pinch and swell structures at the middle upper muschelkalk boundary triassic evidence of earthquake effects seismites in the germanic basin a limestone bed with synsedimentary deformations is described from the middle upper muschelkalk boundary middle triassic of thuringia germany the deformation structures have an elongated geometry in a preferential n s to nnw sse direction and are several metres across in size they are similar to ball and pillow structures but differ from these by absence of significant loading into underlying beds their development is interpreted as a result of bed internal deformation with bed thickening due to lateral contraction and bed thinning due to stretching this deformation mechanism is comparable to the one producing boudinage structures in particular pinch and swell structures the deformation style and size of these structures and their widespread occurrence together with other synsedimentary deformation structures support their interpretation as earthquake induced structures seismites synsedimentary deformation structures are common features that occur in a narrow stratigraphic unit at the middle upper muschelkalk boundary in different parts of the germanic basin and point to tectonically influenced changes in the depositional regime and basin organization further examples of pinch and swell structures from the lower and upper muschelkalk suggest that tectonics significantly influenced the sedimentation in the germanic basin during middle triassic time

purely erosional cyclic and solitary steps created by flow over a cohesive bed an erodible surface exposed to supercritical flow often devolves into a series of steps that migrate slowly upstream each step delineates a headcut with an associated hydraulic jump these steps can form in a bed of cohesive material which once eroded is carried downstream as washload without redeposition here the case of purely erosional one dimensional periodic or cyclic steps in cohesive material is considered the st venant shallow water equations combined with a formulation for sediment erosion are used to construct a complete theory of the erosional case the solution allows wavelength wave height migration speed and bed and water surface profiles to be determined as functions of imposed parameters the analysis also admits a solution for a solitary step or single headcut of self preserving form

numerical modelling of clast rotation during soft sediment deformation a case study in miocene delta deposits a numerical model for a rotated clast in a sedimentary matrix is presented quantifying the deformation in associated soft sediment deformation structures all the structures occur in a southwards prograding deltaic sequence within the miocene ingering formation deposited at the northern margin of the fohnsdorf basin eastern alps austria debris flow and pelitic strata contain boudins pinch and swell structures ptygmatic folds rotated top to s reverse faults and rigid clasts developed under different stress conditions within the same layers the deformation around a 24 10 cm trapezoid shaped rigid clast resembling the clast geometry in metamorphic rocks has been modelled using a 2d finite element modelling software under the chosen initial and boundary conditions the rotational behaviour of the clast mainly depends on the proportions of pure and simple shear best fitting results were attained with a dominantly pure shear deformation 65 85 with stretching parallel and shortening normal to the bedding in this specific model set up the initial sedimentary thickness is reduced by 30 explained by stretching due to sediment creeping and compaction the high amount of pure shear deformation proposed is compatible with the observed layer parallel boudinage and pinch and swell structures rotated faults and ptygmatic folds were caused by the minor component of bedding parallel simple shear

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

identifying the probabilistic structure of drained areas as a function of hypsometry in river networks classical morphological descriptors of river networks have been developed in 2d planar system the third z dimension elevation however is necessary to model landscape evolution particularly in a mountainous region when taking into account transport processes such as in glaciology and erosion this paper aims at analyzing 3d morphometric properties of channel networks on the basis of probabilistic relationships relating the drained area and the elevation the methodology is an extension of the fundamental planar power law description proposed by rodriguez iturbe et al 1992a representing the probability that the drained area a is higher than a threshold area a p a a a where is constant and represents an invariant property of natural river networks a new scaling factor taking into account hypsometry is introduced in the previous power law relationship as where f is a scaling function and is a measure of the system scale and a function of hypsometry the new power law has one empirical parameter a procedure was developed to calibrate this parameter and to calculate the corresponding uncertainty for applications on a single basin and then extended to a set of 70 basins in the southern rocky mountains the results show that the 3d power law exhibits scale invariance properties with respect to when applied to a single basin looking at the entire set of 70 basins the criterion value associated with the uncertainty model shows a moderate loss in scaling quality compared with the basin per basin description but nevertheless remains acceptable this 3d power law provides a geomorphologic basis for applications in mountainous regions where the relation between drained area and hypsometry has to be considered copyright 2014 john wiley sons ltd

