experimental alluvial fans advances in understanding of fan dynamics and processes alluvial fans are depositional systems that develop because of a disparity between the upstream and downstream sediment transport capacity of a system usually at the base of mountain fronts as rivers emerge from the constrained mountain area onto the plain they are dynamic landforms that are prone to abrupt changes on a geomorphological decades to centuries time scale while also being long term deposition features that preserve sedimentary strata and are sensitive indictors of environmental change the complexity of interactions between catchment characteristics climate tectonics internal system feedbacks and environmental processes on field alluvial fans means that it is difficult to isolate individual variables in a field setting therefore the controlled conditions afforded by experimental models has provided a novel technique to overcome some of these complexities the use of experimental models of alluvial fans has a long history and these have been implemented over a range of different research areas utilising various experimental designs using this technique important advances have been made in determining the primary factors influencing fan slope understanding of avulsion dynamics identifying autogenic processes driving change on fan systems independent of any change in external conditions and the mechanics of flow and flood risk on alluvial fans to name a few however experiments cannot be carried out in isolation thus combining the findings from experimental alluvial fans with field research and numerical modelling is important and likewise using these techniques to inform experimental design if this can be achieved there is potential for future experimental developments to explore key alluvial fan issues such as stratigraphic preservation potential and simulating extra terrestrial fan systems

shoreline response to autogenic processes of sediment storage and release in the fluvial system 1 experimentally determined shoreline migration rates show high frequency autogenic variability superimposed on low frequency allogenic shoreline responses induced by eustatic base level change this variability persists even when the shoreline migration is averaged laterally indicating time variation in total sediment discharge reaching the shoreline the magnitude of autogenic variability in shoreline migration rate changes by roughly a factor of 3 depending on the shoreline migration direction it is strongest during transgression when the shoreline is on average migrating against the mean sediment flow and weakest during regression when the shoreline is migrating with the mean sediment flow we propose that this time variation is due to overall sediment storage and release in the fluvial system we use a one dimensional geometric model to model the autogenic signals observed in the experiment the model uses small periodic changes in the fluvial slope to represent the effects of storage and release of supplied sediment due to intrinsic variation in the transport efficiency of the fluvial system the periodic pulses of sediment discharge to the shoreline required in the model to explain the variations in shoreline migration can exceed by an order of magnitude the mean allogenic sediment discharge the slope variability required in the model to explain the autogenic shoreline signals is 1 4 of the mean slope this is well within the range of observed variability in depositional fluvial slopes we propose that at least part of this observed variability is real that is the long profile slope of a depositional river system may have an intrinsic elasticity of a few percent of its mean value even under steady forcing autogenic slope variation of this magnitude could readily produce parasequence scale deposits in the stratigraphic record

a salient region detection and pattern matching based algorithm for center detection of a partially covered tropical cyclone in a sar image spaceborne microwave synthetic aperture radar sar with its high spatial resolution large area coverage day night imaging capability and penetrating cloud capability has been used as an important tool for tropical cyclone monitoring the accuracy of locating tropical cyclone centers has a large impact on the accuracy of tropical cyclone track prediction usually the center of a tropical cyclone can be accurately located if the tropical cyclone eye is fully covered by a sar image in some cases due to the limited coverage of the sar only a part of a tropical cyclone can be imaged without the eye from a sar image processing point of view these facts make the automatic center location of tropical cyclones a challenging work this paper addresses the problem by proposing a semiautomatic center location method based on salient region detection and pattern matching a salient region detection algorithm is proposed in which the salient region map contains mainly the rain bands of a tropical cyclone in a sar image the pattern matching problem is transformed into an optimization problem solved by using the particle swarm optimization algorithm to search the best estimated center of a tropical cyclone to estimate the accuracy of the located center we compare the results with the noaa national hurricane center s best track data experiments demonstrate that the proposed method achieves good accuracy for locating the centers of tropical cyclones from sar images that do not contain a distinguishable eye signature

avulsions and the spatio temporal evolution of debris flow fans debris flows are water laden masses of sediment that move rapidly through channel networks and over alluvial fans where they can devastate people and property episodic shifts in the position of a debris flow channel termed avulsions are critical for debris flow fan evolution and for understanding flow hazards because avulsions distribute debris flow deposits through space and time however both the mechanisms of flow avulsion and their effects on the long term evolution of debris flow fans are poorly understood here we document and analyze the spatial and temporal patterns of debris flow activity obtained by repeat topographic analyses dendrogeomorphic and lichenometric reconstructions and cosmogenic radionuclide dating on 16 fans from japan usa switzerland france and kyrgyzstan where possible we analyze the observed spatio temporal patterns of debris flow activity in conjunction with high resolution topographic data to identify the main controls on avulsion we identify two main processes that control avulsions on debris flow fans operating over distinct time scales first during individual flows or flow surges deposition of sediment plugs locally blocks channels and forces subsequent flows to avulse into alternative flow paths plug deposition is a stochastic process but appears to depend in part on the sequence of flow volumes the geometry of the channel and the composition of the flows second over time scales of tens of events the average locus of debris flow deposition gradually shifts toward the topographically lower parts of a fan highlighting the importance of topographic compensation for fan evolution our documented debris flow avulsions often but not always follow a pattern of channel plugging backstepping of deposition toward the fan apex over one or more flows avulsion and establishment of a new active channel large flows can have contrasting impacts depending on whether or not they follow smaller flows that have deposited channel plugs these results suggest that avulsions and spatio temporal patterns of debris flow fan formation strongly depend on both the magnitude frequency distribution and the sequence of the flows feeding a fan while individual avulsions are generally abrupt and difficult to predict the presence of debris flow plugs and patterns of backstepping may be useful as indicators of impending avulsions over longer time scales the compensational tendency of flows to avulse into topographic depressions on the fan may also be used to identify sectors of the fan that are at risk of future inundation

can synthetic aperture radars be used to estimate hurricane force winds 1 we compare wind fields retrieved from a radarsat i synthetic aperture radar sar image acquired over hurricane ivan on september 10 2004 using the c band geophysical model functions cmod4 and its newest version cmod5 cmod4 has previously been shown to yield very good wind field estimates under low and moderate wind conditions wind directions obtained from streaks imaged by the sar that are well aligned with the mean surface wind direction are used to invert both algorithms to obtain estimates of the wind speed on scales of 1 km these estimates are compared with predictions from a high resolution tropical cyclone model as well as local in situ data it is found that the sar wind speeds using cmod5 agree reasonably well while those from cmod4 significantly under predict the measured wind speeds near the hurricane eye wall that reach values as high as 60 m s 1

the development of a laterally confined laboratory fan delta under sediment supply reduction abstract in previous fan delta experiments the effect of lateral confinement was generally ignored as these fans were usually unconfined with semiconical geometries however in gorge areas fan development is usually laterally confined by valley walls this study investigates autogenic processes of fan deltas in a laterally confined experimental tank the experiment is divided into three phases the sediment supply is held constant within each phase so the autogenic processes of the fan are separated from the allogenic forcings results indicate that laterally confined fan deltas have higher progradation and aggradation potential more regular channel braiding and more even transverse sedimentation than unconfined fans besides responses of fan deltas to sediment supply reduction are investigated in this research at the initiation of the second and third phases sediment feed rates are instantaneously reduced so that the allogenic forcings are predominant observations show that under sediment supply reduction channelization on fan deltas are more pronounced and durations of the fluvial cycles are longer the adjustment of fan morphology becomes slower as the self regulation capacity of the fan decreases with reduced sediment supply

