analogies between mineral sediment and vegetative particle dynamics in fluvial systems abstract riparian vegetation fragments and propagules form part of the organic sediment load of rivers this review paper draws analogies between the transfer of these vegetative particles and that of mineral sediment within river systems whole plants vegetation fragments and propagules are delivered to rivers by physical processes but the timing of seed release and the morphological characteristics of the plants moderate delivery the transport and deposition of plant material is partly controlled by flow patterns but is also influenced by the buoyancy and morphology of the plant material once deposited the vegetative fragments propagules and the plants that develop from them can have significant local effects on flow hydraulics and sediment erodibility producing complex assemblages of physical features aggregate vegetative particles are identified as being particularly important in accelerating vegetation colonisation of exposed river sediments driving landform development and supporting the rapid development of a diverse cover of plants the geomorphological significance of interactions between vegetative particles and fluvial processes is illustrated at different spatial scales at the catchment scale ribbons of mineral and vegetative particles are transferred downstream with inputs continuously supplied throughout the river s course individual particles experience phases of mobilisation transport and deposition as a result along larger rivers down river changes are typically seen in the size and type of mineral sediment and vegetative particles and also the species composition of the vegetative particles coupled with downstream changes in hydroclimatological conditions within a river s active zone marked downstream changes in interactions between fluvial processes vegetation propagules and landforms can result at the patch scale individual vegetative particles particularly aggregate particles deposited on exposed riverine sediments create local hydraulic complexity that induces the scour and deposition of sediment and further plant propagules resulting in a suite of distinctive landforms which may support many plant species within individual reaches patch scale interactions between mineral sediment and vegetative particles are moderated or sieved by the form of the reach and its flow patterns so that the integration of patch scale effects can support the development of different landforms in different locations

source characteristics of the nicaraguan tsunami earthquake of september 2 1992 a large ms 7 2 shallow earthquake took place off the pacific coast of nicaragua on september 2 1992 and set off large tsunamis the ground motion of the main shock was very weak along the whole nicaraguan coast a tsunami as high as 10 m was observed at el transito whereas a height of about 2 m is empirically expected for an earthquake of ms 7 2 the tsunami magnitude mt is estimated to be 7 9 from tide gage data the nicaraguan event is a tsunami earthquake which generates unusually large tsunamis for its earthquake magnitude the source mechanism is studied in detail by using waveforms of body waves and surface waves recorded on global broadband seismographs the possibility of single force source is ruled out from radiation patterns and the amplitude ratio of rayleigh and love waves the main shock is interpreted as a low angle thrust fault with strike 302 dip 16 and slip 87 the cocos plate underthrusting beneath the caribbean plate the seismic moment from surface wave analysis is 3 0 1020 nm mw 7 6 the source dimension is estimated to be 200 km 100 km from the aftershock area the inversion results of body waves suggest bilateral rupture with rupture velocity as low as 1 5 km s and duration time of about 100 s the source process time is unusually long indicating that the associated crustal deformation has a long time constant

sediment characteristics of an extreme flood 1993 upper mississippi river valley the 1993 mississippi river flood was notable for its high magnitude long duration summer occurrence and low sediment discharge a field survey of a 70 km long reach in the vicinity of quincy illinois revealed that the event was characterized by 100 yr flood had remarkably little sedimentological or geomorphological impact on the flood plain within the study reach because the transport effectiveness of floods in large drainage basins is influenced by event sequencing in the same manner as floods in small watersheds and the cohesive flood plain soils were not susceptible to erosion

body wave inversion moment tensors and depths of oceanic intraplate bending earthquakes this paper develops a moment tensor inversion technique suited for analysis of long period body waves from distant shallow earthquakes in addition to the moment tensor the procedure resolves precise source depths 5 km and estimates the duration of faulting the technique is applied to digital sro dwwssn recordings of outer rise intraplate earthquakes these earthquakes result from bending of oceanic plates prior to subduction bending induces horizontal tension near the top of the lithosphere and horizontal compression near its base a neutral surface separates compressional from tensional regimes an examination of 11 bending earthquakes in the period january 1981 to july 1982 indicates that the depth to the neutral surface is not geographically uniform although the seismicity sample is very small the depth of the neutral surface appears to correlate with the position of the trench arc in the evolutionary sequence of uyeda and kanamori 1979 in particular neutral surfaces at strongly coupled chilean type plate boundaries are elevated as much as 15 km above those at weakly coupled mariana type boundaries this correlation implies that nonuniformities in neutral surface height are created by variations in regional compressive stress resulting from contrasts in plate plate coupling to account for the observed heights maximum interplate compressive stresses must be comparable with stresses derived from bending

the tsunami mode of a flat earth and its excitation by earthquake sources summary tsunami generation by earthquakes in a flat isotropic elastic vertically stratified earth underlying a uniform depth incompressible ocean can be studied in terms of the tsunami normal mode of the combined ocean solid earth system we derive in a way that demonstrates their natural extension from traditional approaches to tsunami theory the equations and boundary conditions governing the tsunami mode displacement and stress eigenfunctions then solve the excitation problem by a variational method this leads to a straightforward expression for the far field tsunami displace ments due to a point moment tensor source in the solid earth numerically computed spectra and waveforms reveal clearly the dependence of the far field tsunami on the source depth duration moment and mechanism

bank accretion and the development of vegetated depositional surfaces along modified alluvial channels this paper describes the recovery of stable bank form and development of vegetated depositional surfaces along the banks of channelized west tennessee streams most perennial streams in west tennessee were straightened and dredged since the turn of the century patterns of fluvial ecological responses to channelization have previously been described by a six stage model dendrogeomorphic tree ring techniques allowed the determination of location timing amount and rate of bank sediment deposition channel cross sections and ecological analyses made at 101 locations along 12 streams encompassing bends and straight reaches show that channel and bank processes initially react vertically to channelization through downcutting a depositional surface forms on banks once bed degradation and heightened bank mass wasting processes have eased or slowed the formation of this depositional surface marks the beginning of bank recovery from channelization dominating lateral processes characteristic of stable or natural channels return during the formation and expansion of the depositional surface suggesting a relation with thalweg deflection point bar development and meanderloop extension characteristic woody riparian vegetation begins to grow as this depositional surface develops and becomes part of the process and form of restabilizing banks the depositional surface initially forms low on the bank and tends to maintain a slope of about 24 mean accretion rates ranges from 5 9 cm yr on inside bends to 0 cm yr on most outside bends straight reaches have a mean accretion rate of 4 2 cm yr the relatively stable convex upward depositional surface expands and ultimately attaches to the flood plain the time required for the recovery process to reach equilibrium averaged about 50 years indicative pioneer speccies of woody riparian vegetation include black willow river birch silver maple and boxelder stem densities generally decrease with time after and initial flush of about 160 stems per 100 m2 together bank accretion and vegetative regrowth appear to be the most important environmental processes involved in channel bank recovery from channelization or rejuvenation

deposition and fate of organic carbon in floodplains along a tropical semiarid lowland river tana river kenya inland waters organic carbon oc burial by sedimentation has recently been shown to be an important component in river catchment carbon c budgets however data on oc burial by sedimentation are hitherto largely limited to temperate zones we investigated the deposition and fate of sediment associated oc in the floodplains of the tropical lowland tana river kenya between two main gaging stations garissa and garsen freshly deposited surface sediments and sediment cores were sampled and analyzed for oc total nitrogen content stable isotope signatures 13c of oc and grain size distribution in addition we incubated sediment cores to quantify co2 production as a proxy for oc mineralization while the floodplain receives sediment with a relatively low oc content 1 56 0 42 sediments are enriched with oc inputs from floodplain vegetation to levels above 3 sediment cores show a sharp decrease of oc with depth from 3 to 12 oc in the sub surface to less than 1 oc below approximately 60 cm depth relatively elevated oc mineralization rates 0 14 0 07 mol co2 kgc 1 d 1 were recorded we used these data to make a first assessment of the c burial efficiency of the tana river floodplain in contrast to what is observed in temperate environments over 50 of c present in the top layers is lost in less than a century while significant amounts of oc are buried in the tana river floodplain the high rates of postdepositional loss limit the development of a long term c sink within this tropical floodplain

