress increased referred to as the 06 patch the wake center penetrated it causing average turbulent velocities with horizontal components 3 3 times higher and vertical components 4 2 times higher than in the upstream patch when this patch was positioned where the reynolds stress decayed referred to as the 14 patch the wake center rose above it nevertheless the turbulence in the 14 patch had horizontal components 12 higher and vertical components 22 higher on average than in the 06 patch because its upstream end was closer to the reynolds stress maximum thus the ratio of the patch separation to the length of wake in which the reynolds stress increased was identified as central to quantifying the turbulence within the downstream patch the increased turbulence is likely to be important in determining sedimentary and ecological patch characteristics by increasing retention of particulates in suspension and thus reducing depositional rates of for example larvae nutrients and dead organic matter

case study effect of submerged aquatic plants on turbulence structure in a lowland river interactions of aquatic plants with turbulent flows in fluvial systems have attracted considerable interest while there have been recent advances in theories that describe vegetation flow interactions in idealized laboratory flows their practical application is still problematic due to limited knowledge of effects caused by heterogeneously patchy distributed plants in naturally formed vegetative mosaics in rivers this paper reports on a study in a lowland river aimed at quantification and parameterization of vegetation effects on redistribution of mean and turbulent characteristics of the flow and their consequences for hydraulic resistance the measurements were carried out in summer on a river reach with a patchy mosaic dominated by submerged flexible aquatic plants and repeated at the same water level in early spring before the plants start growing this design of the study allowed for quantitative evaluation of the effects caused by flow plants interactions on bulk flow parameters at comparable submergences of riverbed roughness elements sediment grains and sand bars the study indicates that symmetrical quasi two dimensional open channel flow structure in unvegetated riverbed was transformed into highly fragmented complex flow pattern spatially arranged by patches and free paths in the mosaic despite complexities and three dimensionality of the flow normalized mean velocity profiles in the patches were satisfactory described by hyperbolic tangent function while flow in the free paths similarly to unvegetated channel was in a reasonable agreement with the conventional logarithmic law

channel adjustments bedload transport and sediment sources in a gravel bed river brenta river italy this paper deals with the brenta river the alps italy a gravel bed river strongly affected by human impact the aims of this work are a to reconstruct the channel adjustments that have occurred during the last decades and b to analyse the present condition of the river in terms of bedload transport and sediment sources the study reach which is 23 km long was investigated using historical maps aerial photographs 12 monumented cross sections laser altimetry data and field survey bedload transport rates were estimated by a morphological approach which allows the construction of a sediment budget dramatic channel adjustments have occurred in response to an alteration of sediment fluxes caused by different human interventions gravel mining dams torrent control works major channel adjustments specifically incision up to 8 9 m and narrowing took place between the 1950s and the 1980s on the other hand widening has become the most important process and incision has continued only in the upper part of the study reach in more recent times about the last 20 25 years the estimate of bedload transport rates for the period 1984 1997 was carried out starting from the erosion and deposition volumes of the single sub reaches such an estimate has shown that a a high spatial variability of gravel transport rates exists from 0 up to 73 200 85 400 m3 year and b most of the bedload is supplied by local sources bank erosion is the main source of sediments for bedload transport and its contribution can be estimated as from 9 up to 20 times higher than the upstream contribution finally from a practical point of view results from this study should be taken into account in addressing maintenance sediment management and restoration along a dynamic and unstable river such as the brenta copyright 2007 john wiley sons ltd

pollen and spores date origin of rift basins from texas to nova scotia as early late triassic palynological studies of the nonmarine newark supergroup of eastern north america and of rift basins in the northern gulf of mexico facilitate correlation with well dated marine sections of europe new information emphasizes the chronological link between the newark basins and a gulf of mexico basin and their common history in the rifting of north america from pangea shales from the subsurface south georgia basin are shown to be of late karnian age early late triassic the known time of earliest sedimentation in the culpeper basin is extended from norian late late triassic to mid karnian and the date of earliest sedimentation in the richmond and deep river basins is moved to at least earliest karnian perhaps ladinian the subsurface eagle mills formation in texas and arkansas has been dated palynologically as mid to late karnian the oldest parts of the newark supergroup and the eagle mills formation mostly began deposition in precursor rift basins that formed in ladinian to early karnian time in the southern newark basins sedimentation apparently ceased in late karnian but continued in the northern basins well into the jurassic until genesis of the atlantic ended basin sedimentation

