sediment motion and velocity in a glacier fed stream current understanding of coarse sediment transport e g threshold for motion travel length and virtual velocity in mountain rivers is still quite limited and even less is known about glacial streams however the hydrological characteristics of these systems strong daily discharge fluctuations high water turbidity pose challenges to the use of tracers to monitor bed sediment dynamics as tagged clasts are usually located after bedload events when flow stage has receded e g by means of portable antennas in the case of passive integrated transponders pit the use of stationary antennas still scarcely in use worldwide to detect pit tagged particles has potential advantages in glacier fed streams if water discharge is monitored continuously a stationary antenna provides real time data on the actual discharge at the moment of tracer particles passage this study focuses on incipient motion and virtual velocity of bed particles measured by a stationary antennas system in a steep mountain channel saldur river drainage area 18 6 km2 italian alps where significant daily discharge fluctuations and bedload transport occur as a result of a nivo glacial regime four stationary antennas were installed 50 m apart in the study reach a total of 629 pit tagged clasts were inserted in the studied reach between 2011 and 2014 ranging in size from 35 mm to 580 mm with an overall recovery rate of around 44 critical discharge for sediment entrainment was obtained by detecting the movement of tracers placed immediately upstream of antennas virtual velocity was derived by knowing distances between the antennas and travel time of tracers results on initiation of motion show that the relationship between the size of transported tracers and the discharge measured at the time clasts were passing the stationary antenna is very weak the influence of antecedent flows on incipient motion was thus investigated by dividing the highest discharge recorded between each pit deployment and the subsequent entrainment by the actual critical discharge at the time of movement ratio qmax qc results show that approximately 50 of tracers moved at qmax qc 1 2 and that 73 of tracers moved at qmax qc 1 5 therefore about 30 of tracers had to previously experience a discharge substantially greater than the one that actually mobilized them also coarser particles moved at higher qmax qc ratios suggesting that higher antecedent flows may be needed to destabilize bed clustering results on the virtual velocity of the pit tagged clasts employed in the field show that the virtual velocity turned out to be highly variable ranging from 101 to 10 5 m min 1 and weakly related to either particle size or flow discharge however virtual velocity was well correlated with the highest flow discharge experienced by each tracer normalized by a percentile of the flow duration curve this evidence further stresses the importance of flow history on sediment entrainment and transport finally the pros and cons of the deployed monitoring technology are discussed

formal definition and dating of the gssp global stratotype section and point for the base of the holocene using the greenland ngrip ice core and selected auxiliary records the greenland ice core from northgrip ngrip contains a proxy climate record across the pleistocene holocene boundary of unprecedented clarity and resolution analysis of an array of physical and chemical parameters within the ice enables the base of the holocene as reflected in the first signs of climatic warming at the end of the younger dryas greenland stadial 1 cold phase to be located with a high degree of precision this climatic event is most clearly reflected in an abrupt shift in deuterium excess values accompanied by more gradual changes in d 18 o dust concentration a range of chemical species and annual layer thickness a timescale based on multi parameter annual layer counting provides an age of 11 700 calendar yr b2 k before ad 2000 for the base of the holocene with a maximum counting error of 99 yr a proposal that an archived core from this unique sequence should constitute the global stratotype section and point gssp for the base of the holocene series epoch quaternary system period has been ratified by the international union of geological sciences five auxiliary stratotypes for the pleistocene holocene boundary have also been recognised copyright 2008 john wiley sons ltd

late pleistocene holocene right slip rate and paleoseismology of the nayband fault western margin of the lut block iran the 290 km long nayband strike slip fault bounds the western margin of the lut block and cuts across a region thought to have been quiescent during the last few millennia cl 36 cosmic ray exposure cre and optically stimulated luminescence osl dating of cumulative geomorphic offsets are used to derive the long term slip rate the measured offsets at two sites along the fault range between 9 1 m and 195 15 m with ages from 6 8 0 6 ka to 100 ka yielding minimum and maximum bounds of late pleistocene and holocene slip rates of 1 08 and 2 45 mm yr 1 respectively this moderate slip rate of 1 8 0 7 mm yr 1 averaged over several earthquake cycles is compared to the paleoseismic record retrieved from the first trench excavated across the fault combining the paleoseismic evidence with 18 osl ages obtained from this trench site demonstrates the occurrence of at least four large m 7 earthquakes during the last 17 4 1 3 ka and of two older wearthquakes one before 23 ka and another before 70 5 ka the exposed sediment succession also indicates a significant gap at the end of mis 2 and the beginning of mis 1 the age of the most recent regional incision is accurately bracketed between 6 1 ka and 7 4 ka sediments from the last 7 ka contain evidence of the three younger earthquakes interestingly the penultimate and antepenultimate events occurred between 6 5 0 4 ka and 6 7 0 4 ka within a time interval lasting at most 1 ka whereas the most recent earthquake occurred within the last millennium such an irregular earthquake occurrence suggests the seismic behavior of the nayband fault is not strictly time dependent but possibly related to clustering from this and taking into account the occurrence of the most recent earthquake within the last 800 years the imminence of an earthquake along the nayband fault cannot be discarded although the most recent surface rupturing event seems to have occurred after ad 1200 this event went unnoticed in the historical records this provides a marked illustration of the incompleteness of the historical seismic catalogs in central iran challenging any assessment of regional seismic hazard without appropriate geologic and geochronological information large and infrequent earthquakes are characteristic of the seismic behavior of the slow slipping strike slip faults slicing central and eastern iran also the slip rates summed across central and eastern iran from the iran plateau up to the afghan lowlands appear in agreement with the most recent gps data

the evaluation of grain shear stress from experiments in a pebble bedded flume initial experiments were conducted in a flat bottomed flume with pebbles median diameter slightly below 20 mm with a view to test the validity of the methods which permit differentiation between shear stress due to grain resistance and that due to bedform resistance it is clearly confirmed that represents the total shear stress the method of laursen 1958 is appropriate for evaluation of grain shear stress in the case of pebbly beds indeed the ratio is close to 1 except when the dimensionless flow depth d d50 is less than 4 a close relationship exists between the grain shear stress and the shear calculated from friction velocities a second series of experiments was then carried out in the same flume after creating differences in bedform alternating riffles and pools the ratio produced by laursen s method represents on average 0 40 the relationship between these grain shear stresses and the shear stresses calculated from shear velocities is relatively good here as well and is similar in presentation to that established in the case of flat bed finally as confirmation of the adequacy of laursen s method under the same initial conditions of bottom slope and discharge the grain shear stress for an undulating bed is very close to the total shear stress of a flat bed

formal ratification of the quaternary system period and the pleistocene series epoch with a base at 2 58 ma in june 2009 the executive committee of the international union of geological sciences iugs formally ratified a proposal by the international commission on stratigraphy to lower the base of the quaternary system period to the global stratotype section and point gssp of the gelasian stage age at monte san nicola sicily italy the gelasian until then had been the uppermost stage of the pliocene series epoch the base of the gelasian corresponds to marine isotope stage 103 and has an astronomically tuned age of 2 58 ma a proposal that the base of the pleistocene series epoch be lowered to coincide with that of the quaternary the gelasian gssp was also accepted by the iugs executive committee the gssp at vrica calabria italy which had hitherto defined the basal boundary of both the quaternary and the pleistocene remains available as the base of the calabrian stage age now the second stage of the revised pleistocene in ratifying these proposals the iugs has acknowledged the distinctive qualities of the quaternary by reaffirming it as a full system period correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the pleistocene to that of the quaternary and fully respected the historical and widespread current usage of both the terms quaternary and pleistocene copyright 2009 john wiley sons ltd

what was the transport mode of large boulders in the campine plateau and the lower meuse valley during the mid pleistocene abstract the campine plateau in northeastern belgium a remnant of an alluvial fan deposited by the meuse river during the mid pleistocene is characterised by the presence of boulders with maximum dimensions of up to 2 m embedded in a gravel matrix these boulders originated in the ardennes region and are generally assumed to have been transported by ice rafting processes this paper investigates for the first time quantitatively the possibility of purely hydraulic transport of the boulders taking into account channel and flow characteristics in the boulder provenance area during the mid pleistocene empirical transport relations that describe incipient motion thresholds in nonuniform river beds as a function of the relative grain size or the ratio between the grain size of interest and the median grain size of the channel bed are applied in order to calculate critical water depths for transport of boulders of various sizes results indicate that hydraulic transport of boulders with intermediate diameters

collapse of polar ice sheets during the stage 11 interglacial the magnitude of sea level rise during marine isotope stage 11 about 400 000 years ago is shown to have been probably only 6 to 13 metres in contrast to some earlier estimates of up to 20 metres the ice sheets in greenland and west antarctica are known to be susceptible to climate warming and both are losing mass how the east antarctic ice sheet will respond to warming is less clear recent evidence from shoreline features in bermuda and the bahamas suggested that during marine isotope stage 11 a period of warming that occurred about 400 000 years ago the sea level was 20 metres higher than it is today which pointed to significant melting of the east antarctic ice sheet now an estimate that takes into account post glacial crustal subsidence of the shoreline sites during an anomalously long interglacial period puts the sea level during stage 11 at 6 13 metres higher than today that can be explained by the collapse of the greenland and west antarctic ice sheets with only a small contribution from the east antarctic ice sheet contentious observations of pleistocene shoreline features on the tectonically stable islands of bermuda and the bahamas have suggested that sea level about 400 000 years ago was more than 20 metres higher than it is today1 2 3 4 geochronologic and geomorphic evidence indicates that these features formed during interglacial marine isotope stage mis 11 an unusually long interval of warmth during the ice age1 2 3 4 previous work has advanced two divergent hypotheses for these shoreline features first significant melting of the east antarctic ice sheet in addition to the collapse of the west antarctic ice sheet and the greenland ice sheet1 2 3 or second emplacement by a mega tsunami during mis 11 ref 4 5 here we show that the elevations of these features are corrected downwards by 10 metres when we account for post glacial crustal subsidence of these sites over the course of the anomalously long interglacial on the basis of this correction we estimate that eustatic sea level rose to 6 13 m above the present day value in the second half of mis 11 this suggests that both the greenland ice sheet and the west antarctic ice sheet collapsed during the protracted warm period while changes in the volume of the east antarctic ice sheet were relatively minor thereby resolving the long standing controversy over the stability of the east antarctic ice sheet during mis 11

