flow and suspended sediment division at two highly asymmetric bifurcations in a river delta implications for channel stability the division of sediment at river bifurcations results from the complex interaction between three dimensional flow planform and channel bed morphology as well as the heterogeneity of the bed material sediment division processes cannot be incorporated in their full complexity in scale experiments and are difficult to reproduce with numerical models field measurements are thus necessary to advance our understanding of those processes in river deltas however such measurements are rare we present measurements of the flow and sediment division at two tidally influenced bifurcations of the kapuas river a large sand bedded suspended load dominated river in west kalimantan indonesia at both bifurcations a smaller channel branches off from the side of the main river which makes the planform strongly asymmetric the planform of both bifurcations has been stable at least since the end of the nineteenth century when the region was mapped for the first time based on our measurements we explore possible factors that stabilize the bifurcations we measure the flow velocities with a boat mounted acoustic velocity profiler and determine the sediment concentration from acoustic backscatter calibrated against water samples the side branch of the first bifurcation receives a proportionally lower fraction of sediment than water in contrast the side branch at the second bifurcation receives a proportionally higher fraction of sediment than water a comparison of flow velocity and suspended sand concentration indicates that the bed material sorting strongly influences the division of sediment in particular at one of the bifurcations which is situated in a meander bend

sedimentary characteristics of the gravel sand transition in the river rhine abstract a gravel bed river often changes abruptly into a sand bed river the causes of such so called gravel sand transitions have been elucidated in recent years but detailed observations of gravel sand transitions in large rivers are scarce the present study fills this knowledge gap by investigating the sedimentary characteristics of the gravel sand transition in the river rhine data on bed composition and flow characteristics are used in combination with a novel method for the evaluation of the bed structure the analysis shows that in contrast to common belief the bed structure in the gravel sand transition zone does not change from fully clast supported to fully matrix supported instead there is a strong cross stream variation in bed structure especially upstream of the transition zone the analysis also shows that the downstream decrease in gravel mobility in the gravel sand transition zone which is usually attributed to the change in bed structure and the so called patchiness effect is at least partly caused by the larger scale bend sorting process which concentrates gravel in outer bends where it is only infrequently mobile dune sorting which has been suggested to have an effect on the gravel mobility similar to that of bend sorting was found to be relatively unimportant in the rhine partly because it is strongly counteracted by armoring processes that affect an uncommonly thick sediment layer the gravel sand transition in the rhine with its length of 50 km is much less abrupt than the gravel sand transitions of smaller rivers reported on in the literature although the dependence of the transition length on river size intuitively is correct the exact causes remain unclear

harmonic excitation of mantle rayleigh waves by the 1991 eruption of mount pinatubo philippines an unusually long at least two hours seismic wave train having periods of about 230 sec was recorded at many worldwide seismic stations during the major eruption of mount pinatubo in the philippines on june 15 1991 this wave train exhibits two sharp spectral peaks at 228 and 270 sec the group velocity phase velocity and the particle motion of this wave train indicate that it is a rayleigh wave the most probable excitation mechanism is acoustic coupling of atmospheric oscillations that were set off by continuous thermal energy flux from the volcano the two spectral peaks correspond to the characteristic periods of acoustic and gravity modes of the earth s atmosphere the magnitude of the vertical single force equivalent to the acoustic coupling is 1 6 10 17 dynes over a frequency band of 0 003 to 0 01 hz the results suggest the possibility of using acoustically coupled rayleigh waves for detection characterization and quantification of volcanic eruptions acoustic coupling of the atmosphere and the solid earth provides a unique seismic source with long duration

flow fields bed shear stresses and suspended bed sediment dynamics in bifurcations of a large river 1 channel bifurcations associated with bars and islands are important nodes in braided rivers and may control flow partitioning and thus affect downstream confluences as well as the formation and dynamics of bars however the morphodynamic processes associated with bar formation are poorly understood and previous studies have largely concerned laboratory experiments small natural streams or numerical analyses with large froude numbers high slopes and low shields stresses in these cases the morphologic changes at bifurcations are relatively rapid with predominant bed load transport and the suspended load playing a minor role in this paper the evolution of the flow structure and suspended bed sediment transport along four expansion diffluence units in the rio parana argentina are described the rio parana is a large multichannel river with a bed composed of medium and fine sands and possesses low froude numbers and high suspended bed material transport primary and secondary flow velocity components were measured with an acoustic doppler current profiler adcp along the expansion diffluence units and the backscatter signal of the adcp was calibrated to allow simultaneous measurements of suspended bed sediment concentrations the interactions between these variables show that the cores of primary flow velocity and suspended bed sediment concentration do not necessarily follow the thalweg at the bifurcation and that inertial effects on the suspended bed sediment may influence the morphodynamics of bar formation it is suggested that changes in flow stage as well as the presence of vegetation may further increase the deposition of suspended bed sediment at the bar head this study suggests that the ratio of suspended bed material to bed load is an important factor controlling the morphodynamics of bifurcations in large sand bed braided rivers

directivity and apparent velocity of the coseismic ionospheric disturbances observed with a dense gps array abstract coseismic disturbances in ionosphere have been observed after recent thrust earthquakes off the pacific coast of japan with a dense global positioning system array positive pulses in electron content as large as several times 10 15 electrons m 2 and as long as 4 5 min emerge 10 min after earthquakes and propagate horizontally with apparent velocity of 1 km s close to the sound velocity at the ionospheric height they may have been excited by coseismic uplifts of the sea surface initially as upward propagating compressive pulses of atmosphere which were gradually refracted to propagate horizontally in ionosphere the propagation has strong north south asymmetry and interaction between the movements of charged particles in acoustic waves and geomagnetic fields might have selectively attenuated the northward propagating disturbances

bed load sorting in an alluvial river bed load transport measurements of different grain size fractions in a sand bed river bankfull discharge 10 m 3 s width 15 m depth 1 5 m mean grain diameter 0 5 mm in southwest denmark showed that the transport rate in the central grain sizes varies less than in all other fractions in the bed load this is argued to be related to the role of point bars as sediment reservoirs during net erosion the lower part of the point bar is eroded and deposition takes place at the bar top whereas the situation is reversed during net deposition thus during their growth point bars undergo repeated episodes of erosion and deposition during these episodes the bed load is sorted measurements of input and output of size fractions from the studied meander bend showed that the overall effect of the size sorting is preferential deposition of fine and coarse fractions whereas the central size fractions are preferentially transported through the bend this type of sorting seems to be a general feature in sand bed river bends and affects the often assumed condition of bed load continuity for each size range in meander bends the long term effect of this is 1 bed load becomes better sorted during its down valley passage through meander bends and 2 the central size fraction is less abundant in the bulk sediment of point bars than in the average bed load thus during floods when point bars release sediment to the bed load the size distribution of the bed load is preferentially supplied with sizes on each side of the central fraction

sorting in grain flows at the lee side of dunes abstract sediment sorting at the lee side of ripples dunes and bars has already been recognized long ago a predictive model of the sorting is necessary but unavailable for implementation in sediment transport models for sediment mixtures relevant processes in sedimentological and physical literature are reviewed and compared to the sparse data of sediment sorting a synthesis is given of the most important variables governing the sorting processes for the benefit of future experimentation and modelling these variables are the sorting standard deviation skewness and bimodality of the sediment mixture delivered to the brink point the height of the dune or bar relative to the average grain size of the mixture the velocity of the flow above the brink point relative to the settling velocity for all grain size fractions and the frequency of the grain flows in addition the initiation mechanism and frequency of the grain flows affect the pattern and effectiveness of sorting

detection of ionospheric perturbations using a dense gps array in southern california 1 we present observations of high frequency ionospheric perturbations detected using global positioning system gps data from the southern california integrated gps network scign a densely spaced gps array of about 250 stations centered on the los angeles area we show examples of perturbations with 3 10 minute periods that may result from coupling between the ionosphere and neutral gravity waves generated in the lower atmosphere although the signal to noise ratio of the perturbations is relatively small we show how multi station array processing techniques can take advantage of the high spatial density of the measurements and the coherence of the signal over a region the size of the scign to considerably improve the detection capability

complex variations in sediment transport at three large river bifurcations during discharge waves in the river rhine river bifurcations strongly control the distribution of water and sediment over a river system a good understanding of this distribution process is crucial for river management in this paper an extensive data set from three large bifurcations in the dutch rhine is presented containing data on bed load transport suspended bed sediment transport dune development and hydrodynamics the data show complex variations in sediment transport during discharge waves the objective of this paper is to examine and explain these measured variations in sediment transport it is found that bend sorting upstream of the bifurcations leads to supply limitation particularly in the downstream branch that originates in the outer bend of the main channel tidal water level variations lead to cyclical variations in the sediment distribution over the downstream branches lags in dune development cause complex hysteresis patterns in flow parameters and sediment transport all bifurcations show evidence of sediment waves which probably are intrinsic bifurcation phenomena the complex transport processes at the three bifurcations cause distinct discontinuities in the downstream fining trend of the river differences among the studied river bifurcations are mainly due to differences in sediment mobility shields value because the variations in sediment transport are complex and poorly correlated with the flow discharge prediction of the sediment distribution with existing relationships for one dimensional models is problematic