implications of the 26 december 2004 sumatra andaman earthquake on tsunami forecast and assessment models for great subduction zone earthquakes results from different tsunami forecasting and hazard assessment mod els are compared with observed tsunami wave heights from the 26 december 2004 indian ocean tsunami forecast models are based on initial earthquake information and are used to estimate tsunami wave heights during propagation an empirical forecast relationship based only on seismic moment provides a close estimate to the observed mean regional and maximum local tsunami runup heights for the 2004 indian ocean tsunami but underestimates mean regional tsunami heights at azimuths in line with the tsunami beaming pattern e g sri lanka thailand standard forecast models developed from subfault discretization of earthquake rupture in which deep ocean sea level observations are used to constrain slip are also tested forecast models of this type use tsunami time series measurements at points in the deep ocean as a proxy for the 2004 indian ocean tsunami a transect of deep ocean tsunami amplitudes recorded by satellite altimetry is used to constrain slip along four subfaults of the m 9 sumatra andaman earthquake this proxy model performs well in comparison to observed tsunami wave heights travel times and inundation patterns at banda aceh hypothetical tsunami hazard assessments models based on end member estimates for average slip and rupture length m w 9 0 9 3 are compared with tsunami observations using average slip low end member and rupture length high end member m w 9 14 consistent with many seismic geodetic and tsunami inversions adequately estimates tsunami runup in most regions except the extreme runup in the western aceh province the high slip that occurred in the southern part of the rupture zone linked to runup in this location is a larger fluctuation than expected from standard stochastic slip models in addition excess moment release 9 deduced from geodetic studies in comparison to seismic moment estimates may gen erate additional tsunami energy if the exponential time constant of slip is less than approximately 1 hr overall there is significant variation in assessed runup heights caused by quantifiable uncertainty in both first order source parameters e g rupture length slip length scaling and spatiotemporal complexity of earthquake rupture

the role of vegetation in the formation of anabranching channels in an ephemeral river northern plains arid central australia as the distribution and abundance of vegetation in drylands is often controlled by the greater availability of water along river channels riparian vegetation has the potential to influence significantly dryland river form process and behaviour this paper demonstrates how a small indigenous shrub the inland teatree melaleuca glomerata influences the formation and maintenance of anabranching channels in a reach of the ephemeral marshall river northern plains arid central australia here the marshall is characterized by ridge form anabranching where water and sediment are routed through subparallel multiple channels of variable size which occur within a typically straight channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands by providing a substantial element of boundary roughness dense stands of teatrees growing on channel beds or atop the ridges and islands influence flow velocities flow depths and sediment transport resulting in flow diversion bank and floodplain erosion and especially sediment deposition ridges and islands represent a continuum of forms and their formation and development can be divided into a three stage sequence involving teatree growth and alluvial sedimentation 1 teatrees colonize a flat sandy channel bed initiating the formation of ridges by lee side accretion individual ridges grow laterally vertically and longitudinally and maintain a geometrically similar streamlined lemniscate form that presents minimum drag 2 individual ridges grow in size and interact with neighbouring ridges causing the lemniscate forms to become distorted ridges in the lee of other ridges tend to be protected from the erosive effects of floods and survive whereas individual teatrees or small ridges exposed to flow concentrated between larger ridges tend to be removed 3 ridges lengthen and coalesce with downstream ridges eventually subdividing the channel train into well defined anabranches this sequence turns a channel initially obstructed with dense and chaotic stands of teatrees into a well organized system of ridge form anabranches in the moderate to low gradient marshall river which is colonized by an abundance of within channel vegetation and subject to declining downstream discharges this helps to minimize flow resistance thereby maintaining an efficient water and sediment flux copyright 2000 john wiley sons ltd

distribution of lipid class compounds in bottom sediments of freshwater lakes with different trophic status in japan abstract unbound and bound lipid class compounds mono and di carboxylic acids and hydroxy acids n alkanes n alcohols and perylene were studied in bottom sediments collected from four freshwater lakes in japan with different trophic status lakes motosu biwa haruna and suwa concentrations of some lipid components relative to total organic carbon toc showed positive or negative correlations with the primary productivity of the lakes n saturated c12 c19 fatty acids fa s branched chain fa s unsaturated fa s and c14 c19 fatty alcohols which are probably of autochthonous origin appear to increase with an increase in primary productivity whereas n saturated c20 c32 fa s c20 c30 fatty alcohols dicarboxylic acids n alkanes and perylene which are probably of terrestrial origin appear to decrease with an increase in primary productivity these results indicate that primary productivity of lakes is an important factor controlling the distributions of organic molecules in the bottom sediments on the other hand concentrations of hydroxy acids relative to toc did not show a correlation with primary productivity because these acids are derived from bacterial activity their distributions may be controlled by sedimentary environments such as oxic or anoxic rather than primary productivity

acid and alcohol compositions of wax esters in sediments from different environments abstract wax esters were isolated from three freshwater lake and four coastal marine sediments of which fatty acid and alcohol compositions were determined the acid and alcohol moieties of wax esters from an oligotrophic lake lake motosu sediment were predominated by long chain c 22 c 30 species whereas those found in a eutrophic lake lake shoji sediment involved relatively large amounts of short chain c 14 c 18 species both the nearshore and the deep marine sediments from sagami bay contained wax esters predominated by long chain constituents in contrast a shallow bay tokyo bay sediment contained significant amounts of short chain wax esters the long chain wax esters were thought to originate from cuticular wax of terrestrial plants and the short chain ones were from aquatic organisms thus the distribution of wax ester fatty acids and alcohols appeared to reflect the autochtonous allochtonous source of the organic matter in the sediment but wax ester concentrations decreased rapidly towards the deeper core sections of the sediment from tokyo bay chiefly due to decrease of short chain species unexpectedly high proportions of long chain wax esters in deep marine sediments were considered to be due to this preferential degradation of short chain esters

overbank flow with vegetatively roughened flood plains an experimental and theoretical investigation into the flow characteristics of channels with complex cross sections was undertaken in this study particular attention was given to the problem of non submerged flood plain roughnesses this differs from previous studies in which compound channel flow was primarily investigated for more or less uniform boundary roughnesses in order to achieve more conformity with natural rivers the flood plain and the main channel were separated in the model by a sloping bank two cross sections with varying aspect ratios and flood plain roughnesses were investigated the necessary measurements were carried out by applying ldv and preston tube techniques on the basis of simple turbulence assumptions methods are presented by which the flow resistance in vegetatively roughened flood plains and main channels can be properly predicted as a function of independent and directly determinable basic flow parameters a first verification of this model was accomplished using field

can the sedimentological and morphological structure of rivers be used to predict characteristics of riparian seed banks abstract seeds are transported by flowing water along with sediment and organic matter and form seed banks within the fluvial landforms or geomorphic units of river systems fluvial processes commonly result in observable gradients in sediment characteristics with elevation above the channel bed this study aims to investigate spatial variability in seed bank characteristics that may be attributed to fluvial processes we compared the extent to which four riparian seed bank characteristics abundance species richness seed mass and seed shape are correlated with 1 fluvially influenced gradients in sediment character percentage of organic matter organic median particle size d50 percentage of fine particles fines and the combined percentage of sand and gravel sand gravel and 2 three geomorphic unit types that form with increasing elevation above the channel bed bars benches and the floodplain seed bank abundance and species richness were weakly yet significantly correlated with sediment gradients significantly increasing with increasing fines and decreasing sand gravel seed bank species richness also significantly increased with increasing organic and decreasing d50 conversely seed abundance was highly variable and relationships between sediment qualities and seed mass and shape were nonexistent we suggest that hydrological factors such as inundation frequency operating most clearly at the geomorphic unit scale ultimately drive spatial variability in riparian seed bank characteristics by 1 directly influencing seed inputs and losses from seed banks via erosion and deposition which is complicated by species specific differences in seed morphology and 2 indirectly influencing seed inputs and losses by mediating seed germination and mortality and the establishment success of plants through impacts on sediment moisture and organic matter content further complexity is added by nonfluvial seed inputs from established vegetation the net result of these influences tends toward decreasing potential for seed losses and increasing potential for seed inputs associated with the reduction in inundation frequency observed from bars to the floodplain for those assessing the potential of the seed bank as a seed source for revegetation sediment sampling for seed bank assays targeted at organic flood debris or fine organic rich sediments such as those typically associated with benches and the floodplain should elicit useful estimations of seed bank composition