global boundary stratotype section and point gssp for the anthropocene series where and how to look for potential candidates abstract the anthropocene as a potential new unit of the international chronostratigraphic chart which serves as the basis of the geological time scale is assessed in terms of the stratigraphic markers and approximate boundary levels available to define the base of the unit the task of assessing and selecting potential global boundary stratotype section and point gssp candidate sections a required part of the process in seeking formalisation of the term is now being actively pursued here we review the suitability of different stratified palaeoenvironmental settings and facies as potential hosts for a candidate gssp and auxiliary sections and the relevant stratigraphical markers for correlation published examples are evaluated for their strengths and weaknesses in this respect a marked upturn in abundance of radioisotopes of 239pu or 14c approximately in 1952 and 1954 ce respectively broadly coincident with a downturn in 13c values is applicable across most environments principal palaeoenvironments examined include settings associated with accumulations of anthropogenic material marine anoxic basins coral reefs estuaries and deltas lakes at various latitudes peat bogs snow ice layers speleothems and trees together many of these geographically diverse palaeoenvironments offer annual subannual laminae that can be counted and independently dated radiometrically e g by 210pb examples of possible sections offer the possibility of correlation with annual seasonal resolution from among such examples a small number of potentially representative sites require the acquisition of more systematic and comprehensive datasets with correlation established between sections to allow selection of a candidate gssp and auxiliary stratotypes the assessments in this paper will help find the optimal locations for these sections

multi thread rivers in the polish carpathians occurrence decline and possibilities of restoration multi thread rivers are typified by the presence of interconnected channels separated by mid channel bars or the islands forming as a result of vegetation encroachment on mid channel bars high gradients of channels and valley floors high discharge variability relatively low content of fine cohesive sediments in the alluvial plain coarse bed material and high sediment supply are environmental conditions that favour the development of braided channel pattern under natural conditions of the holocene island braided channel pattern was typical of the rivers in the foreland of the tatra mountains and most likely also those draining the parts of the flysch outer carpathians underlain by thick bedded sandstones complexes these braided channels formed in the rivers flowing through mostly non cohesive floodplains and fed with coarse grained material exceeding competence of the rivers progressive deforestation of mountain catchments with the increasing area of cultivated hillslopes resulted in higher flood peaks and substantially increased sediment supply to river channels coupled with greater humidity of the final stages of the little ice age this led to the transformation of the island braided rivers into bar braided ones throughout the nineteenth century the braided channel morphology expanded downstream to the foreland river reaches in turn over the twentieth century the braided morphology nearly disappeared from polish carpathian rivers mostly as a result of their channelization the effectiveness of these works was however strengthened by a decrease in sediment supply to the rivers caused by land use changes and by the reduced availability of bed material for fluvial transport resulting from in channel gravel mining and partitioning of rivers with dam reservoirs environmental changes which have since occurred in the river catchments and disruption of the continuity of sediment transport by dams limit the feasibility of the restoration of braided channel pattern in polish carpathian rivers to their reaches supporting such morphology under natural conditions of the holocene

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

deciphering boulder mobility and erosion from cosmogenic nuclide exposure dating large boulders are prominent features in many geomorphic systems and are frequently targeted for cosmogenic exposure dating presently there are little data or theory predicting exposure age erosion rate and mobilization frequency of boulders in environments such as channels talus slopes or moraines here we explore the potential for cosmogenic isotope analysis to constrain the transport and erosion history of boulders through a series of numerical experiments we model the statistical evolution of nuclide concentrations around the surface of boulders stable boulders have distinctive radial distributions of surface concentration in comparison to those that are periodically mobile and this can be used to establish boulder stability mean nuclide accumulation rates around the surface of an eroding boulder increase when the radius is smaller than approximately 1 5 e folding lengths 1 2 m of neutron flux intensity whereupon nuclide accumulation on the underside of the boulder becomes non negligible 10 model results for cases of no cosmogenic inheritance and uniform erosion indicate the normalized standard deviation of nuclide surface concentration systematically decreases with increasing number of boulder mobilization events this may be used to constrain the minimum number of times a boulder has moved for up to approximately four events or distinguish between rarely and frequently mobilized boulders using non dimensional scaling relations between surface concentration statistics boulder size and time we propose methods to estimate the minimum age frequency of movement and erosion rate of mobile boulders with application to a range of geomorphic problems

a stratigraphical basis for the anthropocene recognition of intimate feedback mechanisms linking changes across the atmosphere biosphere geosphere and hydrosphere demonstrates the pervasive nature of humankind s influence perhaps to the point that we have fashioned a new geological epoch the anthropocene to what extent will these changes be evident as long lasting signatures in the geological record to establish the anthropocene as a formal chronostratigraphical unit it is necessary to consider a spectrum of indicators of anthropogenically induced environmental change and to determine how these show as stratigraphic signals that can be used to characterize an anthropocene unit and to recognize its base it is important to consider these signals against a context of holocene and earlier stratigraphic patterns here we review the parameters used by stratigraphers to identify chronostratigraphical units and how these could apply to the definition of the anthropocene the onset of the range of signatures is diachronous although many show maximum signatures which post date1945 leading to the suggestion that this date may be a suitable age for the start of the anthropocene

geomorphological records of extreme floods and their relationship to decadal scale climate change extreme rainfall and flood events in steep upland catchments leave geomorphological traces of their occurrence in the form of boulder berms debris cones and alluvial fans constraining the age of these features is critical to understanding i landscape evolution in response to past present and future climate changes and ii the magnitude frequency of extreme ungauged floods in small upland catchments this research focuses on the cambrian mountains of wales uk where lichenometric dating of geomorphological features and palaeohydrological reconstructions is combined with climatological data and documentary flood records our new data from wales highlight a distinct flood rich period between 1900 and 1960 similar to many other uk lichen dated records however this study sheds new light on the underlying climatic controls on upland flooding in small catchments although floods can occur in any season their timing is best explained by the summer north atlantic oscillation snao and shifts between negative wetter than average conditions with regular cyclonic flow and flooding and positive phases drier than average conditions with less frequent cyclonic flow and flooding which vary from individual summers to decadal and multidecadal periods recent wet summer weather flooding and boulder berm deposition in the uk 2007 2012 are related to a pronounced negative phase shift of the snao there is also increasing evidence that recent summer weather extremes in the mid latitudes may be related to arctic amplification and rapid sea ice loss if this is the case continuing and future climate change is likely to mean that i unusual weather patterns become more frequent and ii upland uk catchments will experience heightened flood risk and significant geomorphological changes

structure composition and bulk properties of upland stream gravels upland gravel bedded streams in the u k have received only scant attention from both hydrologists and sedimentologists but are worthy of further investigation the sedimentology of three small streams in teesdale in the pennines has been examined in detail grain size characteristics bedforms structure composition and packing characteristics of these deposits are described and compared where appropriate with published information it is argued that a fuller appreciation of gravel bed composition and morphology should eventually contribute to an improved understanding of sediment transport and deposition mechanisms and hence to improved accuracy in sediment transport and deposition estimates

surface displacements and source parameters of the 2003 bam iran earthquake from envisat advanced synthetic aperture radar imagery 1 the mw 6 6 26 december 2003 bam iran earthquake was one of the first earthquakes for which envisat advanced synthetic aperture radar asar data were available using interferograms and azimuth offsets from ascending and descending tracks we construct a three dimensional displacement field of the deformation due to the earthquake elastic dislocation modeling shows that the observed deformation pattern cannot be explained by slip on a single planar fault which significantly underestimates eastward and upward motions se of bam we find that the deformation pattern observed can be best explained by slip on two subparallel faults eighty five percent of moment release occurred on a previously unknown strike slip fault running into the center of bam with peak slip of over 2 m occurring at a depth of 5 km the remainder occurred as a combination of strike slip and thrusting motion on a southward extension of the previously mapped bam fault 5 km to the east

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

coseismic fault related folding during the south golbaf earthquake of november 20 1989 in southeast iran the south golbaf earthquake of november 20 1989 m s 5 7 m b 5 6 i vii in southeast iran was associated with coseismic surface faulting and folding surface faults 11 km west dipping and 8 km east dipping long with oblique reverse mechanisms developed on both sides of a small holocene playa apparently repeated coseismic fault related folding was responsible for the holocene 20 tilting of the playa deposits above the active fault tip at the ground surface this study provided the first evidence of earthquake folding of holocene playa deposits in iran

surface ruptures of the iranian earthquakes 1900 2014 insights for earthquake fault rupture hazards and empirical relationships abstract a database of iranian earthquakes during the instrumental period 1900 2014 is used to analyze geometric and kinematic aspects of the surface ruptures in different seismotectonic regions of the country majority of the ruptures have occurred along or associated with known geological or active faults thrust and strike slip faults show a maximum surface rupture length of 85 and 125 km respectively excluding the distributed displacements on bedding thrusts during the 1979 tabas earthquake which was summed up differently to 1 5 and 3 0 m maximum displacement on individual faults of thrust mechanism is 1 5 m while strike slip faults show a maximum horizontal displacement of 4 5 m surface rupture zone width of 3 km is observed in an strike slip event and a 4 km distance between the known active fault and the surface rupture of an event suggests that care should be taken in evaluation of setback zone for rupture hazards of some faults with complex geometry kinematics partitioning in space and time of ruptures in earthquakes requires a better understanding of exact kinematics of active fault zones while rerupturing of a fault segment in alternating events complicates the rupture history of the segment simultaneous rupture of several fault segments and sympathetic faulting should be taken into account for evaluation of earthquake hazard in specific regions with such possible seismotectonic setting secondary ruptures and fractures either in the presence or absence of primary surface ruptures develop via different mechanisms and complicate the surface deformations while surface ruptures are frequently associated with earthquakes in eastern iran these features are very rare in zagros and makran regions empirical relations are suggested among surface rupture length maximum displacement and moment magnitude for different earthquake fault mechanisms in iran which may be more compatible to the events within iran using these relations the maximum surface rupture length maximum surface displacement and the associated maximum credible earthquakes are suggested for different regions in iran the suggested values may also be used for estimation of earthquake magnitudes in paleoseismological studies