sediment supply limited bedforms in sand gravel bed rivers the stability of bedforms in mixtures of gravel and sand is not well understood two bedform types are characteristic flow parallel sand ribbons and flow transverse barchans flume experi ments and field data presented here show that gradual transitions exist from sand ribbons to barchans and from barchans to fully de veloped dunes barchans and sand ribbons occur when not enough transportable sediment is available for the formation of fully devel oped ripples or dunes the reason is that a part of the bed sediment is immobile e g with an armor layer which limits the sediment sup ply and thus the volume of sediment available for the formation of bedforms bedform stability diagrams are shown to be extendable to sedi ment supply limited bedforms in sand gravel sediment if the par ticle parameters of the diagrams are derived from the transported sediment instead of the bed sediment barchans and forms transi tional to fully developed dunes plot in the dune stability fields sand ribbons on the other hand plot in the ripple lower plane bed and dune fields in the case of sediment supply limitation bedforms are partly or completely related to the characteristics of the sediment supply from upstream the sediment underlying the bedforms may be a stable armor and the exchange of sediment between this armor and the bedforms may be small or non existent consequently bedform char acteristics in sand gravel mixtures in supply limited conditions often are not predictable from the local hydraulics and sediment charac teristics

ionospheric response to infrasonic acoustic waves generated by natural hazard events recent measurements of gps derived total electron content tec reveal acoustic wave periods of 1 4 min in the f region ionosphere following natural hazard events such as earthquakes severe weather and volcanoes here we simulate the ionospheric responses to infrasonic acoustic waves generated by vertical accelerations at the earth s surface or within the lower atmosphere using a compressible atmospheric dynamics model to perturb a multifluid ionospheric model response dependencies on wave source geometry and spectrum are investigated at middle low and equatorial latitudes results suggest constraints on wave amplitudes that are consistent with observations and that provide insight on the geographical variability of tec signatures and their dependence on the geometry of wave velocity field perturbations relative to the ambient geomagnetic field asymmetries of responses poleward and equatorward from the wave sources indicate that electron perturbations are enhanced on the equatorward side while field aligned currents are driven principally on the poleward side due to alignments of acoustic wave velocities parallel and perpendicular to field lines respectively acoustic wave driven tec perturbations are shown to have periods of 3 4 min which are consistent with the fraction of the spectrum that remains following strong dissipation throughout the thermosphere furthermore thermospheric acoustic waves couple with ion sound waves throughout the f region and topside ionosphere driving plasma disturbances with similar periods and faster phase speeds the associated magnetic perturbations of the simulated waves are calculated to be observable and may provide new observational insight in addition to that provided by gps tec measurements

goce the first seismometer in orbit around the earth the first in situ sounding of a post seismic infrasound wavefront is presented using data from the goce mission the atmospheric infrasounds following the great tohoku earthquake on 11 march 2011 induce variations of air density and vertical acceleration of the goce platform these signals are detected at two positions along the goce orbit corresponding to a crossing and a doubling of the infrasonic wavefront created by seismic surface waves perturbations up to 11 of air density and 1 35 10 7 m s2 of vertical acceleration are observed and modeled with two different solid atmosphere coupling codes these perturbations are a due to acoustic waves creating vertical velocities up to 130 m s amplitudes and arrival times of these perturbations are reproduced respectively within a factor 2 and within a 60 s time window waveforms present a good agreement with observed data the vertical acceleration to air density perturbation ratio is higher for these acoustic waves than for gravity waves combining these two pieces of information offers a new way to distinguish between these two wave types this new type of data is a benchmark for the models of solid atmosphere coupling amplitude and frequency content constrain the infrasound attenuation related to atmosphere viscosity and thermal conductivity observed time shifts between data and synthetics are ascribed to lateral variations of the seismic and atmospheric sound velocities and to the influence of atmospheric winds these effects should be included in future modeling this validation of our modeling tools allows to specify more precisely future observation projects

direct measurement of over pressure of a volcanic blast on the june 1991 eruption at unzen volcano japan over pressure of a volcanic blast has been measured for the first time by a lead plate blastmeter at unzen volcano kyushu japan the over pressure of the volcanic blast on june 8 was 0 28 bar at 2700 m distance from the crater and that was less than 0 06 bar at 4400 m distance the estimated explosive yield of the explosion accompanied by the blast was 1 1 107 kg tnt 5 1020 erg calculated based on the over pressure and distribution of the blast effect the explosion energy is as much as 1 600 of that of the blast at mount st helens on 18 may 1980 the lead plate of the blastmeter at 2700 m has also recorded the collision with some accretionary lapillis the maximum particle velocity of the blast was estimated to be about 75 m sec based on the trace of the collision the significance of over pressure for the prediction of volcanic hazards is also discussed briefly

human induced changes in bed shear stress and bed grain size in the river waal the netherlands during the past 900 years human impact has changed the flow characteristics and bed sediment characteristics of lowland rivers affecting channel stability flood risk navigability and biodiversity we analysed the effect of human activities on the flow and bed sediment characteristics of the river waal the netherlands the objectives were a to reconstruct the historical change in bed shear stress during the past 900 years b to reconstruct the contemporary change in bed grain size and c to identify the main causes of these changes various data types were used such as borehole descriptions historical river maps and modern hydraulic data it was found that the bed shear stress in the river waal strongly increased during the past 900 years in the same period the gravel content of the sandy river bed increased causing a coarsening of the river bed before ad 1870 the shear stress increase and bed coarsening were mainly due to embankment artificial levee construction after ad 1870 the shear stress increase and bed coarsening were mainly due to river narrowing and dredging the systematic grain size difference between present day and historical rivers should be taken into account in river restoration projects copyright 2009 john wiley sons ltd

a large amplitude traveling ionospheric disturbance produced by the may 18 1980 explosion of mount st helens a remarkable long lived large scale traveling ionospheric disturbance tid excited by the may 18 1980 explosion of mount st helens has been detected in total electron content monitor data oscillatory perturbations in the electron column density of the ionosphere with amplitudes about 10 of the nominal daytime content were detected at three stations whose ionospheric penetration points lie between 1610 and 1890 km from mount st helens smaller perturbations were detected at five of six additional stations between 3760 and 4950 km away the period of the tid increased linearly with great circle distance from mount st helens ranging from 37 min at the nearest station to 116 min at the most distant one the tid persisted for at least four cycles at the three close stations and three cycles at the more distant stations and was qualitatively similar to tids produced by the low altitude thermonuclear detonations of the 1960 s the disturbance front of this tid accelerated from an average velocity of 350 m s between mt st helens and the close stations to an average velocity of 550 m s to the more distant ones in analogy with the bomb excited disturbances this tid is interpreted as the ionospheric fluctuations induced by a gravity wave excited by the explosion of mount st helens propagating in the neutral atmosphere a model based on the free wave response of an isothermal atmosphere to a point disturbance provides a good fit to the data at the three closest stations but no such model can account for all of the data modeling of the long distance behavior of the mount st helens tid in terms of upper atmosphere guided gravity waves is complicated by the requirement of exciting them by a ground level explosion a comprehensive explanation would probably include the propagation of energy to ionospheric heights in free modes and the excitation thereby of guided modes there was no evidence for a strong supersonic shock wave in the ionosphere as a result the mount st helens disturbance may prove to be a cleaner test of detailed theories of the point excitation and propagation of gravity waves in a realistic atmosphere than were tids excited by thermonuclear weapons

ionospheric ripples excited by superimposed wave fronts associated with rayleigh waves in the thermosphere 1 coseismic ionospheric disturbances cids associated with the 2011 tohoku earthquake off the pacific coast mw 9 0 tohoku eq were examined using total electron content and seismic wave data a faster cid propagated at 3 0 km s only in the west southwest while a slower cid propagated concentrically at 1 2 km s or slower from the tsunami source area taking the propagation speed and oscillation cycle into account the faster cid was associated with a rayleigh wave but the slower cid was associated with an acoustic or gravity wave the north south asymmetry of the cid associated with the rayleigh wave suggests that the rayleigh wave did not act as a point source of the acoustic wave because a point source propagating in all directions must produce symmetric cid in all directions therefore a superimposed wave front of acoustic waves was excited by the rayleigh wave and produced the north south asymmetry of the faster cid due to the magnetic inclination effect which is different from a well known north south asymmetry of cid excited at the epicenter on the other hand above and south of the tsunami source area the cid with a period of 4 min was excited by a point source located at the tsunami source area because atmospheric waves propagating from a point source produce north south asymmetry in the resulting cid