predicting vertical accretion rates at an archaeological site on the mississippi river floodplain effigy mounds national monument iowa abstract the sny magill unit of effigy mounds national monument iowa contains the largest cluster of prehistoric effigy mounds on public land in north america the mounds are situated atop a low terrace of the upper mississippi river where they are slowly being buried by overbank deposition during floods the terrace surface includes forest soils with argillic bt or cambic bw horizons developed in up to 1 m of loamy overbank deposits on top of pleistocene sand and gravel radiocarbon evidence suggests that overbank deposits have accumulated since the end of the mound building period about 700 years bp yielding a vertical accretion rate of about 0 6 mm yr 1 on the basis of 137cs analysis accretion rates over the past 40 50 years average 1 25 2 07 mm yr 1 with some evidence for a decreasing rate since 1964 if these accretion rates are projected forward several of the effigy mounds could be buried by flood deposits within 150 300 years this 137cs derived estimate agrees closely with an estimate of burial times based on flood frequency and observed flood deposit thickness during recent floods however the floodplain and backwater environments of the upper mississippi river are aggrading much more rapidly than the sny magill terrace surface suggesting that burial of the entire terrace could occur within 80 400 years and the entire mound group could be buried within 150 850 years the projected accretion rates and time to burial are subject to large uncertainties because of environmental change in the watershed including recent trends toward increasing flood stages and decreasing suspended sediment loads

mtsu recovering seismic moments from tsunameter records we define a new magnitude scale m tsu allowing the quantification of the seismic moment m0 of an earthquake based on recordings of its tsunami in the far field by ocean bottom pressure sensors tsunameters deployed in ocean basins far from continental or island shores which are known to affect profoundly and in a nonlinear fashion the amplitude of the tsunami wave the formula for m tsu m tsu log10 m o 20 log10 x c d tsu c s tsu c o where x is the spectral amplitude of the tsunami c d tsu a distance correction and c s tsu a source correction is directly adapted from the mantle magnitude m m introduced for seismic surface waves by okal and talandier like m m its corrections are fully justified theoretically based on the representation of a tsunami wave as a branch of the earth s normal modes even the locking constant c 0 which may depend on the nature of the recording surface amplitude of the tsunami or overpressure at the ocean floor and its units is predicted theoretically m tsu combines the power of a theoretically developed algorithm with the robustness of a magnitude measurement that does not take into account such parameters as focal geometry and exact depth which may not be available under operational conditions in the framework of tsunami warning we verify the performance of the concept on simulations of the great 1946 aleutian tsunami at two virtual gauges and then apply the algorithm to 24 records of 7 tsunamis at dart tsunameters during the years 1994 2003 we find that m tsu generally recovers the seismic moment m 0 within 0 2 logarithmic units even under unfavorable conditions such as excessive focal depth and refraction of the tsunami wave around continental masses finally we apply the algorithm to the jason satellite trace obtained over the bay of bengal during the 2004 sumatra tsunami after transforming the trace into a time series through a simple ad hoc procedure results are surprisingly good with most estimates of the moment being over 1029 dyn cm and thus identifying the source as an exceptionally large earthquake

first indications of the formation of kerogen amorphous fractions by selective preservation role of non hydrolysable macromolecular constituents of eubacterial cell walls abstract two marine kerogens supposed to contain an important bacterial component were analysed and their spectroscopic and pyrolytic features compared with those of the amorphous non hydrolysable macromolecular materials bacterans isolated from extent bacteria examination by transmissio electron microscopy revealed that dontrien lower toarcian shales paris basin is essentially composed of amorphous organic matter and osb3 marl slate formation n e england is exclusively amorphous the formation upon kerogen pyrolysis of series of products 3 methylalkanes dimethylalkanes ethylesters and alcohols characteristic of bacteran pyrolysates is consistent with the contribution of bacterans to the formation of these two kerogens the nature and distribution of the acids of the pyrolysates indicate that bacterial biomass was implicated in osb3 and dontrien kerogen formation via two pathways bacteran selective preservation and incorporation of partly degraded lipids comparison between dontrien and osb3 indicates a weaker contribution of the selective preservation pathway to osb3 kerogen whereas bacteria lipid incorporation may have been more significant in osb3 kerogen the selective preservation pathway was so far considered as restricted to the formation of kerogens having retained some of the morphological features of the source organisms an important point derived from this study is therefore the ability of this pathway to also contribute to the formation of amorphous kerogens

tsunami generation a comparison of traditional and normal mode approaches suxmary techniques to model tsunami generation by earthquakes may be divided into two broad categories according to whether the ocean and solid earth are fully or partially coupled the former category includes normal mode techniques while the latter is comprised of more qraditional approaches including those in which the hydrodynamic equations for the ocean are solved subject to an inhomogeneous time dependent boundary condition at the ocean floor we compare representatives of each approach using a solution for the flat earth tsunami mode excitation due to a point moment tensor earthquake source and a more traditional model in which the ocean floor boundary condition is derived from the static response of an elastic half space to a point moment tensor the results are nearly identical and extend to finite sources according to linear superposition thus establishing the practical equivalence of the two conceptually divergent techniques and assuring the general validity of models with partial coupling

riparian vegetation and fluvial geomorphic processes abstract riparian vegetation and fluvial geomorphic processes and landforms are intimately connected parts of the bottomland landscape relations among vegetation processes and landforms are described here for representative streams of four areas of the united states high gradient streams of the humid east coastal plain streams great plains streams and stream channels of the southwestern united states vegetation patterns suggest that species distributions in the humid east are largely controlled by frequency duration and intensity of floods along channelized streams vegetation distribution is largely controlled by variation in fluvial geomorphic processes cycles of degradation and aggradation in response to increases in channel gradient associated with channelization similarly riparian vegetation of great plains streams may be controlled by fluxes in sediment deposition and erosion along braided streams patterns of riparian vegetation in semi arid regions may be most closely related to patterns of water availability unlike most other streams in more humid environments channel equilibrium conditions control stability of the coincident fluvial landform and attendant vegetation pattern throughout the continent in most situations riparian vegetation patterns are indicative of specific landforms and thus of ambient hydrogeomorphic conditions

effects of oxidative weathering on the composition of organic matter in coal and sedimentary rock abstract the effect of oxidative weathering on the composition of sedimentary organic matter som of lignite subbituminous coal quartzose arenite siliceous mudstone siliceous shale and diatomaceous shale was investigated in hokkaido japan in a subarctic humid climate for 15 samples in total a humic substance extraction method was applied to divide som into lipid c humin c and alkali soluble c the alkali soluble c was further divided into fulvic acid fa c humic acid ha c and a smaller molecular size fraction smsf c which comprised organic molecules able to pass through a dialysis membrane

numerical modelling of floodplain hydraulics and suspended sediment transport and deposition a numerical model is presented for the prediction of floodplain inundation extents flow depths and velocities and patterns of suspended sediment dispersion and deposition the model employs a simplified and novel treatment of fluid flow and a conventional convection diffusion mass balance relationship for suspended sediment transport and deposition these relationships are solved over a finite difference grid with a relatively fine nodal spacing which enables a detailed representation of complex floodplain topography the model is applied to a 600 m reach of the river culm devon uk continuous records of river stage and suspended sediment concentration monitored at the upstream boundary of the study reach provide the data needed to operate the model these data are supplemented by measurements of the in situ settling characteristics of the suspended sediment load model predictions of overbank flow depths and velocities and patterns of suspended sediment concentrations and deposition amounts are presented predicted patterns of overbank deposition are described and compared with field measurements obtained with the aid of astroturf sedimentation traps grain size distributions obtained for samples of deposited sediment retrieved from the sedimentation traps are also examined and compared with model predictions the results of both the field measurement programme and modelling work are shown to have significant implications for the representation of floodplain topography and suspended sediment particle size and settling properties in numerical simulations of overbank processes 1998 john wiley sons ltd

diagenesis of free and bound lipids in terrestrial detritus deposited in a lacustrine sediment recent sediments from an oligotrophic lake loch clair having uniform organic input for 2000 yr show changes in lipid abundance and composition with increasing depth attributed to diagenesis stability of free lipids decreases in the order n alkanes alkan 2 ones sterols n alkanoic acids n alkanols n alkenoic acids diagenetic loss of shorter chain homologues is complete within 400 yr stabilisation of bound relative to free lipids increases the proportion of the former with sediment age and reduces loss of shorter chain bound homologues in an eutrophic lake cross mere shorter chain free and bound sedimentary lipids show increased abundance compared with loch clair the relative importance of higher input of shorter chain lipids derived from aquatic detritus and slower initial diagenesis due to the anoxic hypolimnion as causative factors for this difference between lake types cannot yet be assessed