comparison of typhoon centers from sar and ir images and those from best track data sets this paper compares the typhoon centers from the tropical cyclone best track bt data sets of three meteorological agencies and those from synthetic aperture radar sar and infrared ir images first we carried out algorithm comparison using two newly developed algorithms and one existing wavelet based algorithm which were used to extract typhoon eyes in six sar images and two ir images these case studies showed that the extracted eyes by the three algorithms are consistent with each other the differences among them are relatively small however there is a systematic difference between the extracted centers and the typhoon centers from the three bt data sets which were interpolated to the imaging times first we then compared the typhoon centers determined from 25 sar and 43 ir images with those from the three bt data sets to investigate the performance of the latter at the sea surface and at the cloud top respectively we found that the typhoon centers from the three bt data sets are generally closer to the locations extracted from the sar images showing sea surface imprints of the typhoons than those from the ir images showing cloud top structures of the typhoons

bifurcation dynamics and avulsion duration in meandering rivers by one dimensional and three dimensional models at river bifurcations water and sediment are divided over two branches the dynamics of the bifurcation determine the long term evolution centuries of the downstream branches potentially leading to avulsion but the dynamics are poorly understood the long term evolution can only be studied by one dimensional models because of computational costs for such models a relation describing the sediment division is necessary but only few relations are available and these remain poorly tested so far we study the division of sediment and the morphodynamics on a timescale of decades to centuries by idealized three dimensional modeling of bifurcations with upstream meanders and dominantly bed load transport an upstream meander favors one bifurcate with more sediment and the other with more water leading to destabilization the bifurcations commonly attain a highly asymmetrical division of discharge and sediment after a few decades to a few centuries depending on combinations of the relevant parameters although past work on avulsions focused on slope advantage we found that bifurcations can be quasibalanced by opposing factors such as a bifurcate connected to the inner bend with a downstream slope advantage nearly balanced bifurcations develop much slower than unbalanced bifurcations which explains the observed variation in avulsion duration in natural systems which branch becomes dominant and the timescale to attain model equilibrium are determined by the length of the downstream bifurcates the radius of the upstream bend a possible gradient advantage for one bifurcate and notably the width depth ratio the latter determines the character of the bars which may result in overdeepening and unstable bars the distance between the beginning of the upstream bend and the bifurcation determines the location of such bars and pools which may switch the dominant bifurcate in fact when the bifurcation is quasibalanced by opposing factors any minor disturbance or a different choice of roughness or sediment transport predictor may switch the dominant bifurcate the division of sediment is nearly the same as the division of flow discharge in most runs until the discharge division becomes very asymmetrical so that a bifurcate does not close off entirely this partly explains the sustained existence of residual channels and existence of anastomosing rivers and the potential for reoccupation of old channel courses we develop a new relation for sediment division at bifurcations in one dimensional models incorporating the effect of meandering the flow and sediment divisions predicted by two existing relations and the new relation for one dimensional models are in qualitative agreement with the three dimensional model these one dimensional relations are however of limited value for wider rivers because they lack the highly three dimensional bar dynamics that may switch the direction of bifurcation evolution the potential effects of bed sediment sorting bank erosion and levee formation on bifurcation stability and avulsion duration are discussed

effects of debris flow magnitude frequency distribution on avulsions and fan development shifts in the active channel on a debris flow fan termed avulsions pose a large threat because new channels can bypass mitigation measures and cause damage to settlements and infrastructure recent but limited field evidence suggests that avulsion processes and tendency may depend on the flow size distribution which is difficult to constrain in the field here we investigate how the flow magnitude frequency distribution and the associated flow magnitude sequences affect avulsion on debris flow fans we created three experimental fans with contrasting flow size distributions 1 a uniform distribution 2 a steep double pareto distribution with many flows around the mean and a limited number of large flows and 3 a shallow double pareto distribution with fewer flows around the mean and more abundant large flows the fan formed by uniform flows developed through regular sequences of stepwise channelization backstepping of deposition toward the fan apex and avulsion over multiple flows in contrast the wide range of sizes in the double pareto distributions led to distinct avulsion mechanisms and fan evolution here large flows could overtop channels creating levee breaches that could initiate avulsion immediately or in subsequent events moreover sequences of small to moderately sized flows could deposit channel plugs triggering avulsion in the next large flow this mechanism was most common on the fan formed by a steep double pareto distribution but was rare on the fan formed by a shallow double pareto distribution where large flows were more frequent we infer that some flow size distributions are more likely to cause avulsions especially those that produce abundant sequences of small flows followed by a large flow critically avulsions in our experiments could occur by either large single events or over multiple flows this observation has important implications for hazard assessment on debris flow fans suggesting that attention should be paid to flowhistory as well as flow size

quantifiable effectiveness of experimental scaling of river and delta morphodynamics and stratigraphy laboratory experiments to simulate landscapes and stratigraphy often suffer from scale effects because reducing length and time scales leads to different behaviour of water and sediment classically scaling proceeded from dimensional analysis of the equations of motion and sediment transport and minor concessions such as vertical length scale distortion led to acceptable results in the past decade many experiments were done that seriously violated these scaling rules but nevertheless produced significant and insightful results that resemble the real world in quantifiable ways here we focus on self formed fluvial channels and channel patterns in experiments the objectives of this paper are 1 to identify what aspects of scaling considerations are most important for experiments that simulate morphodynamics and stratigraphy of rivers and deltas 2 to establish a design strategy for experiments based on a combination of relaxed classical scale rules theory of bars and meanders and small scale experiments focussed at specific processes we present a number of small laboratory setups and protocols that we use to rapidly quantify erosional and depositional types of forms and dynamics that develop in the landscape experiments as a function of detailed properties such as effective material strength and to assess potential scale effects most importantly the width to depth ratio of channels determines the bar pattern and meandering tendency the strength of floodplain material determines these channel dimensions and theory predicts that laboratory rivers should have 1 5 times larger width to depth ratios for the same bar pattern we show how floodplain formation can be controlled by adding silt sized silicaflour bentonite medicago sativa alfalfa or partially hydrolyzed polyacrylamide a synthetic polymer to poorly sorted sediment the experiments demonstrate that there is a narrow range of conditions between no mobility of bed or banks and too much mobility the density of vegetation and the volume proportion of silt allow well controllable channel dimensions whereas the polymer proved difficult to control the theory detailed methods of quantification and experimental setups presented here show that the rivers and deltas created in the laboratory seem to behave as natural rivers when the experimental conditions adhere to the relaxed scaling rules identified herein and that required types of fluvio deltaic morphodynamics can be reproduced based on conditions and sediments selected on the basis of a series of small scale experiments