discriminating the tectonic and non tectonic contributions in the ionospheric signature of the 2011 mw7 1 dip slip van earthquake eastern turkey 1 it has previously been suggested that ionospheric perturbations triggered by large dip slip earthquakes might offer additional source parameter information compared to the information gathered from land observations based on 3d modeling of gps and glonass derived total electron content signals recorded during the 2011 van earthquake thrust intra plate event mw 7 1 turkey we confirm that coseismic ionospheric signals do contain important information about the earthquake source namely its slip mode moreover we show that part of the ionospheric signal initial polarity and amplitude distribution is not related to the earthquake source but is instead controlled by the geomagnetic field and the geometry of the global navigation satellite system satellites constellation ignoring these non tectonic effects would lead to an incorrect description of the earthquake source thus our work emphasizes the added caution that should be used when analyzing ionospheric signals for earthquake source studies

correlation analysis for preseismic total electron content anomalies around the 2011 tohoku oki earthquake we can observe the changes of total electron content tec in ionosphere by analyzing the data from global navigation satellite systems gnss satellites up to now preseismic tec anomalies have been reported in several papers however they are not so clear as coseismic tec anomalies and their analysis methods have some problems for practical earthquake prediction one factor making it difficult to detect tec anomalies is large noises in tec data nonnegligible tec disturbances are caused by many natural mechanisms to overcome this difficulty we propose correlation analyses between one gnss station and gnss stations surrounding it first we model tec time series over a few hours using polynomial functions of time second we calculate prediction errors as the departure of the tec time series from the models over time scale of a few minutes and define it as the tec anomaly third we calculate the correlation between anomaly of one gnss station and those at the surrounding stations although such a correlation method has long been used for radio communications in particular for spread spectrum communications and very long baseline interferometry to increase signal to noise ratio it has not been widely applied for tec analysis as a result of our method we demonstrate that the correlation analysis can detect preseismic anomalies about 1 h before the 2011 tohoku oki earthquake on 11 march mw 9 0 20 min before the foreshock on 9 march and 40 min before the aftershock on 7 april mw 7 3

ionospheric signature of surface mine blasts from global positioning system measurements sources such as atmospheric or buried explosions and shallow earthquakes are known to produce infrasonic pressure waves in the atmosphere because of the coupling between neutral particles and electrons at ionospheric altitudes these acoustic and gravity waves induce variations of the ionospheric electron density the global positioning system gps provides a way of directly measuring the total electron content in the ionosphere and therefore of detecting such perturbations in the upper atmosphere in july and august 1996 three large surface mine blasts 1 5 kt each were detonated at the black thunder coal mine in eastern wyoming as part of a seismic and acoustic monitoring experiment we deployed five dual frequency gps receivers at distances ranging from 50 to 200 km from the mine and were able to detect the ionospheric perturbation caused by the blasts the perturbation starts 10 to 15 min after the blast lasts for about 30 min and propagates with an apparent horizontal velocity of 1200 meters per second its amplitude reaches 3 x 10 exp 14 el per square meters in the 7 3 min period band a value close to the ionospheric perturbation caused by the m 6 7 northridge earthquake the small signal to noise ratio of the perturbation can be improved by slant stacking the electron content time series recorded by the different gps receivers taking into account the horizontal propagation of the perturbation the energy of the perturbation is concentrated in the 200 to 300 second period band a result consistent with previous observations and numerical model predictions the 300 second band probably corresponds to gravity modes and shorter periods to acoustic modes respectively using a 1 d stratified velocity model of the atmosphere we show that linear acoustic ray tracing fits arrival times at all gps receivers we interpret the perturbation as a direct acoustic wave caused by the explosion itself this study shows that even relatively small subsurface events can produce ionospheric perturbations that are above the detection threshold of the gps technique by sensing derivative signals which can be detected over a relatively broad region it appears that gps might be particularly useful for source characterization within the first acoustic quiet zone where infrasound would probably be ineffective this suggests that dual frequency gps monitoring could contribute to comprehensive nuclear test ban treaty verification

sediment discharge division at two tidally influenced river bifurcations 1 we characterize and quantify the sediment discharge division at two tidally influenced river bifurcations in response to mean flow and secondary circulation by employing a boat mounted acoustic doppler current profiler adcp to survey transects at bifurcating branches during a semidiurnal tidal cycle the adcp collecting flow velocity and acoustical backscatter data was used to quantify suspended sediment discharge adopting a recently introduced calibration procedure measured profiles of flow velocity and sediment concentration allowed us to compute spatiotemporal distributions of the shear velocity the roughness length and the rouse number spatiotemporal distributions of the settling velocity were obtained by combining the rouse number and shear velocity estimates with in situ measurements from a laser particle size analyzer bed load transport rates were inferred from shear stress estimates the concentration field shows a direct response to bed shear stress stressing the alluvial context of the system the flow in the bifurcation regions is characterized by counter rotating secondary flow cells which stretch over the full width and depth of the cross sections in the downstream branches and persist throughout the entire tidal cycle the pattern of secondary flow suggests the flow approaching the bifurcation is concentrated in two independent threads a two cell structure inhibits the exchange of sediment that would occur in case a single cell would stretch over the full channel width the division of suspended sediment primarily depends on the upstream transverse profile of the suspended sediment concentration which is in turn dependent on geometrical factors such as upstream curvature

holocene evolution of the east texas coast and inner continental shelf along strike variability in coastal retreat rates abstract the low gradient east texas coast and inner continental shelf from sabine lake at the texas louisiana border to the western end of galveston island experienced extreme along strike variations in rates of holocene coastal retreat around 7 7 ka a barrier shoreline was located approximately 55 km offshore toward the western end of galveston island the shoreline retreated 55 km occupying a position on the lagoon side of the island by about 5 3 ka toward the texas louisiana border the shoreline retreated more gradually occupying a position seaward of sabine bank by 5 3 ka between 4 7 ka and 2 8 ka the shoreline at sabine bank retreated 30 km while galveston island prograded seaward bolivar peninsula began to accrete around 1 5 ka heald and sabine banks located on the inner continental shelf above terraced fluvial deposits of the trinity sabine incised valley are the only preserved remnants of these former shoreline positions fluctuating rates of sea level rise were not the forcing mechanism behind episodes of rapid shoreline retreat because these events were localized rather along strike variations in the rate of transgression were caused by the variable inner shelf gradients which increase towards the west and the orientation of the sabine incised valley and associated terraced fluvial deposits which trend northeast southwest parallel to shore as shorelines retreated over fluvial deposits these served as local sand sources that enabled barrier islands to persist figure 1 map of the east texas inner shelf showing locations of sabine heald and shepard banks paleotopographic map of the pleistocene surface thin contours siringan 1993 delineates the trinity sabine incised valley which formed during the last lowstand of sea level thomas and anderson 1994 bathymetric contours are shown as thick lines with bold numbers dots are core locations end page 405 offshore out of equilibrium with sea level once these sand sources became depleted and or sea level reached some critical threshold barrier shorelines became stranded offshore as banks and new shorelines formed landward the geologic setting of coastal areas specifically antecedent topography plays a primary role in controlling coastal evolution to accurately forecast long term centennial to millennial coastal evolution it is essential that impacts associated with variations in the underlying geology of coastal areas be incorporated into coastal forecasting models

origin of hysteresis in bed form response to unsteady flows 1 field and laboratory studies indicate that changes in riverbed morphology often lag changes in water discharge this lagged response produces hysteresis in the relationship between water discharge and bed form geometry to understand these phenomena we performed flume experiments to observe the response of a sand bed to step increases and decreases in water discharge for an abrupt rise in discharge we observed that bed forms grew rapidly by collision and merger of bed forms migrating with different celerities growth rate slowed as bed forms approached equilibrium with the higher discharge regime after an abrupt discharge drop bed form decay occurred through formation of smaller secondary bed forms in equilibrium with the lower discharge which cannibalized the original relict features we present a simple model framework to quantitatively predict time scales of bed form adjustment to flow changes based on equilibrium bed form heights lengths and celerities at low and high flows for rising discharge the model assumes that all bed form collisions result in irreversible merger due to a dispersion of initial celerities for falling discharge we derive a diffusion model for the decay of relict high stage features our models predict the form and time scale of experimental bed form adjustments additional experiments applying slow and fast triangular flood waves show that bed form hysteresis occurs only when the time scale of flow change is faster than the modeled and measured bed form adjustment time we show that our predicted adjustment time scales can also be used to predict the occurrence of bed form hysteresis in natural floods