estimated likelihood of observing a large earthquake on a continental low angle normal fault and implications for low angle normal fault activity the lack of observed continental earthquakes that clearly occurred on low angle normal faults lanfs may indicate that these structures are not seismically active or that these earthquakes are simply rare events to address this we compile all potentially active continental lanfs 24 in total and calculate the likelihood of observing a significant earthquake on them over periods of 1 100 years this probability depends on several factors including the frequency magnitude distribution for either a characteristic or gutenberg richter distribution we calculate a probability of about 0 5 that an earthquake greater than m6 5 large enough to avoid ambiguity in dip angle will be observed on any lanf in a period of 35 years which is the current length of the global centroid moment tensor catalog we then use bayes theorem to illustrate how the absence of observed significant lanf seismicity over the catalog period moderately decreases the likelihood that the structures generate large earthquakes

symmetric and asymmetric lithospheric extension relative effects of frictional plastic and viscous strain softening 1 strain dependent rheologies may play a critical role in the deformation of the lithosphere and particularly in the development of focused shear zones we investigate the effects of strain softening on lithospheric extension using plane strain thermomechanical finite element model experiments parametric softening is specified as a linear decrease of the effective internal angle of friction the effective viscosity or both in the model rheologies the sensitivity of deformation to the choice of softening parameters is investigated in cases where the crust is either strongly or weakly coupled to the mantle lithosphere results are classified according to the symmetry s or asymmetry a of the deformation of the upper and lower lithosphere during rifting strain softening is required for rifting asymmetry but is not always sufficient a range of model tectonic styles occurs including pure and simple shear modes with focused shear zones mode selection is mostly determined by the feedback between two primary controls the dominant rheology and the parametric strain softening mechanisms listed above softening of the dominant rheology promotes asymmetric extension of that part of the lithosphere controlled by the dominant rheology model results are consistent with the proposed primary controls and the factors that contribute to these controls in particular decreasing and increasing the rifting velocity can change the mode by changing the dominant rheology asymmetry is strongest in coupled models which include a decrease in the internal angle of friction and have low rifting velocities

mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition 1 the transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems and the fate of these particles is closely linked to vegetation we describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition patches of rigid emergent and flexible submerged vegetation were considered with two different stem densities for the rigid emergent vegetation flow adjustment was primarily two dimensional with flow deflected in the horizontal plane horizontal shear layers produced a von karman vortex street flow through the patch shifted the vortex street downstream resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished net deposition was enhanced within this region in contrast for the flexible submerged vegetation flow adjustment was three dimensional with shear layers formed in the vertical and horizontal planes because of strong vertical circulation turbulent kinetic energy was elevated directly downstream of the patch consistent with this deposition was not enhanced at any point in the wake this comparison suggests that morphological feedbacks differ between submerged and emergent vegetation further enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced relative to the open channel reduced deposition indicating enhanced resuspension occurred in regions of high turbulence kinetic energy regardless of local mean velocity these observations highlight the importance of turbulence in controlling deposition

mixing layers and coherent structures in vegetated aquatic flows 1 to date flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow with vegetative drag treated as an extension of bed drag however recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer this paper presents laboratory measurements obtained from a scaled seagrass model that demonstrate the applicability of the mixing layer analogy to aquatic systems specifically all vertical profiles of mean velocity contained an inflection point which makes the flow susceptible to kelvin helmholtz instability this instability leads to the generation of large coherent vortices within the mixing layer observed in the model at frequencies between 0 01 and 0 11 hz which dominate the vertical transport of momentum through the layer the downstream advection of these vortices is shown to cause the progressive coherent waving of aquatic vegetation known as the monami when the monami is present the turbulent vertical transport of momentum is enhanced with turbulent stresses penetrating an additional 30 of the plant height into the canopy

tectonic control of triassic sedimentation in southern new brunswick local and regional implications both regional and local tectonics controlled the sediment distribution in the fundy half graben during the triassic locally alluvial fans built out into the basin from the western boundary fault along what is now the south shore of new brunswick the alluvial fan red beds of the honeycomb point formation are covered by fluvial conglomerates of the quaco formation which in turn are buried by a resurgence of alluvial fan deposition represented by the echo cove formation pollen recovered from the upper part of the echo cove formation indicates that regionally the system of triassic jurassic grabens along the eastern seaboard is composed of two separate graben systems one stretching from south carolina to connecticut the other from the gulf of maine to the southern grand banks initial graben formation began at the southern end of each system followed by successive grabens opening toward the north the areal distribution of both graben systems appears to have been controlled by four large transform fault systems from the middle triassic through the jurassic the age and overall distribution of sediments within the fundy basin confirm the existence of a hot spot along the kelvin seamount chain and refines determination of the position and timing of the initial rifting that led to the formation of the present atlantic ocean