refocusing geomorphology field work in four acts abstract geomorphology grew out of natural history natural history is conducted in the field accordingly the early history of geomorphology was dominated by investigations in the field in the attempt to decipher the history of specific landscapes the constraints of transport and accessibility dictated that field excursions be long and often arduous these circumstances changed after the mid twentieth century with the advent of modern transport the introduction of remote sensing instruments and methods and the increasing emphasis on mechanistic analysis of generic landscape forming processes the latter brought to geomorphology an increasingly reductionist perspective field work has become increasingly a matter of relatively short excursions to acquire specific measurements defined by model or theoretical criteria but geomorphology is a system science seeking to understand the compounded effects of many interacting processes these effects include phenomena that emerge from the intersection of simpler physical and biological processes while simple processes might be isolated and successfully analyzed by reductionist means it is not clear that we can reverse the process and understand emergent phenomena by conflating our understanding of individual processes emergence is better understood initially by direct observation and induction this was intuitively understood by early field scientists whose long seasons provided ample opportunity to observe such phenomena recent technological developments have enhanced our ability to comprehend the landscape system but the effort will surely require comprehensive field experience if we are to regain the whole landscape view of the early field workers

far field tsunami hazard from mega thrust earthquakes in the indian ocean summary we evaluate far field tsunami hazard in the indian ocean basin based on hydrodynamic simulations of ten case studies of possible mega earthquakes at the major seismic zones surrounding the basin they represent worst case scenarios of seismic rupture along the full extent of seismogenic faults having supported large earthquakes in the historical record in a series of numerical experiments in which the source parameters of the 2004 sumatra tsunami are allowed to vary one by one while keeping the seismic moment and the fault orientation unchanged we document that the main patterns of far field tsunami amplitudes are remarkably robust with respect to nominal variations in such parameters as hypocentral depth exact centroid location and slip distribution on the fault plane these results validate the concept of modelling case scenarios of potential future earthquakes whose source is by definition imprecise we consider seismic sources located at the extremities of the 2004 sumatra andaman rupture namely along the southern coast of sumatra and in the andaman myanmar province along the makran coast of pakistan and iran and also along the southern coast of java where the possibility of a large interplate thrust earthquake cannot be entirely dismissed the results of our hydrodynamic simulations indicate that the distribution of maximum amplitudes in the indian ocean basin is primarily controlled by the classical effect of source directivity and additionally by refraction and focusing along bathymetric features as a result many provinces in the basin could be threatened by higher tsunami amplitudes than in 2004 this pattern is particularly important along the coast of east africa from somalia to and including south africa in madagascar and the mascarene islands especially under a south sumatra scenario involving an earthquake comparable to or even possibly larger than the 1833 event whose epicentral area is widely believed to be under enhanced seismic risk as a result of stress transfer from the 2004 and 2005 ruptures to the northwest possibly even in the wake of the 2007 bengkulu earthquakes