sedimentation in the riparian zone of an incising river this paper focuses on one aspect of riparian zone change associated with channel incision it presents information on sedimentation within the riparian zone of the river garonne france derived from both historical and contemporary sources the riparian zone investigated is morphologically complex containing a remnant island and cut off channel information drawn from historical and contemporary sources permits the reconstruction of channel planform and cross profile change as well as an assessment of changes in riparian zone sedimentation rates and patterns very significant changes are identified over the last 50 years a change from a multiple thread to single thread channel planform high rates of riparian zone sedimentation of the order of 0 5 to 2 5 cm a 1 clear spatial patterns in over bank sedimentation reflecting topographic and vegetational variations and flood event magnitude and a reduction in morphological and vegetational diversity through the period which is expected to continue as the zone is transformed into an increasingly homogeneous sediment sink copyright 2001 john wiley sons ltd

the interplay of sedimentation and carbon accretion in riparian forests abstract sediment trapping and organic carbon oc accretion in soil are crucial ecosystem services of floodplain forests however interactions between the two processes have scarcely been analyzed at the ecosystem level this study aimed at quantifying oc accretion parameters cap including sedimentation rate oc concentration oc accretion over roughly the last 50 years on both sides of a dike in a danubian floodplain forest in austria additionally we determined soil oc stocks 0 100 cm in depth and modeled both cap and oc stocks in relation to environmental parameters overall mean sedimentation rate and oc accretion of the riparian forest were 0 8 cm y 1 and 3 3 t oc ha 1 y 1 and significantly higher in flooded riparian forest frf 1 0 cm y 1 and 4 1 t oc ha 1 y 1 than in diked riparian forest drf 0 3 cm y 1 and 1 5 t oc ha 1 y 1 in contrast mean oc concentration 0 05 t oc m 3 and oc stocks 238 t oc ha 1 were significantly higher in the drf than in frf 0 05 vs 0 04 t oc m 3 and 286 vs 201 t oc ha 1 modeling revealed tree species fluctuation of groundwater table and the distance to the river as valuable indicators for oc accretion rate the oc concentration and distance to the river were positively and sedimentation negatively correlated with oc stock the dike was consistently ruled out as a significant predictor variable consequently differences among frf and drf seem to be related rather to longer term processes during the last centuries than directly to the dike our findings highlight the relevance of sediment quality i e oc concentration for building up long term soil oc stocks whereas sediment quantity is the main driver of recent oc accretion rates

effects of woody vegetation on overbank sand transport during a large flood rio puerco new mexico abstract distributions of woody vegetation on floodplain surfaces affect flood flow erosion and deposition processes a large flood along the lower rio puerco new mexico in august 2006 caused extensive erosion in a reach that had been sprayed with herbicide in september 2003 for the purpose of saltcedar tamarix spp control large volumes of sediment including a substantial fraction of sand were delivered to the reach downstream which had not been treated with herbicide we applied physically based one dimensional models of flow and suspended sediment transport to compute volume concentrations of sand in suspension in floodplain flow at a site within the sprayed reach and at a site downstream from the sprayed reach we computed the effects of drag on woody stems in reducing the skin friction shear stress velocity of flow and suspended sand transport from open paths into patches of dense stems total flow and suspended sand fluxes were computed for each site using well constrained flood flow depths water surface slopes and measured shrub characteristics results show that flow in open paths carried high concentrations of sand in suspension with nearly uniform vertical distributions drag on woody floodplain stems reduced skin friction shear stresses by two orders of magnitude yet sufficient velocities were maintained to transport sand more than 50 m into fields of dense free surface penetrating stems an increase in shrub canopy extent from 31 in the sprayed reach site to 49 in the downstream site was found to account for 69 of the computed decrease in discharge between the two sites the results demonstrate the need to compute the spatial distribution of skin friction shear stress in order to effectively compute suspended sand transport and to predict the fate of sediment and contaminants carried in suspension during large floods

on tsunami nucleation ii an instantaneous modulated line source abstract tsunami generation on a spherically symmetric self gravitating and elastic earth is investigated using normal mode summations and moment tensor line sources wave cancellation in a line source of length l substantially eliminates tsunamis whose horizontal wavenumber component along the fault exceeds 3 l this results in a preferential beaming of tsunami radiation perpendicular to the fault strike beaming from a source of fixed length occurs in the same fashion irrespective of slip mechanism tsunami radiation patterns from finite sources are thus more uniform than those from point sources the largest far field sea waves from any long shallow fault are likely to be found within 20 azimuth of the perpendicular bisecting great circle although line sources subordinate distinctions in radiation patterns focal mechanism is still a critical element in determining the extent of tsunami excitation the ratio of maximum tsunami amplitude from strike and dip slips of equal moment are 1 10 for faults 400 km in length finite faulting weakens strike slip tsunamis relative to dip slip tsunamis because the beaming and natural radiation directions of strike slips are severely misaligned using an empirical relation linking source process time fault length and moment i predict tsunami energies in the range 1010 1017 j for earthquake moments spanning 2 1018

sedimentation and sediment accretion in michigan coastal wetlands u s a abstract sediment transport and accretion rates were studied for three different types of coastal wetlands of lake michigan u s a a forested intradunal wetland cranberry bog no 1 near stevensville michigan displayed sediments in the form of detritus and exported them very little sedimentary material entered by streamflow these features of bottom land wetlands were confirmed by radioisotope studies on cores which showed low accretion rates of 210 pb the mass fluxes were found to range from 0 01 to 0 2 g cm 2 yr 1 the equivalent linear growths are 0 5 9 0 mm yr 1 the suspended material from this wetland entered a filling shrub bog lake complex known as cranberry bog no 2 a considerable fraction of the incoming sediments were retained in this intradunal basin wetland this was confirmed via radioisotope studies with cores showing higher accretion rates than in the bottom land wetland the river delta wetland at pentwater michigan had little sediment trapping ability large amounts of water and suspended materials entered this riverine wetland but no annual average removal was found radioisotope studies of cores at selected locations within this system showed little or no accretion in stream channels and normal accumulation of organic material in non channel areas no net annual effect on water quality of the streams as they discharged to lake michigan was found storm events caused no notable import or export of suspended material presumably the sand substrate in the vicinity of all three wetlands caused runoff events to be mediated by subsurface flow through this porous soil these three sand based coastal wetlands appear to have little net effect on suspended solids the 210 pb method proved more valuable than 137 cs because of the small depth of occurrence of the latter isotope interpretation of isotope profiles required information on acid fraction soluble profiles results are expressed in terms of mass units since compaction of cores distorts the linear accretion rate delayed transfers of radionuclides appear to have occurred perhaps as a result of integration of atmospheric inputs by the watersheds the total activities of 210 pb and 137 cs are well correlated which indicates particle trapping efficiency as the primary factor for affecting accumulation of both isotopes

floodplain sedimentation and sensitivity summer 1993 flood upper mississippi river valley patterns of overbank sedimentation in the vicinity of and far removed from levee breaks that occurred in response to the 100 year summer 1993 flood in the upper mississippi river valley are elucidated two suites of overbank deposits were associated with the failure of artificial levees within a 70 km long study reach circumjacent sand deposits are a component of the levee break complex that develops in the immediate vicinity of a break site as epitomized by the levee break complex at sny island these features consist of an erosional scoured and or stripped zone together with a horseshoe shaped depositional zone at locales farther removed from the break site the impact of flooding was exclusively depositional and was attributed to the settling of suspended sediment from the water column the overall picture was one of modest scour at break sites and minimal suspended deposition 4 mm at locales farther removed from the breach downriver from the confluence with the missouri river suspended sediment deposition was of a similar magnitude to that observed within the study reach and levee break complexes exhibited a similar morphology but scour at break sites was greatly enhanced and the excavated sand formed extensive deposits on the floodplain surface the different erosional response was probably engendered by the higher sand content and reduced aggregate cohesion of the floodplain soils downriver from the confluence with the missouri river a qualitative comparison serves to highlight the influence that the resistance threshold may have on the sensitivity of floodplains bordering large low gradient rivers to high magnitude floods 1997 john wiley sons ltd