quantitative reconstruction of late holocene surface evolution on an alpine debris flow fan debris flow fans form a ubiquitous record of past debris flow activity in mountainous areas and may be useful for inferring past flow characteristics and consequent future hazard extracting information on past debris flows from fan records however requires an understanding of debris flow deposition and fan surface evolution field scale studies of these processes have been very limited in this paper we document the patterns and timing of debris flow deposition on the surface of the large and exceptionally active illgraben fan in southwestern switzerland we use terrain analysis radiocarbon dating of sediment fill in the illgraben catchment and cosmogenic 10be and 36cl exposure dating of debris flow deposits on the fan to constrain the temporal evolution of the sediment routing system in the catchment and on the fan during the past 3200 years we show that the fan surface preserves a set of debris flow lobes that were predominantly deposited after the occurrence of a large rock avalanche near the fan apex at about 3200 years ago this rock avalanche shifted the apex of the fan and impounded sediment within the illgraben catchment subsequent evolution of the fan surface has been governed by both lateral and radial shifts in the active depositional lobe revealed by the cosmogenic radionuclide dates and by cross cutting geometrical relationships on the fan surface this pattern of frequent avulsion and fan surface occupation provides field scale evidence of the type of large scale compensatory behavior observed in experimental sediment routing systems

stream power controls the braiding intensity of submarine channels similarly to rivers we use physical experiments to investigate the response of submarine braided channels driven by saline density currents to increasing inflow discharge and bed slope we find that similarly to braided rivers only a fraction of submarine braided networks have active sediment transport we then find similar response to imposed change between submarine and fluvial braided systems 1 both the active and total braiding intensities increase with increasing discharge and slope 2 the ratio of active braiding intensity to total braiding intensity is 0 5 in submarine braided systems regardless of discharge and slope and 3 the active braiding intensity scales linearly with dimensionless stream power thus braided submarine channels and braided rivers are similar in some important aspects of their behavior and responses to changes in stream power and bed slope in light of the scale independence of braided channel planform organization these results are likely to apply beyond experimental scales

autogenic erosional surfaces in fluvio deltaic stratigraphy from floods avulsions and backwater hydrodynamics erosional surfaces set the architecture of fluvio deltaic stratigraphy and they have classically been interpreted in terms of changes in boundary conditions such as climate tectonics and base level allogenic forces intrinsic dynamics of sedimentary systems autogenic dynamics can also create a rich stratigraphic architecture and a major knowledge gap exists in parsing the relative roles of autogenic versus allogenic processes emerging theoretical and experimental work suggests that backwater hydrodynamics play an important role in driving transient channel incision in river deltas even those experiencing net aggradation here we identify and quantify two autogenic mechanisms that produce broad erosional surfaces in fluvio deltaic stratigraphy namely floods and avulsions using a simple mass balance model for single threaded delta channel systems we show that flood induced scours begin near the shoreline and avulsion induced scours begin at the avulsion site and both propagate upstream over a distance that scales with the backwater length bed slope and bed grain size we also develop scaling relationships for the maximum scour depths arising from these mechanisms which are functions of characteristic flow depth and formative flood variability we test our theoretical predictions using a flume experiment of river delta evolution governed by persistent backwater hydrodynamics under constant relative sea level results indicate that autogenic dynamics of backwater mediated deltas under conditions of constant base level can result in stratigraphic surfaces and shoreline trajectories similar to those often interpreted to represent multiple sea level cycles our work provides a quantitative framework to decouple autogenic and allogenic controls on erosional surfaces preserved in fluvio deltaic stratigraphy

a hurricane morphology and sea surface wind vector estimation model based on c band cross polarization sar imagery over the last decades data from spaceborne synthetic aperture radar sar have been used in hurricane research however some issues remain when wind is at hurricane strength the wind speed retrievals from single polarization sar may have errors because the backscatter signal may experience saturation and become double valued by comparison wind direction retrievals from cross polarization sar are not possible until now in this paper we develop a 2 d model the symmetric hurricane estimates for wind shew model and combine it with the modified inflow angle model to detect hurricane morphology and estimate the wind vector field imaged by cross polarization sar by fitting shew to the sar derived hurricane wind speed we find the initial closest elliptical symmetrical wind speed fields hurricane center location major and minor axes the azimuthal orientation angle relative to the reference ellipse and maximum wind speed this set of hurricane morphology parameters along with the speed of hurricane motion are input to the inflow angle model modified with an ellipse shaped eye to derive the hurricane wind direction a total of 14 radarsat 2 scansar images are employed to tune the combined model two sar images acquired over hurricane arthur 2014 and hurricane earl 2010 are used to validate this model comparisons between the modeled surface wind vector and measurements from airborne stepped frequency microwave radiometer and dropwindsondes show excellent agreement the proposed method works well in areas with significant radar attenuation by precipitation

the hypanis valles delta the last highstand of a sea on early mars one of the most contentious hypotheses in the geological history of mars is whether the northern lowlands ever contained an oceanic water body arguably the best evidence for an ocean comes from the presence of sedimentary fans around mars dichotomy boundary which separates the northern lowlands from the southern highlands here we describe the palaeogeomorphology of the hypanis valles sediment fan the largest sediment fan complex reported on mars area 970 km2 this has an extensive catchment 4 6 x 105 km2 incorporating hypanis and nanedi valles that we show was active during the late noachian early hesperian period 3 7 ga the fan comprises a series of lobe shaped sediment bodies connected by multiple bifurcating flat topped ridges we interpret the latter as former fluvial channel belts now preserved in inverted relief meter scale thick sub horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins the inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of hypanis valles and descend 500 m in elevation the progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water assuming the elevation of the northern plains basin floor is stable we interpret the hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system at its location at the dichotomy boundary the hypanis valles fan system is topographically open to chryse planitia an extensive plain that opens in turn into the larger northern lowlands basin we conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least chryse planitia given the open topography it is plausible that the hypanis fan system records the existence last highstand and retreat of a large sea in chryse planitia and perhaps even an ocean that filled the northern plains of mars

contrasting morphodynamics in alluvial fans and fan deltas effect of the downstream boundary alluvial fans and fan deltas can in principle have exactly the same upstream conditions but fan deltas by definition have ponding water at their downstream boundary this ponding creates effects on the autogenic behaviour of fan deltas such as backwater adaptation mouth bars and backward sedimentation whereas alluvial fans may lack these effects hence the present authors hypothesize that morphodynamics on alluvial fans are determined primarily by upstream boundary conditions whereas morphodynamics on fan deltas are determined by both the upstream and the downstream boundary condition and changes therein to isolate the effects of the upstream and downstream boundaries five new alluvial fan experiments are compared with the details of three fan deltas published earlier that were formed under very similar and simple conditions similar to the fan deltas the alluvial fans build up by sheet flow whilst quasi regular periods of incision cause temporary channelized flow incision is followed by channel backfilling after which the fan returns to sheet flow the channelization and backfilling in alluvial fans is markedly less pronounced and more prone to autogenic disturbance than in fan deltas the difference is caused by morphodynamics at the downstream boundary in a fan delta the flow expansion of the channel causes deposition of all the sediment which forms a mouth bar and causes strong backfilling in an alluvial fan on the other hand the slope break at the fan perimeter causes some deposition but transport is not reduced to zero consequently the backfilling in alluvial fans is less pronounced than in fan deltas other published experiments support this trend removal of the mouth bar by a river leads to permanent channelization whilst pronounced mouth bar formation in highly channelized deltas promotes backward sedimentation the experimental results for this study predict that when alluvial fans prograde into lakes or deep rivers they transition to fan deltas with increasingly deeper channels and thicker backfill deposits