climate an exceptionally long interglacial ahead today9s comparatively warm climate has been the exception more than the rule during the last 500 000 years or more if recent warm periods or interglacials are a guide then we may soon slip into another glacial period but berger and loutre argue in their perspective that with or without human perturbations the current warm climate may last another 50 000 years the reason is a minimum in the eccentricity of earth9s orbit around the sun

reconstruction of a debris slide initiated flood in the southern kenai mountains alaska abstract a flood initiated by a slide of 84 million m 3 of rock and debris swept the forefeild of grewingk glacier during the fall of 1967 we used high water marks bedforms and scours to estimate flow competence and to reconstruct the flood an estimate of flow competence was obtained by graphing the intermediate clast axis of 34 boulders showing no evidence of transport by the flood against the length of sediment shadows and the depth of flood scour upstream from the boulders projection of the best fit lines of these relationships onto the grain size axis identified the largest clast that had no sediment shadow or associated scour and thus is itself assumed to have been transported the representative clast was 35 cm in diameter this in turn was utilized in a selective entrainment equation derived from a data set of grain sizes encompassing the critical clast size a shear stress of 1100 dyn cm 2 and a flow velocity of 2 4 m s 1 3 km downvalley from the slide were estimated from this equation

feedback between bed load transport and flow resistance in gravel and cobble bed rivers 1 to calculate bed load engineers often use flow resistance equations that provide estimates of bed shear stress in these equations on the basis of the estimate of the appropriate hydraulic radius associated with the bed only the bed roughness ks is commonly set as a constant whatever the bed load intensity however several studies have confirmed the existence of feedback mechanisms between flow resistance and bed load suggesting that a flow dependent bed roughness should be used therefore using a data set composed of 2282 flume and field experimental values this study investigated the importance of these feedback effects new flow resistance equations were proposed for three flow domains domain 1 corresponds to no bed load and a constant bed roughness ks d where d is a representative grain diameter whereas domain 3 corresponds to a high bed load transport rate over a flat bed with a constant bed roughness ks 2 6d between these two domains a transitional domain 2 was identified for which the bed roughness evolved from d to 2 6d with increasing flow conditions in this domain the darcy weisbach resistance coefficient f can be approximated using a constant for a given slope the results using this new flow resistance equation proved to be more accurate than those using equations obtained from simple fittings of logarithmic laws to mean values the data set indicates that distinguishing domains 2 and 3 is still relevant for bed load in particular the data indicate a slope dependence in domain 2 but not in domain 3 a bed load model based on the tractive force concept is proposed finally flow resistance and bed load equations were used together to calculate both shear stress and bed load from the flow discharge the slope and the grain diameter for each run of the data set efficiency tests indicate that new equations implicitly taking a feedback mechanism into account can reduce the error by a factor of 2 when compared to other equations currently in use showing that feedback between flow resistance and bed load can improve field bed load modeling

in situ acoustic measurements of marine gravel threshold and transport measurements of the nearbed turbulent current flow and the bedload transport of marine gravel have been made over three tidal cycles the turbulence in the bottom boundary layer was measured using two electromagnetic current meters and the gravel transport was measured using a passive acoustic system which monitored the interparticle collision noise of locally mobile material visual estimates of bedload were also obtained with an underwater tv camera the acoustic technique unlike a conventional bedload sampler has allowed estimates of transport to be obtained with a temporal resolution comparable with the turbulence data collected this has enabled a detailed comparison to be made between the turbulent flow and the sediment response to the instantaneous flow conditions the results of the study show that of the turbulent bursting events which contribute towards the reynolds stress only the sweeps and outward interactions play a significant role in the transport of coarse sedimentary material the measurements show that it is the instantaneous increases in the horizontal turbulent velocity fluctuations that generate excess shear stresses which drive the transport process

strong motion and teleseismic waveform inversions for the source process of the 2003 bam iran earthquake the bam earthquake m w 6 5 occurred on 26 december 2003 in southeastern iran causing a major disaster in the city of bam a remarkable vertical peak ground acceleration value of 988 cm s2 and two horizontal pulses were recorded inside the damaged city previous analyses showed that the earthquake was caused by a subsurface rupture on an unknown strike slip fault in this study we attempt to determine the precise fault location and source process of the 2003 bam earthquake by performing a multiple time window linear waveform inversion of teleseismic and strong motion data both individually and jointly we examined the general features of the fault location and the source process by analyzing the teleseismic displacement waveforms and determined the precise features and fault geometry by inverting the three components of strong motion velocity records the final estimate of the source process of the 2003 bam earthquake was determined by joint inversion of the datasets our results show that a single fault model characterized by the appropriate location of the hypocenter rake angle variations and the rayleigh like speed of the rupture front can satisfactorily explain the three components of the strong motion records at bam station

theoretical development on the effects of changing flow hydraulics on incipient bed load motion 1 several decades of flume and field measurements have indicated that in rough turbulent flows the critical shields stress increases with increasing slope and associated decreasing relative depth this result contradicts the usual consideration of a decreased critical shields value on very steep slopes because of increased gravitational effects however recent studies have demonstrated that these experimental results could be reproduced with a force balance model if the classical logarithmic velocity profile was replaced with a velocity profile that was more compatible with available velocity measurements over gravel beds these measurements indicate the existence of a roughness layer that is a zone of almost constant velocity close to the bed whose properties mean velocity and turbulence depended on the flow s relative depth unfortunately velocity profile measurements for low relative depth associated with steep slopes are scarce and it is still difficult to include such flow properties in a force balance model flow resistance data on the basis of depth average velocity measurements are very common and cover a wide range of slopes and relative depths in this paper these data are used to fit a velocity profile including a roughness layer when used in a force balance model for incipient motion it adequately reproduced a data set composed of 270 critical shields values measured in a flume with near uniform sediments the relevance of this research to field problems is discussed using a data set composed of 92 critical shields stresses obtained from field measurements finally a model is proposed for field applications taking into account the slope effect

late quaternary active faulting and landscape evolution in relation to the gowk fault in the south golbaf basin s e iran abstract we present ten infra red stimulated luminescence irsl ages of feldspar grains within lake bed sediments and alluvial fan gravels displaced by the gowk fault se iran our results show that lake deposition in the south golbaf basin was ongoing from at least 13 5 ka the deepest exposed sediments until the mid holocene furthermore the south golbaf palaeo lake is likely to have spilled into the neighbouring golbaf basin at 6 3 0 2 ka this event led to a widespread incision of the lake bed and neighbouring alluvial fan surfaces as the drainage systems adjusted to the new base level our constraint on the age of the south golbaf palaeolake combined with measurements of 30 5 m of right lateral displacement of stream channels incised into the lake beds yields a slip rate of 3 8 5 7 mm yr the deposition of alluvial fans around the margins of the south golbaf depression appears to have largely ended by 12 9 0 7 ka right lateral displacements of up to 60 m are observed in streams cut into the fan surfaces yielding a second slip rate estimate of 4 4 4 9 mm yr much of the widespread incision of the 12 9 ka fan surfaces does not appear to have taken place until 6 ka later when overtopping of the south golbaf palaeolake and the adjustment of drainage to a lower base level promoted widespread drainage incision

holocene slip rate on the gowk strike slip fault and implications for the distribution of tectonic strain in eastern iran we provide the first quantitative estimate of the holocene slip rate on the gowk strike slip fault in eastern iran the main active strand of the fault cuts lakebed sediments within the south golbaf pull apart basin numerous channels incised into the palaeolake surface are displaced right laterally by 30 5 m at the fault radiocarbon dating of two terrestrial wood fragments constrains the lake desiccation at a maximum of 7 9 0 1 cal ka bp from which we estimate a minimum slip rate for the gowk fault of 3 8 0 7 mm yr22121 this estimate indicates that the gowk fault is one of the most important structures in the accommodation of regional tectonic strain in eastern iran the gowk fault has generated five destructive earthquakes in the past 30 yr at a minimum rate of 3 8 0 7 mm yr22121 the average interval between earthquakes assuming that the fault typically fails in events involving 223c3 m of slip will be 6602013960 yr the southern 223c90 km of the gowk fault the sarvestan segment has no record of historical earthquakes and constitutes a considerable remaining hazard in this region our estimated rate is consistent with geodetic measurements of deformation across the same area and hence suggests that the slip rate on the gowk fault has been constant since at least 223c8 ka ago determining whether or not holocene and late quaternary variations in slip rate occur in general across eastern iran requires similar quantitative studies of fault slip rate across the major faults of eastern iran

the 2003 december 26 bam earthquake iran mw 6 6 aftershock sequence summary from 2003 december 29 to 2004 january 30 a dense seismological network of 23 stations was installed in the epicentral area of the 2003 december 26 bam earthquake to study the aftershock seismicity we select the 331 earthquakes recorded at a minimum of 10 stations with rms less than 0 1 s and uncertainties less than 1 km to infer the precise geometry of the seismicity in the fault region we also process the data with the double difference technique to confirm the results the aftershock cluster is 25 km long trends north south and is located 5 km west of the bam baravat escarpment exactly beneath the observed surface breaks at depth aftershocks are concentrated between 6 and 20 km beneath the upper layer of relatively low velocity that experienced the maximum slip and they dip slightly westward the southernmost part of the aftershock cluster is narrow and defines the rupture zone that is likely the bam baravat fault at depth however it is unlikely that it is connected at surface to the bam baravat escarpment but more likely to the co seismic ruptures south of bam on the contrary the distribution of the northernmost aftershocks spread into a more complex pattern which is consistent with a northward propagation of the rupture along the fault plane the focal mechanisms are consistent with right lateral strike slip faulting on n s trending faults parallel to the bam baravat escarpment

carbon isotope constraints on the deglacial co2 rise from ice cores the stable carbon isotope ratio of atmospheric co2 13catm is a key parameter in deciphering past carbon cycle changes here we present 13catm data for the past 24 000 years derived from three independent records from two antarctic ice cores we conclude that a pronounced 0 3 per mil decrease in 13catm during the early deglaciation can be best explained by upwelling of old carbon enriched waters in the southern ocean later in the deglaciation regrowth of the terrestrial biosphere changes in sea surface temperature and ocean circulation governed the 13catm evolution during the last glacial maximum 13catm and atmospheric co2 concentration were essentially constant which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then