extension across the indian arabian plate boundary the murray ridge summary seismic reflection profiles from the murray ridge in the gulf of oman northwest indian ocean show a significant component of extension across the predominantly strike slip indian arabian plate boundary the murray ridge lies along the northern section of the plate boundary where its trend becomes more easterly and thus allows a component of extension the dalrymple trough is a 25 km wide steep sided halfgraben bounded by large faults with components of both strike slip and normal motion the throw at the seabed of the main fault on the southeastern side of the halfgraben reaches 1800 m the northwest side of the trough is delineated by a series of smaller antithetic normal faults wide angle seismic gravity and magnetic models show that the murray ridge and dalrymple trough are underlain by a crystalline crust up to 17 km thick which may be continental in origin any crustal thinning due to extension is limited and no new crust has been formed we favour a plate model in which the indian arabian plate boundary was initially located further west than the owen fracture zone possibly along the oman continental margin and suggest that during the oligocene early miocene indian ocean plate reorganization the plate boundary moved to the site of the present owen fracture zone and that motion further west ceased at this time deformation began along the murray ridge with both the uplift of basement highs and subsidence in the troughs tilting the lowest sedimentary unit qalhat seamount was formed at this time subsequent sediments were deposited unconformably on the tilted lower unit and then faulted to produce the present basement topography the normal faulting was accompanied by hanging wall subsidence footwall uplift and erosion flat lying recent sediments show that the major vertical movements have ceased although continuing earthquakes show that some faulting is still active along the plate boundary

the relationship between channel avulsion flow occupancy and aggradation in braided rivers insights from an experimental model experimental modelling of an aggrading braided river has allowed investigation of the relationship between the frequency of channel avulsion a f the duration of time that the braidplain is occupied by flow the spatial pattern of braidplain sedimentation and how these respond to a change in sediment supply s s model results demonstrate a strong positive relationship between s s and a f and that there is no downstream change in a f over the short braidplain distances ca 100 m modelled herein although a f is strongly dependent on s s the degree of channel switching does not influence the rate or spatial pattern of braidplain sedimentation all experiments used a single central input for water and sediment and the channels occupied the centre of the alluvial basin for a longer period of time than the margins for all sediment supply rates and distances downstream despite this spatio temporal pattern in flow occupancy braidplain sedimentation rates were nearly uniform both downstream and across the basin and increased at approximately the same rate as increases in s s as a consequence less frequent and possibly short lived flows at the margins of the braidplain deposited and preserved more sediment per unit time in comparison with the centre of the basin where flow occupancy was higher an approximate order of magnitude change in sediment supply resulted in only a factor of two change in bed slope probably due to both an increase in channelization and adjustment of the channel form that maintained sediment transport through the basin this result suggests that linear diffusion models are unlikely to be applicable in landscape evolution models that possess aggrading multi thread rivers which are capable of self adjustment in channel number and form

feasible optimality of vegetation patterns in river basins 1 we examine mechanisms leading to organization of vegetation patterns within the channel network structure of a semi arid new mexico river basin under the controlling influence of water stress we compare the actual pattern of water stress within the basin to patterns resulting from two algorithms of local stress optimization which proceed from an initial fully random vegetation distribution here we show that the distribution of vegetation and basin water stress derived from an algorithm that maintains local optimization within the network flow path exhibits considerably better agreement with the actual distribution than one that ignores the network structure of the basin these results suggest the pattern of actual vegetation observed within the basin corresponds to a condition of feasible optimality in which organization is constrained by the stochastic nature of local interactions mediated by the network configuration the principles of such organization have important consequences regarding the interaction between land cover change and hydrological dynamics in river basins as well as the biogeographical evolution of landscapes

constraints on plate motions in southern pakistan and the northern arabian sea from the focal mechanisms of small earthquakes the focal mechanism and depth were determined for nine small earthquakes m0 1025 dyn cm m 5 5 that occurred in southern pakistan and the northern arabian sea from an analysis of the vertical component of rayleigh waves in combination with limited first motion data focal parameters were determined from the rayleigh waves by using an event pair method of analysis for earthquakes that are located very close to each other 50 km the event pair method is able to remove a significant proportion of propagation effects at all periods in the range of interest 20 50 s for events separated by more than 100 km the propagation effects are reduced for only the longer periods 40 50 s the earthquakes that were studied provide evidence for a model of plate interactions in the vicinity of the southern pakistan triple junction the owen fracture zone is a transform fault that accommodates right lateral motion between the indian and arabian plates the plate boundary in the vicinity of the murray ridge is also partially made up of transform segments that strike subparallel to the owen fracture zone spreading centers may also exist in the vicinity of the murray ridge but were not documented by seismic or other evidence the slip azimuths for earthquakes along this boundary are significantly more northerly than those predicted by various regional and worldwide models of plate motion the arabian plate is being subducted beneath the eurasian plate along the southern coast of pakistan slip vectors for earthquakes along this boundary trend northnortheasterly in general agreement with predicted directions left lateral motion is documented along the boundary between the indian and eurasian plates in southern pakistan the predicted direction of relative motion between these plates is not significantly different from that observed two of the earthquakes studied appear to be intraplate in nature the depth and focal mechanism of one intraplate event which may have occurred within the accretionary prism along the makran coast however are based on limited data the other intraplate earthquake occurred within the sedimentary deposits along the western edge of the indian subcontinent near the indian eurasian plate boundary appendix is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b83 009 2 50 payment must accompany order