evolution of a bifurcation in a meandering river with adjustable channel widths rhine delta apex the netherlands rivers may dramatically change course on a fluvial plain such an avulsion temporarily leads to two active channels connected at a bifurcation here we study the effect of dynamic meandering at the bifurcation and the effect of channel width adjustment to changing discharge in both downstream branches on the evolution of a bifurcation and coexisting channels as an example we reconstructed the last major avulsion at the rhine delta apex we combined historical and geological data to reconstruct a slowly developing avulsion process spanning 2000 years and involving channel width adjustment and meandering at the bifurcation based on earlier idealised models we developed a one dimensional model for long term morphodynamic prediction of upstream channel and bifurcates connected at the bifurcation node the model predicts flow and sediment partitioning at the node including the effect of migrating meanders at the bifurcation and channel width adjustment bifurcate channel width adaptation to changing discharge partitioning dramatically slows the pacing of bifurcation evolution because the sediment balance for width adjustment and bed evolution are coupled the model further shows that meandering at the bifurcation modulates channel abandonment or enlargement periodically this explains hitherto unrecognised reactivation signals in the sedimentary record of the studied bifurcation meander belts newly identified in our geological reconstruction historical maps show that bifurcation migration due to meander bend dynamics increases the bifurcation angle which increases the rate of closure of one bifurcate the combination of model and reconstruction identifies the relevant timescales for bifurcation evolution and avulsion duration these are the time required to fill one downstream channel over one backwater length the time to translate one meander wavelength downstream and for strong river banks the adaptation timescale to adjust channel width the findings have relevance for all avulsions where channel width can adjust to changing discharge and where meandering occurs copyright 2011 john wiley sons ltd

lower rhine historical flood magnitudes of the last 450years reproduced from grain size measurements of flood deposits using end member modelling abstract objective the objective of this research was to unlock the potential of fluvial archives to create flood chronologies based on grain size characteristics of flood deposits located in two recently formed fluvio lacustrine sequences methods grain size data was compared with contemporaneous discharge measurements for the lower rhine the netherlands regression relations between coarse tail grain size parameters and measured discharge were established for the last 240 years and applied to the older parts of both cores resulting in peak discharge estimates back to ad 1550 results grain size descriptive parameters such as the 95th percentile and end member modelling outcomes correlate well with discharge and turn out to be sensitive proxies for inferring flood magnitudes locally geomorphological changes influence the relation between peak discharge magnitudes and flood bed coarseness but these can be assessed using continuous flood layer and background sedimentation measurements to standardize grain size descriptive parameters conclusion implications flood records distilled from sedimentary archives hold great potential for extending existing records of observed discharge and aid establishment of design discharge for flood protection measures and assessment of non stationarity of the flooding regime due to climatic and anthropogenic forcing

generation and propagation of infrasonic airwaves from volcanic explosions abstract analysis of infrasonic pressure waves generated by active volcanoes is essential to the understanding of volcanic explosion dynamics unlike seismic waves propagating in the earth infrasonic airwaves offer a relatively unfiltered representation of source motions at the vent during an eruption time varying acoustic propagation filters caused by changeable atmospheric conditions are minimal for microphones deployed at intermediate distances johnson et al j volcanol geotherm res in press

atmospheric resonant oscillations by the 2014 eruption of the kelud volcano indonesia observed with the ionospheric total electron contents and seismic signals abstract acoustic waves from volcanic eruptions are often observed as infrasound in near fields part of them propagate upward and disturb the ionosphere and can be observed with total electron content tec data from global navigation satellite system gnss receivers here we report tec variations after the 13 february 2014 plinian eruption of the kelud volcano east java indonesia observed with regional gnss networks significant disturbances in tec were detected with six gnss satellites and wavelet analysis showed that harmonic oscillations started at 16 25 ut and continued for 2 5 h the amplitude spectrum of the tec time series showed peaks at 3 7 mhz 4 8 mhz and 6 8 mhz long wavelength standing waves with a wide range of wavelength trapped in the lower atmosphere are excited by the plinian eruption amplitude spectra of the ground motion recorded by seismometers however had frequency components at discrete wave periods the condition for the resonant oscillations between the atmosphere and the solid earth is satisfied only at these discrete wave period and horizontal wavelength pairs therefore efficient energy transfer from the atmospheric standing waves to the solid earth rayleigh waves occurred at discrete periods and resulted in the harmonic ground motion

lithosphere atmosphere ionosphere coupling after the 2003 explosive eruption of the soufriere hills volcano montserrat resonant coupling between the earth and the atmosphere at frequencies where the solid earth modes overlap the fundamental modes of the atmosphere allows for the triggering of oscillatory acoustic perturbations by ground excitation and vice versa here we describe oscillatory perturbations observed in the solid earth from volumetric borehole strainmeter data and in the atmosphere from gps derived ionospheric total electron content following the july 13 2003 soufri ere hills volcano explosion montserrat lesser antilles spectral analysis shows an amplitude peak at 4 mhz for both datasets with similar waveforms and signal duration using a normal mode summation technique we show that both signals are explained by a single explosive source in the atmosphere similarities in waveforms in particular a double wave train also reported after several other explosion triggered atmospheric perturbations result from the superposition of the dominant fundamental atmospheric modes that trigger resonant coupling with the solid earth around 4 mhz

catastrophic lava dome failure at soufriere hills volcano montserrat 12 13 july 2003 the lava dome collapse of 12 13 july 2003 was the largest of the soufriere hills volcano eruption thus far 1995 2005 and the largest recorded in historical times from any volcano 210 million m3 of dome material collapsed over 18 h and formed large pyroclastic flows which reached the sea the evolution of the collapse can be interpreted with reference to the complex structure of the lava dome which comprised discrete spines and shear lobes and an apron of talus progressive slumping of talus for 10 h at the beginning of the collapse generated low volume pyroclastic flows it undermined the massive part of the lava dome and eventually prompted catastrophic failure from 02 00 to 04 40 13 july 2003 large pyroclastic flows were generated these reached their largest magnitude at 03 35 when the volume flux of material lost from the lava dome probably approached 16 million m3 over two minutes the high flux of pyroclastic flows into the sea caused a tsunami and a hydrovolcanic explosion with an associated pyroclastic surge which flowed inland a vulcanian explosion occurred during or immediately after the largest pyroclastic flows at 03 35 13 july and four further explosions occurred at progressively longer intervals during 13 15 july 2003 the dome collapse lasted approximately 18 h but 170 of the total 210 million m3 was removed in only 2 6 h during the most intense stage of the collapse

preseismic ionospheric anomalies detected before the 2016 kumamoto earthquake on 15 april 2016 the kumamoto earthquake mw 7 3 occurred in japan with no warning signals global navigation satellite system gnss receivers provide useful information on disturbances in the ionosphere by calculating the changes in total electron content tec which is the number of electrons in the ionosphere here we show our recently proposed correlation analysis of tec data which can detect the preseismic ionospheric anomalies from the public gnss data our method detected the ionospheric anomaly several tens of minutes before the 2016 kumamoto earthquake near its epicenter furthermore we gave an indicator to distinguish between the preseismic tec anomalies and the medium scale traveling ionospheric disturbances mstids by calculating the anomalous area rates these results support the hypothesis for existence of the preceding phenomena before large earthquakes

morphodynamic assessment of side channel systems using a simple one dimensional bifurcation model and a comparison with aerial images side channel construction is a common intervention applied to increase a river s conveyance capacity and to increase its ecological value past modelling efforts suggest two mechanisms affecting the morphodynamic change of a side channel 1 a difference in channel slope between the side channel and the main channel and 2 bend flow just upstream of the bifurcation the objective of this paper was to assess the conditions under which side channels generally aggrade or degrade and to assess the characteristic timescales of the associated morphological change we use a one dimensional bifurcation model to predict the development of side channel systems and the characteristic timescale for a wide range of conditions we then compare these results to multitemporal aerial images of four side channel systems we consider the following mechanisms at the bifurcation to be important for side channel development sediment diversion due to the bifurcation angle sediment diversion due to the transverse bed slope partitioning of suspended load mixed sediment processes such as sorting at the bifurcation bank erosion deposition due to vegetation and floodplain sedimentation there are limitations to using a one dimensional numerical model as it can only account for these mechanisms in a parametrized manner but the model reproduces general behaviour of the natural side channels until floodplain forming processes become important the main result is a set of stability diagrams with key model parameters that can be used to assess the development of a side channel system and the associated timescale which will aid in the future design and maintenance of side channel systems