exchanges of sediment between the flood plain and channel of the amazon river in brazil sediment transport through the brazilian sector of the amazon river valley a distance of 2010 km involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at obidos 1200 mt yr 1 the exchanges occur through bank erosion bar deposition settling from diffuse overbank flow and sedimentation in flood plain channels we estimated the magnitude of these exchanges for each of 10 reaches of the valley and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel the annual supply of sediment entering the channel from bank erosion was estimated to average 1570 mt yr 1 1 3 the obidos flux and the amount transferred from channel transport to the bars 380 mt yr 1 and the flood plain 460 mt yr 1 in channelized flow 1230 mt yr 1 in diffuse overbank flow totaled 2070 mt yr 1 1 7 the obidos flux thus deposition on the bars and flood plain exceeded bank erosion by 500 mt yr 1 over a 10 16 yr period sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 mt yr 1 over 16 yr crudely validating the process based calculations of the sediment budget which in turn illuminate the physical controls on each exchange process another 300 400 mt yr 1 are deposited in a delta plain downstream of obidos the components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain which in turn are influenced by tectonic features of the amazon structural trough

the november 20 1960 peru tsunami earthquake source mechanism of a slow event the november 20 1960 peru earthquake excited a tsunami that was anomalously large for an earthquake of moderate magnitude m 6 75 pas body wave first motions combined with observed love to rayleigh wave spectral ratios indicate slip along a shallowly dipping thrust fault rather than a single force mechanism suggestive of a landslide deconvolution of sh waveforms shows a time function consisting of 4 subevents with a total duration of 110 s using this time function body waveform inversion yields a very shallowly dipping thrust faulting mechanism strike 0 dip 6 slip 100 and a seismic moment of 1 9 1027 dyn cm however the time function obtained from the band limited body waveforms cannot fit the surface wave data which show a large increase in amplitude with period and a moment of 3 4 1027 dyn cm both types of data can be modeled by combining the body wave time function and a 130 s cosine time function representing a longer period component this event represents the largest earthquake to occur along this relatively aseismic portion of the peruvian coast the tsunami excitation is not anomalous relative to the measured seismic moment and moment magnitude mw 7 6 the disparity between tsunami height and surface wave magnitude results from underestimation of the earthquake size by conventional magnitude scales due to the long source duration

the origin of the tsunami excited by the 1989 loma prieta earthquake faulting or slumping we investigated the tsunami recorded at monterey california during the 1989 loma prieta earthquake m w 6 9 the first arrival of the tsunami was about 10 min after the origin time of the earthquake using an elastic half space we computed vertical ground displacements for many different fault models for the loma prieta earthquake and used them as the initial condition for computation of tsunamis in monterey bay the synthetic tsunami computed for the uniform dislocation model determined from seismic data can explain the arrival time polarity and amplitude of the beginning of the tsunami however the period of the synthetic tsunami is too long compared with the observed we tested other fault models with more localized slip distribution none of the models could explain the observed period the residual waveform the observed minus the synthetic waveform begins as a downward motion at about 18 min after the origin time of the earthquake and could be interpreted as due to a secondary source near moss landing if the large scale slumping near moss landing suggested by an eyewitness observation occurred about 9 min after the origin time of the earthquake it could explain the residual waveform to account for the amplitude of the observed tsunami the volume of sediments involved in the slumping is approximately 0 013km 3 thus the most likely cause of the tsunami observed at monterey is the combination of the vertical uplift of the sea floor due to the main faulting and a large scale slumping near moss landing

floodplain sedimentation quantities patterns and processes this paper presents the result of measurements of floodplain sedimentation using sediment traps the study was carried out on two embanked floodplains along the rivers rhine and meuse in the netherlands during a 3 day flood in january 1993 raster maps of sediment accumulation were made by interpolating the measurements from the traps using block kriging the sediment maps show clear patterns in sediment accumulation together with the estimated interpolation errors average sediment accumulation ranges between 0 57 and 1 0 kg m 2 high sediment accumulation is found on the levees 4 kg m 2 or more and on low lying areas 1 6 kg m 2 sediment accumulation decreases with distance from the main channel the sedimentation patterns are related to floodplain topography and sediment transporting mechanisms sediment transport by turbulent diffusion as well as by convection can be recognized also flood duration and the process of sediment settling out in ponding water in closed depressions are important the applied method allows comparison of the results with raster based sedimentation models

organic matter processing and soil evolution in a braided river system traditionally braided river research has considered flow sediment transport processes and recently vegetation dynamics in relation to river morphodynamics however if considering the development of woody vegetated patches over a time scale of decades we must consider the extent to which soil forming processes particularly related to soil organic matter impact the alluvial geomorphic vegetation system here we quantify the soil organic matter processing humification that occurs on young alluvial landforms we sampled different geomorphic units ranging from the active river channel to established river terraces in a wandering braided river system for each geomorphic unit soil pits were used to sample sediment soil layers that were analysed in terms of grain size 2 mm and organic matter quantity and quality rock eval method a principal components analysis was used to identify patterns in the dataset results suggest that during the succession from bare river gravels to a terrace soil there is a transition from small amounts of external organic matter supply provided by sedimentation processes e g organic matter transported in suspension and deposited on bars to large amounts of autogenic in situ organic matter production due to plant colonisation this appears to change the time scale and pathways of alluvial succession bio geomorphic succession however this process is complicated by the ongoing possibility of local sedimentation which can serve to isolate surface layers via aggradation from the exogenic supply and erosion which tends to create fresh deposits upon which organic matter processing must re start the result is a complex pattern of organic matter states as well as a general lack of any clear chronosequence within the active river corridor this state reflects the continual battle between deposition events that can isolate organic matter from the surface erosion events that can destroy accumulating organic matter and the early ecosystem processes necessary to assist the co evolution of soil and vegetation a key question emerges over the extent to which the fresh organic matter deposited in the active zone is capable of significantly transforming the local geochemical environment sufficiently to accelerate soil development

nature rehabilitation by floodplain excavation the hydraulic effect of 16 years of sedimentation and vegetation succession along the waal river nl abstract the ewijkse plaat is a floodplain along the waal river nl in 1988 the floodplain was excavated as part of a program for enlargement of the discharge capacity and was assigned as a nature rehabilitation area this paper describes the combined geomorphological and vegetation evolution of the floodplain until 16 years after the initial excavation using elevation data and data on vegetation structure derived from detailed aerial stereographic imagery the impact of these processes on flow velocity and water surface elevation was evaluated by using a hydraulic model within 16 years the excavated amount of sediment was redeposited in the area the dominant geomorphological process after excavation was vertical accretion of the floodplain which resulted in the formation of natural levees the amount of sedimentation was correlated to the across floodplain flow r 2 0 89 in the research period 41 of the sedimentation took place during two single major flood events the creation of pioneer stages by excavation promoted softwood forest establishment which influenced the sedimentation pattern significantly the landscape evolved toward structure rich vegetation nine years after excavation the initial hydraulic gain was lost by the combined effect of sedimentation and vegetation succession implications for river and nature management are discussed

bathymetric effects on body waveforms from shallow subduction zone earthquakes and application to seismic processes in the kurile trench resolution of earthquake source characteristics is limited by structural complexities in the source region this study explores the effects of dipping near source bathymetry and structure on long period teleseismic body waveforms from shallow subduction zone earthquakes ray theory synthetics calculated for shallow double couple sources and velocity structures incorporating planar dipping interfaces suggest that p waveforms are most sensitive to water depth and sea bottom orientation for sources beneath a substantial water layer the seafloor dip of the inner trench slope can give rise to prominent later arrivals and waveform complexity not found on synthetics calculated for horizontal bathymetry sediment thickness and the dip of the sediment crust and crust mantle interfaces generally have lesser effects the high amplitude arrivals result largely from changes in the source takeoff angles of the reverberations these arrivals present difficulties for source depth and time function determination from p waveforms and may cause spurious complexity in the derived pattern of earthquake moment release sh waveforms show little effect of sea bottom orientation or local structure for shallowly dipping thrust faulting events suggesting that sh waveform analysis can stabilize source parameter studies with respect to unknown or incompletely parameterized bathymetry and structure effects of nonhorizontal structure are observed in the p waveforms from shallow kurile trench events ms 5 8 7 2 which show prominent later arrivals not observed on sh waveforms synthetics calculated for a dipping water crust interface provide a better fit to these arrivals than those calculated for a horizontal interface suggesting that the p waveforms show systematic effects of seafloor dip the synthetics are highly sensitive to the assumed orientation of the seafloor the data are fit best for seafloor orientations consistent with the dip of the inner trench slope the distorting effect of the water layer gives rise to systematic differences in p wave complexity between shallow events near the seismic front which occur beneath a thick water layer and show numerous later arrivals and deeper arcward events which occur beneath a thin water layer and show simple waveforms large reverberations in the p waveforms of the october 20 1963 and june 10 1975 kurile tsunami earthquakes have previously been used as evidence for a long source duration and a change in focal mechanism during rupture however sh waveforms suggest simple source time functions with durations of 25 and 43 s inversion of p and sh waveforms and amplitudes yields shallowly dipping thrust mechanisms with no conclusive evidence for a previously proposed steepening of the fault dip during rupture the large p wave reverberations cannot be fit using a point source and a horizontal seafloor detailed modeling of the 1963 event as an upward propagating rupture extending through low velocity sediments to the ocean bottom combined with the effects of the dipping seafloor allow the reverberation amplitudes to be matched the anomalous tsunami excitation appears to be related to the location of the sources at shallow depths within low velocity sediments