changes in natural lead copper zinc and cadmium concentrations in central greenland ice from 8250 to 149 100 years ago their association with climatic changes and resultant variations of dominant source contributions abstract we present here the first reliable time series of pb cu zn and cd in greenland ice for the last climatic cycle they were obtained by analysing various sections of the 3028 8 m grip deep ice core drilled at summit central greenland our results show that climatic changes have led to large variations in the concentrations of natural pb cu zn and cd in the high latitude troposphere of the northern hemisphere between the interglacial and glacial periods concentrations have varied by factors of 320 for pb 100 for cu 36 for zn and 13 for cd based on a good correlation between each heavy metal and al pb and cu are found to have mainly originated from soil and rock dust for both glacial and interglacial periods on the other hand continental biogenic emissions were the main source of cd and to a lesser extent zn in the arctic troposphere during the warm eemian and the pre boreal to holocene transition whereas wind blown dust was the predominant source for these two metals during the cold glacial climatic stages this characteristic change of relative cd and zn contributions from different sources in contrast to that for pb and cu is well documented in the ice from the last deglaciation period 15 000 to 8250 yrs ago after the younger dryas event ended a remarkable increase of cd al and zn al ratios occurred from 13 000 to 9300 yrs ago which is consistent with the progressive expansion of vegetation following the retreat of the north american and north eurasian ice sheets the subsequent decrease of these ratios to holocene values can be explained by the stabilization of atmospheric circulation in the northern high latitude regions which became similar to that for the holocene due to further reduction of the laurentide ice sheet finally the observed variations of the metal al ratios suggest changes in the soil and rock dust source regions in parallel with climatic changes which have altered the mean composition of the crustal particles transported to the arctic

bedload dynamics and associated snowmelt influence in mountainous and semiarid alluvial rivers abstract the influence of snowmelt in semiarid alluvial rivers is determined by the river bed configuration and erosion processes moreover the large amount of available sediment in the floodplains of these rivers limits traditional bedload sampling methodologies and suggests the use of large control volumes and long term studies to understand erosive dynamics in this study bedload monitoring in a large control volume 0 2 hm3 from 2004 to 2010 was used to study erosive processes of the guadalfeo river a semiarid alluvial river in southeastern spain with high mountain influences and a hydrological regime conditioned by snow dynamics the methodological approach to testing the performance of different transport models included characterization of the forcing agents precipitation and snowmelt events hydraulic configuration of the river determination of the river bed material surface and substrate and one off measurements for particular events the results indicate a sediment volume effective runoff relationship that is consistent with the existence of steep channels with a flashy runoff regime although the existence of an armored layer derived from snowmelt events greatly controls the transport dynamics with equivalent fractions of cobble gravel and sand in the measured bedload this apparent predominance of near equal mobility was confirmed by the calibrated hiding function exponent x 0 94 0 97 the thresholds for entrainment and transport efficiency are similar to those observed for mountain rivers that exhibit torrential flow although notable differences can be observed in the dynamics of the processes the strong performance of the original meyer peter and muller model with c 8 is shown to estimate the total transported volume associated with intense events when the variability of d50 is included in the analysis however this model does not sufficiently capture transport because of moderate events rain or snowmelt and thus underestimates bedload on medium and long timescales the calibrated model of parker klingeman adequately represents erosive dynamics with r50 values between 0 03 and 0 041 for moderate and intense events respectively and a flow threshold of 14 2 m3 s 1 that separates these two situations nevertheless these models based on hiding functions present greater dispersion if the variability of diameters related to cobbles and pebbles is considered for such cases the wilcock and crowe model performed better for both intense and moderate events the latter is important in the study area where snowmelt pulses occasionally exceed the critical flow and break the surface layer with significant sediment contributions these processes differentiate the transport dynamics from other studies and are distinctive characteristics that are more closely related to mountainous influences in semiarid environments where pulses of intense snowmelt are common despite its limitations the proposed methodology based on a large check dam has proven to be adequate and representative for assessment of erosion processes

episodic folding inferred from syntectonic carbonate sedimentation the santaren anticline bahamas foreland abstract sedimentation coeval with growth of the santaren anticline provides an excellent opportunity to study the relationships between sedimentation and anticline uplift through time the santaren anticline is a kilometre scale nw se trending fold offshore of cuba in the bahamas foreland of the cuban fold and thrust belt the growth strata associated with this anticline consist of a thick package of carbonate sediments that were deposited without major interruptions from neogene and perhaps before to present day the excellent seismic resolution and age control of a number of seismic horizons within the growth strata allowed us to define 25 growth beds each of them representing between 0 1 and 3 2 ma an analysis of the thickness of these beds allowed us to determine accurate quantitative values of cumulative decompacted thickness and crestal structural relief at the time of their deposition in addition for the same periods sedimentation and fold uplift rates were calculated moreover some information on relationships between sedimentation and fold uplift rates was inferred from the growth stratal geometry growth beds that overlap the fold crest and thin over it indicate that sedimentation rates outpaced fold growth rates during their deposition some overlapping beds have constant thickness indicating that no fold uplift occurred during their sedimentation the rest of the growth beds exhibit onlap offlap geometries that do not indicate a unique sedimentation fold uplift rate relationship only in those cases in which the geometry of the underlying bed at the end of its deposition is known is it possible to infer a specific sedimentation fold uplift rate relationship as a result of this analysis we have been able to 1 illustrate that the geometry of the growth strata associated with the santaren anticline results from competition between sedimentation and tectonic fold uplift 2 document the episodic and non steady nature of fold growth and 3 show that short term rates at the scale of hundreds of thousands years provide much insight into the interplay between sedimentation and tectonic fold uplift that control the growth stratal patterns

critical conditions for particle motion in coarse bed materials of nonuniform size distribution initiation of particle motion in a bed material of nonuniform size distribution may be quantified by qci qcr di dr b where qci is the critical unit discharge at which particle size di enters motion qcr is the critical condition for a reference size dr unaffected by the hiding exposure effects associated with nonuniform size distributions i and r refer to percentiles of the distribution and b varies from 0 equal mobility in entrainment of all particle sizes to 1 5 2 5 full size selective transport currently there is no generally accepted method for predicting the value of b flume and field data are therefore combined to investigate the above relationship thirty seven sets of flume data quantify the relationship between critical unit discharge and particle size for bed materials with uniform size distributions used here to approximate full size selective transport field data quantify the relationship for bed materials of nonuniform size distribution at 24 sites with b ranging from 0 15 to 1 3 intersection of the two relationships clearly demonstrates the hiding exposure effect in some but not all cases dr is close to the median size d50 the exponent has two clusters of values b 1 for sites subject to episodic rain fed floods and data collected by bedload pit trap and tracers and b 1 sites with relatively infrequent bedload transport where particle embedding and consolidation could reduce the mobility of coarser particles and for b 0 7 a looser bed structure with frequent transport events allowing hiding exposure and size selection effects to achieve their balance as yet there is no firm evidence for such a dependency on bed structure but variations in b could potentially be caused by factors outside those determining equal mobility or size selection but appearing to affect b in the same way

initial motion and pivoting characteristics of sand particles in uniform and heterogeneous beds experiments and modelling experiments are described in which the threshold conditions for sediment entrainment are measured for uniform and mixed sand beds beneath both steady and combined steady oscillatory flows derived critical shear stresses are compared with the mixed bed entrainment model of wiberg smith 1987 as predicted by the model coarser grains within a sand mixture are entrained at lower bed shear stresses than progressively finer grains entrainment occurs generally at lower shear stresses than predicted by the model especially under unidirectional flows this may be the result of grains resting in unusually unstable positions during the experiments because the beds are unworked at the start of the experiments the model of wiberg and smith predicts threshold conditions more accurately for the mixed beds if the bed pivoting angle is correctly defined the pivoting angles of the beds used here are measured using a new technique designed specifically for comparison with the threshold data the measured angles repeat the finding that the coarse grains are more mobile than the finer fractions of a mixture the results are poorly described by the pivoting angle model presented by wiberg smith 1987 and are better represented by a model of the form d di d50 after li komar 1986 where and are empirical constants the threshold model is found to be more effective using the improved pivoting relationship the entrainment of grains is found to be easier beneath unidirectional flows than combined flows in accordance with previous authors findings a suggestion that this result is caused by a change in the erosion mechanism beneath wave flows is made wave boundary layers may act as an extended laminar sublayer over bed grains and reduce the erosive efficiency of the overlying current flow the results of the experiment have implications for the natural sorting mechanisms of sediment beds being deposited in near threshold flows

flow hydraulics and geomorphic effects of glacial lake outburst floods in the mount everest region nepal glacial lake outburst floods glofs on 3 september 1977 and 4 august 1985 dramatically modified channels and valleys in the mount everest region of nepal by eroding transporting and depositing large quantities of sediment for tens of kilometres along the flood routes the glof discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff glacier meltwater and monsoonal precipitation referred to as seasonal high flow floods shffs specific stream power values ranged from as low as 1900 w m 2 in wide low gradient valley segments to as high as 51 700 w m 2 in narrow high gradient valley segments bounded by bedrock along the upper 16 km of the glof routes the reach averaged specific stream power of the glofs was 3 2 to 8 0 times greater than the reach averaged specific stream power of the shffs the greatest geomorphic change occurred along the upper 10 to 16 km of the glof routes where the ratio between the glof specific stream power and the shff specific stream power was the greatest there was an abundant supply of sediment and channel valley boundaries consisted primarily of unconsolidated sediment below 11 to 16 km from the source area the geomorphic effects of the glofs were reduced because of the lower specific stream power ratio between the glofs and shffs more resistant bedrock flow boundaries reduced sediment supply and the occurrence of past glofs copyright 2003 john wiley sons ltd

an experimental investigation of the effect of bedslope and grain pivot angle on the threshold of marine gravel transport abstract a theoretical model developed by dyer 1986 for the effect of bedslope on bed shear stress for transport threshold crit under unidirectional flows is tested in a series of laboratory experiments data are presented from 230 laboratory threshold experiments for 1 cm glass spheres with two situation of grain pivot angle on bedslopes ranging from 10 to 15 the experimental results support the dyer model and indicate that for rhombohedral bed packing it can be developed to include the effect of grain pivot angle at threshold