response of plio pleistocene alluvial systems to tectonically induced base level changes vera basin se spain tectonics are perceived to be a major control on the positioning and long term evolution of alluvial systems by increasing slope gradients through uplift and tilting or by changing local base level incision can be stimulated leading to a switch in the active area of sedimentation an example of such a sedimentary response to tectonic activity is provided by well exposed late pliocene early pleistocene alluvial sediments of the salmeron formation from the western margins of the vera basin se spain early stage palaeogeographic reconstructions demonstrate the occurrence of two alluvial fan bodies with distinct palaeocurrent and provenance signatures that suggest sediment source areas from the north sierra lisbona and south sierra de bedar of the study area late stage reconstructions suggest fan abandonment and indicate the occurrence of a braided river system sourced from the sierra de bedar in the south proximal parts of this braided river are incised by up to 100 m into underlying fan sediments sourced from the sierra de bedar in distal areas incision is negligible and the braided system forms a conformable sedimentary succession with underlying fan sediments sourced from the sierra lisbona the switch from alluvial fan to braided river sedimentation and the spatially variable patterns of incision into the alluvial fan bodies can be accounted for by a phase of deformation which affected the vera basin during the early pleistocene extensional faulting resulted in uplift and subsidence leading to localized tilting of depositional surfaces in distal areas of the southern fan increased stream power resulted in headward incision through mid and proximal fan areas once the system became fully trenched distal base level controls became effective in generating an enlarged catchment area and continuing incision the resultant changes dramatically increased both sediment and water discharge to the alluvial system and a switch to braided river sedimentation

a numerical modelling and experimental study of flow width dynamics on alluvial fans alluvial fans are dynamic landforms the evolution of which is controlled by both external environmental forcing climate tectonics and base level change and internal process form feedbacks the latter include changes in flow configuration between sheetflow and channelized flow states driven by aggradation and degradation which may in turn promote changes in sediment transport capacity recent numerical modelling indicates that such feedbacks may lead to dramatic and persistent fan entrenchment in the absence of external forcing however the parameterization of flow width within such models is untested to date and is subject to considerable uncertainty this paper presents results from an experimental study of flow width dynamics on an aggrading fan in which spatial and temporal patterns of fan inundation are monitored continuously using analysis of digital vertical photography observed flow widths are compared with results from a simple theoretical model developed for non equilibrium aggradational conditions results demonstrate that the theoretical model is capable of capturing the first order characteristics of width adjustment over the course of the experiment and indicate that flow width is a function of fan aggradation rate this illustrates that models of alluvial flow width derived for equilibrium conditions may have limited utility in non equilibrium situations despite their widespread use to date

an experimental investigation of autogenic behaviour during alluvial fan evolution the findings from a series of laboratory experiments designed to examine the role of autogenic process form interactions as controls on alluvial fan evolution are presented the experimental approach follows the similarity of processes concept and is therefore not scaled to a real world prototype the experiments were conducted in the university of exeter sediment research facility using a 3 3 m fixed bed experimental table with controlled sediment and water supply fed to the fan apex and evacuation of all sediment that passes the distal boundary the evolution of the fan was recorded using high resolution time lapse overhead photography to permit analysis of fan topography flow patterns channel migration and avulsion on the fan surface over the course of the experimental run the qualitative observations from three experimental scenarios are discussed and evaluated in the context of current understanding of alluvial fan evolution these demonstrate that in the absence of any change in the extrinsic variables there is an autogenic transition from sheetflow to channelised flow as the experimental fans evolve this is consistent with theory that predicts this change in response to a decline in aggradation rate through time

hurricane sea surface inflow angle and an observation based parametric model abstractthis study presents an analysis of near surface 10 m inflow angles using wind vector data from over 1600 quality controlled global positioning system dropwindsondes deployed by aircraft on 187 flights into 18 hurricanes the mean inflow angle in hurricanes is found to be 22 6 2 2 95 confidence composite analysis results indicate little dependence of storm relative axisymmetric inflow angle on local surface wind speed and a weak but statistically significant dependence on the radial distance from the storm center a small but statistically significant dependence of the axisymmetric inflow angle on storm intensity is also found especially well outside the eyewall by compositing observations according to radial and azimuthal location relative to storm motion direction significant inflow angle asymmetries are found to depend on storm motion speed although a large amount of unexplained variability remains generally the largest storm relative inflow angles 50 are found in the fas

quaternary sedimentology of the rose creek fan delta walker lake nevada usa and implications to fan delta facies models the 3 2 km long rose creek fan delta of west central nevada is prograding from an active rift margin into the 32 m deep walker lake a case study of the forms processes and facies of this fan delta reveals that the proximal and medial zones mainly are of sub aerial origin and the distal zone is of lacustrine origin pebbly to bouldery rock avalanche mounds 100 m thick facies a and muddy to bouldery debris flow levees 0 5 to 2 0 m thick facies b dominate the proximal zone whereas mostly matrix supported cobbly pebbly debris flow lobes 0 1 to 1 0 m thick facies c typify the medial zone surficial pebble lags and gully fills facies d are widespread in both zones but in exposures comprise only partings or lenticles between debris flow units the distal fan delta mainly consists of lakeshore to lake bottom tracts formed by extensive wave reworking of debris flow facies nearshore deposits include erosional cobbly boulder lag beaches facies e pebbly constructional beaches attached at headcuts or on barrier spits facies f pebbly upper shoreface facies g and sandy lower shoreface facies h tracts positioned lakeward of the beach and pebbly landward dipping foresets facies i and backshore pond sand and mud facies j present landward of the spits erosional lag beaches fringe the windward north side of the fan delta front attached constructional beaches characterize the central zone and southward elongating barrier spits typify the leeward south side extending from the zone of greatest projection of the fan delta into the lake shoreline facies asymmetry results from largely unidirectional longshore drift caused by high fetch to the north and minimal fetch to the south combined with the arcuate shape of the fan delta front the spits overlie a platform deposited below common wave base consisting of south east trending cones of pebbly gilbert foresets facies k and sandy toesets facies l typically slumped silt and mud facies m fringe both this platform and lower shoreface sand in deeper water this case demonstrates facies types and patterns that are inconsistent with the widely promoted fan delta facies model having a front consisting of an apron of radially directed gilbert foresets deposited where sub aerial flows enter the lake the rose creek fan delta front instead features a sharp contact between sub aerial and lakeshore facies formed where waves erode sort and redistribute heterogeneous debris flow sediment into the various shallow to deep lake facies gilbert foresets are present only in the lee of the fan delta where sediment moving by longshore drift reaches the brink of the spit front this facies scenario results from the infrequency of fan building events versus nearly constant wind induced waves a scenario that in contrast to the popular gilbert model probably is the norm for fan deltas the level of walker lake and thus the position of wave reworking on the rose creek fan delta fluctuated over a range of 157 m during the last 18 kyr producing complex interfingering between sub aerial and lakeshore facies across a 1700 m wide radial belt typifying a wave modified freestand lacustrine fan delta