tsunami earthquakes slow thrust faulting events in the accretionary wedge the november 20 1960 peru october 20 1963 kurile and june 10 1975 kurile earthquakes are classified as tsunami earthquakes based on anomalously large tsunami excitation relative to earthquake magnitude long period surface wave analysis indicates double couple faulting mechanisms for all three events rather than single force mechanisms indicative of submarine landslides the earthquakes have shallow depths 15 km and are located near the trench axis and seaward of most other thrust zone events beneath the accretionary prism body waveform inversion indicates very shallowly dipping thrust faulting mechanisms for the three events with dip angles of 6 8 surface wave spectral amplitudes and deconvolution of sh waveforms suggests anomalously long source durations and large seismic moments relative to ms specifically the 1963 kurile event ms 7 2 shows a duration of 85 s and a moment of 6 0 1027 dyn cm mw 7 8 the 1975 kurile event ms 7 0 shows a duration of 60 s and a moment of 2 0 1027 dyn cm mw 7 5 and the 1960 peru event ms 6 75 shows a time function consisting of four subevents with a total duration of 110 130 s and a seismic moment of 3 4 1027 dyn cm mw 7 6 estimated rupture velocities are about 1 km s or less but there is no evidence of unusually low stress drops the august 1 1968 philippines event previously classified as a tsunami earthquake shows none of the anomalous source properties and teleseismic tsunami height measurements are sparse we do not consider this event a tsunami earthquake most of the anomalous tsunami excitation results from underestimation of earthquake size by ms due to the long source duration the tsunami heights are not significantly anomalous relative to seismic moment the slow nature of these events may result from rupture through the sedimentary rock along the basal decollement of the accretionary prism standard scaling laws when adjusted for the slow seismic velocity in the source region show an mw ms relationship similar to that observed for the tsunami earthquakes and predict ms saturation at about 7 3 rather than 8 0 for typical events

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

formation and dynamics of vegetated fluvial landforms follow the biogeomorphological succession model in a channelized river feedback between hydrogeomorphological processes and riparian plants drives landscape dynamics and vegetation succession in river corridors we describe the consequences of biogeomorphological feedback on the formation and dynamics of vegetated fluvial landforms based on observations from the channelized isere river in france the channel was laterally confined with embankments and mostly straightened from the beginning of the 1970s to the end of the 1990s alternate bars were progressively but heavily colonized by vegetation this context presented an exceptional opportunity to analyse temporal adjustments between fluvial landforms and vegetation succession from bare gravel bars to mature upland forest as the consequence of biogeomorphological interactions based on a gis analysis of aerial photographs between 1948 and 1996 we show that the spatiotemporal organization of vegetated bars within the river channel observed in 1996 resulted from a bioconstruction and biostabilization effect of vegetation and interactions between bars of varying age size and mobility field measurements in 1996 reflected how a strong positive feedback between sedimentary dynamics and riparian vegetation succession resulted in the construction of the vegetated bars a highly significant statistical association of geomorphological and vegetation variables rv of co inertia analysis 0 41 p 0 001 explained 95 of the variability in just one axis supporting the existence of very strong feedback between geomorphological changes i e the transformation of small bare alternate bars to fluvial landforms covered by mature upland forest and vegetation succession such dynamics reflect the fluvial biogeomorphological successions model as described by the authors earlier 2020 john wiley sons ltd

riparian vegetation and island formation along the gravel bed fiume tagliamento italy after more than 300 years of river management scientific knowledge of european river systems has evolved with limited empirical knowledge of truly natural systems in particular little is known of the mechanisms supporting the evolution and maintenance of islands and secondary channels the dynamic gravel bed fiume tagliamento italy provides an opportunity to acquire baseline data from a river where the level of direct engineering intervention along the main stem is remarkably small against a background of a strong alpine to mediterranean climatic and hydrological gradient this paper explores relationships between topography sediment and vegetation at eight sites along the active zone of the tagliamento a conceptual model of island development is proposed which integrates the interactions between large woody debris and vegetation geomorphic features sediment calibre and hydrological regime islands may develop on bare gravel sites or be dissected from the floodplain by channel avulsion depositional and erosional processes result in different island types and developmental stages differences in the apparent trajectories of island development are identified for each of the eight study sites along the river the management implications of the model and associated observations of the role of riparian vegetation in island development are considered in particular the potential impacts of woody debris removal riparian tree management regulation of river flow and sediment regimes and changes in riparian tree species distribution are discussed

analytical model for gravity and rayleigh wave investigation in the layered ocean earth structure in terms of the linear theory of elasticity we analyze the gravity and rayleigh wave excitation and propagation process in a three layered ocean earth model which includes a superficial liquid layer and two layers of sediments soft and hard to compute the oceanic surface wave dispersion function the thomson haskell matrix method is used the solution is obtained by applying the normal mode formalism to the flat homogeneous layered ocean earth structure based on this theory the spectra of the excitation functions are investigated in detail for 45 thrust dip slip and strike slip point sources in the half space a numerical experiment reveals that the rigidity of the rock exerts a strong influence on both gravity and rayleigh waves in the case of rayleigh waves a layered structure of the bottom strongly affects the propagation process the main focus of the present study is to model tsunami and tsunamigenic events it is well known from observations that earthquakes that generate abnormally large tsunamis are mostly thrust events characterized by long source duration 2 4 times longer than typical earthquakes of similar moment and shallow source depth and are located near the trench axis meanwhile typical tsunamigenic earthquakes are generally dip slip and thrust events with depths between 15 and 50 km on this basis and using the distributed model of seismic source the influence of source mechanism location and source duration on the tsunami wave amplitude are investigated here the results of our model computations of the seismic sea waves from tsunami and tsunamigenic earthquake are in good agreement with real observation data

control on sediment and organic carbon delivery to the arctic ocean revealed with space borne synthetic aperture radar ob river siberia an important control on river biogeochemistry and sediment load is the process of water exchange between primary channels and the flood plain particularly in low r elief areas containing lakes ephemeral channels and other aquatic ecosystems flood plain exchange may be a dominant process on the lowland rivers of arctic russia which are among the world s largest in water discharge yet are strikingly deficient in their delivery of sediment to the arctic shelf temporal synthetic aperture radar sar amplitude and interferometric images of the ob river siberia reveal a time varying limnological network controlling water sediment and nutrient exchange between flood plain wetlands and the main channel the amount of hydrologic exchange decreases by one order of magnitude from june to september enhancing sedimentation over as much as 90 of the flood plain and enriching channel waters with colloidal organic carbon this observation combined with russian field measurements of water discharge and sediment load indicates that a major sediment sink on the lower ob flood plain may be responsible for the low amount of sediment delivery by the ob river to its estuary and the kara sea

on tsunami nucleation 1 a point source near field tsunami formation is detailed by means of mode summations using point moment tensor sources with a spherically symmetric self gravitating and elastic earth snapshots of vertical sea surface motion calculated within 200 km and 1000 s of an event typically show an initial tsunami pulse slowly grow and then evolve into dispersed wave trains the general point moment tensor used here produces frequency dependent tsunami radiation patterns of azimuthal degree 2 pure dip and strike slip sources however create waves that are symmetric or antisymmetric about the epicenter with a moment of 1020 n m and a rise time of 25 s these sources generate initial tsunami pulses 40 km wide when buried 10 km beneath an ocean 4 km deep maximum dip slip and strike slip tsunami amplitudes of 209 and 56 cm occur 10 km from the epicenter 75 s after the start of nucleation tsunamis from deeper earthquakes are smaller broader and slower to develop because they are depleted of high frequencies in general characteristics of tsunamis developing in this dynamic model contradict static concepts which base tsunami formation on permanent deformations of an otherwise rigid seafloor supporting incompressible water i find that the permanent strain state of the seafloor is not important in tsunami generation because it is defined by frequencies well below the range of interest 100 2000 s