patterns of historical earthquake rupture in the iranian plateau the iranian plateau accommodates the 35 mrn yr convergence rate be tween the eurasian and arabian plates by strike slip and reverse faults with relatively low slip rates in a zone 1000 km across although these faults have only locally been the subject of paleoseismological studies a rich historical and archeological record spans several thousand years long enough to establish recurrence intervals of 1000 to 5000 yr on individual fault segments several clusters of earthquakes provide evidence of interaction among reverse and strike slip faults probably due to adjacent faults being loaded by individual earthquakes the dasht e bayaz sequence of 1936 to 1997 includes earthquakes on left lateral right lateral and reverse faults the neyshabur sequence of four earthquakes between 1209 and 1405 respected the seg ment boundary between the neyshabur and binalud reverse fault systems the two pairs of earthquakes may have ruptured different faults in each segment similar to the 1971 and 1994 san fernando california earthquakes the 1978 tabas reverse fault earthquake was preceded by the 1968 ferdows earthquake part of the dasht e bayaz sequence the north tabriz fault system ruptured from southeast to north west in three earthquakes from 1721 to 1786 a previous cluster may have struck this region in 855 to 958 the mosha fault north of tehran ruptured in three earthquakes in 958 1665 and 1830 five large earthquakes struck the tehran region from 743 to 1177 but only two that large have struck the area since 1177 other earthquakes occurred in pairs in the talesh mountains near the caspian sea 1863 1896 the iran turkey border 1840 1843 and the nayband gowk fault system both 1981 other historical events did not occur as parts of sequences the historic seismic moment release in iran accounts for only a small part of the plate convergence rate which may be due to aseismic slip or to the iranian historical record long as it is being too short to sample long term deformation across the plateau no historic earthquakes of m 8 have struck iran however several long straight strike slip faults doruneh west neh east neh and nayband have not sustained large historical earthquakes raising the possibility that these long faults could produce earthquakes of m 8 thereby removing at least part of the apparent slip deficit an increased understanding of iran s seismic hazard could be obtained by an extensive paleoseismology program and space geodetic arrays supplementing the abundant historical and archaeological record

atmospheric carbon dioxide concentration across the mid pleistocene transition the dominant period of pleistocene glacial cycles changed during the mid pleistocene from 40 000 years to 100 000 years for as yet unknown reasons here we present a 2 1 million year record of sea surface partial pressure of co2 pco2 based on boron isotopes in planktic foraminifer shells which suggests that the atmospheric partial pressure of co2 pco2 was relatively stable before the mid pleistocene climate transition glacial pco2 was approximately 31 microatmospheres higher before the transition more than 1 million years ago but interglacial pco2 was similar to that of late pleistocene interglacial cycles 450 000 years ago these estimates are consistent with a close linkage between atmospheric co2 concentration and global climate but the lack of a gradual decrease in interglacial pco2 does not support the suggestion that a long term drawdown of atmospheric co2 was the main cause of the climate transition

present day kinematics and fault slip rates in eastern iran derived from 11 years of gps data we analyze new gps data spanning 11 years at 92 stations in eastern iran we use these data to analyze the present day kinematics and the slip rates on most seismogenic faults in eastern iran the east lut west lut kuhbanan anar dehshir and doruneh faults are confirmed as the major faults and are found to currently slip laterally at 5 6 0 6 4 4 0 4 3 6 1 3 2 0 0 7 1 4 0 9 and 1 3 0 8 mm yr respectively slip is right lateral on the ns striking east lut west lut kuhbanan anar and dehshir faults and left lateral on the ew doruneh fault the ns faults slice the eastern iranian crust into five blocks that are moving northward at 6 13 mm yr with respect to the stable afghan crust at the eastern edge of the collision zone the collective behavior of the ns faults might thus allow the arabian promontory to impinge northward into the eurasian crust the ns faults achieve additional ns shortening by rotating counterclockwise in the horizontal plane at current rates up to 0 8 ma modeling the gps and available geological data with a block rotation model suggests that the rotations have been going on at a similar rate 1 0 4 ma over the last 12 ma we identify large strains at the tips of the rotating east lut west lut and kuhbanan faults which we suspect to be responsible for the important historical and instrumental seismicity in those zones

simulation of selected strong motion records of the 2003 mw 6 6 bam earthquake se iran the modal summation ray tracing methods in the wkbj approximation

coulomb stress changes and secondary stress triggering during the 2003 mw 6 6 bam iran earthquake abstract the 26 december 2003 mw 6 6 bam earthquake is one of the most destructive events in the recorded history of iran good variable slip fault models and precise aftershock data enabled us to calculate coulomb stress changes on the surrounding faults optimally oriented faults and the aftershock nodal planes to learn whether they were brought closer to failure we also test the role of secondary stress on the aftershocks triggering calculated stress on the surrounding faults showed that the southern part of the gowk fault and middle part of the dalfard and bam faults received positive stress changes stress also increases at the ends of the ruptured fault plane to expand it our calculations showed that deeper part of the bam fault planes received positive stress changes due to slipping on the shallow depth it can lead to the occurrence of aftershocks and enhance the probability of large events in the future that represent a substantial remaining seismic hazard to the reconstructed city of bam by imparting stress on optimally oriented faults the correlation between coulomb stress changes and aftershock distribution is investigated obtained results showed good correlation between coulomb stress change and seismicity from 331 well located aftershock hypocenters about 270 events 81 are located in the positive stress changes area the imparted stress due to the main shock and secondary aftershocks on the nodal planes of the 158 aftershocks is calculated the results show that the imparted stress due to main shock encouraged about 60 1 of nodal planes and 77 8 of the chosen nodal planes of aftershocks and added secondary aftershock encouraged about 81 6 of chosen nodal planes in other word by adding secondary triggering stress coulomb index for chosen nodal planes increased from 0 778 to 0 816 and about 80 of aftershocks receive greater positive stress changes

comment on when did the anthropocene begin a mid twentieth century boundary is stratigraphically optimal by jan zalasiewicz et al 2015 quaternary international 383 196 203 we offer a comment on the paper when did the anthropocene begin a mid twentieth century boundary is stratigraphically optimal by jan zalasiewicz et al 2015 quaternary international 383 196 203 we consider this proposal in the context of the procedures and terminology employed by the international union of geological sciences which underpin the formal designation of chronostratigraphic units our conclusion is that there is no practical value in establishing the lower boundary of a new interval of geological time in the mid twentieth century equally there is no sound stratigraphical basis for designating an additional chronostratigraphic unit above the holocene in the international geological time scale

when did the anthropocene begin a mid twentieth century boundary level is stratigraphically optimal abstract we evaluate the boundary of the anthropocene geological time interval as an epoch since it is useful to have a consistent temporal definition for this increasingly used unit whether the presently informal term is eventually formalized or not of the three main levels suggested an early anthropocene level some thousands of years ago the beginning of the industrial revolution at 1800 ce common era and the great acceleration of the mid twentieth century current evidence suggests that the last of these has the most pronounced and globally synchronous signal a boundary at this time need not have a global boundary stratotype section and point gssp or golden spike but can be defined by a global standard stratigraphic age gssa i e a point in time of the human calendar we propose an appropriate boundary level here to be the time of the world s first nuclear bomb explosion on july 16th 1945 at alamogordo new mexico additional bombs were detonated at the average rate of one every 9 6 days until 1988 with attendant worldwide fallout easily identifiable in the chemostratigraphic record hence anthropocene deposits would be those that may include the globally distributed primary artificial radionuclide signal while also being recognized using a wide range of other stratigraphic criteria this suggestion for the holocene anthropocene boundary may ultimately be superseded as the anthropocene is only in its early phases but it should remain practical and effective for use by at least the current generation of scientists

applications of grain pivoting and sliding analyses to selective entrapment of gravel and to flow competence evaluations models of sediment threshold by grain pivoting or sliding over underlying particles are examined in order to explore their application to evaluations of selective entrainment of gravel by flowing water of special interest is whether such process based models provide satisfactory evaluations of flow competence and the movement of large clasts by floods a detailed derivation is undertaken focusing first on the fluid flow and forces at the particle level the resulting threshold equation for the particle level velocity is then modified to yield the mean entrainment stress for the flow as a whole this approach is appropriate for considerations of selective entrainment of grains of varying sizes within a deposit the sorting being due to their relative projection distances above the bed and the dependence of their pivoting angles on grain size and shape the resulting threshold equations contain a number of coefficients e g drag and lift whose values are poorly known but can be constrained by requiring agreement with the shields curve for the threshold of grains in uniform deposits if pivoting coefficients based on laboratory measurements with tetrahedral arrangements of particles are used in the models smaller degrees of selective sorting are predicted than found in the field measurements of gravel entrainment however if reasonable modifications of those coefficients are made for expected field conditions then the models yield good agreement with the data sliding models where sorting is due entirely to projection distances of the grains above the bed yield somewhat poorer agreement with the field data however the sliding models may have support from laboratory experiments on gravel entrainment in that the data and theoretical curves have similar concave trends the existing measurements lack documentation of the mechanisms of grain movement so it is not possible to conclusively determine the relative importance of grain pivoting versus sliding in spite of such uncertainties the results are encouraging and it is concluded that pivoting and sliding models for grain entrainment do have potential for field computations of selective entrainment and flow competence

morphodynamics of a 1000 year flood in the kamp river austria and impacts on floodplain morphology this paper investigates the impact of a 1000 year flood in august 2002 on floodplains and valley morphology of an austrian mixed alluvial bed rock river discharges with a recurrence interval between 500 and 2000 years caused distinctive overbank scouring and material deposition in the floodplains after the 1000 year flood those morphologically affected areas were at random intervals documented over the whole longitudinal profile in addition to overbank erosion in curved sections cut offs the river bed locally widened floodplain stripping occurred and local overbank scours were documented along straight parts of the river a hydrodynamic numerical model combined with field measurements was used to analyse the cause of these erosional landforms based on the modelled hydraulic conditions for a one year flood 30 78 m3 s 1 and the catastrophic 2002 event 700 800 m3 s 1 the numerical results allowed a cause effect study with 19 parameters deterministic and statistical analysis anova discriminant analysis showed that the morphodynamic effects of the 2002 flood were influenced by the variability of valley morphology of the kamp river which led partially to supercritical flow during flood constriction these processes were in some cases also anthropogenically influenced lateral constriction and expansion of the valley geometry over short distances led to scouring and aggradation within the inundated areas during the event these morphological features were therefore responsible for the elongated scour holes in the floodplains copyright 2009 john wiley sons ltd