observations of dune interactions from dems using through water structure from motion abstract the role of three dimensionality 3d in modulating both flow and sediment transport remains poorly understood 3d bed elevation measurements are difficult to obtain due to irregular dune shapes and submergence using photogrammetric tools for topographic reconstruction has become popular in surface studies yet water refraction makes through water image capturing of submerged dunes still challenging we show that through water images and structure from motion sfm tools can produce accurate digital elevation models dems of a measured dune field with a high level of detail it is a low cost and non intrusive alternative for submerged bed elevation measurements we provide a detailed sfm workflow introduce and discuss the use of camera coordinates and underwater ground control points and processing steps needed to obtain high accuracy dems our method results in dems with mm resolution in controlled laboratory conditions new data for 23 dune field dems from 6 experiments were obtained and are presented the dune field dem time series provide insights on dune interaction processes in our experiments merging and defect creation were most common merging decreases the number of bedforms and defect creation is responsible for more bedforms dunes continue to interact and jostle after achieving equilibrium simple crests are much more frequently observed than irregular sinuous or double crests two dimensional 2d crest shapes were observed although crest shapes were generally of 3d nature observed dune migration rates are not steady and vary in time and space bedform splitting speeds up dune migration whilst neighbouring dunes tend to accelerate or decelerate we identify a cascade of processes and show that 3d dems at high frequency are required to resolve observed rapid deformations and interaction of dunes the identified dune interaction processes are inherent to sediment flux variability whereas the temporal component of the underlying sediment transport processes is still not well understood in relation to average transport

the key role of fluvial dunes in transport and deposition of sand gravel mixtures a preliminary note abstract sediment transport and deposition in sand gravel bed rivers is shown to depend on dunes the sediment mixture is vertically sorted in avalanches at the lee side of the dunes part of the resulting upward fining sets of the largest dunes that occur during a discharge wave is preserved in the bed furthermore the sediment is entrained and deposited size selectively in the dune troughs which results in an additional upward fining accumulation of lag deposits this deposit is the source for sediment entrained during the next discharge wave which will depend on the relict vertical sorting and on the depth from which it is entrained the entrainment and deposition depth of the sediment depends on the dune trough level below the average bed level and therefore on the dune height thus subsequent discharge waves of decreasing magnitude will leave the upward fining cross bedded sets at depths below the bed surface related to the concurrent dune height this is demonstrated with flume experiments and with new vibrocores collected from the river waal the netherlands

discussion of understanding the influence of slope on the threshold of coarse grain motion revisiting critical stream power by c parker n j clifford and c r thorne geomorphology volume 126 march 2011 pages 51 65 abstract this paper presents a discussion of parker et al 2011 in particular some theoretical developments are presented that give additional material to apprehend the effects of grain size water depth and slope on the critical shields parameter and critical stream power

assessing channel response of a long river influenced by human disturbance article i nfo this paper describes an approach to assess channel changes of a long anthropogenised river the middle loire river over decadal timescales channel changes are evaluated along geomorphically homogeneous river reaches the classic geomorphic parameters active channel width bed slope grain size are complemented with parameters extracted from a 1d hydraulic model width depth ratio effective bed shear stress and specific stream power calculated for the biennial discharge assimilated to bankfull flow conditions the delineation of reaches is undertaken by combining visual inspection with the implementation of simple statistical tests to corroborate discontinuities in flow and sediment transport the 450 km long study area has been divided into 167 homogeneous reaches the general trends observed over the last fiftyyearsarenarrowingoftheactivechannel width and incision of the river bed however changes in bed level and active channel width are not consistently correlated channel changes at the reach scale are mainly controlled by the presence of former sediment extraction sites significant incision is observed at the peak of the in stream sediment mining period this was followed by channel recovery when extractions stopped the 1d numerical model provides a more rigorous manner to derive hydraulic parameters the effective bed shear stress made dimensionless by its critical value and the width depth ratio helps to explain observed channel responses more effectively by relating patterns to geological units along the middle loire

fluvial sediment budget of a modern restrained river the lower reach of the rhine in germany abstract the rhine river is a restrained river which is intensely used for navigation its river bed is subject to human induced erosion and sedimentation processes for river management information on the amount type source transport mode and fate of the sediments moving through the rhine is indispensable the objective of this study was to quantify the downstream fluxes of clay silt sand gravel and cobbles through the rhine between 1991 and 2010 and to identify the sources and sinks of these sediments this was done by analysing a unique dataset containing thousands of sediment transport measurements and by evaluating the sediment budget the river bed of the rhine was found to be subject to a net bed degradation of 3 mm a between 1991 and 2010 bed degradation has been induced by 18th 20th century river training works and nowadays is concentrated in areas with tertiary sands close to the bed surface in areas with mining induced subsidence and in the gravel sand transition zone sediment transport was found to be dominated by suspended clay and silt morphologically relevant however are only the sand gravel and cobble fractions despite the armoured gravely river bed sand is the main morphological agent sediment loads change in the downstream direction sand and fine gravel loads increase due to erosion of the bed whereas coarse gravel and cobble loads decrease due to a reduced sediment mobility caused by the downstream decreasing bed slope approximately one third of the sand and gravel load comes from upstream rhenish massif one third is supplied by bed degradation and one third is supplied artificially by humans for bed stabilisation purposes or as substitute for natural bed load slightly more than one half of the sediment was transported downstream into the north sea basin rhine delta a small amount was lost by abrasion and the remainder must have been deposited in groyne fields on floodplains or in ports the transfer of sand gravel and cobbles from the hinterland towards the rhine delta equalled 0 66 mt a 26 despite the long history of human impact this rate does not differ significantly from the holocene rate of sediment transfer to the rhine delta

evidence of atmospheric gravity waves during the 2008 eruption of okmok volcano from seismic and remote sensing observations 1 okmok volcano erupted on july 12 2008 following an 11 year hiatus detailed inspection of the syn eruptive seismograms revealed the presence of an ultra long period mode at a frequency of 1 7 mhz which is not a characteristic of the background seismic noise at okmok data collected by the national oceanic and atmospheric administration geostationary operational environmental satellite goes and national aeronautical and space administration moderate resolution imaging spectroradiometer modis sensors displayed the propagation of a vigorous ash and steam plume up to about 17 km above sea level we suggest that the observed ultra long period signals represent the response of the seismometer to changes in gravity associated with buoyancy oscillations set off in the lower atmosphere above okmok by the emplacement of the eruption column calculations based on simple modeling of these effects allowed estimation of peak atmospheric pressure perturbations associated with the eruption of less than 1 mbar

life of a bifurcation in a gravel bed braided river channel bifurcation is a key element in braided rivers determining the water and sediment distribution and hence controlling the morphological evolution recent theoretical and experimental findings as well as field observations showed that bifurcations in gravel bed braided rivers are often asymmetrical and highly unstable in this paper field data are presented on a bifurcation in the tagliamento river northeast italy the planform configuration of the bifurcation and its temporal evolution was monitored by an automatic digital camera during a series of seven floods with different magnitudes this remote sensing technique allowed a high temporal resolution pictures were acquired every hour that was proved to be essential in a highly dynamic system as the one considered here digitized maps of the channels provided information on the location of the bifurcation the width of the anabranches the angle between them along with the occurrence and migration of sediment bars data were acquired at two different water levels giving the possibility to compare low and high flow conditions the monitored bifurcation is largely unstable and shows sudden changes in the water distribution mainly driven by the bar migrating in the upstream channel and entering the distributaries a relationship between width asymmetry and flood magnitude was observed confirming previous analyses moreover recent theoretical findings were applied in order to test the possibility to estimate general trends in bifurcation evolution the analysis pointed out the relevance of a correct assessment of the characteristic temporal scales as the bifurcation evolves on a timescale similar to that of bar migration and flood duration understanding the interactions between these processes is therefore crucial in order to increase the ability to model and predict the morphological evolution of a braided network copyright 2012 john wiley sons ltd