experimental study on evolution of lacustrine shallow water delta abstract in the process of delta evolution the flow regime and sediment transport change with the development of topography flow is the dynamic factor of shaping topography while sediment scouring and silting is the direct cause of topography formation and they are constrained and influenced by topographic changes simultaneously in order to explore rules of water and sediment movement and topographic sedimentation of delta under microscale conditions we studied the phenomena rules and evolution mechanism of flow movement sediment transport particle sorting topographic sedimentation and flow path generation merger and recombination under microscale conditions from the perspective of physical experiment the influence of different external conditions on lacustrine shallow water delta evolution and the self organization of delta evolution are studied through comparative experiments under the condition of distinct sediment supplied rates or lake levels and repeatability experiments under the same conditions some rules of flow movement sediment transport and topographic sedimentation such as characteristics of each stage during the process of evolution of lacustrine shallow water delta the periodic change of flow regime and the prediction model the characteristics of sedimentary morphology under different conditions and the influence of stochastic factors on delta evolution are summarized the experiments suggest coupled linkage of interaction of water and sediment self organization of flow path evolution and the equilibrium tendency of delta structure under the action of coupling interaction of multiple factors of water sediment and topographic sedimentation

swiftness of biomorphodynamics in lilliput to giant sized rivers and deltas physical experiments of self formed river channels and floodplains with live vegetation are pathways for understanding that complement numerical modelling recent experiments succeeded in creating braided rivers and dynamic meandering systems with clastic and vegetated floodplains however application of the insights gained from such experiments to natural systems depends on understanding potential scale effects temporal and spatial here we combine review analysis and experiments to identify fundamental problems of biomorphological river pattern formation that are open for further research in experiments we first show by review and analysis that physics based linear bar theory predicts negligible spatial scale effects in bar and bend wavelength relative to channel width time scaling on the other hand remains problematic because it integrates multiple processes of sediment transport floodplain formation and bank failure affected by bank stratigraphy and riparian vegetation as a tentative solution we secondly present experimental methods to assess bank strength effects that can be used in the design of river pattern experiments the third issue is that riparian vegetation has often been represented in experiments by uniformly seeded sprouts of a single plant species whilst spectacularly different patterns are obtained with contrasting seeding protocols showing the need for other experimental procedures and alternative riparian species the main challenge for future experiments is better understanding of temporal scaling of biomorphodynamics

modeling alluvial landform change in the absence of external environmental forcing alluvial fan evolution and morphology are often considered to respond primarily to external forcing e g tectonics climate and base level change here we present a numerical model of alluvial fan evolution that shows that dramatic and persistent fan entrenchment may occur in the absence of such forcing this process is driven by positive autogenic feedbacks between flow width sediment transport and rate of fan aggradation entrenchment is initiated where sediment accommodation space limits continued fan growth our results highlight a need to rethink both the representation of fluvial width adjustment in landscape evolution models and the established framework for the interpretation of fluvial landforms as archives of environmental change

facies and depositional model of alluvial fan dominated by episodic flood events in arid conditions an example from the quaternary poplar fan north western china

balancing aggradation and progradation on a vegetated delta the importance of fluctuating discharge in depositional systems vegetation is an important component of constructional landscapes as plants enhance deposition and provide organic sediment that can increase aggradation rates to combat land loss we conducted two sets of laboratory experiments using alfalfa medicago sativa to determine the effects of plants on channel organization and large scale delta dynamics in the first set we found that rapid vegetation colonization enhanced deposition but inhibited channelization via increased form drag that reduced the shear stress available for sediment entrainment and transport a second set of experiments used discharge fluctuations between flood and base flow or interflood interfloods were critical for reworking the topset via channel incision and lateral migration to create channel relief and prevent rapid plant colonization these low flow periods also greatly reduced the topset slope in the absence of vegetation by removing topset sediment and delivering it to the shoreline floods decreased relief by filling channels with sediment resulting in periods of rapid progradation and enhanced aggradation over the topset surface which was amplified by vegetation the combination of discharge fluctuations and vegetation thus provided a balance of vertical aggradation and lateral progradation we conclude that plants can inhibit channelization in depositional systems and that discharge fluctuations encourage channel network organization to naturally balance against aggradation thus variations in discharge are an important aspect of understanding the ecomorphodynamics of aggrading surfaces and modeling vegetated deltaic systems and the combined influences of plants and discharge variations can act to balance vertical and lateral delta growth

three dimensional model of alluvial stratigraphy theory and applications abstract a three dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution proportion and connectedness of coarse grained channel belt deposits in alluvial strata as a function of channel belt width floodplain width bankfull channel depth channel belt and overbank sedimentation rates avulsion location and period compaction and tectonism tilting and faulting in this model a floodplain surface of variable width and length is occupied by a single channel belt changes in floodplain topography are produced by spatial and temporal variation of channel belt and floodplain deposition rates and by compaction and local or regional tectonism the location and timing of avulsions are determined by local changes in floodplain slope relative to channel b lt slope and by flood magnitude and frequency the diverted channel belt follows the locus of maximum floodplain slope at the end of each simulation architectural parameters are calculated including channel deposit proportion and connectedness and the dimensions of channel belt sandstone bodies three dimensional perspective diagrams mesh surfaces and two dimensional stratigraphic sections can be plotted to illustrate depositional surfaces time planes and the location and geometry of coarse grained channel belt deposits within finer grained overbank deposits the model predicts that channel belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross section orientation upstream from avulsion points sandstone bodies have low width thickness ratios because of aggradation in a fixed channel belt immediately downstream from avulsion points channel belts tend to be connected resulting in sandstone bodies with high width thickness ratios avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period such sequences may produce successions in which channel belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years down valley increases in aggradation rate or down valley decreases in floodplain slope for example associated with a rise in base level may result in an increase in channel belt proportion and connectedness because of high avulsion frequencies in down valley regions of the floodplain down valley decreases in aggradation rate as in alluvial fans foreland basins and during base level fall may result in high avulsion frequencies in up valley parts of the floodplain tectonic tilting and faulting locally increase avulsion probabilities and channel belts generally shift toward areas of maximum subsidence under certain conditions however depositional topography may cause channels to shift away from areas of maximum subsidence channel deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain but distribution clustering of channel belts may not be a reliable indicator of fault geometry or displacement models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified the three dimensional model presented here predicts many of the features of channel behavior observed in modern rivers but there is a pressing need for better models and adequate natural data to test them

autogenic avulsion channelization and backfilling dynamics of debris flow fans alluvial fans develop their semi conical shape by quasi cyclic avulsions of their geomorphologically active sector from a fixed fan apex on debris flow fans these quasi cyclic avulsions are poorly understood partly because physical scale experiments on the formation of fans have been limited largely to turbidite and fluvial fans and deltas in this study debris flow fans were experimentally created under constant extrinsic forcing and autogenic sequences of backfilling avulsion and channelization were observed backfilling avulsion and channelization were gradual processes that required multiple successive debris flow events debris flows avulsed along preferential flow paths given by the balance between steepest descent and flow inertia in the channelization phase debris flows became progressively longer and narrower because momentum increasingly focused on the flow front as flow narrowed resulting in longer run out and deeper channels backfilling commenced when debris flows reached their maximum possible length and channel depth as defined by channel slope and debris flow volume and composition after which they progressively shortened and widened until the entire channel was filled and avulsion was initiated the terminus of deposition moved upstream because the frontal lobe deposits of previous debris flows created a low gradient zone forcing deposition consequently the next debris flow was shorter which led to more in channel sedimentation causing more overbank flow in the next debris flow and resulting in reduced momentum to the flow front and shorter runout this topographic feedback is similar to the interaction between flow and mouth bars forcing backfilling and transitions from channelized to sheet flow in turbidite and fluvial fans and deltas debris flow avulsion cycles are governed by the same large scale topographic compensation that drives avulsion cycles on fluvial and turbidite fans although the detailed processes are unique to debris flow fans this novel result provides a basis for modelling of debris flow fans with applications in hazards and stratigraphy