unified view of sediment transport by currents and waves iii graded beds the problem of suspended load and bed load transport in river and coastal flows over graded beds is addressed two effects are important the degree of exposure of the sediment particles of unequal size within a mixture hiding of smaller particles resting or moving between the larger particles and the nonlinear dependence of transport on particle diameter the former effect can be modeled by modifying the critical bed shear stress through a correction factor and by modifying the effective grain roughness through another correction factor the modeling of the effective bed shear stress parameter is studied by using various alternative methods based on comparison with suspended load and bed load transport data for graded beds in steady and oscillatory flow the most promising method is selected the proposed prediction method is found to work well for the fine sand bed range as well as the coarse sand gravel bed range

the influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers a reply clifford et al 1992 argue that differences in hydraulic conditions at the moment of sediment entrainment in turkey brook flood by flood are attributable to variations in the form drag that arises from cluster microforms while not denying the possibility of variable cluster concentration we show that the time dependent bed consolidation and cementation that arises as a function of interstitial matrix development can also account for variation in the traction threshold clifford et al further postulate that the growth of pebble clusters just prior to bedload entrainment is a cause of the observed differences in traction thresholds at the start and finish of bedload during a flood event this merits further examination however we point out that clusters are not only observed at low flow and therefore already present and able to contribute significant form drag as the next bedload generating flood waxes but that they are known both to survive more or less intact and to entrap mobile particles during bed disturbing events the revelation by clifford et al that flow structure in the river quarme reflects differences in bed rugosity between riffles and pools and that it relates in scale to bed roughness elements perhaps clusters is not surprising there is however some difficulty in distinguishing the precedence of chicken and egg when using this data set to elucidate the cause of cluster spacing nevertheless the inference that flow and form are dynamically linked is in sympathy with our own conclusions that cluster spacing is an equilibrium condition governed by the interplay of flow resistance and sediment transport

seismicity anomalies of the 2003 bam iran earthquake abstract the bam earthquake occurred in an area without any historically recorded major earthquake based on active tectonics and cmt solutions the area is under the influence of shortening and right lateral strike slip faulting seismicity is of a shallow crustal type which is mainly distributed within the koohbanan golbaf lakarkooh shahdad gowk fault systems and the terminal sections of zagros in order to detect temporal seismicity anomalies before this earthquake we compiled a catalog from the isc events and then analyzed it for the magnitude of completeness after declustering this catalog changes in seismicity were assessed by the z value test the temporal variations indicate a relative decrease in z value before the bam earthquake additional to seismic quiescence and decrease in b value before the main shock there are pieces of evidence corresponding to increase in triggered background seismicity after this earthquake

threshold of erosion of submarine bedrock landscapes by tidal currents since sea level stabilized 7000 yr bp shelf seas experiencing semi diurnal tides will have been affected by streaming four times per day if tidal erosion of bedrock were even only marginally efficient the 10 million streamings since then should have left geomorphological imprints we examine high resolution multibeam sonar data from three areas with extreme tidal currents the minas passage bay of fundy experiencing 8 knot surface tidal currents was surveyed in 2007 with a multibeam sonar in an area near to transverse dunes which are evidence for bedload transport the data show local overhanging surfaces near to the sediment rock contact potentially created by abrasion by saltating particles however they are uncommon in the straits of messina where surface currents reach 10 knots surveying revealed ridges lying oblique to the flow that are not obviously broken into separate outcrops by erosion in the bristol channel uk sonar data collected where currents reach 3 4 knots at 1 5 m above the bed reveal outcrops of limestone with superimposed sand dunes but only minor rounding of blocks holocene tidal currents have apparently been generally ineffective at eroding bedrock we examine this issue further by compiling extreme tidal streams around the uk and from them estimate shear stresses representing a macro tidal environment where peak surface currents reach 9 7 knots those data are compared with shear stresses in mountainous rivers where long term rates of erosion are comparable with tectonic uplift rates and are thus geomorphologically significant whereas river stresses reach 102 103 pa the largest tidal stresses are generally 101 and only rarely approach 102 pa too small for quarrying to operate generally however the vertical faces in the minas passage may represent the onset of abrasion given this limited evidence for abrasion we explore conditions in the geological past for tides that may have locally eroded bedrock

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

changes in bedload transport rate associated with episodic sediment supply in a japanese headwater channel abstract we conducted field monitoring of bedload transport rate associated with experimental sediment release in a natural channel to clarify behavior of the supplied sediment on mixed size bed observation of bedload rate at two sites along the 30 m channel reach revealed that downstream migration of finer particles delay compared with coarser particles ratio of the bedload sediment that deposited during the migration was higher for finer sediments these behaviors of the mixed size particles were clear during passage of the sediment wave without changes in water discharge flashing peak of discharge that caused artificially by opening of the dam gate did not destroy channel bed structure including steps and pools formed by coarser sediments and only small amount of bedload was mobilized both reach scale channel features including steps pools and riffles as well as fine scale features i e armour coat likely increased critical shear stress of particles and decreased bedload rate during our experiment extreme sediment supply induced two types of sediment deposition 1 filling the pools in reach sales and 2 the intrusion of fine particles into the coarser sediment that formed an armour layer the all grain size fractions can deposit as type 1 when shear stress of stream water is not enough to entrain bedload particles while deposition type 2 occurs when finer sediment pass over channel bed on which armour coat is well developed deposition of finer sediment into coarser sediment that forms armour coat is affected by grain size distribution of bed surface sediment thus impact of the sediment supply on downstream channel depends on both bedforms and grain size distribution of bed surface sediment over which the supplied sediment pass

particle comminution defines megaflood and superflood energetics abstract the concept of megafloods and superfloods was introduced at the end of the last century to define exceptionally large discharge floods primarily those associated with the failure of quaternary ice dams these floods exceeded by one or two magnitudes historically recorded floods megafloods having peak discharges equalling or exceeding 1 m m3 s 1 herein the sediment associations of exceptional floods are found to be distinctive being dominated by comminuted smashed grain size distributions which contrast to the sediment deposits of more moderate floods a consideration of the energetics of moderate floods superfloods and megafloods with respect to the entrainment dis entrainment suspension and comminution of coarse gravel allows thresholds of energy expenditure to be proposed that reflect general transformations in flood behaviour that relate to distinctive flood deposits a threshold of energy expenditure 20 kj s 1 m 2 is proposed to separate moderate floods from superfloods the latter by this definition can be 0 1 m m3 s 1 this threshold separates floods competent to entrain cobbles and boulders with limited comminution of the load from superfloods that comminute the suspended cobbles and boulders to produce fine granules in suspension the granules are subsequently deposited to form distinct depositional units that are characteristic of superfloods and megafloods the energetic threshold is consistent with the lower range of power expenditures associated with the original definition of a megaflood in terms of peak fluid flux significance exceptional floods occurred in prehistoric times the largest are referred to as megafloods or superfloods to distinguish such exceptional floods from other large floods megafloods were defined as having a peak discharge exceeding 1 m m3 s 1 however many reports of megafloods are flows with a peak discharge smaller than 1 m m3 s 1 recent research has shown that megafloods and superfloods deposit distinctive layers of smashed gravel which is not the case for smaller floods the gravel is smashed by exceptionally high energy expenditures consideration of the energetics of floods to transport gravel allows a robust quantitative definition of superflood based on the energy needed to smash a range of gravel sizes

bedforms and sediment transport processes in the ephemeral streams of kobo basin northern ethiopia abstract bedforms and channel deposits architecture were studied in the ephemeral streams of the structural basin of kobo in northern ethiopia the froude numbers calculated at bankfull flow for a few of the study reaches are in agreement with the extensive occurrence of horizontal planar lamination small bedforms not previously reported in the literature are found and described as produced mainly by scouring rather than accretion processes equations to predict particle entrainment proved that large individual boulders standing scattered on the stream bed can be transported at bankfull flow for long distances direct inspection of the old alluvium and the modern channel deposits allow to identify a typical arrangement within a single bed consisting of divisions with specific characteristics this model of division association is explained in terms of vertical distribution of shear stress and compared with hyperconcentrated flow and traction carpet models in contrast with recent theories of flat asymmetrical bed waves progradation at froude numbers close to unity

offset and evolution of the gowk fault s e iran a major intra continental strike slip system abstract we use drainage reconstructions to estimate long term offsets on the gowk fault an oblique right lateral strike slip fault in eastern iran on which there have been a number of recent large earthquakes a 3 km horizontal offset is inferred from well preserved geomorphology we further identify a total cumulative offset of 12 km which produces a simple reconstruction of geomorphology across the fault filling in pull apart basins restoring rivers to linear courses across the fault trace and aligning structural and bed rock features the probable age of the gowk fault and k ar dating of offset basalts north of the study region suggest an overall slip rate of 1 5 2 4 mm year this is small compared with the overall 10 20 mm year of shear expected between central iran and afghanistan and the deficit is likely to have been accommodated on other faults east of the gowk fault drainage displaced by dextral movement leads to the development of a series of basins along the fault and a longitudinal topographic profile that resembles an asymmetric saw tooth the geomorphic evolution of the fault zone at the surface includes both normal and reverse faulting components reflecting a probable ramp and flat structure in cross section this interpretation is consistent with evidence from the analysis of seismological radar and surface rupture data in recent earthquakes

sediment entrainment and transport in fluviokarst systems the primary geomorphic process active in the development of karst stream systems is generally regarded as bedrock dissolution however physical erosional processes may also be an important geomorphic agent in karst development the objectives of this study were to determine the sediment transport threshold in two fluviokarst streams the source of the sediment was internal to the karst basins the approach used was to calculate basal and critical shear stresses from streams in two karst systems to determine if and how frequently storm induced flows are capable of mobilizing stream sediment the fluviokarst systems investigated as a part of this research are capable of transporting 50 85 of their stream substrates during bankfull discharge conditions based on the discharge and precipitation frequency stream flows capable of entraining d50 and d85 particles occur at intervals of 2 4 and 11 7 months 0 98 yr respectively thus the sediment transport threshold in fluviokarst streams is exceeded by relatively common discharge events q 2004 elsevier b v all rights reserved