geology of the east siberian sea russian arctic from seismic images structures evolution and implications for the evolution of the arctic ocean basin 1 the kinematics and history of the opening of the amerasia basin are closely linked to the geology of the wide shelves surrounding the arctic ocean in this context multichannel seismic reflection data from the virtually unexplored shelf of the east siberian sea russian arctic are discussed in combination with potential field data three seismic marker horizons were defined and mapped their ages were linked to main tectonic and regional events and to onshore findings the data reveal that there is no continuation of the large rift basins from the laptev shelf onto the east siberian shelf and there are no indications for the previously defined several hundred kilometers wide blagoveshchensk basin the east siberian shelf is best described as an epicontinental platform that synsedimentarily subsided continuously since late cretaceous times with stronger subsidence to the northeast resulting in the formation of a large depocenter some form of extensional transtensional stresses affected the area and created relatively small ese wnw striking basins within this depocenter these basins are filled with 6 km thick late cretaceous to tertiary sediments the general dip of the platform of the east siberian shelf toward the northeast may be explained by dip slip movements along a major transform fault that is proposed by the rotation model for the opening of the amerasia basin for the evolution of small sag shaped basins within the east siberian depocenter we suggest a link to the opening of the eurasia basin instead of to the opening of the makarov basin

impacts of cascade reservoirs on the longitudinal variability of fine sediment characteristics a case study of the lancang and nu rivers abstract the lancang river and nu river are parallel rivers located in southwestern china while the lancang river has several dams the nu river has none to explore the impacts of cascade reservoirs on the grain size and mineral composition of fine sediments 9 fine sediment samples from the nu river and 29 samples from the lancang river were collected and tested the results indicate that in the free flowing reaches ffrs of the lancang river the sediment grain sizes fined systematically and the mineral compositions varied slightly and these results were similar to those of the nu river without dams along the whole mainstream in the regulated reaches rrs of the lancang river the sediment grain sizes and mineral compositions indicated discontinuous fluctuations due to the dams trapping in the reservoir head areas the sediments were composed of fine silt or medium silt with 50 clay minerals but the sediments immediately downstream of the dams were fine sand or medium sand with 71 quartz and feldspar the relative abundance of each mineral was altered differently by passing through the rrs quartz chlorite and illite increased by 13 33 and 20 respectively while feldspar and calcite decreased by 26 and 80 respectively and dolomite and pyrite were completely trapped in the cascade reservoirs all these common minerals may be replenished except pyrite which originates from mining areas in the lancang subbasin

sediment deposition within and around a finite patch of model vegetation over a range of channel velocity the interaction between flow and vegetation creates feedbacks to deposition that vary with channel velocity this experimental study describes how channel velocity and stem generated turbulence influence the deposition within and around an emergent patch of model vegetation with a particular focus on deposition within the patch the reynolds number threshold for stem scale turbulence generation was determined using velocity spectra and flow visualization at high channel velocity resuspension occurred in the bare regions of the channel and a nonuniform spatial distribution of net deposition was observed around and within the patch in contrast at low channel velocity there was no or limited resuspension and a uniform distribution of net deposition was observed around and within the patch the deposition inside the patch was enhanced relative to a bare channel control only when the following two criteria were met 1 the absence of stem turbulence and 2 the presence of sediment resuspension in the bare channel comparison to previous lab and field studies further support these criteria

grain size sediment transport and alluvial channel pattern abstract the shields parameter a dimensionless bed shear stress which can be expressed as a ratio of the slope depth and characteristic properties of bed material in an alluvial channel has been observed in natural rivers to take on modal values for the regimes of bedload mixed load and suspension transport dade w b friend p f 1998 grain size sediment transport regime and channel slope in alluvial rivers j geology 106 661 675 such conditions correspond to channel geometries associated with conserved sediment flux and thus to a state of approximate equilibrium in which the channels are neither aggrading nor degrading to a significant degree these findings are extended here to accommodate the effects of channel width in the context of a comprehensive data set on stable perennial rivers the new analysis reconciles existing empirical and theoretical approaches to predict alluvial channel geometry