spatial hydrogeomorphological influences on sediment and nutrient deposition in riparian zones observations from the garonne river france abstract this paper investigates the influence of geomorphological setting on riparian zone sedimentation within a reach of the river garonne france during three major floods the sampling design was stratified to reflect landforms constructed by fluvial processes e g floodplain lateral benches islands side channels and point bars observed sedimentation varied significantly with flood event planform context landform type and associated vegetation cover and in some cases with sample location within the landform lowest sedimentation was associated with the flood with the smallest peak discharge peak sediment concentration and sediment load sites under natural riparian vegetation experienced higher sedimentation than poplar plantations sites on concave outer banks received less sedimentation than those on convex inner banks sedimentation on floodplain sites and higher benches was lower than on low benches point bars and side channels there was considerable interdependence among these patterns reflecting the underlying geomorphological forms and processes meandering rivers tend to evolve through erosion of concave banks and deposition on convex banks point bar features tend to be built along convex banks whilst concave banks are eroded into higher floodplain and bench features as a result concave banks tend to be bordered by higher riparian margins that are less frequently flooded than convex banks where river margins are developed for agriculture the higher less frequently flooded sites are preferentially selected analyses of the quantity calibre nutrient and carbon content of the deposited sediment reveal further significant relationships which reflect the geomorphological structure of the riparian zone sediment particle size coarsens in locations with higher amounts of sedimentation the quantities of total organic carbon toc total organic nitrogen ton and total phosphorus tp all increase as the quantity of deposited sediment increases the concentration of toc and ton also increased significantly with an increase in the percentage of silt plus clay in the deposited sediments based upon the above observations a conceptual model is proposed which considers the spatial pattern in riparian zone sedimentation according to riparian morphology and flood magnitude the implications of channel incision for the functioning of the model are also discussed

channel instability as a control on silting dynamics and vegetation patterns within perifluvial aquatic zones many authors have shown that the sedimentology of former channels and subsequent vegetation changes are controlled by temporal flood events and successional processes and spatial e g distance to the main channel factors river channel instability can disrupt these associations the ain river france has undergone a fluvial metamorphosis during the past 100 years its braided pattern being replaced by a sinuous single thread pattern as a consequence former channels have different geometrical characteristics and sediment trap efficiencies former meandering channels experience more frequent backflows and are more rapidly silted than the older former braided channels the recently abandoned channels are characterized by the development of large sized vegetation species with a relatively slow colonization rate whereas the older channels are colonized predominantly by flood tolerant aquatic plants the locally derived discharge of former channels from groundwater or from their own basin may reduce or prevent sediment entry during flood events and thus may decrease the sedimentation rate in such cases the oligotrophic component of the water from the hillslope aquifer is high and the former channel is usually nutrient poor characterized by oligotrophic species the main river channel also has experienced local incision aggradation and horizontal displacement during recent decades so that the dynamics of the former channels strongly depend on the dynamics of the reach in which they are located in degraded reaches former channels are often dry and helophyte species have been replaced by mesophytes the frequency and magnitude of flow connection between the river channel and the former channel can increase or decrease owing to the movement of the active river channel within the fluvial corridor inducing varying modifications of former channel vegetation patterns river channel instability at various time scales is a key factor controlling process diversity and thus biodiversity in the fluvial corridor it can modify the geometry of abandoned channels groundwater fluxes the amount mobilization and deposition of sediment within the corridor and consequently the vegetation community patterns this increases the complexity of successional patterns because an old former channel may be characterized by pioneer species whereas a younger one can become quickly filled and colonized by terrestrial species copyright c 2000 john wiley sons ltd

vertical accretion sand proxies of gaged floods along the upper little tennessee river blue ridge mountains usa abstract understanding environmental hazards presented by river flooding has been enhanced by paleoflood analysis which uses sedimentary records to document floods beyond historical records bottomland overbank deposits e g natural levees floodbasins meander scars low terraces have the potential as continuous paleoflood archives of flood frequency and magnitude but they have been under utilized because of uncertainty about their ability to derive flood magnitude estimates the purpose of this paper is to provide a case study that illuminates tremendous potential of bottomland overbank sediments as reliable proxies of both flood frequency and magnitude methods involve correlation of particle size measurements of the coarse tail of overbank deposits 0 25 mm sand from three separate sites with historical flood discharge records for the upper little tennessee river in the blue ridge mountains of the southeastern united states results show that essentially all floods larger than a 20 probability event can be detected by the coarse tail of particle size distributions especially if the temporal resolution of sampling is annual or sub annual coarser temporal resolution 1 0 to 2 5 year sample intervals provides an adequate record of large floods but is unable to discriminate individual floods separated by only one to three years measurements of 0 25 mm sand that are normalized against a smoothed trend line through the down column data produce highly significant correlations r 2 values of 0 50 to 0 60 with p values of 0 004 to

reciprocal interactions and adjustments between fluvial landforms and vegetation dynamics in river corridors a review of complementary approaches abstract until recently one way relationships between flow dynamics geomorphology and plant ecology were considered dominantly when studying the functioning of river systems whereby fluvial landforms and hydrogeomorphic processes drive the evolution of riparian plant communities however biological communities may significantly control geomorphic processes and have strong impacts on landform dynamics in order to fully identify the processes linked to river dynamics changes in time and space of fluvial landforms and associated plant communities conceptual multidisciplinary progress is clearly needed to understand the mutual interactions and feedbacks between fluvial landforms and vegetation community dynamics this paper presents a detailed literature review of fluvial geomorphology riparian plant ecology and hydraulic engineering knowledge the historical and recent development of ecological plant succession theory toward the integration of hydrogeomorphic disturbances is discussed as well as the integration of vegetation within geomorphology as a significant landform control factor incorporating both hydrogeomorphic controls on riparian vegetation dynamics and mechanical impacts of vegetation structures on flow properties and sediment dynamics recent progress in ecology hydraulic engineering and fluvial geomorphology emphasises interdependence between biological and physical forms and processes based on this literature review a fluvial biogeomorphic succession concept is proposed to link fluvial landform and riparian vegetation community evolution within a bi directional model the succession of fluvial landforms and associated vegetation communities is composed of four main critical phases that represent a shift in the relative dominance of hydrogeomorphic and ecological processes as a response to biostabilisation and passive bioconstruction processes the positive feedbacks associated with this shift lead to the development of characteristic biogeomorphic structures such as vegetated banks islands or floodplains which are moderated by the biogeomorphic functional roles of ecosystem engineers that induce or reinforce the positive feedbacks this fluvial biogeomorphic succession concept relates the natural darwinian selection and ecological succession theories to fluvial geomorphology

populus nigra l establishment and fluvial landform construction biogeomorphic dynamics within a channelized river populations of the riparian pioneer species populus nigra l which establish on alluvial bars within river channels modulate sediment dynamics and fluvial landforms dense cohorts of p nigra have colonized gravel point bars along the channelized river garonne france during the last 20 years and have enhanced the vertical lateral and longitudinal development of the bars for this period the geomorphic characteristics of two wooded point bars on this laterally stable river are closely linked to the spatial distribution and intensity of establishment and resistance of different cohorts of p nigra furthermore p nigra colonization dynamics were controlled by engineer effects of this same species this relationship is illustrated by a significant correlation between key geomorphic and biological variables measured in situ and characterized with a set of four aerial photographs taken between 2000 and 2010 the development of wooded point bars which are discrete biogeomorphic units over the studied period appear to result from a specific biogeomorphic positive feedback of matter aggregation and vegetation establishment related to sediment trapping and stabilization by pioneer engineer plants we propose a conceptual model of biogeomorphic unit construction for channelized lateral stable rivers we consider the resultant biogeomorphic units as functional from an ecological point of view because p nigra enhances at the cohort scale i its own inherent capacity to resist hydrogeomorphic disturbances and ii its resilience capacity as a result of successful colonization especially downstream of mature poplar stands

geochemical significance of lipids and lipid derived substructures interlaced in kerogen abstract young kerogens isolated from seven freshwater lakes six river mouths and four marine surface sediments were subjected to pyrolysis in vacuo their pyrolysates were trapped and separated subsequently for determination of hydrocarbons fatty acids and alcohols the abundances carbon number distributions of long c12 polymethylene chain lipid compounds and relative abundances of pristenes are proposed as possible indices applicable to discrimination between young kerogens from freshwater lacustrine and marine sediments some oil shale kerogens of eocene and permian age were pyrolyzed in the same way where the chain length distributions of the pyrolysis products showed similar trends as those observed for the pyrolysis of young kerogens