gradation effects in sediment transport to determine the effects of grain size and density gradation in oscillatory sheet flow experiments are conducted in an oscillating water tunnel a formal derivation of a schematised transport model shows that the transport rates per sediment fraction can be determined with and without the assumption of an active layer a technique that measures sediment composition from natural occurring radionuclides is used to determine the transport rates without that assumption of an active layer the measurements on total sediment transport rates and suspended sediment concentrations show that effects of gradation are present the effects of size gradation are mainly in the increased transport rates of the coarse fraction with respect to the uniform coarse material and the availability at the bed under similar conditions the experiments on density graded sediments indicate that total mass transport rates are larger than the mass transport rates of quartz material whilst the transport rates of the quartz fraction show that this fraction is not hindered by the availability at the bed

threshold of coarse sediment transport in broad and narrow natural streams the threshold of coarse sediment transport has been examined in natural streambeds in an upland pennine u k area threshold values of the total boundary shear stress t0 for a given grain size in a narrow natural stream w d 11 efficiency in the entrainment process is related not only to the overall channel geometry but also varies as a function of discharge in channels characterized by compound roughness empirical curves relating t0 and a mean grain size d5 are presented but are limited in application to streams of similar physical and hydraulic characteristics as the ones examined in this investigation considerable divergence is noted between these empirical functions and a summary empirical function for general application obtained from a published source the reasons for this divergence are discussed the influence of grain shape was found not to be important in the initiation of motion criterion this conclusion may reflect the limited range of natural grain shapes in the study streams but might reasonably apply to other field investigations of similar streams modifications of the shields and yalin diagrams are suggested for practical applications in shallow streams with poorly graded bed material the shields parameter may be regarded as an inverse function of the relative protrusion of individual grains in the shallow flow depth d5 d the increased importance of augmented drag forces in the entrainment process in shallow flows is suggested as the physical explanation for the reduced values of the shields parameter however the relationships presented should not be applied to laboratory experiments concerned with well graded sediments therefore beds with little deviation in level in which the shields parameter may be regarded as constant at high reynolds grain numbers consistent estimated field values of a threshold sediment transport parameter might be used to compare field data to threshold values derived from statistical arguments and laboratory experiments reported in the literature

seismotectonic rupture process and earthquake hazard aspects of the 2003 december 26 bam iran earthquake summary the catastrophic 2003 m w 6 6 bam earthquake in southern iran attracted much attention and has been studied with an abundance of observations from synthetic aperture radar teleseismic seismology aftershock studies strong ground motion geomorphology remote sensing and surface field work many reports have focused on the details of one or other data type producing interpretations that either conflict with other data or leave questions unanswered this paper is an attempt to look at all the available data types together to produce a coherent picture of the coseismic faulting in 2003 and to examine its consequences for active tectonics and continuing seismic hazard in the region we conclude that more than 80 per cent of the moment release in the main shock occurred on a near vertical right lateral strike slip fault extending from the city of bam southwards for about 15 km with slip of up t o2mb utmostly restricted to the depth range 2 7 km analysis of the strong ground motion record at bam is consistent with this view and indicates that the extreme damage in the city can be attributed at least in part to the enhancement of ground motion in bam because of its position at the end of the northward propagating rupture little of the slip in the main shock reached the earth s surface and more importantly aftershocks reveal that 12 km vertical extent of a deeper part of the fault system remained unruptured beneath the coseismic rupture plane at depths of 8 20 km this may represent a substantial remaining seismic hazard to the reconstructed city of bam we believe that some oblique reverse slip up to 2 m and less than 20 per cent of the released seismic moment occurred at a restricted depth of 5 7 km on a blind west dipping fault that projects to the surface at the bam baravat escarpment an asymmetric anticline ridge that is the most prominent geomorphological feature in the area this fault did not rupture significantly at shallow levels in 2003 and it may also represent a continuing seismic hazard widespread distributed surface ruptures north of the city are apparently unrelated to substantial slip at depth and may be the result of enhanced ground motion related to northward propagation of the rupture the faulting at bam may be in the early stages of a spatial separation partitioning between the reverse and strike slip components of an oblique convergence across the zone such a separation is common on the continents though in this case the slip vectors between the two faults differ only by 20 as a substantial strike slip component remains on the obliquereverse fault the bam earthquake is one in a series of large earthquakes involving faulting along the western edge of the lut desert in addition to the unruptured parts of the faults near bam itself continuing and substantial hazard is represented by unruptured neighbouring faults particularly blind thrusts along the jebel barez mountains to the south and strike slip faulting at sarvestan to the west

geology of mankind for the past three centuries the effects of humans on the global environment have escalated because of these anthro pogenic emissions of carbon dioxide global climate may depart significantly from natural behaviour for many millennia to come it seems appropriate to assign the term anthropocene to the present in many ways human dominated geological epoch supplementing the holocene the warm period of the past 10 12 millennia

ice sheets and the anthropocene ice could play a role in identifying and defining the anthropocene the recurrence of northern hemisphere glaciation and the stability of the greenland ice sheet are both potentially vulnerable to human impact on the environment however only a very long hiatus in either would be unusual in the context of the quaternary period requiring the definition of a geological boundary human influence can clearly be discerned in several ice core measurements these include a sharp boundary in radioactivity due to atmospheric nuclear testing increases unprecedented at least in the holocene in greenland concentrations of sulphate nitrate and metals such as lead the appearance in ice core air bubbles of previously undetectable compounds such as sf6 and the rise unprecedented in the last 800 ka in concentrations of carbon dioxide and methane some combination of these changes could be used by future generations to clearly identify the onset of a new epoch defined at a particular calendar date however it is not yet clear what the character of the fully developed anthropocene will be and it might be wise to let future generations decide with hindsight when the anthropocene started acknowledging only that we are in the transition towards it

the 1998 march 14 fandoqa earthquake mw 6 6 in kerman province southeast iran re rupture of the 1981 sirch earthquake fault triggering of slip on adjacent thrusts and the active tectonics of the gowk fault zone summary the 1998 march 14 fandoqa earthquake ms 6 6 was the penultimate in a series of five substantial earthquakes on the gowk fault system of southeast iran since 1981 all of which were associated with co seismic surface ruptures we use observations of surface faulting analysis of p and sh body waves sar interferometry and geomorphology to investigate the ruptures in these earthquakes and how they are related both to each other and to the regional active tectonics the 1998 fandoqa earthquake produced 23 km of surface faulting with up to 3 m right lateral strike slip and 1 m vertical offsets sar interferometry and seismic waveforms show that the main rupture plane dipped west at 50 and had a normal component although the surface ruptures were more complicated being downthrown to both the east and the west on steep faults in near surface sediments in addition sar interferometry shows that a nearby thrust with a similar strike but dipping at 6 w moved about 8 cm in a time interval and in a position that makes it likely that its slip was triggered by the fandoqa earthquake the 1998 surface ruptures in the gowk valley followed part of a much longer 80 km set of co seismic ruptures with smaller offsets that were observed after larger earthquakes in 1981 mw 6 6 and 7 1 the main ruptures in these 1981 earthquakes probably occurred on different deeper parts of the same fault system producing only minor reactivation of the shallower faults at the surface although the 1981 1998 earthquake sequence apparently ruptured parts of the same fault system repeatedly these earthquakes had very different rupture characteristics an important lesson for the interpretation of both palaeoseismological trenching investigations and historical accounts of earthquakes the regional kinematics which involve oblique right lateral and convergent motion are evidently achieved by a complex configuration of faults with normal reverse and strike slip components some of the complexity at the surface may be related to a ramp and flat fault geometry at depth but could also be related to the large topographic contrast of 2000 m across the fault system which separates the high kerman plateau from the low dasht e lut desert details of the fault geometry at depth remain speculative but it must be unstable and evolve with time it may be this requirement that causes the principal features of geological flower structures to develop such as series of subparallel faults which accommodate dip slip components of motion

glacial interglacial and millennial scale variations in the atmospheric nitrous oxide concentration during the last 800 000 years we present records of atmospheric nitrous oxide obtained from the ice cores of the european project for ice coring in antarctica epica dome c and dronning maud land sites shedding light on the concentration of this greenhouse gas on glacial interglacial and millennial time scales the extended epica dome c record covers now all interglacials of the last 800 000 years and reveals nitrous oxide variations in concert with climate highest mean interglacial nitrous oxide concentrations of 280 parts per billion by volume are observed during the interglacial corresponding to marine isotope stage 11 around 400 000 years before present at the same time when carbon dioxide and methane reach maximum mean interglacial concentrations the temperature reconstruction at dome c indicates colder interglacials between 800 000 and 440 000 years before present compared to the interglacials of the last 440 000 years in contrast to carbon dioxide and methane which both respond with lower concentrations at lower temperatures nitrous oxide shows mean interglacial concentrations of 4 19 parts per billion by volume higher than the preindustrial holocene value during the interglacials corresponding to marine isotope stage 9 19 at the end of most interglacials nitrous oxide remains substantially longer on interglacial levels than methane nevertheless nitrous oxide shows millennial scale variations at the same time as methane throughout the last 800 000 years we suggest that these millennial scale variations have been driven by a similar mechanism as the dansgaard oeschger events known from the last glacial our data lead to the hypothesis that emissions from the low latitudes drive past variations of the atmospheric nitrous oxide concentration

pivoting analyses of the selective entrainment of sediments by shape and size with application to gravel threshold measured variations of pivoting angles with grain size shape reliability and angularity and imbrication are employed in analyses of grain threshold to examine how these factors influence selective grain entrainment and sorting with a bed of uniform grain sizes as employed experimentally to establish the standard threshold curves such as that of shields the threshold condition depends on grain shape and fabric the analysis demonstrates quantitatively that there should be a series of nearly parallel threshold curves depending on grain pivoting angles for a given grain size the order of increasing flow strength required for entrainment is spheres smooth ellipsoids depending on their reliability angular grains and imbricated ellipsoids depending on their imbrication angles the relative threshold values for these different grain shapes and fabric are predicted according to their respective pivoting angles but remain to be directly tested by actual threshold measurements the pivoting angle of a grain also depends on the ratio of its size to those it rests upon this dependence permits an evaluation of selective entrainment by size of grains from a bed of mixed sizes the condition generally found in natural sediments the pivoting model predicts systematic departures from the standard threshold curves for uniform grain sizes such departures have been found in recent studies of gravel threshold in rivers and offshore tidal currents the pivoting model is compared with those threshold data with reasonable agreement however more controlled measurements are required for a satisfactory test of the model it is concluded that variations in pivoting angles for grain entrainment are significant to the processes of selective sorting by grain size and shape