isotopic evidence for climatic influence on alluvial fan development in death valley california at least three semiarid to arid cycles are recorded by delta sup 13 c values of organic matter in layers of rock varnishes on surfaces of hanaupah canyon and johnson canyon alluvial fans death valley california these isotopic paleoenvironmental signals are interpreted as indicating major periods of fan aggradation during relatively more humid periods and fan entrenchment during subsequent lengthy arid periods

observation of hurricane generated ocean swell refraction at the gulf stream north wall with the radarsat 1 synthetic aperture radar we analyze the refraction of long oceanic waves at the gulf stream s north wall off the florida coast as observed in imagery obtained from the radarsat 1 synthetic aperture radar sar during the passage of hurricane bonnie on august 25 1998 the wave spectra are derived from radarsat 1 sar images from both inside and outside the gulf stream from the image spectra we can determine both the long wave s dominant wavelength and its propagation direction with 180 spl deg ambiguity we find that the wavelength of hurricane generated ocean waves can exceed 200 m the calculated dominant wavelength from the sar image spectra agree very well with in situ measurements made by national oceanic and atmospheric administration national data buoy center buoys since the waves mainly propagate toward the continental shelf from the open ocean we can eliminate the wave propagation ambiguity we also discuss the velocity bunching mechanism we find that in this very long wave case the radarsat 1 sar wave spectra should not be appreciably affected by the azimuth falloff and we find that the ocean swell measurements can be considered reliable we observe that the oceanic long waves change their propagation directions as they leave the gulf stream current a wave current interaction model is used to simulate the wave refraction at the gulf stream boundary in addition the wave shoaling effect is discussed we find that wave refraction is the dominant mechanism at the gulf stream boundary for these very long ocean swells while wave reflection is not a dominant factor we extract 256 by 256 pixel full resolution subimages from the sar image on both sides of the gulf stream boundary and then derive the wave spectra the sar observed swell refraction angles at the gulf stream north wall agree reasonably well with those calculated by the wave current interaction model

geomorphic effects of a large flood on fluvial fans the response of 12 fluvial fans near sydney australia to a large storm between 2 and 4 february 1990 was determined by repeating previously surveyed longitudinal profiles and by undertaking detailed field observations of erosion and deposition peak rainfall intensities occurred on 3 and 4 february when between 173 and 193 8 mm were recorded return periods for 24 h duration peak rainfall ranged between 5 7 and 11 0 years on the annual maximum series at six stations within the study area and return periods for 48 h peak rainfall ranged between 13 5 and 29 4 years of the 12 fans seven were trenched and five untrenched the most significant geomorphic effects of the storm were recorded on the proximal region of the fans however fan response was highly variable with one fan exhibiting no detectable change three fans localized deposition two fans spatially disjunct erosion and deposition two fans channel avulsions and seven fans fanhead trench reworking some fans exhibited more than one type of response a four stage tentative cyclical model of fanhead development was constructed from the field data stage 1 refers to the episodic aggradation of the fanhead by localized deposition spatially disjunct erosion and deposition and or channel avulsions stage 2 represents the initiation of a fanhead trench when progressive aggradation locally exceeds a threshold slope leading to localized erosion this erosion initially creates one or more discontinuous flow aligned scour pools over time the scour pools widen deepen and extend both up and downfan stage 3 refers to the coalescence of discontinuous scour pools into a continuous trench by the removal of intervening log and boulder steps stage 4 represents the backfilling phase of the trench once it has been overwidened and or slope reduced aggradation then continues as for stage one

experimental delta formation in crater lakes and implications for interpretation of martian deltas 1 the morphology of delta deposits in crater lakes on mars is indicative of upstream e g flow discharge and sediment properties and downstream e g basin characteristics parameters from which the hydrological conditions at the time of formation can be inferred to investigate the influences of these parameters on delta morphology we experimentally created deltas in crater shaped basins by feeding a range of constant flow discharges over a feeder channel of various sand textures we reproduced three categorically different types of deltas including most of the types that have been identified on mars our most striking observation is that water level behavior itself a unique function of flow discharge basin size and hypsometry and basin floor permeability can explain most delta morphologies observed on mars stepped retrograding deltas formed during water level rise prograding deltas formed during water level still stand and during water level fall deltas were partially destroyed by erosion on mars numerous retrograding and prograding deltas were preserved most of them without indications of channel incisions or other fluvial modification we conclude that the main difference between a single foreset prograding delta and a multiple foreset retrograding delta is the behavior of the water level in the basin these simple delta morphologies cannot be reconciled with long duration hydrological activity because that would imply crater lake fluctuations due to inherent complex water level histories along with complex sediment delivery histories our experiments and numerical verifications demonstrate that such deltas preferentially form during one aqueous event which parsimoniously argues for short duration hydrological activity

investigating tropical cyclone climate feedbacks using the trmm microwave imager and the quick scatterometer 1 sea surface temperature sst and near surface winds from the tropical rainfall measuring mission trmm microwave imager tmi and the quick scatterometer quikscat are used to calculate globally integrated tropical cyclone induced sst anomalies and power dissipation pd we estimate tropical cyclone induced upper ocean cooling to be 35 higher than our previous estimates based on reanalyzed era40 and ncep surface data annually averaged global pd estimates from tmi are 5 1019 j for the years 1998 to 2006 roughly 30 greater than era40 pd for overlapping years quikscat pd is estimated to be 1 7 1020 j for the years 2000 to 2006 on the basis of these results we conclude that the cyclone induced cooling signal appears to be underrepresented in era40 and ncep reanalysis as postulated in recent observational and modeling studies furthermore we observe a strong positive relationship between pd and ocean surface cooling providing further evidence for the likelihood of cyclone induced climatic feedbacks these results support the hypothesis that tropical cyclones play an active role in the tropical surface ocean heat budget by cooling the tropical upper oceans through enhanced vertical mixing which likely represents a net warming beneath the oceanic mixed layer thus to the degree that vertical mixing is important for regulating the ocean s meridional overturning circulation and poleward heat transport tropical cyclones may be an important contributor to earth s climate system this further confirms the results of emanuel 2001 2002 and sriver and huber 2007b that possible future changes in integrated cyclone intensity associated with warmer sst may provide possible climatic feedbacks through enhanced vertical mixing and increased ocean heat transport thus buffering the tropics to increased temperatures while amplifying the warming at higher latitudes