observations on the movement of coarse gravel using implanted motion sensing radio transmitters motion sensing radio transmitters were implanted in cobbles 72 92 mm diameter and placed in a stream in south west idaho for 43 days during a snowmelt period the radios transmit different pulse rates depending on whether the rocks are at rest or in motion every 30 s a datalogger samples the receiver and records the pulse rate of the transmitters such information can be used to assess numerous properties of particle transport that are beyond the capabilities of conventional tracking methods conclusions include i rocks are more likely to move on rising hydrograph limbs than on falling hydrograph limbs ii the average shields parameter is 0 046 iii rocks move only a fraction of the time between initial and final motion during an event iv the distributions of motion and rest periods are best modeled by gamma functions rather than exponential but the distributions approach exponential as the tails are trimmed copyright 2004 john wiley sons ltd

experimental evidence of dynamic scaling and indications of self organized criticality in braided rivers the evolution of an experimental braided river produced in our laboratory has been monitored and analyzed it has been shown that in addition to the spatial scaling revealed by sapozhnikov and foufoula georgiou 1996a braided rivers also exhibit dynamic scaling this implies that a smaller part of a braided river evolves identically in the statistical sense to a larger one provided the time is renormalized by a factor depending only on the ratio of the spatial scales of those parts the small value of the estimated dynamic exponent z is interpreted as an indication that the evolution of small channels in a braided river system is to a large extent forced by the evolution of bigger channels the presence of dynamic scaling is further interpreted as indicating that braided rivers may be in a critical state and behave as self organized critical systems in a recent paper sapozhnikov and foufoula georgiou 1996a evidence was presented that natural braided rivers ex hibit anisotropic scaling self affinity in their geometrical structure within a range of scales spanning the width of the narrowest channel to the width of the braid plain in simple words within these scales if a small part of a braided river is stretched in a certain way along the mainstream direction and a certain different way along the perpendicular direction then this stretched part looks statistically the same as a bigger part of the river such anisotropically scaled objects are called self affine fractals and are characterized by two fractal exponents nx and ny the ratio nx ny characterizes the scaling anisotropy and the fractal dimension d 5 ny 2 nx 1 1 ny e g see sapozhnikov and foufoula georgiou 1995 indicates how densely the object fills the space in sapozhnikov and foufoula georgiou 1996a three natu ral braided rivers of different scales and different hydrological and sedimentological characteristics aichilik and hulahula in alaska and brahmaputra in bangladesh were analyzed for spatial scaling using the logarithmic correlation integral lci method developed by sapozhnikov and foufoula georgiou 1995 interestingly enough it was observed that despite their different scales 0 5 15 km in braid plain width slopes 7 3 10 23 8 310 25 and types of bed material gravel to sand all three rivers exhibited anisotropic spatial scaling with almost the same fractal exponents nx 5 0 72 0 74 and ny 5 0 51 0 52 the x axis being oriented along the river and the y axis being in the perpendicular direction in simple terms this im plies that if parts of a braided river are stretched by l along the mainstream direction and by l n y n x l 0 7 along the perpen dicular direction the resulting images will look statistically similar to each other similarity within a braided river at the same time the invariance of nx and ny between braided rivers of different sizes and hydrology sedimentology suggests that the same anisotropic scaling as above applied to different riv ers will result in statistically similar images apart possibly from a normalization factor to account for the different mass of each river note that mass here refers to the area i e number of pixels covered with water the presence of such a statistical scale invariance in the spatial structure of braided rivers apart from being interesting in its own right might indicate the presence of universal features in the underlying mechanisms responsible for the formation of braided rivers and deserves further theoretical and experimental investiga tion braided rivers besides their complex geometry at any in stant of time are also highly dynamic systems characterized by intensive erosion sediment transport and deposition and fre quent channel shifting as they evolve predicting the evolution of braided rivers in terms of frequency and magnitude of chan nel shifting is of paramount importance where hydraulic struc tures or land developments are planned or where field use must be made of maps and air photos it is of great practical and theoretical value therefore to study the evolution of braided rivers in addition to their spatial structure in view of the evidence for spatial static scaling in braided rivers the question is asked here as to whether they also show dynamic scaling the presence of dynamic scaling would imply that space and time can be appropriately rescaled such that the evolution of the spatial structure of parts of the river of dif ferent size would be statistically indistinguishable the pres ence of dynamic scaling would also provide a highly desirable integrated framework for studying simultaneously the spatial and temporal structure of braided rivers