fault displacement gradient folds and the structure at lost hills california u s a abstract geometric models of fault propagation folds require that the underlying fault tip propagate upward across layering however related folds can be generated if the tip remains stationary or even moves back along the ramp as a pre existing fault is reactivated fault propagation folds detachment folds as well as those produced when there is no propagation are generated by a displacement gradient along the underlying fault and as a general class can be called fault displacement gradient folds new geometric equations are derived which relate fold shape to displacement gradient and fault propagation folds are a special case of these more general equations growth sequences associated with these structures have been used to distinguish fault propagation folds from fault bend folds when the underlying structure is obscured a displacement gradient fold in which the fault tip retreats back down the ramp generates a growth sequence that in some cases could be confused with that of a fault bend fold the structure at lost hills in the san joaquin valley of california u s a has been interpreted as a fault bend fold but it may be a displacement gradient fold which formed as a pre existing fault was reactivated during a pliocene change in plate motion

the impact of exceptional events on erosion bedload transport and channel stability in a step pool channel sediment transport in the erlenbach a small stream with step pool morphology in the canton of schwyz switzerland has been monitored for more than 20 years during this time three exceptional events events with high sediment yield and long return times that have a large effect on channel morphology have impacted the stream and partly or completely rearranged the existing step pool morphology in the aftermath of the events sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer for the last event dated on the 20 june 2007 observations of boulder mobility and step destruction were used to interpret channel stability boulders with median diameters of up to 135 cm and estimated weights of more than 2 5 tons have moved during the 2007 event using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions even if form resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account for two of the events estimated peak shear stresses at the bed exceeded 1000 pa calculated both from observations of the flow hydraulics and from boulder mobility this suggests that highly energetic flows occur relatively frequently in small steep streams and that large boulders can be transported by fluvial processes in such streams the observations have potential significance for hazard risk mitigation stream engineering and restoration copyright 2009 john wiley sons ltd

evaluation of grain shear stresses required to initiate movement of particles in natural rivers shear stresses were evaluated at different sites on two rivers the first the rulles is characterized by a pebbly bedload and a meandering bed with riffles and pools the second the rouge eau has mainly a sandy rippled bed where meandering is well developed but also flat gravelly sectors without meandering system shear stresses calculated from friction velocities using a redefined y1 roughness height parameter were compared with total shear stresses calculated from the energy grade line and the hydraulic radius divergence between these shear stresses seems to increase in the presence of bedforms and large scale irregularities of the channel the ratio is close to 0 5 in the gravelly sector of the rouge eau and reaches 0 65 in the riffles of the rulles generally located at the inflexion point of the meanders while it is less than 0 3 in the pools of the same river located in the loops and only 0 2 in the sandy rippled sector of the rouge eau grain and bedform shear stresses were evaluated at these same sites by different methods the grain shear stress represents on average 30 per cent of the total shear stress in the riffles of the rulles and the gravelly sector of the rouge eau but less than 15 per cent in the pools in the rulles and the sandy sectors of the rouge eau however it emerges from experiments conducted with marked pebbles and in situ observations of erosion and transport of sandy and gravelly particles that the grain shear stresses are underestimated and cannot explain the movements and modifications actually observed conversely shear stresses calculated from friction velocities at the sites where erosion actually occurred or failed to occur despite very high velocities provide a better explanation of the observed movements

slip distribution aftershocks and co seismic fault of some large persian earthquakes this investigation concentrates on slip distribution aftershocks mainshock location and related co seismic faults for seven continental large earthquakes in the persian plateau most of the earthquakes m s 5 7 7 7 1981 2005 with both measurable surface slip along a mature rupture and a precisely aftershock surveying with a local seismological network in iran are evaluated in most of the case studies we observe an acceptable correlation between maximum surface slip along the fault trace and the asperity an area which is recognized as an obvious gap or an area with lack of aftershocks on a fault plane on the other hand we conclude that the aftershocks which are associated with immeasurable or smaller surface slips mainly concentrate at the outside of the asperities also the mainshocks in most of the earthquakes are in neighboring with the big asperities and segment the co seismic faults we could see a gradual increase in the co seismic slip when the magnitude of the earthquake increases but examples with defuse aftershocks and with no specific pattern are also found

when does bedload transport begin in steep boulder bed streams the paper presents the results of field measurements of critical conditions for bedload motion conducted in the rio cordon a steep boulder bed stream in the italian alps under conditions of high reynolds numbers and low relative submergence poorly explored before two methods have been used to determine threshold of motion the displacement of marked clasts and the flow competence approach which uses the largest grain size diameter transported by each flood event the high values of confirm the great relevance of non bedload effective shear stresses in step pool streams given by the additional form drag associated with this morphology relative submergence effects on the dimensionless critical shear stress have been quantified by considering the relative submergence ratio rh d84 and the major effect of relative size on the mobility of each particle in steep widely graded bed mixtures has been evaluated finally the dimensionless critical unit discharge has also been adopted in the regression equations as the critical hydraulic parameter because it may represent an easier parameter to use than the critical shear stress for steep rough mountain rivers copyright 2006 john wiley sons ltd

the 2003 bam iran earthquake rupture of a blind strike slip fault a magnitude 6 5 earthquake devastated the town of bam in southeast iran on 26 december 2003 surface displacements and decorrelation effects mapped using envisat radar data reveal that over 2 m of slip occurred at depth on a fault that had not previously been identified it is common for earthquakes to occur on blind faults which despite their name usually produce long term surface effects by which their existence may be recognised however in this case there is a complete absence of morphological features associated with the seismogenic fault that destroyed bam

a study of fold characteristics and deformation style using the evolution of the land surface zagros simply folded belt iran abstract deformation styles within a fold thrust belt can be understood in terms of the spatial organization and geometry of the fold structures in young fold thrust belts such as the zagros this geometry is reflected topographically by concordant landform morphology thus the distribution of deformation structures can be characterized using satellite image analysis digital ele vation models the drainage network and geomorphological indicators the two distinct fold types considered in this study fault bend folds and detachment folds both trending nw se interact with streams flowing ne sw from the high zagros mountains into the persian gulf multiple abandoned stream channels cross fault bend folds related to deep seated thrust faults in contrast detachment folds which propagate laterally relatively rapidly are characterized by diverted major stream channels and dendritic minor channels at the fold tips thus these two fold types can be differentiated on the basis of their ge ometry fault bend folds being long linear and asymmetrical can be distinguished from detachment folds which tend to be shorter and symmetrical and on their associated geomorphological structures the spatial organization of these structures in the zagros simply folded belt indicates that deformation is the result of the interaction of footwall collapse and the associ ated formation of long linear fault bend folds and serial folding characterized by relatively short periclinal folds footwall collapse occurs first followed by serial folding to the ne i e in the hanging wall of the fault bend folds often on higher de tachments within the sediment pile 139

a comparison of grab and freeze sampling techniques in the collection of gravel bed river sediment abstract freeze and grab sampling techniques for the collection of bulk sub surface sediments in gravelly rivers are compared data obtained from sampling a substratum of known composition and at over 300 field locations indicate that grab sampling underestimates the proportion by weight of the fine sediment component but collects representative samples of the coarser gravel component as a consequence of this sampling bias the textural characteristics of the composite grab sample means were significantly different p

prediction of sediment transport in step pool channels 1 in mountainous drainage networks sediment mobilized on hillslopes must first pass through steep streams before reaching lower gradient channels the bed of steep channels is typically composed of large relatively immobile boulders and finer more mobile gravel most sediment transport equations overpredict sediment flux in steep streams by several orders of magnitude because they do not account for the stress borne by immobile grains and the limited availability of the more mobile sediment we previously developed and tested in flume experiments a sediment transport equation that accounts for these two effects here we modify the parker 1990 bed load equation to include the resistance borne by steps and selective transport of the relatively mobile sediment using a range of hiding functions we test a number of resistance equations and hiding functions combined with our modified and the original parker equations against measured flow and sediment transport in three steep channels our modified sediment transport equation generally predicts the transported sediment volumes to within an order of magnitude of the measured values whereas the unmodified equations do not the most accurate sediment flux predictions were obtained from using our modified equation combined with a hiding function that calculates highly selective transport of the relatively mobile sediment furthermore this hiding function has a critical shields stress that is similar to those reported for lower gradient channels the effects of the immobile steps on flow and sediment transport are not adequately captured by simply increasing the critical shields stress to values reported in steep streams

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

dimensionless critical shear stress evaluation from flume experiments using different gravel beds flume experiments were conducted using four different gravel beds d50 12 39 mm and a range of marked particles 10 65 mm the shear stresses were evaluated from friction velocities when initial movement of marked particles occurred two kinds of equations were produced first for the threshold of initial movement and second for generalized movement equations of the type 0c a di d50 b as proposed by andrews 1983 are applicable even if the material is relatively well sorted however the values of a and b are lower respectively 0 050 and 0 70 for initial movement generalized movement requires a higher shear stress a 0 068 and b 0 80 d90 of the bed material and y0 the bed roughness parameter were also used as reference values in place of d50 they produced lower values than in natural streams mainly owing to the fact that the material used in the flume is better sorted clusters are less well developed and the bed roughness is lower

test of hack s slope to bed material relationship in the southern eifel uplands germany the local reach gradient of small gravel bed rivers drainage area 0 8 110 km2 in the eifel west germany is adjusted to transport the river bed sediments transport of gravel becomes possible under high flow conditions shields entrainment factor 03 mean bed material size for riffle sections increases with distance downstream for small drainage areas channel slope is a negative exponential function of drainage area while for the larger region the additional influence of bedload size has to be considered good agreement with hack s data 1957 for virginia and maryland u s a is achieved s 0 0066 d50 a 40 r 0 67

threshold studies of gravel size particles under the co linear combined action of waves and currents gravel size sediment beds are tested under the combined influence of simulated wave action and co linear currents in a laboratory flume critical current speed at threshold increases with increasing size superimposed wave energy causes a small reduction in the unidirectional current energy for low values of wave induced near bed current velocities the resistance to erosion increases when the wave period decreases from 10 to 6 s finally combined critical shear stresses are found to be lower than those predicted using the shields curve as modified for oscillatory flow grain protrusion is suggested as a mechanism to explain this divergence