coeval boudinage and folding of oblique single layers under coaxial plane strain layer rotation around the principal stretching axis x abstract we carried out scaled analogue modelling to show the influence of varying layer obliquity on the geometry of single layer folds and boudins which developed simultaneously under coaxial plane strain the initial angle z i between the competent layer and the shortening axis z was gradually changed by turning the layer around the principal stretching axis x although oblique layer rotation was similar fast like that of a corresponding passive plane each layer was crossing different strain fields shortening reduced shortening elongation resulting in coeval boudinage and f1 folding the latter with fold axes parallel to x a rise in z i led to increase of boudinage and decrease of f1 folding the amplitude of f1 folds increased with viscosity ratio between layer and matrix but was hardly affected by z i the arc and wavelength of f1 folds on the other hand increased if z i 45 in cases of low viscosity ratio between layer and matrix boudins were affected by f2 folds with axes subperpendicular to the layer both f1 and f2 folds show increasing interlimb angles at rising z i the structures of the present study are largely not cylindrical and require investigation in three dimensions they are frequent in high pressure low temperature metamorphic rocks of subduction zone settings and in salt walls

flume tank study of surface morphology and stratigraphy of a fan delta the morphodynamics of a river flood on a fan delta and its resultant stratigraphic and sedimentary signatures have been studied by means of a flume experiment under controlled boundary conditions the experiment revealed that deposition was dominant in flood periods when the channels were highly loaded with sediments in contrast erosion was dominant in periods of low flow mouth bars were formed when a subaqueous channel began to backfill the development of a mouth bar began with progradation in the down dip direction and proceeded by aggradation then retrogradation and finally transverse growth a channel bifurcated in multiple stages by sequentially forming mouth bars or by simultaneously forming arrays of mouth bars during the bifurcation the diffluent point moved upstream which resulted in channel migration and the development of a delta lobe flood events triggered fan delta front slide slump deposits

the tectonometamorphic evolution of high pressure low temperature metamorphic rocks of eastern crete greece constraints from microfabrics strain illite crystallinity and paleodifferential stress abstract analysis of strain paleodifferential stress illite crystallinity and microfabrics of quartz and calcite suggest that multiply alternating late oligocene early miocene n s convergence and n s extension caused significant vertical discontinuities in the grade of high pressure low temperature metamorphism of the phyllite quartzite unit pqu of eastern crete constrictional fabrics and parallelism of d2 stretching lineations and fold axes are attributed to enhanced slab pull forces at greater depth of subduction a major d3 extensional detachment is present in the upper part of the pqu where slates with lowest metamorphic grade diagenesis anchizone transition are resting on top of anchimetamorphic rocks the highest metamorphic grade anchi epizone transition has been determined for skythian rocks on top of pre alpine basement revived n s convergence d4 led to e w trending map scale folds and top to the s directed brittle thrusts there is a clear correlation between d2 related metamorphic grade finite strain differential stress and deformation mechanisms at the anchi epizone transition solution precipitation and dislocation creep of quartz and calcite caused maximum finite strains rxz up to 7 at high strain rates and moderate differential stresses 80 200 mpa at the diagenesis anchizone transition deformation was accommodated by cataclasis dislocation glide and solution precipitation creep resulting in relatively low finite strains rxz

folds with axes parallel to the extension direction an experimental study abstract experimental studies of single and multilayer folding have generally considered shortening of layers oriented perpendicular to the maximum extension direction x i e layers parallel to yz or in a more limited number of cases oblique layers still containing the intermediate y axis few experimental studies have considered the case where the extension direction x lies within the layer itself although in nature folds with axes parallel to x are quite commonly seen these folds have often been ascribed to passive rotation of fold axes during continued shear but it has been shown both theoretically and experimentally that active buckle folds can also develop with axes parallel to x single and multilayer analogue model experiments were performed on planar layers oriented initially perpendicular to the intermediate y axis and with the extension direction x lying within the layer itself all experiments were conducted in plane strain either in pure shear or simple shear paraffin waxes of different melting ranges were used as analogues for rocks with a power law rheology stress exponent around 2 3 with a viscosity ratio of ca 30 1 no measurable fold amplification was discernible for shortening of 36 or shear strain of 3 6 neither domed initial perturbations with circular sections parallel to the layer nor cylindrical perturbations elongate parallel to the initial stretching direction were significantly amplified only at much higher viscosity ratios ca 600 1 did active buckle folding develop this folding at high viscosity ratio was associated with flow of the matrix in the x direction around the layer developing a strong linear fabric parallel to x in the matrix immediately adjacent to the layer the development of this flow discontinuity between matrix and layer may be characteristic of active buckling of layers parallel to xz with fold axes parallel to x

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

autocyclic behaviour of fan deltas an analogue experimental study fan deltas are excellent recorders of fan building processes because of their high sedimentation rate particularly in tectonically active settings although previous research focuses mainly on allogenic controls there is clear evidence for autogenically produced storage and release of sediment by flume and numerical modelling that demands further definition of characteristics and significance of autogenically forced facies and stratigraphy analogue experiments were performed on fan deltas with constant extrinsic variables discharge sediment supply sea level and basin relief to demonstrate that fan delta evolution consists of prominent cyclic alternations of channellized flow and sheet flow the channellized flow is initiated by slope induced scouring and subsequent headward erosion to form a channel that connected with the valley while the removed sediment is deposited in a rapidly prograding delta lobe the resulting decrease in channel gradient causes a reduction in flow strength mouth bar formation flow bifurcation and progressive backfilling of the channel in the final stage of channel filling sheet flow coexists for a while with channellized flow semi confined flow although in cycle 1 this phase of semi confined flow was absent subsequent autocyclic incisions are very similar in morphology and gradient however they erode deeper into the delta plain and as a result take more time to backfill the duration of the semi confined flow increases with each subsequent cycle during the period of sheet flow the delta plain aggrades up to the critical gradient required for the initiation of autocyclic incision this critical gradient is dependent on the sediment transport capacity defined by the input conditions these autogenic cycles of erosion and aggradation confirm earlier findings that storage and release of sediment and associated slope variation play an important role in fan delta evolution the erosional surfaces produced by the autocyclic incisions are well preserved by the backfilling process in the deposits of the fan deltas these erosional surfaces can easily be misinterpreted as climate sea level or tectonically produced bounding surfaces

channel dynamics sediment transport and the slope of alluvial fans experimental study a b s t ra c t we present the results of an experimental study of alluvial fan sedimentation under conditions of constant inflow water discharge qw sediment supply qso and median grain size d the study was designed to complement and test a recently formulated model of alluvial fan sedimentation and to emphasize the interactions between and controls on flow channelization and equilibrium fan slope flow channelization and fan sedimentation were studied under conditions of nearly steady uniform aggradation steady conditions were achieved by imposing a steadily rising base level just in balance with the average sediment aggradation rate experimental inflows covered a wide range of conditions allowing examination of the effects of variations in qw q so and d in both bedload and suspension dominated environments experimental results were most consistent with an expanding flow channel model key experimental findings successfully and quantitatively predicted by the expanding flow theory include 1 straight to slightly concave radial profiles of bedload dominated fans 2 distinctly convexo concave profiles of suspension dominated fans 3 a strong inverse relationship between qw and fan slope 4 a strong but secondary relationship between q so and fan slope and 5 near independence of d and fan slope so long as transport stage is high and bedload transport dominant however potential scale effects in the experiments arose from reduced flow reynolds numbers and incorrect geometric scaling of channel widths no confident conclusions regarding the debate over the relative importance of sheetfloods and braided channel flows can be drawn from the experimental data extrapolation to field scale is best accomplished through appropriate application of the theoretical model herein confirmed against experimental data