tectonic stress state in ne japan as part of the okhotsk plate abstract an existing geodetic flow velocity model obtained by using an internal free network adjustment technique is used to derive estimates for various strain rates parameters in ne japan the greatest shortening rates of the principal strains trending e w are located in regions where much steady internal frame invariant plastic flow deformation is observed to be taking place the internal geodetic adjustment technique yielded the internal deformation in the tohoku arc most of the intraplate deformations including the much folding deformations observed in the inner zone are produced from within an interseismic transient elastic loading at a strongly coupled locked japan trench would not be needed the observed ongoing extensive ductile folding deformation in the inner zone of tohoku may mean that the geodetic strain rates causing shortening at 2 3 cm yr probably reflect the more correct level of the deformation which is steady permanent in ne japan as compared with seismic faulting data which indicate 0 5 cm yr shortening the calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework the tectonic stress state in ne japan as part of the okhotsk plate could mostly be influenced by the okhotsk plate which is extruding southward to lessen the significant accumulated contractional deformation in ne asia in the verkhoyansk cherskii mountains the principal strain rates are n s extensional essentially everywhere in ne japan as a result of the southerly extrusion except in its southernmost leading edge in the uetsu fossa magna province where the japan alps rampart rises in front of the extrusion here an e w compressional stress state prevails a second e w contractional zone is found in north central tohoku extending from the sanriku province in the outer zone to the inner zone in the japan sea side being more prevalent in the latter zone the calculated rotation rates from the geodetic flow model are clockwise cw in both of the e w contractional regions ne japan extruding southward faces buttresses in 1 the oga ojika line ool and or a crustal weakness zone between the northern and the southern halves of tohoku approx at 38 5 n latitude and especially 2 the japanese alps rampart these obstacles cause the northern and southernmost tohoku to veer to its right and rotate cw thereby setting up the e w trending compressional deformation in their respective inner zones between the ool or the 38 5 n boundary and the kanto tectonic line ktl the sense of the differential rotations is counterclockwise ccw towards the ocean to the se the northern tohoku north of the ool and the southernmost tohoku south of the ktl cannot rotate ccw towards the ocean because of the izu block s collision in the south and the relatively strong coupling along the subduction interface beneath the japan trench in the north off sanriku the relatively stronger long term coupling between the northern tohoku and the pacific plate at the sanriku coast with respect to that in off fukushima is due to a flatter subduction of the pacific slab there increasing the plates interface contact area the flattening of the subduction dip angle was caused by ccw rotation and shifting of the northern tohoku along the dextral honjo matsushima line roughly corresponding to the ool towards the pacific and overriding of the subduction zone during the formation of the japan sea

effects of river regulation on aeolian landscapes colorado river southwestern usa 1 connectivity between fluvial and aeolian sedimentary systems plays an important role in the physical and biological environment of dryland regions this study examines the coupling between fluvial sand deposits and aeolian dune fields in bedrock canyons of the arid to semiarid colorado river corridor southwestern usa by quantifying significant differences between aeolian landscapes with and without modern fluvial sediment sources this work demonstrates for the first time that the flow and sediment limiting effects of dam operations affect sedimentary processes and ecosystems in aeolian landscapes above the fluvial high water line dune fields decoupled from fluvial sand supply have more ground cover biologic crust and vegetation and less aeolian sand transport than do dune fields that remain coupled to modern fluvial sand supply the proportion of active aeolian sand area also is substantially lower in a heavily regulated river reach marble grand canyon arizona than in a much less regulated reach with otherwise similar environmental conditions cataract canyon utah the interconnections shown here among river flow and sediment aeolian sand transport and biologic communities in aeolian dunes demonstrate a newly recognized means by which anthropogenic influence alters dryland environments because fluvial aeolian coupling is common globally it is likely that similar sediment transport connectivity and interaction with upland ecosystems are important in other dryland regions to a greater degree than has been recognized previously

short and long term changes to bed mobility and bed composition under altered sediment regimes altered flow and sediment transport regimes from impoundment can result in significant channel bed composition changes that exacerbate the geomorphic and ecological effects of flow regulation using long term discharge and cross sectional data in combination with a two fraction sediment transport model we assess changes in the downstream bed of two flow regulated rivers with equivalent dam induced changes in flow but opposite changes in sediment flux supply limitation has led to incision and armoring in one case while supply excess has led to aggradation and embeddedness in the other under limited sediment supply bed elevation variability decreases soon after impoundment while excess sediment supply results in a decades long gradual decrease in both bed elevation variability and depth of incision although the balance of sediment supply and transport differs between dam management styles in both cases both the immediate and more gradual changes can be explained within the framework of a two fraction sediment transport model our results demonstrate the importance of considering bed composition on sediment transport predictions and the development of management strategies for ecosystem maintenance