from source to mouth basin scale morphodynamics of the rhine river abstract in this article we present a unique detailed basin wide morphological analysis of the rhine one of the world s larger rivers the objectives of this study were to characterize the basin scale morphodynamics of the rhine river in the period 1991 2010 by quantifying the downstream fluxes of clay silt sand gravel and cobbles from source to mouth and identifying the sources and sinks of these sediments using sediment budget analyses from source to mouth the rhine traverses four sections with fundamentally different morphodynamic behaviour the alpine impounded free flowing and delta section sediment fluxes are discontinuous primarily because of the presence of a glacial lake trapping all sediments from upstream the lake caused sediment fluxes to be discontinuous already before the anthropocene today s sediment fluxes are strongly influenced by dredging and nourishment operations from a global perspective sediment fluxes in the river s headwaters are large whereas sediment output from the rhine towards the sea is small a special feature of the rhine is the fact that more sediment is transported in upstream direction from the sea into the delta than vice versa on a basin scale nourishment represents the biggest source of gravel and cobbles and tributaries the biggest source of clay silt and sand in the lower rhine delta additional large amounts of clay silt and sand are supplied by the sea dredging represents a main sediment sink for all size fractions for silt and clay also floodplain deposition and deposition in ports represent major sinks the rhine is a typical example of a river in disequilibrium large parts of the river are subject to erosion or sedimentation in contrast to other rivers with erosion upstream and deposition downstream the rhine has net deposition upstream and net erosion downstream although human interventions contributed to the disequilibrium the pristine rhine already was in a state of disequilibrium even today natural factors determine the location of the main sedimentation areas the budget analysis shows that the behaviour of the clay silt sand and gravel cobble fractions strongly differ from each other a particularity is that in many reaches gravel is deposited whereas simultaneously sand is being eroded the budget analysis also shows that sediment dynamics in rivers are much higher than is suggested by echosoundings or transport measurements this study provides valuable insights into the basin scale morphodynamics of the rhine helps to see smaller scale studies of parts of the rhine basin in a correct perspective provides a good data basis to improve numerical prediction models and helps to optimize nourishment dredging and monitoring strategies in the rhine furthermore the rhine represents an excellent reference case for other large river systems for which less data are available knowledge gaps of supra regional importance identified in this study relate to a the fundamental disequilibrium of large river systems b the effect of natural and human factors on the future morphodynamic development of the large river systems c the morphodynamic role of sand in gravel bed rivers and d the long term effects of sediment nourishment

bichromatic excitation of long period rayleigh and air waves by the mount pinatubo and el chichon volcanic eruptions we have detected a new powerful source of low frequency seismic energy which is associated with some violent volcanic eruptions for the two eruptions for which we have identified this new source the spectrum is bichromatic consisting of two narrow phase coherent spectral lines these bands were centered on 3 76 and 5 14 mhz for the april 4 1982 el chichon eruption and on 3 68 and 4 44 mhz for the june 15 1991 mt pinatubo eruption during the latter 8 hour long eruption the resonance frequencies varied by less than 20 hz the strength of the source is sufficient to excite globe circling surface waves we conclude from these observations that volcanoes can excite harmonic tremors at much longer periods than previously observed our preferred source model involves feedback between local atmospheric oscillations and the eruption process the physics responsible for this feedback remains subject to speculations

processing and interpretation of microbarograph signals generated by the explosion of mount st helens following the eruption of the mount st helens volcano on may 18 1980 atmospheric waves were recorded by a network of micrographs located over 7 000 km from the source analysis of these data requires the use of complex processing techniques based on a high resolution method to extract the signals produced by the st helens source from spurious waves or noise in each record this facilitates interpretation of the wave trains in terms of propagation modes it is thus shown that lamb mode l sub 0 is present in the low frequency part of all signals whereas acoustic modes more probably a prime sub 2 are needed to explain all the properties of the high frequency part which is clearly observed for a westward and a southward propagation

estimating bedload transport in a large sand gravel bed river from direct sampling dune tracking and empirical formulas three methods used to estimate river bedload discharges were compared in a large sand gravel bed river the unit and total bedload transport rates estimated by sediment sampling dune tracking method and the equations of van rijn and meyer peter and muller were compared the analysis was based on a large data set obtained from field surveys that combined sediment sampling acoustic doppler profiler adp measurements and multibeam echosoundings of the middle reach of the river loire france for contrasting flow conditions ranging from low flows to 2 year floods for transport stages between 2 and 6 i e between the annual mean discharge and the discharge for a 2 year flood the tested equations predicted fairly well the unit and total bedload discharges and roughly estimated the temporal variability of the bedload during floods for these transport conditions the best agreement with the sediment sampling measurements was observed with the van rijn formula for lower flow conditions the tested formulas provide lower estimates than those sampled to improve the accuracy of the equations for low flows potential solutions include integrating near bed turbulences and non uniformity of bed particles into the models the ability of the formulas to predict the temporal variability of the bedload can be improved by using the bedform roughness to adjust the estimates the bedload transport rates calculated with dune tracking method are lower than the fluxes sampled because a substantial fraction of the bedload does not participate to the dune migration finally a first rating curve that was implemented for the river loire estimates the annual bedload discharge for 2010 to be 480 000 t

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

volcano infrasound a review abstract exploding volcanoes which produce intense infrasound are reminiscent of the veritable explosion of volcano infrasound papers published during the last decade volcano infrasound is effective for tracking and quantifying eruptive phenomena because it corresponds to activity occurring near and around the volcanic vent as opposed to seismic signals which are generated by both surface and internal volcanic processes as with seismology infrasound can be recorded remotely during inclement weather or in the dark to provide a continuous record of a volcano s unrest moreover it can also be exploited at regional or global distances where seismic monitoring has limited efficacy this paper provides a literature overview of the current state of the field and summarizes applications of infrasound as a tool for better understanding volcanic activity many infrasound studies have focused on integration with other geophysical data including seismic thermal electromagnetic radiation and gas spectroscopy and they have generally improved our understanding of eruption dynamics other work has incorporated infrasound into volcano surveillance to enhance capabilities for monitoring hazardous volcanoes and reducing risk this paper aims to provide an overview of volcano airwave studies from analog microbarometer to modern pressure transducer and summarizes how infrasound is currently used to infer eruption dynamics it also outlines the relative merits of local and regional infrasound surveillance highlights differences between array and network sensor topologies and concludes with mention of sensor technologies appropriate for volcano infrasound study

harmonic ionospheric oscillation by the 2010 eruption of the merapi volcano indonesia and the relevance of its amplitude to the mass eruption rate abstract using continuous data from ground based global satellite navigation system gnss receivers in java and sumatra indonesia we studied the response of ionospheric total ionospheric electron content tec to the 2010 nov 5 eruption of the merapi volcano in central java we then compared the results with the case of the 2014 feb 13 eruption of the kelud volcano eastern java the tec showed a quasi periodic oscillation of a frequency 4 mhz with average amplitudes of 0 9 and 1 8 relative to background values lasting for 20 and 120 min for the merapi and kelud eruptions respectively by comparing the two cases together with the 2015 april eruption of the calbuco volcano chile we found the relative tec oscillation amplitude may scale with the mass eruption rate this suggests that the product of such tec oscillation amplitude and the duration provides a new measure for the total volume of the volcanic deposits

bifurcation modelling in a meandering gravel sand bed river the rhine bifurcation at pannerden forms the major distribution point for water supply in the netherlands distributing not only water and sediment but also flooding risks and navigability its morphological stability has been a concern for centuries we present experiences from more than two decades of numerical morphological modelling of this bifurcation with a gravel sand bed and a meandering planform successive computations have shown the importance of upstream approach conditions the necessity to include physical mechanisms for grain sorting and alluvial roughness and the need to assume a thicker active layer of the river bed than is suggested by laboratory flume experiments using a constant discharge the active layer must be thicker in the model to account for river bed variations due to higher frequency discharge variations that are filtered out in morphological modelling we discuss limitations in calibration and verification but argue that notwithstanding these limitations 2d and 3d morphological models are valuable tools not only for pragmatic applications to engineering problems but also for revealing the limitations of established knowledge and understanding of the relevant physical processes the application of numerical models to the pannerden bifurcation appeared to reveal shortcomings in established model formulations that do not pose particular problems in other cases this application is therefore particularly useful for setting the agenda for further research copyright 2012 john wiley sons ltd

explaining artificial side channel dynamics using data analysis and model calculations abstract side channel construction is a common intervention to increase both flood safety and the ecological value of the river three side channels of gameren in the river waal the netherlands show amounts of large aggradation we use bed level measurements and grain size samples to characterize the development of the side channels we relate the bed level changes and the deposited sediment in the side channels to the results of hydrodynamic computations two of the three side channels filled mainly with suspended bed material load in one of these channels the bed level increased enough that vegetation has grown and fine suspended load has settled in the third side channel the bed shear stresses are much smaller and in addition to the suspended bed material load fine sediment settles based on the side channel system at gameren we identify two types of side channels one type fills predominantly with suspended bed material load from the main channel and a second type fills predominantly with fine suspended load this gives an indication of the main mechanisms that lead to the aggradation in artificial side channel systems