experimental study of avulsion frequency and rate of deposition in existing models of alluvial architecture it is typically assumed that mean avulsion frequency is independent of sedimentation rate however if avulsion is driven by superelevation of a river bed above its surrounding flood plain one might expect avulsion rate to increase with sedimentation rate we have carried out a series of experiments with laboratory scale fluvial fans in which we measured the frequency of apical avulsions as a function of mean sedimentation rate on the fan avulsion frequency increased strongly with increasing sedimentation rate and then stabilized as mass flows began to influence deposition in the regime of increasing avulsion frequency the added volume of sediment needed to trigger an avulsion decreased with increasing sedimentation rate although our experimental results cannot simply be scaled up to natural rivers they suggest the possibility of coupling between avulsion frequency and sedimentation rate that would be strong enough to change qualitatively the results of existing models of alluvial architecture these models should be applied with caution until avulsion mechanics are better understood

palaeoflow reconstruction from fan delta morphology on mars abstract alluvial fans and deltas on mars record past hydrological conditions until now these conditions have been inferred from the morphology of the feeder channels and the deposits from images and digital terrain models dtms and from calculations of the bulk fluxes of water and sediment based on the dimensions of upstream channels neither method can distinguish between dilute river like flows and dense sediment laden flows however while the formation time scales for these two sediment transport modes differ by orders of magnitude the objective of this paper is to compare dtm data quantitatively with a morphological model to infer sediment transport mode and formative duration we present a quantitative morphological model for fan and delta formation that assumes as little as possible the model calculates the growth of a sedimentary body in a crater lake represented by a low gradient subaerial cone on top of a high gradient subaqueous cone the volume of the cone is constrained by the influx of sediment while the elevation of the break in slope that is the shoreline is constrained by the influx of water the water and sediment fluxes were calculated with physics based predictors based on the feeder channel small scale morphology such as crater wall irregularities concavity of the fan surface and channel avulsion is ignored the model produces alluvial fans stair stepped fan deltas and gilbert fan deltas as well as hitherto unidentified crater wall drapes the parameters that determine which morphology emerges are the supply of sediment and water to the basin the size of the basin and the duration of the flow a direct comparison between the cone model and hrsc dtm data for five deltas and an alluvial fan demonstrates that single event dilute flows of short duration days to years have created all of the deposits two gilbert fan deltas were formed in overspilling crater lakes from long low gradient upstream channels one alluvial fan was formed in a similar manner except that the damaged crater did not lead to ponding three stair stepped deltas were formed from short high gradient upstream channels that only partially filled the crater lakes

the pulse of calm fan deltas abstract at the heart of interpreting the history of earth surface evolution preserved in the rock record is distinguishing environmental allogenic forcing from internally generated autogenic noise allogenic deposits classically have been recognized by their cyclic nature which apparently results from periodic changes in base level sediment supply or tectonics autogenic deposits which are quite variable in their origin and scale are caused by the nonlinearity of sediment transport and might be expected to have a random or scale free fractal signature here we describe a robust mechanism that generates cyclic deposits by an autogenic process in experimental fan deltas sheet flow over the fan surface induces deposition and an increase in fluvial slope and curvature to a point where the surface geometry is susceptible to a channelization instability similar to channel initiation on hillslopes channelized flow results in incision and degrading of the fan surface to a lower slope releasing a

autogenic incision backfilling cycles and lobe formation during the growth of alluvial fans with supercritical distributaries autogenic cycles of channelization terminal deposit formation channel backfilling and channel abandonment have been observed in the formation of fans and deltas in subcritical flow these terminal deposits are characterized as mouth bars that lead to flow bifurcation backwater and eventual channel backfilling similar although less well characterized cycles also take place on supercritical subaerial and submarine fans this study investigates the hydraulics and morphodynamics of autogenic incision and backfilling cycles associated with supercritical distributive channel flow in alluvial fans the research questions of the study are i how are supercritical autogenic cycles on alluvial fans different from the subcritical cycles ii what are the hydraulic and sediment transport characteristics at the various stages of autogenic feedback cycles and iii what role do the cycles play in the overall fan evolution these questions are investigated in the laboratory and emphasis is placed on measuring the hydraulic and topographic evolution of the systems during the cycles the cycles arise quasi periodically under constant water and sediment discharge periods of sheet like flow are competent to move sediment but not competent enough to carry the full imposed load the net result is preferential deposition near the inlet resulting in fan steepening and an increase in flow competency with time at a sediment supply to capacity ratio of the sheet like flow is unstable to small erosional events near the inlet resulting in the collapse of the distributed flow to a strong channelized state during channelization a graded supercritical fr 1 channel develops and transports eroded and fed sediment up to and through the fan front extending the fan initiating a lobe shaped deposit and reducing the local slope the slopes defined by a sheet like flow with and channelized flow with set the maximum and minimum slopes on the fan respectively once formed graded channels act as bypass conduits linking the inlet with the terminal deposit on average deposits are up to six channel depths in thickness and have volumes approximately five times that of the excavated channel the main distinctive characteristics of the supercritical cycles relate to how the flow interacts with the terminal deposit at the channel to deposit transition the flow undergoes a weak hydraulic jump resulting in rapid sedimentation dechannelization and lateral expansion of the flow and deposition of any remaining sediment on top of the channel fill and floodplain this process often caps the channel as the deposit propagates up channel erasing memory of the excavated channel

forced regressive deposits of a deglaciation sequence example from the late quaternary succession in the lake saint jean basin quebec canada differentiating between forced regressive deposits from deglacial periods in high latitude domains and forced regressive deposits from the onset of glacial periods in low latitude domains is fundamental for the accurate interpretation of glacial cycles within the geological record and then for the reconstruction of palaeogeography and palaeo climate a forced regressive deglacial sequence is documented from the lake saint jean basin quebec canada in this area the late pleistocene to holocene sediments have recorded the laurentide ice sheet retreat accompanied by the invasion of marine waters laflamme gulf from ca 129 cal kyr bp subsequently fluviodeltaic and coastal prograding wedges were deposited they followed the base level fall due to glacio isostatic rebound this succession representing a transition from glacial to post glacial periods within a previously glaciated area was investigated through recent mapping preserved landforms facies analysis and new optical stimulated luminescence and radiocarbon dates three basin scale geological sections share a common lower part made of isolated ice contact fan deposits overlying bedrock throughout the entire basin ice contact fans are capped by glacimarine muds above fluvial and coastal prograding systems were deposited and evolved through four steps i deltaic systems progressively increased in width ii coastal influence on sedimentation increased iii hydrographic drainage systems became more organised and iv deltas graded from steep gilbert delta to low angle foresets mouth bar delta deposited during the base level fall from glacioisostatic rebound the complete succession has been designated as a single falling stage system tract referred to as a deglacial falling stage system tract it is representative of a deglaciation sequence in areas previously covered by ice during glacial periods i e medium to high latitude domains diagnostic criteria are provided to identify such a deglacial falling stage system tract in the geological record which may aid identification of previously unknown glacial cycles