fluvial fan deltas linking channel processes with large scale morphodynamics 1 alluvial fan deltas are built by aggrading and avulsing river channels a numerical model of flow and sediment transport in channels is combined with a condition for channel avulsion to describe evolution of the fan surface the model combines elements of two recent approaches 1 diffusional models of depositional basin filling which describe the evolution of overall morphology and 2 cellular models of channel evolution which provide simplified descriptions of channel dynamics here the cellular formulation is used simply as a template for discretizing a standard set of equations describing flow and sediment transport within channels the basic formulation is thus grid invariant and the results are in actual rather than arbitrary time and length scales the model captures the interaction between microscale channel morphodynamics including converging and diverging flow and avulsion and morphodynamics at the macroscale fan it provides a starting point for the study of a wide range of topics including the three dimensional stratigraphy of fan delta deposits and the response of fan deltas to engineering activities

coupling fine particle and bedload transport in gravel bedded streams abstract fine particles in the silt and clay size range are important determinants of surface water quality since fine particle loading rates are not unique functions of stream discharge this limits the utility of the available models for water quality assessment data from 38 minimally developed watersheds within the united states geological survey stream gauging network in california usa reveal three lines of evidence that fine particle release is coupled with bedload transport first there is a transition in fine particle loading rate as a function of discharge for gravel bedded sediments that does not appear when the sediment bed is composed of sand cobbles boulders or bedrock second the discharge at the transition in the loading rate is correlated with the initiation of gravel mobilization third high frequency particle concentration and discharge data are dominated by clockwise hysteresis where rising limb discharges generally have higher concentrations than falling limb discharges these three observations across multiple watersheds lead to a conceptual model that fine particles accumulate within the sediment bed at discharges less than the transition and then the gravel bed fluidizes with fine particle release at discharges above the transition discharge while these observations were individually recognized in the literature this analysis provides a consistent conceptual model based on the coupling of fine particle dynamics with filtration at low discharges and gravel bed fluidization at higher discharges