accuracy of cross channel sampled sediment transport in large sand gravel bed rivers the accuracy of cross channel integrated sediment transport of bed material is determined with an elaborate set of field measurements in the waal river the netherlands the measurements were done during a discharge wave in the upstream part of the river which has a bimodal sand gravel bed the sampling strategy should take both spatial and temporal aspects into account to obtain maximum accuracy presence of moving bedforms differences in bed sediment grain size in the cross section and presence of preferential transport lanes dictate that at least five subsections for sampling in the cross section are necessary the accuracy of cross channel integrated bedload transport depends mainly on the measurement strategy an uncertainty of 20 bedload and 7 suspended load of cross channel integrated sediment transport is shown to be feasible if 30 samples of bedload and two vertical profiles of suspended bed material load are taken in one subsection provided that the cross section of the river is divid

global positioning system detection and energy estimation of the ionospheric wave caused by the 13 july 2003 explosion of the soufriere hills volcano montserrat 1 volcanic explosions or shallow earthquakes are known to trigger acoustic and gravity waves that propagate in the atmosphere at infrasonic speeds at ionospheric heights coupling between neutral particles and free electrons induces variations of electron density detectable with dual frequency global positioning system gps measurements using gps data collected in the caribbean we identified an ionospheric perturbation after a major volcanic explosion at the soufriere hills volcano montserrat lesser antilles on 13 july 2003 spectral analysis reveals peaks centered at 1 and 4 mhz similar to those in previous observations and consistent with theory suggesting both gravity and acoustic wave components we retrieve a horizontal velocity of 624 m s for the acoustic component which implies upward propagation at 33 consistent with ray tracing results we model the acoustic wave using an n wave pressure source at ground level combined with ray tracing to propagate the neutral pressure wave this accounts for the dispersive characteristics of the atmosphere while conserving total acoustic energy plasma velocity is derived from neutral velocity using a finite difference solution of the magnetohydrodynamic momentum equation the continuity equation for charge densities is used to compute corresponding electron density variations which are then numerically integrated along satellite to receiver line of sights simultaneously accounting for the satellite displacements we minimize the misfit between observed and model waveforms to estimate a total acoustic energy release of 1 53 x 10 10 j for the primary explosion event at soufriere hills volcano associated with the peak dome collapse this method can be applied to any explosion of sufficient magnitude provided gps data are available at near to medium range from the source

three dimensional waveform modeling of ionospheric signature induced by the 2004 sumatra tsunami 1 the sumatra december 26th 2004 tsunami produced internal gravity waves in the neutral atmosphere and large disturbances in the overlying ionospheric plasma to corroborate the tsunamigenic hypothesis of these perturbations we reproduce with a 3d numerical modeling of the ocean atmosphere ionosphere coupling the tsunami signature in the total electron content tec data measured by the jason 1 and topex poseidon satellite altimeters the agreement between the observed and synthetic tec shows that ionospheric remote sensing can provide new tools for offshore tsunami detection and monitoring

sediment supply and the development of the coarse surface layer in gravel bedded rivers the bed surface of most gravel rivers is considerably coarser than the sub surface or the gravel load transported over it a phenomenon affecting river dynamics morphology and ecology the coarse surface layer often called an armour or pavement has been attributed to an inherent tendency for small grains to settle between larger ones during active transport of all sizes1 2 and to selective erosion or trapping of finer particles when the coarse grains are relatively immobile3 4 where bedload supply is cut off below dams selective erosion causes coarsening5 6 using a simple quantitative model we propose that surface coarsening develops in gravel bedded rivers when local bedload supply from upstream is less than the ability of the flow to transport that load we present laboratory results which support this hypothesis and show that supply reduction causes changes in bedforms and progressive confinement of active bedload transport to a narrow band of finer bed surface bordered by a coarse less active bed it may therefore be possible to relate the degree of river bed surface coarsening to sediment supply resulting from land use

total electron content anomalies associated with global vei4 volcanic eruptions during 2002 2015 abstract in previous studies little attention has been paid to the total electron content tec anomalies preceding the volcanic eruption we analyze the coupling relationship between volcanic eruption and tec anomalies and discuss the spatial distribution of tec anomalies associated with volcanic geographical location we utilize the global ionosphere map gim data from the center for orbit determination in europe code to analyze tec variations before the global volcanic eruptions indicated by vei volcanic explosivity index 4 from 2002 to 2015 with the sliding interquartile range method the results indicate the occurrence rate of tec anomalies before great volcanic eruptions is related with the volcanic type and geographical position the occurrence rate of tec anomalies before stratovolcano and caldera eruptions is higher than that before shield and pyroclastic shield eruptions and the occurrence rate of tec anomalies has a descending trend from low latitudes to high latitudes the tec anomalies before the volcanic eruptions in low mid latitudes are within the volcanic affected areas but do not coincide with the volcanic foci the corresponding tec anomalies could be observed in the conjugated region and all the tec anomalies in the volcanic affected areas are usually close to bounds of equatorial anomaly zones however the tec anomalies preceding these eruptions in high latitudes usually surround the volcano and no tec anomalies appear in the conjugated region these conclusions have potential applications to the prediction of great volcanic eruptions in the future

virtual array beamforming of gps tec observations of coseismic ionospheric disturbances near the geomagnetic south pole triggered by teleseismic megathrusts we identified co seismic ionospheric disturbances cid in antarctica generated by the 2010 maule and the 2011 tohoku oki earthquakes analyzing tec data with a modified beamforming technique beamforming in antarctica however is not straightforward due to the effects of array deformation and atmospheric neutral wave ionospheric plasma coupling we take these effects into account and present a method to invert for the seismically generated acoustic wave using tec observations the back azimuths speeds and waveforms obtained by the beamform are in excellent agreement with the hypothesis that the tec signals are generated by the passage of rayleigh waves from the maule and tohoku oki earthquakes the tohoku oki earthquake is 12 500 km from antarctica making this the farthest observation of cids to date using gps

unique and remarkable dilatometer measurements of pyroclastic flow generated tsunamis pyroclastic flows entering the sea may cause tsunamis at coastal volcanoes worldwide but geophysically monitored field occurrences are rare we document the process of tsunami generation during a prolonged gigantic collapse of the soufriere hills volcano lava dome on montserrat on 12 13 july 2003 tsunamis were initiated by large volume pyroclastic flows entering the ocean we reconstruct the collapse from seismic records and report unique and remarkable borehole dilatometer observations which recorded clearly the passage of wave packets at periods of 250 500 s over several hours strain signals are consistent in period and amplitude with water loading from passing tsunamis each wave packet can be correlated with individual pyroclastic flow packages recorded by seismic data proving that multiple tsunamis were initiated by pyroclastic flows any volcano within a few kilometers of water and capable of generating hot pyroclastic flows or cold debris flows with volumes greater than 5 10 6 m 3 may generate significant and possibly damaging tsunamis during future eruptions

dunes in the world s big rivers are characterized by low angle lee side slopes and a complex shape dunes form critical agents of bedload transport in all of the world s big rivers and constitute appreciable sources of bed roughness and flow resistance dunes also generate stratification that is the most common depositional feature of ancient riverine sediments however current models of dune dynamics and stratification are conditioned by bedform geometries observed in small rivers and laboratory experiments for these dunes the downstream lee side is often assumed to be simple in shape and sloping at the angle of repose here we show using a unique compilation of high resolution bathymetry from a range of large rivers that dunes are instead characterized predominantly by low angle lee side slopes 10 complex lee side shapes with the steepest portion near the base of the lee side slope and a height that is often only 10 of the local flow depth this radically different shape of river dunes demands that such geometries are incorporated into predictions of flow resistance water levels and flood risk and calls for rethinking of dune scaling relationships when reconstructing palaeoflow depths and a fundamental reappraisal of the character and origin of low angle cross stratification within interpretations of ancient alluvial sediments dunes in the world s big rivers are dominated by lee side slopes with angles of less than 10 according to a bedform analysis of high resolution bathymetric datasets

stochastic prediction of sediment transport in sand gravel bed rivers classical deterministic bedload transport predictors are applied to sand gravel bed rivers the turbulent bed shear stress is modeled according to a probability distribution to obtain realistic bedload transport rates at incipient motion in extending the predictors to stochastic predictors for nonuniform sediment many parameters that represent near bed turbulence and the particle size distribution must be chosen the parameters that give realistic results are chosen by analyzing the results of a new experimental flume dataset with relatively large water depths choosing other combinations of parameters may give equal total bedload transport rates but at the cost of large errors in fractional transport rates attention is given to the hiding exposure phenomenon and a hindrance effect related to nonuni form sediment validation based on two independent field datasets shows that successful predictions of particle sizes near the threshold for motion are feasible using the stochastic approach while the deterministic approach gives successful predictions well above incipient motion