molecular characterization of suspended and sedimentary organic matter in an arctic delta curie point pyrolysis gas chromatography cupy gc and curie point pyrolysis gas chromatography mass spectrometry cupy gc ms were used to characterize the macromolecular organic content of suspended particles in surface waters at intermediate water depths and in the surface sediments of the lena delta and the adjacent laptev sea eastern siberia the chromatograms of the pyrolysates of the lena river particles revealed several compound classes of biogenic significance polysaccharides phenolic substances and lipid constituents of higher plants the pyrolysates of the surface suspended particles of the laptev sea suggested mixed inputs some fatty acids phytadienes and n alkylnitriles were assigned to planktonic organisms pyrolysis products from terrigenous material encountered in the river were also present at intermediate water depths major differences with respect to the surface particles were evident in all cases we observed a substantial decrease of the precursors of phytadienes and the fatty acids that undergo biotransformation processes a peculiar pattern of three series of c14 c16 and cl8 alkanes and alkenes normal alkane the alki ene the e alk 2 ene and the z alk 2 ene was the prominent feature of these pyrolysates further investigations of the particle solvent extract and the corresponding residue suggested that these alkenes as well as the fatty acids derived from wax esters the composition of the sedimentary material in the laptev sea indicated preservation of the refractory terrigenous constituents however the presence of some algal constituents suggested that a fraction of marine derived macromolecules9 is resistant to degradation the arctic ocean is unique because of its ice cover and limited water exchange with surrounding oceans the marginal seas occupy 70 of this area and their physiography is such that broad shallow continental shelves coincide with the outflow of major rivers arctic environments have been poorly investigated in this respect the role of the arctic ocean and adjacent marginal seas in the global carbon budget has been neglected among other high latitude ecosystems the siberian aquatorium is of interest because of considerable discharge of major world rivers such as the lena yana ob and yenisei the lena river ranked the eighth largest world river discharging to the ocean has an annual water discharge entering the laptev sea of 525 km3 and a sediment discharge of 17 6 x 1 o6 t yr l which corresponds to an

earthquake mechanisms and tsunami generation the kurile islands event of 13 october 1963 abstract investigations of tsunamigenesis on a spherically symmetric and elastic earth using normal mode summations and moment tensor line sources are extended to include general double couple mechanisms so that computed tsunami waveforms can be compared with specific observations amplitudes of 19 tide gauge records of the kurile islands sea wave of 13 october 1963 are reproduced within a factor of 2 by either a single line source 250 km in length or by a triplet of parallel line sources separated by 42 km both models predict a strong beaming of tsunami strength with wave heights toward the northwest and southeast three to eight times larger than those in the northeast and southwest for faults over 150 km in length 2 of the 6 moment tensor components dominate tsunami production this fact motivated the coining of a new parameter tsunami moment m t by cataloging tsunami fields produced by suites of fault mechanisms i find that m t is approximately proportional to the tsunamigenic potential of earthquakes despite the critical role of fault mechanism in tsunami generation many sources have nearly equal tsunami moment and nearly equal ability for sea wave excitation estimates of shallow source strength from measurements of elastic surface waves have questionable integrity at both long 100 sec and short 30 sec periods amplitudes of high frequency waves suffer from saturation due to source size and duration while low frequency amplitudes are unstable with respect to small perturbations in fault mechanism because of the influence of the earth9s surface many tsunami earthquakes may be artifacts of underestimated source strength resulting from the inefficiency of shallow nearly vertical dip slip faults to produce long period surface waves

laboratory thermal conversion of sedimentary lipids to kerogen like matter a laboratory heating experiment was conducted in an attempt to evaluate the possible role of lipids as precursors for petroleum hydrocarbons lipids were extracted from a recent lake sediment lake haruna japan and heated under n2 atmosphere at 125 370 c for 1 7 days a significant amount of lipids was polymerized to kerogen like matter lipid derived kerogen at the low temperature of 175 c for 1 day the polymerization follows first order kinetics and the half life of lipids is calculated to be 104 105 yr at 0 30 c the lipid derived kerogen generated a significant amount 62 mg g of n alkanes c14 c36 on heating at 350 c for 1 day the results indicate a possible occurrence of lower temperature thermal polymerization of lipids in a relatively early stage of diagenesis as one of the formation pathways of kerogen with high hydrocarbon producing potential

seismic potential for large and great interplate earthquakes along the chilean and southern peruvian margins of south america a quantitative reappraisal the seismic potential of the chilean and southern peruvian margins of south america is reevaluated to delineate those areas or segments of the margin that may be expected to experience large or great interplate earthquakes within the next 20 years 1984 2004 long term estimates of seismic potential or the conditional probability of recurrence within a specified period of time are based on 1 statistical analysis of historic repeat time data using weibull distributions and 2 deterministic estimates of recurrence times based on the time predictable model of earthquake recurrence both methods emphasize the periodic nature of large and great earthquake recurrence and are compared with estimates of probability based on the assumption of poisson type behavior the estimates of seismic potential presented in this study are long term forecasts only as the temporal resolution or standard deviation of both methods is taken to range from 15 to 25 of the average or estimated repeat time at present the valparaiso region of central chile 32 35 s has a high potential or probability of recurrence in the next 20 years coseismic uplift data associated with previous shocks in 1822 and 1906 suggest that this area may have already started to rerupture in 1971 1973 average repeat times also suggest this area is due for a great shock within the next 20 years flanking segments of the chilean margin coquimbo illapel 30 32 s and talca concepcion 35 38 s presently have poorly constrained but possibly quite high potentials for a series of large or great shocks within the next 20 years in contrast the rupture zone of the great 1960 earthquake 37 46 s has the lowest potential along the margin and is not expected to rerupture in a great earthquake within the next 100 years in the north the seismic potentials of the mollendo arica 17 18 s and arica antofagasta 18 24 s segments which last ruptured during great earthquakes in 1868 and 1877 are also high but poorly constrained

diagenesis of extractable and bound fatty acids in possible source rocks in japan abstract n fatty acids in marine shales and mudstones of middel miocene age from north east japan were analyzed to investigate their stratigraphic distribution and diagenetic change with burial depth the free and esterified fatty acids showed strong even carbon predominance in sediments as old as middle miocene secondarily extractable n fatty acids showed relatively higher abundances of higher molecular weight fatty acids and lower cpi fa values than the free and esterified fatty acids on the other hand the kerogen form fatty acids were composed of relatively lower molecular weight acids 21 and the cpi fa values decreased systematically with a close relationship with the change of various parameters of organic maturation it is concluded that the thermocatalytic effect of clay minerals was essential for the diagenesis of secondarily extractable and kerogen form fatty acids while diagenesis of extractable fatty acids most of which are supposed to have been present in the pore space of the sedimentary rock was poorly affected by clay minerals

tsunami recorded on the open ocean floor on march 14 1979 a sizeable earthquake ms 7 6 richter scale occurred on the continental shelf adjacent to s w mexico near petatlan in the state of guerrero this earthquake generated a small tsunami that was recorded in deep water 1000 km away thus providing for the first time a glance at a tsunami traveling in the open ocean the same sea floor pressure record displays conspicuous signals associated with vertical sea floor motions generated at the passage of the first rayleigh seismic wave r1 seismic and tsunami travel velocities are in agreement with our present understanding of the phenomena and tsunami detectability in deep water is demonstrated to be well within present day state of the art in the design of sea floor pressure transducers as calculations anticipate the e m signals associated with the passage of the tsunami were too faint to be detected

overbank sedimentation from the historic a d 2011 flood along the lower mississippi river usa in this study we document sedimentary characteristics of overbank flood deposits associated with the epic a d 2011 flood along the lower mississippi river southern usa and directly compare the findings to sedimentation from a comparable flood event in 1973 with the general purpose of understanding how extreme floods contribute to floodplain depositional patterns and accretion rates of embanked fluvial systems the thicknesses of the 2011 flood deposits averaged 138 mm along natural levee crests 9 mm on meander scrolls and 3 mm in backswamps these thicknesses are considerably less than those documented for the 1973 flood sampled at the same locations we contend that less sedimentation in 2011 occurred because the flood was not supplied with much upstream sediment from the missouri river further the 2011 sediments are coarser than in 1973 indicating that the higher 2011 flood levels were associated with more energetic overbank flows that flushed fine grained sediments downstream within the narrow embanked floodplain corridor the largest recorded flood in north american history is only marginally preserved in the embanked floodplain stratigraphy of the alluvial valley of earth s third largest fluvial system