generalized hydraulic geometry insights based on fluvial instability analysis and a physical model 1 the power law dependencies between channel morphology and river flows known as at station hydraulic geometry hg have been recently shown to have exponents that systematically vary with scale contributing area to explain these empirical trends a generalized hg model whose parameters are explicit functions of scale was derived by dodov and foufoula georgiou 2004 based on a statistical multiscaling formalism in this paper we attempt to provide a physical explanation for this scale dependence the hypothesis we pose is that it arises from the scale dependence of fluvial instability which induces systematic variation in river planform geometry e g sinuosity meander wavelength and radius of curvature and consequent variations in channel cross sectional shape with scale in other words we postulate that the scale dependent hg is a direct consequence of the systematic increase of channel cross sectional asymmetry over reaches of increasing scale to test this hypothesis we employ both a direct analysis of observations and also a physical model of meandering rivers which is based on linearization of the fully coupled equations of mass and momentum balance for water and sediment we show that the hg emerging from this physical model is scale dependent and agrees with the empirical observations and the statistical multiscaling model

the search for a topographic signature of life landscapes are shaped by the uplift deformation and breakdown of bedrock and the erosion transport and deposition of sediment life is important in all of these processes over short timescales the impact of life is quite apparent rock weathering soil formation and erosion slope stability and river dynamics are directly influenced by biotic processes that mediate chemical reactions dilate soil disrupt the ground surface and add strength with a weave of roots over geologic time biotic effects are less obvious but equally important biota affect climate and climatic conditions dictate the mechanisms and rates of erosion that control topographic evolution apart from the obvious influence of humans does the resulting landscape bear an unmistakable stamp of life the influence of life on topography is a topic that has remained largely unexplored erosion laws that explicitly include biotic effects are needed to explore how intrinsically small scale biotic processes can influence the form of entire landscapes and to determine whether these processes create a distinctive topography

a generalized exner equation for sediment mass balance 1 the advance of morphodynamics research into new areas has led to a proliferation of forms of sediment mass balance equation without a general equation it is often difficult to know what these problem specific versions of sediment mass balance leave out to address this we derive a general form of the standard exner equation for sediment mass balance that includes effects of tectonic uplift and subsidence soil formation and creep compaction and chemical precipitation and dissolution the complete equation 17 allows for independent evolution of two critical interfaces that between bedrock and sediment or soil and that between sediment and flow by eliminating terms from the general equation it is straightforward to derive mass balance equations applicable to a wide range of problems such as short term bed evolution basin evolution bedrock uplift and soil formation and carbonate precipitation and transport dropping terms makes explicit what is not being considered in a given problem and can be done by inspection or by a formal scaling analysis of the terms scaling analysis leads directly to dimensionless numbers that measure the relative importance of terms in the equation for example the relative influence of spatial versus temporal changes in sediment load on bed evolution combining scaling analysis with time averaging shows how the relative importance of terms in the equation can change with timescale for example the term representing bed evolution due to temporal change in sediment load tends to zero as timescale increases

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

present day motion along the owen fracture zone and dalrymple trough in the arabian sea all plate motion data available for describing the present day motion between the arabian and indian plates are analyzed to understand the present day tectonic role of the presumed plate boundary the owen fracture zone and dalrymple trough in the northern arabian sea all prior plate motion models are shown to be inconsistent with some of the data along the presumed boundary in particular published global plate motion models predict some convergence across the owen fracture zone and dalrymple trough convergence along the owen fracture zone is contradicted by earthquake focal mechanisms which show right lateral strike slip convergence along the dalrymple trough is contradicted by observed normal faulting in the trough and by normal and strike slip focal mechanisms for earthquakes occurring along or near the trough the sense and rate of motion is further constrained by spreading rates along the sheba ridge northwest of the owen fracture zone and along the carlsberg ridge southeast of the owen fracture zone to estimate the present day motion we determine 43 3 m y average spreading rates from sheba ridge carlsberg ridge and central indian ridge magnetic profiles and have combined them with eight transform azimuths and 15 earthquake slip vectors along these ridges and the arabia india boundary we determine an arabia india euler vector that predicts 2 mm yr of right lateral strike slip motion along the owen fracture zone with a 95 confidence interval of 0 7 mm yr which excludes the faster rates of slips predicted by several prior models the direction of motion is 35 50 counterclockwise from that predicted by published global plate motion models if we omit the data along the arabia india boundary the motion differs insignificantly from zero suggesting that magnetic profiles from the carlsberg and sheba ridges give spreading rates too imprecise to detect the slow arabia india motion if the owen fracture zone and dalrymple trough are regarded as a plate boundary it is the slowest slipping plate boundary known on earth with motion about 100 times slower than the fastest slipping faults along the east pacific rise