downstream fining in large sand bed rivers abstract downstream fining of bed sediments is a well known phenomenon in gravel bed rivers but also occurs in large sand bed rivers the underlying processes however are not necessarily the same due to the difference in sediment mobility grain size distribution width and geographical setting downstream fining studies focusing on large sand bed rivers are scarce nevertheless in this paper the processes that affect downstream fining in gravel bed rivers are reviewed and it is evaluated to what extent they are relevant for large sand bed rivers furthermore several new downstream fining processes are discussed ending in a conceptual model of downstream fining in large sand bed rivers in deriving the conceptual model downstream fining processes are divided into three categories abrasion selective transport and sediment addition extraction abrasion rates in large sand bed rivers are small due to the durable lithologies the small grain size the high degree of rounding the dominance of grinding as abrasion process and the dominant suspended transport mode of the bed sediment only in the upstream part of large sand bed rivers abrasion rates may be somewhat higher selective transport rates in large sand bed rivers everywhere overrun abrasion rates but are small compared to selective transport rates in gravel bed rivers because the unimodal sediments in sand bed rivers exhibit stronger hiding exposure effects during threshold of motion conditions but especially because many sand bed rivers though not all are in state of fully mobilised transport making differences in threshold of motion between coarse and fine grains relatively unimportant selective transport in these rivers is probably mainly the result of the presence of suspended load transport in combination with the effects of dune and perhaps bend sorting which are all processes that act on a relatively large scale within sand bed rivers the degree of selective transport probably decreases downstream due to the change in mixture bimodality and sorting efficiency there are indications that coarse grains may sometimes even be more mobile than fine grains in the downstream part of sand bed rivers note that in contrast to abrasion selective transport only produces a stable downstream fining pattern if the river profile is concave generally a stronger profile concavity leads to a higher aggradation rate and a stronger downstream fining trend sediment addition and extraction processes can obscure the effects of abrasion and selective transport in sand bed rivers overbank sedimentation for instance may significantly decrease the downstream fining rate in large sand bed rivers because especially fine grains are removed from the bed dredging can also strongly affect the downstream fining trend depending on the volume and the grain size of the sediment involved meander migration may cause a nett loss of coarse grains from the channel in aggrading circumstances increasing the downstream fining rate river bifurcations can cause a discontinuity in the downstream fining pattern because bend sorting upstream of the bifurcation causes the river branch that originates in the outer bend of the main channel to be much coarser than the other branch all these addition and extraction processes not only have a direct effect on the grain size composition of the river bed but also indirectly influence downstream fining by their effect on the longitudinal bed profile other sediment addition and extraction processes such as tributary confluences non alluvial sediment sources and dumping are less common in large sand bed rivers but can locally have a great effect a full determination of the relative importance of all downstream fining processes in large sand bed rivers requires extensive field measurements the construction of detailed fractionwise sediment balances and the development of numerical downstream fining models that incorporate all processes described above

explosion energy of the 2004 eruption of the asama volcano central japan inferred from ionospheric disturbances 1 the japanese dense array of global positioning system recorded ionospheric disturbances as changes in total electron content 12 minutes after the september 1 2004 eruption of the asama volcano central japan the disturbance had a period of one and a quarter minutes and propagated as fast as 1 1 km s suggesting its origin as the acoustic wave generated by the explosion by comparing the disturbance amplitudes with those by a surface mine blast with a known energy the overall asama explosion energy is inferred to be about 2 1014 j

predicting the migration rates of subaqueous dunes in this paper we develop a simple physically based method for predicting what fraction of sediment moving over the crests of dunes will bypass their lee faces the bypass fraction is found by calculating a characteristic excursion length for every grain size making up a particular train of dunes all particles with excursion lengths greater than the downstream span of the lee face of the average dune are assumed not to contribute to dune propagation bypass fractions based on distributions of excursion lengths account for the discrepancies between total sediment discharge and dune migration rate measured by stein 1965 and guy et al 1966 in laboratory flumes as well as by us in the north loup river of nebraska calculations and these data agree over sediment transporting conditions associated with the entire stability field for dunes composed of medium sand the two laboratory studies show that commonly 30 60 of all sand moving over fully developed dunes is not deposited on slip faces measurements from the north loup river reveal that of all sediment moving over the dune crests there roughly 45 is not being captured on lee faces even though 99 of sediment is transported within 2 cm of the bed the method developed herein successfully estimates measured values for the bypass fraction from 0 to 80 our analysis indicates that the division between grains that are deposited versus those that are bypassing falls within the range of sand sizes making up the suspended load at dune crests

ionospheric detection and localization of volcano eruptions on the example of the april 2015 calbuco events using data from ground based gnss receivers located in southern chile we study the ionospheric total electron content tec response to two eruptions of the calbuco volcano that occurred on 22 23 april 2015 in both cases the tec response showed quasi periodic signals with several consecutive wave trains the averaged amplitude of the observed co volcanic tec perturbations amounted 0 45 tecu for the first eruption and 0 16 tecu for the second one we compare amplitudes of the tec response to volcano eruptions of different intensity from our and previously published data and we show that both the intensity and the background ionospheric conditions define the amplitude of ionospheric co volcanic disturbances cvid the relative contribution however scales with the eruption intensity the travel time diagrams allowed to estimate the propagation speed of the observed co volcanic tec perturbations as 900 1200 m s which is close to the acoustic or shock acoustic waves speed at the ionospheric height the spectrograms are consistent with the conclusion on the acoustic nature of the observed tec perturbations finally we use the approximation of a spherical wave propagating at a constant velocity from a point source and for the first time we calculate the location of the volcanic source and the onset time of the volcano eruption from ionospheric measurements we show that even from 30 sec ionospheric gps data it is possible to localize the eruptive source within several degrees of latitude longitude

the response of subaqueous dunes to floods in sand and gravel bed reaches of the dutch rhine the branches of the river rhine in the netherlands characterized by a sand gravel bed in the upstream part and a sand bed in the downstream part of the river system show migrating dunes especially during floods in the last 20 years these dunes have been studied extensively high resolution echo sounding measurements of these dunes made with single and multibeam equipment were analysed for three different sections of the rhine river system during several floods this analysis was done to quantify the growth decay and migration rates of the dunes during floods in addition the migrating dunes were used to calculate bedload transport rates with dune tracking the results of dune growth and decay and migration rate are shown to be very different for the various sections during the various floods and these differences are related to differences in grain size of the bed and to differences in the distribution of discharge over the main channel and the floodplain the relations are used to show that the growth and migration rate of dunes and the calculated bedload transport rates during the rising stage of a flood wave can be predicted from the mobility of the bed material with simple power relations

paleoslope reconstruction in sandy suspended load dominant rivers constraining the depositional gradient of ancient alluvial river systems can aid in reconstructing landscapes and estimating paleodischarge by establishing boundaries on the climatic and tectonic history of continental sequences we present three methods for estimating ancient depositional gradients based on the interpreted mode of sediment transport for the range of particle sizes found on the beds of modern rivers or preserved in channel fills for sandy rivers with suspension as the dominant mode of sediment transport these methods take advantage of observations that can be directly obtained from preserved strata including measurements of paleo flow depth and grain size the first method relates river slope to shields number at bankfull flow the second method is similar to the first but allows for variation in shields number at bankfull flow with grain diameter the final method relies on criteria required for both suspended and bed material load sediment transport in the same system and is the most comprehensive and physically justified method we present each method and test them with modern river datasets to verify accuracy and help constrain uncertainty the first step to adapting them to ancient systems results indicate that all methods estimate slope within a factor of two these methods are potentially very powerful for interpreting sandy fluvial deposits because they can provide reasonably accurate quantitative estimates of paleoslope an elusive yet important environmental variable

ionospheric disturbances induced by a missile launched from north korea on 12 december 2012 1 ionospheric disturbances caused by a missile launched from north korea on 12 december 2012 were investigated by using the gps total electron content tec the spatial characteristic of the front edge of v shaped disturbances produced by missiles and rockets was first determined considering the launch direction and the height of estimated ionospheric points at which gps radio signal pierces the ionosphere the missile passed through the ionosphere at heights of 391 425 and 435 km at 0056 30 0057 00 and 0057 30 ut respectively the observed velocities of the missile were 2 8 and 3 2 km s at that time which was estimated from the traveling speed of the front edge of v shaped disturbances westward and eastward v shaped disturbances propagated at 1 8 2 6 km s the phase velocities of the westward and eastward v shaped disturbances were much faster than the speed of acoustic waves reported in previous studies suggesting that sources other than acoustic waves may have played an important role furthermore the plasma density depletion that is often observed following missile and rocket launches was not found this suggests that the depletion resulting from the missile s exhaust was not strong enough to be observed in the tec distribution in the topside ionosphere