toward a unified science of the earth s surface opportunities for synthesis among hydrology geomorphology geochemistry and ecology 1 the earth s surface is shaped by the interaction of tectonics water sediment solutes and biota over a wide range of spatial and temporal scales and across diverse environments development of a predictive science of earth surface dynamics integrates many disciplines and approaches including hydrology geomorphology ocean and atmospheric science sedimentary and structural geology geochemistry and ecology this paper discusses challenges opportunities and a few example problems that can serve as pathways toward this integration

increase in coarse sediment transport associated with disturbance of gravel river beds by signal crayfish pacifastacus leniusculus there is growing acknowledgement of the interaction between animals and the river bed on which they live and the implications of biological activity for geomorphic processes it has been observed that signal crayfish pacifastacus leniusculus disturb gravel substrates potentially promoting sediment transport and impacting ecological communities however the mechanisms involved and the extent of their impact remain poorly understood especially in relation to other processes that affect grain mobility in gravel bed rivers a series of flume experiments using loose and water worked gravel beds of narrowly graded grain sizes that were exposed to 6 h of crayfish activity under low velocity flows showed a substantial increase in the number of grains entrained by subsequent higher velocity flows when compared with control runs in which crayfish were never introduced crayfish alter the topography of their substrate by constructing pits and mounds which affect grain protrusion when walking and foraging they also alter gravel fabric by reorienting and changing the friction angle of surface grains in water worked surfaces this fabric rearrangement is shown to lead to a statistically significant partial reversal of the structuring that had been achieved by antecedent flow for these previously water worked surfaces the increase in entrainment arising from disturbance by crayfish was statistically significant with grain transport nearly twice as great this suggests that signal crayfish an increasingly widespread invasive species in temperate latitudes beyond their native nw north america have the potential to enhance coarse grained bedload flux by altering the surface structure of gravel river beds and reducing the stability of surface grains this study illustrates further the importance of acknowledging the impact of mobile organisms in conditioning the river bed when assessing sediment entrainment mechanics in the context of predicting bedload flux

quantification of chemical weathering rates across an actively eroding hillslope abstract chemical weathering rates for landscapes are difficult to quantify because the timescales over which weathering occurs are often unknown in this study we use timescales defined by prior cosmogenic nuclide analyses and a suite of geochemical measurements to calculate weathering rates in saprolite and soil and to determine how these rates vary across an eroding hillslope we also estimate the relative contributions of solute and erosional mass loss to landscape lowering analyses were conducted on a soil mantled hillslope developed on a granodiorite pluton in southern nsw australia mass loss in solution accounts for 35 to 55 of the total mass loss from the hillslope saprolite close to the soil saprolite boundary is less weathered at the ridge than at distance from the ridge the calculated flux of silica from the saprolite is 5 tons km 2 yr 1 and does not vary with distance from the ridge or overlying soil thickness the assumption of steady state but spatially variable erosion rates with a temporally constant thickness of soil and saprolite allows us to calculate the downslope variation in the rate of solute losses soil silica weathering rates initially increase from 12 tons km 2 yr 1 at the ridge crest to 20 tons km 2 yr 1 on the convex region of the hillslope and then decrease to 13 tons km 2 yr 1 by the time soils have been transported 45 50 m soils closer to the surface are more weathered than deeper soils this geochemical stratification suggests that the soil column does not become thoroughly vertically mixed as soils move down slope dependence of solute loss on transport distance may explain the previously noted discrepancy between the observed soil thickness and that predicted based on curvature variation of solute loss with transport distance may also contribute to the linear dependence of soil thickness on distance from the ridge